WO2023184490A1 - 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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WO2023184490A1
WO2023184490A1 PCT/CN2022/084835 CN2022084835W WO2023184490A1 WO 2023184490 A1 WO2023184490 A1 WO 2023184490A1 CN 2022084835 W CN2022084835 W CN 2022084835W WO 2023184490 A1 WO2023184490 A1 WO 2023184490A1
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secondary battery
coating layer
core
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PCT/CN2022/084835
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French (fr)
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陈培培
张立美
蒋耀
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 EP22934326.4A priority Critical patent/EP4318704A4/en
Priority to CN202280039981.3A priority patent/CN117425995A/zh
Priority to PCT/CN2022/084835 priority patent/WO2023184490A1/zh
Publication of WO2023184490A1 publication Critical patent/WO2023184490A1/zh
Priority to US18/607,120 priority patent/US20240283036A1/en

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    • H—ELECTRICITY
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    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C01P2004/86—Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M2300/0025—Organic electrolyte
    • 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 technical field of lithium batteries, and in particular to a secondary battery, a battery module, a battery pack and an electrical device.
  • lithium-ion batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields. Due to the great development of lithium-ion batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance.
  • lithium manganese phosphate cathode active materials Compared with other cathode active materials, lithium manganese phosphate cathode active materials have higher safety and cycle life.
  • the disadvantage of lithium manganese phosphate is poor rate performance. Currently, this is usually solved by coating or doping. One question. However, it is still hoped that the rate performance, cycle performance, high temperature stability, etc. of lithium manganese phosphate cathode active materials can be further improved.
  • This application was made in view of the above-mentioned problems, and its purpose is to provide a secondary battery, a battery module, a battery pack and a power device to solve the problem of poor cycle performance of lithium manganese phosphate secondary batteries.
  • a first aspect of the present application provides a secondary battery, including a positive electrode sheet and a non-aqueous electrolyte, wherein the positive electrode sheet includes a positive electrode active material with a core-shell structure, and the positive electrode active material includes a core and a shell covering the core.
  • the chemical formula of the core is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x is any value within the range of -0.100-0.100, and y is within the range of 0.001-0.500 Any value within the range, 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, One or more elements from the group consisting of Sn, Sb, Nb and Ge, optionally one or more elements from the group consisting of Fe, Ti, V, Ni, Co and Mg, R is selected from B, Si, N One or more elements in the group consisting of and S, optionally, R is an element selected from the group consisting of B, Si, N and S; the values of 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 cla
  • the non-aqueous electrolyte solution includes a first additive, and the first additive includes one or more of the group consisting of a compound represented by Formula 1 and a compound represented by Formula 2,
  • R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C6 haloalkyl group, a C1 to C6 alkoxy group, a C2 to C6 alkenyl group, or a C2 to C6 alkynyl group. any of;
  • R 3 , R 4 , R 5 and R 6 each independently represent a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C6 haloalkyl group, a C1 to C6 alkoxy group, a C2 to C6 alkenyl group, Any one of a C2-C6 alkynyl group and a C2-C6 alkynyloxy group, and R 3 , R 4 , R 5 , and R 6 do not represent a hydrogen atom at the same time.
  • 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 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 additive is introduced into the non-aqueous electrolyte to form a layer of polymer on the surface of the coating layer during the charging process of the lithium-ion battery, preventing the coating layer from dissolving, reducing the dissolution of manganese ions, and at the same time reducing the catalytic activity of the coating carbon , reducing the consumption of active lithium and further improving the high-temperature cycle and storage performance of secondary batteries.
  • R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, a C1-C4 alkyl group, C1-C4 Any one of haloalkyl groups, C1-C4 alkoxy groups, C2-C4 alkenyl groups, C2-C4 alkynyl groups, optionally, R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, Any one of a C1-C4 alkyl group, a C1-C2 haloalkyl group, and a C2-C3 alkenyl group.
  • R 3 , R 4 , R 5 , and R 6 each independently represent a hydrogen atom, a halogen atom, C1 to C4 Any one of an alkyl group, a C1 to C4 haloalkyl group, a C1 to C4 alkoxy group, a C2 to C4 alkenyl group, a C2 to C4 alkynyl group, or a C2 to C4 alkynyloxy group, optionally, R 3 , R 4 , R 5 and R 6 each independently represent a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C2 haloalkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, Any one of C2 to C4 alkynyloxy groups, and R 3 , R 4 , R 5 , and
  • the first additive includes at least one of the following compounds:
  • the content of the first additive is W1% by weight based on the total weight of the non-aqueous electrolyte, and W1 is 0.01 to 20, optionally 0.2 to 8 or 0.5 to 5.
  • W1 is 0.01 to 20, optionally 0.2 to 8 or 0.5 to 5.
  • the first additive is any one of the following compounds
  • the polymer formed by each of the above first additives during the charging process is more stable, and therefore, the dissolution of Mn in the cathode active material of the present application is more efficiently improved.
  • the above-mentioned non-aqueous electrolyte further includes a second additive.
  • the second additive includes vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, difluorophosphate, and vinyl sulfate.
  • One or more of the group consisting of lithium oxalate and borate will form a film on the positive electrode to form a low-resistance CEI film, further improving the secondary battery capacity and rate performance.
  • the content of the second additive is W2% by weight based on the total weight of the non-aqueous electrolyte, and W2 is 0.01 to 20, optionally 0.2 to 8 or 0.3 to 5; to form a low impedance with appropriate thickness.
  • CEI film is W2% by weight based on the total weight of the non-aqueous electrolyte, and W2 is 0.01 to 20, optionally 0.2 to 8 or 0.3 to 5; to form a low impedance with appropriate thickness.
  • the content of the first additive is W1% by weight based on the total weight of the non-aqueous electrolyte
  • W1 is 0.01 to 20 (such as 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2 , 3, 4, 5, 8, 10, 12, 15, 18 or 20), optionally 0.2 to 8 or 0.5 to 5, optionally the mass ratio of W2/W1 is A, A is 0.1 to 10 ( For example, 0.1, 0.2, 0.3, 0.4, 0.5, 1,, 2, 3, 4, 5, 6, 7, 8, 9 or 10), optionally 0.2 to 5.
  • the second additive can be used to effectively alleviate the problem of increased cathode impedance caused by the first additive, and further optimize the improvement effect of the first additive on battery capacity and rate performance.
  • the above-mentioned non-aqueous electrolyte further includes a third additive.
  • the third additive includes a chain sulfate ester compound, a sulfite compound, a sultone compound containing an unsaturated bond, a disulfonic acid compound, and a nitrile compound. , one or more of the group consisting of aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate ester compounds, and borate ester compounds.
  • the above-mentioned third additive can improve the capacity, cycle performance, etc. of the secondary battery according to its own performance. Those skilled in the art can select the corresponding third additive according to actual needs.
  • the above-mentioned non-aqueous electrolyte also includes an organic solvent.
  • organic solvent is not particularly limited and can be selected according to actual needs.
  • the organic solvent includes dimethyl carbonate, diethyl carbonate.
  • dipropyl carbonate ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone, methyl formate, ethyl formate, methyl acetate
  • ester ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, and tetrahydrofuran.
  • the above-mentioned non-aqueous electrolyte solution further includes an electrolyte salt.
  • the electrolyte salt includes LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ), Li(FSO 2 ) 2 N, LiCF 3 SO 3 , LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiBOB, LiDFOB, LiTFOP, one or more of the group consisting of, x and y represent positive integers, optionally, x and y are each independently 0, 1, 2 or 3, non-aqueous electrolyte
  • the concentration range of the medium electrolyte salt is 0.5M ⁇ 2M, and the optional range is 0.8M ⁇ 1.5M, which can ensure the smooth and rapid migration of Li + in the positive and negative electrodes.
  • 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 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 ratio of W1/(C1+C2+C3) is defined as Q, and Q is 0.05 to 1 (such as 0.05, 0.06, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1), optionally 0.1 to 1.
  • Q is 0.05 to 1 (such as 0.05, 0.06, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1), optionally 0.1 to 1.
  • 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 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. As a result, impurity phases in the coating layer can be effectively avoided, thereby 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. As a result, the cycle performance and rate performance of the secondary battery are further improved.
  • the ratio of z to 1-z is from 1:999 to 1:9, optionally from 1:499 to 1:249. As a result, the cycle performance and rate performance of the secondary battery are further improved.
  • 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 above embodiment improves 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 2-25 nm.
  • 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 When the thickness of the second coating layer is in the range of 2-15nm, the surface structure of the second coating layer is stable and side reactions with the electrolyte are small. Therefore, interface side reactions can be effectively reduced, thereby improving the high-temperature performance of the secondary battery.
  • the thickness of the third coating layer ranges from 2 to 20 nm, the electrical conductivity of the material can be improved and the compaction density performance of the battery pole piece prepared using the cathode active material can be improved.
  • the manganese element content is in the range of 10 wt%-35 wt%, optionally in the range of 15 wt%-30 wt%, more optionally
  • the content of phosphorus is in the range of 17% to 20% by weight, and the content of phosphorus is in the range of 12% to 25% by weight, optionally in the range of 15% to 20% by weight, and the weight ratio of manganese to phosphorus 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 Improve the cycle, storage and compaction density performance of secondary batteries; and avoid problems such as low voltage platforms that may occur 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 with 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 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 (ton), optionally 2.2 g/cm or more and 2.8 g/cm 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, and especially the high temperature stability is significantly improved, thereby providing power consumption devices with the secondary battery, battery module or battery pack of the present application.
  • High power cycle stability and high temperature operating stability are particularly preferred.
  • 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 arbitrarily combined, that is, 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).
  • the term “coating layer” refers to the material layer coated on the lithium manganese phosphate core.
  • the material layer can completely or partially cover the lithium manganese phosphate core.
  • the term “coating layer” is used " is only for convenience of description and is not intended to limit the present invention.
  • the term “thickness of the coating layer” refers to the thickness of the material layer coating the lithium manganese phosphate core in the radial direction of the lithium manganese phosphate core.
  • the inventor of the present application found in actual operations that the existing manganese phosphate lithium cathode active material has serious manganese ion dissolution during the deep charge and discharge process. Although there are attempts in the prior art to coat lithium manganese phosphate with lithium iron phosphate to reduce interface side reactions, this coating cannot prevent the eluted manganese from continuing to migrate into the electrolyte. The eluted manganese is reduced to metallic manganese after migrating to the negative electrode.
  • the metallic manganese produced in this way is equivalent to a "catalyst", which can catalyze the decomposition of the SEI film (solid electrolyte interphase, solid electrolyte interface film) on the surface of the negative electrode to produce by-products; part of the by-products is gas, thus causing secondary battery failure. expansion, affecting the safety performance of the secondary battery; in addition, another part of the by-product is deposited on the surface of the negative electrode, which will hinder the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase, thus affecting the dynamic performance of the secondary battery. In addition, in order to replenish the lost SEI film, the electrolyte and active lithium inside the battery are continuously consumed, which will have an irreversible impact on the capacity retention rate of the secondary battery.
  • the cathode active material can Achieving significantly reduced manganese ion dissolution and reduced lattice change rate, it is used in secondary batteries to improve the cycle performance, rate performance, safety performance of the battery and increase the capacity of the battery.
  • 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.
  • One embodiment of the present application provides a secondary battery, including 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 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, y is any value in the range of 0.001-0.500, z is any value in the range of 0.001-0.100, and 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 elements from the group consisting of Ge, optionally one or more elements from the group consisting of Fe, Ti, V, Ni, Co and Mg, R is selected from the group consisting of 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 coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating the
  • the non-aqueous electrolyte solution includes a first additive, and the first additive includes one or more of the group consisting of a compound represented by Formula 1 and a compound represented by Formula 2,
  • R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C6 haloalkyl group, a C1 to C6 alkoxy group, a C2 to C6 alkenyl group, or a C2 to C6 alkynyl group. any of;
  • R 3 , R 4 , R 5 and R 6 each independently represent a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a C1 to C6 haloalkyl group, a C1 to C6 alkoxy group, a C2 to C6 alkenyl group, Any one of a C2-C6 alkynyl group and a C2-C6 alkynyloxy group, and R 3 , R 4 , R 5 , and R 6 do not represent a hydrogen atom at the same time.
  • 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.
  • the composite current collector 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 above-mentioned limitation on the numerical range of y is not only a limitation on the stoichiometric number of each element as A, but also on each element as A. Limitation of the sum of the stoichiometric numbers of elements. 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. Similarly, for the case where R is two or more elements, the limitation on the numerical range of the R stoichiometric number in this application also has the above meaning.
  • 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. 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.
  • 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 dissolution of manganese ions reduces the migration of manganese ions to the negative electrode, reduces the consumption of electrolyte due to the decomposition of the SEI film, improves the cycle performance and safety performance of secondary batteries, and can also promote the adjustment of Mn-O bonds and reduce the lithium ion migration barrier.
  • the core by coating the core with a first coating layer including crystalline pyrophosphate, the migration resistance of manganese can be further increased, its dissolution can be reduced, and surface miscellaneous lithium can be reduced 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 secondary batteries; by further coating crystalline phosphoric acid with excellent ability to conduct lithium ions
  • the salt coating layer can effectively reduce the interfacial side reactions on the surface of the positive electrode 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. Battery 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 lithium deintercalation process of the material, and improves the structural stability of the lithium manganese phosphate cathode material. properties, 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 change of the Mn-O bond length, thereby improving electronic conductivity and lowering the lithium ion migration barrier , promote lithium ion migration 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, thereby improving the dynamic properties of the secondary battery.
  • transition metal such as manganese
  • the first additive is introduced into the non-aqueous electrolyte to form a layer of polymer on the surface of the coating layer during the charging process of the lithium-ion battery, preventing the coating layer from dissolving, reducing the dissolution of manganese ions, and at the same time reducing the catalytic activity of the coating carbon , reducing the consumption of active lithium and further improving the high-temperature cycle and storage performance of secondary batteries.
  • the main characteristic peak positions in the XRD pattern of lithium manganese phosphate doped with A element and R element are consistent with those of undoped LiMnPO 4 , indicating that no impurity phase is introduced during the doping process. Therefore, the improvement in core performance mainly comes from the elements. Doping, not impurities.
  • 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.
  • 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, the matching degree between the core and the first cladding layer is improved compared with the non-doped elements. can be brought closer 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.
  • R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, a C1-C4 alkyl group, C1-C4 Any one of haloalkyl groups, C1-C4 alkoxy groups, C2-C4 alkenyl groups, C2-C4 alkynyl groups, optionally, R 1 and R 2 each independently represent a hydrogen atom, a halogen atom, Any one of a C1-C4 alkyl group, a C1-C2 haloalkyl group, and a C2-C3 alkenyl group.
  • R 3 , R 4 , R 5 , and R 6 each independently represent a hydrogen atom, a halogen atom, or C1 to C4 Any one of alkyl, C1-C4 haloalkyl, C1-C4 alkoxy, C2-C4 alkenyl, C2-C4 alkynyl, C2-C4 alkynyloxy, optionally, R 3.
  • R 4 , R 5 and R 6 each independently represent a hydrogen atom, a halogen atom, a C1-C3 alkyl group, a C1-C2 haloalkyl group, a C1-C4 alkoxy group, a C2-C4 alkenyl group, C2 Any one of ⁇ C4 alkynyloxy groups, and R 3 , R 4 , R 5 and R 6 do not simultaneously represent a hydrogen atom.
  • the first additive includes at least one of the following compounds:
  • the content of the first additive is W1% by weight based on the total weight of the non-aqueous electrolyte, and W1 is 0.01 to 20, optionally 0.2 to 8 or 0.5 to 5.
  • W1 is 0.01 to 20, optionally 0.2 to 8 or 0.5 to 5.
  • the first additive is any one of the following compounds
  • the polymer formed by each of the above first additives during the charging process is more stable, and therefore, the dissolution of Mn in the cathode active material of the present application is more efficiently improved.
  • the above-mentioned non-aqueous electrolyte further includes a second additive, and the second additive includes one of the group consisting of vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium difluoroborate.
  • the second additive includes one of the group consisting of vinyl sulfate, lithium difluorophosphate, lithium difluorodioxalate phosphate, and lithium difluoroborate.
  • Each of the above-mentioned second additives will form a film on the positive electrode to form a low-resistance CEI film (catheode electrolyte interface film), further improving the secondary battery capacity and rate performance.
  • the content of the second additive is W2% by weight based on the total weight of the non-aqueous electrolyte, and W2 is 0.01 to 20, optionally 0.2 to 8 or 0.3 to 5; to form a low impedance with appropriate thickness.
  • CEI film is W2% by weight based on the total weight of the non-aqueous electrolyte, and W2 is 0.01 to 20, optionally 0.2 to 8 or 0.3 to 5; to form a low impedance with appropriate thickness.
  • the content of the first additive is W1% by weight, W1 is 0.01 to 20, optionally 0.2 to 8 or 0.5 to 5, optionally W2/W1
  • the mass ratio is A, with A ranging from 0.1 to 10, optionally from 0.2 to 5.
  • the above-mentioned non-aqueous electrolyte further includes a third additive.
  • the third additive includes a chain sulfate ester compound, a sulfite compound, a sultone compound containing an unsaturated bond, a disulfonic acid compound, and a nitrile compound. , one or more of the group consisting of aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate ester compounds, and borate ester compounds.
  • the above-mentioned third additive can improve the capacity, cycle performance, etc. of the secondary battery according to its own performance. Those skilled in the art can select the corresponding third additive according to actual needs.
  • the above-mentioned non-aqueous electrolyte also includes an organic solvent.
  • organic solvent is not particularly limited and can be selected according to actual needs.
  • the organic solvent includes dimethyl carbonate, diethyl carbonate.
  • dipropyl carbonate ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ⁇ -butyrolactone, methyl formate, ethyl formate, methyl acetate
  • ester ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, and tetrahydrofuran.
  • the above-mentioned non-aqueous electrolyte solution further includes an electrolyte salt.
  • the electrolyte salt includes LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ), Li(FSO 2 ) 2 N, LiCF 3 SO 3 , LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiBOB, LiDFOB, LiTFOP, one or more of the group consisting of, x and y represent positive integers, optionally, x and y are each independently 0, 1, 2 or 3, non-aqueous electrolyte
  • the concentration range of the electrolyte salt mentioned in is 0.5M ⁇ 2M, and the optional range is 0.8M ⁇ 1.5M, which can ensure the smooth and rapid migration of Li + in the positive and negative electrodes.
  • 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 cathode activity.
  • the dynamic performance and safety performance of the secondary battery 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 ratio of W1/(C1+C2+C3) is defined as Q, and Q is 0.05 to 1 (such as 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 ), optionally 0.1 to 1.
  • Q is 0.05 to 1 (such as 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 ), optionally 0.1 to 1.
  • 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 effectively reduced, thereby further improving the high temperature of the secondary battery. 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 within the above range can effectively avoid the following situation: if the content of phosphorus element is too large, the covalency of P-O may be too strong and affect the conductivity of small polarons, thereby affecting the conductivity of small polarons. Affects the electrical conductivity of the material; if the phosphorus content is too small, it may reduce the stability of the pyrophosphate in the core, the first cladding layer and/or the phosphate lattice structure in the second cladding layer, thus affecting the material overall 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, thereby affecting the performance of 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 between Li+ and Mn2+ in the LiMnPO4 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/T24533-2009.
  • 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.
  • 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. In addition, the sources of raw materials are wide, the cost is low, and the process is simple, which is conducive to industrialization.
  • 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.
  • the positive electrode film layer may also include other positive electrode active materials known in the art for secondary batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for secondary batteries can also be used.
  • lithium transition metal oxides may include, but are not limited to, lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide , at least one of lithium nickel manganese oxide and its modified compounds.
  • lithium-containing phosphates with an olivine structure 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 ), phosphoric acid At least one of a composite material of lithium manganese and carbon, a composite material of lithium manganese iron phosphate, or a composite material of lithium manganese iron 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
  • phosphoric acid At least one of a composite material of lithium manganese and carbon, a composite material of lithium manganese iron phosphate, or a composite material of lithium manganese iron 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 additive is selected from the following compounds:
  • 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 After uniformity, 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 with the second coating layer
  • step S4 Add 1586.8g of the pyrophosphate-coated material obtained in step S4 to the second coating layer suspension (coating material content is 47.1g) obtained in step S5, stir and mix thoroughly for 6 hours, and mix After uniformity, it is 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 dry at 700°C After sintering for 10 hours, the three-layer coated material was 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 2.0g/cm 3 .
  • a lithium sheet is used as the negative electrode, and compound 1 (the first additive, the mass content in the electrolyte is 2%), lithium difluorophosphate (the second additive, the mass content in the electrolyte is 1%), LiPF 6 ( As the electrolyte salt, the mass content in the electrolyte is 1%) in a solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1:
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • the positive active materials and batteries in Examples 2 to 29 and Comparative Examples 1 to 3 were prepared in a manner similar to Example 1.
  • the differences in the preparation of the positive active materials are shown in Tables 1 to 6, where Comparative Examples 2 and 3
  • the first layer is not coated, so there are no steps S3 and S4; Comparative Example 1 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, and 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 (1540.25mm 2 ) 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 5 g of the positive active material prepared above in 100 mL 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 as follows Discharge from 0.1C 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 F 1 of the battery cell using a balance that automatically converts units based on the dial data, then completely places the battery core in deionized water (density is known to be 1g/cm 3 ), and measures the battery core at this time.
  • 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.

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Abstract

本申请提供了二次电池、电池模块、电池包和用电装置。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，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添加剂，第一添加剂包括式1所示化合物、式2所示化合物组成的组中的一种或多种。利用正极活性材料、或者正极活性材料和非水电解液的组合提高了磷酸锰锂二次电池的倍率性能、循环性能和高温稳定性。

Description

二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及锂电池技术领域，尤其涉及一种二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着锂离子电池的应用范围越来越广泛，锂离子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，以及电动工具、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。由于锂离子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。
与其他正极活性材料相比，磷酸锰锂正极活性材料具有较高的安全性和循环寿命，但是磷酸锰锂的缺点在于倍率性能较差，目前通常是通过包覆或掺杂等手段来解决这一问题。但仍然希望能够进一步提升磷酸锰锂正极活性材料的倍率性能、循环性能、高温稳定性等。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种二次电池、电池模块、电池包和用电装置，以解决磷酸锰锂二次电池的循环性能差的问题。
为了达到上述目的，本申请的第一方面提供了一种二次电池，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组成的组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组成的组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Li aMP 2O 7和/或M b(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Li aMP 2O 7或M b(P 2O 7) c保持电中性，晶态焦磷酸盐Li aMP 2O 7和M b(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和Al组成的组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和Al组成的组中的一种或多种元素，第三包覆层为碳；
非水电解液包括第一添加剂，所述第一添加剂包括式1所示化合物、式2所示化合物组成的组中的一种或多种，
Figure PCTCN2022084835-appb-000001
R 1、R 2各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基中的任意一种；
R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基、C2～C6的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
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所述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，非水电解液中引入第一添加剂，在锂离子电池充电过程中在包覆层表面形成一层聚合物，防止包覆层溶解，减小锰离子溶出，同时降低包覆碳的催化活性，减小活性锂消耗，进一步改善了二次电池的高温循环和存储性能。
上述式1的化合物在现有技术中常见的式1化合物中进行选择，在一些实施方式中，R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基中的任意一种，可选地，R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C2的卤代烷基、C2～C3的烯基中的任意一种。
上述式2的的化合物在现有技术中常见的式2化合物中进行选择，在一些实施方式中，R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基、C2～C4的炔氧基中的任意一种，可选地，R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C3的烷基、C1～C2的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
进一步地，在一些实施方式中，第一添加剂包括如下化合物中的至少一种：
Figure PCTCN2022084835-appb-000002
Figure PCTCN2022084835-appb-000003
过多的第一添加剂会使正极阻抗增大，使二次电池容量异常、倍率性能变差。此外，过多的第一添加剂在锂离子充电过程中会氧化产气，恶化二次电池的高温循环和存储性能。在一些实施方式中，基于非水电解液的总重量，第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5。当第一添加剂在电解液中的质量占比处于上述范围时，既能防止焦磷酸盐和磷酸盐的包覆层的溶解，降低包覆碳的催化活性，又能避免对正极阻抗的增加，进而进一步改善二次电池的高温循环和存储性能，又不影响锂离子电池容量和倍率性能。
在一些实施方式中，第一添加剂如下化合物中的任意一种；
Figure PCTCN2022084835-appb-000004
上述各第一添加剂在充电过程中形成的聚合物更为稳定，因此，更高效地改善了本申请的正极活性材料的中Mn的溶出。
由于第一添加剂会在正极形成一层聚合物，防止包覆层溶解，减小锰离子溶出，同时降低包覆碳的催化活性，减小活性锂消耗，但同时会使正极阻抗增大，恶化二次电池容量和倍率性能。为了解决第一添加剂带来的负面影响，在一些实施方式中，上述非水电解液还包括第二添加剂，第二添加剂包括硫酸乙烯酯、二氟磷酸锂、二氟二草酸磷酸锂、二氟草酸硼酸锂组成的组中的一种或多种。上述各第二添加剂均会在正极成膜，形成低阻抗CEI膜，进一步改善二次电池容量和倍率性能。
在一些实施方式中，基于非水电解液的总重量，第二添加剂的含量为W2重量％，W2为0.01至20，可选地为0.2至8或0.3至5；以形成厚度合适的低阻抗CEI膜。
在一些实施方式中，基于非水电解液的总重量，第一添加剂的含量为W1重量％，W1为0.01至20(比如为0.01、0.05、0.1、0.2、0.3、0.4、0.5、1、2、3、4、5、8、10、12、15、18或20)，可选地为0.2至8或0.5至5，可选地W2/W1的质量比为A，A为0.1至10(比如为0.1、0.2、0.3、0.4、0.5、1、、2、3、4、5、6、7、8、9或10)，可选地0.2至5。当第一添加剂和第二添加剂的用量满足上述条件时，可以利用第二添加剂有效缓解第一添加剂造成的正极阻抗增大的问题，进一步优化第一添加剂对电池容量和倍率性能的改善效果。
在一些实施方式中，上述非水电解液还包括第三添加剂，第三添加剂包括链状硫酸酯化合物、亚硫酸酯化合物、含有不饱和键的磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、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。上述第三添加 剂可以根据自身性能改善二次电池的容量、循环性能等，本领域技术人员可以根据实际需求来选择相应的第三添加剂。
在一些实施方式中，上述非水电解液还包括有机溶剂，有机溶剂的种类没有特别的限制，可根据实际需求进行选择，可选地，所述有机溶剂包括碳酸二甲酯、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、丙酸丁酯、四氢呋喃组成的组中的一种或多种。
在一些实施方式中，上述非水电解液还包括电解质盐。可选地，电解质盐包括LiN(C xF 2x+1SO 2)(C yF 2y+1SO 2)、Li(FSO 2) 2N、LiCF 3SO 3、LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiBOB、LiDFOB、LiTFOP组成的组中的一种或几种，x、y表示正整数，可选地，x、y各自独立地为0、1、2或3，非水电解液中电解质盐的浓度范围为0.5M～2M，可选为0.8M～1.5M，可以保证Li +平稳快速的在正负极迁移。
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。
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。
在一些实施方式中，定义W1/(C1+C2+C3)的比值为Q，Q为0.05至1(比如为0.05、0.06、0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9或1)，可选为0.1至1。通过控制Q值在上述范围内，避免当Q值小于上述范围时，第一添加剂在包覆层上形成的聚合物较少，不能有效抑制锰离子溶出和减小包覆碳催化氧化电解液分解，进而改善高温循环和存储性能的效果不显著；当Q值大于上述范围时，过多的添加剂作用于包覆层上，使得正极阻抗太大，导致电池的克容量和倍率性能改善受限。
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°。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。
在任意实施方式中，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，提升了二次电池的综合性能。
在任意实施方式中，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，因此能够有效减轻界面副反应，从而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改善二次电池的克容量和倍率性能。
在任意实施方式中，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，尤其是高温稳定性也有明显改善，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高温运行稳定性。
附图说明
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。
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
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)。
需要说明的是，在本文中，术语“包覆层”是指包覆在磷酸锰锂内核上的物质层，所述物质层可以完全或部分地包覆磷酸锰锂内核，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”是指包覆在磷酸锰锂内核上的所述物质层在磷酸锰锂内核径向上的厚度。
本申请发明人在实际作业中发现，目前现有的磷酸锰锂正极活性材料在深度充放电过程中，锰离子溶出比较严重。虽然现有技术中有尝试对磷酸锰锂进行磷酸铁锂包覆，从而减少界面副反应，但这种包覆无法阻止溶出的锰继续向电解液中迁移。溶出的锰在迁移到负极后，被还原成金属锰。这样产生的金属锰相当于“催化剂”，能够催化负极表面的SEI膜(solid electrolyte interphase，固态电解质界面膜)分解，产生副产物；所述副产物的一部分为气体，因此导致会二次电池发生膨胀，影响二次电池的安全性能；另外，所述副产物的另一部分沉积在负极表面，会阻碍锂离子进出负极的通道，造成二次电池阻抗增加，从而影响二次电池的动力学性能。此外，为补充损失的SEI膜，电解液和电池内部的活性锂被不断消耗，会给二次电池容量保持率带来不可逆的影响。
发明人在进行大量研究后发现，通过对磷酸锰锂进行改性以及对磷酸锰锂的多层包覆，能够得到一种新型的具有核-壳结构的正极活性材料，所述正极活性材料能够实现显著降低的锰离子溶出以及降低的晶格变化率，其用于二次电池中，能够改善电池的循环性能、倍率性能、安全性能并且提高电池的容量。
[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。
本申请的一个实施方式提供一种二次电池，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组成的组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组成的组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Li aMP 2O 7和/或M b(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Li aMP 2O 7或M b(P 2O 7) c保持电中性，晶态焦磷酸盐Li aMP 2O 7和M b(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和Al组成的组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和Al组成的组中的一种或多种元素，第三包覆层为碳；
非水电解液包括第一添加剂，所述第一添加剂包括式1所示化合物、式2所示化合物组成的组中的一种或多种，
Figure PCTCN2022084835-appb-000005
R 1、R 2各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基中的任意一种；
R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基、C2～C6的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
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。
除非另有说明，否则上述内核的化学式中，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。
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。
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。
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，不仅可有效减少锰离子溶出，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，进而提高了二次电池的动力学性能。
同时，非水电解液中引入第一添加剂，在锂离子电池充电过程中在包覆层表面形成一层聚合物，防止包覆层溶解，减小锰离子溶出，同时降低包覆碳的催化活性，减小活性锂消耗，进一步改善了二次电池的高温循环和存储性能。
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。
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，在所述内核中掺杂了A和R元素后，与不掺杂元素相比，所述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。
上述式1的化合物在现有技术中常见的式1化合物中进行选择，在一些实施方式中，R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基中的任意一种，可选地，R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C2的卤代烷基、C2～C3的烯基中的任意一种。
上述式2的化合物在现有技术中常见的式2化合物中进行选择，在一些实施方式中，R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的 卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基、C2～C4的炔氧基中的任意一种，可选地，R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C3的烷基、C1～C2的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
进一步地，在一些实施方式中，第一添加剂包括如下化合物中的至少一种：
Figure PCTCN2022084835-appb-000006
在一些实施方式中，基于非水电解液的总重量，第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5。当第一添加剂在电解液中的质量占比处于上述范围时，既能防止焦磷酸盐和磷酸盐的包覆层的溶解，降低包覆碳的催化活性，又能避免对正极阻抗的增加，进而进一步改善二次电池的高温循环和存储性能，又不影响锂离子电池容量和倍率性能。
在一些实施方式中，第一添加剂如下化合物中的任意一种；
Figure PCTCN2022084835-appb-000007
上述各第一添加剂在充电过程中形成的聚合物更为稳定，因此，更高效地改善了本申请的正极活性材料的中Mn的溶出。
在一些实施方式中，上述非水电解液还包括第二添加剂，第二添加剂包括硫酸乙烯酯、二氟磷酸锂、二氟二草酸磷酸锂、二氟草酸硼酸锂组成的组中的一种或多种。上述各第二添加剂均会在正极成膜，形成低阻抗CEI膜(catheode electrolyte interface膜)，进一步改善二次电池容量和倍率性能。
在一些实施方式中，基于非水电解液的总重量，第二添加剂的含量为W2重量％，W2为0.01至20，可选地为0.2至8或0.3至5；以形成厚度合适的低阻抗CEI膜。
在一些实施方式中，基于非水电解液的总重量，第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5，可选地W2/W1的质量比为A，A为0.1至10，可选地0.2至5。当第一添加剂和第二添加剂的用量满足上述条件时，可以利用第二添加剂有效缓解第一添加剂造成的正极阻抗增大的问题，进一步优化第一添加剂对电池容量和倍率性能的改善效果。
在一些实施方式中，上述非水电解液还包括第三添加剂，第三添加剂包括链状硫酸酯化合物、亚硫酸酯化合物、含有不饱和键的磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、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。上述第三添加剂可以根据自身性能改善二次电池的容量、循环性能等，本领域技术人员可以根据实际需求来选择相应的第三添加剂。
在一些实施方式中，上述非水电解液还包括有机溶剂，有机溶剂的种类没有特别的限制，可根据实际需求进行选择，可选地，所述有机溶剂包括碳酸二甲酯、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、丙酸丁酯、四氢呋喃组成的组中的一种或多种。
在一些实施方式中，上述非水电解液还包括电解质盐。可选地，电解质盐包括LiN(C xF 2x+1SO 2)(C yF 2y+1SO 2)、Li(FSO 2) 2N、LiCF 3SO 3、LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiBOB、LiDFOB、LiTFOP组成的组中的一种或几种，x、y表示正整数，可选地，x、y各自独立地为0、1、2或3，非水电解液中所述电解质盐的浓度范围为0.5M～2M，可选为0.8M～1.5M，可以保证Li +平稳快速的在正负极迁移。
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，由此能够对所述内核进行充分包覆，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。
在一些实施方式中，定义W1/(C1+C2+C3)的比值为Q，Q为0.05至1(比如为0.05、0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9或1)，可选为0.1至1。通过控制Q值在上述范围内，避免当Q值小于上述范围时，不能保证足够的第一添加剂作用于包覆层上，抑制锰离子溶出和减小包覆碳催化氧化电解液分解效果不显著，进而不能显著改善高温循环和存储性能；当Q值大于上述范围时，过多的添加剂作用于包覆层上，使得正极阻抗太大，锂离子电池的克容量和倍率性能提升受到影响。
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，因此能够有效减轻界面副反应，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。
本上述实施方式中，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LiMnPO4晶格中，Li+与Mn2+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/T24533-2009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。在一些实施方式中，正极膜层还可包含本领域公知的用于二次电池的其它正极活性材料。作为示例，正极活性材料可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二次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和图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，第一添加剂选自如下化合物：
化合物1：
Figure PCTCN2022084835-appb-000008
化合物2:
Figure PCTCN2022084835-appb-000009
化合物3：
Figure PCTCN2022084835-appb-000010
化合物4：
Figure PCTCN2022084835-appb-000011
化合物5：
Figure PCTCN2022084835-appb-000012
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6小时。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6小时，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10小时，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4小时，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2小时得到溶液，之后将该溶液升温到80℃并保持此温度4小时，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6小时，混合均匀后，转入120℃烘箱中干燥6小时，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6小时得到溶液，之后将该溶液升温到120℃并保持此温度6小时，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6小时，混合均匀后，转入120℃烘箱中干燥6小时，然后700℃烧结8小时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6小时，混合均匀后，转入150℃烘箱中干燥6小时，然后在700℃下烧结10小时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)，作为有机溶剂，将碳酸亚乙酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，向其中加入化合物1(作为第一添加剂，在电解液中的质量含量为2％)、二氟磷酸锂(作为第二添加剂，在电解液中的质量含量为1％)、LiPF 6(作为电解质盐，在电解液中的质量含量为1％)，搅拌均匀，得到电解液。
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，采用化合物1(第一添加剂，在电解液中的质量含量为2％)、二氟磷酸锂(第二添加剂，在电解液中的质量含量为1％)、LiPF 6(作为电解质盐，在电解液中的质量含量为1％)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，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29和对比例1至3
以类似于实施例1的方式制备实施例2至29和对比例1至3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2和3未包覆第一层，因此没有步骤S3、S4；对比例1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 PCTCN2022084835-appb-000013
Figure PCTCN2022084835-appb-000014
Figure PCTCN2022084835-appb-000015
Figure PCTCN2022084835-appb-000016
Figure PCTCN2022084835-appb-000017
Figure PCTCN2022084835-appb-000018
Figure PCTCN2022084835-appb-000019
Figure PCTCN2022084835-appb-000020
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°/分钟对样品进行测试，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5分钟，按照1/3C放电至2.5V。静置5分钟，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5分钟，记录此时的充电容量为C0。按照1/3C放电至2.5V，静置5分钟，再按照3C充电至4.3V，静置5分钟，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(1540.25mm 2)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5分钟，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F 1，然后将电芯完全置于去离子水(密度已知为1g/cm 3)中，测量此时的电芯的重力F 2，电芯受到的浮力F 浮即为F 1-F 2，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＝(F 1-F 2)/(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5分钟，然后按照1C放电至2.5V，容量记为D n(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 PCTCN2022084835-appb-000021
Figure PCTCN2022084835-appb-000022
Figure PCTCN2022084835-appb-000023
Figure PCTCN2022084835-appb-000024
Figure PCTCN2022084835-appb-000025
Figure PCTCN2022084835-appb-000026
Figure PCTCN2022084835-appb-000027
Figure PCTCN2022084835-appb-000028
Figure PCTCN2022084835-appb-000029
Figure PCTCN2022084835-appb-000030

Claims (24)

  1. 一种二次电池，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组成的组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组成的组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Li aMP 2O 7和/或M b(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Li aMP 2O 7或M b(P 2O 7) c保持电中性，所述晶态焦磷酸盐Li aMP 2O 7和M b(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和Al组成的组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和Al组成的组中的一种或多种元素，
    所述第三包覆层为碳；
    所述非水电解液包括第一添加剂，所述第一添加剂包括式1所示化合物、式2所示化合物组成的组中的一种或多种，
    Figure PCTCN2022084835-appb-100001
    R 1、R 2各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基中的任意一种；
    R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C6的烷基、C1～C6的卤代烷基、C1～C6的烷氧基、C2～C6的烯基、C2～C6的炔基、C2～C6的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
  2. 根据权利要求1所述的二次电池，其中，
    R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基中的任意一种，可选R 1、R 2各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C2的卤代烷基、C2～C3的烯基中的任意一种；和/或，
    R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C4的烷基、C1～C4的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔基、C2～C4的炔氧基中的任意一种，可选R 3、R 4、R 5、R 6各自独立地表示氢原子、卤原子、C1～C3的烷基、C1～C2的卤代烷基、C1～C4的烷氧基、C2～C4的烯基、C2～C4的炔氧基中的任意一种，并且R 3、R 4、R 5、R 6不同时表示氢原子。
  3. 根据权利要求1或2所述的二次电池，其中，所述第一添加剂包括如下化合物中的至少一种：
    Figure PCTCN2022084835-appb-100002
    Figure PCTCN2022084835-appb-100003
  4. 根据权利要求1-3中任一项所述的二次电池，其中，基于所述非水电解液的总重量，所述第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5。
  5. 根据权利要求1-4中任一项所述的二次电池，其中，所述第一添加剂如下化合物中的任意一种；
    Figure PCTCN2022084835-appb-100004
  6. 根据权利要求1-5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硫酸乙烯酯、二氟磷酸锂、二氟二草酸磷酸锂、二氟草酸硼酸锂组成的组中的一种或多种。
  7. 根据权利要求6所述的二次电池，其中，基于所述非水电解液的总重量，所述第二添加剂的含量为W2重量％，W2为0.01至20，可选地为0.2至8或0.3至5；
  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重量，所述第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5，W2/W1的质量比为A，A为0.1至10，可选地0.2至5。
  9. 根据权利要求1-8中任一项所述的二次电池，其中，所述非水电解液还包括第三添加剂，所述第三添加剂包括链状硫酸酯化合物、亚硫酸酯化合物、含有不饱和键的磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、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。
  10. 根据权利要求1-9中任一项所述的二次电池，其中，所述非水电解液还包括有机溶剂和电解质盐，
    可选地，所述有机溶剂包括碳酸二甲酯、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、丙酸丁酯、四氢呋喃组成的组中的一种或多种；和/或，
    可选地，所述电解质盐包括LiN(C xF 2x+1SO 2)(C yF 2y+1SO 2)、Li(FSO 2) 2N、LiCF 3SO 3、LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiBOB、LiDFOB、LiTFOP组成的 组中的一种或几种，x、y表示正整数，可选地，x、y各自独立地为0、1、2或3，所述非水电解液中所述电解质盐的浓度范围为0.5M～2M，可选为0.8M～1.5M。
  11. 根据权利要求1-10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。
  12. 根据权利要求11所述的二次电池，其中，
    基于所述非水电解液的总重量，所述第一添加剂的含量为W1重量％，W1为0.01至20，可选地为0.2至8或0.5至5，定义W1/(C1+C2+C3)的比值为Q，Q为0.05至1，可选为0.1至1。
  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°。
  14. 根据权利要求1-13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。
  15. 根据权利要求1-14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。
  16. 根据权利要求1-15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。
  17. 根据权利要求1-16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。
  18. 根据权利要求1-17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％。
  19. 根据权利要求1-18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％。
  20. 根据权利要求1-19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。
  21. 根据权利要求1-20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。
  22. 一种电池模块，包括权利要求1-21中任一项所述的二次电池。
  23. 一种电池包，包括权利要求22所述的电池模块。
  24. 一种用电装置，包括选自权利要求1-21中任一项所述的二次电池、权利要求22所述的电池模块或权利要求23所述的电池包中的至少一种。
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