Study On Preparation And Electrochemical Performance Of Si/C Composite Anode Material For Lithium Ion Battery

Anode material is one of the key factors, which is to improve thecapacity, enery and cycle performance of lithium ion battery. Althoughthere are many advantages of graphite anode material, but it has theshortages that low specific capacity (372mAh/g), poor in high rateperformance and embedded in organic solvent easily. Silicon as the anodematerial in lithium ion battery, it has the highest lithium storagecapacity(4200mAh/g), but silicon have been produced th“evolume effect”in the cycle process, and lead to practical applications have beenrestricted. In order to make full use of their own advantages, silicon andcarbon were made into composite material, the aim is to restraint thevolume effect of silicon by carbon, and obtained the silicon/carbon (Si/C)composite anode material with high capacity and good cycleperformance.In this paper, Si/C composite anode material was prepared via highenergy ball-milling method and high temperature pyrolysis method. Thetests of SEM, XRD, galvanostatic charge-discharge, CV, EIS were used toanalyse of milling time, pyrolysis temperature and silicon content toinfluence on the morphology, structure and electrochemical performanceof composite material.Silicon/artificial graphite (Si/AG) composite anode material wasprepared via high energy ball-milling using silicon powder and artificialgraphite as raw materials, the milling time and silicon content were in therange of4h~24h and5%~40%. The results of tests showed that siliconwas embedded in the gap of graphite, the longer milling time, the bettereffect of degree of dispersion of silicon and combined with graphite, butthe worse the destruction of graphite; meanwhile, the more silicon, theworse compound effect; the structure of the silicon and graphite were notdestroyed. The specific lithium extraction capacity of composite wasincreased and then decreased as milling time and silicon content wereincreased. When milling time was fixed，in the first cycle, the specificlithium extraction capacity of composite material with different siliconcontent were528~1700mAh/g and the coulombic efficiency was about 70%~80%; cycle performance of composite was stability after10cycles,its reversible specific capacity were309~567mAh/g after40cycles.Silicon content was in10%~20%, the specific lithium extraction capacityand cycle performance of composite material were the best.Silicon/artificial graphite/pyrolysis carbon (Si/AG/C) compositeanode material was prepared via high temperature pyrolysis method usingsilicon, artificial graphite and sucrose as raw materials, temperature wasin600~900℃, artificial graphite content was30%, the silicon contentwas in10%~40%. The results showed that graphite and silicon werewrapped by pyrolysis carbon, the higher temperature, the better effect ofbe wrapped; meanwhile, the more silicon, the worse effect of be wrapped;silicon and graphite were still kept crystal type after high temperaturepyrolysis. When silicon content was constant, the specific lithiumextraction capacity and cycle stability of composite was respectivelyincreased and strengthened as temperature was increased; the capacity ofcomposite was kept at418~543mAh/g. While temperature was constantand silicon content was increased, the specific lithium extraction capacityof composite was increased and then decreased, meanwhile, the cyclestability of composite was strengthened and then weakened. The lesssilicon, the higher coulombic efficiency and the faster was increased. Inthe first cycle, the specific lithium extraction capacity of compositematerial with different silicon content were1090~1865mAh/g and thecoulombic efficiency was about63%~69%; If silicon less then20%, thecycle performance of composite was stability after5cycles, however,silecon more then20%, the cycle performance of composite was stabilityafter25cycles. Its reversible specific capacity were350~640mAh/g andthe coulombic efficiency was about90%~97%after40cycles，siliconwas20%, the reversible specific capacity capacity and cycle performanceof composite material were the best, the reversible specific capacity were640mAh/g and the coulombic efficiency was about93%.In the same cycle case, the reversible capacity of Si/AG compositematerial was less than the Si/AG/C composite material, but the coulombicefficiency was higher than Si/AG/C composite material. The carboncarrier dispersed the expansion stress and inhibition volume effect of silicon in the Si/AG and Si/AG/C composite material, the compositematerial not only overcome the low specific capacity of graphite and thevolume effect of silicon, but also have high reversible capacity and goodcycle performance.