Surface Treatments for Controlling Solid Electrolyte Interphase Formation on Sn/Graphene Composite Anodes for High Performance Li-Ion Batteries

Sn is a candidate anode material for high energy density Li-ion batteries, owing to its high specific capacity, low cost, and high electronic conductivity, but its practical applications are hindered by mechanical degradation induced by the large volume change during cycling. Graphene can be used as a buffer material for Sn volume expansion while also improving mechanical strength and electronic conductivity of the composite structure. We report here the synthesis of a composite of Sn nanoparticles and graphene through surface functionalization of graphene using diazonium grafting and subsequent Sn nanoparticle deposition. We further applied two types of surface treatments on the anode surface to improve the nucleation of the solid electrolyte interphase, which is formed due to the reduction of the electrolyte solution. These treatments include refunctionalizing the anode surface with graphene oxide sheets or sulfophenyl groups, which provide ample sites on the anode surface for the nucleation of the solid electrolyte interphase. These treatments result in the formation of a stable layer of solid electrolyte interphase, as evidenced from lower and stable charge transfer resistance at the anode interface during cycling. The anodes treated with layers of graphene oxide and sulfophenyl groups delivered reversible capacities which were 39% and 85% higher than the untreated anode. We related the enhanced electrochemical performance of the treated anodes to the formation of a stable solid electrolyte interphase layer.