Lithium battery development and research on composite materials for negative electrodes

　　 Currently, commercial materials for lithium-ion battery anodes are all carbon materials, including graphitic carbon materials, such as graphitized medium-phase carbon microbeads and some pyrolytic hard carbons. At present, the actual specific capacity of these carbon materials usually does not exceed 400mA·h/g. Although the specific capacity of most cathode materials currently used is usually higher (120~180mA·h/g), due to the vibration of low-density carbon materials , plus the current collector paper for the negative electrode uses heavy copper paper, and the positive electrode uses lighter aluminum foil paper, so the actual material of the positive electrode with specific capacity is larger than the negative electrode. Therefore, the specific energy of the battery must be further improved, and the insertion performance of lithium is the key to research and development. As electronic products become more popular, the demand for special high-energy batteries is also increasing. At present, only certain materials cannot fully meet the relevant needs. Although carbon materials have good cycle performance, their specific capacity is low; other electrochemical properties of carbon materials with high specific capacities will be affected. Alloy materials have high specific energy, but due to the large volume expansion during lithium insertion, the material cycle performance is far from meeting the requirements. Tin-based composite oxides have good cycling properties, but the first irreversible capacity loss has not yet been solved. From this perspective, it is a logical choice to combine the advantages of various materials and purposefully combine them to avoid their own shortcomings. The formation of composite anode materials is a logical choice. At present, research on composite materials has achieved certain results.

　　Considering the first loss of irreversible capacity of the material, some people have proposed using lithium-containing transition metal nitrides to compensate, and using the reaction of lithium and tin oxide to solve the first loss of irreversible capacity. Tin oxide material.

　　Given the poor cycling of alloy materials, the idea of dispersing active materials in another inert material to form composites has been proposed. These efforts include using excess copper to form an inert grid to improve electrochemical cycling of copper-tin alloys. HisashiTamai et al. used organotin to prepare dispersed nanoscale tin compounds in carbon gratings to improve material recycling. For example, graphite-tin compounds are prepared by ball milling, composite materials composed of conductive polymer/metal alloys are studied, and the surfaces of silicon particles are carbon coated by CVD. Improved silicon particles do not break after repeated cycles; prepare electrodes composed of conductive polymers and lithium alloys. Obviously, all of these improve the electrochemical cycle of alloy materials to a certain extent.

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