WO2015172627A1 - 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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WO2015172627A1
WO2015172627A1 PCT/CN2015/077333 CN2015077333W WO2015172627A1 WO 2015172627 A1 WO2015172627 A1 WO 2015172627A1 CN 2015077333 W CN2015077333 W CN 2015077333W WO 2015172627 A1 WO2015172627 A1 WO 2015172627A1
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active material
lithium
fluorine
positive electrode
containing oxygen
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PCT/CN2015/077333
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French (fr)
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张艳丽
何向明
王莉
李建军
高剑
尚玉明
张玉峰
金玉红
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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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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B9/00—General methods of preparing halides
    • C01B9/08—Fluorides
    • 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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—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
    • 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
    • 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
    • H01M4/36—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
    • H01M4/582—Halogenides
    • 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 the field of positive electrode active materials for lithium ion batteries, and in particular to a method for preparing a metal fluoride-coated lithium-transition metal oxide positive electrode active material.
  • Lithium-ion batteries have high energy density, large specific power, good cycle performance, no memory effect, no pollution, etc., and have been widely used in various electronic products such as mobile phones, mobile phones, video cameras, and notebook computers.
  • lithium-transition metal oxide cathode active material is the most widely used and most successfully used cathode active material in lithium ion batteries.
  • the performance of lithium-transition metal oxide cathode active materials has direct performance on lithium ion batteries. Influence, in practical applications, the lithium-transition metal oxide positive active material is in direct contact with the electrolyte, and the interaction between them causes deterioration of the chemical properties of the lithium-transition metal oxide positive active material, affecting the stability of the lithium ion battery. Sex.
  • the electrolyte will slowly decompose, and some harmful by-products will be eroded to erode the lithium-transition metal oxide cathode active material. Therefore, the lithium ion battery has a rapid decline in capacity during the cycle. Problems such as poor cycle performance can even cause battery safety problems.
  • a surface coating method is generally employed to avoid direct contact between the lithium-transition metal oxide positive electrode active material and the electrolyte.
  • One of the methods is to coat the surface of the lithium-transition metal oxide positive active material with a metal fluoride, and the metal fluoride as a coating layer can reduce the influence of the acid formed near the lithium-transition metal oxide positive active material, and inhibit lithium.
  • the reaction between the transition metal oxide positive active material and the electrolyte prevents the lithium ion battery from rapidly decreasing in capacity, and can improve the cycle performance and high rate performance of the lithium ion battery.
  • a method of coating a metal fluoride on a surface of a lithium-transition metal oxide positive active material is generally a method of immersing a lithium-transition metal oxide positive active material in a metal soluble salt solution, and then adding a soluble fluoride solution to cause fluoride and The metal soluble salt reacts and forms a metal fluoride coating on the surface of the lithium-transition metal oxide positive active material, followed by drying and high temperature heat treatment.
  • This method is complicated in operation, requires a large amount of solvent, requires high raw material cost, increases production cost, and is difficult to be used in industrial production, and this method easily introduces impurities into the metal fluoride coating layer, thereby affecting lithium-transition metal oxidation. Electrochemical performance of the positive electrode active material.
  • a method for preparing a positive active material for a lithium ion battery comprising:
  • the mixture is sintered in an inert atmosphere to obtain a metal fluoride-coated lithium-transition metal oxide positive electrode active material which decomposes during the sintering to release hydrogen fluoride gas.
  • the invention adopts the method of directly performing sintering to coat the surface of the lithium-transition metal oxide positive electrode active material with metal fluoride, and can form a uniform continuous coating layer on the surface of the lithium-transition metal oxide positive electrode active material, and the method not only operates Simple, low cost, suitable for industrial production, and the thickness of the metal fluoride layer is controllable, the metal fluoride layer can effectively isolate the contact between the lithium-transition metal oxide positive active material and the electrolyte, and prevent the lithium ion battery from being Performance degradation during use.
  • FIG. 1 is a flow chart showing a method for preparing a metal fluoride positive electrode active material according to a first embodiment of the present invention.
  • FIG. 2 is a flow chart showing a method for preparing a metal fluoride positive electrode active material according to a second embodiment of the present invention.
  • FIG. 3 is a flow chart showing a method of preparing a metal fluoride on a surface of a lithium-transition metal oxide positive electrode active material according to a third embodiment of the present invention.
  • FIG. 4 is a flow chart showing a method of preparing a metal fluoride on a surface of a lithium-transition metal oxide positive active material according to a fourth embodiment of the present invention.
  • Figure 5 is a scanning electron micrograph of a carbon-coated fluorinated ferrous core shell composite of Example 1 of the present invention.
  • Fig. 6 is a XRD test chart of the carbon-coated ferrous fluoride core-shell composite of Example 1 of the present invention.
  • Figure 7 is a transmission electron micrograph of a carbon-coated ferrous fluoride core-shell composite of Example 1 of the present invention.
  • Figure 8 is a scanning electron micrograph of a carbon-coated fluorinated ferrous core shell composite of Example 2 of the present invention.
  • Figure 9 is a comparison diagram of the cycle performance test of the carbon-coated fluorinated ferrous core shell composite and the ferrous fluoride not coated with carbon according to Example 2 of the present invention.
  • a first embodiment of the present invention provides a method for preparing a metal fluoride positive electrode active material, including:
  • the metallocene is an organometallic compound formed by linking a transition metal to cyclopentadiene.
  • a typical metallocene is formed by linking two cyclopentadienyl anions and a divalent oxidation state metal center, and has the formula (C 5 H 5 ) 2 M.
  • the metallocene can be decomposed into metal elements and carbon clusters during the sintering process.
  • the carbon cluster refers to an atomic group composed of ten to several hundred carbon atoms, and the carbon cluster has high reactivity.
  • the metallocene may be one or more of ferrocene, cobaltocene, nickel pentoxide and manganese pentano.
  • the metallocene is a solid.
  • the morphology of the metallocene is not limited, for example, the metallocene may be in the form of a powder.
  • the metallocene has a particle size of 200 mesh or less.
  • the fluorine-containing oxygen-free compound can release hydrogen fluoride gas during heating or sintering. Further, the fluorine-containing oxygen-free compound is decomposed to release the hydrogen fluoride gas, and the remaining impurities are impurities which are easily removed.
  • the impurities may be gases, and other impurities other than hydrogen fluoride do not participate in the reaction of generating metal fluoride.
  • the fluorine-containing oxygen-free compound may be one or more of a fluorine-containing oxygen-free organic substance and a fluorine-containing oxygen-free inorganic substance.
  • the fluorine-containing oxygen-free organic material may be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), polyvinyl fluoride (PVF), and trifluoromethylbenzene.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • FEP fluorinated ethylene propylene copolymer
  • PVF polyvinyl fluoride
  • trifluoromethylbenzene One or several.
  • the fluorine-containing oxygen-free inorganic substance may be one or more of NH 4 F and NH 4 HF 2 .
  • the fluorine-containing oxygen-free compound may be a solid (for example, PVDF) or a liquid (for example, trifluoromethylbenzene).
  • the fluorine-containing oxygen-free compound is a solid, the morphology of the fluorine-containing oxygen-free compound is not limited.
  • the fluorine-containing oxygen-free compound may be in the form of a powder. The smaller the particle size of the fluorine-containing oxygen-free compound, the more favorable the decomposition reaction in the subsequent sintering process.
  • the fluorine-containing oxygen-free compound has a particle size of 200 mesh or less.
  • step S12 the metallocene and the fluorine-containing oxygen-free compound are mixed in such a manner that the metallocene and the fluorine-containing oxygen-free compound can be uniformly mixed.
  • the metallocene and the fluorine-containing oxygen-free compound can be mixed at normal temperature.
  • the metallocene and the fluorine-containing oxygen-free compound may be mixed in an oxygen-free environment to prevent the first mixture from being mixed with oxygen to oxidize the metal fluoride particles formed in the subsequent sintering process.
  • a solid metallocene may be immersed in a liquid fluorine-containing oxygen-free compound to form a suspension, thereby forming a fluorine-containing oxygen-free compound film on the surface of the solid metallocene, to obtain the first mixture.
  • a solid metallocene may also be dissolved in the liquid fluorine-containing oxygen-free compound to form a mixed solution to obtain the first mixture.
  • the solid powdered metallocene can be mixed with a solid powdered or liquid fluorine-containing oxygen-free compound by grinding or ball milling.
  • the metallocene and the fluorine-containing oxygen-free compound are mixed by a ball milling method, and the ball milling method can not only uniformly mix the metallocene and the fluorine-containing oxygen-free compound, but also further reduce the metallocene or the
  • the particle size of the fluorine-containing oxygen-free compound is more favorable for the progress of the decomposition reaction in the subsequent sintering process.
  • the metallocene and the fluorine-containing oxygen-free compound are both solid.
  • the metal element in the metallocene has a lowest non-zero valence m+.
  • the mixing ratio of the metallocene to the fluorine-containing oxygen-free compound is a ratio of (m-0.1):1 to (m+0.1):1 in terms of a stoichiometric ratio of a fluorine element to a metal element.
  • the stoichiometric ratio of the fluorine element to the metal element in the metallocene and the fluorine-containing oxygen-free compound is (m-0.1): 1 to m: 1, and hydrogen fluoride generated by decomposition of the fluorine-containing oxygen-free compound in the range It can be completely reacted to form metal fluoride without generating excess hydrogen fluoride gas.
  • the sintering temperature is a temperature at which both the metallocene and the fluorine-containing oxygen-free compound can be decomposed.
  • the sintering temperature is from 400 ° C to 1000 ° C. More preferably, the sintering temperature is from 500 ° C to 900 ° C. Most preferably, the sintering temperature is from 600 ° C to 800 ° C. If the sintering temperature is too low, the degree of graphitization of the formed carbon layer is low; if the sintering temperature is too high, the metal fluoride is easily oxidized.
  • the sintering time is from 1 hour to 10 hours. Preferably, the sintering time is from 2 hours to 5 hours.
  • the inert atmosphere further protects the resulting metal fluoride from oxidation.
  • the inert atmosphere may be one or more of argon, nitrogen and helium.
  • the metallocene is decomposed to form a metal element and a carbon cluster
  • the fluorine-containing oxygen-free compound is decomposed to release a hydrogen fluoride gas
  • the metal element reacts with the hydrogen fluoride gas to form metal fluoride particles
  • the carbon cluster adsorbs to the surface of the metal fluoride particle to form a carbon coating layer, and finally forms a core-shell composite structure of carbon-coated metal fluoride.
  • the carbon-coated metal fluoride carbon layer is a uniform continuous carbon layer. Due to the presence of the elemental element of the metal during the sintering process, the carbon cluster may be graphitized during the formation of the carbon layer, and thus the carbon layer is a graphitized carbon layer. Due to the presence of reducing carbon clusters during the sintering process, the valence state of the metal element in the carbon-coated metal fluoride is the lowest non-zero valence state m+ of the metal element.
  • the carbon-coated metal fluoride has a carbon layer thickness of 5 nm to 50 nm.
  • the carbon-coated metal fluoride has a carbon layer thickness of 10 nm to 20 nm.
  • the carbon layer has a mass of 30% to 60% by mass of the carbon coated metal fluoride.
  • the carbon layer has a mass of from 30% to 40% by mass of the carbon coated metal fluoride.
  • the carbon layer in the mass range can ensure the metal fluoride has a high capacity while improving the conductivity of the metal fluoride.
  • the thickness of the carbon layer and the mass percentage of the carbon layer to the metal-coated metal fluoride can be regulated by adjusting the ratio of the carbon element and the metal element in the first mixture.
  • the carbon-coated metal fluoride is a spherical particle.
  • the carbon-coated metal fluoride of the spherical particles has a diameter of 50 nm to 1 ⁇ m. This may be because the fluorine-containing oxygen-free inorganic material has a lower decomposition temperature and a faster decomposition speed, and more hydrogen fluoride gas can be rapidly generated during the sintering process, so that the metal fluoride crystal can be used from the beginning.
  • the crystal faces are grown to finally form a metal fluoride of spherical particles.
  • the carbon-coated metal fluoride is a rod-shaped particle. Further, since the fluorine-containing oxygen-free organic substance can also decompose the carbon clusters during the sintering process, the carbon-coated metal fluoride having a thick carbon layer in the range of 5 nm to 50 nm can be obtained.
  • the carbon-coated metal fluoride of the rod-shaped particles has a length of 500 nm to 1.2 ⁇ m and a width of 50 nm to 1 ⁇ m.
  • the fluorine-containing oxygen-free organic matter has a higher decomposition temperature and a slower decomposition rate, and the amount of hydrogen fluoride gas generated during the initial growth of the metal fluoride crystal is less, so the metal fluoride crystal preferentially follows a crystal.
  • the surface is grown to form a metal fluoride of the rod-shaped particles.
  • the metal fluoride and the fluorine-containing oxygen-free compound are mixed and then sintered to simultaneously complete the growth of the metal fluoride and the coating of the carbon layer, and the preparation method of the present invention is simpler than the prior art. Easy to operate and low cost, it can be applied to large-scale industrial production.
  • the metallocene has a low boiling point, generally lower than 300 ° C, the metallocene will sublime to form a gas during the sintering process, so that after reacting with the hydrogen fluoride gas, a metal fluoride having a small particle size and uniformity can be formed. The particles ultimately form a carbon coated metal fluoride particle having a smaller particle size and uniformity.
  • the metal simple substance and the metal fluoride particle do not Oxidation occurs during the sintering to form impurities such as metal oxides, so that metal fluoride particles having higher purity can be obtained.
  • the carbon layer of the carbon-coated metal fluoride is a uniform continuous graphitized carbon layer, and the graphitized carbon layer can provide more space for volume expansion and contraction of the metal fluoride than the amorphous carbon layer. More electron transport channels allow metal fluorides to have better electrical conductivity. Therefore, the metal fluoride positive electrode active material prepared by the invention not only has high specific capacity and energy density, but also has good electrical conductivity, high coulombic efficiency and more stable cycle performance.
  • a second embodiment of the present invention provides a method for preparing a metal fluoride positive electrode active material, comprising:
  • the metal particles are elemental and may be one of Ti, V, Mn, Fe, Bi, Co, Ni, Cu, Zn, Sn, Ag, Pb, Ca or Ba particles.
  • the metal particles can be nanoparticles.
  • the metal particles may have a particle diameter of between 20 nm and 1 ⁇ m.
  • the metal particles may have a particle diameter of between 20 nm and 500 nm.
  • the metal particles can be prepared by an aqueous solution reduction method, a sol-gel method, a vapor deposition method, an evaporation-coacervation method, and a pyrolysis metal compound.
  • the metal element in the metal particle has a lowest non-zero valence state m+.
  • the mixing ratio of the metal particles to the fluorine-containing oxygen-free compound is a ratio of (m-0.1):1 to (m+0.1):1 in terms of a stoichiometric ratio of a fluorine element to a metal element.
  • the stoichiometric ratio of the fluorine element to the metal element in the metallocene and the fluorine-containing oxygen-free compound is (m-0.1): 1 to m: 1, and the hydrogen fluoride produced by the decomposition of the fluorine-containing oxygen-free compound may be All reactions form metal fluorides without generating excess hydrogen fluoride gas.
  • the anaerobic carbon source can be either a solid or a liquid.
  • the oxygen-free carbon source is capable of decomposing carbon clusters during the sintering process.
  • the oxygen-free carbon source may be one of polyethylene, polypropylene, polystyrene, polyphenylene naphthalene, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene copolymer, and polyvinyl fluoride or Several.
  • the oxygen-free carbon source does not contain oxygen, and therefore does not oxidize the metal particles during the sintering to form metal oxide impurities.
  • the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source are mixed in such a manner that the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source can be uniformly mixed.
  • the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source can be mixed at normal temperature.
  • the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source may be mixed in an oxygen-free environment to prevent mixing of oxygen in the second mixture to cause metal fluoride formed in the subsequent sintering process.
  • the particles are oxidized.
  • the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source are all solid, and the solid metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source may be mixed by grinding or ball milling.
  • the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source are mixed by a ball milling method, and the ball metal is not only used to mix the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source. Uniformity can further reduce the particle size of the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source, and is more favorable for the sintering reaction during the subsequent sintering process.
  • the sintering temperature is a temperature at which both the oxygen-free carbon source and the fluorine-containing oxygen-free compound can be decomposed.
  • the sintering temperature is from 400 ° C to 1000 ° C. More preferably, the sintering temperature is from 500 ° C to 900 ° C. Most preferably, the sintering temperature is from 600 ° C to 800 ° C. If the sintering temperature is too low, the degree of graphitization of the formed carbon layer is low; if the sintering temperature is too high, the metal fluoride is susceptible to oxidation.
  • the sintering time is from 1 hour to 10 hours. Preferably, the sintering time is from 2 hours to 5 hours.
  • the inert atmosphere further protects the resulting metal fluoride from oxidation.
  • the inert atmosphere may be one or more of argon, nitrogen and helium.
  • the fluorine-containing oxygen-free compound is decomposed to release hydrogen fluoride gas, and the oxygen-free carbon source is decomposed to generate carbon clusters.
  • the metal particles react with the hydrogen fluoride gas to form metal fluoride particles, and at the same time, the carbon clusters adsorb to the surface of the metal fluoride particles to form a carbon coating layer, thereby finally forming a core-shell composite structure of carbon-coated metal fluoride.
  • the carbon-coated metal fluoride carbon layer is a uniform continuous carbon layer. Due to the presence of the metal particles during the sintering process, the carbon clusters may be graphitized during the formation of the carbon layer, and thus the carbon layer is a graphitized carbon layer.
  • the valence state of the metal element in the metal fluoride positive electrode active material is the lowest non-zero valence state m+ of the metal element due to the presence of a reducing carbon cluster during the sintering process.
  • the metal fluoride, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source are mixed and then sintered to simultaneously complete the growth of the metal fluoride and the coating of the carbon layer, and the present invention is compared with the prior art.
  • the preparation method is simple, easy to operate and low in cost, and can be applied to large-scale industrial production.
  • the metal element and the metal fluoride particles are not oxidized during the sintering process.
  • impurities such as metal oxides, metal fluoride particles having higher purity can be obtained.
  • the carbon layer of the carbon-coated metal fluoride is a uniform continuous graphitized carbon layer, and the graphitized carbon layer can provide more space for volume expansion and contraction of the metal fluoride than the amorphous carbon layer. More electron transport channels allow the metal fluoride to have better electrical conductivity. Therefore, the metal fluoride positive electrode active material prepared by the invention not only has high specific capacity and energy density, but also has good electrical conductivity, high coulombic efficiency and more stable cycle performance.
  • the metal compound, the fluorine-containing compound, and the oxygen-free carbon source may be mixed and sintered to prepare a carbon-coated metal fluoride, which may be decomposed during the sintering process.
  • the metal particles having a smaller particle diameter are formed, thereby providing metal particles for the preparation of the metal fluoride positive electrode active material, and a metal fluoride positive electrode active material having a smaller particle diameter can be obtained.
  • the present invention can also provide a method for preparing a metal fluoride layer on a surface of a lithium-transition metal oxide positive active material, which can avoid the lithium-transition metal oxide positive active material and electrolyte Direct contact suppresses the reaction between the lithium-transition metal oxide positive active material and the electrolyte, prevents the lithium-transition metal oxide positive active material from rapidly decreasing in capacity during use, and can improve the use of the lithium- Cyclic performance and high rate performance of a lithium ion battery of a transition metal oxide positive active material.
  • a third embodiment of the present invention further provides a method for preparing a metal fluoride on a surface of a lithium-transition metal oxide positive active material, comprising:
  • the third mixture is sintered in an inert atmosphere to obtain a metal fluoride-coated lithium-transition metal oxide positive active material.
  • the lithium-transition metal oxide positive active material is a lithium intercalation compound capable of reversibly inserting and extracting lithium ions during charge and discharge of a lithium battery.
  • the lithium-transition metal oxide positive electrode active material may be undoped or doped spinel structure lithium manganate, layered lithium manganate, lithium nickelate, lithium cobaltate, lithium iron phosphate, lithium nickel manganese One or more of an oxide and a lithium nickel cobalt manganese oxide.
  • the spinel-structured lithium manganate may be represented by a chemical formula of Li x Mn 2-y L y O 4 , which may be represented by a chemical formula of Li x Ni 1-y L y O 2
  • the lithium cobaltate The chemical formula may be represented by Li x Co 1-y L y O 2
  • the chemical formula of the layered lithium manganate may be Li x Mn 1-y L y O 2
  • the chemical formula of the lithium iron phosphate may be Li x Fe 1- y L y PO 4 indicates that the chemical formula of the lithium nickel manganese oxide can be represented by Li x Ni 0.5+za Mn 1.5-zb L a R b O 4
  • the chemical formula of the lithium nickel cobalt manganese oxide can be Li x Ni c Co d Mn e L f O 2 represents, where 0.1 ⁇ x ⁇ 1.1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1.5, 0 ⁇ az ⁇
  • L and R are selected from one or more of an alkali metal element, an alkaline earth metal element, a Group 13 element, a Group 14 element, a transition group element, and a rare earth element.
  • L and R are selected from the group consisting of Mn, Ni, Cr. At least one of Co, V, Ti, Al, Fe, Ga, Nd, and Mg.
  • the lithium-transition metal oxide positive electrode active material may have a particle diameter of 20 nm to 10 ⁇ m.
  • the particle diameter of the metal particles is smaller than the particle diameter of the lithium-transition metal oxide positive electrode active material, so that the metal particles can be sufficiently in contact with the surface of the lithium-transition metal oxide positive electrode active material, thereby being more advantageous.
  • the metal fluoride is nucleated on the surface of the lithium-transition metal oxide positive active material during the subsequent sintering.
  • the lithium-transition metal oxide positive electrode active material has a particle diameter of 10 to 500 times the particle diameter of the metal particles. More preferably, the lithium-transition metal oxide positive electrode active material has a particle diameter of 100 to 500 times the particle diameter of the metal particles.
  • step S32 the metal particles, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide positive electrode active material are mixed in such a manner that the metal particles, the fluorine-containing oxygen-free compound, and the lithium-transition can be obtained.
  • the metal oxide positive active material can be uniformly mixed.
  • the metal particles, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide positive electrode active material can be mixed at normal temperature.
  • the metal particles, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide positive electrode active material may be mixed in an inert atmosphere.
  • the fluorine-containing oxygen-free compound may be a solid, and the metal particles, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide positive electrode active material may be mixed by grinding or ball milling.
  • the metal particles, the fluorine-containing oxygen-free compound and the lithium-transition metal oxide positive electrode active material are mixed by a ball milling method, and the metal particles, the fluorine-containing oxygen-free compound and the ball are not only used by ball milling.
  • the lithium-transition metal oxide positive electrode active material is uniformly mixed, and the particle size of the metal particles, the fluorine-containing oxygen-free compound and the lithium-transition metal oxide positive electrode active material can be further reduced, which is more favorable for sintering in the subsequent sintering process.
  • the reaction proceeds.
  • the lithium-transition metal oxide positive active material may have a mass of 50% to 99% by mass of the third mixture.
  • the lithium-transition metal oxide positive active material may have a mass of 80% to 99% by mass of the third mixture. More preferably, the lithium-transition metal oxide positive active material may have a mass of from 90% to 97% by mass of the third mixture.
  • the lithium-transition metal oxide positive electrode active material in the mass range can ensure that the metal fluoride-coated lithium-transition metal oxide positive electrode active material has good conductivity and can cover the coated metal fluoride layer. The contact of the lithium-transition metal oxide positive active material with the electrolytic solution is effectively insulated.
  • the temperature of the sintering is a temperature at which the fluorine-containing oxygen-free compound can be decomposed.
  • the sintering conditions are the same as those of the first embodiment of the present invention.
  • step S33 during the sintering process, the fluorine-containing oxygen-free compound is decomposed to release hydrogen fluoride gas, and the metal particles react with the hydrogen fluoride gas to form a metal fluoride, and the metal fluoride is in the lithium-transition metal oxide.
  • the surface of the positive electrode active material is nucleated and gradually grown to finally form a metal fluoride-coated lithium-transition metal oxide positive electrode active material.
  • the metal fluoride layer of the metal fluoride-coated lithium-transition metal oxide positive active material is a uniform continuous coating layer.
  • the thickness of the metal fluoride layer can be adjusted by the ratio of the metal particles to the fluorine-containing oxygen-free compound in the third mixture.
  • the metal fluoride layer may have a thickness of 0.2 nm to 50 nm, and the metal fluoride layer in the thickness range can effectively isolate the lithium-transition while ensuring the conductivity of the lithium-transition metal oxide positive active material.
  • the metal fluoride-coated lithium-transition metal oxide positive active material has a metal fluoride coating layer having a thickness of from 1 nm to 5 nm.
  • the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free organic substance
  • the fluorine-containing oxygen-free organic substance can decompose a carbon cluster during the sintering process, the carbon cluster can be adsorbed on the metal fluoride layer.
  • a carbon layer is formed on the surface of the metal fluoride layer to form a three-layered core-shell type positive electrode material, which is a lithium-transition metal oxide positive active material and a metal fluoride from the inside to the outside. Compound layer and carbon layer.
  • the carbon cluster may be graphitized during the formation of the carbon layer, so the carbon layer of the core-shell cathode material is a graphitized carbon layer, and the graphitized carbon layer
  • the core-shell type positive electrode material can provide more space for volume expansion and contraction and more electron transport channels, so that the core-shell type positive electrode material can have better conductivity.
  • the third embodiment of the present invention coats the surface of the lithium-transition metal oxide positive active material with a metal fluoride by directly performing the sintering method, which is not only simple in operation, low in cost, and is suitable for industrial production, and the metal fluoride layer
  • the thickness of the metal fluoride layer can effectively block the contact of the lithium-transition metal oxide positive active material with the electrolyte, and prevent the performance degradation of the lithium ion battery during use.
  • the metal compound, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide positive electrode active material may be mixed and sintered to prepare a metal fluoride-coated lithium-transition metal oxide.
  • a positive electrode active material which can be decomposed to form metal particles during the sintering process, thereby providing metal particles having a smaller particle diameter for the preparation of the metal fluoride-coated lithium-transition metal oxide positive electrode active material.
  • a fourth embodiment of the present invention further provides a method for preparing a metal fluoride on a surface of the lithium-transition metal oxide cathode active material, comprising:
  • the fourth mixture is sintered in an inert atmosphere to obtain a metal fluoride-coated lithium-transition metal oxide positive electrode active material.
  • the mixing mode of the mixing is the same as the mixing mode of the third embodiment of the present invention.
  • the lithium-transition metal oxide positive active material may have a mass of 50% to 99% by mass of the fourth mixture.
  • the lithium-transition metal oxide positive active material may have a mass of 80% to 99% by mass of the fourth mixture. More preferably, the lithium-transition metal oxide positive active material may have a mass of 90% to 97% by mass of the fourth mixture.
  • the lithium-transition metal oxide positive electrode active material in the mass range can ensure that the metal fluoride-coated lithium-transition metal oxide positive electrode active material has good conductivity and can cover the coated metal fluoride layer. The contact of the lithium-transition metal oxide positive active material with the electrolytic solution is effectively insulated.
  • the sintering conditions are the same as those of the first embodiment of the present invention.
  • step S43 the metallocene is decomposed to form a metal element, and the fluorine-containing oxygen-free compound is decomposed to release hydrogen fluoride gas, and the metal element reacts with the hydrogen fluoride gas to form metal fluoride particles. Since the metallocene has a low boiling point, the metallocene can be sublimated into a gas and uniformly distributed around the positive electrode active material during the sintering process, thereby finally forming a uniform continuous metal on the surface of the positive electrode active material. Fluoride coating.
  • the thickness of the metal fluoride layer can be adjusted by the ratio of the metallocene to the fluorine-containing oxygen-free compound in the fourth mixture.
  • the metal fluoride layer may have a thickness of 0.2 nm to 50 nm, and the metal fluoride layer in the thickness range can effectively isolate the lithium-transition while ensuring the conductivity of the lithium-transition metal oxide positive active material. Contact of the metal oxide positive active material with the electrolyte. More preferably, the metal fluoride-coated lithium-transition metal oxide positive active material has a metal fluoride coating layer having a thickness of from 1 nm to 5 nm.
  • the core-shell type positive electrode material is a lithium-transition metal oxide positive electrode active material, a metal fluoride and a carbon layer from the inside to the outside.
  • the carbon cluster may be graphitized during the formation of the carbon layer, so the carbon layer of the core-shell cathode material is a graphitized carbon layer, and the graphitized carbon layer
  • the core-shell type positive electrode material can provide more space for volume expansion and contraction and more electron transport channels, so that the core-shell type positive electrode material can have better conductivity.
  • the surface of the lithium-transition metal oxide positive active material is coated with a metal fluoride by directly performing sintering, and a uniform continuous coating layer can be formed on the surface of the lithium-transition metal oxide positive active material.
  • the method is not only simple in operation, low in cost, and is suitable for industrial production, and the thickness of the metal fluoride layer is controllable, and the metal fluoride layer can effectively isolate the contact between the lithium-transition metal oxide positive active material and the electrolyte to prevent contact. The performance of lithium ion batteries deteriorates during use.
  • the ferrocene and PVDF were mixed at a molar ratio of fluorine/iron of 2:1, and ball-milled at a speed of 500 rpm/min for 2 hours to obtain a first mixture.
  • the first mixture was placed in a stainless steel container, the container was placed in a glove box and filled with argon gas, and then the first mixture was reacted at 600 ° C for 5 hours to obtain a carbon-coated ferrous fluoride.
  • the carbon-coated ferrous fluoride is a rod-shaped particle having a length of about 1 ⁇ m, a width of between 100 nm and 1 ⁇ m, and a carbon layer thickness of about 20 nm.
  • the diffraction peak of the XRD pattern of the reaction product is consistent with the diffraction peak of the standard map of ferrous fluoride, which proves that the above preparation method can produce ferrous fluoride having a pure phase and good crystallinity.
  • the carbon-coated ferrous fluoride carbon layer has lattice fringes with a stripe pitch of 0.34 nm, which is consistent with the layer spacing of the graphite, and the carbon layer of the carbon-coated ferrous fluoride is graphitized carbon.
  • the carbon-coated ferrous fluoride has a first lithium storage capacity of 300 mAh ⁇ g -1 when used for a positive electrode of a lithium ion battery, the coulombic efficiency is above 96%, and the capacity loss rate per cycle is 0.66% within 50 cycles. .
  • the ferrocene and NH 4 F were mixed at a fluorine/iron element ratio of 2.05:1, and ball-milled at a speed of 400 rpm/min for 1 hour to obtain a first mixture.
  • the first mixture was placed in a stainless steel container, the container was placed in a glove box to be filled with nitrogen, and then the first mixture was reacted at 650 ° C for several hours to obtain a carbon-coated ferrous fluoride.
  • the carbon-coated ferrous fluoride is a spherical particle having a diameter of between 100 nm and 1 ⁇ m and a carbon layer having a thickness of about 10 nm.
  • the carbon coated ferrous fluoride is used for the positive electrode of a lithium ion battery, the first lithium storage capacity of 330 mAh ⁇ g -1 is achieved, the coulombic efficiency is above 95%, and the capacity loss rate per cycle is 0.72 within 40 cycles. %, see Figure 9, the carbon-coated ferrous fluoride has better coulombic efficiency and more stable cycle performance than ferrous fluorite without carbon coating.
  • Cobalt and NH 4 HF 2 were mixed at a fluorine/carbon element ratio of 1.95:1, and ground until homogeneous to obtain a first mixture.
  • the first mixture was placed in a stainless steel container, and the container was placed in a glove box filled with helium gas, and then reacted at 550 ° C for 4 hours to obtain a carbon-coated manganese fluoride.
  • the carbon-coated manganese fluoride is a spherical particle having a diameter of 50 nm to 0.5 ⁇ m and a carbon layer thickness of about 15 nm.
  • the carbon coated manganese fluoride When used for the positive electrode of a lithium ion battery, it has a first lithium storage capacity of 380 mAh ⁇ g -1 , a coulombic efficiency of 95% or more, and a capacity loss rate of 0.52% per cycle within 80 cycles.
  • Nickel pentoxide, NH 4 F and lithium cobaltate were mixed and ball-milled at a speed of 400 rpm/min for 1 hour to obtain a fourth mixture.
  • the molar ratio of nickel to nickel and NH 4 F in the fourth mixture is 2.05:1, and the mass of lithium cobaltate is 85% by mass of the fourth mixture.
  • the fourth mixture is placed in a stainless steel container, the container is placed in a glove box to be filled with nitrogen, and then the fourth mixture is reacted at 650 ° C for a small time to obtain a core-shell type positive electrode material, which is from the inside to the inside.
  • the outer layers are lithium cobaltate, NiF 2 and graphitized carbon layers.
  • the core-shell type positive electrode material was applied to a positive electrode of a lithium ion battery, and had a first lithium storage capacity of 140 mAh ⁇ g -1 , a Coulomb efficiency of 95% or more, and a capacity loss rate of 0.72% per cycle within 40 cycles.

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Abstract

一种锂离子电池正极材料的制备方法，包括：提供茂金属、含氟无氧化合物及锂-过渡金属氧化物正极活性材料；将该茂金属、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合得到一混合物；以及将该混合物在惰性气氛中进行烧结，得到金属氟化物包覆的锂-过渡金属氧化物正极活性材料，该含氟无氧化合物在所述烧结过程中发生分解释放出氟化氢气体。

Description

锂离子电池正极活性材料的制备方法 技术领域
本发明涉及锂离子电池正极活性材料领域，具体涉及一种金属氟化物包覆的锂-过渡金属氧化物正极活性材料的制备方法。
背景技术
锂离子电池具有能量密度高、比功率大、循环性能好、无记忆效应、无污染等特点，在手机、移动电话、摄像机、笔记本电脑等各种电子产品中得到了广泛的应用。其中，锂-过渡金属氧化物正极活性材料是锂离子电池中使用最广泛、商业化最成功的正极活性材料，锂-过渡金属氧化物正极活性材料的性能好坏对锂离子电池性能有直接的影响，在实际应用中，锂-过渡金属氧化物正极活性材料与电解液直接接触，它们之间的相互作用会引起锂-过渡金属氧化物正极活性材料化学性质的恶化，影响锂离子电池的稳定性。另外，在锂离子电池工作过程中，电解液会有缓慢分解的现象，进而产生一些有害的副产物侵蚀锂-过渡金属氧化物正极活性材料，因此锂离子电池在循环过程中存在容量快速下降，循环性能变差等问题，甚至会引发电池的安全性问题。为了克服锂-过渡金属氧化物正极活性材料和电解液的相互作用，通常采用表面包覆的方法避免锂-过渡金属氧化物正极活性材料和电解液的直接接触。其中一种方法是在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物，金属氟化物作为包覆层可以减少锂-过渡金属氧化物正极活性材料附近形成的酸的影响，抑制锂-过渡金属氧化物正极活性材料与电解液之间的反应，防止锂离子电池容量快速降低，可改善锂离子电池的循环性能及高倍率性能。
然而，目前在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物的方法一般为将锂-过渡金属氧化物正极活性材料浸入金属可溶性盐溶液，然后加入可溶性氟化物溶液，使氟化物和金属可溶性盐发生反应并在锂-过渡金属氧化物正极活性材料表面形成金属氟化物包覆层，之后再进行干燥和高温加热处理。这种方法操作过程复杂，需要使用大量的溶剂、原料成本高、增加了生产成本，难以用于工业化生产，且这种方法容易将杂质引入金属氟化物包覆层，从而影响锂-过渡金属氧化物正极活性材料的电化学性能。
发明内容
有鉴于此，确有必要提供一种操作简单、成本较低、适用于工业化生产的锂-过渡金属氧化物正极活性材料表面包覆金属氟化物的制备方法。
一种锂离子电池正极活性材料的制备方法，包括：
提供茂金属、含氟无氧化合物及锂-过渡金属氧化物正极活性材料；
将该茂金属、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合得到一混合物；以及
将该混合物在惰性气氛中进行烧结，得到金属氟化物包覆的锂-过渡金属氧化物正极活性材料，该含氟无氧化合物在所述烧结过程中发生分解释放出氟化氢气体。
本发明采用直接进行烧结的方法在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物，可以在该锂-过渡金属氧化物正极活性材料表面生成均匀连续的包覆层，该方法不仅操作简单、成本较低、适用于工业化生产，而且该金属氟化物层的厚度可控，该金属氟化物层能有效隔绝锂-过渡金属氧化物正极活性材料与电解液的接触，防止锂离子电池在使用过程中的性能退化。
 附图说明
图1为本发明第一实施例金属氟化物正极活性材料制备方法的流程图。
图2为本发明第二实施例金属氟化物正极活性材料制备方法的流程图。
图3为本发明第三实施例在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物制备方法的流程图。
图4为本发明第四实施例在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物制备方法的流程图。
图5为本发明实施例1碳包覆氟化亚铁核壳复合物的扫描电镜照片。
图6为本发明实施例1碳包覆氟化亚铁核壳复合物的XRD测试图。
图7为本发明实施例1碳包覆氟化亚铁核壳复合物的透射电镜照片。
图8为本发明实施例2碳包覆氟化亚铁核壳复合物的扫描电镜照片。
图9为本发明实施例2碳包覆氟化亚铁核壳复合物与未进行碳包覆的氟化亚铁的循环性能测试对比图。
具体实施方式
请参阅图1，本发明第一实施例提供一种金属氟化物正极活性材料的制备方法，包括：
S11，提供茂金属和含氟无氧化合物；
S12，将该茂金属和该含氟无氧化合物混合得到一第一混合物；以及
S13，将该第一混合物在惰性气氛中进行烧结，得到碳包覆金属氟化物。
在步骤S11中，该茂金属为过渡金属与环戊二烯相连所形成的有机金属化合物。典型的茂金属是由两个环戊二烯阴离子和二价氧化态金属中心连接而成，通式为(C5H5)2M。该茂金属可在所述烧结过程中分解为金属单质和碳团簇。所述碳团簇是指十到数百个碳原子组成的原子团，该碳团簇具有较高的反应活性。优选地，该茂金属可为二茂铁、二茂钴、二茂镍和二茂锰中的一种或几种。
该茂金属为固体。该茂金属的形貌不限，例如该茂金属可为粉末状。该茂金属的粒度越小，越有利于后续烧结过程中分解反应的进行。优选地，该茂金属的粒度小于等于200目。
该含氟无氧化合物可在加热或烧结的过程中释放出氟化氢气体。此外，该含氟无氧化合物发生分解释放出氟化氢气体后剩余的杂质为容易去除的杂质，例如该杂质可为气体，并且除氟化氢外，其它的所述杂质不参与生成金属氟化物的反应。该含氟无氧化合物可为含氟无氧有机物和含氟无氧无机物中的一种或几种。优选地，该含氟无氧有机物可为聚偏氟乙烯（PVDF）、聚四氟乙烯（PTFE）、氟化乙烯丙烯共聚物（FEP）、聚氟乙烯（PVF）中和三氟甲基苯的一种或几种。该含氟无氧无机物可为NH4F和NH4HF2中的一种或几种。
该含氟无氧化合物可为固体（例如PVDF），也可为液体（例如三氟甲基苯）。当该含氟无氧化合物为固体时，该含氟无氧化合物的形貌不限。优选地，该含氟无氧化合物可为粉末状。该含氟无氧化合物的粒度越小，越有利于后续烧结过程中分解反应的进行。优选地，该含氟无氧化合物的粒度小于等于200目。
在步骤S12中，将该茂金属与该含氟无氧化合物进行混合的混合方式只要能使该茂金属与该含氟无氧化合物混合均匀即可。该茂金属与该含氟无氧化合物可在常温下进行混合。优选地，茂金属与该含氟无氧化合物可在无氧的环境下进行混合，以防止该第一混合物中混入氧而使后续烧结过程中生成的金属氟化物颗粒发生氧化。在一实施例中，可将固态的茂金属浸渍在液态的含氟无氧化合物中形成一悬浮液，从而在该固态的茂金属表面形成一层含氟无氧化合物膜，得到所述第一混合物。在一实施例中，也可将固态的茂金属溶解在所述液态的含氟无氧化合物中形成一混合溶液，得到所述第一混合物。在另一实施例中，可将固体粉末状的茂金属与固体粉末状或液体的含氟无氧化合物采取研磨或球磨的方法进行混合。优选地，该茂金属与该含氟无氧化合物采用球磨的方法进行混合，采用球磨的方法不仅能使该茂金属与该含氟无氧化合物混合均匀，还可进一步减小该茂金属或该含氟无氧化合物的粒度，更有利于后续烧结过程中分解反应的进行。优选地，该茂金属与该含氟无氧化合物均为固体。
该茂金属中的金属元素具有一最低的非零价态m+。该茂金属与该含氟无氧化合物的混合比例按照氟元素与金属元素的化学计量比为(m-0.1):1到(m+0.1):1进行配比。优选地，该茂金属与该含氟无氧化合物中氟元素与金属元素的化学计量比为(m-0.1):1到m:1，该范围内所述含氟无氧化合物分解产生的氟化氢可全部反应生成金属氟化物，不会产生多余的氟化氢气体。
在步骤S13中，所述烧结的温度为能使该茂金属和该含氟无氧化合物均能发生分解的温度。优选地，所述烧结温度为400°C至1000°C。更为优选地，所述烧结温度为500°C至900°C。最为优选地，所述烧结温度为600°C至800°C。若所述烧结温度过低，则所形成的碳层石墨化程度较低；若所述烧结温度过高，则所述金属氟化物易氧化。所述烧结的时间为1小时至10小时。优选地，所述烧结时间为2小时至5小时。若所述烧结时间过短，则上述反应不充分，若所述烧结时间过长，则所述金属氟化物易氧化。该惰性气氛可进一步保护生成的金属氟化物不被氧化。优选地，该惰性气氛可为氩气、氮气和氦气中的一种或几种。
在所述烧结过程中，该茂金属发生分解生成金属单质和碳团簇，该含氟无氧化合物发生分解释放出氟化氢气体，该金属单质和该氟化氢气体反应生成金属氟化物颗粒，同时，该碳团簇吸附到该金属氟化物颗粒的表面形成碳包覆层，最终形成了碳包覆金属氟化物的核壳复合结构。
所述碳包覆金属氟化物的碳层为均匀连续的碳层。由于在所述烧结过程中该金属单质的存在，该碳团簇在形成碳层的过程中可发生石墨化，因此该碳层为石墨化碳层。由于所述烧结过程中具有还原性的碳团簇的存在，该碳包覆金属氟化物中金属元素的价态为该金属元素的最低非零价态m+。
该碳包覆金属氟化物的碳层厚度为5nm至50nm。优选地，该碳包覆金属氟化物的碳层厚度为10nm至20nm。该碳层的质量为该碳包覆金属氟化物质量的30%至60%。优选地，该碳层的质量为该碳包覆金属氟化物质量的30%至40%。该质量范围内的碳层在提高该金属氟化物的导电性的同时，可以保证该金属氟化物具有较高的容量。可通过调控所述第一混合物中碳元素和金属元素的比例来对该碳层的厚度和该碳层占该碳包覆金属氟化物的质量百分数来进行调控。
当该含氟无氧化合物为含氟无氧无机物时，该碳包覆金属氟化物为球形颗粒。该球形颗粒的碳包覆金属氟化物的直径为50nm至1μm。这可能是因为该含氟无氧无机物的分解温度较低、分解速度较快，在所述烧结过程中可快速产生较多的氟化氢气体，因此该金属氟化物晶体从一开始即可在各个晶面进行生长，最终形成了球形颗粒的金属氟化物。
当该含氟无氧化合物为含氟无氧有机物时，该碳包覆金属氟化物为棒状颗粒。此外，由于该含氟无氧有机物也可在所述烧结过程中分解出碳团簇，因此可得到上述5nm至50nm的范围内厚度较厚碳层的碳包覆金属氟化物。该棒状颗粒的碳包覆金属氟化物的长度为500nm至1.2μm，宽度为50nm至1μm。这可能是因为该含氟无氧有机物的分解温度较高、分解速度较慢，在金属氟化物晶体刚开始生长的过程中氟化氢气体产生的量较少，因此该金属氟化物晶体优先沿一个晶面进行生长，从而形成了棒状颗粒的金属氟化物。
本发明第一实施例通过将茂金属和含氟无氧化合物混合后再进行烧结，同步完成金属氟化物的生长和碳层的包覆，与现有技术相比，本发明的制备方法工艺简单、容易操作且成本较低，可适用于大规模的工业化生产。
由于该茂金属的沸点较低，一般低于300°C，该茂金属在所述烧结过程中会升华形成气体，因此在与氟化氢气体发生反应后，可形成粒度较小且均匀的金属氟化物颗粒，最终形成粒度较小且均匀的碳包覆金属氟化物颗粒。
由于所述烧结在惰性气氛中进行，且该含氟无氧化合物中不含有氧元素，同时所述茂金属分解生成的碳团簇具有还原性，因此该金属单质和该金属氟化物颗粒不会在所述烧结过程中发生氧化而生成金属氧化物等杂质，从而能获得纯度较高的金属氟化物颗粒。
另外，该碳包覆金属氟化物的碳层为均匀连续的石墨化碳层，与无定形碳层相比，该石墨化碳层能为金属氟化物提供更多的体积膨胀和收缩的空间及更多的电子输运通道，使得金属氟化物具有更好的导电性能。因此，本发明制备的金属氟化物正极活性材料不仅具有较高的比容量和能量密度，同时具备较好的导电性能、较高的库仑效率和更稳定的循环性能。
请参阅图2，本发明第二实施例提供一种制备金属氟化物正极活性材料的制备方法，包括：
S21，提供金属颗粒、所述含氟无氧化合物及无氧碳源；
S22，将该金属颗粒、该含氟无氧化合物及该无氧碳源混合得到一第二混合物；以及
S23，将该第二混合物在惰性气氛中进行烧结，得到碳包覆金属氟化物。
在步骤S21中，该金属颗粒为单质，可为Ti、V、Mn、Fe、Bi、Co、Ni、Cu、Zn、Sn、Ag、Pb、Ca或Ba颗粒中的一种。该金属颗粒可为纳米颗粒。优选地，该金属颗粒的粒径可在20nm至1μm之间。优选地，为了获得粒径更小、性能更好的正极活性材料，该金属颗粒的粒径可在20nm至500nm之间。该金属颗粒可采用水溶液还原法、溶胶-凝胶法、气相沉积法、蒸发-凝聚法及高温分解金属化合物等方法来进行制备。
该金属颗粒中的金属元素具有一最低的非零价态m+。该金属颗粒与该含氟无氧化合物的混合比例按照氟元素与金属元素的化学计量比为(m-0.1):1到(m+0.1):1进行配比。优选地，该茂金属与该含氟无氧化合物中氟元素与金属元素的化学计量比为(m-0.1):1到m:1，该范围内该含氟无氧化合物分解产生的氟化氢可全部反应生成金属氟化物，不会产生多余的氟化氢气体。
所述无氧碳源可为固体，也可为液体。优选地，所述无氧碳源能在所述烧结过程中分解出碳团簇。优选地，所述无氧碳源可为聚乙烯、聚丙烯、聚苯乙烯、聚苯萘、聚偏氟乙烯、聚四氟乙烯、氟化乙烯丙烯共聚物和聚氟乙烯中的一种或几种。所述无氧碳源中不含氧元素，因此不会在所述烧结过程中使金属颗粒发生氧化而生成金属氧化物杂质。
在步骤S22中，将该金属颗粒、该含氟无氧化合物及该无氧碳源进行混合的混合方式只要能使该金属颗粒、该含氟无氧化合物及该无氧碳源混合均匀即可。该金属颗粒、该含氟无氧化合物及该无氧碳源可在常温下进行混合。优选地，该金属颗粒、该含氟无氧化合物及该无氧碳源可在无氧的环境下进行混合，以防止所述第二混合物中混入氧而使后续烧结过程中生成的金属氟化物颗粒发生氧化。优选地，该金属颗粒、该含氟无氧化合物及该无氧碳源均为固体，可将该固体的金属颗粒、含氟无氧化合物及无氧碳源采取研磨或球磨的方法进行混合。优选地，该金属颗粒、该含氟无氧化合物及该无氧碳源采用球磨的方法进行混合，采用球磨的方法不仅能使该金属颗粒、该含氟无氧化合物及该无氧碳源混合均匀，还可进一步减小该金属颗粒、该含氟无氧化合物及该无氧碳源的粒度，更有利于后续烧结过程中烧结反应的进行。
在步骤S23中，所述烧结的温度为能使该无氧碳源和该含氟无氧化合物均能发生分解的温度。优选地，所述烧结温度为400°C至1000°C。更为优选地，所述烧结温度为500°C至900°C。最为优选地，所述烧结温度为600°C至800°C。若所述烧结温度过低，则所形成的碳层石墨化程度较低；若所述烧结温度过高，则所述金属氟化物易发生氧化。所述烧结的时间为1小时至10小时。优选地，所述烧结时间为2小时至5小时。若所述烧结时间过短，则上述反应不充分，若所述烧结时间过长，则所述金属氟化物易氧化。该惰性气氛可进一步保护生成的金属氟化物不被氧化。优选地，该惰性气氛可为氩气、氮气和氦气中的一种或几种。
在所述烧结过程中，该含氟无氧化合物发生分解释放出氟化氢气体，该无氧碳源发生分解产生碳团簇。该金属颗粒和该氟化氢气体反应生成金属氟化物颗粒，同时，该碳团簇吸附到该金属氟化物颗粒的表面形成碳包覆层，最终形成了碳包覆金属氟化物的核壳复合结构。
所述碳包覆金属氟化物的碳层为均匀连续的碳层。由于在所述烧结过程中该金属颗粒的存在，该碳团簇在形成碳层的过程中可发生石墨化，因此该碳层为石墨化碳层。由于在所述烧结过程中具有还原性的碳团簇的存在，该金属氟化物正极活性材料中所述金属元素的价态为该金属元素的最低非零价态m+。
本发明第二实施例通过将金属颗粒、含氟无氧化合物及无氧碳源混合后再进行烧结，同步完成金属氟化物的生长和碳层的包覆，与现有技术相比，本发明的制备方法工艺简单、容易操作且成本较低，可适用于大规模的工业化生产。
由于所述烧结在惰性气氛中进行，且该含氟无氧化合物和该无氧碳源中不含有氧元素，因此该金属单质和该金属氟化物颗粒不会在所述烧结过程中发生氧化而生成金属氧化物等杂质，能获得纯度较高的金属氟化物颗粒。
另外，该碳包覆金属氟化物的碳层为均匀连续的石墨化碳层，与无定形碳层相比，该石墨化碳层能为金属氟化物提供更多的体积膨胀和收缩的空间及更多的电子输运通道，使得所述金属氟化物具有更好的导电性能。因此，本发明制备的金属氟化物正极活性材料不仅具有较高的比容量和能量密度，同时具备较好的导电性能、较高的库仑效率和更稳定的循环性能。
本发明第二实施例还可将所述金属化合物、所述含氟化合物以及所述无氧碳源混合后进行烧结制备碳包覆金属氟化物，该金属化合物在所述烧结过程中可发生分解生成粒径较小的金属颗粒，从而为金属氟化物正极活性材料的制备提供金属颗粒，并可获得粒径较小的金属氟化物正极活性材料。
此外，本发明还可提供一种在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物层的制备方法，该金属氟化物层可避免该锂-过渡金属氧化物正极活性材料和电解液的直接接触，抑制该锂-过渡金属氧化物正极活性材料与电解液之间的反应，防止该锂-过渡金属氧化物正极活性材料在使用过程中容量快速的降低，同时能够改善使用该锂-过渡金属氧化物正极活性材料的锂离子电池的循环性能及高倍率性能。
请参阅图3，本发明第三实施例进一步提供一种在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物的制备方法，包括：
S31，提供所述金属颗粒、所述含氟无氧化合物及锂-过渡金属氧化物正极活性材料；
S32，将该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合得到一第三混合物；以及
S33，将该第三混合物在惰性气氛中进行烧结，得到金属氟化物包覆的锂-过渡金属氧化物正极活性材料。
在步骤S31中，该锂-过渡金属氧化物正极活性材料为可在锂电池充放电过程中可逆地插入及脱出锂离子的嵌锂化合物。所述锂-过渡金属氧化物正极活性材料可以为未掺杂或掺杂的尖晶石结构的锰酸锂、层状锰酸锂、镍酸锂、钴酸锂、磷酸铁锂、锂镍锰氧化物及锂镍钴锰氧化物中的一种或多种。具体地，该尖晶石结构的锰酸锂可以由化学式LixMn2-yLyO4表示，该镍酸锂可以由化学式LixNi1-yLyO2表示，该钴酸锂的化学式可以由LixCo1-yLyO2表示，该层状锰酸锂的化学式可以由LixMn1-yLyO2，该磷酸铁锂的化学式可以由LixFe1-yLyPO4表示，该锂镍锰氧化物的化学式可以由LixNi0.5+z-aMn1.5-z-bLaRbO4表示，该锂镍钴锰氧化物的化学式可以由LixNicCodMneLfO2表示，其中0.1≤x≤1.1，0≤y<1，0≤z<1.5，0≤a-z<0.5，0≤b+z<1.5，0<c<1，0<d<1, 0<e<1，0≤f≤0.2，c+d+e+f=1。L和R选自碱金属元素、碱土金属元素、第13族元素、第14族元素、过渡族元素及稀土元素中的一种或多种，优选地，L和R选自Mn、Ni、Cr、Co、V、Ti、Al、Fe、Ga、Nd及Mg中的至少一种。
该锂-过渡金属氧化物正极活性材料的粒径可为20nm至10μm。优选地，该金属颗粒的粒径小于该锂-过渡金属氧化物正极活性材料的粒径，以使该金属颗粒可充分与该锂-过渡金属氧化物正极活性材料的表面接触，从而更有利于在后续的烧结过程中该金属氟化物在该锂-过渡金属氧化物正极活性材料表面的形核。优选地，该锂-过渡金属氧化物正极活性材料的粒径为该金属颗粒粒径的10到500倍。更为优选地，该锂-过渡金属氧化物正极活性材料的粒径为该金属颗粒粒径的100到500倍。
在步骤S32中，将该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料进行混合的混合方式只要能使该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合均匀即可。该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料可在常温下进行混合。优选地，该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料可在惰性气氛中进行混合。优选地，该含氟无氧化合物可为固体，可将该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料采取研磨或球磨的方法进行混合。优选地，该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料采用球磨的方法进行混合，采用球磨的方法不仅能使该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合均匀，还可进一步减小该金属颗粒、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料的粒径，更有利于后续烧结过程中烧结反应的进行。
该锂-过渡金属氧化物正极活性材料的质量可为该第三混合物质量的50%到99%。优选地，该锂-过渡金属氧化物正极活性材料的质量可为该第三混合物质量的80%到99%。更为优选地，该锂-过渡金属氧化物正极活性材料的质量可为该第三混合物质量的90%到97%。该质量范围内的锂-过渡金属氧化物正极活性材料既能保证该金属氟化物包覆的锂-过渡金属氧化物正极活性材料具有较好的导电性，又能使包覆的金属氟化物层有效隔绝该锂-过渡金属氧化物正极活性材料与电解液的接触。
在步骤S33中，所述烧结的温度为能使该含氟无氧化合物能发生分解的温度。在本实施例中，所述烧结的条件与本发明第一实施例的烧结条件相同。
在步骤S33中，在所述烧结过程中，该含氟无氧化合物发生分解释放出氟化氢气体，该金属颗粒和该氟化氢气体反应生成金属氟化物，该金属氟化物在该锂-过渡金属氧化物正极活性材料表面进行形核，并逐渐生长，最终形成了金属氟化物包覆的锂-过渡金属氧化物正极活性材料。
该金属氟化物包覆的锂-过渡金属氧化物正极活性材料的金属氟化物层为均匀连续的包覆层。该金属氟化物层的厚度可通过该第三混合物中该金属颗粒和该含氟无氧化合物的比例进行调控。优选地，该金属氟化物层的厚度可为0.2nm至50nm，该厚度范围内的金属氟化物层在保证该锂-过渡金属氧化物正极活性材料导电性的同时，可有效隔绝该锂-过渡金属氧化物正极活性材料与电解液的接触。更为优选地，该金属氟化物包覆锂-过渡金属氧化物正极活性材料的金属氟化物包覆层厚度为1nm至5nm。
进一步地，当该含氟无氧化合物为含氟无氧有机物时，由于该含氟无氧有机物可在所述烧结过程中分解出碳团簇，该碳团簇可吸附在该金属氟化物层表面，在该金属氟化物层表面形成碳层，从而形成一个三层结构的核壳型正极材料，该核壳型正极材料从内到外依次为锂-过渡金属氧化物正极活性材料、金属氟化物层及碳层。由于在所述烧结过程中该金属颗粒的存在，该碳团簇在形成碳层的过程中可发生石墨化，因此该核壳型正极材料的碳层为石墨化碳层，该石墨化碳层能为该核壳型正极材料提供更多的体积膨胀和收缩的空间及更多的电子输运通道，能使该核壳型正极材料具有更好的导电性能。
本发明第三实施例采用直接进行烧结的方法在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物，该方法不仅操作简单、成本较低、适用于工业化生产，而且该金属氟化物层的厚度可控，该金属氟化物层能有效隔绝锂-过渡金属氧化物正极活性材料与电解液的接触，防止锂离子电池在使用过程中的性能退化。
本发明第三实施例还可将所述金属化合物、所述含氟无氧化合物及所述锂-过渡金属氧化物正极活性材料混合后进行烧结制备金属氟化物包覆的锂-过渡金属氧化物正极活性材料，该金属化合物在所述烧结过程中可发生分解生成金属颗粒，从而为金属氟化物包覆的锂-过渡金属氧化物正极活性材料的制备提供粒径较小的金属颗粒。
请参阅图4，本发明第四实施例进一步提供一种在所述锂-过渡金属氧化物正极活性材料表面包覆金属氟化物的制备方法，包括：
S41，提供所述茂金属、所述含氟无氧化合物及所述锂-过渡金属氧化物正极活性材料；
S42，将该茂金属、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合得到一第四混合物；以及
S43，将该第四混合物在惰性气氛中进行烧结，得到金属氟化物包覆的锂-过渡金属氧化物正极活性材料。
在步骤S42中，所述混合的混合方式与本发明第三实施例中混合的混合方式相同。该锂-过渡金属氧化物正极活性材料的质量可为该第四混合物质量的50%到99%。优选地，该锂-过渡金属氧化物正极活性材料的质量可为该第四混合物质量的80%到99%。更为优选地，该锂-过渡金属氧化物正极活性材料的质量可为该第四混合物质量的90%到97%。该质量范围内的锂-过渡金属氧化物正极活性材料既能保证该金属氟化物包覆的锂-过渡金属氧化物正极活性材料具有较好的导电性，又能使包覆的金属氟化物层有效隔绝该锂-过渡金属氧化物正极活性材料与电解液的接触。
在步骤S43中，所述烧结的条件与本发明第一实施例的烧结条件相同。
在步骤S43中，该茂金属发生分解生成金属单质，该含氟无氧化合物发生分解释放出氟化氢气体，该金属单质和该氟化氢气体反应生成金属氟化物颗粒。由于该茂金属的沸点较低，在所述烧结过程中，该茂金属可升华为气体并均匀的分布在该正极活性材料的周围，因此，最终可在该正极活性材料表面形成均匀连续的金属氟化物包覆层。
该金属氟化物层的厚度可通过该第四混合物中该茂金属和该含氟无氧化合物的比例进行调控。优选地，该金属氟化物层的厚度可为0.2nm至50nm，该厚度范围内的金属氟化物层在保证该锂-过渡金属氧化物正极活性材料导电性的同时，可有效隔绝该锂-过渡金属氧化物正极活性材料与电解液的接触。更为优选地，该金属氟化物包覆锂-过渡金属氧化物正极活性材料的金属氟化物包覆层厚度为1nm至5nm。
进一步地，该茂金属发生分解后还能生成碳团簇，该碳团簇可吸附到该金属氟化物包覆层的表面形成碳包覆层，最终形成了三层结构的核壳型正极材料，该核壳型正极材料从内到外依次为锂-过渡金属氧化物正极活性材料、金属氟化物及碳层。由于在所述烧结过程中该金属单质的存在，该碳团簇在形成碳层的过程中可发生石墨化，因此该核壳型正极材料的碳层为石墨化碳层，该石墨化碳层能为该核壳型正极材料提供更多的体积膨胀和收缩的空间及更多的电子输运通道，能使该核壳型正极材料具有更好的导电性能。
本发明第四实施例采用直接进行烧结的方法在锂-过渡金属氧化物正极活性材料表面包覆金属氟化物，可以在该锂-过渡金属氧化物正极活性材料表面生成均匀连续的包覆层，该方法不仅操作简单、成本较低、适用于工业化生产，而且该金属氟化物层的厚度可控，该金属氟化物层能有效隔绝锂-过渡金属氧化物正极活性材料与电解液的接触，防止锂离子电池在使用过程中的性能退化。
实施例1
将二茂铁和PVDF按照氟/铁元素摩尔比2:1比例混合，以500rpm/min速度球磨2小时得到一第一混合物。将该第一混合物置于不锈钢容器中，将容器置于手套箱中充氩气，然后将该第一混合物于600°C下反应5小时，得到碳包覆氟化亚铁。
请参阅图5，该碳包覆氟化亚铁为棒状颗粒，该棒状颗粒的长度约1μm，宽度在100nm~1μm之间，碳层厚度约为20nm。请参阅图6，该反应产物的XRD图谱的衍射峰与氟化亚铁的标准图谱的衍射峰一致，证明上述制备方法可制备出纯相且结晶度良好的氟化亚铁。请参阅图7，该碳包覆氟化亚铁的碳层具有晶格条纹，条纹间距为0.34nm，与石墨的层间距相符，证明该碳包覆氟化亚铁的碳层为石墨化碳层。将该碳包覆氟化亚铁用于锂离子电池正极时具有300mAh·g-1的首次储锂容量，库伦效率在96%以上，循环50次之内每次循环的容量损失率为0.66%。
实施例2
将二茂铁和NH4F按照氟/铁元素比2.05:1比例混合，以400rpm/min速度球磨1小时得到一第一混合物。将该第一混合物置于不锈钢容器中，将容器置于手套箱中充氮气，然后将该第一混合物在650°C反应小时，得到碳包覆氟化亚铁。
请参阅图8，该碳包覆氟化亚铁为球形颗粒，该球形颗粒直径在100nm~1μm之间，碳层厚度约为10nm。将该碳包覆氟化亚铁用于锂离子电池正极时，具有330mAh·g-1的首次储锂容量，库伦效率在95%以上，循环40次之内每次循环的容量损失率为0.72%，请参阅图9，该碳包覆氟化亚铁与未包覆碳的氟化亚铁相比，具有更好的库仑效率和更稳定的循环性能。
实施例3
将二茂钴和NH4HF2按照氟/碳元素比1.95:1比例混合，研磨至混合均匀得到一第一混合物。将该第一混合物置于不锈钢容器中，将容器置于手套箱中充氦气，然后在550°C反应4小时，得到碳包覆氟化锰。
该碳包覆氟化锰为球形颗粒，该球形颗粒直径在50nm~0.5μm之间，碳层厚度约为15nm。该碳包覆氟化锰用于锂离子电池正极时，具有380mAh·g-1的首次储锂容量，库伦效率在95%以上，循环80次之内每次循环的容量损失率为0.52%。
实施例4
将50nm的铁颗粒和PVDF按照氟/铁元素摩尔比2:1比例混合，以500rpm/min速度球磨2小时得到一第二混合物。将该第二混合物置于不锈钢容器中，将容器置于手套箱中充氩气，然后将该第二混合物于600°C下反应5小时，得到碳包覆氟化亚铁。将该碳包覆氟化亚铁用于锂离子电池正极时具有300mAh·g-1的首次储锂容量，库伦效率在96%以上，循环50次之内每次的容量损失率为0.66%。
实施例5
将100nm的铁颗粒、PVDF和钴酸锂混合，以500rpm/min速度球磨2小时得到一第三混合物，该铁颗粒与该PVDF中氟/铁元素的摩尔比为2:1，该钴酸锂的质量为该第三混合物质量的80%。将该第三混合物置于不锈钢容器中，将容器置于手套箱中充氩气，然后将该第三混合物于600°C下反应5小时，得到氟化亚铁包覆钴酸锂壳核复合结构。将该氟化亚铁包覆钴酸锂的壳核复合结构用于锂离子电池正极时，在50次放电和再充电循环后，氟化亚铁包覆钴酸锂在室温30°C和电流密度0.8Ma/cm2的容量保持率为93%。这些结果证明了，随着循环次数的增加，氟化亚铁包覆钴酸锂容量保持率较高。
实施例6
将二茂镍、NH4F与钴酸锂混合，以400rpm/min速度球磨1小时得到一第四混合物。该第四混合物中二茂镍和NH4F的氟/镍元素摩尔比为2.05:1，钴酸锂的质量为该第四混合物质量的85%。将该第四混合物置于不锈钢容器中，将容器置于手套箱中充氮气，然后将该第四混合物在650°C反应小时，得到核壳型正极材料，该核壳型正极材料从里到外分别为钴酸锂、NiF2及石墨化碳层。将该核壳型正极材料应用于锂离子电池正极，具有140mAh·g-1的首次储锂容量，库伦效率在95%以上，循环40次之内每次循环的容量损失率为0.72%。
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. 一种锂离子电池正极活性材料的制备方法，包括：
    提供茂金属、含氟无氧化合物及锂-过渡金属氧化物正极活性材料；
    将该茂金属、该含氟无氧化合物及该锂-过渡金属氧化物正极活性材料混合得到一混合物；以及
    将该混合物在惰性气氛中进行烧结，得到金属氟化物包覆的锂-过渡金属氧化物正极活性材料，该含氟无氧化合物在所述烧结过程中发生分解释放出氟化氢气体。
  2. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，该茂金属为二茂铁、二茂钴、二茂镍和二茂锰中的一种或几种。
  3. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，该含氟无氧化合物为含氟无氧有机物。
  4. 如权利要求3所述的锂离子电池正极活性材料的制备方法，其特征在于，该含氟无氧有机物为聚偏氟乙烯、聚四氟乙烯、氟化乙烯丙烯共聚物和聚氟乙烯中的一种或几种。
  5. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，该含氟无氧化合物为含氟无氧无机物。
  6. 如权利要求5所述的锂离子电池正极活性材料的制备方法，其特征在于，该含氟无氧无机物为NH4F和NH4HF2中的一种或几种。
  7. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，该茂金属中的金属元素具有一最低非零价态m+，该茂金属与该含氟无氧化合物中氟元素与金属元素的化学计量比为(m-0.1):1到(m+0.1):1。
  8. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，该锂-过渡金属氧化物正极活性材料的质量为该混合物质量的50%到99%。
  9. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，所述烧结温度为400至1000°C，所述烧结的时间为1小时至10小时。
  10. 如权利要求1所述的锂离子电池正极活性材料的制备方法，其特征在于，所述烧结温度为600至800°C，所述烧结的时间为2小时至5小时。
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