Study on the Influence of Defective Graphene on the Li Diffusion Performance in Si/Defective Graphene Composite Anodes: an Ab Initio Molecular Dynamics Study

Si/C composites are the most promising alternatives for anodes of lithium-ion batteries, as they can effectively address the challenges associated with volume expansion and structural degradation commonly encountered in Si-based anodes. Research results showed that the Li diffusion performance in Si/C composites was highly dependent on the C-layer structure, where ion channels were needed for Li diffusion. In order to illustrate how defective graphene promotes Li diffusion behaviors, the Li diffusion properties in Si/defective-graphene (SV and Si/DV5-8-5 defects) composites are investigated by <i>ab initio</i> molecular dynamics (AIMD) in this paper. The structural evolutions of Si/defective-graphene composites during the Li diffusion process are analyzed, and the effects of various graphene defects on Li diffusion are presented. The mean squared displacements of Li atoms are studied, and the Li diffusion coefficients are calculated. It is discovered that the defective-graphene layer could provide voids for Li atoms to diffuse in; therefore, the Li diffusion speeds in Si/defective-graphene composites are faster. The diffusion coefficients for Li atoms are increased from 1.88 × 10^-4 to 2.47 × 10^-4 cm²/s by the introduction of defects into Si/graphene composites.