Secondary battery, battery module, battery pack, and electric device

Abstract

The application relates to the technical field of batteries, in particular to a secondary battery, a battery module, a battery pack and a power utilization device, which comprises a positive electrode sheet and a nonaqueous electrolyte, wherein the secondary battery comprises a positive electrode sheet and a nonaqueous electrolyte, the positive electrode sheet comprises a positive electrode active material with a core-shell structure, 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, the A comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, the R comprises one or more elements selected from B, Si, N and S; the shell comprises a first coating layer covering the inner core; the first coating layer comprises a crystalline pyrophosphate LiaMP2O7 and / or Mb(P2O7) c , the nonaqueous electrolyte comprises an organic solvent, the organic solvent comprises a first solvent, and the first solvent comprises one or more compounds shown in formula 1.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, battery module, battery pack, and electrical device. Background Technology

[0002] In recent years, with the development of lithium-ion rechargeable battery technology, lithium-ion rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, and have also found wide applications in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. Due to the significant advancements in lithium-ion rechargeable batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0003] Lithium manganese phosphate, as a positive electrode active material for lithium-ion secondary batteries, has advantages such as high capacity, good safety, and low cost. However, its poor rate performance limits its commercial application. Summary of the Invention

[0004] This application provides a secondary battery, a battery module, a battery pack, and an electrical device to solve the problem of poor rate performance of secondary batteries when lithium manganese phosphate is used as the positive electrode active material of lithium-ion secondary batteries.

[0005] A first aspect of the present invention provides a secondary battery comprising a positive electrode and a non-aqueous electrolyte, wherein,

[0006] The positive electrode includes a core-shell structured positive electrode active material, which comprises a core and a shell covering the core.

[0007] The chemical formula of the kernel 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, 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 includes 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 may be selected from one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, R includes one or more elements selected from B, Si, N, and S, and optionally, R includes one element selected from B, Si, N, and S; the values ​​of x, y, and z satisfy the following condition: keeping the entire nucleus electrically neutral;

[0008] The shell includes a first covering layer that covers the core;

[0009] The first coating layer comprises crystalline pyrophosphate LiaMP2O7 and / or Mb(P2O7). c Where 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate LiaMP2O7 or Mb(P2O7) possible. c Maintaining electroneutrality, crystalline pyrophosphates LiaMP2O7 and Mb(P2O7) c Each of the M elements independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al;

[0010] The non-aqueous electrolyte includes an organic solvent, which includes a first solvent, and the first solvent includes one or more compounds shown in Formula 1.

[0011] Formula 1

[0012] R1 and R2 are each independently one of C1~C10 alkyl and C1~C10 haloalkyl. Optionally, R1 and R2 are each independently one of methyl, ethyl, propyl, butyl, pentyl, hexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, and fluorohexyl. Further optionally, R1 and R2 are each independently one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl, and fluoropropyl.

[0013] The surface oxygen valence state of core-shell structured positive electrode active materials is below -1.90.

[0014] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of values ​​for 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 consists of two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the range of values ​​for y defined in this application, and the sum of y1, y2...yn must also fall within this range. Similarly, for the case where R consists of two or more elements, the limitation on the range of values ​​for the stoichiometric coefficients of R in this application has the same meaning.

[0015] In this article, "crystalline state" refers to a crystallinity of 50% or higher, i.e., 50%-100%. Crystallinity less than 50% is referred to as the glassy state. The crystalline pyrophosphate and crystalline phosphate described in this application have a crystallinity of 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.

[0016] This application provides a novel core-shell structured lithium manganese phosphate cathode active material by doping element A at the manganese site and element R at the phosphorus site of lithium manganese phosphate to obtain a doped lithium manganese phosphate core and coating the core surface with a layer. When this cathode active material is applied to a secondary battery, it can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery.

[0017] Meanwhile, the first solvent in the non-aqueous electrolyte has a good ability to dissociate lithium salts, but compared to carbonates, the first organic solvent reacts with Li... + The effect of the first solvent is very small. As the first solvent gradually dominates the first solvation layer, Li + The desolvation energy gradually decreases, which is beneficial to Li + Rapid insertion and extraction at the interface enhances the rate performance of the secondary battery. Furthermore, the first solvent has a low viscosity, allowing lithium ions extracted from the positive electrode active material to rapidly migrate and insert into the negative electrode side. Driven by concentration polarization, lithium ions at the positive electrode material interface are rapidly transferred to the electrolyte, further improving the rate performance of the secondary battery.

[0018] Furthermore, by limiting the surface oxygen valence state of the positive electrode active material to the above range, the interfacial side reactions between the positive electrode material and the electrolyte can be reduced, thereby improving the cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0019] In any embodiment of the first aspect, the shell further includes a second covering layer covering the first covering layer.

[0020] In any embodiment of the first aspect, the second coating layer comprises crystalline phosphate XPO4, wherein X comprises one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0021] In any embodiment of the first aspect, the shell further includes a third covering layer covering the second covering layer.

[0022] In any embodiment of the first aspect, the third coating layer comprises carbon.

[0023] In any embodiment of the first aspect, the first solvent comprises at least one of the following compounds:

[0024] , ,

[0025] , ,

[0026] , ,

[0027] , ,

[0028] , ,

[0029] and ;

[0030] In any embodiment of the first aspect, optionally, the first solvent comprises at least one of the following compounds:

[0031] , ,

[0032] and .

[0033] When the above-mentioned substances are selected as the first solvent, the electrolyte viscosity is lower and the wettability is better, thus improving the lithium-ion transport capacity and thereby better improving the rate performance of the secondary battery; at the same time, the above-mentioned first solvents have better chemical stability and better resistance to oxidation of the positive electrode active material.

[0034] In any embodiment of the first aspect, the mass percentage of the first solvent is w1, based on the total mass of the organic solvent, and w1 ranges from 20% to 80%; alternatively, w1 ranges from 30% to 75%. By controlling the above-mentioned mass percentage, the rechargeable battery can have good cycle performance and storage performance while improving the fast charging performance of the battery using the first solvent.

[0035] In any embodiment of the first aspect, optionally, the organic solvent further includes a second solvent, the second solvent comprising one or more of the group consisting of chain carbonates and cyclic carbonates; further optionally, based on the total mass of the organic solvent, the mass percentage of the second solvent is w2, the range of w2 being 20% ​​to 80%; optionally, the range of w2 is 25% to 70%. This utilizes the second solvent in combination with the first solvent to improve the cycle performance of the secondary battery.

[0036] In any embodiment of the first aspect, the aforementioned non-aqueous electrolyte further includes a first additive, which comprises one or more of the group consisting of sulfonyl lactones and cyclic sulfates. The introduction of sulfonyl lactones or cyclic sulfates into the non-aqueous electrolyte allows them to form a layer of polymers with strong ion-conducting capabilities, such as ester sulfates, on the surface of the positive electrode active material during the secondary battery charging process. This polymer can further improve the rate performance of the secondary battery and effectively inhibit the catalytic oxidation of the first solvent by the positive electrode active material, thereby improving the cycle and storage performance of the secondary battery. Furthermore, sulfonyl lactones or cyclic sulfates can form a film on the negative electrode more readily than the first solvent, reducing the reaction between α-H on the first solvent and the active lithium reduced from the negative electrode, thereby further improving the cycle and storage performance of the secondary battery.

[0037] In any embodiment of the first aspect, the sulfonyl lactone comprises at least one of the compounds shown in Formula 2.

[0038] Formula 2

[0039] p represents 1, 2, or 3.

[0040] R 11 It represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl, C1-C12 haloalkyl, C1-C12 alkoxy, and C1-C12 haloalkoxy; optionally, R 11 It represents one of hydrogen atom, halogen atom, C1~C6 alkyl, C1~C3 haloalkyl, C1~C3 alkoxy, and C1~C3 haloalkoxy; optionally, the alkoxy is a chain alkoxy or a cyclic alkoxy, optionally the cyclic alkoxy shares a carbon atom with the parent ring of the sulfonyl lactone, and further optionally the cyclic alkoxy has 4, 5 or 6 carbon atoms;

[0041] Each R 12 Each of the following groups independently represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, and 4- to 7-membered sulfonyl lactone group; optionally, each R 12Each of the following can be independently represented: a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, or a 5- or 6-membered sulfonyl lactone group; optionally, the sulfonyl lactone group shares a carbon atom with the parent ring of the sulfonyl lactone, and optionally the sulfonyl lactone group is a 5-membered ring.

[0042] R 11 and R 12 The carbon atoms bonded to each other can form 5 to 10-membered cycloalkyl groups;

[0043] R 13 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C6 ester group, C1-C12 alkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, C6-C20 aryl group, or benzyl group; optionally, R 13 The term "sulfonyl lactone" refers to one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C3 ester group, C1-C3 alkyl group, C1-C3 haloalkyl group, C2-C6 alkenyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, C6-C10 aryl group, or benzyl group. The aforementioned sulfonyl lactones are commonly used in the field, widely available, and relatively inexpensive.

[0044] In any embodiment of the first aspect, the above-mentioned cyclic sulfate ester includes at least one of the compounds shown in Formula 3.

[0045] Formula 3

[0046] q represents 1, 2, or 3.

[0047] R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C1-C12 alkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, C2-C6 ester group, and 4- to 7-membered cyclic sulfate ester group; optionally, R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, double bond, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, C2-C3 ester group, and 4- to 5-membered cyclic sulfate group; optionally, the cyclic sulfate group and the cyclic sulfate share a carbon atom.

[0048] Each R 15 Each of the following independently represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, and C6-C20 aryl group; optionally, each R 15Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, and C6-C10 aryl group.

[0049] Or R 14 and R 15 Together with their respective linked carbon atoms, they form 4 to 7-membered cyclic sulfate groups, and optionally, R 14 and R 15 Together with their respective linked carbon atoms, they form a 5-membered cyclic sulfate ester group.

[0050] The aforementioned cyclic sulfates are commonly used cyclic sulfates in this field, with wide availability and low cost.

[0051] In any embodiment of the first aspect, optionally, the sulfonyl lactone comprises at least one of the following compounds:

[0052] .

[0053] In any embodiment of the first aspect, optionally, the cyclic sulfate ester comprises at least one of the following compounds:

[0054] .

[0055] Further, optionally, sulfonyl lactones include at least one of the following compounds:

[0056] .

[0057] Further, optionally, the cyclic sulfate ester includes at least one of the following compounds:

[0058] .

[0059] The aforementioned sulfonyl lactones and cyclic sulfates are more likely to form polymers at the positive electrode.

[0060] In any embodiment of the first aspect, based on the total mass of the non-aqueous electrolyte, the content of the first additive is W3, and 0.01% ≤ W3 ≤ 20%, optionally 0.1% ≤ W3 ≤ 10%, and further optionally 0.3% ≤ W3 ≤ 5%. This avoids the increase in positive and negative electrode impedance caused by the introduction of excessive sulfonyl lactones or cyclic sulfates, thereby ensuring a significant improvement in the capacity and rate performance of the lithium-ion battery.

[0061] In any embodiment of the first aspect, the non-aqueous electrolyte further includes a second additive, which comprises one or more of the group consisting of sulfite compounds, disulfonate compounds, nitrile compounds, aromatic compounds, phosphonitrile compounds, acid anhydride compounds, phosphite compounds, phosphate compounds, and borate compounds. The aforementioned second additive helps to form a denser and more stable interfacial film on the surface of the positive and / or negative electrode active materials, thereby further improving at least one of the cycle performance, storage performance, and rate performance of the secondary battery.

[0062] In any embodiment of the first aspect, based on the total mass of the non-aqueous electrolyte, the content of the second additive is W4, 0.01% ≤ W4 ≤ 20%, optionally 0.05% ≤ W4 ≤ 5%, and further optionally 0.1% ≤ W4 ≤ 3%, so that the effect of the second additive can be fully utilized.

[0063] In any implementation of the first aspect, based on the kernel weight, the coating amount of the first coating layer is C1 weight%, where C1 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably greater than 0 and less than or equal to 2.

[0064] In any implementation of the first aspect, based on the kernel weight, the coverage of the second coating layer is C2 weight%, where C2 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably 2-4.

[0065] In any implementation of the first aspect, based on the kernel weight, the coverage of the third coating layer is C3 weight%, where C3 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably greater than 0 and less than or equal to 2.

[0066] In the core-shell structured positive electrode active material of the above embodiments, the coating amount of the three coating layers is preferably within the above range, thereby enabling sufficient coating of the core and further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0067] In any embodiment of the first aspect, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°.

[0068] In any embodiment of the first aspect, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0069] In the above-described embodiments, both the first and second coating layers of the positive electrode active material are made of crystalline materials. Their interplanar spacing and angle range are within the above-described range, which can more effectively avoid impurity phases in the coating layer, thereby further improving the specific capacity, cycle performance and rate performance of the material.

[0070] In any embodiment of the first aspect, 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.

[0071] In any implementation of the first aspect, in the core, the ratio of z to 1-z is 1:999 to 1:9, optionally 1:499 to 1:249. This further improves the cycle performance and rate performance of the secondary battery.

[0072] In any embodiment of the first aspect, the carbon in the third coating layer is a mixture of SP2-form carbon and SP3-form carbon. Optionally, the molar ratio of SP2-form carbon to SP3-form carbon is any value within the range of 0.1-10, and optionally any value within the range of 2.0-3.0. By limiting the molar ratio of SP2-form carbon to SP3-form carbon within the aforementioned range, the above embodiments better improve the overall performance of the secondary battery.

[0073] In any embodiment of the first aspect, the thickness of the first coating layer is 1-10 nm. In the above embodiments, when the thickness of the first coating layer is in the range of 1-10 nm, it is possible to avoid the adverse effects on the kinetic properties of the material that may occur when it is too thick, and it is possible to avoid the problem that it cannot effectively hinder the migration of transition metal ions when it is too thin.

[0074] In any embodiment of the first aspect, the thickness of the second coating layer is 2-15 nm. In the above embodiments, when the thickness of the second coating layer is in the range of 2-15 nm, the surface structure of the second coating layer is stable, and the side reactions with the electrolyte are small. Therefore, it can more effectively reduce interfacial side reactions, thereby significantly improving the high-temperature performance of the secondary battery.

[0075] In any embodiment of the first aspect, the thickness of the third coating layer is 2-25 nm. In the above embodiments, when the thickness of the third coating layer is in the range of 2-20 nm, the electrical conductivity of the material can be further improved and the compaction density performance of the battery electrode prepared using the positive electrode active material can be improved.

[0076] In any embodiment of the first aspect, based on the weight of the positive electrode active material having a core-shell structure, the manganese content is in the range of 10 wt% to 35 wt%, optionally in the range of 15 wt% to 30 wt%, more preferably in the range of 17 wt% to 20 wt%, the phosphorus content is in the range of 12 wt% to 25 wt%, optionally in the range of 15 wt% to 20 wt%, and the weight ratio of manganese to phosphorus is in the range of 0.90 to 1.25, optionally in the range of 0.95 to 1.20.

[0077] In the core-shell structured positive electrode active material of the above embodiments, the content of manganese element is within the above range, which can effectively avoid the problems of poor material structure stability and density reduction that may be caused by excessive manganese element content, thereby more effectively improving the cycle, storage and compaction density performance of the secondary battery; and can avoid the problems of low voltage platform that may be caused by excessive manganese element content, thereby improving the energy density of the secondary battery.

[0078] In the core-shell structured positive electrode active material of the above embodiments, the phosphorus content is within the above range, which can effectively avoid the following situations: if the phosphorus content is too high, it may cause the covalentity of PO to be too strong, affecting the conductivity of small polarons, thereby affecting the conductivity of the 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 material.

[0079] In the core-shell structured positive electrode active material of the above embodiments, the weight ratio of manganese to phosphorus is within the above range, which can effectively avoid the following situations: if the weight ratio is too large, it may lead to an increase in the dissolution of transition metals, affecting the stability of the material and the cycle and storage performance of the secondary battery; if the weight ratio is too small, it may cause the discharge voltage plateau of the material to drop, thereby reducing the energy density of the secondary battery.

[0080] In any embodiment of the first aspect, the lattice change rate of the core-shell structured positive electrode active material before and after complete lithium insertion / extraction is 4% or less, preferably 3.8% or less, and more preferably 2.0-3.8%. The core-shell structured positive electrode active material of the above embodiments can achieve a lattice change rate of less than 4% before and after lithium insertion / extraction. Therefore, using the positive electrode active material can more effectively improve the specific capacity and rate performance of the secondary battery.

[0081] In any embodiment of the first aspect, the Li / Mn antisite defect concentration of the core-shell structured positive electrode active material is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%. By keeping the Li / Mn antisite defect concentration within the above range, Mn can be more effectively avoided. 2+ Hinder Li+ This enhances the transport capacity and rate performance of the positive electrode active material.

[0082] In any embodiment of the first aspect, the compaction density of the core-shell structured positive electrode active material at 3T (tons) is 2.2 g / cm³. 3 The above can be optionally 2.2 g / cm³. 3 Above and 2.8 g / cm 3 Therefore, increasing the compaction density increases the weight of the active material per unit volume, which is more conducive to improving the volumetric energy density of the secondary battery.

[0083] In any embodiment of the first aspect, the surface oxygen valence state of the positive electrode active material having a core-shell structure is -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 material and the electrolyte can be further reduced, thereby improving the cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0084] A second aspect of this application also provides a battery module comprising a secondary battery, wherein the secondary battery is any of the aforementioned secondary batteries described in this application.

[0085] A third aspect of this application also provides a battery pack, which includes a battery module, the battery module being the aforementioned battery module of this application.

[0086] A fourth aspect of this application also provides an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack, wherein the aforementioned secondary battery, battery module, and battery pack are all secondary batteries, battery modules, and battery packs provided in this application.

[0087] Therefore, the battery module and battery pack of this application have high cycle performance and rate characteristics, thereby providing high power cycle stability and rate characteristics for electrical devices with the secondary battery, battery module or battery pack of this application.

[0088] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0089] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced 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.

[0090] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0091] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0092] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0093] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0094] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0095] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0096] The accompanying drawings are not drawn to scale.

[0097] Explanation of reference numerals in the attached figures:

[0098] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0099] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0100] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, battery module, battery pack, and power-consuming device of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0101] 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.

[0102] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0103] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0104] 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.

[0105] 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.

[0106] 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).

[0107] In this document, the term "cladding layer" refers to a layer of material covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Similarly, the term "thickness of cladding layer" refers to the thickness of the layer of material covering the core in the radial direction of the core.

[0108] In this document, the term "source" refers to a compound that is the source of a certain element. For example, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, elements, halides, oxides, and hydroxides.

[0109] [Rechargeable Battery]

[0110] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0111] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0112] A first aspect of the present invention provides a secondary battery comprising a positive electrode and a non-aqueous electrolyte, wherein,

[0113] The positive electrode includes a core-shell structured positive electrode active material, which comprises a core and a shell covering the core.

[0114] The chemical formula of the kernel 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, z is any value in the range of 0.001 to 0.100, A includes 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 may be selected from one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, R includes one or more elements selected from B, Si, N, and S, and optionally, R includes one element selected from B, Si, N, and S; the values ​​of x, y, and z satisfy the following condition: keeping the entire core electrically neutral;

[0115] The shell includes a first covering layer that covers the core;

[0116] The first coating layer comprises crystalline pyrophosphate LiaMP2O7 and / or Mb(P2O7). c Where 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate LiaMP2O7 or Mb(P2O7) available. c Maintaining electroneutrality, crystalline pyrophosphates LiaMP2O7 and Mb(P2O7) c Each of the M elements independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al;

[0117] The non-aqueous electrolyte includes an organic solvent, which includes a first solvent, and the first solvent includes one or more compounds shown in Formula 1.

[0118] Formula 1

[0119] R1 and R2 are each independently one of C1~C10 alkyl and C1~C10 haloalkyl. Optionally, R1 and R2 are each independently one of methyl, ethyl, propyl, butyl, pentyl, hexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, and fluorohexyl. Further optionally, R1 and R2 are each independently one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl, and fluoropropyl.

[0120] The surface oxygen valence state of the core-shell structured positive electrode active material is below -1.90.

[0121] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of values ​​for 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 consists of two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the range of values ​​for y defined in this application, and the sum of y1, y2...yn must also fall within this range. Similarly, for the case where R consists of two or more elements, the limitation on the range of values ​​for the stoichiometric coefficients of R in this application has the same meaning.

[0122] The secondary battery of this application utilizes an improved positive electrode active material with a coating layer and an improved electrolyte composition, which not only effectively enhances the rate performance of the secondary battery but also improves its cycle performance. Specifically:

[0123] The positive electrode active material of this application can improve the specific capacity, 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 manganese dissolution, 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, the migration resistance of manganese can be further increased, reducing its dissolution, and reducing the surface lithium content and the contact between the core and the electrolyte, thereby reducing interfacial side reactions, reducing gas production, and improving the high-temperature storage performance, cycle performance, and safety performance of the secondary battery.

[0124] 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 material, greatly reduces the dissolution of manganese 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.

[0125] 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 form or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. In addition, ensuring the electrical neutrality of the system can, in some cases, generate lithium vacancies in the material, thereby improving the material's kinetic performance.

[0126] As can be seen, this application provides a novel core-shell structured lithium manganese phosphate cathode active material by doping element A at the manganese site and element R at the phosphorus site of lithium manganese phosphate to obtain a doped lithium manganese phosphate core and coating the core surface with a layer. When this cathode active material is applied to secondary batteries, it can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of secondary batteries.

[0127] Meanwhile, the first solvent in the non-aqueous electrolyte has a good ability to dissociate lithium salts, but compared to carbonates, the first organic solvent reacts with Li... + The effect of the first solvent is very small. As the first solvent gradually dominates the first solvation layer, Li + The desolvation energy gradually decreases, which is beneficial to Li + Rapid insertion and extraction at the interface enhances the rate performance of the secondary battery. Furthermore, the first solvent has a low viscosity, allowing lithium ions extracted from the positive electrode active material to rapidly migrate and insert into the negative electrode side. Driven by concentration polarization, lithium ions at the positive electrode material interface are rapidly transferred to the electrolyte, further improving the rate performance of the secondary battery.

[0128] Furthermore, oxygen's stable valence state is -2. The closer the valence state is to -2, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. Under normal circumstances, its surface valence state is below -1.7. 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 material and the electrolyte can be reduced, thereby improving the cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0129] The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0130] In any embodiment of the first aspect, the shell further includes a second covering layer covering the first covering layer.

[0131] By further coating the cathode active material with a crystalline phosphate coating layer that has excellent lithium-ion conductivity, the interfacial side reactions on the surface of the cathode active material can be effectively reduced, thereby improving the high-temperature cycling and storage performance of the secondary battery.

[0132] In any embodiment of the first aspect, the second coating layer comprises crystalline phosphate XPO4, wherein X comprises one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0133] In any embodiment of the first aspect, the shell further includes a third covering layer covering the second covering layer.

[0134] By further coating the battery with a third coating layer (such as a carbon layer), the safety and kinetic performance of the secondary battery can be further improved.

[0135] In any embodiment of the first aspect, the third coating layer comprises carbon.

[0136] [Non-aqueous electrolyte]

[0137] The first solvent used in this application may be any carboxylic acid ester covered by Formula 1 above. In some embodiments, the first solvent includes at least one of the following compounds:

[0138] , ,

[0139] , ,

[0140] , ,

[0141] , ,

[0142] , ,

[0143] and .

[0144] In some embodiments, the first solvent optionally includes at least one of the following compounds:

[0145] , ,

[0146] and .

[0147] When the above-mentioned substances are selected as the first solvent, the electrolyte viscosity is lower and the wettability is better, thus improving the lithium-ion transport capacity and thereby better improving the rate performance of the secondary battery; at the same time, the above-mentioned first solvents have better chemical stability and better resistance to oxidation of the positive electrode active material.

[0148] While the first solvent offers advantages such as low viscosity and high conductivity, it readily reacts chemically with the positive and negative electrodes of the secondary battery, thus affecting the battery's cycle performance. In some embodiments, the mass percentage of the first solvent is w1, based on the total mass of the organic solvent, and w1 ranges from 20% to 80% (e.g., 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%); alternatively, w1 ranges from 30% to 75%. By controlling the above mass percentage, the first solvent can be used to improve the battery's fast-charging performance while simultaneously providing good cycle and storage performance.

[0149] In this application, when using the first solvent as the solvent for the non-aqueous electrolyte, in order to ensure the secondary battery has the highest possible cycle performance and storage performance, in some embodiments, the organic solvent optionally includes a second solvent, which may include one or more of the group consisting of chain carbonates and cyclic carbonates; further optionally, based on the total mass of the organic solvent, the mass percentage of the second solvent is w2, and w2 ranges from 20% to 80% (e.g., 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%); optionally, w2 ranges from 25% to 70%. This utilizes the combination of the second solvent and the first solvent to improve the cycle performance of the secondary battery.

[0150] There are no particular restrictions on the types of chain carbonates or cyclic carbonates in the second solvent mentioned above, and they can be selected according to actual needs. Optionally, the second solvent may include one or more of the following: dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and methyl propionate.

[0151] In some embodiments of the first aspect, the solvent of the above-mentioned non-aqueous electrolyte may also include commonly used solvents such as tetrahydrofuran, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone, which will not be described in detail in this application.

[0152] Typically, non-aqueous electrolytes may also optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0153] Furthermore, in some embodiments, the aforementioned non-aqueous electrolyte further includes a first additive, which comprises one or more of the group consisting of sulfonyl lactones and cyclic sulfates. The introduction of sulfonyl lactones or cyclic sulfates into the non-aqueous electrolyte allows them to form a layer of polymers with strong ion-conducting capabilities, such as ester sulfates, on the surface of the positive electrode active material during the secondary battery charging process. This polymer can further improve the rate performance of the secondary battery and effectively inhibit the catalytic oxidation of the first solvent by the positive electrode active material, thereby improving the cycle and storage performance of the secondary battery. In addition, sulfonyl lactones or cyclic sulfates can form a film on the negative electrode more readily than the first solvent, reducing the reaction between α-H on the first solvent and the active lithium reduced from the negative electrode, thereby further improving the cycle and storage performance of the secondary battery.

[0154] The sulfonyl lactones and cyclic sulfates used in the above embodiments of this application can be corresponding substances commonly used in the prior art. In some embodiments, the sulfonyl lactones include at least one of the compounds shown in Formula 2.

[0155] Formula 2

[0156] p represents 1, 2, or 3.

[0157] R 11 It represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl, C1-C12 haloalkyl, C1-C12 alkoxy, and C1-C12 haloalkoxy; optionally, R 11 It represents one of hydrogen atom, halogen atom, C1~C6 alkyl, C1~C3 haloalkyl, C1~C3 alkoxy, and C1~C3 haloalkoxy; optionally, the alkoxy is a chain alkoxy or a cyclic alkoxy, optionally the cyclic alkoxy shares a carbon atom with the parent ring of the sulfonyl lactone, and further optionally the cyclic alkoxy has 4, 5 or 6 carbon atoms;

[0158] Each R 12 Each of the following groups independently represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, and 4- to 7-membered sulfonyl lactone group; optionally, each R 12 Each of the following can be independently represented: a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C3 haloalkyl group, a C1-C3 alkoxy group, a C1-C3 haloalkoxy group, or a 5- or 6-membered sulfonyl lactone group; optionally, the sulfonyl lactone group shares a carbon atom with the parent ring of the sulfonyl lactone, and optionally the sulfonyl lactone group is a 5-membered ring.

[0159] R 11 and R 12 The carbon atoms bonded to each other can form 5 to 10-membered cycloalkyl groups;

[0160] R13 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C6 ester group, C1-C12 alkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, C6-C20 aryl group, or benzyl group; optionally, R 13 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C3 ester group, C1-C3 alkyl group, C1-C3 haloalkyl group, C2-C6 alkenyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, C6-C10 aryl group, or benzyl group.

[0161] The aforementioned sulfonyl lactones are commonly used sulfonyl lactones in this field, with wide availability and low cost.

[0162] In some embodiments, the above-mentioned cyclic sulfates include at least one of the compounds shown in Formula 3.

[0163] Formula 3

[0164] q represents 1, 2, or 3.

[0165] R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C1-C12 alkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, C2-C6 ester group, and 4- to 7-membered cyclic sulfate ester group; optionally, R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, double bond, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, C2-C3 ester group, and 4- to 5-membered cyclic sulfate group; optionally, the cyclic sulfate group and the cyclic sulfate share a carbon atom.

[0166] Each R 15 Each of the following independently represents one of the following: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, and C6-C20 aryl group; optionally, each R 15 Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C6 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, and C6-C10 aryl group.

[0167] Or R 14 and R 15 Together with their respective linked carbon atoms, they form 4 to 7-membered cyclic sulfate groups, and optionally, R 14 and R 15 Together with their respective linked carbon atoms, they form a 5-membered cyclic sulfate ester group.

[0168] The aforementioned cyclic sulfates are commonly used cyclic sulfates in this field, with wide availability and low cost.

[0169] In some embodiments, the sulfonyl lactone optionally includes at least one of the following compounds:

[0170] .

[0171] In some embodiments, the cyclic sulfate ester optionally includes at least one of the following compounds:

[0172] .

[0173] Further, optionally, sulfonyl lactones include at least one of the following compounds:

[0174] .

[0175] Further, optionally, the cyclic sulfate ester includes at least one of the following compounds:

[0176] .

[0177] The aforementioned sulfonyl lactones and cyclic sulfates are more likely to form polymers at the positive electrode.

[0178] While sulfonyl lactones and cyclic sulfates can improve the cycle and storage performance of secondary batteries compared to the first solvent, excessive use may increase the positive and negative electrode impedance, affecting the rate capability of the secondary battery. Those skilled in the art can refer to the conventional dosages of sulfonyl lactones and cyclic sulfates in the non-aqueous electrolyte of this application to select their dosage. In some embodiments, based on the total mass of the non-aqueous electrolyte, the content of the first additive is W3, and 0.01% ≤ W3 ≤ 20% (e.g., 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, or 20%), optionally 0.1% ≤ W3 ≤ 10%, and further optionally 0.3% ≤ W3 ≤ 5%. By effectively suppressing the decrease in cycle performance caused by the first solvent and avoiding the increase in positive and negative electrode impedance caused by excessive sulfonyl lactones or cyclic sulfates, a significant improvement in the capacity and rate capability of the lithium-ion battery is ensured.

[0179] In some embodiments, the non-aqueous electrolyte used in this application further includes a second additive, which comprises one or more of the group consisting of sulfite compounds, disulfonate compounds, nitrile compounds, aromatic compounds, phosphonitrile compounds, acid anhydride compounds, phosphite compounds, phosphate compounds, and borate compounds. The aforementioned second additive helps to form a denser and more stable interfacial film on the surface of the positive and / or negative electrode active materials, thereby further improving at least one of the cycle performance, storage performance, and rate performance of the secondary battery.

[0180] In some embodiments, based on the total mass of the non-aqueous electrolyte, the content of the second additive is W4, 0.01% ≤ W4 ≤ 20%, optionally 0.05% ≤ W4 ≤ 5%, and further optionally 0.1% ≤ W4 ≤ 3%, so that the effect of the second additive can be fully utilized.

[0181] The following are examples of some second additives.

[0182] Sulfite compounds

[0183] The sulfite compound is preferably a cyclic sulfite compound, specifically selected from one or more of the compounds shown in Formula 4.

[0184] Formula 4

[0185] In Equation 4, R 28 It is selected from substituted or unsubstituted C1-C6 alkylene groups and substituted or unsubstituted C2-C6 alkenyl groups, wherein the substituent is selected from one or more of halogen atoms, C1-C3 alkyl groups, and C2-C4 alkenyl groups.

[0186] In Equation 4, optionally, R 28 It is selected from substituted or unsubstituted C1-C4 alkylene groups and substituted or unsubstituted C2-C4 alkenyl groups, wherein the substituent is selected from one or more of halogen atoms, C1-C3 alkyl groups and C2-C4 alkenyl groups.

[0187] Optionally, the sulfite compound may be selected from one or more of vinyl sulfite (ES), propylene sulfite (PS), and butylene sulfite (BS).

[0188] disulfonate compounds

[0189] The disulfonate compound is a compound containing two sulfonic acid groups (-S(=O)2O-), preferably selected from disulfonate methylene ester compounds, which may be selected from one or more of the compounds shown in Formula 5. In Formula 5, R 24 R 25 R 26 R 27Each is independently selected from hydrogen atoms, halogen atoms, substituted or unsubstituted C1-C10 alkyl groups, substituted or unsubstituted C2-C10 alkenyl groups, wherein the substituents are selected from one or more of halogen atoms, C1-C3 alkyl groups, and C2-C4 alkenyl groups.

[0190] Formula 5

[0191] In Equation 5, optionally, R 24 R 25 R 26 R 27 Each is independently selected from hydrogen atoms, halogen atoms, substituted or unsubstituted C1-C4 alkyl groups, and substituted or unsubstituted C2-C6 alkenyl groups, wherein the substituents are selected from one or more of halogen atoms, C1-C3 alkyl groups, and C2-C4 alkenyl groups.

[0192] Optionally, the disulfonate compound may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

[0193] .

[0194] Alternatively, the disulfonate compound may be selected from methane disulfonate methylene (MMDS), with the following specific structure:

[0195] .

[0196] Nitrile compounds

[0197] The nitrile compound can be any one or more of the compounds shown in Formula 6 or Formula 7.

[0198] Formula 6, Formula 7.

[0199] In Formulas 6 and 7: R5 is selected from substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted C2-C12 alkenyl, and substituted or unsubstituted C2-C12 alkyne; R6, R7, and R8 are each independently selected from substituted or unsubstituted C0-C12 alkylene, substituted or unsubstituted C2-C12 alkenyl, and substituted or unsubstituted C2-C12 alkyne, wherein the substituent is selected from one or more of halogen atoms, nitrile groups, C1-C6 alkyl groups, C2-C6 alkenyl groups, and C1-C6 alkoxy groups. Optionally, R5 is selected from substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C2-C10 alkenyl, and substituted or unsubstituted C2-C10 alkyne, and R6, R7, and R8 are each independently selected from substituted or unsubstituted C0-C10 alkylene, substituted or unsubstituted C2-C10 alkenyl, and substituted or unsubstituted C2-C10 alkyne, wherein the substituent is selected from halogen atoms.

[0200] Further optionally, in Formula 6, R5 is selected from C1-C6 alkylene, C2-C6 alkenyl, and C2-C6 alkyne; optionally, R5 is selected from C2-C4 alkylene, C2-C4 alkenyl, and C2-C4 alkyne; in Formula 7, R6, R7, and R8 are each independently selected from C0-C6 alkylene, C2-C6 alkenyl, and C2-C6 alkyne; optionally, R6 is selected from C0-C1 alkylene, and R7 and R8 are each independently selected from C2-C4 alkylene, C2-C4 alkenyl, and C2-C4 alkyne.

[0201] In some embodiments, the nitrile compound is selected from one or more of oxonium, butadione, glutaronitrile, adiponitrile, heptanonitrile, octadione, nonadione, decanadione, undecanedione, dodecanedione, tetramethylsuccinate, methylglutaronitrile, butenonitrile, 2-pentenonitrile, hex-2-enonitrile, hex-3-enonitrile, oct-4-enonitrile, oct-4-ynedione, 1,2,3-propanetricarbonyl, 1,3,5-pentanetricarbonyl, and 1,3,6-hexanetrionitrile.

[0202] Aromatic compounds

[0203] The aromatic compound may be selected from one or more of the following: cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (ortho, meta, para), diphenyl ether, fluorobenzene, difluorobenzene (ortho, meta, para), anisole, 2,4-difluoroanisole, and partially hydrogenated terphenyl compounds (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, ortho-cyclohexylbiphenyl).

[0204] Optionally, the aromatic compound may be selected from one or more of biphenyl, terphenyl (ortho, meta, para), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene. Further, the aromatic compound may be selected from one or more of biphenyl, ortho-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene.

[0205] Phosphazene compounds

[0206] The phosphazene compound is preferably a cyclic phosphazene compound. The cyclic phosphazene compound may be selected from one or more of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0207] Optionally, the cyclic phosphazene compound may be selected from one or more of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene.

[0208] Further optionally, the cyclic phosphazene compound may be selected from methoxypentafluorocyclotriphosphazene or ethoxypentafluorocyclotriphosphazene.

[0209] acid anhydride compounds

[0210] The acid anhydride compound can be a chain anhydride or a cyclic anhydride. Specifically, the acid anhydride compound can be selected from one or more of acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, 2-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfono-propionic anhydride.

[0211] Optionally, the anhydride compound may be selected from one or more of succinic anhydride, maleic anhydride, and 2-allyl succinic anhydride. More preferably, the anhydride compound may be selected from one or two of succinic anhydride and 2-allyl succinic anhydride.

[0212] Phosphite compounds

[0213] The phosphite compound may be selected from silane phosphite compounds, specifically one or more of the compounds shown in Formula 8. In Formula 8, R 31 R 32 R 33 R 34 R 35 R 36 R 37 R 38 R 39 Each is independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.

[0214] Formula 8

[0215] Optionally, the silane phosphite compound may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

[0216]

[0217] Phosphate compounds

[0218] The phosphate compound may be selected from silane phosphate compounds, specifically one or more of the compounds shown in Formula 9. In Formula 9, R 41 R 42 R 43 R 44 R 45 R 46 R 47 R 48 R 49 Each is independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.

[0219] Formula 9

[0220] Optionally, the silane phosphate compound may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

[0221]

[0222] Boronate compounds

[0223] The borate ester compound may be selected from silane borate ester compounds, specifically one or more of the compounds shown in Formula 10. In Formula 10, R 51 R 52 R 53 R 54 R 55 R 56 R 57 R 58 R 59 Each is independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.

[0224] Formula 10

[0225] Optionally, the silane borate compound may be specifically selected from one or more of the following compounds, but this application is not limited thereto:

[0226]

[0227] In addition, the non-aqueous electrolyte of the secondary battery in this application also includes lithium salts. There are no particular restrictions on the type of lithium salt, which can be selected according to actual needs. For example, the lithium salt can be selected from LiN(C) x’ F 2x’+1 SO2)(C y’ F 2y ' +1 The lithium salt is selected from one or more of the following: SO2, LiPF6, LiBF4, LiBOB, LiAsF6, Li(FSO2)2N, LiCF3SO3, and LiClO4, wherein x' and y' are natural numbers, such as 0, 1, 2, 3, 4, 5, or 6, respectively. In some embodiments, the concentration range of the above lithium salt is 0.5 mol / L to 2.5 mol / L, preferably 0.8 mol / L to 2 mol / L.

[0228] [Positive electrode plate]

[0229] A positive electrode typically 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 including a positive electrode active material.

[0230] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0231] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0232] In the positive electrode active material of the secondary battery described above, which has a core and a shell covering the core, the main characteristic peak positions of the lithium manganese phosphate doped with A and R elements are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in core performance mainly comes from elemental doping, rather than impurity phases. After preparing the above-mentioned positive electrode active material, the inventors of this application used focused ion beam (FIB) to cut the middle region of the prepared positive electrode active material particles. Tests using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0233] In an optional implementation, when A includes 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 Where n1 + n2 + n3 + n4 = y, and 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 Rz 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.

[0234] 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 specific capacity of the material. The value of y limits the total amount of all dopants. If y is too small, the doping amount is too low, and 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 site. 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 0.001-0.100.

[0235] Through process control (e.g., thorough mixing and grinding of 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 XRD pattern of lithium manganese phosphate doped with A and R elements 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 positive electrode active material described in this application, the inventors used focused ion beam (FIB) to cut the middle region of the prepared positive electrode active material particles. Testing using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0236] In this application, "crystalline state" refers to a crystallinity of 50% or higher, i.e., 50%-100%. Crystallinity less than 50% is referred to as the glassy state. The crystallinity of the crystalline pyrophosphate and crystalline phosphate 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.

[0237] 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 techniques in the art, such as density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, or by, for example, X-ray diffraction.

[0238] 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:

[0239] A certain amount of positive electrode active material powder is taken, and the total scattering intensity is measured by X-rays. It is the sum of the scattering intensities of all matter in space. It is only related to the intensity of the primary rays, the chemical structure of the positive electrode active material powder, and the total number of electrons participating in diffraction, i.e., the mass, and is independent of the order state of the sample. Then, crystalline scattering and non-crystalline scattering are separated from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0240] 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.

[0241] 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.

[0242] 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 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, the matching degree between the core and the first coating layer is improved compared to undoped elements, allowing for a tighter bonding between the core and the pyrophosphate coating layer.

[0243] 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 material's stability. Crystalline phosphate has a very stable structure and excellent lithium-ion conductivity; therefore, using crystalline phosphate for coating can effectively reduce interfacial side reactions on the surface of the positive electrode active material, thereby improving the high-temperature cycling and 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.

[0244] The primary 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.

[0245] Each covering layer in this application can be a complete covering or a partial covering.

[0246] In some implementations, based on the kernel weight, the coverage of the first coating layer is C1 weight%, where C1 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably greater than 0 and less than or equal to 2.

[0247] In any implementation of the first aspect, based on the kernel weight, the coverage of the second coating layer is C2 weight%, where C2 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably 2-4.

[0248] In any implementation of the first aspect, based on the kernel weight, the coverage of the third coating layer is C3 weight%, where C3 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, and more preferably greater than 0 and less than or equal to 2.

[0249] In the core-shell structured positive electrode active material of the above embodiments, the coating amount of the three coating layers is preferably within the above range, thereby enabling sufficient coating of the core and further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0250] For the first coating layer, by keeping the coating amount within the above range, the following situations can be avoided: too little coating amount means that the coating layer is too thin, which may not be able to effectively hinder the migration of transition metals; too much coating amount means that the coating layer is too thick, which will affect the migration of Li+, and thus affect the rate performance of the material.

[0251] For the second coating layer, by keeping the coating amount within the above range, the following situations can be avoided: too much coating amount may affect the overall plateau voltage of the material; too little coating amount may not achieve sufficient coating effect.

[0252] 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.

[0253] In the core-shell structured positive electrode active material of the above embodiments, the coating amount of the three coating layers is preferably within the above range, thereby enabling sufficient coating of the core and further improving the kinetic performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0254] In any embodiment, the interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°.

[0255] In any embodiment, the interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

[0256] The crystalline pyrophosphates and crystalline phosphates in the coating layer can be characterized using conventional techniques in the art, or for example, by transmission electron microscopy (TEM). Under TEM, the core and coating layer can be distinguished by measuring the interplanar spacing.

[0257] The specific testing methods for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer may include the following steps:

[0258] Take a certain amount of the coated positive electrode active material sample powder into a test tube, and inject a solvent such as alcohol into the test tube. 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, obtain the original TEM test image, and save the original image.

[0259] Open the original image obtained from the TEM test in the diffractometer software and perform a 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 included angle is calculated according to the Bragg equation.

[0260] 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.

[0261] In the above-described embodiments, both the first and second coating layers of the positive electrode active material are made of crystalline materials, and their interplanar spacing and angles are within the aforementioned range. This effectively avoids impurity phases in the coating layers, thereby improving the specific capacity, cycle performance, and rate performance of the material. Furthermore, 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, cycle stability, and high-temperature storage performance of the secondary battery.

[0262] In some implementations, the ratio of y to 1-y in the core is 1:10 to 1:1, optionally 1:4 to 1:1. When the above conditions are met, the energy density and cycle performance of the secondary battery using the aforementioned positive electrode active material can be further improved.

[0263] In some implementations, the ratio of z to 1-z in the core is from 1:999 to 1:9, 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.

[0264] In some embodiments, 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 in the range of 0.1-10, and can be any value in the range of 2.0-3.0.

[0265] 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.

[0266] In this application, "about" for a certain value represents a range, specifically a range of ±10% of that value.

[0267] By selecting the morphology of carbon in the carbon coating layer, the overall electrical 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 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 insertion / 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 benefiting the optimization of secondary battery function and the improvement of its cycle performance.

[0268] 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.

[0269] The structure and characteristics of the third coating carbon can be determined by Raman spectroscopy. The specific testing method is as follows: by dividing the energy spectrum of the Raman test, the Id / Ig ratio is obtained (where Id is the peak intensity of SP3 carbon and Ig is the peak intensity of SP2 carbon), thereby confirming the molar ratio between the two.

[0270] In some embodiments, the thickness of the first coating layer is 1-10 nm; and / or the thickness of the second coating layer is 2-15 nm; and / or the thickness of the third coating layer is 2-25 nm.

[0271] 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 any of the above values.

[0272] 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 any of the above values.

[0273] 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.

[0274] When the thickness of the first coating layer is in the range of 1-10 nm, it can avoid the adverse effects on the dynamic properties of the 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.

[0275] When the thickness of the second coating layer is in the range of 2-15 nm, the surface structure of the second coating layer is stable and the side reactions with the electrolyte are small. Therefore, it can more effectively reduce the interfacial side reactions, thereby further improving the high-temperature performance of the secondary battery.

[0276] When the thickness of the third coating layer is in the range of 2-25 nm, the electrical conductivity of the material can be further improved and the compaction performance of the battery electrode prepared using the positive electrode active material can be better improved.

[0277] 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.

[0278] In some embodiments, based on the weight of the positive electrode active material, the manganese content is in the range of 10 wt%-35 wt%, preferably in the range of 15 wt%-30 wt%, and more preferably in the range of 17 wt%-20 wt%, the phosphorus content is in the range of 12 wt%-25 wt%, preferably in the range of 15 wt%-20 wt%, and the weight ratio of manganese to phosphorus is in the range of 0.90-1.25, preferably in the range of 0.95-1.20.

[0279] 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.

[0280] In the above embodiments, limiting the manganese content within the above range can effectively avoid problems such as poor material structure stability and decreased density that may be caused by excessive manganese content, thereby effectively improving the cycle, storage and compaction performance of the secondary battery; and can also avoid problems such as low voltage platform that may be caused by excessive manganese content, thereby further improving the energy density of the secondary battery.

[0281] In the above embodiments, limiting the phosphorus content within the above range can effectively avoid the following situations: if the phosphorus content is too high, it may cause the covalent nature of PO to be too strong, affecting the conductivity of small polarons, thereby affecting the conductivity of the 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 material.

[0282] 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 specific 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 material to drop, thereby reducing the energy density of the secondary battery.

[0283] 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.

[0284] 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 2.0-3.8%.

[0285] 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 lattice change rate before and after lithium insertion / extraction. The smaller the lattice change rate, the smaller the interfacial stress, and the easier the Li+ transport. Therefore, reducing the lattice change rate of the core will enhance the Li+ transport capability, thereby improving the rate performance of the secondary battery. The core-shell structured cathode active material of the above embodiments can achieve a lattice change rate of less than 4% before and after lithium insertion / extraction, thus using the cathode active material can improve the rate performance of the secondary battery. The lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).

[0286] In some embodiments, the Li / Mn antisite defect concentration of the core-shell structured positive electrode active material is less than 4%, preferably less than 2.2%, and more preferably 1.5-2.2%.

[0287] The Li / Mn inversion defect in this application refers to the Li / Mn inversion defect in the LiMnPO4 lattice. + With Mn 2+ The positions of the Li and Mn antisite defects have been interchanged. Accordingly, the Li / Mn antisite defect concentration refers to the concentration relative to Mn. 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.

[0288] The core-shell structured positive electrode active material of the above embodiments 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 transport efficiency and enhances the specific capacity and rate performance of the positive electrode active material.

[0289] In some embodiments, the compaction density of the positive electrode active material at 3T is 2.2 g / cm³. 3 The above can be optionally 2.2 g / cm³. 3 Above and 2.8 g / cm 3 The higher the compaction density, the greater the weight of active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of the battery cell. Compaction density can be measured according to GB / T 24533-2009.

[0290] In some embodiments, the surface oxygen valence state of the core-shell structured positive electrode active material is -1.90 to -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. By limiting the surface oxygen valence state of the positive electrode active material to the aforementioned range as described above, the above embodiments can reduce interfacial side reactions between the positive electrode material and the electrolyte, thereby improving the cell's cycle life, high-temperature storage gas generation, and other performance characteristics.

[0291] This application also provides a method for preparing a positive electrode active material, comprising the following steps:

[0292] 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 z O4, 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 includes 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 may be selected from one or more elements selected from Fe, Ti, V, Ni, Co, and Mg. R includes one or more elements selected from B, Si, N, and S, and optionally, R is an element selected from B, Si, N, and S.

[0293] Coating steps: Provide LiaMP2O7 and / or Mb(P2O7) separately. c And an XPO4 suspension, the core material is added to the above suspension and mixed, and then sintered to obtain a positive electrode active material, wherein 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values ​​of a, b and c satisfy the following conditions: making crystalline pyrophosphate LiaMP2O7 or Mb(P2O7) available. c Maintaining electrical neutrality; each of M independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al; X includes one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al;

[0294] The positive electrode active material has a core-shell structure, comprising a core and a shell covering the core. 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 comprises crystalline pyrophosphate LiaMP2O7 and / or Mb(P2O7).c The second coating layer comprises crystalline phosphate XPO4, and the third coating layer comprises carbon.

[0295] In some implementations, the step of providing the core material includes the following steps:

[0296] Step (1): Mix and stir the manganese source, element A dopant and acid in a container to obtain manganese salt particles doped with element A;

[0297] 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, 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 includes 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 may be selected from one or more elements selected from Fe, Ti, V, Ni, Co, and Mg. R includes one or more elements selected from B, Si, N, and S, and optionally, R is an element selected from B, Si, N, and S.

[0298] 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.

[0299] In some embodiments, the dopant of element A includes one or more elements selected from the group consisting of their respective elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide, as well as one or more of the elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge.

[0300] In some embodiments, the dopant of element R includes one or more of the following: inorganic acid, succinic acid, organic acid, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide selected from B, Si, N, and S.

[0301] 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.

[0302] 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.

[0303] In this application, the lithium source may be any lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source may be one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0304] 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.

[0305] In some alternative 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.

[0306] In some alternative embodiments, the slurry in step (2) is dried to obtain powder, and then the powder is sintered to obtain a core doped with elements A and R.

[0307] In some embodiments, step (1) is performed at a temperature of 20-120°C, optionally 40-120°C; and / or

[0308] The stirring in step (1) is carried out at 400-700 rpm for 1-9 hours, optionally 3-7 hours.

[0309] 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.

[0310] In some embodiments, step (2) is performed at a temperature of 20-120°C, optionally 40-120°C, for 1-12 hours. Optionally, the reaction temperature in step (2) can be performed at approximately 30°C, approximately 50°C, approximately 60°C, approximately 70°C, approximately 80°C, approximately 90°C, approximately 100°C, approximately 110°C, or approximately 120°C; the mixing in step (2) is performed 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, approximately 10 hours, approximately 11 hours, or approximately 12 hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of the above values.

[0311] 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.

[0312] In some embodiments, optionally, during the preparation of dilute manganese acid particles doped with elements A and R, the pH of the solution is controlled to be 3.5-6; alternatively, the pH of the solution is controlled to be 4-6; more preferably, the pH of the solution is controlled to be 4-5. 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.

[0313] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles to the lithium source and the phosphorus source is 1:0.5-2.1:0.5-2.1. 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.

[0314] In some embodiments, optionally, the sintering conditions in the preparation of A and R-doped lithium manganese phosphate are: sintering at 600-950°C for 4-10 hours in an inert gas or a mixture of inert gas and hydrogen; 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 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 material core, which will also affect the overall performance. If the sintering time is too long, the material core particles will be too large, which will affect the specific capacity, compaction density and rate performance.

[0315] In some alternative embodiments, the protective atmosphere may optionally be a mixture of 70-90% nitrogen and 10-30% hydrogen by volume.

[0316] In some embodiments, the coating step includes:

[0317] 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 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.

[0318] 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.

[0319] 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.

[0320] In some embodiments, the source of element M includes one or more elements selected from the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, hydroxide, etc.

[0321] In some embodiments, the source of element X includes one or more elements selected from the group consisting of their respective elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide, such as Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

[0322] 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.

[0323] As an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0324] In some embodiments, 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 3.5-6.5, then stirred and reacted for 1-5 hours, then the solution is heated to 50-120°C and held at that temperature for 2-10 hours, and / or sintering is carried out at 650-800°C for 2-6 hours.

[0325] 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 4.5 hours, or approximately 5 hours. Optionally, in the first coating step, the reaction time can be within any range of the above-mentioned values.

[0326] Optionally, in the first coating step, the pH of the solution is controlled to be 4-6. 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 heating temperature and holding time can be within any range of the above values.

[0327] 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.

[0328] In the first coating step, by controlling the sintering temperature and time within the above range, the following situations can be 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 high-temperature 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 high-temperature storage performance of the secondary battery; when the sintering time is too long, the thickness of the first coating layer will increase, affecting the migration of Li+, thereby affecting the specific capacity and rate performance of the material.

[0329] In some embodiments, 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 1-10 hours, the solution is then heated to 60-150°C and held at that temperature for 2-10 hours, and / or sintering is carried out at 500-700°C for 6-10 hours.

[0330] 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.

[0331] 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.

[0332] 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)-(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 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.

[0333] 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.

[0334] In the second coating step, by controlling the sintering temperature and time within the above range, the following situations can be 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 material surface reactivity and thus affecting the cycle and high-temperature storage performance of the secondary battery; when the sintering temperature is too high, impurity phases will appear in the second coating layer, which will also affect its effect of reducing the material surface reactivity and thus affect the cycle and high-temperature 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 material and thus reducing the energy density of the material.

[0335] In some embodiments, the sintering in the third coating step is performed at 700-800°C for 6-10 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.

[0336] In the third coating step, by controlling the sintering temperature and time within the above range, the following situations can be 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 specific capacity of the material; when the sintering temperature is too high, the graphitization degree of the third coating layer will be too high, affecting the transport of Li+ and thus affecting the specific capacity of the material; when the sintering time is too short, the coating layer will be too thin, affecting its conductivity and thus affecting the specific capacity of the material; when the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the material.

[0337] In the first, second, and third coating steps described above, the drying is 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 is 3-9 hours, optionally 4-8 hours, more preferably 5-7 hours, and most preferably about 6 hours.

[0338] 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 stability, high-temperature cycling performance, and rate performance. Furthermore, the raw materials are widely available, inexpensive, and the process is simple, facilitating industrialization.

[0339] In some embodiments, the positive electrode active material may be other positive electrode active materials known in the art for use in batteries. As an example, other positive electrode active materials may also include at least one of the following: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0340] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0341] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0342] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0343] [Negative electrode plate]

[0344] 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, the negative electrode film layer including a negative electrode active material.

[0345] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0346] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0347] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0348] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0349] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0350] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0351] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0352] [Isolation membrane]

[0353] In some embodiments, the secondary battery also includes a separator. 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.

[0354] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0355] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0356] 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.

[0357] 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0358] 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. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0359] In some implementations, refer to Figure 2 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 forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within 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 selected by those skilled in the art according to specific practical needs.

[0360] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0361] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0362] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0363] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0364] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and 5 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, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0365] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided 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 include, 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.

[0366] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0367] Figure 6This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0368] [Example]

[0369] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0370] The first solvent is selected from the following solvents:

[0371] Solvent 1: Solvent 2: ;

[0372] Solvent 3: Solvent 4: ;

[0373] Solvent 5: Solvent 6 .

[0374] The first additive is selected from the following compounds:

[0375] Additive 1: Additive 2: Additive 3: ;

[0376] Additive 4: Additive 5: Additive 6: ;

[0377] Additive 7: Additive 8: Additive 9: .

[0378] I. Battery fabrication

[0379] Example 1:

[0380] Step 1: Preparation of positive electrode active material

[0381] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0382] 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 h. 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 h until homogeneous mixing and the reaction was terminated without bubble generation, 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.

[0383] 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

[0384] Take 1793.1 g of manganese oxalate, 368.3 g of lithium carbonate, 1146.6 g of ammonium dihydrogen phosphate, and 4.9 g of dilute sulfuric acid prepared in (1), add them to 20 L of deionized water, stir thoroughly, and react uniformly at 80°C for 10 h 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 h to obtain the above-mentioned core material.

[0385] Step S3: Preparation of the first coating layer suspension

[0386] 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 h to obtain a solution. The solution was then heated to 80 °C and maintained at this temperature for 4 h to obtain the first coating layer suspension.

[0387] Step S4: Coating with the first coating layer

[0388] 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.

[0389] Step S5: Preparation of the second coating layer suspension

[0390] 3.7 g lithium carbonate, 11.6 g ferrous carbonate, 11.5 g ammonium dihydrogen phosphate and 12.6 g oxalic acid dihydrate were dissolved in 1500 mL deionized water, stirred and reacted for 6 h to obtain a solution. The solution was then heated to 120 °C and maintained at this temperature for 6 h to obtain a second coating layer suspension.

[0391] Step S6: Coating with the second coating layer

[0392] 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.

[0393] Step S7: Preparation of the third coating layer aqueous solution

[0394] Dissolve 37.3g of sucrose in 500g of deionized water, then stir and dissolve completely to obtain a sucrose aqueous solution.

[0395] Step S8: Coating with the third coating layer

[0396] 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 an oven at 150°C and dried for 6 hours. Then, it was sintered at 700°C for 10 hours to obtain the three-layer coated material.

[0397] Step 2: Preparation of the positive electrode sheet

[0398] The three-layer coated positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared above were added to N-methylpyrrolidone (NMP) at a weight ratio of 97.0:1.2:1.8, and stirred until homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry was prepared at a ratio of 0.280 g / 1540.25 mm. 2 The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0399] Step 3: Preparation of the negative electrode sheet

[0400] Artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were dissolved in deionized water at a weight ratio of 90:5:2:2:1 and stirred until homogeneous to prepare a cathode slurry. The cathode slurry was then uniformly coated onto a copper foil (cathode current collector) at a ratio of 0.117 g / 1540.25 mm². After drying, cold pressing, and slitting, the cathode sheet was obtained.

[0401] Step 4: Preparation of electrolyte

[0402] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), solvent 1 is used as the first solvent, and a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3 / 7 is used as the second solvent. Additive 1 is used as the first additive, and LiPF6 is used as the lithium salt. The first solvent, second solvent, first additive, and lithium salt constitute the electrolyte. The mass ratio of the first solvent and the second solvent is 1:1. Based on the total mass of the electrolyte, the mass content of the first additive is 3%, and the mass content of the lithium salt is 12.5%.

[0403] Step 5: Preparation of the separating membrane

[0404] The PP-PE copolymer microporous film with a thickness of 20μm and an average pore size of 80nm (from Zogo Electronics Technology Co., Ltd., model 20) was used.

[0405] Step 6: Preparation of the full cell

[0406] 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 electrodes are then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the electrolyte, and sealed to obtain a full battery (hereinafter also referred to as "full battery").

[0407] [Preparation of button cells]

[0408] The prepared positive electrode active material, polyvinylidene fluoride (PVDF), and acetylene black were added to N-methylpyrrolidone (NMP) in a weight ratio of 90:5:5, 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 amount was 0.2 g / cm², and the compaction density was 2.0 g / cm³.

[0409] A lithium sheet is used as the negative electrode. Solvent 1 is used as the first solvent, and a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as the second solvent. Additive 1 is used as the first additive, and LiPF6 is used as the lithium salt. The electrolyte consists of the first solvent, the second solvent, the first additive, and the lithium salt. The mass ratio of the first solvent to the second solvent is 1:1. Based on the total mass of the electrolyte, the mass content of the first additive is 3%, and the mass content of the lithium salt is 1 mol / L. Together with the positive electrode prepared above, they are assembled into a coin cell (hereinafter referred to as "coin cell") in a coin cell box.

[0410] Examples 2 to 27 and Comparative Examples 1 to 19

[0411] The positive electrode active materials and batteries of Examples 2 to 27 and Comparative Examples 1 to 19 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 1-6. Comparative Examples 1-2, 4-10 and 12 were not coated with the first layer, so steps S3 and S4 were not performed. Comparative Examples 1-11 were not coated with the second layer, so steps S5 and S6 were not performed.

[0412] Note: 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.

[0413] Table 1: Raw materials for kernel preparation

[0414]

[0415] Table 2: Preparation of the first coating layer suspension (step S3)

[0416]

[0417] Table 3: Covering of the first coating layer (step S4)

[0418]

[0419]

[0420] Table 4: Preparation of the second coating layer suspension (step S5)

[0421]

[0422] Table 5: Covering of the second coating layer (step S6)

[0423]

[0424] Table 6: Covering of the third coating layer (step S8)

[0425]

[0426]

[0427] Examples 30-42: Investigation of other coating materials

[0428] Examples 30-42 were carried out in a manner similar to that in Example 1, with the differences shown in Tables 7-9 below.

[0429] Table 7: Investigation of the material of the first coating layer

[0430]

[0431] Table 8: Investigation of the Second Coating Material

[0432]

[0433] II. Performance Evaluation

[0434] 1. Method for testing lattice change rate:

[0435] Under a constant temperature environment of 25℃, the positive electrode active material sample was placed in an XRD (model Bruker D8 Discover) and tested at 1° / min. The test data was 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 each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0436] 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 500nm 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, with (v0-v1) / v0×100% as the lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction.

[0437] 2. Li / Mn antisite defect concentration

[0438] 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.

[0439] 3. Compacted density

[0440] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm). Then place the mold on a compaction density instrument. Apply a pressure of 3T and read the thickness of the powder under pressure (thickness after depressurization) on the instrument. Calculate the compaction density using ρ=m / v, where the area value used is the standard small image area of ​​1540.25mm².

[0441] 4. 3C charging constant current ratio

[0442] Under a constant temperature environment of 25°C, the fresh full cells 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 time was recorded as C0. After discharging at 1 / 3C to 2.5V, standing for 5 minutes, and then charging at 3C to 4.3V, and standing for 5 minutes, the charging capacity at this time was recorded as C1. The constant current ratio of 3C charging is C1 / C0×100%.

[0443] The higher the constant current ratio during 3C charging, the better the rate performance of the secondary battery.

[0444] 5. Dissolution test of transition metal Mn (and Fe doped at Mn sites)

[0445] 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 cells were then disassembled, and the negative electrode was removed. Thirty circular pieces with a unit area (1540.25 mm²) were randomly selected from the negative electrode and inductively coupled plasma emission spectroscopy (ICP) was performed using an Agilent ICP-OES730. Based on the ICP results, the amounts of Fe (if the positive electrode active material is doped at Mn sites) and Mn were calculated, thereby calculating the amount of Mn (and the Fe doped at Mn sites) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0446] 6. Surface oxygen valence state

[0447] 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.

[0448] 7. Measurement of manganese and phosphorus elements in positive electrode active materials

[0449] Dissolve 5 g of the prepared positive electrode active material in 100 ml of aqua regia (concentrated hydrochloric acid: concentrated nitric acid = 1:3) (concentrated hydrochloric acid concentration ~37%, concentrated nitric acid concentration ~65%). Use ICP to test the content of each element in the solution, and 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.

[0450] 8. Method for measuring the initial specific capacity of button cells

[0451] At 2.5-4.3V, the coin cells prepared in the above embodiments and comparative examples were charged to 4.3V at 0.1C, and 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.

[0452] 9. Cell expansion test after 30 days of storage at 60℃:

[0453] 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. The full cells were removed after every 48 hours of storage, allowed to stand for 1 hour, and then the open-circuit voltage (OCV) and internal resistance (IMP) were measured. After cooling to room temperature, the cell volume was measured using the water displacement method. The water displacement method involved 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 process, the weight F2 of the battery cell at this moment is measured, and the buoyant force F_buoyancy on the battery cell is F1-F2. Then, according to Archimedes' principle, F_buoyancy... The cell volume V is calculated to be V = (F1 - F2) / .

[0454] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire experiment until the end of storage.

[0455] After 30 days of storage, the cell volume was measured, and the percentage increase in cell volume after storage was calculated relative to the cell volume before storage.

[0456] 10. Cyclic performance test of the full battery at 45°C

[0457] Under constant temperature conditions of 45℃, charge at 1C to 4.3V within the range of 2.5-4.3V, then charge at constant voltage at 4.3V until the current is ≤0.05mA, let stand for 5 minutes, and then discharge at 1C to 2.5V. Record the capacity as Dn (n=0,1,2,……). Repeat the above process until the capacity fades to 80%, and record the number of repetitions at this point. This number of cycles corresponds to 80% capacity retention at 45℃.

[0458] 11. Interplanar spacing and angle testing

[0459] 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. Then, stir and disperse the mixture thoroughly 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 F200s G2) for testing. Obtain the original TEM test image and save it in the original image format (xx.dm3).

[0460] 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.

[0461] By comparing the obtained interplanar spacing and corresponding angle data with their standard values, different materials in the coating layer can be identified.

[0462] 12. Coating thickness test

[0463] 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. Then, the slice was subjected to TEM testing to obtain the original TEM test image, which was saved in the original image format (xx.dm3).

[0464] 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.

[0465] Measure the thickness of the selected particle at three locations and take the average value.

[0466] 13. Determination of the molar ratio of SP2 and SP3 forms in the third coating layer of carbon.

[0467] This test was performed using Raman spectroscopy. By splitting the energy spectrum from the Raman test, the Id / Ig ratio was obtained, where Id is the peak intensity of SP3 carbon and Ig is the peak intensity of SP2 carbon, thus confirming the molar ratio between the two.

[0468] The performance test results for all embodiments and comparative examples are shown in the table below.

[0469] Table 9: Powder properties of positive electrode active materials in Examples 1-29 and Comparative Examples 1-17 and battery performance of the prepared batteries

[0470]

[0471] As shown in Table 9, compared with the comparative example, the embodiment achieves 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.

[0472] Table 10: Thickness of each layer of the positive electrode active material prepared in Examples 1-14 and Comparative Examples 3-4 and 12, and the weight ratio of manganese and phosphorus.

[0473]

[0474] As can be seen from Table 10, by doping the manganese and phosphorus sites of lithium manganese iron phosphate (containing 35% manganese and about 20% phosphorus) and applying a three-layer coating, 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 9, it can be seen that the reduction of manganese and phosphorus in the positive electrode active material leads to a decrease in the amount of manganese iron dissolved and an improvement in the battery performance of the secondary battery prepared from it.

[0475] Table 11: Powder properties of the positive electrode active materials in Examples 30-42 and battery performance of the prepared batteries

[0476]

[0477] As shown in Table 11, the use of a first coating layer and a second coating layer 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.

[0478] The first solvent, second solvent, and first additive in the electrolyte of Example 4 were sequentially replaced with the corresponding substances and contents listed in Table 12 to form the corresponding batteries of Examples 43 to 71. The contents W1% and W2% are added together to equal 100%, and the content W3% of the first additive is based on electrolyte measurement.

[0479] Table 12

[0480]

[0481] The initial gram capacity (mAh / g) at 0.1C, the constant current ratio at 3C charging (%), the number of cycles with 80% capacity retention at 45℃, and the cell expansion rate (%) after 30 days of storage at 60℃ were tested according to the above test methods, and the test results are recorded in Table 13.

[0482] Table 13

[0483]

[0484] Furthermore, the electrolyte in the full cells of Examples 1 to 29 was replaced with: ethylene carbonate (EC) / ethyl methyl carbonate (EMC) organic solvents were mixed uniformly at a volume ratio of 3 / 7, and 12.5% ​​by weight (based on the weight of the ethylene carbonate / ethyl methyl carbonate solvent) of LiPF6 was added and dissolved in the organic solvent, and stirred uniformly to obtain the electrolyte; the electrolyte in the coin cells was replaced with: 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 as the electrolyte. The cyclic Mn and Fe dissolution amounts (ppm), 0.1C coin capacity (mAh / g), 3C charge constant current ratio (%), 80% capacity retention cycle number at 45°C, and 60°C storage cell expansion rate (%) of the coin cells or full cells formed in Comparative Examples 18 to 46 were tested according to the above method, and the test results are recorded in Table 14.

[0485] Table 14

[0486]

[0487] As can be seen from the comparison between Table 9 and Table 14, the electrolyte composition of this application can further improve the rate performance and cycle performance of secondary batteries.

[0488] Based on the electrolyte of Example 4, a second additive was further added. Table 15 indicates the types of additives and their content in the electrolyte. The initial coin cell capacity (mAh / g), 3C charging constant current ratio (%), 80% capacity retention cycle number at 45°C, and cell expansion rate at 60°C were tested using the above method, and the test results are recorded in Table 15.

[0489] Table 15

[0490]

[0491]

[0492]

[0493]

[0494] A comparison of the data in Table 15 and the data in Example 4 shows that the use of the second additive can further improve the cycle performance.

[0495] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, comprising: Including the positive electrode and the non-aqueous electrolyte, among which, The positive electrode sheet includes a core-shell structured positive electrode active material, wherein 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 z O4, 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 includes 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 values ​​of x, y, and z satisfy the following condition: maintaining the entire core electrically neutral; The shell includes a first covering layer that covers the core; The first coating layer comprises crystalline pyrophosphate LiaMP2O7 and / or Mb(P2O7). c Where 0≤a≤2, 1≤b≤4, 1≤c≤6, and the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate LiaMP2O7 or Mb(P2O7) available. c Maintaining electroneutrality, the crystalline pyrophosphates LiaMP2O7 and Mb(P2O7) c Each of the M elements independently includes one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al; The non-aqueous electrolyte includes an organic solvent, which includes a first solvent, and the first solvent includes one or more compounds of Formula 1. Formula 1 R1 and R2 are each independently one of C1~C10 alkyl and C1~C10 haloalkyl; The surface oxygen valence state of the core-shell structured positive electrode active material is below -1.90; Based on the total mass of the organic solvent, the mass percentage of the first solvent is w1, and the range of w1 is 20% to 80%.

2. The secondary battery according to claim 1, wherein, A is one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, and R includes one or more elements selected from B, Si, N, and S.

3. The secondary battery according to claim 1, wherein, The R includes an element selected from B, Si, N, and S.

4. The secondary battery according to claim 1, wherein, R1 and R2 are each independently one of methyl, ethyl, propyl, butyl, pentyl, hexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl, and fluorohexyl.

5. The secondary battery according to claim 3, wherein, R1 and R2 are each independently one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl, and fluoropropyl.

6. The secondary battery according to claim 1, wherein, The shell also includes a second covering layer that covers the first covering layer.

7. The secondary battery according to claim 6, characterized in that, The second coating layer comprises crystalline phosphate XPO4, wherein X comprises one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.

8. The secondary battery according to claim 6, wherein, The shell also includes a third covering layer that covers the second covering layer.

9. The secondary battery according to claim 8, wherein, The third coating layer comprises carbon.

10. The secondary battery according to claim 1, wherein, The first solvent includes at least one of the following compounds: 、 、 、 、 、 、 、 、 、 、 and .

11. The secondary battery according to claim 10, wherein, The first solvent includes at least one of the following compounds: 、 、 and .

12. The secondary battery according to claim 1, wherein, The range of w1 is 30% to 75%.

13. The secondary battery according to claim 1, wherein, The organic solvent further includes a second solvent, which comprises one or more of the group consisting of chain carbonates and cyclic carbonates.

14. The secondary battery according to claim 13, wherein, Based on the total mass of the organic solvent, the mass percentage of the second solvent is w2, and the range of w2 is 20% to 70%.

15. The secondary battery according to claim 14, wherein, The range of w2 is 25% to 70%.

16. The secondary battery according to claim 1, wherein, The non-aqueous electrolyte also includes a first additive, which comprises one or more of the group consisting of sulfonyl lactones and cyclic sulfates.

17. The secondary battery according to claim 16, wherein, The sulfonyl lactone includes at least one of the compounds shown in Formula 2. Formula 2 p represents 1, 2, or 3. R 11 It represents one of the following: hydrogen atom, halogen atom, C1~C12 alkyl, C1~C12 haloalkyl, C1~C12 alkoxy, and C1~C12 haloalkoxy. Each R 12 Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, or 4- to 7-membered sulfonyl lactone group; R 11 and R 12 It may or may not form a 5- to 10-membered cycloalkyl group with the carbon atoms it is attached to; R 13 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C6 ester group, C1-C12 alkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, C6-C20 aryl group, or benzyl group; And / or, The cyclic sulfate includes at least one of the compounds shown in Formula 3. Formula 3 q represents 1, 2, or 3. R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C1~C12 alkyl group, C1~C12 haloalkyl group, C2~C12 alkenyl group, C1~C12 alkoxy group, C1~C12 haloalkoxy group, C2~C6 ester group, and 4 to 7-membered cyclic sulfate ester group; Each R 15 Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C12 alkyl group, C1-C12 haloalkyl group, C1-C12 alkoxy group, C1-C12 haloalkoxy group, and C6-C20 aryl group. Or R 14 and R 15 Together with their respective bonded carbon atoms, they form 4 to 7-membered cyclic sulfate groups.

18. The secondary battery according to claim 17, wherein, R 11 It represents one of the following: hydrogen atom, halogen atom, C1~C6 alkyl, C1~C3 haloalkyl, C1~C3 alkoxy, and C1~C3 haloalkoxy.

19. The secondary battery according to claim 18, wherein, The alkoxy group is a chain alkoxy group or a cyclic alkoxy group.

20. The secondary battery according to claim 19, wherein, The cyclic alkoxy group shares a carbon atom with the parent ring of the sulfonyl lactone.

21. The secondary battery according to claim 19, wherein, The cyclic alkoxy group has 4, 5, or 6 carbon atoms.

22. The secondary battery according to claim 17, wherein, Each R 12 Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C3 alkyl group, C1-C3 haloalkyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, or 5- to 6-membered sulfonyl lactone group.

23. The secondary battery according to claim 22, wherein, The sulfonyl lactone group shares a carbon atom with the parent ring of the sulfonyl lactone.

24. The secondary battery according to claim 22, wherein, The sulfonyl lactone group is a 5-membered ring.

25. The secondary battery according to claim 17, wherein, R 13 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, C2-C3 ester group, C1-C3 alkyl group, C1-C3 haloalkyl group, C2-C6 alkenyl group, C1-C3 alkoxy group, C1-C3 haloalkoxy group, C6-C10 aryl group, or benzyl group.

26. The secondary battery according to claim 17, wherein, R 14 It represents one of the following: hydrogen atom, halogen atom, carbonyl group, double bond, C1~C6 alkyl group, C1~C3 haloalkyl group, C1~C3 alkoxy group, C1~C3 haloalkoxy group, C2~C3 ester group, and 4 to 5-membered cyclic sulfate ester group.

27. The secondary battery according to claim 26, wherein, The cyclic sulfate group shares a carbon atom with the cyclic sulfate group.

28. The secondary battery according to claim 17, wherein, Each R 15 Each of the following can be independently represented: hydrogen atom, halogen atom, C1-C6 alkyl, C1-C3 haloalkyl, C1-C3 alkoxy, C1-C3 haloalkoxy, and C6-C10 aryl.

29. The secondary battery according to claim 17, wherein, R 14 and R 15 Together with their respective connected carbon atoms, they form a 5-membered cyclic sulfate ester group.

30. The secondary battery according to claim 17, wherein, The sulfonyl lactone includes at least one of the following compounds: 。 31. The secondary battery according to claim 17, wherein, The cyclic sulfate ester includes at least one of the following compounds: 。 32. The secondary battery according to claim 30, wherein, The sulfonyl lactone includes at least one of the following compounds: 。 33. The secondary battery according to claim 31, wherein, The cyclic sulfate ester includes at least one of the following compounds: 。 34. The secondary battery according to claim 16 or 17, wherein, Based on the total mass of the non-aqueous electrolyte, the content of the first additive is W3, and 0.01%≤W3≤20%.

35. The secondary battery according to claim 34, wherein, 0.1%≤W3≤10%。 36. The secondary battery according to claim 35, wherein, 0.3%≤W3≤5%。 37. The secondary battery according to claim 16, wherein, The non-aqueous electrolyte further includes a second additive, which comprises one or more of the following groups: sulfite compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, and borate ester compounds.

38. The secondary battery according to claim 37, wherein, Based on the total mass of the non-aqueous electrolyte, the content of the second additive is W4, and 0.01%≤W4≤20%.

39. The secondary battery according to claim 38, wherein, 0.05%≤W4≤5%。 40. The secondary battery according to claim 39, wherein, 0.1%≤W4≤3%。 41. The secondary battery according to claim 1, wherein, Based on the weight of the core, the coating amount of the first coating layer is C1% by weight, where C1 is greater than 0 and less than or equal to 6.

42. The secondary battery according to claim 41, wherein, Based on the weight of the core, C1 is greater than 0 and less than or equal to 5.

5.

43. The secondary battery according to claim 41, wherein, C1 is greater than 0 and less than or equal to 2.

44. The secondary battery according to claim 6, wherein, Based on the weight of the core, the coating amount of the second coating layer is C2% by weight, where C2 is greater than 0 and less than or equal to 6.

45. The secondary battery according to claim 44, wherein, C2 is greater than 0 and less than or equal to 5.

5.

46. ​​The secondary battery according to claim 45, wherein, C2 is 2-4.

47. The secondary battery according to claim 8, wherein, Based on the weight of the core, the coating amount of the third coating layer is C3% by weight, where C3 is greater than 0 and less than or equal to 6.

48. The secondary battery according to claim 47, wherein, C3 is greater than 0 and less than or equal to 5.

5.

49. The secondary battery according to claim 48, wherein, C3 is greater than 0 and less than or equal to 2.

50. The secondary battery according to claim 1, wherein, The interplanar spacing of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the included angle of the crystal orientation (111) ranges from 18.00° to 32.00°.

51. The secondary battery according to claim 6, wherein, The interplanar spacing of the crystalline phosphate in the second coating layer ranges from 0.244 to 0.425 nm, and the included angle of the crystal orientation (111) ranges from 20.00° to 37.00°.

52. The secondary battery according to claim 1, wherein, In the kernel, the ratio of y to 1-y is 1:10 to 1:1; and / or In the kernel, the ratio of z to 1-z is between 1:9 and 1:

999.

53. The secondary battery according to claim 52, wherein, The ratio of y to 1-y is between 1:4 and 1:

1.

54. The secondary battery according to claim 52, wherein, The ratio of z to 1-z is between 1:499 and 1:

249.

55. The secondary battery according to claim 8, wherein, The carbon in the third coating layer is a mixture of SP2 and SP3 carbon.

56. The secondary battery according to claim 55, wherein, The molar ratio of SP2 carbon to SP3 carbon is any value within the range of 0.1-10.

57. The secondary battery according to claim 56, wherein, The molar ratio of SP2 carbon to SP3 carbon is any value within the range of 2.0-3.

0.

58. The secondary battery according to claim 1, wherein, The thickness of the first coating layer is 1-10 nm.

59. The secondary battery according to claim 6, wherein, The thickness of the second coating layer is 2-15 nm.

60. The secondary battery according to claim 8, wherein, The thickness of the third coating layer is 2-25 nm.

61. The secondary battery according to claim 1, wherein, Based on the gravimeter of the positive electrode active material The manganese content ranges from 10% to 35% by weight; The phosphorus content ranges from 12% to 25% by weight.

62. The secondary battery according to claim 61, wherein, The manganese content is in the range of 15%-30% by weight.

63. The secondary battery according to claim 62, wherein, The manganese content is in the range of 17%-20% by weight.

64. The secondary battery according to claim 63, wherein, The phosphorus content is in the range of 15%-20% by weight.

65. The secondary battery according to claim 61, wherein, The weight ratio of manganese to phosphorus ranges from 0.90 to 1.

25.

66. The secondary battery according to claim 65, wherein, The weight ratio of manganese to phosphorus ranges from 0.95 to 1.

20.

67. The secondary battery according to claim 1, wherein, The lattice change rate of the core-shell structured positive electrode active material before and after complete lithium insertion / extraction is less than 4%.

68. The secondary battery according to claim 67, wherein, The lattice change rate of the core-shell structured positive electrode active material before and after complete lithium insertion / extraction is less than 3.8%.

69. The secondary battery according to claim 68, wherein, The lattice change rate of the core-shell structured positive electrode active material before and after complete lithium insertion / extraction is 2.0-3.8%.

70. The secondary battery according to claim 1, wherein, The concentration of Li / Mn antisite defects in the core-shell structured positive electrode active material is below 4%.

71. The secondary battery according to claim 1, wherein, The concentration of Li / Mn antisite defects in the core-shell structured positive electrode active material is below 2.2%.

72. The secondary battery according to claim 70, wherein, The Li / Mn antisite defect concentration of the core-shell structured positive electrode active material is 1.5-2.2%.

73. The secondary battery according to claim 1, wherein, The surface oxygen valence state of the core-shell structured positive electrode active material is -1.90 to -1.

98.

74. A battery module comprising a secondary battery, wherein, The secondary battery is any one of claims 1 to 73.

75. A battery pack comprising a battery module, wherein the battery module is the battery module of claim 74.

76. An electrical device comprising a secondary battery, a battery module, or a battery pack, wherein, The secondary battery is selected from any one of claims 1 to 73, the battery module is the battery module of claim 74, or the battery pack is the battery pack of claim 75.

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