Defect mediated lithium adsorption on graphene-based silicon composite electrode for high capacity and high stability lithium-ion battery

Carbon-coated silicon materials are considered as promising anode materials in high-capacity lithium-ion batteries (LIBs). Theoretically, using graphene as the anode material in the LIB would afford high electrical conductivity, mechanical stability of Si, and suppression of the unstable solid–electrolyte interface. However, its usage is hindered by its electrochemical characteristic, which is not electrochemically active when combined with lithium. Therefore, research on graphene as the anode and coated material in LIBs has been conducted using defect engineering to enhance the storage capacity of graphene. Although the electrochemical characteristics of various defects in graphene have been studied experimentally and theoretically, graphene-based composite anode materials such as graphene–silicon composite electrodes have rarely been studied from the electrochemical and mechanical perspectives. In this study, lithium adsorptions are conducted on various defected graphene and graphene–silicon composites using density functional theory calculation. The formation energies of Li on the various defected graphene are assessed, and the mechanical strengths of the graphene–silicon composites are analyzed. Our calculations validate that the defects in graphene enhance the electrochemical adsorptions and interfacial mechanical strengths of the graphene and graphene–silicon composites. During lithiation, the defects mediate greater interfacial adhesion of the silicon–graphene composite. Hence, we elucidate that defected graphene increases the electro-chemo mechanical stabilities of silicon composites in high-capacity LIBs.