Preparation method of high-volume silicon-carbon negative electrode material

Abstract

The invention relates to a method for preparing a modified graphite negative electrode material of a lithium ion power battery. The method particularly comprises the following steps: adding asphalt and resin into a kneading kettle with heating and stirring devices, heating until the asphalt and the resin are melted into liquid, continuously stirring, stopping heating after mixing uniformly and cooling to obtain a composite coating material block; performing coarse crushing on the composite coating material block and performing ultrafine crushing by using an airflow crushing machine or a cryogenic crushing machine to obtain composite coating material ultrafine powder; completely mixing the composite coating material ultrafine powder and graphite to obtain uniform powder; and performing heating, heat preservation and natural cooling on the uniform powder under the protection of inert gas, and sieving after cooling to obtain the modified graphite negative electrode material of the lithium ion power battery. The most outstanding innovation points are that the coating material precursor is subjected to compound treatment and coated by the graphite; the mixing uniformity of various coating material precursors is guaranteed, any solvents are not required, and environmental friendliness is realized; in addition, the process is simple, low in cost and easy in industrialized production.

Description

technical field [0001] The invention relates to the field of lithium-ion batteries, in particular to a method for preparing a silicon-carbon negative electrode material used for the negative electrode of a lithium-ion battery. The silicon-carbon negative electrode material prepared by the method adopts a composite material formed of pitch and resin to coat silicon powder , to improve its cycle performance. [0002] This application is based on the invention patent application "a preparation method of modified graphite anode material for lithium ion power battery" filed in China on December 14, 2012, the patent number is: 2012105410709, and part of the content is quoted here. Background technique [0003] Since Japan's Sony Corporation took the lead in developing and commercializing lithium-ion batteries in 1990, lithium-ion batteries have developed rapidly. Today lithium-ion batteries have been widely used in various fields of civil and military use. With the continuous ad...

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Problems solved by technology

The main problem of the composite material prepared by this method is: due to the large specific surface area and the inability to completely prevent the micro-oxidation during the ball milling process, the first irreversible capacity is large;

[0007] (2) Polymer wrapping silicon powder for carbonization: This method can well disperse silicon powder in the carbon matrix and improve its cycle performance; but since the polymer is carbonized to form amorphous carbon, it cannot fully reflect The stability and conductivity of graphitic carbon materials, and may increase the first irreversible capacity of composite materials due to the amorphous structure, so the overall performance is not ideal; (3) carbonization after asphalt is used as a binder to bond silicon powder and graphite: Pitch can not only be used as a binder to uniformly combine graphite and silicon, but also act as a surface coating after carbonization

The main advantage of using resin as the coating material is that the resin has good fluidity at low temperature. It can not only cover the surface, but also easily penetrate into the material particles through micropores, which is beneficial to improving the tap density and electronic conductivity of the material. It can also be cured by heating, introducing catalysts or ultraviolet radiation. During the pyrolysis process of the resin, it will not melt and deform, and will not produce obvious expansion, but there are still some problems, mainly: the yield of carbon materials obtained by resin pyrolysis Low, brittle, high volatile content during resin pyrolysis, high specific surface area, strong cohesive force of resin, easy to cause coating particles to stick together, easy to cause damage to the coating layer when pulverized after heat treatment

The above problems affect the cycle efficiency, cycle stability and compressibility of the resin coating material.

Pitch, petroleum tar, coal tar or their mixtures are used as coating materials. Compared with resin pyrolytic carbon, the specific surface area of ​​pitch pyrolytic carbon is smaller, and the affinity with materials is better, and the structure is stronger. During the heating process, it will be deformed due to melting. If the dosage is too much, it will easily cause the particles of the coating material to stick to each other. If the dosage is too small, it will easily cause uneven coating, and it will easily expand during the heating process, which will affect the electrical properties of the material.

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