WO2015127841A1 - 锂离子电池正极活性材料的制备方法 - Google Patents

锂离子电池正极活性材料的制备方法 Download PDF

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WO2015127841A1
WO2015127841A1 PCT/CN2015/071319 CN2015071319W WO2015127841A1 WO 2015127841 A1 WO2015127841 A1 WO 2015127841A1 CN 2015071319 W CN2015071319 W CN 2015071319W WO 2015127841 A1 WO2015127841 A1 WO 2015127841A1
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particles
limpo
linpo
active material
positive electrode
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French (fr)
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戴仲葭
何向明
王莉
李建军
尚玉明
高剑
王要武
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江苏华东锂电技术研究院有限公司
清华大学
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Publication of WO2015127841A1 publication Critical patent/WO2015127841A1/zh
Priority to US15/243,723 priority Critical patent/US9923204B2/en

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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
    • 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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/06—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances
    • H01B1/08—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of other non-metallic substances oxides
    • 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
    • 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
    • H01M4/364—Composites as mixtures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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 invention relates to a preparation method of a cathode active material for a lithium ion battery, in particular to a method for preparing a transition metal phosphate LiM x N 1-x PO 4 cathode active material.
  • Lithium metal phosphate LiMPO 4 having an olivine structure is a positive active material mainly used for lithium ion batteries, and has the advantages of low raw material price, abundant storage, no pollution to the environment, stable chemical properties, and good safety. Among them, lithium iron phosphate (LiFePO 4 ) has a theoretical capacity of 170 mAh/g and excellent cycle performance. However, the voltage platform of lithium iron phosphate 3.4V severely limits the increase in energy density of lithium ion batteries. Lithium manganese phosphate (LiMnPO 4 ), lithium cobalt phosphate (LiCoPO 4 ), lithium nickel phosphate (LiNiPO 4 ) can greatly improve the energy density of lithium ion batteries.
  • LiMnPO 4 lithium cobalt phosphate
  • LiNiPO 4 lithium nickel phosphate
  • the prior art solves the above problems by preparing a material of a doped metal lithium phosphate LiM x N 1-x PO 4 (for example, LiMn x Fe 1-x PO 4 or LiMn x Mg 1-x PO 4 ).
  • the commonly used methods for preparing the doped metal lithium phosphate salt LiM x N 1-x PO 4 are solvothermal method and solid phase synthesis method.
  • the solvothermal method is specifically: dissolving a phosphorus source, a lithium source, two or more metal sources in an organic solvent in a certain ratio, and heating in a solvothermal reaction vessel to obtain the doped metal lithium phosphate.
  • the solvothermal method can prepare the doped metal lithium phosphate salt with good morphology, particle size controllability and good crystal form.
  • the solid phase synthesis method is specifically: mixing a phosphorus source, a lithium source, two or more metal sources and a solvent in a certain ratio and ball milling, and then calcining at a high temperature in an inert atmosphere to obtain the doped metal lithium phosphate.
  • the solid phase synthesis method can prepare the doped metal lithium phosphate salt which is stoichiometrically controlled, but in the conventional solid phase synthesis method, the phosphorus source, the lithium source and the metal source generally adopt a powder of phosphate (such as ammonium dihydrogen phosphate).
  • phosphate such as ammonium dihydrogen phosphate
  • lithium carbonate or lithium hydroxide organic metal salts or inorganic metal salts (such as ferrous oxalate / manganese, ferrous acetate / manganese or manganese carbonate) as a precursor of sintering, Li, P, O and other elements in these powders Diffusion transfer and recrystallization into the doped metal lithium phosphate LiM x N 1-x PO 4 crystal during sintering, due to the complex diffusion of elements such as Li, P, O during high-temperature sintering, and recrystallization
  • the growth of new crystals is affected by factors such as temperature, interfacial properties, crystal defects, etc.
  • the lithium metal phosphate LiM x N 1-x PO 4 synthesized by the conventional solid phase method has many structural defects and its shape. The appearance and particle size are difficult to precisely control.
  • a method for preparing a lithium ion positive electrode active material comprising: providing LiMPO 4 particles and LiNPO 4 particles, wherein the LiMPO 4 particles and the LiNPO 4 particles are orthorhombic crystals having a space group of Pnma, Wherein M is Fe, Mn, Co or Ni, N and M are different elements, N is a divalent metal; the LiMPO 4 particles and the LiNPO 4 particles are mixed to obtain a precursor; and the precursor is sintered A LiM x N 1-x PO 4 particle positive active material was obtained, where 0 ⁇ x ⁇ 1.
  • the preparation method of the lithium ion positive electrode active material provided by the invention adopts the LiMPO 4 particles and the LiNPO 4 particles with the same crystal structure as the precursor, and the LiM x N 1-x PO 4 positive electrode active material is prepared by the solid phase synthesis method, and can be precisely controlled.
  • Stoichiometry of LiMn x Fe 1-x PO 4 particles Because of the presence and concentration of Mn in the Fe element only differences between the particles and the LiMPO 4 LiNPO 4 particles during sintering and therefore, the particles and the LiMPO 4 LiNPO 4 particles can still maintain its original crystalline structure, morphology And particle size, only M element and N element will undergo diffusion transfer to form LiM x N 1-x PO 4 particles. Therefore, the morphology and particle size of the LiM x N 1-x PO 4 positive active material can be controlled by controlling the morphology and particle size of LiMPO 4 particles and LiNPO 4 particles.
  • FIG. 1 is a flow chart of a method for preparing a positive active material for a lithium ion battery according to the present invention.
  • 2a and 2b are XRD test views of the precursor of Example 1 before and after sintering, respectively.
  • Figure 3 is a scanning electron micrograph of LiMn 0.4 Fe 0.6 PO4 particles in Example 1 of the present invention.
  • FIG. 4a, 4b are scanning electron micrographs of LiMnPO 4 particles in Examples 1 to 5 of the present invention
  • Fig. 4c is a transmission electron micrograph of LiMnPO 4 particles in Examples 1 to 5 of the present invention
  • Figure 4d is a first to fifth embodiment of the present invention. A Fourier transform of a transmission electron micrograph of LiMnPO 4 particles.
  • FIG. 4i, 4j are scanning electron micrographs of LiFePO 4 particles in Examples 1 to 5 of the present invention
  • FIG. 4k is a transmission electron micrograph of LiFePO 4 particles in Examples 1 to 5 of the present invention
  • FIG. 4l is Examples 1 to 5 of the present invention.
  • Fig. 6 is a distribution map of Fe element and Mn element of LiMn 0.4 Fe 0.6 PO 4 /C particles in Example 3 of the present invention.
  • a method for preparing a lithium ion positive electrode active material comprising:
  • LiMPO 4 particles and LiNPO 4 particles wherein the LiMPO 4 particles and the LiNPO 4 particles are both orthorhombic crystals having a space group of Pnma, wherein M is Fe, Mn, Co or Ni, N and M are different elements, and N is a divalent metal;
  • the precursor is sintered to obtain a LiM x N 1-x PO 4 particle positive active material, wherein 0 ⁇ x ⁇ 1.
  • the LiMPO 4 particles and the LiNPO 4 particles have the same crystal structure, and both are orthorhombic crystals, and the space group is Pnma olivine crystal.
  • M may be Fe, Mn, Co or Ni.
  • N may be a divalent metal, and N and M are different elements.
  • N may be Fe, Mn, Co, Ni, Mg, Ca, Zn, Cu, Al, B, Cr, Nb, Sc, Ti, V, Be, Sr, Ba, Zr or La.
  • the LiMPO 4 particles or the LiNPO 4 particles may be one or more of spherical particles, rod-shaped particles, and flake particles.
  • the LiMPO 4 particles or the LiNPO 4 particles may be tabular particles, and the flake particles have a larger contact area during the sintering process of step S4, which is more favorable for M element and N during sintering.
  • the element undergoes diffusion transfer.
  • the LiMPO 4 particles or the LiNPO 4 particles may be nanoparticles, the nanoparticles having higher reactivity and being more favorable for the solid phase reaction during sintering. More preferably, the LiMPO 4 particles and the LiNPO 4 particles may both be nano-flaky particles.
  • the morphology of the LiMPO 4 particles may be the same as or different from the morphology of the LiNPO 4 particles.
  • the size of the LiMPO 4 particles may be the same as or different from the size of the LiNPO 4 particles. Since the LiMPO 4 particles and the LiMPO 4 particles are already intact crystals, and the crystal structures of the two are the same, only Fe and Mn elements per unit volume are between the LiMPO 4 particles and the LiNPO 4 particles.
  • the LiMPO 4 particles lose the M element, and the N element is obtained to form LiM x N 1-x PO 4 particles, and the LiM x N 1-x PO 4 particles inherit the morphology of the LiNPO 4 particles, Crystal structure and particle size; the LiNPO 4 particles lose the N element, and the M element is formed to form LiM x N 1-x PO 4 particles, the LiM x N 1-x PO 4 particles inheriting the morphology of the LiNPO 4 particles, Crystal structure and particle size.
  • the morphology and particle size of the LiM x N 1-x PO 4 can thus be controlled by controlling the morphology and particle size of the LiMPO 4 particles and the LiNPO 4 particles.
  • the morphology of the LiMPO 4 is the same as that of the LiNPO 4 and the particle size is also the same to prepare the LiM x N 1-x PO 4 particles having a uniform morphology and particle size, so that LiM x The N 1-x PO 4 positive active material has more excellent properties.
  • the ratio of the LiMPO 4 particles and the LiNPO 4 particles is not limited, and may be determined according to the value of x in the LiM x N 1-x PO 4 particles actually required, for example, when preparing When the value of x in the LiM x N 1-x PO 4 particles is 4, the LiMPO 4 particles and the LiNPO 4 particles may be mixed at a molar ratio of 4:6. When N is one of Fe, Mn, Co or Ni, the LiMPO 4 particles and the LiNPO 4 particles are mixed in an arbitrary ratio to obtain a LiM x N 1-x PO 4 positive active material having a relatively high capacity. .
  • the LiMPO 4 particles and the The molar ratio of the LiNPO 4 particles is such that the Li value of the LiM x N 1-x PO 4 is greater than 0.9, so that the LiM x N 1-x PO 4 has a higher capacity.
  • the LiMPO 4 particles and the LiNPO 4 particles may be uniformly mixed to obtain the precursor, such that the LiMPO 4 particles and the LiNPO 4 particles have the largest contact area.
  • the manner in which the LiNPO 4 particles and the LiMPO 4 particles are mixed is not limited, but the crystal structure and morphology of the LiNPO 4 particles and the LiMPO 4 particles are destroyed as much as possible during mixing, for example, The mixing was carried out by ultrasonication in a suspension. When the LiNPO 4 particles and the LiMPO 4 particles are nanoparticles, the mixing may be performed by grinding without damaging the morphology and crystal structure of the LiNPO 4 particles and the LiMPO 4 particles.
  • step S4 before the sintering, the step of adding a carbon source to the precursor may be further included, and the carbon source and the precursor are sintered together.
  • the carbon source may be decomposed during the sintering process to coat a surface of the LiMPO 4 particles and the LiNPO 4 particles with a single carbon layer, and after the sintering is completed, LiM x N 1-x PO 4 /C is obtained. Particles.
  • the elemental carbon layer can prevent coalescence of the LiMPO 4 particles and the LiNPO 4 particles during sintering, so that the LiM x N 1-x PO 4 particles obtained by sintering do not coalesce, and On the one hand, the conductivity of the LiM x N 1-x PO 4 particles can be improved.
  • the carbon source can be cracked into elemental carbon during the sintering of step S4.
  • the carbon source may be one or more of sucrose, glucose, spartan 80, phenolic resin, epoxy resin, furan resin, polyacrylic acid, polyacrylonitrile, polyethylene glycol, and polyvinyl alcohol.
  • the amount of the carbon source added can be determined according to actual needs.
  • the carbon source is added in an amount of from 5% to 15% by mass of the LiMPO 4 particles and the LiNPO 4 particles.
  • the manner in which the carbon source is added to the precursor is not limited as long as the precursor and the carbon source can be mixed together.
  • the carbon source may be added when the LiMPO 4 particles and the LiNPO 4 particles are mixed, the carbon source and the precursor may be mixed, and then sintered; or after the precursor is obtained, The precursor and the carbon source are mixed and then sintered; the carbon source may also be impregnated onto the precursor by dipping the precursor into a solution of a carbon source compound, and then performing sintering.
  • the LiMPO 4 particles, the LiNPO 4 particles, and the carbon source in the precursor may be uniformly mixed and then sintered, so that the carbon layer can be uniformly distributed during sintering.
  • Coating on the surface of all of the LiMPO 4 particles and the LiNPO 4 particles better prevents coalescence of the precursor.
  • a grinding manner LiMPO 4 with the particles, the particles and the carbon source LiNPO 4, LiMPO 4 the particles in said precursor, said particles and LiNPO 4 The carbon source is uniformly mixed.
  • the sintering temperature may be from 300 ° C to 1200 ° C.
  • the sintering temperature may be from 500 ° C to 1000 ° C.
  • the sintering time can be from 2 hours to 20 hours.
  • the sintering time may be from 4 hours to 10 hours.
  • the precursor is sintered under an inert atmosphere.
  • the nano-flaky LiMnPO 4 particles and the nano-platelet LiFePO 4 particles were mixed at a molar ratio of 4:6 and ground for 15 minutes to obtain a precursor, and the precursor was sintered at 650 ° C for 5 hours in a nitrogen atmosphere to obtain LiMn 0.4 Fe. 0.6 PO 4 granules.
  • the diffraction peaks of LiMnPO 4 and LiFePO 4 disappear in the XRD pattern, and a new diffraction peak between the diffraction peaks of LiMnPO 4 and LiFePO 4 appears, and the intensity of the new diffraction peak changes significantly.
  • the new diffraction peak is the diffraction peak of LiMn 0.4 Fe 0.6 PO 4 , indicating that LiMnPO 4 particles and LiFePO 4 particles completely react in the sintering process and produce pure phase and good crystallinity olivine LiMn 0.4 Fe 0.6 PO 4 particles. It can be seen from Fig. 3 and Figs.
  • LiMn 0.4 Fe 0.6 PO 4 particles obtained by sintering is consistent with the morphology of LiMnPO 4 particles and LiFePO 4 particles, and both are nano-flaky particles.
  • the LiMn 0.4 Fe 0.6 PO 4 particles are slightly agglomerated, the LiMn 0.4 Fe 0.6 PO 4 particle size remains consistent with the size of the LiMnPO 4 particles and the LiFePO 4 particles.
  • the nano-flaky LiMnPO 4 particles, nano-platelet LiFePO 4 particles and sucrose were mixed and ground for 15 minutes to obtain a precursor.
  • the molar ratio of LiMnPO 4 particles to LiFePO 4 particles was 2:8, and the mass of sucrose was LiMnPO 4 particles and LiFePO 4 particles.
  • the precursor was sintered at 650 ° C for 5 hours in a nitrogen atmosphere at a mass ratio of 15% to obtain LiMn 0.2 Fe 0.8 PO 4 /C particles.
  • the LiMn 0.2 Fe 0.8 PO 4 /C particles were used as a positive electrode active material to assemble a lithium ion battery.
  • the positive electrode was composed of a mixture of LiMn 0.2 Fe 0.8 PO 4 /C particles having a mass percentage of 80%, 5% acetylene black, 5% conductive graphite, and 10% polyvinylidene fluoride.
  • the button cell battery was tested for battery performance after standing at room temperature for a period of time.
  • This example is basically the same as Example 2 except that the molar ratio of LiMnPO 4 particles to LiFePO 4 particles is 4:6, and LiMn 0.4 Fe 0.6 PO 4 /C particles are obtained after sintering.
  • This comparative example is basically the same as the above-mentioned Example 2 except that the nano-flaky LiFePO 4 particles and sucrose are mixed and ground for 15 minutes to obtain a precursor, and the precursor is sintered to obtain LiFePO 4 /C particles.
  • the present comparative example is basically the same as the above-mentioned Example 2, except that the nano-flaky LiMnPO 4 particles and sucrose are mixed and ground for 15 minutes to obtain a precursor, and the precursor is sintered to obtain LiMnPO 4 /C particles.
  • the diffraction peaks of LiMnPO 4 and LiFePO 4 do not appear in the XRD test chart of Example 3 of the present invention, but LiMn 0.4 Fe 0.6 PO 4 between the diffraction peaks of LiMnPO 4 and LiFePO 4 appears.
  • the diffraction peaks indicate that all of the LiMnPO 4 particles and the LiFePO 4 particles in the third embodiment of the present invention react to form LiMn 0.4 Fe 0.6 PO 4 particles, and the crystallinity of the LiMn 0.4 Fe 0.6 PO 4 particles is good.
  • the morphology and particle size of LiMn 0.4 Fe 0.6 PO 4 /C particles in Example 3 of the present invention are consistent with the morphology and particle size of LiMnPO 4 particles and LiFePO 4 particles, and LiMn
  • the crystal growth direction of 0.4 Fe 0.6 PO 4 /C particles is consistent with the crystal growth direction of LiMnPO 4 particles and LiFePO 4 particles, and both grow along the bc crystal plane.
  • the LiMn 0.4 Fe 0.6 PO 4 /C particles do not coalesce. phenomenon. As can be seen from FIG.
  • the distribution map of the Mn element in the LiMn 0.4 Fe 0.6 PO 4 /C particles of Example 3 is identical to the distribution map of the Fe element, and it is confirmed that the solid phase reaction in the sintering process of Example 3 has been completely completed.
  • Elemental detection of the LiMn 0.4 Fe 0.6 PO 4 /C particles by inductively coupled plasma atomic emission spectrometry (ICP-AES) revealed that the molar ratio of Mn:Fe in LiMn 0.4 Fe 0.6 PO 4 /C particles was 4: 5.983, the error from the expected stoichiometry is less than 1%, indicating that the preparation method can precisely control the stoichiometry of the LiMn 0.4 Fe 0.6 PO 4 particles.
  • This example is basically the same as Example 2 except that the molar ratio of LiMnPO 4 particles to LiFePO 4 particles is 6:4.
  • This example is basically the same as Example 2 except that the molar ratio of LiMnPO 4 particles to LiFePO 4 particles is 8:2.
  • LiMn x Fe 1-x PO 4 particles/C prepared in Examples 2 to 5 of the present invention and LiFePO 4 /C particles of Comparative Example 1 and LiMnPO 4 / Comparative Example 2 Compared with the C particles, it has stable cycle performance, good rate performance, good capacity retention and high energy density. Among them, LiMn 0.4 Fe 0.6 prepared in Example 3 of the present invention at 0.1 C rate.
  • the discharge capacity of the PO 4 /C particles was increased by 60% compared to the LiMnPO 4 /C particles of Comparative Example 2, reaching 160.6 mAh/g, and the high capacity was maintained after multiple cycles, LiMn 0.4 Fe 0.6 PO 4 / C particles and the energy density increased by 53% compared to Comparative Example 1 LiFePO 4 / C particles, LiMn 0.4 Fe 0.6 PO 4 / C particles both higher capacity and higher energy density.
  • the preparation method of the lithium ion positive electrode active material provided by the invention adopts the LiMPO 4 particles and the LiNPO 4 particles with the same crystal structure as the precursor, and the LiM x N 1-x PO 4 positive electrode active material is prepared by the solid phase synthesis method, and can be precisely controlled. Stoichiometry of LiMn x Fe 1-x PO 4 particles. Because of the presence and concentration of Mn in the Fe element only differences between the particles and the LiMPO 4 LiNPO 4 particles during sintering and therefore, the particles and the LiMPO 4 LiNPO 4 particles can still maintain its original crystalline structure, morphology And particle size, only M element and N element will undergo diffusion transfer to form LiM x N 1-x PO 4 particles.
  • the morphology and particle size of the LiM x N 1-x PO 4 positive active material can be controlled by controlling the morphology and particle size of LiMPO 4 particles and LiNPO 4 particles.
  • the positive active material of the lithium ion battery prepared by the preparation method of the invention has stable cycle performance, good rate performance, good capacity retention and high energy density.

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Abstract

一种锂离子正极活性材料的制备方法，包括：提供LiMPO4颗粒和LiNPO4颗粒，所述LiMPO4颗粒和所述LiNPO4颗粒均为正交晶系、空间群为Pnma的橄榄石型晶体，其中M为Fe、Mn、Co或Ni，N为二价金属，N与M为不同的元素；将所述LiMPO4颗粒和所述LiNPO4颗粒混合得到前驱体；以及将所述前驱体进行烧结，得到LiMxN1-xPO4颗粒正极活性材料，其中0<x<1。

Description

锂离子电池正极活性材料的制备方法 技术领域
本发明涉及一种锂离子电池正极活性材料的制备方法，尤其涉及一种掺杂过渡金属磷酸盐LiMxN1-xPO4正极活性材料的制备方法。
背景技术
具有橄榄石结构的金属磷酸锂盐LiMPO4是一种主要用于锂离子电池的正极活性材料，具有原材料价格低廉、储藏丰富，对环境无污染，化学性质稳定，安全性好等优点。其中磷酸铁锂（LiFePO4）具有170mAh/g的理论容量和优良的循环性能，然而磷酸铁锂3.4V的电压平台严重限制了锂离子电池能量密度的提高。磷酸锰锂（LiMnPO4）、磷酸钴锂（LiCoPO4）、磷酸镍锂（LiNiPO4）能极大地提高锂离子电池的能量密度，然而，这几种材料的电子电导率和锂离子扩散速率较低，限制了其应用。现有技术通过制备掺杂金属磷酸锂盐LiMxN1-xPO4（例如LiMnxFe1-xPO4或LiMnxMg1-xPO4）材料来解决上述问题。
目前制备所述掺杂金属磷酸锂盐LiMxN1-xPO4常用的方法有溶剂热法和固相合成法。溶剂热法具体为：按一定比例将磷源、锂源、两种或两种以上金属源溶解于有机溶剂中，在溶剂热反应釜中加热进行反应得到所述掺杂金属磷酸锂盐。该溶剂热法可制备出形貌、颗粒尺寸可控且晶型较好的所述掺杂金属磷酸锂盐，然而由于该溶剂热法在反应过程中的溶液条件复杂、且不同的金属离子在溶剂热反应中的结晶行为不同，因此该溶剂热法制备出的所述掺杂金属磷酸锂盐其化学计量不可控。固相合成法具体为：按一定比例将磷源、锂源、两种或两种以上金属源及溶剂混合并球磨，之后在惰性氛围下高温煅烧获得所述掺杂金属磷酸锂盐。固相合成法可制备出化学计量可控的所述掺杂金属磷酸锂盐，但传统固相合成法中磷源、锂源及金属源一般采用粉体的磷酸盐（如磷酸二氢铵）、碳酸锂或氢氧化锂、有机金属盐或无机金属盐（如草酸亚铁/锰、醋酸亚铁/锰或碳酸锰)作为烧结的前驱体，这些粉体中的Li、P、O等元素在烧结过程中进行扩散转移并重新结晶生长为所述掺杂金属磷酸锂盐LiMxN1-xPO4晶体，由于高温烧结过程中Li、P、O等元素的扩散现象复杂，并且重新结晶生长为新的晶体会受到温度、界面性质、晶体缺陷等因素的影响，传统固相法合成的所述掺杂金属磷酸锂盐LiMxN1-xPO4晶体结构缺陷较多，且其形貌、颗粒尺寸难以精确调控。
发明内容
有鉴于此，确有必要提供一种形貌、颗粒尺寸及化学计量均可控的掺杂金属磷酸锂盐LiMxN1-xPO4正极活性材料的制备方法。
一种锂离子正极活性材料的制备方法，包括：提供LiMPO4颗粒和LiNPO4颗粒，所述LiMPO4颗粒和所述LiNPO4颗粒均为正交晶系、空间群为Pnma的橄榄石型晶体，其中M为Fe、Mn、Co或Ni， N与M为不同的元素，N为二价金属；将所述LiMPO4颗粒和所述LiNPO4颗粒混合得到前驱体；以及将所述前驱体进行烧结，得到LiMxN1-xPO4颗粒正极活性材料，其中0<x<1。
本发明提供的锂离子正极活性材料的制备方法，以晶体结构相同的LiMPO4颗粒和LiNPO4颗粒为前驱体，采用固相合成法制备LiMxN1-xPO4正极活性材料，可精确控制LiMnxFe1-xPO4颗粒的化学计量。由于该LiMPO4颗粒和该LiNPO4颗粒间仅Fe元素和Mn元素的浓度存在差异，因此在烧结过程中，该LiMPO4颗粒和该LiNPO4颗粒仍可保持其原有的晶型结构、形貌和颗粒尺寸，仅M元素和N元素会发生扩散转移而形成LiMxN1-xPO4颗粒。故可通过控制LiMPO4颗粒及LiNPO4颗粒的形貌、颗粒尺寸来控制LiMxN1-xPO4正极活性材料的形貌和颗粒尺寸。
 附图说明
图1为本发明提供的锂离子电池正极活性材料的制备方法流程图。
图2a和图2b分别为本发明实施例1前驱体进行烧结前和进行烧结后的的XRD测试图。
图3为本发明实施例1中LiMn0.4Fe0.6PO4颗粒的扫描电镜照片。
图4a、4b为本发明实施例1至5中LiMnPO4颗粒的扫描电镜照片，图4c为本发明实施例1至5中LiMnPO4颗粒的透射电镜照片，图4d为本发明实施例1至5中LiMnPO4颗粒透射电镜照片的傅立叶变换图。
图4e、4f为本发明实施例3中LiMn0.4Fe0.6PO4/C颗粒的扫描电镜照片，图4g为本发明实施例3中LiMn0.4Fe0.6PO4/C颗粒的透射电镜照片，图4h为本发明实施例3中LiMn0.4Fe0.6PO4/C颗粒透射电镜照片的傅立叶变换图。
图4i、4j为本发明实施例1至5中LiFePO4颗粒的扫描电镜照片，图4k为本发明实施例1至5中LiFePO4颗粒的透射电镜照片，图4l为本发明实施例1至5中LiFePO4颗粒透射电镜照片的傅立叶变换图。
图5为本发明对比例1（x=0）、实施例2（x=2）、实施例3（x=4）、实施例4（x=6）、实施例5（x=8）、对比例2（x=1）中LiMnxFe1-xPO4/C颗粒的XRD测试图。
图6为本发明实施例3中LiMn0.4Fe0.6PO4/C颗粒Fe元素和Mn元素的分布映射图。
图7a为本发明对比例1（x=0）、实施例2（x=2）、实施例3（x=4）、实施例4（x=6）、实施例5（x=8）、对比例2（x=1）中正极活性材料LiMnxFe1-xPO4/C颗粒的在不同倍率下的循环性能测试对比图。
图7b为本发明对比例1（x=0）、实施例2（x=2）、实施例3（x=4）、实施例4（x=6）、实施例5（x=8）、对比例2（x=1）中正极活性材料LiMnxFe1-xPO4/C颗粒的在不同倍率下的能量密度对比图。
具体实施方式
下面将结合具体实施方式及附图，对本发明提供的锂离子正极活性材料的制备方法作进一步的详细说明。
请参阅图1，一种锂离子正极活性材料的制备方法，包括：
S1，提供LiMPO4颗粒和LiNPO4颗粒，所述LiMPO4颗粒和所述LiNPO4颗粒均为正交晶系、空间群为Pnma的橄榄石型晶体，其中M为Fe、Mn、Co或Ni， N与M为不同的元素，N为二价金属；
S2，将所述LiMPO4颗粒和所述LiNPO4颗粒混合得到前驱体；以及
S3，将所述前驱体进行烧结，得到LiMxN1-xPO4颗粒正极活性材料，其中0<x<1。
在步骤S1中，所述LiMPO4颗粒和所述LiNPO4颗粒具有相同的晶体结构，均为正交晶系、空间群为Pnma的橄榄石型晶体。M可为Fe、Mn、Co或Ni。N可为二价金属，N与M为不同的元素。优选地，N可为Fe、Mn、Co、Ni、Mg、Ca、Zn、Cu、Al、B、Cr、Nb、Sc、Ti、V、Be、Sr、Ba、Zr或La。
所述LiMPO4颗粒或所述LiNPO4颗粒可为球形颗粒、棒状颗粒和片状颗粒中的一种或几种。优选地，所述LiMPO4颗粒或所述LiNPO4颗粒可为片状颗粒，在步骤S4的烧结过程中，所述片状颗粒具有更大的接触面积，更有利于烧结过程中M元素和N元素进行扩散转移。优选地，所述LiMPO4颗粒或所述LiNPO4颗粒可为纳米颗粒，所述纳米颗粒具有更高的反应活性，更有利于烧结过程中固相反应的进行。更为优选地，所述LiMPO4颗粒和所述LiNPO4颗粒可均为纳米片状颗粒。
所述LiMPO4颗粒的形貌与所述LiNPO4颗粒的形貌既可以相同，也可以不同。当所述LiMPO4颗粒的形貌与所述LiNPO4颗粒的形貌相同时，所述LiMPO4颗粒的尺寸与所述LiNPO4颗粒的尺寸既可以相同，也可以不同。由于所述LiMPO4颗粒和所述LiMPO4颗粒已经是完整的晶体，且二者的晶体结构相同，故所述LiMPO4颗粒和所述LiNPO4颗粒之间仅单位体积内的Fe元素和Mn元素的摩尔浓度存在差异，因此，在步骤S4的烧结过程中，仅所述LiMPO4颗粒M元素和所述LiNPO4颗粒的N元素会发生扩散，而所述LiMPO4颗粒与所述LiNPO4颗粒的形貌、晶体结构和颗粒尺寸均不会发生变化。当步骤S4烧结完毕后，所述LiMPO4颗粒失去M元素、得到N元素形成LiMxN1-xPO4颗粒，该LiMxN1-xPO4颗粒继承了所述LiNPO4颗粒形貌、晶体结构和颗粒尺寸；所述LiNPO4颗粒失去N元素、得到M元素形成LiMxN1-xPO4颗粒，该LiMxN1-xPO4颗粒继承了所述LiNPO4颗粒的形貌、晶体结构和颗粒尺寸。因此可通过控制所述LiMPO4颗粒及所述LiNPO4颗粒的形貌和颗粒尺寸来控制所述LiMxN1-xPO4的形貌和颗粒尺寸。优选地，所述LiMPO4的形貌与所述LiNPO4的形貌相同且颗粒尺寸也相同，以便制备出形貌、颗粒尺寸均一的所述LiMxN1-xPO4颗粒，使LiMxN1-xPO4正极活性材料具有更优良的性能。
在步骤S3中，所述LiMPO4颗粒和所述LiNPO4颗粒的比例不限，可根据实际所需的所述LiMxN1-xPO4颗粒中x的值来进行确定，例如当要制备的所述LiMxN1-xPO4颗粒中x值为4时，可将所述LiMPO4颗粒和所述LiNPO4颗粒按照摩尔比4：6的比例进行混合。当N为Fe、Mn、Co或Ni中的一种时，所述LiMPO4颗粒和所述LiNPO4颗粒以任意比例进行混合均可获得容量较高的LiMxN1-xPO4正极活性材料。当N为Mg、Ca、Zn、Cu、Al、B、Cr、Nb、Sc、Ti、V、Be、Sr、Ba、Zr或La中的一种时，优选地，所述LiMPO4颗粒和所述LiNPO4颗粒的摩尔比使所述LiMxN1-xPO4的x值大于0.9，以使所述LiMxN1-xPO4具有较高的容量。
优选地，可将所述LiMPO4颗粒和所述LiNPO4颗粒混合均匀后得到所述前驱体，使所述所述LiMPO4颗粒和所述LiNPO4颗粒具有最大的接触面积。将所述LiNPO4颗粒和所述LiMPO4颗粒进行混合的方式不限，但要尽量避免在混合过程中破坏所述LiNPO4颗粒和所述LiMPO4颗粒的晶型结构和形貌，例如可采用在悬浊液中进行超声的方式进行混合。当所述LiNPO4颗粒和所述LiMPO4颗粒为纳米颗粒时，可采用研磨的方式进行混合而不会破坏所述LiNPO4颗粒和所述LiMPO4颗粒的形貌和晶体结构。
在步骤S4中，在进行所述烧结前，可进一步包括一在所述前驱体中加入一碳源的步骤，使所述碳源和所述前驱体一起进行烧结。该碳源在所述烧结过程中，可进行分解从而在所述LiMPO4颗粒和所述LiNPO4颗粒表面包覆一单质碳层，并在烧结完毕后得到LiMxN1-xPO4/C颗粒。所述单质碳层一方面可阻止烧结过程中所述LiMPO4颗粒和所述LiNPO4颗粒发生聚结，从而使烧结得到的所述LiMxN1-xPO4颗粒不会发生聚结，另一方面可提高所述LiMxN1-xPO4颗粒的导电性能。
所述碳源在步骤S4的烧结过程中可裂解成单质碳。优选地，所述碳源可为蔗糖、葡萄糖、司班80、酚醛树脂、环氧树脂、呋喃树脂、聚丙烯酸、聚丙烯腈、聚乙二醇和聚乙烯醇中的一种或几种。所述碳源的加入量可根据实际需要进行确定。优选地，所述碳源的加入量为所述LiMPO4颗粒和所述LiNPO4颗粒质量和的5%至15%。
将所述碳源加入所述前驱体的方式不限，只要能将所述前驱体和所述碳源混合在一起即可。可在将所述LiMPO4颗粒和所述LiNPO4颗粒混合时加入所述碳源，使所述碳源和所述前驱体混合，然后再进行烧结；也可在得到所述前驱体后，将所述前驱体和所述碳源进行混合，然后再进行烧结；也可通过将所述前驱体浸渍到一碳源化合物溶液中，使所述碳源浸渍到所述前驱体上，然后再进行烧结。优选地，可使所述前驱体中的所述LiMPO4颗粒、所述LiNPO4颗粒及所述碳源混合均匀后再进行所述烧结，从而使在烧结过程中，所述碳层能均匀地包覆在所有所述LiMPO4颗粒和所述LiNPO4颗粒的表面，更好地防止所述前驱体发生聚结。在本发明实施例中，采用将所述LiMPO4颗粒、所述LiNPO4颗粒和所述碳源一起进行研磨的方式，使所述前驱体中的所述LiMPO4颗粒、所述LiNPO4颗粒和所述碳源混合均匀。
在步骤S4中，所述烧结温度可为300℃至1200℃。优选地，所述烧结温度可为500℃至1000℃。所述烧结时间可为2小时至20小时。优选地，所述烧结时间可为4小时至10小时。优选地，可在惰性气氛下对所述前驱体进行烧结。
实施例1
将0.016mol的MnSO4和0.048mol的LiOH·H2O溶解于20mL乙二醇和去离子水的混合溶液中（乙二醇和去离子水的体积比为4：1），与0.016mol H3PO4混合后于180℃下进行溶剂热反应，反应12小时后即得到纳米片状LiMnPO4颗粒；
将0.016mol的FeSO4和0.048mol的LiOH·H2O溶解于20mL乙二醇和去离子水的混合溶液中（乙二醇和去离子水的体积比为4：1），与0.016mol H3PO4混合后于180℃下进行溶剂热反应，反应12小时后即得到纳米片状LiFePO4颗粒；
将纳米片状LiMnPO4颗粒及纳米片状LiFePO4颗粒按照摩尔比4：6的比例混合后研磨15min得到前驱体，将所述前驱体在氮气气氛中650℃下烧结5小时，得到LiMn0.4Fe0.6PO4颗粒。
从图2可以看出，在进行烧结后，XRD图谱中LiMnPO4及LiFePO4的衍射峰消失，出现了位于LiMnPO4及LiFePO4的衍射峰之间的新衍射峰，该新衍射峰的强度明显变大，该新衍射峰即为LiMn0.4Fe0.6PO4的衍射峰，说明LiMnPO4颗粒及LiFePO4颗粒在烧结过程中完全反应并生成了纯相、结晶度良好的橄榄石型LiMn0.4Fe0.6PO4颗粒。从图3及图4a、4b、4i、4j可以看出，烧结所得到的LiMn0.4Fe0.6PO4颗粒的形貌与LiMnPO4颗粒及LiFePO4颗粒的形貌一致，均为纳米片状颗粒，且虽然LiMn0.4Fe0.6PO4颗粒略有聚结，但LiMn0.4Fe0.6PO4颗粒尺寸仍与LiMnPO4颗粒及LiFePO4颗粒的尺寸保持一致。
实施例2
将0.016mol的MnSO4和0.048mol的LiOH·H2O溶解于20mL乙二醇和去离子水的混合溶液中（乙二醇和去离子水的体积比为4：1），与0.016mol H3PO4混合后于180℃下进行溶剂热反应，反应12小时后即得到纳米片状LiMnPO4颗粒；
将0.016mol的FeSO4和0.048mol的LiOH·H2O溶解于20mL乙二醇和去离子水的混合溶液中（乙二醇和去离子水的体积比为4：1），与0.016mol H3PO4混合后于180℃下进行溶剂热反应，反应12小时后即得到纳米片状LiFePO4颗粒；
将纳米片状LiMnPO4颗粒、纳米片状LiFePO4颗粒及蔗糖混合后研磨15min得到前驱体，LiMnPO4颗粒与LiFePO4颗粒的摩尔比为2：8，蔗糖的质量为LiMnPO4颗粒与LiFePO4颗粒质量和的15%，将所述前驱体在氮气气氛中在650℃下烧结5小时，得到LiMn0.2Fe0.8PO4/C颗粒。
将该LiMn0.2Fe0.8PO4/C颗粒作为正极活性材料组装锂离子电池。正极由质量百分比为80%的LiMn0.2Fe0.8PO4/C颗粒、5%的乙炔黑、5%的导电石墨及10%的聚偏氟乙烯混合组成。以金属锂为负极，Celgard 2400微孔聚丙烯膜为隔膜，以1mol/L LiPF6/EC+DMC+EMC（3:1:1体积比）为电解液，在氩气气氛手套箱中组成CR2032型纽扣电池，在室温下静置一段时间后进行电池性能测试。
实施例3
本实施例与实施例2基本相同，其区别仅在于，LiMnPO4颗粒与LiFePO4颗粒的摩尔比为4：6，烧结后得到LiMn0.4Fe0.6PO4/C颗粒。
对比例1
本对比例与上述实施例2基本相同，其区别仅在于，将纳米片状LiFePO4颗粒及蔗糖混合后研磨15min得到前驱体，烧结该前驱体得到LiFePO4/C颗粒。
对比例2
本对比例与上述实施例2基本相同，其区别仅在于，将纳米片状LiMnPO4颗粒及蔗糖混合后研磨15min得到前驱体，烧结该前驱体得到LiMnPO4/C颗粒。
从图5可以看出，本发明实施例3的XRD测试图中没有出现LiMnPO4及LiFePO4的衍射峰，而是出现了位于LiMnPO4及LiFePO4的衍射峰之间的LiMn0.4Fe0.6PO4的衍射峰，说明本发明实施例3中LiMnPO4颗粒及LiFePO4颗粒全部反应生成了LiMn0.4Fe0.6PO4颗粒，且LiMn0.4Fe0.6PO4颗粒的结晶度较好。从图4a至图4l中可以看出，本发明实施例3中LiMn0.4Fe0.6PO4/C颗粒的形貌及颗粒尺寸与LiMnPO4颗粒和LiFePO4颗粒的形貌及颗粒尺寸一致，且LiMn0.4Fe0.6PO4/C颗粒的晶体生长方向与LiMnPO4颗粒和LiFePO4颗粒的晶体生长方向一致，均沿bc晶面生长，另外，该LiMn0.4Fe0.6PO4/C颗粒没有出现聚结的现象。从图5可以看出，实施例3的LiMn0.4Fe0.6PO4/C颗粒中Mn元素的分布映射和Fe元素的分布映射一致，证明实施例3烧结过程中固相反应已反应完全。采用电感耦合等离子体原子发射光谱法（ICP-AES）对所述LiMn0.4Fe0.6PO4/C颗粒进行元素检测，发现LiMn0.4Fe0.6PO4/C颗粒中Mn：Fe的摩尔比为4：5.983，与预期化学计量的误差小于1%，说明该制备方法可对所述LiMn0.4Fe0.6PO4颗粒的化学计量进行精确的调控。
实施例4
本实施例与实施例2基本相同，其区别仅在于，LiMnPO4颗粒与LiFePO4颗粒的摩尔比为6：4。
实施例5
本实施例与实施例2基本相同，其区别仅在于，LiMnPO4颗粒与LiFePO4颗粒的摩尔比为8：2。
从图7a和图7b可以看出，本发明实施例2到实施例5制备的LiMnxFe1-xPO4颗粒/C与对比例1的LiFePO4/C颗粒及对比例2的LiMnPO4/C颗粒及相比，兼具稳定的循环性能、良好的倍率性能、较好的容量保持率及较高的能量密度，其中，在0.1C倍率下，本发明实施例3制备的LiMn0.4Fe0.6PO4/C颗粒的放电容量比对比例2的LiMnPO4/C颗粒的放电容量提高了60%，达到160.6mAh/g，且多次循环后仍可保持较高的容量，LiMn0.4Fe0.6PO4/C颗粒的能量密度与对比例1的LiFePO4/C颗粒相比提高了53%，LiMn0.4Fe0.6PO4/C颗粒兼具较高的容量和较高的能量密度。
本发明提供的锂离子正极活性材料的制备方法，以晶体结构相同的LiMPO4颗粒和LiNPO4颗粒为前驱体，采用固相合成法制备LiMxN1-xPO4正极活性材料，可精确控制LiMnxFe1-xPO4颗粒的化学计量。由于该LiMPO4颗粒和该LiNPO4颗粒间仅Fe元素和Mn元素的浓度存在差异，因此在烧结过程中，该LiMPO4颗粒和该LiNPO4颗粒仍可保持其原有的晶型结构、形貌和颗粒尺寸，仅M元素和N元素会发生扩散转移而形成LiMxN1-xPO4颗粒。故可通过控制LiMPO4颗粒及LiNPO4颗粒的形貌、颗粒尺寸来控制LiMxN1-xPO4正极活性材料的形貌和颗粒尺寸。利用本发明制备方法制备的锂离子电池正极活性材料兼具稳定的循环性能、良好的倍率性能、较好的容量保持率及较高的能量密度。
另外，本领域技术人员还可在本发明精神内做其他变化，当然，这些依据本发明精神所做的变化，都应包含在本发明所要求保护的范围之内。

Claims (10)

  1. 一种锂离子正极活性材料的制备方法，包括：
    提供LiMPO4颗粒和LiNPO4颗粒，所述LiMPO4颗粒和所述LiNPO4颗粒均为正交晶系、空间群为Pnma的橄榄石型晶体，其中M为Fe、Mn、Co或Ni，N与M为不同的元素，N为二价金属；
    将所述LiMPO4颗粒和所述LiNPO4颗粒混合得到前驱体；以及
    将所述前驱体进行烧结，得到LiMxN1-xPO4颗粒正极活性材料，其中0<x<1。
  2. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，所述LiNPO4颗粒和所述LiMPO4颗粒均为纳米颗粒。
  3. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，所述LiNPO4颗粒和所述LiMPO4颗粒均为片状颗粒。
  4. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，所述LiNPO4颗粒和所述LiMPO4颗粒均为纳米片状颗粒，且所述LiNPO4颗粒和所述LiMPO4颗粒的颗粒尺寸相同。
  5. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，N为Fe、Mn、Co、Ni、Mg、Ca、Zn、Cu、Al、B、Cr、Nb、Sc、Ti、V、Be、Sr、Ba、Zr或La。
  6. 如权利要求5所述的锂离子正极活性材料的制备方法，其特征在于，当N为Mg、Ca、Zn、Cu、Al、B、Cr、Nb、Sc、Ti、V、Be、Sr、Ba、Zr或La时，所述LiMPO4颗粒和所述LiNPO4颗粒的摩尔比使所述LiMxN1-xPO4的x值大于0.9。
  7. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，将所述LiMPO4颗粒和所述LiNPO4颗粒混合均匀得到所述前驱体。
  8. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，在进行所述烧结前，进一步包括一在所述前驱体中加入一碳源的步骤，使所述碳源和所述前驱体一起进行烧结，并得到LiMxN1-xPO4/C颗粒。
  9. 如权利要求8所述的锂离子正极活性材料的制备方法，其特征在于，所述碳源的质量为所述LiMPO4颗粒及所述LiNPO4颗粒质量和的5%至15%。
  10. 如权利要求1所述的锂离子正极活性材料的制备方法，其特征在于，所述烧结温度为500℃至1000℃，所述烧结时间为4小时至10小时。
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