Novel cobalt oxide-nanobubble-decorated reduced graphene oxide sphere with superior electrochemical properties prepared by nanoscale Kirkendall diffusion process

Abstract

In this study, a novel metal oxide-reduced graphene oxide (RGO) composite structure, denoted as a "nanobubble-decorated RGO sphere," was fabricated and characterized for potential use in Li-ion batteries. The nanobubble-decorated RGO sphere consists of an RGO sphere uniformly decorated with hollow metal oxide nanopowder. Reduction of the composite powder prepared by spray pyrolysis under H-2/Ar gas mixture formed RGO spheres decorated with metal nanopowders. The metal nanopowders were transformed into hollow metal oxide nanopowders, or nanobubbles, by the nanoscale Kirkendall diffusion process. Cobalt oxide nanobubble-decorated RGO spheres, prepared as the first target material, showed excellent Li-storage properties. The cobalt oxide-RGO composite powders, tested at the current density of 2 A g(-1) for 200 cycles before and after the nanoscale Kirkendall diffusion, showed discharge capacities of 932 and 1156 mA h g(-1), respectively; their capacity retentions measured from the second cycle onward were 89% and 99%, respectively. (C) 2015 Elsevier Ltd. All rights reserved.