WO2023240617A1 - 具有核-壳结构的正极活性材料及制备方法、正极极片、二次电池、电池模块、电池包和用电装置 - Google Patents

具有核-壳结构的正极活性材料及制备方法、正极极片、二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023240617A1
WO2023240617A1 PCT/CN2022/099523 CN2022099523W WO2023240617A1 WO 2023240617 A1 WO2023240617 A1 WO 2023240617A1 CN 2022099523 W CN2022099523 W CN 2022099523W WO 2023240617 A1 WO2023240617 A1 WO 2023240617A1
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optionally
active material
elements
range
core
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PCT/CN2022/099523
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English (en)
French (fr)
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蒋耀
欧阳楚英
张欣欣
邓斌
徐波
王志强
袁天赐
陈尚栋
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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 JP2024501212A priority Critical patent/JP2024529322A/ja
Priority to CN202280082208.5A priority patent/CN118382943A/zh
Priority to PCT/CN2022/099523 priority patent/WO2023240617A1/zh
Priority to KR1020247016141A priority patent/KR20240093614A/ko
Priority to EP22932480.1A priority patent/EP4322254A1/en
Priority to CN202280013384.3A priority patent/CN116964781A/zh
Priority to PCT/CN2022/126838 priority patent/WO2023066394A1/zh
Priority to KR1020247007998A priority patent/KR20240046889A/ko
Priority to JP2024515538A priority patent/JP2024534988A/ja
Priority to EP22882998.2A priority patent/EP4418363A1/en
Publication of WO2023240617A1 publication Critical patent/WO2023240617A1/zh
Priority to US18/635,016 priority patent/US20240254003A1/en
Priority to US18/641,410 priority patent/US20240282969A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G45/00—Compounds of manganese
    • C01G45/12—Manganates manganites or permanganates
    • C01G45/1221—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof
    • C01G45/1228—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof of the type [MnO2]n-, e.g. LiMnO2, Li[MxMn1-x]O2
    • H—ELECTRICITY
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C01B25/377—Phosphates of heavy metals of manganese
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 secondary batteries, and in particular to a cathode active material with a core-shell structure, a preparation method of the cathode active material, a cathode plate, a secondary battery, a battery module, a battery pack and an electrical device.
  • secondary 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 secondary batteries, higher requirements have been put forward for their energy density, cycle performance and safety performance. As the existing cathode active material of secondary batteries, lithium manganese phosphate is prone to produce Li/Mn anti-site defects during the charge and discharge process, and the manganese dissolution is serious, which affects the gram capacity of the secondary battery and leads to the safety performance of the secondary battery. and cycle performance deteriorates.
  • This application was made in view of the above problems, and its purpose is to provide a positive electrode active material with a core-shell structure, a preparation method of the positive electrode active material, a positive electrode plate, a secondary battery, a battery module, a battery pack and an electricity consumption
  • the device is used to solve the problems that existing lithium manganese phosphate cathode active materials are prone to Li/Mn anti-site defects and serious manganese dissolution during the charge and discharge process, thereby solving the problem of low capacity, poor safety performance and poor cycle performance of secondary batteries. question.
  • the first aspect of the present application provides a cathode active material with a core-shell structure, which includes a core and a shell covering the core,
  • the kernel contains Li m A _ _ Any value of Any value within the range, optionally any value selected from the range 0.001-0.1, n is selected from any value within the range 0.001-0.5, optionally any value selected from the range 0.001-0.1, A is selected B One or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally selected from Ti, V, Fe, Ni, Mg and one or more elements from Co, C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N , D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br;
  • the shell includes a first cladding layer covering the core and a second cladding layer covering the first cladding layer;
  • the first coating layer includes crystalline pyrophosphate M a P 2 O 7 and oxide M′ b O c , where a is greater than 0 and less than or equal to 4, optionally greater than 0 and less than or equal to 3, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al or A plurality of elements, optionally one or more elements selected from Li and Fe, M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide elements and One or more elements in Sb, optionally selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo,
  • the second cladding layer contains carbon.
  • the inventor of the present application found in actual operations that Li/Mn anti-site defects are easily generated in the lithium manganese phosphate cathode active material during deep charge and discharge processes, and manganese dissolution is relatively serious.
  • the eluted manganese is reduced to metallic manganese after migrating to the negative electrode.
  • the metal manganese produced 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.
  • Part of the by-products produced are gases, which can easily cause the battery to expand and affect the safety of the secondary battery.
  • Performance and the other part is deposited on the surface of the negative electrode, blocking the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase and affecting the dynamic performance and cycle performance of the battery.
  • the electrolyte and active lithium inside the battery are continuously consumed, which has an irreversible impact on the capacity retention rate of the secondary battery.
  • the applicant unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li site, Mn site, P site and O site of the compound LiMnPO 4 , the surface of the compound is coated with crystalline pyrophosphate and oxide.
  • the first coating layer and the second coating layer containing carbon are coated on the surface of the first coating layer to obtain the cathode active material, which can greatly reduce the generation of Li/Mn anti-site defects, reduce manganese dissolution and reduce lattice changes efficiency, increase the capacity of secondary batteries, and improve the cycle performance, high-temperature storage performance and safety performance of secondary batteries.
  • the above limitation on the numerical range of The limitation of the stoichiometric number of each element as A is also the limitation of the sum of the stoichiometric numbers of each element as A.
  • the respective stoichiometric numbers x1, x2...xn of A1, A2...An must fall within the numerical range of x defined in this application, and x1
  • the sum of , x2...xn also needs to fall within this numerical range.
  • the limitation on the numerical range of the stoichiometric numbers of B, C, and D in this application also has the above meaning.
  • the above-mentioned limitation on the numerical range of a is not only a limitation on the stoichiometric number of each element as M, but also on each As a definition of the sum of the stoichiometric numbers of the elements of M.
  • M is two or more elements M1, M2...Mn
  • the stoichiometric numbers a1, a2...an of M1, M2...Mn must each fall within the numerical range of a defined in this application, and a1 The sum of , a2...an also needs to fall within this numerical range.
  • M' in the chemical formula M' b O c is two or more elements
  • the limitation on the numerical range of the stoichiometric number b of M' in this application also has the above meaning.
  • the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326nm, and the angle between the crystallographic directions (111) is 26.41°-32.57°;
  • the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310nm; and/or,
  • the angle between the crystallographic directions (111) of the pyrophosphate in the first coating layer is 29.00°-30.00°.
  • the angle between the interplanar spacing and the crystal direction (111) of the pyrophosphate in the first coating layer is within the above range, the impurity phase in the coating layer can be effectively avoided, thereby increasing the gram capacity of the material and improving the secondary battery. cycle performance and rate performance.
  • x is any value in the range of 0.001-0.005; and/or,
  • y is any value in the range 0.01-0.5, optionally any value in the range 0.25-0.5; and/or,
  • z is any value within the range of 0.001-0.005; and/or,
  • n is any value within the range of 0.001-0.005.
  • x, y, z, n within the above range can further reduce the generation of Li/Mn anti-site defects, reduce manganese dissolution and reduce the lattice change rate, thereby further increasing the capacity of the secondary battery and improving the secondary battery. cycle performance, high temperature storage performance and safety performance.
  • the ratio of 1-y to y is 1 to 4, optionally 1.5 to 3.
  • y represents the sum of stoichiometric numbers of Mn-site doping elements.
  • the ratio of m to x is 1 to 1200, optionally 9 to 1100, and more optionally 190-998.
  • x represents the sum of stoichiometric numbers of Li-site doping elements.
  • the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core.
  • the coating amount of the first coating layer is within the above range, the dissolution of manganese can be further suppressed, while further promoting the transmission of lithium ions, maintaining low impedance of the secondary battery, and improving the dynamic performance of the secondary battery.
  • the weight ratio of pyrophosphate and oxide in the first coating layer is from 1:3 to 3:1, optionally from 1:3 to 1:1.
  • the appropriate ratio of pyrophosphate and oxide is conducive to giving full play to the synergistic effect of the two, which can further inhibit the dissolution of manganese while maintaining a low impedance of the secondary battery.
  • the crystallinity of the pyrophosphate in the first coating layer is from 10% to 100%, optionally from 50% to 100%.
  • the pyrophosphate with a certain degree of crystallinity is beneficial to maintaining the structural stability of the first coating layer and reducing lattice defects.
  • this is conducive to giving full play to the role of pyrophosphate in hindering manganese dissolution.
  • it is also conducive to reducing the surface miscellaneous lithium content and reducing the valence state of surface oxygen, thereby reducing the interface side reactions between the cathode material and the electrolyte and reducing the impact on electrolysis. fluid consumption and improve the cycle performance and safety performance of secondary batteries.
  • the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.
  • the carbon-containing layer as the second coating layer can function as a "barrier” to avoid direct contact between the positive active material and the electrolyte, thereby reducing the corrosion of the active material by the electrolyte and improving the safety performance of the battery at high temperatures.
  • it has strong electrical conductivity, which can reduce the internal resistance of the battery, thereby improving the dynamic performance of the secondary battery.
  • the coating amount of the second coating layer is within the above range, the kinetic performance and safety performance of the secondary battery can be further improved while maintaining a higher gram capacity of the positive active material.
  • A in the cathode active material, is any element selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W.
  • A is Mg or Nb. ;and / or,
  • B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.
  • B is selected from Fe, Ti, V, Co and At least two elements in Mg, more optionally, B is a combination of Fe element and at least one element selected from Ti, V, Co and Mg; and/or,
  • C is any element selected from B, S, Si and N, optionally, C is S; and/or,
  • D is any element selected from S, F, Cl and Br. Alternatively, D is F.
  • doping elements it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to Further reduce surface oxygen activity and reduce interface side reactions between the positive active material and the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.
  • the Li/Mn anti-site defect concentration of the cathode active material is 4% or less, optionally 2% or less.
  • the Li/Mn anti-site defect refers to the interchange of positions of Li + and Mn 2+ in the LiMnPO 4 crystal lattice. Since the Li + transport channel is a one-dimensional channel, Mn 2+ is difficult to migrate in the Li + transport channel. Therefore, the anti-site defective Mn 2+ will hinder the transport of Li + .
  • the Li/Mn antisite defect concentration By controlling the Li/Mn antisite defect concentration at a low level, the gram capacity of the cathode active material and the rate performance of the secondary battery can be improved.
  • the lattice change rate of the cathode active material before and after complete deintercalation of lithium is 9.8% or less, optionally 6% or less, and more preferably 4% or less.
  • the lithium deintercalation process of LiMnPO 4 is a two-phase reaction.
  • the interface stress of the two phases is determined by the lattice change rate. The smaller the lattice change rate, the smaller the interface stress and the easier Li + transport. Therefore, reducing the lattice change rate of the core will be beneficial to enhancing the Li + transport capability, thereby improving the rate performance of secondary batteries.
  • the surface oxygen valence state of the cathode active material is -1.55 or less, optionally -1.88 or less, and more preferably -1.98 to -1.88. This is because the higher the valence state of oxygen in the compound, the stronger its ability to obtain electrons, that is, the stronger its oxidizing property.
  • the cathode active material of the present application by controlling the surface valence state of oxygen at a lower level, the reactivity on the surface of the cathode material can be reduced, and the interface side reaction between the cathode active material and the electrolyte can be reduced, thereby improving the performance of the secondary battery. Cycling performance and high temperature storage performance.
  • the compacted density of the positive active material at 3 tons (T) is 1.89g/cm or more, optionally 2.0g/cm or more, more optionally 2.2g/cm cm 3 and above.
  • a second aspect of this application provides a method for preparing a cathode active material, including the following steps:
  • the core contains Li m A x Mn 1-y B y P 1-z C z O 4-n D n , where m is selected from any value in the range of 0.5-1.2, optionally from any value in the range 0.9-1.1, x is selected from any value in the range 0.001-0.5, optionally any value in the range 0.001-0.1, y is selected from any value in the range 0.001-0.5, z n is selected from any value within the range of 0.001-0.2, optionally from any value within the range of 0.001-0.1, n is selected from any value within the range of 0.001-0.5, optionally from the range of 0.001-0.1 Any value, A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W or multiple elements, B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb
  • Coating step Provide a powder containing pyrophosphate M a P 2 O 7 and a suspension containing a carbon source and an oxide M′ b O c , and combine the core material and the powder containing pyrophosphate M a P 2 O 7 Mix with a suspension containing carbon source and oxide M' b O c , and sinter to obtain a positive active material, in which a is greater than 0 and less than or equal to 4, optionally greater than 0 and less than or equal to 3, and b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al , optionally one or more elements selected from Li and Fe, M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide elements and Sb One or more elements, optionally selected from Li
  • the positive active material has a core-shell structure, which includes a core and a shell covering the core.
  • the core includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n
  • the shell includes a coating a first cladding layer of the core and a second cladding layer covering the first cladding layer, the first cladding layer comprising crystalline pyrophosphate M a P 2 O 7 and oxide M′ b O c , and the second cladding layer covering the first cladding layer.
  • the cladding contains carbon.
  • the applicant unexpectedly discovered that by doping specific elements in specific amounts at the same time at the Li site, Mn site, P site and O site of the compound LiMnPO 4 , the surface of the compound is coated with crystalline pyrophosphate and oxide.
  • the first coating layer and the second coating layer containing carbon are coated on the surface of the first coating layer to obtain the cathode active material, which can greatly reduce the generation of Li/Mn anti-site defects, reduce manganese dissolution and reduce lattice changes efficiency, increase the capacity of secondary batteries, and improve the cycle performance, high-temperature storage performance and safety performance of secondary batteries.
  • the step of providing the core material includes the following steps:
  • Step (1) Mix a manganese source, a source of element B, an acid and an optional solvent to obtain a mixture;
  • Step (2) Mix the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C, a source of element D and an optional solvent, dry and sinter to obtain Li m A x Mn 1-y B Core material of y P 1-z C z O 4-n D n .
  • step (1) is mixed at 60°C-120°C; and/or, in step (1), mixing is carried out by stirring at 200-800 rpm.
  • step (2) mixing is performed for 8-15 hours.
  • step (2) sintering is performed at 600°C-900°C for 6-14 hours.
  • the source of element A is one or more selected from the group consisting of elemental elements, oxides, phosphates, oxalates, carbonates and sulfates of element A; and/or ,
  • the source of element B is one or more selected from elemental elements, oxides, phosphates, oxalates, carbonates and sulfates of element B; and/or,
  • the source of element C is one or more selected from sulfate, borate, nitrate and silicate of element C; and/or,
  • the source of element D is one or more selected from the group consisting of elemental elements and ammonium salts of element D.
  • the powder comprising pyrophosphate M a P 2 O 7 is prepared by the following steps:
  • drying is performed at 100°C-300°C for 4-8h, optionally at 150°C-200°C Drying at °C; and/or sintering at 500°C-800°C and under inert gas protection for 4-10h, optionally sintering at 650°C-800°C.
  • the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10 hours.
  • a third aspect of the present application provides a positive electrode sheet, which 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 the positive electrode active material of the first aspect of the application or the second aspect of the application.
  • the cathode active material prepared by the preparation method of the aspect, and the content of the cathode active material in the cathode film layer is more than 10% by weight, based on the total weight of the cathode film layer.
  • the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer.
  • a fourth aspect of the present application provides a secondary battery, including the positive active material of the first aspect of the present application or the positive active material prepared by the preparation method of the second aspect of the present application, or the positive electrode sheet of the third aspect of the present application.
  • a fifth aspect of the present application provides a battery module, including the secondary battery of the fourth aspect of the present application.
  • a sixth aspect of the present application provides a battery pack, including the battery module of the fifth aspect of the present application.
  • a seventh aspect of the present application provides an electrical device, including at least one selected from the group consisting of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, and the battery pack of the sixth aspect of the present application. kind.
  • FIG. 1 is a schematic diagram of a cathode active material with a core-shell structure according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 2 .
  • Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .
  • FIG. 7 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
  • a 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) can be added to the method in any order.
  • the method may include steps (a), (b) and (c), and may also include step (a). , (c) and (b), and 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 median particle diameter D v 50 refers to the particle diameter corresponding to when the cumulative volume distribution percentage of the positive active material reaches 50%.
  • the median particle diameter Dv 50 of the positive electrode active material can be measured using laser diffraction particle size analysis. For example, refer to the standard GB/T 19077-2016 and use a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.
  • coating layer refers to the material layer coating the core.
  • the material layer can completely or partially cover the core.
  • thickness of the coating layer refers to the thickness of the material layer coating the core in the radial direction of the core.
  • source refers to a compound that is the source of a certain element.
  • types of “source” include but are not limited to carbonates, sulfates, nitrates, elements, Halides, oxides and hydroxides, etc.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery normally includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions such as lithium ions
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • the electrolyte is between the positive electrode piece and the negative electrode piece and mainly plays the role of conducting active ions.
  • the present application provides a cathode active material with a core-shell structure, which includes a core and a shell covering the core.
  • the kernel contains Li m A _ _ Any value of Any value within the range, optionally any value selected from the range 0.001-0.1, n is selected from any value within the range 0.001-0.5, optionally any value selected from the range 0.001-0.1, A is selected B One or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, optionally selected from Ti, V, Fe, Ni, Mg and one or more elements from Co, C is one or more elements selected from B, S, Si and N, optionally one or more elements selected from S, Si and N , D is one or more elements selected from S, F, Cl and Br, optionally one or more elements selected from F, Cl and Br;
  • the shell includes a first cladding layer covering the core and a second cladding layer covering the first cladding layer;
  • the first coating layer includes crystalline pyrophosphate M a P 2 O 7 and oxide M′ b O c , where a is greater than 0 and less than or equal to 4, optionally greater than 0 and less than or equal to 3, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al or A plurality of elements, optionally one or more elements selected from Li and Fe, M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide elements and One or more elements in Sb, optionally selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo,
  • the second cladding layer contains carbon.
  • the cathode active material with a core-shell structure of the present application includes a core 11 , a first coating layer 12 covering the core 11 , and a second coating layer 13 coating the first coating layer 12 .
  • the core 11 includes Li m A Doping can also effectively reduce surface activity, thereby inhibiting Mn dissolution and interface side reactions between the cathode active material and the electrolyte; P-site doping makes the change rate of the Mn-O bond length faster and reduces the small polaron migration potential of the material.
  • O-site doping has a good effect on reducing interface side reactions; P-site and O-site doping also affects Mn dissolution and kinetic properties of anti-site defects; therefore, doping Impurities reduce the concentration of anti-site defects in the material, improve the dynamic properties and gram capacity of the material, and can also change the morphology of the particles, thereby increasing the compaction density.
  • the first coating layer 12 includes crystalline pyrophosphate and oxide; since the migration barrier of transition metal in pyrophosphate is high (>1eV), it can effectively inhibit the dissolution of transition metal; and the oxide has a high structure Stability, and low surface activity, therefore, oxide coating can effectively reduce interface side reactions, thereby improving the high-temperature cycle and high-temperature storage performance of the battery.
  • the second coating layer 13 is a carbon-containing layer, it can effectively improve the conductive performance and desolvation ability of the cathode active material.
  • the "barrier" function of the second coating layer 13 can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active material by the electrolyte.
  • the cathode active material of the present application can reduce the generation of Li/Mn anti-site defects by element doping and surface coating of lithium manganese phosphate, effectively inhibit Mn dissolution during the lithium deintercalation process, and at the same time promote the migration of lithium ions. Thereby improving the rate performance of the battery core and improving the cycle performance, high temperature performance and safety performance of the secondary battery.
  • the position of the main characteristic peak of the cathode active material of this application is basically consistent with that of LiMnPO 4 before doping, indicating that the doped lithium manganese phosphate cathode active material has no impurity phase, and the improvement of secondary battery performance mainly comes from element doping. Impurity, not caused by impurity phase.
  • LimAxMn1 - yByP1 -zCzO4 - nDn remains electrically neutral throughout.
  • the above limitation on the numerical range of The limitation of the stoichiometric number of each element as A is also the limitation of the sum of the stoichiometric numbers of each element as A.
  • the respective stoichiometric numbers x1, x2...xn of A1, A2...An must fall within the numerical range of x defined in this application, and x1
  • the sum of , x2...xn also needs to fall within this numerical range.
  • the limitation on the numerical range of the stoichiometric numbers of B, C, and D in this application also has the above meaning.
  • the above-mentioned limitation on the numerical range of a is not only a limitation on the stoichiometric number of each element as M, but also on each As a definition of the sum of the stoichiometric numbers of the elements of M.
  • M is two or more elements M1, M2...Mn
  • the stoichiometric numbers a1, a2...an of M1, M2...Mn must each fall within the numerical range of a defined in this application, and a1 The sum of , a2...an also needs to fall within this numerical range.
  • M' in the chemical formula M' b O c is two or more elements
  • the limitation on the numerical range of the stoichiometric number b of M' in this application also has the above meaning.
  • one of x1, x2, x3, and x4 is zero, and the rest are not zero; more optionally, two of x1, x2, x3, and x4 are zero, and the rest are not zero; also optionally, Three of x1, x2, x3, and x4 are zero, and the rest are not zero.
  • the core Li m A x Mn 1-y B y P 1-z C z O 4-n D n it is advantageous to dope one, two, three or four of the above A elements in the Li position, which is optional.
  • the ground is doped with one, two or three of the above A elements; in addition, the Mn position is doped with one or two B elements, the phosphorus position is doped with one or two C elements, and the O position is doped with one One or two D elements are advantageous, which is beneficial to uniform distribution of doping elements.
  • the values of m, x, y, z, and n are such that the entire core remains electrically neutral.
  • the size of m is affected by the valence sizes of A, B, C, and D and the sizes of x, y, z, and n influence to ensure that the entire system is electrically neutral. If the value of m is too small, the lithium content of the entire core system will be reduced, affecting the gram capacity of the material.
  • the x, y, z, and n values will limit the total amount of all doping elements. If the doping amount is too small, the doping elements will not be effective. If y exceeds 0.5, the Mn content in the system will be low, affecting the material. voltage platform.
  • the C 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 0.001-0.2.
  • the entire core system remains electrically neutral, ensuring that there are as few defects and impurities in the cathode active material as possible. If there is an excess of transition metal (such as manganese) in the cathode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely to precipitate in the form of elemental substances, or form a heterogeneous phase inside the crystal lattice, maintaining the electrical neutrality. Sex can minimize such impurities. In addition, ensuring the electrical neutrality of the system can also generate lithium vacancies in the material in some cases, thereby making the material's dynamic properties better.
  • transition metal such as manganese
  • the inventor of the present application cut out the middle region of the prepared cathode active material particles through a focused ion beam (FIB for short), and analyzed it through a transmission electron microscope (TEM for short) and X-ray energy spectroscopy (EDS for short). Tests were conducted and it was found that each element was evenly distributed and no aggregation occurred.
  • FIB focused ion beam
  • EDS X-ray energy spectroscopy
  • the values of a, b, and c satisfy conditions such that M a P 2 O 7 and M' b O c remain electrically neutral.
  • the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326nm, and the angle between the crystallographic directions (111) is 26.41°-32.57°;
  • the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310nm (for example, 0.303nm); and/or,
  • the angle between the crystallographic directions (111) of the pyrophosphate in the first coating layer is 29.00°-30.00° (for example, 29.496°).
  • the angle between the interplanar spacing and the crystal direction (111) of the pyrophosphate in the first coating layer is within the above range, the impurity phase in the coating layer can be effectively avoided, thereby increasing the gram capacity of the material and improving the secondary battery. cycle performance and rate performance.
  • x is any value in the range of 0.001-0.005; and/or,
  • y is any value in the range 0.01-0.5, optionally any value in the range 0.25-0.5; and/or,
  • z is any value within the range of 0.001-0.005; and/or,
  • n is any value within the range of 0.001-0.005.
  • x, y, z, n within the above range can further reduce the generation of Li/Mn anti-site defects, reduce manganese dissolution and reduce the lattice change rate, thereby further increasing the capacity of the secondary battery and improving the secondary battery. cycle performance, high temperature storage performance and safety performance.
  • the ratio of 1-y to y is 1 to 4, optionally 1.5 to 3.
  • y represents the sum of stoichiometric numbers of Mn-site doping elements.
  • the ratio of m to x is 1 to 1200, optionally 9 to 1100, and more optionally 190-998.
  • x represents the sum of stoichiometric numbers of Li-site doping elements.
  • the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally 4-5.6% by weight, based on the weight of the core.
  • the coating amount of the first coating layer is within the above range, the dissolution of manganese can be further suppressed, while further promoting the transmission of lithium ions, maintaining low impedance of the secondary battery, and improving the dynamic performance of the secondary battery.
  • the weight ratio of pyrophosphate and oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.
  • the appropriate ratio of pyrophosphate and oxide is conducive to giving full play to the synergistic effect of the two, which can further inhibit the dissolution of manganese while maintaining a low impedance of the secondary battery.
  • the thickness of the first cladding layer is 1-100 nm. Therefore, the migration barrier of the transition metal in the first coating layer is relatively high, which can effectively reduce the dissolution of the transition metal.
  • the oxides have high stability and can effectively reduce interface side reactions, thus improving the high-temperature stability of the material.
  • the thickness of the second cladding layer is 1-100 nm.
  • the crystallinity of the pyrophosphate in the first coating layer ranges from 10% to 100%, optionally from 50% to 100%.
  • the pyrophosphate with a certain degree of crystallinity is beneficial to maintaining the structural stability of the first coating layer and reducing lattice defects.
  • this is conducive to giving full play to the role of pyrophosphate in hindering manganese dissolution.
  • it is also conducive to reducing the surface miscellaneous lithium content and reducing the valence state of surface oxygen, thereby reducing the interface side reactions between the cathode material and the electrolyte and reducing the impact on electrolysis. fluid consumption and improve the cycle performance and safety performance of secondary batteries.
  • the crystallinity of the pyrophosphate of the first coating layer of the cathode active material can be tested by conventional technical means in the art, such as by density method, infrared spectroscopy, differential scanning calorimetry and nuclear magnetism. Measured by resonance absorption methods, it can also be tested by, for example, X-ray diffraction.
  • a specific X-ray diffraction method for testing the crystallinity of the first coating layer pyrophosphate 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 the pyrophosphate 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.
  • the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.
  • the carbon-containing layer as the second coating layer can function as a "barrier” to avoid direct contact between the positive active material and the electrolyte, thereby reducing the corrosion of the active material by the electrolyte and improving the safety performance of the battery at high temperatures.
  • it has strong electrical conductivity, which can reduce the internal resistance of the battery, thereby improving the dynamic performance of the secondary battery.
  • the coating amount of the second coating layer is within the above range, the kinetic performance and safety performance of the secondary battery can be further improved while maintaining a higher gram capacity of the positive active material.
  • A is any element selected from Zn, Al, Na, K, Mg, Nb, Mo and W, optionally, A is Mg or Nb; and/or ,
  • B is at least two elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.
  • B is selected from Fe, Ti, V, Co and At least two elements in Mg, more optionally, B is a combination of Fe element and at least one element selected from Ti, V, Co and Mg; and/or,
  • C is any element selected from B, S, Si and N, optionally, C is S; and/or,
  • D is any element selected from S, F, Cl and Br. Alternatively, D is F.
  • doping elements it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to Further reduce surface oxygen activity and reduce interface side reactions between the positive active material and the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.
  • the Li/Mn anti-site defect concentration of the cathode active material is 4% or less, optionally 2% or less.
  • the Li/Mn anti-site defect refers to the interchange of positions of Li + and Mn 2+ in the LiMnPO 4 crystal lattice. Since the Li + transport channel is a one-dimensional channel, Mn 2+ is difficult to migrate in the Li + transport channel. Therefore, the anti-site defective Mn 2+ will hinder the transport of Li + .
  • the anti-site defect concentration can be measured in accordance with JIS K 0131-1996, for example.
  • the lattice change rate of the cathode active material before and after complete deintercalation of lithium is 9.8% or less, optionally 6% or less, and more optionally 4% or less.
  • the lithium deintercalation process of LiMnPO 4 is a two-phase reaction.
  • the interface stress of the two phases is determined by the lattice change rate.
  • the lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD).
  • the surface oxygen valence state of the cathode active material is -1.55 or less, optionally -1.88 or less, and more optionally -1.98 ⁇ -1.88. This is because the higher the valence state of oxygen in the compound, the stronger its ability to obtain electrons, that is, the stronger its oxidizing property.
  • the cathode active material of the present application by controlling the surface valence state of oxygen at a lower level, the reactivity on the surface of the cathode material can be reduced, and the interface side reaction between the cathode active material and the electrolyte can be reduced, thereby improving the performance of the secondary battery. Cycling performance and high temperature storage performance. Surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).
  • EELS electron energy loss spectroscopy
  • the positive active material has a compacted density of 3 tons (T) of 1.89 g/cm or more, optionally 2.0 g/cm 3 or more, and more optionally 2.2 g/cm 3 or more.
  • T 3 tons
  • the compacted density can be measured according to GB/T 24533-2009, for example.
  • the cathode active material has an average discharge voltage of more than 3.5 V and a discharge capacity of more than 140 mAh/g; optionally, the average discharge voltage is more than 3.6 V and the discharge capacity is more than 145 mAh/g.
  • the average discharge voltage of undoped LiMnPO 4 is above 4.0V, its discharge gram capacity is low, usually less than 120mAh/g. Therefore, the energy density is low; adjusting the lattice change rate by doping can make it The discharge gram capacity is greatly increased, and the overall energy density is significantly increased while the average discharge voltage drops slightly.
  • m is selected from any value in the range of 0.97-1.01.
  • x is selected from any value in the range of 0.001-0.005.
  • y is selected from any value in the range of 0.25-0.5.
  • a is any value in the range of 1-4, for example, a is 1, 2, 3, or 4.
  • b is any value within the range of 1-2, for example, b is 1 or 2.
  • c is any value in the range of 1-5, optionally any value in the range of 1-3, for example, c is 1, 2, 3, 4, or 5.
  • This application provides a preparation method of cathode active material, including the following steps:
  • the core contains Li m A x Mn 1-y B y P 1-z C z O 4-n D n , where m is selected from any value in the range of 0.5-1.2, optionally from any value in the range 0.9-1.1, x is selected from any value in the range 0.001-0.5, optionally any value in the range 0.001-0.1, y is selected from any value in the range 0.001-0.5, z n is selected from any value within the range of 0.001-0.2, optionally from any value within the range of 0.001-0.1, n is selected from any value within the range of 0.001-0.5, optionally from the range of 0.001-0.1 Any value, A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, optionally one or more elements selected from Al, Mg, Nb, Mo and W or multiple elements, B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb
  • Coating step Provide a powder containing pyrophosphate M a P 2 O 7 and a suspension containing a carbon source and an oxide M′ b O c , and combine the core material and the powder containing pyrophosphate M a P 2 O 7 Mix with a suspension containing carbon source and oxide M' b O c , and sinter to obtain a positive active material, in which a is greater than 0 and less than or equal to 4, optionally greater than 0 and less than or equal to 3, and b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al , optionally one or more elements selected from Li and Fe, M′ is selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide elements and Sb One or more elements, optionally selected from Li
  • the positive active material has a core-shell structure, which includes a core and a shell covering the core.
  • the core includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n
  • the shell includes a coating a first cladding layer of the core and a second cladding layer covering the first cladding layer, the first cladding layer comprising crystalline pyrophosphate M a P 2 O 7 and oxide M′ b O c , and the second cladding layer covering the first cladding layer.
  • the cladding contains carbon.
  • A, B, C, D, M, M′, m, x, y, z, n, a, b and c are defined as above.
  • the applicant unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li site, Mn site, P site and O site of the compound LiMnPO 4 , the surface of the compound is coated with crystalline pyrophosphate and oxide.
  • the first coating layer and the second coating layer containing carbon are coated on the surface of the first coating layer to obtain the cathode active material, which can greatly reduce the generation of Li/Mn anti-site defects, reduce manganese dissolution and reduce lattice changes efficiency, increase the capacity of secondary batteries, and improve the cycle performance, high-temperature storage performance and safety performance of secondary batteries.
  • the step of providing core material includes the following steps:
  • Step (1) Mix a manganese source, a source of element B, an acid and an optional solvent to obtain a mixture;
  • Step (2) Mix the mixture with a lithium source, a phosphorus source, a source of element A, a source of element C, a source of element D and an optional solvent, dry and sinter to obtain Li m A x Mn 1-y B Core material of y P 1-z C z O 4-n D n .
  • step (1) is performed at 60°C-120°C, optionally at 70°C-120°C (for example, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C ° C or about 120 ° C); and/or, in step (1), mixing is performed by stirring at a speed of 200-800 rpm (such as 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm), optionally stirring 1 -9h (more optionally 3-7h, such as 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).
  • 200-800 rpm such as 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm
  • stirring 1 -9h more optionally 3-7h, such as about 2 hours, about 3 hours, about 4 hours, about 5 hours, about
  • step (2) mixing is performed for 8-15 hours (eg, about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, or about 15 hours ), optionally at 20-120°C, optionally 40-120°C (for example, about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C °C or about 120 °C).
  • 8-15 hours eg, about 8 hours, about 9 hours, about 10 hours, about 11 hours, about 12 hours, about 13 hours, about 14 hours, or about 15 hours
  • 20-120°C optionally 40-120°C (for example, about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C °C or about 120 °C).
  • the prepared core and the cathode active material produced therefrom have fewer lattice defects, which is beneficial to inhibiting manganese dissolution 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.
  • step (2) mixing is performed at a pH of 3.5-6, optionally a pH of 4-6, more optionally a pH of 4-5.
  • the pH can be adjusted by methods commonly used in the art, for example, by adding acid or alkali.
  • the mixture obtained in step (1) is filtered, dried, and ground to obtain element B-doped manganese salt particles with a particle size D v 50 of 50-200 nm, and the element B-doped manganese salt particles are
  • the doped manganese salt particles are used in step (2) to be mixed with a lithium source, a phosphorus source, a source of element A, a source of element C, a source of element D and an optional solvent.
  • the molar ratio of the mixture or element B-doped manganese salt particles to the lithium source and phosphorus source is 1:0.4-2.1:0.1-2.1, optionally It is about 1:0.4-0.5:0.1-1.
  • step (2) sintering is performed at 600-900°C for 4-10 hours; optionally, sintering can be performed at about 650°C, about 700°C, about 750°C, about 800°C, about 850°C Or sintering at 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, in an inert gas or Sintering under the protection of a mixed atmosphere of inert gas and hydrogen.
  • the protective atmosphere is a mixed gas of 70-90 volume % nitrogen and 10-30 volume % hydrogen; the sintering temperature and sintering time can be within any range of any of the above values. , can improve the crystallinity of the core, reduce the generation of impurities, and maintain a certain particle size of the core, thereby increasing the gram capacity and compaction density of the positive active material, and improving the overall performance of the secondary battery, including rate performance.
  • step (2) drying is performed by spray drying equipment.
  • step (2) grinding is performed while mixing.
  • a powder comprising pyrophosphate M a P 2 O 7 is prepared by the following steps:
  • drying is at 100°C-300°C for 4-8h, optionally at 150°C-200°C; and /Or, sintering is performed at 500°C-800°C for 4-10 hours under inert gas protection, and optionally, sintering is performed at 650°C-800°C.
  • the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10 h.
  • the preparation method of the present application has no special restrictions on the source of materials.
  • the source of a certain element may include the element, sulfate, halide, nitrate, phosphate, oxalate, carbonate, oxide and One or more of the hydroxides, provided that the source can achieve the purpose of the preparation method of the present application.
  • the source of element A is selected from one or more of elements, oxides, phosphates, oxalates, carbonates and sulfates of element A; and/or,
  • the source of element B is one or more selected from elemental elements, oxides, phosphates, oxalates, carbonates and sulfates of element B; and/or,
  • the source of element C is one or more selected from sulfate, borate, nitrate and silicate of element C; and/or,
  • the source of element D is one or more selected from the group consisting of elemental elements and ammonium salts of element D.
  • the source of element M is one or more selected from the group consisting of elemental elements, carbonates, sulfates, halides, nitrates, organic acid salts, oxides and hydroxides of element M.
  • the source of element M' is one or more selected from the group consisting of elemental substances, carbonates, sulfates, halides, nitrates, organic acid salts, oxides and hydroxides of element M' .
  • the addition amounts of the respective sources of elements A, B, C, D, M, and M' depend on the target doping amount, and the ratio of the amounts of lithium source, manganese source, and phosphorus source conforms to the stoichiometric ratio.
  • 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 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 carbon source is one or more selected from starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
  • the present application provides a positive electrode sheet, which 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 the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned preparation method, And the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.
  • the content of the cathode active material in the cathode film layer is 90-99.5% by weight, based on the total weight of the cathode film layer. Ensure that the secondary battery has higher capacity and better cycle performance, high-temperature storage performance and safety performance.
  • 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 positive electrode film layer may also include other positive electrode active materials known in the art for use in batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate and modified compounds thereof.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium-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)), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ) , at least one of composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composite materials of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate
  • 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 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.
  • 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 electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is liquid and includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally also includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the 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. 2 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. 4 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.
  • the electrical device 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 can be used as a power source for the power-consuming device, or as an energy storage unit of the power-consuming device.
  • Electric devices 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, electric golf carts, electric Trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • secondary batteries, battery modules or battery packs can be selected according to its usage requirements.
  • Fig. 7 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.
  • Step S1 Preparation of doped manganese oxalate
  • Step S2 Preparation of core containing Li 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001
  • Step S3 Preparation of lithium iron pyrophosphate powder
  • Step S4 Prepare a suspension containing aluminum oxide and sucrose
  • Step S5 Preparation of two coating layers
  • the cathode active materials of Examples 1-2 to 1-59 and Comparative Examples 1 to 12 were prepared in a method similar to Example 1-1. The differences in the preparation of the cathode active materials are shown in Table 1-4.
  • Comparative Examples 1-9 do not involve steps S3-S5; Comparative Example 10 does not involve step S4; Comparative Example 11 does not involve step S3.
  • step S3 of preparing lithium iron pyrophosphate (Li 2 FeP 2 O 7 ) powder the sintering temperature in the powder sintering step is 550°C and the sintering time is 1h to control the crystallinity of Li 2 FeP 2 O 7 to 30 %, other conditions are the same as Example 1-1.
  • step S3 of preparing lithium iron pyrophosphate (Li 2 FeP 2 O 7 ) powder the sintering temperature in the powder sintering step is 550°C and the sintering time is 2h to control the crystallinity of Li 2 FeP 2 O 7 to 50 %, other conditions are the same as Example 1-1.
  • step S3 of preparing lithium iron pyrophosphate (Li 2 FeP 2 O 7 ) powder the sintering temperature in the powder sintering step is 600°C and the sintering time is 3h to control the crystallinity of Li 2 FeP 2 O 7 to 70 %, other conditions are the same as Example 1-1.
  • the sintering temperature in the powder sintering step is 500°C to control the crystallinity of Li 2 FeP 2 O 7 to 10%, other conditions are the same as Same as Example 1-1.
  • the double-layer coated lithium manganese phosphate 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 92:2.5:5.5 ), stir and mix evenly to obtain 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.
  • the mass ratio of the negative active material artificial graphite, conductive agent superconducting carbon black (Super-P), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethylcellulose (CMC-Na) is 95%: Dissolve 1.5%: 1.8%: 1.7% in deionized water, stir thoroughly and mix evenly to obtain a negative electrode slurry with a viscosity of 3000 mPa.s and a solid content of 52%; coat the negative electrode slurry on a 6 ⁇ m negative electrode current collector copper foil , then baked at 100°C for 4 hours to dry, and rolled to obtain a negative electrode piece with a compacted density of 1.75g/ cm3 .
  • 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").
  • Lithium sheets were used as the negative electrode, and a solution of 1 mol/L LiPF 6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) with a volume ratio of 1:1:1 was used as the electrolyte.
  • liquid, together with the positive electrode sheet prepared above, are assembled into a button battery (hereinafter also referred to as a "button battery") in a buckle box.
  • ACSTEM Spherical aberration electron microscopy
  • the button battery prepared above was left for 5 minutes in a constant temperature environment of 25°C, discharged at 0.1C to 2.5V, left for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than Equal to 0.05mA, let stand for 5 minutes; then discharge to 2.5V according to 0.1C.
  • the discharge capacity at this time is the initial gram capacity, recorded as D0, the discharge energy is the initial energy, recorded as E0, and the average discharge voltage V of the buckle is E0 /D0.
  • the above-prepared full cell was stored at 100% state of charge (SOC) at 60°C. 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. 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 positive active material sample is prepared into a buckle, and the above 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 positive electrode active material sample prepared above Take 5 g of the positive electrode active material sample prepared above and prepare a buckle according to the above buckle preparation method. 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 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. 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
  • the crystallinity is the ratio of the crystalline part scattering to the total scattering intensity.
  • the existence of the first coating layer is beneficial to reducing the Li/Mn anti-site defect concentration of the obtained material and the amount of Fe and Mn dissolution after cycling, and improving the performance of the battery.
  • the lattice change rate, anti-site defect concentration and Fe and Mn dissolution of the resulting material can be significantly reduced, and the gram capacity and compaction of the battery can be improved. density, and improve the high-temperature storage performance, safety performance and cycle performance of the battery.
  • Example 1-1 and Examples 1-37 to 1-40 Based on Example 1-1 and Examples 1-37 to 1-40, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the dissolution amount of Fe and Mn after recycling of the obtained material gradually decreases, corresponding to the battery The high-temperature storage performance, safety performance and cycle performance at 45°C have also been improved, but the discharge capacity has slightly decreased.
  • the total amount of the second coating layer is 3-5% by weight, the overall performance of the corresponding battery is optimal.
  • Example 1-1 and Examples 1-41 to 1-44 it can be seen that when Li 2 FeP 2 O 7 and Al 2 O 3 coexist in the first coating layer, especially Li 2 FeP 2 O 7 and Al 2 When the weight ratio of O 3 is 1:3 to 3:1, the battery performance is significantly improved.

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Abstract

本申请提供一种具有核-壳结构的正极活性材料、正极活性材料的制备方法、正极极片、二次电池、电池模块、电池包和用电装置；正极活性材料包括含有Li mA xMn 1-yB yP 1-zC zO 4-nD n的内核、包覆内核的含晶态焦磷酸盐M aP 2O 7和氧化物M' bO c的第一包覆层以及包覆第一包覆层的含碳的第二包覆层。本申请正极活性材料能减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。

Description

具有核-壳结构的正极活性材料及制备方法、正极极片、二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及二次电池技术领域，尤其涉及一种具有核-壳结构的正极活性材料、该正极活性材料的制备方法、正极极片、二次电池、电池模块、电池包和用电装置。
背景技术
近年来，随着二次电池的应用范围越来越广泛，二次电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，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。由于二次电池取得了极大的发展，因此对其能量密度、循环性能和安全性能等也提出了更高的要求。作为二次电池现有的正极活性材料，磷酸锰锂在充放电过程中，容易产生Li/Mn反位缺陷，锰溶出较严重，影响了二次电池的克容量，导致二次电池的安全性能和循环性能变差。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种具有核-壳结构的正极活性材料、正极活性材料的制备方法、正极极片、二次电池、电池模块、电池包和用电装置，以解决现有的磷酸锰锂正极活性材料在充放电过程中容易产生Li/Mn反位缺陷，锰溶出较严重的问题，从而解决二次电池的容量低、安全性能和循环性能差等问题。
为了达到上述目的，本申请第一方面提供了一种具有核-壳结构的正极活性材料，其包括内核及包覆内核的壳，
内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，m选自0.5-1.2范围 内的任意数值、可选地为选自0.9-1.1范围内的任意数值，x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，y选自0.001-0.5范围内的任意数值，z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种元素；
壳包括包覆内核的第一包覆层以及包覆第一包覆层的第二包覆层；
其中，第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，其中，a大于0且小于或等于4、可选为大于0且小于或等于3，b大于0且小于或等于2，c大于0且小于或等于5，M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素、可选地为选自Li和Fe中的一种或多种元素，M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素、可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中的一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W中的一种或多种元素；
第二包覆层包含碳。
本申请发明人在实际作业中发现：磷酸锰锂正极活性材料在深度充放电过程中，易产生Li/Mn反位缺陷，锰溶出比较严重。溶出的锰在迁移到负极后，被还原成金属锰。这些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，产生的副产物一部分为气体，容易导致电池发生膨胀，影响二次电池的安全性能，另一部分沉积在负极表面，阻碍锂离子进出负极的通道，造成二次电池的阻抗增加，影响电池的动力学性能和循环性能。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，给二次电池的容量保持率带来不可逆的影响。
由此，本申请人意外地发现：通过在化合物LiMnPO 4的Li位、Mn位、P位和O位同时以特定量掺杂特定元素、在化合物表面包覆含晶态焦磷酸盐和氧化物的第一包覆层并在第一包覆层表面包覆含碳的第二包覆层以获得正极活性材料，能够大大减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。
除非另有说明，否则化学式Li mA xMn 1-yB yP 1-zC zO 4-nD n中，当A为两种以上元素时，上述对于x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x1、x2……xn各自均需落入本申请对x限定的数值范围内，且x1、x2……xn之和也需落入该数值范围内。类似地，对于B、C、D为两种以上元素的情况，本申请中对B、C、D化学计量数的数值范围的限定也具有上述含义。
除非另有说明，否则化学式M aP 2O 7中，当M为两种以上元素时，上述对于a数值范围的限定不仅是对每种作为M的元素的化学计量数的限定，也是对各个作为M的元素的化学计量数之和的限定。例如当M为两种以上元素M1、M2……Mn时，M1、M2……Mn各自的化学计量数a1、a2……an各自均需落入本申请对a限定的数值范围内，且a1、a2……an之和也需落入该数值范围内。类似地，对于化学式M′ bO c中M′为两种以上元素的情况，本申请中对M′化学计量数b的数值范围的限定也具有上述含义。
在第一方面的任意实施方式中，第一包覆层中焦磷酸盐的晶面间距为0.293-0.326nm，晶向(111)的夹角为26.41°-32.57°；
可选地，所述第一包覆层中焦磷酸盐的晶面间距为0.300-0.310nm；和/或，
可选地，所述第一包覆层中焦磷酸盐的晶向(111)的夹角为29.00°-30.00°。
当第一包覆层中焦磷酸盐的晶面间距和晶向(111)的夹角在上述范围时，能够有效避免包覆层中的杂质相，从而提升材料的克容量，提高二次电池的循环性能和倍率性能。
在第一方面的任意实施方式中，x为0.001-0.005范围内的任意数值；和/或，
y为0.01-0.5范围内的任意数值，可选地为0.25-0.5范围内的任意数值；和/或，
z为0.001-0.005范围内的任意数值；和/或，
n为0.001-0.005范围内的任意数值。
由此，x、y、z、n在上述范围内，能进一步减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，从而进一步提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。
在第一方面的任意实施方式中，内核中，1-y与y的比值为1至4，可选为1.5至3。此处y表示Mn位掺杂元素的化学计量数之和。在满足上述条件时，正极活性材料所制二次电池的能量密度和循环性能可进一步提升。
在第一方面的任意实施方式中，内核中，m与x的比值为1到1200，可选为9到1100，更可选为190-998。此处x表示Li位掺杂元素的化学计量数之和。在满足上述条件时，正极活性材料所制二次电池的能量密度和循环性能可进一步提升。
在第一方面的任意实施方式中，第一包覆层的包覆量大于0重量％且小于或等于7重量％，可选为4-5.6重量％，基于内核的重量计。
当第一包覆层的包覆量在上述范围内时，能够进一步抑制锰溶出，同时进一步促进锂离子的传输，维持二次电池具备低阻抗，改善二次电池的动力学性能。
在第一方面的任意实施方式中，第一包覆层中焦磷酸盐和氧化物 的重量比为1:3至3:1，可选为1:3至1:1。
焦磷酸盐和氧化物的合适配比有利于充分发挥二者的协同作用，能够进一步抑制锰溶出，同时维持二次电池具备较低的阻抗。
在第一方面的任意实施方式中，第一包覆层中焦磷酸盐的结晶度为10％至100％，可选为50％至100％。
在本申请磷酸锰锂正极活性材料的第一包覆层中，具备一定结晶度的焦磷酸盐有利于保持第一包覆层的结构稳定，减少晶格缺陷。这一方面有利于充分发挥焦磷酸盐阻碍锰溶出的作用，另一方面也有利于减少表面杂锂含量、降低表面氧的价态，从而减少正极材料与电解液的界面副反应，减少对电解液的消耗，改善二次电池的循环性能和安全性能。
在第一方面的任意实施方式中，第二包覆层的包覆量为大于0重量％且小于或等于6重量％，可选为3-5重量％，基于内核的重量计。
作为第二包覆层的含碳层一方面可以发挥“屏障”功能，避免正极活性材料与电解液直接接触，从而减少电解液对活性材料的腐蚀，提高电池在高温下的安全性能。另一方面，其具备较强的导电能力，可降低电池内阻，从而改善二次电池的动力学性能。第二包覆层的包覆量在上述范围时，能够在保持正极活性材料较高克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
在第一方面的任意实施方式中，正极活性材料中，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的任一种元素，可选地，A为Mg或Nb；和/或，
B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的至少两种元素，可选地，B为选自Fe、Ti、V、Co和Mg中的至少两种元素，更可选地，B为Fe元素与选自Ti、V、Co和Mg中的至少一种元素的组合；和/或，
C为选自B、S、Si和N中的任一种元素，可选地，C为S；和/或，
D为选自S、F、Cl和Br中的任一种元素，可选地，D为F。
通过在上述范围内对掺杂元素进行选择，有利于增强掺杂效果， 一方面进一步减小晶格变化率，从而抑制锰的溶出，减少电解液和活性锂的消耗，另一方面也有利于进一步降低表面氧活性，减少正极活性材料与电解液的界面副反应，从而改善电池的循环性能和高温储存性能。
在第一方面的任意实施方式中，正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2％以下。在本申请的正极活性材料中，Li/Mn反位缺陷是指LiMnPO 4晶格中，Li +和Mn 2+的位置发生互换。由于Li +传输通道为一维通道，Mn 2+在Li +传输通道中难以迁移，因此，反位缺陷的Mn 2+会阻碍Li +的传输。通过将Li/Mn反位缺陷浓度控制在低水平，能够改善正极活性材料的克容量和二次电池的倍率性能。
在第一方面的任意实施方式中，正极活性材料在完全脱嵌锂前后的晶格变化率为9.8％以下，可选为6％以下，更可选为4％以下。LiMnPO 4的脱嵌锂过程是两相反应。两相的界面应力由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。
在第一方面的任意实施方式中，正极活性材料的表面氧价态为-1.55以下，可选为-1.88以下，更可选为-1.98～-1.88。这是由于氧在化合物中的价态越高，其得电子能力越强，即氧化性越强。而在本申请的正极活性材料中，通过将氧的表面价态控制在较低水平，可降低正极材料表面的反应活性，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高温储存性能。
在第一方面的任意实施方式中，正极活性材料在3吨(T)下的压实密度为1.89g/cm 3以上，可选为2.0g/cm 3以上，更可选地为2.2g/cm 3以上。正极活性材料的压实密度越高，即单位体积活性物质的重量越大，将更有利于提升二次电池的体积能量密度。
本申请第二方面提供了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：内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，m选自0.5-1.2范围内的任意数值、可选地为选自0.9-1.1范围内的任 意数值，x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，y选自0.001-0.5范围内的任意数值，z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种元素；
包覆步骤：提供包含焦磷酸盐M aP 2O 7的粉末和包含碳源及氧化物M′ bO c的悬浊液，将内核材料、包含焦磷酸盐M aP 2O 7的粉末与包含碳源及氧化物M′ bO c的悬浊液混合，烧结，获得正极活性材料，其中，a大于0且小于或等于4、可选为大于0且小于或等于3，b大于0且小于或等于2，c大于0且小于或等于5，M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素、可选地为选自Li和Fe中的一种或多种元素，M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素、可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中的一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W中的一种或多种元素；
其中，正极活性材料具有核-壳结构，其包括内核及包覆内核的壳，内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，壳包括包覆内核的第一包覆层以及包覆第一包覆层的第二包覆层，第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，第二包覆层包含碳。
由此，本申请人意外地发现：通过在化合物LiMnPO 4的Li位、 Mn位、P位和O位同时以特定量掺杂特定元素、在化合物表面包覆含晶态焦磷酸盐和氧化物的第一包覆层并在第一包覆层表面包覆含碳的第二包覆层以获得正极活性材料，能够大大减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。
本申请第二方面的任意实施方式中，提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素B的源、酸和可选的溶剂混合，得到混合物；
步骤(2)：将混合物与锂源、磷源、元素A的源、元素C的源和元素D的源及可选的溶剂混合，干燥，烧结，得到包含Li mA xMn 1-yB yP 1-zC zO 4-nD n的内核材料。
本申请第二方面的任意实施方式中，步骤(1)在60℃-120℃下进行混合；和/或，步骤(1)中，通过以200-800rpm转速搅拌进行混合。
本申请第二方面的任意实施方式中，步骤(2)中，混合进行8-15小时。
本申请第二方面的任意实施方式中，步骤(2)中，烧结在600℃-900℃下进行6-14小时。
本申请第二方面的任意实施方式中，元素A的源为选自元素A的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
元素B的源为选自元素B的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
元素C的源为选自元素C的硫酸盐、硼酸盐、硝酸盐和硅酸盐中的一种或多种；和/或，
元素D的源为选自元素D的单质和铵盐中的一种或多种。
本申请第二方面的任意实施方式中，包含焦磷酸盐M aP 2O 7的粉末通过以下步骤制备：
将元素M的源、磷源与可选的溶剂混合，得到混合物，调节混 合物的pH为4-6，继续混合，经干燥、烧结即可。
本申请第二方面的任意实施方式中，制备包含焦磷酸盐M aP 2O 7的粉末的步骤中，干燥为在100℃-300℃下干燥4-8h，可选为在150℃-200℃下干燥；和/或，烧结为在500℃-800℃及惰性气体保护下烧结4-10h，可选为在650℃-800℃下烧结。
本申请第二方面的任意实施方式中，包覆步骤中的烧结温度为500-800℃，烧结时间为4-10h。
本申请第三方面提供一种正极极片，其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，正极膜层包括本申请第一方面的正极活性材料或通过本申请第二方面的制备方法制备的正极活性材料，并且正极活性材料在正极膜层中的含量为10重量％以上，基于正极膜层的总重量计。
本申请第三方面的任意实施方式中，正极活性材料在正极膜层中的含量为90-99.5重量％，基于正极膜层的总重量计。以保证二次电池具有较高的容量和较好的循环性能、高温存储性能和安全性能。
本申请的第四方面提供一种二次电池，包括本申请第一方面的正极活性材料或者通过本申请第二方面的制备方法制备的正极活性材料或者本申请第三方面的正极极片。
本申请的第五方面提供一种电池模块，包括本申请第四方面的二次电池。
本申请的第六方面提供一种电池包，包括本申请第五方面的电池模块。
本申请的第七方面提供一种用电装置，包括选自本申请的第四方面的二次电池、本申请的第五方面的电池模块和本申请的第六方面的电池包中的至少一种。
附图说明
图1为本申请一实施方式的具有核-壳结构的正极活性材料的示意图。
图2是本申请一实施方式的二次电池的示意图。
图3是图2所示的本申请一实施方式的二次电池的分解图。
图4是本申请一实施方式的电池模块的示意图。
图5是本申请一实施方式的电池包的示意图。
图6是图5所示的本申请一实施方式的电池包的分解图。
图7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；11内核；12第一包覆层；13第二包覆层。
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正极活性材料、正极活性材料的制备方法、正极极片、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。
本申请中“某数值以下”、“某数值以上”的范围表示以某数值为上限或下限所限定的范围。
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，方法包括步骤(a)和(b)，表示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，提到方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到方法，例如，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，“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)。
如果没有特别的说明，在本申请中，中值粒径D v50是指，正极活性材料累计体积分布百分数达到50％时所对应的粒径。在本申请中，正极活性材料的中值粒径Dv 50可采用激光衍射粒度分析法测定。例如参照标准GB/T 19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。
如果没有特别的说明，在本申请中，术语“包覆层”是指包覆在内核上的物质层，物质层可以完全或部分地包覆内核，使用“包覆层”只是为了便于描述，并不意图限制本发明。同样地，术语“包覆层的 厚度”是指包覆在内核上的物质层在内核径向上的厚度。
如果没有特别的说明，在本申请中，术语“源”是指作为某种元素的来源的化合物，作为实例，“源”的种类包括但不限于碳酸盐、硫酸盐、硝酸盐、单质、卤化物、氧化物和氢氧化物等。
[二次电池]
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解液。在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。电解液在正极极片和负极极片之间，主要起到传导活性离子的作用。
[正极活性材料]
本申请提供了一种具有核-壳结构的正极活性材料，其包括内核及包覆内核的壳，
内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，m选自0.5-1.2范围内的任意数值、可选地为选自0.9-1.1范围内的任意数值，x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，y选自0.001-0.5范围内的任意数值，z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种 元素；
壳包括包覆内核的第一包覆层以及包覆第一包覆层的第二包覆层；
其中，第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，其中，a大于0且小于或等于4、可选为大于0且小于或等于3，b大于0且小于或等于2，c大于0且小于或等于5，M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素、可选地为选自Li和Fe中的一种或多种元素，M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素、可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中的一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W中的一种或多种元素；
第二包覆层包含碳。
如图1所示，本申请的具有核-壳结构的正极活性材料包括内核11、包覆内核11的第一包覆层12以及包覆第一包覆层12的第二包覆层13。其中，内核11包括Li mA xMn 1-yB yP 1-zC zO 4-nD n；在内核11中，通过Li和Mn位掺杂减小了晶格变化率；Mn位掺杂还能有效降低表面活性，从而抑制Mn溶出和正极活性材料与电解液的界面副反应；P位掺杂使Mn-O键长的变化速率更快，降低材料的小极化子迁移势垒，从而有利于电子电导率；O位掺杂对减小界面副反应有良好的作用；P位和O位的掺杂还对反位缺陷的Mn溶出及动力学性能产生影响；因此，掺杂减小了材料中反位缺陷浓度，提高材料的动力学性能和克容量，还可以改变颗粒的形貌，从而提升压实密度。第一包覆层12包括晶态焦磷酸盐和氧化物；由于过渡金属在焦磷酸盐中的迁移势垒较高(>1eV)，能够有效抑制过渡金属的溶出；而氧化物具有高的结构稳定性，并且表面活性低，因此，通过氧化物包覆能有效减轻界面副反应，从而改善电池的高温循环和高温存储等性能。另外，由于第二包覆层13为含碳层，因而能够有效改善正极活性材料 的导电性能和去溶剂化能力。此外，第二包覆层13的“屏障”作用可以进一步阻碍锰离子迁移到电解液中，并减少电解液对活性材料的腐蚀。因此，本申请正极活性材料通过对磷酸锰锂进行元素掺杂和表面包覆，能够减少Li/Mn反位缺陷的产生，有效抑制脱嵌锂过程中的Mn溶出，同时促进锂离子的迁移，从而改善电芯的倍率性能，提高二次电池的循环性能、高温性能和安全性能。需要指出的是，本申请的正极活性材料与LiMnPO 4掺杂前的主要特征峰的位置基本一致，说明掺杂的磷酸锰锂正极活性材料没有杂质相，二次电池性能的改善主要来自元素掺杂，而不是杂质相导致的。
在一些实施方式中，Li mA xMn 1-yB yP 1-zC zO 4-nD n整个保持电中性。
除非另有说明，否则化学式Li mA xMn 1-yB yP 1-zC zO 4-nD n中，当A为两种以上元素时，上述对于x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x1、x2……xn各自均需落入本申请对x限定的数值范围内，且x1、x2……xn之和也需落入该数值范围内。类似地，对于B、C、D为两种以上元素的情况，本申请中对B、C、D化学计量数的数值范围的限定也具有上述含义。
除非另有说明，否则化学式M aP 2O 7中，当M为两种以上元素时，上述对于a数值范围的限定不仅是对每种作为M的元素的化学计量数的限定，也是对各个作为M的元素的化学计量数之和的限定。例如当M为两种以上元素M1、M2……Mn时，M1、M2……Mn各自的化学计量数a1、a2……an各自均需落入本申请对a限定的数值范围内，且a1、a2……an之和也需落入该数值范围内。类似地，对于化学式M′ bO c中M′为两种以上元素的情况，本申请中对M′化学计量数b的数值范围的限定也具有上述含义。
在一些实施方式中，当A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种、两种、三种或四种元素时，A x为Q x1H x2E x3K x4，其中x1+x2+x3+x4＝x，且x1、x2、x3、x4均为正数且不同时为零，Q、H、E、K各自独立地为选自Zn、Al、Na、K、Mg、Nb、Mo和 W的一种。可选地，x1、x2、x3、x4之一为零，其余不为零；更可选地，x1、x2、x3、x4中的两个为零，其余不为零；还可选地，x1、x2、x3、x4中的三个为零，其余不为零。内核Li mA xMn 1-yB yP 1-zC zO 4-nD n中，在Li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Mn位掺杂一种或两种B元素、在磷位掺杂一种或两种C元素、在O位掺杂一种或两种D元素均是有利的，这样有利于使掺杂元素均匀分布。
在一些实施方式中，m、x、y、z和n的值满足以下条件：使整个内核保持电中性。
内核Li mA xMn 1-yB yP 1-zC zO 4-nD n中，m的大小受A、B、C、D的价态大小以及x、y、z和n的大小的影响，以保证整个体系呈现电中性。如果m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。x、y、z、n值会限制所有掺杂元素的总量，如果掺杂量过少，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。C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0.001-0.2。
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。
通过工艺控制(例如，对各种源的材料进行充分混合、研磨)，能够保证各元素在晶格中均匀分布，不出现聚集的情况。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正极活性材料后，通过聚焦离子束(简称FIB)切取已制备好的正极活性材料颗粒 的中间区域，通过透射电子显微镜(简称TEM)以及X射线能谱分析(简称EDS)进行测试发现，各元素分布均匀，未出现聚集。
在一些实施方式中，a、b和c的值满足以下条件：使M aP 2O 7和M′ bO c保持电中性。
在一些实施方式中，第一包覆层中焦磷酸盐的晶面间距为0.293-0.326nm，晶向(111)的夹角为26.41°-32.57°；
可选地，所述第一包覆层中焦磷酸盐的晶面间距为0.300-0.310nm(例如0.303nm)；和/或，
可选地，所述第一包覆层中焦磷酸盐的晶向(111)的夹角为29.00°-30.00°(例如29.496°)。
当第一包覆层中焦磷酸盐的晶面间距和晶向(111)的夹角在上述范围时，能够有效避免包覆层中的杂质相，从而提升材料的克容量，提高二次电池的循环性能和倍率性能。
在一些实施方式中，x为0.001-0.005范围内的任意数值；和/或，
y为0.01-0.5范围内的任意数值，可选地为0.25-0.5范围内的任意数值；和/或，
z为0.001-0.005范围内的任意数值；和/或，
n为0.001-0.005范围内的任意数值。
由此，x、y、z、n在上述范围内，能进一步减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，从而进一步提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。
在一些实施方式中，内核中，1-y与y的比值为1至4，可选为1.5至3。此处y表示Mn位掺杂元素的化学计量数之和。在满足上述条件时，正极活性材料所制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，内核中，m与x的比值为1到1200，可选为9到1100，更可选为190-998。此处x表示Li位掺杂元素的化学计量数之和。在满足上述条件时，正极活性材料所制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，第一包覆层的包覆量大于0重量％且小于或 等于7重量％，可选为4-5.6重量％，基于内核的重量计。
当第一包覆层的包覆量在上述范围内时，能够进一步抑制锰溶出，同时进一步促进锂离子的传输，维持二次电池具备低阻抗，改善二次电池的动力学性能。
在一些实施方式中，第一包覆层中焦磷酸盐和氧化物的重量比为1:3至3:1，可选为1:3至1:1。
焦磷酸盐和氧化物的合适配比有利于充分发挥二者的协同作用，能够进一步抑制锰溶出，同时维持二次电池具备较低的阻抗。
在一些实施方式中，第一包覆层的厚度为1-100nm。由此，过渡金属在第一包覆层中的迁移势垒较高，可有效减少过渡金属的溶出。其中的氧化物具有较高稳定性，可以有效减轻界面副反应，从而提升材料的高温稳定性。
在一些实施方式中，第二包覆层的厚度为1-100nm。
在一些实施方式中，第一包覆层中焦磷酸盐的结晶度为10％至100％，可选为50％至100％。
在本申请磷酸锰锂正极活性材料的第一包覆层中，具备一定结晶度的焦磷酸盐有利于保持第一包覆层的结构稳定，减少晶格缺陷。这一方面有利于充分发挥焦磷酸盐阻碍锰溶出的作用，另一方面也有利于减少表面杂锂含量、降低表面氧的价态，从而减少正极材料与电解液的界面副反应，减少对电解液的消耗，改善二次电池的循环性能和安全性能。
在一些实施方式中，正极活性材料的第一包覆层焦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焦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，在一些实施方式中，包覆层中的焦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。
在一些实施方式中，第二包覆层的包覆量为大于0重量％且小于或等于6重量％，可选为3-5重量％，基于内核的重量计。
作为第二包覆层的含碳层一方面可以发挥“屏障”功能，避免正极活性材料与电解液直接接触，从而减少电解液对活性材料的腐蚀，提高电池在高温下的安全性能。另一方面，其具备较强的导电能力，可降低电池内阻，从而改善二次电池的动力学性能。第二包覆层的包覆量在上述范围时，能够在保持正极活性材料较高克容量的前提下，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，正极活性材料中，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的任一种元素，可选地，A为Mg或Nb；和/或，
B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的至少两种元素，可选地，B为选自Fe、Ti、V、Co和Mg中的至少两种元素，更可选地，B为Fe元素与选自Ti、V、Co和Mg中的至少一种元素的组合；和/或，
C为选自B、S、Si和N中的任一种元素，可选地，C为S；和/或，
D为选自S、F、Cl和Br中的任一种元素，可选地，D为F。
通过在上述范围内对掺杂元素进行选择，有利于增强掺杂效果，一方面进一步减小晶格变化率，从而抑制锰的溶出，减少电解液和活性锂的消耗，另一方面也有利于进一步降低表面氧活性，减少正极活性材料与电解液的界面副反应，从而改善电池的循环性能和高温储存性能。
在一些实施方式中，正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2％以下。在本申请的正极活性材料中，Li/Mn反位缺 陷是指LiMnPO 4晶格中，Li +和Mn 2+的位置发生互换。由于Li +传输通道为一维通道，Mn 2+在Li +传输通道中难以迁移，因此，反位缺陷的Mn 2+会阻碍Li +的传输。通过将Li/Mn反位缺陷浓度控制在低水平，能够改善正极活性材料的克容量和二次电池的倍率性能。本申请中，反位缺陷浓度例如可根据JIS K 0131-1996测定。
在一些实施方式中，正极活性材料在完全脱嵌锂前后的晶格变化率为9.8％以下，可选为6％以下，更可选为4％以下。LiMnPO 4的脱嵌锂过程是两相反应。两相的界面应力由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。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。
在一些任意实施方式中，正极活性材料的表面氧价态为-1.55以下，可选为-1.88以下，更可选为-1.98～-1.88。这是由于氧在化合物中的价态越高，其得电子能力越强，即氧化性越强。而在本申请的正极活性材料中，通过将氧的表面价态控制在较低水平，可降低正极材料表面的反应活性，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高温储存性能。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。
在一些实施方式中，正极活性材料在3吨(T)下的压实密度为1.89g/cm 3以上，可选为2.0g/cm 3以上，更可选地为2.2g/cm 3以上。正极活性材料的压实密度越高，即单位体积活性物质的重量越大，将更有利于提升二次电池的体积能量密度。本申请中，压实密度例如可根据GB/T 24533-2009测定。
在一些实施方式中，正极活性材料的扣电平均放电电压为3.5V以上，放电克容量在140mAh/g以上；可选为平均放电电压3.6V以上，放电克容量在145mAh/g以上。
尽管未掺杂的LiMnPO 4的平均放电电压在4.0V以上，但它的放电克容量较低，通常小于120mAh/g，因此，能量密度较低；通过掺杂调整晶格变化率，可使其放电克容量大幅提升，在平均放电电压微 降的情况下，整体能量密度有明显升高。
在一些实施方式中，m选自0.97-1.01范围内的任意数值。
在一些实施方式中，x选自0.001-0.005范围内的任意数值。
在一些实施方式中，y选自0.25-0.5范围内的任意数值。
在一些实施方式中，a为1-4范围内的任意数值，例如a为1、2、3、4。
在一些实施方式中，b为1-2范围内的任意数值，例如b为1、2。
在一些实施方式中，c为1-5范围内的任意数值，可选为1-3范围内的任意数值，例如c为1、2、3、4、5。
[正极活性材料的制备方法]
本申请提供了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：内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，m选自0.5-1.2范围内的任意数值、可选地为选自0.9-1.1范围内的任意数值，x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，y选自0.001-0.5范围内的任意数值，z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种元素；
包覆步骤：提供包含焦磷酸盐M aP 2O 7的粉末和包含碳源及氧化物M′ bO c的悬浊液，将内核材料、包含焦磷酸盐M aP 2O 7的粉末与包含碳源及氧化物M′ bO c的悬浊液混合，烧结，获得正极活性材料，其中，a大于0且小于或等于4、可选为大于0且小于或等于3，b大于 0且小于或等于2，c大于0且小于或等于5，M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素、可选地为选自Li和Fe中的一种或多种元素，M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素、可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中的一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W中的一种或多种元素；
其中，正极活性材料具有核-壳结构，其包括内核及包覆内核的壳，内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，壳包括包覆内核的第一包覆层以及包覆第一包覆层的第二包覆层，第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，第二包覆层包含碳。其中，A、B、C、D、M、M′、m、x、y、z、n、a、b和c的定义如上述。
由此，本申请人意外地发现：通过在化合物LiMnPO 4的Li位、Mn位、P位和O位同时以特定量掺杂特定元素、在化合物表面包覆含晶态焦磷酸盐和氧化物的第一包覆层并在第一包覆层表面包覆含碳的第二包覆层以获得正极活性材料，能够大大减少Li/Mn反位缺陷的产生、减少锰溶出并降低晶格变化率，提高二次电池的容量，改善二次电池的循环性能、高温存储性能和安全性能。
在一些实施方式中，提供内核材料的步骤包括以下步骤：
步骤(1)：将锰源、元素B的源、酸和可选的溶剂混合，得到混合物；
步骤(2)：将混合物与锂源、磷源、元素A的源、元素C的源和元素D的源及可选的溶剂混合，干燥，烧结，得到包含Li mA xMn 1-yB yP 1-zC zO 4-nD n的内核材料。
在一些实施方式中，步骤(1)在60℃-120℃、可选为在70℃-120℃(例如约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃)下进行；和/或，步骤(1)中，通过以200-800rpm(例如200rpm、300rpm、400rpm、500rpm、600rpm、700rpm、800rpm)转速 搅拌进行混合，可选为搅拌1-9h(更可选为3-7h，例如约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)。
在一些实施方式中，步骤(2)中，混合进行8-15h(例如约8小时、约9小时、约10小时、约11小时、约12小时、约13小时、约14小时或约15小时)，可选地在20-120℃、可选为40-120℃(例如约30℃、约50℃、约60℃、约70℃、约80℃、约90℃、约100℃、约110℃或约120℃)的温度下混合。
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，步骤(2)中，在pH为3.5-6条件下混合，可选地pH为4-6，更可选地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pH，例如可通过添加酸或碱。
在一些可选实施方式中，将步骤(1)获得的混合物过滤，烘干，并进行研磨以得到粒径D v50为50-200nm的经元素B掺杂的锰盐颗粒，将经元素B掺杂的锰盐颗粒用于步骤(2)中与锂源、磷源、元素A的源、元素C的源和元素D的源及可选的溶剂混合。
在一些实施方式中，可选地，在步骤(2)中，混合物或经元素B掺杂的锰盐颗粒与锂源、磷源的摩尔比为1：0.4-2.1：0.1-2.1，可选为约1：0.4-0.5：0.1-1。
在一些实施方式中，步骤(2)中，在600-900℃下烧结4-10小时；可选地，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，在惰性气体或惰性气体与氢气混合气氛保护下烧结，更可选地，保护气氛为70-90体积％氮气和10-30体积％氢气的混合气体；烧结的温度、烧结时间可在上述任意数值的任意范围内，能提高内核的结晶度， 减少杂相生成，使内核维持一定的颗粒度，从而提高正极活性材料的克容量、压实密度，提高二次电池的整体性能包括倍率性能。
在一些可选实施方式中，步骤(2)中，通过喷雾干燥设备进行干燥。
在一些可选实施方式中，步骤(2)中，混合的同时进行研磨。
在一些实施方式中，包含焦磷酸盐M aP 2O 7的粉末通过以下步骤制备：
将元素M的源、磷源与可选的溶剂混合，得到混合物，调节混合物的pH为4-6，继续混合，经干燥、烧结即可。
在一些实施方式中，制备包含焦磷酸盐M aP 2O 7的粉末的步骤中，干燥为在100℃-300℃下干燥4-8h，可选为在150℃-200℃下干燥；和/或，烧结为在500℃-800℃下及惰性气体保护下烧结4-10h，可选为在650℃-800℃下烧结。
在一些实施方式中，包覆步骤中的烧结温度为500-800℃，烧结时间为4-10h。
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、磷酸盐、草酸盐、碳酸盐、氧化物和氢氧化物中的一种或多种，前提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，元素A的源选自元素A的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
元素B的源为选自元素B的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
元素C的源为选自元素C的硫酸盐、硼酸盐、硝酸盐和硅酸盐中的一种或多种；和/或，
元素D的源为选自元素D的单质和铵盐中的一种或多种。
在一些实施方式中，元素M的源为选自元素M的单质、碳酸盐、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物和氢氧化物中的一种或多种。
在一些实施方式中，元素M’的源为选自元素M’的单质、碳酸盐、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物和氢氧化物中的一种或多种。
元素A、B、C、D、M、M’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。
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，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，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，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，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。
本申请中，作为示例，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。
[正极极片]
本申请提供了一种正极极片，其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，正极膜层包括前述的正极活性材料或通过前述的制备方法制备的正极活性材料，并且正极活性材料在正极膜层中的含量为10重量％以上，基于正极膜层的总重量计。
在一些实施方式中，正极活性材料在正极膜层中的含量为90-99.5重量％，基于正极膜层的总重量计。保证二次电池具有较高的容量和较好的循环性能、高温存储性能和安全性能。
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。
在一些实施方式中，正极膜层还可包含本领域公知的用于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及其改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，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。
[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，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。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解 质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，电解质为液态的，且包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，电解液还可选地包括添加剂。作为示例，添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[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2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3，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能够盖设于开口，以封闭容纳腔。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4是作为一个示例的电池模块4。参照图4，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5和图6是作为一个示例的电池包1。参照图5和图6，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，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。二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。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7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。本发明实施例中各成分的含量，如果没有特别说明，均以不含结晶水的质量计。
本申请制备例及实施例涉及的原材料来源如下：
名称 化学式 厂家 规格
碳酸锰 MnCO 3 山东西亚化学工业有限公司 1Kg
碳酸锂 Li 2CO 3 山东西亚化学工业有限公司 1Kg
碳酸镁 MgCO 3 山东西亚化学工业有限公司 1Kg
碳酸锌 ZnCO 3 武汉鑫儒化工有限公司 25Kg
碳酸亚铁 FeCO 3 西安兰之光精细材料有限公司 1Kg
硫酸镍 NiCO 3 山东西亚化学工业有限公司 1Kg
硫酸钛 Ti(SO 4) 2 山东西亚化学工业有限公司 1Kg
硫酸钴 CoSO 4 厦门志信化学有限公司 500g
二氯化钒 VCl 2 上海金锦乐实业有限公司 1Kg
二水合草酸 C 2H 2O 4 ●2H 2O 上海金锦乐实业有限公司 1Kg
磷酸二氢铵 NH 4H 2PO 4 上海澄绍生物科技有限公司 500g
蔗糖 C 12H 22O 11 上海源叶生物科技有限公司 100g
硫酸 H 2SO 4 深圳海思安生物技术有限公司 质量分数60％
硝酸 HNO 3 安徽凌天精细化工有限公司 质量分数60％
亚硅酸 H 2SiO 3 上海源叶生物科技有限公司 100g
硼酸 H 3BO 3 常州市启迪化工有限公司 1Kg
实施例1-1
步骤S1：制备掺杂的草酸锰
将1.3mol MnSO 4·H 2O与0.7mol FeSO 4·H 2O在混料机中充分混合6小时；将混合物转移至反应釜中，加入10L去离子水和2mol二水合草酸，加热至80℃，之后以600rpm转速搅拌6小时，反应终止(无气泡产生)，得到Fe掺杂的草酸锰的悬浮液；过滤悬浮液，滤饼在120℃下烘干，研磨，得到粒径D v50为100nm左右的Fe掺杂的草酸锰颗粒；
步骤S2：制备包含Li 0.994Mo 0.001Mn 0.65Fe 0.35P 0.999Si 0.001O 3.999F 0.001的内核
取1mol Fe掺杂的草酸锰颗粒、0.497mol碳酸锂、0.001mol的Mo(SO 4) 3、含有0.999mol磷酸的浓度85％的磷酸水溶液、0.001mol的H 4SiO 4、0.0005mol的NH 4HF 2和0.005mol蔗糖加入到20L去离子水中，将混合物转入砂磨机中充分研磨搅拌10小时，得到浆料；将浆料转移到喷雾干燥设备中进行喷雾干燥造粒，设定干燥温度为250℃，干燥4小时，得到颗粒；在氮气(90％v/v)+氢气(10％v/v)保护气氛中，将颗粒在700℃下烧结10小时，得到内核材料。采用电感耦合等离子体发射光谱(ICP)对内核材料进行元素含量检测，得到内核化学式为上述所示。
步骤S3：制备焦磷酸铁锂粉末
将4.77g碳酸锂、7.47g碳酸亚铁、14.84g磷酸二氢铵和1.3g二水合草酸溶于50ml去离子水中。混合物的pH为5，搅拌2小时使反 应混合物充分反应。然后将反应后的溶液升温到80℃并保持该温度4小时，得到包含Li 2FeP 2O 7的悬浊液，将悬浊液进行过滤，用去离子水洗涤，并在120℃下干燥4h，得到粉末。将粉末在650℃、氮气气氛下烧结8小时，并自然冷却至室温后进行研磨，得到Li 2FeP 2O 7粉末。
步骤S4：制备包含三氧化二铝和蔗糖的悬浊液
将4.71g纳米级Al 2O 3(粒径约20nm)和3.73g蔗糖(以C 12H 22O 11计，下同)加入150ml去离子水中，搅拌6小时充分混合，然后将混合物升温至120℃并保持该温度6小时，得到包含三氧化二铝和蔗糖的悬浊液。
步骤S5：两层包覆层的制备
将157.21g上述内核与1.57g上述焦磷酸铁锂(Li 2FeP 2O 7)粉末加入到上一步骤制备获得的包含三氧化二铝和蔗糖的悬浊液中，搅拌混合均匀后转入真空烘箱中在150℃下干燥6小时，然后通过砂磨分散所得产物，分散后将产物在氮气气氛中于700℃下烧结6小时，得到双层包覆的磷酸锰锂。
实施例1-2至1-59及对比例1至12
以类似于实施例1-1的方法制作实施例1-2至1-59和对比例1至12的正极活性材料，正极活性材料的制备中的不同之处参见表1-4。
其中，对比例1-9不涉及步骤S3-S5；对比例10不涉及步骤S4；对比例11不涉及步骤S3。
Figure PCTCN2022099523-appb-000001
Figure PCTCN2022099523-appb-000002
Figure PCTCN2022099523-appb-000003
Figure PCTCN2022099523-appb-000004
Figure PCTCN2022099523-appb-000005
Figure PCTCN2022099523-appb-000006
Figure PCTCN2022099523-appb-000007
Figure PCTCN2022099523-appb-000008
Figure PCTCN2022099523-appb-000009
Figure PCTCN2022099523-appb-000010
Figure PCTCN2022099523-appb-000011
Figure PCTCN2022099523-appb-000012
Figure PCTCN2022099523-appb-000013
Figure PCTCN2022099523-appb-000014
Figure PCTCN2022099523-appb-000015
Figure PCTCN2022099523-appb-000016
Figure PCTCN2022099523-appb-000017
Figure PCTCN2022099523-appb-000018
Figure PCTCN2022099523-appb-000019
Figure PCTCN2022099523-appb-000020
Figure PCTCN2022099523-appb-000021
Figure PCTCN2022099523-appb-000022
Figure PCTCN2022099523-appb-000023
实施例2-1
除在制备焦磷酸铁锂(Li 2FeP 2O 7)粉末的步骤S3中，在粉末烧结步骤中的烧结温度为550℃，烧结时间为1h以控制Li 2FeP 2O 7的结晶度为30％，其他条件与实施例1-1相同。
实施例2-2
除在制备焦磷酸铁锂(Li 2FeP 2O 7)粉末的步骤S3中，在粉末烧结步骤中的烧结温度为550℃，烧结时间为2h以控制Li 2FeP 2O 7的结晶度为50％，其他条件与实施例1-1相同。
实施例2-3
除在制备焦磷酸铁锂(Li 2FeP 2O 7)粉末的步骤S3中，在粉末烧结步骤中的烧结温度为600℃，烧结时间为3h以控制Li 2FeP 2O 7的结晶度为70％，其他条件与实施例1-1相同。
实施例2-4
除在制备焦磷酸铁锂(Li 2FeP 2O 7)粉末的步骤S3中，在粉末烧结步骤中的烧结温度为500℃以控制Li 2FeP 2O 7的结晶度为10％，其他条件与实施例1-1相同。
正极极片的制备
将上述制备的双层包覆的磷酸锰锂正极活性材料、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为92：2.5：5.5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。
负极极片的制备
将负极活性材料人造石墨、导电剂超导炭黑(Super-P)、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照质量比为 95％：1.5％：1.8％：1.7％溶于去离子水中，充分搅拌混合均匀后，得到粘度3000mPa.s、固含52％的负极浆料；将负极浆料涂覆在6μm的负极集流体铜箔上，之后在100℃烘烤4小时以烘干，辊压，得到压实密度为1.75g/cm 3的负极极片。
隔离膜
采用聚丙烯膜。
电解液的制备
将碳酸乙烯酯、碳酸二甲酯和1,2-丙二醇碳酸酯按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。
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、PVDF、乙炔黑以90：5：5的重量比加入至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1mol/L的LiPF 6在体积比1：1：1的碳酸亚乙酯(EC)+碳酸二乙酯(DEC)+碳酸二甲酯(DMC)中的溶液作为电解液，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”)。
正极活性材料的性质测试
1.内核化学式及不同包覆层组成的测定：
采用球差电镜仪(ACSTEM)对正极活性材料内部微观结构和表 面结构进行高空间分辨率表征，结合三维重构技术得到正极活性材料的内核化学式及第一、二包覆层的组成。
2.扣式电池初始克容量测试：
在2.5～4.3V下，将上述制得的扣式电池按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5min，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为D0。
3.扣电平均放电电压(V)测试：
将上述制得的扣式电池在25℃恒温环境下，静置5min，按照0.1C放电至2.5V，静置5min，按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5min；然后按照0.1C放电至2.5V，此时的放电容量为初始克容量，记为D0，放电能量为初始能量，记为E0，扣电平均放电电压V即为E0/D0。
4.全电池60℃胀气测试：
在60℃下，存储100％充电状态(SOC)的上述制得的全电池。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。
另外，测量电芯残余容量。在2.5～4.3V下，将全电池按照1C充 电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5min，记录此时的充电容量为电芯残余容量。
5.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，将上述制得的全电池按照1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA。静置5min，然后按照1C放电至2.5V，记录此时的放电容量为D0。重复前述充放电循环，直至放电容量降低到D0的80％。记录此时电池经过的循环圈数。
6.晶格变化率测试：
在25℃恒温环境下，将上述制得的正极活性材料样品置于XRD(型号为Bruker D8Discover)中，采用1°/min对样品进行测试，并对测试数据进行整理分析，参照标准PDF卡片，计算出此时的晶格常数a0、b0、c0和v0(a0、b0和c0表示晶胞各个方面上的长度大小，v0表示晶胞体积，可通过XRD精修结果直接获取)。
采用上述扣电制备方法，将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。
7.Li/Mn反位缺陷浓度测试：
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。
8.过渡金属溶出测试：
将45℃下循环至容量衰减至80％后的全电池采用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。
9.表面氧价态测试：
取5g上述制得的正极活性材料样品按照上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。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。
10.压实密度测量：
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，用于测试的容器的面积为1540.25mm 2)，通过ρ＝m/v，计算出压实密度。
11.X射线衍射法测试焦磷酸盐和磷酸盐的结晶度
取5g上述制得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、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与散射总强度之比。
12.晶面间距和夹角
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。
以上的结果见表5-9。
Figure PCTCN2022099523-appb-000024
Figure PCTCN2022099523-appb-000025
Figure PCTCN2022099523-appb-000026
Figure PCTCN2022099523-appb-000027
Figure PCTCN2022099523-appb-000028
Figure PCTCN2022099523-appb-000029
Figure PCTCN2022099523-appb-000030
Figure PCTCN2022099523-appb-000031
Figure PCTCN2022099523-appb-000032
Figure PCTCN2022099523-appb-000033
综合实施例1-1至1-59以及对比例1-9可知，第一包覆层的存在有利于降低所得材料的Li/Mn反位缺陷浓度和循环后Fe和Mn溶出量，提高电池的扣电克容量，并改善电池的高温存储性能、安全性能和循环性能。当在Li位、Mn位、磷位和氧位分别掺杂其他元素时，可显著降低所得材料的晶格变化率、反位缺陷浓度和Fe和Mn溶出量，提高电池的克容量和压实密度，并改善电池的高温存储性能、安全性能和循环性能。
综合实施例1-33至1-36可知，随着第一包覆层的量从3.2％增加至6.4％，所得材料的循环后Fe和Mn溶出量逐渐下降，对应电池的高温存储性能、安全性能和45℃下的循环性能也得到改善，但扣电克容量略有下降。可选地，当第一包覆层的总量为4-6.4重量％时，对应电池的综合性能最佳。
综合实施例1-1以及实施例1-37至1-40可知，随着第二包覆层的量从1％增加至6％，所得材料的循环后Fe和Mn溶出量逐渐下降，对应电池的高温存储性能、安全性能和45℃下的循环性能也得到改善，但扣电克容量却略有下降。可选地，当第二包覆层的总量为3-5重量％时，对应电池的综合性能最佳。
综合实施例1-1、实施例1-41至1-44可知，当第一包覆层中同时存在Li 2FeP 2O 7和Al 2O 3、特别是Li 2FeP 2O 7和Al 2O 3的重量比为1：3至3：1时，对电池性能的改善明显。
Figure PCTCN2022099523-appb-000034
Figure PCTCN2022099523-appb-000035
Figure PCTCN2022099523-appb-000036
Figure PCTCN2022099523-appb-000037
Figure PCTCN2022099523-appb-000038

Claims (23)

  1. 一种具有核-壳结构的正极活性材料，其包括内核及包覆所述内核的壳，
    所述内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，所述m选自0.5-1.2范围内的任意数值、可选地为选自0.9-1.1范围内的任意数值，所述x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述y选自0.001-0.5范围内的任意数值，所述z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，所述B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，所述C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，所述D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种元素；
    所述壳包括包覆所述内核的第一包覆层以及包覆所述第一包覆层的第二包覆层；
    其中，所述第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，其中，所述a大于0且小于或等于4、可选地为大于0且小于或等于3，所述b大于0且小于或等于2，所述c大于0且小于或等于5，所述M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al中的一种或多种元素、可选地为选自Li和Fe中的一种或多种元素，所述M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素、可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、 Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中的一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W中的一种或多种元素；
    所述第二包覆层包含碳。
  2. 根据权利要求1所述的正极活性材料，其中，所述内核中，
    1-y与y的比值为1至4，可选为1.5至3；和/或，
    m与x的比值为1到1200，可选为9-1100，更可选为190-998。
  3. 根据权利要求1或2所述的正极活性材料，其中，
    所述x为0.001-0.005范围内的任意数值；和/或，
    所述y为0.01-0.5范围内的任意数值，可选地为0.25-0.5范围内的任意数值；和/或，
    所述z为0.001-0.005范围内的任意数值；和/或，
    所述n为0.001-0.005范围内的任意数值。
  4. 根据权利要求1-3中任一项所述的正极活性材料，其中，
    所述第一包覆层的包覆量大于0重量％且小于或等于7重量％，可选为4-5.6重量％，基于所述内核的重量计。
  5. 根据权利要求1-4中任一项所述的正极活性材料，其中，
    所述第一包覆层中焦磷酸盐和氧化物的重量比为1:3至3:1，可选为1:3至1:1。
  6. 根据权利要求1-5中任一项所述的正极活性材料，其中，
    所述第一包覆层中焦磷酸盐的晶面间距为0.293-0.326nm，晶向(111)的夹角为26.41°-32.57°；
    可选地，所述第一包覆层中焦磷酸盐的晶面间距为0.300-0.310nm；和/或，
    可选地，所述第一包覆层中焦磷酸盐的晶向(111)的夹角为 29.00°-30.00°。
  7. 根据权利要求1-6中任一项所述的正极活性材料，其中，
    所述第一包覆层中焦磷酸盐的结晶度为10％至100％，可选为50％至100％。
  8. 根据权利要求1-7中任一项所述的正极活性材料，其中，
    所述第二包覆层的包覆量为大于0重量％且小于或等于6重量％，可选为3-5重量％，基于所述内核的重量计。
  9. 根据权利要求1-8中任一项所述的正极活性材料，其中，
    所述A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的任一种元素，可选地，所述A为Mg或Nb；和/或，
    所述B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的至少两种元素，可选地，所述B为选自Fe、Ti、V、Co和Mg中的至少两种元素，更可选地，所述B为Fe元素与选自Ti、V、Co和Mg中的至少一种元素的组合；和/或，
    所述C为选自B、S、Si和N中的任一种元素，可选地，所述C为S；和/或，
    所述D为选自S、F、Cl和Br中的任一种元素，可选地，所述D为F。
  10. 根据权利要求1-9中任一项所述的正极活性材料，其中，
    所述正极活性材料的Li/Mn反位缺陷浓度为4％以下，可选为2％以下。
  11. 根据权利要求1-10中任一项所述的正极活性材料，其中，
    所述正极活性材料在完全脱嵌锂前后的晶格变化率为9.8％以下，可选为6％以下，更可选为4％以下。
  12. 根据权利要求1-11中任一项所述的正极活性材料，其中，
    所述正极活性材料的表面氧价态为-1.55以下，可选为-1.88以下，更可选为-1.98～-1.88。
  13. 根据权利要求1-12中任一项所述的正极活性材料，其中，
    所述正极活性材料在3吨下的压实密度为1.89g/cm 3以上，可选为2.0g/cm 3以上，更可选为2.2g/cm 3以上。
  14. 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：所述内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，其中，所述m选自0.5-1.2范围内的任意数值、可选地为选自0.9-1.1范围内的任意数值，所述x选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述y选自0.001-0.5范围内的任意数值，所述z选自0.001-0.2范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述n选自0.001-0.5范围内的任意数值、可选地为选自0.001-0.1范围内的任意数值，所述A为选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素、可选地为选自Al、Mg、Nb、Mo和W中的一种或多种元素，所述B为选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素、可选地为选自Ti、V、Fe、Ni、Mg和Co中的一种或多种元素，所述C为选自B、S、Si和N中的一种或多种元素、可选地为选自S、Si和N中的一种或多种元素，所述D为选自S、F、Cl和Br中的一种或多种元素、可选地为选自F、Cl和Br中的一种或多种元素；
    包覆步骤：提供包含焦磷酸盐M aP 2O 7的粉末和包含碳源及氧化物M′ bO c的悬浊液，将所述内核材料、包含焦磷酸盐M aP 2O 7的粉末与包含碳源及氧化物M′ bO c的悬浊液混合，烧结，获得正极活性材料，其中，所述a大于0且小于或等于4、可选为大于0且小于或等于3，所述b大于0且小于或等于2，所述c大于0且小于或等于5，所述M为选自Li、Fe、Ni、Mg、Co、Cu、Zn、Ti、Ag、Zr、Nb和Al 中的一种或多种元素、可选为选自Li和Fe中的一种或多种元素，所述M′为选自碱金属、碱土金属、过渡金属、第IIIA族元素、第IVA族元素、镧系元素和Sb中的一种或多种元素，可选地为选自Li、Be、B、Na、Mg、Al、Si、P、K、Ca、Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、As、Se、Sr、Y、Zr、Nb、Mo、Tc、Ru、Rh、Pd、Ag、Cd、In、Sn、Sb、Te、W、La和Ce中一种或多种元素、更可选地为选自Mg、Al、V、Cu、Zn、Zr和W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，其包括内核及包覆所述内核的壳，所述内核包含Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述壳包括包覆所述内核的第一包覆层以及包覆所述第一包覆层的第二包覆层，所述第一包覆层包含晶态焦磷酸盐M aP 2O 7和氧化物M′ bO c，所述第二包覆层包含碳。
  15. 根据权利要求14所述的制备方法，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B的源、酸和可选的溶剂混合，得到混合物；
    步骤(2)：将所述混合物与锂源、磷源、元素A的源、元素C的源和元素D的源及可选的溶剂混合，干燥，烧结，得到包含Li mA xMn 1-yB yP 1-zC zO 4-nD n的内核材料；
    可选地，所述步骤(1)在60℃-120℃下进行混合；和/或，所述步骤(1)中，通过以200-800rpm转速搅拌进行混合；
    可选地，所述步骤(2)中，所述混合进行8-15小时；
    可选地，所述步骤(2)中，所述烧结在600℃-900℃下进行6-14小时。
  16. 根据权利要求14或15所述的制备方法，其中，所述元素A的源为选自元素A的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
    所述元素B的源为选自元素B的单质、氧化物、磷酸盐、草酸盐、碳酸盐和硫酸盐中的一种或多种；和/或，
    所述元素C的源为选自元素C的硫酸盐、硼酸盐、硝酸盐和硅酸盐中的一种或多种；和/或，
    所述元素D的源为选自元素D的单质和铵盐中的一种或多种。
  17. 根据权利要求14-16中任一项所述的制备方法，其中，
    所述的包含焦磷酸盐M aP 2O 7的粉末通过以下步骤制备：
    将元素M的源、磷源与可选的溶剂混合，得到混合物，调节所述混合物的pH为4-6，继续混合，经干燥、烧结即可；
    可选地，所述干燥为在100℃-300℃下干燥4-8h，可选为在150℃-200℃下干燥；和/或，所述烧结为在500℃-800℃及惰性气体保护下烧结4-10h，可选为在650℃-800℃下烧结。
  18. 根据权利要求14-17中任一项所述的制备方法，其中，
    所述包覆步骤中的烧结温度为500℃-800℃，烧结时间为4-10h。
  19. 一种正极极片，其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，所述正极膜层包括权利要求1-13中任一项所述的正极活性材料或通过权利要求14-18中任一项所述的制备方法制备的正极活性材料，并且所述正极活性材料在所述正极膜层中的含量为10重量％以上，基于所述正极膜层的总重量计；
    可选地，所述正极活性材料在所述正极膜层中的含量为90-99.5重量％，基于所述正极膜层的总重量计。
  20. 一种二次电池，包括权利要求1-13中任一项所述的正极活性材料或者通过权利要求14-18中任一项所述的制备方法制备的正极活性材料或者权利要求19所述的正极极片。
  21. 一种电池模块，其特征在于，包括权利要求20所述的二次 电池。
  22. 一种电池包，其特征在于，包括权利要求21所述的电池模块。
  23. 一种用电装置，其特征在于，包括选自权利要求20所述的二次电池、权利要求21所述的电池模块和权利要求22所述的电池包中的至少一种。
PCT/CN2022/099523 2021-10-22 2022-06-17 具有核-壳结构的正极活性材料及制备方法、正极极片、二次电池、电池模块、电池包和用电装置 WO2023240617A1 (zh)

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CN104577115A (zh) * 2014-12-26 2015-04-29 青海时代新能源科技有限公司 一种锂离子电池正极材料、其制备方法及应用
CN108511715A (zh) * 2018-03-27 2018-09-07 中南大学 一种表面包覆焦磷酸锂的锂离子电池三元材料、制备及其应用
CN114256448A (zh) * 2020-09-25 2022-03-29 比亚迪股份有限公司 磷酸锰铁锂复合材料及其制备方法和锂离子电池

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CN104577115A (zh) * 2014-12-26 2015-04-29 青海时代新能源科技有限公司 一种锂离子电池正极材料、其制备方法及应用
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