Three-Dimensional Holey-Graphene/Niobia Composite Architectures for Ultrahigh-Rate Energy Storage

Abstract

Nanostructured electrode materials have shown considerable promise for electrochemical energy storage with ultrahigh energy density or powder density. However, such performance was often achieved in electrodes with rather low mass loading (e.g., ~1 mg cm-2 or less), which cannot be readily scaled to electrodes having practical levels of mass loading (e.g., > 10 mg cm-2) due to ion diffusion limitations in thicker electrodes. As a result, the scaled areal capacity or current density of these nanostructured electrodes rarely exceeds those of today’s Li-ion batteries. To sustain the same gravimetric capacity and current density in thicker electrodes with 10 times greater mass loading (e.g., 10 vs. 1 mg cm-2) requires to deliver 10 times more charges over 10 times longer distance, which represents a fundamental scientific challenge in electrode architecture design rather than a simple engineering scaling matter. Herein we report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 mg cm-2). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, while its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward towards practical applications.