Origin of Reduced Graphene Oxide Enhancements in Electrochemical Energy Storage

Reduced graphene oxide (RGO) has become a common substrate upon which active intercalation materials are anchored for electrochemical applications such as supercapacitors and lithium ion batteries. The unique attributes of RGO, including high conductivity and porous macrostructure, are often credited for enhanced cycling and capacity performance. Here we focus on probing the electrochemical response of alpha-MnO2/RGO composite used as an electrode in a lithium ion battery cell and elucidating the mechanistic aspects of the RGO on the commonly observed improvements in cycling and capacity. We find that electron storage properties of RGO enables better electrode kinetics, more rapid diffusion of Li+ to intercalation sites, and a greater capacitance effect during discharge. Further investigation of the length of the one-dimensional nanowire morphology of the alpha-MnO2 has allowed us to differentiate between the innate characteristics of the MnO2 and those of the RGO. RGO coupled with long nanowires (>5 mu m) exhibited the best performance in all tests and retained similar to 150 mAh/g capacity after 20 cycles at 0.4C rate.