Dynamic processes in Si and Si/C anodes in lithium-ion batteries during cycling

Si is one of the most attractive anode materials because of its extremely high theoretical capacity. In this study, we find that the (111) plane of crystalline Si in the anode is still present after 100cycles and infer that it is the intercalation site of Li+ ions. We believe that Li+ ions are inserted into the tetrahedral sites of crystalline Si, and the (111) plane of Si collapses; meanwhile, expansion parallel to 〈220〉 crystal orientation occurs. After full lithiation, the crystalline Si is converted to amorphous silicon. In a Si/ composite anode, although the addition of amorphous carbon may improve the cycling performance of Si anode, the activation process is prolonged as the amount of amorphous carbon increased. We determine that amorphous carbon may reduce the diffusion of Li+, which increases the overpotential and results in the lower formation of the saturated Li/Si alloy.