Cathode material composition, method of making the same, and cathode sheet, secondary battery, and power using device comprising the same

Abstract

A positive electrode material composition, a method for preparing the same, a positive electrode sheet comprising the same, a secondary battery, and an electric device. The positive electrode material composition comprises a positive electrode active material having a core-shell structure and an organic polysiloxane compound, wherein the positive electrode active material comprises an inner core and a shell covering the inner core, the inner core has a chemical formula of Li 1+x Mn 1‑ y A y P 1‑z R z O4, the shell comprises a first coating layer covering the inner core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The positive electrode material composition can enable the secondary battery to have a higher energy density, and meanwhile, improved cycle performance, safety performance and / or rate performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode material composition, its preparation method, and a positive electrode sheet, secondary battery, and electrical device containing the same. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their safety performance has received increasing attention. Lithium manganese phosphate has become one of the most popular cathode active materials due to its advantages such as high capacity, good safety performance, and abundant raw material sources. However, lithium manganese phosphate is prone to manganese ion dissolution during charging, leading to rapid capacity decay. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode material composition, a method for preparing the same, and a positive electrode sheet, a secondary battery, and an electrical device comprising the same, which enables the secondary battery using the positive electrode material composition to have a high energy density while also improving cycle performance, safety performance, and / or rate performance.

[0004] The first aspect of this application provides a cathode material composition comprising a core-shell structured cathode active material and an organopolysiloxane compound, wherein the cathode active material includes a core and a shell covering the core, and the core has the chemical formula Li. 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, optionally any value in the range of -0.005 to 0.002, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 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, optionally 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, optionally one element selected from B, Si, N, and S. The values ​​of x, y, and z satisfy the following condition: maintaining the entire core electrically neutral. 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 crystalline pyrophosphate Li. a MP2O7 and / or M b(P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c In each of the elements M, M is independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c Maintaining electrical neutrality; the second coating layer comprises 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; the third coating layer is carbon.

[0005] After extensive research, the inventors discovered that by modifying lithium manganese phosphate and applying multilayer coating, a novel core-shell structured positive electrode active material can be obtained. This material significantly reduces manganese ion dissolution and lattice change rate. When used in secondary batteries, it improves cycle performance, rate performance, safety performance, and battery capacity. Combining the positive electrode active material with an organopolysiloxane compound can mitigate electrolyte erosion of the positive electrode active material surface and reduce manganese ion dissolution, thereby enhancing the electrochemical performance of the positive electrode active material. Therefore, positive electrode sheets and secondary batteries using the positive electrode material composition of this application can achieve higher energy density while maintaining improved cycle performance, safety performance, and / or rate performance.

[0006] In any embodiment of this application, the organopolysiloxane compound comprises at least one structural unit represented by Formula 1.

[0007]

[0008] R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate ester, carboxylic acid ester, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon, C1-C20 halogenated aliphatic hydrocarbon, C1-C20 heteroaliphatic hydrocarbon, C1-C20 halogenated heteroaliphatic hydrocarbon, C6-C20 aromatic hydrocarbon, C6-C20 halogenated aromatic hydrocarbon, C2-C20 heteroaromatic hydrocarbon, C2-C20 halogenated heteroaromatic hydrocarbon. Optionally, R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, phenyl. More preferably, R1 and R2 independently represent H or at least one of the following functional groups: -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl. This can further reduce manganese ion dissolution, thereby significantly improving the cycle performance and storage performance of the secondary battery.

[0009] In any embodiment of this application, the organopolysiloxane compound includes one or more selected from linear polysiloxanes and cyclic polysiloxanes. Optionally, the organopolysiloxane compound is selected from linear polysiloxanes.

[0010] Therefore, this can further alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, reduce manganese ion dissolution, and thus significantly improve the cycle performance and storage performance of the secondary battery. Because the electrons in the ring structure of cyclic polysiloxanes have a certain degree of delocalization, compared with linear polysiloxanes, their Si-O framework has a lower affinity for electron-rich F-containing ions, resulting in a slightly lower removal rate of F-containing ions in the electrolyte, a slightly weaker effect in reducing manganese ion dissolution, and a slightly poorer improvement effect on the cycle performance of the secondary battery.

[0011] In any embodiment of this application, the linear polysiloxane further comprises end-capping groups. Optionally, the end-capping groups comprise at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxyalkyl, amino, C1-C8 aminoalkyl, carboxyl, and C1-C8 carboxyalkyl.

[0012] In any embodiment of this application, the linear polysiloxane includes one or more of the following: polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, terminal epoxy-terminated polydimethylsiloxane, terminal hydroxyl-terminated polydimethylsiloxane, terminal polyether polydimethylsiloxane, side-chain aminopropyl polysiloxane, side-chain hydroxymethyl polysiloxane, side-chain hydroxypropyl polysiloxane, side-chain polyether-grafted polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane. Optionally, the linear polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, end-group polyether polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane.

[0013] In any embodiment of this application, the cyclic polysiloxane comprises one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrosiloxane, and cyclic polymethyltrifluoropropylsiloxane. Optionally, the cyclic polysiloxane comprises one or more of 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentapolydimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, hexadecylcyclooctasiloxane, and tetradecylcycloheptasiloxane.

[0014] In any embodiment of this application, the number average molecular weight of the organopolysiloxane compound is below 300,000, and can be selected as 400 to 80,000. This enables the secondary battery to simultaneously achieve good kinetic performance and high-temperature storage performance.

[0015] In any embodiment of this application, the mass percentage of polar functional groups in the organopolysiloxane compound is α, where 0 ≤ α < 50%, and optionally, 5% ≤ α ≤ 30%. This can better improve the cycle performance and storage performance of the secondary battery.

[0016] In any embodiment of this application, the content of the organopolysiloxane compound is from 0.01% to 2% by weight, optionally from 0.1% to 2% by weight, based on the total weight of the cathode material composition. This can better improve the cycle performance and storage performance of the secondary battery.

[0017] In any embodiment of this application, the coating amount of the first 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, and more preferably greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

[0018] In any embodiment of this application, the coating amount of the second 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 preferably 2% to 4% by weight, based on the weight of the core.

[0019] In any embodiment of this application, the coating 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, and more preferably greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

[0020] In the core-shell structured positive electrode active material described in this application, the coating amount of the three coating layers is preferably within the above-mentioned range, thereby enabling sufficient coating of the core and further improving the cycle performance, safety performance, and / or rate performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0021] In any embodiment of this application, the thickness of the first coating layer is 1 nm to 10 nm. This avoids the adverse effects on the kinetic performance of the positive electrode active material that may occur when the first coating layer is too thick, and also avoids the problem that the first coating layer cannot effectively hinder the migration of transition metal ions when it is too thin.

[0022] In any embodiment of this application, the thickness of the second coating layer is 2 nm to 15 nm. In this case, the surface structure of the second coating layer is stable, and the side reactions with the electrolyte are minimal. Therefore, it can effectively reduce interfacial side reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0023] In any embodiment of this application, the thickness of the third coating layer is 2 nm to 25 nm. This can improve the conductivity of the positive electrode active material and increase the compaction density of the positive electrode sheet prepared using the positive electrode active material.

[0024] In any embodiment of this application, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 nm to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°.

[0025] In any embodiment of this application, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 nm to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0026] Crystalline pyrophosphate and crystalline phosphate within the aforementioned interplanar spacing and angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during lithium insertion / extraction, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0027] In any embodiment of this application, in the core, the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1. This further improves the cycle performance and rate performance of the secondary battery.

[0028] In any embodiment of this application, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. This further improves the cycle performance and rate performance of the secondary battery.

[0029] In any embodiment of this application, the carbon in the third coating layer is a mixture of SP2 and SP3 carbon. Optionally, the molar ratio of SP2 to SP3 carbon is any value within the range of 0.1 to 10, and optionally any value within the range of 2.0 to 3.0. By limiting the molar ratio of SP2 to SP3 carbon to the above range, this application improves the overall performance of the secondary battery.

[0030] In any embodiment of this application, based on the weight of the positive electrode active material, the manganese content is in the range of 10% to 35% by weight, preferably in the range of 15% to 30% by weight, and more preferably in the range of 17% to 20% by weight. This effectively avoids problems such as decreased structural stability and reduced density of the positive electrode active material that may be caused by excessive manganese content, thereby improving the cycle life, storage, and compaction density performance of the secondary battery; and also avoids problems such as a low voltage plateau that may be caused by insufficient manganese content, thereby improving the energy density of the secondary battery.

[0031] In any embodiment of this application, based on the weight of the positive electrode active material, the phosphorus content is in the range of 12% to 25% by weight, and optionally in the range of 15% to 20% by weight. This effectively avoids the following situations: if the phosphorus content is too high, it may lead to excessive covalentity of PO, affecting the conductivity of small polarons, thereby affecting the conductivity of the positive electrode active material; if the phosphorus content is too low, it may reduce the stability of the pyrophosphate lattice structure in the core, the first coating layer, and / or the phosphate lattice structure in the second coating layer, thereby affecting the overall stability of the positive electrode active material.

[0032] In any embodiment of this application, based on the weight of the positive electrode active material, the weight ratio of manganese to phosphorus ranges from 0.90 to 1.25, and can be optionally from 0.95 to 1.20. This effectively avoids the following situations: if the weight ratio is too high, it may lead to increased manganese ion dissolution, affecting the stability of the positive electrode active material and the cycle performance and storage performance of the secondary battery; if the weight ratio is too low, it may cause a decrease in the discharge voltage plateau of the positive electrode active material, thereby reducing the energy density of the secondary battery.

[0033] In any embodiment of this application, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is less than 4%, preferably less than 3.8%, and more preferably 2.0% to 3.8%. In this case, the positive electrode active material can improve the capacity utilization and rate performance of the secondary battery.

[0034] In any embodiment of this application, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2.2% or less, and more preferably 1.5% to 2.2%. By keeping the Li / Mn antisite defect concentration within the above range, Mn... 2+ Hinder Li + This improves the transmission efficiency and enhances the capacity utilization and rate performance of the positive electrode active material.

[0035] In any embodiment of this application, the compaction density of the positive electrode active material at 3T is 2.2 g / cm³. 3 The above can be selected as 2.2g / cm. 3 Above and 2.8g / cm 3 The following is a summary. Therefore, this is beneficial for improving the volumetric energy density of secondary batteries.

[0036] In any embodiment of this application, the surface oxygen valence state of the positive electrode active material is below -1.90, and can be selected as -1.90 to -1.98. Therefore, by limiting the surface oxygen valence state of the positive electrode active material to the above range as described above, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and storage performance of the secondary battery.

[0037] In any embodiment of this application, the positive electrode material composition further comprises a conductive agent and a binder. Optionally, the binder content is 1.79% to 10% by weight, based on the total weight of the positive electrode material composition; alternatively, the conductive agent content is 0.2% to 10% by weight, based on the total weight of the positive electrode material composition.

[0038] In any embodiment of this application, the powder resistivity of the cathode material composition at 12 MPa is 4 Ω / cm to 55 Ω / cm, optionally 4 Ω / cm to 40 Ω / cm. This enables the secondary battery to have better kinetic performance.

[0039] In any embodiment of this application, the specific surface area of ​​the positive electrode material composition is 8m². 2 / g to 20m 2 / g, optional 8m 2 / g to 15m 2 / g. This allows secondary batteries to have better electrochemical performance.

[0040] A second aspect of this application provides a method for preparing a cathode material composition, comprising the following steps: providing a core material, a coating step, and a mixing step.

[0041] The steps for providing the core material: the core has the chemical formula Li 1+x Mn 1-y A 、 P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, optionally any value in the range of -0.005 to 0.002, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 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, optionally 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, optionally R is one element selected from B, Si, N and S, and the values ​​of x, y and z satisfy the following condition: keeping the entire core electrically neutral.

[0042] Coating steps: Provide Li separately a MP2O7 and / or M b (P2O7) cAnd an XPO4 suspension, the core material is added to the suspension and mixed, and then sintered to obtain a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell covering the core, the shell comprising 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 comprising crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c In each of the elements M, M is independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c To maintain electrical neutrality, the second coating layer comprises 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, and the third coating layer is carbon.

[0043] Mixing step: The obtained positive electrode active material is mixed uniformly with an organopolysiloxane compound, an optional binder and an optional conductive agent to obtain a positive electrode material composition.

[0044] In any embodiment of this application, the step of providing kernel material includes step (1) and step (2).

[0045] Step (1): Mix and stir the manganese source, dopant of element A and acid in a container to obtain manganese salt particles doped with element A.

[0046] Step (2): The manganese salt particles doped with element A are mixed with a lithium source, a phosphorus source, and a dopant of element R in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, a core doped with elements A and R is obtained, wherein the core doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R zO4, where x is any value in the range of -0.100 to 0.100, optionally any value in the range of -0.005 to 0.002, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 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, 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, optionally one element selected from B, Si, N, and S.

[0047] In any embodiment of this application, step (1) is performed at a temperature of 20°C to 120°C, optionally 40°C to 120°C.

[0048] In any embodiment of this application, the stirring in step (1) is carried out at 400 rpm to 700 rpm for 1 hour to 9 hours, or optionally 3 hours to 7 hours.

[0049] When the heating temperature and stirring time during the core particle preparation process are within the above range, the obtained core and the positive electrode active material made from it have fewer lattice defects, which is beneficial to suppress the dissolution of manganese ions, reduce the interfacial side reactions between the positive electrode active material and the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0050] In any embodiment of this application, step (2) is performed at a temperature of 20°C to 120°C, optionally 40°C to 120°C, for 1 hour to 10 hours.

[0051] In any embodiment of this application, the dopant of element A is one or more elements selected from the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

[0052] In any embodiment of this application, the dopant of element R is one or more of the 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.

[0053] In any embodiment of this application, the coating step includes a first coating step, a second coating step, and a third coating step.

[0054] First coating step: Dissolve the source of element M, phosphorus source, acid, and optionally lithium source in a solvent to obtain a first coating layer suspension; thoroughly mix the core obtained in the core material provision step with the first coating layer suspension obtained in the first coating step, dry, and then sinter to obtain the material coated by the first coating layer.

[0055] Second coating step: Dissolve the source of element X, phosphorus source and acid in solvent to obtain a second coating layer suspension; mix the material coated by the first coating layer obtained in the first coating step with the second coating layer suspension obtained in the second coating step, dry, and then sinter to obtain a material coated by two coating layers.

[0056] The third coating step: Dissolve the carbon source in a solvent to obtain a third coating layer solution; then add the material coated by the two coating layers obtained in the second coating step to the third coating layer solution, mix evenly, dry, and then sinter to obtain a material coated by the three coating layers, i.e., the positive electrode active material.

[0057] In any embodiment of this application, in the first coating step, the pH of the solution containing the source of element M, the phosphorus source, and the acid, and optionally the lithium source, is controlled to be 3.5 to 6.5, then stirred and reacted for 1 to 5 hours, and then the solution is heated to 50°C to 120°C and maintained at that temperature for 2 to 10 hours.

[0058] In any embodiment of this application, in the first coating step, the sintering is carried out at 650°C to 800°C for 2 to 6 hours.

[0059] By controlling the conditions of the first coating step within the above range, it is possible to guarantee or even improve the capacity performance, cycle performance, high-temperature storage performance, and rate performance of the secondary battery prepared using the positive electrode active material.

[0060] In any embodiment of this application, in the second coating step, after dissolving the source of element X, the phosphorus source and the acid in a solvent, the mixture is stirred and reacted for 1 to 10 hours, and then the solution is heated to 60°C to 150°C and maintained at that temperature for 2 to 10 hours.

[0061] In any embodiment of this application, in the second coating step, sintering is carried out at 500°C to 700°C for 6 to 10 hours.

[0062] In the steps of providing the core material and the first coating step and the second coating step, before sintering, that is, in the preparation of the core material in which the chemical reaction occurs (steps (1) and (2)) and in the preparation of the first coating layer suspension and the second coating layer suspension, by selecting the reaction temperature and reaction time as described above, the following situations can be avoided: when the reaction temperature is too low, the reaction cannot occur or the reaction rate is slow; when the temperature is too high, the product decomposes or forms an impurity phase; when the reaction time is too long, the product particle size is large, which may increase the time and difficulty of subsequent processes; when the reaction time is too short, the reaction is incomplete and less product is obtained.

[0063] In any embodiment of this application, the sintering in the third coating step is carried out at 700°C to 800°C for 6 to 10 hours.

[0064] By controlling the conditions of the third coating step within the above range, the capacity utilization and compaction density of the positive electrode active material can be improved.

[0065] The method for preparing the positive electrode active material described in this application uses widely available and inexpensive raw materials, and has a simple process, which is conducive to industrialization.

[0066] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode material composition of the first aspect of this application or a positive electrode material composition prepared by the method of the second aspect of this application, and the content of the positive electrode material composition in the positive electrode film layer is 50% by weight or more, based on the total weight of the positive electrode film layer.

[0067] In any embodiment of this application, the content of the positive electrode material composition in the positive electrode film layer is 90% to 100% by weight, based on the total weight of the positive electrode film layer.

[0068] In any embodiment of this application, the solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 90°, optionally between 3° and 60°, and further between 10° and 30°. When the contact angle is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance.

[0069] In any embodiment of this application, the porosity of the positive electrode film is 15% to 50%, optionally 15% to 30%. When the porosity is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance.

[0070] In any embodiment of this application, the resistance of the positive electrode film is greater than 0 and less than or equal to 6Ω. This enables the secondary battery to have better dynamic performance.

[0071] In any embodiment of this application, the adhesion force between the positive electrode film layer and the positive electrode current collector is greater than or equal to 0.5 MPa. This is beneficial to the performance of the secondary battery.

[0072] In any embodiment of this application, the areal density of the positive electrode film is 0.006 g / cm³. 2 Up to 0.065 g / cm 2 This is beneficial for increasing the volumetric energy density of secondary batteries.

[0073] In any embodiment of this application, the electrolyte absorption rate of the positive electrode film is from 0.0125 μg / s to 100 μg / s, and optionally from 0.5 μg / s to 40 μg / s. This is beneficial for improving the electrochemical performance of the secondary battery.

[0074] The positive electrode sheet of this application, when used in secondary batteries, can improve the energy density, cycle performance, safety performance, and / or rate performance of secondary batteries.

[0075] The fourth aspect of this application provides a secondary battery, including the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared by the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0076] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0077] The positive electrode sheet, secondary battery, and electrical device of this application include the positive electrode material composition of this application, and therefore have at least the same advantages as the positive electrode material composition. Attached Figure Description

[0078] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0079] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0080] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0081] Figure 3This is a schematic diagram of one embodiment of the battery module of this application.

[0082] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0083] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0084] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0085] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0086] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode material composition, its preparation method, and embodiments of the positive electrode sheet, secondary battery, and power device comprising the same. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0087] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0088] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0089] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0090] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0091] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0092] Unless otherwise specified, 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, the condition "A or B" is satisfied by any of the following conditions: 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).

[0093] In this article, the terms "multiple" or "various" refer to two or more kinds.

[0094] In this article, “about” refers to a range of values, specifically the range of ±10% of that value.

[0095] In this document, the term "coating layer" refers to a layer of material coating the lithium manganese phosphate core, which may completely or partially coat the lithium manganese phosphate core. The use of "coating layer" is for descriptive purposes only and is not intended to limit the invention. Furthermore, each coating layer may be a complete or partial coating. Similarly, the term "coating layer thickness" refers to the thickness of the material coating the lithium manganese phosphate core in the radial direction of the lithium manganese phosphate core.

[0096] In this document, the median particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. In this application, the median particle size Dv50 of the material can be determined using laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvern Master Size 3000) in accordance with standard GB / T19077-2016.

[0097] In this document, substituents of compounds are disclosed by groups or ranges. It is expressly anticipated that such descriptions include each individual subcombination of members of these groups and ranges. For example, it is expressly anticipated that the term “C1-C8 alkyl” individually discloses C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7, and C7-C8 alkyl groups.

[0098] In this document, the term "aliphatic hydrocarbon group" includes alkyl, alkenyl, and alkynyl groups, and the term "heteroaliphatic hydrocarbon group" refers to an aliphatic hydrocarbon group containing heteroatoms (e.g., N, O, S, etc.). The term "heteroalkyl group" refers to an alkyl group containing heteroatoms (e.g., N, O, S, etc.), such as alkoxy, alkylthio, etc.

[0099] The inventors of this application discovered in practical operation that existing lithium manganese phosphate (LiMnPO4) cathode active materials suffer from significant manganese ion dissolution during deep charge-discharge processes. Although existing technologies have attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the dissolved manganese ions from migrating further into the electrolyte. After migrating to the negative electrode, the dissolved manganese ions are reduced to metallic manganese. This metallic manganese acts as a "catalyst," catalyzing the decomposition of the SEI (solid electrolyte interphase) film on the negative electrode surface, producing byproducts. Some of these byproducts are gaseous, causing the secondary battery to expand and affecting its safety performance. Additionally, another portion of these byproducts deposits on the negative electrode surface, obstructing the channels for lithium ions to enter and exit the negative electrode, increasing the secondary battery impedance and thus affecting its kinetic performance. Furthermore, to replenish the lost SEI film, the electrolyte and the active lithium inside the battery are continuously consumed, which also has an irreversible impact on the capacity retention rate of the secondary battery.

[0100] After extensive research, the inventors discovered that by modifying lithium manganese phosphate and applying multilayer coating, a novel core-shell structured positive electrode active material can be obtained. This material significantly reduces manganese ion dissolution and lattice change rate. When used in secondary batteries, it improves cycle performance, rate performance, safety performance, and battery capacity. Furthermore, the inventors found that combining the positive electrode active material with an organopolysiloxane compound can mitigate the erosion of the positive electrode active material surface by the electrolyte, thereby facilitating the full utilization of the material's electrochemical performance.

[0101] Positive electrode material composition

[0102] Specifically, the first aspect of this application proposes a cathode material composition comprising a cathode active material having a core-shell structure and an organopolysiloxane compound.

[0103] The positive electrode active material includes a core and a shell covering the core. The chemical formula of the core is Li. 1+x Mn 1- y A y P 1-z R zO4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, and z is any value in the range of 0.001 to 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, optionally 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, optionally one element selected from B, Si, N, and S. The values ​​of x, y, and z satisfy the condition that the entire core remains electrically neutral. 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 crystalline pyrophosphate Li. a MP2O7 and / or M b (P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c In each of the elements M, M is independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c Maintaining electrical neutrality; the second coating layer comprises 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; the third coating layer is carbon.

[0104] Unless otherwise stated, in the above-described core chemical formula, when A comprises two or more elements, the limitation on the numerical range of y applies not only to the stoichiometric coefficient of each element as A, but also to the sum of the stoichiometric coefficients of all elements as A. For example, when A comprises two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the numerical range of y defined in this application, and the sum of y1, y2...yn must also fall within this numerical range. Similarly, for the case where R comprises two or more elements, the limitation on the numerical range of the stoichiometric coefficient of R in this application has the same meaning.

[0105] In an optional implementation, when A is one, two, three, or four elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, A y For Q n1 D n2 E n3 K n4 Let n1 + n2 + n3 + n4 = y, where n1, n2, n3, and n4 are all positive numbers and not all zero simultaneously. Q, D, E, and K are each independently selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge. Optionally, at least one of Q, D, E, and K is Fe. Optionally, one of n1, n2, n3, and n4 is zero, and the others are not zero; more preferably, two of n1, n2, n3, and n4 are zero, and the others are not zero; even more preferably, three of n1, n2, n3, and n4 are zero, and the others are not zero. The kernel Li... 1+x Mn 1-y A y P 1-z R z In O4, it is advantageous to dope one, two, three or four of the aforementioned A elements at the manganese sites, and optionally, one, two or three of the aforementioned A elements are doped. In addition, it is advantageous to dope one or two R elements at the phosphorus sites, which is beneficial to make the doped elements uniformly distributed.

[0106] The kernel Li 1+x Mn 1-y A y P 1-z R z In O4, the value of x is influenced by the valence states of A and R, as well as the values ​​of y and z, to ensure the overall system remains electrically neutral. If the value of x is too small, the lithium content of the entire core system will decrease, affecting the capacity of the positive electrode active material. The value of y limits the total amount of all dopants. If y is too small, i.e., the doping amount is too low, the dopants will not play a role. If y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. The R element is doped at the P position. Since the PO tetrahedron is relatively stable, and a large z value would affect the stability of the material, the z value is limited to 0.001 to 0.100.

[0107] The positive electrode active material of this application can improve the capacity utilization, cycle performance, and safety performance of secondary batteries. Although the mechanism is not yet clear, it is speculated that the lithium manganese phosphate positive electrode active material of this application has a core-shell structure. By doping the manganese and phosphorus sites of the lithium manganese phosphate core with elements A and R respectively, it can not only effectively reduce the dissolution of manganese ions, thereby reducing the number of manganese ions migrating to the negative electrode and reducing the electrolyte consumed due to SEI film decomposition, thus improving the cycle performance and safety performance of the secondary battery, but also promote Mn-O bond adjustment, lower the lithium ion migration barrier, promote lithium ion migration, and improve the rate performance of the secondary battery; by coating the core with a first coating layer including crystalline pyrophosphate, it can further improve the capacity utilization, cycle performance, and safety performance of the secondary battery. The process involves increasing the migration resistance of manganese ions, reducing their dissolution, and decreasing the content of surface lithium impurities and the contact between the core and the electrolyte. This reduces interfacial side reactions and gas generation, thereby improving the high-temperature storage performance, cycle performance, and safety performance of the secondary battery. Further coating with a crystalline phosphate coating layer, which has excellent lithium-ion conductivity, can effectively reduce interfacial side reactions between the positive electrode active material and the electrolyte, thus improving the high-temperature cycle and storage performance of the secondary battery. Finally, further coating with a carbon layer as a third coating layer can further enhance the safety and kinetic performance of the secondary battery.

[0108] Furthermore, in the core, the element A doped at the manganese site of lithium manganese phosphate helps to reduce the lattice change rate of lithium manganese phosphate during the lithium insertion / extraction process, improves the structural stability of the lithium manganese phosphate cathode active material, greatly reduces the dissolution of manganese ions and reduces the oxygen activity on the particle surface; the element R doped at the phosphorus site also helps to change the ease of Mn-O bond length change, thereby improving electronic conductivity and reducing the lithium ion migration barrier, promoting lithium ion migration and improving the rate performance of the secondary battery.

[0109] Furthermore, maintaining the electrical neutrality of the entire core system ensures that defects and impurities in the cathode active material are minimized. If an excess of transition metal (such as manganese) exists in the cathode active material, due to the relatively stable structure of the material system itself, the excess transition metal is likely to precipitate as elemental or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. Additionally, ensuring system electrical neutrality can, in some cases, generate lithium vacancies in the cathode active material, thereby improving its kinetic performance.

[0110] The cathode material composition of this application comprises a cathode active material and an organopolysiloxane compound. The inventors of this application have discovered that using the aforementioned cathode active material in combination with the organopolysiloxane compound can alleviate the corrosion of the cathode active material surface by the electrolyte and reduce manganese ion dissolution, thereby improving the electrochemical performance of the cathode active material. A possible reason is that the Si-O framework of the organopolysiloxane compound can remove F-containing ions from the electrolyte, thereby reducing the electrolyte acidity and alleviating the corrosion of the cathode active material surface by acidic substances in the electrolyte; the organopolysiloxane compound also has a certain degree of hydrophobicity, and when it is prepared together with the cathode active material into a cathode electrode sheet, the contact angle between the resulting cathode electrode sheet and the electrolyte increases, thereby alleviating the corrosion of the cathode active material surface by the electrolyte.

[0111] Therefore, positive electrode sheets and electrical devices such as secondary batteries using the positive electrode material composition of this application can have high energy density and improve cycle performance, safety performance, and / or rate performance.

[0112] The cores prepared in this application have an average particle size ranging from 50 nm to 500 nm, and a Dv50 ranging from 200 nm to 300 nm. The primary particle size of the cores is consistently within the range of 50 nm to 500 nm, with a Dv50 of 200 nm to 300 nm. If the average particle size of the cores is too large (exceeding 500 nm), the capacity of the secondary battery using this material will be affected; if the average particle size of the cores is too small, its specific surface area is too large, making it prone to aggregation and difficult to achieve uniform coating.

[0113] By controlling the process (e.g., thoroughly mixing and grinding materials from various sources), it is possible to ensure that each element is uniformly distributed in the crystal lattice and that no aggregation occurs. The main characteristic peak positions in the X-ray diffraction (XRD) pattern of lithium manganese phosphate doped with elements A and R are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in the core performance mainly comes from elemental doping, rather than impurity phases. After preparing the cathode active material described in this application, the inventors used focused ion beam (FIB) to cut the middle region (core region) of the prepared cathode active material particles. Tests conducted using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0114] In this application, "crystalline" refers to a crystallinity of 50% or higher, i.e., 50% to 100%. Crystallinity less than 50% is referred to as glassy (or amorphous). The crystallinity of the crystalline pyrophosphate and crystalline phosphate described in this application is 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity not only fully utilize the pyrophosphate coating's ability to inhibit manganese ion dissolution and the phosphate coating's excellent lithium ion conduction capabilities, reducing interfacial side reactions, but also enable better lattice matching between the pyrophosphate and phosphate coatings, thus achieving a tighter bond between the coatings.

[0115] In this application, the crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the positive electrode active material can be tested by conventional technical means in the art, such as by density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, or by, for example, X-ray diffraction.

[0116] A specific X-ray diffraction method for testing the crystallinity of the first coating layer crystalline pyrophosphate and the second coating layer crystalline phosphate of the positive electrode active material may include the following steps: Take a certain amount of positive electrode active material powder, and measure the total scattering intensity by X-rays. This is the sum of the scattering intensities of all matter in space, and is only related to the intensity of the primary rays, the chemical structure of the positive electrode active material powder, and the total number and mass of electrons participating in the diffraction, but is independent of the order state of the sample; then separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0117] It should be noted that, in this application, the crystallinity of pyrophosphate and phosphate in the coating layer can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time.

[0118] In this application, since metal ions are difficult to migrate in pyrophosphate, pyrophosphate, as the first coating layer, can effectively isolate the doped metal ions from the electrolyte. Crystalline pyrophosphate has a stable structure; therefore, coating with crystalline pyrophosphate can effectively suppress the dissolution of transition metals and improve cycle performance.

[0119] The bonding between the first coating layer and the core is similar to that of a heterojunction, and the strength of this bonding is limited by the degree of lattice matching. When the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly. A tight bonding ensures that the coating layer will not detach during subsequent cycling, which is beneficial for ensuring the long-term stability of the cathode active material. The degree of bonding between the first coating layer and the core is mainly measured by calculating the mismatch between the lattice constants of the core and the coating. In this application, after doping the core with A and R elements, compared with undoped elements, the matching degree between the core and the first coating layer is improved, and the core and the pyrophosphate coating layer can bond more tightly.

[0120] Crystalline phosphate was chosen as the second coating layer primarily because of its high lattice matching (mismatch of only 3%) with the first coating layer, crystalline pyrophosphate. Secondly, phosphate itself is more stable than pyrophosphate, and coating pyrophosphate with phosphate helps improve the stability of the positive electrode active material. Crystalline phosphate has a very stable structure and excellent lithium-ion conductivity; therefore, using crystalline phosphate for coating can effectively reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. The lattice matching between the second and first coating layers is similar to the bonding between the first coating layer and the core; when the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly.

[0121] The main reason for using carbon as the third coating layer is its excellent electronic conductivity. Since electrochemical reactions occur in secondary batteries, requiring electrons, carbon, with its superior conductivity, can be used to coat the positive electrode active material to increase electron transport between particles and between different locations on the particles. Carbon coating effectively improves the conductivity and desolvation capability of the positive electrode active material.

[0122] In some embodiments, the average particle size of the primary particles of the positive electrode active material ranges from 50 nm to 500 nm, and the volume median particle size (Dv50) is in the range of 200 nm to 300 nm. Since particle agglomeration can occur, the actual measured size of the agglomerated secondary particles may be from 500 nm to 40,000 nm. The size of the positive electrode active material particles affects the processing of the material and the compaction density performance of the electrode sheet. By selecting an average particle size of the primary particles within the above range, the following situations can be effectively avoided: if the average particle size of the primary particles of the positive electrode active material is too small, it may cause particle agglomeration, making dispersion difficult and requiring more binder, resulting in poor electrode sheet brittleness; if the average particle size of the primary particles of the positive electrode active material is too large, it may result in larger gaps between particles, reducing the compaction density.

[0123] The above scheme can effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during the lithium insertion / extraction process, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0124] In some embodiments, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 nm to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°; the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 nm to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0125] The first and second coating layers of the positive electrode active material described in this application both use crystalline materials. The crystalline pyrophosphate and crystalline phosphate in the coating layers can be characterized using conventional techniques in the art, or for example, by transmission electron microscopy (TEM). Under TEM, the core and coating layers can be distinguished by measuring the interplanar spacing.

[0126] The specific testing method for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer can include the following steps: Take a certain amount of the coated positive electrode active material sample powder into a test tube, inject a solvent such as alcohol into the test tube, and then stir and disperse it thoroughly. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM sample chamber for testing to obtain the original TEM image. Open the original image obtained from the above TEM test in the diffractometer software, and perform Fourier transform to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The angle can be calculated according to the Bragg equation.

[0127] The interplanar spacing range of crystalline pyrophosphates differs from that of crystalline phosphates, and can be directly determined by the value of the interplanar spacing.

[0128] Crystalline pyrophosphate and crystalline phosphate within the aforementioned interplanar spacing and angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during lithium insertion / extraction, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0129] In the kernel, x is any value in the range of -0.100 to 0.100, for example, x can be 0.001, 0, -0.001, -0.002, -0.003, -0.004, or -0.005. Optionally, x is any value in the range of -0.005 to 0.002.

[0130] In the kernel, y is any value in the range of 0.001 to 0.500. For example, y can be 0.001, 0.100, 0.200, 0.300, 0.350, 0.400, 0.450, or 0.500.

[0131] In the kernel, z is any value in the range of 0.001 to 0.100, for example, z can be 0.001, 0.002, 0.003, 0.004, 0.005, or 0.100.

[0132] In some embodiments, the ratio of y to 1-y in the core is 1:10 to 1:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements A. When the above conditions are met, the energy density and cycle performance of the secondary battery using the positive electrode active material can be further improved.

[0133] In some embodiments, the ratio of z to 1-z in the core is from 1:9 to 1:999, optionally from 1:499 to 1:249. Here, z represents the sum of the stoichiometric coefficients of the p-site doping elements R. When the above conditions are met, the energy density and cycle performance of the secondary battery using the positive electrode active material can be further improved.

[0134] In some embodiments, the carbon in the third coating layer is a mixture of SP2 carbon and SP3 carbon. Optionally, the molar ratio of SP2 carbon to SP3 carbon is any value in the range of 0.1 to 10, and can be any value in the range of 2.0 to 3.0.

[0135] In some embodiments, the molar ratio of SP2 carbon to SP3 carbon may be about 0.1, about 0.2, about 0.3, 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 any range of the above values.

[0136] By selecting the morphology of carbon in the carbon coating layer, the overall electrochemical performance of the secondary battery can be improved. Specifically, by using a mixture of SP2 and SP3 carbon morphologies and limiting the ratio of SP2 to SP3 carbon within a certain range, the following situations can be effectively avoided: if the carbon in the coating layer is all amorphous SP3, the conductivity is poor; if it is all graphitized SP2, although the conductivity is good, there are few lithium-ion pathways, which is not conducive to lithium-ion insertion and extraction. In addition, limiting the molar ratio of SP2 to SP3 carbon within the above-mentioned range can achieve both good conductivity and ensure lithium-ion pathways, thus improving the kinetic and cycle performance of the secondary battery.

[0137] The mixing ratio of SP2 and SP3 carbon forms in the third coating layer can be controlled by sintering conditions, such as sintering temperature and sintering time. For example, when using sucrose as a carbon source to prepare the third coating layer, after the sucrose is pyrolyzed at high temperature and deposited on the second coating layer under high temperature, a carbon coating layer with both SP2 and SP3 forms will be produced. The ratio of SP2 to SP3 carbon can be adjusted by selecting high-temperature pyrolysis and sintering conditions.

[0138] The structure and characteristics of the third coating carbon layer can be determined by Raman spectroscopy. The specific testing method is as follows: by dividing the energy spectrum of the Raman test, I is obtained. d / I g (I d For the peak intensity of SP3 carbon, I g (The peak intensity of the SP2 form of carbon) was used to confirm the molar ratio between the two.

[0139] In some embodiments, the coating amount of the first 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, and more preferably greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

[0140] In some embodiments, the coating amount of the second 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, and more preferably 2% to 4% by weight, based on the weight of the core.

[0141] In some embodiments, the coating 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, and more preferably greater than 0 and less than or equal to 2% by weight, based on the weight of the core.

[0142] In this application, the coverage of each layer is not zero.

[0143] In the core-shell structured positive electrode active material described in this application, the coating amount of the three coating layers is preferably within the above-mentioned range, thereby enabling sufficient coating of the core and further improving the cycle performance, safety performance, and / or rate performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0144] For the first coating layer, keeping the coating amount within the aforementioned range effectively avoids the following situations: insufficient coating amount means a thin coating layer, which may not effectively hinder the migration of transition metals; excessive coating amount means an excessively thick coating layer, which may affect Li... + The migration of these molecules affects the rate performance of the positive electrode active material.

[0145] For the second coating layer, by keeping the coating amount within the above range, the following situations can be effectively avoided: too much coating amount may affect the overall plateau voltage of the positive electrode active material; too little coating amount may not achieve sufficient coating effect.

[0146] For the third coating layer, the carbon coating mainly plays the role of enhancing electron transport between particles. However, since the structure also contains a large amount of amorphous carbon, the carbon density is low. Therefore, if the coating amount is too large, it will affect the compaction density of the electrode.

[0147] In some embodiments, the thickness of the first coating layer is 1 nm to 10 nm.

[0148] In some embodiments, the thickness of the second coating layer is 2 nm to 15 nm.

[0149] In some embodiments, the thickness of the third coating layer is 2 nm to 25 nm.

[0150] In some embodiments, the thickness of the first coating layer may be 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 any range of the above values.

[0151] In some embodiments, the thickness of the second coating layer may be 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 any range of the above values.

[0152] In some embodiments, the thickness of the third coating layer may be 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 any range of any of the above values.

[0153] When the thickness of the first coating layer is in the range of 1 nm to 10 nm, it can avoid the adverse effects on the kinetic performance of the positive electrode active material that may occur when it is too thick, and it can also avoid the problem that it may not be able to effectively hinder the migration of transition metal ions when it is too thin.

[0154] When the thickness of the second coating layer is in the range of 2nm to 15nm, the surface structure of the second coating layer is stable and the side reactions with the electrolyte are small. Therefore, it can effectively reduce the interface side reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0155] When the thickness of the third coating layer is in the range of 2 nm to 25 nm, it can improve the conductivity of the positive electrode active material and increase the compaction density of the positive electrode sheet prepared using the positive electrode active material.

[0156] The thickness of the coating layer is mainly tested by FIB. The specific method may include the following steps: randomly select a single particle from the positive electrode active material powder to be tested, cut a thin slice with a thickness of about 100 nm from the middle position or near the middle position of the selected particle, and then perform TEM test on the thin slice to measure the thickness of the coating layer. Measure 3-5 positions and take the average value.

[0157] In some embodiments, based on the weight of the positive electrode active material, the manganese content is in the range of 10% to 35% by weight, preferably in the range of 15% to 30% by weight, and more preferably in the range of 17% to 20% by weight.

[0158] In some embodiments, the phosphorus content, based on the weight of the positive electrode active material, is in the range of 12% to 25% by weight, and optionally in the range of 15% to 20% by weight.

[0159] In some embodiments, the weight ratio of manganese to phosphorus ranges from 0.90 to 1.25, and is optionally from 0.95 to 1.20.

[0160] In this application, when only the core of the positive electrode active material contains manganese, the manganese content can correspond to the content of the core.

[0161] In this application, limiting the content of manganese element within the above-mentioned range can effectively avoid problems such as poor structural stability and decreased density of the positive electrode active material that may be caused by excessive manganese element content, thereby improving the cycle, storage and compaction density performance of the secondary battery; and can also avoid problems such as low voltage platform that may be caused by excessive manganese element content, thereby improving the energy density of the secondary battery.

[0162] In this application, limiting the phosphorus content within the aforementioned range effectively avoids the following situations: if the phosphorus content is too high, it may lead to excessive covalentity of PO, affecting the conductivity of small polarons and thus affecting the conductivity of the positive electrode active material; if the phosphorus content is too low, it may reduce the stability of the pyrophosphate lattice structure in the core, the first coating layer, and / or the phosphate lattice structure in the second coating layer, thereby affecting the overall stability of the positive electrode active material.

[0163] The weight ratio of manganese to phosphorus has the following effects on the performance of secondary batteries: If the weight ratio is too high, it means that there is too much manganese, which increases the dissolution of manganese ions, affecting the stability and capacity of the positive electrode active material, and thus affecting the cycle performance and storage performance of the secondary battery; if the weight ratio is too low, it means that there is too much phosphorus, which is prone to the formation of impurity phases, which will cause the discharge voltage plateau of the positive electrode active material to drop, thereby reducing the energy density of the secondary battery.

[0164] The measurement of manganese and phosphorus can be performed using conventional techniques in the field. In particular, the content of manganese and phosphorus 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, and then the content of manganese is measured and converted to obtain its weight percentage.

[0165] In some embodiments, the lattice change rate of the core-shell structured positive electrode active material before and after complete lithium insertion / extraction is less than 4%, preferably less than 3.8%, and more preferably 2.0% to 3.8%.

[0166] The lithium insertion / extraction process of lithium manganese phosphate (LiMnPO4) is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change before and after lithium insertion / extraction; the smaller the rate of lattice change, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + The core-shell structured cathode active material described in this application achieves a lattice change rate of less than 4% before and after lithium insertion / extraction, thus improving the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD) patterns.

[0167] In some embodiments, the Li / Mn antisite defect concentration of the core-shell structured positive electrode active material is below 4%, optionally below 2.2%, and more preferably from 1.5% to 2.2%. The Li / Mn antisite defect mentioned in this application refers to the Li / Mn antisite defect in the LiMnPO4 lattice. + With Mn 2+ The positions of the Li / Mn antisite defects are interchanged. Accordingly, the Li / Mn antisite defect concentration refers to the concentration relative to the Mn concentration. 2+ Interchangeable Li + Zhan Li + Percentage of the total amount. In this application, the concentration of Li / Mn antisite defects can be tested, for example, according to JIS K 0131-1996.

[0168] The core-shell structured positive electrode active material described in this application can achieve the aforementioned low Li / Mn antisite defect concentration. Although the mechanism is not yet fully understood, the inventors of this application speculate that due to the presence of Li in the LiMnPO4 lattice... + With Mn 2+ The positions will be swapped, and Li + The transmission channel is a one-dimensional channel, therefore Mn 2+ In Li + Migration will be difficult within the channel, thus hindering Li + Therefore, the core-shell structured positive electrode active material described in this application, due to its low Li / Mn antisite defect concentration within the aforementioned range, can avoid Mn transport. 2+ Hinder Li + This improves the transmission efficiency and enhances the capacity utilization and rate performance of the positive electrode active material.

[0169] In some embodiments, the core-shell structured positive electrode active material has a compaction density of 2.2 g / cm³ at 3T. 3 The above can be selected as 2.2g / cm. 3 Above and 2.8g / cm 3 The higher the compaction density, the greater the weight of the positive electrode active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of secondary batteries. Compaction density can be measured according to GB / T 24533-2009.

[0170] In some embodiments, the surface oxygen valence state of the core-shell structured positive electrode active material is below -1.90, optionally between -1.90 and -1.98. The stable valence state of oxygen is -2; the closer the valence state is to -2, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. Typically, its surface valence state is below -1.7. This application, by limiting the surface oxygen valence state of the positive electrode active material to the above range as described above, can mitigate interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and storage performance 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).

[0171] In some embodiments, the organopolysiloxane compound comprises at least one structural unit represented by Formula 1.

[0172]

[0173] R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate ester, carboxylic acid ester, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon, C1-C20 halogenated aliphatic hydrocarbon, C1-C20 heteroaliphatic hydrocarbon, C1-C20 halogenated heteroaliphatic hydrocarbon, C6-C20 aromatic hydrocarbon, C6-C20 halogenated aromatic hydrocarbon, C2-C20 heteroaromatic hydrocarbon, C2-C20 halogenated heteroaromatic hydrocarbon. Optionally, R1 and R2 each independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, phenyl. More preferably, R1 and R2 each independently represent H or at least one of the following functional groups: -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl.

[0174] These functional groups can complex manganese ions and / or react with acidic substances in the electrolyte, thereby reducing manganese ion dissolution and further improving the cycle performance and storage performance of the secondary battery.

[0175] When these functional groups also have electron-withdrawing properties, the Si in the Si-O framework of organopolysiloxane compounds becomes more electron-deficient, thereby further enhancing the affinity with F-containing ions in the electrolyte, further mitigating the erosion of the positive electrode active material surface by acidic substances in the electrolyte, reducing the dissolution of manganese ions, and thus significantly improving the cycle performance and storage performance of secondary batteries.

[0176] In some embodiments, the organopolysiloxane compound includes one or more selected from linear polysiloxanes and cyclic polysiloxanes. Optionally, the organopolysiloxane compound is selected from linear polysiloxanes.

[0177] Therefore, this can further alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, reduce manganese ion dissolution, and thus significantly improve the cycle performance and storage performance of the secondary battery. Because the electrons in the ring structure of cyclic polysiloxanes have a certain degree of delocalization, compared with linear polysiloxanes, their Si-O framework has a lower affinity for electron-rich F-containing ions, resulting in a slightly lower removal rate of F-containing ions in the electrolyte, a slightly weaker effect in reducing manganese ion dissolution, and a slightly poorer improvement effect on the cycle performance of the secondary battery.

[0178] In some embodiments, the linear polysiloxane may further comprise end-capping groups. Optionally, the end-capping groups comprise at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxyalkyl, amino, C1-C8 aminoalkyl, carboxyl, and C1-C8 carboxyalkyl.

[0179] In some embodiments, the molecular formula of the cyclic polysiloxane may be as shown in Formula 2, where n represents the degree of polymerization of the structural unit shown in Formula 1. Optionally, n ≤ 12, n ≤ 11, n ≤ 10, n ≤ 9, or n ≤ 8.

[0180]

[0181] As an example, the linear polysiloxanes include, but are not limited to, one or more of the following: polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, epoxy-terminated polysiloxane, hydroxyl-terminated polydimethylsiloxane, polyether-terminated polydimethylsiloxane, side-chain aminopropylpolysiloxane, side-chain hydroxymethylpolysiloxane, side-chain hydroxypropylpolysiloxane, side-chain polyether-grafted polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane. Optionally, the linear polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, end-group polyether polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane.

[0182] As an example, the cyclic polysiloxane includes, but is not limited to, one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrosiloxane, and cyclic polymethyltrifluoropropylsiloxane. Optionally, the cyclic polysiloxane includes one or more of 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentapolydimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, hexadecylcyclooctasiloxane, and tetradecylcycloheptasiloxane.

[0183] In some embodiments, the number average molecular weight of the organopolysiloxane compound is below 300,000, for example, it can be 400 to 300,000, 400 to 200,000, 400 to 100,000, 400 to 80,000, 400 to 50,000, 400 to 20,000, 400 to 10,000, 1,000 to 100,000, 1,000 to 50,000, 1,000 to 20,000, or 1,000 to 10,000. The number average molecular weight of the organopolysiloxane compound can be determined by methods known in the art, such as gel permeation chromatography (GPC). The testing instrument can be a PL-GPC 220 high-temperature gel permeation chromatograph. In this application, "organopolysiloxane compound" can be either an oligomer or a polymer.

[0184] When the number-average molecular weight of organopolysiloxane compounds is within a suitable range, secondary batteries can simultaneously achieve good kinetic performance and high-temperature storage performance. This effectively avoids the following situations: if the number-average molecular weight of the organopolysiloxane compound is too low, its hydrophobicity may be poor, which may prevent the effective increase of the contact angle between the positive electrode film and the electrolyte, and thus may not effectively mitigate the erosion of the positive electrode active material surface by the electrolyte, resulting in a potentially insignificant improvement in the cycle performance and storage performance of the secondary battery; if the number-average molecular weight of the organopolysiloxane compound is too high, its hydrophobicity may be too strong, which may also be detrimental to the dispersion of the slurry, thereby affecting the improvement of the secondary battery performance.

[0185] In some embodiments, the mass percentage of polar functional groups in the organopolysiloxane compound is α, where 0 ≤ α < 50%, and optionally, 5% ≤ α ≤ 30%.

[0186] In this application, "the mass percentage of polar functional groups in the organopolysiloxane compound" refers to the mass proportion of polar functional groups in R1, R2, and the end-capping group in the organopolysiloxane compound. In this application, polar functional groups include one or more of the following: -COOH, -OH, -SH, -CN, -SCN, amino groups (including -NH2, -NH-), phosphate ester groups, carboxylic ester groups (-COO-), amide groups (-CONH-), aldehyde groups (-CHO), sulfonyl groups (-S(=O)2-), polyether segments, halogen atoms, alkoxy groups, and epoxy groups. When the aforementioned polar functional groups are directly connected to silicon atoms, α represents the mass fraction of these polar functional groups in the organopolysiloxane compound. When the aforementioned polar functional groups are not directly connected to silicon atoms, α represents the sum of the mass fractions of the polar functional groups and the divalent to tetravalent methyl groups (e.g., -CH2, -CH-, -C-, etc.) directly connected to them in the organopolysiloxane compound. Here, "divalent to tetravalent methyl groups" refers to the carbon atom directly connected to the polar functional group and located between the polar functional group and the silicon atom, as well as other nonpolar functional groups connected to the carbon atom. Taking polymethyltrifluoropropylsiloxane as an example, α refers to the mass percentage of -CF3, excluding the ethylidene; taking polymethylchloropropylsiloxane as an example, α refers to the mass percentage of -CH2Cl, excluding the ethylidene; taking hydroxypropyl-terminated polydimethylsiloxane as an example, α refers to the mass percentage of -CH2OH. The mass percentage of polar functional groups in organopolysiloxane compounds can be determined by methods known in the art, such as titration (e.g., acid-base titration, redox titration, precipitation titration), infrared spectroscopy, and nuclear magnetic resonance spectroscopy.

[0187] When the content of polar functional groups in organopolysiloxane compounds is within a suitable range, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte is better. This can better alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, and better improve the cycle performance and storage performance of the secondary battery. It also effectively avoids the following situation: when the content of polar functional groups in organopolysiloxane compounds is too high, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte will not be further enhanced, but may lead to a smaller contact angle between the positive electrode film and the electrolyte, resulting in a less significant improvement in the cycle performance of the secondary battery.

[0188] In some embodiments, the content of the organopolysiloxane compound is from 0.01% to 2% by weight, optionally from 0.1% to 2% by weight, based on the total weight of the cathode material composition.

[0189] When the content of organopolysiloxane compounds is within a suitable range, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte is better, thus better mitigating the erosion of the positive electrode active material surface by acidic substances in the electrolyte, and better improving the cycle performance and storage performance of the secondary battery. It also effectively avoids the following situations: if the content of organopolysiloxane compounds is too high, it may affect the electrolyte wettability of the positive electrode film, affecting the kinetic performance of the secondary battery. Furthermore, since organopolysiloxane compounds do not contribute capacity, a high content will also reduce the energy density of the secondary battery. If the content of organopolysiloxane compounds is too low, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte is not significant, and they cannot effectively mitigate the erosion of the positive electrode active material surface by acidic substances in the electrolyte, thus the improvement effect on the cycle performance and high-temperature storage performance of the secondary battery may not be significant.

[0190] In some embodiments, the positive electrode material composition may further include a binder. The binder may be a known adhesive substance, and optionally, the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0191] Optionally, the binder content is from 1.79% to 10% by weight, or optionally from 2% to 5% by weight, based on the total weight of the cathode material composition.

[0192] In some embodiments, the positive electrode material composition may further include a conductive agent. The conductive agent may be a substance known in the art that can perform electron conduction; optionally, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] Optionally, the conductive agent content is from 0.2% to 10% by weight, or optionally from 0.5% to 5% by weight, based on the total weight of the positive electrode material composition.

[0194] In some embodiments, the powder resistivity of the cathode material composition at 12 MPa is 4 Ω / cm to 55 Ω / cm, optionally 4 Ω / cm to 40 Ω / cm. Adjusting the powder resistivity of the cathode material composition within a suitable range can improve the kinetic performance of the secondary battery. The powder resistivity of the cathode material composition can be determined by methods known in the art. For example, it can be tested using a powder resistivity tester, referring to GB / T 30835-2014. An exemplary testing method includes the steps of: weighing a certain amount of the sample powder to be tested and placing it in a special mold, setting the test pressure, and thus obtaining the powder resistivity at different pressures. In this application, the test pressure can be set to 12 MPa. The testing instrument can be a Suzhou Jinglü ST2722-SZ type four-probe powder resistivity tester.

[0195] In some embodiments, the specific surface area of ​​the cathode material composition is 8 m². 2 / g to 20m 2 / g, optional 8m 2 / g to 15m 2 / g. Adjusting the specific surface area of ​​the cathode material composition within a suitable range can reduce interfacial side reactions between the cathode electrode and the electrolyte, decrease the volume expansion of the secondary battery, and thus enable the secondary battery to have better electrochemical performance. The specific surface area of ​​the cathode material composition can be determined by methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0196] Preparation method

[0197] The second aspect of this application provides a method for preparing a cathode material composition, which can prepare the cathode material composition of the first aspect of this application.

[0198] Specifically, the preparation method includes the following steps: providing core material, coating, and mixing.

[0199] The steps for providing the core material: the core has the chemical formula Li 1+x Mn 1-y A y P 1-z R zO4, where x is any value in the range of -0.100 to 0.100, optionally any value in the range of -0.005 to 0.002, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 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, optionally 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, optionally R is one element selected from B, Si, N and S, and the values ​​of x, y and z satisfy the following condition: keeping the entire core electrically neutral.

[0200] Coating steps: Provide Li separately a MP2O7 and / or M b (P2O7) c And an XPO4 suspension, the core material is added to the suspension and mixed, and then sintered to obtain a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell covering the core, the shell comprising 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 comprising crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c In each of the elements M, M is independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c To maintain electrical neutrality, the second coating layer comprises 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, and the third coating layer is carbon.

[0201] Mixing step: The obtained positive electrode active material is mixed uniformly with an organopolysiloxane compound, an optional binder and an optional conductive agent to obtain a positive electrode material composition.

[0202] In some implementations, the step of providing the core material includes steps (1) and (2).

[0203] Step (1): Mix and stir the manganese source, dopant of element A and acid in a container to obtain manganese salt particles doped with element A.

[0204] Step (2): The manganese salt particles doped with element A are mixed with a lithium source, a phosphorus source, and a dopant of element R in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, a core doped with elements A and R is obtained, wherein the core doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, optionally any value in the range of -0.005 to 0.002, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 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, 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, optionally one element selected from B, Si, N, and S.

[0205] The preparation method of this application does not have any particular restrictions on the source of materials. The source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide. The precursor is from this source to achieve the purpose of the preparation method of this application.

[0206] In some embodiments, the dopant of element A is one or more elements selected from the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

[0207] In some embodiments, the dopant of element R is one or more of the inorganic acids, flavonoids, organic acids, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements selected from B, Si, N, and S.

[0208] In this application, the manganese source can be any manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source can be one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0209] In this application, the acid may be one or more organic acids selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, siliceous acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.

[0210] In this application, the lithium source can be any lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0211] In this application, the phosphorus source may be any phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the phosphorus source may be one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0212] In some embodiments, after the manganese source, the dopant of element A and the acid are reacted in a solvent to obtain a suspension of manganese salt doped with element A, the suspension is filtered, dried and sand-milled to obtain manganese salt particles doped with element A with a particle size of 50-200 nm.

[0213] In some embodiments, the slurry in step (2) is dried to obtain powder, and then the powder is sintered to obtain a core doped with element A and element R.

[0214] In some embodiments, step (1) is performed at a temperature of 20°C to 120°C, optionally 40°C to 120°C.

[0215] In some embodiments, the stirring in step (1) is carried out at 400 rpm to 700 rpm for 1 hour to 9 hours, or optionally 3 hours to 7 hours.

[0216] Optionally, the reaction temperature in step (1) can be about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C; the stirring in step (1) can be carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, or about 9 hours; optionally, the reaction temperature and stirring time in step (1) can be within any range of the above values.

[0217] In some embodiments, step (2) is carried out at a temperature of 20°C to 120°C, optionally 40°C to 120°C, for 1 hour to 12 hours. Optionally, the reaction temperature in step (2) can be carried out at about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C; the mixing in step (2) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours, or about 12 hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of the above values.

[0218] When the temperature and time during the core particle preparation process are within the above range, the obtained core and the positive electrode active material made from it have fewer lattice defects, which is beneficial to suppress the dissolution of manganese ions, reduce the interfacial side reactions between the positive electrode active material and the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0219] In some embodiments, optionally, during the preparation of lithium manganese phosphate particles doped with elements A and R, the solution pH is controlled to be 3.5 to 6; alternatively, the solution pH is controlled to be 4 to 6; and more preferably, the solution pH is controlled to be 4 to 5. It should be noted that the pH of the resulting mixture can be adjusted using methods commonly used in the art, for example, by adding an acid or a base.

[0220] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles doped with element A to the lithium source and the phosphorus source is 1:(0.5-2.1):(0.5-2.1), and more preferably, the molar ratio of the manganese salt particles doped with element A to the lithium source and the phosphorus source is about 1:1:1.

[0221] In some embodiments, optionally, the sintering conditions in the preparation of A and R-doped lithium manganese phosphate are: sintering at 600°C to 950°C for 4 to 10 hours in an inert gas or a mixture of inert gas and hydrogen atmosphere; optionally, the sintering can be carried out at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values. In the preparation of lithium manganese phosphate doped with elements A and R, if the sintering temperature is too low or the sintering time is too short, the crystallinity of the cathode active material core will be low, which will affect the overall performance. If the sintering temperature is too high, impurity phases are likely to appear in the cathode active material core, which will also affect the overall performance. If the sintering time is too long, the cathode active material core particles will be too large, which will affect the capacity, compaction density and rate performance.

[0222] In some embodiments, the protective atmosphere may optionally be a mixture of 70-90% by volume nitrogen and 10-30% by volume hydrogen.

[0223] In some embodiments, the coating step includes a first coating step, a second coating step, and a third coating step.

[0224] First coating step: Dissolve the source of element M, phosphorus source, acid, and optionally lithium source in a solvent to obtain a first coating layer suspension; thoroughly mix the core obtained in the core material provision step with the first coating layer suspension obtained in the first coating step, dry, and then sinter to obtain the material coated by the first coating layer.

[0225] Second coating step: Dissolve the source of element X, phosphorus source and acid in solvent to obtain a second coating layer suspension; mix the material coated by the first coating layer obtained in the first coating step with the second coating layer suspension obtained in the second coating step, dry, and then sinter to obtain a material coated by two coating layers.

[0226] The third coating step: Dissolve the carbon source in a solvent to obtain a third coating layer solution; then add the material coated by the two coating layers obtained in the second coating step to the third coating layer solution, mix evenly, dry, and then sinter to obtain a material coated by the three coating layers, i.e., the positive electrode active material.

[0227] In some embodiments, the source of element M is one or more elements selected from the group consisting of the elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0228] In some embodiments, the source of element X is one or more elements selected from the group consisting of the elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0229] The amount of each of the elements A, R, M, and X sources added depends on the target doping amount, and the ratio of the amounts of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0230] As an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0231] In some embodiments, during the first coating step, the pH of the solution containing the dissolved source of element M, the phosphorus source, and the acid, and optionally the lithium source, is controlled to be 3.5 to 6.5. The solution is then stirred and reacted for 1 to 5 hours, followed by heating the solution to 50°C to 120°C and maintaining that temperature for 2 to 10 hours. In some embodiments, during the first coating step, sintering is performed at 650°C to 800°C for 2 to 6 hours.

[0232] Optionally, in the first coating step, the reaction proceeds fully. Optionally, in the first coating step, the reaction proceeds for approximately 1.5 hours, approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 45 hours, or approximately 5 hours. Optionally, in the first coating step, the reaction time can be within any range of the above-mentioned values.

[0233] Optionally, in the first coating step, the pH of the solution is controlled to be between 4 and 6. Optionally, in the first coating step, the solution is heated to approximately 55°C, approximately 60°C, approximately 70°C, approximately 80°C, approximately 90°C, approximately 100°C, approximately 110°C, or approximately 120°C, and held at this temperature for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; Optionally, in the first coating step, the temperature and holding time can be within any range of the above values.

[0234] Optionally, in the first coating step, the sintering can be performed at about 650°C, about 700°C, about 750°C, or about 800°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours; optionally, the sintering temperature and sintering time can be within any range of the above values.

[0235] In the first coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: When the sintering temperature in the first coating step is too low and the sintering time is too short, the crystallinity of the first coating layer will be low and there will be more amorphous substances, which will reduce the effect of inhibiting metal dissolution, thereby affecting the cycle performance and storage performance of the secondary battery; when the sintering temperature is too high, impurities will appear in the first coating layer, which will also affect its effect of inhibiting metal dissolution, thereby affecting the cycle performance and storage performance of the secondary battery; when the sintering time is too long, the thickness of the first coating layer will increase, affecting the Li + The migration of these molecules affects the capacity utilization and rate performance of the positive electrode active material.

[0236] In some embodiments, 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 to 10 hours. The solution is then heated to 60°C to 150°C and maintained at that temperature for 2 to 10 hours. In some embodiments, in the second coating step, sintering is performed at 500°C to 700°C for 6 to 10 hours.

[0237] Optionally, in the second coating step, the reaction proceeds fully. Optionally, in the second coating step, the reaction proceeds for approximately 1.5 hours, approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 4.5 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours. Optionally, in the second coating step, the reaction time can be within any range of the above-mentioned values.

[0238] Optionally, in the second coating step, the solution is heated to approximately 65°C, approximately 70°C, approximately 80°C, approximately 90°C, approximately 100°C, approximately 110°C, approximately 120°C, approximately 130°C, approximately 140°C, or approximately 150°C, and held at this temperature for approximately 2 hours, approximately 3 hours, approximately 4 hours, approximately 5 hours, approximately 6 hours, approximately 7 hours, approximately 8 hours, approximately 9 hours, or approximately 10 hours; optionally, in the second coating step, the heating temperature and holding time can be within any range of the above values.

[0239] In the steps of providing the core material and the first coating step and the second coating step, before sintering, that is, in the preparation of the core material in which the chemical reaction occurs (steps (1) and (2)) and in the preparation of the first coating layer suspension and the second coating layer suspension, by selecting appropriate reaction temperature and reaction time as described above, the following situations can be effectively avoided: when the reaction temperature is too low, the reaction cannot occur or the reaction rate is slow; when the temperature is too high, the product decomposes or forms an impurity phase; when the reaction time is too long, the product particle size is large, which may increase the time and difficulty of subsequent processes; when the reaction time is too short, the reaction is incomplete and less product is obtained.

[0240] Optionally, in the second coating step, the sintering can be carried out at about 550°C, about 600°C, or about 700°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values.

[0241] In the second coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: When the sintering temperature in the second coating step is too low and the sintering time is too short, the crystallinity of the second coating layer will be low, with more amorphous phases, reducing the performance of the surface reactivity of the positive electrode active material, thereby affecting the cycle performance and storage performance of the secondary battery; when the sintering temperature is too high, impurities will appear in the second coating layer, which will also affect its effect of reducing the surface reactivity of the positive electrode active material, thereby affecting the cycle performance and storage performance of the secondary battery; when the sintering time is too long, the thickness of the second coating layer will increase, affecting the voltage plateau of the positive electrode active material, thereby reducing the energy density of the secondary battery.

[0242] In some embodiments, the sintering in the third coating step is performed at 700°C to 800°C for 6 to 10 hours. Optionally, in the third coating step, the sintering can be performed at about 700°C, about 750°C, or about 800°C for about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; alternatively, the sintering temperature and sintering time can be within any range of the above values.

[0243] In the third coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: when the sintering temperature in the third coating step is too low, the graphitization degree of the third coating layer will decrease, affecting its conductivity and thus affecting the capacity performance of the positive electrode active material; when the sintering temperature is too high, the graphitization degree of the third coating layer will be too high, affecting the Li +The transmission of the cathode material can affect its capacity utilization, etc.; if the sintering time is too short, the coating layer will be too thin, affecting its conductivity and thus affecting the capacity utilization of the cathode material; if the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the cathode material, etc.

[0244] In the first, second, and third coating steps described above, the drying can be carried out at a drying temperature of 100°C to 200°C, optionally 110°C to 190°C, more preferably 120°C to 180°C, even more preferably 120°C to 170°C, and most preferably 120°C to 160°C. The drying time can be 3 hours to 9 hours, optionally 4 hours to 8 hours, more preferably 5 hours to 7 hours, and most preferably about 6 hours.

[0245] The positive electrode active material prepared by the method described in this application results in a reduced dissolution of Mn and Mn-site dopant elements in the secondary battery after cycling, and improved high-temperature storage performance, cycle performance, and rate performance. Furthermore, the raw materials are widely available, inexpensive, and the process is simple, facilitating industrialization.

[0246] Positive electrode sheet

[0247] A third aspect of this application provides a positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer comprises a positive electrode material composition according to the first aspect of this application or a positive electrode material composition prepared by the method according to the second aspect of this application, and the content of the positive electrode material composition in the positive electrode film layer is 50% by weight or more, based on the total weight of the positive electrode film layer. The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0248] In some embodiments, the positive electrode material composition may optionally be present in the positive electrode film layer at a content of 90% to 100% by weight, based on the total weight of the positive electrode film layer.

[0249] The positive electrode film layer does not exclude components other than the positive electrode material composition of the first aspect of this application or the positive electrode material composition prepared by the method of the second aspect of this application. For example, the positive electrode film layer may also include other positive electrode active materials besides the three-layer coated positive electrode active materials mentioned above. Optionally, the other positive electrode active materials may include at least one of lithium transition metal oxides and their modified compounds. As an example, the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0250] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0251] In some embodiments, the solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 90°, optionally between 3° and 60°, and further between 10° and 30°. When the contact angle is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance. It also effectively avoids the following situations: if the contact angle is too small, it cannot effectively mitigate the erosion of the positive electrode active material surface by acidic substances in the electrolyte, and its effect on improving cycle performance may not be significant; if the contact angle is too large, it may cause poor electrolyte wettability of the positive electrode film, affecting the rate performance and cycle performance of the secondary battery. The solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent has a well-known meaning in the art and can be tested using methods known in the art, such as referring to GB / T 30693-2014 for measurement. An exemplary testing method includes the following steps: at room temperature, a non-aqueous organic solvent is dropped onto the surface of the positive electrode, and its contact angle is measured over 60 seconds using a contact angle meter. The testing instrument can be an LSA200 optical contact angle meter from LAUDA Scientific, Germany. The non-aqueous organic solvent can be any non-aqueous organic solvent known in the art for use in non-aqueous electrolytes for secondary batteries; optionally, the non-aqueous organic solvent is ethylene carbonate (EC).

[0252] In some embodiments, the porosity of the positive electrode film is 15% to 50%, optionally 15% to 30%. When the porosity is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance. It effectively avoids the following situations: if the porosity is too low, the electrolyte wettability of the positive electrode film may deteriorate, affecting the rate performance and cycle performance of the secondary battery; if the porosity is too high, it may affect the overall energy density of the secondary battery. The porosity of the positive electrode film has a well-known meaning in the art and can be tested using methods known in the art, such as by peeling off the positive electrode film with tape and measuring according to GB / T 24586-2009. Porosity P = [(V2-V1) / V2] × 100%. V1 (cm 3 V² (cm²) represents the true volume, which can be determined using an inert gas with a small molecular diameter (such as helium) via a displacement method, combined with Archimedes' principle and Bohr's law. 3 V represents the apparent volume, V² = S × H × A, where S (cm²) 2 ) represents the area, H (cm) represents the thickness, and A represents the number of samples.

[0253] In some embodiments, the resistance of the positive electrode film is greater than 0 and less than or equal to 6Ω. This ensures that the positive electrode has good conductivity, resulting in better dynamic performance of the secondary battery. The resistance of the positive electrode film is a term known in the art and can be tested using methods known in the art, such as an electrode resistance meter. An exemplary testing method is as follows: Take a single-sided coated and cold-pressed positive electrode (if it is a double-sided coated positive electrode, the positive electrode film on one side can be wiped off first) and place it parallel between the two conductive terminals of the electrode resistance meter. Apply a certain pressure to fix it, thus obtaining the resistance of the positive electrode film. Optionally, the diameter of the conductive terminals can be 14mm, the applied pressure can be 15-27MPa, and the sampling time range can be 10-20s. The testing instrument can be an IEST BER1000 electrode resistance meter from Yuaneng Technology Co., Ltd.

[0254] In some embodiments, the adhesion force between the positive electrode film and the positive electrode current collector is greater than or equal to 0.5 MPa. Within this range, it can prevent the occurrence of powder shedding from the positive electrode sheet, thereby benefiting the performance of the secondary battery. The adhesion force between the positive electrode film and the positive electrode current collector is a term known in the art and can be tested using methods known in the art. An exemplary test method is as follows: Cut the positive electrode sheet into a test sample 100mm long and 10mm wide; take a stainless steel plate 25mm wide, apply double-sided tape (e.g., 11mm wide), and attach the test sample to the double-sided tape on the stainless steel plate. Roll the sample back and forth three times with a 2000g roller (e.g., at a rolling speed of 300mm / min); bend the test sample 180°, manually peel the positive electrode film layer from the positive electrode current collector by 25mm, fix the test sample on a testing machine (e.g., INSTRON 336), ensuring the peeling surface is aligned with the force line of the testing machine. The testing machine continuously peels at 30mm / min. The average value of the obtained peeling force curve at a stable point is taken as the peeling force F0; the adhesion force between the positive electrode film layer and the positive electrode current collector = F0 / width of the test sample.

[0255] In some embodiments, the areal density of the positive electrode film is 0.006 g / cm³. 2 Up to 0.065 g / cm 2 This is beneficial for improving the volumetric energy density of secondary batteries. The areal density of the positive electrode film is a well-known concept in the art and can be tested using methods known in the art. An exemplary test method is as follows: Take a positive electrode sheet coated on one side and cold-pressed (if it is a positive electrode sheet coated on both sides, the positive electrode film on one side can be wiped off first) and cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; then wipe off the positive electrode film of the above-weighed positive electrode sheet, weigh the positive current collector, and record it as M0; the areal density of the positive electrode film = (M1-M0) / S1.

[0256] In some embodiments, the electrolyte absorption rate of the positive electrode film is from 0.0125 μg / s to 100 μg / s, and optionally from 0.5 μg / s to 40 μg / s. This ensures good wettability of the electrolyte in the electrode assembly, allowing it to quickly penetrate the electrode assembly and form an SEI film on the surface of the positive electrode in a timely manner, thereby improving the electrochemical performance of the secondary battery.

[0257] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0258] It should be noted that the parameters of each positive electrode film layer given in this application (such as contact angle, porosity, resistance, adhesion, areal density, and electrolyte absorption rate) refer to the parameters of the positive electrode film layer on one side of the positive electrode current collector. When the positive electrode film layer is disposed on both sides of the positive electrode current collector, if the parameters of the positive electrode film layer on either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0259] In addition, the above-mentioned tests on the parameters of the positive electrode film can be conducted by sampling during the preparation of the positive electrode sheet or battery, or by sampling from the prepared battery.

[0260] When the test samples are taken from the prepared battery, as an example, the sampling can be carried out in the following steps: discharge the battery (for safety reasons, the battery is generally left fully discharged); remove the positive electrode after disassembling the battery, and soak the positive electrode in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); then remove the positive electrode and dry it at a certain temperature and time (e.g., 60°C for 4 hours). After drying, remove the positive electrode, and then samples can be taken from the dried positive electrode to test the parameters related to the positive electrode film layer mentioned above in this application.

[0261] Secondary batteries

[0262] A fourth aspect of this application provides a secondary battery that includes the positive electrode of the third aspect of this application.

[0263] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery consists of an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts the active ions.

[0264] [Positive electrode plate]

[0265] The positive electrode used in the secondary battery of this application is the positive electrode described in any embodiment of the third aspect of this application.

[0266] [Negative electrode plate]

[0267] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0268] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0269] In some embodiments, the negative electrode film may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0270] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0271] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0272] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0273] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0274] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0275] [Electrolytes]

[0276] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0277] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0278] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0279] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0280] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0281] [Isolation membrane]

[0282] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0283] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0284] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0285] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0286] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0287] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0288] In some implementations, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0289] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer package, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0290] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0291] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0292] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0293] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0294] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0295] Electrical appliances

[0296] The fifth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0297] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0298] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0299] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0300] Example

[0301] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0302] The sources of raw materials involved in the embodiments of this application are as follows:

[0303] name Chemical formula factory Specification manganese carbonate <![CDATA[MnCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg lithium carbonate <![CDATA[Li2CO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Magnesium carbonate <![CDATA[MgCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Zinc carbonate <![CDATA[ZnCO3]]> Wuhan Xinru Chemical Co., Ltd. 25Kg Ferrous carbonate <![CDATA[FeCO3]]> Xi'an Lanzhiguang Fine Materials Co., Ltd. 1Kg Nickel sulfate <![CDATA[NiCO3]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Titanium sulfate <![CDATA[Ti(SO4)2]]> Shandong Xiya Chemical Industry Co., Ltd. 1Kg Cobalt sulfate <![CDATA[CoSO4]]> Xiamen Zhixin Chemical Co., Ltd. 500g Vanadium dichloride <![CDATA[VCl2]]> Shanghai Jinjinle Industrial Co., Ltd. 1Kg Oxalic acid dihydrate <![CDATA[C2H2O4.2(H2O)]]> Shanghai Jinjinle Industrial Co., Ltd. 1Kg Ammonium dihydrogen phosphate <![CDATA[NH4H2PO4]]> Shanghai Chengshao Biotechnology Co., Ltd. 500g sucrose <![CDATA[C 12 H 22 O 11 ]]> Shanghai Yuanye Biotechnology Co., Ltd. 100g dilute sulfuric acid <![CDATA[H2SO4]]> Shenzhen Haisi'an Biotechnology Co., Ltd. Quality score 60% dilute nitric acid <![CDATA[HNO3]]> Anhui Lingtian Fine Chemical Co., Ltd. Quality score 60% Silicate <![CDATA[H2SiO3]]> Shanghai Yuanye Biotechnology Co., Ltd. 100g, mass fraction 99.8%

[0304] I. Battery Manufacturing

[0305] Example 1

[0306] Step 1: Preparation of positive electrode active material

[0307] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0308] 689.6 g of manganese carbonate, 455.27 g of ferrous carbonate, 4.65 g of cobalt sulfate, and 4.87 g of vanadium dichloride were added to a mixer and mixed thoroughly for 6 hours. The resulting mixture was then transferred to a reaction vessel, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred thoroughly at 500 rpm for 6 hours until homogeneous and the reaction was terminated without bubble formation, yielding a Fe, Co, and V co-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and milled to obtain manganese oxalate particles with a particle size of 100 nm.

[0309] Step S2: Preparation of core Li 0.997 Mn 0.60 Fe 0.393 V 0.004 Co 0.003 P 0.997 S 0.003 O4

[0310] Take 1793.1g of manganese oxalate, 368.3g of lithium carbonate, 1146.6g of ammonium dihydrogen phosphate, and 4.9g of dilute sulfuric acid prepared in (1), add them to 20L of deionized water, stir thoroughly, and react uniformly at 80°C for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, and dry at 250°C to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700°C for 4 hours to obtain the above-mentioned core material.

[0311] Step S3: Preparation of the first coating layer suspension

[0312] To prepare 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, and the pH was controlled at 5. The solution was then stirred and reacted at room temperature for 2 hours to obtain a solution. The solution was then heated to 80 °C and maintained at this temperature for 4 hours to obtain the first coating layer suspension.

[0313] Step S4: Coating with the first coating layer

[0314] The 1571.9g of doped lithium manganese phosphate core material obtained in step S2 was added to the first coating layer suspension (coating material content of 15.7g) obtained in step S3. The mixture was stirred and mixed thoroughly for 6 hours. After being mixed evenly, the mixture was dried in an oven at 120℃ for 6 hours and then sintered at 650℃ for 6 hours to obtain the pyrophosphate coated material.

[0315] Step S5: Preparation of the second coating layer suspension

[0316] 3.7g lithium carbonate, 11.6g ferrous carbonate, 11.5g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate were dissolved in 1500mL deionized water, stirred and reacted for 6 hours to obtain a solution. The solution was then heated to 120℃ and maintained at this temperature for 6 hours to obtain a second coating layer suspension.

[0317] Step S6: Coating with the second coating layer

[0318] The 1586.8g of pyrophosphate-coated material obtained in step S4 was added to the second coating suspension (coating material content of 47.1g) obtained in step S5. The mixture was stirred and mixed thoroughly for 6 hours. After mixing evenly, the mixture was dried in an oven at 120℃ for 6 hours and then sintered at 700℃ for 8 hours to obtain the two-layer coated material.

[0319] Step S7: Preparation of the third coating layer aqueous solution

[0320] Dissolve 37.3g of sucrose in 500g of deionized water, then stir and dissolve completely to obtain a sucrose aqueous solution.

[0321] Step S8: Covering with the third coating layer

[0322] 1633.9g of the two-layer coated material obtained in step S6 was added to the sucrose solution obtained in step S7 and stirred together for 6 hours. After mixing evenly, the mixture was placed in a 150°C oven and dried for 6 hours. Then, it was sintered at 700°C for 10 hours to obtain the three-layer coated material, which is the positive electrode active material.

[0323] Step 2: Preparation of the positive electrode sheet

[0324] A positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups -CH2NH2 and -CH2NH-, mass percentage α approximately 12%, number average molecular weight 3700) were mixed in a mixer at a weight ratio of 93.4:1.5:4.5:0.6 until the materials were uniformly mixed to obtain a positive electrode material composition. Then, the above positive electrode material composition was added to N-methylpyrrolidone (NMP) and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was then coated with a surface density of 0.018 g / cm³. 2 The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0325] Step 3: Preparation of the negative electrode sheet

[0326] A negative electrode slurry was prepared by dissolving artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then coated with a solution to achieve a surface density of 0.0075 g / cm³. 2 The coating is uniformly applied to the copper foil of the negative electrode current collector, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0327] Step 4: Preparation of electrolyte

[0328] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed evenly at a volume ratio of 3 / 7. 12.5% ​​by weight (based on the weight of the ethylene carbonate / ethyl methyl carbonate solvent) of LiPF6 is added and dissolved in the organic solvent. The mixture is stirred evenly to obtain the electrolyte.

[0329] Step 5: Preparation of the separating membrane

[0330] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0331] Step 6: Preparation of the full cell

[0332] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, injected with the electrolyte, and sealed to obtain a full cell (hereinafter also referred to as "full cell").

[0333] [Preparation of button cells]

[0334] A positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups -CH2NH2 and -CH2NH-, mass percentage α approximately 12%, number average molecular weight 3700) were mixed in a mixer at a weight ratio of 89.4:5:5:0.6 until the materials were uniformly mixed to obtain a positive electrode material composition. Then, the above positive electrode material composition was added to N-methylpyrrolidone (NMP) and stirred in a drying chamber to form a slurry. The slurry was coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating surface density was 0.015 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0335] A lithium sheet is 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 is used as the electrolyte. The lithium sheet and the positive electrode prepared above are assembled into a coin cell in a coin cell box to form a coin cell (hereinafter also referred to as "coin cell").

[0336] Example 2-29

[0337] The positive electrode active materials of Examples 2-29 were prepared in a manner similar to that of Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 1 to 6. All other processes are the same as those of Example 1.

[0338] Examples 30-42

[0339] The positive electrode active materials of Examples 30-42 were prepared in a manner similar to that of Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 7 and 8. All other processes are the same as those of Example 1.

[0340] Examples 43-47

[0341] Except for adjusting the weight percentage of aminoethylaminopropylpolydimethylsiloxane in the cathode material composition during the preparation of the full cell and the coin cell, the process is the same as in Example 1. The differences are shown in Table 9.

[0342] Example 43

[0343] Preparation of full cellsThe positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93.99:1.5:4.5:0.01 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0344] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 89.99:5:5:0.01 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0345] Example 44

[0346] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and alkylaminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93.9:1.5:4.5:0.1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0347] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 89.9:5:5:0.1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0348] Example 45

[0349] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93:1.5:4.5:1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0350] Preparation of button cellsThe positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (with polar functional groups -CH2NH2 and -CH2NH-, a mass percentage α of approximately 12%, and a number average molecular weight of 3700) are mixed in a mixer at a weight ratio of 89:5:5:1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0351] Example 46

[0352] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 92:1.5:4.5:2 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0353] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (with polar functional groups -CH2NH2 and -CH2NH-, a mass percentage α of approximately 12%, and a number average molecular weight of 3700) are mixed in a mixer at a weight ratio of 88:5:5:2 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0354] Example 47

[0355] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 89:1.5:4.5:5 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0356] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 85:5:5:5 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0357] Examples 48-65

[0358] Except for replacing the aminoethylaminopropylpolydimethylsiloxane in the cathode material composition with the following organopolysiloxane compounds in the preparation of the full cell and the coin cell, the process is the same as in Example 1. The differences are shown in Table 9.

[0359] Example 48: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 1200).

[0360] Example 49: Polymethylchloropropylsiloxane (polar functional group is -CH2Cl, mass percentage α is about 30.2%, number average molecular weight is 2500).

[0361] Example 50: Polymethyltrifluoropropylsiloxane (polar functional group is -CF3, mass percentage α is about 44.0%, number average molecular weight is 1400).

[0362] Example 51: Mercaptopropyl polysiloxane (polar functional group is -CH2SH, mass percentage α is about 15.0%, number average molecular weight is 2000).

[0363] Example 52: Hydroxyl-terminated polydimethylsiloxane (polar functional group is -OH, mass percentage α is about 3.4%, number average molecular weight is 1000).

[0364] Example 53: Methoxy-terminated polydimethylsiloxane (the polar functional group is methoxy, the mass percentage α is about 3.1%, and the number average molecular weight is 2800).

[0365] Example 54: Terminal polyether polydimethylsiloxane (polar functional group is polyether segment, mass percentage α is about 10.0%, number average molecular weight is 2110).

[0366] Example 55: Side-chain phosphate ester grafted polydimethylsiloxane (polar functional group is phosphate ester group, mass percentage α is about 1.4%, number average molecular weight is 15600),

[0367] Example 56: 1,3,5,7-octamethylcyclotetrasiloxane (mass percentage of polar functional groups α is about 0%, molecular weight is 280).

[0368] Example 57: Cyclopentadimethylsiloxane (mass percentage of polar functional groups α is about 0%, molecular weight is 370).

[0369] Example 58: Terminal polyether polydimethylsiloxane (polar functional group is polyether segment, mass percentage α is about 55.0%, number average molecular weight is 25132).

[0370] Example 59: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 400).

[0371] Example 60: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 10,000).

[0372] Example 61: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 50,000).

[0373] Example 62: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 80,000).

[0374] Example 63: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 100,000).

[0375] Example 64: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 300,000).

[0376] Example 65: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 400,000).

[0377] Comparative Examples 1-18

[0378] The positive electrode active materials of Comparative Examples 1-18 were prepared in a manner similar to that of Example 1. The differences in the preparation of the positive electrode active materials are shown in Tables 1 to 6. Comparative Examples 1-2, 4-10 and 12 were not coated with the first coating layer, so steps S3 and S4 were omitted; Comparative Examples 1-11 were not coated with the second coating layer, so steps S5 and S6 were omitted.

[0379] Full cells and coin cells of Comparative Examples 1-18 were prepared in a manner similar to that of Example 1, except that aminoethylaminopropylpolydimethylsiloxane was not added to the positive electrode material composition, and all other processes were the same as those of Example 1.

[0380] In addition, in all embodiments and comparative examples of this application, unless otherwise specified, the first coating layer material and / or the second coating layer material used are assumed to be crystalline.

[0381]

[0382]

[0383]

[0384] Table 2: Preparation of the first coating layer suspension (step S3)

[0385]

[0386] Table 3: Coverage of the first coating layer (step S4)

[0387]

[0388] Table 4: Preparation of the second coating layer suspension (step S5)

[0389]

[0390] Table 5: Covering of the second coating layer (step S6)

[0391]

[0392] Table 6: Covering with the third coating layer (step S8)

[0393]

[0394]

[0395] Table 7: Investigation of the material of the first coating layer

[0396]

[0397] Table 8: Investigation of the Second Coating Material

[0398]

[0399] Table 9: Investigation of organopolysiloxane compounds

[0400]

[0401] II. Performance Evaluation

[0402] 1. Methods for measuring lattice change rate

[0403] Under a constant temperature environment of 25℃, the positive electrode active material sample was placed in an X-ray powder diffractometer (model Bruker D8 Discover) and tested at a rate of 1° / minute. The test data were then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of the unit cell in each direction, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0404] Using the coin cell preparation method described in the above embodiments, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0405] 2. Li / Mn antisite defect concentration

[0406] The XRD results obtained from the "lattice change rate measurement method" are compared with the PDF (Powder Diffraction File) card of the standard crystal to determine the Li / Mn antisite defect concentration. Specifically, the XRD results obtained from the "lattice change rate measurement method" are imported into the General Structure Analysis System (GSAS) software to automatically obtain refined results, which include the occupancy of different atoms. The Li / Mn antisite defect concentration is then obtained by reading the refined results.

[0407] 3. Surface oxygen valence state

[0408] 5g of the positive electrode active material sample prepared above was used to prepare a coin cell according to the coin cell preparation method described in the above embodiments. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in DMC for 8 hours. Then, it was dried, scraped off, and particles with a particle size of less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of the surface oxygen after charging.

[0409] 4. Compacted density

[0410] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T (tons) and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using ρ = m / v.

[0411] 5. Powder resistivity test:

[0412] A suitable amount of the positive electrode material composition sample powder used to prepare the full battery is placed in a special mold of a powder resistivity tester. The powder resistivity under different pressures is obtained by setting the test pressure. In this application, the test pressure is 12 MPa. The testing instrument is a Suzhou Jinglü ST2722-SZ four-probe powder resistivity tester.

[0413] 6. Specific surface area test:

[0414] Five grams of the cathode material composition sample powder used to prepare the full battery were taken, and the specific surface area was measured using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method.

[0415] 7. Contact Angle Test

[0416] At room temperature, ethylene carbonate (EC) droplets were dropped onto the surface of the positive electrode film, and the solid-liquid contact angle was measured over 60 seconds using an LSA 200 optical contact angle meter from LAUDA Scientific, Germany.

[0417] 8. Method for measuring the initial specific capacity of button cells

[0418] The coin cells prepared in the above embodiments and comparative examples were charged to 4.3V at 0.1C, then charged at 4.3V at a constant voltage until the current was less than or equal to 0.05mA. After standing for 5 minutes, they were discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0419] 9. 3C charging constant current ratio

[0420] Under a constant temperature of 25°C, the fresh full batteries prepared in the above embodiments and comparative examples were allowed to stand for 5 minutes, then discharged at 1 / 3C to 2.5V. After standing for 5 minutes, they were charged at 1 / 3C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After standing for 5 minutes, the charging capacity at this point was recorded as C0. The batteries were then discharged at 1 / 3C to 2.5V, allowed to stand for 5 minutes, and then charged at 3C to 4.3V. After standing for 5 minutes, the charging capacity at this point was recorded as C1. The 3C charging constant current ratio is C1 / C0 × 100%. A higher 3C charging constant current ratio indicates better rate performance of the secondary battery.

[0421] 10. Battery swelling test after 30 days of storage at 60°C.

[0422] The full cells prepared in the above-described embodiments and comparative examples were stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. After every 48 hours of storage, the full cells were removed, allowed to stand for 1 hour, and then the open-circuit voltage (OCV) and internal resistance (IMP) were tested. After cooling to room temperature, the cell volume was measured using the water displacement method. The water displacement method involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion of dial data, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery at this moment is measured, and the buoyant force F on the battery is measured. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The battery volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0423] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire testing process until the end of storage.

[0424] After 30 days of storage, the battery volume was measured, and the percentage increase in battery volume after storage was calculated relative to the battery volume before storage.

[0425] 11. Cyclic performance test of the full battery at 45°C

[0426] Under a constant temperature environment of 45℃, the full battery is charged at 1C to 4.3V, then charged at 4.3V at a constant voltage until the current is ≤0.05mA. After resting for 5 minutes, it is discharged at 1C to 2.5V, and the capacity is recorded as D0. The above process is repeated until the capacity decays to 80% of D0. The number of repetitions at this point is recorded, which is the number of cycles corresponding to 80% capacity retention at 45℃.

[0427] 12. Dissolution test of transition metal Mn (and Fe doped at Mn sites)

[0428] The full cells prepared in the above-described embodiments and comparative examples, after being cycled at 45°C until their capacity decayed to 80%, were discharged at a rate of 0.1C to a cutoff voltage of 2.0V. The batteries were then disassembled, and the negative electrode was removed. Thirty unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0429] 13. Measurement of manganese and phosphorus elements in positive electrode active materials

[0430] Dissolve 5g of the prepared positive electrode active material in 100mL of aqua regia (concentrated hydrochloric acid:concentrated nitric acid = 1:3). Use ICP to test the content of each element in the solution. Then measure and convert the content of manganese or phosphorus (amount of manganese or phosphorus / amount of positive electrode active material × 100%) to obtain its weight percentage.

[0431] 14. Coating thickness test

[0432] The thickness of the coating layer was tested by cutting a thin slice of about 100 nm thickness from the middle of a single particle of the positive electrode active material prepared above using FIB, and then performing TEM testing on the slice to obtain the original TEM image.

[0433] Open the original images obtained from the TEM test in DigitalMicrograph software, identify the cladding layer using the lattice spacing and angle information, and measure the thickness of the cladding layer.

[0434] Measure the thickness of the selected particle at three locations and take the average value.

[0435] 15. Interplanar spacing and angle testing

[0436] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Stir and disperse for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the sample chamber of a TEM (Talos F200sG2) for testing and obtain the original TEM test image.

[0437] Open the original image obtained from the TEM test in DigitalMicrograph software and perform a Fourier transform (the software will automatically complete this step after clicking) to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The included angle is calculated according to the Bragg equation.

[0438] By comparing the obtained interplanar spacing and corresponding angle data with their standard values, different materials in the coating layer can be identified.

[0439] 16. Determination of the molar ratio of SP2 and SP3 forms in the third coating layer of carbon

[0440] This test was performed using Raman spectroscopy. I was obtained by peak separation of the Raman spectrum.d / I g I d For the peak intensity of SP3 carbon, I g The peak intensity of the SP2 carbon was used to confirm the molar ratio between the two.

[0441] 17. Determination of the core chemical formula and composition of different coating layers

[0442] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of different coating layers of the positive electrode active material were obtained.

[0443] Table 10 shows the performance data of the positive electrode active material, positive electrode material composition, positive electrode sheet, button cell or full cell measured according to the above performance test methods in Examples 1-29 and Comparative Examples 1-18.

[0444] Table 11 shows the thickness of each coating layer and the weight ratio of manganese and phosphorus in the positive electrode active materials prepared in Examples 1-14 and Comparative Examples 3-4 and 12.

[0445] Table 12 shows the interplanar spacing and angle between the first and second coating layers in the positive electrode active materials prepared in Examples 1, 30-42.

[0446] Table 13 shows the performance data of the positive electrode active material, positive electrode material composition, positive electrode sheet, button cell or all-electric cell in Examples 30-42, measured according to the above performance test methods.

[0447] Table 14 shows the performance data of the positive electrode material composition, positive electrode sheet, button cell or full cell in Examples 43-65, measured according to the above performance test methods.

[0448]

[0449]

[0450] Table 11

[0451]

[0452] Table 12

[0453]

[0454]

[0455]

[0456] As shown in Table 10, compared with the comparative example, the embodiments achieve a smaller lattice change rate, a smaller Li / Mn antisite defect concentration, a larger compaction density, a surface oxygen valence state closer to -2, less Mn and Fe dissolution after cycling, and better battery performance, such as better high-temperature storage performance and high-temperature cycling performance. Combining the positive electrode active material of the embodiments of this application with an organopolysiloxane compound can further alleviate the erosion of the positive electrode active material surface by the electrolyte, reduce the amount of Mn and Fe dissolution after cycling, and thus further improve the battery's cycle performance.

[0457] As can be seen from Table 11, by doping and coating the manganese and phosphorus sites of lithium manganese iron phosphate (containing 35% manganese and about 20% phosphorus), the manganese content and the weight ratio of manganese to phosphorus in the positive electrode active material are significantly reduced. In addition, comparing Examples 1-14 with Comparative Examples 3, 4, and 12, and referring to Table 10, it can be seen that the reduction of manganese and phosphorus in the positive electrode active material will reduce the amount of manganese and iron ions dissolved and improve the performance of the battery prepared from it.

[0458] As shown in Table 12, the interplanar spacing and included angle of the first and second coating layers in the positive electrode active material of this application are both within the range described in this application. As shown in Table 13, using the first and second coating layers containing other elements within the scope of this application also yielded a positive electrode active material with good performance and achieved good battery performance results.

[0459] As can be seen from Table 14, when the positive electrode active material is the same, selecting an organopolysiloxane compound that meets one or more of the following criteria—content of polar functional groups, number-average molecular weight, and amount added—to be used in combination with the positive electrode active material can further improve the cycle performance of the battery without affecting the energy density and kinetic performance.

[0460] Based on Examples 1 and 43-47, it can also be seen that as the amount of organopolysiloxane compound added increases, the powder resistance of the positive electrode active material composition first decreases and then increases. The possible reason is that when the amount of organopolysiloxane compound added is within a certain range, its hydrophobicity reduces the interaction between conductive agents, alleviates the aggregation of conductive agents, and thus allows for the formation of a better conductive network.

[0461] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode material composition comprising a positive electrode active material having a core-shell structure and an organic polysiloxane compound, wherein, the positive electrode active material comprises an inner core and a shell covering the inner core, The chemical formula of the inner core is Li 1+x Mn 1-y A y P 1-z R z O4, x is any numerical value in the range of -0.100 to 0.100, y is any numerical value in the range of 0.001 to 0.500, z is any numerical value in the range of 0.001 to 0.100, the 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, the R is one or more elements selected from B, Si, N, and S, the values of x, y, and z satisfy the following condition: to maintain the entire inner core electrically neutral; The shell comprises a first cladding layer cladding the inner core, a second cladding layer cladding the first cladding layer, and a third cladding layer cladding the second cladding layer, the first cladding layer comprising a crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c , 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c M in each case independently is selected from Fe, Ni, Mg, Co, Cu, one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; the values of a, b, and c satisfy the following conditions: a > 0, b > 0, c > 0, a + b + c = 1, and a < 1; and the crystal state of the phosphate Li a MP2O7or M b (P2O7) c maintaining electrical neutrality; the second coating layer comprises a crystal state phosphate XPO4, X being one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; and the third coating layer is carbon.

2. The cathode material composition of claim 1, wherein, The chemical formula of the inner core is Li 1+x Mn 1-y A y P 1- z R z O4, x is any number in the range of -0.005 to 0.

002.

3. The cathode material composition of claim 1, wherein, The chemical formula of the core is Li 1+x Mn 1-y A y P 1- z R z O4, the A is one or more elements of Fe, Ti, V, Ni, Co and Mg.

4. The cathode material composition of claim 1, wherein, the R is one element selected from B, Si, N and S.

5. The cathode material composition of claim 1, wherein, the organic polysiloxane compound comprises at least one structural unit represented by Formula 1, R1, R2 each independently represent H or at least one selected from the group consisting of -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, C2-C20 halogenated heteroaromatic hydrocarbon group.

6. The cathode material composition of claim 5, wherein, R1, R2 each independently represent H or at least one selected from the group consisting of -COOH, -OH, -SH, amino, phosphate, polyether segment, C1-C8 alkyl group, C1-C8 halogenated alkyl group, C1-C8 heteroalkyl group, C1-C8 halogenated heteroalkyl group, C2-C8 alkenyl group, C2-C8 halogenated alkenyl group, phenyl group.

7. The cathode material composition of claim 5, wherein, R1, R2 each independently represent H or at least one selected from the group consisting of -OH, -SH, amino, phosphate, polyether segment, C1-C8 alkyl group, C1-C8 halogenated alkyl group, C1-C8 heteroalkyl group, C1-C8 halogenated heteroalkyl group, C2-C8 alkenyl group, C2-C8 halogenated alkenyl group.

8. The positive electrode material composition according to any one of claims 1 to 7, wherein, the organic polysiloxane compound comprises one or more selected from linear structure polysiloxane, cyclic structure polysiloxane.

9. The positive electrode material composition according to any one of claims 1 to 7, wherein, the organic polysiloxane compound is selected from linear structure polysiloxane.

10. The cathode material composition of claim 8, wherein, the linear structure polysiloxane further comprises a capping group.

11. The cathode material composition of claim 10, wherein, the capping group comprises at least one selected from the group consisting of polyether, C1-C8 alkyl group, C1-C8 halogenated alkyl group, C1-C8 heteroalkyl group, C1-C8 halogenated heteroalkyl group, C2-C8 alkenyl group, C2-C8 halogenated alkenyl group, C6-C20 aromatic hydrocarbon group, C1-C8 alkoxy group, C2-C8 epoxy group, hydroxyl group, C1-C8 hydroxylalkyl group, amino group, C1-C8 aminoalkyl group, carboxyl group, C1-C8 carboxylalkyl group.

12. The positive electrode material composition according to claim 8, wherein, The linear structure polysiloxane includes one or more of polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrogenosiloxane, carboxy-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxyl-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, epoxy-terminated polysiloxane, hydroxyl-terminated polydimethylsiloxane, polyether-terminated polydimethylsiloxane, side-chain aminopropylpolysiloxane, side-chain hydroxymethylpolysiloxane, side-chain hydroxypropylpolysiloxane, side-chain polyether-grafted polydimethylsiloxane, side-chain phosphate-ester-grafted polydimethylsiloxane, and / or The cyclic structure polysiloxane includes one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrogenosiloxane, cyclic polymethyltrifluoropropylsiloxane.

13. The cathode material composition of claim 8, wherein, The linear structure polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, polyether-terminated polydimethylsiloxane, side-chain phosphate-ester-grafted polydimethylsiloxane.

14. The cathode material composition of claim 8, wherein, The cyclic structure polysiloxane includes one or more of 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, hexadecamethylcyclooctasiloxane, tetradecamethylcyclotetrasiloxane.

15. The cathode material composition according to any one of claims 1 to 7, wherein, The number average molecular weight of the organopolysiloxane compound is 300,000 or less.

16. The cathode material composition according to any one of claims 1 to 7, wherein, The number average molecular weight of the organopolysiloxane compound is 400 to 80,000.

17. The cathode material composition according to any one of claims 1 to 7, wherein, The mass percentage content of the polar functional group in the organopolysiloxane compound is a, and 0≤a<50%.

18. The cathode material composition according to any one of claims 1 to 7, wherein, The mass percentage content of the polar functional group in the organopolysiloxane compound is a, and 5%≤a≤30%.

19. The cathode material composition of any of claims 1-7, wherein, The content of the organopolysiloxane compound is 0.01 to 2% by mass, based on the total weight of the positive electrode material composition.

20. The cathode material composition of any of claims 1-7, wherein, The content of the organopolysiloxane compound is 0.1 to 2% by mass, based on the total weight of the positive electrode material composition.

21. The positive electrode material composition according to any one of claims 1 to 7, wherein The coating amount of the first coating layer is greater than 0 and 6% by mass or less, based on the weight of the core; and / or The coating amount of the second coating layer is greater than 0 and 6% by mass or less, based on the weight of the core; and / or The coating amount of the third coating layer is greater than 0 and 6% by mass or less, based on the weight of the core.

22. The positive electrode material composition according to any one of claims 1 to 7, wherein the first coating layer has a coating amount of greater than 0 and less than or equal to 5.5% by weight based on the weight of the core; and / or the second coating layer has a coating amount of greater than 0 and less than or equal to 5.5% by weight based on the weight of the core; and / or the third coating layer has a coating amount of greater than 0 and less than or equal to 5.5% by weight based on the weight of the core.

23. The positive electrode material composition according to any one of claims 1 to 7, wherein the first coating layer has a coating amount of greater than 0 and less than or equal to 2% by weight based on the weight of the core; and / or the second coating layer has a coating amount of 2% to 4% by weight based on the weight of the core; and / or the third coating layer has a coating amount of greater than 0 and less than or equal to 2% by weight based on the weight of the core.

24. The positive electrode material composition according to any one of claims 1 to 7, wherein the first coating layer has a thickness of 1 nm to 10 nm; and / or the second coating layer has a thickness of 2 nm to 15 nm; and / or the third coating layer has a thickness of 2 nm to 25 nm.

25. The positive electrode material composition according to any one of claims 1 to 7, wherein the crystalline pyrophosphate in the first coating layer has a range of 0.293 nm to 0.470 nm in interplanar spacing of crystal face and a range of 18.00° to 32.00° in included angle of crystal direction (111); and / or the crystalline phosphate in the second coating layer has a range of 0.244 nm to 0.425 nm in interplanar spacing of crystal face and a range of 20.00° to 37.00° in included angle of crystal direction (111).

26. The positive electrode material composition according to any one of claims 1 to 7, wherein in the core, the ratio of y to 1-y is 1:10 to 1:1; and / or in the core, the ratio of z to 1-z is 1:9 to 1:

999.

27. The positive electrode material composition according to any one of claims 1 to 7, wherein in the core, the ratio of y to 1-y is 1:4 to 1:1; and / or in the core, the ratio of z to 1-z is 1:499 to 1:

249.

28. The cathode material composition of any one of claims 1-7, wherein, the carbon of the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.

29. The cathode material composition of claim 28, wherein, the molar ratio of the SP2 form carbon to the SP3 form carbon is any value in the range of 0.1 to 10.

30. The cathode material composition of claim 28, wherein, the molar ratio of the SP2 form carbon to the SP3 form carbon is any value in the range of 2.0 to 3.

0.

31. The positive electrode material composition according to any one of claims 1 to 7, wherein the content of manganese element is in the range of 10% to 35% by weight based on the weight of the positive electrode active material; and / or the content of phosphorus element is in the range of 12% to 25% by weight based on the weight of the positive electrode active material; and / or the weight ratio of manganese element to phosphorus element is in the range of 0.90 to 1.25 based on the weight of the positive electrode active material.

32. The positive electrode material composition according to any one of claims 1 to 7, wherein the content of manganese element is in the range of 17 to 20% by weight based on the weight of the positive electrode active material; and / or, the content of phosphorus element is in the range of 15 to 20% by weight based on the weight of the positive electrode active material; and / or, the weight ratio of manganese element and phosphorus element is in the range of 0.95 to 1.20 based on the weight of the positive electrode active material.

33. The cathode material composition of any one of claims 1-7, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 4% or less; (2) the Li / Mn anti-site defect concentration of the positive electrode active material is 4% or less; (3) the positive electrode active material has a compaction density of 2.2 g / cm3 at 3T 3 above; (4) the surface oxygen valence state of the positive electrode active material is -1.90 or less.

34. The cathode material composition of any of claims 1-7, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 3.8% or less; (2) the Li / Mn anti-site defect concentration of the positive electrode active material is 2.2% or less; (3) 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; (4) the surface oxygen valence state of the positive electrode active material is -1.90 to -1.

98.

35. The cathode material composition of any of claims 1-7, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 2.0% to 3.8%; (2) the Li / Mn anti-site defect concentration of the positive electrode active material is 1.5% to 2.2%.

36. The cathode material composition of any of claims 1-7, wherein, It further comprises a conductive agent and a binder.

37. The cathode material composition of claim 36, wherein, The content of the binder is 1.79 to 10% by weight based on the total weight of the positive electrode material composition.

38. The cathode material composition of claim 36, wherein, The content of the conductive agent is 0.2 to 10% by weight based on the total weight of the positive electrode material composition.

39. The positive electrode material composition according to any one of claims 1-7, wherein, the powder resistivity of the positive electrode material composition at 12 MPa is 4 to 55 Ω / cm; and / or, The specific surface area of the positive electrode material composition is 8 m 2 / g to 20 m 2 / g.

40. The positive electrode material composition according to any one of claims 1-7, wherein, the powder resistivity of the positive electrode material composition at 12 MPa is 4 to 40 Ω / cm; and / or, The specific surface area of the positive electrode material composition is 8 m 2 / g to 15 m 2 / g.

41. A method for preparing a positive electrode material composition, comprising the steps of: The step of 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 numerical value within a range of -0.100 to 0.100, y is any numerical value within a range of 0.001 to 0.500, z is any numerical value within a range of 0.001 to 0.100, the 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, the R is one or more elements selected from B, Si, N, and S, and the values of x, y, and z satisfy a condition that the entire core remains electrically neutral; coating step: providing Li a MP2O7and / or M b (P2O7) c and XPO4suspension, adding the inner core material into the above suspension and mixing, and obtaining the positive electrode active material by sintering, wherein the positive electrode active material has a core-shell structure including the inner core and a shell coating the inner core, the shell including 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, the first coating layer including a crystalline pyrophosphate Li a MP2O7and / or M b (P2O7) c , 0≤a≤2, 1≤b≤4, 1≤c≤6, the crystalline pyrophosphate Li a MP2O7and M b (P2O7) c each independently is one or more elements selected from the group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and the values of a, b and c satisfy the following conditions: the crystalline pyrophosphate Li a MP2O7or M b (P2O7) c is kept electrically neutral, the second coating layer includes a crystalline phosphate XPO4, the 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, and the third coating layer is carbon. a mixing step of uniformly mixing the obtained positive electrode active material with an organopolysiloxane compound to obtain a positive electrode material composition.

42. The method of claim 41, wherein, The inner core has a chemical formula of Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any number in the range of -0.005 to 0.

002.

43. The method of claim 41, wherein, The A is one or more elements selected from the group consisting of Fe, Ti, V, Ni, Co, and Mg.

44. The method of claim 41, wherein, The R is one element selected from the group consisting of B, Si, N, and S.

45. The method of claim 41, wherein, The obtained positive electrode active material is uniformly mixed with an organopolysiloxane compound, a binder, and / or a conductive agent to obtain a positive electrode material composition.

46. The method of claim 41, wherein, The step of providing a core material comprises the steps of: 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; Step (2): mixing the manganese salt particles doped with element A with a lithium source, a phosphorus source, and a dopant of element R in a solvent and obtaining a slurry, and obtaining a core doped with elements A and R after sintering under protection of an inert gas atmosphere, wherein the core doped with elements A and R is Li 1+x Mn 1-y A y P 1-z R z O4, x is any numerical value in the range of -0.100 to 0.100, y is any numerical value in the range of 0.001 to 0.500, z is any numerical value in the range of 0.001 to 0.100, the 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, and the R is one or more elements selected from B, Si, N, and S.

47. The method according to claim 46, wherein, the mixing in the step (1) is performed at a temperature of 20 to 120°C; and / or the stirring in the step (1) is performed at 400 to 700 rpm for 1 to 9 hours; and / or the stirring in the step (1) is performed at 400 to 700 rpm for 1 to 9 hours; and / or The step (2) is mixing at a temperature of 20°C to 120°C for 1 hour to 10 hours.

48. The method of claim 46, wherein, The step (1) is mixing at a temperature of 40°C to 120°C; and / or The stirring in the step (1) is at 400 rpm to 700 rpm for 3 hours to 7 hours; and / or The step (2) is mixing at a temperature of 40°C to 120°C for 1 hour to 10 hours.

49. The method of claim 46, wherein, The dopant of A is one or more of the 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, each in one or more of the forms of simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, hydroxide; and / or, The dopant of R is one or more of the elements selected from the group consisting of B, Si, N and S, each in one or more of the forms of inorganic acid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide, hydroxide.

50. The method of any one of claims 41-46, wherein, The coating step comprises: a first coating step: dissolving a source of element M, a phosphorus source and an acid, and optionally a lithium source, in a solvent to obtain a first coating layer suspension; mixing the core obtained in the step of providing a core material with the first coating layer suspension obtained in the first coating step, drying, and then sintering to obtain a first coating layer coated material; 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; mixing the first coating layer coated 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 two-layer coating layer coated material; a 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 to 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.

51. The method of claim 50, wherein, In the first coating step, the pH of the solution in which the source of element M, the phosphorus source and the acid, and optionally the lithium source, is controlled to be 3.5 to 6.5, then stirred and reacted for 1 hour to 5 hours, then the solution is warmed to 50°C to 120°C and maintained at this temperature for 2 hours to 10 hours; and / or, The sintering in the first coating step is at 650°C to 800°C for 2 hours to 6 hours; and / or, In the second coating step, after dissolving the source of element X, the phosphorus source and the acid in a solvent, stirring and reacting for 1 hour to 10 hours, then the solution is warmed to 60°C to 150°C and maintained at this temperature for 2 hours to 10 hours; and / or, The sintering in the second coating step is at 500°C to 700°C for 6 hours to 10 hours; and / or, The sintering in the third coating step is at 700°C to 800°C for 6 hours to 10 hours.

52. 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 the positive electrode material composition according to any one of claims 1 to 40, or the positive electrode material composition produced by the method according to any one of claims 41 to 51, and the content of the positive electrode material composition in the positive electrode film layer is 50% by weight or more based on the total weight of the positive electrode film layer.

53. The cathode sheet of Claim 52, wherein, The content of the positive electrode material composition in the positive electrode film layer is 90% to 100% by weight based on the total weight of the positive electrode film layer.

54. The cathode sheet of claim 52 or 53, wherein, The positive electrode sheet satisfies at least one of the following conditions (1) to (6): (1) the solid-liquid contact angle between the positive electrode film layer and a non-aqueous organic solvent is between 3° and 90°; (2) the porosity of the positive electrode film layer is 15% to 50%; (3) the electrical resistance of the positive electrode film layer is greater than 0 and less than or equal to 6 Ω; (4) the adhesive force of the positive electrode film layer to the positive electrode current collector is greater than or equal to 0.5 MPa; (5) the face density of the positive electrode film layer is 0.006 g / cm 2 to 0.065 g / cm 2 ; (6) the liquid absorption rate of the positive electrode film layer to an electrolyte solution is 0.0125 μg / s to 100 μg / s.

55. The cathode sheet of either claim 52 or 53, wherein, The positive electrode sheet satisfies at least one of the following conditions (1) to (6): (1) the solid-liquid contact angle between the positive electrode film layer and a non-aqueous organic solvent is between 3° and 60°; (2) the porosity of the positive electrode film layer is 15% to 30%; (3) the electrical resistance of the positive electrode film layer is greater than 0 and less than or equal to 6 Ω; (4) the adhesive force of the positive electrode film layer to the positive electrode current collector is greater than or equal to 0.5 MPa; (5) the face density of the positive electrode film layer is 0.006 g / cm 2 to 0.065 g / cm 2 ; (6) the liquid absorption rate of the positive electrode film layer to an electrolyte solution is 0.5 μg / s to 40 μg / s.

56. The cathode sheet of either claim 52 or 53, wherein, The solid-liquid contact angle between the positive electrode film layer and a non-aqueous organic solvent is between 10° and 30°.

57. A secondary battery comprising the positive electrode material composition according to any one of claims 1 to 40, or the positive electrode material composition produced by the method according to any one of claims 41 to 51, or the positive electrode sheet according to any one of claims 52 to 56.

58. An electric device comprising the secondary battery according to claim 57.

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