Preparation And Properties Of Silicon Carbon-graphite Composite Anode Materials

With the promotion of electronic terminal products and the vigorous development of new energy vehicles,the market has put forward higher requirements for the energy density and cycle performance of lithium ion batteries,but the theoretical specific capacity of traditional commercial graphite anode materials is lower,Silicon materials have high capacity advantages and have high hopes in the energy storage industry.When used as a negative electrode material for lithium ion batteries,it can greatly increase the volume energy density of lithium ion batteries,but silicon has poor conductivity as a semiconductor material,and at the same time,the huge volume expansion during charge and discharge makes the electrode powder crack and destroy the final,the electrode fails,which makes it difficult to apply silicon materials to actual production.In order to improve the short board of silicon-based anode materials for lithium ion batteries,lithium ion battery anode materials with high specific capacity,long cycle life and reasonable price are prepared.In this paper,nano silicon and artificial graphite are used as raw materials,and asphalt is used to treat nano silicon and artificial silicon.The graphite material is coated twice to prepare a silicon carbon-graphite composite material with high gram capacity and excellent cycle performance.(1)Screening and evaluation of commercial graphite materials and nano silicon/carbon materials.After electrochemical tests,it was found that the specific discharge capacity of nano-silicon reached 3605mAh/g for the first time,but the specific charging capacity was only 619mAh/g.The specific charge capacity is 354.9mAh/g.In addition,electrical performance tests were conducted under the same conditions after combining silicon and graphite,and it was found that the charging specific capacity of the composite system after mixing 3%nano-silicon and artificial graphite is 431.6mAh/g,which is 1.2 times that of graphite about.According to the calculation of the addition ratio of nano silicon and graphite,it is found that the actual charging specific capacity of nano silicon should be about 2800mAh/g.(2)Using bitumen as a carbon source to coat and modify silicon graphite to improve the first coulombic efficiency and cycle performance of the composite anode material.Through experiments,it was found that the cycle stability of the composite material improved with the increase of the amount of asphalt.Further investigation found that the silicon-carbon-graphite composite material had the best electrical properties after being carbonized at 1000? after adding 10%pitch.After 50 cycles in the constant current charge and discharge test,the specific charge capacity was 420.4mAh/g,and the cycle retention rate was as high as 97.82%.The carbonized material added with 10%bitumen at 1000? performed equally well under high magnification conditions during the magnification test.(3)The silicon carbon graphite composite material was prepared in batches by mechanical mixing method,and the full battery was fabricated for electrochemical performance test.The design capacity of the full battery was 1500mAh,and it was 1130.1mAh after 200 cycles,and the cycle retention rate was 87.47%.