Hollow Graphene as an Expansion-Inhibiting Electrical Interconnector for Silicon Electrodes in Lithium-Ion Batteries

Abstract

Huge volume changes of silicon particles upon alloying and dealloying reactions with lithium are a major reason for the poor cycle performance of silicon-based anodes for lithium-ion batteries. To suppress dimensional changes of silicon is a key strategy in attempts to improve the electrochemical performance of silicon-based anodes. Here, we demonstrate that a conductive agent can be exploited to offset the mechanical strain imposed on silicon electrodes caused by volume expansion of silicon associated with lithiation. Hollow graphene particles as a conductive agent inhibit volume expansion by absorbing the swelling of silicon upon lithiation through flattening the free voids surrounded by the graphene shell. As a result, silicon electrodes with hollow graphene showed a height expansion of 20.4% after full lithiation with a capacity retention of 69% after 200 cycles, while the silicon electrode with conventional carbon black showed an expansion of 76.8% under the same conditions with a capacity retention of 38%. Some of the deflated hollow graphene returns to its initial shape on delithiation due to the mechanical flexibility of the graphene shell layer. Such a robust microstructure of a silicon electrode incorporating hollow graphene that serves as both an expansion inhibitor and a conductive agent greatly improves capacity retention compared with silicon electrodes with the conventionally used carbon black.