Preparation And Electrochemical Study Of Silicom-Carbon Composite Anode Materials For Lithium Ion Batteries

Silicon is a promising alternative anode material for high performancelithium-ion batteries，owning to its extremely high theoretical capacity(4200mAh/g), appropriate insertion potential (0.2V vs. Li/Li+), natureabundance and environmental friendliness. However, the gigantic volumeexpansion (up to300%) during Li alloying and dealloying leads to theparticles crumbling and pulverization, eventually resulting in electricaldeactivation, which is believed to be the main reason for rapid capacityfading of silicon anode materials. In addition, for the high-powerlithium-ion batteries, silicon s low conductivity resulting from itssemiconductor nature also limits its rate performance. To overcome theseproblems, many researches try to minimize the volume expansion as wellas improve the conductivity of silicon, which are regarded as two biggestobstacles for silicon anode in the way to practical application. As aneffective strategy, silicon/carbon composite has been employed extensively to overcome the above problems. In this paper, two different siliconsources, nano-silicon and mesoporous silica SBA-15, are used to preparethe silicon/carbon composites and their electrochemical performance aredeeply investigated.A porous spherical Si/GNS@C composite was synthesized by spraydrying method and in situ thermal reduction technique. A reversiblecapacity in excess of1024.3mAh/g after200cycles was recorded at thecurrent density of0.5A/g and602.3mAh/g was obtained at8A/g,exhibiting good cycle stability and excellent rate performance. In thespecial structure of the Si/GNS@C composite, the pore structure as well asthe high flexibility of graphene can ease the volume expansion in thelithiation process and the open three-dimension conductive network allowsrapid lithium-ion and electron transmission. These collaborative functioncontributes to the excellent cycle stability and rate performance.We also investigated the lotus root-like mesoporous silicon/carboncomposite (LRP-Si/C) prepared by magnesiothermic reduction andchemical vapor deposition (CVD) method. The effects of the raw materialratio，mixing method and reaction temperature on the phase compositionand morphology of the LRP-Si are studied. The electrochemical testsrevealed the excellent cycling and rate performances of the mesoporous silicon/carbon composite material， which maintained the reversiblecapacity of1633.1mAh/g at a current density of0.5A/g after70cycles,and attained580.1mAh/g even at8A/g.The mesoporous structure of LRP-Si/C offers sufficient void space toabsorb the huge volume expansions of silicon and also provides channelsfor fast transfer of the lithium-ion, while the surface carbon layer increasesthe conductivity of the LRP-Si/C electrode. These lead to the excellentelectrochemical properties of LRP-Si/C.