WO2024065145A1 - 正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 - Google Patents

正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 Download PDF

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WO2024065145A1
WO2024065145A1 PCT/CN2022/121540 CN2022121540W WO2024065145A1 WO 2024065145 A1 WO2024065145 A1 WO 2024065145A1 CN 2022121540 W CN2022121540 W CN 2022121540W WO 2024065145 A1 WO2024065145 A1 WO 2024065145A1
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group
coating
positive electrode
optionally
electrode active
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PCT/CN2022/121540
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English (en)
French (fr)
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袁天赐
蒋耀
张欣欣
欧阳楚英
吴凌靖
康伟斌
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 PCT/CN2022/121540 priority Critical patent/WO2024065145A1/zh
Publication of WO2024065145A1 publication Critical patent/WO2024065145A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • 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
    • 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 belongs to the field of battery technology, and specifically relates to a positive electrode active material, a preparation method thereof, a positive electrode plate containing the same, a secondary battery, and an electrical device.
  • lithium manganese phosphate has become one of the most popular positive electrode active materials due to its advantages such as high capacity, good safety performance and abundant raw material sources.
  • lithium manganese phosphate is prone to manganese ion dissolution during charging, resulting in rapid capacity decay.
  • the purpose of the present application is to provide a positive electrode active material, a preparation method thereof, a positive electrode plate, a secondary battery and an electrical device containing the same, which can enable a secondary battery using the positive electrode active material to have a higher energy density and improved cycle performance, safety performance, and/or rate performance.
  • the present application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, wherein the core comprises LimAxMn1 - yByP1 - zCzO4 - nDn , wherein A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, wherein B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, wherein C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises
  • the D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, the m is selected from the range of 0.900 to 1.100, optionally selected from the range of 0.900 to 1.006, the x is selected from the range of 0 to 0.100, optionally selected from the range of 0.001 to 0.005, the y is selected from the range of 0.001 to 0.500, optionally selected from the range of 0.100 to 0.450, the z is selected from the range of 0.001 to 0.100, the n is selected from the range of 0 to 0.100, optionally selected from the range of 0.001 to 0.005, and the core is electrically neutral; the shell comprises phosphate MPO 4 , borate XaBbOc and carbon, and the shell includes one or more coating layers, each coating layer independently includes one or more of phosphate MPO4 , borate XaBbOc and carbon, the M includes one or more metal elements selected from transition metals, Group IA
  • the present invention can effectively inhibit the dissolution of manganese ions during the process of lithium insertion and extraction by doping lithium manganese phosphate with specific elements and coating the surface, while promoting the migration of lithium ions. Therefore, the positive electrode sheet and electrical devices such as secondary batteries using the positive electrode active material of the present invention can have a higher energy density and improved cycle performance, safety performance, and/or rate performance.
  • the shell includes a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, the third coating layer contains carbon, and the first coating layer includes phosphate MPO 4 , the second coating layer includes borate X a B b O c , or the first coating layer includes borate X a B b O c , and the second coating layer includes phosphate MPO 4.
  • the first coating layer includes phosphate MPO 4
  • the second coating layer includes borate X a B b O c .
  • the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, and can be optionally 1% to 5% by weight, based on the weight of the core.
  • the function of the first coating layer can be effectively exerted, and the dynamic performance of the secondary battery will not be affected due to the excessive thickness of the coating layer.
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, and can be optionally 1% to 5% by weight, based on the weight of the core, thereby further suppressing the dissolution of manganese ions and further promoting the transmission of lithium ions and electrons.
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, and can be optionally 2% to 5% by weight, based on the weight of the core, thereby effectively increasing the gram capacity of the positive electrode active material.
  • the total coating amount of the first coating layer and the second coating layer is greater than 0 and less than or equal to 7% by weight, and can be optionally 4% to 5.6% by weight, based on the weight of the core.
  • the cycle performance, safety performance, and/or rate performance of the secondary battery can be further improved without sacrificing the gram capacity of the positive electrode active material.
  • the weight ratio of the phosphate MPO 4 to the borate X a B b O c is 1:3 to 3:1, and can be 1:3 to 1:1. This is conducive to the synergistic effect of phosphate and borate.
  • the interplanar spacing of the phosphate MPO 4 is 0.345 nm to 0.358 nm, and the angle of the crystal orientation (111) is 24.25° to 26.45°, thereby further improving the cycle performance and rate performance of the secondary battery.
  • the crystallinity of the phosphate MPO 4 is 10% to 100 %, and can be 50% to 100%; and/or the crystallinity of the borate XaBbOc is 10% to 100%, and can be 50% to 100%.
  • the ratio of y to 1-y is 1:10 to 10:1, and can be 1:4 to 1:1.
  • the energy density and cycle performance of the secondary battery can be further improved.
  • the ratio of z to 1-z is 1:9 to 1:999, and can be 1:499 to 1:249.
  • the energy density and cycle performance of the secondary battery can be further improved.
  • the B in the core, includes one or more elements selected from Fe, Ti, V, Ni, Co and Mg, and optionally includes at least two elements selected from Fe, Ti, V, Ni, Co and Mg. This can further reduce the surface oxygen activity and inhibit the dissolution of manganese ions.
  • b:c is 1:3.
  • the Li/Mn antisite defect concentration of the positive electrode active material is 4% or less, and can be optionally 2% or less, thereby improving the gram capacity and rate performance of the positive electrode active material.
  • the lattice change rate of the positive electrode active material is 8% or less, and can be optionally 4% or less, thereby improving the rate performance of the secondary battery.
  • the surface oxygen valence of the positive electrode active material is less than -1.88, and may be -1.98 to -1.88, thereby improving the cycle performance and high temperature storage performance of the secondary battery.
  • the compaction density of the positive electrode active material under 3 tons is 2.0 g/cm 3 or more, and can be 2.2 g/cm 3 or more, which is beneficial to improve the volume energy density of the secondary battery.
  • a second aspect of the present application provides a method for preparing a positive electrode active material, comprising the following steps of providing a core material and a coating step.
  • the step of providing a core material comprises LimAxMn1-yByP1-zCzO4 - nDn , the A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, Si and N one or more elements, the D includes one or more elements selected from Group VIA and Group VIIA, optionally including one or more elements selected
  • Coating step providing coating solutions comprising phosphate MPO 4 , borate X a B b O c and a carbon source respectively, adding the core material into the coating solution and mixing, and sintering to obtain a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising phosphate MPO 4 , borate X a B b O c and carbon, and the shell comprising one or more coating layers, each coating layer independently comprising phosphate MPO 4 , borate X a B b O c and carbon.
  • the M comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al
  • the X comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al
  • the a is selected from the range of 1 to 4
  • the b is selected from the range of 1 to 7
  • the c is selected from the range of 2 to 12
  • the values of a, b and c satisfy the following condition: the borate XaBbOc is kept electrically neutral.
  • the step of providing a core material comprises the following steps: step (1): mixing and stirring a manganese source, a source of element B and an acid in a container to obtain manganese salt particles doped with element B; step (2): mixing the manganese salt particles doped with element B with a source of lithium, a source of phosphorus, a source of element C, an optional source of element A and an optional source of element D in a solvent to obtain a slurry, and sintering under the protection of an inert gas atmosphere to obtain a core material.
  • the step (1) is carried out at a temperature of 20°C to 120°C, optionally 25°C to 80°C.
  • the stirring in step (1) is performed at 500 rpm to 700 rpm for 60 minutes to 420 minutes, and optionally 120 minutes to 360 minutes.
  • the doping elements By controlling the reaction temperature, stirring rate and mixing time during doping, the doping elements can be evenly distributed and the crystallinity of the material after sintering can be higher, thereby improving the gram capacity and rate performance of the positive electrode active material.
  • the source of the element A is selected from one or more of a simple substance of the element A, a carbonate, a sulfate, a halide, a nitrate, an organic acid salt, an oxide and a hydroxide.
  • the source of the element B is selected from one or more of a simple substance of the element B, a carbonate, a sulfate, a halide, a nitrate, an organic acid salt, an oxide and a hydroxide.
  • the source of the element C is selected from one or more of a simple substance of the element C, a sulfate, a halide, a nitrate, an organic acid salt, an oxide, a hydroxide and an inorganic acid of the element C.
  • the source of the element D is selected from one or more of a simple substance of the element D and an ammonium salt.
  • the sintering in step (2) is carried out at 600° C. to 800° C. for 4 to 10 hours in an inert gas or a mixed atmosphere of inert gas and hydrogen.
  • the coating step comprises, in optional order, a step of coating phosphate MPO 4 , a step of coating borate X a B b O c , and a step of coating carbon.
  • the first coating step is a step of coating phosphate MPO 4
  • the second coating step is a step of coating borate X a B b O c
  • the third coating step is a step of coating carbon
  • the positive electrode active material thus obtained has a core-shell structure, which includes the core and a shell coating the core, the shell includes a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer
  • the first coating layer includes phosphate MPO 4
  • the second coating layer includes borate X a B b O c
  • the third coating layer contains carbon.
  • the step of coating phosphate MPO 4 includes the following steps: providing a coating liquid containing phosphate MPO 4 , adding the material to be coated into the above coating liquid, mixing evenly, drying, and then sintering to obtain the material coated with phosphate MPO 4 .
  • the step of coating the borate XaBbOc comprises the following steps: providing a coating solution containing the borate XaBbOc , then adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain the borate XaBbOc coated material .
  • the step of coating carbon includes the following steps: providing a coating liquid containing a carbon source, then adding the material to be coated into the above coating liquid, mixing evenly, drying, and then sintering to obtain a carbon-coated material.
  • the coating solution containing phosphate MPO 4 is prepared by the following method: adding a source of element M and a source of phosphorus to a solvent, stirring evenly to obtain a mixture, and then heating the mixture to 60°C to 120°C and maintaining it for 2 hours to 8 hours to obtain a coating solution.
  • the coating solution containing the borate XaBbOc is prepared by the following method: adding a source of element X and a source of boron into a solvent, stirring the mixture evenly , and obtaining a coating solution.
  • the sintering in the step of coating the phosphate MPO 4 is sintering at 500° C. to 800° C. for 4 hours to 10 hours.
  • the sintering in the step of coating the borate XaBbOc is sintering at 300°C to 500° C for 2 hours to 10 hours.
  • the sintering in the carbon coating step is sintering at 500° C. to 800° C. for 4 hours to 10 hours.
  • the gram capacity and rate performance of the positive electrode active material can be further improved.
  • the third aspect of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application, and the content of the positive electrode active material in the positive electrode film layer is more than 10 weight%, and can be optionally 90 weight% to 99.5 weight%, based on the total weight of the positive electrode film layer.
  • the positive electrode plate of the present application is used in a secondary battery, and can improve the energy density, cycle performance, safety performance, and/or rate performance of the secondary battery.
  • the fourth aspect of the present application provides a secondary battery, comprising the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application or the positive electrode plate of the third aspect of the present application.
  • a fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application.
  • the positive electrode sheet, secondary battery, and electrical device of the present application include the positive electrode active material of the present application, and thus have at least the same advantages as the positive electrode active material.
  • FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application.
  • FIG. 2 is an exploded schematic diagram of an embodiment of a battery cell of the present application.
  • FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.
  • FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.
  • FIG7 is a comparison diagram of the XRD spectrum of the core of the positive electrode active material prepared in Example 1-1 and the standard XRD spectrum of lithium manganese phosphate (00-033-0804).
  • the embodiments of the positive electrode active material, the preparation method thereof, the positive electrode sheet, the secondary battery and the electric device containing the positive electrode active material of the present application are specifically disclosed with appropriate reference to the drawings.
  • unnecessary detailed descriptions are omitted.
  • detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art.
  • drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: 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 size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • the median particle size Dv50 of the material can be measured by laser diffraction particle size analysis.
  • a laser particle size analyzer such as Malvern Master Size 3000 is used for measurement.
  • coating refers to the material layer coated on the kernel, and described material layer can coat the kernel completely or partially, and using “ coating " is just for the convenience of description, and is not intended to limit the present invention.
  • each layer of coating can be to coat completely, and also can be to coat partially.
  • thickness of coating refers to the thickness of described material layer coated on the kernel in the kernel radial direction.
  • the term “source” refers to a compound that is the source of a certain element.
  • examples of the “source” include, but are not limited to, carbonates, sulfates, nitrates, simple substances, halides, oxides, and hydroxides.
  • the terms “plurality”, “multiple”, and “multi-layers” refer to two, two or more layers.
  • a numerical value indicates a range, which means a range of ⁇ 10% of the numerical value.
  • the inventors of the present application found in actual operation that the manganese ion dissolution of lithium manganese phosphate LiMnPO4 positive electrode active material is relatively serious during the deep charge and discharge process.
  • the prior art has attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce the interface side reaction, this coating cannot prevent the dissolved manganese ions from migrating into the electrolyte.
  • the dissolved manganese ions migrate to the negative electrode, they are reduced to metallic manganese.
  • the metallic manganese produced is equivalent to a "catalyst" that can catalyze the decomposition of the SEI film (solid electrolyte interphase) on the surface of the negative electrode.
  • Part of the by-products produced are gases, which easily cause the battery to swell and affect the safety performance of the secondary battery.
  • the other part is deposited on the surface of the negative electrode, which hinders the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase and affecting the kinetic performance of the secondary battery.
  • the active lithium ions inside the electrolyte and the battery are also continuously consumed, which also brings irreversible effects on the capacity retention rate of the secondary battery.
  • the inventors found that for lithium manganese phosphate positive electrode active materials, the serious dissolution of manganese ions and high surface reactivity may be caused by the Jan-Taylor effect of Mn 3+ and the change in the size of Li + channels after delithiation.
  • the inventors modified lithium manganese phosphate to obtain a positive electrode active material that can significantly reduce the dissolution of manganese ions and the lattice change rate, thereby having good cycle performance, safety performance, and/or rate performance.
  • the first aspect of the present application proposes a positive electrode active material with a core-shell structure, which includes a core and a shell covering the core.
  • the inner core includes LimAxMn1 - yByP1 - zCzO4 - nDn , the A includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, the B includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, the C includes one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, the D includes one or more elements selected from Group VIA and Group VIIA, the m is selected from the range of 0.900 to 1.100, the x is selected from the range of 0 to 0.100, the y is selected from the range of 0.001 to 0.500, the z is selected from the range of 0.001 to 0.100, the n is selected from the range of 0 to 0.100, and the inner core is electrically neutral.
  • the shell includes phosphate MPO4 , borate XaBbOc and carbon, and the shell includes one or more coating layers, each coating layer independently includes one or more of phosphate MPO4 , borate XaBbOc and carbon, the M includes one or more metal elements selected from transition metals, group IA, group IIA, group IIIA, group IVA, group VA and lanthanides, the X includes one or more metal elements selected from transition metals, group IA, group IIA, group IIIA, group IVA, group VA and lanthanides, the a is selected from the range of 1 to 4, the b is selected from the range of 1 to 7, the c is selected from the range of 2 to 12, and the values of a, b and c satisfy the following condition: the borate XaBbOc remains electrically neutral.
  • the above-mentioned limitation on the numerical range of x is not only a limitation on the stoichiometric number of each element as A, but also a limitation on the sum of the stoichiometric numbers of each element as A.
  • the stoichiometric numbers x1, x2...xn of A1, A2...An each need to fall within the numerical range of x defined in this application, and the sum of x1, x2...xn also needs to fall within the 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 lithium manganese phosphate positive electrode active material of the present application has a core-shell structure, and the core includes Li m A x Mn 1-y B y P 1-z C z O 4-n D n .
  • the element B doped at the Mn position of the core helps to reduce the lattice change rate of the lithium manganese phosphate during the lithium insertion and extraction process, improves the structural stability of the lithium manganese phosphate positive electrode active material, greatly reduces the dissolution of manganese ions and reduces the oxygen activity on the particle surface.
  • the element C doped at the P position helps to change the difficulty of the Mn-O bond length change, thereby reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the secondary battery.
  • the element A doped at the Li position also helps to reduce the lattice change rate of the lithium manganese phosphate during the lithium insertion and extraction process.
  • the element D doped at the O position helps to reduce interface side reactions.
  • the shell includes phosphate MPO 4 , borate X a B b O c and carbon.
  • Phosphate has excellent lithium ion conductivity and can reduce the surface impurity lithium content.
  • Borates have excellent lithium ion and electron conductivity, and can reduce the surface impurity lithium content and inhibit the dissolution of manganese ions, thereby reducing interface side reactions and gas production, and improving cycle performance. Carbon can effectively improve the conductivity and desolvation ability of positive electrode active materials.
  • the present application can effectively inhibit the dissolution of manganese ions during the lithium insertion and extraction process by performing specific element doping and surface coating on lithium manganese phosphate, while promoting the migration of lithium ions, thereby improving the cycle performance, safety performance, and/or rate performance of the secondary battery.
  • the positions of the main characteristic peaks of the core of the positive electrode active material of the present application are basically consistent with those of LiMnPO 4 before doping, indicating that the core of the doped lithium manganese phosphate positive electrode active material of the present application has no impurity phase, and the improvement in the performance of the secondary battery mainly comes from element doping, rather than impurity phase.
  • the shell includes multiple coating layers, and each coating layer independently includes one or more of phosphate MPO 4 , borate X a B b O c and carbon.
  • the shell includes a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, the third coating layer contains carbon, and the first coating layer includes phosphate MPO 4 , the second coating layer includes borate X a B b O c , or the first coating layer includes borate X a B b O c , and the second coating layer includes phosphate MPO 4 .
  • the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, and can be optionally 1% to 5% by weight, based on the weight of the core.
  • the coating amount of the second coating layer is greater than 0 and less than or equal to 6 weight %, and can be optionally 1 weight % to 5 weight %, based on the weight of the core.
  • the coating amount of the first coating layer and/or the second coating layer is within the above range, the impurity lithium content can be reduced, the dissolution of manganese ions can be inhibited, and the transmission of lithium ions and electrons can be promoted; in addition, the cycle performance and storage performance of the secondary battery can be further improved without sacrificing the gram capacity of the positive electrode active material.
  • the coating amount of the first coating layer and/or the second coating layer is too small, it may lead to insufficient inhibition of manganese ion dissolution, and the improvement of lithium ion and electron transmission performance is not significant; if the coating amount of the first coating layer and/or the second coating layer is too large, it may cause the coating layer to be too thick as a whole, increase the battery impedance, and affect the kinetic performance of the secondary battery. At the same time, because the coating layer does not provide capacity, excessive coating will reduce the gram capacity of the positive electrode active material.
  • the total coating amount of the first coating layer and the second coating layer is greater than 0 and less than or equal to 7% by weight, and optionally 4% to 5.6% by weight, based on the weight of the core.
  • the coating amount of the third coating layer is greater than 0 and less than or equal to 6% by weight, optionally 1% to 6% by weight, and more optionally 2% to 5% by weight, based on the weight of the kernel.
  • the carbon-containing layer can play a "barrier" function on the one hand, avoiding direct contact between the positive electrode active material and the electrolyte, thereby reducing the erosion of the electrolyte on the positive electrode active material and improving the safety performance of the secondary battery at high temperatures.
  • it has a strong electrical conductivity, which can reduce the battery impedance, thereby improving the kinetic performance of the secondary battery.
  • the coating amount of the third coating layer is within the above range, the kinetic performance and safety performance of the secondary battery can be further improved without sacrificing the gram capacity of the positive electrode active material.
  • the first coating layer includes phosphate MPO 4
  • the second coating layer includes borate X a B b O c
  • the third coating layer includes carbon
  • the first coating layer may optionally include phosphate, which has excellent lithium ion conductivity and can reduce the surface impurity lithium content.
  • the second coating layer may optionally include borate, which has excellent lithium ion conductivity and electron conductivity, and can reduce the surface impurity lithium content and inhibit the dissolution of manganese ions, thereby reducing the interface side reaction and reducing the gas production, and improving the cycle performance.
  • the main reason for selecting borate as the second coating layer is that compared with phosphate, its surface activity is lower, thereby further reducing the surface impurity lithium content, reducing the decomposition of the electrolyte, and further inhibiting the dissolution of manganese ions.
  • the third coating layer is a carbon-containing layer, so it can effectively improve the conductivity and desolvation ability of the positive electrode active material.
  • the third coating layer is located in the outermost layer, and its "barrier" effect can further hinder the migration of manganese ions into the electrolyte and reduce the erosion of the electrolyte on the positive electrode active material. Therefore, the positive electrode sheet and electrical devices such as secondary batteries using the positive electrode active material of the present application can have improved cycle performance, safety performance, and/or rate performance.
  • the first coating layer includes phosphate MPO 4 , and the coating amount of the first coating layer is greater than 0 and less than or equal to 6% by weight, optionally 1% to 5% by weight, and more optionally 1% to 3% by weight, based on the weight of the core.
  • the coating amount of the first coating layer is within the above range, it can reduce the content of impurities of lithium, inhibit the dissolution of manganese ions, and promote the transmission of lithium ions.
  • the coating amount of the first coating layer is too small, it may lead to insufficient inhibition of manganese ion dissolution, and at the same time, the improvement of lithium ion transmission performance is not significant; if the coating amount of the first coating layer is too large, it may cause the coating layer to be too thick, increase the battery impedance, and affect the dynamic performance of the secondary battery.
  • the second coating layer includes borate XaBbOc , and the coating amount of the second coating layer is greater than 0 and less than or equal to 6% by weight, optionally 1% to 5% by weight, and more optionally 2% to 5% by weight, based on the weight of the core.
  • the coating amount of the second coating layer is within the above range, the dissolution of manganese ions can be further suppressed, and the transmission of lithium ions and electrons can be further promoted.
  • the coating amount of the second coating layer is too small, it may lead to insufficient inhibition of manganese ion dissolution, and the improvement of lithium ion and electron transmission performance is not significant; if the coating amount of the second coating layer is too large, it may cause the coating layer to be too thick, increase the battery impedance, and affect the kinetic performance of the secondary battery. At the same time, because the coating layer does not provide capacity, excessive coating will reduce the gram capacity of the positive electrode active material. Therefore, when the coating amount of the second coating layer is within the above range, the cycle performance and storage performance of the secondary battery can be further improved without sacrificing the gram capacity of the positive electrode active material.
  • the weight ratio of the phosphate MPO 4 to the borate X a B b O c is 1: 3 to 3: 1, and optionally 1: 3 to 1: 1.
  • the appropriate ratio of phosphate and borate is conducive to giving full play to the synergistic effect of the two, which can effectively hinder the dissolution of manganese ions, effectively reduce the surface impurity lithium content, and reduce interface side reactions.
  • m is selected from the range of 0.900 to 1.100, for example, m can be 0.900, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 1.000, 1.001, 1.002, 1.003, 1.004, 1.005, 1.006.
  • m is selected from the range of 0.900 to 1.006.
  • the x is selected from the range of 0 to 0.100, for example, 0, 0.001, 0.005.
  • the x is selected from the range of 0.001 to 0.1, 0.001 to 0.005.
  • y is selected from the range of 0.001 to 0.500, for example, y may be 0.100, 0.200, 0.250, 0.300, 0.350, 0.400, 0.450. Optionally, y is selected from the range of 0.100 to 0.450.
  • z is selected from the range of 0.001 to 0.100, for example, z can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.100.
  • n is selected from the range of 0 to 0.100, for example, 0, 0.001, 0.005, 0.08, 0.1.
  • n is selected from the range of 0.001 to 0.1, 0.001 to 0.005.
  • the x is selected from the range of 0 to 0.100
  • the n is selected from the range of 0 to 0.100, that is, the Li position and the O position of the lithium manganese phosphate may be undoped or doped.
  • the x is selected from the range of 0.001 to 0.100, that is, the element A is doped at the Li position of the lithium manganese phosphate.
  • the n is selected from the range of 0.001 to 0.100, that is, the element D is doped at the O position of the lithium manganese phosphate.
  • the x is selected from the range of 0.001 to 0.100
  • the n is selected from the range of 0.001 to 0.1, that is, the Li position and the O position of the lithium manganese phosphate are doped at the same time.
  • the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1.
  • y represents the sum of the stoichiometric numbers of the doping elements at the Mn position.
  • the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249.
  • y represents the sum of the stoichiometric coefficients of the P-site doping elements.
  • the A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W.
  • the Li-site doping element within the above range, the lattice change rate can be further reduced, thereby further improving the rate performance of the secondary battery.
  • the B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, more optionally, the B includes one or more elements selected from Fe, Ti, V, Ni, Co and Mg, and further optionally, the B includes at least two elements selected from Fe, Ti, V, Ni, Co and Mg.
  • Simultaneous doping of two or more of the above elements at the Mn position in the lithium manganese phosphate positive electrode active material is conducive to enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese ions and reducing the consumption of electrolyte and active lithium ions. On the other hand, it is also conducive to further reducing the surface oxygen activity and reducing the interface side reaction between the positive electrode active material and the electrolyte, thereby improving the cycle performance and high temperature storage performance of the secondary battery.
  • the C includes one or more elements selected from B (boron), S, Si and N.
  • the D includes one or more elements selected from S, F, Cl and Br.
  • the M includes one or more selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al.
  • X includes one or more selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al.
  • b:c is 1:3.
  • the interplanar spacing of the phosphate MPO 4 is 0.345 nm to 0.358 nm, and the angle of the crystal direction (111) is 24.25° to 26.45°.
  • the interplanar spacing of the phosphate MPO 4 and the angle of the crystal direction (111) are within the above range, the impurity phase in the coating layer can be effectively avoided, thereby increasing the gram capacity of the positive electrode active material and improving the cycle performance and rate performance of the secondary battery.
  • the crystallinity of the phosphate MPO 4 is 10% to 100%, optionally 50% to 100%; and/or, the crystallinity of the borate XaBbOc is 10% to 100%, optionally 50% to 100%.
  • Phosphates and borates with a certain degree of crystallinity are conducive to maintaining the structural stability of the coating layer and reducing lattice defects. On the one hand, this is conducive to giving full play to the role of phosphates in reducing the content of surface impurities and reducing the valence state of surface oxygen.
  • the crystallinity of phosphate and borate can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature, sintering time, etc.
  • the crystallinity of phosphate and borate can be measured by methods known in the art, such as X-ray diffraction, density method, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption method.
  • the Li/Mn antisite defect concentration of the positive electrode active material is less than 4%, optionally less than 2%.
  • Li/Mn antisite defects refer to the positions of Li + and Mn2 + in the LiMnPO4 lattice.
  • the Li/Mn antisite defect concentration refers to the percentage of Li + that is interchanged with Mn2 + in the total amount of Li + in the positive electrode active material. Since the Li + transport channel is a one-dimensional channel, Mn2 + is difficult to migrate in the Li + transport channel, and therefore, the antisite defect Mn2 + will hinder the transmission of Li + .
  • the antisite defect concentration can be determined, for example, according to JIS K0131-1996.
  • the lattice change rate of the positive electrode active material is 8% or less, optionally 6% or less, and more optionally 4% or less.
  • the lithium insertion and extraction process of LiMnPO 4 is a two-phase reaction.
  • the interfacial stress of the two phases is determined by the lattice change rate. The smaller the lattice change rate, the smaller the interfacial stress, and the easier the Li + transmission. Therefore, reducing the lattice change rate of the core will help enhance the transmission capacity of Li + , thereby improving the rate performance of the secondary battery.
  • the positive electrode active material may have an average discharge voltage of 3.5V or more, and a discharge capacity in grams of 140mAh/g or more; and may have an average discharge voltage of 3.6V or more, and a discharge capacity in grams of 145mAh/g or more.
  • the average discharge voltage of undoped LiMnPO 4 is above 4.0V, its discharge capacity in grams is relatively low, usually less than 120mAh/g, and therefore the energy density of the secondary battery is relatively low; by adjusting the lattice change rate through doping, the discharge capacity in grams can be greatly increased, and the overall energy density of the secondary battery can be significantly increased with a slight decrease in the average discharge voltage.
  • the surface oxygen valence of the positive electrode active material is below -1.88, and can be optionally -1.98 to -1.88. This is because the higher the valence of oxygen in the compound, the stronger its electron-accepting ability, that is, the stronger its oxidizing property.
  • the surface valence of oxygen in the compound the stronger its electron-accepting ability, that is, the stronger its oxidizing property.
  • the reactivity of the surface of the positive electrode active material can be reduced, and the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high temperature storage performance of the secondary battery.
  • the compaction density of the positive electrode active material at 3 tons (T) is 2.0 g/cm 3 or more, and optionally 2.2 g/cm 3 or more.
  • the compaction density can be determined, for example, according to GB/T 24533-2009.
  • the second aspect of the present application provides a method for preparing the positive electrode active material of the first aspect of the present application, which includes the following steps of providing a core material and a coating step.
  • the step of providing a core material comprises LimAxMn1-yByP1-zCzO4 - nDn , the A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, Si and N one or more elements, the D includes one or more elements selected from Group VIA and Group VIIA, optionally including one or more elements selected
  • Coating step providing coating solutions comprising phosphate MPO 4 , borate X a B b O c and a carbon source respectively, adding the core material into the coating solution and mixing, and sintering to obtain a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising phosphate MPO 4 , borate X a B b O c and carbon, and the shell comprising one or more coating layers, each coating layer independently comprising phosphate MPO 4 , borate X a B b O c and carbon.
  • the M comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al
  • the X comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al
  • the a is selected from the range of 1 to 4
  • the b is selected from the range of 1 to 7
  • the c is selected from the range of 2 to 12
  • the values of a, b and c satisfy the following condition: the borate XaBbOc is kept electrically neutral.
  • the preparation method of the present application has no particular restrictions on the source of the core material.
  • the core material in the preparation method of the present application can be commercially available, or can be prepared by the method of the present application.
  • the core material is prepared by the method described below.
  • the step of providing the core material comprises the following steps: step (1): mixing and stirring a manganese source, a source of element B and an acid in a container to obtain manganese salt particles doped with element B; step (2): mixing the manganese salt particles doped with element B with a source of lithium, a source of phosphorus, a source of element C, an optional source of element A and an optional source of element D in a solvent to obtain a slurry, and sintering under the protection of an inert gas atmosphere to obtain the core material.
  • the step (1) is performed at a temperature of 20°C to 120°C, optionally 25°C to 80°C.
  • the stirring in step (1) is performed at 500 rpm to 700 rpm for 60 minutes to 420 minutes, and optionally 120 minutes to 360 minutes.
  • the doping elements By controlling the reaction temperature, stirring rate and mixing time during doping, the doping elements can be evenly distributed, lattice defects can be reduced, manganese ion dissolution can be inhibited, and the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the gram capacity and rate performance of the positive electrode active material.
  • the source of a certain element may include one or more of the element's simple substance, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide, provided that the source can achieve the purpose of the preparation method of the present application.
  • the source of manganese is selected from one or more of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.
  • the source of element A is selected from one or more of element A, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide.
  • the source of element B is selected from one or more of a simple substance, carbonate, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide of element B.
  • element B is iron, and optionally, the source of iron is selected from one or more of ferrous carbonate, ferric hydroxide and ferrous sulfate.
  • the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acids such as oxalic acid, etc., and can be oxalic acid.
  • the acid is a dilute acid with a concentration of 60% by weight or less.
  • the source of element C is selected from one or more of a simple substance, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide and inorganic acid of element C.
  • the inorganic acid of element C is selected from one or more of phosphoric acid, nitric acid, sulfuric acid, boric acid, silicic acid and orthosilicic acid.
  • the source of element D is selected from one or more of a simple substance of element D and an ammonium salt.
  • the source of lithium is selected from one or more of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.
  • the source of phosphorus is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and phosphoric acid.
  • the solvent used is a solvent commonly used in the art, for example, at least one selected from ethanol and water (eg, deionized water).
  • the pH of the solution is controlled to be 4 to 6. It should be noted that in the present application, the pH of the obtained mixture can be adjusted by methods commonly used in the art, for example, by adding acid or base.
  • step (2) the molar ratio of the manganese salt particles doped with element B to the lithium source and the phosphorus source is 1:(0.5-2.1):(0.5-2.1).
  • the amount of each source of elements A, B, C, D added may depend on the target doping amount.
  • the sintering conditions are: sintering at 600°C to 800°C for 4 to 10 hours in an inert gas or a mixed atmosphere of inert gas and hydrogen.
  • the crystallinity of the sintered material is higher, thereby improving the gram capacity and rate performance of the positive electrode active material.
  • the mixture of inert gas and hydrogen is nitrogen (70% to 90% by volume) + hydrogen (10% to 30% by volume).
  • the carbon source is an organic carbon source, and the organic carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
  • the coating step includes a step of coating phosphate MPO 4 , a step of coating borate XaBbOc , and a step of coating carbon in an optional order.
  • the specific coating order of the above coating steps is not specifically limited and can be adaptively adjusted according to the specific structure of the shell of the desired positive electrode active material.
  • the step of coating phosphate MPO 4 includes the following steps: providing a coating solution containing phosphate MPO 4 , adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain a material coated with phosphate MPO 4.
  • the material to be coated can be a core material, a material coated with one coating layer, or a material coated with two coating layers according to actual conditions.
  • the step of coating the borate XaBbOc comprises the following steps: providing a coating solution containing the borate XaBbOc , then adding the material to be coated into the coating solution, mixing evenly, drying, and then sintering to obtain the material coated with the borate XaBbOc .
  • the material to be coated can be a core material, a material coated with one coating layer , or a material coated with two coating layers according to actual conditions.
  • the step of coating carbon includes the following steps: providing a coating liquid containing a carbon source, then adding the material to be coated into the coating liquid, mixing evenly, drying, and then sintering to obtain a carbon-coated material.
  • the material to be coated can be a core material, a material coated with a coating layer, or a material coated with two coating layers according to actual conditions.
  • the first coating step is a step of coating borate XaBbOc
  • the second coating step is a step of coating phosphate MPO4
  • the third coating step is a step of coating carbon
  • the positive electrode active material obtained has a core-shell structure, comprising the core and a shell coating the core, the shell comprising a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer
  • the first coating layer comprises borate XaBbOc
  • the second coating layer comprises phosphate MPO4
  • the third coating layer comprises carbon
  • the first coating step is a step of coating phosphate MPO 4
  • the second coating step is a step of coating borate X a B b O c
  • the third coating step is a step of coating carbon.
  • the positive electrode active material thus obtained has a core-shell structure, which includes the core and a shell coating the core, the shell includes a first coating layer coating the core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer
  • the first coating layer includes phosphate MPO 4
  • the second coating layer includes borate X a B b O c
  • the third coating layer contains carbon.
  • the solvent used is a solvent commonly used in the art.
  • the solvent can be independently selected from at least one of ethanol and water (eg, deionized water).
  • the drying can be carried out at a drying temperature of 100°C to 200°C, optionally 110°C to 190°C, more optionally 120°C to 180°C, even more optionally 120°C to 170°C, most optionally 120°C to 160°C, and the drying time is 3 hours to 9 hours, optionally 4 hours to 8 hours, more optionally 5 hours to 7 hours, and most optionally about 6 hours.
  • the coating solution containing phosphate MPO 4 is commercially available, or alternatively, prepared by the following method: adding a source of element M and a source of phosphorus to a solvent, stirring evenly to obtain a mixture, and then heating the mixture to 60°C to 120°C for 2 to 8 hours to obtain a coating solution.
  • the pH of the mixture is 4 to 6. It should be noted that in the present application, the pH of the mixture can be adjusted by methods commonly used in the art, for example, by adding an acid or a base.
  • the source of element M is selected from one or more of a simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element M.
  • the source of phosphorus is selected from one or more of diammonium hydrogen phosphate, diammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.
  • the coating solution containing the borate XaBbOc is commercially available, or alternatively, prepared by the following method: adding a source of element X and a source of boron to a solvent, stirring evenly , to obtain a coating solution.
  • the source of element X is selected from one or more of a simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element X.
  • the source of boron is selected from one or more of boric acid, borate, and boron oxide.
  • the sintering in the step of coating phosphate MPO 4 is sintering at 500°C to 800°C for 4 to 10 hours.
  • the sintering can be sintered at about 500°C, about 600°C, about 700°C or about 800°C for about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, the sintering temperature and sintering time can be within any range of the above values.
  • the sintering temperature in the step of coating phosphate MPO 4 is too low and the sintering time is too short, the phosphate MPO 4 will have low crystallinity and more amorphous state, and at the same time its coating effect is poor, the inhibition of manganese ion dissolution is insufficient, and the improvement of lithium ion transmission performance is not significant; when the sintering temperature is too high and the sintering time is too long, the thickness of the formed coating layer will increase, the battery impedance will increase, and the kinetic performance and energy density of the secondary battery will be affected.
  • the sintering in the step of coating the borate XaBbOc is sintering at 300°C to 500°C for 2 hours to 10 hours.
  • the sintering may be sintered at about 300°C, about 350° C , about 400°C, about 450°C or about 500°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; alternatively, the sintering temperature and sintering time may be within any range of the above values.
  • the sintering temperature in the step of coating the borate XaBbOc is too low and the sintering time is too short, the borate XaBbOc will have low crystallinity and more amorphous state, and its coating effect will be poor, the inhibition of manganese ion dissolution will be insufficient, and the improvement of lithium ion and electron transport performance will not be significant; when the sintering temperature is too high and the sintering time is too long, the thickness of the formed coating layer will increase, the battery impedance will increase, and the kinetic performance and energy density of the secondary battery will be affected.
  • the sintering in the step of coating carbon is sintering at 500° C. to 800° C. for 4 to 10 hours.
  • the sintering may be sintered at about 500° C., about 600° C., about 700° C. or about 800° C. for about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; alternatively, the sintering temperature and sintering time may be within any range of the above values.
  • the following situations can be avoided: when the sintering temperature in the step of coating the carbon is too low, the graphitization degree of the carbon material will decrease, affecting its conductivity, thereby affecting the specific capacity of the positive electrode active material; when the sintering temperature is too high, the graphitization degree of the carbon material will be too high, affecting the transmission of Li + , thereby affecting the specific capacity of the positive electrode active material, etc.; when the sintering time is too short, the formed coating layer will be too thin, affecting its conductivity, thereby affecting the specific capacity of the positive electrode active material; when the sintering time is too long, the formed coating layer will be too thick, affecting the compaction density of the positive electrode active material, etc.
  • the median particle size Dv50 of the primary particles of the core-shell structured lithium manganese phosphate positive electrode active material of the present application is 50 nm to 2000 nm.
  • the third aspect of the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application, and the content of the positive electrode active material in the positive electrode film layer is 10% by weight or more, and can be 90% by weight to 99.5% by weight, based on the total weight of the positive electrode film layer.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer does not exclude other positive electrode active materials other than the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application.
  • the positive electrode film layer may also include other positive electrode active materials other than the above-mentioned positive electrode active materials of the present application.
  • the other positive electrode active materials may include at least one of lithium transition metal oxides and modified compounds thereof.
  • the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.
  • the positive electrode film layer may further include a positive electrode conductive agent.
  • a positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode film layer may further include a positive electrode binder.
  • the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly.
  • the solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the fourth aspect of the present application provides a secondary battery, which includes the positive electrode plate of the third aspect of the present application.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be used continuously by recharging the active materials after the battery is discharged.
  • secondary batteries include electrode assemblies and electrolytes, and the electrode assemblies include positive electrode sheets, negative electrode sheets, and separators.
  • the separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.
  • the electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.
  • the secondary battery mentioned in the embodiments or implementations of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity.
  • the secondary battery mentioned in the present application may include a battery cell, a battery module or a battery pack, etc.
  • a battery cell is the smallest unit that makes up a secondary battery, which can realize the function of charging and discharging alone.
  • the present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape.
  • Figure 1 is a battery cell 5 of a square structure as an example.
  • the battery cell includes an electrode assembly, and the single cell may further include an outer package.
  • the electrode assembly may be made of a positive electrode sheet, a negative electrode sheet, and a separator, etc., by a winding process and/or a lamination process, and the outer package may be used to encapsulate the above-mentioned electrode assembly.
  • the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer package may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.
  • battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 3, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can be further fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • Figures 4 and 5 are schematic diagrams of a battery pack 1 as an example.
  • 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 body 2 and a lower box body 3, and the upper box body 2 is used to cover the lower box body 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 positive electrode plate used in the secondary battery of the present application is the positive electrode plate described in any embodiment of the third aspect of the present application.
  • 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 and including a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its 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 active material may be a negative electrode active material for a secondary battery known in the art.
  • the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.
  • the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material.
  • the tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.
  • the present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a negative electrode conductive agent.
  • a negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the negative electrode film layer may further include a negative electrode binder.
  • the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • the negative electrode film layer may further include other additives.
  • the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing.
  • the negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them uniformly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode plate described in the present application also includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.
  • the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.
  • the present application has no specific limitation on the type of the electrolyte, which can be selected according to the needs.
  • the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, an electrolyte solution).
  • the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.
  • the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiC
  • the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (MSM), ethyl methyl sulfone (MSM), ethy
  • the electrolyte may further include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include a separator.
  • the separator is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.
  • the present application has no particular restrictions on the type of the separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After vacuum packaging, standing, forming, shaping and other processes, a battery cell is obtained.
  • Multiple battery cells can also be further connected in series, in parallel or in mixed connection to form a battery module.
  • Multiple battery modules can also be connected in series, in parallel or in mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.
  • the fifth aspect of the present application provides an electrical device, which includes the secondary battery of the present application.
  • the secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device.
  • the electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • the electrical device may select a specific type of secondary battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.
  • Fig. 6 is a schematic diagram of an electric device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used as a power source.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the electric device is usually required to be light and thin, and a battery cell may be used as a power source.
  • the reactor was heated to 80°C and stirred at a speed of 600rpm for 6 hours until the reaction was terminated (no bubbles were generated), to obtain a co-doped manganese oxalate suspension.
  • the suspension was then filtered, the filter cake was dried at 120°C, and then ground to obtain co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100nm.
  • Preparation of co-doped lithium manganese phosphate Add the dihydrate manganese oxalate particles (1793.4 g) obtained in the previous step, 369.0 g lithium carbonate (calculated as Li 2 CO 3 , the same below), 1.6 g dilute sulfuric acid with a concentration of 60% (calculated as 60% H 2 SO 4 , the same below) and 1148.9 g diammonium phosphate (calculated as NH 4 H 2 PO 4 , the same below) to 20 liters of deionized water, and stir the mixture for 10 hours to mix it evenly to obtain a slurry.
  • the slurry is transferred to a spray drying device for spray drying and granulation, the drying temperature is set to 250° C., and dried for 4 hours to obtain a powder.
  • a nitrogen (90 volume %) + hydrogen (10 volume %) protective atmosphere the above powder is sintered at 700° C. for 4 hours to obtain 1572.1 g of co-doped lithium manganese phosphate, i.e., the core.
  • the material coated with the first coating layer is added to the coating liquid of the second coating layer, stirred and mixed evenly, and then transferred to a vacuum oven and dried at 150°C for 6 hours, and then the obtained product is dispersed by sand milling, and then the obtained product is sintered at 400°C for 10 hours to obtain a material coated with two coating layers.
  • sucrose was dissolved in 500 ml of deionized water, and then stirred and fully dissolved to obtain a third coating layer coating solution.
  • the material coated with the above two coating layers is added to the coating liquid of the third coating layer, stirred and mixed evenly, and then transferred to a vacuum oven and dried at 150°C for 6 hours, and then sintered at 700°C in a nitrogen atmosphere for 6 hours to obtain a material coated with three coating layers, i.e., the positive electrode active material.
  • the positive electrode active material, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) prepared above were added to N-methylpyrrolidone (NMP) at a weight ratio of 92:2.5:5.5, and stirred and mixed to obtain positive electrode slurry. Then, the positive electrode slurry was evenly coated on aluminum foil at a coating surface density of 0.018g/ cm2 , and dried, cold pressed and cut to obtain positive electrode sheets.
  • NMP N-methylpyrrolidone
  • the negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) were dissolved in solvent deionized water at a weight ratio of 90:5:2:2:1, and stirred and mixed to prepare negative electrode slurry.
  • the negative electrode slurry was evenly coated on the negative electrode current collector copper foil at a coating surface density of 0.0075g/ cm2 , and the negative electrode sheet was obtained after drying, cold pressing and slitting.
  • ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3:7 as organic solvents, 12.5 wt% (based on the weight of the organic solvent) of LiPF6 was added and dissolved in the organic solvent, and stirred uniformly to obtain an electrolyte.
  • a commercially available PP-PE copolymer microporous film (from Zhuogao Electronic Technology Co., Ltd., Model 20) with a thickness of 20 ⁇ m and an average pore size of 80 nm was used.
  • the positive electrode sheet, separator, and negative electrode sheet obtained above are stacked in order, with the separator placed between the positive and negative electrodes to play a role of isolation, and then wound to obtain an electrode assembly.
  • the electrode assembly is placed in an outer package, injected with the above electrolyte and packaged to obtain a full battery (hereinafter also referred to as "full battery").
  • the positive electrode active material prepared above, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and stirred in a drying room to form a slurry.
  • NMP N-methylpyrrolidone
  • the slurry was coated on aluminum foil, dried, and cold pressed to form a positive electrode sheet.
  • the coating surface density was 0.015g/ cm2
  • the compaction density was 2.0g/ cm3 .
  • a lithium sheet was used as the negative electrode, and a solution of 1 mol/L LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 are the same as those in Example 1-1, except that vanadium dichloride and cobalt sulfate are not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used.
  • Example 1-7 to 1-10 are the same as those of Example 1-3, except that the amounts of sucrose used are 74.6 g, 149.1 g, 186.4 g and 223.7 g, respectively, so that the corresponding coating amounts of the carbon layer as the third coating layer are 31.4 g, 62.9 g, 78.6 g and 94.3 g, respectively.
  • Example 1-11 to 1-14 are the same as those of Example 1-7, except that the amounts of various raw materials are adjusted according to the coating amounts shown in Table 1 so that the amounts of LiFePO 4 /Li 3 BO 3 are 23.6 g/39.3 g, 31.4 g/31.4 g, 39.3 g/23.6 g and 47.2 g/15.7 g, respectively.
  • Example 1-15 The conditions of Example 1-15 were the same as those of Example 1-14, except that 492.80 g of zinc carbonate was used instead of ferrous carbonate during the preparation of the co-doped lithium manganese phosphate core.
  • Example 1-16 to 1-18 are the same as those of Example 1-7, except that Example 1-16 uses 466.4 g of nickel carbonate, 5.0 g of zinc carbonate and 7.2 g of titanium sulfate instead of ferrous carbonate in the preparation process of the co-doped lithium manganese phosphate core, Example 1-17 uses 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride in the preparation process of the co-doped lithium manganese phosphate core, and Example 1-18 uses 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride and 2.5 g of magnesium carbonate in the preparation process of the co-doped lithium manganese phosphate core.
  • Example 1-19 Except that in Example 1-19, 369.4 g of lithium carbonate and 1.05 g of 60% dilute nitric acid were used instead of dilute sulfuric acid in the preparation process of the co-doped lithium manganese phosphate core, and in Example 1-20, 369.7 g of lithium carbonate and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation process of the co-doped lithium manganese phosphate core, the conditions of Examples 1-19 to 1-20 were the same as those of
  • Example 1-21 uses 632.0g of manganese carbonate, 463.30g of ferrous carbonate, 30.5g of vanadium dichloride, 21.0g of magnesium carbonate and 0.78g of silicic acid in the preparation process of the co-doped lithium manganese phosphate core; and Example 1-22 uses 746.9g of manganese carbonate, 289.6g of ferrous carbonate, 60.9g of vanadium dichloride, 42.1g of magnesium carbonate and 0.78g of silicic acid in the preparation process of the co-doped lithium manganese phosphate core, the conditions of Examples 1-21 to 1-22 are the same as those of Example 1-20.
  • Example 1-23 uses 804.6g manganese carbonate, 231.7g ferrous carbonate, 1156.2g ammonium dihydrogen phosphate, 1.2g boric acid (mass fraction 99.5%) and 370.8g lithium carbonate in the preparation process of the co-doped manganese phosphate lithium core; and
  • Example 1-24 uses 862.1g manganese carbonate, 173.8g ferrous carbonate, 1155.1g ammonium dihydrogen phosphate, 1.86g boric acid (mass fraction 99.5%) and 371.6g lithium carbonate in the preparation process of the co-doped manganese phosphate lithium core, the conditions of Examples 1-23 to 1-24 are the same as those of Example 1-22.
  • Example 1-25 The conditions of Example 1-25 are the same as those of Example 1-20, except that 370.1 g of lithium carbonate, 1.56 g of silicic acid and 1147.7 g of diammonium phosphate are used in the preparation process of the co-doped lithium manganese phosphate core of Example 1-25.
  • Example 1-26 The conditions of Example 1-26 are the same as those of Example 1-20, except that 368.3 g of lithium carbonate, 4.9 g of 60% by mass dilute sulfuric acid, 919.6 g of manganese carbonate, 224.8 g of ferrous carbonate, 3.7 g of vanadium dichloride, 2.5 g of magnesium carbonate and 1146.8 g of diammonium phosphate are used in the preparation process of the co-doped lithium manganese phosphate core in Example 1-26.
  • Example 1-27 The conditions of Example 1-27 are the same as those of Example 1-20, except that 367.9 g of lithium carbonate, 6.5 g of 60% dilute sulfuric acid and 1145.4 g of diammonium phosphate are used in the preparation process of the co-doped lithium manganese phosphate core in Example 1-27.
  • Examples 1-28 to 1-33 Except that 1034.5g of manganese carbonate, 108.9g of ferrous carbonate, 3.7g of vanadium dichloride and 2.5g of magnesium carbonate are used in the preparation process of the co-doped lithium manganese phosphate core in Examples 1-28 to 1-33, the amounts of lithium carbonate used are 367.6g, 367.2g, 366.8g, 366.4g, 366.0g and 332.4g, the amounts of diammonium dihydrogen phosphate used are 1144.5g, 1143.4g, 1142.2g, 1141.1g, 1139.9g and 1138.8g, and the amounts of dilute sulfuric acid with a concentration of 60% are 8.2g, 9.8g, 11.4g, 13.1g, 14.7g and 16.3g, respectively.
  • the conditions of Examples 1-28 to 1-33 are the same as those of Example 1-20.
  • Example 1-34 are the same as those of Example 1-1, except that coating with the second coating layer in Example 1-1 is first performed and then coating with the first coating layer in Example 1-1 is performed in the preparation of the positive electrode active material.
  • Example 1-35 The conditions of Example 1-35 are the same as those of Example 1-1, except that 3.84 g of molybdenum sulfate (calculated as Mo(SO 4 ) 3 ) and 0.57 g of ammonium bifluoride (calculated as NH 4 HF 2 ) are added in the preparation of the co-doped lithium manganese phosphate core.
  • Comparative Example 2 Except for using 689.5 g of manganese carbonate and additionally adding 463.3 g of ferrous carbonate, other conditions of Comparative Example 2 are the same as those of Comparative Example 1.
  • Comparative Example 3 The other conditions of Comparative Example 3 are the same as those of Comparative Example 1, except that 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used, and 1.6 g of 60% strength dilute sulfuric acid is additionally added.
  • Comparative Example 4 The other conditions of Comparative Example 4 are the same as those of Comparative Example 1 except that 689.5 g of manganese carbonate, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used, and 463.3 g of ferrous carbonate and 1.6 g of 60% concentrated dilute sulfuric acid are additionally added.
  • Coating of the first coating layer 3.7g lithium carbonate, 11.6g ferrous carbonate, 11.5 diammonium phosphate, and 12.6g dihydrated oxalic acid were dissolved in 500mL deionized water, and then stirred for 6 hours to allow the mixture to react fully, and then the reacted solution was heated to 120°C and maintained at this temperature for 6 hours to obtain a first coating layer suspension.
  • the sintering temperature in the coating sintering step was 600°C, and the sintering time was 4 hours to control the crystallinity of LiFePO 4 to 8%.
  • Coating of the second coating layer 42.4 g lithium hydroxide and 20.6 g boron oxide were added to 500 mL deionized water to obtain a second coating layer coating solution.
  • the coating sintering step only drying treatment was performed without high temperature sintering treatment, so that the crystallinity of Li 3 BO 3 was 5%.
  • the internal microstructure and surface structure of the positive electrode active material were characterized with high spatial resolution using spherical aberration electron microscopy (ACSTEM), and the core chemical formula of the positive electrode active material and the composition of the first coating layer and the second coating layer were obtained using three-dimensional reconstruction technology.
  • ACSTEM spherical aberration electron microscopy
  • the button cell prepared above was charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V until the current was less than or equal to 0.05mA, left to stand for 5 minutes, and then discharged to 2.0V at 0.1C.
  • the discharge capacity at this time was the initial gram capacity, recorded as D0.
  • the button battery prepared as above was placed in a constant temperature environment of 25°C, left standing for 5 minutes, discharged to 2.5V at 0.1C, left standing for 5 minutes, charged to 4.3V at 0.1C, then charged at a constant voltage at 4.3V until the current was less than or equal to 0.05mA, and left standing for 5 minutes; then discharged to 2.5V at 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 button battery is E0/D0.
  • the prepared full battery at 100% state of charge (SOC) was stored at 60°C.
  • the open circuit voltage (OCV) and AC internal resistance (IMP) of the battery were measured before, during and after storage to monitor the SOC, and the volume of the battery was measured.
  • the full battery was taken out after each 48 hours of storage, and the open circuit voltage (OCV) and internal resistance (IMP) were tested after standing for 1 hour, and the battery volume was measured by the water displacement method after cooling to room temperature.
  • the water displacement method is to first measure the gravity F1 of the battery separately using a balance that automatically converts the dial data, and then completely place the battery in deionized water (density is known to be 1g/ cm3 ), and measure the gravity F2 of the battery at this time.
  • the batteries of all embodiments maintained a SOC of more than 99% throughout the test until the end of storage.
  • the full battery prepared above was charged to 4.3V at 1C, and then charged at a constant voltage at 4.3V until the current was less than or equal to 0.05mA. After standing for 5 minutes, it was discharged to 2.5V at 1C, and the discharge capacity at this time was recorded as D0. The above charge and discharge cycle was repeated until the discharge capacity was reduced to 80% of D0. The number of cycles the battery had gone through was recorded at this time.
  • the full battery is discharged at a rate of 0.1C to a cut-off voltage of 2.0V. Then the battery is disassembled, the negative electrode plate is taken out, and 30 discs of unit area (1540.25 mm2 ) are randomly selected from the negative electrode plate and tested by inductively coupled plasma emission spectroscopy (ICP) using Agilent ICP-OES730. According to the ICP results, the amount of Fe (if the Mn position of the positive electrode active material is doped with Fe) and Mn is calculated, thereby calculating the dissolution amount of Mn (and Fe doped at the Mn position) after cycling.
  • the test standard is based on EPA-6010D-2014.
  • the positive electrode active material samples prepared above were placed in XRD (model: Bruker D8 Discover), and the samples were tested at 1°/min.
  • the test data were sorted and analyzed, and the lattice constants a0, b0, c0 and v0 were calculated with reference to the standard PDF card (a0, b0 and c0 represent the lengths of the unit cell in each direction, v0 represents the unit cell volume, which can be directly obtained through the XRD refinement results).
  • the positive electrode active material sample is prepared into a button battery by the above-mentioned button battery preparation method, and the button battery is charged at a small rate of 0.05C until the current is reduced to 0.01C. Then the positive electrode plate in the button battery is taken out and immersed in dimethyl carbonate (DMC) for 8 hours. Then it is dried, powdered, and particles with a particle size of 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 the fresh sample, and (v0-v1)/v0 ⁇ 100% is shown in the table as the lattice change rate (unit cell volume change rate) before and after complete lithium deintercalation.
  • DMC dimethyl carbonate
  • the XRD results tested in the "lattice change rate measurement method” are compared with the PDF (Powder Diffraction File) card of the standard crystal to obtain the Li/Mn antisite defect concentration.
  • the XRD results tested in the "lattice change rate measurement method” are imported into the General Structural Analysis System (GSAS) software to automatically obtain the refinement results, which include the occupancy of different atoms.
  • the Li/Mn antisite defect concentration is obtained by reading the refinement results.
  • the buckle battery takes 5g of the above-prepared positive electrode active material sample and prepare it into a buckle battery according to the above-mentioned buckle battery preparation method.
  • the buckle battery is charged at a small rate of 0.05C until the current decreases to 0.01C.
  • DMC dimethyl carbonate
  • the obtained particles are measured by electron energy loss spectroscopy (EELS, the instrument model used is Talos F200S) to obtain the energy loss near edge structure (ELNES), which reflects the state density and energy level distribution of the element.
  • ELNES energy loss near edge structure
  • the positive electrode active material powder prepared as above Take 5g of the positive electrode active material powder prepared as above and measure the total scattering intensity by X-ray. It is the sum of the scattering intensities of the entire space matter and is only related to the intensity of the primary rays, the chemical structure, and the total number of electrons participating in the diffraction, that is, the mass, but has nothing to do with the order state of the sample. Then separate the crystalline scattering and non-crystalline scattering from the diffraction pattern, and the degree of crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.
  • the original image obtained by the above TEM test was opened in the DigitalMicrograph software, and Fourier transform was performed (automatically completed by the software after clicking the operation) to obtain the diffraction pattern.
  • the distance from the diffraction spot to the center position in the diffraction pattern was measured to obtain the crystal plane spacing, and the angle was calculated according to the Bragg equation.
  • Table 1 shows the positive electrode active material compositions of Examples 1-1 to 1-35 and Comparative Examples 1 to 7.
  • Table 2 shows the performance data of the positive electrode active materials, positive electrode sheets, buckle or full electricity of Examples 1-1 to 1-35 and Comparative Examples 1 to 7 measured according to the above performance test method.
  • Table 3 shows the performance data of the positive electrode active materials, positive electrode sheets, buckle or full electricity of Examples 2-1 to 2-3 measured according to the above performance test method.
  • Examples 1-1 to 1-35 and Comparative Examples 1 to 7 that the presence of the first coating layer and the second coating layer is beneficial to reducing the Li/Mn antisite defect concentration of the obtained material and the amount of Fe and Mn dissolved after cycling, increasing the gram capacity of the battery, and improving the safety performance and cycle performance of the battery.
  • the lattice change rate, antisite defect concentration and Fe and Mn dissolved amount of the obtained material can be significantly reduced, the gram capacity of the battery can be increased, and the safety performance and cycle performance of the battery can be improved.
  • the interplanar spacing of the phosphate in the coating layer is 0.348nm, and the angle of the crystal direction (111) is 25.562°.
  • Figure 7 is a comparison diagram of the XRD spectrum of the positive electrode active material core prepared in Example 1-1 and the standard XRD spectrum of lithium manganese phosphate (00-033-0804). As shown in Figure 7, the positions of the main characteristic peaks of the positive electrode active material core of the present application and the lithium manganese phosphate before doping are basically consistent, indicating that the positive electrode active material core of the present application has no impurity phase, and the improvement of the secondary battery performance mainly comes from element doping, rather than impurity phase.

Abstract

本申请提供一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置。所述正极活性材料包括内核及包覆所述内核的壳，所述内核包括Li mA xMn 1- yB yP 1-zC zO 4-nD n，所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种。本申请提供的正极活性材料能使二次电池具有较高的能量密度以及兼顾改善的循环性能、安全性能、和/或倍率性能。

Description

正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 技术领域
本申请属于电池技术领域，具体涉及一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置。
背景技术
近年来，二次电池被广泛应用于水力、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。随着二次电池的应用及推广，其安全性能受到越来越多的关注。磷酸锰锂由于具有容量高、安全性能好及原材料来源丰富等优势成为了目前最受关注的正极活性材料之一，然而磷酸锰锂在充电时容易发生锰离子溶出，导致容量迅速衰减。
发明内容
本申请的目的在于提供一种正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置，其能使应用所述正极活性材料的二次电池具有较高的能量密度以及兼顾改善的循环性能、安全性能、和/或倍率性能。
本申请第一方面提供一种具有核-壳结构的正极活性材料，其包括内核及包覆所述内核的壳，所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，可选地包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，可选地包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，可选地包括选自B(硼)、S、Si和N中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，可选地包括选自S、F、Cl和Br中的一种或多种元素，所述m选自0.900至1.100的范围，可选地选自0.900至1.006的范围，所述x选自0至0.100的范围，可选地选自0.001至0.005的范围，所述y选自0.001至0.500的范围，可选地选自0.100至0.450的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，可选地选自0.001至0.005的范围，并且所述内核为电中性的；所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述X包括 选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
本申请通过对磷酸锰锂进行特定的元素掺杂和表面包覆，能够有效抑制脱嵌锂过程中的锰离子溶出，同时促进锂离子的迁移。因此，采用本申请正极活性材料的正极极片以及二次电池等用电装置能够具有较高的能量密度以及兼顾改善的循环性能、安全性能、和/或倍率性能。
在本申请的任意实施方式中，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第三包覆层包含碳，并且所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，或者所述第一包覆层包括硼酸盐X aB bO c，所述第二包覆层包括磷酸盐MPO 4。可选地，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c。由此，采用本申请正极活性材料的正极极片以及二次电池等用电装置能够具有改善的循环性能、安全性能、和/或倍率性能。
在本申请的任意实施方式中，所述第一包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计。由此能够有效发挥第一包覆层的功能，同时不会由于包覆层过厚而影响二次电池的动力学性能。
在本申请的任意实施方式中，所述第二包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计。由此能够进一步抑制锰离子溶出，同时进一步促进锂离子和电子的传输。
在本申请的任意实施方式中，所述第三包覆层的包覆量为大于0且小于等于6重量％，可选为2重量％至5重量％，基于所述内核的重量计。由此能够有效提升正极活性材料的克容量。
在本申请的任意实施方式中，所述第一包覆层和所述第二包覆层的包覆总量为大于0且小于等于7重量％，可选为4重量％至5.6重量％，基于所述内核的重量计。由此，能够在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的循环性能、安全性能、和/或倍率性能。
在本申请的任意实施方式中，所述磷酸盐MPO 4和所述硼酸盐X aB bO c的重量比为1:3至3:1，可选为1:3至1:1。由此有利于发挥磷酸盐和硼酸盐的协同作用。
在本申请的任意实施方式中，所述磷酸盐MPO 4的晶面间距为0.345nm至0.358nm，晶向(111)的夹角为24.25°至26.45°。由此能够进一步提升二次电池的循环性能和倍率性能。
在本申请的任意实施方式中，所述磷酸盐MPO 4的结晶度为10％至100％，可选为50％至100％；和/或所述硼酸盐X aB bO c的结晶度为10％至100％，可选为50％至100％。一方面有利于充分发挥磷酸盐减少表面杂锂含量、降低表面氧的价态的作用，另一方面也有利于充分发挥硼酸盐阻碍锰离子溶出、促进锂离子和电子传输的作用，从而减少正极活性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。
在本申请的任意实施方式中，在所述内核中，y与1-y的比值为1:10至10:1，可选为1:4至1:1。由此二次电池的能量密度和循环性能可进一步提升。
在本申请的任意实施方式中，在所述内核中，z与1-z的比值为1:9至1:999，可选为1:499至1:249。由此二次电池的能量密度和循环性能可进一步提升。
在本申请的任意实施方式中，在所述内核中，所述B包括选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，可选地包括选自Fe、Ti、V、Ni、Co和Mg中的至少两种元素。由此能够进一步降低表面氧活性和抑制锰离子的溶出。
在本申请的任意实施方式中，b:c为1:3。
在本申请的任意实施方式中，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。由此能够提升正极活性材料的克容量和倍率性能。
在本申请的任意实施方式中，所述正极活性材料的晶格变化率为8％以下，可选为4％以下。由此能够改善二次电池的倍率性能。
在本申请的任意实施方式中，所述正极活性材料的表面氧价态为-1.88以下，可选为-1.98至-1.88。由此能够改善二次电池的循环性能和高温存储性能。
在本申请的任意实施方式中，所述正极活性材料在3吨下的压实密度为2.0g/cm 3以上，可选为2.2g/cm 3以上。由此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一种正极活性材料的制备方法，包括以下提供内核材料的步骤和包覆步骤。
提供内核材料的步骤：所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，可选地包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，可选地包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，可选地包括选自B(硼)、S、Si和N中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，可选地包括选自S、F、Cl和Br中的一种或多种元素，所述m选自0.900至1.100的范围，可选地选自0.900至1.006的范围，所述x选自0至0.100的范围，可选地选自0.001至0.005的范围，所述y选自0.001至0.500的范围，可选地选自0.100至0.450的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，可选地选自0.001至0.005的范围，并且所述内核为电中性的。
包覆步骤：分别提供包括磷酸盐MPO 4、硼酸盐X aB bO c和碳源的包覆液，将所述内核材料加入到上述包覆液中并混合，经烧结获得正极活性材料，其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述X包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的 一种或多种元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
在本申请的任意实施方式中，所述提供内核材料的步骤包括以下步骤：步骤(1)：将锰的源、元素B的源和酸在容器中混合并搅拌，得到掺杂有元素B的锰盐颗粒；步骤(2)：将所述掺杂有元素B的锰盐颗粒与锂的源、磷的源、元素C的源、可选的元素A的源和可选的元素D的源在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到内核材料。
在本申请的任意实施方式中，所述步骤(1)在20℃至120℃，可选为25℃至80℃的温度下进行。
在本申请的任意实施方式中，所述步骤(1)中所述搅拌在500rpm至700rpm下进行60分钟至420分钟，可选为120分钟至360分钟。
通过控制掺杂时的反应温度、搅拌速率和混合时间，能够使掺杂元素均匀分布，并且烧结后材料的结晶度更高，从而可提升正极活性材料的克容量和倍率性能等。
在本申请的任意实施方式中，所述元素A的源选自元素A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。
在本申请的任意实施方式中，所述元素B的源选自元素B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。
在本申请的任意实施方式中，所述元素C的源选自元素C的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物、氢氧化物以及元素C的无机酸中的一种或多种。
在本申请的任意实施方式中，所述元素D的源选自元素D的单质和铵盐中的一种或多种。
通过在上述范围内选择各掺杂元素的源，能够有效改善正极活性材料的性能。
在本申请的任意实施方式中，所述步骤(2)中所述烧结为在惰性气体或惰性气体与氢气混合气氛下在600℃至800℃下烧结4小时至10小时。
在本申请的任意实施方式中，所述包覆步骤包括任选顺序的包覆磷酸盐MPO 4的步骤、包覆硼酸盐X aB bO c的步骤和包覆碳的步骤。
在本申请的任意实施方式中，可选地，第一包覆步骤为包覆磷酸盐MPO 4的步骤，第二包覆步骤为包覆硼酸盐X aB bO c的步骤，第三包覆步骤为包覆碳的步骤，由此所获得的正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，所述第三包覆层包含碳。
在本申请的任意实施方式中，所述包覆磷酸盐MPO 4的步骤包括以下步骤：提供包含磷酸盐MPO 4的包覆液，将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到磷酸盐MPO 4包覆的材料。
在本申请的任意实施方式中，所述包覆硼酸盐X aB bO c的步骤包括以下步骤：提供包含硼酸盐X aB bO c的包覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到硼酸盐X aB bO c包覆的材料。
在本申请的任意实施方式中，所述包覆碳的步骤包括以下步骤：提供包含碳源的包 覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到碳包覆的材料。
在本申请的任意实施方式中，所述包含磷酸盐MPO 4的包覆液通过以下方法制备：将元素M的源和磷的源加入到溶剂中，搅拌均匀，得到混合物，然后将混合物升温至60℃至120℃保持2小时至8小时，得到包覆液。
在本申请的任意实施方式中，所述包含硼酸盐X aB bO c的包覆液通过以下方法制备：将元素X的源和硼的源加入到溶剂中，搅拌均匀，得到包覆液。
在本申请的任意实施方式中，所述包覆磷酸盐MPO 4的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时。
在本申请的任意实施方式中，所述包覆硼酸盐X aB bO c的步骤中的所述烧结为在300℃至500℃下烧结2小时至10小时。
在本申请的任意实施方式中，所述包覆碳的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时。
通过控制包覆时的烧结温度和时间，可以进一步提升正极活性材料的克容量和倍率性能等。
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，所述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，可选为90重量％至99.5重量％，基于所述正极膜层的总重量计。
本申请的正极极片用于二次电池中，能够改善二次电池能量密度、循环性能、安全性能、和/或倍率性能。
本申请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通过本申请第二方面的方法制备的正极活性材料或本申请第三方面的正极极片。
本申请第五方面提供一种用电装置，包括本申请第四方面的二次电池。
本申请的正极极片、二次电池、用电装置包括本申请的正极活性材料，因而至少具有与所述正极活性材料相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的电池单体的一实施方式的示意图。
图2是本申请的电池单体的一实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
图7是实施例1-1制备的正极活性材料内核的XRD谱图与磷酸锰锂XRD标准谱图 (00-033-0804)的对比图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5电池单体，51壳体，52电极组件，53盖板。
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、其制备方法以及包含其的正极极片、二次电池及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
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，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本文中，中值粒径Dv50是指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，材料的中值粒径Dv50可采用激光衍射粒度分析法测定。例如参照标准GB/T19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。
在本文中，术语“包覆层”是指包覆在内核上的物质层，所述物质层可以完全或部分地包覆内核，使用“包覆层”只是为了便于描述，并不意图限制本发明。另外，每一层包覆层可以是完全包覆，也可以是部分包覆。同样地，术语“包覆层的厚度”是指包覆在内核上的所述物质层在内核径向上的厚度。
在本文中，术语“源”是指作为某种元素的来源的化合物，作为实例，所述“源”的种类包括但不限于碳酸盐、硫酸盐、硝酸盐、单质、卤化物、氧化物和氢氧化物等。
在本文中，术语“多个”、“多种”、“多层”是指两个、两种或两层以上。
在本文中，“约”某个数值表示一个范围，表示该数值±10％的范围。
本申请发明人在实际作业中发现：磷酸锰锂LiMnPO 4正极活性材料在深度充放电过程中，锰离子溶出比较严重。虽然现有技术有尝试对磷酸锰锂进行磷酸铁锂包覆，从而减少界面副反应，但这种包覆无法阻止溶出的锰离子向电解液中迁移。溶出的锰离子在迁移到负极后，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，影响二次电池的动力学性能。此外，为补充损失的SEI膜，电解液和电池内部的活性锂离子还被不断消耗，由此还给二次电池的容量保持率带来不可逆的影响。
发明人经过大量研究后发现，对于磷酸锰锂正极活性材料，锰离子溶出严重和表面反应活性高等问题可能是由于脱锂后Mn 3+的姜-泰勒效应和Li +通道大小变化引起的。为此，发明人通过对磷酸锰锂进行改性，得到了能够显著降低锰离子溶出和降低晶格变化率，进而具备良好的循环性能、安全性能、和/或倍率性能的正极活性材料。
正极活性材料
具体而言，本申请的第一方面提出了一种具有核-壳结构的正极活性材料，其包括内核及包覆所述内核的壳。
所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，所述m选自0.900至1.100的范围，所述x选自0至0.100的范围，所述y选自0.001至0.500的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，并且所述内核为电中性的。
所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，所述X包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2 至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
除非另有说明，否则上述化学式中，当A为两种以上元素时，上述对于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和D为两种以上元素的情况，本申请中对B、C和D化学计量数的数值范围的限定也具有上述含义。
本申请的磷酸锰锂正极活性材料具有核-壳结构，内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n。所述内核在磷酸锰锂的Mn位掺杂的元素B有助于减小脱嵌锂过程中磷酸锰锂的晶格变化率，提高磷酸锰锂正极活性材料的结构稳定性，大大减少锰离子的溶出并降低颗粒表面的氧活性。在P位掺杂的元素C有助于改变Mn-O键长变化的难易程度，从而降低锂离子迁移势垒，促进锂离子迁移，提高二次电池的倍率性能。在Li位掺杂的元素A也有助于减小脱嵌锂过程中磷酸锰锂的晶格变化率。在O位掺杂的元素D有助于减少界面副反应。所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳。磷酸盐具有优异的导锂离子的能力，并可减少表面杂锂含量。硼酸盐具有优异的导锂离子的能力和导电子的能力，并可减少表面杂锂含量、抑制锰离子溶出，由此能够减少界面副反应和降低产气量，提高循环性能。碳能够有效改善正极活性材料的导电性能和去溶剂化能力。
因此，本申请通过对磷酸锰锂进行特定的元素掺杂和表面包覆，能够有效抑制脱嵌锂过程中的锰离子溶出，同时促进锂离子的迁移，从而改善二次电池的循环性能、安全性能、和/或倍率性能。
需要指出的是，本申请的正极活性材料内核与LiMnPO 4掺杂前的主要特征峰的位置基本一致，说明本申请的掺杂的磷酸锰锂正极活性材料内核没有杂质相，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，所述壳包括多层包覆层，且各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种。
在一些实施方式中，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第三包覆层包含碳，并且所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，或者所述第一包覆层包括硼酸盐X aB bO c，所述第二包覆层包括磷酸盐MPO 4。
在一些实施方式中，所述第一包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计。
在一些实施方式中，所述第二包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计。
当第一包覆层和/或第二包覆层的包覆量在上述范围内时，能够降低杂锂含量、抑制锰离子溶出，同时促进锂离子和电子的传输；此外，还能够在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的循环性能和存储性能。并能够有效避免以下情况：若第一包覆层和/或第二包覆层的包覆量过小，则可能会导致对锰离子溶出的抑制作用不充分，同时对锂离子和电子传输性能的改善也不显著；若第一包覆层和/或第二包覆层的 包覆量过大，则可能会导致包覆层整体过厚，增大电池阻抗，影响二次电池的动力学性能，同时由于包覆层不提供容量，过多包覆会降低正极活性材料的克容量。
在一些实施方式中，可选地，所述第一包覆层和所述第二包覆层的包覆总量为大于0且小于等于7重量％，可选为4重量％至5.6重量％，基于所述内核的重量计。由此，能够在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的循环性能、安全性能、和/或倍率性能。
在一些实施方式中，所述第三包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至6重量％，更可选为2重量％至5重量％，基于所述内核的重量计。作为第三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，从而减少电解液对正极活性材料的侵蚀，提高二次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，可降低电池阻抗，从而改善二次电池的动力学性能。然而，由于碳材料的克容量较低，因此当第三包覆层的用量过大时，可能会降低正极活性材料整体的克容量。因此，当所述第三包覆层的包覆量在上述范围内时，能够在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的动力学性能和安全性能。
在一些实施方式中，可选地，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，所述第三包覆层包含碳。
第一包覆层可选为包括磷酸盐，磷酸盐具有优异的导锂离子的能力，并可减少表面杂锂含量。第二包覆层可选为包括硼酸盐，硼酸盐具有优异的导锂离子的能力和导电子的能力，并可减少表面杂锂含量、抑制锰离子的溶出，由此能够减少界面副反应和降低产气量，提高循环性能，此外选择硼酸盐作为第二包覆层的主要原因是与磷酸盐相比，其表面活性更低，由此能够进一步减少表面杂锂含量、减少电解液的分解，以及进一步抑制锰离子溶出。第三包覆层为含碳层，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，第三包覆层位于最外层，其“屏障”作用可以进一步阻碍锰离子迁移到电解液中，并减少电解液对正极活性材料的侵蚀。因此，采用本申请正极活性材料的正极极片以及二次电池等用电装置能够具有改善的循环性能、安全性能、和/或倍率性能。
在一些实施方式中，所述第一包覆层包括磷酸盐MPO 4，并且所述第一包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，更可选为1重量％至3重量％，基于所述内核的重量计。当所述第一包覆层的包覆量在上述范围内时，能够降低杂锂含量、抑制锰离子溶出，同时促进锂离子的传输。并能够有效避免以下情况：若第一包覆层的包覆量过小，则可能会导致对锰离子溶出的抑制作用不充分，同时对锂离子传输性能的改善也不显著；若第一包覆层的包覆量过大，则可能会导致包覆层过厚，增大电池阻抗，影响二次电池的动力学性能。
在一些实施方式中，所述第二包覆层包括硼酸盐X aB bO c，并且所述第二包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，更可选为2重量％至5重量％，基于所述内核的重量计。当所述第二包覆层的包覆量在上述范围内时，能够进一步抑制锰离子的溶出，同时能够进一步促进锂离子和电子的传输。并能够有效避免以下情况：若第二包覆层的包覆量过小，则可能会导致对锰离子溶出的抑制作用不充分，同时对锂离子和电子传输性能的改善也不显著；若第二包覆层的包覆量过大，则可能会导致 包覆层过厚，增大电池阻抗，影响二次电池的动力学性能，同时由于包覆层不提供容量，过多包覆会降低正极活性材料的克容量。因此，当所述第二包覆层的包覆量在上述范围内时，能够在不牺牲正极活性材料克容量的前提下，进一步改善二次电池的循环性能和存储性能。
在一些实施方式中，可选地，所述磷酸盐MPO 4和所述硼酸盐X aB bO c的重量比为1:3至3:1，可选为1:3至1:1。磷酸盐和硼酸盐的合适配比有利于充分发挥二者的协同作用，既可有效阻碍锰离子溶出，又可有效减少表面杂锂含量，减少界面副反应。
在所述内核中，所述m选自0.900至1.100的范围，例如m可以为0.900、0.991、0.992、0.993、0.994、0.995、0.996、0.997、0.998、1.000、1.001、1.002、1.003、1.004、1.005、1.006。可选地，所述m选自0.900至1.006的范围。
在所述内核中，所述x选自0至0.100的范围，例如为0、0.001、0.005。可选地，所述x选自0.001至0.1，0.001至0.005的范围。
在所述内核中，所述y选自0.001至0.500的范围，例如y可以为0.100、0.200、0.250、0.300、0.350、0.400、0.450。可选地，所述y选自0.100至0.450的范围。
在所述内核中，所述z选自0.001至0.100的范围，例如z可以为0.001、0.002、0.003、0.004、0.005、0.006、0.007、0.008、0.009、0.100。
在所述内核中，所述n选自0至0.100的范围，例如为0、0.001、0.005、0.08、0.1。可选地，所述n选自0.001至0.1，0.001至0.005的范围。
所述x选自0至0.100的范围，所述n选自0至0.100的范围，即在磷酸锰锂的Li位和O位可以不进行掺杂，也可以进行掺杂。
在一些实施例方式中，可选地，所述x选自0.001至0.100的范围，即在磷酸锰锂的Li位掺杂了元素A。
在一些实施例方式中，可选地，所述n选自0.001至0.100的范围，即在磷酸锰锂的O位掺杂了元素D。
在一些实施例方式中，可选地，所述x选自0.001至0.100的范围，并且所述n选自0.001至0.1的范围，即在磷酸锰锂的Li位和O位同时进行了掺杂。
在一些实施方式中，可选地，在所述内核中，y与1-y的比值为1:10至10:1，可选为1:4至1:1。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，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，可选地，在所述内核中，z与1-z的比值为1:9至1:999，可选为1:499至1:249。此处y表示P位掺杂元素的化学计量数之和。在满足上述条件时，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，可选地，所述A包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素。通过在上述范围内对Li位掺杂元素进行选择，能够进一步减小晶格变化率，从而进一步改善二次电池的倍率性能。
在一些实施方式中，可选地，所述B包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，更可选地，所述B包括选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，进一步可选地，所述B包括选自Fe、Ti、V、Ni、Co和Mg中的至少两种元素。在磷酸锰锂正极活性材料中的Mn位同时掺杂两种以上的上述元 素有利于增强掺杂效果，一方面进一步减小晶格变化率，从而抑制锰离子的溶出，减少电解液和活性锂离子的消耗，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，从而改善二次电池的循环性能和高温存储性能。
在一些实施方式中，可选地，所述C包括选自B(硼)、S、Si和N中的一种或多种元素。通过在上述范围内对P位掺杂元素进行选择，能够进一步改善二次电池的倍率性能。
在一些实施方式中，可选地，所述D包括选自S、F、Cl和Br中的一种或多种元素，通过在上述范围内对O位掺杂元素进行选择，能够进一步减轻界面的副反应，提升二次电池的高温稳定性。
在一些实施方式中，可选地，所述M包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种。
在一些实施方式中，可选地，所述X包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种。
在一些实施方式中，可选地，b:c为1:3。
在一些实施方式中，可选地，所述磷酸盐MPO 4的晶面间距为0.345nm至0.358nm，晶向(111)的夹角为24.25°至26.45°。当磷酸盐MPO 4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，从而提升正极活性材料的克容量，提升二次电池的循环性能和倍率性能。
在一些实施方式中，可选地，所述磷酸盐MPO 4的结晶度为10％至100％，可选为50％至100％；和/或，所述硼酸盐X aB bO c的结晶度为10％至100％，可选为50％至100％。具备一定结晶度的磷酸盐和硼酸盐有利于保持包覆层的结构稳定，减少晶格缺陷。这一方面有利于充分发挥磷酸盐减少表面杂锂含量、降低表面氧的价态的作用，另一方面也有利于充分发挥硼酸盐阻碍锰离子溶出、促进锂离子和电子传输的作用，从而减少正极活性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。
需要说明的是，在本申请中，磷酸盐和硼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。磷酸盐和硼酸盐的结晶度可通过本领域中已知的方法测量，例如通过X射线衍射法、密度法、红外光谱法、差示扫描量热法和核磁共振吸收方法等方法测量。
在一些实施方式中，可选地，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。Li/Mn反位缺陷是指LiMnPO 4晶格中，Li +和Mn 2+的位置发生互换。Li/Mn反位缺陷浓度指的是正极活性材料中与Mn 2+发生互换的Li +占Li +总量的百分比。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。在本申请的正极活性材料中，通过将Li/Mn反位缺陷浓度控制在低水平，能够提升正极活性材料的克容量和倍率性能。本申请中，反位缺陷浓度例如可根据JIS K0131-1996测定。
在一些实施方式中，可选地，所述正极活性材料的晶格变化率为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。
在一些实施方式中，可选地，所述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，二次电池的能量密度较低；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，二次电池整体能量密度有明显升高。
在一些实施方式中，可选地，所述正极活性材料的表面氧价态为-1.88以下，可选为-1.98至-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。而在本申请的磷酸锰锂正极活性材料中，通过将氧的表面价态控制在较低水平，可降低正极活性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存储性能。
在一些实施方式中，可选地，所述正极活性材料在3吨(T)下的压实密度为2.0g/cm 3以上，可选为2.2g/cm 3以上。正极活性材料的压实密度越高，即单位体积活性材料的重量越大，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。
制备方法
本申请的第二方面提供本申请的第一方面的正极活性材料的制备方法，其包括以下提供内核材料的步骤和包覆步骤。
提供内核材料的步骤：所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，可选地包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，可选地包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，可选地包括选自B(硼)、S、Si和N中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，可选地包括选自S、F、Cl和Br中的一种或多种元素，所述m选自0.900至1.100的范围，可选地选自0.900至1.006的范围，所述x选自0至0.100的范围，可选地选自0.001至0.005的范围，所述y选自0.001至0.500的范围，可选地选自0.100至0.450的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，可选地选自0.001至0.005的范围，并且所述内核为电中性的。
包覆步骤：分别提供包括磷酸盐MPO 4、硼酸盐X aB bO c和碳源的包覆液，将所述内核材料加入到上述包覆液中并混合，经烧结获得正极活性材料，其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述X包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的 一种或多种元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
本申请的制备方法对内核材料的来源没有特别的限制。可选地，本申请制备方法中的内核材料可以是市售获得的，也可以是通过本申请的方法制备获得的。可选地，所述内核材料通过下文中所述方法制备获得。
在一些实施方式中，可选地，所述提供内核材料的步骤包括以下步骤：步骤(1)：将锰的源、元素B的源和酸在容器中混合并搅拌，得到掺杂有元素B的锰盐颗粒；步骤(2)：将所述掺杂有元素B的锰盐颗粒与锂的源、磷的源、元素C的源、可选的元素A的源和可选的元素D的源在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到内核材料。
在一些实施方式中，可选地，所述步骤(1)在20℃至120℃，可选为25℃至80℃的温度下进行。
在一些实施方式中，所述步骤(1)中所述搅拌在500rpm至700rpm下进行60分钟至420分钟，可选为120分钟至360分钟。
通过控制掺杂时的反应温度、搅拌速率和混合时间，能够使掺杂元素均匀分布，减少晶格缺陷，抑制锰离子溶出，减少正极活性材料与电解液的界面副反应，从而可提升正极活性材料的克容量和倍率性能等。
需要说明的是，在本申请中，某种元素的来源可包括该元素的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物或氢氧化物中的一种或多种，前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，可选地，在步骤(1)中，所述锰的源选自单质锰、二氧化锰、磷酸锰、草酸锰、碳酸锰中的一种或多种。
在一些实施方式中，可选地，所述元素A的源选自元素A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，可选地，所述元素B的源选自元素B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。可选地，元素B为铁，并且可选地，所述铁的源选自碳酸亚铁、氢氧化铁、硫酸亚铁中的一种或多种。
在一些实施方式中，可选地，在步骤(1)中，所述酸选自盐酸、硫酸、硝酸、磷酸、有机酸如草酸等中的一种或多种，可选为草酸。在一些实施方式中，所述酸为浓度为60重量％以下的稀酸。
在一些实施方式中，可选地，在步骤(2)中，所述元素C的源选自元素C的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物、氢氧化物以及元素C的无机酸中的一种或多种。在一些实施方式中，可选地，元素C的无机酸选自磷酸、硝酸、硫酸、硼酸、亚硅酸、原硅酸中的一种或多种。
在一些实施方式中，可选地，在步骤(2)中，所述元素D的源选自元素D的单质和铵盐中的一种或多种。
在一些实施方式中，可选地，在步骤(2)中，所述锂的源选自碳酸锂、氢氧化锂、磷酸锂、磷酸二氢锂中的一种或多种。
在一些实施方式中，可选地，在步骤(2)中，所述磷的源选自磷酸氢二铵、磷酸二氢铵、磷酸铵和磷酸中的一种或多种。
在一些实施方式中，在步骤(2)中，所使用的溶剂为本领域通常使用的溶剂。例如，可选自乙醇、水(例如去离子水)中的至少一种。
在一些实施方式中，可选地，在步骤(1)中，，控制溶液pH为4至6。需要说明的是，在本申请中可通过本领域通常使用的方法调节所得混合物的pH，例如可通过添加酸或碱。
在一些实施方式中，可选地，在步骤(2)中，所述掺杂有元素B的锰盐颗粒与锂的源、磷的源的摩尔比为1:(0.5-2.1):(0.5-2.1)。
元素A、B、C、D各自的源的加入量可取决于目标掺杂量。
在一些实施方式中，可选地，在步骤(2)中，烧结条件为：在惰性气体或惰性气体与氢气混合气氛下在600℃至800℃下烧结4小时至10小时。由此，烧结后材料的结晶度更高，从而可提升正极活性材料的克容量和倍率性能等。在一些实施方式中，可选地，惰性气体与氢气混合物为氮气(70体积％至90体积％)+氢气(10体积％至30体积％)。
在一些实施方式中，可选地，所述碳的源为有机碳源，并且所述有机碳源选自淀粉、蔗糖、葡萄糖、聚乙烯醇、聚乙二醇、柠檬酸中的一种或多种。
在一些实施方式中，可选地，所述包覆步骤包括任选顺序的包覆磷酸盐MPO 4的步骤、包覆硼酸盐X aB bO c的步骤和包覆碳的步骤。上述各包覆步骤的具体包覆顺序不受具体的限制，可根据所需的正极活性材料的壳的具体结构进行适应性调整。
可选地，所述包覆磷酸盐MPO 4的步骤包括以下步骤：提供包含磷酸盐MPO 4的包覆液，将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到磷酸盐MPO 4包覆的材料。所述待包覆的材料可根据实际情况采用内核材料、一层包覆层包覆的材料或两层包覆层包覆的材料。
可选地，所述包覆硼酸盐X aB bO c的步骤包括以下步骤：提供包含硼酸盐X aB bO c的包覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到硼酸盐X aB bO c包覆的材料。所述待包覆的材料可根据实际情况采用内核材料、一层包覆层包覆的材料或两层包覆层包覆的材料。
可选地，所述包覆碳的步骤包括以下步骤：提供包含碳源的包覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到碳包覆的材料。所述待包覆的材料可根据实际情况采用内核材料、一层包覆层包覆的材料或两层包覆层包覆的材料。
在一些实施方式中，第一包覆步骤为包覆硼酸盐X aB bO c的步骤，第二包覆步骤为包覆磷酸盐MPO 4的步骤，第三包覆步骤为包覆碳的步骤，由此所获得的正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第一包覆层包括硼酸盐X aB bO c，所述第二包覆层包括磷酸盐MPO 4，所述第三包覆层包含碳。
在一些实施方式中，第一包覆步骤为包覆磷酸盐MPO 4的步骤，第二包覆步骤为包覆硼酸盐X aB bO c的步骤，第三包覆步骤为包覆碳的步骤，由此所获得的正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆 层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，所述第三包覆层包含碳。
在一些实施方式中，在上述各包覆步骤中，所使用的溶剂为本领域通常使用的溶剂。例如，所述溶剂可各自独立地选自乙醇、水(例如去离子水)中的至少一种。
在一些实施方式中，可选地，在上述各包覆步骤中，所述干燥均可以在100℃至200℃、可选为110℃至190℃、更可选为120℃至180℃、甚至更可选为120℃至170℃、最可选为120℃至160℃的干燥温度下进行，干燥时间为3小时至9小时、可选为4小时至8小时，更可选为5小时至7小时，最可选为约6小时。
在一些实施方式中，所述包含磷酸盐MPO 4的包覆液是市售可得的，或者可选地，通过以下方法制备：将元素M的源和磷的源加入到溶剂中，搅拌均匀，得到混合物，然后将混合物升温至60℃至120℃保持2小时至8小时，得到包覆液。可选地，所述混合物的pH为4至6。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混合物的pH，例如可通过添加酸或碱。可选地，元素M的源选自元素M的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。可选地，磷的源选自磷酸氢二铵、磷酸二氢铵、磷酸铵和磷酸中的一种或多种。
在一些实施方式中，所述包含硼酸盐X aB bO c的包覆液是市售可得的，或者可选地，通过以下方法制备：将元素X的源和硼的源加入到溶剂中，搅拌均匀，得到包覆液。可选地，元素X的源选自元素X的单质、碳酸盐、硫酸盐、氯化盐、硝酸盐、有机酸盐、氧化物、氢氧化物中的一种或多种。可选地，硼的源选自硼酸、硼酸盐、氧化硼中的一种或多种。
在一些实施方式中，所述包覆磷酸盐MPO 4的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时。可选地，所述烧结可在约500℃、约600℃、约700℃或约800℃下烧结约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述包覆磷酸盐MPO 4的步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述包覆磷酸盐MPO 4的步骤中的烧结温度过低以及烧结时间过短时，会导致磷酸盐MPO 4的结晶度低，非晶态较多，同时其包覆效果差，对锰离子溶出的抑制作用不充分，对锂离子传输性能的改善也不显著；而烧结温度过高以及烧结时间过长时，会使形成的包覆层的厚度增加，增大电池阻抗，影响二次电池的动力学性能和能量密度。
在一些实施方式中，所述包覆硼酸盐X aB bO c的步骤中的所述烧结为在300℃至500℃下烧结2小时至10小时。可选地，所述烧结可在约300℃、约350℃、约400℃、约450℃或约500℃下烧结约2小时、约3小时、约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述包覆硼酸盐X aB bO c的步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述包覆硼酸盐X aB bO c的步骤中的烧结温度过低以及烧结时间过短时，会导致硼酸盐X aB bO c的结晶度低，非晶态较多，同时其包覆效果差，对锰离子溶出的抑制作用不充分，同时对锂离子和电子传输性能的改善也不显著；而烧结温度过高以 及烧结时间过长时，会使形成的包覆层的厚度增加，增大电池阻抗，影响二次电池的动力学性能和能量密度。
在一些实施方式中，所述包覆碳的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时。可选地，所述烧结可在约500℃、约600℃、约700℃或约800℃下烧结约4小时、约5小时、约6小时、约7小时、约8小时、约9小时或约10小时；可选地，所述烧结的温度、烧结时间可在上述任意数值的任意范围内。
在所述包覆碳的步骤中，通过将烧结温度和时间控制在以上范围内，可以避免以下情况：当所述包覆碳的步骤中的烧结温度过低时，会导致碳材料的石墨化程度下降，影响其导电性，从而影响正极活性材料的克容量发挥；烧结温度过高时，会造成碳材料的石墨化程度过高，影响Li +的传输，从而影响正极活性材料的克容量发挥等；烧结时间过短时，会导致形成的包覆层过薄，影响其导电性，从而影响正极活性材料的克容量发挥；烧结时间过长时，会导致形成的包覆层过厚，影响正极活性材料的压实密度等。
在一些实施方式中，可选地，本申请的核壳结构的磷酸锰锂正极活性材料的一次颗粒的中值粒径Dv50为50nm至2000nm。
正极极片
本申请的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，所述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，可选为90重量％至99.5重量％，基于所述正极膜层的总重量计。所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置于所述正极集流体的两个相对表面中的任意一者或两者上。
正极膜层并不排除除了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方法制备的正极活性材料之外的其他正极活性材料，例如正极膜层还可以包括本申请上述正极活性材料以外的其他正极活性材料，可选地，所述其他正极活性材料可以包括锂过渡金属氧化物及其改性化合物中的至少一种。作为示例，所述其他正极活性材料可包括锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其各自的改性化合物中的至少一种。
在一些实施方式中，所述正极膜层还可选地包括正极导电剂。本申请对所述正极导电剂的种类没有特别的限制，作为示例，所述正极导电剂包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的至少一种。
在一些实施方式中，所述正极膜层还可选地包括正极粘结剂。本申请对所述正极粘结剂的种类没有特别的限制，作为示例，所述正极粘结剂可包括聚偏氟乙烯(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、含氟丙烯酸酯类树脂中的至少一种。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可选自聚丙烯(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。
所述正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
二次电池
本申请的第四方面提供了一种二次电池，其包括本申请第三方面的正极极片。
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，二次电池包括电极组件和电解质，电极组件包括正极极片、负极极片和隔离膜。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。电解质在正极极片和负极极片之间起到传导活性离子的作用。
本申请的实施例或实施方式中所提到的二次电池是指包括一个或多个电池单体以提供更高的电压和容量的单一的物理模块。例如，本申请中所提到的二次电池可以包括电池单体、电池模块或电池包等。电池单体是组成二次电池的最小单元，其独自能够实现充放电的功能。本申请对电池单体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。如图1是作为一个示例的方形结构的电池单体5。
在一些实施方式中，电池单体包括电极组件，单体电池还可包括外包装。电极组件可通过卷绕工艺和/或叠片工艺由正极极片、负极极片以及隔离膜等制成，外包装可用于封装上述电极组件。外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)和聚丁二酸丁二醇酯(PBS)中的一种或多种。
在一些实施方式中，如图2所示，外包装可包括壳体51和盖板53。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用于盖设所述开口，以封闭所述容纳腔。电极组件52封装于所述容纳腔。电池单体5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
在本申请的一些实施例中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个电池单体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电池单体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，多个电池单体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根据电池包的应用和容量进行调节。图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，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用于盖设下箱体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。
[正极极片]
本申请的二次电池中使用的正极极片为本申请第三方面任一实施例所述的正极极片。
[负极极片]
在一些实施方式中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面且包括负极活性材料的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，所述负极活性材料包括但不限于天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料、钛酸锂中的至少一种。所述硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物、硅合金材料中的至少一种。所述锡基材料可包括单质锡、锡氧化物、锡合金材料中的至少一种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池负极活性材料的传统公知的材料。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，所述负极膜层还可选地包括负极导电剂。本申请对所述负极导电剂的种类没有特别的限制，作为示例，所述负极导电剂可包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的至少一种。
在一些实施方式中，所述负极膜层还可选地包括负极粘结剂。本申请对所述负极粘结剂的种类没有特别的限制，作为示例，所述负极粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，所述负极膜层还可选地包括其他助剂。作为示例，其他助剂可包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铜、铜合金、镍、镍合金、钛、钛合金、银、银合金中的至少一种。作为示例，高分子材料基层可选自聚丙烯(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。
所述负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。所述负极浆料通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。
所述负极极片并不排除除了所述负极膜层以外的其他附加功能层。例如在某些实施例中，本申请所述的负极极片还包括夹在所述负极集流体和所述负极膜层之间、设置于所述负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施例中，本申请所述的负极极片还包括覆盖在所述负极膜层表面的保护层。
[电解质]
本申请对所述电解质的种类没有具体的限制，可根据需求进行选择。例如，所述电解质可以选自固态电解质及液态电解质(即电解液)中的至少一种。
在一些实施方式中，所述电解质采用电解液，所述电解液包括电解质盐和溶剂。
所述电解质盐的种类不受具体的限制，可根据实际需求进行选择。在一些实施方式中，作为示例，所述电解质盐可包括六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)中的至少一种。
所述溶剂的种类不受具体的限制，可根据实际需求进行选择。在一些实施方式中，作为示例，所述溶剂可包括碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的至少一种。
在一些实施方式中，所述电解液中还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，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、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
[隔离膜]
采用电解液的二次电池、以及一些采用固态电解质的二次电池中，还包括隔离膜。所述隔离膜设置在所述正极极片和所述负极极片之间，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。本申请对所述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，所述隔离膜的材质可以包括玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。所述隔离膜可以是单层薄膜，也可以是多层复合薄膜。当所述隔离膜为多层复合薄膜时，各层的材料相同或不同。
本申请的二次电池的制备方法是公知的。在一些实施方式中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到电池单体。多个电池单体还可以进一步经由串联或并联或混联组成电池模块。多个电池模块还可以经由串联或并联或混联形成电池包。在一些实施方式中，多个电池单体还可以直接组成电池包。
用电装置
本申请的第五方面提供一种用电装置，所述用电装置包括本申请的二次电池。所述二次电池可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、平板电脑、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。
所述用电装置可以根据其使用需求来选择二次电池的具体类型，例如电池单体、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。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高功率和高能量密度的需求，可以采用电池包或电池模块作为电源。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用电池单体作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
本申请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
正极活性材料的制备
(1)共掺杂磷酸锰锂内核的制备
制备共掺杂的草酸锰：将689.5g碳酸锰(以MnCO 3计，下同)、455.2g碳酸亚铁(以FeCO 3计，下同)、4.6g硫酸钴(以CoSO 4计，下同)和4.9g二氯化钒(以VCl 2计，下同)在混料机中充分混合6小时。将混合物转移至反应釜中，并加入5升去离子水和1260.6g二水合草酸(以C 2H 2O 4.2H 2O计，下同)。将反应釜加热至80℃，以600rpm的转速搅拌6小时，直至反应终止(无气泡产生)，得到共掺杂的草酸锰悬浮液。然后过滤所述悬浮液，将滤饼在120℃下烘干，之后进行研磨，得到中值粒径Dv50为100nm的共掺杂的二水草酸锰颗粒。
制备共掺杂的磷酸锰锂：将前一步骤获得的二水草酸锰颗粒(1793.4g)、369.0g碳酸锂(以Li 2CO 3计，下同)，1.6g浓度为60％的稀硫酸(以60％H 2SO 4计，下同)和1148.9g磷酸二氢铵(以NH 4H 2PO 4计，下同)加入到20升去离子水中，将混合物搅拌10小时使其混合均匀，得到浆料。将所述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，得到粉料。在氮气(90体积％)+氢气(10体积％)保护气氛中，将上述粉料在700℃下烧结4小时，得到1572.1g的共掺杂的磷酸锰锂，即内核。
(2)第一包覆层的包覆
将3.7g碳酸锂、11.6g碳酸亚铁、11.5g磷酸二氢铵、0.43g二水合草酸溶于1500mL去离子水中，得到混合物，然后搅拌6小时使上述混合物充分反应。然后将反应后的溶液升温到120℃并保持该温度6小时，得到包含LiFePO 4的第一包覆层包覆液。
将1572.1g上述共掺杂的磷酸锰锂(内核)加入到第一包覆层包覆液中，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，再将所得产物在700℃下烧结6小时，得到第一包覆层包覆的材料。
(3)第二包覆层的包覆
将42.4g氢氧化锂和20.6g氧化硼加入到500mL去离子水中，得到第二包覆层包覆液。
将上述第一包覆层包覆的材料加入到第二包覆层包覆液中，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，再将所得产物在400℃下烧结10小时，得到两层包覆层包覆的材料。
(4)第三包覆层的包覆
将74.6g蔗糖溶于500ml去离子水中，然后搅拌并充分溶解，得到第三包覆层包覆液。
将上述两层包覆层包覆的材料加入到第三包覆层包覆液中，搅拌混合均匀后转入真空烘箱中在150℃下干燥6小时，然后在氮气气氛、700℃下烧结6小时，得到三层包覆层包覆的材料，即正极活性材料。
正极极片的制备
将上述制备的正极活性材料、导电剂乙炔黑和粘结剂聚偏二氟乙烯(PVDF)按照重量比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。然后将正极浆料按照涂覆面密度0.018g/cm 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、硬碳、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)和增稠剂羧甲基纤维素钠(CMC)按照重量比为90:5:2:2:1溶于溶剂去离子水中，搅拌混合均匀后 制备成负极浆料。将负极浆料按照涂覆面密度0.0075g/cm 2均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，作为有机溶剂，将碳酸亚乙酯(EC)和碳酸甲乙酯(EMC)按照体积比3:7混合均匀，加入12.5重量％(基于所述有机溶剂的重量计)LiPF 6溶解于上述有机溶剂中，搅拌均匀，得到电解液。
隔离膜的制备
使用市售的厚度为20μm、平均孔径为80nm的PP-PE共聚物微孔薄膜(来自卓高电子科技公司，型号20)。
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，并卷绕得到电极组件。将电极组件置于外包装中，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、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按照重量比90:5:5加入至N-甲基吡咯烷酮(NMP)中，在干燥房中搅拌制成浆料。在铝箔上涂覆上述浆料，干燥、冷压制成正极极片。涂覆面密度为0.015g/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”)。
实施例1-2至1-35
除了正极活性材料的制备以外，其他均与实施例1-1的工艺相同。
实施例1-2至1-6
在共掺杂磷酸锰锂内核的制备过程中，除不使用二氯化钒和硫酸钴、使用463.4g的碳酸亚铁，1.6g的60％浓度的稀硫酸，1148.9g的磷酸二氢铵和369.0g碳酸锂以外，实施例1-2至1-6中磷酸锰锂内核的制备条件与实施例1-1相同。
在包覆第一包覆层、第二包覆层和第三包覆层的过程中，除所使用的原料按照表1中所示包覆量与实施例1-1对应的包覆量的比值对应调整，以使实施例1-2至1-6中LiFePO 4/Li 3BO 3的用量分别为12.6g/37.7g、15.7g/47.1g、18.8g/56.5g、22.0/66.0g和25.1g/75.4g，实施例1-2至1-6中蔗糖的用量为37.3g以外，其他条件与实施例1-1相同。
实施例1-7至1-10
除蔗糖的用量分别为74.6g、149.1g、186.4g和223.7g以使作为第三包覆层的碳层的对应包覆量分别为31.4g、62.9g、78.6g和94.3g以外，实施例1-7至1-10的条件与实施例1-3相同。
实施例1-11至1-14
在包覆第一包覆层、第二包覆层和第三包覆层的过程中，除所使用的原料按照表1中所示包覆量对应调整各种原料的用量以使LiFePO 4/Li 3BO 3的用量分别为23.6g/39.3g、31.4g/31.4g、39.3g/23.6g和47.2g/15.7g以外，实施例1-11至1-14的条件与实施例1-7相同。
实施例1-15
除在共掺杂磷酸锰锂内核的制备过程中使用492.80g碳酸锌代替碳酸亚铁以外，实施例1-15的条件与实施例1-14相同。
实施例1-16至1-18
除实施例1-16在共掺杂磷酸锰锂内核的制备过程中使用466.4g的碳酸镍、5.0g的碳酸锌和7.2g的硫酸钛代替碳酸亚铁，实施例1-17在共掺杂的磷酸锰锂内核的制备过程中使用455.2g的碳酸亚铁和8.5g的二氯化钒，实施例1-18在共掺杂的磷酸锰锂内核的制备过程中使用455.2g的碳酸亚铁、4.9g的二氯化钒和2.5g的碳酸镁以外，实施例1-16至1-18的条件与实施例1-7相同。
实施例1-19至1-20
除实施例1-19在共掺杂磷酸锰锂内核的制备过程中使用369.4g的碳酸锂、和以1.05g的60％浓度的稀硝酸代替稀硫酸，实施例1-20在共掺杂的磷酸锰锂内核的制备过程中使用369.7g的碳酸锂、和以0.78g的亚硅酸代替稀硫酸以外，实施例1-19至1-20的条件与
实施例1-18相同。
实施例1-21至1-22
除实施例1-21在共掺杂磷酸锰锂内核的制备过程中使用632.0g碳酸锰、463.30g碳酸亚铁、30.5g的二氯化钒、21.0g的碳酸镁和0.78g的亚硅酸；实施例1-22在共掺杂磷酸锰锂内核的制备过程中使用746.9g碳酸锰、289.6g碳酸亚铁、60.9g的二氯化钒、42.1g的碳酸镁和0.78g的亚硅酸以外，实施例1-21至1-22的条件与实施例1-20相同。
实施例1-23至1-24
除实施例1-23在共掺杂磷酸锰锂内核的制备过程中使用804.6g碳酸锰、231.7g碳酸亚铁、1156.2g的磷酸二氢铵、1.2g的硼酸(质量分数99.5％)和370.8g碳酸锂；实施例1-24在共掺杂磷酸锰锂内核的制备过程中使用862.1g碳酸锰、173.8g碳酸亚铁、1155.1g的磷酸二氢铵、1.86g的硼酸(质量分数99.5％)和371.6g碳酸锂以外，实施例1-23至1-24的条件与实施例1-22相同。
实施例1-25
除实施例1-25在共掺杂磷酸锰锂内核的制备过程中使用370.1g碳酸锂、1.56g的亚硅酸和1147.7g的磷酸二氢铵以外，实施例1-25的条件与实施例1-20相同。
实施例1-26
除实施例1-26在共掺杂磷酸锰锂内核的制备过程中使用368.3g碳酸锂、4.9g质量分数为60％的稀硫酸、919.6g碳酸锰、224.8g碳酸亚铁、3.7g二氯化钒、2.5g碳酸镁和1146.8g的磷酸二氢铵以外，实施例1-26的条件与实施例1-20相同。
实施例1-27
除实施例1-27在共掺杂磷酸锰锂内核的制备过程中使用367.9g碳酸锂、6.5g浓度为60％的稀硫酸和1145.4g的磷酸二氢铵以外，实施例1-27的条件与实施例1-20相同。
实施例1-28至1-33
除实施例1-28至1-33在共掺杂磷酸锰锂内核的制备过程中使用1034.5g碳酸锰、108.9g碳酸亚铁、3.7g二氯化钒和2.5g碳酸镁，碳酸锂的使用量分别为：367.6g、367.2g、366.8g、366.4g、366.0g和332.4g，磷酸二氢铵的使用量分别为：1144.5g、1143.4g、 1142.2g、1141.1g、1139.9g和1138.8g，浓度为60％的稀硫酸的使用量分别为：8.2g、9.8g、11.4g、13.1g、14.7g和16.3g以外，实施例1-28至1-33的条件与实施例1-20相同。
实施例1-34
除在正极活性材料的制备中首先进行实施例1-1中的第二包覆层的包覆、再进行实施例1-1中的第一包覆层的包覆以外，实施例1-34的条件与实施例1-1相同。
实施例1-35
除在共掺杂磷酸锰锂内核的制备中加入了3.84g硫酸钼(以Mo(SO 4) 3计)和0.57g氟化氢铵(以NH 4HF 2计)以外，实施例1-35的条件与实施例1-1相同。
实施例2-1至2-3
除了正极活性材料的制备以外，其他均与实施例1-1的工艺相同。
实施例2-1
在包覆第一包覆层过程中，除在包覆烧结步骤中的烧结温度为650℃，烧结时间为2小时以控制LiFePO 4的结晶度为30％以外，其他条件与实施例1-1相同。
在包覆第二包覆层过程中，除在包覆烧结步骤中的烧结温度为300℃，烧结时间为2小时以控制Li 3BO 3的结晶度为30％以外，其他条件与实施例1-1相同。
实施例2-2
在包覆第一包覆层过程中，除在包覆烧结步骤中的烧结温度为650℃，烧结时间为3小时以控制LiFePO 4的结晶度为50％以外，其他条件与实施例1-1相同。
在包覆第二包覆层过程中，除在包覆烧结步骤中的烧结温度为350℃，烧结时间为2小时以控制Li 3BO 3的结晶度为50％以外，其他条件与实施例1-1相同。
实施例2-3
在包覆第一包覆层过程中，除在包覆烧结步骤中的烧结温度为650℃，烧结时间为4小时以控制LiFePO 4的结晶度为70％以外，其他条件与实施例1-1相同。
在包覆第二包覆层过程中，除在包覆烧结步骤中的烧结温度为400℃，烧结时间为2小时以控制Li 3BO 3的结晶度为70％以外，其他条件与实施例1-1相同。
对比例1至7
除了按照如下方法制备正极活性材料以外，其他均与实施例1-1的工艺相同。
对比例1
制备草酸锰：将1149.3g碳酸锰加至反应釜中，并加入5升去离子水和1260.6g二水合草酸(以C 2H 2O 4·2H 2O计，下同)。将反应釜加热至80℃，以600rpm的转速搅拌6小时，直至反应终止(无气泡产生)，得到草酸锰悬浮液，然后过滤所述悬浮液，将滤饼在120℃下烘干，之后进行研磨，得到中值粒径Dv50为100nm的二水草酸锰颗粒。
制备碳包覆的磷酸锰锂：取1789.6g上述获得的二水草酸锰颗粒、369.4g碳酸锂(以Li 2CO 3计，下同)，1150.1g磷酸二氢铵(以NH 4H 2PO 4计，下同)和31g蔗糖(以C 12H 22O 11计，下同)加入到20升去离子水中，将混合物搅拌10小时使其混合均匀，得到浆料。将所述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，得到粉料。在氮气(90体积％)+氢气(10体积％)保护气氛中，将上述粉料在700℃下烧结4小时，得到碳包覆的磷酸锰锂。
对比例2
除使用689.5g的碳酸锰和额外添加463.3g的碳酸亚铁以外，对比例2的其他条件与对比例1相同。
对比例3
除使用1148.9g的磷酸二氢铵和369.0g碳酸锂，并额外添加1.6g的60％浓度的稀硫酸以外，对比例3的其他条件与对比例1相同。
对比例4
除使用689.5g的碳酸锰、1148.9g的磷酸二氢铵和369.0g碳酸锂，并额外添加463.3g的碳酸亚铁、1.6g的60％浓度的稀硫酸以外，对比例4的其他条件与对比例1相同。
对比例5
除额外增加以下包覆步骤之外，其他条件与对比例4相同，最终得到非晶态磷酸铁锂(用量为62.8g)、碳包覆的正极活性材料。
将14.7g碳酸锂、46.1g碳酸亚铁、45.8g磷酸二氢铵和50.2g二水合草酸溶于500mL去离子水中，然后搅拌6小时使混合物充分反应，然后将反应后的溶液升温到120℃并保持该温度6小时，得到包覆液。包覆烧结步骤中的烧结温度为600℃，烧结时间为4小时以控制LiFePO 4的结晶度为8％。
对比例6
除额外增加以下包覆步骤之外，其他条件与对比例4相同，最终得到非晶态硼酸三锂(用量为62.8g)、碳包覆的正极活性材料。
将56.5g氢氧化锂和27.5g氧化硼加入到500mL去离子水中，得到包覆液。包覆烧结步骤中仅进行干燥处理不进行高温烧结处理，由此Li 3BO 3的结晶度为5％。
对比例7
除额外增加以下包覆步骤之外，其他条件与对比例4相同，最终得到非晶态磷酸铁锂(用量为15.7g)、非晶态硼酸三锂(用量为47.1g)、碳包覆的正极活性材料。
第一包覆层的包覆：将3.7g碳酸锂、11.6g碳酸亚铁、11.5磷酸二氢铵、12.6g二水合草酸溶于500mL去离子水中，然后搅拌6小时使混合物充分反应，然后将反应后的溶液升温到120℃并保持该温度6小时，得到第一包覆层悬浊液。包覆烧结步骤中的烧结温度为600℃，烧结时间为4小时以控制LiFePO 4的结晶度为8％。
第二包覆层的包覆：将42.4g氢氧化锂和20.6g氧化硼加入到500mL去离子水中，得到第二包覆层包覆液。包覆烧结步骤中仅进行干燥处理不进行高温烧结处理，由此Li 3BO 3的结晶度为5％。
相关参数测试
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包覆层、第二包覆层的组成。
2.扣式电池初始克容量测试：
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5分钟，然后按照0.1C放电至2.0V，此时的放电容量为初始克容量，记为D0。
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5分钟，按照0.1C放电至2.5V，静置5分钟，按照0.1C充电至4.3V，然后在4.3V下恒压充电至电流小于等于0.05mA，静置5分钟；然后按照0.1C放电至2.5V，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池的开路电压(OCV)和交流内阻(IMP)以监控SOC，并测量电池的体积。在每存储48小时后取出全电池，静置1小时后测试开路电压(OCV)、内阻(IMP)，并在冷却至室温后用排水法测量电池体积。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池的重力F 1，然后将电池完全置于去离子水(密度已知为1g/cm 3)中，测量此时的电池的重力F 2，电池受到的浮力F 浮即为F 1-F 2，然后根据阿基米德原理F 浮＝ρ×g×V 排，计算得到电池体积V＝(F 1-F 2)/(ρ×g)。
由OCV、IMP测试结果来看，本测试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，测量电池体积，并计算相对于存储前的电池体积，存储后的电池体积增加的百分比。
5.全电池45℃下循环性能测试：
在45℃的恒温环境下，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5分钟，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.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。
7.晶格变化率测量方法：
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 D8 Discover)中，采用1°/分钟对样品进行测试，并对测试数据进行整理分析，参照标准PDF卡片，计算出此时的晶格常数a0、b0、c0和v0(a0、b0和c0表示晶胞各个方向上的长度大小，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，将所述正极活性材料样品制备成扣电，并对上述扣电以0.05C小倍率进行充电，直至电流减小至0.01C。然后将扣电中的正极极片取出，并置于碳酸二甲酯(DMC)中浸泡8小时。然后烘干，刮粉，并筛选出其中粒径小于500nm的颗粒。取样并按照与上述测试新鲜样品同样的方式计算出其晶胞体积v1，将(v0-v1)/v0×100％作为其完全脱嵌锂前后的晶格变化率(晶胞体积变化率)示于表中。
8.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。
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(吨)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射线衍射法测试磷酸盐和硼酸盐的结晶度：
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。
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。
表1示出实施例1-1至1-35、对比例1至7的正极活性材料组成。
表2示出实施例1-1至1-35、对比例1至7的正极活性材料、正极极片、扣电或全电按照上述性能测试方法测得的性能数据。
表3示出实施例2-1至2-3的正极活性材料、正极极片、扣电或全电按照上述性能测试方法测得的性能数据。
表1
Figure PCTCN2022121540-appb-000001
表2
Figure PCTCN2022121540-appb-000002
表3
Figure PCTCN2022121540-appb-000003
综合实施例1-1至1-35以及对比例1至7可知，第一包覆层和第二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，提高电池的克容量，并改善电池的安全性能和循环性能。当在Mn位和P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，并改善电池的安全性能和循环性能。此外，包覆层中的磷酸盐的晶面间距为0.348nm，晶向(111)的夹角为25.562°。
综合实施例1-2至1-6可知，随着第一包覆层和第二包覆层的总量从3.2％增加至6.4％，所得材料的Li/Mn反位缺陷浓度逐渐下降，循环后Fe和Mn溶出量逐渐下降，对应电池的安全性能和45℃下的循环性能也得到改善，但克容量略有下降。可选地，当第一包覆层和第二包覆层的总量为4重量％至5.6重量％时，对应电池的综合性能最佳。
综合实施例1-3以及实施例1-7至1-10可知，随着第三包覆层的量从1％增加至6％，所得材料循环后Fe和Mn溶出量逐渐下降，对应电池的安全性能和45℃下的循环性能也得到改善，但克容量却略有下降。可选地，当第三包覆层的总量为2重量％至5重量％时，对应电池的综合性能最佳。
综合实施例1-11至1-15以及对比例5至6可知，当第一包覆层中存在LiFePO 4，第二包覆层中存在Li 3BO 3，且LiFePO 4和Li 3BO 3的重量比为1:3至3:1，并且尤其是1:3至1:1时，对电池性能的改善更加明显。
图7是实施例1-1制备的正极活性材料内核的XRD谱图与磷酸锰锂XRD标准谱图(00-033-0804)的对比图。如图7所示，本申请的正极活性材料内核与磷酸锰锂掺杂前的主要特征峰的位置基本一致，说明本申请的正极活性材料内核没有杂质相，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。
由表3可以看出，随着磷酸盐和硼酸盐的结晶度逐渐增加，对应正极活性材料的晶格变化率、Li/Mn反位缺陷浓度和Fe和Mn溶出量逐渐下降，电池的克容量逐渐增加，安全性能和循环性能也逐渐改善。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (20)

  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，
    所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，可选地包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，可选地包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，可选地包括选自B(硼)、S、Si和N中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，可选地包括选自S、F、Cl和Br中的一种或多种元素，所述m选自0.900至1.100的范围，可选地选自0.900至1.006的范围，所述x选自0至0.100的范围，可选地选自0.001至0.005的范围，所述y选自0.001至0.500的范围，可选地选自0.100至0.450的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，可选地选自0.001至0.005的范围，并且所述内核为电中性的；
    所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述X包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
  2. 根据权利要求1所述的正极活性材料，其中，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第三包覆层包含碳，并且所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，或者所述第一包覆层包括硼酸盐X aB bO c，所述第二包覆层包括磷酸盐MPO 4，可选地，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c。
  3. 根据权利要求2所述的正极活性材料，其中，
    所述第一包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计；和/或，
    所述第二包覆层的包覆量为大于0且小于等于6重量％，可选为1重量％至5重量％，基于所述内核的重量计；和/或，
    所述第三包覆层的包覆量为大于0且小于等于6重量％，可选为2重量％至5重量％，基于所述内核的重量计。
  4. 根据权利要求2或3所述的正极活性材料，其中，所述第一包覆层和所述第二包覆层的包覆总量为大于0且小于等于7重量％，可选为4重量％至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，所述磷酸盐MPO 4和所述硼酸盐X aB bO c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，所述磷酸盐MPO 4的晶面间距为0.345nm至0.358nm，晶向(111)的夹角为24.25°至26.45°。
  7. 根据权利要求1-6中任一项所述的正极活性材料，其中，
    所述磷酸盐MPO 4的结晶度为10％至100％，可选为50％至100％；和/或，
    所述硼酸盐X aB bO c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，
    在所述内核中，y与1-y的比值为1:10至10:1，可选为1:4至1:1；和/或，
    在所述内核中，z与1-z的比值为1:9至1:999，可选为1:499至1:249；和/或，
    在所述内核中，所述B包括选自Fe、Ti、V、Ni、Co和Mg中的一种或多种元素，可选地包括选自Fe、Ti、V、Ni、Co和Mg中的至少两种元素。
  9. 根据权利要求1-8中任一项所述的正极活性材料，其中，b:c为1:3。
  10. 根据权利要求1-9中任一项所述的正极活性材料，其中，所述正极活性材料满足如下条件(1)至(4)中的至少一者：
    (1)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；
    (2)所述正极活性材料的晶格变化率为8％以下，可选为4％以下；
    (3)所述正极活性材料的表面氧价态为-1.88以下，可选为-1.98至-1.88；
    (4)所述正极活性材料在3吨下的压实密度为2.0g/cm 3以上，可选为2.2g/cm 3以上。
  11. 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：所述内核包括Li mA xMn 1-yB yP 1-zC zO 4-nD n，所述A包括选自IA族、IIA族、IIIA族、IIB族、VB族和VIB族中的一种或多种元素，可选地包括选自Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，所述B包括选自IA族、IIA族、IIIA族、IVA族、VA族、IIB族、IVB族、VB族、VIB族和VIIIB族中的一种或多种元素，可选地包括选自Ti、V、Zr、Fe、Ni、Mg、Co、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，所述C包括选自IIIA族、IVA族、VA族和VIA族中的一种或多种元素，可选地包括选自B(硼)、S、Si和N中的一种或多种元素，所述D包括选自VIA族和VIIA族中的一种或多种元素，可选地包括选自S、F、Cl和Br中的一种或多种元素，所述m选自0.900至1.100的范围，可选地选自0.900至1.006的范围，所述x选自0至0.100的范围，可选地选自0.001至0.005的范围，所述y选自0.001至0.500的范围，可选地选自0.100至0.450的范围，所述z选自0.001至0.100的范围，所述n选自0至0.100的范围，可选地选自0.001至0.005的范围，并且所述内核为电中性的；
    包覆步骤：分别提供包括磷酸盐MPO 4、硼酸盐X aB bO c和碳源的包覆液，将所述内核材料加入到上述包覆液中并混合，经烧结获得正极活性材料，其中，所述正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括磷酸盐MPO 4、硼酸盐X aB bO c和碳，并且所述壳包括一层或多层包覆层，各层包覆层分别独立地包括磷酸盐MPO 4、硼酸盐X aB bO c和碳中的一种或多种，所述M包括选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述X包括 选自过渡金属、IA族、IIA族、IIIA族、IVA族、VA族和镧系中的一种或多种金属元素，可选地包括选自Li、Fe、Ni、Mg、Mn、Co、Cu、Zn、Ti、Ag、Zr、Nb、Sb和Al中的一种或多种元素，所述a选自1至4的范围，所述b选自1至7的范围，所述c选自2至12的范围，且所述a、b和c的值满足以下条件：使硼酸盐X aB bO c保持电中性。
  12. 根据权利要求11所述的方法，其中，所述提供内核材料的步骤包括以下步骤：步骤(1)：将锰的源、元素B的源和酸在容器中混合并搅拌，得到掺杂有元素B的锰盐颗粒；步骤(2)：将所述掺杂有元素B的锰盐颗粒与锂的源、磷的源、元素C的源、可选的元素A的源和可选的元素D的源在溶剂中混合并得到浆料，在惰性气体气氛保护下烧结后得到内核材料。
  13. 根据权利要求12所述的方法，其中，
    所述步骤(1)在20℃至120℃，可选为25℃至80℃的温度下进行；和/或，
    所述步骤(1)中所述搅拌在500rpm至700rpm下进行60分钟至420分钟，可选为120分钟至360分钟；和/或，
    所述步骤(2)中所述烧结为在惰性气体或惰性气体与氢气混合气氛下在600℃至800℃下烧结4小时至10小时。
  14. 根据权利要求12或13所述的方法，其中，
    所述元素A的源选自元素A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；和/或，
    所述元素B的源选自元素B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；和/或，
    所述元素C的源选自元素C的单质、硫酸盐、卤化物、硝酸盐、有机酸盐、氧化物、氢氧化物以及元素C的无机酸中的一种或多种；和/或，
    所述元素D的源选自元素D的单质和铵盐中的一种或多种。
  15. 根据权利要求11-14中任一项所述的方法，其中，所述包覆步骤包括任选顺序的包覆磷酸盐MPO 4的步骤、包覆硼酸盐X aB bO c的步骤和包覆碳的步骤，
    可选地，第一包覆步骤为包覆磷酸盐MPO 4的步骤，第二包覆步骤为包覆硼酸盐X aB bO c的步骤，第三包覆步骤为包覆碳的步骤，由此所获得的正极活性材料具有核-壳结构，其包括所述内核及包覆所述内核的壳，所述壳包括包覆所述内核的第一包覆层、包覆所述第一包覆层的第二包覆层以及包覆所述第二包覆层的第三包覆层，所述第一包覆层包括磷酸盐MPO 4，所述第二包覆层包括硼酸盐X aB bO c，所述第三包覆层包含碳；
    可选地，所述包覆磷酸盐MPO 4的步骤包括以下步骤：提供包含磷酸盐MPO 4的包覆液，将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到磷酸盐MPO 4包覆的材料；
    可选地，所述包覆硼酸盐X aB bO c的步骤包括以下步骤：提供包含硼酸盐X aB bO c的包覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到硼酸盐X aB bO c包覆的材料；
    可选地，所述包覆碳的步骤包括以下步骤：提供包含碳源的包覆液，然后将待包覆的材料加入到上述包覆液中，混合均匀，干燥，然后烧结，得到碳包覆的材料。
  16. 根据权利要求15所述的方法，其中，
    所述包含磷酸盐MPO 4的包覆液通过以下方法制备：将元素M的源和磷的源加入到溶剂中，搅拌均匀，得到混合物，然后将混合物升温至60℃至120℃保持2小时至8小时，得到包覆液；和/或，
    所述包含硼酸盐X aB bO c的包覆液通过以下方法制备：将元素X的源和硼的源加入到溶剂中，搅拌均匀，得到包覆液。
  17. 根据权利要求15或16所述的方法，其中，
    所述包覆磷酸盐MPO 4的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时；和/或，
    所述包覆硼酸盐X aB bO c的步骤中的所述烧结为在300℃至500℃下烧结2小时至10小时；和/或，
    所述包覆碳的步骤中的所述烧结为在500℃至800℃下烧结4小时至10小时。
  18. 一种正极极片，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1-10中任一项所述的正极活性材料或通过权利要求11-17中任一项所述的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，可选为90重量％至99.5重量％，基于所述正极膜层的总重量计。
  19. 一种二次电池，包括权利要求1-10中任一项所述的正极活性材料或通过权利要求11-17中任一项所述的方法制备的正极活性材料或者权利要求18所述的正极极片。
  20. 一种用电装置，包括权利要求19所述的二次电池。
PCT/CN2022/121540 2022-09-27 2022-09-27 正极活性材料、其制备方法以及包含其的正极极片、二次电池及用电装置 WO2024065145A1 (zh)

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