Formation of Stable Solid-Electrolyte Interphase Layer on Few-Layer Graphene-Coated Silicon Nanoparticles for High-Capacity Li-Ion Battery Anodes

Silicon-based anode materials exhibit higher specific and volumetric capacities than other materials and have therefore received much attention for potential use in lithium-ion batteries. However, the continuous growth of a solid-electrolyte interphase at the surface of silicon is a primary cause of chronic capacity fading of silicon electrodes. In this paper, we report the formation of an electrochemically stable solid-electrolyte interphase layer on the surfaces of the few-layer graphene-coated silicon nanoparticles. During the first lithiation, electrolyte molecules were electrochemically decomposed and deposited on the surface of few-layer graphene, thus forming a stable protective layer. When combined with an ionic liquid electrolyte based on pyrrolidinium and bis(fluorosulfonyl)-imide, an anode containing 75% few-layer graphene-coated silicon delivered a reversible capacity of 1770 mAh g(-1) (1430 mAh/cc(electrode)) at a current density of 400 mAh g(-1) (2 mAh cm(-2)) after 200 cycles. Averaged over the first 200 cycles, the half-cell exhibits a capacity loss of only 7.2% with a Coulombic efficiency of 99.4%. The results of our study demonstrate that the few layer graphene coating may lead to an ideal candidate for the generation of a stable protecting layer for a silicon anode that is otherwise harmed by side reactions with electrolytes during cycling.