WO2023206394A1 - 二次电池、电池模块、电池包和用电装置 - Google Patents

二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023206394A1
WO2023206394A1 PCT/CN2022/090386 CN2022090386W WO2023206394A1 WO 2023206394 A1 WO2023206394 A1 WO 2023206394A1 CN 2022090386 W CN2022090386 W CN 2022090386W WO 2023206394 A1 WO2023206394 A1 WO 2023206394A1
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optionally
group
secondary battery
core
coating layer
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PCT/CN2022/090386
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English (en)
French (fr)
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张立美
陈培培
刘姣
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/090386 priority Critical patent/WO2023206394A1/zh
Priority to CN202280011969.1A priority patent/CN116830298A/zh
Publication of WO2023206394A1 publication Critical patent/WO2023206394A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of battery technology, and in particular to a secondary battery, battery module, battery pack and electrical device.
  • lithium-ion secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and are used in power tools, electric bicycles, electric motorcycles, and electric vehicles. It is widely used in many fields such as military equipment, aerospace and so on. As lithium-ion secondary batteries have achieved great development, higher requirements have been placed on their energy density, cycle performance and safety performance.
  • lithium manganese phosphate As the cathode active material of lithium-ion secondary batteries, lithium manganese phosphate has the advantages of high capacity, good safety and low cost. However, lithium manganese phosphate has poor rate performance, which restricts its commercial application.
  • the present application provides a secondary battery, a battery module, a battery pack and a power device to solve the problem of poor rate performance of the secondary battery when lithium manganese phosphate is used as the positive active material of the lithium ion secondary battery.
  • a first aspect of the present invention provides a secondary battery.
  • the secondary battery includes a positive electrode sheet and a non-aqueous electrolyte, wherein the positive electrode sheet includes a positive active material with a core-shell structure, and the positive active material includes a core and a non-aqueous electrolyte.
  • the shell covering the core.
  • the chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value in the range of -0.100-0.100, and y is in the range of 0.001-0.500 Any value within, z is any value within the range of 0.001-0.100, A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn , one or more elements among Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg, R is selected from B, Si, N and S One or more elements, optionally, R is an element selected from B, Si, N and S; the values of x, y and z satisfy the following conditions: the entire core remains electrically neutral; the shell includes a first cladding layer covering the core, a second cladding layer covering the first cladding layer, and a third cladding layer covering the second cladding layer, wherein
  • R 1 and R 2 are each independently one of C1-C10 alkyl and C1-C10 haloalkyl.
  • R 1 and R 2 are each independently methyl, ethyl, propyl, butyl, One of pentyl, hexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl and fluorohexyl, further optionally, R 1 and R 2 are independently Ground is one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl and fluoropropyl.
  • the above limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A, but also on the stoichiometric number of each element as A.
  • Limitation of the sum of stoichiometric numbers For example, when A is two or more elements A1, A2...An, the stoichiometric numbers y1, y2...yn of A1, A2...An each need to fall within the numerical range of y defined in this application, and y1 , y2...yn and the sum must also fall within this numerical range.
  • the limitation on the numerical range of the R stoichiometric number in this application also has the above meaning.
  • crystalline means that the degree of crystallinity is above 50%, that is, between 50% and 100%. Crystallinity less than 50% is called glassy state.
  • the crystalline pyrophosphates and crystalline phosphates described herein have a crystallinity of 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating layer's ability to hinder the elution of manganese ions and the phosphate coating layer's excellent ability to conduct lithium ions and reduce interface side reactions, but also enable The pyrophosphate coating layer and the phosphate coating layer can achieve better lattice matching, thereby achieving a tight bond between the coating layer and the coating layer.
  • This application obtains a doped lithium manganese phosphate core by doping element A at the manganese position of lithium manganese phosphate and doping element R at the phosphorus position, and sequentially performs three-layer coating on the surface of the core, thereby providing a new type of core-
  • the shell-structured lithium manganese phosphate cathode active material can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of the secondary battery when the cathode active material is used in secondary batteries.
  • the first solvent in the non-aqueous electrolyte has a good ability to dissociate lithium salt, but compared to carbonate, the interaction between the first organic solvent and Li + is very small.
  • the first solvent gradually Dominating the first solvation layer, the desolvation energy of Li + will gradually decrease, which is conducive to the rapid insertion and extraction of Li + at the interface, thereby improving the rate performance of the secondary battery.
  • the first solvent has a low viscosity, which allows the lithium ions extracted from the positive electrode active material to quickly migrate and embed into the negative electrode side. Driven by concentration polarization, the lithium ions at the interface of the positive electrode material are quickly transferred to the electrolyte. to further improve the rate performance of secondary batteries.
  • the above-mentioned first solvent includes at least one of the following compounds:
  • the first solvent includes at least one of the following compounds:
  • the viscosity of the electrolyte is lower and the wettability is better, so the transmission ability of lithium ions is better, thereby better improving the rate performance of the secondary battery; at the same time, the above-mentioned first solvents Better chemical stability and better oxidation tolerance of the positive active material.
  • the mass percentage of the first solvent is w1, and w1 ranges from 20% to 80%; optionally, w1 ranges from 30% to 75%.
  • the first solvent can be used to improve the fast charging performance of the battery, and at the same time, the secondary battery can have good cycle performance and storage performance.
  • the organic solvent also includes a second solvent
  • the second solvent includes one or more of the group consisting of chain carbonates and cyclic carbonates; further optionally , based on the total mass of the organic solvent, the mass percentage of the second solvent is w2, and the range of w2 is 20% to 80%; optionally, the range of w2 is 25% to 70%.
  • the second solvent is used to cooperate with the first solvent to improve the cycle performance of the secondary battery.
  • the above-mentioned non-aqueous electrolyte further includes a first additive, and the first additive includes one or more from the group consisting of sultone and cyclic sulfate. Sultones or cyclic sulfates are introduced into the non-aqueous electrolyte.
  • Sultones or cyclic sulfates are introduced into the non-aqueous electrolyte.
  • they form a layer of polymers with strong ion conductivity, such as ester-based sulfates, on the surface of the positive active material.
  • the polymer can not only further improve the rate performance of the secondary battery, but also effectively inhibit the catalytic oxidation of the first solvent by the positive electrode active material, thereby improving the cycle and storage performance of the secondary battery.
  • sultone or cyclic sulfate can form a film on the negative electrode better than the first solvent, reducing the reaction of ⁇ -H on the first solvent with the active lithium obtained by the reduction of the negative electrode, thereby further improving the cycle and performance of the secondary battery. Storage performance.
  • the above-mentioned sultone includes at least one of the compounds represented by Formula 2,
  • p means 1, 2 or 3,
  • R 11 represents one of hydrogen atom, halogen atom, C1 ⁇ C12 alkyl group, C1 ⁇ C12 haloalkyl group, C1 ⁇ C12 alkoxy group, C1 ⁇ C12 haloalkoxy group; optionally, R 11 represents hydrogen atom, halogen One of atom, C1 ⁇ C6 alkyl, C1 ⁇ C3 haloalkyl, C1 ⁇ C3 alkoxy, C1 ⁇ C3 haloalkoxy; optionally the alkoxy group is a chain alkoxy group or a cyclic alkoxy group , optionally the cyclic alkoxy group shares one carbon atom with the parent ring of sultone, and further optionally the cyclic alkoxy group has a carbon number of 4, 5 or 6;
  • Each R 12 independently represents a hydrogen atom, a halogen atom, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, or a 4 to 7-membered sultone group.
  • each R 12 independently represents a hydrogen atom, a halogen atom, a C1 ⁇ C3 alkyl group, a C1 ⁇ C3 haloalkyl group, a C1 ⁇ C3 alkoxy group, a C1 ⁇ C3 haloalkoxy group, a 5- to 6-membered
  • the sultone groups optionally, the sultone group shares one carbon atom with the parent ring of the sultone, and optionally the sultone group is a 5-membered ring;
  • R 11 and R 12 and the carbon atoms to which they are connected can form a 5- to 10-membered cycloalkyl group
  • R 13 represents a hydrogen atom, a halogen atom, a carbonyl group, a C2 to C6 ester group, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C2 to C12 alkenyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, One of C6 ⁇ C20 aryl or benzyl; optionally, R 13 represents a hydrogen atom, a halogen atom, a carbonyl group, a C2 ⁇ C3 ester group, a C1 ⁇ C3 alkyl group, a C1 ⁇ C3 haloalkyl group, C2 ⁇ C6 One of alkenyl, C1 ⁇ C3 alkoxy, C1 ⁇ C3 haloalkoxy, C6 ⁇ C10 aryl or benzyl.
  • the above-mentioned sultone is a commonly used sultone in this
  • the above-mentioned cyclic sulfate ester includes at least one of the compounds represented by Formula 3,
  • q means 1, 2 or 3
  • R 14 represents a hydrogen atom, a halogen atom, a carbonyl group, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C2 to C12 alkenyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, or a C2 to C6 ester group, One of the 4 to 7-membered cyclic sulfate groups; optionally, R 14 represents a hydrogen atom, a halogen atom, a carbonyl group, a double bond, a C1 to C6 alkyl group, a C1 to C3 haloalkyl group, or a C1 to C3 alkoxy group One of the group, C1 ⁇ C3 haloalkoxy group, C2 ⁇ C3 ester group, 4 to 5-membered cyclic sulfate ester group; optionally the cyclic sulfate ester group and
  • Each R 15 independently represents one of a hydrogen atom, a halogen atom, a C1-C12 alkyl group, a C1-C12 haloalkyl group, a C1-C12 alkoxy group, a C1-C12 haloalkoxy group, or a C6-C20 aryl group; it can Optionally, each R 15 independently represents one of a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C3 haloalkyl group, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or a C6 to C10 aryl group. kind;
  • R 14 and R 15 together with their respective linked carbon atoms form a 4 to 7-membered cyclic sulfate ester group. Further optionally, R 14 and R 15 together with their respective linked carbon atoms form a 5-membered cyclic sulfate ester group. base.
  • cyclic sulfate ester is a cyclic sulfate ester commonly used in this field, with wide sources and low cost.
  • the sultone includes at least one of the following compounds:
  • the cyclic sulfate ester includes at least one of the following compounds:
  • the sultone includes at least one of the following compounds:
  • the cyclic sulfate ester includes at least one of the following compounds:
  • the content of the first additive is W3, and 0.01% ⁇ W3 ⁇ 20%, optionally 0.1% ⁇ W3 ⁇ 10%, and further can be Choose 0.3% ⁇ W3 ⁇ 5%. This avoids the increase in the resistance of the positive and negative electrodes caused by introducing too much sultone or cyclic sulfate, thereby ensuring a significant improvement in the capacity and rate performance of lithium-ion batteries.
  • the non-aqueous electrolyte further includes a second additive
  • the second additive includes a sulfite compound, a disulfonate compound, a nitrile compound, an aromatic compound, a phosphazene compound, an acid anhydride compound, and a phosphorous acid
  • ester compounds phosphate ester compounds, and borate ester compounds.
  • the above-mentioned second additive helps to form a denser and more stable interface film on the surface of the positive electrode and/or negative electrode active material, thereby further improving at least one of the cycle performance, storage performance, and rate performance of the secondary battery.
  • the content of the second additive is W4, 0.01% ⁇ W4 ⁇ 20%, optionally 0.05% ⁇ W4 ⁇ 5%, further optionally 0.1% ⁇ W4 ⁇ 3%. So that the role of the second additive can be fully exerted.
  • the coating amount of the first coating layer is C1 weight %, C1 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, More optionally, it can be greater than 0 and less than or equal to 2.
  • the coating amount of the second coating layer is C2 weight %, C2 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, more optionally 2-4 .
  • the coating amount of the third coating layer is C3% by weight, and C3 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, more optionally greater than 0 and less than or equal to 5.5. Less than or equal to 2.
  • the coating amount of the three coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the gram capacity of the cathode active material. Under the premise of further improving the dynamic performance and safety performance of secondary batteries.
  • the interplanar distance of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the angle range of the crystal direction (111) ranges from 18.00° to 32.00°;
  • the interplanar distance 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°.
  • the first coating layer and the second coating layer in the cathode active material of the above embodiments both use crystalline materials, and their crystal plane spacing and included angle range are within the above range, which can more effectively avoid Impurity phase, thereby further improving the gram capacity, cycle performance and rate performance of the material.
  • the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1.
  • the cycle performance and rate performance of the secondary battery are further improved.
  • the ratio of z to 1-z is 1:999 to 1:9, optionally 1:499 to 1:249.
  • the carbon of the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.
  • the molar ratio of SP2 form carbon and SP3 form carbon is in the range of 0.1-10. Any value, selectable as any value in the range of 2.0-3.0. The above embodiments better improve the overall performance of the secondary battery by limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range.
  • the thickness of the first cladding layer is 1-10 nm; and/or the thickness of the second cladding layer is 2-15 nm; and/or the thickness of the third cladding layer is 2-10 nm. 25nm.
  • the thickness of the first cladding layer ranges from 1 to 10 nm, it can avoid the possible adverse effects on the dynamic properties of the material when it is too thick, and it can avoid the inability to effectively block the transition metal when it is too thin. The problem of ion migration.
  • 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 reaction with the electrolyte is small.
  • the interface side reaction can be more effectively alleviated, thereby more significantly improving the performance of the second coating layer.
  • the thickness of the third coating layer ranges from 2 to 20 nm, the electrical conductivity of the material can be further improved and the compaction density performance of the battery pole piece prepared using the cathode active material can be improved.
  • the content of manganese element is in the range of 10%-35% by weight, optionally in the range of 15%-30% by weight, based on the weight of the cathode active material having a core-shell structure. , more optionally in the range of 17%-20% by weight, the content of phosphorus element in the range of 12%-25% by weight, optionally in the range of 15%-20% by weight, the weight of manganese element and phosphorus element
  • the ratio range is 0.90-1.25, optional 0.95-1.20.
  • the content of manganese element is within the above range, which can effectively avoid problems such as deterioration in structural stability and density reduction that may be caused by excessive manganese element content, thereby It can more effectively improve the performance of secondary batteries such as cycle, storage and compaction density; and can avoid problems such as low voltage platform that may be caused if the manganese content is too small, thus improving the energy density of secondary batteries.
  • the content of phosphorus element is within the above range, which can effectively avoid the following situation: if the content of phosphorus element is too large, the covalent nature of P-O may be too strong and affect the performance of the cathode active material. Small polarons conduct electricity, thereby affecting the conductivity of the material; if the content of phosphorus is too small, it may cause pyrophosphate in the core, the first cladding layer, and/or the phosphate lattice in the second cladding layer. The stability of the structure decreases, thus affecting the overall stability of the material.
  • the weight ratio of manganese element to phosphorus element is within the above range, which can effectively avoid the following situation: if the weight ratio is too large, it may lead to increased dissolution of transition metals, affecting The stability of the material and the cycle and storage performance of the secondary battery; if the weight ratio is too small, the discharge voltage platform of the material may decrease, thereby reducing the energy density of the secondary battery.
  • the lattice change rate of the cathode active material having a core-shell structure before and after complete deintercalation of lithium is 4% or less, optionally 3.8% or less, and more preferably 2.0-3.8%.
  • the positive electrode active material having a core-shell structure according to the above embodiment can achieve a lattice change rate of 4% or less before and after deintercalation of lithium. Therefore, the use of positive active materials can more effectively improve the gram capacity and rate performance of secondary batteries.
  • the Li/Mn anti-site defect concentration of the cathode active material having a core-shell structure is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%.
  • the positive electrode active material having a core-shell structure has a compacted density of 2.2 g/cm or more at 3 T (tons), optionally 2.2 g/cm or more and 2.8 g /cm 3 or less. Therefore, increasing the compaction density will increase the weight of the active material per unit volume, which is more conducive to increasing the volumetric energy density of the secondary battery.
  • the surface oxygen valence state of the cathode active material having a core-shell structure is -1.90 or less, optionally -1.90 to -1.98. Therefore, by limiting the surface oxygen valence state of the positive electrode active material within the above range, the interface side reaction between the positive electrode material and the electrolyte can be further reduced, thereby improving the battery cell cycle, high-temperature storage gas production and other performances.
  • a second aspect of the present application also provides a battery module.
  • the battery module includes a secondary battery, and the secondary battery is any of the above-mentioned secondary batteries of the present application.
  • a third aspect of the present application also provides a battery pack.
  • the battery pack includes a battery module, and the battery module is the above-mentioned battery module of the present application.
  • a fourth aspect of the present application also provides an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack.
  • a secondary battery which includes at least one of a secondary battery, a battery module, or a battery pack.
  • the above secondary batteries, battery modules, and battery packs are all provided by the present application. Secondary batteries, battery modules, and battery packs.
  • the battery module and battery pack of the present application have higher cycle performance and rate characteristics, thereby providing higher power cycle stability and rate for electrical devices equipped with the secondary battery, battery module or battery pack of the present application. characteristic.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be combined in any combination, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 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.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • 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).
  • coating layer refers to a material layer coated on the core.
  • the material layer may completely or partially cover the core.
  • the use of “coating layer” is only for convenience of description and is not intended to limit this article. invention.
  • the term “thickness of the coating layer” refers to the thickness of the material layer coating the core in the radial direction of the core.
  • source refers to a compound that is the source of a certain element.
  • types of “source” include but are not limited to carbonates, sulfates, nitrates, elements, halides, and oxides. and hydroxides, etc.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery normally includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions such as lithium ions
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte is between the positive electrode piece and the negative electrode piece and mainly plays the role of conducting active ions.
  • a first aspect of the present invention provides a secondary battery.
  • the secondary battery includes a positive electrode sheet and a non-aqueous electrolyte, wherein the positive electrode sheet includes a positive active material with a core-shell structure, and the positive active material includes a core and a non-aqueous electrolyte.
  • the shell covering the core.
  • the chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value in the range of -0.100-0.100, and y is in the range of 0.001-0.500 Any value within, z is any value within the range of 0.001-0.100, A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn , one or more elements among Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg, R is selected from B, Si, N and S One or more elements, optionally, R is an element selected from B, Si, N and S; the values of x, y and z satisfy the following conditions: the entire core remains electrically neutral; the shell includes a first cladding layer covering the core, a second cladding layer covering the first cladding layer, and a third cladding layer covering the second cladding layer, wherein
  • R 1 and R 2 are each independently one of C1-C10 alkyl and C1-C10 haloalkyl.
  • R 1 and R 2 are each independently methyl, ethyl, propyl, butyl, One of pentyl, hexyl, fluoromethyl, fluoroethyl, fluoropropyl, fluorobutyl, fluoropentyl and fluorohexyl, further optionally, R 1 and R 2 are independently Ground is one of methyl, ethyl, propyl, fluoromethyl, fluoroethyl and fluoropropyl.
  • the above limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A, but also on the stoichiometric number of each element as A.
  • Limitation of the sum of stoichiometric numbers For example, when A is two or more elements A1, A2...An, the stoichiometric numbers y1, y2...yn of A1, A2...An each need to fall within the numerical range of y defined in this application, and y1 , y2...yn and the sum must also fall within this numerical range.
  • the limitation on the numerical range of the R stoichiometric number in this application also has the above meaning.
  • the secondary battery of the present application utilizes a positive active material with a coating layer and an improvement in the composition of the electrolyte, which not only effectively improves the rate performance of the secondary battery, but also improves the cycle performance of the secondary battery. specifically:
  • the cathode active material of the present application can improve the gram capacity, cycle performance and safety performance of the secondary battery.
  • the lithium manganese phosphate cathode active material of the present application has a core-shell structure.
  • the core by coating the core with a first coating layer including crystalline pyrophosphate, it can further increase the migration resistance of manganese, reduce its dissolution, and reduce the surface miscellaneous lithium content , Reduce the contact between the core and the electrolyte, thereby reducing interface side reactions, reducing gas production, and improving the high-temperature storage performance, cycle performance and safety performance of the secondary battery; by further coating the crystalline phosphate with excellent ability to conduct lithium ions
  • the coating layer can effectively reduce the interfacial side reactions on the surface of the positive active material, thereby improving the high-temperature cycle and storage performance of the secondary battery; by further coating the carbon layer as the third coating layer, the secondary battery can be further improved safety performance and dynamic performance.
  • the element A doped at the manganese position of lithium manganese phosphate also helps to reduce the lattice change rate of lithium manganese phosphate during the deintercalation process of lithium, and improves the performance of the lithium manganese phosphate cathode material.
  • Structural stability greatly reducing the dissolution of manganese and reducing 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 lithium ion migration Barrier, promote the migration of lithium ions and improve the rate performance of secondary batteries.
  • the entire core system remains electrically neutral, ensuring that there are as few defects and impurities in the cathode active material as possible. If there is an excess of transition metal (such as manganese) in the cathode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely to precipitate in the form of elemental substances, or form a heterogeneous phase inside the crystal lattice, maintaining the electrical neutrality. Sex can minimize such impurities. In addition, ensuring the electrical neutrality of the system can also generate lithium vacancies in the material in some cases, thereby making the material's dynamic properties better.
  • transition metal such as manganese
  • this application obtains a doped lithium manganese phosphate core by doping element A at the manganese position of lithium manganese phosphate and doping element R at the phosphorus position, and sequentially performs three-layer coating on the surface of the core, providing a new type of lithium manganese phosphate with
  • the core-shell structure of lithium manganese phosphate cathode active material can significantly improve the high-temperature cycle performance, cycle stability and high-temperature storage performance of secondary batteries when the cathode active material is used in secondary batteries.
  • the first solvent in the non-aqueous electrolyte has a good ability to dissociate lithium salt, but compared to carbonate, the interaction between the first organic solvent and Li + is very small.
  • the first solvent gradually Dominating the first solvation layer, the desolvation energy of Li + will gradually decrease, which is conducive to the rapid insertion and extraction of Li + at the interface, thereby improving the rate performance of the secondary battery.
  • the first solvent has a low viscosity, which allows the lithium ions extracted from the positive electrode active material to quickly migrate and embed into the negative electrode side. Driven by concentration polarization, the lithium ions at the interface of the positive electrode material are quickly transferred to the electrolyte. to further improve the rate performance of secondary batteries.
  • the first solvent used in this application can be any carboxylic acid ester covered in the aforementioned formula 1.
  • the above-mentioned first solvent includes at least one of the following compounds:
  • the first solvent includes at least one of the following compounds:
  • the viscosity of the electrolyte is lower and the wettability is better, so the transmission ability of lithium ions is better, thereby better improving the rate performance of the secondary battery; at the same time, the above-mentioned first solvents Better chemical stability and better oxidation tolerance of the positive active material.
  • the first solvent has the advantages of low viscosity and high conductivity, it is prone to chemical reactions with the positive and negative electrodes of the secondary battery, thereby affecting the cycle performance of the secondary battery.
  • the mass percentage of the first solvent is w1, and w1 ranges from 20% to 80% (such as 20%, 25%, 30%, 35%, 40%, 45% , 50%, 55%, 60%, 65%, 70%, 75% or 80%); optionally, w1 ranges from 30% to 75%.
  • the first solvent can be used to improve the fast charging performance of the battery, and at the same time, the secondary battery can have good cycle performance and storage performance.
  • the organic solvent when using the first solvent as the solvent of the non-aqueous electrolyte, in order to ensure that the secondary battery has high cycle performance and storage performance as much as possible, in some embodiments, optionally, the organic solvent also includes a second Solvent, the second solvent includes one or more of the group consisting of chain carbonate and cyclic carbonate; further optionally, based on the total mass of the organic solvent, the mass percentage of the second solvent is w2, and the w2 The range is 20% to 80% (such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%); Optionally, the range of w2 is 25% to 70%.
  • the second solvent is used to cooperate with the first solvent to improve the cycle performance of the secondary battery.
  • the types of chain carbonate and cyclic carbonate of the above-mentioned second solvent are not particularly limited and can be selected according to actual needs.
  • the second solvent can include dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. , Methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate , one or more of propyl acetate, methyl propionate, ethyl propionate, and methyl propionate.
  • the solvent of the above-mentioned non-aqueous electrolyte may also include commonly used solvents such as tetrahydrofuran, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone. This application will no longer Let’s go over them one by one.
  • the non-aqueous electrolyte solution optionally also includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the above-mentioned non-aqueous electrolyte further includes a first additive
  • the first additive includes one or more from the group consisting of sultone and cyclic sulfate.
  • Sultones or cyclic sulfates are introduced into the non-aqueous electrolyte.
  • they form a layer of polymers with strong ion conductivity, such as ester-based sulfates, on the surface of the positive active material.
  • the polymer can not only further improve the rate performance of the secondary battery, but also effectively inhibit the catalytic oxidation of the first solvent by the positive electrode active material, thereby improving the cycle and storage performance of the secondary battery.
  • sultone or cyclic sulfate can form a film on the negative electrode better than the first solvent, reducing the reaction of ⁇ -H on the first solvent with the active lithium obtained by the reduction of the negative electrode, thereby further improving the cycle and performance of the secondary battery. Storage performance.
  • the sultones and cyclic sulfates used in the above embodiments of the present application can be corresponding substances commonly used in the prior art.
  • the above sultones include at least one of the compounds represented by Formula 2. ,
  • p means 1, 2 or 3,
  • R 11 represents one of hydrogen atom, halogen atom, C1 ⁇ C12 alkyl group, C1 ⁇ C12 haloalkyl group, C1 ⁇ C12 alkoxy group, C1 ⁇ C12 haloalkoxy group; optionally, R 11 represents hydrogen atom, halogen One of atom, C1 ⁇ C6 alkyl, C1 ⁇ C3 haloalkyl, C1 ⁇ C3 alkoxy, C1 ⁇ C3 haloalkoxy; optionally the alkoxy group is a chain alkoxy group or a cyclic alkoxy group , optionally the cyclic alkoxy group shares one carbon atom with the parent ring of sultone, and further optionally the cyclic alkoxy group has a carbon number of 4, 5 or 6;
  • Each R 12 independently represents a hydrogen atom, a halogen atom, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, or a 4 to 7-membered sultone group.
  • each R 12 independently represents a hydrogen atom, a halogen atom, a C1 ⁇ C3 alkyl group, a C1 ⁇ C3 haloalkyl group, a C1 ⁇ C3 alkoxy group, a C1 ⁇ C3 haloalkoxy group, a 5- to 6-membered
  • the sultone groups optionally, the sultone group shares one carbon atom with the parent ring of the sultone, and optionally the sultone group is a 5-membered ring;
  • R 11 and R 12 and the carbon atoms to which they are connected can form a 5- to 10-membered cycloalkyl group
  • R 13 represents a hydrogen atom, a halogen atom, a carbonyl group, a C2 to C6 ester group, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C2 to C12 alkenyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, One of C6 ⁇ C20 aryl or benzyl; optionally, R 13 represents a hydrogen atom, a halogen atom, a carbonyl group, a C2 ⁇ C3 ester group, a C1 ⁇ C3 alkyl group, a C1 ⁇ C3 haloalkyl group, C2 ⁇ C6 One of alkenyl, C1 ⁇ C3 alkoxy, C1 ⁇ C3 haloalkoxy, C6 ⁇ C10 aryl or benzyl.
  • the above-mentioned sultone is a commonly used sultone in this field, with wide sources and low cost.
  • the above-mentioned cyclic sulfate ester includes at least one of the compounds represented by Formula 3,
  • q means 1, 2 or 3
  • R 14 represents a hydrogen atom, a halogen atom, a carbonyl group, a C1 to C12 alkyl group, a C1 to C12 haloalkyl group, a C2 to C12 alkenyl group, a C1 to C12 alkoxy group, a C1 to C12 haloalkoxy group, or a C2 to C6 ester group, One of the 4 to 7-membered cyclic sulfate groups; optionally, R 14 represents a hydrogen atom, a halogen atom, a carbonyl group, a double bond, a C1 to C6 alkyl group, a C1 to C3 haloalkyl group, or a C1 to C3 alkoxy group One of the group, C1 ⁇ C3 haloalkoxy group, C2 ⁇ C3 ester group, 4 to 5-membered cyclic sulfate ester group; optionally the cyclic sulfate ester group and
  • Each R 15 independently represents one of a hydrogen atom, a halogen atom, a C1-C12 alkyl group, a C1-C12 haloalkyl group, a C1-C12 alkoxy group, a C1-C12 haloalkoxy group, or a C6-C20 aryl group; it can Optionally, each R 15 independently represents one of a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C3 haloalkyl group, a C1 to C3 alkoxy group, a C1 to C3 haloalkoxy group, or a C6 to C10 aryl group. kind;
  • R 14 and R 15 together with their respective linked carbon atoms form a 4 to 7-membered cyclic sulfate ester group. Further optionally, R 14 and R 15 together with their respective linked carbon atoms form a 5-membered cyclic sulfate ester group. base.
  • cyclic sulfate ester is a cyclic sulfate ester commonly used in this field, with wide sources and low cost.
  • the sultone includes at least one of the following compounds:
  • the cyclic sulfate ester includes at least one of the following compounds:
  • the sultone includes at least one of the following compounds:
  • the cyclic sulfate ester includes at least one of the following compounds:
  • sultone and cyclic sulfate can improve the cycle performance and storage performance of the secondary battery. However, if they are used in excessive amounts, they may increase the resistance of the positive and negative electrodes of the secondary battery. To affect the rate of the secondary battery, those skilled in the art can refer to the conventional dosages of existing sultones and cyclic sulfate esters to select their dosages in the non-aqueous electrolyte of the present application.
  • the content of the first additive is W3, and 0.01% ⁇ W3 ⁇ 20% (such as 0.01%, 0.05%, 0.1%, 0.2%, 0.5%, 1 %, 2%, 3%, 4%, 5%, 10%, 15% or 20%), optionally 0.1% ⁇ W3 ⁇ 10%, further optionally 0.3% ⁇ W3 ⁇ 5%.
  • the non-aqueous electrolyte solution used in the present application further includes a second additive.
  • the second additive includes a sulfite compound, a disulfonate compound, a nitrile compound, an aromatic compound, a phosphazene compound, an acid anhydride compound, One or more of the group consisting of phosphate ester compounds, phosphate ester compounds, and borate ester compounds.
  • the above-mentioned second additive helps to form a denser and more stable interface film on the surface of the positive electrode and/or negative electrode active material, thereby further improving at least one of the cycle performance, storage performance, and rate performance of the secondary battery.
  • the content of the second additive is W4, 0.01% ⁇ W4 ⁇ 20%, optionally 0.05% ⁇ W4 ⁇ 5%, further optionally 0.1% ⁇ W4 ⁇ 3%. So that the role of the second additive can be fully exerted.
  • the sulfite compound is preferably a cyclic sulfite compound, specifically one or more of the compounds represented by Formula 4.
  • R 28 is selected from substituted or unsubstituted C1 to C6 alkylene, substituted or unsubstituted C2 to C6 alkenylene, wherein the substituent is selected from halogen atoms, C1 to C3 alkyl, C2 to One or more types of C4 alkenyl groups.
  • R 28 is selected from substituted or unsubstituted C1 ⁇ C4 alkylene, substituted or unsubstituted C2 ⁇ C4 alkenylene, wherein the substituent is selected from halogen atoms, C1 ⁇ C3 alkyl One or more of C2-C4 alkenyl groups.
  • the sulfite compound may be selected from one or more of ethylene sulfite (ES for short), propylene sulfite (PS for short), butylene sulfite (BS for short).
  • ES ethylene sulfite
  • PS propylene sulfite
  • BS butylene sulfite
  • the methylene disulfonate compound can be selected from the group consisting of formula 5. one or more of the compounds shown.
  • R 24 , R 25 , R 26 , and R 27 are each independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C1 to C10 alkyl group, and a substituted or unsubstituted C2 to C10 alkenyl group, where , the substituent is selected from one or more types of halogen atoms, C1-C3 alkyl groups, and C2-C4 alkenyl groups.
  • R 24 , R 25 , R 26 , and R 27 are each independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C4 alkyl group, a substituted or unsubstituted C2-C6 Alkenyl group, wherein the substituent is selected from one or more of halogen atoms, C1-C3 alkyl groups, and C2-C4 alkenyl groups.
  • the disulfonate compound may be specifically selected from one or more of the following compounds, but the application is not limited thereto:
  • the disulfonate compound may be selected from methylene methane disulfonate (abbreviated as
  • the nitrile compound may be any one of the compounds represented by Formula 6 or Formula 7,
  • R 5 is selected from substituted or unsubstituted C1 to C12 alkylene, substituted or unsubstituted C2 to C12 alkenylene, substituted or unsubstituted C2 to C12 alkynylene
  • R 6 , R 7 and R 8 are each independently selected from substituted or unsubstituted C0 ⁇ C12 alkylene, substituted or unsubstituted C2 ⁇ C12 alkenylene, substituted or unsubstituted C2 ⁇ C12 alkynylene, wherein, substituted The group is selected from one or more of halogen atoms, nitrile groups, C1-C6 alkyl groups, C2-C6 alkenyl groups, and C1-C6 alkoxy groups.
  • R 5 is selected from substituted or unsubstituted C1 to C10 alkylene, substituted or unsubstituted C2 to C10 alkenylene, substituted or unsubstituted C2 to C10 alkynylene
  • R 6 , R 7 , R 8 is each independently selected from substituted or unsubstituted C0-C10 alkylene, substituted or unsubstituted C2-C10 alkenylene, substituted or unsubstituted C2-C10 alkynylene, wherein the substituent is selected from halogen atom.
  • R 5 is selected from C 1 to C 6 alkylene, C 2 to C 6 alkenylene, C 2 to C 6 alkynylene, optionally, R 5 is selected from C 2 to C 4 alkylene, C 2 to C 4 alkenylene, C 2 to C 4 alkynylene; in formula 7, R 6 , R 7 , and R 8 are each independently selected from C 0 to C 6 Alkyl group, C 2 to C 6 alkenylene group, C 2 to C 6 alkynylene group, optionally, R 6 is selected from C 0 to C 1 alkylene group, R 7 and R 8 are each independently selected from C 2 ⁇ C 4 alkylene group, C 2 ⁇ C 4 alkenylene group, C 2 ⁇ C 4 alkynylene group.
  • the above-mentioned nitrile compound is selected from the group consisting of ethanedonitrile, sebaconitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, sebaconitrile, undecane dinitrile, Dialkanedonitrile, tetramethylsuccinonitrile, methylglutaronitrile, butenedonitrile, 2-pentenedonitrile, hex-2-enedonitrile, hex-3-enedonitrile, oct-4-ene One or more of dinitrile, octy-4-ynediconitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, and 1,3,6-hexanetricarbonitrile.
  • the aromatic compound may be selected from cyclohexylbenzene, fluorinated cyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butyl Benzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (ortho-, meta-, para-), diphenyl ether, fluorobenzene, difluorobenzene (ortho- body, meta body, para body), anisole, 2,4-difluoroanisole, partially hydrogenated compounds of terphenyl (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2 - one or more of diphenylcyclohexane, o-cyclohexy
  • the aromatic compound may be selected from one or more of biphenyl, terphenyl (ortho, meta, para), fluorobenzene, cyclohexylbenzene, tert-butylbenzene, and tert-amylbenzene.
  • the aromatic compound may be selected from one or more of biphenyl, o-terphenyl, fluorobenzene, cyclohexylbenzene, and tert-amylbenzene.
  • the phosphazene compound is preferably a cyclic phosphazene compound.
  • the cyclic phosphazene compound may be selected from one of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene. species or several species.
  • the cyclic phosphazene compound may be selected from one or more of methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and phenoxypentafluorocyclotriphosphazene.
  • the cyclic phosphazene compound may be selected from methoxypentafluorocyclotriphosphazene or ethoxypentafluorocyclotriphosphazene.
  • the acid anhydride compound may be a chain acid anhydride or a cyclic acid anhydride. Specifically, the acid anhydride compound may be selected from acetic acid
  • One or more of sulfo-propionic anhydrides are provided.
  • the acid anhydride compound may be selected from one or more of succinic anhydride, maleic anhydride, and 2-allylsuccinic anhydride. Further optionally, the acid anhydride compound may be selected from one or both of succinic anhydride and 2-allylsuccinic anhydride.
  • the phosphite compound can be selected from silane phosphite compounds, specifically one or more of the compounds represented by Formula 8.
  • R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 , and R 39 are each independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.
  • silane phosphite compound may be specifically selected from one or more of the following compounds, but the application is not limited thereto:
  • the phosphate ester compound may be selected from silane phosphate ester compounds, specifically one or more of the compounds represented by Formula 9.
  • R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , and R 49 are each independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.
  • silane phosphate compound may be specifically selected from one or more of the following compounds, but the application is not limited thereto:
  • the borate compound can be selected from silane borate compounds, specifically one or more of the compounds represented by Formula 10.
  • R 51 , R 52 , R 53 , R 54 , R 55 , R 56 , R 57 , R 58 , and R 59 are each independently selected from halogen-substituted or unsubstituted C1 to C6 alkyl groups.
  • the silane borate compound may be specifically selected from one or more of the following compounds, but the application is not limited thereto:
  • the non-aqueous electrolyte of the secondary battery of the present application also includes lithium salt.
  • the type of lithium salt is not particularly limited and can be selected according to actual needs.
  • the lithium salt can be selected from LiN(C x' F 2x'+1 SO 2 )(C y' F 2y'+1 SO 2 ), LiPF 6 , LiBF 4 , LiBOB, LiAsF 6 , Li(FSO 2 ) 2 N , LiCF 3 SO 3 and LiClO 4 , where x' and y' are natural numbers, such as 0, 1, 2, 3, 4, 5 or 6 independently.
  • the concentration of the above-mentioned lithium salt ranges from 0.5 mol/L to 2.5 mol/L, preferably from 0.8 mol/L to 2 mol/L.
  • the positive electrode sheet usually includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material.
  • the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • Composite current collectors can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the main characteristic peak position in the XRD pattern of lithium manganese phosphate doped with A element and R element is the same as that of undoped LiMnPO 4
  • the consistency indicates that the doping process does not introduce impurity phases. Therefore, the improvement in core performance mainly comes from element doping rather than impurity phases.
  • the inventor of the present application cut out the middle region of the prepared cathode active material particles through focused ion beam (FIB for short), and analyzed it through transmission electron microscope (TEM for short) and X-ray energy spectroscopy analysis (EDS for short). ) conducted tests and found that each element was evenly distributed and no aggregation occurred.
  • A when A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge
  • Q, D, E, 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.
  • one of n1, n2, n3, and n4 is zero, and the rest are not zero; more optionally, two of n1, n2, n3, and n4 are zero, and the rest are not zero; also optionally, Three of n1, n2, n3, and n4 are zero, and the rest are not zero.
  • the size of x is affected by the valence sizes of A and R and the sizes of y and z to ensure that the entire system is electrically neutral sex. If the value of x is too small, the lithium content of the entire core system will be reduced, affecting the gram capacity of the material.
  • the y value will limit the total amount of all doping elements. If y is too small, that is, the doping amount is too small, the doping elements will have no effect. If y exceeds 0.5, the Mn content in the system will be less, affecting the material's properties. voltage platform.
  • the R element is doped at the P position. Since the PO tetrahedron is relatively stable and an excessive z value will affect the stability of the material, the z value is limited to 0.001-0.100.
  • crystalline means that the degree of crystallinity is above 50%, that is, between 50% and 100%. Crystallinity less than 50% is called glassy state.
  • the crystallinity of the crystalline pyrophosphate and crystalline phosphate of the present application ranges from 50% to 100%. Pyrophosphate and phosphate with a certain degree of crystallinity are not only conducive to giving full play to the pyrophosphate coating layer's ability to hinder the elution of manganese ions and the phosphate coating layer's excellent ability to conduct lithium ions and reduce interface side reactions, but also enable The pyrophosphate coating layer and the phosphate coating layer can achieve better lattice matching, thereby achieving a tighter combination of the coating layers.
  • the crystallinity of the first coating layer material crystalline pyrophosphate and the second coating layer material crystalline phosphate of the cathode active material can be tested by conventional technical means in the art, such as by density method, Measurements by infrared spectroscopy, differential scanning calorimetry and nuclear magnetic resonance absorption methods can also be performed, for example, by X-ray diffraction.
  • 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 cathode active material may include the following steps:
  • the crystallinity is the ratio of the crystalline part scattering to the total scattering intensity.
  • 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, sintering time, and the like.
  • pyrophosphate serves as the first coating layer to effectively isolate the doped metal ions from the electrolyte.
  • the structure of crystalline pyrophosphate is stable. Therefore, crystalline pyrophosphate coating can effectively inhibit the dissolution of transition metals and improve cycle performance.
  • the bond between the first cladding layer and the core is similar to a heterojunction, and the strength of the bond is limited by the degree of lattice matching.
  • the degree of bonding between the first cladding layer and the core is measured mainly by calculating the mismatch between the lattice constants of the core and the cladding. In this application, after the A and R elements are doped in the core, compared with undoped elements, the matching between the core and the first cladding layer is improved, and the core and the pyrophosphate cladding layer can be closer ground together.
  • Crystalline phosphate was chosen as the second coating layer, firstly, because it has a high lattice match with the first layer of coating crystalline pyrophosphate (the mismatch is only 3%); secondly, phosphate Its own stability is better than that of pyrophosphate, and coating pyrophosphate with it will help improve the stability of the material.
  • the structure of crystalline phosphate is very stable and has excellent ability to conduct lithium ions. Therefore, coating with crystalline phosphate can effectively reduce interfacial side reactions on the surface of the cathode active material, thereby improving the high temperature of secondary batteries. Looping and storage performance.
  • the lattice matching between the second cladding layer and the first cladding layer is similar to the above-mentioned combination between the first cladding layer and the core.
  • the lattice mismatch is less than 5%, the lattice matching is relatively small. Well, the two are easily combined closely.
  • carbon is used as the third layer of coating. Since electrochemical reactions occur when used in secondary batteries, electrons are required to participate. Therefore, in order to increase electron transmission between particles and at different locations on the particles, materials with excellent conductive properties can be used. Carbon is used to coat the positive active material. Carbon coating can effectively improve the conductive properties and desolvation ability of cathode active materials.
  • Each coating layer in this application can be completely covered or partially covered.
  • the coating amount of the first coating layer is C1 weight %, C1 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, more optionally Greater than 0 and less than or equal to 2.
  • the coating amount of the second coating layer is C2 weight %, C2 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, more optionally 2-4 .
  • the coating amount of the third coating layer is C3% by weight, and C3 is greater than 0 and less than or equal to 6, optionally greater than 0 and less than or equal to 5.5, more optionally greater than 0 and less than or equal to 5.5. Less than or equal to 2.
  • the coating amount of each layer is not zero.
  • the coating amount of the three coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the gram of the cathode active material.
  • the dynamic performance and safety performance of secondary batteries can be further improved.
  • the coating amount is within the above range, the following situations can be avoided: Too little coating means that the thickness of the coating layer is thin, which may not effectively hinder the migration of transition metals; Excessive amount means that the coating layer is too thick, which will affect the migration of Li + and thus affect the rate performance of the material.
  • the coating amount within the above range, the following situations can be avoided: too much coating may affect the overall platform voltage of the material; too little coating may not achieve sufficient Covering effect.
  • the carbon coating mainly plays the role of enhancing electron transmission between particles.
  • the structure also contains a large amount of amorphous carbon, the density of carbon is low. Therefore, if the coating amount is too high, If it is large, it will affect the compaction density of the pole piece.
  • the coating amount of the three coating layers is preferably within the above range, so that the core can be fully coated without sacrificing the gram capacity of the cathode active material. Under the premise of further improving the dynamic performance and safety performance of secondary batteries.
  • the interplanar distance of the crystalline pyrophosphate in the first coating layer ranges from 0.293 to 0.470 nm, and the angle range of the crystal orientation (111) ranges from 18.00° to 32.00°; the second coating layer
  • the interplanar spacing range of the crystalline phosphate is 0.244-0.425nm, and the angle range of the crystal direction (111) is 20.00°-37.00°.
  • the crystalline pyrophosphate and crystalline phosphate in the coating layer can be characterized by conventional technical means in the art, or by means of a transmission electron microscope (TEM), for example. Under TEM, the core and cladding layers can be distinguished by testing the interplanar spacing.
  • TEM transmission electron microscope
  • the specific testing method for the interplanar spacing and angle of crystalline pyrophosphate and crystalline phosphate in the coating layer may include the following steps:
  • the difference between the interplanar spacing range of crystalline pyrophosphate and the existence of crystalline phosphate can be directly judged by the value of the interplanar spacing.
  • the first coating layer and the second coating layer in the cathode active material of the above embodiment are both made of crystalline materials, and their interplanar spacing and included angle range are within the above range.
  • impurity phases in the coating layer can be effectively avoided, thereby improving the gram capacity, cycle performance and rate performance of the material.
  • crystalline pyrophosphate and crystalline phosphate within the above-mentioned crystal plane spacing and included angle range can more effectively suppress the lattice change rate of lithium manganese phosphate and the dissolution of manganese ions during the lithium deintercalation process, thus improving the secondary High-temperature cycle performance, cycle stability and high-temperature storage performance of the battery.
  • the ratio of y to 1-y is 1:10 to 1:1, optionally 1:4 to 1:1.
  • the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249.
  • z represents the sum of stoichiometric numbers of the P-site doping elements R.
  • the carbon in the third coating layer is a mixture of SP2 form carbon and SP3 form carbon.
  • the molar ratio of SP2 form carbon to SP3 form carbon is any value in the range of 0.1-10. Choose any value in the range 2.0-3.0.
  • the molar ratio of SP2 form carbon to SP3 form carbon can be about 0.1, about 0.2, about 03, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 2 , about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10, or within any range of any of the above values.
  • the overall electrical performance of the secondary battery is improved.
  • the following situation can be avoided: If the carbon in the cladding layer is all amorphous SP3 form, the conductivity is poor; if they are all graphitized SP2 form, although the conductivity is good, there are few lithium ion paths, which is not conducive to the deintercalation of lithium.
  • limiting the molar ratio of SP2 form carbon to SP3 form carbon within the above range can not only achieve good conductivity, but also ensure the passage of lithium ions, so it is conducive to the optimization of secondary battery functions and the improvement of cycle performance. .
  • the mixing ratio of the SP2 form and the SP3 form of the third cladding carbon can be controlled by sintering conditions such as sintering temperature and sintering time.
  • sintering conditions such as sintering temperature and sintering time.
  • sucrose is used as the carbon source to prepare the third coating layer
  • the sucrose is cracked at high temperature and deposited on the second coating layer.
  • both SP3 and SP2 forms will be produced. of carbon coating.
  • the ratio of SP2 form carbon and SP3 form carbon can be controlled by selecting high temperature cracking conditions and sintering conditions.
  • the structure and characteristics of the carbon in the third coating layer can be measured by Raman spectroscopy.
  • the specific test method is as follows: by peak splitting the energy spectrum of the Raman test, Id/Ig is obtained (where Id is the peak of SP3 form carbon Intensity, Ig is the peak intensity of SP2 form carbon), thereby confirming the molar ratio of the two.
  • the thickness of the first cladding layer is 1-10 nm; and/or the thickness of the second cladding layer is 2-15 nm; and/or the thickness of the third cladding layer is 2-25 nm.
  • the thickness of the first cladding layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or any range of any of the above values.
  • the thickness of the second cladding 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 14nm, about 15nm, or within any range of any of the above values.
  • the thickness of the third cladding 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 13nm, about 14nm, about 15nm, about 16nm, about 17nm, about 18nm, about 19nm, about 20nm, about 21nm, about 22nm, about 23nm, about 24nm or about 25nm, or within any range of any of the above values.
  • the thickness of the first cladding layer ranges from 1 to 10 nm, it can avoid the possible adverse effects on the dynamic properties of the material when it is too thick, and can avoid the problem that when it is too thin, it may not be able to effectively hinder the migration of transition metal ions. .
  • 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 reaction with the electrolyte is small. Therefore, the interface side reaction can be more effectively alleviated, thereby further improving the secondary battery. high temperature performance.
  • the electrical conductivity of the material can be further improved and the compaction performance of the battery pole piece prepared using the cathode active material can be better improved.
  • the thickness test of the coating layer is mainly carried out through 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 slice with a thickness of about 100nm from the middle position or near the middle position of the selected particle, and then Conduct TEM test on the sheet, measure the thickness of the coating layer, measure 3-5 positions, and take the average value.
  • the manganese element content is in the range of 10%-35% by weight, optionally in the range of 15%-30% by weight, more optionally in the range of 17%-20% by weight, based on the weight of the cathode active material.
  • the content of phosphorus element is in the range of 12% by weight - 25% by weight, optionally in the range of 15% by weight - 20% by weight, and the weight ratio range of manganese element and phosphorus element is 0.90-1.25, optionally in the range of 0.90-1.25. 0.95-1.20.
  • the content of manganese may correspond to the content of the core.
  • limiting the content of manganese element within the above range can effectively avoid problems such as deterioration of material structure stability and decrease in density that may be caused if the content of manganese element is too high, thereby effectively improving the cycle life of the secondary battery. , storage and compression performance; and can avoid problems such as low voltage platform that may be caused if the manganese content is too small, thereby further improving the energy density of secondary batteries.
  • limiting the content of phosphorus element to the above range can effectively avoid the following situation: if the content of phosphorus element is too large, the covalent nature of P-O may be too strong and affect the conductivity of small polarons, thereby affecting the conductivity of small polarons.
  • the electrical conductivity of the material if the phosphorus content is too small, it may reduce the stability of the core, the pyrophosphate in the first cladding layer, and/or the phosphate lattice structure in the second cladding layer, thus affecting the overall material. stability.
  • the weight ratio of manganese to phosphorus content has the following impact on the performance of secondary batteries: If the weight ratio is too large, it means that there is too much manganese element, and the dissolution of manganese ions increases, which affects the stability and gram capacity of the cathode active material, which in turn affects the secondary battery.
  • the measurement of manganese and phosphorus elements can be carried out using conventional technical means in this field.
  • the following method is used to determine the content of manganese and phosphorus: dissolve the material in dilute hydrochloric acid (concentration 10-30%), use ICP to test the content of each element in the solution, and then measure and convert the content of manganese. Get its weight ratio.
  • the lattice change rate of the cathode active material with a core-shell structure before and after complete deintercalation of lithium is less than 4%, optionally less than 3.8%, and more preferably 2.0-3.8%.
  • the lithium deintercalation process of lithium manganese phosphate is a two-phase reaction.
  • the interfacial stress of the two phases is determined by the lattice change rate before and after lithium deintercalation.
  • the cathode active material having a core-shell structure of the above embodiment can achieve a lattice change rate of 4% or less before and after deintercalation of lithium. Therefore, use of the cathode active material can improve the rate performance of the secondary battery.
  • the lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).
  • the Li/Mn anti-site defect concentration of the cathode active material having a core-shell structure is 4% or less, optionally 2.2% or less, and more preferably 1.5-2.2%.
  • the Li/Mn anti-site defect in this application refers to the interchange of positions of Li + and Mn 2+ in the LiMnPO 4 crystal lattice.
  • the Li/Mn antisite defect concentration refers to the percentage of Li + exchanged with Mn 2+ to the total amount of Li + .
  • the Li/Mn antisite defect concentration can be tested in accordance with JIS K 0131-1996, for example.
  • the cathode active material with the core-shell structure of the above embodiment can achieve the above-mentioned lower Li/Mn anti-site defect concentration.
  • the mechanism is not very clear, the inventor of the present application speculates that because Li + and Mn 2+ will exchange positions in the LiMnPO 4 lattice, and the Li + transmission channel is a one-dimensional channel, Mn 2+ is in Li + It will be difficult to migrate in the channel, thus hindering the transport of Li + . Therefore, the cathode active material with a core-shell structure described in this application has a low Li/Mn anti-site defect concentration within the above range. Therefore, it can avoid Mn 2+ from hindering the transport of Li + and at the same time improve the cathode activity. Gram capacity play and rate performance of the material.
  • the positive active material has a compacted density of 2.2 g/cm or more at 3T, optionally 2.2 g/cm or more and 2.8 g/cm or less.
  • the higher the compaction density the greater the weight of the active material per unit volume. Therefore, increasing the compaction density is beneficial to increasing the volumetric energy density of the battery core.
  • the compacted density can be measured according to GB/T 24533-2009.
  • the surface oxygen valence state of the cathode active material is -1.90 or less, optionally -1.90 to -1.98.
  • the stable valence state of oxygen is originally -2. The closer the valence state is to -2, the stronger its ability to obtain electrons, that is, the stronger its oxidizing ability.
  • its surface valence state is below -1.7.
  • EELS electron energy loss spectroscopy
  • This application also provides a preparation method of cathode active material, including the following steps:
  • the step of providing core material the core chemical formula is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value within the range of -0.100-0.100, and y is within 0.001-0.500 Any value within the range, z is any value within the range of 0.001-0.100, and the A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, One or more elements among Ga, Sn, Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg, the R is selected from B, Si , one or more elements in N and S, optionally, the R is an element selected from B, Si, N and S;
  • Coating step Provide Li a MP 2 O 7 and/or M b (P 2 O 7 ) c and XPO 4 suspension respectively, add the core material to the above suspension and mix, and obtain the positive electrode through sintering Active material, where 0 ⁇ a ⁇ 2, 1 ⁇ b ⁇ 4, 1 ⁇ c ⁇ 6, the values of a, b and c satisfy the following conditions: making crystalline pyrophosphate Li a MP 2 O 7 or M b (P 2 O 7 ) c remains electrically neutral; M is each independently one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; X One or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al;
  • the positive active material has a core-shell structure, which includes the inner core and a shell covering the inner core.
  • the shell includes a first coating layer covering the inner core, and a first coating layer covering the first outer core.
  • a second coating layer of the coating layer and a third coating layer coating the second coating layer the first coating layer comprising crystalline pyrophosphate Li a MP 2 O 7 and/or M b ( P 2 O 7 ) c
  • the second coating layer includes crystalline phosphate XPO 4
  • the third coating layer is carbon.
  • the step of providing core material includes the following steps:
  • Step (1) Mix and stir the manganese source, the dopant of element A and the acid in a container to obtain manganese salt particles doped with element A;
  • Step (2) Mix the manganese salt particles doped with element A with a lithium source, a phosphorus source and a dopant of element R in a solvent to obtain a slurry, and then sinter under the protection of an inert gas atmosphere to obtain doping.
  • element A and element R there is a core of element A and element R, wherein the core doped with element A and element R is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is at -0.100- Any value within the range of 0.100, y is any value within the range of 0.001-0.500, z is any value within the range of 0.001-0.100, and the A is selected from Zn, Al, Na, K, Mg, Mo, W , one or more elements among Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements among Fe, Ti, V, Ni, Co and Mg
  • the R is one or more elements selected from the group consisting of B, Si, N and S, optionally, the R is one element selected from the group consisting of B, Si, N and S.
  • the preparation method of the present application has no particular limitation on the source of materials.
  • the source of a certain element may include one of the elements, sulfates, halides, nitrates, organic acid salts, oxides or hydroxides of the element. or more, the precursor is the source that can achieve the purpose of the preparation method of the present application.
  • the dopant of element A is selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and one or more of the respective elements, carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides of one or more elements in Ge.
  • the dopant of the element R is an inorganic acid, a acid, an organic acid, a sulfate, a chloride salt, or one or more elements selected from B, Si, N, and S.
  • the manganese source may be a manganese-containing material known in the art that can be used to prepare lithium manganese phosphate.
  • the manganese source may be one or more selected from the group consisting of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.
  • the acid may be one or more selected from organic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, silicic acid, etc., and organic acids such as oxalic acid.
  • the acid is a dilute organic acid with a concentration of 60% by weight or less.
  • the lithium source may be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate.
  • the lithium source is one or more selected from the group consisting of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.
  • the phosphorus source may be a phosphorus-containing material known in the art that can be used to prepare lithium manganese phosphate.
  • the phosphorus source is one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and phosphoric acid.
  • the dopant of element A and the acid react in a solvent to obtain a manganese salt suspension doped with element A
  • the suspension is filtered, Dry and sand grind to obtain element A-doped manganese salt particles with a particle size of 50-200 nm.
  • 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.
  • the step (1) is mixed at a temperature of 20-120°C, optionally 40-120°C; and/or
  • the stirring in step (1) is carried out at 400-700 rpm for 1-9 hours, optionally 3-7 hours.
  • the reaction temperature in step (1) may 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. °C; the stirring described in step (1) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours; optionally,
  • the reaction temperature and stirring time in step (1) can be within any range of any of the above values.
  • the step (2) is mixed at a temperature of 20-120°C, optionally 40-120°C, for 1-12 hours.
  • the reaction temperature in step (2) 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. °C; the mixing described in step (2) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, About 11 hours or about 12 hours; optionally, the reaction temperature and mixing time in step (2) can be within any range of any of the above values.
  • the prepared core and the cathode active material produced therefrom have fewer lattice defects, which is beneficial to inhibiting the dissolution of manganese ions and reducing the interaction between the cathode active material and the electrolyte. Interfacial side reactions, thereby improving the cycle performance and safety performance of secondary batteries.
  • the pH of the solution is controlled to be 3.5-6, optionally, the pH of the solution is controlled to be 4-6, more preferably Optionally, the pH of the solution is controlled to be 4-5. It should be noted that in this application, the pH of the resulting mixture can be adjusted by methods commonly used in the art, for example, by adding acid or alkali.
  • the molar ratio of the manganese salt particles to the lithium source and the phosphorus source is 1:0.5-2.1:0.5-2.1, and more optionally, the doped
  • the molar ratio of the manganese salt particles mixed with element A to the lithium source and phosphorus source is about 1:1:1.
  • the sintering conditions in the process of preparing A element and R element doped lithium manganese phosphate are: sintering at 600-950°C for 4-10 seconds under an inert gas or a mixed atmosphere of inert gas and hydrogen. hours; optionally, the sintering can be performed 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 any of the above values.
  • the protective atmosphere is a mixed gas of 70-90% nitrogen by volume and 10-30% hydrogen by volume.
  • the coating step includes:
  • the first coating step dissolve the source of element M, the phosphorus source and the acid, and optionally the lithium source in a solvent to obtain a first coating layer suspension; combine the core obtained in the core step with the first coating The first coating layer suspension obtained in the step is thoroughly mixed, dried, and then sintered to obtain a material covered by the first coating layer;
  • the second coating step dissolve the source of element
  • the second coating layer suspension obtained in the second coating step is thoroughly mixed, dried, and then sintered to obtain a material covered with two coating layers;
  • the third coating step Dissolve the carbon source in the solvent and fully dissolve it to obtain a third coating layer solution; then add the two-layer coating layer-coated material obtained in the second coating step to the third coating layer layer solution, mix evenly, dry, and then sinter to obtain a material coated with three coating layers, that is, the positive electrode active material.
  • the source of the element M is elemental carbonic acid of one or more elements selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al.
  • the source of the element One or more of carbonates, sulfates, chlorides, nitrates, organic acid salts, oxides, and hydroxides.
  • the carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
  • the pH of the solution in which the source of element M, the phosphorus source and the acid, and optionally the lithium source are dissolved is controlled to be 3.5-6.5, and then stirred and reacted for 1-5 h, and then The solution is heated to 50-120°C and maintained at this temperature for 2-10 hours, and/or sintering is performed at 650-800°C for 2-6 hours.
  • the reaction proceeds fully.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours or about 5 hours.
  • the reaction time of the reaction can be within any range of any of the above values.
  • the pH of the solution is controlled to be 4-6.
  • 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 keep at this 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, the first coating In this step, the heating temperature and holding time may be within any range of any of the above values.
  • the sintering may 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 any of the above values.
  • the first coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the first coating step is too low and the sintering time is too short, it will lead to The crystallinity of the first coating layer is low and there are many amorphous substances, which will reduce the effect of inhibiting metal dissolution, thereby affecting the cycle performance and high-temperature storage performance of the secondary battery; and when the sintering temperature is too high, it will cause the second The presence of impurities in the first coating layer will also affect its effect of inhibiting metal dissolution, thereby affecting the cycle and high-temperature storage performance of the secondary battery. When the sintering time is too long, the thickness of the first coating layer will increase, affecting The migration of Li+ affects the gram capacity and rate performance of the material.
  • the second coating step after the source of element And maintain this temperature for 2-10 hours, and/or, sintering is performed at 500-700°C for 6-10 hours.
  • the reaction proceeds fully.
  • the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours hours, about 9 hours or about 10 hours.
  • the reaction time of the reaction can be within any range of any of the above values.
  • the solution is heated to about 65°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C, about 120°C, about 130°C, About 140°C or about 150°C, and maintained 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;
  • the temperature and holding time of the heating can be within any range of any of the above values.
  • the sintering may be performed 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;
  • the sintering temperature and sintering time may be within any range of any of the above values.
  • the second coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the second coating step is too low and the sintering time is too short, it will lead to The second coating layer has low crystallinity and a large amount of amorphous state, which reduces the surface reactivity of the material and affects the cycle and high-temperature storage performance of the secondary battery.
  • the sintering temperature is too high, the second coating layer will The presence of impurities in the coating will also affect its effect of reducing the surface reactivity of the material, thereby affecting the cycle and high-temperature storage performance of the secondary battery.
  • the sintering time is too long, the thickness of the second coating will increase, affecting The voltage platform of the material, thereby reducing the energy density of the material, etc.
  • the sintering in the third coating step is performed at 700-800°C for 6-10 hours.
  • the sintering may 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;
  • the sintering temperature and sintering time may be within any range of any of the above values.
  • the third coating step by controlling the sintering temperature and time within the above range, the following situation can be avoided: when the sintering temperature in the third coating step is too low, the third coating layer The degree of graphitization decreases, affecting its conductivity, thereby affecting the gram capacity of the material; when the sintering temperature is too high, the degree of graphitization of the third coating layer will be too high, affecting the transmission of Li + , thereby affecting the gram capacity of the material.
  • the drying temperature is 100°C to 200°C, optionally 110°C to 190°C, and more optionally 120°C to 180°C. , or even more optionally, it can be carried out at a drying temperature of 120°C to 170°C, and the most optional drying temperature is 120°C to 160°C.
  • the drying time is 3-9 hours, optionally 4-8 hours, and even more optionally 5-7 hours. hours, optimally about 6 hours.
  • the cathode active material prepared by the cathode active material preparation method described in the present application can reduce the dissolution of Mn and Mn-site doping elements in the secondary battery after cycling, and has high-temperature stability, high-temperature cycle performance and rate. Performance is improved.
  • the sources of raw materials are wide, the cost is low, and the process is simple, which is conducive to industrialization.
  • the positive active material may be other positive active materials known in the art for batteries.
  • other cathode active materials may also include at least one of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive electrode film layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene tripolymer. At least one of a meta-copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer and a fluorine-containing acrylate resin.
  • the positive electrode film layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), At least one of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 1 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG. 6 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the first solvent is selected from the following solvents:
  • the first additive is selected from the following compounds:
  • Additive 1 Additive 2: Additive 3:
  • Additive 4 Additive 5: Additive 6:
  • Additive 7 Additive 8: Additive 9:
  • Step 1 Preparation of cathode active material
  • Step S1 Preparation of Fe, Co, V and S co-doped manganese oxalate
  • 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 O 4
  • Step S3 Preparation of the first coating layer suspension
  • Li 2 FeP 2 O 7 solution dissolve 7.4g lithium carbonate, 11.6g ferrous carbonate, 23.0g ammonium dihydrogen phosphate and 12.6g oxalic acid dihydrate in 500mL deionized water, control the pH to 5, then stir and keep at room temperature The reaction was carried out for 2 hours to obtain a solution, and then the temperature of the solution was raised to 80°C and maintained at this temperature for 4 hours to obtain a first coating layer suspension.
  • Step S4 Coating of the first coating layer
  • step S2 Add 1571.9g of the doped lithium manganese phosphate core material obtained in step S2 to the first coating layer suspension (coating material content is 15.7g) obtained in step S3, stir and mix thoroughly for 6 hours, and mix evenly Finally, it was transferred to an oven at 120°C for drying for 6 hours, and then sintered at 650°C for 6 hours to obtain the pyrophosphate-coated material.
  • Step S5 Preparation of the second coating layer suspension
  • Step S6 Coating of the second coating layer
  • step S4 Add 1586.8g of the pyrophosphate-coated material obtained in step S4 to the second coating layer suspension obtained in step S5 (coating material content is 47.1g), stir and mix thoroughly for 6 hours, and mix evenly Finally, it was transferred to an oven at 120°C for drying for 6 hours, and then sintered at 700°C for 8 hours to obtain a two-layer coated material.
  • Step S7 Preparation of the third coating layer aqueous solution
  • sucrose aqueous solution Dissolve 37.3g of sucrose in 500g of deionized water, then stir and fully dissolve to obtain a sucrose aqueous solution.
  • Step S8 Coating of the third coating layer
  • step S6 Add 1633.9g of the two-layer coating material obtained in step S6 to the sucrose solution obtained in step S7, stir and mix together for 6 hours. After mixing evenly, transfer to a 150°C oven to dry for 6 hours, and then sinter at 700°C for 10 hours. A three-layer coated material is obtained.
  • the three-layer-coated cathode active material prepared above, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 97.0:1.2:1.8 , stir and mix evenly to obtain the positive electrode slurry. Then, the positive electrode slurry is evenly coated on the aluminum foil at a density of 0.280g/ 1540.25mm2 , dried, cold pressed, and cut to obtain the positive electrode piece.
  • NMP N-methylpyrrolidone
  • negative active material artificial graphite artificial graphite, hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC) in a weight ratio of 90:5:2:2:1 Dissolve in solvent deionized water, stir and mix evenly to prepare negative electrode slurry.
  • the negative electrode slurry is evenly coated on the negative electrode current collector copper foil at a density of 0.117g/ 1540.25mm2 , and then dried, cold pressed, and cut to obtain the negative electrode piece.
  • a commercially available PP-PE copolymer microporous film with a thickness of 20 ⁇ m and an average pore diameter of 80 nm was used.
  • the positive electrode piece, isolation film, and negative electrode piece obtained above are stacked in order, so that the isolation film is between the positive and negative electrodes to play an isolation role, and the bare battery core is obtained by winding.
  • the bare battery core is placed in the outer packaging, the above-mentioned electrolyte is injected and packaged to obtain a full battery (hereinafter also referred to as "full battery").
  • the positive electrode active material prepared above, 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 room to form a slurry.
  • NMP N-methylpyrrolidone
  • the above slurry is coated on aluminum foil, dried and cold pressed to form a positive electrode sheet.
  • the coating amount is 0.2g/cm 2 and the compacted density is
  • Lithium sheet was used as the negative electrode, solvent 1 was used as the first solvent, and a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1 was used as the third solvent.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • Additive 1 is used as the first additive
  • LiPF 6 is used as the lithium salt.
  • the first solvent, the second solvent, the first additive and the lithium salt form the electrolyte.
  • the mass ratio of the first solvent to the second solvent is 1 :1.
  • the mass content of the first additive is 3%
  • the mass content of the lithium salt is 1 mol/L.
  • Example 2 to 27 and Comparative Examples 1 to 19 were prepared in a manner similar to Example 1.
  • the differences in the preparation of the positive active materials are shown in Tables 1-6, where Comparative Examples 1-2 , 4-10 and 12 are not coated with the first layer, so there are no steps S3 and S4; Comparative Example 1-11 is not coated with the second layer, so there are no steps S5-S6.
  • the first coating layer material and/or the second coating layer material used are in the crystalline state by default.
  • the positive active material sample is prepared into a buckle, and the buckle is charged at a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in dimethyl carbonate (DMC) for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. Take a sample and calculate its unit cell volume v1 in the same way as the above-mentioned test of fresh samples, and use (v0-v1)/v0 ⁇ 100% as the lattice change rate (unit cell volume change rate) before and after complete deintercalation of lithium. in the table.
  • DMC dimethyl carbonate
  • the fresh full batteries prepared in the above examples and comparative examples were allowed to stand for 5 minutes, and then discharged to 2.5V at 1/3C. Let it stand for 5 minutes, charge at 1/3C to 4.3V, and then charge at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this time as C0. Discharge to 2.5V according to 1/3C, let it sit for 5 minutes, then charge to 4.3V according to 3C, let it stand for 5 minutes, record the charging capacity at this time as C1.
  • the 3C charging constant current ratio is C1/C0 ⁇ 100%.
  • the full cells prepared in the above embodiments and comparative examples were discharged to a cut-off voltage of 2.0V using a 0.1C rate after being cycled at 45°C until the capacity decayed to 80%. Then disassemble the battery, take out the negative electrode piece, randomly pick 30 discs of unit area (1540.25mm2) on the negative electrode piece, and use Agilent ICP-OES730 to test the inductively coupled plasma emission spectrum (ICP). Calculate the amounts of Fe (if the Mn site of the cathode active material is doped with Fe) and Mn based on the ICP results, and then calculate the dissolution amount of Mn (and Fe doped at the Mn site) after cycles. The test standard is based on EPA-6010D-2014.
  • the cathode active material sample prepared above Take 5 g of the cathode active material sample prepared above and prepare a buckle according to the buckle preparation method described in the above embodiment. Charge with a small rate of 0.05C until the current is reduced to 0.01C. Then take out the positive electrode piece from the battery and soak it in DMC for 8 hours. Then it is dried, scraped into powder, and particles with a particle size less than 500nm are screened out. The obtained particles were measured with electron energy loss spectroscopy (EELS, the instrument model used was Talos F200S) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. According to the density of states and energy level distribution, the number of occupied electrons is calculated by integrating the valence band density of states data, thereby deducing the valence state of the charged surface oxygen.
  • EELS electron energy loss spectroscopy
  • Dissolve 5g of the positive active material prepared above in 100ml aqua regia (concentrated hydrochloric acid: concentrated nitric acid 1:3) (concentrated hydrochloric acid concentration ⁇ 37%, concentrated nitric acid concentration ⁇ 65%), and use ICP to test the content of each element of the solution. content, and then measure and convert the content of manganese element or phosphorus element (amount of manganese element or phosphorus element/amount of cathode active material * 100%) to obtain its weight ratio.
  • the button batteries prepared in the above examples and comparative examples were charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V until the current was less than or equal to 0.05mA, left to stand for 5 minutes, and then charged at 0.1 C is discharged to 2.0V.
  • the discharge capacity at this time is the initial gram capacity, recorded as D0.
  • the full cells prepared in each of the above-described Examples and Comparative Examples were stored at 60° C. at 100% state of charge (SOC). Measure the open circuit voltage (OCV) and AC internal resistance (IMP) of the battery cells before, after and during storage to monitor SOC, and measure the volume of the battery cells. The full battery was taken out after every 48 hours of storage, and the open circuit voltage (OCV) and internal resistance (IMP) were tested after leaving it for 1 hour. After cooling to room temperature, the cell volume was measured using the drainage method.
  • SOC state of charge
  • the drainage method is to first separately measure the gravity F1 of the battery cell using a balance that automatically converts units based on the dial data, then completely place the battery core in deionized water (density is known to be 1g/cm3), and measure the gravity of the battery core at this time.
  • F2 the buoyancy force F on the battery core is F1-F2.
  • F float ⁇ g ⁇ V row
  • the thickness test of the coating layer mainly uses FIB to cut a slice with a thickness of about 100nm from the middle of a single particle of the cathode active material prepared above, and then perform a TEM test on the slice to obtain the original TEM test picture and save the original picture format (xx.dm3) .
  • the thickness of the selected particles was measured at three locations and averaged.
  • This test is performed by Raman spectroscopy. By peak splitting the energy spectrum of the Raman test, Id/Ig is obtained, where Id is the peak intensity of SP3 form carbon, and Ig is the peak intensity of SP2 form carbon, thereby confirming the molar ratio of the two.
  • the electrolyte in the full battery of the above-mentioned embodiments 1 to 29 was replaced with: the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) was mixed evenly according to the volume ratio of 3/7, and 12.5% by weight ( Based on the weight of ethylene carbonate/ethyl methyl carbonate solvent) LiPF 6 is dissolved in the above organic solvent, stir evenly to obtain an electrolyte; replace the electrolyte of the button battery with: use 1 mol/L LiPF 6 in a volume ratio of 1 : A 1:1 solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) is the electrolyte.
  • EC organic solvent
  • EMC ethylene carbonate
  • DMC dimethyl carbonate
  • the electrolyte composition of the present application can further improve the rate performance and cycle performance of the secondary battery.
  • Table 15 indicates the type of additive and the content of the additive in the electrolyte.

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Abstract

本申请提供一种二次电池、电池模块、电池包和用电装置。该二次电池包括正极极片以及非水电解液，正极极片包括具有核-壳结构的正极活性材料，正极活性材料包括内核及包覆内核的壳，内核的化学式为Li1+xMn1-yAyP1-zRzO4，A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，R为选自B、Si、N和S中的一种或多种元素；第一包覆层包括晶态焦磷酸盐LiaMP2O7和/或Mb(P2O7)c，第二包覆层包括晶态磷酸盐XPO4，第三包覆层为碳；非水电解液包括第一溶剂，第一溶剂包括式1所示化合物中的一种或多种。

Description

二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及电池技术领域，特别是涉及一种二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着锂离子二次电池技术的发展，锂离子二次电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，并在电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域有着广泛应用。由于锂离子二次电池取得了极大的发展，因此对其能量密度、循环性能和安全性能等也提出了更高的要求。
磷酸锰锂作为锂离子二次电池的正极活性材料，具有容量高、安全性好、成本低的优点。然而磷酸锰锂的倍率性能较差，制约了其商业化应用。
发明内容
本申请提供了一种二次电池、电池模块、电池包和用电装置，以解决以磷酸锰锂作为锂离子二次电池的正极活性材料时，二次电池的倍率性能差的问题。
本发明的第一方面提供了一种二次电池，该二次电池包括正极极片以及非水电解液，其中，正极极片包括具有核-壳结构的正极活性材料，正极活性材料包括内核及包覆内核的壳，内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中一种或多种元素，R为选自B、Si、N和S中的一种或多种元素，可选地，R为选自B、Si、N和S中的一种元素；x、y和z的值满足以下条件：使整个内核保持电中性；壳包括包覆内核的第一包覆层、包覆第一包覆层的第二包覆层以及包覆第二包覆层的第三包覆层，其中，第一包覆层包括晶态焦磷酸盐LiaMP 2O 7和/或Mb(P 2O 7) c，其中，0≤a≤2，1≤b≤4，1≤c≤6，a、b和c的值满足以下条件：使晶态焦磷酸盐LiaMP 2O 7或Mb(P 2O 7) c保持电中性，晶态焦磷酸盐LiaMP 2O 7和Mb(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素，第二包覆层包括晶态磷酸盐XPO 4，其中，X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；第三包覆层为碳；非水电解液包括有机溶剂，有机溶剂包括第一溶剂，第一溶剂包 括式1所示化合物中的一种或多种，
Figure PCTCN2022090386-appb-000001
R 1和R 2分别独立地为C1～C10烷基、C1～C10卤代烷基中的一种，可选地，R 1和R 2分别独立地为甲基、乙基、丙基、丁基、戊基、己基、氟代甲基、氟代乙基、氟代丙基、氟代丁基、氟代戊基、氟代己基中的一种，进一步可选地，R 1和R 2分别独立地为甲基、乙基、丙基、氟代甲基、氟代乙基、氟代丙基中的一种。
除非另有说明，否则上述化学式中，当A为两种以上元素时，上述对于y数值范围的限定不仅是对每种作为A的元素的化学计量数的限定，也是对各个作为A的元素的化学计量数之和的限定。例如当A为两种以上元素A1、A2……An时，A1、A2……An各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于R为两种以上元素的情况，本申请中对R化学计量数的数值范围的限定也具有上述含义。
本文中，晶态意指结晶度在50％以上，即50％-100％。结晶度小于50％的称为玻璃态。本申请所述的晶态焦磷酸盐和晶态磷酸盐的结晶度为50％至100％。具备一定结晶度的焦磷酸盐和磷酸盐不但有利于充分发挥焦磷酸盐包覆层阻碍锰离子溶出和磷酸盐包覆层优异的导锂离子的能力、减少界面副反应的功能，而且能够使得焦磷酸盐包覆层和磷酸盐包覆层能够更好的进行晶格匹配，从而能够实现包覆层和包覆层之间紧密的结合。
本申请通过在磷酸锰锂的锰位掺杂元素A并在磷位掺杂元素R得到掺杂的磷酸锰锂内核并在内核表面依次进行三层包覆，提供了一种新型的具有核-壳结构的磷酸锰锂正极活性材料，将该正极活性材料应用于二次电池中，能够显著改善二次电池的高温循环性能、循环稳定性和高温储存性能。
同时，非水电解液中的第一溶剂具有很好的解离锂盐的能力，但相对于碳酸酯而言，第一有机溶剂与Li +的作用力却很小，随着第一溶剂逐渐主导第一溶剂化层，Li +去溶剂化能会逐渐降低，这有利于Li +在界面处的快速嵌入和脱出，进而提升二次电池的倍率性能。此外，第一溶剂具有较低的粘度，可使正极活性材料脱出的锂离子迅速迁移并嵌入到负极侧，在浓差极化的驱动下，使正极材料界面处的锂离子快速转移到电解液中，进一步提高二次电池的倍率性能。
在第一方面的任意实施方式中，上述第一溶剂包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000002
Figure PCTCN2022090386-appb-000003
在第一方面的任意实施方式中，可选地，第一溶剂包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000004
当第一溶剂选择上述各物质时，电解液粘度更低，浸润性更好，因此锂离子的传输能力更好，进而更好地提升了二次电池的倍率性能；同时上述各第一溶剂的化学稳定性更好，对正极活性材料的氧化耐受性更好。
在第一方面的任意实施方式中，基于有机溶剂的总质量，第一溶剂的质量百分数为w1，w1的范围为20％～80％；可选地，w1的范围为30％～75％。通过上述质量百分数的控制，可以在利用第一溶剂在提高电池快速充电性能的同时，使二次电池具有良好的循环性能和存储性能。
在第一方面的任意实施方式中，可选地，有机溶剂还包括第二溶剂，第二溶剂包括链状碳酸酯、环状碳酸酯组成的组中的一种或多种；进一步可选地，基于有机溶剂的总质量，第二溶剂的质量百分数为w2，w2的范围为20％～80％；可选 地，w2的范围为25％～70％。以利用第二溶剂与第一溶剂配合提升二次电池的循环性能。
在第一方面的任意实施方式中，上述非水电解液还包括第一添加剂，第一添加剂包含磺酸内酯、环状硫酸酯组成的组中的一种或多种。非水电解液中引入磺酸内酯或环状硫酸酯，在二次电池充电过程中它们在正极活性材料表面形成一层导离子能力强的聚合物，如酯基硫酸物等。该聚合物既可以进一步改善二次电池的倍率性能，又可以有效抑制正极活性材料对第一溶剂的催化氧化，进而改善二次电池的循环和存储性能。此外，磺酸内酯或环状硫酸酯可优于第一溶剂在负极成膜，减小第一溶剂上的α-H与负极还原得到的活性锂反应，进而进一步改善二次电池的循环和存储性能。
在第一方面的任意实施方式中，上述磺酸内酯包括式2所示化合物中的至少一种，
Figure PCTCN2022090386-appb-000005
p表示1、2或3，
R 11表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基中的一种；可选地，R 11表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基中的一种；可选地烷氧基为链状烷氧基或环状烷氧基，可选地环状烷氧基与磺酸内酯的母环共用一个碳原子，进一步可选地环状烷氧基为碳原子数为4、5或6；
各R 12分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、4至7元磺酸内酯基中的一种；可选地，各R 12分别独立地表示氢原子、卤原子、C1～C3烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、5至6元磺酸内酯基中的一种；可选地，磺酸内酯基与磺酸内酯的母环共用一个碳原子，可选地磺酸内酯基为5元环；
R 11和R 12与各自连接的碳原子可形成5至10元的环烷基；
R 13表示氢原子、卤原子、羰基、C2～C6的酯基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基或苄基中的一种；可选地，R 13表示氢原子、卤原子、羰基、C2～C3的酯基、C1～C3烷基、C1～C3卤代烷基、C2～C6烯基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基或苄基中的一种。上述磺酸内酯为本领域常用的磺酸内酯，来源广泛，成本较低。
在第一方面的任意实施方式中，上述环状硫酸酯包括式3所示化合物中的至少一种，
Figure PCTCN2022090386-appb-000006
q表示1、2或3
R 14表示氢原子、卤原子、羰基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C2～C6的酯基、4至7元的环状硫酸酯基中的一种；可选地，R 14表示氢原子、卤原子、羰基、双键、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C2～C3的酯基、4至5元的环状硫酸酯基中的一种；可选地环状硫酸酯基与环状硫酸酯共用一个碳原子；
各R 15分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基中的一种；可选地，各R 15分别独立地表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基中的一种；
或者R 14和R 15与各自链接的碳原子共同形成4至7元的环状硫酸酯基，进一步可选地，R 14和R 15与各自链接的碳原子共同形成5元的环状硫酸酯基。
上述环状硫酸酯为本领域常用的环状硫酸酯，来源广泛，成本较低。
在第一方面的任意实施方式中，可选地，磺酸内酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000007
在第一方面的任意实施方式中，可选地，环状硫酸酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000008
进一步可选地，磺酸内酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000009
进一步可选地，环状硫酸酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000010
上述磺酸内酯和环状硫酸酯更容易在正极形成聚合物。
在第一方面的任意实施方式中，基于非水电解液的总质量，上述第一添加剂的含量为W3，且0.01％≤W3≤20％，可选地0.1％≤W3≤10％，进一步可选地0.3％≤W3≤5％。避免引入过多的磺酸内酯或环状硫酸酯导致的正负极阻抗增大，进而保证了锂离子电池的容量和倍率性能的显著提升。
在第一方面的任意实施方式中，非水电解液还包括第二添加剂，第二添加剂包括亚硫酸酯化合物、二磺酸酯化合物、腈化合物、芳香化合物、磷腈化合物、酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物组成的组中的一种或多种。上述第二添加剂有助于在正极和/或负极活性材料表面形成更为致密且稳定的界面膜，从而进一步提升二次电池的循环性能、存储性能、倍率性能中的至少一者。
在第一方面的任意实施方式中，基于非水电解液的总质量，第二添加剂的含量为W4，0.01％≤W4≤20％，可选地0.05％≤W4≤5％，进一步可选地0.1％≤W4≤3％。以使第二添加剂的作用得到充分发挥。
在第一方面的任意实施方式中，基于内核的重量计，第一包覆层的包覆量为C1重量％，C1大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2。和/或基于内核的重量计，第二包覆层的包覆量为C2重量％，C2大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为2-4。和/或基于内核的重量计，第三包覆层的包覆量为C3重量％，C3大于0且小于或等 于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2。上述实施方式的具有核-壳结构的正极活性材料中，三层包覆层的包覆量优选在上述范围内，由此能够对内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
在第一方面的任意实施方式中，第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。上述实施方式的正极活性材料中的第一包覆层和第二包覆层均使用晶态物质，它们的晶面间距和夹角范围在上述范围内，能够更有效地避免包覆层中的杂质相，从而进一步提升材料的克容量，循环性能和倍率性能。
在第一方面的任意实施方式中，在内核中，y与1-y的比值为1：10至1：1，可选为1：4至1：1。由此，进一步提升二次电池的循环性能和倍率性能。
在第一方面的任意实施方式中，在内核中，z与1-z的比值为1：999至1：9，可选为1：499至1：249。由此，进一步提升二次电池的循环性能和倍率性能。
在第一方面的任意实施方式中，第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。上述实施方式通过将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，更好地提升了二次电池的综合性能。
在第一方面的任意实施方式中，第一包覆层的厚度为1-10nm；和/或第二包覆层的厚度为2-15nm；和/或第三包覆层的厚度为2-25nm。在上述实施方式中，当第一包覆层的厚度范围为1-10nm时，能够避免过厚时可能产生的对材料的动力学性能的不利影响，且能够避免过薄时不能有效阻碍过渡金属离子的迁移的问题。当第二包覆层的厚度在2-15nm范围内时，第二包覆层的表面结构稳定，与电解液的副反应小，因此能够更有效地减轻界面副反应，从而更显著地提升二次电池的高温性能。当第三包覆层的厚度范围为2-20nm时，能够进一步提升材料的电导性能并且改善使用正极活性材料制备的电池极片的压实密度性能。
在第一方面的任意实施方式中，基于具有核-壳结构的正极活性材料的重量计，锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
上述实施方式的具有核-壳结构的正极活性材料中，锰元素的含量在上述范围内，能够有效避免若锰元素含量过大可能会引起的材料结构稳定性变差、密度下降等问题，从而更有效地提升二次电池的循环、存储和压实密度等性能；且能够避 免若锰元含量过小可能会导致的电压平台低等问题，从而提升二次电池的能量密度。
上述实施方式的具有核-壳结构的正极活性材料中，磷元素的含量在上述范围内，能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响材料的电导率；若磷元素的含量过小，可能会使内核、第一包覆层中的焦磷酸盐和/或第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响材料整体的稳定性。
上述实施方式的具有核-壳结构的正极活性材料中，锰元素与磷元素的重量比在上述范围内，能够有效避免以下情况：若该重量比过大，可能会导致过渡金属溶出增加，影响材料的稳定性和二次电池的循环及存储性能；若该重量比过小，可能会使材料的放电电压平台下降，从而使二次电池的能量密度降低。
在第一方面的任意实施方式中，具有核-壳结构的正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。上述实施方式的具有核-壳结构的正极活性材料能够实现4％以下的脱嵌锂前后的晶格变化率。因此使用正极活性材料能够更有效地改善二次电池的克容量和倍率性能。
在第一方面的任意实施方式中，具有核-壳结构的正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。通过Li/Mn反位缺陷浓度在上述范围内，能够更有效地避免Mn 2+阻碍Li +的传输，同时进一步提升正极活性材料的克容量和倍率性能。
在第一方面的任意实施方式中，具有核-壳结构的正极活性材料在3T(吨)下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。由此，提高压实密度，则单位体积活性材料的重量增大，更有利于提高二次电池的体积能量密度。
在第一方面的任意实施方式中，具有核-壳结构的正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。由此，通过如上将正极活性材料的表面氧价态限定在上述范围内，能够进一步减轻正极材料与电解液的界面副反应，从而改善电芯的循环，高温存储产气等性能。
本申请的第二方面还提供一种电池模块，该电池模块包括二次电池，该二次电池为本申请的任意一种上述二次电池。
本申请的第三方面还提供一种电池包，该电池包包括电池模块，该电池模块为本申请的上述电池模块。
本申请的第四方面还提供一种用电装置，该用电装置包括二次电池、电池模块或电池包中的至少一种，上述二次电池、电池模块和电池包均为本申请的提供的二次电池、电池模块、电池包。
由此，本申请的电池模块、电池包具有较高的循环性能、倍率特性，进而为具有本申请二次电池、电池模块或电池包的用电装置提供了较高的动力循环稳定性和倍率特性。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请一实施方式的二次电池的示意图。
图2是图1所示的本申请一实施方式的二次电池的分解图。
图3是本申请一实施方式的电池模块的示意图。
图4是本申请一实施方式的电池包的示意图。
图5是图4所示的本申请一实施方式的电池包的分解图。
图6是本申请一实施方式的二次电池用作电源的用电装置的示意图。
在附图中，附图并未按照实际的比例绘制。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53顶盖组件。
具体实施方式
下面结合附图和实施例对本申请的实施方式作进一步详细描述。以下实施例的详细描述和附图用于示例性地说明本申请的原理，但不能用来限制本申请的范围，即本申请不限于所描述的实施例。
以下，适当地参照附图详细说明具体公开了本申请的二次电池、电池模块、电池包和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这 种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本文中，术语“包覆层”是指包覆在内核上的物质层，所述物质层可以完全或部分地包覆内核，使用“包覆层”只是为了便于描述，并不意图限制本发明。同样地，术语“包覆层的厚度”是指包覆在内核上的所述物质层在内核径向上的厚度。
在本文中，术语“源”是指作为某种元素的来源的化合物，作为实例，所述“源”的种类包括但不限于碳酸盐、硫酸盐、硝酸盐、单质、卤化物、氧化物和氢氧化物等。
[二次电池]
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解液。在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。电解液在正极极片和负极极片之间，主要起到传导活性离子的作用。
本发明的第一方面提供了一种二次电池，该二次电池包括正极极片以及非水电解液，其中，正极极片包括具有核-壳结构的正极活性材料，正极活性材料包括内核及包覆内核的壳，内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中一种或多种元素，R为选自B、Si、N和S中的一种或多种元素，可选地，R为选自B、Si、N和S中的一种元素；x、y和z的值满足以下条件：使整个内核保持电中性；壳包括包覆内核的第一包覆层、包覆第一包覆层的第二包覆层以及包覆第二包覆层的第三包覆层，其中，第一包覆层包括晶态焦磷酸盐LiaMP 2O 7和/或Mb(P 2O 7) c，其中，0≤a≤2，1≤b≤4，1≤c≤6，a、b和c的值满足以下条件：使晶态焦磷酸盐LiaMP 2O 7或Mb(P 2O 7) c保持电中性，晶态焦磷酸盐LiaMP 2O 7和Mb(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素，第二包覆层包括晶态磷酸盐XPO 4，其中，X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；第三包覆层为碳；非水电解液包括有机溶剂，有机溶剂包括第一溶剂，第一溶剂包括式1所示化合物中的一种或多种，
Figure PCTCN2022090386-appb-000011
R 1和R 2分别独立地为C1～C10烷基、C1～C10卤代烷基中的一种，可选地，R 1和R 2分别独立地为甲基、乙基、丙基、丁基、戊基、己基、氟代甲基、氟代乙基、氟代丙基、氟代丁基、氟代戊基、氟代己基中的一种，进一步可选地，R 1和R 2分别独立地为甲基、乙基、丙基、氟代甲基、氟代乙基、氟代丙基中的一种。
除非另有说明，否则上述化学式中，当A为两种以上元素时，上述对于y数值范围的限定不仅是对每种作为A的元素的化学计量数的限定，也是对各个作为A的元素的化学计量数之和的限定。例如当A为两种以上元素A1、A2……An时，A1、A2……An各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于R为两种以上元素的情况，本申请中对R化学计量数的数值范围的限定也具有上述含义。
本申请的二次电池利用具有包覆层的正极活性材料以及电解液组成的改进，不仅有效提升了二次电池的倍率性能，而且改善了二次电池的循环性能。具体地：
本申请的正极活性材料能够提高二次电池的克容量、循环性能和安全性能。虽然机理尚不清楚，但推测是本申请的磷酸锰锂正极活性材料为核-壳结构，其中通过对磷酸锰锂内核的锰位和磷位分别掺杂元素A和元素R，不仅可有效减少锰溶出，进而减少迁移到负极的锰离子，减少因SEI膜分解而消耗的电解液，提高二次电池的循环性能和安全性能，还能够促进Mn-O键调整，降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能；通过对内核包覆包括晶态焦磷酸盐的第一包覆层，能够进一步增大锰的迁移阻力，减少其溶出，并减少表面杂锂含量、减少内核与电解液的接触，从而减少界面副反应、减少产气，提高二次电池的高温存储性能、循环性能和安全性能；通过进一步包覆具有优异导锂离子的能力的晶态磷酸盐包覆层，可以使正极活性材料的表面的界面副反应有效降低，进而改善二次电池的高温循环及存储性能；通过再进一步包覆碳层作为第三包覆层，能够进一步提升二次电池的安全性能和动力学性能。
此外，在所述内核中，在磷酸锰锂的锰位掺杂的元素A还有助于减小该材料在脱嵌锂过程中磷酸锰锂的晶格变化率，提高磷酸锰锂正极材料的结构稳定性，大大减少锰的溶出并降低颗粒表面的氧活性；在磷位掺杂的元素R还有助于改变Mn-O键长变化的难易程度，从而改善电子电导并降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能。
另外，整个内核体系保持电中性，能够保证正极活性材料中的缺陷和杂相尽量少。如果正极活性材料中存在过量的过渡金属(例如锰)，由于该材料体系本身结构较稳定，那么多余的过渡金属很可能会以单质的形式析出，或在晶格内部形成杂相，保持电中性可使这样的杂相尽量少。另外，保证体系电中性还可以在部分情况下使材料中产生锂空位，从而使材料的动力学性能更优异。
可见，本申请通过在磷酸锰锂的锰位掺杂元素A并在磷位掺杂元素R得到掺杂的磷酸锰锂内核并在内核表面依次进行三层包覆，提供了一种新型的具有核-壳结构的磷酸锰锂正极活性材料，将该正极活性材料应用于二次电池中，能够显著改善二次电池的高温循环性能、循环稳定性和高温储存性能。
同时，非水电解液中的第一溶剂具有很好的解离锂盐的能力，但相对于碳酸酯而言，第一有机溶剂与Li +的作用力却很小，随着第一溶剂逐渐主导第一溶剂化层，Li +去溶剂化能会逐渐降低，这有利于Li +在界面处的快速嵌入和脱出，进而提升二次电池的倍率性能。此外，第一溶剂具有较低的粘度，可使正极活性材料脱出的锂离子迅速迁移并嵌入到负极侧，在浓差极化的驱动下，使正极材料界面处的锂离子快速转移到电解液中，进一步提高二次电池的倍率性能。
[非水电解液]
用于本申请的第一溶剂可以为前述式1内所涵盖的任意羧酸酯，在一些实施方式中，上述第一溶剂包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000012
在一些实施方式中，可选地，第一溶剂包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000013
当第一溶剂选择上述各物质时，电解液粘度更低，浸润性更好，因此锂离子的传输能力更好，进而更好地提升了二次电池的倍率性能；同时上述各第一溶剂的化学稳定性更好，对正极活性材料的氧化耐受性更好。
第一溶剂虽然具有低粘度、高电导率的优势，但是其容易与二次电池的正极和负极发生化学反应，进而影响二次电池的循环性能。在一些实施方式中，基于 有机溶剂的总质量，第一溶剂的质量百分数为w1，w1的范围为20％～80％(比如20％、25％、30％、35％、40％、45％、50％、55％、60％、65％、70％、75％或80％)；可选地，w1的范围为30％～75％。通过上述质量百分数的控制，可以在利用第一溶剂在提高电池快速充电性能的同时，使二次电池具有良好的循环性能和存储性能。
本申请在使用第一溶剂作为非水电解液的溶剂时，为了既可以尽可能保证二次电池具有高的循环性能和存储性能，在一些实施方式中，可选地，有机溶剂还包括第二溶剂，第二溶剂包括链状碳酸酯、环状碳酸酯组成的组中的一种或多种；进一步可选地，基于有机溶剂的总质量，第二溶剂的质量百分数为w2，所述w2的范围为20％～80％(比如20％、25％、30％、35％、40％、45％、50％、55％、60％、65％、70％、75％或80％)；可选地，所述w2的范围为25％～70％。以利用第二溶剂与第一溶剂配合提升二次电池的循环性能。
上述第二溶剂的链状碳酸酯、环状碳酸酯种类没有特别的限制，可根据实际需求进行选择，可选地，第二溶剂可包括碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、γ-丁内酯、甲酸甲酯、甲酸乙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸甲酯中的一种或几种。
在第一方面的一些实施例中，上述非水电解液的溶剂还可以包括四氢呋喃、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜等常用溶剂，本申请不再一一赘述。
通常，非水电解液还可选地包括添加剂。作为示例，添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
进一步地，在一些实施方式中，上述非水电解液还包括第一添加剂，第一添加剂包含磺酸内酯、环状硫酸酯组成的组中的一种或多种。非水电解液中引入磺酸内酯或环状硫酸酯，在二次电池充电过程中它们在正极活性材料表面形成一层导离子能力强的聚合物，如酯基硫酸物等。该聚合物既可以进一步改善二次电池的倍率性能，又可以有效抑制正极活性材料对第一溶剂的催化氧化，进而改善二次电池的循环和存储性能。此外，磺酸内酯或环状硫酸酯可优于第一溶剂在负极成膜，减小第一溶剂上的α-H与负极还原得到的活性锂反应，进而进一步改善二次电池的循环和存储性能。
用于本申请上述实施方式的磺酸内酯和环状硫酸酯可以为现有技术中常用的相应物质，在一些实施方式中，上述磺酸内酯包括式2所示化合物中的至少一种，
Figure PCTCN2022090386-appb-000014
p表示1、2或3，
R 11表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基中的一种；可选地，R 11表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基中的一种；可选地烷氧基为链状烷氧基或环状烷氧基，可选地环状烷氧基与磺酸内酯的母环共用一个碳原子，进一步可选地环状烷氧基为碳原子数为4、5或6；
各R 12分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、4至7元磺酸内酯基中的一种；可选地，各R 12分别独立地表示氢原子、卤原子、C1～C3烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、5至6元磺酸内酯基中的一种；可选地，磺酸内酯基与磺酸内酯的母环共用一个碳原子，可选地所酸内酯基为5元环；
R 11和R 12与各自连接的碳原子可形成5至10元的环烷基；
R 13表示氢原子、卤原子、羰基、C2～C6的酯基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基或苄基中的一种；可选地，R 13表示氢原子、卤原子、羰基、C2～C3的酯基、C1～C3烷基、C1～C3卤代烷基、C2～C6烯基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基或苄基中的一种。
上述磺酸内酯为本领域常用的磺酸内酯，来源广泛，成本较低。
在一些实施方式中，上述环状硫酸酯包括式3所示化合物中的至少一种，
Figure PCTCN2022090386-appb-000015
q表示1、2或3，
R 14表示氢原子、卤原子、羰基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C2～C6的酯基、4至7元的环状硫酸酯基中的一种；可选地，R 14表示氢原子、卤原子、羰基、双键、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C2～C3的酯基、4至5元的环状硫酸酯基中的一种；可选地环状硫酸酯基与环状硫酸酯共用一个碳原子；
各R 15分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基中的一种；可选地，各R 15 分别独立地表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基中的一种；
或者R 14和R 15与各自链接的碳原子共同形成4至7元的环状硫酸酯基，进一步可选地，R 14和R 15与各自链接的碳原子共同形成5元的环状硫酸酯基。
上述环状硫酸酯为本领域常用的环状硫酸酯，来源广泛，成本较低。
在一些实施方式中，可选地，磺酸内酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000016
在一些实施方式中，可选地，环状硫酸酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000017
进一步可选地，磺酸内酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000018
进一步可选地，环状硫酸酯包括如下化合物中的至少一种：
Figure PCTCN2022090386-appb-000019
上述磺酸内酯和环状硫酸酯更容易在正极形成聚合物。
磺酸内酯和环状硫酸酯相对于第一溶剂，虽然可以改善二次电池的循环性能和存储性能，但是，如果其用量过多则有可能导致二次电池的正负极阻抗增大，影响二次电池的倍率，本领域技术人员可以以现有磺酸内酯和环状硫酸酯的常规用量为参考选择其在本申请非水电解液中的用量。在一些实施方式中，基于非水电解液的总质量，上述第一添加剂的含量为W3，且0.01％≤W3≤20％(比如0.01％、0.05％、0.1％、0.2％、0.5％、1％、2％、3％、4％、5％、10％、15％或20％)，可选地0.1％≤W3≤10％，进一步可选地0.3％≤W3≤5％。在有效抑制第一溶剂导致的循环性能下降的基础上，避免引入过多的磺酸内酯或环状硫酸酯导致的正负极阻抗增大，进而保证了锂离子电池的容量和倍率性能的显著提升。
在一些实施方式中，用于本申请的非水电解液还包括第二添加剂，第二添加剂包括亚硫酸酯化合物、二磺酸酯化合物、腈化合物、芳香化合物、磷腈化合物、酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物组成的组中的一种或多种。上述第二添加剂有助于在正极和/或负极活性材料表面形成更为致密且稳定的界面膜，从而进一步提升二次电池的循环性能、存储性能、倍率性能中的至少一者。
在一些实施方式中，基于非水电解液的总质量，第二添加剂的含量为W4，0.01％≤W4≤20％，可选地0.05％≤W4≤5％，进一步可选地0.1％≤W4≤3％。以使第二添加剂的作用得到充分发挥。
以下对部分第二添加剂进行举例说明。
亚硫酸酯化合物
亚硫酸酯化合物优选为环状亚硫酸酯化合物，具体可选自式4所示的化合物中的一种或几种。
Figure PCTCN2022090386-appb-000020
在式4中，R 28选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基，其中，取代基选自卤素原子、C1～C3烷基、C2～C4烯基中的一种或 几种。
在式4中，可选地，R 28选自取代或未取代的C1～C4亚烷基、取代或未取代的C2～C4亚烯基，其中，取代基选自卤素原子、C1～C3烷基、C2～C4烯基中的一种或几种。
可选地，亚硫酸酯化合物可选自亚硫酸乙烯酯(简称为ES)、亚硫酸丙烯酯(简称为PS)、亚硫酸丁烯酯(简称为BS)中的一种或几种。
二磺酸酯化合物
二磺酸酯化合物为含有两个磺酸基(-S(＝O) 2O-)的化合物，优选选自二磺酸亚甲酯化合物，二磺酸亚甲酯化合物可选自式5所示的化合物中的一种或几种。在式5中，R 24、R 25、R 26、R 27各自独立地选自氢原子、卤素原子、取代或未取代的C1～C10烷基、取代或未取代的C2～C10烯基，其中，取代基选自卤素原子、C1～C3烷基、C2～C4烯基中的一种或几种。
Figure PCTCN2022090386-appb-000021
在式5中，可选地，R 24、R 25、R 26、R 27各自独立地选自氢原子、卤素原子、取代或未取代的C1～C4烷基、取代或未取代的C2～C6烯基，其中，取代基选自卤素原子、C1～C3烷基、C2～C4烯基中的一种或几种。
可选地，二磺酸酯化合物可具体选自以下化合物中的一种或几种，但本申请不限于此：
Figure PCTCN2022090386-appb-000022
进一步可选地，二磺酸酯化合物可选自甲烷二磺酸亚甲酯(简称为
MMDS)，具体结构如下：
Figure PCTCN2022090386-appb-000023
腈化合物
腈化合物可以为式6或式7示出的化合物中的任意一种或中，
Figure PCTCN2022090386-appb-000024
在式6、式7中：R 5选自取代或未取代的C1～C12亚烷基、取代或未取代的C2～C12亚烯基、取代或未取代的C2～C12亚炔基，R 6、R 7、R 8各自独立地选自取代或未取代的C0～C12亚烷基、取代或未取代的C2～C12亚烯基、取代或未取代的C2～C12亚炔基，其中，取代基选自卤素原子、腈基、C1～C6烷基、C2～C6烯基、C1～C6烷氧基中的一种或几种。可选地，R 5选自取代或未取代的C1～C10亚烷基、取代或未取代的C2～C10亚烯基、取代或未取代的C2～C10亚炔基，R 6、R 7、R 8各自独立地选自取代或未取代的C0～C10亚烷基、取代或未取代的C2～C10亚烯基、取代或未取代的C2～C10亚炔基，其中，取代基选自卤素原子。
进一步可选地，在式6中，R 5选自C 1～C 6亚烷基、C 2～C 6亚烯基、C 2～C 6亚炔基，可选地，R 5选自C 2～C 4亚烷基、C 2～C 4亚烯基、C 2～C 4亚炔基；在式7中，R 6、R 7、R 8各自独立地选自C 0～C 6亚烷基、C 2～C 6亚烯基、C 2～C 6亚炔基，可选地，R 6选自C 0～C 1亚烷基，R 7、R 8各自独立地选自C 2～C 4亚烷基、C 2～C 4亚烯基、C 2～C 4亚炔基。
在一些实施例中，上述腈化合物选自乙二腈、丁二腈、戊二腈、己二腈、庚二腈、辛二腈、壬二腈、癸二腈、十一烷二腈、十二烷二腈、四甲基琥珀腈、甲基戊二腈、丁烯二腈、2-戊烯二腈、己-2-烯二腈、己-3-烯二腈、辛-4-烯二腈、辛-4-炔二腈、1,2,3-丙三甲腈、1,3,5-戊三甲腈、1,3,6-己烷三腈中的一种或几种。
芳香化合物
芳香化合物可选自环己基苯、氟代环己基苯化合物(1-氟-2-环己基苯、1-氟-3-环己基苯、1-氟-4-环己基苯)、叔丁基苯、叔戊基苯、1-氟-4-叔丁基苯、联苯、三联苯(邻位体、间位体、对位体)、二苯基醚、氟苯、二氟苯(邻位体、间位体、对位体)、茴香醚、2,4-二氟茴香醚、三联苯的部分氢化物(1,2-二环己基苯、2-苯基双环己基、1,2-二苯基环己烷、邻环己基联苯)中的一种或几种。
可选地，芳香化合物可选自联苯、三联苯(邻位体、间位体、对位体)、氟苯、环己基苯、叔丁基苯、叔戊基苯中的一种或几种，进一步可选地，芳香化合物可选自联苯、邻三联苯、氟苯、环己基苯、叔戊基苯中的一种或几种。
磷腈化合物
磷腈化合物优选为环状磷腈化合物。环状磷腈化合物可选自甲氧基五氟环三磷腈、乙氧基五氟环三磷腈、苯氧基五氟环三磷腈、乙氧基七氟环四磷腈中的一种或几种。
可选地，环状磷腈化合物可选自甲氧基五氟环三磷腈、乙氧基五氟环三磷腈、苯氧基五氟环三磷腈中的一种或几种。
进一步可选地，环状磷腈化合物可选自甲氧基五氟环三磷腈或乙氧基五氟环三磷腈。
酸酐化合物
酸酐化合物可为链状酸酐或环状酸酐。具体地，酸酐化合物可选自乙酸
酐、丙酸酐、琥珀酸酐、马来酸酐、2-烯丙基琥珀酸酐、戊二酸酐、衣康酸酐、3-
磺基-丙酸酐中的一种或几种。
可选地，酸酐化合物可选自琥珀酸酐、马来酸酐、2-烯丙基琥珀酸酐中的一种或几种。进一步可选地，酸酐化合物可选自琥珀酸酐、2-烯丙基琥珀酸酐中的一种或两种。
亚磷酸酯化合物
亚磷酸酯化合物可选自硅烷亚磷酸酯化合物，具体可选自式8所示的化合物中的一种或几种。在式8中，R 31、R 32、R 33、R 34、R 35、R 36、R 37、R 38、R 39各自独立地选自卤素取代或未取代的C1～C6烷基。
Figure PCTCN2022090386-appb-000025
可选地，硅烷亚磷酸酯化合物可具体选自以下化合物中的一种或几种，但本申请不限于此：
Figure PCTCN2022090386-appb-000026
磷酸酯化合物
磷酸酯化合物可选自硅烷磷酸酯化合物，具体可选自式9所示的化合物中的一种或几种。在式9中，R 41、R 42、R 43、R 44、R 45、R 46、R 47、R 48、R 49各自独立地选自卤素取代或未取代的C1～C6烷基。
Figure PCTCN2022090386-appb-000027
可选地，硅烷磷酸酯化合物可具体选自以下化合物中的一种或几种，但本申请不限于此：
Figure PCTCN2022090386-appb-000028
硼酸酯化合物
硼酸酯化合物可选自硅烷硼酸酯化合物，具体可选自式10所示的化合物中的一种或几种。在式10中，R 51、R 52、R 53、R 54、R 55、R 56、R 57、R 58、R 59各自独立地选自卤素取代或未取代的C1～C6烷基。
Figure PCTCN2022090386-appb-000029
可选地，硅烷硼酸酯化合物可具体选自以下化合物中的一种或几种，但本申请不限于此：
Figure PCTCN2022090386-appb-000030
另外，本申请的二次电池的非水电解液还包括锂盐，锂盐的种类没有特别的限制，可根据实际需求进行选择。比如锂盐可选自LiN(C x’F 2x’+1SO 2)(C y’F 2y’+1SO 2)、LiPF 6、LiBF 4、LiBOB、LiAsF 6、Li(FSO 2) 2N、LiCF 3SO 3以及LiClO 4中的一种或几种，其中，x’、y’为自然数，比如各自独立地为0、1、2、3、4、5或6等。在一些实施方式中，上述锂盐的浓度范围为0.5mol/L～2.5mol/L，优选0.8mol/L～2mol/L。
[正极极片]
正极极片通常包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，正极膜层包括正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请二次电池中的上述具有内核及包覆内核的壳的正极活性材料中，A元素和R元素掺杂后的磷酸锰锂的XRD图中的主要特征峰位置与未掺杂的LiMnPO 4的一致，说明掺杂过程没有引入杂质相，因此，内核性能的改善主要是来自元素掺杂，而不是杂相导致的。本申请发明人在制备上述正极活性材料后，通过聚焦离子束(简称FIB)切取已制备好的正极活性材料颗粒的中间区域，通过透射电子显微镜(简称TEM)以及X射线能谱分析(简称EDS)进行测试发现，各元素分布均匀，未出现聚集。
在一个可选的实施方式中，当A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种、两种、三种或四种元素时，A y为Q n1D n2E n3K n4，其中n1+n2+n3+n4＝y，且n1、n2、n3、n4均为正数且不同时为零，Q、D、E、K各自独立地为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge的一种，可选地，Q、D、E、K中至少一个为Fe。可选地，n1、n2、n3、n4之一为零，其余不为零；更可选地，n1、n2、n3、n4中的两个为零，其余不为零；还可选地，n1、n2、n3、n4中的三个为 零，其余不为零。所述内核Li 1+xMn 1-yA yP 1-zR zO 4中，在锰位掺杂一种、两种、三种或四种上述A元素是有利的，可选地，掺杂一种、两种或三种上述A元素；此外，在磷位掺杂一种或两种R元素是有利的，这样有利于使掺杂元素均匀分布。
所述内核Li 1+xMn 1-yA yP 1-zR zO 4中，x的大小受A和R的价态大小以及y和z的大小的影响，以保证整个体系呈现电中性。如果x的值过小，会导致整个内核体系的含锂量降低，影响材料的克容量发挥。y值会限制所有掺杂元素的总量，如果y过小，即掺杂量过少，掺杂元素起不到作用，如果y超过0.5，会导致体系中的Mn含量较少，影响材料的电压平台。所述R元素掺杂在P的位置，由于P-O四面体较稳定，而z值过大会影响材料的稳定性，因此将z值限定为0.001-0.100。
通过工艺控制(例如，对各种源的材料进行充分混合、研磨)，能够保证各元素在晶格中均匀分布，不出现聚集的情况。A元素和R元素掺杂后的磷酸锰锂的XRD图中的主要特征峰位置与未掺杂的LiMnPO 4的一致，说明掺杂过程没有引入杂质相，因此，所述内核性能的改善主要是来自元素掺杂，而不是杂相导致的。本申请发明人在制备本申请所述的正极活性材料后，通过聚焦离子束(简称FIB)切取已制备好的正极活性材料颗粒的中间区域，通过透射电子显微镜(简称TEM)以及X射线能谱分析(简称EDS)进行测试发现，各元素分布均匀，未出现聚集。
本申请中，晶态意指结晶度在50％以上，即50％-100％。结晶度小于50％的称为玻璃态。本申请晶态焦磷酸盐和晶态磷酸盐的结晶度为50％至100％。具备一定结晶度的焦磷酸盐和磷酸盐不但有利于充分发挥焦磷酸盐包覆层阻碍锰离子溶出和磷酸盐包覆层优异的导锂离子的能力、减少界面副反应的功能，而且能够使得焦磷酸盐包覆层和磷酸盐包覆层能够更好的进行晶格匹配，从而能够实现包覆层更紧密的结合。
本申请中，正极活性材料的第一包覆层物质晶态焦磷酸盐和第二包覆层物质晶态磷酸盐的结晶度可以通过本领域中常规的技术手段来测试，例如通过密度法、红外光谱法、差示扫描量热法和核磁共振吸收方法测量，也可以通过例如，X射线衍射法来测试。
具体的X射线衍射法测试正极活性材料的第一包覆层晶态焦磷酸盐和第二包覆层晶态磷酸盐的结晶度的方法可以包括以下步骤：
取一定量的正极活性材料粉末，通过X射线测得总散射强度，它是整个空间物质的散射强度之和，只与初级射线的强度、正极活性材料粉末化学结构、参加衍射的总电子数即质量多少有关，而与样品的序态无关；然后从衍射图上将结晶散射和非结晶散射分开，结晶度即是结晶部分散射对散射总强度之比。
需要说明的是，在本申请中，包覆层中的焦磷酸盐和磷酸盐的结晶度例如可通过调整烧结过程的工艺条件例如烧结温度、烧结时间等进行调节。
本申请中，由于金属离子在焦磷酸盐中难以迁移，因此焦磷酸盐作为第一 包覆层可以将掺杂金属离子与电解液进行有效隔离。晶态焦磷酸盐的结构稳定，因此，晶态焦磷酸盐包覆能够有效抑制过渡金属的溶出，改善循环性能。
第一包覆层与核之间的结合类似于异质结，其结合的牢固程度受晶格匹配程度的限制。晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。紧密的结合能够保证在后续的循环过程中，包覆层不会脱落，有利于保证材料的长期稳定性。第一包覆层与核之间的结合程度的衡量主要通过计算核与包覆各晶格常数的失配度来进行。本申请中，在内核中掺杂了A和R元素后，与不掺杂元素相比，内核与第一包覆层的匹配度得到改善，内核与焦磷酸盐包覆层之间能够更紧密地结合在一起。
选择晶态磷酸盐作为第二包覆层，首先，是因为它与第一层包覆物晶态焦磷酸盐的晶格匹配度较高(失配度仅为3％)；其次，磷酸盐本身的稳定性好于焦磷酸盐，用其包覆焦磷酸盐有利于提高材料的稳定性。晶态磷酸盐的结构很稳定，其具有优异导锂离子的能力，因此，使用晶态磷酸盐进行包覆能够使正极活性材料的表面的界面副反应得到有效降低，从而改善二次电池的高温循环及存储性能。第二包覆层和第一包覆层之间的晶格匹配方式等，与上述第一包覆层和核之间的结合情况相似，晶格失配在5％以下时，晶格匹配较好，两者容易结合紧密。
碳作为第三层包覆的主要原因是碳层的电子导电性较好。由于在二次电池中应用时发生的是电化学反应，需要有电子的参与，因此，为了增加颗粒与颗粒之间的电子传输，以及颗粒上不同位置的电子传输，可以使用具有优异导电性能的碳来对正极活性材料进行包覆。碳包覆可有效改善正极活性材料的导电性能和去溶剂化能力。
本申请的各包覆层可以是完全包覆，也可以是部分包覆。
在一些实施方式中，基于内核的重量计，第一包覆层的包覆量为C1重量％，C1大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2。和/或基于内核的重量计，第二包覆层的包覆量为C2重量％，C2大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为2-4。和/或基于内核的重量计，第三包覆层的包覆量为C3重量％，C3大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2。
本申请中，每一层的包覆量均不为零。
上述实施方式中的具有核-壳结构的正极活性材料中，三层包覆层的包覆量优选在上述范围内，由此能够对内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
对于第一包覆层而言，通过包覆量在上述范围内，则能够避免以下情况：包覆量过少则意味着包覆层厚度较薄，可能无法有效阻碍过渡金属的迁移；包覆量过大则意味着包覆层过厚，会影响Li +的迁移，进而影响材料的倍率性能。
对于第二包覆层而言，通过包覆量在上述范围内，则能够避免以下情况：包覆量过多，可能会影响材料整体的平台电压；包覆量过少，可能无法实现足够的包覆效果。
对于第三包覆层而言，碳包覆主要起到增强颗粒间的电子传输的作用，然而由于结构中还含有大量的无定形碳，因此碳的密度较低，因此，如果包覆量过大，会影响极片的压实密度。
上述实施方式的具有核-壳结构的正极活性材料中，三层包覆层的包覆量优选在上述范围内，由此能够对内核进行充分包覆，并同时在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
在任意实施方式中，第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
对于包覆层中的晶态焦磷酸盐和晶态磷酸盐，可通过本领域中常规的技术手段进行表征，也可以例如借助透射电镜(TEM)进行表征。在TEM下，通过测试晶面间距可以区分内核和包覆层。
包覆层中的晶态焦磷酸盐和晶态磷酸盐的晶面间距和夹角的具体测试方法可以包括以下步骤：
取一定量的经包覆的正极活性材料样品粉末于试管中，并在试管中注入溶剂如酒精，然后进行充分搅拌分散，然后用干净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM样品腔中进行测试，得到TEM测试原始图片，保存原始图片。
将上述TEM测试所得原始图片在衍射仪软件中打开，并进行傅里叶变换得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角根据布拉格方程进行计算得到。
晶态焦磷酸盐的晶面间距范围和晶态磷酸盐的存在差异，可通过晶面间距的数值直接进行判断。
上述实施方式的正极活性材料中的第一包覆层和第二包覆层均使用晶态物质，它们的晶面间距和夹角范围在上述范围内。由此，能够有效避免包覆层中的杂质相，从而提升材料的克容量，循环性能和倍率性能。而且在上述晶面间距和夹角范围内的晶态焦磷酸盐和晶态磷酸盐，能够更有效地抑制脱嵌锂过程中磷酸锰锂的晶格变化率和锰离子溶出，从而提升二次电池的高温循环性能、循环稳定性和高温储存性能。
在一些实施方式中，在内核中，y与1-y的比值为1：10至1：1，可选为1：4至1：1。在满足上述条件时，使用所述正极活性材料的二次电池的能量密度和循环性能可进一步提升。
在一些实施方式中，在内核中，z与1-z的比值为1：9至1：999，可选为1：499至1：249。此处z表示P位掺杂元素R的化学计量数之和。在满足上述条件时，使用正极活性材料的二次电池的能量密度和循环性能可进一步提升。
在一些实施方式中，第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
在一些实施方式中，SP2形态碳与SP3形态碳的摩尔比可为约0.1、约0.2、约03、约0.4、约0.5、约0.6、约0.7、约0.8、约0.9、约1、约2、约3、约4、约5、约6、约7、约8、约9或约10，或在上述任意值的任意范围内。
本申请中，“约”某个数值表示一个范围，表示该数值±10％的范围。
通过选择碳包覆层中碳的形态，从而提升二次电池的综合电性能。具体来说，通过使用SP2形态碳和SP3形态碳的混合形态并将SP2形态碳和SP3形态碳的比例限制在一定范围内，能够避免以下情况：如果包覆层中的碳都是无定形SP3形态，则导电性差；如果都是石墨化的SP2形态，则虽然导电性良好，但是锂离子通路少，不利于锂的脱嵌。另外，将SP2形态碳与SP3形态碳的摩尔比限制在上述范围内，既能实现良好的导电性，又能保证锂离子的通路，因此有利于二次电池功能的优化及其循环性能的改善。
第三包覆层碳的SP2形态和SP3形态的混合比可以通过烧结条件例如烧结温度和烧结时间来控制。例如，在使用蔗糖作为碳源制备第三包覆层的情况下，使蔗糖在高温下进行裂解后，在第二包覆层上沉积同时在高温作用下，会产生既有SP3形态也有SP2形态的碳包覆层。SP2形态碳和SP3形态碳的比例可以通过选择高温裂解条件和烧结条件来调控。
第三包覆层碳的结构和特征可通过拉曼(Raman)光谱进行测定，具体测试方法如下：通过对Raman测试的能谱进行分峰，得到Id/Ig(其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度)，从而确认两者的摩尔比。
在一些实施方式中，第一包覆层的厚度为1-10nm；和/或第二包覆层的厚度为2-15nm；和/或第三包覆层的厚度为2-25nm。
在一些实施方式中，第一包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm或约10nm，或在上述任意数值的任意范围内。
在一些实施方式中，第二包覆层的厚度可为约2nm、约3nm、约4nm、 约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm，或在上述任意数值的任意范围内。
在一些实施方式中，第三层包覆层的厚度可为约2nm、约3nm、约4nm、约5nm、约6nm、约7nm、约8nm、约9nm、约10nm、约11nm、约12nm、约13nm、约14nm、约15nm、约16nm、约17nm、约18nm、约19nm、约20nm、约21nm、约22nm、约23nm、约24nm或约25nm，或在上述任意数值的任意范围内。
当第一包覆层的厚度范围为1-10nm时，能够避免过厚时可能产生的对材料的动力学性能的不利影响，且能够避免过薄时可能无法有效阻碍过渡金属离子的迁移的问题。
当第二包覆层的厚度在2-15nm范围内时，第二包覆层的表面结构稳定，与电解液的副反应小，因此能够更有效地减轻界面副反应，从而进一步提升二次电池的高温性能。
当第三包覆层的厚度范围为2-25nm时，能够进一步提升材料的电导性能并且更好地改善使用该正极活性材料制备的电池极片的压密性能。
包覆层的厚度大小测试主要通过FIB进行，具体方法可以包括以下步骤：从待测正极活性材料粉末中随机选取单个颗粒，从所选颗粒中间位置或中间位置附近切取100nm左右厚度的薄片，然后对薄片进行TEM测试，量取包覆层的厚度，测量3-5个位置，取平均值。
在一些实施方式中，基于正极活性材料的重量计，锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内，磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
在本申请中，在仅正极活性材料的内核中含有锰的情况下，锰的含量可与内核的含量相对应。
在上述实施方式中，将锰元素的含量限制在上述范围内，能够有效避免若锰元素含量过大可能会引起的材料结构稳定性变差、密度下降等问题，从而有效提升二次电池的循环、存储和压密等性能；且能够避免若锰元含量过小可能会导致的电压平台低等问题，从而进一步提升二次电池的能量密度。
上述实施方式中，将磷元素的含量限制在上述范围内，能够有效避免以下情况：若磷元素的含量过大，可能会导致P-O的共价性过强而影响小极化子导电，从而影响材料的电导率；若磷含量过小，可能会使内核、第一包覆层中的焦磷酸盐和/或第二包覆层中的磷酸盐晶格结构的稳定性下降，从而影响材料整体的稳定性。
锰与磷含量重量比大小对二次电池的性能具有以下影响：该重量比过大， 意味着锰元素过多，锰离子溶出增加，影响正极活性材料的稳定性和克容量发挥，进而影响二次电池的循环性能及存储性能；该重量比过小，意味着磷元素过多，则容易形成杂相，会使材料的放电电压平台下降，从而使二次电池的能量密度降低。
锰元素和磷元素的测量可采用本领域中常规的技术手段进行。特别地，采用以下方法测定锰元素和磷元素的含量：将材料在稀盐酸中(浓度10-30％)溶解，利用ICP测试溶液各元素的含量，然后对锰元素的含量进行测量和换算，得到其重量占比。
在一些实施方式中，具有核-壳结构的正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
磷酸锰锂(LiMnPO 4)的脱嵌锂过程是两相反应。两相的界面应力由脱嵌锂前后的晶格变化率大小决定，晶格变化率越小，界面应力越小，Li +传输越容易。因此，减小内核的晶格变化率将有利于增强Li +的传输能力，从而改善二次电池的倍率性能。上述实施方式的具有核-壳结构的正极活性材料能够实现4％以下的脱嵌锂前后的晶格变化率，因此使用所述正极活性材料能够改善二次电池的倍率性能。晶格变化率可通过本领域中已知的方法，例如X射线衍射图谱(XRD)测得。
在一些实施方式中，具有核-壳结构的正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。
本申请的Li/Mn反位缺陷，指的是LiMnPO 4晶格中，Li +与Mn 2+的位置发生互换。相应地，Li/Mn反位缺陷浓度指的是与Mn 2+发生互换的Li +占Li +总量的百分比。本申请中，Li/Mn反位缺陷浓度例如，可以依据JIS K 0131-1996进行测试。
上述实施方式的具有核-壳结构的正极活性材料能够实现上述较低的Li/Mn反位缺陷浓度。虽然机理尚不十分清楚，但本申请发明人推测，由于LiMnPO 4晶格中，Li +与Mn 2+会发生位置互换，而Li +传输通道为一维通道，因此Mn 2+在Li +通道中将难以迁移，进而阻碍Li +的传输。由此，本申请所述的具有核-壳结构的正极活性材料由于Li/Mn反位缺陷浓度较低，在上述范围内，因此，能够避免Mn 2+阻碍Li +的传输，同时提升正极活性材料的克容量发挥和倍率性能。
在一些实施方式中，正极活性材料在3T下的压实密度为2.2g/cm 3以上，可选地为2.2g/cm 3以上且2.8g/cm 3以下。压实密度越高，单位体积活性材料的重量越大，因此提高压实密度有利于提高电芯的体积能量密度。压实密度可依据GB/T 24533-2009测量。
在一些实施方式中，正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。氧的稳定价态本为-2价，价态越接近-2价，其得电子能力越强，即氧化性越强，通常情况下，其表面价态在-1.7以下。上述实施方式通过如上所述将正极活性材料的表面氧价态限定在上述范围内，能够减轻正极材料与电解液的界面副反应，从而改善电芯的循环，高温存储产气等性能。
表面氧价态可通过本领域中已知的方法测量，例如通过电子能量损失谱(EELS)测量。
本申请还提供一种正极活性材料的制备方法，包括以下步骤：
提供内核材料的步骤：所述内核化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；
包覆步骤：分别提供Li aMP 2O 7和/或M b(P 2O 7) c以及XPO 4悬浊液，将所述内核材料加入到上述悬浊液中并混合，经烧结获得正极活性材料，其中0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐Li aMP 2O 7或M b(P 2O 7) c保持电中性；M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；
其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第一包覆层包括晶态焦磷酸盐Li aMP 2O 7和/或M b(P 2O 7) c，所述第二包覆层包括晶态磷酸盐XPO 4，所述第三包覆层为碳。
在一些实施方式中，所述提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素A的掺杂剂和酸在容器中混合并搅拌，得到掺杂有元素A的锰盐颗粒；
步骤(2)：将所述掺杂有元素A的锰盐颗粒与锂源、磷源和元素R的掺杂剂在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到掺杂有元素A和元素R的内核，其中，所述掺杂有元素A和元素R的内核为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素。
本申请的制备方法对材料的来源并没有特别的限制，某种元素的来源可包括该元素的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物或氢氧化物中的一种或多种，前体是该来源可实现本申请制备方法的目的。
在一些实施方式中，所述元素A的掺杂剂为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在一些实施方式中，所述元素R的掺杂剂为选自B、Si、N和S中的一种或多种元素各自的无机酸、亚酸、有机酸、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种；
本申请中，锰源可为本领域已知的可用于制备磷酸锰锂的含锰物质。作为示例，所述锰源可为选自单质锰、二氧化锰、磷酸锰、草酸锰、碳酸锰中的一种或多种。
本申请中，酸可为选自盐酸、硫酸、硝酸、磷酸、硅酸、亚硅酸等有机酸和有机酸如草酸中的一种或多种。在一些实施方式中，所述酸为浓度为60重量％以下的稀的有机酸。
本申请中，锂源可为本领域已知的可用于制备磷酸锰锂的含锂物质。作为示例，所述锂源为选自碳酸锂、氢氧化锂、磷酸锂、磷酸二氢锂中的一种或多种。
本申请中，磷源可为本领域已知的可用于制备磷酸锰锂的含磷物质。作为示例，所述磷源为选自磷酸氢二铵、磷酸二氢铵、磷酸铵和磷酸中的一种或多种。
在一些可选实施方式中，在所述锰源、所述元素A的掺杂剂与所述酸在溶剂中反应得到掺杂有元素A的锰盐悬浮液后，将所述悬浮液过滤，烘干，并进行砂磨以得到粒径为50-200nm的经元素A掺杂的锰盐颗粒。
在一些可选实施方式中，将步骤(2)中的浆料进行干燥得到粉料，然后将粉料烧结得到掺杂有元素A和元素R的内核。
在一些实施方式中，所述步骤(1)在20-120℃、可选为40-120℃的温度下进行混合；和/或
所述步骤(1)中所述搅拌在400-700rpm下进行1-9小时，可选地为3-7小时。
可选地，所述步骤(1)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；所述步骤(1)中所述搅拌进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时或约9小时；可选地，所述步骤(1)中的反应温度、搅拌时间可在上述任意数值的任意范围内。
在一些实施方式中，所述步骤(2)在20-120℃、可选为40-120℃的温度下进行混合1-12小时。可选地，所述步骤(2)中的反应温度可在约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃进行；所述步 骤(2)中所述混合进行约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时、约10小时、约11小时或约12小时；可选地，所述步骤(2)中的反应温度、混合时间可在上述任意数值的任意范围内。
当内核颗粒制备过程中的温度和时间处于上述范围内时，制备获得的内核以及由其制得的正极活性材料的晶格缺陷较少，有利于抑制锰离子溶出，减少正极活性材料与电解液的界面副反应，从而改善二次电池的循环性能和安全性能。
在一些实施方式中，可选地，在制备A元素和R元素掺杂的稀酸锰颗粒的过程中，控制溶液pH为3.5-6，可选地，控制溶液pH为4-6，更可选地，控制溶液pH为4-5。需要说明的是，在本申请中可通过本领域通常使用的方法调节所得混合物的pH，例如可通过添加酸或碱。
在一些实施方式中，可选地，在步骤(2)中，所述锰盐颗粒与锂源、磷源的摩尔比为1：0.5-2.1：0.5-2.1，更可选地，所述掺杂有元素A的锰盐颗粒与锂源、磷源的摩尔比为约1：1：1。
在一些实施方式中，可选地，制备A元素和R元素掺杂的磷酸锰锂过程中的烧结条件为：在惰性气体或惰性气体与氢气混合气氛下在600-950℃下烧结4-10小时；可选地，所述烧结可在约650℃、约700℃、约750℃、约800℃、约850℃或约900℃下烧结约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。在制备A元素和R元素掺杂的磷酸锰锂过程中，烧结温度过低以及烧结时间过短时，会导致材料内核的结晶度较低，会影响整体的性能发挥，而烧结温度过高时，材料内核中容易出现杂相，从而影响整体的性能发挥；烧结时间过长时，材料内核颗粒长的较大，从而影响克容量发挥，压实密度和倍率性能等。
在一些可选实施方式中，可选地，保护气氛为70-90体积％氮气和10-30体积％氢气的混合气体。
在一些实施方式中，所述包覆步骤包括：
第一包覆步骤：将元素M的源、磷源和酸以及任选地锂源，溶于溶剂中，得到第一包覆层悬浊液；将内核步骤中获得的内核与第一包覆步骤获得的第一包覆层悬浊液充分混合，干燥，然后烧结，得到第一包覆层包覆的材料；
第二包覆步骤：将元素X的源、磷源和酸溶于溶剂中，得到第二包覆层悬浊液；将第一包覆步骤中获得的第一包覆层包覆的材料与第二包覆步骤获得的第二包覆层悬浊液充分混合，干燥，然后烧结，得到两层包覆层包覆的材料；
第三包覆步骤：将碳源溶于溶剂中，充分溶解得到第三包覆层溶液；然后将第二包覆步骤中获得的两层包覆层包覆的材料加入所述第三包覆层溶液中，混合 均匀，干燥，然后烧结得到三层包覆层包覆的材料，即正极活性材料。
在一些实施方式中，所述元素M的源为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
在一些实施方式中，所述元素X的源为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素各自的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。
所述元素A、R、M、X各自的源的加入量取决于目标掺杂量，锂源、锰源和磷源的用量之比符合化学计量比。
作为示例，所述碳源为选自淀粉、蔗糖、葡萄糖、聚乙烯醇、聚乙二醇、柠檬酸中的一种或多种。
在一些实施方式中，所述第一包覆步骤中，控制溶解有元素M的源、磷源和酸以及任选地锂源的溶液pH为3.5-6.5，然后搅拌并反应1-5h，然后将所述溶液升温至50-120℃，并保持该温度2-10小时，和/或，烧结在650-800℃下进行2-6小时。
可选地，在第一包覆步骤中，所述反应充分进行。可选地，在第一包覆步骤中，所述反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时或约5小时。可选地，第一包覆步骤中，所述反应的反应时间可在上述任意数值的任意范围内。
可选地，在第一包覆步骤中，控制溶液pH为4-6。可选地，在第一包覆步骤中，将所述溶液升温至约55℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，第一包覆步骤中，所述升温的温度和保持时间可在上述任意数值的任意范围内。
可选地，在所述第一包覆步骤中，所述烧结可在约650℃、约700℃、约750℃、或约800℃下烧结约2小时、约3小时、约4小时、约5小时或约6小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第一包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述第一包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第一包覆层的结晶度低，非晶态物质较多，这样会导致抑制金属溶出的效果下降，从而影响二次电池的循环性能和高温存储性能；而烧结温度过高时，会导致第一包覆层出现杂相，也会影响到其抑制金属溶出的效果，从而影响二次电池的循环和高温存储性能等；烧结时间过长时，会使第一包覆层的厚度增加，影响Li+的迁移，从而影响材料的克容量发挥和倍率性能等。
在一些实施方式中，所述第二包覆步骤中，将元素X的源、磷源和酸溶于溶剂后，搅拌并反应1-10小时，然后将所述溶液升温至60-150℃，并保持该温度2-10小时，和/或，烧结在500-700℃下进行6-10小时。
可选地，在第二包覆步骤中，所述反应充分进行。可选地，在第二包覆步骤中，所述反应进行约1.5小时、约2小时、约3小时、约4小时、约4.5小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时。可选地，第二包覆步骤中，所述反应的反应时间可在上述任意数值的任意范围内。
可选地，在第二包覆步骤中，将所述溶液升温至约65℃、约70℃、约80℃、约90℃、约100℃、约110℃、约120℃、约130℃、约140℃或约150℃，并在该温度下保持约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，第二包覆步骤中，所述升温的温度和保持时间可在上述任意数值的任意范围内。
在所述提供内核材料的步骤和所述第一包覆步骤和所述第二包覆步骤中，在烧结之前，即，在发生化学反应的内核材料的制备中(步骤(1)-(2))以及在第一包覆层悬浮液和第二包覆层悬浮液的制备中，通过如上所述选择适当的反应温度和反应时间，从而能够避免以下情况：反应温度过低时，则反应无法发生或反应速率较慢；温度过高时，产物分解或形成杂相；反应时间过长时，产物粒径较大，可能会增加后续工艺的时间和难度；反应时间过短时，则反应不完全，获得的产物较少。
可选地，在第二包覆步骤中，所述烧结可在约550℃、约600℃或约700℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第二包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述第二包覆步骤中的烧结温度过低以及烧结时间过短时，会导致第二包覆层的结晶度低，非晶态较多，降低材料表面反应活性的性能下降，从而影响二次电池的循环和高温存储性能等；而烧结温度过高时，会导致第二包覆层出现杂相，也会影响到其降低材料表面反应活性的效果，从而影响二次电池的循环和高温存储性能等；烧结时间过长时，会使第二包覆层的厚度增加，影响材料的电压平台，从而使材料的能量密度下降等。
在一些实施方式中，所述第三包覆步骤中的烧结在700-800℃下进行6-10小时。可选地，在第三包覆步骤中，所述烧结可在约700℃、约750℃或约800℃下烧结约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述第三包覆步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述第三包覆步骤中的烧结温度过低时，会导致第三包覆层的石 墨化程度下降，影响其导电性，从而影响材料的克容量发挥；烧结温度过高时，会造成第三包覆层的石墨化程度过高，影响Li +的传输，从而影响材料的克容量发挥等；烧结时间过短时，会导致包覆层过薄，影响其导电性，从而影响材料的克容量发挥；烧结时间过长时，会导致包覆层过厚，影响材料的压实密度等。
在上述第一包覆步骤、第二包覆步骤、第三包覆步骤中，所述干燥均在100℃至200℃、可选为110℃至190℃、更可选为120℃至180℃、甚至更可选为120℃至170℃、最可选为120℃至160℃的干燥温度下进行，干燥时间为3-9小时、可选为4-8小时，更可选为5-7小时，最可选为约6小时。
通过本申请所述的正极活性材料的制备方法所制备的正极活性材料，其制备的二次电池在循环后Mn与Mn位掺杂元素的溶出量降低，且高温稳定性、高温循环性能和倍率性能得到改善。另外，原料来源广泛、成本低廉，工艺简单，有利于实现工业化。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的其他正极活性材料。作为示例，其他正极活性材料还可以包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂 (例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图3是作为一个示例的电池模块4。参照图3，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和5，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
[实施例]
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
其中，第一溶剂选自如下溶剂：
溶剂1：
Figure PCTCN2022090386-appb-000031
溶剂2:
Figure PCTCN2022090386-appb-000032
溶剂3：
Figure PCTCN2022090386-appb-000033
溶剂4：
Figure PCTCN2022090386-appb-000034
溶剂5：
Figure PCTCN2022090386-appb-000035
溶剂6
Figure PCTCN2022090386-appb-000036
第一添加剂选自如下化合物：
添加剂1：
Figure PCTCN2022090386-appb-000037
添加剂2：
Figure PCTCN2022090386-appb-000038
添加剂3：
Figure PCTCN2022090386-appb-000039
添加剂4：
Figure PCTCN2022090386-appb-000040
添加剂5：
Figure PCTCN2022090386-appb-000041
添加剂6：
Figure PCTCN2022090386-appb-000042
添加剂7：
Figure PCTCN2022090386-appb-000043
添加剂8：
Figure PCTCN2022090386-appb-000044
添加剂9：
Figure PCTCN2022090386-appb-000045
I.电池制备
实施例1：
步骤1：正极活性材料的制备
步骤S1：制备Fe、Co、V和S共掺杂的草酸锰
将689.6g碳酸锰、455.27g碳酸亚铁、4.65g硫酸钴、4.87g二氯化钒加入混料机中充分混合6h。然后将得到的混合物转入反应釜中，并加入5L去离子水和1260.6g二水合草酸，加热至80℃，以500rpm的转速充分搅拌6h，混合均匀，直至反应终止无气泡产生，得到Fe、Co、和V共掺杂的草酸锰悬浮液。然后将悬浮液过滤，在120℃下烘干，再进行砂磨，得到粒径为100nm的草酸锰颗粒。
步骤S2：制备内核Li 0.997Mn 0.60Fe 0.393V 0.004Co 0.003P 0.997S 0.003O 4
取(1)中制备的草酸锰1793.1g以及368.3g碳酸锂、1146.6g磷酸二氢铵和4.9g稀硫酸，将它们加入到20L去离子水中，充分搅拌，在80℃下均匀混合反应10h，得到浆料。将所述浆料转入喷雾干燥设备中进行喷雾干燥造粒，在250℃的温度下进行干燥，得到粉料。在保护气氛(90％氮气和10％氢气)中，在700℃下将所述粉料在辊道窑中进行烧结4h，得到上述内核材料。
步骤S3：第一包覆层悬浊液的制备
制备Li 2FeP 2O 7溶液，将7.4g碳酸锂，11.6g碳酸亚铁，23.0g磷酸二氢铵和12.6g二水合草酸溶于500mL去离子水中，控制pH为5，然后搅拌并在室温下反应2h得到溶液，之后将该溶液升温到80℃并保持此温度4h，得到第一包覆层悬浊液。
步骤S4：第一包覆层的包覆
将步骤S2中获得的掺杂后的1571.9g磷酸锰锂内核材料加入到步骤S3中获得的第一包覆层悬浊液(包覆物质含量为15.7g)中，充分搅拌混合6h，混合均匀后，转入120℃烘箱中干燥6h，然后在650℃下烧结6h得到焦磷酸盐包覆后的材料。
步骤S5：第二包覆层悬浊液的制备
将3.7g碳酸锂、11.6g碳酸亚铁、11.5g磷酸二氢铵和12.6g二水合草酸溶于1500mL去离子水中，然后搅拌并反应6h得到溶液，之后将该溶液升温到120℃并保持此温度6h，得到第二包覆层悬浊液。
步骤S6：第二包覆层的包覆
将步骤S4中获得的1586.8g的焦磷酸盐包覆后的材料加入到步骤S5中得到的第二包覆层悬浊液(包覆物质含量为47.1g)中，充分搅拌混合6h，混合均匀后，转入120℃烘箱中干燥6h，然后700℃烧结8h得到两层包覆后的材料。
步骤S7：第三包覆层水溶液的制备
将37.3g蔗糖溶于500g去离子水中，然后搅拌并充分溶解，得到蔗糖水溶液。
步骤S8：第三包覆层的包覆
将步骤S6中获得的两层包覆的材料1633.9g加入到步骤S7中得到的蔗糖溶液中，一同搅拌混合6h，混合均匀后，转入150℃烘箱中干燥6h，然后在700℃下烧结10h得到三层包覆后的材料。
步骤2：正极极片的制备
将上述制备的三层包覆后的正极活性材料、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为97.0：1.2：1.8加入到N-甲基吡咯烷酮(NMP)中，搅拌混合均匀，得到正极浆料。然后将正极浆料按0.280g/1540.25mm 2均匀涂覆于铝箔上，经烘干、冷压、分切，得到正极极片。
步骤3：负极极片的制备
将负极活性物质人造石墨、硬碳、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC)按照重量比为90：5：2：2：1溶于溶剂去离子水中，搅拌混合均匀后制备成负极浆料。将负极浆料按0.117g/1540.25mm 2均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切，得到负极极片。
步骤4：电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，采用溶剂1作为第一溶剂，碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合形成的混合液作为第二溶剂，采用添加剂1作为第一添加剂，采用LiPF 6作为锂盐均匀，其中第一溶剂、第二溶剂、第一添加剂和锂盐组成电解液，第一溶剂和第二溶剂的质量比为1:1，以电解液的总质量计，第一添加剂的质量含量为3％，锂盐的质量含量为12.5％。
步骤5：隔离膜的制备
使用市售的厚度为20μm、平均孔径为80nm的PP-PE共聚物微孔薄膜(来自卓高电子科技公司，型号20)。
步骤6：全电池的制备
将上述获得的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，并卷绕得到裸电芯。将裸电芯置于外包装中，注入上述电解液并封装，得到全电池(下文也称“全电”)。
【扣式电池的制备】
将上述制备的正极活性材料、聚偏二氟乙烯(PVDF)、乙炔黑以90：5：5的重量比加入至N-甲基吡咯烷酮(NMP)中，在干燥房中搅拌制成浆料。在铝箔上涂覆上述浆料，干燥、冷压制成正极极片。涂覆量为0.2g/cm 2，压实密度为
2.0g/cm 3。
采用锂片作为负极，采用溶剂1作为第一溶剂，体积比1：1：1的碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸二甲酯(DMC)形成的混合液作为第二溶剂，采用添加剂1作为第一添加剂，采用LiPF 6作为锂盐均匀，其中第一溶剂、第二溶剂、第一添加剂和锂盐组成电解液，第一溶剂和第二溶剂的质量比为1:1，以电解液的总质量计，第一添加剂的质量含量为3％，锂盐的质量含量为1mol/L。与上述制备的正极极片一起在扣电箱中组装成扣式电池(下文也称“扣电”)。
实施例2至27和对比例1至19
以类似于实施例1的方式制备实施例2至27和对比例1至19中的正极活性材料和电池，正极活性材料的制备中的不同之处参见表1-6，其中对比例1-2、4-10和12未包覆第一层，因此没有步骤S3、S4；对比例1-11未包覆第二层，因此没有步骤S5-S6。
注：本申请所有实施例和对比例中，如未标明，则使用的第一包覆层物质和/或第二包覆层物质均默认为晶态。
表1：内核的制备原料
Figure PCTCN2022090386-appb-000046
Figure PCTCN2022090386-appb-000047
Figure PCTCN2022090386-appb-000048
Figure PCTCN2022090386-appb-000049
Figure PCTCN2022090386-appb-000050
Figure PCTCN2022090386-appb-000051
Figure PCTCN2022090386-appb-000052
Figure PCTCN2022090386-appb-000053
Figure PCTCN2022090386-appb-000054
Figure PCTCN2022090386-appb-000055
II.性能评价
1.晶格变化率测试方法：
在25℃恒温环境下，将正极活性材料样品置于XRD(型号为Bruker D8 Discover)中，采用1°/min对样品进行测试，并对测试数据进行整理分析，参照标准PDF卡片，计算出此时的晶格常数a0、b0、c0和v0(a0,b0和c0表示晶胞各个方面上的长度大小，v0表示晶胞体积，可通过XRD精修结果直接获取)。
采用上述实施例中扣电制备方法，将所述正极活性材料样品制备成扣电，并对上述扣电以0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于碳酸二甲酯(DMC)中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。取样并按照与上述测试新鲜样品同样的方式计算出其晶胞体积v1，将(v0-v1)/v0×100％作为其完全脱嵌锂前后的晶格变化率(晶胞体积变化率)示于表中。
2.Li/Mn反位缺陷浓度
将“晶格变化率测量方法”中测试的XRD结果与标准晶体的PDF(Powder Diffraction File)卡片对比，得出Li/Mn反位缺陷浓度。具体而言，将“晶格变化率测量方法”中测试的XRD结果导入通用结构分析系统(GSAS)软件中，自动获得精修结果，其中包含了不同原子的占位情况，通过读取精修结果获得Li/Mn反位缺陷浓度。
3.压实密度
取5g的上述制得的正极活性材料粉末放于压实专用模具(美国CARVER模具，型号13mm)中，然后将模具放在压实密度仪器上。施加3T的压力，在设备上读出压力下粉末的厚度(卸压后的厚度)，通过ρ＝m/v，计算出压实密度，其中使用的面积值为标准的小图片面积1540.25mm 2。
4.3C充电恒流比
在25℃恒温环境下，将上述各个实施例和对比例制备的新鲜全电池静置5min，按照1/3C放电至2.5V。静置5min，按照1/3C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5min，记录此时的充电容量为C0。按照1/3C放电至2.5V，静置5min，再按照3C充电至4.3V，静置5min，记录此时的充电容量为C1。3C充电恒流比即为C1/C0×100％。
3C充电恒流比越高，说明二次电池的倍率性能越好。
5.过渡金属Mn(以及Mn位掺杂的Fe)溶出测试
将45℃下循环至容量衰减至80％后的上述各个实施例和对比例制备的全电池采用0.1C倍率进行放电至截止电压2.0V。然后将电池拆开，取出负极极片，在负极极片上随机取30个单位面积(1540.25mm2)的圆片，用Agilent ICP-OES730测试电感耦合等离子体发射光谱(ICP)。根据ICP结果计算其中Fe(如果正极活性材料的Mn位掺杂有Fe的话)和Mn的量，从而计算循环后Mn(以及Mn位掺杂的Fe)的溶出量。测试标准依据EPA-6010D-2014。
6.表面氧价态
取5g上述制得的正极活性材料样品按照上述实施例中所述扣电制备方法制备成扣电。对扣电采用0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于DMC中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。将所得颗粒用电子能量损失谱(EELS，所用仪器型号为Talos F200S)进行测量，获取能量损失近边结构(ELNES)，其反映元素的态密度和能级分布情况。根据态密度和能级分布，通过对价带态密度数据进行积分，算出占据的电子数，从而推算出充电后的表面氧的价态。
7.正极活性材料中锰元素和磷元素的测量
将5g上述制得的正极活性材料在100ml逆王水(浓盐酸：浓硝酸＝1：3)中(浓盐酸浓度～37％，浓硝酸浓度～65％)溶解，利用ICP测试溶液各元素的含量，然后对锰元素或磷元素的含量进行测量和换算(锰元素或磷元素的量/正极活性材料的量*100％)，得到其重量占比。
8.扣式电池初始克容量测量方法
在2.5-4.3V下，将上述各实施例和对比例制备的扣式电池按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5min，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为D0。
10.全电池60℃存储30天电芯膨胀测试：
在60℃下，存储100％充电状态(SOC)的上述各个实施例和对比例制备的全电池。在存储前后及过程中测量电芯的开路电压(OCV)和交流内阻(IMP)以监控SOC，并测量电芯的体积。其中在每存储48h后取出全电池，静置1h后测试开路电压(OCV)、内阻(IMP)，并在冷却至室温后用排水法测量电芯体积。排水法即先用表盘数据自动进行单位转换的天平单独测量电芯的重力F1，然后将电芯完全置于去离子水(密度已知为1g/cm3)中，测量此时的电芯的重力F2，电芯受到的浮力F浮即为F1-F2，然后根据阿基米德原理F浮＝ρ×g×V 排，计算得到电芯体积V＝(F1-F2)/(ρ×g)。
由OCV、IMP测试结果来看，本实验过程中直至存储结束，全部实施例的电池始终保持99％以上的SOC。
存储30天后，测量电芯体积，并计算相对于存储前的电芯体积，存储后的电芯体积增加的百分比。
11.全电池45℃下循环性能测试
在45℃的恒温环境下，在2.5-4.3V下，按照1C充电至4.3V，然后在4.3V下恒压充电至电流≤0.05mA，静置5min，然后按照1C放电至2.5V，容量记为Dn(n＝0,1,2,……)。重复前述过程，直至容量衰减(fading)到80％，记录此时的重复次数，即为45℃下80％容量保持率对应的循环圈数。
12.晶面间距和夹角测试
取1g上述制得的各正极活性材料粉末于50mL的试管中，并在试管中注入10mL质量分数为75％的酒精，然后进行充分搅拌分散30分钟，然后用干 净的一次性塑料吸管取适量上述溶液滴加在300目铜网上，此时，部分粉末将在铜网上残留，将铜网连带样品转移至TEM(Talos F200s G2)样品腔中进行测试，得到TEM测试原始图片，保存原始图片格式(xx.dm3)。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，并进行傅里叶变换(点击操作后由软件自动完成)得到衍射花样，量取衍射花样中衍射光斑到中心位置的距离，即可得到晶面间距，夹角根据布拉格方程进行计算得到。
通过得到的晶面间距和相应夹角数据，与其标准值比对，即可对包覆层的不同物质进行识别。
13.包覆层厚度测试
包覆层的厚度大小测试主要通过FIB从上述制得的正极活性材料单个颗粒中间切取100nm左右厚度的薄片，然后对薄片进行TEM测试，得到TEM测试原始图片，保存原始图片格式(xx.dm3)。
将上述TEM测试所得原始图片在DigitalMicrograph软件中打开，通过晶格间距和夹角信息，识别出包覆层，量取包覆层的厚度。
对所选颗粒测量三个位置处的厚度，取平均值。
14.第三层包覆层碳中SP2形态和SP3形态摩尔比的测定
本测试通过拉曼(Raman)光谱进行。通过对Raman测试的能谱进行分峰，得到Id/Ig，其中Id为SP3形态碳的峰强度，Ig为SP2形态碳的峰强度，从而确认两者的摩尔比。
所有实施例和对比例的性能测试结果参见下面的表格。
Figure PCTCN2022090386-appb-000056
Figure PCTCN2022090386-appb-000057
Figure PCTCN2022090386-appb-000058
Figure PCTCN2022090386-appb-000059
Figure PCTCN2022090386-appb-000060
表12
Figure PCTCN2022090386-appb-000061
按照上述测试方法测试0.1C扣电初始克容量(mAh/g)、3C充电恒流比(％)、45℃容量保持率80％循环圈数、60℃存储30天电芯膨胀率(％)，并将测试结果记录在表13中。
表13
Figure PCTCN2022090386-appb-000062
Figure PCTCN2022090386-appb-000063
Figure PCTCN2022090386-appb-000064
而且，将上述实施例1至29的全电池中的电解液替换为：将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5重量％(基于碳酸乙烯酯/碳酸甲乙酯溶剂的重量计)LiPF 6溶解于上述有机溶剂中，搅拌均匀，得到电解液；将扣电池的电解液替换为：采用1mol/L的LiPF 6在体积比1：1：1的碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸二甲酯(DMC)中的溶液为电解液。对形成的对比例18至46的扣电池或全电池的循环后Mn和Fe溶出量(ppm)、0.1C扣电容量(mAh/g)(mAh/g)、3C充电恒流比(％)、45℃容量保持率80％循环圈数、60℃存储电芯膨胀率(％)按照上述方法进行检测，检测结果记录在表14中。
表14
Figure PCTCN2022090386-appb-000065
Figure PCTCN2022090386-appb-000066
根据表9和表14的对比可以看出，本申请的电解液组成可以进一步提高二次电池的倍率性能和循环性能。
在实施例4的电解液基础上，进一步添加第二添加剂，表15中指出了添加剂的种类以及添加剂在电解液中的含量。采用上述方法测试扣电初始克容量(mAh/g)、3C充电恒流比(％)、45℃容量保持率80％循环圈数、60℃存储电芯膨胀率(％)，并将测试结果记录在表15中。
表15
Figure PCTCN2022090386-appb-000067
Figure PCTCN2022090386-appb-000068
根据表8的数据和实施例4的数据比较可以看出，当时使用第二添加剂时，可以进一步提高循环性能。
虽然已经参考优选实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (20)

  1. 一种二次电池，包括：包括正极极片以及非水电解液，其中，
    所述正极极片包括具有核-壳结构的正极活性材料，所述正极活性材料包括内核及包覆所述内核的壳，
    所述内核的化学式为Li 1+xMn 1-yA yP 1-zR zO 4，其中x为在-0.100-0.100范围内的任意数值，y为在0.001-0.500范围内的任意数值，z为在0.001-0.100范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ni、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，可选为Fe、Ti、V、Ni、Co和Mg中一种或多种元素，所述R为选自B、Si、N和S中的一种或多种元素，可选地，所述R为选自B、Si、N和S中的一种元素；所述x、y和z的值满足以下条件：使整个内核保持电中性；
    所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，其中，
    所述第一包覆层包括晶态焦磷酸盐LiaMP 2O 7和/或Mb(P 2O 7) c，其中，0≤a≤2，1≤b≤4，1≤c≤6，所述a、b和c的值满足以下条件：使晶态焦磷酸盐LiaMP 2O 7或Mb(P 2O 7) c保持电中性，所述晶态焦磷酸盐LiaMP 2O 7和Mb(P 2O 7) c中的M各自独立地为选自Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素，
    所述第二包覆层包括晶态磷酸盐XPO 4，其中，所述X为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb或Al中的一种或多种元素；
    第三包覆层为碳；
    所述非水电解液包括有机溶剂，所述有机溶剂包括第一溶剂，所述第一溶剂包括式1所示化合物中的一种或多种，
    Figure PCTCN2022090386-appb-100001
    R 1和R 2分别独立地为C1～C10烷基、C1～C10卤代烷基中的一种，可选地，R 1和R 2分别独立地为甲基、乙基、丙基、丁基、戊基、己基、氟代甲基、氟代乙基、氟代丙基、氟代丁基、氟代戊基、氟代己基中的一种，进一步可选地R 1和R 2分别独立地为甲基、乙基、丙基、氟代甲基、氟代乙基、氟代丙基中的一种。
  2. 根据权利要求1所述的二次电池，其中，所述第一溶剂包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100002
    Figure PCTCN2022090386-appb-100003
    可选地，所述第一溶剂包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100004
  3. 根据权利要求1或2所述的二次电池，其中，基于所述有机溶剂的总质量，所述第一溶剂的质量百分数为w1，所述w1的范围为20％～80％；可选地，所述w1的范围为30％～75％；
    可选地，所述有机溶剂还包括第二溶剂，所述第二溶剂包括链状碳酸酯、环状碳酸酯组成的组中的一种或多种；进一步可选地，基于所述有机溶剂的总质量，所述第二溶剂的质量百分数为w2，所述w2的范围为20％～70％；可选地，所述w2的范围为25％～70％。
  4. 根据权利要求1至3中任一项所述的二次电池，其中，所述非水电解液还包括第一添加剂，所述第一添加剂包含磺酸内酯、环状硫酸酯组成的组中的一种或多种。
  5. 根据权利要求4所述的二次电池，其中，所述磺酸内酯包括式2所示化合物中的至少一种，
    Figure PCTCN2022090386-appb-100005
    p表示1、2或3，
    R 11表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基中的一种；可选地，R 11表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基中的一种；可选地所述烷氧基为链状烷氧基或环状烷氧基，可选地所述环状烷氧基与所述磺酸内酯的母环共用一个碳原子，进一步可选地环状烷氧基为碳原子数为4、5或6；
    各R 12分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、4至7元磺酸内酯基中的一种；可选地，各R 12分别独立地表示氢原子、卤原子、C1～C3烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、5至6元磺酸内酯基中的一种；可选地，所述磺酸内酯基与所述磺酸内酯的母环共用一个碳原子，可选地所述磺酸内酯基为5元环；
    R 11和R 12与各自连接的碳原子可形成5至10元的环烷基；
    R 13表示氢原子、卤原子、羰基、C2～C6的酯基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基或苄基中的一种；可选地，R 13表示氢原子、卤原子、羰基、C2～C3的酯基、C1～C3烷基、C1～C3卤代烷基、C2～C6烯基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基或苄基中的一种；
    和/或，
    所述环状硫酸酯包括式3所示化合物中的至少一种，
    Figure PCTCN2022090386-appb-100006
    q表示1、2或3，
    R 14表示氢原子、卤原子、羰基、C1～C12烷基、C1～C12卤代烷基、C2～C12烯基、C1～C12烷氧基、C1～C12卤代烷氧基、C2～C6的酯基、4至7元的环状硫酸酯基中的一种；可选地，R 14表示氢原子、卤原子、羰基、双键、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C2～C3的酯基、4至5元的环状硫酸酯基中的一种；可选地所述环状硫酸酯基与所述环状硫酸酯共用一个碳原子；
    各R 15分别独立地表示氢原子、卤原子、C1～C12烷基、C1～C12卤代烷基、C1～C12烷氧基、C1～C12卤代烷氧基、C6～C20芳基中的一种；可选地，各R 15分别独 立地表示氢原子、卤原子、C1～C6烷基、C1～C3卤代烷基、C1～C3烷氧基、C1～C3卤代烷氧基、C6～C10芳基中的一种；
    或者R 14和R 15与各自链接的碳原子共同形成4至7元的环状硫酸酯基，进一步可选地，R 14和R 15与各自链接的碳原子共同形成5元的环状硫酸酯基；
    可选地，所述磺酸内酯包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100007
    可选地，所述环状硫酸酯包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100008
    进一步可选地，所述磺酸内酯包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100009
    进一步可选地，所述环状硫酸酯包括如下化合物中的至少一种：
    Figure PCTCN2022090386-appb-100010
  6. 根据权利要求4或5所述的二次电池，其中，基于所述非水电解液的总质量， 所述第一添加剂的含量为W3，且0.01％≤W3≤20％，可选地0.1％≤W3≤10％，进一步可选地0.3％≤W3≤5％。
  7. 根据权利要求1至6中任一项所述的二次电池，其中，所述非水电解液还包括第二添加剂，所述第二添加剂包括亚硫酸酯化合物、二磺酸化合物、腈化合物、芳香化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物组成的组中的一种或多种。
  8. 根据权利要求7所述的二次电池，其中，基于所述非水电解液的总质量，所述第二添加剂的含量为W4，且0.01％≤W4≤20％，可选地0.05％≤W4≤5％，进一步可选地0.1％≤W4≤3％。
  9. 根据权利要求1-8中任一项所述的二次电池，其中，
    基于所述内核的重量计，所述第一包覆层的包覆量为C1重量％，C1大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2；和/或
    基于所述内核的重量计，所述第二包覆层的包覆量为C2重量％，C2大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为2-4；和/或
    基于所述内核的重量计，所述第三包覆层的包覆量为C3重量％，C3大于0且小于或等于6，可选为大于0且小于或等于5.5，更可选为大于0且小于或等于2。
  10. 根据权利要求1-9中任一项所述的二次电池，其中，
    所述第一包覆层中的晶态焦磷酸盐的晶面间距范围为0.293-0.470nm，晶向(111)的夹角范围为18.00°-32.00°；
    所述第二包覆层中的晶态磷酸盐的晶面间距范围为0.244-0.425nm，晶向(111)的夹角范围为20.00°-37.00°。
  11. 根据权利要求1-10中任一项所述的二次电池，其中，
    在所述内核中，y与1-y的比值为1：10至1：1，可选为1：4至1：1；和/或
    在所述内核中，z与1-z的比值为1：9至1：999，可选为1：499至1：249。
  12. 根据权利要求1-11中任一项所述的二次电池，其中，
    所述第三包覆层的碳为SP2形态碳与SP3形态碳的混合物，可选地，所述SP2形态碳与SP3形态碳的摩尔比为在0.1-10范围内的任意数值，可选为在2.0-3.0范围内的任意数值。
  13. 根据权利要求1-12中任一项所述的二次电池，其中，
    所述第一包覆层的厚度为1-10nm；和/或
    所述第二包覆层的厚度为2-15nm；和/或
    所述第三包覆层的厚度为2-25nm。
  14. 根据权利要求1-13中任一项所述的二次电池，其中，
    基于正极活性材料的重量计，
    锰元素含量在10重量％-35重量％范围内，可选在15重量％-30重量％范围内，更可选在17重量％-20重量％范围内；
    磷元素的含量在12重量％-25重量％范围内，可选在15重量％-20重量％范围内，
    可选地，锰元素和磷元素的重量比范围为0.90-1.25，可选为0.95-1.20。
  15. 根据权利要求1-14中任一项所述的二次电池，其中，
    所述具有核-壳结构的正极活性材料在完全脱嵌锂前后的晶格变化率为4％以下，可选为3.8％以下，更可选为2.0-3.8％。
  16. 根据权利要求1-15中任一项所述的二次电池，其中，
    所述具有核-壳结构的正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2.2％以下，更可选为1.5-2.2％。
  17. 根据权利要求1-16中任一项所述的二次电池，其中，
    所述具有核-壳结构的正极活性材料的表面氧价态为-1.90以下，可选地为-1.90至-1.98。
  18. 一种电池模块，包括二次电池，其中，所述二次电池为权利要求1至17中任一项所述的二次电池。
  19. 一种电池包，包括电池模块，其中所述电池模块为权利要求18所述的电池模块。
  20. 一种用电装置，包括二次电池或电池模块或电池包，其中，所述二次电池选自权利要求1至17中任一项所述的二次电池、所述电池模块为权利要求18所述的电池模块或所述电池包为权利要求19所述的电池包。
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