Electrochemical Lithiation of Graphene-Supported Silicon and Germanium for Rechargeable Batteries

Binder-free graphene-supported Ge nanowires, Si nanowires, and Si nanocrystals were studied for use as negative electrode materials in rechargeable lithium ion batteries (LIBs). Graphene obtained from reduced graphene oxide (RGO) helped stabilize electrochemical cycling of all of the nanomaterials. However, differential capacity plots revealed competition between RGO and Si/Ge lithiation. At high Si/Ge loading (>50% w/w) and low cycle rates (<C/10), only lithiation of Si and Ge occurs, but at higher cycle rates (>C/10), RGO lithiation begins to dominate. Under those conditions, only Ge nanowires exhibited significant lithiation relative to RGO, most likely due to the inherently faster lithiation of Ge compared to Si.