Positive electrode active material, positive electrode sheet, secondary battery, battery module, battery pack, and power using device

Abstract

The application provides a positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. The positive electrode active material comprises a compound Li a A x Mn 1‑y B y P 1‑z C z O 4‑n D n , A comprises one or more elements selected from group IA, group IIA, group IIIA, group IIB, group VB and group VIB; B comprises one or more elements selected from group IA, group IIA, group IIIA, group IVA, group VA, group IIB, group IVB, group VB, group VIB and group VIII; C comprises one or more elements selected from group IIIA, group IVA, group VA and group VIA; and D comprises one or more elements selected from group VIA and group VIIA. The material can improve the rate performance, reduce the dissolution of Mn and Mn site doping elements, and significantly improve the cycle performance and high-temperature stability of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] With the rapid development of the new energy field, lithium ion batteries are widely used in various large-scale power devices, energy storage systems and various consumer products due to their excellent electrochemical performance, no memory effect, small environmental pollution and other advantages, especially in the field of new energy vehicles such as pure electric vehicles and hybrid electric vehicles. Among them, lithium manganese phosphate positive electrode active material has the advantages of high working voltage, wide raw material sources and small environmental pollution, and is considered to be a positive electrode active material that can replace lithium iron phosphate and become a power lithium ion battery.

[0003] However, in the prior art, the cycle performance, high-temperature storage performance and safety performance of the secondary battery using lithium manganese phosphate positive electrode active material have not been comprehensively improved, which greatly limits the wider application of lithium manganese phosphate batteries. Therefore, the industry is still looking forward to designing a lithium manganese phosphate positive electrode active material with high specific capacity, good cycle performance and safety performance. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a positive electrode active material, a preparation method of the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device, so as to solve the problems of easy generation of Li / Mn anti-site defects and serious manganese dissolution of the existing lithium manganese phosphate positive electrode active material during charging and discharging, thereby solving the problems of low capacity, poor safety performance and cycle performance of the secondary battery.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode active material comprising a compound represented by formula (I),

[0006] Li a A x Mn 1-y B y P 1-z C z O 4-n D n

[0007] (I)

[0008] wherein,

[0009] A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB;

[0010] B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB, and Group VIII;

[0011] C comprises one or more elements selected from Group IIIA, Group IVA, Group VA, and Group VIA;

[0012] D comprises one or more elements selected from Group VIA and Group VIIA;

[0013] a is selected from the range of 0.85 to 1.15;

[0014] x is selected from the range of 0 to 0.1;

[0015] y is selected from the range of 0.001 to 0.999;

[0016] z is selected from the range of 0 to 0.5;

[0017] n is selected from the range of 0 to 0.5.

[0018] Thus, the present application is able to obtain significantly improved rate capability, while significantly reducing the dissolution of Mn and Mn-site doped elements, to obtain significantly improved cycle performance and / or high-temperature stability, and the gravimetric capacity and tap density of the material are also improved, by doping specific elements at the Mn site of the compound LiMnPO4, and optionally at the Li site, P site, and / or O site, in specific amounts.

[0019] In any embodiment, A comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, Ga, In, Cd, V, Ta, Cr, Zn, Al, Na, K, Mg, Nb, Mo, and W, optionally comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; and / or,

[0020] B comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, In, Pb, Bi, Cd, Hf, Ta, Cr, Ru, Rh, Pd, Os, Ir, Pt, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, optionally comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or, C comprises one or more elements selected from B (boron), S, Si, and N; and / or, D comprises one or more elements selected from S, F, Cl, and Br.

[0021] Thus, the rate performance, gravimetric capacity, tap density, cycle performance and / or high temperature performance of the secondary battery can be further improved, the elution of Mn and Mn-site doping elements can be further reduced, and the cycle performance and / or high temperature performance of the secondary battery can be improved.

[0022] In any embodiment, A comprises any one element selected from Zn, Al, Na, K, Mg, Nb, Mo and W, optionally any one element selected from Mg and Nb; and / or,

[0023] B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, more optionally at least two elements selected from Fe, Ti, V, Ni, Co and Mg, further optionally at least two elements selected from Fe, Ti, V, Co and Mg, more further optionally Fe and one or more elements selected from Ti, V, Co and Mg; and / or,

[0024] C comprises any one element selected from B (boron), S, Si and N, optionally S; and / or,

[0025] D comprises any one element selected from S, F, Cl and Br, optionally F.

[0026] Thus, the rate performance of the secondary battery can be further improved, the elution of Mn and Mn-site doping elements can be further reduced, the cycle performance and / or high temperature performance of the secondary battery can be improved, and the gravimetric capacity and tap density of the material can be further improved.

[0027] In any embodiment, a is selected from the range of 0.9 to 1.1, optionally from the range of 0.97 to 1.01; and / or,

[0028] x is selected from the range of 0 to 0.005, optionally from the range of 0.001 to 0.1; and / or,

[0029] y is selected from the range of 0.001 to 0.5, optionally from the range of 0.01 to 0.5, optionally from the range of 0.25 to 0.5; and / or,

[0030] z is selected from the range of 0 to 0.5, optionally from the range of 0.001 to 0.5, optionally from the range of 0.001 to 0.1, more optionally from the range of 0.001 to 0.005; and / or,

[0031] n is selected from the range of 0 to 0.1, optionally from the range of 0.001 to 0.1.

[0032] Therefore, the gram capacity of the material can be further improved, the rate performance and / or the kinetic performance of the secondary battery can be further improved, and the cycle performance and / or the high-temperature performance of the battery can be further improved.

[0033] In any embodiment, x is 0, z is selected from the range of 0.001 to 0.5, and n is selected from the range of 0.001 to 0.1; or,

[0034] x is selected from the range of 0.001 to 0.1, z is 0, and n is selected from the range of 0.001 to 0.1; or,

[0035] x is selected from the range of 0.001 to 0.1, z is selected from the range of 0.001 to 0.5, and n is 0; or,

[0036] x is 0, z is 0, and n is selected from the range of 0.001 to 0.1; or,

[0037] x is 0, z is selected from the range of 0.001 to 0.5, and n is 0; or,

[0038] x is selected from the range of 0.001 to 0.1, z is selected from the range of 0.001 to 0.5, and n is selected from the range of 0.001 to 0.1.

[0039] Therefore, by doping specific elements at the Mn site of the compound LiMnPO4 and optionally at the Li site, the P site and / or the O site in specific amounts, especially by doping specific elements at the Mn site and the P site of LiMnPO4 or at the Li site, the Mn site, the P site and the O site of LiMnPO4 in specific amounts, the rate performance can be significantly improved, the dissolution of Mn and the Mn site doping element can be significantly reduced, the cycle performance and / or the high-temperature stability can be significantly improved, and the gram capacity and the compaction density of the material can be significantly improved.

[0040] In any embodiment, y:z is selected from the range of 0.002 to 999, optionally from the range of 0.025 to 999, and more optionally from the range of 0.2 to 600. Therefore, the defects of the material can be reduced, the integrity of the framework structure of the material can be improved, the structural stability of the material can be effectively improved, and the cycle stability of the secondary battery can be improved.

[0041] In any embodiment, z:n is selected from the range of 0.002 to 500, optionally from the range of 0.2 to 100, and more optionally from the range of 0.2 to 50. Therefore, the defects of the material can be further reduced, the integrity of the framework structure of the material can be further improved, the structural stability of the material can be effectively improved, and the cycle stability of the secondary battery can be improved.

[0042] In any embodiment,

[0043] A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W;

[0044] B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge;

[0045] C comprises one or more elements selected from the group consisting of B (boron), S, Si and N;

[0046] D comprises one or more elements selected from the group consisting of S, F, Cl and Br;

[0047] a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, and n is selected from the range of 0.001 to 0.1.

[0048] Thus, the present application can obtain obviously improved rate performance by simultaneously doping specific elements in specific amounts at the Li site, Mn site, P site and O site of the compound LiMnPO4, significantly reduces the dissolution of Mn and Mn site doping elements, and obtains significantly improved cycle performance and / or high temperature stability, and the gram capacity and compaction density of the material can also be improved.

[0049] In any of the embodiments,

[0050] B comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from the group consisting of Zn, Fe, Ti, V, Ni, Co and Mg;

[0051] C is one or more elements selected from the group consisting of B, Si, N and S;

[0052] a is selected from the range of 0.9 to 1.1, x is 0, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, and n is 0.

[0053] Thus, the present application can improve the rate performance, reduce the dissolution of Mn and Mn site doping elements, improve the cycle performance and / or high temperature stability, and improve the gram capacity and compaction density of the material by simultaneously doping specific elements in specific amounts at the Mn site and P site of the compound LiMnPO4.

[0054] In any of the embodiments, the positive electrode active material comprises a core and a shell coating the core, and the core comprises the compound of formula I described above;

[0055] The shell comprises one or more coating layers; the coating layer has ionic conductivity or electronic conductivity.

[0056] The present application provides a novel positive electrode active material with a core-shell structure by doping a specific element in a specific amount at the Mn site of the compound LiMnPO4 and optionally at the Li site, the P site and / or the O site to obtain a doped lithium manganese phosphate core and setting a coating layer with ionic conductivity or electronic conductivity on the surface of the core, and applying the positive electrode active material to a secondary battery, which can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0057] In any embodiment, the shell comprises one coating layer;

[0058] Optionally, the coating layer comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0059] Thus, the present application uses the above-mentioned material to obtain a coating layer with ionic conductivity or electronic conductivity, thereby improving the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0060] In any embodiment, the shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer;

[0061] Optionally, the first coating layer and the second coating layer each independently comprise one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0062] Thus, the present application uses the above-mentioned material as the material of the coating layer and sets two coating layers, which can further improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0063] In any embodiment, the first coating layer comprises one or more selected from pyrophosphate, phosphate, oxide and boride, and the second coating layer comprises one or more selected from carbon and doped carbon.

[0064] Thus, the present application uses the first coating layer of a specific material and the second coating layer of a specific material, which can further improve the rate performance, further reduce the dissolution of Mn and Mn site doping elements, thereby improving the cycle performance and / or high-temperature stability of the secondary battery.

[0065] In any embodiment, the shell comprises a first coating layer coating the core, a second coating layer coating the first coating layer and a third coating layer coating the second coating layer;

[0066] Optionally, each of the first coating layer, the second coating layer and the third coating layer independently comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0067] Thus, the application adopts the above-mentioned materials as the material of the coating layer, and sets three coating layers to further reduce the elution of Mn and Mn-site doped elements, and further improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0068] In any embodiment, the first coating layer comprises pyrophosphate, the second coating layer comprises one or more selected from the group consisting of phosphate, oxide and boride, and the third coating layer comprises one or more selected from the group consisting of carbon and doped carbon.

[0069] Thus, the application adopts the first coating layer of a specific material, the second coating layer of a specific material and the third coating layer of a specific material, further improves the rate performance, further reduces the elution of Mn and Mn-site doped elements, thereby improving the cycle performance and / or high-temperature stability of the secondary battery, and further improves the gravimetric capacity and the compaction density of the material.

[0070] In any embodiment, each of the one or more coating layers independently comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0071] In any embodiment, the pyrophosphate is M b (P2O7) c ; and / or,

[0072] The phosphate is X m (PO4) q ; and / or,

[0073] The doping element in the doped carbon comprises one or more selected from the group consisting of Group IIIA, Group VA, Group VIA and Group VIIA; and / or,

[0074] The oxide is M' d O e ; and / or,

[0075] The boride is Z v B w ; and / or,

[0076] The polymer comprises one or more selected from the group consisting of polysaccharide and its derivative, and polysiloxane;

[0077] wherein,

[0078] M, X and Z each independently comprise one or more elements selected from Group IA, Group IIA, Group IIIA, Group IB, Group IIB, Group IVB, Group VB, Group VIIB and Group VIII; b is selected from the range of 1 to 4, c is selected from the range of 1 to 6; m is selected from the range of 1 to 2, q is selected from the range of 1 to 4; M' comprises one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide series elements and Sb, d is greater than 0 and less than or equal to 2, e is greater than 0 and less than or equal to 5; v is selected from the range of 1 to 7, w is selected from the range of 1 to 2.

[0079] Thus, the present application is able to further reduce the elution of Mn and Mn-site doped elements, further improve the specific capacity and tap density of the material, and further improve the rate capability, high-temperature cycle performance and high-temperature storage performance of the secondary battery by employing the above material as the coating layer.

[0080] In any embodiment, M, X and Z each independently comprise one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; and / or,

[0081] The doped elements in the carbon doping include one or more elements selected from nitrogen, phosphorus, sulfur, boron and fluorine; and / or,

[0082] M' comprises one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, and can optionally comprise one or more elements selected from Mg, Al, Si, Zn, Zr and Sn; and / or,

[0083] The polysiloxane is selected from one or more of linear structure polysiloxane and cyclic structure polysiloxane; and / or,

[0084] The polysaccharide is selected from one or more of plant polysaccharide and marine polysaccharide.

[0085] Thus, the present application is able to further reduce the elution of Mn and Mn-site doped elements, and further improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery by employing the above specific material as the coating layer.

[0086] In any embodiment, the positive electrode active material comprises a core and a shell coating the core,

[0087] The core comprises Li a Mn 1-y By P 1-z C z O4, wherein a is selected from the range of 0.9 to 1.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, Zn and Ge, and C comprises one or more elements selected from B (boron), S, Si and N;

[0088] The shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer,

[0089] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;

[0090] The second coating layer comprises carbon.

[0091] Thus, the positive electrode active material of the present application can improve the specific capacity, cycle performance and safety performance of the secondary battery. Although the mechanism is not clear, it is speculated that the lithium manganese phosphate positive electrode active material of the present application is a core-shell structure, in which the manganese sites and phosphorus sites of the lithium manganese phosphate core are doped with elements respectively, which not only can effectively reduce the dissolution of manganese, and further reduce the manganese ions migrated to the negative electrode, reduce the electrolyte consumed due to the decomposition of SEI film, improve the cycle performance and safety performance of the secondary battery, but also can promote the adjustment of Mn-O bond, reduce the lithium ion migration barrier, promote the migration of lithium ions, and improve the rate performance of the secondary battery; by coating the core with a first coating layer comprising pyrophosphate and phosphate, the migration resistance of manganese can be further increased, the dissolution thereof can be reduced, and the surface lithium content can be reduced, the contact between the core and the electrolyte can be reduced, thereby reducing the interface side reaction, reducing the gas production, and improving the high-temperature storage performance, cycle performance and safety performance of the secondary battery; by further coating the carbon-containing layer as the second coating layer, the safety performance and kinetic performance of the secondary battery can be further improved.

[0092] In any embodiment, the positive electrode active material comprises a core and a shell coating the core,

[0093] The core comprises Li a Mn 1-y B y P 1-z C zO4, wherein a is selected from the range of 0.9 to 1.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, and C comprises one or more elements selected from B (boron), S, Si, and N;

[0094] The shell comprises a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, wherein,

[0095] The first coating layer comprises pyrophosphate Li f QP2O7and / or Q g (P2O7) h wherein 0≤f≤2, 1≤g≤4, 1≤h≤6, pyrophosphate Li f QP2O7and / or Q g (P2O7) h Q in each of the above is independently one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al;

[0096] The second coating layer comprises a crystalline phosphate XPO4, wherein X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al;

[0097] The third coating layer comprises carbon.

[0098] The present application provides a novel lithium manganese phosphate positive electrode active material with a core-shell structure by doping elements at the manganese site of lithium manganese phosphate and doping elements at the phosphorus site to obtain a doped lithium manganese phosphate core, and sequentially performing three-layer coating on the surface of the core. The positive electrode active material is applied to a secondary battery, which can significantly improve the high-temperature cycle performance, cycle stability, and high-temperature storage performance of the secondary battery.

[0099] In any embodiment, one or more coating layers of the shell that are farthest from the core each independently comprise one or more selected from polysiloxane, polysaccharide, and polysaccharide derivatives.

[0100] Thus, the uniformity of the coating can be improved, the interface side reaction caused by high voltage can be effectively blocked, thereby improving the high-temperature cycle performance and high-temperature storage performance of the material; and the coating layer has good electronic conductivity and ionic conductivity, which helps to improve the capacity of the material and reduces the heat generation of the battery cell.

[0101] In any embodiment, the polysiloxane comprises a structural unit represented by formula (i),

[0102]

[0103]

[0104] wherein R1and R2are independently selected from the group consisting of H, -COOH, -OH, -SH, -CN, -SCN, amino, phosphate, carboxylate, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic, C1-C20 halogenated aliphatic, C1-C20 heteroaliphatic, C1-C20 halogenated heteroaliphatic, C6-C20 aromatic, C6-C20 halogenated aromatic, C2-C20 heteroaromatic, and C2-C20 halogenated heteroaromatic;

[0105] Optionally, R1and R2are independently selected from the group consisting of H, amino, phosphate, polyether segment, C1-C8 alkyl, C1-C8 halogenated alkyl, C1-C8 heteroalkyl, C1-C8 halogenated heteroalkyl, C2-C8 alkenyl, and C2-C8 halogenated alkenyl.

[0106] In any embodiment, the polysiloxane further comprises a capping group comprising at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 halogenated alkyl, C1-C8 heteroalkyl, C1-C8 halogenated heteroalkyl, C2-C8 alkenyl, C2-C8 halogenated alkenyl, C6-C20 aromatic, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxylalkyl, amino, C1-C8 aminoalkyl, carboxyl, C1-C8 carboxylalkyl.

[0107] In any embodiment, the polysiloxane comprises one or more of polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl functionalized polysiloxane, epoxy terminated polysiloxane, methoxy terminated polydimethylsiloxane, hydroxypropyl terminated polydimethylsiloxane, polymethylchloropropylsiloxane, hydroxyl terminated polydimethylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, aminoethyl aminopropyl polydimethylsiloxane, end group polyether polydimethylsiloxane, side chain aminopropyl polysiloxane, aminopropyl terminated polydimethylsiloxane, side chain phosphate grafted polydimethylsiloxane, side chain polyether grafted polydimethylsiloxane, 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentadimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, cyclic polymethylvinylsiloxane, hexadecamethylcyclooctasiloxane, tetradecamethylcyclotetrasiloxane, and cyclic polydimethylsiloxane.

[0108] In any of the embodiments, the number average molecular weight of the polysiloxane, the polysaccharide, and the polysaccharide derivative is each independently 300,000 or less, optionally 10,000 to 200,000, more optionally 20,000 to 120,000, further optionally 400 to 80,000.

[0109] In any of the embodiments, the mass percentage of the polar functional group in the polysiloxane is a, and 0 < a < 50%, optionally 5% < a < 30%.

[0110] In any of the embodiments, the substituent bonded to the sugar unit in the polysaccharide and the polysaccharide derivative each independently includes at least one of the group consisting of -OH, -COOH and salts thereof, -R-OH, -SO3H and salts thereof, -R-OH, -R-SO3H and salts thereof, sulfate group, and alkoxy group, wherein R represents an alkylene group, optionally a C1-C5 alkylene group.

[0111] Optionally, the substituent bonded to the sugar unit in the polysaccharide and the polysaccharide derivative each independently includes at least one of the group consisting of -OH, -COOH, -COOLi, -COONa, -COOK, -SO3H, -SO3Li, -SO3Na, -SO3K, -CH2-SO3H, -CH2-SO3Li, -CH2-SO3Na, -CH2-SO3K, methoxy group, and ethoxy group.

[0112] In any of the embodiments, the polysaccharide includes one or more selected from the group consisting of pectin, carboxymethyl starch, hydroxypropyl starch, dextrin, cellulose ether, carboxymethyl chitosan, hydroxyethyl cellulose, carboxymethyl cellulose, carboxypropyl methyl cellulose, guar gum, sorgo gum, gum arabic, lithium alginate, sodium alginate, potassium alginate, fucoidan, agar, carrageenan, furcellaran, xanthan gum, and fenugreek gum.

[0113] In any of the embodiments, the mass percentage of the substituent bonded to the sugar unit in the polysaccharide and the polysaccharide derivative is each independently 20% to 85%, optionally 30% to 78%.

[0114] In any of the embodiments, the degree of lattice mismatch between the material of the core and the material of the shell is less than 10%. Thereby, the contact between the core and the shell (or the coating layer) can be made good to prevent the detachment of the shell (or the coating layer).

[0115] In any of the embodiments, the content of the lithium ion source is 0.1 to 10% by mass based on the weight of the positive electrode active material.

[0116] The content of manganese element is in the range of 10wt%-35wt%, optionally in the range of 13.3wt%-33.2wt%, more optionally in the range of 15wt%-30wt%, further optionally in the range of 17wt%-20wt%; and / or,

[0117] The content of phosphorus element is in the range of 12wt%-25wt%, optionally in the range of 15wt%-20wt%, more optionally in the range of 16.8wt%-19.5wt%; and / or,

[0118] The weight ratio of manganese element and phosphorus element is in the range of 0.71-1.85, optionally in the range of 0.90-1.25, more optionally in the range of 0.95-1.20.

[0119] The content of manganese element in the application is in the above range, which can effectively reduce the problems of poor material structure stability, density reduction and the like, thereby improving the performance of the secondary battery such as cycle, storage and compaction density; and can reduce the problem of too low voltage platform, thereby improving the energy density of the secondary battery.

[0120] In any embodiment, the surface of the positive electrode active material is coated with one or more of carbon and doped carbon; optionally, the surface of the positive electrode active material is coated with carbon. In this way, the conductivity of the positive electrode active material can be improved.

[0121] In any embodiment, the doping element in the doped carbon includes one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine. It is convenient to control the performance of the doped carbon layer.

[0122] In any embodiment, in the core,

[0123] (1-y):y is in the range of 0.1-999, optionally in the range of 0.1-10 or in the range of 0.67-999, more optionally in the range of 1 to 10, further optionally in the range of 1 to 4, more further optionally in the range of 1.5 to 3; and / or,

[0124] a:x is in the range of 1 to 1200, optionally in the range of 9 to 1100, more optionally in the range of 190-998.

[0125] In this way, the energy density and cycle performance of the positive electrode active material can be further improved.

[0126] In any embodiment, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. In this way, the cycle performance and rate performance of the secondary battery are further improved.

[0127] In any embodiment, the shell has a coating amount of 0.1% to 6% by weight based on the weight of the core. The coating amount of the shell according to the present application is preferably within the above range, thereby enabling sufficient coating of the core while further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive active material.

[0128] In any embodiment, the first coating layer has a coating amount of greater than 0% by weight and less than or equal to 7% by weight, optionally greater than 0% and less than or equal to 6% by weight, more optionally greater than 0% and less than or equal to 5.5% by weight or 4 to 5.6% by weight, further optionally greater than 0% and less than or equal to 2% by weight, based on the weight of the core; and / or,

[0129] The second coating layer has a coating amount of greater than 0% by weight and less than or equal to 6% by weight, optionally greater than 0% and less than or equal to 5.5% by weight, more optionally 2 to 4% by weight or 3 to 5% by weight, based on the weight of the core; and / or,

[0130] The third coating layer has a coating amount of greater than 0% and less than or equal to 6% by weight, optionally greater than 0% and less than or equal to 5.5% by weight, more optionally greater than 0% and less than or equal to 2% by weight, based on the weight of the core.

[0131] In any embodiment, the shell further comprises a fourth coating layer coating the third coating layer and a fifth coating layer coating the fourth coating layer; wherein,

[0132] The fourth coating layer and the fifth coating layer each independently have a coating amount of 0.01% to 10% by weight, optionally 0.05% to 10% by weight, more optionally 0.1% to 5% by weight, further 0.1% to 2% by weight, based on the weight of the core.

[0133] In the positive active material having a core-shell structure according to the present application, the coating amount of each layer is preferably within the above range, thereby enabling sufficient coating of the core while further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive active material.

[0134] In any embodiment, the shell is located on 40% to 90% of the surface of the core, optionally 60% to 80% of the surface. This enables sufficient coating of the core, thereby improving the kinetic performance and safety performance of the secondary battery.

[0135] In any embodiment, the shell has a thickness of 1 to 15 nm.

[0136] In any embodiment, the first coating layer has a thickness of 1 to 10 nm, optionally 2 to 10 nm; and / or,

[0137] The thickness of the second coating layer is 2-25 nm, optionally 2-15 nm, more optionally 3-15 nm; and / or,

[0138] The thickness of the third cladding layer is 2-25 nm, and can be optionally 5-25 nm.

[0139] In the present application, the first coating layer has the above-mentioned thickness range, which can further reduce the adverse effects on the kinetic properties of the material and can alleviate the problem of being unable to effectively hinder the migration of transition metal ions.

[0140] The second coating layer has the above-mentioned thickness range, so that the surface structure of the second coating layer is stable and the side reaction with the electrolyte is small, thereby effectively reducing the interface side reaction and improving the high temperature performance of the secondary battery.

[0141] The third coating layer has the above-mentioned thickness range, which can enhance the electrical conductivity of the material and improve the compaction density performance of the battery pole piece prepared using the positive electrode active material.

[0142] In any embodiment, the one or more coating layers each independently comprise one or more selected from pyrophosphate, phosphate and oxide, and the one or more selected from pyrophosphate, phosphate and oxide are crystalline;

[0143] Optionally, the crystallinity of the pyrophosphate, phosphate, and oxide are each independently from 10% to 100%, more preferably from 50% to 100%.

[0144] Herein, crystalline means a crystallinity of 50% or more, i.e., 50%-100%. A crystallinity of less than 50% is called a glassy state. The crystallinity of the crystalline pyrophosphate and crystalline phosphate of the present application is 50% to 100%.

[0145] Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating's ability to hinder manganese dissolution and the phosphate coating's excellent lithium ion conductivity and reduce interface side reactions, but also enable the pyrophosphate coating and the phosphate coating to better lattice match, thereby achieving a close bond between the coatings.

[0146] In any embodiment, in the shell, the weight ratio of pyrophosphate to phosphate and the weight ratio of pyrophosphate to oxide are each independently 1:3 to 3:1, and can be optionally 1:3 to 1:1. Thus, by having the pyrophosphate and phosphate in a suitable weight ratio range or the pyrophosphate and oxide in a suitable weight ratio range, manganese dissolution can be effectively hindered, the surface impurity lithium content can be effectively reduced, and interfacial side reactions can be reduced, thereby improving the high-temperature storage performance, safety performance, and cycle performance of the secondary battery.

[0147] In any embodiment, the one or more coating layers each independently comprises carbon, and the carbon is a mixture of SP2 carbon and SP3 carbon, and optionally, the molar ratio of SP2 carbon to SP3 carbon in the carbon is any value in the range of 0.07-13, more optionally any value in the range of 0.1-10, and further optionally any value in the range of 2.0-3.0.

[0148] The present application improves the comprehensive performance of the secondary battery by limiting the molar ratio of SP2 carbon to SP3 carbon in the above range.

[0149] In any embodiment, the one or more coating layers each independently comprises doped carbon, and the mass content of the doping element in the doped carbon is less than 30%, and optionally, the mass content of the doping element in the doped carbon is less than 20%. The doping element in the above content range can sufficiently improve the conductivity of the pure carbon layer, and effectively avoid excessive surface activity caused by excessive doping of the doping element, thereby effectively controlling the interface side reaction caused by excessive doping of the coating layer.

[0150] In any embodiment, the one or more coating layers each independently comprises doped carbon, and the mass content of the doping element in the doped carbon is less than 30%, and optionally, the mass content of the doping element in the doped carbon is less than 20%. The doping element in the above content range can sufficiently improve the conductivity of the pure carbon layer, and effectively avoid excessive surface activity caused by excessive doping of the doping element, thereby effectively controlling the interface side reaction caused by excessive doping of the coating layer.

[0151] The doping element is nitrogen and / or sulfur, and the mass content of the doping element in the doped carbon is 1%-15%.

[0152] The doping element is phosphorus, boron and / or fluorine, and the mass content of the doping element in the doped carbon is 0.5%-5%.

[0153] Optionally, the doping element is nitrogen, phosphorus, sulfur, boron or fluorine.

[0154] Since the atomic radius of nitrogen and sulfur atoms is closer to that of carbon atoms, it is not easy to damage the carbon skeleton, and therefore, when the doping amount of nitrogen and sulfur atoms is in the above relatively wide range, the conductivity of the doped carbon layer can be sufficiently improved, and the lithium ion transmission and lithium ion desolvation capacity can be promoted.

[0155] Since the atomic radius of phosphorus, boron and / or fluorine atoms is different from that of carbon atoms, excessive doping can easily damage the carbon skeleton, and therefore, when the doping amount of phosphorus, boron and / or fluorine atoms is in the above relatively small range, the conductivity of the doped carbon layer can be sufficiently improved, and the lithium ion transmission and lithium ion desolvation capacity can be promoted.

[0156] In any embodiment, the one or more coating layers each independently comprise a pyrophosphate having an interplanar spacing ranging from 0.293 nm to 0.470 nm, optionally from 0.297 nm to 0.462 nm or from 0.293 nm to 0.326 nm, more optionally from 0.300 nm to 0.310 nm, and an angle of incidence ranging from 18.00° to 32.57°, optionally from 18.00° to 32.00° or from 26.41° to 32.57°, more optionally from 19.211° to 30.846°, further optionally from 29.00° to 30.00°; and / or,

[0157] The one or more coating layers each independently comprise a phosphate having an interplanar spacing ranging from 0.244 nm to 0.425 nm, optionally from 0.345 nm to 0.358 nm, and an angle of incidence ranging from 20.00° to 37.00°, optionally from 24.25° to 26.45°;

[0158] Optionally, the first coating layer or the second coating layer comprises a phosphate.

[0159] In the positive electrode active material of the present application, both the first coating layer and the second coating layer use crystalline substances, and their interplanar spacing and angle of incidence range within the above-mentioned ranges. Thus, impurity phases in the coating layer can be effectively reduced, thereby improving the gravimetric capacity, cycle performance and rate capability of the material.

[0160] In any embodiment, the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 50% or less, optionally 9.8% or less, more optionally 8.1% or less, further optionally 7.5% or less, more further optionally 6% or less, more further optionally 4% or less, more further optionally 3.8% or less, more further optionally from 2.0% to 3.8%.

[0161] Therefore, using the positive electrode active material can improve the gravimetric capacity and rate capability of the secondary battery.

[0162] In any embodiment, the Li / Mn antisite defect concentration of the positive electrode active material is 5.3% or less, optionally 5.1% or less, more optionally 4% or less, further optionally 2.2% or less, more further optionally 2% or less, more further optionally from 1.5% to 2.2% or 0.5% or less.

[0163] By having the Li / Mn antisite defect concentration within the above-mentioned range, Mn 2+ can be avoided from hindering the transmission of Li + , while improving the gravimetric capacity and rate capability of the positive electrode active material.

[0164] In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm 3 In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm

[0165] In any embodiment, the compaction density of the positive electrode active material at 3T is 1.89 g / cm

[0166] In any embodiment, the surface oxygen valence state of the positive electrode active material is -1.55 or less, optionally -1.82 or less, more optionally -1.88 or less, further optionally -1.90 or less, or -1.98 to -1.88, more further optionally -1.98 to -1.89, more further optionally -1.98 to -1.90.

[0167] In any embodiment, the surface oxygen valence state of the positive electrode active material is -1.55 or less, optionally -1.82 or less, more optionally -1.88 or less, further optionally -1.90 or less, or -1.98 to -1.88, more further optionally -1.98 to -1.89, more further optionally -1.98 to -1.90.

[0168] The second aspect of the present application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0169] reacting a manganese source with a source of element B to obtain a manganese salt doped with element B;

[0170] mixing a lithium source, a phosphorus source, optionally a source of element A, optionally a source of element C, optionally a source of element D, and the manganese salt doped with element B, drying, and sintering to obtain a core Li a A x Mn 1-y B y P 1-z C z O 4-n D n ; wherein A, B, C, D, a, x, y, z and n are defined as in the first aspect of the present application.

[0171] Thus, by doping specific elements in the Mn site of the compound LiMnPO4 and optionally in the Li site, P site and / or O site in specific amounts, the application can obtain significantly improved rate performance, while significantly reducing the dissolution of Mn and Mn site doping elements, obtaining significantly improved cycle performance and / or high temperature stability, and the gravimetric capacity and tap density of the material can also be improved.

[0172] In any embodiment, the method specifically comprises the following steps:

[0173] mixing and stirring a manganese source, a source of element B and an acid in a solvent to generate a suspension of manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain manganese salt doped with element B;

[0174] adding a lithium source, a phosphorus source, an optional source of element A, an optional source of element C, an optional source of element D, a solvent and the manganese salt doped with element B into a reaction vessel to grind and mix to obtain a slurry;

[0175] transferring the obtained slurry to a spray drying device for spray drying granulation to obtain granules;

[0176] sintering the obtained granules to obtain a core Li a A x Mn 1-y B y P 1-z C z O 4-n D n ; wherein the definitions of A, B, C, D, a, x, y, z and n are as in the first aspect of the application.

[0177] In any embodiment, in the step of preparing the slurry, a lithium source, a phosphorus source, an optional source of element A, an optional source of element C, an optional source of element D, a carbon source, a source of carbon layer doping elements, a solvent and the manganese salt doped with element B are added into a reaction vessel to grind and mix to obtain a slurry; the other steps are the same as above; and the positive electrode active material is obtained;

[0178] The positive electrode active material comprises a core and a shell covering the core, the core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , and the shell comprises doped carbon, the doping elements in the doped carbon comprising one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine; wherein the definitions of A, B, C, D, a, x, y, z and n are as in the first aspect of the application.

[0179] In any embodiment, the method further comprises the step of:

[0180] coating the mixture of one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer on the surface of the inner core by dry coating or wet coating to obtain the positive electrode active material;

[0181] The positive electrode active material comprises an inner core and a shell coating the inner core, the inner core is Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the shell comprises one or more coating layers, each coating layer independently comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer; wherein the definitions of A, B, C, D, a, x, y, z and n are as in the first aspect of the application; optionally, the polymer comprises one or more selected from polysiloxane, polysaccharide and polysaccharide derivative.

[0182] In any embodiment, the method further comprises the step of:

[0183] providing a pyrophosphate M b (P2O7) c powder, a suspension liquid comprising a phosphate X m (PO4) q and / or an oxide M' d O e , wherein the suspension liquid further comprises a source of carbon and / or a source of doped carbon;

[0184] adding the inner core, the pyrophosphate M b (P2O7) c powder into the suspension liquid and mixing, to obtain the positive electrode active material by sintering; wherein,

[0185] The positive electrode active material comprises an inner core and a shell coating the inner core, the shell comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer, the inner core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the first coating layer comprises a pyrophosphate M b (P2O7) c and one or more selected from a phosphate X m (PO4) q and an oxide M'd O e one or more of carbon and doped carbon, optionally, the doping element in the doped carbon comprises one or more of nitrogen, phosphorus, sulfur, boron and fluorine, wherein A, B, C, D, a, x, y, z and n are defined as in the first aspect of the present application, M, X, M', b, c, d, e, m, q are defined as in the first aspect of the present application.

[0186] In any embodiment, the method further comprises the steps of:

[0187] providing a pyrophosphate MP2O7 powder, a phosphate XPO4 suspension comprising a source of carbon;

[0188] adding the core, the pyrophosphate MP2O7 powder into the XPO4 suspension comprising a source of carbon and mixing, obtaining the positive electrode active material by sintering; wherein,

[0189] the positive electrode active material comprises a core and a shell coating the core, the shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer, the core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, the second coating layer comprises carbon, wherein A, B, C, D, a, x, y, z and n are defined as in the first aspect of the present application, M and X are defined as in the first aspect of the present application.

[0190] In any embodiment, the method further comprises the steps of:

[0191] respectively providing a pyrophosphate M b (P2O7) c suspension, a suspension comprising one or more of phosphate X m (PO4) q , oxide M' d O e and boride and a suspension comprising a source of carbon and / or a source of doped carbon;

[0192] mixing the core with all the suspensions above, sintering, obtaining the positive electrode active material; wherein,

[0193] the positive electrode active material comprises a core and a shell coating the core,

[0194] the core comprises Li a Mn 1-y By P 1-z C z O4, the shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, the first coating layer includes pyrophosphate M b (P2O7) c The second coating layer includes a phosphate selected from X m (PO4) q , oxide M′ d O e and one or more of borides, and the third coating layer is selected from one or more of carbon and doped carbon, wherein A, B, C, D, a, x, y, z and n are defined as in the first aspect of the present application, and M, X, M′, b, c, d, e, m, q are defined as in the first aspect of the present application.

[0195] In any embodiment, the method further comprises the steps of:

[0196] Provide Li f QP2O7 and / or Q g (P2O7) h and XPO4 suspension, adding the core into the suspension and mixing, and sintering to obtain the positive electrode active material; wherein,

[0197] The positive electrode active material includes a core and a shell covering the core, and the core includes Li a A x Mn 1-y B y P 1-z C z O 4-n D n The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, wherein the first coating layer includes pyrophosphate Li f QP2O7 and / or Q g (P2O7) h , the second coating layer includes phosphate XPO4, and the third coating layer includes carbon, wherein A, B, C, D, a, x, y, z and n are defined as in the first aspect of the present application, and Q, X, f, g and h are defined as in the first aspect of the present application.

[0198] In any embodiment, the method further comprises the steps of:

[0199] The first coating step: dissolving the source of element Q, phosphorus source and acid and optionally lithium source in a solvent to obtain a coating containing Li f QP2O7 and / or Q g (P2O7) ha first coating layer suspension; mixing the core with the first coating layer suspension, drying, and sintering to obtain a material coated with the first coating layer;

[0200] a second coating step: dissolving a source of element X, a phosphorus source, and an acid in a solvent to obtain a second coating layer suspension containing XPO4; mixing the material coated with the first coating layer obtained in the first coating step with the second coating layer suspension, drying, and sintering to obtain a material coated with two coating layers;

[0201] a third coating step: dissolving a carbon source in a solvent to obtain a third coating layer solution; then adding the material coated with two coating layers obtained in the second coating step into the third coating layer solution, mixing uniformly, drying, and then sintering to obtain a material coated with three coating layers, i.e., a positive electrode active material.

[0202] In any of the embodiments, the method further comprises the following steps:

[0203] respectively providing pyrophosphate M b (P2O7) c powder, one or more powders selected from phosphate X m (PO4) q , oxide M' d O e and boride, and a carbon source powder and / or a carbon-doped source powder;

[0204] mixing and grinding the core with all the powders described above, drying to obtain a positive electrode active material; wherein,

[0205] the positive electrode active material comprises a core and a shell coating the core,

[0206] the core comprises Li a Mn 1-y B y P 1-z C z O4, the shell comprises a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, the first coating layer comprises pyrophosphate M b (P2O7) c , the second coating layer comprises one or more selected from phosphate X m (PO4) q , oxide M' d O e and boride, and the third coating layer is selected from one or more of carbon and carbon-doped carbon, wherein A, B, C, D, a, x, y, z and n and M, X, M', b, c, d, e, m, q are defined as in the first aspect of the application;

[0207] Optionally, the drying is performed by a spray granulation dryer.

[0208] In any embodiment, the method further comprises the step of:

[0209] providing a polymer, the polymer comprising one or more selected from the group consisting of polysiloxane, polysaccharide, and polysaccharide derivative;

[0210] coating the positive active material with the polymer by dry coating or wet coating to obtain a material comprising a core and a shell coating the core;

[0211] one or more coating layers of the shell that are furthest from the core each independently comprise one or more selected from the group consisting of polysiloxane, polysaccharide, and polysaccharide derivative.

[0212] In any embodiment, the source of element A is selected from at least one of elemental A, oxide, phosphate, oxalate, carbonate, and sulfate of element A; and / or,

[0213] the source of element B is selected from at least one of elemental B, oxide, phosphate, oxalate, carbonate, halide, nitrate, organic acid salt, hydroxide, and sulfate of element B, optionally at least one of elemental B, oxide, phosphate, oxalate, carbonate, and sulfate of element B, optionally at least one of elemental B, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide of element B, optionally at least one of elemental B, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element B; and / or,

[0214] the source of element C is selected from at least one of elemental C, halide, organic acid salt, oxide, hydroxide, inorganic acid, organic acid, sulfate, borate, nitrate, and silicate of element C, optionally at least one of sulfate, borate, nitrate, and silicate of element C, optionally at least one of elemental C, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid of element C, optionally at least one of inorganic acid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element C; and / or,

[0215] the source of element D is selected from at least one of elemental D and ammonium salt of element D.

[0216] In any embodiment, in the step of preparing the manganese salt doped with element B,

[0217] the stirring is performed at a temperature in the range of 20-120 °C, optionally in the range of 25-80 °C or 40-120 °C, further optionally in the range of 60-120 °C, and / or,

[0218] The grinding and mixing is performed at a stirring rate of 200-800 rpm, optionally 400-700 rpm, for 1-9 hours, more optionally 500-700 rpm for 60-420 minutes, further optionally 3-7 hours or 120-360 minutes.

[0219] In any embodiment, in the step of preparing the slurry, the grinding and mixing is performed for 1-15 hours, optionally 8-15 hours; and the mixing is performed at a temperature of 20-120°C, more optionally 40-120°C, for 1-10 hours.

[0220] In any embodiment, in the step of preparing the core, the sintering is performed at a temperature in the range of 600-900°C for 6-14 hours.

[0221] In any embodiment, in the step of preparing the slurry, the carbon source is added to the reaction vessel for the grinding and mixing.

[0222] In any embodiment, the MP2O7 powder is prepared by the following method:

[0223] The source of element M and the source of phosphorus are added to a solvent to obtain a mixture, the pH of the mixture is adjusted to 4-6, and the mixture is stirred and reacted sufficiently, and then dried and sintered to obtain, wherein M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.

[0224] In any embodiment, in the method of preparing the MP2O7 powder,

[0225] The drying step is performed at a temperature of 100-300°C, optionally 150-200°C, for 4-8 hours.

[0226] In any embodiment, in the method of preparing the MP2O7 powder,

[0227] The sintering step is performed at a temperature of 500-800°C, optionally 650-800°C, under an inert gas atmosphere, for 4-10 hours.

[0228] In any embodiment, in the coating step, the sintering temperature is 500-800°C, and the sintering time is 4-10 hours.

[0229] In any embodiment, in the first coating step,

[0230] The pH of the solution in which the source of element Q, the source of phosphorus and the acid, and optionally the source of lithium, are dissolved is controlled to be 3.5-6.5, and then stirred and reacted for 1-5 hours, and then the solution is heated to a temperature of 50-120°C and maintained at this temperature for 2-10 hours, and / or,

[0231] sintering is performed at 650-800°C for 2-6 hours.

[0232] In any embodiment, the second coating step is performed at a temperature of 20- 60°C.

[0233] After dissolving the source of element X, the phosphorus source and the acid in a solvent, the solution is stirred and reacted for 1-10h, then the solution is warmed to 60-150°C and kept at this temperature for 2-10h, and / or,

[0234] sintering is performed at 500-700°C for 6-10 hours.

[0235] In any embodiment, the sintering in the third coating step is performed at 700- 800°C for 6-10 hours.

[0236] A third aspect of the present application provides a positive electrode tab, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a first positive electrode active material, the first positive electrode active material being the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application; optionally, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, more optionally 95-99.5% by weight, based on the total weight of the positive electrode film layer.

[0237] In any embodiment, the positive electrode tab further comprises a second positive electrode active material, and the second positive electrode active material is different from the first positive electrode active material.

[0238] In any embodiment, the second positive electrode active material comprises LiE t Co s F (1-t-s) O2, spinel lithium manganate and spinel lithium titanate, wherein E comprises one or more elements selected from Group VIII, F comprises one or more elements selected from Group IIIA and VIIB, t is selected from the range of 0 to 0.9, and the sum of t and s is selected from the range of 0.3 to 1.

[0239] In any embodiment, E comprises one or more elements selected from Ni, Fe, Ru and Rh, and F comprises one or more elements selected from Mn, Al, Ga and In.

[0240] In any embodiment, the second positive electrode active material is selected from LiNi t Co s Mn (1-t-s) O2, LiNi t Co s Al (1-t-s)one or more of O2, LiCoO2, spinel lithium manganate and spinel lithium titanate; wherein t is independently selected from 0.3-0.9, optionally 0.33-0.8, the sum of t and s is independently selected from 0.3-0.9, optionally 0.66-0.9.

[0241] In any embodiment, the mass ratio of the first active material to the second active material is 1:7-7:1, optionally 1:4-4:1.

[0242] In any embodiment, the second positive active material has a mass ratio of LiNi

[0243] LiNi t Co s Mn (1-t-s) O2, t, (1-t-s) and s are in a ratio of 5:2:3 or 3:1:1 or 8:1:1; and / or,

[0244] LiNi t Co s Al (1-t-s) O2, t, s and (1-t-s) are in a ratio of 5:2:3 or 3:1:1 or 8:1:1.

[0245] In any embodiment, the sum of the mass of the first positive active material and the second positive active material accounts for 88%-98.7% of the mass of the positive electrode sheet.

[0246] A fourth aspect of the present application provides a secondary battery comprising the positive electrode material of the first aspect of the present application or the positive active material prepared by the method of the second aspect of the present application or the positive electrode sheet of the third aspect of the present application.

[0247] A fifth aspect of the present application provides a battery module comprising the secondary battery of the fourth aspect of the present application.

[0248] A sixth aspect of the present application provides a battery pack comprising the battery module of the fifth aspect of the present application.

[0249] A seventh aspect of the present application provides an electric device comprising at least one selected from the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application and the battery pack of the sixth aspect of the present application.

[0250] 1. A positive active material having a chemical formula Li a A x Mn 1-y B y P 1-z C z O 4-n D n ,

[0251] wherein A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W,

[0252] B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge,

[0253] C comprises one or more elements selected from the group consisting of B (boron), S, Si and N,

[0254] D comprises one or more elements selected from the group consisting of S, F, Cl and Br,

[0255] a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the positive electrode active material is electrically neutral.

[0256] 2. The positive electrode active material according to item 1, wherein A, C and D are each independently any one element within the respective ranges described above, and B is at least two elements within the range thereof;

[0257] Optionally,

[0258] A is any one element selected from the group consisting of Mg and Nb, and / or,

[0259] B is at least two elements selected from the group consisting of Fe, Ti, V, Co and Mg, optionally Fe and one or more elements selected from the group consisting of Ti, V, Co and Mg, and / or,

[0260] C is S, and / or,

[0261] D is F.

[0262] 3. The positive electrode active material according to item 1 or 2, wherein x is selected from the range of 0.001 to 0.005; and / or, y is selected from the range of 0.01 to 0.5, optionally from the range of 0.25 to 0.5; and / or, z is selected from the range of 0.001 to 0.005; and / or, n is selected from the range of 0.001 to 0.005.

[0263] 4. The positive electrode active material according to any one of items 1 to 3, wherein (1-y):y is in the range of 1 to 4, optionally in the range of 1.5 to 3, and a:x is in the range of 9 to 1100, optionally in the range of 190 to 998.

[0264] 5. The positive electrode active material according to any one of items 1 to 4, wherein the lattice change rate thereof is 8% or less, optionally 4% or less.

[0265] 6. The positive electrode active material according to any one of items 1 to 5, wherein the Li / Mn anti-site defect concentration thereof is 2% or less, optionally 0.5% or less.

[0266] 7. The positive electrode active material according to any one of items 1 to 6, wherein the surface oxygen valence state thereof is -1.82 or less, optionally -1.89 to -1.98.

[0267] 8. The positive electrode active material according to any one of items 1 to 7, wherein the tap density thereof at 3T is 2.0 g / cm3 or more, optionally 2.2 g / cm3 or more. 3 3

[0268] 9. The positive electrode active material according to any one of items 1 to 8, wherein the surface thereof is coated with carbon.

[0269] 10. A method of producing a positive electrode active material, comprising the steps of:

[0270] (1) dissolving and stirring a manganese source, a source of element B, and an acid in a solvent to produce a suspension of a manganese salt doped with element B, filtering the suspension, and drying the filter cake to obtain a manganese salt doped with element B;

[0271] (2) adding a lithium source, a phosphorus source, a source of element A, a source of element C, a source of element D, a solvent, and the manganese salt doped with element B obtained in step (1) into a reaction vessel, grinding and mixing to produce a slurry;

[0272] (3) transferring the slurry obtained in step (2) to a spray-drying apparatus to perform spray-drying granulation to obtain granules;

[0273] (4) sintering the granules obtained in step (3) to obtain a positive electrode active material.

[0274] 11. The method according to item 10, wherein the source of element A is selected from at least one of an elemental substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element A, the source of element B is selected from at least one of an elemental substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element B, the source of element C is selected from at least one of a sulfate, a borate, a nitrate, and a silicate of element C, and the source of element D is selected from at least one of an elemental substance and an ammonium salt of element D.

[0275] 12. The method according to item 10 or 11, wherein the stirring of step (1) is performed at a temperature in the range of 60 to 120°C, and / or,

[0276] the stirring of step (1) is performed at a stirring rate in the range of 200 to 800 rpm.

[0277] ​​13. The method of any one of items 10 to 12, wherein the milling and mixing of step (2) is performed for 8-15 hours.

[0278] 14. The method of any one of items 10 to 13, wherein the sintering of step (4) is performed at a temperature range of 600-900 °C for 6-14 hours.

[0279] 15. The method of any one of items 10 to 14, wherein in step (2) further comprises adding a carbon source to the reaction vessel together with the milling and mixing.

[0280] 16. A positive electrode tab comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of any one of items 1-9 or the positive electrode active material prepared by the method of any one of items 10-15, and the content of the positive electrode active material in the positive electrode film layer is 10 wt% or more, optionally 95-99.5 wt%, based on the total weight of the positive electrode film layer.

[0281] 17. A secondary battery comprising the positive electrode active material of any one of items 1-8 or the positive electrode active material prepared by the method of any one of items 10-15 or the positive electrode tab of item 16.

[0282] 18. A battery module comprising the secondary battery of item 17.

[0283] 19. A battery pack comprising the battery module of item 18.

[0284] 20. An electric device comprising at least one selected from the secondary battery of item 17, the battery module of item 18, and the battery pack of item 19.

[0285] 1) A positive electrode active material having a core-shell structure comprising an inner core and a shell coating the inner core,

[0286] the inner core comprising Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, optionally one or more of Fe, Ti, V, Ni, Co, and Mg, R is selected from one or more of B, Si, N, and S;

[0287] The shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer,

[0288] wherein the first coating layer comprises a pyrophosphate MP2O7 and a phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0289] The second coating layer comprises carbon.

[0290] 2) The positive electrode active material according to item 1), wherein,

[0291] The interplanar spacing of the phosphate of the first coating layer is 0.345-0.358 nm, and the included angle of the crystal direction (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate of the first coating layer is 0.293-0.326 nm, and the included angle of the crystal direction (111) is 26.41°-32.57°.

[0292] 3) The positive electrode active material according to item 1) or 2), wherein,

[0293] In the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1.

[0294] 4) The positive electrode active material according to any one of items 1) to 3), wherein,

[0295] In the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249.

[0296] 5) The positive electrode active material according to any one of items 1) to 4), wherein,

[0297] The coating amount of the first coating layer is greater than 0 wt% and less than or equal to 7 wt%, optionally 4-5.6 wt%, based on the weight of the core.

[0298] 6) The positive electrode active material according to any one of items 1) to 5), wherein,

[0299] The weight ratio of the pyrophosphate and the phosphate in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.

[0300] 7) The positive electrode active material according to any one of items 1) to 6), wherein,

[0301] The crystallinity of the pyrophosphate and the phosphate is each independently 10% to 100%, optionally 50% to 100%.

[0302] 8) The positive electrode active material according to any one of items 1) to 7), wherein,

[0303] The second coating layer has a coating amount of greater than 0 wt% and less than or equal to 6 wt%, optionally 3-5 wt%, based on the weight of the core.

[0304] 9) The positive electrode active material according to any one of 1) to 8), wherein,

[0305] A is selected from at least two of Fe, Ti, V, Ni, Co and Mg.

[0306] 10) The positive electrode active material according to any one of 1) to 9), wherein,

[0307] The positive electrode active material has a Li / Mn antisite defect concentration of 4% or less, optionally 2% or less.

[0308] 11) The positive electrode active material according to any one of 1) to 10), wherein,

[0309] The positive electrode active material has a lattice change rate of 6% or less, optionally 4% or less.

[0310] 12) The positive electrode active material according to any one of 1) to 11), wherein,

[0311] The positive electrode active material has a surface oxygen valence state of -1.88 or less, optionally -1.98 to -1.88.

[0312] 13) The positive electrode active material according to any one of 1) to 12), wherein,

[0313] The positive electrode active material has a compaction density of 2.0 g / cm 3 or less at 3 tons, optionally 2.2 g / cm 3 or less.

[0314] 14) A method of preparing a positive electrode active material, comprising the steps of:

[0315] providing a core material: the core comprises Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S;

[0316] Coating step: providing MP2O7 powder and XPO4 suspension containing a source of carbon, mixing the core material, MP2O7 powder into the XPO4 suspension containing a source of carbon and mixing, obtaining the positive active material via sintering, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0317] wherein the positive active material has a core-shell structure comprising a core and a shell coating the core, the shell comprising a first coating layer coating the core and a second coating layer coating the first coating layer, the first coating layer comprising pyrophosphate MP2O7 and phosphate XPO4, the second coating layer comprising carbon.

[0318] 15) The method of preparing the positive active material of item 14), the step of providing the core material comprising the steps of:

[0319] Step (1): mixing a source of manganese, a source of element A and an acid in a container and stirring to obtain manganese salt particles doped with element A;

[0320] Step (2): mixing the manganese salt particles doped with element A with a source of lithium, a source of phosphorus and a source of element R in a solvent and obtaining a slurry, sintering under inert gas atmosphere to obtain lithium manganese phosphate doped with element A and element R, wherein the lithium manganese phosphate doped with element A and element R is Li 1+x Mn 1-y A y P 1-z R z O4, wherein x = -0.100-0.100, y = 0.001-0.500, z = 0.001-0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, R is selected from one or more of B, Si, N and S.

[0321] 16) The method of item 15), wherein,

[0322] Step (1) is performed at a temperature of 20-120 °C, optionally 25-80 °C; and / or,

[0323] The stirring in step (1) is performed at 500-700 rpm for 60-420 minutes, optionally 120-360 minutes.

[0324] 17) The method of any one of items 15) to 16), wherein,

[0325] the source of element A is selected from one or more of an elemental form, a sulfate, a halide, a nitrate, an organic acid salt, an oxide, or a hydroxide of element A; and / or, the source of element R is selected from one or more of an elemental form, a sulfate, a halide, a nitrate, an organic acid salt, an oxide, or a hydroxide of element R, and an inorganic acid of element R.

[0326] 18) The method of any one of 14) to 17), wherein,

[0327] The MP2O7 powder is prepared by the following method:

[0328] adding a source of element M and a source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to be 4-6, stirring and reacting sufficiently, and then drying, sintering to obtain, wherein M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0329] 19) The method of 18), wherein,

[0330] The drying step is drying at 100-300°C, optionally 150-200°C, for 4-8h.

[0331] 20) The method of any one of 18) to 19), wherein,

[0332] The sintering step is sintering at 500-800°C, optionally 650-800°C, under an inert gas atmosphere for 4-10h.

[0333] 21) The method of any one of 14) to 20), wherein,

[0334] The sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10h.

[0335] 22) A positive electrode tab comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of any one of 1) to 13) or prepared by the method of any one of 14) to 21), and the content of the positive electrode active material in the positive electrode film layer is 10% by weight or more based on the total weight of the positive electrode film layer.

[0336] 23) The positive electrode tab of 22), wherein the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight based on the total weight of the positive electrode film layer.

[0337] 24) A secondary battery comprising the positive electrode active material of any one of 1) to 13) or prepared by the method of any one of 14) to 21), or the positive electrode tab of 22) or 23).

[0338] 25) A battery module comprising the secondary battery of item 24).

[0339] 26) A battery pack comprising the battery module of item 25).

[0340] 27) An electric device comprising at least one selected from the secondary battery of item 24), the battery module of item 25), and the battery pack of item 26).

[0341] (1). A positive electrode active material having a core-shell structure, comprising a core and a shell covering the core,

[0342] the chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any numerical value within the range of -0.100-0.100, y is any numerical value within the range of 0.001-0.500, z is any numerical value within the range of 0.001-0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, which can be optionally one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, and R is one or more elements selected from B, Si, N, and S, which can be optionally one element selected from B, Si, N, and S.

[0343] the values of x, y, and z satisfy the following condition: maintaining the entire core electrically neutral;

[0344] the shell comprises a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, wherein

[0345] the first coating layer comprises a crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c wherein 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values of a, b, and c satisfy the following condition: maintaining the crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c electrically neutral,

[0346] the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) ceach M in the formula (1) is independently one or more elements selected from the group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al,

[0347] the second coating layer includes a crystalline phosphate XPO4, wherein X is one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al;

[0348] the third coating layer is carbon.

[0349] (2) The positive electrode active material having a core-shell structure according to item (1), wherein

[0350] the first coating layer has a crystalline pyrophosphate with an interplanar spacing ranging from 0.293 nm to 0.470 nm and an angle of 18.00° to 32.00° with respect to the (111) direction; and the second coating layer has a crystalline phosphate with an interplanar spacing ranging from 0.244 nm to 0.425 nm and an angle of 20.00° to 37.00° with respect to the (111) direction.

[0351] (3) The positive electrode active material having a core-shell structure according to item (1) or (2), wherein, in the inner core, the ratio of y to 1-y is 1:10 to 1:1, and optionally 1:4 to 1:1.

[0352] (4) The positive electrode active material having a core-shell structure according to any one of items (1) to (4), wherein, in the inner core, the ratio of z to 1-z is 1:9 to 1:999, and optionally 1:499 to 1:249.

[0353] (5) The positive electrode active material having a core-shell structure according to any one of items (1) to (4), wherein the carbon of the third coating layer is a mixture of SP2 form carbon and SP3 form carbon, and optionally, the molar ratio of SP2 form carbon to SP3 form carbon is any value in the range of 0.1 to 10, and optionally any value in the range of 2.0 to 3.0.

[0354] (6) The positive electrode active material having a core-shell structure according to any one of items (1) to (5), wherein

[0355] the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, and optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally greater than 0 and less than or equal to 2% by weight, based on the weight of the inner core; and / or

[0356] the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, and optionally greater than 0 and less than or equal to 5.5% by weight, and more optionally 2% to 4% by weight, based on the weight of the inner core; and / or

[0357] The amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally greater than 0 and less than or equal to 5.5% by weight, more optionally greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

[0358] (7) The positive electrode active material having a core-shell structure according to any one of (1) to (6), wherein the thickness of the first coating layer is 1 to 10 nm; and / or

[0359] the thickness of the second coating layer is 2 to 15 nm; and / or

[0360] the thickness of the third coating layer is 2 to 25 nm.

[0361] (8) The positive electrode active material having a core-shell structure according to any one of (1) to (7), wherein,

[0362] the content of manganese element is in the range of 10% to 35% by weight, optionally in the range of 15% to 30% by weight, more optionally in the range of 17% to 20% by weight, and the content of phosphorus element is in the range of 12% to 25% by weight, optionally in the range of 15% to 20% by weight, based on the weight of the positive electrode active material, and the weight ratio of manganese element to phosphorus element is in the range of 0.90 to 1.25, optionally in the range of 0.95 to 1.20.

[0363] (9) The positive electrode active material having a core-shell structure according to any one of (1) to (8), wherein the lattice change rate of the positive electrode active material having a core-shell structure before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, more optionally in the range of 2.0 to 3.8%.

[0364] (10) The positive electrode active material having a core-shell structure according to any one of (1) to (9), wherein the Li / Mn antisite defect concentration of the positive electrode active material having a core-shell structure is 4% or less, optionally 2.2% or less, more optionally in the range of 1.5 to 2.2%.

[0365] (11) The positive electrode active material having a core-shell structure according to any one of (1) to (10), wherein the tap density of the positive electrode active material having a core-shell structure at 3T is 2.2 g / cm 3 or more and 2.8 g / cm 3 or more and 2.8 g / cm 3 or more.

[0366] (12) The positive electrode active material having a core-shell structure according to any one of (1) to (11), wherein the surface oxygen valence state of the positive electrode active material having a core-shell structure is -1.90 or less, optionally in the range of -1.90 to -1.98.

[0367] (13) A method for preparing a positive electrode active material, comprising the steps of:

[0368] providing a core material having a chemical formula of Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any number in a range of -0.100-0.100, y is any number in a range of 0.001-0.500, z is any number in a range of 0.001-0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, which can be one or more elements selected from Fe, Ti, V, Ni, Co and Mg, R is one or more elements selected from B, Si, N and S, which can be one element selected from B, Si, N and S;

[0369] coating the core material with a suspension of Li a MP2O7and / or M b (P2O7) c PO4, wherein 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values of a, b and c satisfy the following conditions: the crystalline pyrophosphate Li a MP2O7or M b (P2O7) c PO4 remains electrically neutral; each M is independently one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; and X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;

[0370] wherein the positive electrode active material has a core-shell structure comprising a core and a shell coating the core, the shell comprising a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, the first coating layer comprising a crystalline pyrophosphate Li a MP2O7and / or M b (P2O7) c PO4, the second coating layer comprising a crystalline phosphate XPO4, and the third coating layer being carbon.

[0371] (14) The method for preparing a positive electrode active material of item (13), wherein the step of providing a core material comprises the steps of:

[0372] Step (1): mixing and stirring a manganese source, a dopant of element A, and an acid in a container to obtain manganese salt particles doped with element A;

[0373] Step (2): mixing the manganese salt particles doped with element A, a lithium source, a phosphorus source, and a dopant of element R in a solvent to obtain a slurry, and sintering under protection of an inert gas atmosphere to obtain a core doped with elements A and R, wherein the core doped with elements A and R is Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100-0.100, y is any value in the range of 0.001-0.500, z is any value in the range of 0.001-0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, which can be one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, and R is one or more elements selected from B, Si, N, and S, which can be one element selected from B, Si, N, and S.

[0374] (15) The method for preparing the positive electrode active material of item (14), wherein,

[0375] Step (1) is performed at a temperature of 20-120°C, which can be 40-120°C; and / or

[0376] The stirring in step (1) is performed at 400-700 rpm for 1-9 h, which can be 3-7 h.

[0377] (16) The method for preparing the positive electrode active material of item (14), wherein step (2) is performed at a temperature of 20-120°C, which can be 40-120°C, and mixing is performed for 1-10 h.

[0378] (17) The method for preparing the positive electrode active material of any one of items (14)-(16), wherein,

[0379] The dopant of element A is one or more of the simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or,

[0380] The dopant of element R is one or more of inorganic acids, organic acids, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements selected from B, Si, N, and S.

[0381] (18) The method for preparing a positive electrode active material according to any one of (13) to (17), wherein the coating step comprises:

[0382] First coating step: dissolving a source of element M, a phosphorus source, an acid, and optionally a lithium source in a solvent to obtain a first coating layer suspension; thoroughly mixing the core obtained in the core step with the first coating layer suspension obtained in the first coating step, drying, and then sintering to obtain a material coated with the first coating layer;

[0383] Second coating step: dissolving the source of element X, the phosphorus source and the acid in a solvent to obtain a second coating layer suspension; fully mixing the first coating layer material obtained in the first coating step with the second coating layer suspension obtained in the second coating step, drying, and then sintering to obtain a material coated with two coating layers;

[0384] The third coating step: dissolving the carbon source in a solvent and fully dissolving it to obtain a third coating layer solution; then adding the material coated with two coating layers obtained in the second coating step to the third coating layer solution, mixing them evenly, drying, and then sintering to obtain a material coated with three coating layers, i.e., the positive electrode active material.

[0385] (19) The method for preparing a positive electrode active material according to item (18), wherein:

[0386] In the first coating step, the pH of the solution containing the source of element M, the phosphorus source, the acid, and optionally the lithium source is controlled to be 3.5-6.5, and then stirred and reacted for 1-5 hours, and then the solution is heated to 50-120° C. and maintained at this temperature for 2-10 hours, and / or,

[0387] Sintering is carried out at 650-800°C for 2-6 hours.

[0388] (20) The method for preparing a positive electrode active material according to any one of (18) to (19), wherein:

[0389] In the second coating step, the source of element X, the phosphorus source and the acid are dissolved in a solvent, stirred and reacted for 1-10 hours, and then the solution is heated to 60-150° C. and maintained at this temperature for 2-10 hours, and / or,

[0390] Sintering is carried out at 500-700°C for 6-10 hours.

[0391] (21) The method for producing the positive electrode active material according to any one of (18) to (20), wherein the sintering in the third coating step is performed at 700 to 800°C for 6 to 10 hours.

[0392] (22) A positive electrode tab comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material having a core-shell structure according to any one of (1) to (12) or produced by the method for producing the positive electrode active material according to any one of (13) to (21), and the content of the positive electrode active material in the positive electrode film layer is 90 to 99.5% by weight, optionally 95 to 99.5% by weight, based on the total weight of the positive electrode film layer.

[0393] (23) A secondary battery comprising the positive electrode active material having a core-shell structure according to any one of (1) to (12) or produced by the method for producing the positive electrode active material according to any one of (13) to (21) or the positive electrode tab according to (22).

[0394] (24) A battery module comprising the secondary battery according to (23).

[0395] (25) A battery pack comprising the battery module according to (24).

[0396] (26) An electric device comprising at least one selected from the secondary battery according to (23), the battery module according to (24), and the battery pack according to (25). BRIEF DESCRIPTION OF DRAWINGS

[0397] Figure 1 is a schematic view of the positive electrode active material having a core-shell structure with two coating layers in one embodiment of the present application.

[0398] Figure 2 is an X-ray diffraction (XRD) pattern of the positive electrode active material prepared in Example I-2 and undoped LiMnPO4.

[0399] Figure 3 is a schematic view of the positive electrode active material having a core-shell structure with three coating layers in one embodiment of the present application.

[0400] Figure 4 is a schematic view of the secondary battery in one embodiment of the present application.

[0401] Figure 5 is an exploded view of the secondary battery in one embodiment of the present application. Figure 4

[0402] Figure 6 is a schematic view of the battery module in one embodiment of the present application.​

[0403] Figure 7 is a schematic view of a battery pack according to an embodiment of the present application.

[0404] Figure 8 is Figure 7 is an exploded view of a battery pack according to an embodiment of the present application.

[0405] Figure 9 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0406] Figure 10 is an EDS spectrum of a positive electrode active material prepared in Example I-2 of the present application.

[0407] Explanation of Reference Numerals:

[0408] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0409] Hereinafter, embodiments of a positive electrode active material and a method for manufacturing the same, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device according to the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters well known, repeated description of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0410] The ranges disclosed herein are meant to be inclusive of the endpoints and include the end values in the range. Ranges can be combined to form new ranges, e.g., a range of "60-120 and 80-110" is understood to include 60-110 and 80-120. Further, if a minimum range value is listed as 1 and a maximum range value is listed as 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, wherein both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0411] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0412] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0413] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0414] Unless otherwise specified, "including" and "comprising" mentioned in the present application means open-ended, and can also be closed-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0415] If not specifically stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0416] [Secondary battery]

[0417] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating active materials through charging after the battery is discharged.

[0418] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging of the battery, active ions (e.g., lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing the active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, and mainly functions to conduct the active ions.

[0419] [Positive active material]

[0420] One embodiment of the present application provides a positive active material including a compound represented by Formula (I),

[0421] Li a A x Mn 1-y B y P 1-z C z O 4-n D n

[0422] (I)

[0423] wherein,

[0424] A includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB, and Group VIB;

[0425] B includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB, and Group VIII;

[0426] C includes one or more elements selected from Group IIIA, Group IVA, Group VA, and Group VIA;

[0427] D includes one or more elements selected from Group VIA and Group VIIA;

[0428] a is selected from the range of 0.85 to 1.15;

[0429] x is selected from the range of 0 to 0.1 ;

[0430] y is selected from the range of 0.001 to 0.999;

[0431] z is selected from the range of 0 to 0.5;

[0432] n is selected from the range of 0 to 0.5.

[0433] Unless otherwise specified, in the above chemical formulae, when A is more than one element, the above limitation on the value range of x is not only a limitation on the stoichiometric number of each element as A, but also a limitation on the sum of the stoichiometric numbers of each element as A. For example, when A is more than one element A1, A2,..., An, the stoichiometric numbers x1, x2,..., xn of A1, A2,..., An respectively each need to fall within the value range of x limited by the present application, and the sum of x1, x2,..., xn also needs to fall within the value range. Similarly, for the case where B, C and D are more than one element, the limitation on the value range of the stoichiometric numbers of B, C and D in the present application also has the above meaning.

[0434] The positive electrode active material of the present application is obtained by element doping in the compound LiMnPO4, wherein A, B, C and D are respectively elements doped at the Li site, Mn site, P site and O site of the compound LiMnPO4. Without wishing to be bound by theory, it is believed that the performance improvement of lithium manganese phosphate is related to reducing the lattice change rate of lithium manganese phosphate during lithium deintercalation and reducing the surface activity. Reducing the lattice change rate can reduce the difference in lattice constant between the two phases at the grain boundary, reduce the interface stress, and enhance the Li +The transmission capacity at the interface is improved, thereby improving the rate performance of the positive active material. High surface activity is prone to cause serious interface side reactions, which aggravates gas production, electrolyte consumption and interface damage, thereby affecting the cycle performance of the battery. In the present application, Li and / or Mn site doping can reduce the lattice change rate. Mn site doping can also effectively reduce the surface activity, thereby inhibiting Mn dissolution and the interface side reaction between the positive active material and the electrolyte. P site doping makes the change rate of the Mn-O bond length faster, reduces the small polaron migration barrier of the material, thereby being beneficial to the electronic conductivity. O site doping has a good effect on reducing the interface side reaction. P site and / or O site doping also affects the Mn dissolution and the kinetic performance of the anti-site defects. Therefore, doping reduces the concentration of anti-site defects in the material, improves the kinetic performance and specific capacity of the material, and can also change the morphology of the particles, thereby improving the compaction density. The present applicant has unexpectedly found that by doping a specific element at the Mn site of the compound LiMnPO4 and optionally at the Li site, P site and / or O site in a specific amount, the rate performance can be significantly improved, the dissolution of Mn and the Mn site doping element can be significantly reduced, the cycle performance and / or high temperature stability can be significantly improved, and the specific capacity and compaction density of the material are also improved.

[0435] In some embodiments, A comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, Ga, In, Cd, V, Ta, Cr, Zn, Al, Na, K, Mg, Nb, Mo and W, and / or A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W; and / or,

[0436] B comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, In, Pb, Bi, Cd, Hf, Ta, Cr, Ru, Rh, Pd, Os, Ir, Pt, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and / or B comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; and / or, C comprises one or more elements selected from B (boron), S, Si and N; and / or, D comprises one or more elements selected from S, F, Cl and Br.

[0437] In some embodiments, A comprises any one element selected from Zn, Al, Na, K, Mg, Nb, Mo and W, and / or A comprises any one element selected from Mg and Nb; and / or,

[0438] B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, more optionally at least two elements selected from Fe, Ti, V, Ni, Co and Mg, further optionally at least two elements selected from Fe, Ti, V, Co and Mg, more further optionally Fe and one or more elements selected from Ti, V, Co and Mg; and / or,

[0439] C comprises any one element selected from B (boron), S, Si and N, optionally S; and / or,

[0440] D comprises any one element selected from S, F, Cl and Br, optionally F.

[0441] By selecting the doping elements for Li site within the above range, the lattice change rate during delithiation can be further reduced, thereby further improving the rate performance of the battery. By selecting the doping elements for Mn site within the above range, the electronic conductivity can be further improved and the lattice change rate can be further reduced, thereby improving the rate performance and gravimetric capacity of the battery. By selecting the doping elements for P site within the above range, the rate performance of the battery can be further improved. By selecting the doping elements for O site within the above range, the side reaction at the interface can be further reduced, thereby improving the high-temperature performance of the battery.

[0442] In some embodiments, a is selected from the range of 0.9 to 1.1, optionally from the range of 0.97 to 1.01; and / or,

[0443] x is selected from the range of 0.001 to 0.005; and / or,

[0444] y is selected from the range of 0.001 to 0.5, optionally from the range of 0.01 to 0.5, optionally from the range of 0.25 to 0.5; and / or,

[0445] z is selected from the range of 0.001 to 0.5, optionally from the range of 0.001 to 0.1, more optionally from the range of 0.001 to 0.005; and / or,

[0446] n is selected from the range of 0 to 0.1, optionally from the range of 0.001 to 0.005.

[0447] Alternatively, x is selected from the range of 0 to 0.005, optionally from the range of 0.001 to 0.1; and / or,

[0448] y is selected from the range of 0.001 to 0.5, optionally from the range of 0.01 to 0.5, optionally from the range of 0.25 to 0.5; and / or,

[0449] z is selected from the range of 0 to 0.5, optionally from the range of 0.001 to 0.5, optionally from the range of 0.001 to 0.1, more optionally from the range of 0.001 to 0.005; and / or,

[0450] n is selected from the range of 0 to 0.1, optionally from the range of 0.001 to 0.1.

[0451] By selecting the value of y within the above range, the gravimetric capacity and rate capability of the material can be further improved. By selecting the value of x within the above range, the kinetics of the material can be further improved. By selecting the value of z within the above range, the rate capability of the secondary battery can be further improved. By selecting the value of n within the above range, the high temperature performance of the secondary battery can be further improved.

[0452] In some embodiments, x is 0, z is selected from the range of 0.001 to 0.5, and n is selected from the range of 0.001 to 0.1; or,

[0453] x is selected from the range of 0.001 to 0.1, z is 0, and n is selected from the range of 0.001 to 0.1; or,

[0454] x is selected from the range of 0.001 to 0.1, z is selected from the range of 0.001 to 0.5, and n is 0; or,

[0455] x is 0, z is 0, and n is selected from the range of 0.001 to 0.1; or,

[0456] x is 0, z is selected from the range of 0.001 to 0.5, and n is 0; or,

[0457] x is selected from the range of 0.001 to 0.1, z is selected from the range of 0.001 to 0.5, and n is selected from the range of 0.001 to 0.1.

[0458] Thus, by doping specific elements at the Mn site of the compound LiMnPO4, and optionally at the Li site, P site, and / or O site, in specific amounts, and especially by doping specific elements at the Mn site and P site of the compound LiMnPO4, or at the Li site, Mn site, P site, and O site of the compound LiMnPO4, in specific amounts, the present application can significantly improve the rate capability, significantly reduce the dissolution of Mn and Mn site doping elements, significantly improve the cycle performance and / or high temperature stability, and significantly increase the gravimetric capacity and tap density of the material.

[0459] In some embodiments, y:z is selected from the range of 0.002 to 999, optionally from the range of 0.025 to 999 or 0.002 to 500, more optionally from the range of 0.2 to 600, for example 0.2, 0.25, 1, 2, 3, 4, 5, 6, 8, 10, 12, 13, 15, 17, 20, 70, 80, 84, 67, 91, 100, 134, 150, 182, 200, 250, 300, 320, 350, 400, 420, 450, 500, 600, 999 or a range between any two of the aforementioned values. In this way, the defects of the material can be reduced, the integrity of the framework structure of the material can be improved, the structural stability of the material can be effectively improved, and thus the cycle stability of the secondary battery can be improved.

[0460] In some embodiments, z:n is selected from the range of 0.002 to 500, optionally from the range of 0.2 to 100, more optionally from the range of 0.2 to 50, for example 0.2, 0.8, 1, 1.25, 4, 5, 50 or a range between any two of the aforementioned values. In this way, the defects of the material can be further reduced, the integrity of the framework structure of the material can be further improved, the structural stability of the material can be effectively improved, and the cycle stability of the secondary battery can be improved.

[0461] In some embodiments,

[0462] A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W;

[0463] B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge;

[0464] C comprises one or more elements selected from B (boron), S, Si and N;

[0465] D comprises one or more elements selected from S, F, Cl and Br;

[0466] a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, and n is selected from the range of 0.001 to 0.1.

[0467] In this way, by simultaneously doping specific elements at the Li site, Mn site, P site and O site of the compound LiMnPO4 in specific amounts, the application can obtain significantly improved rate performance, significantly reduce the dissolution of Mn and Mn site doping elements, obtain significantly improved cycle performance and / or high temperature stability, and the specific capacity and compaction density of the material can also be improved.

[0468] In some embodiments,

[0469] B comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Zn, Fe, Ti, V, Ni, Co and Mg;

[0470] C is one or more elements selected from B, Si, N and S;

[0471] a is selected from the range of 0.9 to 1.1, x is 0, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, and n is 0.

[0472] Thus, by simultaneously doping specific elements in the Mn site and P site of the compound LiMnPO4 in specific amounts, the present application can improve the rate capability, reduce the dissolution of Mn and Mn site doping elements, improve the cycle performance and / or high temperature stability, and increase the gram capacity and compaction density of the material.

[0473] The average particle size of the inner core prepared in the present application is in the range of 50-500nm, D v 50 is 200-300nm. The primary particle size of the inner core is in the range of 50-500nm, D v 50 is 200-300nm. Thus, the gram capacity of the secondary battery is improved, and the uniformity of the coating layer coated on the inner core is improved.

[0474] In the present application, the median particle size D v 50 refers to the particle size corresponding to the cumulative volume distribution percentage of 50% of the material. In the present application, the median particle size D v 50 can be measured by laser diffraction particle size analysis method. For example, refer to the standard GB / T19077-2016, and use a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.

[0475] By process control (e.g., sufficient mixing, grinding of materials from various sources), it can be ensured that the elements are uniformly distributed in the crystal lattice without aggregation. The main characteristic peak position in the XRD pattern of the lithium manganese phosphate doped with B element and C element is consistent with that of the undoped LiMnPO4, indicating that the doping process does not introduce impurity phases, and therefore, the improvement of the core performance is mainly from element doping, rather than caused by impurity phases. After the inventors of the present application prepared the positive electrode active material of the present application, the middle region of the prepared positive electrode active material particles was cut by a focused ion beam (FIB for short), and it was found by transmission electron microscopy (TEM for short) and X-ray energy spectrum analysis (EDS for short) that the elements were uniformly distributed and no aggregation occurred.

[0476] In some embodiments, the positive electrode active material comprises a core and a shell coating the core, the core comprising the compound of formula (I) described above;

[0477] The shell comprises one or more coating layers; the coating layer has ionic conductivity or electronic conductivity.

[0478] The present application provides a new type of positive electrode active material with core-shell structure by doping a specific amount of a specific element at the Mn site of the compound LiMnPO4 and optionally at the Li site, P site and / or O site to obtain a doped lithium manganese phosphate core, and setting a coating layer with ionic conductivity or electronic conductivity on the surface of the core. The application of the positive electrode active material in a secondary battery can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0479] In some embodiments, the shell comprises one coating layer;

[0480] Optionally, the coating layer comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0481] Thus, the present application uses the above-mentioned material to obtain a coating layer with ionic conductivity or electronic conductivity, thereby improving the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0482] In some embodiments, the shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer;

[0483] Optionally, the first coating layer and the second coating layer each independently comprise one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0484] Thus, the present application uses the above-mentioned material as the material of the coating layer, and sets two coating layers to further improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0485] In some embodiments, the first coating layer comprises one or more selected from pyrophosphate, phosphate, oxide and boride, and the second coating layer comprises one or more selected from carbon and doped carbon.

[0486] Thus, the present application employs the first coating layer of a specific material and the second coating layer of a specific material, which can further improve the rate performance, further reduce the dissolution of Mn and Mn-site doped elements, and thus improve the cycle performance and / or high-temperature stability of the secondary battery.

[0487] In some embodiments, the shell comprises a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer.

[0488] Optionally, the first coating layer, the second coating layer and the third coating layer each independently comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0489] Thus, the present application employs the above-mentioned materials as the material of the coating layer, and sets three coating layers, which can further reduce the dissolution of Mn and Mn-site doped elements, and further improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0490] In some embodiments, the first coating layer comprises pyrophosphate, the second coating layer comprises one or more selected from phosphate, oxide and boride, and the third coating layer comprises one or more selected from carbon and doped carbon.

[0491] Thus, the present application employs the first coating layer of a specific material, the second coating layer of a specific material and the third coating layer of a specific material, which further improves the rate performance, further reduces the dissolution of Mn and Mn-site doped elements, and thus improves the cycle performance and / or high-temperature stability of the secondary battery, and further improves the gravimetric capacity and the tap density of the material.

[0492] In some embodiments, one or more coating layers each independently comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride and polymer.

[0493] In some embodiments, the pyrophosphate is M b (P2O7) c ; and / or,

[0494] The phosphate is X m (PO4) q ; and / or,

[0495] The doping elements in the doped carbon include one or more selected from the group consisting of Group IIIA, Group VA, Group VIA and Group VIIA; and / or,

[0496] The oxide is M' d O e ; and / or,

[0497] The boride is Z v B w ; and / or,

[0498] The polymer includes one or more selected from the group consisting of polysaccharides and derivatives thereof, polysiloxanes;

[0499] wherein,

[0500] M, X and Z each independently include one or more elements selected from Group IA, Group IIA, Group IIIA, Group IB, Group IIB, Group IVB, Group VB, Group VIIB and Group VIII; b is selected from the range of 1 to 4, c is selected from the range of 1 to 6; m is selected from the range of 1 to 2, q is selected from the range of 1 to 4; M' includes one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide series elements and Sb, d is greater than 0 and less than or equal to 2, e is greater than 0 and less than or equal to 5; v is selected from the range of 1 to 7, w is selected from the range of 1 to 2.

[0501] Thus, by employing the above-mentioned material as a coating layer, the present application can further reduce the elution of Mn and Mn-site doping elements, further improve the specific capacity and tap density of the material, and further improve the rate performance, high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0502] In some embodiments, M, X and Z each independently include one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; and / or,

[0503] The doping elements in the doped carbon include one or more selected from the group consisting of nitrogen, phosphorus, sulfur, boron and fluorine; and / or,

[0504] M' includes one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, which can optionally include one or more elements selected from Mg, Al, Si, Zn, Zr and Sn; and / or,

[0505] The polysiloxane is selected from one or more of linear structure polysiloxane and cyclic structure polysiloxane; and / or,

[0506] The polysaccharide is selected from one or more of plant polysaccharide and marine polysaccharide.

[0507] Therefore, by using the above specific material as the coating layer, the dissolution of Mn and Mn site doped elements can be further reduced, and the high-temperature cycle performance and high-temperature storage performance of the secondary battery can be further improved.

[0508] In some embodiments, the positive active material comprises a core and a shell coating the core,

[0509] The core comprises Li a Mn 1-y B y P 1-z C z O4, wherein a is selected from the range of 0.9 to 1.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, Zn and Ge, and C comprises one or more elements selected from B (boron), S, Si and N;

[0510] The shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer,

[0511] The first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;

[0512] The second coating layer comprises carbon.

[0513] As Figure 1As shown, the lithium manganese phosphate cathode active material of the present application is a core-shell structure with two layers of coating, the inner core helps to reduce the lattice change rate of lithium manganese phosphate during the process of lithium extraction and insertion, improve the structural stability of lithium manganese phosphate cathode material, greatly reduce the dissolution of manganese and reduce the oxygen activity on the surface of the particles. The element C doped at the phosphorus site helps to change the difficulty of Mn-O bond length change, thereby reducing the lithium ion migration barrier, promoting lithium ion migration and improving the rate performance of the secondary battery. The first coating layer of the cathode active material of the present application includes pyrophosphate and phosphate. Since the migration barrier of transition metal in pyrophosphate is high (>1eV), it can effectively inhibit the dissolution of transition metal. And the phosphate has excellent lithium ion conductivity and can reduce the content of surface lithium. In addition, since the second coating layer is a carbon-containing layer, it can effectively improve the conductivity and desolvation ability of LiMnPO4. In addition, the "barrier" effect of the second coating layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the electrolyte to the active material. Therefore, by specific element doping and surface coating of lithium manganese phosphate, the present application can effectively inhibit the Mn dissolution during the process of lithium extraction and insertion, while promoting the migration of lithium ions, thereby improving the rate performance of the battery, and improving the cycle performance and high temperature performance of the secondary battery.

[0514] It should be noted that, as Figure 2 shown, by comparing the XRD spectra of LiMnPO4 before and after doping, it can be seen that the main characteristic peaks of the cathode active material of the present application are basically the same as those of LiMnPO4 before doping, indicating that the doped lithium manganese phosphate cathode active material has no impurity phase, and the improvement of the performance of the secondary battery is mainly due to the element doping, not the impurity phase.

[0515] In some embodiments, the cathode active material includes an inner core and a shell coating the inner core,

[0516] The inner core includes Li a Mn 1-y B y P 1-z C z O4, wherein a is selected from the range of 0.9 to 1.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, and C includes one or more elements selected from B (boron), S, Si and N;

[0517] The shell includes a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, wherein

[0518] The first coating layer includes pyrophosphate Lif QP2O7and / or Q g (P2O7) h wherein, 0≤f≤2, 1≤g≤4, 1≤h≤6, the pyrophosphate Li f QP2O7and / or Q g (P2O7) h Q in each of QP2O7and / or Q is independently one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;

[0519] The second coating layer comprises a crystalline phosphate XPO4, wherein X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al;

[0520] The third coating layer comprises carbon.

[0521] The positive electrode active material of the present application can improve the specific capacity, cycle performance and safety performance of the secondary battery. Although the mechanism is not clear, it is speculated that the lithium manganese phosphate positive electrode active material of the present application is a core-shell structure, wherein by doping element B and element C to the manganese site and the phosphorus site of the lithium manganese phosphate core respectively, not only can the manganese dissolution be effectively reduced, and then the manganese ions migrated to the negative electrode are reduced, the electrolyte consumed due to the decomposition of the SEI film is reduced, the cycle performance and safety performance of the secondary battery are improved, but also the Mn-O bond adjustment can be promoted, the lithium ion migration barrier is reduced, the lithium ion migration is promoted, and the rate performance of the secondary battery is improved; by coating the core with a first coating layer comprising a pyrophosphate, the migration resistance of manganese can be further increased, the dissolution thereof is reduced, and the surface lithium content is reduced, the contact between the core and the electrolyte is reduced, thereby reducing the interface side reaction, reducing the gas production, and improving the high-temperature storage performance, cycle performance and safety performance of the secondary battery; by further coating a phosphate coating layer with excellent lithium ion conductivity, the interface side reaction on the surface of the positive electrode active material can be effectively reduced, and the high-temperature cycle and storage performance of the secondary battery is improved; by further coating a carbon layer as a third coating layer, the safety performance and kinetic performance of the secondary battery can be further improved. In addition, in the core, the element B doped at the manganese site of the lithium manganese phosphate also helps to reduce the lattice change rate of the lithium manganese phosphate during the lithium extraction process, improve the structural stability of the lithium manganese phosphate positive material, greatly reduce the dissolution of manganese and reduce the oxygen activity on the surface of the particles; the element C doped at the phosphorus site also helps to change the difficulty of the Mn-O bond length change, thereby improving the electronic conductivity and reducing the lithium ion migration barrier, promoting the lithium ion migration, and improving the rate performance of the secondary battery.

[0522] Figure 3A schematic diagram of an ideal three-layer coated positive electrode active material. As shown, the innermost circle schematically represents the core, and the first, second, and third coating layers are sequentially arranged from the inside to the outside. This diagram represents an ideal state in which each layer is completely coated. In practice, each coating layer can be completely coated or partially coated.

[0523] In addition, the entire core system remains electrically neutral, which can ensure that defects and impurities in the positive electrode active material are as few as possible. If excess transition metals (e.g., manganese) are present in the positive electrode active material, the excess transition metals are likely to be precipitated in the form of an element or to form impurities in the crystal lattice due to the stable structure of the material system itself. Maintaining electrical neutrality can minimize such impurities. In addition, maintaining electrical neutrality can also generate lithium vacancies in the material in some cases, thereby making the material more excellent in dynamic performance.

[0524] In some embodiments, one or more coating layers of the shell that are farthest from the core each independently comprise one or more selected from polysiloxane, polysaccharide, and polysaccharide derivatives.

[0525] Thus, the uniformity of the coating can be improved, the interface side reactions caused by high voltage can be effectively blocked, and the high-temperature cycle performance and high-temperature storage performance of the material can be improved. In addition, the coating layer has good electronic conductivity and ionic conductivity, which helps to improve the capacity of the material and reduces the heat generation of the battery.

[0526] In some embodiments, the polysiloxane comprises a structural unit represented by formula (i),

[0527]

[0528] wherein R1and R2are independently selected from H, -COOH, -OH, -SH, -CN, -SCN, amino, phosphate, carboxylate, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon group, C1-C20 halogenated aliphatic hydrocarbon group, C1-C20 heteroaliphatic hydrocarbon group, C1-C20 halogenated heteroaliphatic hydrocarbon group, C6-C20 aromatic hydrocarbon group, C6-C20 halogenated aromatic hydrocarbon group, C2-C20 heteroaromatic hydrocarbon group, and C2-C20 halogenated heteroaromatic hydrocarbon group;

[0529] Optionally, R1and R2are independently selected from H, amino, phosphate, polyether segment, C1-C8 alkyl, C1-C8 halogenated alkyl, C1-C8 heteroalkyl, C1-C8 halogenated heteroalkyl, C2-C8 alkenyl, and C2-C8 halogenated alkenyl.

[0530] In some embodiments, the polysiloxane further comprises a capping group comprising at least one of the group consisting of polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 halo-heteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon group, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxylalkyl, amino, C1-C8 aminoalkyl, carboxyl, C1-C8 carboxyalkyl.

[0531] In some embodiments, the polysiloxane comprises one or more selected from the group consisting of polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxy-functionalized polysiloxane, epoxy-terminated polysiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, polymethylchloropropylsiloxane, hydroxyl-terminated polydimethylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, aminoethyl aminopropyl polydimethylsiloxane, end group polyether polydimethylsiloxane, side chain aminopropyl polysiloxane, aminopropyl terminated polydimethylsiloxane, side chain phosphate grafted polydimethylsiloxane, side chain polyether grafted polydimethylsiloxane, 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentadimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, cyclic polymethylvinylsiloxane, hexadecamethylcyclooctasiloxane, tetradecamethylcyclotetrasiloxane, and cyclic polydimethylsiloxane.

[0532] In some embodiments, the number average molecular weight of the polysiloxane, the polysaccharide, and the polysaccharide derivative is each independently 300,000 or less, optionally 10,000 to 200,000, more optionally 20,000 to 120,000, and further optionally 400 to 80,000.

[0533] In some embodiments, the mass percentage of the polar functional groups in the polysiloxane is a, and 0≤a<50%, and optionally 5%≤a≤30%.

[0534] In some embodiments, the substituent attached to the sugar unit in the polysaccharide and the polysaccharide derivative each independently comprises at least one of the group consisting of -OH, -COOH and salts thereof, -R-OH, -SO3H and salts thereof, -R-OH, -R-SO3H and salts thereof, sulfate group, alkoxy group, wherein R represents an alkylene group, and optionally represents a C1-C5 alkylene group.

[0535] Optionally, the substituents attached to the sugar units in the polysaccharide and polysaccharide derivatives each independently include at least one of the group consisting of the following functional groups: -OH, -COOH, -COOLi, -COONa, -COOK, -SO3H, -SO3Li, -SO3Na, -SO3K, -CH2-SO3H, -CH2-SO3Li, -CH2-SO3Na, -CH2-SO3K, methoxy, ethoxy.

[0536] In some embodiments, the polysaccharide includes one or more selected from pectin, carboxymethyl starch, hydroxypropyl starch, dextrin, cellulose ether, carboxymethyl chitosan, hydroxyethyl cellulose, carboxymethyl cellulose, carboxypropyl methyl cellulose, guar gum, sesbania gum, gum arabic, lithium alginate, sodium alginate, potassium alginate, fucoidan, agar, carrageenan, carrageenan, xanthan gum and fenugreek gum.

[0537] In some embodiments, the weight percentage of substituents attached to the sugar units in the polysaccharide and polysaccharide derivatives is independently 20% to 85%, optionally 30% to 78%.

[0538] In some embodiments, the lattice mismatch between the core material and the shell material is less than 10%, thereby ensuring good contact between the core and the shell (or coating) to prevent the shell (or coating) from falling off.

[0539] In some embodiments, based on the weight of the positive electrode active material,

[0540] The manganese content is in the range of 10 wt% to 35 wt%, optionally in the range of 13.3 wt% to 33.2 wt%, more optionally in the range of 15 wt% to 30 wt%, further optionally in the range of 17 wt% to 20 wt%; and / or,

[0541] The phosphorus content is in the range of 12 wt% to 25 wt%, optionally in the range of 15 wt% to 20 wt%, and more optionally in the range of 16.8 wt% to 19.5 wt%; and / or,

[0542] The weight ratio of manganese element to phosphorus element ranges from 0.71 to 1.85, optionally from 0.90 to 1.25, and more preferably from 0.95 to 1.20.

[0543] In the present application, in the case where manganese is contained only in the core of the positive electrode active material, the content of manganese may correspond to the content of the core.

[0544] In the present application, the content of manganese element is limited in the above range, which can further improve the stability and density of the material, thereby improving the cycle, storage and compaction performance of the secondary battery; and can maintain a high voltage platform, thereby improving the energy density of the secondary battery.

[0545] In the present application, the content of phosphorus element is limited in the above range, which can effectively reduce the influence of small polarons conduction on the electrical conductivity of the material, and further improve the stability of the crystal lattice structure, thereby affecting the overall stability of the material.

[0546] The weight ratio of the contents of manganese and phosphorus has the following effects on the performance of the secondary battery: it can further reduce manganese dissolution, further improve the stability and specific capacity of the positive active material, and thereby affect the cycle performance and storage performance of the secondary battery; it can reduce impurities, further reduce the discharge voltage platform of the material, thereby reducing the energy density of the secondary battery.

[0547] The measurement of manganese element and phosphorus element can be performed by using conventional technical means in the art. In particular, the content of manganese element and phosphorus element is determined by the following method: the material is dissolved in dilute hydrochloric acid (concentration 10-30%), the content of each element in the solution is tested by ICP, then the content of manganese element is measured and converted to obtain its weight ratio.

[0548] In some embodiments, the surface of the positive active material is coated with one or more of carbon and doped carbon; optionally, the surface of the positive active material is coated with carbon. In this way, the conductivity of the positive active material can be improved.

[0549] In some embodiments, the doping elements in the doped carbon include one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine. This facilitates the performance control of the doped carbon layer.

[0550] In some embodiments, in the core,

[0551] (1-y):y is in the range of 0.1-999, optionally in the range of 0.1-10 or in the range of 0.67-999, more optionally in the range of 1 to 10, further optionally in the range of 1 to 4, and more further optionally in the range of 1.5 to 3; and / or,

[0552] a:x is in the range of 1 to 1200, optionally in the range of 9 to 1100, and more optionally in the range of 190-998.

[0553] Here y represents the sum of the stoichiometric number of Mn site doping elements. When the above conditions are met, the energy density and cycle performance of the positive active material can be further improved.

[0554] In some embodiments, the ratio of z to 1-z in the core is 1:9 to 1:999, optionally 1:499 to 1:249. When the above conditions are met, the energy density and cycle performance of the positive electrode active material can be further improved.

[0555] In some embodiments, the amount of the shell is 0.1% to 6% based on the weight of the core. The amount of the shell of the present application is preferably within the above range, which can sufficiently coat the core and at the same time further improve the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0556] In some embodiments, the amount of the first shell is greater than 0% by weight and less than or equal to 7% by weight, optionally greater than 0% and less than or equal to 6% by weight, more optionally greater than 0% and less than or equal to 5.5% by weight or 4-5.6% by weight, further optionally greater than 0% and less than or equal to 2% by weight, based on the weight of the core; and / or,

[0557] The amount of the second shell is greater than 0% by weight and less than or equal to 6% by weight, optionally greater than 0% and less than or equal to 5.5% by weight, more optionally 2-4% by weight or 3-5% by weight, based on the weight of the core; and / or,

[0558] The amount of the third shell is greater than 0% and less than or equal to 6% by weight, optionally greater than 0% and less than or equal to 5.5% by weight, more optionally greater than 0% and less than or equal to 2% by weight, based on the weight of the core.

[0559] In some embodiments, the shell further comprises a fourth shell coating the third shell and a fifth shell coating the fourth shell; wherein,

[0560] The amount of the fourth shell and the fifth shell is each independently 0.01% by weight to 10% by weight, optionally 0.05% by weight to 10% by weight, more optionally 0.1% by weight to 5% by weight, further 0.1% by weight to 2% by weight, based on the weight of the core.

[0561] In the positive electrode active material having a core-shell structure of the present application, the amount of each shell is preferably within the above range, which can sufficiently coat the core and at the same time further improve the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0562] In some embodiments, the shell is located on 40% to 90% of the surface of the core, optionally 60% to 80% of the surface. This can sufficiently coat the core and thus improve the kinetic performance and safety performance of the secondary battery.

[0563] In some embodiments, the shell has a thickness of 1-15 nm.

[0564] In some embodiments, the first coating layer has a thickness of 1-10 nm, optionally 2-10 nm; and / or,

[0565] The second coating layer has a thickness of 2-25 nm, optionally 2-15 nm, more optionally 3-15 nm; and / or,

[0566] The third coating layer has a thickness of 2-25 nm, optionally 5-25 nm.

[0567] In some embodiments, the first coating layer has a thickness of about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or within any range of any of the aforementioned values.

[0568] In some embodiments, the second coating layer has a thickness of about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or within any range of any of the aforementioned values.

[0569] In some embodiments, the third coating layer has a thickness of about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm, or about 25 nm, or within any range of any of the aforementioned values.

[0570] In the present application, the first coating layer has the above thickness range, which can further reduce the adverse effects on the kinetic performance of the material, and can reduce the problem of not being able to effectively hinder the migration of transition metal ions.

[0571] The second coating layer has the above thickness range, so that the surface structure of the second coating layer is stable, and the side reaction with the electrolyte is small, thus the interface side reaction can be effectively alleviated, thereby improving the high-temperature performance of the secondary battery.

[0572] The third coating layer has the above thickness range, which can improve the electrical conductivity of the material and improve the compaction density performance of the battery pole piece prepared using the positive electrode active material.

[0573] The thickness of the coating layer is tested mainly by FIB, and the specific method can include the following steps: randomly selecting a single particle from the positive electrode active material powder to be tested, cutting a thin slice with a thickness of about 100 nm from the middle position or the vicinity of the middle position of the selected particle, and then performing TEM testing on the thin slice to measure the thickness of the coating layer. The thickness of the coating layer is measured at 3-5 positions, and the average value is taken.

[0574] In some embodiments, the one or more coating layers each independently comprise one or more selected from the group consisting of pyrophosphate, phosphate and oxide, and the one or more selected from the group consisting of pyrophosphate, phosphate and oxide is crystalline.

[0575] Optionally, the crystallinity of the pyrophosphate, phosphate and oxide is each independently 10% to 100%, more optionally 50% to 100%.

[0576] Herein, crystalline means that the crystallinity is above 50%, i.e. 50%-100%. The crystallinity below 50% is referred to as glassy. The crystallinity of the crystalline pyrophosphate and the crystalline phosphate of the present application is 50% to 100%.

[0577] The pyrophosphate and the phosphate with certain crystallinity not only facilitate the full play of the functions of the pyrophosphate coating layer in hindering the dissolution of manganese and the excellent lithium ion conducting ability of the phosphate coating layer, reducing the interface side reaction, but also enable the pyrophosphate coating layer and the phosphate coating layer to better perform lattice matching, thereby enabling the tight combination between the coating layers.

[0578] It should be noted that in the present application, the crystallinity can be adjusted, for example, by adjusting the process conditions of the sintering process, such as the sintering temperature, the sintering time, etc. The crystallinity can be measured by methods known in the art, such as by X-ray diffraction method, density method, infrared spectroscopy method, differential scanning calorimetry method and nuclear magnetic resonance absorption method, etc. The method for testing the crystallinity of the positive electrode active material by X-ray diffraction method can include the following steps:

[0579] A certain amount of positive electrode active material powder is taken, and the total scattering intensity is measured by X-ray, which is the sum of the scattering intensities of the entire space matter, and only related to the intensity of the primary ray, the chemical structure of the positive electrode active material powder, the total number of electrons participating in diffraction, i.e. the mass, and not related to the order state of the sample; then the crystalline scattering and the non-crystalline scattering are separated from the diffraction graph, and the crystallinity is the ratio of the crystalline part scattering to the total scattering intensity.

[0580] In some embodiments, the weight ratio of pyrophosphate and phosphate and the weight ratio of pyrophosphate and oxide in the shell are each independently 1:3 to 3:1, optionally 1:3 to 1:1. In this way, by the pyrophosphate and phosphate being in a suitable weight ratio range or the pyrophosphate and oxide being in a suitable weight ratio range, the manganese dissolution can be effectively inhibited, the surface lithium impurity content can be effectively reduced, the interface side reaction can be reduced, and thus the high-temperature storage performance, safety performance, and cycle performance of the secondary battery can be improved.

[0581] In some embodiments, the one or more coating layers each independently comprise carbon, and the carbon is a mixture of SP2 form carbon and SP3 form carbon, optionally, in the carbon, the molar ratio of SP2 form carbon to SP3 form carbon is any value in the range of 0.07-13, more optionally any value in the range of 0.1-10, further optionally any value in the range of 2.0-3.0.

[0582] In some embodiments, the molar ratio of SP2 form carbon to SP3 form carbon can be about 0.1, about 0.2, about 03, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10, or in any range of any of the above values.

[0583] In this application, "about" a certain value means a range, which means the range of ±10% of the value.

[0584] By selecting the form of carbon in the carbon coating layer, the comprehensive electrical performance of the secondary battery can be improved. Specifically, by using a mixed form of SP2 form carbon and SP3 form carbon and limiting the ratio of SP2 form carbon to SP3 form carbon within a certain range, the following situations can be avoided: if the carbon in the coating layer is all amorphous SP3 form, the conductivity is poor; if it is all graphitized SP2 form, although the conductivity is good, the lithium ion path is less, which is not conducive to the deintercalation of lithium. In addition, by limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range, both good conductivity and lithium ion path can be achieved, thus being conducive to the realization of the function of the secondary battery and its cycle performance. The mixing ratio of SP2 form carbon and SP3 form carbon can be controlled by sintering conditions such as sintering temperature and sintering time. The molar ratio of SP2 form carbon to SP3 form carbon can be determined by Raman spectroscopy, and the specific test method is as follows: by peak separation of the energy spectrum of Raman test, Id / Ig (wherein Id is the peak intensity of SP3 form carbon, Ig is the peak intensity of SP2 form carbon) is obtained, so as to confirm the molar ratio of the two.

[0585] In some embodiments, each of the one or more coating layers independently comprises doped carbon, and in the doped carbon, the mass content of the doping element is less than 30%; optionally, in the doped carbon, the mass content of the doping element is less than 20%. The doping element in the above content range can sufficiently improve the conductivity of the pure carbon layer, and effectively avoid excessive surface activity caused by excessive doping element, thereby effectively controlling the interface side reaction caused by excessive doping of the coating layer.

[0586] In some embodiments, each of the one or more coating layers independently comprises doped carbon, and in the doped carbon,

[0587] The doping element is nitrogen element and / or sulfur element, and the mass content of the doping element in the doped carbon is 1% to 15%; or,

[0588] The doping element is phosphorus element, boron element and / or fluorine element, and the mass content of the doping element in the doped carbon is 0.5% to 5%;

[0589] Optionally, the doping element is nitrogen, phosphorus, sulfur, boron or fluorine.

[0590] Since the atomic radius of nitrogen atom and sulfur atom is closer to that of carbon atom, it is not easy to damage the carbon skeleton, therefore, when the doping amount of nitrogen atom and sulfur atom is in the above relatively wide range, the conductivity of the doped carbon layer can be sufficiently improved, and the lithium ion transmission and lithium ion desolvation capacity can be promoted.

[0591] Since the atomic radius of phosphorus atom, boron atom and / or fluorine atom is different from that of carbon atom, excessive doping can easily damage the carbon skeleton, therefore, when the doping amount of phosphorus atom, boron atom and / or fluorine atom is in the above relatively small range, the conductivity of the doped carbon layer can be sufficiently improved, and the lithium ion transmission and lithium ion desolvation capacity can be promoted.

[0592] In some embodiments, each of the one or more coating layers independently comprises pyrophosphate, the interplanar spacing of the pyrophosphate ranges from 0.293 nm to 0.470 nm, optionally from 0.297 nm to 0.462 nm or from 0.293 nm to 0.326 nm, more optionally from 0.300 nm to 0.310 nm, the included angle of the crystal direction (111) ranges from 18.00° to 32.57°, optionally from 18.00° to 32.00° or from 26.41° to 32.57°, more optionally from 19.211° to 30.846°, further optionally from 29.00° to 30.00°; and / or,

[0593] The one or more coating layers independently include phosphate, the interplanar spacing of the phosphate is in the range of 0.244-0.425 nm, optionally 0.345-0.358 nm, and the angle of the crystal orientation (111) is in the range of 20.00°-37.00°, optionally 24.25°-26.45°;

[0594] Optionally, the first coating layer or the second coating layer comprises phosphate.

[0595] The first and second coating layers of the positive electrode active material of the present application are both crystalline, and their interplanar spacing and angle ranges are within the above-mentioned ranges. This effectively reduces the impurity phase in the coating layers, thereby improving the material's specific capacity, cycle performance, and rate performance.

[0596] In some embodiments, the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is less than 50%, optionally less than 9.8%, more optionally less than 8.1%, further optionally less than 7.5%, further optionally less than 6%, further optionally less than 4%, further optionally less than 3.8%, and further optionally less than 2.0-3.8%.

[0597] By reducing the lattice change rate, Li ion transport can be made easier, that is, the mobility of Li ions in the material is stronger, which is beneficial to improving the rate performance of the secondary battery. The lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).

[0598] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is 5.3% or less, optionally 5.1% or less, more optionally 4% or less, further optionally 2.2% or less, further optionally 2% or less, further optionally 1.5%-2.2% or 0.5% or less.

[0599] The so-called Li / Mn antisite defect refers to the Li + With Mn 2+ The positions of Li / Mn are interchanged. The concentration of Li / Mn antisite defects refers to the concentration of Li / Mn antisite defects in the positive electrode active material. 2+ Li exchange occurs + Occupy + The percentage of total antisite defect Mn 2+ Will hinder Li + The transport of Li / Mn antisite defects can be improved by reducing the concentration of Li / Mn antisite defects, thereby improving the specific capacity and rate performance of the positive electrode active material. The concentration of Li / Mn antisite defects can be measured by methods known in the art, such as XRD.

[0600] In some embodiments, the positive electrode active material has a compaction density of 1.89 g / cm at 3T. 3 Above, 1.95g / cm2 is optional 3 Above, 1.98g / cm2 is optional 3 Above, further optional 2.0g / cm 3 Above, further optional 2.2g / cm 3 Above, further optionally 2.2g / cm 3 Above and 2.8g / cm 3 Below or 2.2g / cm 3 Above and 2.65g / cm 3 the following.

[0601] The higher the compaction density, the greater the weight of the active material per unit volume. Therefore, increasing the compaction density is beneficial to increasing the volumetric energy density of the battery cell. The compaction density can be measured according to GB / T24533-2009.

[0602] In some embodiments, the surface oxygen valence state of the positive electrode active material is -1.55 or less, optionally -1.82 or less, more optionally -1.88 or less, further optionally -1.90 or less or -1.98 to -1.88, further optionally -1.98 to -1.89, further optionally -1.98 to -1.90.

[0603] By reducing the surface oxygen valence state, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature stability of the secondary battery. The surface oxygen valence state can be measured by methods known in the art, such as electron energy loss spectroscopy (EELS).

[0604] [Method for preparing positive electrode active material]

[0605] The present application provides a method for preparing a positive electrode active material, which comprises the following steps:

[0606] reacting a manganese source with a source of element B to obtain a manganese salt doped with element B;

[0607] The lithium source, phosphorus source, optional source of element A, optional source of element C, optional source of element D and manganese salt doped with element B are mixed, dried and sintered to obtain the core Li a A x Mn 1-y B y P 1-z C z O 4-n D n ; wherein, A, B, C, D, a, x, y, z and n are defined as in [positive electrode active material].

[0608] Thus, by doping specific elements in the Mn site of the compound LiMnPO4 and optionally in the Li site, P site and / or O site in specific amounts, the present application can obtain significantly improved rate capability, while significantly reducing the dissolution of Mn and Mn site doping elements, obtaining significantly improved cycle performance and / or high temperature stability, and the gravimetric capacity and tap density of the material can also be improved.

[0609] In some embodiments, the method specifically comprises the following steps:

[0610] Mixing and stirring a manganese source, a source of element B and an acid in a solvent to generate a suspension of manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain manganese salt doped with element B;

[0611] Grinding and mixing a lithium source, a phosphorus source, an optional source of element A, an optional source of element C, an optional source of element D, a solvent and the manganese salt doped with element B in a reaction vessel to obtain a slurry;

[0612] Transferring the obtained slurry to a spray drying device for spray drying granulation to obtain granules;

[0613] Sintering the obtained granules to obtain the core Li a A x Mn 1-y B y P 1-z C z O 4-n D n ; wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive electrode active material].

[0614] In some embodiments, in the step of preparing the slurry, a lithium source, a phosphorus source, an optional source of element A, an optional source of element C, an optional source of element D, a carbon source, a source of carbon layer doping elements, a solvent and the manganese salt doped with element B are ground and mixed in a reaction vessel to obtain a slurry; the other steps are the same as above; and a positive electrode active material is obtained;

[0615] The positive electrode active material comprises a core and a shell covering the core, the core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , and the shell comprises doped carbon, the doping elements in the doped carbon comprising one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine; wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive electrode active material].

[0616] In some embodiments, the solvent in the step of preparing the manganese salt doped with element B and the step of preparing the slurry can each independently be a solvent conventionally used by those skilled in the art in the preparation of manganese salts and lithium manganese phosphates, for example, it can each independently be selected from at least one of ethanol, water (e.g., deionized water), etc.

[0617] In some embodiments, the method further comprises the following steps:

[0618] coating a mixture of one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer on the surface of the inner core by dry coating or wet coating to obtain the positive electrode active material;

[0619] The positive electrode active material comprises an inner core and a shell coating the inner core, the inner core is Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the shell comprises one or more coating layers, each coating layer independently comprises one or more selected from pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer; wherein the definitions of A, B, C, D, a, x, y, z, and n are as in [positive electrode active material]; optionally, the polymer comprises one or more selected from polysiloxane, polysaccharide, and polysaccharide derivative.

[0620] In some embodiments, the method further comprises the following steps:

[0621] providing a pyrophosphate M b (P2O7) c powder, a suspension liquid comprising a phosphate X m (PO4) q and / or an oxide M′ d O e , wherein the suspension liquid further comprises a source of carbon and / or a source of doped carbon;

[0622] adding the inner core, the pyrophosphate M b (P2O7) c powder to the suspension liquid and mixing to obtain the positive electrode active material by sintering; wherein,

[0623] The positive electrode active material comprises an inner core and a shell coating the inner core, the shell comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer, the inner core comprises Li a A x Mn 1-y B y P1-z C z O 4-n D n , the first coating layer comprises pyrophosphate M b (P2O7) c and one or more selected from phosphate X m (PO4) q and oxide M' d O e , the second coating layer comprises one or more selected from carbon and doped carbon, optionally, the doping element in the doped carbon comprises one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine, wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive electrode active material], the definitions of M, X, M', b, c, d, e, m, q are as in [positive electrode active material].

[0624] In some embodiments, the method further comprises the following steps:

[0625] providing a pyrophosphate MP2O7 powder, a phosphate XPO4 suspension comprising a source of carbon;

[0626] adding the core, the pyrophosphate MP2O7 powder into the XPO4 suspension comprising the source of carbon and mixing, obtaining the positive electrode active material via sintering; wherein,

[0627] the positive electrode active material comprises a core and a shell coating the core, the shell comprises a first coating layer coating the core and a second coating layer coating the first coating layer, the core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, the second coating layer comprises carbon, wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive electrode active material], the definitions of M and X are as in [positive electrode active material].

[0628] In some embodiments, the method further comprises the following steps:

[0629] respectively providing a pyrophosphate M b (P2O7) c suspension, a suspension comprising one or more selected from phosphate X m (PO4) q , oxide M' d O e and boride and a suspension comprising a source of carbon and / or a source of doped carbon;

[0630] The core is mixed with all the above suspensions, sintered to obtain the positive active material; wherein,

[0631] The positive active material comprises a core and a shell covering the core,

[0632] The core comprises Li a Mn 1-y B y P 1-z C z O4, the shell comprises a first shell layer covering the core, a second shell layer covering the first shell layer and a third shell layer covering the second shell layer, the first shell layer comprises pyrophosphate M b (P2O7) c , the second shell layer comprises one or more selected from phosphate X m (PO4) q , oxide M' d O e and boride, the third shell layer is selected from one or more of carbon and doped carbon, wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive active material], the definitions of M, X, M', b, c, d, e, m, q are as in [positive active material].

[0633] In some embodiments, the method further comprises the following steps:

[0634] Li f QP2O7and / or Q g (P2O7) h and XPO4suspensions are provided respectively, the core is added into the above suspensions and mixed, and the positive active material is obtained by sintering; wherein,

[0635] The positive active material comprises a core and a shell covering the core, the core comprises Li a A x Mn 1-y B y P 1-z C z O 4-n D n , the shell comprises a first shell layer covering the core, a second shell layer covering the first shell layer and a third shell layer covering the second shell layer, the first shell layer comprises pyrophosphate Li f QP2O7and / or Q g (P2O7) h , the second shell layer comprises phosphate XPO4, and the third shell layer comprises carbon, wherein the definitions of A, B, C, D, a, x, y, z and n are as in [positive active material], the definitions of Q, X, f, g and h are as in [positive active material].

[0636] In some embodiments, the method further comprises the following steps:

[0637] First coating step: dissolving a source of element Q, a phosphorus source and an acid, and optionally a lithium source, in a solvent to obtain a first coating layer suspension containing Li f QP2O7and / or Q g (P2O7) h ; mixing the core with the first coating layer suspension, drying, and sintering to obtain a first coating layer coated material;

[0638] Second coating step: dissolving a source of element X, a phosphorus source and an acid in a solvent to obtain a second coating layer suspension containing XPO4; mixing the first coating layer coated material obtained in the first coating step with the second coating layer suspension, drying, and sintering to obtain a two-layer coating layer coated material;

[0639] Third coating step: dissolving a carbon source in a solvent to obtain a third coating layer solution; then adding the two-layer coating layer coated material obtained in the second coating step into the third coating layer solution, mixing uniformly, drying, and then sintering to obtain a three-layer coating layer coated material, i.e., a positive electrode active material.

[0640] In some embodiments, the method further comprises the following steps:

[0641] respectively providing pyrophosphate M b (P2O7) c powder, one or more powders selected from phosphate X m (PO4) q , oxide M' d O e , and boride, and a carbon source powder and / or a carbon-doped source powder;

[0642] mixing and grinding the core with all the powders described above, drying to obtain a positive electrode active material; wherein,

[0643] the positive electrode active material comprises a core and a shell coating the core,

[0644] the core comprises Li a Mn 1-y B y P 1-z C z O4, the shell comprises a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, the first coating layer comprises pyrophosphate M b (P2O7) c , the second coating layer comprises one or more powders selected from phosphate X m (PO4) q , oxide M'd O e and borides, and the third coating layer is selected from one or more of carbon and doped carbon, wherein A, B, C, D, a, x, y, z and n and M, X, M', b, c, d, e, m, q are as defined in [positive electrode active material];

[0645] Optionally, drying is performed by a spray granulation dryer.

[0646] In some embodiments, the method further comprises the step of:

[0647] providing a polymer, the polymer comprising one or more selected from polysiloxane, polysaccharide and polysaccharide derivative;

[0648] coating the positive electrode active material with the polymer by dry coating or wet coating to obtain a material comprising a core and a shell coating the core;

[0649] one or more coating layers of the shell furthest from the core each independently comprises one or more selected from polysiloxane, polysaccharide and polysaccharide derivative.

[0650] In any of the embodiments, the source of element A is selected from at least one of elemental A, oxide, phosphate, oxalate, carbonate and sulfate of element A; and / or,

[0651] the source of element B is selected from at least one of elemental B, oxide, phosphate, oxalate, carbonate, halide, nitrate, organic acid salt, hydroxide and sulfate of element B, optionally at least one of elemental B, oxide, phosphate, oxalate, carbonate and sulfate of element B, optionally at least one of elemental B, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide of element B, optionally at least one of elemental B, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide and hydroxide of element B; and / or,

[0652] the source of element C is selected from at least one of elemental C, halide, organic acid salt, oxide, hydroxide, inorganic acid, organic acid, sulfate, borate, nitrate and silicate of element C, optionally at least one of sulfate, borate, nitrate and silicate of element C, optionally at least one of elemental C, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide and inorganic acid of element C, optionally at least one of inorganic acid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide, hydroxide of element C; and / or,

[0653] the source of element D is selected from at least one of elemental D and ammonium salt of element D.

[0654] In some embodiments, the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, an organic acid such as oxalic acid, and the like, for example, can be oxalic acid. In some embodiments, the acid is a dilute acid having a concentration of 60 wt% or less.

[0655] In some embodiments, the manganese source can be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the manganese source can be selected from one or a combination of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate.

[0656] In some embodiments, the lithium source can be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the lithium source can be selected from one or a combination of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate.

[0657] In some embodiments, the phosphorus source can be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate, for example, the phosphorus source can be selected from one or a combination of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0658] The amount of each source of elements A, B, C, D added depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0659] In any embodiment, in the step of preparing the manganese salt doped with element B,

[0660] The stirring is performed at a temperature in the range of 20-120°C, optionally in the range of 25-80°C or 40-120°C, further optionally in the range of 60-120°C, and / or,

[0661] The stirring is performed at a stirring rate of 200-800 rpm, optionally 400-700 rpm, more optionally 500-700 rpm, further optionally for 1-9 hours, or 60-420 minutes, or 3-7 hours or 120-360 minutes.

[0662] In some embodiments, in the step of preparing the slurry, the grinding and mixing are performed for 1-15 hours, optionally 8-15 hours; optionally, the mixing is performed at a temperature of 20-120°C, more optionally 40-120°C, for 1-10 hours.

[0663] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be uniformly distributed, and the material after sintering has a higher crystallinity, thereby improving the specific capacity and rate performance of the material, etc.

[0664] In some embodiments, the filter cake can be washed before drying the filter cake in the step of preparing the manganese salt doped with element B.

[0665] In some embodiments, the drying in the step of preparing the manganese salt doped with element B can be performed by means and under conditions known to those skilled in the art, for example, the drying temperature can be in the range of 120-300°C. Alternatively, the filter cake can be ground into particles after drying, for example, ground to a median particle size Dv 50 In some embodiments, the median particle size Dv 50 In some embodiments, the median particle size Dv 50 The median particle size Dv

[0666] In some embodiments, in the step of preparing the slurry, a carbon source is also added to the reaction vessel for grinding and mixing together. In this way, the method can obtain a positive electrode active material coated with carbon on the surface. Alternatively, the carbon source includes one or a combination of several of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid. The amount of the carbon source is usually in the range of 0.1%-5% of the amount of the lithium source in terms of molar ratio. The grinding can be performed by a suitable grinding method known in the art, for example, by sand grinding.

[0667] The temperature and time for the spray drying can be the temperature and time conventionally used in the art for spray drying, for example, at 100-300°C for 1-6 hours.

[0668] In some embodiments, in the step of preparing the core, the sintering is performed at a temperature in the range of 600-900°C for 6-14 hours.

[0669] In some embodiments, the sintering is performed under a protective atmosphere, which can be nitrogen, inert gas, hydrogen, or a mixture thereof.

[0670] In some embodiments, the MP2O7 powder is a commercially available product, or the MP2O7 powder is prepared by the following method:

[0671] The source of element M and the source of phosphorus are added to a solvent to obtain a mixture, the pH of the mixture is adjusted to 4-6, stirred and reacted sufficiently, and then dried and sintered to obtain, wherein M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0672] In some embodiments, in the method of preparing the MP2O7 powder,

[0673] The drying step is drying at 100-300°C, optionally 150-200°C, for 4-8h.

[0674] In some embodiments, in the method of preparing the MP2O7 powder,

[0675] The sintering step is sintering at 500-800°C, optionally 650-800°C, under an inert gas atmosphere for 4-10h.

[0676] In some embodiments, the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10h.

[0677] In some embodiments, optionally, the XPO4 suspension containing the source of carbon is commercially available, or is prepared by mixing the source of lithium, the source of X, the source of phosphorus and the source of carbon uniformly in a solvent, and then heating the reaction mixture to 60-120°C for 2-8h to obtain the XPO4 suspension containing the source of carbon. Optionally, in the process of preparing the XPO4 suspension containing the source of carbon, the pH of the mixture is adjusted to 4-6.

[0678] In some embodiments, in the step of preparing the positive electrode active material, the mass ratio of the inner core, the MP2O7 powder and the XPO4 suspension containing the source of carbon is: 1: (0.001-0.05): (0.001-0.05).

[0679] In some embodiments, in the first coating step,

[0680] The pH of the solution in which the source of element Q, the source of phosphorus and the acid, and optionally the source of lithium, is dissolved is controlled to be 3.5-6.5, then stirred and reacted for 1-5h, then the solution is heated to 50-120°C and kept at this temperature for 2-10h, and / or,

[0681] The sintering is carried out at 650-800°C for 2-6h.

[0682] In some embodiments, in the second coating step,

[0683] After dissolving the source of element X, the source of phosphorus and the acid in a solvent, stirring and reacting for 1-10h, then heating the solution to 60-150°C and keeping at this temperature for 2-10h, and / or,

[0684] The sintering is carried out at 500-700°C for 6-10h.

[0685] In some embodiments, the sintering in the third coating step is carried out at 700-800°C for 6-10h.

[0686] [Positive electrode sheet]

[0687] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a first positive electrode active material, the first positive electrode active material being the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned method; optionally, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, more optionally 95-99.5% by weight, based on the total weight of the positive electrode film layer.

[0688] In some embodiments, the positive electrode tab further includes a second positive electrode active material, and the second positive electrode active material is different from the first positive electrode active material.

[0689] In some embodiments, the second positive electrode active material includes LiE t Co s F (1-t-s) O2, spinel lithium manganate, and spinel lithium titanate, wherein E includes one or more elements selected from Group VIII, F includes one or more elements selected from Group IIIA and Group VIIB, t is selected from the range of 0 to 0.9, and the sum of t and s is selected from the range of 0.3 to 1.

[0690] In some embodiments, E includes one or more elements selected from Ni, Fe, Ru, and Rh, and F includes one or more elements selected from Mn, Al, Ga, and In.

[0691] In some embodiments, the second positive electrode active material is selected from LiNi t Co s Mn (1-t-s) O2, LiNi t Co s Al (1-t-s) O2, LiCoO2, spinel lithium manganate, and spinel lithium titanate; wherein t is independently selected from the range of 0.3-0.9, optionally 0.33-0.8, and the sum of t and s is independently selected from the range of 0.3-0.9, optionally 0.66-0.9.

[0692] In some embodiments, the mass ratio of the first active material to the second active material is 1:7-7:1, optionally 1:4-4:1.

[0693] In some embodiments, the second positive electrode active material includes LiNi

[0694] LiNi t Co s Mn (1-t-s) O2, the ratio of t, (1-t-s), and s is 5:2:3 or 3:1:1 or 8:1:1; and / or,

[0695] LiNi tCo s Al (1-t-s) The ratio of t, s, and (1-t-s) in O2 is 5:2:3 or 3:1:1 or 8:1:1.

[0696] In some embodiments, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 88-98.7% of the mass of the positive electrode tab.

[0697] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0698] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0699] In some embodiments, the positive electrode active material can also employ a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or two or more thereof can be used in combination.

[0700] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0701] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0702] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0703] [Positive electrode sheet]

[0704] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0705] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0706] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. As a metal foil, for example, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0707] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0708] In some embodiments, the negative electrode film layer can also optionally include a binder. As an example, the binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0709] In some embodiments, the negative electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0710] In some embodiments, the negative electrode film layer can also optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0711] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0712] [Electrolyte]

[0713] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0714] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0715] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0716] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0717] In some embodiments, the electrolyte can also optionally include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0718] [Separator]

[0719] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0720] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0721] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly by a winding process or a stacking process.

[0722] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0723] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0724] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, Figure 4 is a square structure secondary battery 5 as an example.

[0725] In some embodiments, referring to Figure 5 , the outer package can comprise a shell 51 and a cover plate 53. The shell 51 can comprise a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be used to form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the person skilled in the art can select according to the specific actual needs.

[0726] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the person skilled in the art according to the application and capacity of the battery module.

[0727] Figure 6 is a battery module 4 as an example. Referring to Figure 6In the battery module 4, the plurality of secondary batteries 5 can be arranged in series along the length direction of the battery module 4. Of course, the plurality of secondary batteries 5 can be arranged in any other manner. The plurality of secondary batteries 5 can be further fixed by fasteners.

[0728] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0729] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0730] Figure 7 and Figure 8 is a battery pack 1 as an example. Referring to Figure 7 and Figure 8 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0731] In addition, the present application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0732] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0733] Figure 9 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0734] [Embodiment]

[0735] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0736] The sources of raw materials involved in the examples of this application are as follows:

[0737]

[0738]

[0739] [Cathode active material including core and battery preparation]

[0740] Example I-1

[0741] 1) Preparation of positive electrode active materials

[0742] Preparation of doped manganese oxalate: 1.3 mol of MnSO4﹒H2O and 0.7 mol of FeSO4﹒H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reactor and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reactor was heated to 80°C and stirred at 600 rpm for 6 hours. The reaction was terminated (no bubbles were generated) to obtain an Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C and then ground to obtain a median particle size Dv 50 Fe-doped manganese oxalate particles with a size of about 100 nm.

[0743] Preparation of doped lithium manganese phosphate: Take 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2 and 0.005 mol of sucrose and add them to 20L of deionized water. Transfer the mixture to a sand mill and grind and stir thoroughly for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C, dry for 4 hours, and obtain particles. In a protective atmosphere of nitrogen (90 volume %) + hydrogen (10 volume %), sinter the above powder at 700°C for 10 hours to obtain carbon-coated Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001The positive active material can be detected for element content by inductively coupled plasma emission spectrometry (ICP).

[0744] 2) Preparation of button cell

[0745] The positive active material, polyvinylidene fluoride (PVDF) and acetylene black described above are added to N-methyl pyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a dry room to make a slurry. The slurry is coated on an aluminum foil, dried, and cold-pressed to make a positive electrode sheet. The coating amount is 0.2 g / cm 2 , and the compacted density is 2.0 g / cm 3 .

[0746] A lithium sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in a volume ratio of 1:1:1 of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) is used as the electrolyte, which is assembled with the positive electrode sheet prepared above in a button cell box to form a button cell (hereinafter also referred to as "button").

[0747] 3) Preparation of full cell

[0748] The positive active material, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) described above are uniformly mixed in a weight ratio of 92:2.5:5.5 in an N-methyl pyrrolidone solvent system, coated on an aluminum foil and dried and cold-pressed to obtain a positive electrode sheet. The coating amount is 0.4 g / cm 2 , and the compacted density is 2.4 g / cm 3 .

[0749] The negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR) and thickening agent sodium carboxymethyl cellulose (CMC) are uniformly mixed in a weight ratio of 90:5:2:2:1 in deionized water, coated on a copper foil, dried and cold-pressed to obtain a negative electrode sheet. The coating amount is 0.2 g / cm 2 , and the compacted density is 1.7 g / cm 3 .

[0750] A polyethylene (PE) porous polymer film is used as a separator film, and the positive electrode sheet, the separator film and the negative electrode sheet are stacked in order with the separator film in the middle to play a role of separation, and wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the same electrolyte as in the preparation of the button cell described above and packaged to obtain a full cell (hereinafter also referred to as "full").

[0751] Example I-2

[0752] Example I-1 Except that in "1) Preparation of the positive active material", the amount of high-purity Li2CO3 is changed to 0.4885 mol, Mo(SO4)3 is replaced by MgSO4, the amount of FeSO4-H2O is changed to 0.68 mol, 0.02 mol of Ti(SO4)2 is added in the preparation of the doped manganese oxalate, and H4SiO4 is replaced by HNO3, the rest is the same as in Example I-1.

[0753] Example I-3

[0754] Example I-1 Except that in "1) Preparation of the positive active material", the amount of high-purity Li2CO3 is changed to 0.496 mol, Mo(SO4)3 is replaced by W(SO4)3, and H4SiO4 is replaced by H2SO4, the rest is the same as in Example I-1.

[0755] Example I-4

[0756] Example I-1 Except that in "1) Preparation of the positive active material", the amount of high-purity Li2CO3 is changed to 0.4985 mol, 0.001 mol of Mo(SO4)3 is replaced by 0.0005 mol of Al2(SO4)3, and NH4HF2 is replaced by NH4HCl2, the rest is the same as in Example I-1.

[0757] Example I-5

[0758] Example I-1 Except that in "1) Preparation of the positive active material", 0.7 mol of FeSO4-H2O is changed to 0.69 mol, 0.01 mol of VCl2 is added in the preparation of the doped manganese oxalate, the amount of Li2CO3 is changed to 0.4965 mol, 0.001 mol of Mo(SO4)3 is replaced by 0.0005 mol of Nb2(SO4)5, and H4SiO4 is replaced by H2SO4, the rest is the same as in Example I-1.

[0759] Example I-6

[0760] Example I-1 Except that in "1) Preparation of the positive active material", the amount of FeSO4-H2O is changed to 0.68 mol, 0.01 mol of VCl2 and 0.01 mol of MgSO4 are added in the preparation of the doped manganese oxalate, the amount of Li2CO3 is changed to 0.4965 mol, 0.001 mol of Mo(SO4)3 is replaced by 0.0005 mol of Nb2(SO4)5, and H4SiO4 is replaced by H2SO4, the rest is the same as in Example I-1.

[0761] Example I-7

[0762] Example I-6

[0763] Example I-8

[0764] Example I-6

[0765] Example I-9

[0766] Example I-1 except that in "1) Preparation of the positive electrode active material", the amount of FeSO4-H2O was changed to 0.68 mol, 0.01 mol of VCl2and 0.01 mol of MgSO4were added in the preparation of the doped manganese oxalate, the amount of Li2CO3was changed to 0.4975 mol, 0.001 mol of Mo(SO4)3was changed to 0.0005 mol of Nb2(SO4)5, and NH4HF2was changed to NH4HBr2.

[0767] Example I-10

[0768] Example I-1 except that in "1) Preparation of the positive electrode active material", the amount of FeSO4-H2O was changed to 0.68 mol, 0.01 mol of VCl2and 0.01 mol of MgSO4were added in the preparation of the doped manganese oxalate, the amount of Li2CO3was changed to 0.4975 mol, 0.001 mol of Mo(SO4)3was changed to 0.0005 mol of Nb2(SO4)5, and NH4HF2was changed to NH4HBr2.

[0769] Example I-11

[0770] Example I-1 except that in "1) Preparation of the positive electrode active material", the amount of FeSO4-H2O was changed to 0.69 mol, 0.01 mol of VCl2was added in the preparation of the doped manganese oxalate, the amount of Li2CO3was changed to 0.499 mol, Mo(SO4)3was changed to MgSO4, and NH4HF2was changed to NH4HBr2.

[0771] Example I-12

[0772] The preparation method was the same as that in Example I-1, except that in "1) Preparation of Positive Electrode Active Material", the amount of MnSO4﹒H2O was changed to 1.36 mol, the amount of FeSO4﹒H2O was changed to 0.6 mol, 0.04 mol of VCl2 was added when preparing doped manganese oxalate, the amount of Li2CO3 was changed to 0.4985 mol, Mo(SO4)3 was replaced by MgSO4, and H4SiO4 was replaced by HNO3. 0.99 7Mg 0.001 Mn 0.68 Fe 0.3 V 0.02 P 0.999 N 0.001 O 3.999 F 0.001

[0773] Example I-13

[0774] The preparation was the same as that of Example I-12 except that the amount of MnSO4.H2O was changed to 1.16 mol and the amount of FeSO4.H2O was changed to 0.8 mol in “1) Preparation of positive electrode active material”.

[0775] Example I-14

[0776] The preparation was the same as that of Example I-12 except that the amount of MnSO4.H2O was changed to 1.3 mol and the amount of VCl2 was changed to 0.1 mol in “1) Preparation of positive electrode active material”.

[0777] Example I-15

[0778] The preparation method was the same as that in Example I-1, except that in "1) Preparation of Positive Electrode Active Material", the amount of MnSO4﹒H2O was changed to 1.2 mol, 0.1 mol of VCl2 was added when preparing doped manganese oxalate, the amount of Li2CO3 was changed to 0.494 mol, 0.001 mol of Mo(SO4)3 was replaced by 0.005 mol of MgSO4, and H4SiO4 was replaced by H2SO4.

[0779] Example I-16

[0780] Example I-1 except that in "1) Preparation of the positive active material", the amount of MnSO4-H2O is changed to 1.2 mol, 0.1 mol of VCl2is added in the preparation of the doped manganese oxalate, the amount of Li2CO3is changed to 0.467 mol, 0.001 mol of Mo(SO4)3is replaced by 0.005 mol of MgSO4, 0.001 mol of H4SiO4is replaced by 0.005 mol of H2SO4, and 1.175 mol of phosphoric acid with a concentration of 85% is replaced by 1.171 mol of phosphoric acid with a concentration of 85%.

[0781] Example I-17

[0782] Example I-1 except that in "1) Preparation of the positive active material", the amount of MnSO4-H2O is changed to 1.2 mol, 0.1 mol of VCl2is added in the preparation of the doped manganese oxalate, the amount of Li2CO3is changed to 0.492 mol, 0.001 mol of Mo(SO4)3is replaced by 0.005 mol of MgSO4, H4SiO4is replaced by H2SO4, and 0.0005 mol of NH4HF2is replaced by 0.0025 mol.

[0783] Example I-18

[0784] Example I-1 except that in "1) Preparation of the positive active material", the amount of FeSO4-H2O is changed to 0.5 mol, 0.1 mol of VCl2and 0.1 mol of CoSO4are added in the preparation of the doped manganese oxalate, the amount of Li2CO3is changed to 0.492 mol, 0.001 mol of Mo(SO4)3is replaced by 0.005 mol of MgSO4, H4SiO4is replaced by H2SO4, and 0.0005 mol of NH4HF2is replaced by 0.0025 mol.

[0785] Example I-19

[0786] Example I-18 except that in "1) Preparation of the positive active material", the amount of FeSO4-H2O is changed to 0.4 mol, and 0.1 mol of CoSO4is changed to 0.2 mol.

[0787] Example I-20

[0788] Example I-18 except that in "1) Preparation of the positive active material", the amount of MnSO4-H2O is changed to 1.5 mol, the amount of FeSO4-H2O is changed to 0.1 mol, and the amount of CoSO4is changed to 0.3 mol.

[0789] Example I-21

[0790] Except that in “1) Preparation of positive electrode active material”, 0.1 mol of CoSO 4 was replaced with 0.1 mol of NiSO 4 , the rest was the same as Example I-18.

[0791] Example I-22

[0792] The preparation method was the same as that of Example I-18 except that in “1) Preparation of positive electrode active material” the amount of MnSO4.H2O was changed to 1.5 mol, the amount of FeSO4.H2O was changed to 0.2 mol, and 0.1 mol of CoSO4 was replaced by 0.2 mol of NiSO4.

[0793] Example I-23

[0794] The preparation was the same as that of Example I-18 except that in “1) Preparation of positive electrode active material” the amount of MnSO4.H2O was changed to 1.4 mol, the amount of FeSO4.H2O was changed to 0.3 mol, and the amount of CoSO4 was changed to 0.2 mol.

[0795] Example I-24

[0796] The following are the same as in Example I-1, except that in "1) Preparation of Positive Electrode Active Material", 1.3 mol of MnSO4﹒H2O was changed to 1.2 mol, 0.7 mol of FeSO4﹒H2O was changed to 0.5 mol, 0.1 mol of VCl2 and 0.2 mol of CoSO4 were added when preparing doped manganese oxalate, the amount of Li2CO3 was changed to 0.497 mol, 0.001 mol of Mo(SO4)3 was replaced by 0.005 mol of MgSO4, H4SiO4 was replaced by H2SO4, and 0.0005 mol of NH4HF2 was changed to 0.0025 mol.

[0797] Example I-25

[0798] The preparation was the same as that of Example I-18 except that in “1) Preparation of positive electrode active material” the amount of MnSO4.H2O was changed to 1.0 mol, the amount of FeSO4.H2O was changed to 0.7 mol, and the amount of CoSO4 was changed to 0.2 mol.

[0799] Example I-26

[0800] Example I-1 except that in "1) Preparation of the positive active material", the amount of MnSO4-H2O was changed to 1.4 mol, the amount of FeSO4-H2O was changed to 0.3 mol, 0.1 mol of VCl2 and 0.2 mol of CoSO4 were added in the preparation of the doped manganese oxalate, the amount of Li2CO3 was changed to 0.4825 mol, 0.001 mol of Mo(SO4)3 was replaced by 0.005 mol of MgSO4, the amount of H4SiO4 was changed to 0.1 mol, the amount of phosphoric acid was changed to 0.9 mol and the amount of NH4HF2 was changed to 0.04 mol.

[0801] Example I-27

[0802] Example I-1 except that in "1) Preparation of the positive active material", the amount of MnSO4-H2O was changed to 1.4 mol, the amount of FeSO4-H2O was changed to 0.3 mol, 0.1 mol of VCl2 and 0.2 mol of CoSO4 were added in the preparation of the doped manganese oxalate, the amount of Li2CO3 was changed to 0.485 mol, 0.001 mol of Mo(SO4)3 was replaced by 0.005 mol of MgSO4, the amount of H4SiO4 was changed to 0.08 mol, the amount of phosphoric acid was changed to 0.92 mol and the amount of NH4HF2 was changed to 0.05 mol.

[0803] Examples I-28 to I-41

[0804] The stirring speed, the temperature, the time of the stirring and grinding in the sand mill, the sintering temperature and the sintering time in the preparation of the doped manganese oxalate were changed, as shown in Table 13.

[0805] Examples I-42 to I-54

[0806] The sources of lithium, manganese, phosphorus and doping elements A, B, C, D were changed, as shown in Table 14.

[0807] Example I-55

[0808] (1) Preparation of the doped manganese oxalate

[0809] 1.2 mol of MnSO4-H2O and 0.79 mol of FeSO4-H2O were mixed in a mixer for 6 hours; the mixture was transferred into a reaction kettle, 10 L of deionized water and 2 mol of oxalic acid dihydrate, 0.01 mol of VCl2 were added, heated to 80°C, then stirred at a speed of 600 rpm for 6 hours, the reaction was terminated (no gas bubbles were generated), a suspension of Fe-doped manganese oxalate was obtained; the suspension was filtered, the filter cake was dried at 120°C, ground, and a Dv50 of 2.5 μm was obtained. 50Fe-doped manganese oxalate particles of about 100 nm;

[0810] (2) Preparation of doped lithium manganese phosphate

[0811] Take 1 mol of Fe-doped manganese oxalate particles, 0.45 mol of lithium carbonate, 0.05 mol of MgSO4, 0.9 mol of phosphoric acid in 85% concentration phosphoric acid aqueous solution, 0.1 mol of H4SiO4, 0.05 mol of NH4HF2 and 0.005 mol of sucrose into 20 L of deionized water, and the mixture is transferred into a sand mill for intensive grinding and stirring for 10 hours to obtain a slurry; the slurry is transferred to a spray drying device for spray drying and granulation, and the drying temperature is set to 250°C, and the granulation is dried for 4 hours to obtain particles; the particles are sintered at 700°C for 10 hours in a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere to obtain a positive electrode active material. The elemental content is detected by inductively coupled plasma emission spectrometry (ICP), and the chemical formula of the positive electrode active material is Li 0.9 Mg 0.05 Mn 0.6 Fe 0.395 V 0.00 5P 0.9 Si 0.1 O 3.9 F 0.1 .

[0812] Example I-56

[0813] Except that in step (2), the lithium carbonate is 0.55 mol, the MgSO4 is 0.001 mol, and the NH4HF2 is 0.001 mol, the rest is the same as Preparation Example B55; a positive electrode active material Li 1.1 Mg 0.001 Mn 0.6 Fe 0.395 V 0.005 P 0.9 Si 0.1 O 3.998 F 0.002 .

[0814] Example I-57

[0815] Except that in step (2), the MgSO4 is 0.1 mol, the 85% concentration phosphoric acid aqueous solution contains 0.95 mol of phosphoric acid, the H4SiO4 is 0.05 mol, and the NH4HF2 is 0.025 mol, the rest is the same as Preparation Example B55; a positive electrode active material Li 0.9 Mg 0.1 Mn 0.6 Fe 0.395 V 0.005 P 0.95Si 0.05 O 3.95 F 0.05 .

[0816] Example I-58

[0817] Except that in step (1) MnSO4-H2O was 1.998 mol, FeSO4-H2O was 0.002 mol and VCl2 was not used; and except that in step (2) lithium carbonate was 0.475 mol, the aqueous solution of phosphoric acid having a concentration of 85% contained 0.96 mol of phosphoric acid, H4SiO4 was 0.04 mol, and NH4HF2 was 0.01 mol; and the rest was the same as in Preparation Example B55; to obtain a positive electrode active material Li 0.95 Mg 0.05 Mn 0.999 Fe 0.001 P 0.96 Si 0.04 O 3.99 F 0.01 .

[0818] Example I-59

[0819] Except that in step (1) MnSO4-H2O was 1.98 mol, FeSO4-H2O was 0.02 mol and VCl2 was not used; and except that in step (2) lithium carbonate was 0.475 mol, the aqueous solution of phosphoric acid having a concentration of 85% contained 0.96 mol of phosphoric acid, H4SiO4 was 0.04 mol, and NH4HF2 was 0.01 mol; and the rest was the same as in Preparation Example B55; to obtain a positive electrode active material Li 0.95 Mg 0.05 Mn 0.9 9Fe 0.01 P 0.96 Si 0.04 O 3.99 F 0.01 .

[0820] Example I-60

[0821] Except that in step (1) MnSO4-H2O was 1.6 mol, FeSO4-H2O was 0.4 mol and VCl2 was not used; and except that in step (2) lithium carbonate was 0.475 mol, the aqueous solution of phosphoric acid having a concentration of 85% contained 0.96 mol of phosphoric acid, H4SiO4 was 0.04 mol, and NH4HF2 was 0.01 mol; and the rest was the same as in Preparation Example B55; to obtain a positive electrode active material Li 0.95 Mg 0.05 Mn 0. 8Fe 0.2 P 0.96 Si 0.04O 3.99 F 0.01 .

[0822] Example I-61

[0823] Preparation of Fe, Co and V co-doped manganese oxalate: 689.5 g of manganese carbonate (as MnC03, same below), 455.2 g of ferrous carbonate (as FeC03, same below), 4.6 g of cobalt sulfate (as CoS04, same below) and 4.9 g of vanadium dichloride (as VCl2, same below) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C and stirred at a speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), obtaining a Fe, Co, V and S co-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C, followed by grinding, obtaining Fe, Co and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0824] Preparation of Fe, Co, V and S co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles obtained in the previous step (1793.4 g), 314 g of lithium carbonate (as Li2C03, same below), 89.8 g of MgS04, 1.6 g of dilute sulfuric acid with a concentration of 60% (as 60% H2S04, same below) and 1148.9 g of ammonium dihydrogen phosphate (as NH4H2P04, same below) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to make it uniform, obtaining a slurry. The slurry was transferred to a spray drying device for spray drying granulation, and the drying temperature was set to 250°C and dried for 4 hours, obtaining a powder. The above-mentioned powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, obtaining Li 0.85 Mg 0.075 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.999 S 0.00 1O4.

[0825] Example I-62

[0826] Without adding MgS04, the mass of lithium carbonate was 425 g, and the rest was the same as in Example I-61, obtaining Li 1.15 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.999 S 0.001 O4.

[0827] Example I-63

[0828] Without adding CoSO4, VCl2 and MgSO4, the mass of MnCO3 is 1.149 g, the mass of FeCO3 is 1157 g, the mass of Li2CO3 is 425 g, and the rest is the same as in Example I-61, to obtain Li 1.15 Mn 0.001 Fe 0.999 P 0.999 S 0.00 1O4.

[0829] Example I-64

[0830] Without adding Mo(SO4)3, the amount of Li2CO3 is adjusted to 0.575 mol, the amount of MnSO4-H2O is adjusted to 0.002 mol, the amount of FeSO4-H2O is adjusted to 1.998 mol, the concentration of phosphoric acid is adjusted to 85% phosphoric acid aqueous solution to 0.5 mol, 0.001 mol of H4SiO4 is replaced with 0.5 mol of H2SO4, the amount of MnC2O4-2H2O is adjusted to 0.875 mol, the amount of NH4HF2 is adjusted to 0.25 mol, and the rest is the same as in Example I-1, to obtain Li 1.15 Mn 0.001 Fe 0.999 P 0.5 S 0.5 O 3.5 F 0.5 .

[0831] Example I-65

[0832] Without adding MgSO4, the amount of Li2CO3 is changed to 0.499 mol, and the rest is the same as in Example I-12, to obtain Li 0.998 Mn 0.68 Fe 0.3 V 0.02 P 0.999 N 0.001 O 3.999 F 0.001 .

[0833] Example I-66

[0834] Without adding HNO3, the concentration of phosphoric acid is adjusted to 85% phosphoric acid aqueous solution to 1 mol, and the rest is the same as in Example I-12, to obtain Li 0.997 Mg 0.001 Mn 0.68 Fe 0.3 V 0.02 PO 3.999 F 0.001 .

[0835] Example I-67

[0836] Without adding NH4HF2, the rest is the same as Example I-12 to obtain Li 0.997 Mg 0.001 Mn 0.68 Fe 0.3 V 0.02 P 0.999 N 0.00 1O4.

[0837] Example I-68

[0838] Without adding MgSO4 and HNO3, the amount of Li2CO3 was changed to 0.499 mol, the concentration of phosphoric acid was adjusted to 1 mol of 85% phosphoric acid aqueous solution, and the rest was the same as in Example I-12 to obtain Li 0.998 Mn 0.68 Fe 0.3 V 0.02 PO 3.999 F 0.001 .

[0839] Example I-2-1

[0840] 1) Preparation of positive electrode active materials

[0841] Preparation of doped manganese oxalate: 1.3 mol of MnSO4﹒H2O and 0.7 mol of FeSO4﹒H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reactor and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reactor was heated to 80°C and stirred at 600 rpm for 6 hours. The reaction was terminated (no bubbles were generated) to obtain an Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C and then ground to obtain a median particle size Dv 50 Fe-doped manganese oxalate particles with a size of about 100 nm.

[0842] Preparation of doped lithium manganese phosphate: Take 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, 0.05 mol of sucrose and 0.025 mol of ethylenediamine and add them to 20L of deionized water. Transfer the mixture to a sand mill and grind and stir it for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, set the drying temperature to 250°C, dry it for 4 hours, and obtain particles. In a protective atmosphere of nitrogen (90 volume %) + hydrogen (10 volume %), sinter the above powder at 700°C for 10 hours to obtain Li doped with carbon layer. 0.994 Mo 0.001Mn 0.65 Fe 0.35 P 0.999 Si 0.00 1O 3.999 F 0.001 .

[0843] 2) Preparation of button cell

[0844] The above positive active material, polyvinylidene fluoride (PVDF) and acetylene black were added into N-methyl pyrrolidone (NMP) in a weight ratio of 90:5:5, and stirred in a dry room to make a slurry. The slurry was coated on an aluminum foil, dried, and cold-pressed to make a positive electrode sheet. The coating amount was 0.2 g / cm 2 , and the compacted density was 2.0 g / cm 3 .

[0845] Lithium sheet was used as the negative electrode, and a solution of 1 mol / L LiPF6 in a volume ratio of 1:1:1 of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) was used as the electrolyte. The above prepared positive electrode sheet was assembled into a button cell (hereinafter also referred to as "button") in a button cell box.

[0846] 3) Preparation of full cell

[0847] The above positive active material, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) were uniformly mixed in a weight ratio of 92:2.5:5.5 in an N-methyl pyrrolidone solvent system, coated on an aluminum foil, dried and cold-pressed to obtain a positive electrode sheet. The coating amount was 0.4 g / cm 2 , and the compacted density was 2.4 g / cm 3 .

[0848] The negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR) and thickening agent sodium carboxymethyl cellulose (CMC) were uniformly mixed in a weight ratio of 90:5:2:2:1 in deionized water, coated on a copper foil, dried and cold-pressed to obtain a negative electrode sheet. The coating amount was 0.2 g / cm 2 , and the compacted density was 1.7 g / cm 3 .

[0849] A polyethylene (PE) porous polymer film was used as a separator film, and the positive electrode sheet, the separator film and the negative electrode sheet were stacked in order with the separator film between the positive and negative electrodes to play a role of separation, and wound to obtain a bare cell. The bare cell was placed in an outer package, injected with the same electrolyte as in the preparation of the button cell and packaged to obtain a full cell (hereinafter also referred to as "full").

[0850] Example I-2-2

[0851] Example 1 was repeated except that in "1) Preparation of positive active material", the amount of high-purity Li2CO3 was changed to 0.4885 mol, Mo(SO4)3 was replaced with MgSO4, the amount of FeSO4-H2O was changed to 0.68 mol, 0.02 mol of Ti(SO4)2 was added in the preparation of manganese oxalate-doped, and H4SiO4 was replaced with HNO3.

[0852] Comparative Example I-1

[0853] Preparation of manganese oxalate: 1 mol of MnSO4-H2O was added to a reaction vessel, and 10 L of deionized water and 1 mol of oxalic acid dihydrate (as oxalic acid) were added. The reaction vessel was heated to 80°C, and stirred at 600 rpm for 6 hours, and the reaction was terminated (no gas bubbles were generated), to obtain a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C, and then ground, to obtain manganese oxalate particles having a median particle diameter Dv50-200 nm. 50 Preparation of manganese oxalate: 1 mol of MnSO4-H2O was added to a reaction vessel, and 10 L of deionized water and 1 mol of oxalic acid dihydrate (as oxalic acid) were added. The reaction vessel was heated to 80°C, and stirred at 600 rpm for 6 hours, and the reaction was terminated (no gas bubbles were generated), to obtain a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C, and then ground, to obtain manganese oxalate particles having a median particle diameter Dv50-200 nm.

[0854] Preparation of lithium manganese phosphate: 1 mol of the above manganese oxalate particles, 0.5 mol of lithium carbonate, 1 mol of phosphoric acid in an 85% concentration aqueous solution of phosphoric acid, and 0.005 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill, and thoroughly ground and stirred for 10 hours, to obtain a slurry. The slurry was transferred to a spray-drying apparatus, and spray-dried and granulated, with the drying temperature set to 250°C, and dried for 4 hours, to obtain granules. The above powder was sintered at 700°C for 10 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, to obtain carbon-coated LiMnPO4.

[0855] Comparative Example I-2

[0856] Example 1 was repeated except that in Comparative Example I-1, 1 mol of MnSO4-H2O was replaced with 0.85 mol of MnSO4-H2O and 0.15 mol of FeSO4-H2O, and the mixture was added to the reaction vessel after being thoroughly mixed in a mixer for 6 hours.

[0857] Comparative Example I-3

[0858] Example 1 was repeated except that in "1) Preparation of positive active material", the amount of MnSO4-H2O was changed to 1.9 mol, 0.7 mol of FeSO4-H2O was replaced with 0.1 mol of ZnSO4, the amount of Li2CO3 was changed to 0.495 mol, 0.001 mol of Mo(SO4)3 was replaced with 0.005 mol of MgSO4, the amount of phosphoric acid was changed to 1 mol, and H4SiO4 and NH4HF2 were not added. Comparative Example I-3

[0859] Comparative Example I-4

[0860] Example I-1 was repeated except that in "1) Preparation of the positive active material", the amount of MnS04.H20 was changed to 1.2 mol, the amount of FeS04.H20 was changed to 0.8 mol, the amount of Li2C03was changed to 0.45 mol, 0.001 mol of Mo(S04)3was replaced with 0.005 mol of Nb2(S04)5, 0.999 mol of phosphoric acid was replaced with 1 mol, 0.0005 mol of NH4HF2was replaced with 0.025 mol, and H4Si04was not added.

[0861] Comparative Example I-5

[0862] Example I-1 was repeated except that in "1) Preparation of the positive active material", the amount of MnS04.H20 was changed to 1.4 mol, the amount of FeS04.H20 was changed to 0.6 mol, the amount of Li2C03was changed to 0.38 mol, 0.001 mol of Mo(S04)3was replaced with 0.12 mol of MgS04.

[0863] Comparative Example I-6

[0864] Example I-1 was repeated except that in "1) Preparation of the positive active material", the amount of MnS04.H20 was changed to 0.8 mol, 0.7 mol of FeS04.H20 was replaced with 1.2 mol of ZnS04, the amount of Li2C03was changed to 0.499 mol, and 0.001 mol of Mo(S04)3was replaced with 0.001 mol of MgS04.

[0865] Comparative Example I-7

[0866] Example I-1 was repeated except that in "1) Preparation of the positive active material", the amount of MnS04.H20 was changed to 1.4 mol, the amount of FeS04.H20 was changed to 0.6 mol, the amount of Li2C03was changed to 0.534 mol, 0.001 mol of Mo(S04)3was replaced with 0.001 mol of MgS04, the amount of phosphoric acid was changed to 0.88 mol, the amount of H4Si04was changed to 0.12 mol, and the amount of NH4HF2was changed to 0.025 mol.

[0867] Comparative Example I-8

[0868] Example I-1 was repeated except that in "1) Preparation of the positive active material", the amount of MnS04-H20 was changed to 1.2 mol, the amount of FeS04-H20 was changed to 0.8 mol, the amount of Li2C03was changed to 0.474 mol, 0.001 mol of Mo(S04)3was replaced with 0.001 mol of MgS04, the amount of phosphoric acid was changed to 0.93 mol, the amount of H4Si04was changed to 0.07 mol, and the amount of NH4HF2was changed to 0.06 mol.

[0869]

Double-coated positive active material and preparation of a battery

[0870] Example II-1-1

[0871] (1) Preparation of the positive active material

[0872] Preparation of a lithium manganese phosphate core co-doped with phosphorus

[0873] Preparation of Fe, Co, and V co-doped manganese oxalate: 689.5 g of manganese carbonate (as MnC03, hereinafter), 455.2 g of ferrous carbonate (as FeC03, hereinafter), 4.6 g of cobalt sulfate (as CoS04, hereinafter), and 4.9 g of vanadium dichloride (as VCl2, hereinafter) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, hereinafter) were added. The reaction kettle was heated to 80°C and stirred at a speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), resulting in a suspension of Fe, Co, V, and S co-doped manganese oxalate. The suspension was then filtered and the filter cake was dried at 120°C, after which it was ground, resulting in Fe, Co, and V co-doped manganese oxalate dihydrate particles having a median particle size Dv50 of 100 nm.

[0874] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles obtained in the previous step (1793.4 g), 369.0 g of lithium carbonate (as Li2C03, hereinafter), 1.6 g of dilute sulfuric acid having a concentration of 60% (as 60% H2S04, hereinafter), and 1148.9 g of ammonium dihydrogen phosphate (as NH4H2P04, hereinafter) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to homogenize it, resulting in a slurry. The slurry was transferred to a spray-drying apparatus and spray-dried granulation was performed, with a drying temperature of 250°C and a drying time of 4 hours, resulting in a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, resulting in 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate.

[0875] Preparation of lithium iron pyrophosphate and lithium iron phosphate

[0876] Preparation of lithium iron pyrophosphate powder: 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react sufficiently by stirring for 2 hours. Then, the reacted solution was warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and after natural cooling to room temperature, the powder was ground to obtain a Li2FeP2O7 powder.

[0877] Preparation of lithium iron phosphate suspension: 11.1 g of lithium carbonate, 34.8 g of ferrous carbonate, 34.5 g of ammonium dihydrogen phosphate, 1.3 g of oxalic acid dihydrate and 74.6 g of sucrose (C 12 H 22 O 11 were dissolved in 150 ml of deionized water to obtain a mixture, and then the mixture was allowed to react sufficiently by stirring for 6 hours. Then, the reacted solution was warmed to 120°C and maintained at this temperature for 6 hours to obtain a suspension containing LiFePO4.

[0878] Coating

[0879] The above Fe, Co, V and S co-doped lithium manganese phosphate (LiMnPO4) of 1572.1 g and the above lithium iron pyrophosphate (Li2FeP2O7) powder of 15.72 g were added to the lithium iron phosphate (LiFePO4) suspension prepared in the above step, and after stirring and mixing uniformly, the mixture was transferred into a vacuum oven and dried at 150°C for 6 hours. Then, the obtained product was dispersed by sand milling. After dispersion, the obtained product was sintered at 700°C for 6 hours in a nitrogen atmosphere to obtain a target product of double-coated lithium manganese phosphate.

[0880] (2) Preparation of positive electrode sheet

[0881] The above prepared double-coated lithium manganese phosphate positive active material, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were added to N-methyl pyrrolidone (NMP) at a weight ratio of 92:2.5:5.5, and stirred and mixed uniformly to obtain a positive electrode slurry. Then, the positive electrode slurry was uniformly coated on an aluminum foil at 0.280 g / 1540.25 mm 2 after drying, cold pressing and slitting to obtain a positive electrode sheet.

[0882] (3) Preparation of negative electrode sheet

[0883] The negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickening agent sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water according to a weight ratio of 90:5:2:2:1, and after stirring and mixing uniformly, a negative electrode slurry was prepared. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil at 0.117 g / 1540.25 mm 2 The negative electrode current collector copper foil was dried, cold-pressed, and cut to obtain a negative electrode sheet.

[0884] (4) Preparation of electrolyte

[0885] In an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), as an organic solvent, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) was mixed uniformly according to a volume ratio of 3 / 7, 12.5% by weight (based on the weight of the organic solvent) LiPF6 was added and dissolved in the above-mentioned organic solvent, and stirred uniformly to obtain an electrolyte.

[0886] (5) Separator

[0887] A PP-PE copolymer microporous film (from Zhuogao Electronics Technology Co., Ltd., model 20) with a thickness of 20 μm and an average pore size of 80 nm was used.

[0888] (6) Preparation of full battery

[0889] The positive electrode sheet, the separator, and the negative electrode sheet obtained above were stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, and were wound to obtain a bare battery cell. The bare battery cell was placed in an outer package, injected with the above-mentioned electrolyte and packaged to obtain a full battery (hereinafter also referred to as "full").

[0890] (7) Preparation of button cell

[0891] The double-coated lithium manganese phosphate positive electrode active material prepared above, PVDF, and acetylene black were added to NMP in a weight ratio of 90:5:5, and a slurry was prepared by stirring in a dry room. The slurry was coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet. The coating amount was 0.2 g / cm 2 , and the compacted density was 2.0 g / cm 3 .

[0892] A lithium sheet was used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte, which was assembled with the positive electrode sheet prepared above in a button cell box to obtain a button cell (hereinafter also referred to as "button").

[0893] Examples II-1-2 to II-1-6

[0894] In the preparation of the co-doped lithium manganese phosphate core, the preparation conditions of the lithium manganese phosphate core in Examples II-1-2 to II-1-6 were the same as those in Example II-1-1, except that vanadium dichloride and cobalt sulfate were not used, 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate, and 369.0 g of lithium carbonate were used.

[0895] Further, in the preparation of the lithium iron pyrophosphate and lithium iron phosphate and the process of coating the first coating layer and the second coating layer, the use amounts of Li2FeP2O7 / LiFePO4 in Examples II-1-2 to II-1-6 were 12.6 g / 37.7 g, 15.7 g / 47.1 g, 18.8 g / 56.5 g, 22.0 g / 66.0 g, and 25.1 g / 75.4 g, respectively, and the use amount of sucrose in Examples II-1-2 to II-1-6 was 37.3 g, except that the use amounts of the raw materials were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example II-1-1, and the other conditions were the same as those in Example II-1-1.

[0896] Examples II-1-7 to II-1-10

[0897] The conditions of Examples II-1-7 to II-1-10 were the same as those in Example II-1-3, except that the use amounts of sucrose were 74.6 g, 149.1 g, 186.4 g, and 223.7 g, respectively, so that the corresponding coating amounts of the carbon layer as the second coating layer were 31.4 g, 62.9 g, 78.6 g, and 94.3 g, respectively.

[0898] Examples II-1-11 to II-1-14

[0899] The conditions of Examples II-1-11 to II-1-14 were the same as those in Example II-1-7, except that the use amounts of the raw materials were adjusted according to the coating amount shown in Table 1 in the preparation of the lithium iron pyrophosphate and lithium iron phosphate so that the use amounts of Li2FeP2O7 / LiFePO4 were 23.6 g / 39.3 g, 31.4 g / 31.4 g, 39.3 g / 23.6 g, and 47.2 g / 15.7 g, respectively.

[0900] Example II-1-15

[0901] The conditions of Example II-1-15 were the same as those in Example II-1-14, except that 492.80 g of ZnCO3 was used instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core.

[0902] Examples II-1-16 to II-1-18

[0903] Example II-1-16 to II-1-18 except that in the preparation of the co-doped lithium manganese phosphate core, 466.4 g of NiCO3, 5.0 g of zinc carbonate, and 7.2 g of titanium sulfate were used instead of ferrous carbonate in Example II-1-16, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used in the preparation of the co-doped lithium manganese phosphate core in Example II-1-17, and 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride, and 2.5 g of magnesium carbonate were used in the preparation of the co-doped lithium manganese phosphate core in Example II-1-18, the conditions of Examples II-1-17 to II-1-19 were the same as those of Example II-1-7.

[0904] Examples II-1-19 to II-1-20

[0905] Example II-1-19 to II-1-20 except that in the preparation of the co-doped lithium manganese phosphate core, 369.4 g of lithium carbonate, and 1.05 g of 60% concentration of dilute nitric acid were used instead of dilute sulfuric acid in Example II-1-19, and 369.7 g of lithium carbonate, and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core in Example II-1-20, the conditions of Examples II-1-19 to II-1-20 were the same as those of Example II-1-18.

[0906] Examples II-1-21 to II-1-22

[0907] Example II-1-21 to II-1-22 except that in the preparation of the co-doped lithium manganese phosphate core, 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid were used in Example II-1-21, and 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid were used in the preparation of the co-doped lithium manganese phosphate core in Example II-1-22, the conditions of Examples II-1-21 to II-1-22 were the same as those of Example II-1-20.

[0908] Examples II-1-23 to II-1-24

[0909] Example II-1-23 to II-1-24 except that in the preparation of the co-doped lithium manganese phosphate core, 804.6 g of manganese carbonate, 231.7 g of ferrous carbonate, 1156.2 g of ammonium dihydrogen phosphate, 1.2 g of boric acid (mass fraction 99.5%), and 370.8 g of lithium carbonate were used in Example II-1-23, and 862.1 g of manganese carbonate, 173.8 g of ferrous carbonate, 1155.1 g of ammonium dihydrogen phosphate, 1.86 g of boric acid (mass fraction 99.5%), and 371.6 g of lithium carbonate were used in the preparation of the co-doped lithium manganese phosphate core in Example II-1-24, the conditions of Examples II-1-23 to II-1-24 were the same as those of Example II-1-22.

[0910] Example II-1-25

[0911] The conditions of Example II-1-25 are the same as those of Example II-1-20, except that 370.1 g of lithium carbonate, 1.56 g of silicic acid, and 1147.7 g of ammonium dihydrogen phosphate are used in the preparation of the core of the co-doped lithium manganese phosphate.

[0912] Example II-1-26

[0913] The conditions of Example II-1-26 are the same as those of Example II-1-20, except that 368.3 g of lithium carbonate, 4.9 g of dilute sulfuric acid with a mass fraction of 60%, 919.6 g of manganese carbonate, 224.8 g of ferrous carbonate, 3.7 g of vanadic dichloride, 2.5 g of magnesium carbonate, and 1146.8 g of ammonium dihydrogen phosphate are used in the preparation of the core of the co-doped lithium manganese phosphate.

[0914] Example II-1-27

[0915] The conditions of Example II-1-27 are the same as those of Example II-1-20, except that 367.9 g of lithium carbonate, 6.5 g of dilute sulfuric acid with a concentration of 60%, and 1145.4 g of ammonium dihydrogen phosphate are used in the preparation of the core of the co-doped lithium manganese phosphate.

[0916] Examples II-1-28 to II-1-33

[0917] The conditions of Examples II-1-28 to II-1-33 are the same as those of Example II-1-20, except that 1034.5 g of manganese carbonate, 108.9 g of ferrous carbonate, 3.7 g of vanadic dichloride, and 2.5 g of magnesium carbonate are used in the preparation of the core of the co-doped lithium manganese phosphate, the amount of lithium carbonate used is 367.6 g, 367.2 g, 366.8 g, 366.4 g, 366.0 g, and 332.4 g, respectively, the amount of ammonium dihydrogen phosphate used is 1144.5 g, 1143.4 g, 1142.2 g, 1141.1 g, 1139.9 g, and 1138.8 g, respectively, and the amount of dilute sulfuric acid with a concentration of 60% used is 8.2 g, 9.8 g, 11.4 g, 13.1 g, 14.7 g, and 16.3 g, respectively.

[0918] Example II-1-34

[0919] Core Li 1.1 Mn 0.6 Fe 0.393 Mg 0.007 P 0.9 Si0.1 Preparation of O4:

[0920] Preparation of Fe and Mg co-doped manganese oxalate: 689.5 g of manganese carbonate (as MnCO3, same below), 455.2 g of ferrous carbonate (as FeCO3, same below) and 5.90 g of magnesium carbonate (as MgCO3, same below) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C and stirred at a speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), obtaining a Fe and Mg co-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C, followed by grinding, obtaining Fe and Mg co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0921] Preparation of Fe, Mg and Si co-doped lithium manganese phosphate: the manganese oxalate dihydrate particles obtained in the previous step (1791.3 g), 406.3 g of lithium carbonate (as Li2CO3, same below), 7.8 g of silicic acid (as H2SiO3, same below) and 1035.0 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, setting the drying temperature to 250°C and drying for 4 hours, obtaining a powder. The above powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, obtaining 1574.0 g of Fe, Mg and Si co-doped lithium manganese phosphate.

[0922] The other conditions refer to Example II-1-1.

[0923] Example II-1-35

[0924] Core LiMn 0.50 Fe 0.50 P 0.995 N 0.005 Preparation of O4.

[0925] Preparation of Fe-doped manganese oxalate: 574.7 g of manganese carbonate (as MnC03, same below) and 579.27 g of ferrous carbonate (as FeC03, same below) were thoroughly mixed in a blender for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80 °C and stirred at 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), resulting in a Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120 °C before being ground, resulting in Fe-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0926] Preparation of Fe and N co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles obtained in the previous step (1794.4 g), 369.4 g of lithium carbonate (as Li2C03, same below), 5.25 g of dilute nitric acid (as 60% HN03, same below), and 1144.3 g of ammonium dihydrogen phosphate (as NH4H2P04, same below) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to homogenize, resulting in a slurry. The slurry was transferred to a spray-drying apparatus and spray-dried granulated at a drying temperature of 250 °C for 4 hours, resulting in a powder. The powder was sintered at 700 °C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, resulting in 1572.2 g of Fe and N co-doped lithium manganese phosphate.

[0927] The other conditions refer to Example II-1-1.

[0928] Example II-1-36

[0929] Preparation of core LiMn 0.909 Fe 0.091 P 0.99 N 0.01 O4, 1044.6 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 369.4 g of lithium carbonate were used, and additionally 105.4 g of ferrous carbonate and 10.5 g of dilute nitric acid (as 60% HN03, same below) were added, and the rest was the same as in Example II-1-1.

[0930] Example II-1-37

[0931] Preparation of core LiMn 0.091 Fe 0.909 P 0.995 N 0.005When O4 is used, 104.5g of manganese carbonate, 1138.5g of ammonium dihydrogen phosphate and 371.3g of lithium carbonate are used, and 1052.8g of ferrous carbonate and 5.25g of dilute nitric acid (calculated as 60% HNO3, the same below) are additionally added. The rest is the same as Example II-1-1.

[0932] Example II-1-38

[0933] In the preparation process of lithium iron pyrophosphate and lithium iron phosphate and the process of coating the first coating layer and the second coating layer, except that the raw materials used are adjusted according to the ratio of the coating amount shown in Table 4 and the coating amount corresponding to Example II-1-1, so that the amount of Li2FeP2O7 / LiFePO4 is 62.9g / 47.1g respectively, other conditions are the same as Example II-1-1.

[0934] Example II-1-39

[0935] In the preparation of silver pyrophosphate, 463.4 g of silver oxide (calculated as Ag2O, the same below) and 230.6 g of phosphoric acid (calculated as 85% H3PO4, the same below) are thoroughly mixed. The mixture is heated to 450°C while stirring continuously for 2 hours to allow the reaction mixture to fully react. The resulting solution is then held at 450°C for 4 hours, yielding a viscous paste containing Ag4P2O7. This solid is then washed with deionized water, ground in a ball mill filled with ethanol for 4 hours, and dried under an infrared lamp to yield Ag4P2O7 powder. The remaining steps are the same as in Example II-1-1.

[0936] Example II-1-40

[0937] Except that during the preparation of Fe, Co, V and S co-doped lithium manganese phosphate, the powder was sintered at 650°C for 43.5 hours in a protective atmosphere of nitrogen (90 volume %) + hydrogen (10 volume %), everything else is the same as Example II-1-21.

[0938] Example II-1-41

[0939] Core LiMn 0.999 Fe 0.001 P 0.995 N 0.005 Preparation of O4

[0940] Preparation of Fe-doped manganese oxalate: 1148.0 g of manganese carbonate (as MnCO3, same below) and 11.58 g of ferrous carbonate (as FeCO3, same below) were mixed thoroughly in a mixer for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C, followed by grinding, to obtain Fe-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0941] Preparation of Fe and N co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles (1789.9 g) obtained in the previous step, 369.4 g of lithium carbonate (as Li2CO3, same below), 5.25 g of dilute nitric acid (as 60% HNO3, same below) and 1144.3 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to make it uniform, to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, with a drying temperature set at 250°C and dried for 4 hours to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere to obtain 1567.7 g of Fe and N co-doped lithium manganese phosphate.

[0942] The other conditions of Examples II-1-41 are the same as those of Example II-1-1.

[0943] Example II-2-1

[0944] Except that the sintering temperature in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP2O7) was 550°C and the sintering time was 1 h to control the crystallinity of Li2FeP2O7 to be 30%, and the sintering temperature in the coating sintering step in the preparation of lithium iron phosphate (LiFePO4) was 650°C and the sintering time was 2 h to control the crystallinity of LiFePO4 to be 30%, the other conditions were the same as those of Example II-1-1.

[0945] Example II-2-2

[0946] Example II-1-1 except that the sintering temperature in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP207) was 550°C and the sintering time was 2h to control the crystallinity of Li2FeP207 to be 50%, and the sintering temperature in the coating sintering step in the preparation of lithium iron phosphate (LiFeP04) was 650°C and the sintering time was 3h to control the crystallinity of LiFeP04 to be 50%.

[0947] Example II-2-3

[0948] Example II-1-1 except that the sintering temperature in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP207) was 600°C and the sintering time was 3h to control the crystallinity of Li2FeP207 to be 70%, and the sintering temperature in the coating sintering step in the preparation of lithium iron phosphate (LiFeP04) was 650°C and the sintering time was 4h to control the crystallinity of LiFeP04 to be 70%.

[0949] Example II-2-4

[0950] Example II-1-1 except that the sintering temperature in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP207) was 650°C and the sintering time was 4h to control the crystallinity of Li2FeP207 to be 100%, and the sintering temperature in the coating sintering step in the preparation of lithium iron phosphate (LiFeP04) was 700°C and the sintering time was 6h to control the crystallinity of LiFeP04 to be 100%.

[0951] Examples II-3-1 to II-3-12

[0952] Except that the heating temperature / stirring time in the reaction kettle of Example II-3-1 is 60°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-2 is 70°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-3 is 80°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-4 is 90°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-5 is 100°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-6 is 110°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-7 is 120°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-8 is 130°C / 120 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-9 is 100°C / 60 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-10 is 100°C / 90 minutes, the heating temperature / stirring time in the reaction kettle of Example II-3-11 is 100°C / 150 minutes, and the heating temperature / stirring time in the reaction kettle of Example II-3-12 is 100°C / 180 minutes, other conditions of Examples II-3-1 to II-3-12 are the same as those of Example II-1-1.

[0953] Examples II-4-1 to II-4-7

[0954] Examples II-4-1 to II-4-4: Except that the drying temperature / drying time in the drying step in the preparation of lithium iron pyrophosphate (Li2FeP2O7) is 100°C / 4h, 150°C / 6h, 200°C / 6h and 200°C / 6h, respectively, and the sintering temperature and sintering time in the sintering step in the preparation of lithium iron pyrophosphate (Li2FeP2O7) is 700°C / 6h, 700°C / 6h, 700°C / 6h and 600°C / 6h, respectively, other conditions are the same as those of Example II-1-7.

[0955] Examples II-4-5 to II-4-7: Except that the drying temperature / drying time in the drying step in the coating process is 150°C / 6h, 150°C / 6h and 150°C / 6h, respectively, and the sintering temperature and sintering time in the sintering step in the coating process is 600°C / 4h, 600°C / 6h and 800°C / 8h, respectively, other conditions are the same as those of Example II-1-12.

[0956] Example II-5-1:

[0957] (1) Preparation of the Co-doped lithium manganese phosphate core: The same as "Preparation of the Co-doped lithium manganese phosphate core" of Example II-1-1.

[0958] (2) Preparation of lithium iron pyrophosphate and suspension containing aluminum trioxide and sucrose:

[0959] Preparation of lithium iron pyrophosphate powder: 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react sufficiently by stirring for 2 hours. Then, the reacted solution was warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and after natural cooling to room temperature, was ground to obtain a Li2FeP2O7 powder.

[0960] Preparation of a suspension containing aluminum trioxide and sucrose: 47.1 g of nano Al2O3 (particle size of about 20 nm) and 74.6 g of sucrose (C 12 H 22 O 11 were dissolved in 1500 ml of deionized water, and then the mixture was allowed to mix sufficiently by stirring for 6 hours. Then, the resulting solution was warmed to 120°C and maintained at this temperature for 6 hours to obtain a suspension containing aluminum trioxide and sucrose.

[0961] (3) Coating

[0962] The 1572.1 g of the above-mentioned Fe, Co, V and S co-doped lithium manganese phosphate and 15.72 g of the above-mentioned lithium iron pyrophosphate (Li2FeP2O7) powder were added to the suspension containing aluminum trioxide and sucrose prepared in the previous step, and after stirring to mix uniformly, were transferred to a vacuum oven and dried at 150°C for 6 hours. Then, the resulting product was dispersed by sand milling. After dispersion, the resulting product was sintered at 700°C for 6 hours in a nitrogen atmosphere to obtain the target product, double-coated lithium manganese phosphate.

[0963] Example II-5-2

[0964] In the preparation of the Co-doped lithium manganese phosphate core, except that 463.4 g of ferrous carbonate, 1.6 g of 60% concentrated dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate were used instead of vanadium dichloride and cobalt sulfate, the conditions for the preparation of the lithium manganese phosphate core of Example II-5-2 were the same as those of Example II-5-1.

[0965] Further, in the preparation of the lithium iron pyrophosphate and the suspension containing the aluminum trioxide and the sucrose, and in the process of coating the first coating layer and the second coating layer, the raw materials used are adjusted according to the ratio of the coating amount shown in Table 24 to the coating amount corresponding to Example II-5-1, so that the amount of Li2FeP2O7 / Al2O3 in Example II-5-2 is 12.6 g / 37.68 g, and the amount of sucrose in Example II-5-2 is 37.3 g, and the other conditions are the same as those in Example II-5-1.

[0966] Example II-5-3

[0967] Step S1: Preparation of doped manganese oxalate

[0968] 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours; the mixture was transferred to a reaction kettle, 10 L of deionized water and 2 mol of dihydrate oxalic acid were added, heated to 80°C, and then stirred at a speed of 600 rpm for 6 hours, and the reaction was terminated (no gas bubbles were generated), to obtain a suspension of Fe-doped manganese oxalate; the suspension was filtered, the filter cake was dried at 120°C, and ground to obtain Fe-doped manganese oxalate particles with a particle size D v 50 is Fe-doped manganese oxalate particles with a particle size of about 100 nm;

[0969] Step S2: Preparation of a core containing Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001

[0970] 1 mol of Fe-doped manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, 0.999 mol of phosphoric acid in an 85% concentration aqueous solution of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added to 20 L of deionized water, and the mixture was transferred to a sand mill for thorough grinding and stirring for 10 hours to obtain a slurry; the slurry was transferred to a spray drying device for spray drying and granulation, and the drying temperature was set to 250°C, and the granulation was dried for 4 hours to obtain particles; the particles were sintered at 700°C for 10 hours in a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere to obtain a core material. The element content of the core material was detected by inductively coupled plasma emission spectrometry (ICP), and the chemical formula of the core material was obtained as shown above.

[0971] Step S3: Preparation of lithium iron pyrophosphate powder ​

[0972] A mixture of 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate was dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react for 2 hours with stirring. The reacted solution was then warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and ground after natural cooling to room temperature to obtain a Li2FeP2O7 powder.

[0973] Step S4: Preparation of a suspension containing aluminum trioxide and sucrose

[0974] A mixture of 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate was dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react for 2 hours with stirring. The reacted solution was then warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and ground after natural cooling to room temperature to obtain a Li2FeP2O7 powder. 12 H 22 O 11 A mixture of 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate was dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react for 2 hours with stirring. The reacted solution was then warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and ground after natural cooling to room temperature to obtain a Li2FeP2O7 powder.

[0975] Step S5: Preparation of a two-layered coating layer

[0976] A mixture of 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate and 1.3 g of oxalic acid dihydrate was dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react for 2 hours with stirring. The reacted solution was then warmed to 80°C and maintained at this temperature for 4 hours to obtain a suspension containing Li2FeP2O7. The suspension was filtered, washed with deionized water, and dried at 120°C for 4 hours to obtain a powder. The powder was sintered at 650°C for 8 hours in a nitrogen atmosphere, and ground after natural cooling to room temperature to obtain a Li2FeP2O7 powder.

[0977] Example II-5-4

[0978] In the step S3 of preparing the lithium iron pyrophosphate (Li2FeP2O7) powder, the sintering temperature in the sintering step of the powder was 550°C, and the sintering time was 1 h to control the crystallinity of the Li2FeP2O7 to be 30%, and the other conditions were the same as in Example II-5-3.

[0979] Example II-5-5

[0980] Preparation of doped manganese oxalate:MnSO4H2O, 0.7 mol of FeSO4H2O were mixed thoroughly in a mixer for 6 hours. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction kettle was heated to 80°C, and stirred at a rotation speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain Fe-doped manganese oxalate particles with a median particle size Dv 50 of about 100 nm.

[0981] Preparation of the core: mol of the above manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, 0.999 mol of phosphoric acid aqueous solution with a concentration of 85%, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sand mill for thorough grinding and stirring for 10 hours, to obtain a slurry. The slurry was transferred into a spray drying device for spray drying and granulation, with a drying temperature set to 250°C, and dried for 4 hours, to obtain particles. The above powder was sintered at 700°C for 10 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, to obtain carbon-coated Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 , i.e., the core. The elemental content can be detected by inductively coupled plasma emission spectroscopy (ICP).

[0982] Coating of the coating layer: The ammonia-ethyl-amino-propyl polydimethylsiloxane was dissolved in xylene to form a coating liquid, and then the prepared core was added thereto and stirred uniformly to form a mixed slurry. The mixed slurry was placed in a wet pack machine, dried at 120°C for 4 hours in a nitrogen atmosphere, to obtain a positive electrode active material. The mass percentage content of the polar functional groups (i.e., -CH2NH2and -CH2NH-) of the ammonia-ethyl-amino-propyl polydimethylsiloxane was 12%, and the number average molecular weight was 3700. The coating amount was 1% by weight, based on the weight of the prepared core.

[0983] The preparation of button cells and full cells is described in Example II-1-1.

[0984] Example II-5-6

[0985] Step S1: Preparation of Fe, Co, V, and S co-doped manganese oxalate

[0986] Manganese carbonate 689.6 g, ferrous carbonate 455.27 g, cobalt sulfate 4.65 g, vanadium dichloride 4.87 g were added into a mixer and mixed for 6 hours. Then the mixture was transferred into a reactor, 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added, heated to 80 °C, and stirred at 500 rpm for 6 hours until the reaction was complete and no bubbles were generated. A Fe, Co, and V co-doped manganese oxalate suspension was obtained. The suspension was then filtered, dried at 120 °C, and then sand-milled to obtain manganese oxalate particles with a particle size of 100 nm.

[0987] Step S2: Preparation of the inner core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4

[0988] Manganese oxalate 1793.1 g prepared in (1) and 368.3 g of lithium carbonate, 1146.6 g of ammonium dihydrogen phosphate, and 4.9 g of dilute sulfuric acid were taken and added to 20 L of deionized water, stirred well, and mixed uniformly at 80 °C for 10 hours to obtain a slurry. The slurry was transferred to a spray drying device for spray drying and granulation, and dried at a temperature of 250 °C to obtain a powder. The powder was sintered in a roller kiln at 700 °C for 4 hours in a protective atmosphere (90% nitrogen and 10% hydrogen) to obtain the above-mentioned inner core material.

[0989] Step S3: Preparation of the first coating layer suspension

[0990] A Li2FeP2O7 solution was prepared by dissolving 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate, and 12.6 g of oxalic acid dihydrate in 500 mL of deionized water, controlling the pH to be 5, then stirring and reacting at room temperature for 2 hours to obtain a solution, and then heating the solution to 80 °C and maintaining this temperature for 4 hours to obtain the first coating layer suspension.

[0991] Step S4: Coating of the first coating layer

[0992] The doped 1571.9 g of lithium manganese phosphate inner core material obtained in step S2 was added to the first coating layer suspension (coating material content 15.7 g) obtained in step S3, stirred and mixed well for 6 hours, and then transferred to a 120 °C oven for drying for 6 hours, and then sintered at 650 °C for 6 hours to obtain the pyrophosphate coated material.

[0993] Step S5: Preparation of the second coating layer suspension

[0994] A solution was prepared by dissolving 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate in 1500 mL of deionized water, then stirring and reacting for 6 hours, after which the solution was heated to 120°C and maintained at this temperature for 6 hours to obtain a second coating layer suspension.

[0995] Step S6: Coating of the second coating layer

[0996] The 1586.8 g of pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension obtained in step S5 (coating material content 47.1 g), and the mixture was stirred thoroughly for 6 hours. After the mixture was uniformly mixed, it was transferred to a 120°C oven for drying for 6 hours, and then sintered at 700°C for 8 hours to obtain a two-layer coated material.

[0997] Step S7: Preparation of a third coating layer aqueous solution

[0998] 37.3 g of sucrose was dissolved in 500 g of deionized water, and then stirred and thoroughly dissolved to obtain a sucrose aqueous solution.

[0999] Step S8: Coating of the third coating layer

[1000] The two-layer coated material obtained in step S6, 1633.9 g, was added to the sucrose solution obtained in step S7, and the mixture was stirred thoroughly for 6 hours. After the mixture was uniformly mixed, it was transferred to a 150°C oven for drying for 6 hours, and then sintered at 700°C for 10 hours to obtain a three-layer coated material.

[1001] Step S9: Coating of the fourth coating layer

[1002] The hydroxyl-terminated polydimethylsiloxane was dissolved in xylene to form a fourth coating solution, and then the three-layer coated material obtained in step S8 was added thereto and stirred uniformly to form a mixed slurry. The mixed slurry was placed in a wet packer and dried at 120°C for 4 hours in a nitrogen atmosphere to obtain a four-layer coated positive electrode active material. The mass percentage content of the polar functional group (i.e., -OH) of the hydroxyl-terminated polydimethylsiloxane was 3.4%, and the number average molecular weight was 1000. The coating amount was 1% by weight, based on the weight of the three-layer coated material obtained in step S8.

[1003] The preparation of button cells and full cells is described in Example II-1-1.

[1004] Example II-5-7

[1005] Preparation of doped manganese oxalate:MnSO4H2O, 0.7 mol of FeSO4H2O were mixed thoroughly in a mixer for 6 hours. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction kettle was heated to 80°C, and stirred at a rotation speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain Fe-doped manganese oxalate particles with a median particle size Dv 50 of about 100 nm.

[1006] Preparation of the core: mol of the above manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, 0.999 mol of phosphoric acid in an 85% phosphoric acid aqueous solution, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.005 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sand mill for thorough grinding and stirring for 10 hours, to obtain a slurry. The slurry was transferred into a spray drying device for spray drying and granulation, with a drying temperature set at 250°C, and dried for 4 hours, to obtain particles. The above powder was sintered at 700°C for 10 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, to obtain carbon-coated Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 , i.e., the core. The elemental content can be detected by inductively coupled plasma emission spectroscopy (ICP).

[1007] Coating of the coating layer: The carboxymethyl chitosan was dissolved in deionized water to form a coating liquid, and then the core material was added thereto and stirred uniformly to form a mixed slurry. The mixed slurry was placed in a wet packaging machine, and dried at 120°C for 4 hours in a nitrogen atmosphere, to obtain a positive electrode active material. The mass percentage content of the substituents connected to the sugar units in the carboxymethyl chitosan was 60.2%, and the number average molecular weight was 26,000. The coating amount was 1% by weight, based on the weight of the core.

[1008] The preparation of button cells and full cells is described in Example II-1-1.

[1009] Comparative Example II-1

[1010] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was charged into a reaction vessel, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (C2H2O4 2H2O, hereinafter the same) were added. The reaction vessel was heated to 80°C, and stirred at 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a manganese oxalate suspension, which was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain manganese oxalate dihydrate particles having a median particle diameter Dv50 of 100 nm.

[1011] Preparation of carbon-coated lithium manganese phosphate: 1789.6 g of the manganese oxalate dihydrate particles obtained above, 369.4 g of lithium carbonate (Li2CO3, hereinafter the same), 1150.1 g of ammonium dihydrogen phosphate (NH4H2PO4, hereinafter the same), and 31 g of sucrose (C12H22O11, hereinafter the same) were added to 20 liters of deionized water, and the mixture was stirred for 10 hours to homogenize, to obtain a slurry. The slurry was transferred to a spray-drying apparatus to perform spray-drying granulation, and the drying temperature was set to 250°C, and dried for 4 hours to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, to obtain carbon-coated lithium manganese phosphate. 12 H 22 O 11 The slurry was transferred to a spray-drying apparatus to perform spray-drying granulation, and the drying temperature was set to 250°C, and dried for 4 hours to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, to obtain carbon-coated lithium manganese phosphate.

[1012] Comparative Example II-2

[1013] The other conditions of Comparative Example II-2 were the same as those of Comparative Example II-1, except that 689.5 g of manganese carbonate was used, and 463.3 g of ferrous carbonate was additionally added.

[1014] Comparative Example II-3

[1015] The other conditions of Comparative Example II-3 were the same as those of Comparative Example II-1, except that 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate were used, and 1.6 g of dilute sulfuric acid at a concentration of 60% was additionally added.

[1016] Comparative Example II-4

[1017] The other conditions of Comparative Example II-4 were the same as those of Comparative Example II-1, except that 689.5 g of manganese carbonate, 1148.9 g of ammonium dihydrogen phosphate, and 369.0 g of lithium carbonate were used, and 463.3 g of ferrous carbonate, 1.6 g of dilute sulfuric acid at a concentration of 60% was additionally added.

[1018] Comparative Example II-5

[1019] Example II-4 except for the additional step of preparing the lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water, and then the mixture was stirred for 6 hours to allow the reaction mixture to react sufficiently. The reacted solution was then warmed to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFeP04. The other conditions of Comparative Example II-4 were the same as those of Example II-4 except that the sintering temperature in the coating and sintering step during the preparation of lithium iron phosphate (LiFeP04) was 600°C, the sintering time was 4 hours to control the crystallinity of LiFeP04 to 8%, and the amount of LiFeP04 used in the preparation of the carbon-coated material was 62.8 g.

[1020] Comparative Example II-6

[1021] Example II-4 except for the additional step of preparing the lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water, and then the mixture was stirred for 6 hours to allow the reaction mixture to react sufficiently. The reacted solution was then warmed to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFeP04. The other conditions of Comparative Example II-4 were the same as those of Example II-4 except that the sintering temperature in the coating and sintering step during the preparation of lithium iron phosphate (LiFeP04) was 600°C, the sintering time was 4 hours to control the crystallinity of LiFeP04 to 8%, and the amount of LiFeP04 used in the preparation of the carbon-coated material was 62.8 g.

[1022] Comparative Example II-7

[1023] Example II-4 except for the additional step of preparing the lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water, and then the mixture was stirred for 6 hours to allow the reaction mixture to react sufficiently. The reacted solution was then warmed to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFeP04. The other conditions of Comparative Example II-4 were the same as those of Example II-4 except that the sintering temperature in the coating and sintering step during the preparation of lithium iron phosphate (LiFeP04) was 600°C, the sintering time was 4 hours to control the crystallinity of LiFeP04 to 8%, and the amount of LiFeP04 used in the preparation of the carbon-coated material was 62.8 g.

[1024] Example II-4 except for the additional step of preparing the lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 ml of deionized water, and then the mixture was stirred for 6 hours to allow the reaction mixture to react sufficiently. The reacted solution was then warmed to 120°C and maintained at that temperature for 6 hours to obtain a suspension containing LiFeP04. The other conditions of Comparative Example II-4 were the same as those of Example II-4 except that the sintering temperature in the coating and sintering step during the preparation of lithium iron phosphate (LiFeP04) was 600°C, the sintering time was 4 hours to control the crystallinity of LiFeP04 to 8%, and the amount of LiFeP04 used in the preparation of the carbon-coated material was 62.8 g. 12 H 22 O 11The lithium phosphate 15.7 g obtained in step 1 was added to the lithium phosphate (LiFeP04) and sucrose suspension prepared in step 2, and the sintering temperature in the coating and sintering step in the preparation process was 600°C, and the sintering time was 4 h to control the crystallinity of LiFeP04 to be less than 8%, and the other conditions were the same as those in Example II-1, to obtain an amorphous lithium pyrophosphate, an amorphous lithium phosphate, and a carbon-coated positive electrode active material.

[1025] The lithium phosphate 15.7 g obtained in step 1 was added to the lithium phosphate (LiFeP04) and sucrose suspension prepared in step 2, and the sintering temperature in the coating and sintering step in the preparation process was 600°C, and the sintering time was 4 h to control the crystallinity of LiFeP04 to be less than 8%, and the other conditions were the same as those in Example II-1, to obtain an amorphous lithium pyrophosphate, an amorphous lithium phosphate, and a carbon-coated positive electrode active material.

[1026] Examples III-8 to III-11 were implemented

[1027] Except that the drying temperature / drying time in the drying step in the preparation process of lithium pyrophosphate (Li2FeP207) was 80°C / 3h, 80°C / 3h, 80°C / 3h, respectively, in Comparative Examples II-8 to II-10; the sintering temperature and sintering time in the sintering step in the preparation process of lithium pyrophosphate (Li2FeP207) were 400°C / 3h, 400°C / 3h, 350°C / 2h, respectively, in Comparative Examples II-8 to II-10; the drying temperature / drying time in the drying step in the preparation process of lithium phosphate (LiFeP04) was 80°C / 3h in Comparative Example II-11; and the amount of Li2FeP207 / LiFeP04 was 47.2 g / 15.7 g, 15.7 g / 47.2 g, 62.8 g / 0 g, 0 g / 62.8 g, respectively, in Comparative Examples II-8 to II-11, the other conditions were the same as those in Example II-1-7.

[1028] The preparation of the positive electrode sheet, the preparation of the negative electrode sheet, the preparation of the electrolyte, the preparation of the separator, and the preparation of the battery in the above examples and comparative examples were the same as the process in Example II-1-1.

[1029]

Three-layer-coated positive electrode active material and battery preparation

[1030] Example III-1:

[1031] Step 1: Preparation of positive electrode active material

[1032] Step S1: Preparation of Fe, Co, V, and S co-doped manganese oxalate

[1033] Manganese carbonate 689.6 g, ferrous carbonate 455.27 g, cobalt sulfate 4.65 g, vanadium dichloride 4.87 g were added into a mixer and mixed for 6 h. The resulting mixture was then transferred into a reactor, 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added, heated to 80 °C, and stirred at 500 rpm for 6 h until the reaction was complete and no bubbles were generated. A Fe, Co, and V co-doped manganese oxalate suspension was obtained. The suspension was then filtered, dried at 120 °C, and then sand milled to obtain manganese oxalate particles with a particle size of 100 nm.

[1034] Step S2: Preparation of the inner core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4

[1035] Manganese oxalate 1793.1 g prepared in (1) and 368.3 g of lithium carbonate, 1146.6 g of ammonium dihydrogen phosphate, and 4.9 g of dilute sulfuric acid were taken and added to 20 L of deionized water, stirred well, and mixed uniformly at 80 °C for 10 h to obtain a slurry. The slurry was transferred to a spray drying device for spray drying and granulation, and dried at a temperature of 250 °C to obtain a powder. The powder was sintered in a roller kiln at 700 °C for 4 h in a protective atmosphere (90% nitrogen and 10% hydrogen) to obtain the above-mentioned inner core material.

[1036] Step S3: Preparation of the first coating layer suspension

[1037] A Li2FeP2O7 solution was prepared by dissolving 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate, and 12.6 g of oxalic acid dihydrate in 500 mL of deionized water, controlling the pH to be 5, then stirring and reacting at room temperature for 2 h to obtain a solution, and then heating the solution to 80 °C and maintaining this temperature for 4 h to obtain the first coating layer suspension.

[1038] Step S4: Coating of the first coating layer

[1039] The doped 1571.9 g of lithium manganese phosphate inner core material obtained in step S2 was added to the first coating layer suspension (coating material content 15.7 g) obtained in step S3, stirred and mixed well for 6 h, and then transferred into a 120 °C oven to dry for 6 h, and then sintered at 650 °C for 6 h to obtain the pyrophosphate coated material.

[1040] Step S5: Preparation of the second coating layer suspension

[1041] A solution was prepared by dissolving 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate in 1500 mL of deionized water, then stirring and reacting for 6 h to obtain a solution, and then heating the solution to 120°C and maintaining the temperature for 6 h to obtain a second coating layer suspension.

[1042] Step S6: Coating of the second coating layer

[1043] The 1586.8 g of pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension (coating material content 47.1 g) obtained in step S5, and the mixture was stirred for 6 h. After the mixture was uniformly mixed, it was transferred to a 120°C oven for drying for 6 h, and then sintered at 700°C for 8 h to obtain a two-layer coated material.

[1044] Step S7: Preparation of a third coating layer aqueous solution

[1045] 37.3 g of sucrose was dissolved in 500 g of deionized water, and then stirred and fully dissolved to obtain a sucrose aqueous solution.

[1046] Step S8: Coating of the third coating layer

[1047] The two-layer coated material 1633.9 g obtained in step S6 was added to the sucrose solution obtained in step S7, and the mixture was stirred for 6 h. After the mixture was uniformly mixed, it was transferred to a 150°C oven for drying for 6 h, and then sintered at 700°C for 10 h to obtain a three-layer coated material.

[1048] Step 2: Preparation of a positive electrode sheet

[1049] The three-layer coated positive electrode active material prepared above, a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) were added to N-methyl pyrrolidone (NMP) at a weight ratio of 97.0:1.2:1.8, and the mixture was stirred and uniformly mixed to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil at 0.280 g / 1540.25 mm 2 after drying, cold pressing, and slitting, a positive electrode sheet was obtained.

[1050] Step 3: Preparation of a negative electrode sheet

[1051] A negative electrode active material artificial graphite, a hard carbon, a conductive agent acetylene black, a binder styrene butadiene rubber (SBR), and a thickening agent sodium carboxymethyl cellulose (CMC) were dissolved in a solvent deionized water at a weight ratio of 90:5:2:2:1, and the mixture was stirred and uniformly mixed to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil at 0.117 g / 1540.25 mm 2 after drying, cold pressing, and slitting, a negative electrode sheet was obtained.

[1052] Step 4: Preparation of electrolyte

[1053] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7, 12.5 wt% (based on the weight of the ethylene carbonate / ethyl methyl carbonate solvent) of LiPF6 was added and dissolved in the above organic solvent, and stirred evenly to obtain an electrolyte.

[1054] Step 5: Preparation of isolation membrane

[1055] A commercially available PP-PE copolymer microporous film (from Zhuogao Electronic Technology Co., Ltd., Model 20) with a thickness of 20 μm and an average pore size of 80 nm was used.

[1056] Step 6: Preparation of the full battery

[1057] The positive electrode sheet, separator, and negative electrode sheet obtained above are stacked in order, with the separator placed between the positive and negative electrodes to act as a barrier, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the above electrolyte, and encapsulated to obtain a full battery (hereinafter also referred to as a "full battery").

[1058] (Preparation of button cell)

[1059] The prepared positive electrode active material, polyvinylidene fluoride (PVDF), and acetylene black were added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5 and stirred in a drying room to form a slurry. The slurry was coated on aluminum foil, dried, and cold pressed to form a positive electrode sheet. The coating amount was 0.2g / cm 2 , compacted density is 2.0g / cm 3 .

[1060] A lithium sheet was used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. Together with the positive electrode sheet prepared above, they were assembled into a button battery (hereinafter also referred to as "button battery") in a button box.

[1061] Examples III-2 to III-53 and Comparative Examples III-1 to III-17

[1062] The positive electrode active materials and batteries in Examples III-2 to III-53 and Comparative Examples III-1 to III-17 are prepared in a similar manner to Example III-1, with the differences in the preparation of the positive electrode active materials being as shown in Tables 1-6, wherein Comparative Examples III-1 to III-2, Comparative Examples III-4 to III-10 and Comparative Example III-12 are not coated with a first layer, and thus do not have steps S3, S4; Comparative Examples III-1 to III-11 are not coated with a second layer, and thus do not have steps S5-S6.

[1063] Note: In all examples and comparative examples of the present application, if not specified, the first coating layer material and / or the second coating layer material used are both crystalline by default.

[1064] Table 1: Preparation of the core

[1065]

[1066]

[1067]

[1068]

[1069]

[1070] *The determination method is described in the section “Material Performance Test” below.

[1071] Table 2: Preparation of the first coating layer suspension (step S3)

[1072]

[1073] *The determination method is described in the section “Material Performance Test” below.

[1074] **The mass of the first coating layer coating material is increased or decreased by the same multiple as the mass of the raw material used for the first coating layer suspension.

[1075] Table 3: Coating of the first coating layer (step S4)

[1076]

[1077]

[1078]

[1079]

[1080] *The determination method is described in the section “Material Performance Test” below.

[1081] Table 4: Preparation of the second coating suspension (step S5)

[1082]

[1083] * The measurement method is described in the section "Material property testing" below.

[1084] ** The mass of the second coating material is increased or decreased by the same multiple as the mass of the raw material used for the second coating suspension.

[1085] Table 5: Coating of the second coating layer (step S6)

[1086]

[1087]

[1088]

[1089]

[1090]

[1091] * The measurement method is described in the section "Material property testing" below.

[1092] Table 6: Coating of the third coating layer (step S8)

[1093]

[1094]

[1095]

[1096]

[1097]

[1098]

[1099]

[1100] Examples III-30 to III-42: Investigation of further coating materials

[1101] Examples III-30 to III-42 were carried out in a similar manner to Example III-1, with the differences being as indicated in Tables 7-8 below.

[1102] Table 7: Investigation of the first coating material

[1103]

[1104]

[1105] Table 8: Investigation of the second coating material

[1106]

[1107]

[1108] Examples III-2-1 to III-2-24

[1109] The sintering temperature and sintering time in steps S4, S6 and S8 were changed, and the rest was the same as in Example III-1, see Table 30.

[1110] Examples III-3-1 to III-3-20

[1111] The reaction temperature and reaction time in the preparation of the core were changed, and the rest was the same as in Example III-1, see Table 31.

[1112] Example III-4-1

[1113] Step S1 : Preparation of Fe, Co, V and S co-doped manganese oxalate

[1114] 689.6 g of manganese carbonate, 455.27 g of ferrous carbonate, 4.65 g of cobalt sulfate, 4.87 g of vanadium dichloride were added to a mixer and mixed for 6 h. Then the obtained mixture was transferred into a reaction kettle, 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added, heated to 80 °C, and stirred at a speed of 500 rpm for 6 h, mixed uniformly until the reaction was terminated and no bubbles were generated, to obtain a Fe, Co, and V co-doped manganese oxalate suspension. Then the suspension was filtered, dried at 120 °C, and then sand-milled to obtain manganese oxalate particles with a particle size of 100 nm.

[1115] Step S2: Preparation of the core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4

[1116] Manganese oxalate 1793.1 g prepared in (1) and 368.3 g lithium carbonate, 1146.6 g ammonium dihydrogen phosphate and 4.9 g dilute sulfuric acid were taken and added to 20 L of deionized water, stirred well, and mixed uniformly at 80°C for 10 h to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, dried at a temperature of 250°C to obtain a powder. The powder was sintered in a roller kiln at 700°C for 4 h in a protective atmosphere (90% nitrogen and 10% hydrogen) to obtain a core material. The element content of the core material was detected by inductively coupled plasma emission spectrometry (ICP), and the core chemical formula was obtained as shown above.

[1117] Step S3: Preparation of the first coating layer suspension

[1118] Preparation of a Li2FeP2O7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled at 5, then stirred and reacted at room temperature for 2 h to obtain a solution, and then the solution was warmed to 80°C and kept at this temperature for 4 h to obtain a first coating layer suspension.

[1119] Step S4: Coating of the first coating layer

[1120] The doped 1571.9 g of lithium manganese phosphate core material obtained in step S2 was added to the first coating layer suspension (coating material content 15.7 g) obtained in step S3, stirred well and mixed for 6 h, after uniform mixing, it was transferred to a 120°C oven for drying for 6 h, and then sintered at 650°C for 6 h to obtain a pyrophosphate coated material.

[1121] Step S5: Preparation of the second coating layer suspension

[1122] 47.1 g of nano-sized Al2O3 (particle size about 20 nm) was dissolved in 1500 mL of deionized water, stirred for 2 h to obtain a second coating layer suspension.

[1123] Step S6: Coating of the second coating layer

[1124] The 1586.8 g of pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension (coating material content 47.1 g) obtained in step S5, stirred well and mixed for 6 h, after uniform mixing, it was transferred to a 120°C oven for drying for 6 h, and then sintered at 700°C for 8 h to obtain a two-layer coated material.

[1125] Step S7: Preparation of the third coating layer aqueous solution

[1126] 37.3 g of sucrose was dissolved in 500 g of deionized water, then stirred and fully dissolved to obtain a sucrose aqueous solution.

[1127] Step S8: coating of the third coating layer

[1128] The two-layer coated material 1633.9 g obtained in step S6 was added to the sucrose solution obtained in step S7, and stirred and mixed together for 6 h. After uniform mixing, it was transferred into an oven at 150 ℃ for drying for 6 h, and then sintered at 700 ℃ for 10 h to obtain a three-layer coated material.

[1129] Core: Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4; the first coating layer is 1% crystalline Li2FeP2O7; the second coating layer is 3% crystalline Al2O3; and the third coating layer is 1% carbon with a SP2 / SP3 molar ratio of 2.2.

[1130] Example III-4-2

[1131] Except that the amount of sucrose in step S8 is 111.9 g and sintering is carried out at 600 ℃ for 9 h, the rest is the same as Example III-4-1.

[1132] The core, the first coating layer and the second coating layer are the same as Example III-4-1; and the third coating layer is 3% carbon with a SP2 / SP3 molar ratio of 2.3.

[1133] Example III-4-3

[1134] Step S1: preparation of doped manganese oxalate

[1135] 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours; the mixture was transferred to a reaction kettle, 10 L of deionized water and 2 mol of dihydrate oxalic acid were added, heated to 80 ℃, and then stirred at a speed of 600 rpm for 6 hours, and the reaction was terminated (no gas bubbles were generated), to obtain a suspension of Fe-doped manganese oxalate; the suspension was filtered, the filter cake was dried at 120 ℃, and ground to obtain Fe-doped manganese oxalate particles with a particle size Dv 50 of about 100 nm;

[1136] Step S2: preparation of Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O3.999 F 0.001 core

[1137] Take 1 mol Fe-doped manganese oxalate particles, 0.497 mol lithium carbonate, 0.001 mol Mo(SO4)3, 0.999 mol phosphoric acid aqueous solution with a concentration of 85%, 0.001 mol H4SiO4, 0.0005 mol NH4HF2 and 0.005 mol sucrose into 20 L of deionized water, and transfer the mixture into a sand mill for sufficient grinding and stirring for 10 hours to obtain a slurry; the slurry is transferred to a spray drying device for spray drying and granulation, and the drying temperature is set to 250°C, and the drying is performed for 4 hours to obtain particles; the particles are sintered at 700°C for 10 hours in a nitrogen (90% v / v) + hydrogen (10% v / v) protective atmosphere to obtain a core material. The element content of the core material is detected by inductively coupled plasma emission spectrometry (ICP), and the chemical formula of the core material is obtained as shown above.

[1138] Step S3: Preparation of the first coating layer suspension

[1139] Preparation of a Li2FeP2O7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate are dissolved in 500 mL of deionized water, the pH is controlled to be 5, then stirred and reacted at room temperature for 2 h to obtain a solution, and then the solution is heated to 80°C and kept at this temperature for 4 h to obtain a first coating layer suspension.

[1140] Step S4: Coating of the first coating layer

[1141] The doped 157.2 g of lithium manganese phosphate core material obtained in step S2 is added to the first coating layer suspension (coating material content is 1.572 g) obtained in step S3, and stirred and mixed for 6 h, and then transferred into a 120°C oven for drying for 6 h, and then sintered at 650°C for 6 h to obtain a pyrophosphate coated material.

[1142] Step S5: Preparation of the second coating layer suspension

[1143] 4.71 g of nano-Al2O3 (particle size about 20 nm) is dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a second coating layer suspension.

[1144] Step S6: Coating of the second coating layer

[1145] The 158.772 g of pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension (coating material content 4.71 g) obtained in step S5, and mixed by stirring for 6 h. After mixing was complete, the mixture was dried in an oven at 120°C for 6 h, and then sintered at 700°C for 8 h to obtain a material coated with two layers.

[1146] Step S7: Preparation of a third coating layer aqueous solution

[1147] 37.3 g of sucrose was dissolved in 500 g of deionized water, and then stirred and dissolved completely to obtain a sucrose aqueous solution.

[1148] Step S8: Coating of a third coating layer

[1149] The 1633.9 g of material coated with two layers obtained in step S6 was added to the sucrose solution obtained in step S7, and mixed by stirring for 6 h. After mixing was complete, the mixture was dried in an oven at 150°C for 6 h, and then sintered at 700°C for 10 h to obtain a material coated with three layers.

[1150] Core: Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 ; the first coating layer was 1% crystalline Li2FeP2O7; the second coating layer was 3% crystalline Al2O3; and the third coating layer was 1% carbon, with a SP2 to SP3 molar ratio of 2.2.

[1151] Example III-4-4

[1152] Except for the following differences, the rest was the same as in Example III-4-3:

[1153] Step S3: 53.3 g of aluminum chloride, 34.5 g of ammonium dihydrogen phosphate, and 18.9 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 4, and then the solution was stirred and reacted at room temperature for 2 h to obtain a solution. The solution was then warmed to 80°C and maintained at this temperature for 4 h to obtain a first coating layer suspension.

[1154] Step S4: sintering at 680°C for 8 h, and the rest was the same as in step S4 of Example III-4-3.

[1155] The core, the second coating layer, and the third coating layer were the same as in Example III-4-3; and the first coating layer was 1% crystalline Al4(P2O7)3.

[1156]

Two positive electrode active materials are mixed and used, and a battery is prepared

[1157] Example IV-1

[1158] The core material of Example I-1 was mixed with lithium nickel cobalt manganese oxide LiNi 0.5 Co 0.2 Mn 0.3 O2 in a mass ratio of 1:1 as a positive electrode active material.

[1159] Preparation of the positive electrode tab: the slurry of the positive electrode active material was uniformly coated on both sides of the current collector aluminum foil at a coating amount of 0.019 g / cm 2 , vacuum dried at high temperature of 100-120°C for 14h, roll-pressed to compact, to obtain the positive electrode tab P4.

[1160] Preparation of the negative electrode tab: the negative electrode active material artificial graphite, the conductive agent super-p, the binder SBR, and the thickening agent CMC-Na were dissolved in deionized water in a mass ratio of 95%:1.5%:1.8%:1.7%, and after being fully stirred and mixed uniformly, a negative electrode slurry with a viscosity of 3000 mPa.s and a solid content of 52% was obtained; the negative electrode slurry was coated on a negative electrode current collector copper foil of 6μm, and then baked at 100°C for 4 hours to dry, roll-pressed to obtain a negative electrode tab with a compacted density of 1.75 g / cm3.

[1161] Separator film: a polypropylene film was used.

[1162] Preparation of the electrolyte: ethylene carbonate, dimethyl carbonate, and 1,2-propanediol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte. In the electrolyte, the concentration of LiPF6 was 1 mol / L.

[1163] Preparation of the full battery: the above positive electrode tab was used, and the negative electrode tab, the separator film, and the positive electrode tab were sequentially arranged to form a bare cell by the winding method, and the aluminum tab and the copper tab were punched out to obtain a bare cell; the two bare cells were welded together by the copper tab and the copper tab, and the aluminum tab and the aluminum tab by the adapter piece, and then the bare cell was wrapped and insulated, and then the bare cell was put into an aluminum shell, and the top cover and the aluminum shell were welded to form a dry cell, and then the dry cell was baked to remove water, and then the electrolyte was injected, and then the battery was formed and aged, and accordingly a full battery was obtained.

[1164] Preparation of the button cell: the above positive electrode tab and the negative electrode and the electrolyte were assembled into a button cell (hereinafter also referred to as “button”) in a button cell box.

[1165] Example IV-2

[1166] The core material of Example I-1 was mixed with lithium nickel cobalt aluminum oxide LiNi 0.33 Co0.33 Al 0.34 O2 was mixed as a positive active material at a mass ratio of 1:1.

[1167] The rest was the same as in Example IV-1.

[1168] Battery test

[1169] 1. Lattice change rate test method:

[1170] At 25°C, the positive active material sample was placed in an XRD (model: Bruker D8 Discover) and tested at 1° / min, and the test data was analyzed and collated, and the lattice constants a0, b0, c0and v0at this time were calculated (a0, b0and c0represent the length of each aspect of the unit cell, and v0represents the volume of the unit cell, which can be directly obtained through XRD refinement results) by referring to the standard PDF card.

[1171] The positive active material sample was prepared into a coin cell using the coin cell preparation method in the above examples, and the coin cell was charged at a small rate of 0.05C until the current decreased to 0.01C. Then the positive electrode sheet in the coin cell was taken out and soaked in dimethyl carbonate (DMC) for 8 hours. Then it was dried, scraped and sieved to obtain particles with a particle size of less than 500 nm. The sample was taken and the unit cell volume v1was calculated in the same way as the fresh sample, and the lattice change rate (unit cell volume change rate) before and after complete deintercalation of lithium was calculated as (v0-v1) / v0x 100%.

[1172] 2. Li / Mn anti-site defect concentration:

[1173] The XRD results tested in the "lattice change rate measurement method" were compared with the standard crystal PDF (Powder Diffraction File) card to obtain the Li / Mn anti-site defect concentration. Specifically, the XRD results tested in the "lattice change rate measurement method" were imported into the general structure analysis system (GSAS) software to automatically obtain the refinement results, which included the occupation of different atoms. The Li / Mn anti-site defect concentration was obtained by reading the refinement results.

[1174] 3. Compaction density:

[1175] 5g of the above prepared positive active material powder was placed in a compaction special mold (CARVER mold, model 13mm, USA), and then the mold was placed on a compaction density instrument. A pressure of 3T was applied, and the thickness of the powder under pressure (thickness after unloading) was read on the device, and the compaction density was calculated by p=m / v, where the area value used was the standard small picture area 1540.25mm 2.

[1176] 4.3C charge constant current ratio:

[1177] Fresh full cells prepared in each of the above examples and comparative examples were rested for 5 min at 25°C, and discharged at 1 / 3C to 2.5V. After resting for 5 min, the cells were charged at 1 / 3C to 4.3V, and then charged at 4.3V to a current less than or equal to 0.05 mA. After resting for 5 min, the charge capacity at this time was recorded as C0. The cells were discharged at 1 / 3C to 2.5V, rested for 5 min, and then charged at 3C to 4.3V, rested for 5 min, and the charge capacity at this time was recorded as C1. The 3C charge constant current ratio was C1 / C0 x 100%.

[1178] The higher the 3C charge constant current ratio, the better the rate performance of the secondary battery.

[1179] 5. Transition metal Mn (and Mn-site doped Fe) dissolution test:

[1180] Full cells prepared in each of the above examples and comparative examples, which were cycled at 45°C to a capacity decay of 80%, were discharged at a rate of 0.1C to a cut-off voltage of 2.0V. Then the cells were disassembled, and the negative electrode sheets were removed. Thirty circular pieces of unit area (1540.25 mm 2 ) were randomly taken from the negative electrode sheets, and inductively coupled plasma emission spectroscopy (ICP) was tested using an Agilent ICP-OES 730. The amount of Fe (if the Mn site of the posi...

Claims

1. A positive electrode active material comprising a compound represented by Formula (I), wherein, A B C D (I) a x y z n wherein, the A comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, Ga, In, Cd, V, Ta, Cr, Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Rb, Cs, Be, Ca, Sr, Ba, In, Pb, Bi, Cd, Hf, Ta, Cr, Ru, Rh, Pd, Os, Ir, Pt, Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from boron, S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br, the a is selected from the range of 0.85 to 1.15, the x is selected from the range of 0.001 to 0.1, the y is selected from the range of 0.001 to 0.999, the z is selected from the range of 0.001 to 0.5, and the n is selected from the range of 0.001 to 0.

5. Li a A x Mn 1-y B y P 1-z C z O 4-n D n (I) 2. The positive electrode active material according to claim 1, wherein, the A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; and / or, the B comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

3. The positive electrode active material according to claim 1 or 2, wherein, the A comprises any one element selected from Mg and Nb; and / or, the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or, the C is S; and / or, the D is F. B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge. B is at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. B is at least two elements selected from Fe, Ti, V, Co, and Mg. B is Fe, with one or more elements selected from Ti, V, Co, and Mg.

8. The positive electrode active material according to claim 1, wherein, the a is selected from the range of 0.9 to 1.1; and / or, the x is selected from the range of 0.001 to 0.005; and / or, the y is selected from the range of 0.001 to 0.5; and / or, the z is selected from the range of 0.001 to 0.1; and / or, the n is selected from the range of 0.001 to 0.

1. the a is selected from the range of 0.97 to 1.01; and / or, the y is selected from the range of 0.01 to 0.5; and / or, the z is selected from the range of 0.001 to 0.

005. the y is selected from the range of 0.25 to 0.

5.

11. The positive electrode active material according to claim 1, wherein, ​ ​ ​ ​ 4. The positive electrode active material according to claim 3, wherein ​ 5. The positive electrode active material according to claim 4, wherein ​ 6. The positive electrode active material according to claim 5, wherein ​ 7. The positive electrode active material according to claim 6, wherein ​ ​ ​ ​ ​ ​ ​ 9. The positive electrode active material according to claim 8, wherein ​ ​ ​ 10. The positive electrode active material according to claim 9, wherein ​ ​ x is selected from the range of 0.001 to 0.1, z is selected from the range of 0.001 to 0.5, and n is selected from the range of 0.001 to 0.

1.

12. The positive electrode active material according to claim 1, wherein y:z is selected from the range of 0.002 to 999; and / or z:n is selected from the range of 0.002 to 500.

13. The positive electrode active material according to claim 12, wherein y:z is selected from the range of 0.025 to 999; and / or z:n is selected from the range of 0.2 to 100.

14. The positive electrode active material according to claim 13, wherein y:z is selected from the range of 0.2 to 600; and / or z:n is selected from the range of 0.2 to 50.

15. The positive electrode active material of claim 1, wherein, A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from the group consisting of boron, S, Si, and N; D comprises one or more elements selected from the group consisting of S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, and n is selected from the range of 0.001 to 0.

1.

16. The positive electrode active material according to claim 1, wherein the positive electrode active material comprises a core and a shell that coats the core, the core comprises the compound of Formula I; the shell comprises one or more coating layers; the coating layers have ionic or electronic conductivity.

17. The positive electrode active material according to claim 16, wherein each of the one or more coating layers independently comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer.

18. The positive electrode active material according to claim 17, wherein the shell comprises one coating layer.

19. The positive electrode active material according to claim 18, wherein the coating layer comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer.

20. The positive electrode active material of claim 16, wherein, the shell comprises a first coating layer that coats the core and a second coating layer that coats the first coating layer.

21. The positive electrode active material according to claim 20, wherein each of the first and second coating layers independently comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer.

22. The positive electrode active material according to claim 21, wherein the first coating layer comprises one or more selected from the group consisting of pyrophosphate, phosphate, oxide, and boride, and the second coating layer comprises one or more selected from the group consisting of carbon and doped carbon.

23. The positive electrode active material of claim 16, wherein, the shell comprises a first coating layer that coats the core, a second coating layer that coats the first coating layer, and a third coating layer that coats the second coating layer.

24. The positive electrode active material according to claim 23, wherein each of the first, second, and third coating layers independently comprises one or more selected from the group consisting of pyrophosphate, phosphate, carbon, doped carbon, oxide, boride, and polymer.

25. The positive electrode active material according to claim 23, wherein the first coating layer comprises pyrophosphate, the second coating layer comprises one or more selected from the group consisting of phosphate, oxide, and boride, and the third coating layer comprises one or more selected from the group consisting of carbon and doped carbon.

26. The positive electrode active material according to claim 16, wherein The degree of lattice mismatch between the material of the core and the material of the shell is less than 10%.

27. The positive electrode active material according to claim 1, wherein based on the weight of the positive electrode active material, the content of manganese element is in the range of 10% to 35% by weight; and / or, the content of phosphorus element is in the range of 12% to 25% by weight; and / or, the weight ratio of manganese element to phosphorus element is in the range of 0.71 to 1.

85.

28. The positive electrode active material according to claim 27, wherein based on the weight of the positive electrode active material, the content of manganese element is in the range of 13.3% to 33.2% by weight; and / or, the content of phosphorus element is in the range of 15% to 20% by weight; and / or, the weight ratio of manganese element to phosphorus element is in the range of 0.90 to 1.

25.

29. The positive electrode active material according to claim 28, wherein based on the weight of the positive electrode active material, the content of manganese element is in the range of 15% to 30% by weight; and / or, the content of phosphorus element is in the range of 16.8% to 19.5% by weight; and / or, the weight ratio of manganese element to phosphorus element is in the range of 0.95 to 1.

20.

30. The positive electrode active material according to claim 29, wherein based on the weight of the positive electrode active material, the content of manganese element is in the range of 17% to 20% by weight.

31. The positive electrode active material according to claim 1, wherein The positive electrode active material is coated with one or more of carbon and doped carbon on the surface.

32. The positive electrode active material of claim 1, wherein the positive electrode active material is coated with carbon on the surface.

33. The positive electrode active material according to claim 31, wherein The doping element in the doped carbon comprises one or more selected from nitrogen, phosphorus, sulfur, boron and fluorine.

34. The positive electrode active material according to claim 1, wherein In the compound represented by formula (I), (1-y):y is in the range of 0.1 to 999; and / or, a: x is in the range of 1 to 1200.

35. The positive electrode active material according to claim 34, wherein In the compound represented by formula (I), (1-y):y is in the range of 0.1 to 10 or in the range of 0.67 to 999; and / or, a: x is in the range of 9 to 1100, more optionally in the range of 190 to 998.

36. The positive electrode active material according to claim 35, wherein (1-y):y is in the range of 1 to 10; and / or, a: x is in the range of 190 to 998.

37. The positive electrode active material according to claim 36, wherein (1-y):y is in the range of 1 to 4.

38. The positive electrode active material according to claim 37, wherein (1-y):y is in the range of 1.5 to 3.

39. The positive electrode active material according to claim 1, wherein In the compound represented by formula (I), the ratio of z to 1-z is 1:9 to 1:

999.

40. The positive electrode active material according to claim 39, wherein In the compound represented by formula (I), the ratio of z to 1-z is 1:499 to 1:

249.

41. The positive electrode active material according to claim 16, wherein The coating amount of the shell is 0.1% to 6% based on the weight of the core.

42. The positive electrode active material according to claim 16, wherein The shell is located on the surface of 40% to 90% of the core.

43. The positive electrode active material according to claim 42, wherein The shell is located on the surface of 60% to 80% of the core.

44. The positive electrode active material according to claim 16, wherein The thickness of the shell is 1-15nm, the shell comprises a first coating layer, or the shell comprises a first and a second coating layer, or the shell comprises a first to a third coating layer.

45. The positive electrode active material according to claim 44, wherein The thickness of the first coating layer is 1-10nm; and / or, The thickness of the second coating layer is 2-25nm; and / or, The thickness of the third coating layer is 2-25nm.

46. The positive electrode active material according to claim 45, wherein The thickness of the first coating layer is 2-10nm; and / or, The thickness of the second coating layer is 2-15nm; and / or, The thickness of the third coating layer is 5-25nm.

47. The positive electrode active material according to claim 46, wherein The thickness of the second coating layer is 3-15nm.

48. The positive electrode active material of claim 16, wherein, The one or more coating layers each independently include one or more selected from pyrophosphate, phosphate, and oxide, and one or more selected from the pyrophosphate, the phosphate, and the oxide is crystalline.

49. The positive electrode active material according to claim 48, wherein The crystallinity of the pyrophosphate, the phosphate, and the oxide is each independently 10% to 100%.

50. The positive electrode active material according to claim 49, wherein The crystallinity of the pyrophosphate, the phosphate, and the oxide is each independently 50% to 100%.

51. The cathode active material of claim 16, wherein, The one or more coating layers each independently include carbon, and the carbon is a mixture of SP2-form carbon and SP3-form carbon.

52. The positive electrode active material according to claim 16, wherein The molar ratio of the SP2-form carbon to the SP3-form carbon in the carbon is any value in the range of 0.07 to 13.

53. The positive electrode active material according to claim 52, wherein The molar ratio of the SP2-form carbon to the SP3-form carbon in the carbon is any value in the range of 0.1 to 10.

54. The positive electrode active material according to claim 53, wherein The molar ratio of the SP2-form carbon to the SP3-form carbon in the carbon is any value in the range of 2.0 to 3.

0.

55. The positive electrode active material according to claim 16, wherein, The one or more coating layers each independently include doped carbon, and the mass content of a doping element in the doped carbon is 30% or less.

56. The positive electrode active material according to claim 55, wherein The mass content of the doping element in the doped carbon is 20% or less.

57. The positive electrode active material according to claim 55, wherein The one or more coating layers each independently include doped carbon, and the mass content of a doping element in the doped carbon is 30% or less. The doping element is a nitrogen element and / or a sulfur element, and the mass content of the doping element in the doped carbon is 1% to 15%; or, The doping element is a phosphorus element, a boron element, and / or a fluorine element, and the mass content of the doping element in the doped carbon is 0.5% to 5%.

58. The positive electrode active material according to claim 57, wherein The doping element is nitrogen, phosphorus, sulfur, boron, or fluorine.

59. The positive electrode active material according to claim 16, wherein, The one or more coating layers each independently include pyrophosphate, and the interplanar spacing of the pyrophosphate is in the range of 0.293 to 0.470 nm, and the angle of the crystal orientation (111) is in the range of 18.00° to 32.57°; and / or, The one or more coating layers each independently include phosphate, and the interplanar spacing of the phosphate is in the range of 0.244 to 0.425 nm.

60. The positive electrode active material according to claim 59, wherein The interplanar spacing of the pyrophosphate is in the range of 0.297 to 0.462 nm.

61. The positive electrode active material according to claim 60, wherein The interplanar spacing of the pyrophosphate is in the range of 0.293 to 0.326 nm.

62. The positive electrode active material according to claim 61, wherein The interplanar spacing of the pyrophosphate is in the range of 0.300 to 0.310 nm.

63. The positive electrode active material of claim 59, wherein, The angle of the crystal orientation (111) of the pyrophosphate is in the range of 18.00° to 32.00°.

64. The positive electrode active material according to claim 63, wherein The angle of the crystal orientation (111) of the pyrophosphate is in the range of 26.41° to 32.57°.

65. The positive electrode active material according to claim 64, wherein The angle of the crystal orientation (111) of the pyrophosphate is in the range of 19.211° to 30.846°.

66. The positive electrode active material according to claim 65, wherein The angle of the crystal orientation (111) of the pyrophosphate is in the range of 29.00° to 30.00°.

67. The cathode active material of claim 59, wherein, The interplanar spacing of the phosphate is in the range of 0.345 to 0.358 nm.

68. The cathode active material of claim 59, wherein, The angle of the crystal orientation (111) of the phosphate is in the range of 20.00° to 37.00°.

69. The positive electrode active material according to claim 68, wherein The phosphate has a range of 24.25°-26.45° for the included angle of the crystal orientation (111).

70. The cathode active material of claim 44, wherein, The first coating layer or the second coating layer comprises a phosphate.

71. The cathode active material of claim 1, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 50% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 5.3% or less; and / or The positive electrode active material has a compaction density of 1.89 g / cm3 at 3T 3 above; and / or The surface oxygen valence state of the positive electrode active material is -1.55 or less.

72. The positive electrode active material of claim 71, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 9.8% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 5.1% or less; and / or The positive electrode active material has a compaction density of 1.95 g / cm 3 above; and / or The surface oxygen valence state of the positive electrode active material is -1.82 or less.

73. The positive electrode active material of claim 71, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 8.1% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 4% or less; and / or The positive electrode active material has a compaction density of 1.98 g / cm 3 above; and / or The surface oxygen valence state of the positive electrode active material is -1.88 or less.

74. The positive electrode active material according to claim 73, wherein The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 7.5% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 2.2% or less; and / or The positive electrode active material has a compaction density of 2.0 g / cm 3 above; and / or The surface oxygen valence state of the positive electrode active material is -1.90 or less.

75. The positive electrode active material of claim 74, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 6% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 2% or less; and / or The positive electrode active material has a compaction density of 2.2 g / cm 3 above; and / or The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

88.

76. The positive electrode active material of claim 75, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 4% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 1.5%-2.2%; and / or The positive electrode active material has a compaction density of 2.2 g / cm3 at 3T 3 above and 2.8 g / cm3 3 below; and / or The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

89.

77. The positive electrode active material of claim 76, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 3.8% or less; and / or The Li / Mn antisite defect concentration of the positive electrode active material is 0.5% or less; and / or The positive electrode active material has a compaction density of 2.2 g / cm 3 above and 2.65 g / cm 3 below; and / or The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

90.

78. The positive electrode active material of claim 77, wherein, The positive electrode active material satisfies at least one of the following conditions: The lattice change rate before and after complete deintercalation of lithium is 2.0-3.8%.

79. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a first positive electrode active material, the first positive electrode active material being the positive electrode active material of any one of claims 1 to 78.

80. The cathode sheet of Claim 79, wherein, The content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight based on the total weight of the positive electrode film layer.

81. The cathode sheet of Claim 80, wherein, The content of the positive electrode active material in the positive electrode film layer is 95-99.5% by weight based on the total weight of the positive electrode film layer.

82. The positive electrode sheet of claim 79, further comprising a second positive electrode active material, and the second positive electrode active material is different from the first positive electrode active material.

83. The cathode sheet of Claim 82, wherein, the second positive electrode active material comprises one or more selected from LiEtCosF(l-t-s)02, spinel lithium manganate, and spinel lithium titanate, wherein E comprises one or more elements selected from Group VIII, F comprises one or more elements selected from Group IIIA and Group VIIB, t is selected from a range of 0 to 0.9, and the sum of t and s is selected from a range of 0.3 to 1.

84. The cathode sheet of Claim 81, wherein, E comprises one or more elements selected from Ni, Fe, Ru, and Rh, and F comprises one or more elements selected from Mn, Al, Ga, and In.

85. The positive electrode sheet of claim 82, wherein, the second positive electrode active material comprises one or more selected from LiNitCosMn(l-t-s)02, LiNitCosAl(l-t-s)02, LiCo02, spinel lithium manganate, and spinel lithium titanate; wherein t is independently selected from 0.3-0.9, and the sum of t and s is independently selected from 0.3-0.

9.

86. The cathode sheet of Claim 85, wherein, t is independently selected from 0.33-0.8, and the sum of t and s is independently selected from 0.66-0.

9.

87. The cathode sheet of Claim 82 wherein, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:7-7:

1.

88. The cathode sheet of Claim 87, wherein, the mass ratio of the first positive electrode active material to the second positive electrode active material is 1:4-4:

1.

89. The cathode sheet of Claim 82, wherein, the sum of the mass of the first positive electrode active material and the second positive electrode active material is 88%-98.7% of the mass of the positive electrode sheet.

90. A secondary battery comprising the positive electrode active material of any one of claims 1-78, or the positive electrode sheet of any one of claims 79-89.

91. A battery module comprising the secondary battery of claim 90.

92. A battery pack comprising the battery module of claim 91.

93. An electrical device comprising at least one selected from the secondary battery of claim 90, the battery module of claim 91, and the battery pack of claim 92.

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