WO2015172625A1

WO2015172625A1 - Method for preparing active material for positive electrode of lithium-ion battery

Info

Publication number: WO2015172625A1
Application number: PCT/CN2015/077331
Authority: WO
Inventors: 张艳丽; 何向明; 王莉; 尚玉明; 李建军; 高剑
Original assignee: 江苏华东锂电技术研究院有限公司; 清华大学
Priority date: 2014-05-16
Filing date: 2015-04-24
Publication date: 2015-11-19
Also published as: CN103996851A

Abstract

A method for preparing the active material for the positive electrode of a lithium-ion battery, comprising: providing metal particles, a compound containing fluorine but not oxygen, and a carbon source containing no oxygen; mixing the metal particles, the compound containing fluorine but not oxygen, and the carbon source containing no oxygen to obtain a mixture; sintering the mixture in an inert atmosphere to obtain a carbon-covered metal fluoride, the compound containing fluorine but not oxygen decomposing and generating hydrogen fluoride gas during sintering.

Description

Method for preparing lithium ion battery positive active material

Technical field

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 positive electrode active material.

Background technique

At present, lithium-ion batteries have been widely used in portable electronic products, but in the field of electric vehicles and large-scale energy storage, they need higher energy density, so it is necessary to seek high-energy density lithium-ion battery cathode active materials. Lithium cobaltate or lithium iron phosphate, which is currently used as a positive electrode active material for lithium ion batteries, is limited to one electron redox reaction, so its specific capacity is low.

Metal fluorides can undergo multi-electron redox reactions and therefore have a higher specific capacity. At the same time, the metal fluoride has a high redox voltage caused by a strong covalent bond (MF bond) between the metal atom and the fluorine atom. Therefore, the metal fluoride has a high theoretical energy density and is a high energy density lithium. An alternative positive active material for an ion battery. However, the MF bond of the metal fluoride is a high electronegativity valence bond, so that the metal fluoride has a large energy gap, so that the metal fluoride is not electrically conductive, and there is still a volume due to its application to the positive electrode active material of the lithium ion battery. Problems such as low coulombic efficiency due to expansion and poor cycle performance.

In order to overcome the problems of the metal fluoride positive electrode active material, one solution is to coat the surface of the metal fluoride particles with a carbon layer to increase the conductivity of the metal fluoride and to buffer the volume change during charging and discharging. However, the existing method of coating the surface of the metal fluoride with a carbon layer is to directly mix the metal fluoride and the carbon source and then sinter at a high temperature, which not only makes the metal fluoride easily oxidized to generate impurities, but also The carbon layer formed by this method is an amorphous carbon layer, and the amorphous carbon layer has poor conductivity, so the electrochemical performance of the carbon-coated metal fluoride prepared by this method is still poor.

Summary of the invention

In view of this, it is indeed necessary to provide a method for preparing a metal fluoride positive electrode active material which is simple in preparation method, low in cost, and suitable for industrial production and can improve the conductivity of metal fluoride.

A method for preparing a positive active material for a lithium ion battery, comprising:

Providing metal particles, fluorine-containing oxygen-free compounds, and an oxygen-free carbon source;

Mixing the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source to obtain a mixture;

The mixture is sintered in an inert atmosphere to obtain a carbon-coated metal fluoride which decomposes during the sintering to release hydrogen fluoride gas.

The invention combines the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source and then performs sintering to simultaneously complete the growth of the metal fluoride and the coating of the carbon layer, and the preparation method of the invention is compared with the prior art. Simple, easy to operate and low in cost, it can be applied to large-scale industrial production; in addition, the preparation method of the present invention can form a graphitized carbon layer on the surface of metal fluoride particles, which can provide more metal fluoride The volume expansion and contraction space and more electron transport channels, therefore, the metal fluoride positive electrode active material prepared by the invention not only has higher specific capacity and energy density, but also has better conductivity and higher conductivity. Coulomb efficiency and more stable cycle performance.

DRAWINGS

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.

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.

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.

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.

detailed description

Referring to FIG. 1 , a first embodiment of the present invention provides a method for preparing a metal fluoride positive electrode active material, including:

S11, providing a metallocene and a fluorine-containing oxygen-free compound;

S12, mixing the metallocene and the fluorine-containing oxygen-free compound to obtain a first mixture;

S13, sintering the first mixture in an inert atmosphere to obtain a carbon-coated metal fluoride.

In step S11, 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. Preferably, 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 smaller the particle size of the metallocene, the more favorable the decomposition reaction during the subsequent sintering process. Preferably, 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. For example, 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. Preferably, the fluorine-containing oxygen-free organic material may be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), polyvinyl fluoride (PVF), and 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). When the fluorine-containing oxygen-free compound is a solid, the morphology of the fluorine-containing oxygen-free compound is not limited. Preferably, 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. Preferably, the fluorine-containing oxygen-free compound has a particle size of 200 mesh or less.

In 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. Preferably, 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. In one embodiment, 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. In one embodiment, 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. In another embodiment, the solid powdered metallocene can be mixed with a solid powdered or liquid fluorine-containing oxygen-free compound by grinding or ball milling. Preferably, 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. Preferably, 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. Preferably, 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.

In the step S13, the sintering temperature is a temperature at which both the metallocene and the fluorine-containing oxygen-free compound can be decomposed. Preferably, 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. If the sintering time is too short, the above reaction is insufficient, and if the sintering time is too long, the metal fluoride is easily oxidized. The inert atmosphere further protects the resulting metal fluoride from oxidation. Preferably, the inert atmosphere may be one or more of argon, nitrogen and helium.

During the sintering process, the metallocene is decomposed to form a metal element and a carbon cluster, and the fluorine-containing oxygen-free compound is decomposed to release a hydrogen fluoride gas, and the metal element reacts with the hydrogen fluoride gas to form metal fluoride particles, and at the same time, 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. Preferably, 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. Preferably, 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.

When the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free inorganic substance, 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 μm. 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.

When the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free organic material, 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 μm and a width of 50 nm to 1 μm. This may be because 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.

In the first embodiment of the present invention, 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.

Since 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.

Since the sintering is carried out in an inert atmosphere, and the fluorine-containing oxygen-free compound does not contain an oxygen element, and the carbon cluster formed by the decomposition of the metallocene has a reducing property, 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.

In addition, 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.

Referring to FIG. 2, a second embodiment of the present invention provides a method for preparing a metal fluoride positive electrode active material, comprising:

S21, providing metal particles, the fluorine-containing oxygen-free compound, and an oxygen-free carbon source;

S22, mixing the metal particles, the fluorine-containing oxygen-free compound and the oxygen-free carbon source to obtain a second mixture;

S23, sintering the second mixture in an inert atmosphere to obtain a carbon-coated metal fluoride.

In step S21, 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. Preferably, the metal particles may have a particle diameter of between 20 nm and 1 μm. Preferably, in order to obtain a positive electrode active material having a smaller particle diameter and better performance, 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. Preferably, 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. Preferably, the oxygen-free carbon source is capable of decomposing carbon clusters during the sintering process. Preferably, 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.

In step S22, 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. Preferably, 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. Preferably, 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. Preferably, 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.

In step S23, the sintering temperature is a temperature at which both the oxygen-free carbon source and the fluorine-containing oxygen-free compound can be decomposed. Preferably, 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. If the sintering time is too short, the above reaction is insufficient, and if the sintering time is too long, the metal fluoride is easily oxidized. The inert atmosphere further protects the resulting metal fluoride from oxidation. Preferably, the inert atmosphere may be one or more of argon, nitrogen and helium.

During the sintering process, 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.

In the second embodiment of the present invention, 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.

Since the sintering is performed in an inert atmosphere, and the fluorine-containing oxygen-free compound and the oxygen-free carbon source do not contain oxygen, the metal element and the metal fluoride particles are not oxidized during the sintering process. By forming impurities such as metal oxides, metal fluoride particles having higher purity can be obtained.

In addition, 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.

In a second embodiment of the present invention, 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.

In addition, 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.

Referring to FIG. 3, 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:

S31, providing the metal particles, the fluorine-containing oxygen-free compound, and a lithium-transition metal oxide cathode active material;

S32, mixing the metal particles, the fluorine-containing oxygen-free compound and the lithium-transition metal oxide positive electrode active material to obtain a third mixture;

S33, the third mixture is sintered in an inert atmosphere to obtain a metal fluoride-coated lithium-transition metal oxide positive active material.

In step S31, 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. Specifically, 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 , and the chemical formula of the layered lithium manganate may be Li _x Mn _1-y L _y O ₂ , and 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 , and 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 < 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 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. Preferably, 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 μm. Preferably, 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. Preferably, 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.

In 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. Preferably, 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. Preferably, 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. Preferably, 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. Preferably, 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.

In step S33, the temperature of the sintering is a temperature at which the fluorine-containing oxygen-free compound can be decomposed. In the present embodiment, the sintering conditions are the same as those of the first embodiment of the present invention.

In 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. Preferably, 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.

Further, when the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free organic substance, since 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. Due to the presence of the metal particles during the sintering process, 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.

According to a third embodiment of the present invention, 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.

Referring to FIG. 4, 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:

S41, providing the metallocene, the fluorine-containing oxygen-free compound, and the lithium-transition metal oxide cathode active material;

S42, mixing the metallocene, the fluorine-containing oxygen-free compound and the lithium-transition metal oxide positive electrode active material to obtain a fourth mixture;

S43, the fourth mixture is sintered in an inert atmosphere to obtain a metal fluoride-coated lithium-transition metal oxide positive electrode active material.

In step S42, 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. Preferably, 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.

In the step S43, the sintering conditions are the same as those of the first embodiment of the present invention.

In 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. Preferably, 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.

Further, after the metallocene is decomposed, carbon clusters can be formed, and the carbon clusters can be adsorbed onto the surface of the metal fluoride coating layer to form a carbon coating layer, thereby finally forming a three-layer core-shell cathode material. 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. Due to the presence of the metal element in the sintering process, 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.

In the fourth embodiment of the present invention, 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.

Example 1

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.

Referring to FIG. 5, the carbon-coated ferrous fluoride is a rod-shaped particle having a length of about 1 μm, a width of between 100 nm and 1 μm, and a carbon layer thickness of about 20 nm. Referring to Fig. 6, 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. Referring to FIG. 7, 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. Floor. 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. .

Example 2

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.

Referring to FIG. 8, the carbon-coated ferrous fluoride is a spherical particle having a diameter of between 100 nm and 1 μm and a carbon layer having a thickness of about 10 nm. When 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.

Example 3

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 μm and a carbon layer thickness of about 15 nm. When the carbon coated manganese fluoride is 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.

Example 4

50 nm of iron particles and PVDF were mixed at a fluorine/iron molar ratio of 2:1, and ball milled at 500 rpm/min for 2 hours to obtain a second mixture. The second mixture was placed in a stainless steel container, the container was placed in a glove box filled with argon gas, and then the second mixture was reacted at 600 ° C for 5 hours to obtain a carbon-coated ferrous fluoride. When the carbon-coated ferrous fluoride is used for the positive electrode of a lithium ion battery, the first lithium storage capacity of 300 mAh·g ^-1 is obtained, the coulombic efficiency is 96% or more, and the capacity loss rate per time is 50% within 60 cycles.

Example 5

100 nm of iron particles, PVDF and lithium cobaltate were mixed and ball-milled at 500 rpm for 2 hours to obtain a third mixture having a molar ratio of fluorine particles to iron/iron in the PVDF of 2:1. The mass is 80% of the mass of the third mixture. The third mixture is placed in a stainless steel container, the container is placed in a glove box and filled with argon gas, and then the third mixture is reacted at 600 ° C for 5 hours to obtain a ferrous fluoride-coated lithium cobaltate shell core composite. structure. When the ferrous fluoride coated lithium cobaltate core-shell composite structure is used for the positive electrode of a lithium ion battery, after 50 cycles of discharge and recharge, the ferrous fluoride coated lithium cobalt oxide at room temperature 30 ° C and current The capacity retention ratio of the density of 0.8 Ma/cm ² was 93%. These results demonstrate that the capacity retention of ferrous fluoride coated lithium cobaltate is higher as the number of cycles increases.

Example 6

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.

In addition, those skilled in the art can make other changes in the spirit of the present invention. Of course, the changes made in accordance with the spirit of the present invention should be included in the scope of the present invention.

Claims

A method for preparing a positive active material for a lithium ion battery, comprising:

Providing metal particles, fluorine-containing oxygen-free compounds, and an oxygen-free carbon source;

Mixing the metal particles, the fluorine-containing oxygen-free compound, and the oxygen-free carbon source to obtain a mixture;

The mixture is sintered in an inert atmosphere to obtain a carbon-coated metal fluoride which decomposes during the sintering to release hydrogen fluoride gas.
The method for preparing a positive electrode active material for a lithium ion battery according to claim 1, wherein the carbon layer of the carbon-coated metal fluoride is a graphitized carbon layer, and the valence state of the metal element in the carbon-coated metal fluoride It is the lowest non-zero valence state m+ of the metal element.
The method for preparing a positive electrode active material for a lithium ion battery according to claim 1, wherein the metal particles are elemental, and the metal particles are Ti, V, Mn, Fe, Bi, Co, Ni, Cu, Zn, Sn. One of Ag, Pb, Ca or Ba particles.
The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free organic material.
The method for preparing a positive electrode active material for a lithium ion battery according to claim 4, wherein the fluorine-containing oxygen-free organic substance is in a polyvinylidene fluoride, a polytetrafluoroethylene, a fluorinated ethylene propylene copolymer, and a polyvinyl fluoride. One or several.
The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein the fluorine-containing oxygen-free compound is a fluorine-containing oxygen-free inorganic material.
The method for producing a positive electrode active material for a lithium ion battery according to claim 6, wherein the fluorine-containing oxygen-free inorganic substance is one or more of NH 4 F and NH 4 HF 2 .
The method for preparing a positive electrode active material for a lithium ion battery according to claim 1, wherein a stoichiometric ratio of the fluorine element to the metal element in the metal particle and the fluorine-containing oxygen-free compound is (m-0.1): 1 to (m+0.1): 1.
The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein the sintering temperature is 400 to 1000 ° C, and the sintering time is 1 hour to 10 hours.
The method for producing a positive electrode active material for a lithium ion battery according to claim 1, wherein the sintering temperature is 600 to 800 ° C, and the sintering time is 2 hours to 5 hours.