Graphite is a allotrope of carbon, and the two are closely related. Graphite is the most stable form of carbon. The material is high temperature resistant, corrosion resistant, has good electrical and thermal conductivity and stable chemical properties, and is lighter than aluminum. In addition to being used as a cathode material for lithium-ion batteries, high-quality graphite can be used in fuel cells, solar cells, semiconductors, light-emitting diodes and nuclear reactors. Graphite, with its advantages of high electronic conductivity, small volume change before and after lithium insertion, high capacity of lithium insertion and low potential of lithium insertion, has become a mainstream commercial cathode material for lithium ion batteries.
Methods of obtaining graphite and modification of graphite anode materials
There are two ways to obtain graphite: one is the natural ore, the other is the synthesis of coal tar. The graphite material used in lithium-ion batteries is generally prepared by blending 55% synthetic graphite with 45% natural graphite of low purity. As the solvent molecules in the electrolyte are particularly sensitive to graphite, thus inducing many harmful reactions, so when graphite is used as electrode material, it should be modified. At present, more graphite is spheroidized, surface treated and doped modified.
1. The anisotropy of flake graphite leads to the low specific capacity of negative electrode. By spherification of flake graphite, the specific capacity, first cycle efficiency and cycling performance of negative electrode materials can be obviously improved. In the actual industrial production, the spheroidizing treatment is carried out by the wind impact shaper
2. By oxidation, the disordered carbon atoms on the surface of natural graphite can be eliminated so that the surface REDOX reaction can proceed uniformly. After oxidation treatment, the surface forms covalently bonded functional groups such as -COO- and -OH. These functional groups can form bonding and stable SEI membranes during the first discharge cycle, thus increasing the life span.
3. C-f structure is formed on the surface of natural graphite through fluorination treatment to enhance the structural stability of graphite and prevent the graphite flake from falling off during the cycle.
4. Coating modification is based on graphite carbon material as core, coating amorphous carbon material or metal and its oxides on the surface. Amorphous carbon material can improve the diffusion property of Li+ and the charging and discharging property of graphite material with large current.
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