Preparation And Properties Of Silicon Carbon Composite Anode For Lithium Ion Battery

In the 21 st century,Lithium-ion batteries are the most promising chemical power sources.At present,graphite-based carbon materials are commonly used as anode material for commercial lithium-ion batteries.The ultimate lithium storage capacity of such materials is only 372 m Ah/g and can't enough to meet the development needs of high-performance lithium ions.Due to its high theoretical capacity(up to 4200 m Ah/g,more than ten times that of current commercial graphite cathodes),low discharge potential,and abundant reserves,silicon anode materials are considered to be one of the most promising cathode materials for lithium ion batteries.However,as anode materials of lithium ion batteries,silicon generates up to 300% expansion effect during charge and discharge cycles,and as a semiconductor,silicon has low electronic conductivity,these two problems have greatly limited the development of silicon negative electrodes.In this paper,silicon-based carbon composites were prepared by waste silicon powder from the photovoltaic industry which are coated by organic carbon source.By introducing carbon which has good mechanical properties as the second phase,the expansion effect of silicon materials can be alleviated effectively,and carbon can also make the overall conductivity of composite materials increase.In this way,the electrochemical properties of silicon anode materials are improved simultaneously.Si/SiO_x was prepared by oxidized and heat-treated silicon micro-powder.Phenolic resin and bitumen were used as thermal pyrolysis carbon sources to prepare silicon-based carbon composites.The phenolic resin was determined to be the optimal pyrolytic carbon source through testing and comparing.The silicon-based carbon composite anode materials were prepared at different temperatures and heating rates,then test their electrochemical properties.Through the comparison test to determine the best preparation technology: pyrolysis temperature is 850?,the heating rate is 5? / min,and the pyrolysis time is 120 min.The silicon carbon composite anode materials were prepared under this condition and show a performance: the capacity for the first time was 1135 m Ah/g.After 100 cycles,the capacity of anode material was 816 m Ah/g,capacity retention rate reached 71.9%.In order to further enhance the cycle stability of the anode material,based on the silicon-based carbon anode materials which were coated by phenolic resin,the secondary silicon-based carbon composite anode material was prepared by once again coating organic carbon with bitumen.The initial capacity of the anode material after secondary bitumen coating can reach 1180 m Ah/g.After 150 cycles,the anode material has a capacity of 950 m Ah/g,the capacity retention rate reaches 80.5%,and the secondary coating of bitumen can enhance the cycle stability of the anode material effectively.