WO2017166863A1 - 一种橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料及其制备方法 - Google Patents

一种橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料及其制备方法 Download PDF

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WO2017166863A1
WO2017166863A1 PCT/CN2016/109096 CN2016109096W WO2017166863A1 WO 2017166863 A1 WO2017166863 A1 WO 2017166863A1 CN 2016109096 W CN2016109096 W CN 2016109096W WO 2017166863 A1 WO2017166863 A1 WO 2017166863A1
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lithium
manganese
salt
layered lithium
rich manganese
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French (fr)
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杨成浩
郑锋华
熊训辉
刘美林
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South China University of Technology SCUT
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Complex oxides containing nickel and at least one other metal element
    • C01G53/42—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2
    • C01G53/44—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Complex oxides containing nickel and at least one other metal element containing alkali metals, e.g. LiNiO2 containing manganese of the type (MnO2)n-, e.g. Li(NixMn1-x)O2 or Li(MyNixMn1-x-y)O2
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/80—Compounds containing nickel, with or without oxygen or hydrogen, and containing one or more other elements
    • C01G53/82—Compounds containing nickel, with or without oxygen or hydrogen, and containing two or more other elements
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
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    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C—CHEMISTRY; METALLURGY
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • Lithium-ion batteries have the advantages of high energy density, small self-discharge and good safety performance, making them widely used in portable electronic products such as mobile phone batteries, laptop batteries, and mobile power supplies.
  • how to further improve the energy density of lithium-ion batteries is the key to promoting the widespread application of lithium-ion batteries in electric vehicles and hybrid vehicles.
  • the specific capacity of the positive electrode material is relatively low relative to the negative electrode material, which is one of the important factors that it is difficult for lithium ion batteries to obtain high energy density and hinder their further development. Therefore, research and improvement of cathode materials is the key to the development of lithium-ion batteries.
  • cathode materials which have been commercialized mainly include LiCoO 2 and ternary materials having a layered structure, LiMn 2 O 4 having a spinel structure, and LiFePO 4 having an olivine structure.
  • the actual specific capacity of these positive electrode materials is low, both below 200 mAh/g.
  • layered lithium-rich manganese-based positive electrode materials have attracted wide interest due to their specific capacity exceeding 250 mAh/g and high operating voltage of 4.8V.
  • the layered lithium-rich manganese-based positive electrode material has poor rate performance, and has disadvantages such as specific capacity attenuation and pressure drop during the cycle.
  • the problem of specific capacity attenuation and pressure drop of the layered lithium-rich manganese-based cathode material during the cycle is mainly caused by the following two points. First, the active material is lost due to the reaction between the electrolyte and the lithium-rich manganese-based material itself, followed by The layered lithium-rich manganese-based material will transform to the spinel structure during the cycle, the layered structure is destroyed, and the Li + diffusion channel is blocked.
  • the methods for improving the cycle performance and rate performance of layered lithium-rich manganese-based cathode materials are mainly bulk phase doping and surface coating.
  • Bulk phase doping is to replace some ions in the bulk of the layered lithium-rich manganese-based cathode material with metal ions (Al 3+ , Ti 4+ or Fe 2+ , etc.), thereby stabilizing the material structure, improving its cycle stability and suppressing pressure. Drop the problem.
  • the surface coating is coated with a nano-level protective film on the surface of the lithium-rich manganese-based positive electrode material, thereby preventing the lithium-rich manganese-based positive electrode material from directly contacting and reacting with the electrolyte to improve the circulation of the layered lithium-rich manganese-based positive electrode material. Stability and the purpose of suppressing pressure drop problems.
  • the preparation method is simple and easy to operate, and can effectively improve the structural stability of the layered lithium-rich manganese-based positive electrode material, improve its cycle performance and suppress the pressure drop during the cycle.
  • a preparation method of olivine-type structure LiMPO4 surface-modified layered lithium-rich manganese-based cathode material comprises the following steps:
  • the mixed alkali solution obtained in the step 2) is added to the reaction vessel, the volume of the mixed alkali solution is 30%-50% of the volume of the reaction vessel, and the pH is controlled between 9-12 and the temperature is between 60-80 ° C;
  • the nickel salt, the cobalt salt and the manganese salt solution prepared in the step 1) are respectively uniformly added to the reaction vessel through a peristaltic pump, and the pH value in the whole process is between 9-12 and the temperature is between 60-80 ° C;
  • the precipitate is uniformly mixed with the lithium salt, and calcined at 450-550 ° C for 3-5 hours, and then calcined at 750-950 ° C for 10-16 hours to obtain a pure phase layered lithium-rich manganese-based cathode material;
  • the molar ratio of the substance to the lithium salt is 1: (1.05-1.1);
  • the lithium source, the transition metal source, the phosphorus source, and the additive are all dissolved in deionized water according to a molar ratio of 1:1:1: (1-5), and then the pure phase layered lithium-rich manganese-based cathode material obtained in the step 6) is added. , slowly evaporating at 80-100 ° C to form a gel;
  • the nickel salt is one or more of nickel sulfate, nickel nitrate and nickel acetate
  • the cobalt salt is one or more of cobalt sulfate, cobalt nitrate and cobalt acetate
  • manganese The salt is one or more of manganese sulfate, manganese nitrate, and manganese acetate.
  • the base in the step 2) is one or two of a sodium hydroxide solution and a potassium hydroxide solution, and the concentration is 2-5 mol/L; and the molar ratio of sodium hydroxide to ammonia water is 2:1.
  • the lithium salt in the step 6) is one or more of lithium hydroxide, lithium carbonate and lithium acetate.
  • step 6 the temperature is raised to 450-550 ° C at a heating rate of 5 ° C / min, the temperature is maintained for 3-5 hours, and then the temperature is raised to 750-950 ° C at a heating rate of 1-5 ° C / min, and the temperature is maintained at 10 -16 hours.
  • the lithium source described in the step 7) is one or more of lithium hydroxide, lithium dihydrogen phosphate and lithium carbonate.
  • the transition metal source in the step 7) is one or more of ferrous sulfate, ferrous nitrate, ferrous oxalate and ferrous acetate.
  • the phosphorus source described in the step 7) is one or more of dihydrogen phosphate, ammonium hydrogen phosphate and phosphoric acid; the additive is one or more of citric acid, tartaric acid, glucose and sucrose. And the amount of the control additive is 20-50% of the mass of the transition metal source.
  • step 8 the temperature is raised to 400-600 ° C at a heating rate of 1-5 ° C / min, and the temperature is maintained for 4-6 hours.
  • the present invention has the following advantages and technical effects:
  • the preparation method of the invention is simple, low in cost and environmentally friendly, and is suitable for large-scale industrial production.
  • the surface modification of the layered lithium-rich manganese-based positive electrode material by using the olivine-type structure LiMPO 4 can effectively improve the cycle stability and inhibit the pressure drop of the material during the cycle.
  • Example 1 is an XRD pattern of a LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material prepared in Example 1 and a pure phase layered lithium-rich manganese-based cathode material (before surface modification).
  • Example 2 is an SEM image of an olivine-type structure LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material prepared in Example 1 of the present invention.
  • Fig. 3 is a SEM image of the pure phase layered lithium-rich manganese-based positive electrode material (before surface modification) used in Example 1.
  • Example 4 is a graph showing a discharge cycle of a LiFePO 4 coated layered surface-modified manganese-based positive electrode material prepared in Example 1 and a pure phase layered lithium-rich manganese-based positive electrode material at a current density of 0.5 C.
  • FIG. 5 is a graph showing charge and discharge curves of the LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material prepared in Example 1 during the first 100 cycles of charge and discharge cycles.
  • the pure phase layered lithium-rich manganese-based positive electrode material prepared in Example 1 of Figure 6 was made into a sufficient electrical curve during the first 100 cycles of charge and discharge cycles.
  • the above mixed alkali solution was added to the reaction vessel in a volume of 30% of the volume of the reactor, and the pH was controlled to be 9, and the temperature was 60 °C.
  • the above prepared nickel salt, cobalt salt and manganese salt solution were uniformly added to the reaction vessel through a peristaltic pump, and the pH was controlled at 9 and the temperature was 60 ° C throughout the process.
  • the precipitate was uniformly mixed with 4.67 mol of lithium carbonate (molar ratio of precipitate to lithium salt was 1:1.05), and the temperature was raised to 450 ° C for 5 hours at a heating rate of 1 ° C / min, and then the temperature was raised at 1 ° C / min. When the temperature is raised to 750 ° C for 16 hours, a pure phase layered lithium-rich manganese-based positive electrode material can be obtained.
  • the obtained gel was vacuum dried at 100 ° C, crushed, and heated at a heating rate of 1 ° C / min to 400 ° C for 6 hours to obtain an olivine-type structure LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material. .
  • FIG. 1 is the XRD pattern of the LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material prepared in Example 1, and b in FIG. 1 is the pure phase layered lithium-rich manganese-based cathode obtained in Example 1.
  • XRD pattern of the material It can be seen from Fig. 1 that the layered lithium-rich manganese-based cathode material after LiFePO 4 surface modification is basically the same as the pure phase layer lithium-rich manganese-based cathode material before modification, that is to say, LiFePO 4 coating does not lead to layer rich
  • the structure of the lithium manganese based cathode material changes.
  • FIGS. 2 and 3 The SEM images of the LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material and the layered lithium-rich manganese-based cathode material obtained in Example 1 (before coating modification) are shown in FIGS. 2 and 3. It can be seen from the comparison of Fig. 2 and Fig. 3 that the nano-sized LiFePO 4 is uniformly coated on the surface of the layered lithium-rich manganese-based positive electrode material particles.
  • the LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material prepared in Example 1 (or pure phase layered lithium-rich manganese-based cathode material) and the conductive carbon black super P and the binder PVDF were in an 8:1:1 mass. After mixing in proportion, 0.4 g of N-methylpyrrolidone was added and stirred uniformly, and the obtained slurry was coated on a current collector aluminum foil, and dried at 120 ° C to obtain a positive electrode sheet, using a lithium metal sheet as a negative electrode, a polypropylene as a separator, and LiPF 6 .
  • a CR2032 button test battery was assembled in an argon-filled glove box. The obtained battery was subjected to a charge and discharge test at a rate of 0.5 C. The resulting cycle curve is shown in FIG.
  • the initial discharge specific capacity of the layered lithium-rich manganese-based positive electrode material modified by LiFePO4 prepared in Example 1 was 280 mAh/g, and after 100 cycles, the specific discharge capacity was 249.8 mAh/g, and the cycle was repeated.
  • the retention rate is approximately 89.2%.
  • the initial discharge specific capacity of the battery made of the pure phase layered lithium-rich manganese-based positive electrode material prepared in Example 1 was 208.3 mAh/g, and the discharge specific capacity was 143.1 mAh after 100 cycles. /g, the cycle retention rate is only 68.7%.
  • the layered lithium-rich manganese-based positive electrode material modified by LiFePO 4 has a relatively small pressure drop, while the pure phase layered lithium-rich manganese-based positive electrode material produces a large pressure drop.
  • the nano-LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material has stable structure, high specific capacity, good cycle stability, and can effectively inhibit the laminar lithium-rich manganese-based cathode material during charge-discharge cycle.
  • the resulting pressure drop problem It can be seen from the above results that the nano-LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material has stable structure, high specific capacity, good cycle stability, and can effectively inhibit the laminar lithium-rich manganese-based cathode material during charge-discharge cycle.
  • the resulting pressure drop problem is the pressure drop problem.
  • the above mixed alkali solution was added to the reaction vessel in a volume of 50% by volume of the reactor, and the pH was controlled to be 12 and the temperature was 80 °C.
  • the prepared nickel salt, cobalt salt and manganese salt solution were uniformly added to the reaction vessel through a peristaltic pump, and the pH value was 12 and the temperature was 80 ° C.
  • the precipitate was uniformly mixed with 7 mol of lithium hydroxide (the molar ratio of the precipitate to the lithium salt was 1:1.1), and the temperature was raised to 550 ° C for 4 hours at a heating rate of 5 ° C / min, and then the temperature was raised at 5 ° C / min.
  • the temperature is raised to 850 ° C for 13 hours, a pure phase layered lithium-rich manganese-based positive electrode material can be obtained.
  • the obtained gel was vacuum dried at 120 ° C, crushed, and heated at a heating rate of 5 ° C / min to 600 ° C for 4 hours to obtain an olivine-type structure LiFePO 4 surface-modified layered lithium-rich manganese-based cathode material. .
  • the NaOH solution and 2.12 mol of ammonia water were dissolved in deionized water to prepare a mixed alkali solution.
  • the concentration of the NaOH solution was 6 mol/L, and the molar concentration of the ammonia water was 3.5 mol/L.
  • the above mixed alkali solution was added to the reaction vessel, and its volume accounted for 40% of the volume of the reaction vessel, and the pH was controlled to be 10 and the temperature was 70 °C.
  • the prepared nickel salt, cobalt salt and manganese salt solution were separately added to the reaction vessel through a peristaltic pump at a constant rate, and the pH value was 9.5 and the temperature was 75 ° C.
  • the nickel salt, the cobalt salt and the manganese salt are added, and after standing for 16 hours, the precipitate is filtered, the precipitate is washed, and dried.
  • the obtained gel was vacuum dried at 110 ° C, crushed, and heated at a heating rate of 3.5 ° C / min to 500 ° C for 5 hours to obtain an olivine-type structure LiFePO 4 surface-modified layered lithium-rich manganese-based positive electrode. material.
  • the above mixed alkali solution was added to the reaction vessel in a volume of 35% of the volume of the reaction vessel, and the pH was controlled to be 10 and the temperature was 65 °C.
  • the nickel salt, the cobalt salt and the manganese salt are added, and after standing for 16 hours, the precipitate is filtered, the precipitate is washed, and dried.
  • the precipitate was uniformly ground with 4.24 mol of lithium carbonate (the molar ratio of precipitate to lithium salt was 1:1.06), and the temperature was raised to 450 ° C for 4.5 hours at a temperature increase rate of 1 ° C / min, and then at 1 ° C / min. When the heating rate is raised to 750 ° C for 1 hour, a pure phase layered lithium-rich manganese-based positive electrode material can be obtained.
  • the obtained gel is vacuum dried at 120 ° C, crushed, and heated at a heating rate of 5 ° C / min to 600 ° C for 4.5 hours to obtain an olivine-type structure LiMPO 4 coated layered lithium-rich manganese-based positive electrode. material.
  • the precipitate was uniformly mixed with 8.18 mol of lithium hydroxide (the molar ratio of the precipitate to the lithium salt was 1:1.08), and the temperature was raised to 550 ° C at a heating rate of 5 ° C / min for 6 hours, and then at 1 ° C / When the heating rate of min is raised to 750 ° C for 1 hour, a pure phase layered lithium-rich manganese-based positive electrode material can be obtained.
  • the obtained gel is vacuum dried at 120 ° C, crushed, and heated at a heating rate of 5 ° C / min to 600 ° C for 4 hours to obtain an olivine-type structure LiMPO 4 surface-modified layered lithium-rich manganese-based positive electrode. material.

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Abstract

本发明公开了一种橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料及其制备方法。该制备方法是：先通过共沉淀法和高温烧结法制备出纯相层状富锂锰基正极材料，然后利用溶胶-凝胶法将橄榄石型结构的LiMPO4均匀地包覆和掺杂到层状富锂锰基复合电极材料表面。本发明通过利用橄榄石型结构LiMPO4对层状富锂锰基正极材料进行表面修饰，可有效提高其循环稳定性、抑制材料在循环过程中产生压降。本发明的制备方法简单，成本低，环境友好，适用于大规模工业生产。

Description

一种橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料及其制备方法
技术领域
本发明属于锂离子电池电极材料制备技术领域，具体涉及一种橄榄石型结构LiMPO4 (M= Ni, Co, Mn, Fe, Cu, Al, Mo, Mg) 表面修饰层状富锂锰基正极材料及其制备方法。
背景技术
锂离子电池具有能量密度高，自放电小和安全性能好等优势，使其被广泛地应用于手机电池、笔记本电池、移动电源等便携式电子产品。近年来，如何进一步提高锂离子电池的能量密度，是促进锂离子电池在电动汽车和混合动力汽车领域广泛应用的关键。相对于负极材料，正极材料的比容量较低，这是锂离子电池很难获得高能量密度和阻碍其进一步发展的重要因素之一。因此，研究和提高正极材料是锂离子电池发展关键。目前，已经商业化的正极材料主要有，层状结构的LiCoO2与三元材料、尖晶石结构的LiMn2O4和橄榄石型结构的LiFePO4等。但是，这些正极材料的实际比容量较低，都在200mAh/g以下。近年来，层状富锂锰基正极材料因其超过250mAh/g的比容量和4.8V高工作电压，引起广泛的兴趣。但是，层状富锂锰基正极材料存在倍率性能差，循环过程中会产生比容量衰减和产生压降等缺点。层状富锂锰基正极材料在循环过程中比容量衰减和压降等问题主要是由以下两点引起的，首先是电解液与富锂锰基材料本身发生反应所导致活性物质损失，其次是层状富锂锰基材料在循环过程中会向尖晶石结构转变，层状结构遭到破坏，Li+扩散通道被堵塞。
研究发现，提高层状富锂锰基正极材料循环性能和倍率性能的方法主要有体相掺杂和表面包覆两种。体相掺杂，就是利用金属离子（Al3+、Ti4+或Fe2+等）替代层状富锂锰基正极材料本体中部分离子，进而稳定材料结构，改善其循环稳定性能和抑制压降问题。表面包覆，是在富锂锰基正极材料表面包覆一层纳米级保护膜，从而防止富锂锰基正极材料与电解液直接接触和反应，以达到改善层状富锂锰基正极材料循环稳定性能和抑制压降问题的目的。
发明内容
本发明提供一种橄榄石型结构LiMPO4 (M= Ni, Co, Mn, Fe, Cu, Mo, Mg) 表面修饰层状富锂锰基正极材料及其制备方法。该制备方法简单易操作，可有效提高层状富锂锰基正极材料结构稳定性，提高其循环性能和抑制其在循环过程中的压降问题。
本发明所述的橄榄石型结构LiMPO4 (M= Ni, Co, Mn, Fe, Cu, Mo, Mg) 表面修饰层状富锂锰基正极材料的制备方法，包括利用共沉淀法制备纯相层状富锂锰基正极材料和利用橄榄石型结构LiMPO4 (M= Ni, Co, Mn, Fe, Cu, Mo, Mg) 对其进行表面修饰。并且以质量分数计: 橄榄石型结构LiMPO4 (M= Ni, Co, Mn, Fe, Cu, Al, Mo, Mg) 包覆层所占质量分数为1-10%，富锂材料所占质量分数为90-99%。
本发明的目的通过以下技术方案实现。
一种橄榄石型结构LiMPO4 表面修饰层状富锂锰基正极材料的制备方法，包括以下步骤：
1)称取镍盐、钴盐和锰盐分别溶解在去离子水中，配制成浓度均为0.5-2mol/L的盐溶液；所述镍盐、钴盐和锰盐是按照化学式Li1.2MnxNiyCo0.8-x-yO2中Ni、Co和Mn元素的摩尔比称取，其中， 0.4≤x≤0.6， 0.1≤y≤0.2；
2) 将碱和氨水溶解在去离子水中配制成混合碱溶液；其中，碱的浓度为2-10mol/L，氨水的摩尔浓度为2-5mol/L；
3) 将步骤2）所得混合碱溶液加入到反应釜中，混合碱溶液的体积占反应釜容积30%-50%，并且控制pH值在9-12之间、温度在60-80℃之间；
4) 将步骤1）配制好的镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值在9-12之间、温度在60-80℃之间；
5) 镍盐、钴盐和锰盐加入完，静置陈化12-20小时后，然后将沉淀过滤，洗涤沉淀，烘干；
6) 将沉淀物与锂盐均匀混合，并在450-550℃预烧3-5小时，然后在750-950℃煅烧10-16小时，即得到纯相层状富锂锰基正极材料；所述沉淀物与锂盐的摩尔比为1：(1.05-1.1)；
7) 将锂源、过渡金属源、磷源、添加剂按照摩尔比1：1：1：(1-5)全部溶于去离子水中，然后加入步骤6）所得的纯相层状富锂锰基正极材料，在80-100℃下慢慢蒸干，形成凝胶；
8) 将步骤7）所得凝胶在100-120℃下真空烘干，破碎，在400℃-600℃预烧4-6小时，即得到橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料。
进一步地，步骤1)中，所述的镍盐为硫酸镍、硝酸镍和醋酸镍中的一种或几种；钴盐为硫酸钴、硝酸钴和醋酸钴中的一种或几种；锰盐为硫酸锰、硝酸锰和醋酸锰中的一种或几种。
进一步地，步骤2)所述的碱为氢氧化钠溶液和氢氧化钾溶液中的一种或两种，并且浓度为2-5mol/L；氢氧化钠与氨水的摩尔比为2：1。
进一步地，步骤6)所述的锂盐为氢氧化锂、碳酸锂和醋酸锂中的一种或几种。
进一步地，步骤6)中是以5℃/min的升温速率升温到450-550℃，保温3-5小时，然后再以1-5℃/min的升温速率升温到750-950℃，保温10-16小时。
进一步地，步骤7)所述的锂源为氢氧化锂、磷酸二氢锂和碳酸锂中的一种或几种。
进一步地，步骤7)所述的过渡金属源为硫酸亚铁、硝酸亚铁、草酸亚铁和醋酸亚铁中的一种或几种。
进一步地，步骤7)中所述的磷源为磷酸二氢氨、磷酸氢氨和磷酸中的一种或几种；所述的添加剂为柠檬酸、酒石酸、葡萄糖和蔗糖中的一种或几种，并且控制添加剂的用量为过渡金属源质量的20～50%。
进一步地，步骤8)中是以1-5℃/min的升温速率升温到400-600℃，保温4-6小时。
由上述制备方法制得的一种橄榄石型结构LiMPO4 表面修饰层状富锂锰基正极材料，所述层状富锂锰基正极材料的化学式为：Li1.2MnxNiyCo0.8-x-yO2，其中，x、y为摩尔数，0.4≤x≤0.6， 0.1≤y≤0.2；所述层状富锂锰基正极材料的橄榄石型结构LiMPO4包覆层为LiNiPO4，LiCoPO4， LiMnPO4，LiFePO4，LiCuPO4，LiAlPO4， LiMoPO4或LiMgPO4，并且控制橄榄石型结构LiMPO4包覆层的质量为层状富锂锰基正极材料质量的1～10%。
与现有技术相比，本发明具有如下优点与技术效果：
1、本发明的制备方法简单，成本低，环境友好，适用于大规模工业生产。
2、本发明通过利用橄榄石型结构LiMPO4对层状富锂锰基正极材料进行表面修饰，可有效提高其循环稳定性、抑制材料在循环过程中产生压降。
附图说明
图1为实施例1制得的LiFePO4表面修饰层状富锂锰基正极材料和纯相层状富锂锰基正极材料（表面修饰前）的XRD图谱。
图2为本发明实施例1制得的橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料的SEM图。
图3为实施例1中用到的纯相层状富锂锰基正极材料（表面修饰前）的SEM图。
图4为实施例1制得的LiFePO4包覆层状表面修饰锰基正极材料和纯相层状富锂锰基正极材料在0.5C电流密度下的放电循环曲线图。
图5为实施例1制得的LiFePO4表面修饰层状富锂锰基正极材料在前100圈充放电循环过程中充放电曲线图。
图6实施例1制得的纯相层状富锂锰基正极材料制成在前100圈充放电循环过程中充分电曲线。
具体实施方式
下面以LiFePO4包覆层状富锂锰基正极材料为具体实施例对本发明作进一步说明，但本发明并不局限于这些实施例。
实施例1
1. 按照层状富锂锰基正极材料化学式Li1.2Mn0.54Ni0.13Co0.13O2中所示Mn：Ni：Co = 0.54:0.13:0.13的摩尔比分别称取2mol硫酸锰、0.48mol硫酸钴和0.48mol硫酸镍溶解在去离子水中，配制成浓度为0.5mol/L的盐溶液。
2. 将5.92mol NaOH溶液和 3mol氨水溶解在去离子水中配制成混合碱溶液，NaOH溶液浓度为2mol/L，氨水浓度为2mol/L。
3. 将上述混合碱溶液加入到反应釜中，其体积占反应釜容积30%，并且控制pH值为9、温度为60℃。
4. 将上述配制好镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中控制pH值在9、温度为60℃。
5. 待镍盐、钴盐和锰盐溶液加入完，静置陈化12小后，将沉淀过滤、洗涤、烘干。
6. 将沉淀物与4.67mol碳酸锂混合均匀（沉淀物与锂盐的摩尔比为1：1.05），以1℃/min的升温速率升温到450℃预烧5小时后，以1℃/min的升温速率升温到750℃煅烧16小时，即可得到纯相层状富锂锰基正极材料。
7. 将0.101mol碳酸锂、0.101mol草酸亚铁、0.101mol磷酸二氢氨和0.101mol柠檬酸全部溶于去离子水中，加入所制备层状富锂锰基正极材料，在80℃下慢慢蒸干，形成凝胶。
8. 将所得凝胶在100℃下真空烘干，破碎，以1℃/min的升温速率升温到400℃煅烧6小时，即得到橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料。
图1中的a为实施例1制得的LiFePO4表面修饰层状富锂锰基正极材料的XRD图谱，图1中的b为实施例1中制得的纯相层状富锂锰基正极材料的XRD图谱。从图1可以看出，LiFePO4表面修饰后层状富锂锰基正极材料与改性前的纯相层状富锂锰基正极材料基本一致，也就是说LiFePO4包覆没有导致层状富锂锰基正极材料结构发生改变。实施例1所得的LiFePO4表面修饰层状富锂锰基正极材料和层状富锂锰基正极材料(包覆改性前的)的SEM图如图2和图3所示。由图2和图3对比可以得知，纳米级LiFePO4均匀地包覆在层状富锂锰基正极材料颗粒表面。
将实施例1制备的LiFePO4表面修饰层状富锂锰基正极材料（或纯相层状富锂锰基正极材料）与导电炭黑super P、粘结剂PVDF按照8：1：1的质量比例混合后，加入0.4g N-甲基吡咯烷酮搅拌均匀后，将所得浆料涂在集流体铝箔上，在120℃干燥制得正极片，以金属锂片作为负极、聚丙烯为隔膜和LiPF6为电解液，在充满氩气的手套箱中组装得到CR2032型纽扣实验电池。将所得实施电池在倍率为0.5C倍率下进行充放电测试，所得的循环曲线如图4所示。
图4中的A和B分别为实施例1制得的LiFePO4表面修饰层状富锂锰基正极材料和纯相层状富锂锰基正极材料制成的在0.5C电流密度下的循环曲线。由图4A可知，以实施例1制备的LiFePO4表面修饰的层状富锂锰基正极材料的初始放电比容量为280mAh/g，经过100次循环后，其放电比容量为249.8mAh/g，循环保持率约为89.2%。由图4B可知，由实施例1制备的纯相层状富锂锰基正极材料制成的电池的初始放电比容量为208.3mAh/g，在经过100次循环后，其放电比容量为143.1mAh/g，循环保持率仅为68.7%。此外通过图5和图6可知LiFePO4表面修饰的层状富锂锰基正极材料产生压降比较小，而纯相层状富锂锰基正极材料产生较大的压降。由以上结果可知，采用纳米LiFePO4表面修饰层状富锂锰基正极材料结构稳定、比容量高、循环稳定性好，并且能够有效地抑制层状富锂锰基正极材料在充放电循环过程中产生的压降问题。
实施例2
1. 按照层状富锂锰基正极材料化学式中Li1.2Mn0.5Ni0.15Co0.15O2中所示Mn：Ni：Co = 0.54:0.13:0.13的摩尔比分别称取3mol 硝酸锰、0.72mol硝酸钴和0.72mol硝酸镍溶解在去离子水中，配制成浓度为2mol/L的盐溶液;
2. 将2.65mol NaOH溶液和1.3mol氨水溶解在去离子水中配制成混合碱溶液，NaOH溶液浓度为10mol/L，氨水摩尔浓度为5mol/L。
3. 将上述混合碱溶液加入到反应釜中，其体积占反应釜容积50%，并且控制pH值为12、温度为80℃。
4. 将上述配制好镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值为12、温度为80℃。
5. 待镍盐、钴盐和锰盐加入完，静置陈化20小时后，然后将沉淀过滤，洗涤沉淀，烘干。
6. 将沉淀物与7mol氢氧化锂混合均匀（沉淀物与锂盐的摩尔比为1：1.1），以5℃/min的升温速率升温到550℃预烧4小时，然后以5℃/min的升温速率升温到850℃煅烧13小时，即可得到纯相层状富锂锰基正极材料。
7. 将0.202mol碳酸锂、0.202mol硝酸亚铁、0.202mol磷酸二氢氨和1.01mol酒石酸全部溶于去离子水，然后加入所制备层状富锂锰基正极材，在100℃下慢慢蒸干，形成凝胶。
8. 将所得凝胶在120℃下真空烘干，破碎，以5℃/min的升温速率升温到600℃煅烧4小时，即得到橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料。
对实施例2所得的橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料的制备及电化学性能分析：称取0.4g所得的LiFePO4表面修饰层状富锂锰基正极材料，加入0.05g的乙炔黑作导电剂和0.05g的PVDF（HSV900）作粘结剂，充分研磨后，加入0.4g的NMP分散混合，调浆均匀后于铜箔上拉浆制片，烘干后在厌氧手套箱中以金属钠片为对电极，组装成CR2025扣式电池。在25℃下，以500mA/g在2-4.8V间进行100次充放电循环，采用纳米LiFePO4表面修饰层状富锂锰基正极材料结构稳定、比容量高、循环稳定性好，并且能够有效地抑制层状富锂锰基正极材料在充放电循环过程中产生的压降问题，显示了优异的电化学性能。
实施例3
1. 按照层状富锂锰基正极材料化学式中Li1.2Mn0.52Ni0.14Co0.14O2中所示Mn：Ni：Co = 0.54:0.13:0.13的摩尔比分别称取1.85mol醋酸锰、0.45mol醋酸钴和0.45mol醋酸镍溶解在去离子水中，配制成浓度为1.2mol/L的盐溶液;
2. 将4.15mol NaOH溶液和2.12mol氨水溶解在去离子水中配制成混合碱溶液，NaOH溶液浓度为6mol/L，氨水摩尔浓度为3.5mol/L。
3. 将上述混合碱溶液加入到反应釜中，其体积占反应釜容积40%，控制pH值为10、温度为70℃。
4. 将上述配制好的镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值为9.5、温度为75℃。
5. 镍盐、钴盐和锰盐加入完，静置陈化16小时后，将沉淀过滤，洗涤沉淀，烘干。
6. 将沉淀物与4.4 mol醋酸锂混合均匀（沉淀物与锂盐的摩尔比为1：1.07），以3.5℃/min的升温速率升温到500℃预烧4小时，以3.5℃/min的升温速率升温到850℃煅烧13小时，即可得到纯相层状富锂锰基正极材料。
7. 将0.141mol碳酸锂、0.141mol硫酸亚铁、0.141mol磷酸二氢氨和0.423mol酒石酸全部溶于去离子水，然后加入所制备层状富锂锰基正极材，在80℃下慢慢蒸干，形成凝胶。
8. 将所得凝胶在110℃下真空烘干，破碎，以3.5℃/min的升温速率升温到500℃煅烧5小时，即可得到橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料。
对实施例3所得的橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料的制备及电化学性能分析：称取0.4g所得的LiFePO4表面修饰层状富锂锰基正极材料，加入0.05g的乙炔黑作导电剂和0.05g的PVDF（HSV900）作粘结剂，充分研磨后，加入0.4g的NMP分散混合，调浆均匀后于铜箔上拉浆制片，烘干后在厌氧手套箱中以金属钠片为对电极，组装成CR2025扣式电池。在25℃下，以500mA/g在2-4.8V间进行100次充放电循环，采用纳米LiFePO4表面修饰层状富锂锰基正极材料结构稳定、比容量高、循环稳定性好，并且能够有效地抑制层状富锂锰基正极材料在充放电循环过程中产生的压降问题，显示了优异的电化学性能。
实施例4
1. 按照层状富锂锰基正极材料化学式中Li1.2Mn0.6Ni0.1Co0.1O2中所示Mn：Ni：Co = 0.6:0.1:0.1的摩尔比分别称取2mol硫酸锰、0.33mol硫酸钴和0.33mol硫酸镍溶解去离子水中，配制成浓度为1mol/L的盐溶液。
2. 将7.15mol NaOH溶液和1.5mol氨水溶解在去离子水中配制成混合碱溶液，NaOH溶液浓度为3mol/L，氨水摩尔浓度为4mol/L。
3. 将上述混合碱溶液加入到反应釜中，其体积占反应釜容积的35%，并且控制pH值为10，温度为65℃。
4. 将上述配制好镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值在10、温度为65℃。
5. 镍盐、钴盐和锰盐加入完，静置陈化16小时后，然后将沉淀过滤，洗涤沉淀，烘干。
6. 将沉淀物与4.24mol碳酸锂研磨均匀（沉淀物与锂盐的摩尔比为1：1.06），并以1℃/min的升温速率升温到450℃预烧4.5小时，然后以1℃/min的升温速率升温到750℃煅烧11小时，即可得到纯相层状富锂锰基正极材料。
7. 将0.141mol碳酸锂、0.141mol草酸亚铁、0.141mol磷酸二氢氨和0.423mol酒石酸全部溶于去离子水，然后加入所制备层状富锂锰基正极材，在80℃下慢慢蒸干，形成凝胶。
8. 将所得凝胶在120℃下真空烘干，破碎，以5℃/min的升温速率升温到600℃煅烧4.5小时，即可得到橄榄石型结构LiMPO4 包覆层状富锂锰基正极材料。
对实施例4所得的橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料的制备及电化学性能分析：称取0.4g所得的LiFePO4表面修饰层状富锂锰基正极材料，加入0.05g的乙炔黑作导电剂和0.05g的PVDF（HSV900）作粘结剂，充分研磨后，加入0.4g的NMP分散混合，调浆均匀后于铜箔上拉浆制片，烘干后在厌氧手套箱中以金属钠片为对电极，组装成CR2025扣式电池。在25℃下，以500mA/g在2-4.8V间进行100次充放电循环，采用纳米LiFePO4表面修饰层状富锂锰基正极材料结构稳定、比容量高、循环稳定性好，并且能够有效地抑制层状富锂锰基正极材料在充放电循环过程中产生的压降问题，显示了优异的电化学性能。
实施例5
1. 按照层状富锂锰基正极材料化学式中Li1.2Mn0.48Ni0.16Co0.16O2中所示Mn：Ni：Co = 0.48:0.16:0.16的摩尔比分别称取3mol硝酸锰、1mol硝酸钴和1mol硝酸镍溶解去离子水中，配制成浓度为1mol/L的盐溶液。
2. 将6.65mol NaOH溶液和1.13mol氨水溶解在去离子水中配制成混合碱溶液，NaOH溶液浓度为3.5mol/L，氨水摩尔浓度为4.5mol/L。
3. 将上述混合碱溶液加入到反应釜中，占反应釜容积45%，并且控制pH值在11、温度为75℃。
4. 将上述配制好镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值在11、温度为75℃。
5. 待镍盐、钴盐和锰盐加入完，静置陈化11小时后，然后将沉淀过滤，洗涤沉淀，烘干。
6. 将沉淀物与8.18mol氢氧化锂混合均匀（沉淀物与锂盐的摩尔比为1：1.08），并以5℃/min的升温速率升温到550℃预烧6小时，然后在以1℃/min的升温速率升温到750℃煅烧11小时，即可得到纯相层状富锂锰基正极材料。
7. 将0.202mol碳酸锂、0.202mol硫酸亚铁、0.202mol磷酸二氢氨和1.01mol酒石酸全部溶于去离子水，然后加入所制备层状富锂锰基正极材，在80℃下，慢慢蒸干，形成凝胶。
8. 将所得凝胶在120℃下真空烘干，破碎，以5℃/min的升温速率升温到600℃煅烧4小时，即可得到橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料。
对实施例5所得的橄榄石型结构LiFePO4表面修饰层状富锂锰基正极材料的制备及电化学性能分析：称取0.4g所得的LiFePO4表面修饰层状富锂锰基正极材料，加入0.05g的乙炔黑作导电剂和0.05g的PVDF（HSV900）作粘结剂，充分研磨后，加入0.4g的NMP分散混合，调浆均匀后于铜箔上拉浆制片，烘干后在厌氧手套箱中以金属钠片为对电极，组装成CR2025扣式电池。在25℃下，以500mA/g在2-4.8V间进行100次充放电循环，采用纳米LiFePO4表面修饰层状富锂锰基正极材料结构稳定、比容量高、循环稳定性好，并且能够有效地抑制层状富锂锰基正极材料在充放电循环过程中产生的压降问题，显示了优异的电化学性能。

Claims (10)

  1. 一种橄榄石型结构LiMPO4 表面修饰层状富锂锰基正极材料的制备方法，其特征在于，包括以下步骤：
    1)称取镍盐、钴盐和锰盐分别溶解在去离子水中，配制成浓度均为0.5-2mol/L的盐溶液；所述镍盐、钴盐和锰盐是按照化学式Li1.2MnxNiyCo0.8-x-yO2中Ni、Co和Mn元素的摩尔比称取，其中， 0.4≤x≤0.6， 0.1≤y≤0.2；
    2) 将碱和氨水溶解在去离子水中配制成混合碱溶液；其中，碱的浓度为2-10mol/L，氨水的摩尔浓度为2-5mol/L；
    3) 将步骤2）所得混合碱溶液加入到反应釜中，混合碱溶液的体积占反应釜容积30%-50%，并且控制pH值在9-12之间、温度在60-80℃之间；
    4) 将步骤1）配制好的镍盐、钴盐和锰盐溶液通过蠕动泵分别匀速加入反应釜中，整个过程中的pH值在9-12之间、温度在60-80℃之间；
    5) 镍盐、钴盐和锰盐溶液加入完，静置陈化12-20小时后，然后将沉淀过滤，洗涤沉淀，烘干；
    6) 将沉淀物与锂盐均匀混合，并在450-550℃预烧3-5小时，然后在750-950℃煅烧10-16小时，即得到纯相层状富锂锰基正极材料；所述沉淀物与锂盐的摩尔比为1：(1.05-1.1)；
    7) 将锂源、过渡金属源、磷源、添加剂按照摩尔比1：1：1：(1-5)全部溶于去离子水中，然后加入步骤6）所得的纯相层状富锂锰基正极材料，在80-100℃下蒸干，形成凝胶；
    8) 将步骤7）所得凝胶在100-120℃下真空烘干，破碎，在400℃-600℃预烧4-6小时，即得到橄榄石型结构LiMPO4表面修饰层状富锂锰基正极材料。
  2. 根据权利要求1所述的制备方法，其特征在于，步骤1)中，所述的镍盐为硫酸镍、硝酸镍和醋酸镍中的一种或几种；钴盐为硫酸钴、硝酸钴和醋酸钴中的一种或几种；锰盐为硫酸锰、硝酸锰和醋酸锰中的一种或几种。
  3. 根据权利要求1所述的制备方法，其特征在于，步骤2)所述的碱为氢氧化钠溶液和氢氧化钾溶液中的一种或两种，并且浓度为2-5mol/L；氢氧化钠与氨水的摩尔比为2：1。
  4. 根据权利要求1所述的制备方法，其特征在于，步骤6)所述的锂盐为氢氧化锂、碳酸锂和醋酸锂中的一种或几种。
  5. 根据权利要求1所述的制备方法，其特征在于，步骤6)中是以1-5℃/min的升温速率升温到450-550℃，保温3-5小时，然后再以1-5℃/min的升温速率升温到750-950℃，保温10-16小时。
  6. 根据权利要求1所述的制备方法，其特征在于，步骤7)所述的锂源为氢氧化锂、磷酸二氢锂和碳酸锂中的一种或几种。
  7. 据权利要求1所述的制备方法，其特征在于，步骤7)所述的过渡金属源为硫酸亚铁、硝酸亚铁、草酸亚铁和醋酸亚铁中的一种或几种。
  8. 根据权利要求1所述的制备方法，其特征在于，步骤7)中所述的磷源为磷酸二氢氨、磷酸氢氨和磷酸中的一种或几种；所述的添加剂为柠檬酸、酒石酸、葡萄糖和蔗糖中的一种或几种，并且控制添加剂的用量为过渡金属源质量的20～50%。
  9. 根据权利要求1所述的制备方法，其特征在于，步骤8)中是以1-5℃/min的升温速率升温到400-600℃，保温4-6小时。
  10. 由权利要求1-9任一项所述的制备方法制得的一种橄榄石型结构LiMPO4 表面修饰层状富锂锰基正极材料，其特征在于，所述层状富锂锰基正极材料的化学式为：Li1.2MnxNiyCo0.8-x-yO2，其中，x、y为摩尔数，0.4≤x≤0.6， 0.1≤y≤0.2；所述层状富锂锰基正极材料的橄榄石型结构LiMPO4包覆层为LiNiPO4，LiCoPO4， LiMnPO4，LiFePO4，LiCuPO4，LiAlPO4， LiMoPO4或LiMgPO4，并且控制橄榄石型结构LiMPO4包覆层的质量为层状富锂锰基正极材料质量的1～10%。
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