Secondary batteries and battery modules, battery packs and electrical devices containing them.

Abstract

This application provides a secondary battery, as well as a battery module, battery pack, and power consumption device comprising the same. The secondary battery includes a positive electrode and a non-aqueous electrolyte. The positive electrode includes a core-shell structured positive electrode active material, comprising a core and a shell covering the core. The core has the chemical formula Li. 1+x Mn 1‑y A y P 1‑z R z O4, the shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer; the non-aqueous electrolyte includes a first additive, which includes one or more compounds shown in Formula 1. This application enables secondary batteries to simultaneously possess high energy density and good rate performance, cycle performance, storage performance, and safety performance. O=C=N-R1-N=C=O Formula 1.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a secondary battery and a battery module, battery pack and power-consuming device containing the same. Background Technology

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

[0003] The purpose of this application is to provide a secondary battery and a battery module, battery pack and power device containing the same, which aims to enable the secondary battery to have both high energy density and good rate performance, cycle performance, storage performance and safety performance.

[0004] The first aspect of this application provides a secondary battery, including a positive electrode and a non-aqueous electrolyte, wherein...

[0005] 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.

[0006] 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, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be one or more elements selected from Fe, Ti, V, Ni, Co and Mg, R is one or more elements selected from B, Si, N and S, and optionally, R is one element selected from B, Si, N and S;

[0007] The values ​​of x, y, and z satisfy the following condition: keeping the entire kernel electrically neutral;

[0008] The shell includes a first covering layer covering the core, a second covering layer covering the first covering layer, and a third covering layer covering the second covering layer, wherein...

[0009] The first coating layer comprises crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, where the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c Maintaining electrical neutrality, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c Each of the M elements is independently selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0010] The second coating layer comprises crystalline phosphate XPO4, wherein X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0011] The third coating layer is carbon;

[0012] The non-aqueous electrolyte includes a first additive, which includes one or more compounds of Formula 1.

[0013]

[0014] R1 represents R a At least one of the following groups, substituted or unsubstituted: C2-C10 divalent alkyl, C2-C10 divalent heteroalkyl, C6-C18 divalent aryl, C7-C18 divalent arylalkyl, C7-C18 divalent alkylaryl, C8-C18 divalent alkylarylalkyl, C13-C18 divalent arylalkylaryl, C2-C18 divalent heteroaryl, C3-C18 divalent heteroarylalkyl, C3-C18 divalent alkyl heteroaryl, C4-C18 divalent alkyl heteroarylalkyl, C5-C18 divalent heteroarylalkyl heteroaryl, C3-C18 divalent alicyclic, C4-C18 divalent alicyclic alkyl, C4-C18 divalent alkyl alicyclic, C5-C18 divalent alkyl alicyclic alkyl, C7-C18 divalent alicyclic alkyl alicyclic, C2-C18 divalent heteroaryl, C3-C18 divalent heteroaryl alkyl, C3-C18 divalent alkyl heteroaryl, C4-C18 divalent alkyl heteroaryl alkyl and C5-C18 divalent heteroaryl alkyl heteroaryl.

[0015] Optionally, R a It includes one or more selected from halogen atoms, -CN, -NCO, -OH, -COOH, -SOOH, carboxylic acid ester group, sulfonate ester group, sulfate ester group, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C2-C10 oxaalkyl, phenyl, and benzyl.

[0016] After extensive research, the inventors discovered that by doping and modifying lithium manganese phosphate and by multi-layer coating it, a novel core-shell structured positive electrode active material can be obtained. This positive electrode active material can reduce manganese ion dissolution and lattice change rate, thereby improving the rate performance, cycle performance, storage performance, safety performance, and capacity utilization of the secondary battery. When the non-aqueous electrolyte contains the first additive shown in Formula 1, it can react with trace amounts of water in the non-aqueous electrolyte to generate -NHCOOH, reducing HF generation and lowering the acidity of the non-aqueous electrolyte, thereby reducing the dissolution of the coating layer, manganese ion dissolution, and gas generation. Simultaneously, the first additive shown in Formula 1 can also form a uniform and dense interfacial film on the surface of the negative electrode active material, reducing the reduction reaction of dissolved manganese ions at the negative electrode. Therefore, the secondary battery of this application can simultaneously possess high energy density and excellent rate performance, cycle performance, storage performance, and safety performance.

[0017] In any embodiment of this application, R1 represents R a At least one of the following groups, substituted or unsubstituted: C2-C10 alkylene, C2-C10 oxaalkylene, C2-C10 azaalkylene, phenylene, o-phthalimide, m-phthalimide, terephthalimide, monomethylphenylene, dimethylphenylene, trimethylphenylene, tetramethylphenylene, monoethylphenylene, diethylphenylene, triethylphenylene, tetraethylphenylene, diphenylene, terphenylene, tetraphenylene, diphenylene Methyl, cyclobutylene, o-cyclobutyldimethyl, m-cyclobutyldimethyl, p-cyclobutyldimethyl, cyclopentylene, o-cyclopentyldimethyl, m-cyclopentyldimethyl, p-cyclopentyldimethyl, cyclohexylene, monomethylcyclohexylene, dimethylcyclohexylene, trimethylcyclohexylene, tetramethylcyclohexylene, o-cyclohexyldimethyl, m-cyclohexyldimethyl, p-cyclohexyldimethyl, dicyclohexylmethane, methylcyclohexyl, naphthylene, anthraceneylene, and perhydroanthraceneylene. Optionally, R a It includes one or more selected from fluorine atom, -CN, -NCO, -OH, -COOH, -SOOH, carboxylic acid ester group, sulfonate ester group, sulfate ester group, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C2-C10 oxaalkyl, phenyl, benzyl.

[0018] When R1 represents the above-mentioned substituent, it can further reduce the generation of HF and lower the acidity of non-aqueous electrolytes, while also helping to form a uniform, dense, and low-resistance interface film on the surface of the negative electrode active material, thereby further enhancing the improvement effect on the cycle performance and storage performance of secondary batteries.

[0019] In any embodiment of this application, the first additive comprises at least one of the following compounds:

[0020]

[0021]

[0022] During the research process, the inventors discovered that using at least one of the above-mentioned compounds H1 to H38 as a first additive can further reduce the generation of HF and reduce the acidity of non-aqueous electrolytes. At the same time, it helps to form a uniform, dense, and low-resistance interface film on the surface of the negative electrode active material, thereby further enhancing the improvement effect on the cycle performance and storage performance of secondary batteries.

[0023] In any embodiment of this application, the content of the first additive is W1% by weight, where W1 is 0.01 to 20, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte. This significantly improves the cycle performance and storage performance of the secondary battery without affecting its capacity utilization and rate performance.

[0024] In any embodiment of this application, 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, 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, based on the weight of the core.

[0025] In any embodiment of this application, 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, optionally greater than 0 and less than or equal to 5.5, and more preferably 2 to 4, based on the weight of the core.

[0026] In any embodiment of this application, 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, 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, based on the weight of the core.

[0027] 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, cycle performance, storage performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0028] In any embodiment of this application, W1 / (C1+C2+C3) is 0.001 to 2, optionally 0.01 to 1.5, and more preferably 0.05 to 1. This significantly enhances the improvement effect on the cycle performance and storage performance of the secondary battery, while also improving the capacity utilization and rate performance of the secondary battery.

[0029] In any embodiment of this application, the non-aqueous electrolyte further includes a second additive, the second additive comprising ethylene sulfate, lithium difluorophosphate, lithium difluorodioxarate phosphate, and R2[FSO3]. - ] a 、R2[C b F 2b+1 SO3 - ] a One or more of the following, where a represents 1 to 5, b represents an integer from 1 to 6, and R2 represents a metal cation or an organic cation. Optionally, the metal cation includes those selected from Li. + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Cu 2+ Ni 2+ and Ni 3+ One or more of the following. Optionally, the organic cation includes those selected from NH4. + N(CH3)4 + N(CH2CH3)4 + One or more of them.

[0030] When a non-aqueous electrolyte contains both a first additive and a second additive, it helps to significantly improve the cycle performance and storage performance of the secondary battery, while also enhancing the capacity utilization and rate performance of the secondary battery.

[0031] In any embodiment of this application, the content of the second additive is W2% by weight, where W2 is 0.01 to 20, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte. This effectively improves the capacity utilization and rate performance of the secondary battery.

[0032] In any embodiment of this application, the non-aqueous electrolyte further includes a third additive, which comprises one or more of the following: cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonate compounds, nitrile compounds, phosphonitrile compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, acid anhydride compounds, phosphite compounds, phosphate compounds, and borate ester compounds. The third additive helps to form a denser and more stable interfacial film on the surface of the positive and / or negative electrode active materials, thereby contributing to further improvement in at least one of the cycle performance, storage performance, and rate performance of the secondary battery.

[0033] In any embodiment of this application, the content of the third additive is W3% by weight, where W3 is 0.01 to 10, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte.

[0034] In any embodiment of this application, the thickness of the first coating layer is 1-10 nm. This avoids the adverse effects on the material's kinetic properties that may occur when the coating is too thick, and also avoids the problem that it cannot effectively hinder the migration of transition metal ions when the coating is too thin.

[0035] In any embodiment of this application, the thickness of the second coating layer is 2-15 nm. In this case, the surface structure of the second coating layer is stable, and the side reactions with the electrolyte are minimal. Therefore, it can effectively reduce interfacial side reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0036] In any embodiment of this application, the thickness of the third coating layer is 2-25 nm. This can improve the conductivity of the positive electrode active material and increase the compaction density of the positive electrode sheet prepared using the positive electrode active material.

[0037] In any embodiment of this application, in the core, the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1. This further improves the cycle performance and rate performance of the secondary battery.

[0038] In any embodiment of this application, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. This further improves the cycle performance and rate performance of the secondary battery.

[0039] In any embodiment of this application, 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°.

[0040] In any embodiment of this application, 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°.

[0041] Crystalline pyrophosphate and crystalline phosphate within the aforementioned interplanar spacing and angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during lithium insertion / extraction, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0042] In any embodiment of this application, the carbon in the third coating layer is a mixture of SP2 and SP3 carbon. Optionally, the molar ratio of SP2 to SP3 carbon is any value within the range of 0.1-10, and optionally any value within the range of 2.0-3.0. By limiting the molar ratio of SP2 to SP3 carbon to the above range, this application improves the overall performance of the secondary battery.

[0043] In any embodiment of this application, based on the weight of the positive electrode active material, the manganese content is in the range of 10 wt% to 35 wt%, preferably in the range of 15 wt% to 30 wt%, and more preferably in the range of 17 wt% to 20 wt%. This effectively avoids problems such as decreased structural stability and reduced density of the positive electrode active material that may be caused by excessive manganese content, thereby improving the cycle life, storage, and compaction density performance of the secondary battery; and it also avoids problems such as a low voltage plateau that may be caused by insufficient manganese content, thereby improving the energy density of the secondary battery.

[0044] In any embodiment of this application, based on the weight of the positive electrode active material, the phosphorus content is in the range of 12%-25% by weight, and optionally in the range of 15%-20% by weight. This effectively avoids the following situations: if the phosphorus content is too high, it may lead to excessive covalentity of PO, affecting the conductivity of small polarons, thereby affecting the conductivity of the positive electrode active material; if the phosphorus content is too low, it may reduce the stability of the pyrophosphate lattice structure in the core, the first coating layer, and / or the phosphate lattice structure in the second coating layer, thereby affecting the overall stability of the positive electrode active material.

[0045] In any embodiment of this application, based on the weight of the positive electrode active material, the weight ratio of manganese to phosphorus ranges from 0.90 to 1.25, and can be optionally 0.95 to 1.20. This effectively avoids the following situations: if the weight ratio is too high, it may lead to increased manganese ion dissolution, affecting the stability of the positive electrode active material and the cycle performance and storage performance of the secondary battery; if the weight ratio is too low, it may cause a decrease in the discharge voltage plateau of the positive electrode active material, thereby reducing the energy density of the secondary battery.

[0046] In any embodiment of this application, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is less than 4%, preferably less than 3.8%, and more preferably 2.0-3.8%. In this case, the positive electrode active material can improve the capacity utilization and rate performance of the secondary battery.

[0047] In any embodiment of this application, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%. By keeping the Li / Mn antisite defect concentration within the above range, Mn... 2+ Hinder Li + This improves the transmission efficiency and enhances the capacity utilization and rate performance of the positive electrode active material.

[0048] In any embodiment of this application, the compaction density of the positive electrode active material at 3T is 2.2 g / cm³. 3 The above can be selected as 2.2g / cm. 3 Above and 2.8g / cm 3 The following is a summary. Therefore, this is beneficial for improving the volumetric energy density of secondary batteries.

[0049] In any embodiment of this application, the surface oxygen valence state of the positive electrode active material is below -1.90, and can be selected as -1.90 to -1.98. Therefore, by limiting the surface oxygen valence state of the positive electrode active material to the above range as described above, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0050] A second aspect of this application provides a battery module that includes the secondary battery of the first aspect of this application.

[0051] A third aspect of this application provides a battery pack that includes the battery module of the second aspect of this application.

[0052] The fourth aspect of this application provides an electrical device that includes at least one selected from the secondary battery of the first aspect of this application, the battery module of the second aspect of this application, or the battery pack of the third aspect of this application.

[0053] The battery module, battery pack, and power device of this application include the secondary battery of this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0056] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0057] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0058] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0059] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0060] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0061] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0062] 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 included herein. 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.

[0063] 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.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0066] 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.

[0067] 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.

[0068] 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).

[0069] It should be noted that, in this document, the term "coating layer" refers to a material layer coating the lithium manganese phosphate core. This material layer may completely or partially coat the lithium manganese phosphate core. The use of "coating layer" is for ease of description only and is not intended to limit the invention. Furthermore, each coating layer may be a complete or partial coating. Similarly, the term "coating layer thickness" refers to the thickness of the material layer coating the lithium manganese phosphate core in the radial direction of the lithium manganese phosphate core.

[0070] In this document, the median particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. In this application, the median particle size Dv50 of the material can be determined using laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvem Master Size 3000) in accordance with standard GB / T19077-2016.

[0071] In this article, “about” refers to a range of values, specifically the range of ±10% of that value.

[0072] In this article, the terms "multiple" or "various" refer to two or more kinds.

[0073] In this paper, heteroatoms may include N, O, S, Si, etc.

[0074] In this document, the term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched structures. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, isopropyl), butyl (e.g., n-butyl, isobutyl, sec-butyl, tert-butyl), and pentyl (e.g., n-pentyl, isopentyl, neopentyl).

[0075] In this document, the term "heteroalkyl" refers to a group obtained by substituting at least one carbon atom of an alkyl group with a heteroatom. For example, an oxaalkyl group is a group obtained by substituting at least one carbon atom of an alkyl group with an oxygen atom. The number of heteroatoms in a heteroalkyl group can be one or more, and the multiple heteroatoms can be the same or different.

[0076] In this document, the term "alkenyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon double bond, including both straight-chain and branched structures, and the number of carbon-carbon double bonds can be one or more. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, allyl, and butadiene.

[0077] In this document, the term "alkynyl" refers to an unsaturated hydrocarbon group containing a carbon-carbon triple bond, including both straight-chain and branched structures, and may contain one or more carbon-carbon triple bonds. Examples of alkynyl groups include, but are not limited to, ethynyl, propynyl, butynyl, and butadiynyl.

[0078] In this document, the term "aryl" refers to a closed aromatic ring or ring system. Unless otherwise specified, the "aryl" structure can be monocyclic, polycyclic, or fused-ring. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthraceneyl, phenanthryl, diphenyl, triphenyl, tetraphenyl, triphenylene, pyrene, etc. alkyl, peryl, indene, benzo[phenanthrene], fluorenyl, 9,9-dimethylfluorenyl, spirodifluorenyl.

[0079] In this document, the term "heteroaryl" refers to an aryl group in which one or more atoms in the ring are elements other than carbon (such as N, O, S, Si, etc.). Examples of heteroaryl groups include, but are not limited to, pyrroleyl, furanyl, thiopheneyl, indolyl, benzofuranyl, benzothiopheneyl, dibenzofuran, dibenzothiophene, carbazoyl, indobenzocarbazoyl, indolocarbazoyl, pyridyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazinyl, oxazolyl, isoxazolyl, thiazoyl, and isothiazolyl. The number of heteroatoms in a heteroaryl group can be one or more, and the heteroatoms can be the same or different.

[0080] The term "alicyclic group" refers to a carbocyclic system with aliphatic properties, including cyclized alkyl, alkenyl, and alkynyl groups, whose structure can be monocyclic or polycyclic (such as fused rings, bridged rings, and spirocyclic rings). Examples of alicyclic groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopentenyl, cyclohexenyl, and cyclohexynyl.

[0081] The term "heterocyclic alicyclic group" refers to an alicyclic group in which one or more atoms are elements other than carbon (such as N, O, S, Si, etc.). The number of heteroatoms in a heterocyclic alicyclic group can be one or more, and these heteroatoms can be the same or different. Examples of heterocyclic alicyclic groups include, but are not limited to, ethylene oxide, aziridine propane, and proprolactone.

[0082] In this article, when each substituent is "divalent" or "analytical", it refers to a group formed by removing two H atoms from the molecule.

[0083] In this document, when a substituent represents a group consisting of certain groups, it includes groups formed by these groups bonded together by single bonds. For example, when a substituent represents "at least one of the groups consisting of C2-C10 divalent alkyl and C6-C18 divalent aryl", the substituent alone discloses a C2-C10 divalent alkyl, a C6-C18 divalent aryl, an alkylaryl or arylalkyl or alkylarylalkyl or arylalkylaryl formed by a single bond between a C2-C10 divalent alkyl and a C6-C18 divalent aryl.

[0084] Throughout this specification, substituents of compounds are disclosed by groups or ranges. It is expressly intended that such descriptions include each individual sub-combination of members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 alkyl" individually discloses C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6 alkyl.

[0085] The inventors of this application discovered in practical operation that existing lithium manganese phosphate cathode active materials suffer from significant manganese ion dissolution during deep charge-discharge processes. Although existing technologies have attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the dissolved manganese ions from migrating further into the non-aqueous electrolyte. After migrating to the negative electrode, the dissolved manganese ions are reduced to metallic manganese. This metallic manganese acts as a "catalyst," catalyzing the decomposition of the SEI film (solid electrolyte interphase) on the negative electrode surface, producing byproducts. Part of these byproducts is gaseous, causing expansion of the secondary battery and affecting its safety performance. Additionally, another portion of these byproducts deposits on the negative electrode surface, obstructing the channels for lithium ions to enter and exit the negative electrode, increasing the battery impedance and affecting its kinetic performance. Furthermore, to replenish the lost SEI film, the non-aqueous electrolyte and the active lithium ions inside the battery are continuously consumed, irreversibly impacting the battery's capacity retention rate.

[0086] After careful consideration, the inventors designed a secondary battery based on the positive electrode and non-aqueous electrolyte. This secondary battery can simultaneously possess high energy density, good rate performance, cycle performance, storage performance, and safety performance.

[0087] Specifically, the first aspect of this application provides a secondary battery.

[0088] Secondary batteries

[0089] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery includes an electrode assembly and a non-aqueous electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing lithium ions to pass through. The non-aqueous electrolyte, located between the positive and negative electrodes, conducts lithium ions.

[0090] [Positive electrode plate]

[0091] The positive electrode used in the secondary battery of this application includes at least a positive electrode active material with a core-shell structure, wherein the positive electrode active material includes a core and a shell covering the core.

[0092] 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, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and may be one or more elements selected from Fe, Ti, V, Ni, Co, and Mg, R is one or more elements selected from B, Si, N, and S, and optionally, R is 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.

[0093] The shell includes a first coating layer covering the core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer. The first coating layer includes crystalline pyrophosphate Li. a MP2O7 and / or M b (P2O7) c 0≤a≤2, 1≤b≤4, 1≤c≤6, where the values ​​of a, b, and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c Maintaining electrical neutrality, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) cEach of the elements M is independently selected from one or more elements chosen from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al. The second coating layer comprises crystalline phosphate XPO4, where X is selected from one or more elements chosen from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al. The third coating layer is carbon.

[0094] Unless otherwise stated, in the above-described core chemical formula, when A comprises two or more elements, the limitation on the numerical range of y applies not only to the stoichiometric coefficient of each element as A, but also to the sum of the stoichiometric coefficients of all elements as A. For example, when A comprises two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the numerical range of y defined in this application, and the sum of y1, y2...yn must also fall within this numerical range. Similarly, for the case where R comprises two or more elements, the limitation on the numerical range of the stoichiometric coefficient of R in this application has the same meaning.

[0095] In an optional implementation, when A is one, two, three, or four elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, A y For Q n1 D n2 E n3 K n4 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 R z In O4, it is advantageous to dope one, two, three or four of the aforementioned A elements at the manganese sites, and optionally, one, two or three of the aforementioned A elements are doped. In addition, it is advantageous to dope one or two R elements at the phosphorus sites, which is beneficial to make the doped elements uniformly distributed.

[0096] The kernel Li 1+x Mn 1-y Ay P 1-z R z In O4, the value of x is influenced by the valence states of A and R, as well as the values ​​of y and z, to ensure the overall system remains electrically neutral. If the value of x is too small, the lithium content of the entire core system will decrease, affecting the capacity of the positive electrode active material. The value of y limits the total amount of all dopants. If y is too small, i.e., the doping amount is too low, the dopants will not play a role. If y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. The R element is doped at the P position. Since the PO tetrahedron is relatively stable, and a large z value would affect the stability of the material, the z value is limited to 0.001 to 0.100.

[0097] After extensive research, the inventors discovered that by doping and modifying lithium manganese phosphate and by multi-layer coating it, a novel positive electrode active material with a core-shell structure can be obtained. This positive electrode active material can reduce manganese ion dissolution and reduce lattice change rate, thereby improving the rate performance, cycle performance, storage performance, safety performance, and capacity utilization of secondary batteries.

[0098] Although the mechanism is not yet clear, it is speculated that: by doping the manganese and phosphorus sites of the lithium manganese phosphate core with elements A and R respectively, not only can manganese ion dissolution be effectively reduced, thereby reducing the number of manganese ions migrating to the negative electrode and reducing the consumption of non-aqueous electrolyte due to SEI film decomposition, thus improving the cycle performance and safety of the secondary battery, but it can 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 ions can be further increased. By reducing its dissolution, surface lithium content, and contact between the core and non-aqueous electrolyte, interfacial side reactions and gas generation are reduced, thereby improving the cycle performance, storage performance, and safety performance of the secondary battery. Further coating with a crystalline phosphate coating layer with excellent lithium-ion conductivity can effectively reduce interfacial side reactions between the positive electrode active material and the non-aqueous electrolyte, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. Further coating with a carbon layer as a third coating layer can further enhance the safety and kinetic performance of the secondary battery.

[0099] Furthermore, in the core, the element A doped at the manganese site of lithium manganese phosphate helps to reduce the lattice change rate of lithium manganese phosphate during the lithium insertion / extraction process, improves the structural stability of the lithium manganese phosphate cathode active material, greatly reduces the dissolution of manganese ions and reduces the oxygen activity on the particle surface; the element R doped at the phosphorus site also helps to change the ease of Mn-O bond length change, thereby improving electronic conductivity and reducing the lithium ion migration barrier, promoting lithium ion migration and improving the rate performance of the secondary battery.

[0100] Furthermore, maintaining the electrical neutrality of the entire core system ensures that defects and impurities in the cathode active material are minimized. If an excess of transition metal (such as manganese) exists in the cathode active material, due to the relatively stable structure of the material system itself, the excess transition metal is likely to precipitate as elemental or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. Additionally, ensuring system electrical neutrality can, in some cases, generate lithium vacancies in the cathode active material, thereby improving its kinetic performance.

[0101] The cores prepared in this application have an average particle size range of 50-500 nm and a median particle size Dv50 of 200-300 nm. The primary particle size of the cores is also within the range of 50-500 nm, with a median particle size Dv50 of 200-300 nm. If the average particle size of the cores is too large (exceeding 500 nm), the capacity of the secondary battery using this material will be affected; if the average particle size of the cores is too small, its specific surface area is large, making it prone to aggregation and difficult to achieve uniform coating.

[0102] By controlling the process (e.g., thoroughly mixing and grinding materials from various sources), it is possible to ensure that each element is uniformly distributed in the crystal lattice and that no aggregation occurs. The main characteristic peak positions in the X-ray diffraction (XRD) pattern of lithium manganese phosphate doped with elements A and R are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in the core performance mainly comes from elemental doping, rather than impurity phases. After preparing the cathode active material described in this application, the inventors used focused ion beam (FIB) to cut the middle region (core region) of the prepared cathode active material particles. Tests conducted using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0103] In this application, "crystalline" refers to a crystallinity of 50% or higher, i.e., 50% to 100%. Crystallinity less than 50% is referred to as glassy (or amorphous). The crystallinity of the crystalline pyrophosphate and crystalline phosphate described in this application is 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity not only fully utilize the pyrophosphate coating's ability to inhibit manganese ion dissolution and the phosphate coating's excellent lithium ion conduction capabilities, reducing interfacial side reactions, but also enable better lattice matching between the pyrophosphate and phosphate coatings, thus achieving a tighter bond between the coatings.

[0104] In this application, the crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the positive electrode active material can be tested by conventional technical means in the art, such as by density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption method, or by, for example, X-ray diffraction.

[0105] A specific X-ray diffraction method for testing the crystallinity of the first coating layer crystalline pyrophosphate and the second coating layer crystalline phosphate of the positive electrode active material may include the following steps: Take a certain amount of positive electrode active material powder, and measure the total scattering intensity by X-rays. This is the sum of the scattering intensities of all matter in space, and is only related to the intensity of the primary rays, the chemical structure of the positive electrode active material powder, and the total number and mass of electrons participating in the diffraction, but is independent of the order state of the sample; then separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0106] 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.

[0107] 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 non-aqueous electrolyte. Crystalline pyrophosphate has a stable structure; therefore, coating with crystalline pyrophosphate can effectively reduce the dissolution of transition metal ions and improve the cycle performance of the secondary battery.

[0108] The bonding between the first coating layer and the core is similar to that of a heterojunction, and the strength of this bonding is limited by the degree of lattice matching. When the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly. A tight bonding ensures that the coating layer will not detach during subsequent cycling, which is beneficial for ensuring the long-term stability of the cathode active material. The degree of bonding between the first coating layer and the core is mainly measured by calculating the mismatch between the lattice constants of the core and the coating. In this application, after doping the core with A and R elements, compared with undoped elements, the matching degree between the core and the first coating layer is improved, and the core and the pyrophosphate coating layer can bond more tightly.

[0109] Crystalline phosphate was chosen as the second coating layer primarily because of its high lattice matching (mismatch of only 3%) with the first coating layer, crystalline pyrophosphate. Secondly, phosphate itself is more stable than pyrophosphate, and coating pyrophosphate with phosphate helps improve the stability of the positive electrode active material. Crystalline phosphate has a very stable structure and excellent lithium-ion conductivity; therefore, using crystalline phosphate for coating can effectively reduce interfacial side reactions between the positive electrode active material and the non-aqueous electrolyte, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery. The lattice matching between the second and first coating layers is similar to the bonding between the first coating layer and the core; when the lattice mismatch is below 5%, the lattice matching is good, and the two easily bond tightly.

[0110] The main reason for using carbon as the third coating layer is its excellent electronic conductivity. Since electrochemical reactions occur in secondary batteries, requiring electrons, carbon, with its superior conductivity, can be used to coat the positive electrode active material to increase electron transport between particles and between different locations on the particles. Carbon coating effectively improves the conductivity and desolvation capability of the positive electrode active material.

[0111] In some embodiments, the average particle size of the primary particles of the positive electrode active material ranges from 50 to 500 nm, with a median particle size (Dv50) in the range of 200 to 300 nm. Due to particle agglomeration, the actual measured size of the agglomerated secondary particles may be 500 to 40000 nm. The size of the positive electrode active material particles affects the material processing and the compaction density performance of the electrode sheet. By selecting an average particle size of the primary particles within the above range, the following situations can be avoided: if the average particle size of the primary particles of the positive electrode active material is too small, it may cause particle agglomeration, making dispersion difficult and requiring more binder, resulting in poor electrode sheet brittleness; if the average particle size of the primary particles of the positive electrode active material is too large, it may result in larger gaps between particles, reducing the compaction density.

[0112] The above scheme can effectively reduce the lattice change rate of lithium manganese phosphate and the amount of manganese ion dissolution during the lithium insertion / extraction process, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0113] In some embodiments, 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°; 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°.

[0114] The first and second coating layers of the positive electrode active material described in this application both use crystalline materials. The crystalline pyrophosphate and crystalline phosphate in the coating layers can be characterized using conventional techniques in the art, or for example, by transmission electron microscopy (TEM). Under TEM, the core and coating layers can be distinguished by measuring the interplanar spacing.

[0115] The specific testing method for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer can include the following steps: Take a certain amount of the coated positive electrode active material sample powder into a test tube, inject a solvent such as alcohol into the test tube, and then stir and disperse it thoroughly. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM sample chamber for testing to obtain the original TEM image. Open the original image obtained from the above TEM test in the diffractometer software, and perform Fourier transform to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The angle can be calculated according to the Bragg equation.

[0116] 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.

[0117] Crystalline pyrophosphate and crystalline phosphate within the aforementioned interplanar spacing and angle range can more effectively reduce the lattice change rate and manganese ion dissolution of lithium manganese phosphate during lithium insertion / extraction, thereby improving the high-temperature cycle performance and high-temperature storage performance of secondary batteries.

[0118] In some embodiments, the ratio of y to 1-y in the core is 1:10 to 1:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements A. When the above conditions are met, the energy density and cycle performance of the secondary battery using the positive electrode active material can be further improved.

[0119] In some embodiments, the ratio of z to 1-z in the core is from 1:9 to 1:999, optionally from 1:499 to 1:249. Here, z represents the sum of the stoichiometric coefficients of the p-site doping elements R. When the above conditions are met, the energy density and cycle performance of the secondary battery using the positive electrode active material can be further improved.

[0120] In some embodiments, the carbon in the third coating layer is a mixture of SP2 carbon and SP3 carbon. Optionally, the molar ratio of SP2 carbon to SP3 carbon is any value in the range of 0.1-10, and can be any value in the range of 2.0-3.0.

[0121] 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.

[0122] By selecting the morphology of carbon in the carbon coating layer, the overall electrochemical performance of the secondary battery can be improved. Specifically, by using a mixture of SP2 and SP3 carbon morphologies and limiting the ratio of SP2 to SP3 carbon within a certain range, the following situations can be avoided: if the carbon in the coating layer is all amorphous SP3, the conductivity is poor; if it is all graphitized SP2, although the conductivity is good, there are few lithium-ion pathways, which is not conducive to lithium-ion insertion and extraction. In addition, limiting the molar ratio of SP2 to SP3 carbon within the above-mentioned range can achieve both good conductivity and ensure lithium-ion pathways, thus improving the kinetic and cycle performance of the secondary battery.

[0123] 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.

[0124] 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, Id / Ig (where Id is the peak intensity of SP3 carbon and Ig is the peak intensity of SP2 carbon) is obtained, thereby confirming the molar ratio of the two.

[0125] In some embodiments, 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, 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, based on the weight of the core.

[0126] In some embodiments, 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, optionally greater than 0 and less than or equal to 5.5, and more preferably 2 to 4, based on the weight of the core.

[0127] In some embodiments, 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, 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, based on the weight of the core.

[0128] In this application, the coverage of each layer is not zero.

[0129] In the core-shell structured positive electrode active material described in this application, the coating amount of the three coating layers is preferably within the above-mentioned range, thereby enabling sufficient coating of the core and further improving the kinetic performance, cycle performance, storage performance and safety performance of the secondary battery without sacrificing the specific capacity of the positive electrode active material.

[0130] 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 the coating layer is too thin, which may not effectively hinder the migration of transition metals; too much coating amount means the coating layer is too thick, which may affect Li + The migration of these molecules affects the rate performance of the secondary battery.

[0131] 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 positive electrode active material; too little coating amount may not achieve sufficient coating effect.

[0132] 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.

[0133] In some embodiments, the thickness of the first coating layer is 1-10 nm.

[0134] In some embodiments, the thickness of the second coating layer is 2-15 nm.

[0135] In some embodiments, the thickness of the third coating layer is 2-25 nm.

[0136] In some embodiments, the thickness of the first coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or any range of the above values.

[0137] In some embodiments, the thickness of the second coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or any range of the above values.

[0138] 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.

[0139] When the thickness of the first coating layer is in the range of 1-10 nm, it can avoid the adverse effects on the kinetic performance of the positive electrode active material that may occur when it is too thick, and it can also avoid the problem that it may not be able to effectively hinder the migration of transition metal ions when it is too thin.

[0140] When the thickness of the second coating layer is in the range of 2-15nm, the surface structure of the second coating layer is stable and the side reactions with non-aqueous electrolytes are small. Therefore, it can effectively reduce interfacial side reactions, thereby improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0141] When the thickness of the third coating layer is in the range of 2-25 nm, it can improve the conductivity of the positive electrode active material and increase the compaction density of the positive electrode sheet prepared using the positive electrode active material.

[0142] 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.

[0143] In some embodiments, based on the weight of the positive electrode active material, the manganese content is in the range of 10 wt% to 35 wt%, preferably in the range of 15 wt% to 30 wt%, and more preferably in the range of 17 wt% to 20 wt%.

[0144] In some embodiments, the phosphorus content, based on the weight of the positive electrode active material, is in the range of 12%-25% by weight, and optionally in the range of 15%-20% by weight.

[0145] In some embodiments, the weight ratio of manganese to phosphorus ranges from 0.90 to 1.25, and may be 0.95 to 1.20.

[0146] 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.

[0147] In this application, limiting the content of manganese element within the above-mentioned range can effectively avoid problems such as poor structural stability and decreased density of the positive electrode active material that may be caused by excessive manganese element content, thereby improving the cycle, storage and compaction density performance of the secondary battery; and can also avoid problems such as low voltage platform that may be caused by excessive manganese element content, thereby improving the energy density of the secondary battery.

[0148] In this application, limiting the phosphorus content within the aforementioned range effectively avoids the following situations: if the phosphorus content is too high, it may lead to excessive covalentity of PO, affecting the conductivity of small polarons and thus affecting the conductivity of the positive electrode active material; if the phosphorus content is too low, it may reduce the stability of the pyrophosphate lattice structure in the core, the first coating layer, and / or the phosphate lattice structure in the second coating layer, thereby affecting the overall stability of the positive electrode active material.

[0149] The weight ratio of manganese to phosphorus has the following effects on the performance of secondary batteries: If the weight ratio is too high, it means that there is too much manganese, which increases the dissolution of manganese ions, affecting the stability and capacity of the positive electrode active material, and thus affecting the cycle performance and storage performance of the secondary battery; if the weight ratio is too low, it means that there is too much phosphorus, which is prone to forming impurities, which will cause the discharge voltage plateau of the positive electrode active material to drop, thereby reducing the energy density of the secondary battery.

[0150] 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.

[0151] 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%.

[0152] The lithium intercalation / deintercalation process of lithium manganese phosphate (LiMnPO4) is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change before and after lithium intercalation / deintercalation; the smaller the rate of lattice change, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. +The core-shell structured cathode active material described in this application achieves a lattice change rate of less than 4% before and after lithium insertion / extraction, thus improving the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD) patterns.

[0153] In some embodiments, the Li / Mn antisite defect concentration of the core-shell structured positive electrode active material is less than 4%, optionally less than 2.2%, and more preferably 1.5-2.2%.

[0154] The Li / Mn inversion defect described 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.

[0155] The core-shell structured positive electrode active material described in this application can achieve the aforementioned low Li / Mn antisite defect concentration. Although the mechanism is not yet fully understood, the inventors of this application speculate that due to the presence of Li in the LiMnPO4 lattice... + With Mn 2+ The positions will be swapped, and Li + The transmission channel is a one-dimensional channel, therefore Mn 2+ In Li + Migration will be difficult within the channel, thus hindering Li + Therefore, the core-shell structured positive electrode active material described in this application, due to its low Li / Mn antisite defect concentration within the aforementioned range, can avoid Mn transport. 2+ Hinder Li + This improves the transmission efficiency and enhances the capacity utilization and rate performance of the positive electrode active material.

[0156] In some embodiments, the core-shell structured positive electrode active material has a compaction density of 2.2 g / cm³ at 3 tons. 3 The above is an option, specifically 2.2 g / cm³. 3 Above and 2.8g / cm 3 The higher the compaction density, the greater the weight of the positive electrode active material per unit volume. Therefore, increasing the compaction density is beneficial for improving the volumetric energy density of secondary batteries. Compaction density can be measured according to GB / T 24533-2009.

[0157] In some embodiments, the surface oxygen valence state of the core-shell structured positive electrode active material is below -1.90, and can be selected as -1.90 to -1.98.

[0158] 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. This application, by limiting the surface oxygen valence state of the positive electrode active material to the above-mentioned range as described above, can reduce the interfacial side reactions between the positive electrode active material and the non-aqueous electrolyte, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0159] The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0160] This application also provides a method for preparing a positive electrode active material, which includes the following steps of providing a core material and a coating step.

[0161] 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, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be one or more elements selected from Fe, Ti, V, Ni, Co and Mg, R is one or more elements selected from B, Si, N and S, and optionally, R is one element selected from B, Si, N and S.

[0162] Coating steps: Provide Li separately a MP2O7 and / or M b (P2O7) 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, 0≤a≤2, 1≤b≤4, 1≤c≤6, wherein the values ​​of a, b and c satisfy the following condition: making crystalline pyrophosphate Li a MP2O7 or M b (P2O7) cMaintaining electrical neutrality; each of M is independently selected from one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; each of X is selected from one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al. The positive electrode active material has a core-shell structure, comprising the 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 Li. a MP2O7 and / or M b (P2O7) c The second coating layer comprises crystalline phosphate XPO4, and the third coating layer is carbon.

[0163] In some implementations, the step of providing the core material includes steps (1) and (2).

[0164] 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.

[0165] 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, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be one or more elements selected from Fe, Ti, V, Ni, Co and Mg, R is one or more elements selected from B, Si, N and S, and optionally, R is one element selected from B, Si, N and S.

[0166] 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.

[0167] Optionally, the dopant of element A is one or more elements selected from the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

[0168] Optionally, the dopant of element R is one or more of the inorganic acids, flavonoids, organic acids, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements selected from B, Si, N, and S.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] In some embodiments, after the manganese source, the dopant of element A and the acid are reacted in a solvent to obtain a suspension of manganese salt doped with element A, the suspension is filtered, dried and sand-milled to obtain manganese salt particles doped with element A with a particle size of 50-200 nm.

[0174] In some embodiments, the slurry in step (2) is dried to obtain powder, and then the powder is sintered to obtain a core doped with element A and element R.

[0175] In some embodiments, step (1) is performed at a temperature of 20-120°C, optionally 40-120°C. The stirring in step (1) is carried out at 400-700 rpm for 1-9 hours, optionally 3-7 hours.

[0176] 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.

[0177] 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) can be 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.

[0178] 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 helps to reduce manganese ion dissolution and reduce interfacial side reactions between the positive electrode active material and the non-aqueous electrolyte, thereby improving the cycle performance and safety performance of the secondary battery.

[0179] In some embodiments, optionally, during the preparation of lithium manganese phosphate particles doped with elements A and R, the solution pH is controlled to be 3.5-6; alternatively, the solution pH is controlled to be 4-6; and more preferably, the solution pH 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.

[0180] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles doped with element A to the lithium source and the phosphorus source is 1:(0.5-2.1):(0.5-2.1), and more preferably, the molar ratio of the manganese salt particles doped with element A to the lithium source and the phosphorus source is about 1:1:1.

[0181] 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 under an inert gas or a mixture of inert gas and hydrogen atmosphere; optionally, the sintering can be carried out at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C, or about 900°C for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values. In the preparation of lithium manganese phosphate doped with elements A and R, if the sintering temperature is too low or the sintering time is too short, the crystallinity of the cathode active material core will be low, which will affect the overall performance. If the sintering temperature is too high, impurity phases are likely to appear in the cathode active material core, which will also affect the overall performance. If the sintering time is too long, the cathode active material core particles will be too large, which will affect the capacity, compaction density and rate performance.

[0182] Optionally, the protective atmosphere is a mixture of 70-90% by volume nitrogen and 10-30% by volume hydrogen.

[0183] In some embodiments, the coating step includes a first coating step, a second coating step, and a third coating step.

[0184] First coating step: Dissolve the source of element M, phosphorus source, acid, and optionally lithium source in a solvent to obtain a first coating layer suspension; thoroughly mix the core obtained in the core material provision step with the first coating layer suspension obtained in the first coating step, dry, and then sinter to obtain the material coated by the first coating layer.

[0185] 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.

[0186] 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.

[0187] As an example, the source of element M is one or more of the following: elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0188] As an example, the source of element X is one or more of the elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, including their elemental form, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

[0189] 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.

[0190] As an example, the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0191] In some embodiments, during the first coating step, the pH of the solution containing the dissolved source of element M, phosphorus source, acid, and optionally lithium source is controlled to be 3.5-6.5, then stirred and reacted for 1-5 hours, and then the solution is heated to 50-120°C and maintained at that temperature for 2-10 hours. In some embodiments, during the first coating step, sintering is carried out at 650-800°C for 2-6 hours.

[0192] 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.

[0193] Optionally, in the first coating step, the solution pH is controlled to be 4-6.

[0194] Optionally, in the first coating step, the solution is heated to about 55°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, or about 120°C, and held at that temperature 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, in the first coating step, the temperature and holding time can be within any range of the above values.

[0195] 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.

[0196] In the first coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: When the sintering temperature in the first coating step is too low and the sintering time is too short, the crystallinity of the first coating layer will be low and there will be more amorphous substances, which will reduce the effect of reducing 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 reducing 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 Li + The migration of these molecules can affect the capacity utilization and rate performance of secondary batteries.

[0197] In some embodiments, in the second coating step, the source of element X, the phosphorus source, and the acid are dissolved in a solvent, stirred, and reacted for 1-10 hours. The solution is then heated to 60-150°C and maintained at that temperature for 2-10 hours. In some embodiments, in the second coating step, sintering is performed at 500-700°C for 6-10 hours.

[0198] 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.

[0199] 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.

[0200] 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.

[0201] 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.

[0202] In the second coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: When the sintering temperature in the second coating step is too low and the sintering time is too short, the crystallinity of the second coating layer will be low, with more amorphous states, reducing the performance of the positive electrode active material's surface reactivity, 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 second coating layer, which will also affect its effect on reducing the surface reactivity of the positive electrode active material, 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 second coating layer will increase, affecting the voltage plateau of the positive electrode active material, thereby reducing the energy density of the secondary battery.

[0203] 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.

[0204] In the third coating step, by controlling the sintering temperature and time within the above range, the following situations can be effectively avoided: when the sintering temperature in the third coating step is too low, the graphitization degree of the third coating layer will decrease, affecting its conductivity and thus affecting the capacity performance of the positive electrode active material; when the sintering temperature is too high, the graphitization degree of the third coating layer will be too high, affecting the Li + The transmission of the cathode material can affect its capacity utilization, etc.; if the sintering time is too short, the coating layer will be too thin, affecting its conductivity and thus affecting the capacity utilization of the cathode material; if the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the cathode material, etc.

[0205] In the first, second, and third coating steps described above, the drying can be carried out at a drying temperature of 100°C to 200°C, optionally 110°C to 190°C, more preferably 120°C to 180°C, even more preferably 120°C to 170°C, and most preferably 120°C to 160°C. The drying time can be 3-9 hours, optionally 4-8 hours, more preferably 5-7 hours, and most preferably about 6 hours.

[0206] The positive electrode active material prepared by the method described in this application results in a reduced dissolution of Mn and Mn-site dopant elements in the secondary battery after cycling, and improved high-temperature storage performance, cycle performance, and rate performance. Furthermore, the raw materials are widely available, inexpensive, and the process is simple, facilitating industrialization.

[0207] The positive electrode sheet of this application may include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. Specifically, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector. The positive electrode film layer includes the positive electrode active material described in this application.

[0208] In some embodiments, optionally, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer. More optionally, the content of the positive electrode active material in the positive electrode film layer is 95-99.5% by weight, based on the total weight of the positive electrode film layer.

[0209] The positive electrode film layer does not exclude other positive electrode active materials besides the core-shell structure positive electrode active materials provided in this application. For example, in some embodiments, the positive electrode film layer may also include at least one of layered lithium transition metal oxides and their modified compounds. As an example, the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0210] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0211] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode 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 resins.

[0212] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0213] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0214] [Negative electrode plate]

[0215] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0216] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0217] In some embodiments, the negative electrode film may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0218] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0219] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0220] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0221] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0222] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0223] [Isolation membrane]

[0224] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0225] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0226] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0227] [Non-aqueous electrolyte]

[0228] Secondary batteries include non-aqueous electrolytes, which act as a bridge for lithium ions to pass through. They play a crucial role in transporting lithium ions between the positive and negative electrodes, and are essential for the capacity, cycle performance, storage performance, rate performance, and safety performance of secondary batteries.

[0229] Currently, the most widely used commercial non-aqueous electrolyte system is a mixed carbonate solution of lithium hexafluorophosphate. However, lithium hexafluorophosphate has poor thermal stability at high temperatures, and it decomposes to form PF5 at higher temperatures. PF5 has strong Lewis acidity and can interact with the lone pair electrons on the oxygen atoms in organic solvent molecules, causing the organic solvent to decompose. In addition, PF5 is highly sensitive to trace amounts of water in the non-aqueous electrolyte, and will generate HF upon contact with water, thereby increasing the acidity of the non-aqueous electrolyte. This can easily damage the coating layer on the surface of the positive electrode active material, especially the first coating layer containing crystalline pyrophosphate and the second coating layer containing crystalline phosphate, accelerating the dissolution of manganese ions and affecting the cycle performance and storage performance of the secondary battery.

[0230] The inventors conducted further research and ingeniously added a first additive, as shown in Formula 1, to the non-aqueous electrolyte. This additive can reduce the dissolution of the coating layer, thereby significantly improving the cycle performance and storage performance of the secondary battery.

[0231] Specifically, the non-aqueous electrolyte of this application includes at least a first additive, which includes one or more compounds of Formula 1.

[0232]

[0233] R1 represents R aAt least one of the following groups, substituted or unsubstituted: C2-C10 divalent alkyl, C2-C10 divalent heteroalkyl, C6-C18 divalent aryl, C7-C18 divalent arylalkyl, C7-C18 divalent alkylaryl, C8-C18 divalent alkylarylalkyl, C13-C18 divalent arylalkylaryl, C2-C18 divalent heteroaryl, C3-C18 divalent heteroarylalkyl, C3-C18 divalent alkyl heteroaryl, C4-C18 divalent alkyl heteroarylalkyl, C5-C18 divalent heteroarylalkyl heteroaryl, C3-C18 divalent alicyclic, C4-C18 divalent alicyclic alkyl, C4-C18 divalent alkyl alicyclic, C5-C18 divalent alkyl alicyclic alkyl, C7-C18 divalent alicyclic alkyl alicyclic, C2-C18 divalent heteroaryl, C3-C18 divalent heteroaryl alkyl, C3-C18 divalent alkyl heteroaryl, C4-C18 divalent alkyl heteroaryl alkyl and C5-C18 divalent heteroaryl alkyl heteroaryl.

[0234] R a The halogen atom includes one or more selected from halogen atoms, -CN, -NCO, -OH, -COOH, -SOOH, carboxylic acid ester groups, sulfonate ester groups, sulfate ester groups, C1-C10 alkyl groups, C2-C10 alkenyl groups, C2-C10 alkynyl groups, C2-C10 oxaalkyl groups, phenyl groups, and benzyl groups. Optionally, the halogen atom includes one or more selected from fluorine atoms, chlorine atoms, and bromine atoms. More preferably, the halogen atom is selected from fluorine atoms.

[0235] When the non-aqueous electrolyte contains the first additive shown in Formula 1, it can react with trace amounts of water in the non-aqueous electrolyte to generate -NHCOOH, reducing HF generation and lowering the acidity of the non-aqueous electrolyte, thereby reducing the dissolution of the coating layer, the dissolution of manganese ions, and the generation of gas. Simultaneously, the first additive shown in Formula 1 can also form a uniform and dense interfacial film on the surface of the negative electrode active material, reducing the reduction reaction of dissolved manganese ions at the negative electrode. Therefore, when the non-aqueous electrolyte contains the first additive shown in Formula 1, the cycle performance and storage performance of the secondary battery can be significantly improved, particularly its high-temperature cycle performance and high-temperature storage performance.

[0236] In some implementations, R1 represents R aAt least one of the following groups, substituted or unsubstituted: C2-C10 alkylene, C2-C10 oxaalkylene, C2-C10 azaalkylene, phenylene, o-phthalimide, m-phthalimide, terephthalimide, monomethylphenylene, dimethylphenylene, trimethylphenylene, tetramethylphenylene, monoethylphenylene, diethylphenylene, triethylphenylene, tetraethylphenylene, diphenylene, terphenylene, tetraphenylene, diphenylene Methyl, cyclobutylene, o-cyclobutyldimethyl, m-cyclobutyldimethyl, p-cyclobutyldimethyl, cyclopentylene, o-cyclopentyldimethyl, m-cyclopentyldimethyl, p-cyclopentyldimethyl, cyclohexylene, monomethylcyclohexylene, dimethylcyclohexylene, trimethylcyclohexylene, tetramethylcyclohexylene, o-cyclohexyldimethyl, m-cyclohexyldimethyl, p-cyclohexyldimethyl, dicyclohexylmethane, methylcyclohexyl, naphthylene, anthraceneylene, and perhydroanthraceneylene. Optionally, R a It includes one or more selected from fluorine atom, -CN, -NCO, -OH, -COOH, -SOOH, carboxylic acid ester group, sulfonate ester group, sulfate ester group, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C2-C10 oxaalkyl, phenyl, benzyl.

[0237] When R1 represents the above-mentioned substituent, it can further reduce the generation of HF and lower the acidity of non-aqueous electrolytes, while also helping to form a uniform, dense, and low-resistance interface film on the surface of the negative electrode active material, thereby further enhancing the improvement effect on the cycle performance and storage performance of secondary batteries.

[0238] In some embodiments, the first additive includes at least one of the following compounds:

[0239]

[0240]

[0241] During the research process, the inventors discovered that using at least one of the above-mentioned compounds H1 to H38 as a first additive can further reduce the generation of HF and reduce the acidity of non-aqueous electrolytes. At the same time, it helps to form a uniform, dense, and low-resistance interface film on the surface of the negative electrode active material, thereby further enhancing the improvement effect on the cycle performance and storage performance of secondary batteries.

[0242] The inventors also discovered during their research that when the non-aqueous electrolyte contains excessive amounts of the first additive, the negative electrode interface impedance increases, thereby affecting the capacity utilization and rate performance of the secondary battery. Therefore, the content of the first additive in the non-aqueous electrolyte should not be too high. In some embodiments, the content of the first additive is W1% by weight, where W1 is 0.01 to 20, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte. When the content of the first additive is within a suitable range, it can reduce HF generation and lower the acidity of the non-aqueous electrolyte without worsening the negative electrode interface impedance, thereby significantly improving the cycle performance and storage performance of the secondary battery, while not affecting its capacity utilization and rate performance.

[0243] In some embodiments, the coating amount C1 (wt%) of the first coating layer, the coating amount C2 (wt%) of the second coating layer, and the content W1 (wt%) of the first additive satisfy the following: W1 / (C1+C2+C3) is 0.001 to 2. Optionally, W1 / (C1+C2+C3) is 0.01 to 2, 0.01 to 1.5, 0.01 to 1.5, 0.05 to 1.5, 0.05 to 1, or 0.1 to 1. When W1 / (C1+C2+C3) is within a suitable range, it can significantly enhance the improvement effect on the cycle performance and storage performance of the secondary battery, while improving the capacity utilization and rate performance of the secondary battery. It can effectively avoid the following situations: When W1 / (C1+C2+C3) is small, there is not enough first additive to reduce the generation of HF and reduce the acidity of non-aqueous electrolyte, so the dissolution of manganese ions and the generation of gas cannot be significantly reduced, and the effect of further improving the cycle performance and storage performance of secondary battery is not obvious; when W1 / (C1+C2+C3) is large, the negative electrode interface impedance increases, affecting the capacity utilization and rate performance of secondary battery.

[0244] In some embodiments, the non-aqueous electrolyte further includes a second additive, the second additive comprising ethylene sulfate (DTD), lithium difluorophosphate (LiPO2F2), lithium difluorodioxarate phosphate (LiDODFP), and R2[FSO3]. - ] a 、R2[C b F 2b+ 1SO3 - ] a One or more of the following, where a represents 1 to 5, b represents an integer from 1 to 6, and R2 represents a metal cation or an organic group cation.

[0245] The second additive helps form a low-resistance interfacial film on the surface of the negative electrode active material, thereby improving the capacity utilization and rate performance of the secondary battery. Therefore, when the non-aqueous electrolyte contains both the first and second additives, it significantly improves the cycle performance and storage performance of the secondary battery, while also enhancing its capacity utilization and rate performance.

[0246] a represents the average valence of the metal cation or the organic cation R2. b represents an integer from 1 to 6, for example, b represents 1, 2, 3, 4, 5 or 6, and optionally b represents 1, 2 or 3.

[0247] Optionally, the metal cation includes those selected from Li. + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Cu 2+ Ni 2+ and Ni 3+ One or more of them.

[0248] Optionally, the organic cation includes those selected from NH4. + N(CH3)4 + N(CH2CH3)4 + One or more of them.

[0249] Alternatively, R2[FSO3 - ] a This indicates lithium fluorosulfonate (LiFSO3).

[0250] Optionally, R2[C b F 2b+1 SO3 - ] a It represents lithium trifluoromethanesulfonate (LiCF3SO3).

[0251] The inventors also discovered during their research that when the non-aqueous electrolyte contains excessive amounts of the second additive, its effect on reducing the negative electrode interface impedance does not further increase, while the viscosity and conductivity of the non-aqueous electrolyte may be affected, thereby impacting the capacity utilization and rate performance of the secondary battery. Therefore, the content of the second additive in the non-aqueous electrolyte should not be too high. In some embodiments, the content of the second additive is W2% by weight, where W2 is 0.01 to 20, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte. When the content of the second additive is within a suitable range, it can effectively improve the capacity utilization and rate performance of the secondary battery.

[0252] The inventors also discovered during their research that the ratio of the content of the first additive (W1 wt%) to the content of the second additive (W2 wt%) also affects the electrochemical performance of the secondary battery. In some embodiments, W1 / W2 is 0.01 to 20. Optionally, W1 / W2 is 0.01 to 10, 0.1 to 10, 0.1 to 8, 0.1 to 5, 0.2 to 5, 0.5 to 5, or 1 to 5. When W1 / W2 is within a suitable range, the synergistic effect between the two additives can be better utilized, thereby further enhancing the improvement effect on the cycle performance and storage performance of the secondary battery, while improving the capacity utilization and rate performance of the secondary battery. This effectively avoids the following situations: when W1 / W2 is large, the second additive cannot effectively reduce the negative electrode interface impedance, thus the further improvement effect on the capacity utilization and rate performance of the secondary battery may not be significant; when W1 / W2 is small, the generation of HF and the acidity of the non-aqueous electrolyte cannot be significantly reduced, thus the improvement effect on the cycle performance and storage performance of the secondary battery may not be significant.

[0253] In some embodiments, the non-aqueous electrolyte further includes a third additive, which comprises one or more of the following: cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate compounds, sulfite compounds, sulfonyl lactone compounds, disulfonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, acid anhydride compounds, phosphite compounds, phosphate compounds, and borate ester compounds. When the non-aqueous electrolyte contains both the first and third additives, or both the first, second, and third additives, the third additive helps to form a denser and more stable interfacial film on the surface of the positive and / or negative electrode active materials, thereby helping to further improve at least one of the cycle performance, storage performance, and rate performance of the secondary battery. In some embodiments, the content of the third additive is W3% by weight, where W3 is 0.01 to 10, optionally 0.1 to 10, and more preferably 0.3 to 5, based on the total weight of the non-aqueous electrolyte.

[0254] This application does not impose any particular restrictions on the type of third additive, as long as it does not impair the purpose of this application. For example, the third additive can be selected from the following specific substances in any ratio.

[0255] (a) Cyclic carbonate compounds containing carbon-carbon unsaturated bonds

[0256] Cyclic carbonate compounds containing carbon-carbon unsaturated bonds may include one or more of the compounds shown in Formula 2-1. R3 represents a C1-C6 alkylene group, a substituted or unsubstituted C2-C6 straight-chain alkenyl group, with an alkenyl or alkynyl group substituted on the branch chain, wherein the substituent is selected from one or more of halogen atoms, C1-C6 alkyl groups, and C2-C6 alkenyl groups.

[0257]

[0258] Optionally, the cyclic carbonate compound containing carbon-carbon unsaturated bonds may include, but is not limited to, one or more of the following compounds.

[0259]

[0260] (b) Halogen-substituted cyclic carbonate compounds

[0261] Halogen-substituted cyclic carbonate compounds may include one or more of the compounds shown in Formula 2-2. R4 represents a halogen-substituted C1-C6 alkylene group or a halogen-substituted C2-C6 alkenyl group.

[0262]

[0263] Optionally, the halogen-substituted cyclic carbonate compound may include, but is not limited to, one or more of fluoroethylene carbonate (FEC), fluoropropylene carbonate (FPC), trifluoropropylene carbonate (TFPC), trans or cis-4,5-difluoro-1,3-dioxane-2-one (hereinafter collectively referred to as DFEC).

[0264] (c) Sulfate compounds

[0265] The sulfate compound may be a cyclic sulfate compound other than ethylene sulfate (DTD). Other cyclic sulfate compounds may include one or more of the compounds shown in Formulas 2-3. R5 represents a substituted or unsubstituted C1-C6 alkylene group or a substituted or unsubstituted C2-C6 alkenyl group, wherein the substituent is selected from one or more of a halogen atom, a C1-C3 alkyl group, and a C2-C4 alkenyl group.

[0266]

[0267] Optionally, the sulfate compound may include, but is not limited to, one or more of the following compounds.

[0268]

[0269] Further optionally, the sulfate compound includes one or more of propylene sulfate (TMS) and 4-methylethyl sulfate (PLS).

[0270] (d) Sulfite compounds

[0271] The sulfite compound may be a cyclic sulfite compound, specifically including one or more of the compounds shown in Formulas 2-4. R6 represents a substituted or unsubstituted C1-C6 alkylene group or a substituted or unsubstituted C2-C6 alkenyl group, wherein the substituent is selected from one or more of a halogen atom, a C1-C3 alkyl group, or a C2-C4 alkenyl group.

[0272]

[0273] Optionally, the sulfite compound may include one or more of vinyl sulfite (ES), propylene sulfite (PS), and butyl sulfite (BS).

[0274] (e) Sulfonolactone compounds

[0275] The sulfonyl lactone compound may include one or more of the compounds shown in Formulas 2-5. R7 represents a substituted or unsubstituted C1-C6 alkylene group or a substituted or unsubstituted C2-C6 alkenyl group, wherein the substituent is selected from one or more of a halogen atom, a C1-C3 alkyl group, or a C2-C4 alkenyl group.

[0276]

[0277] Alternatively, the sulfonyl lactone compound may include, but is not limited to, one or more of the following compounds.

[0278]

[0279] Further optionally, the sulfonate compound may include one or more of 1,3-propanesulfonate lactone (PS) and 1,3-propenesulfonate lactone (PES).

[0280] (f) Disulfonate compounds

[0281] Disulfonate compounds are compounds containing two sulfonic acid groups (-S(=O)2O-), and optionally, disulfonate compounds are methylene disulfonate compounds.

[0282] The disulfonate methylene ester compound may include one or more of the compounds shown in formulas 2-6. R8 to R 11Each of the following can be independently represented: a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C2-C10 alkenyl group, wherein the substituent is selected from one or more of the halogen atom, C1-C3 alkyl group, and C2-C4 alkenyl group.

[0283]

[0284] Optionally, the disulfonate compound may include, but is not limited to, one or more of the following compounds.

[0285]

[0286] Alternatively, the disulfonate compound may be methylene disulfonate.

[0287] (g) Nitrile compounds

[0288] The nitrile compound may be a dinitrile or a trinitrile compound. Optionally, the nitrile compound may include one or more of the compounds shown in Formulas 2-7 and 2-8. R 12 Represents substituted or unsubstituted C1-C12 alkylene, substituted or unsubstituted C1-C12 oxaalkylene, substituted or unsubstituted C2-C12 alkenylene, substituted or unsubstituted C2-C12 ynylene, R 13 To R 15 Each of the following can be independently represented as a substituted or unsubstituted C0-C12 alkylene group, a substituted or unsubstituted C1-C12 oxaalkylene group, a substituted or unsubstituted C2-C12 alkenylene group, or a substituted or unsubstituted C2-C12 alkyne group, wherein the substituent is selected from one or more of a halogen atom, a nitrile group, a C1-C6 alkyl group, a C2-C6 alkenyl group, or a C1-C6 alkoxy group.

[0289]

[0290]

[0291] Optionally, the nitrile compound may include one or more of the following: ethylenedionitrile, malononitrile, butadionitrile, glutaronitrile, adiponitrile, heptanonitrile, octanilide, nonadionitrile, decanadionitrile, undecanedionitrile, dodecanedionitrile, tetramethylsuccinate, methylglutaronitrile, butenonitrile, 2-pentenonitrile, hex-2-enonitrile, hex-3-enonitrile, oct-4-enonitrile, oct-4-ynedionitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, and 1,3,6-hexanetrionitrile.

[0292] (h) Phosphazene compounds

[0293] The phosphazene compound may be a cyclic phosphazene compound. Cyclic phosphazene compounds may include one or more of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene. Optionally, the cyclic phosphazene compound may include one or more of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene. Further optionally, the cyclic phosphazene compound may include methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, or a combination thereof.

[0294] (i) Aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds

[0295] Aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds may include one or more of cyclohexylbenzene, fluorocyclohexylbenzene compounds (e.g., 1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-pentylbenzene, 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 (e.g., 1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl). Optionally, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds may include one or more of biphenyl, terphenyl (ortho, meta, para), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-pentylbenzene. Further optionally, the aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds may include one or more of biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene.

[0296] (j) Acid anhydride compounds

[0297] The acid anhydride compound can be a chain anhydride or a cyclic anhydride. Specifically, the acid anhydride compound may include one or more of acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, 2-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, and 3-sulfonyl-propionic anhydride. Optionally, the acid anhydride compound may include one or more of succinic anhydride, maleic anhydride, and 2-allyl succinic anhydride. Further optionally, the acid anhydride compound may include succinic anhydride, 2-allyl succinic anhydride, or a combination thereof.

[0298] (k) Phosphite compounds

[0299] The phosphite compound may be a silane phosphite compound, specifically including one or more of the compounds shown in formulas 2-9, R 16 To R 24 Each can be used independently to represent a halogen-substituted or unsubstituted C1-C6 alkyl group.

[0300]

[0301] Optionally, the silane phosphite compound may include, but is not limited to, one or more of the following compounds.

[0302]

[0303] (l) Phosphate compounds

[0304] Phosphate compounds may be silane phosphate compounds, specifically including one or more of the compounds shown in Formulas 2-10, R 25 To R 33 Each can be used independently to represent a halogen-substituted or unsubstituted C1-C6 alkyl group.

[0305]

[0306] Optionally, the silane phosphate compound may include, but is not limited to, one or more of the following compounds.

[0307]

[0308] (m) Boronate compounds

[0309] The borate ester compound may be a silane borate ester compound, specifically including one or more of the compounds shown in Formula 2-11, R 34 To R 42 Each can be used independently to represent a halogen-substituted or unsubstituted C1-C6 alkyl group.

[0310]

[0311] Alternatively, the silane borate compound may include, but is not limited to, one or more of the following compounds:

[0312]

[0313] In some embodiments, the third additive may optionally include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC). These third additives are electrochemically reducing additives with a higher reduction potential than organic solvents. Therefore, they can preferentially undergo electrochemical reduction on the surface of the negative electrode active material to form a high-performance interfacial film, reducing the degree of damage to the interfacial film by organic solvents. Consequently, secondary batteries using these additives can have better electrochemical and safety performance.

[0314] The non-aqueous electrolyte also includes lithium salts and organic solvents. This application does not impose any particular restrictions on the types of lithium salts and organic solvents; they can be selected according to actual needs.

[0315] As an example, the organic solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylic acid esters. This application does not specifically limit the types of chain carbonates, cyclic carbonates, and carboxylic acid esters; they can be selected according to actual needs. Optionally, the organic solvent may include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (GBL), methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), methyl propionate (PP), and tetrahydrofuran (THF).

[0316] As an example, the lithium salt may include LiN(C) m F 2m+1 SO2)(C n F 2n+1 The electrolyte comprises one or more of the following: SO2), LiPF6, LiBF4, LiBOB, LiAsF6, Li(FSO2)2N, and LiClO4, where m and n are natural numbers. When the non-aqueous electrolyte includes the above-mentioned lithium salts, it helps to form a dense, stable, and low-resistance interfacial film on the surface of the positive and / or negative electrode active materials, effectively improving at least one of the cycle performance, storage performance, and rate performance of the secondary battery.

[0317] Cyclic carbonates have a high dielectric constant, which is beneficial for the dissociation of lithium salts. In some embodiments, the content of the cyclic carbonate can be more than 20% by weight, optionally from 20% to 80% by weight, and more preferably from 20% to 50% by weight, based on the total weight of the organic solvent. Optionally, the cyclic carbonate includes one or more of ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC).

[0318] Chain carbonates have a low dielectric constant and a weak ability to dissociate lithium salts, but they have low viscosity and good flowability, which can increase the migration rate of lithium ions. In some embodiments, the content of the chain carbonate can be more than 10% by weight, optionally from 10% to 80% by weight, based on the total weight of the organic solvent. Optionally, the chain carbonate includes one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0319] Carboxylic acid esters have the advantages of low viscosity and high dielectric constant, which can improve the conductivity of non-aqueous electrolytes. In some embodiments, the content of the carboxylic acid ester can be from 0% by weight to 70% by weight, optionally from 0% by weight to 60% by weight, based on the total weight of the organic solvent. Optionally, the carboxylic acid ester includes one or more of methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), and methyl propionate (PP).

[0320] Increasing the lithium salt content increases the total number of migratable lithium ions, but simultaneously increases the viscosity of the non-aqueous electrolyte, thus slowing down the lithium ion migration rate. Therefore, there is an optimal value for the lithium salt content. In some embodiments, the lithium salt content can be from 6% to 39% by weight, optionally from 10% to 31% by weight, more preferably from 11% to 24% by weight, and even more preferably from 12% to 20% by weight, based on the total weight of the non-aqueous electrolyte.

[0321] The non-aqueous electrolyte of this application can be prepared according to conventional methods in the art. For example, the additives, the organic solvent, and the lithium salt can be mixed evenly to obtain the non-aqueous electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the additives and the lithium salt can be added to the organic solvent and mixed evenly to obtain the non-aqueous electrolyte.

[0322] In this application, the components and their contents in the non-aqueous electrolyte can be determined using methods conventional in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0323] It should be noted that the non-aqueous electrolyte of this application can also be obtained from a secondary battery. An exemplary method for obtaining a non-aqueous electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage and then centrifuging it, followed by taking an appropriate amount of the centrifuged liquid for testing.

[0324] [Outer Packaging]

[0325] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the non-aqueous electrolyte.

[0326] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0327] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0328] In some implementations, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. A non-aqueous electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0329] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0330] Battery Module

[0331] In some embodiments, the secondary battery according to this application can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0332] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0333] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0334] Battery pack

[0335] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0336] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0337] Electrical appliances

[0338] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0339] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0340] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0341] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0342] Example

[0343] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0344] The sources of raw materials involved in the embodiments of this application are as follows:

[0345]

[0346]

[0347] I. Battery Manufacturing

[0348] Example 1

[0349] Step 1: Preparation of positive electrode active material

[0350] Step S1: Preparation of Fe, Co, V and S co-doped manganese oxalate

[0351] 689.6 g of manganese carbonate, 455.27 g of ferrous carbonate, 4.65 g of cobalt sulfate, and 4.87 g of vanadium dichloride were added to a mixer and mixed thoroughly for 6 hours. The resulting mixture was then transferred to a reaction vessel, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred thoroughly at 500 rpm for 6 hours until homogeneous and the reaction was terminated without bubble formation, yielding a Fe, Co, and V co-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and milled to obtain manganese oxalate particles with a particle size of 100 nm.

[0352] 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

[0353] Take 1793.1g of manganese oxalate, 368.3g of lithium carbonate, 1146.6g of ammonium dihydrogen phosphate, and 4.9g of dilute sulfuric acid prepared in (1), add them to 20L of deionized water, stir thoroughly, and react uniformly at 80°C for 10 hours to obtain a slurry. Transfer the slurry to a spray drying equipment for spray drying and granulation, and dry at 250°C to obtain a powder. In a protective atmosphere (90% nitrogen and 10% hydrogen), sinter the powder in a roller kiln at 700°C for 4 hours to obtain the above-mentioned core material.

[0354] Step S3: Preparation of the first coating layer suspension

[0355] To prepare a Li2FeP2O7 solution, 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, and the pH was controlled at 5. The solution was then stirred and reacted at room temperature for 2 hours to obtain a solution. The solution was then heated to 80 °C and maintained at this temperature for 4 hours to obtain the first coating layer suspension.

[0356] Step S4: Coating with the first coating layer

[0357] 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.

[0358] Step S5: Preparation of the second coating layer suspension

[0359] 3.7g lithium carbonate, 11.6g ferrous carbonate, 11.5g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate were dissolved in 1500mL deionized water, stirred and reacted for 6 hours to obtain a solution. The solution was then heated to 120℃ and maintained at this temperature for 6 hours to obtain a second coating layer suspension.

[0360] Step S6: Coating with the second coating layer

[0361] 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.

[0362] Step S7: Preparation of the third coating layer aqueous solution

[0363] Dissolve 37.3g of sucrose in 500g of deionized water, then stir and dissolve completely to obtain a sucrose aqueous solution.

[0364] Step S8: Coating with the third coating layer

[0365] 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.

[0366] Step 2: Preparation of the positive electrode sheet

[0367] 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.

[0368] Step 3: Preparation of the negative electrode sheet

[0369] A negative electrode slurry was prepared by dissolving artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then prepared at a concentration of 0.117 g / 1540.25 mm. 2 The coating is uniformly applied to the copper foil of the negative electrode current collector, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0370] Step 4: Preparation of non-aqueous electrolyte

[0371] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed uniformly at a volume ratio of 1:1:1 as an organic solvent. Then, 12.5 wt% (based on the total weight of the non-aqueous electrolyte) of LiPF6 and 1 wt% (based on the total weight of the non-aqueous electrolyte) of compound H38 were added and dissolved in the organic solvent, and stirred uniformly to obtain the non-aqueous electrolyte.

[0372] Step 5: Preparation of the separating membrane

[0373] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0374] Step 6: Preparation of the full cell

[0375] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, injected with the aforementioned non-aqueous electrolyte, and sealed to obtain a full cell (hereinafter also referred to as "full cell").

[0376] [Preparation of button cells]

[0377] 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 then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0378] A lithium sheet is used as the negative electrode, and together with the positive electrode sheet prepared above and the non-aqueous electrolyte, they are assembled into a coin cell (hereinafter also referred to as "coin cell") in a coin cell box.

[0379] Examples 2-67 and Comparative Examples 1-18

[0380] The positive electrode active materials, non-aqueous electrolytes, and batteries of Examples 2-67 and Comparative Examples 1-18 were prepared in a manner similar to that of Example 1. Examples 30-42 were identical to Example 1 except for the first or second coating layer material. Examples 43-67 were identical to Example 1 except for the preparation process of the non-aqueous electrolyte. Differences in the preparation of the positive electrode active materials are shown in Tables 1-8. Comparative Examples 1-2, 4-10, and 12 did not have a first coating layer, therefore steps S3 and S4 were omitted; Comparative Examples 1-11 did not have a second coating layer, therefore steps S5-S6 were omitted. Differences in the preparation of the non-aqueous electrolytes are shown in Table 9.

[0381] In addition, in all embodiments and comparative examples of this application, unless otherwise specified, the first coating layer material and / or the second coating layer material used are assumed to be crystalline.

[0382]

[0383]

[0384]

[0385] Table 2: Preparation of the first coating layer suspension (step S3)

[0386]

[0387] Table 3: Coverage of the first coating layer (step S4)

[0388]

[0389] Table 4: Preparation of the second coating layer suspension (step S5)

[0390]

[0391] Table 5: Covering of the second coating layer (step S6)

[0392]

[0393] Table 6: Covering with the third coating layer (step S8)

[0394]

[0395]

[0396] Table 7: Investigation of the material of the first coating layer

[0397]

[0398] Table 8: Investigation of the Second Coating Material

[0399]

[0400] Table 9: Preparation of non-aqueous electrolyte (Step 4)

[0401]

[0402]

[0403] II. Performance Evaluation

[0404] 1. Methods for measuring lattice change rate

[0405] Under a constant temperature environment of 25℃, the positive electrode active material sample was placed in an X-ray powder diffractometer (model Bruker D8 Discover) and tested at a rate of 1° / minute. The test data were then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of the unit cell in each direction, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0406] Using the coin cell preparation method described in the above embodiments, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0407] 2. Li / Mn antisite defect concentration

[0408] 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.

[0409] 3. Compacted density

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

[0411] 4. Surface oxygen valence state

[0412] 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.

[0413] 5. Dissolution test of transition metal Mn (and Fe doped at Mn sites)

[0414] The full cells prepared in the above-described embodiments and comparative examples, after being cycled at 45°C until their capacity decayed to 80%, were discharged at a rate of 0.1C to a cutoff voltage of 2.0V. The batteries were then disassembled, and the negative electrode was removed. Thirty unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0415] 6. Measurement of manganese and phosphorus elements in positive electrode active materials

[0416] Dissolve 5g of the prepared positive electrode active material in 100mL of aqua regia (concentrated hydrochloric acid:concentrated nitric acid = 1:3). Use ICP to test the content of each element in the solution. Then measure and convert the content of manganese or phosphorus (amount of manganese or phosphorus / amount of positive electrode active material × 100%) to obtain its weight percentage.

[0417] 7. Method for measuring the initial specific capacity of button cells

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

[0419] 8. 3C charging constant current ratio

[0420] 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 point 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 point was recorded as C1. The constant current ratio for 3C charging is C1 / C0 × 100%.

[0421] The higher the constant current ratio during 3C charging, the better the rate performance of the secondary battery.

[0422] 9. Battery swelling test after 30 days of storage at 60°C.

[0423] The full cells prepared in the above-described embodiments and comparative examples were stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) of the cells were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. 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 involves first measuring the cell's weight F1 separately using a balance with automatic unit conversion of dial data, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery at this moment is measured, and the buoyant force F on the battery is measured. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The battery volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0424] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire testing process until the end of storage.

[0425] After 30 days of storage, the battery volume was measured, and the percentage increase in battery volume after storage was calculated relative to the battery volume before storage.

[0426] 10. Cyclic performance test of the full battery at 45°C

[0427] Under a constant temperature environment of 45℃, the full battery is charged at 1C to 4.3V, then charged at 4.3V at a constant voltage until the current is ≤0.05mA. After resting for 5 minutes, it is discharged at 1C to 2.5V, and the capacity is recorded as D0. The above process is repeated until the capacity decays to 80% of D0. The number of repetitions at this point is recorded, which is the number of cycles corresponding to 80% capacity retention at 45℃.

[0428] 11. Interplanar spacing and angle testing

[0429] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Stir and disperse for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the sample chamber of a TEM (Talos F200sG2) for testing and obtain the original TEM test image.

[0430] 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.

[0431] By comparing the obtained interplanar spacing and corresponding angle data with their standard values, different materials in the coating layer can be identified.

[0432] 12. Coating thickness test

[0433] The thickness of the coating layer was tested by cutting a thin slice of about 100 nm thickness from the middle of a single particle of the positive electrode active material prepared above using FIB, and then performing TEM testing on the slice to obtain the original TEM image.

[0434] 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.

[0435] Measure the thickness of the selected particle at three locations and take the average value.

[0436] 13. Determination of the molar ratio of SP2 and SP3 forms in the third coating layer of carbon

[0437] 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.

[0438] 14. Determination of core chemical formula and composition of different coating layers

[0439] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of different coating layers of the positive electrode active material were obtained.

[0440] Table 10 shows the powder properties of the positive electrode active materials in Examples 1-42 and Comparative Examples 1-18, as well as the properties of the prepared positive electrode sheets and batteries.

[0441] Table 11 shows the thickness of each coating layer of the positive electrode active material prepared in Examples 1-14 and Comparative Examples 3-4 and 12, as well as the weight ratio of manganese and phosphorus.

[0442] Table 12 shows the interplanar spacing and angle between the first and second coating materials in Examples 1, 30-42.

[0443]

[0444]

[0445] Table 11

[0446]

[0447] Table 12

[0448]

[0449] As shown in Table 10, by doping and modifying lithium manganese phosphate and applying multilayer coating, the resulting positive electrode active material achieves a smaller lattice change rate, a lower 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 cycling performance and high-temperature storage performance. The presence of the first additive in the non-aqueous electrolyte helps reduce HF generation and lower the acidity of the non-aqueous electrolyte, thereby reducing manganese ion dissolution and gas generation. Simultaneously, the first additive can also form a uniform and dense interfacial film on the surface of the negative electrode active material, reducing the reduction reaction of dissolved manganese ions at the negative electrode. Therefore, when the non-aqueous electrolyte contains the first additive, the battery's cycle performance and storage performance can be further improved.

[0450] As can be seen from Table 11, 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 10, it can be seen that the reduction of manganese and phosphorus in the positive electrode active material will reduce the amount of manganese and iron ions dissolved and improve the performance of the battery prepared by it.

[0451] Examples 30-42 are identical to Example 1 except for the first or second coating layer material. As can be seen from Examples 30-42, using a first and second coating layer containing other elements within the scope of this application also yields a positive electrode active material with good performance and achieves good battery performance. Table 12 shows that the interplanar spacing and included angle of the first and second coating layers in this application are within the range described in this application.

[0452] Examples 43-67 were identical to Example 1 except for the preparation process of the aqueous electrolyte. Table 13 shows the performance of the batteries prepared in Examples 43-60. Table 14 shows the performance of the batteries prepared in Examples 61-67.

[0453]

[0454] As can be seen from Examples 1 and 43-52, the effect of different types of the first additive on improving battery performance varies slightly.

[0455] Based on Examples 1 and 53-60, it can be seen that when the non-aqueous electrolyte also contains an appropriate amount of a second additive and / or a third additive, it helps to further improve the battery's specific capacity, rate performance, high-temperature cycle performance, and high-temperature storage performance.

[0456] Based on Examples 1 and 61-67, it can be seen that as the content of the first additive increases from 0.01% by weight to 20% by weight, the amount of Fe and Mn leaching after cycling of the resulting material gradually decreases, and the storage performance of the corresponding battery at 60°C is also improved. However, the specific capacity, 3C charging constant current ratio, and cycling performance at 45°C will decrease to varying degrees when the content of the first additive is high.

[0457] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery comprising a positive electrode sheet and a nonaqueous electrolyte, wherein the positive electrode sheet comprises a positive electrode active material having a core-shell structure, the positive electrode active material comprising an inner core and a shell covering the inner core, The chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O4, x is any numerical value in the range of -0.100 to 0.100, y is any numerical value in the range of 0.001 to 0.500, z is any numerical value in the range of 0.001 to 0.100, the A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and the R is one or more elements selected from B, Si, N, and S. the values of x, y, and z satisfy a condition to maintain the entire inner core electrically neutral; the shell comprises a first coating layer covering the inner core, a second coating layer covering the first coating layer, and a third coating layer covering the second coating layer, wherein said first cladding layer comprising a crystalline pyrophosphate Li a MP2O7 and / or M b (P2O7) c with 0≤a≤2, 1≤b≤4, 1≤c≤6, the values of a, b and c satisfying the condition that the crystalline pyrophosphate Li a MP2O7 or M b (P2O7) c remains electrically neutral, the crystalline pyrophosphate Li a MP2O7 and M b (P2O7) c M in each case independently is one or more elements selected from the group consisting of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, the second coating layer comprises a crystalline phosphate XPO4, the X being one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, the third coating layer is carbon; the nonaqueous electrolyte comprises a first additive, the first additive comprising one or more of compounds represented by Formula 1, Formula 1 R1represents at least one member of the group consisting of substituted or unsubstituted C1-C10alkyl, C1-C10heteroalkyl, C6-C18aryl, C7-C18arylalkyl, C7-C18alkylaryl, C8-C18alkylarylalkyl, C13-C18arylalkylaryl, C2-C18heteroaryl, C3-C18heteroarylalkyl, C3-C18alkylheteroaryl, C4-C18alkylheteroarylalkyl, C5-C18heteroarylalkylheteroaryl, C3-C18cycloalkyl, C4-C18cycloalkylalkyl, C4-C18alkylcycloalkyl, C5-C18alkylcycloalkylalkyl, C7-C18cycloalkylalkylcycloalkyl, C2-C18heterocycloalkyl, C3-C18heterocycloalkylalkyl, C3-C18alkylheterocycloalkyl, C4-C18alkylheterocycloalkylalkyl, and C5-C18heterocycloalkylalkylheterocycloalkyl. a R1represents at least one member of the group consisting of substituted or unsubstituted C1-C10alkyl, C1-C10heteroalkyl, C6-C18aryl, C7-C18arylalkyl, C7-C18alkylaryl, C8-C18alkylarylalkyl, C13-C18arylalkylaryl, C2-C18heteroaryl, C3-C18heteroarylalkyl, C3-C18alkylheteroaryl, C4-C18alkylheteroarylalkyl, C5-C18heteroarylalkylheteroaryl, C3-C18cycloalkyl, C4-C18cycloalkylalkyl, C4-C18alkylcycloalkyl, C5-C18alkylcycloalkylalkyl, C7-C18cycloalkylalkylcycloalkyl, C2-C18heterocycloalkyl, C3-C18heterocycloalkylalkyl, C3-C18alkylheterocycloalkyl, C4-C18alkylheterocycloalkylalkyl, and C5-C18heterocycloalkylalkylheterocycloalkyl.

2. The secondary battery according to claim 1, wherein the A is one or more elements selected from the group consisting of Fe, Ti, V, Ni, Co, and Mg.

3. The secondary battery according to claim 1, wherein the R is one element selected from the group consisting of B, Si, N, and S.

4. The secondary battery according to claim 1, wherein R a one or more selected from the group consisting of a halogen atom, -CN, -NCO, -OH, -COOH, -SOOH, a carboxylate group, a sulfonate group, a sulfate group, a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C2-C10 oxaalkyl group, a phenyl group, a benzyl group.

5. The secondary battery according to claim 1, wherein R1represents at least one member of the group consisting of substituted or unsubstituted C2-C10alkylene, C2-C10oxyalkylene, C2-C10azaalkylene, phenylene, o-xylylene, m-xylylene, p-xylylene, monomethylphenylene, dimethylphenylene, trimethylphenylene, tetramethylphenylene, monoethylphenylene, diethylphenylene, triethylphenylene, tetraethylphenylene, bisphenylene, trisphenylene, tetrakisphenylene, diphenylmethane, cyclobutylene, o-cyclobutylxylene, m-cyclobutylxylene, p-cyclobutylxylene, cyclopentylene, o-cyclopentylxylene, m-cyclopentylxylene, p-cyclopentylxylene, cyclohexylene, monomethylcyclohexylene, dimethylcyclohexylene, trimethylcyclohexylene, tetramethylcyclohexylene, o-cyclohexylxylene, m-cyclohexylxylene, p-cyclohexylxylene, dicyclohexylmethane, methylcyclohexyl, naphthylene, anthrylene, and perhydronaphthylene. a R1represents at least one member of the group consisting of substituted or unsubstituted C2-C10alkylene, C2-C10oxyalkylene, C2-C10azaalkylene, phenylene, o-xylylene, m-xylylene, p-xylylene, monomethylphenylene, dimethylphenylene, trimethylphenylene, tetramethylphenylene, monoethylphenylene, diethylphenylene, triethylphenylene, tetraethylphenylene, bisphenylene, trisphenylene, tetrakisphenylene, diphenylmethane, cyclobutylene, o-cyclobutylxylene, m-cyclobutylxylene, p-cyclobutylxylene, cyclopentylene, o-cyclopentylxylene, m-cyclopentylxylene, p-cyclopentylxylene, cyclohexylene, monomethylcyclohexylene, dimethylcyclohexylene, trimethylcyclohexylene, tetramethylcyclohexylene, o-cyclohexylxylene, m-cyclohexylxylene, p-cyclohexylxylene, dicyclohexylmethane, methylcyclohexyl, naphthylene, anthrylene, and perhydronaphthylene.

6. The secondary battery according to claim 2, wherein R a one or more of a fluorine atom, -CN, -NCO, -OH, -COOH, -SOOH, carboxylate, sulfonate, sulfate, C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C2-C10 oxaalkyl, phenyl, benzyl.

7. The secondary battery according to claim 1 or 5, wherein the first additive comprises at least one of the following compounds: 。 8. The secondary battery according to claim 1, wherein a content of the first additive is W1% by weight, W1 being 0.01 to 20, based on the total weight of the nonaqueous electrolyte; and / or, a coating amount of the first coating layer is C1% by weight, C1 being greater than 0 and less than or equal to 6, based on the weight of the inner core; and / or a coating amount of the second coating layer is C2% by weight, C2 being greater than 0 and less than or equal to 6, based on the weight of the inner core; and / or a coating amount of the third coating layer is C3% by weight, C3 being greater than 0 and less than or equal to 6, based on the weight of the inner core.

9. The secondary battery according to claim 8, wherein W1 is 0.1 to 10.

10. The secondary battery according to claim 8, wherein W1 is 0.3 to 5.

11. The secondary battery according to claim 8, wherein C1 is greater than 0 and less than or equal to 5.

5.

12. The secondary battery according to claim 8, wherein C1 is greater than 0 and less than or equal to 2.

13. The secondary battery according to claim 8, wherein C2 is greater than 0 and less than or equal to 5.

5.

14. The secondary battery according to claim 8, wherein C2 is 2 to 4.

15. The secondary battery according to claim 8, wherein C3 is greater than 0 and less than or equal to 5.

5.

16. The secondary battery according to claim 8, wherein C3 is greater than 0 and less than or equal to 2.

17. The secondary battery according to claim 8, wherein W1 / (C1+C2+C3) is 0.001 to 2.

18. The secondary battery according to claim 17, wherein W1 / (C1+C2+C3) is 0.01 to 1.

5.

19. The secondary battery of claim 17, wherein, W1 / (C1+C2+C3) is 0.05 to 1.

20. The secondary battery of claim 1, wherein, The nonaqueous electrolyte further includes a second additive including one or more of ethylene sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, R2[FSO3 - ] a , R2[C b F 2b+1 SO3 - ] a , a represents 1 to 5, b represents an integer of 1 to 6, and R2 represents a metal cation or an organic group cation.

21. The secondary battery according to claim 20, wherein The metal cations include one or more selected from Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Al 3+ , Fe 2+ , Fe 3+ , Cu 2+ , Ni 2+ , and Ni 3+ .

22. The secondary battery of claim 20, wherein, The organic-based cation comprises one or more selected from NH4 + , N(CH3)4 + , N(CH2CH3)4 + .

23. The secondary battery of claim 20, wherein, a content of the second additive is W2% by weight, W2 being 0.01 to 20, based on the total weight of the nonaqueous electrolyte.

24. The secondary battery according to claim 23, wherein W2 is 0.1 to 10.

25. The secondary battery of claim 23, wherein, W2 is 0.3 to 5.

26. The secondary battery of claim 1, wherein, the nonaqueous electrolyte further comprises a third additive, the third additive comprising one or more of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sulfonolide compound, a disulfonate compound, a nitrile compound, a phosphazene compound, an aromatic hydrocarbon and a halogenated aromatic hydrocarbon compound, an anhydride compound, a phosphite compound, a phosphate compound, a borate compound.

27. The secondary battery of claim 26, wherein, a content of the third additive is W3% by weight, W3 being 0.01 to 10.

28. The secondary battery of claim 27, wherein, W3 is 0.1 to 10.

29. The secondary battery of claim 27, wherein, W3 is 0.3 to 5.

30. The secondary battery according to claim 1, wherein the first coating layer has a thickness of 1-10 nm; and / or the second coating layer has a thickness of 2-15 nm; and / or the third coating layer has a thickness of 2-25 nm.

31. The secondary battery according to claim 1, wherein in the core, the ratio of y to 1-y is 1:10 to 1:1; and / or, in the core, the ratio of z to 1-z is 1:9 to 1:

999.

32. The secondary battery of claim 1, wherein, the ratio of y to 1-y is 1:4 to 1:1; and / or, the ratio of z to 1-z is 1:499 to 1:

249.

33. 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 direction (111) ranges from 18.00° to 32.00°; 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 direction (111) ranges from 20.00° to 37.00°.

34. The secondary battery of claim 1, wherein, the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.

35. The secondary battery of claim 34, wherein, the molar ratio of the SP2 form carbon to the SP3 form carbon is any value ranging from 0.1 to 10.

36. The secondary battery of claim 34, wherein, the molar ratio of the SP2 form carbon to the SP3 form carbon is any value ranging from 2.0 to 3.

0.

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

38. The secondary battery of claim 37, wherein, the manganese element content ranges from 15% to 30% by weight.

39. The secondary battery of claim 37, wherein, the manganese element content ranges from 17% to 20% by weight.

40. The secondary battery of claim 37, wherein, the phosphorus element content ranges from 12% to 25% by weight.

41. The secondary battery of claim 37, wherein, the phosphorus element content ranges from 15% to 20% by weight.

42. The secondary battery of claim 37, wherein, the weight ratio of the manganese element to the phosphorus element ranges from 0.90 to 1.

25.

43. The secondary battery of claim 42, wherein, the weight ratio of the manganese element to the phosphorus element ranges from 0.95 to 1.

20.

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

45. The secondary battery of claim 44, wherein, the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 3.8% or less.

46. The secondary battery of claim 44, wherein, the lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 2.0-3.8%.

47. The secondary battery of claim 44, wherein, the Li / Mn antisite defect concentration of the positive electrode active material is 2.2% or less.

48. The secondary battery of claim 44, wherein, the Li / Mn antisite defect concentration of the positive electrode active material is 1.5-2.2%.

49. The secondary battery of claim 44, wherein, The positive electrode active material has a compaction density of 2.2 g / cm 3 above and 2.8 g / cm 3 below.

50. The secondary battery of claim 44, wherein, the surface oxygen valence state of the positive electrode active material is -1.90 to -1.

98.

51. A battery module comprising the secondary battery according to any one of claims 1-50.

52. A battery pack comprising the battery module according to claim 51.

53. An electric device comprising at least one selected from the group consisting of the secondary battery according to any one of claims 1 to 50, the battery module according to claim 51, or the battery pack according to claim 52.

Images