Phase and Morphology Evolution Induced Lithium Storage Capacity Enhancement of Porous CoO Nanowires Intertwined with Reduced Graphene Oxide Nanosheets

A simple and cost-effective process is developed for the synthesis of a high-performance anode consisting of porous CoO nanowires intertwined with reduced graphene oxide sheets (CoO-NWs/rGO). When tested in a lithium-ion battery, the CoO-NWs/rGO exhibits high initial reversible capacity (similar to 960 mAh g(-1)) and excellent rate capability. More importantly, its performance is further enhanced when CoO-NWs/rGO is discharged/charged for >100 cycles. For example, the specific capacity of the CoO-NWs/rGO can reach up to 1195 mAh g(-1) after similar to 130 cycles. This enhancement of the electrochemical performance of the CoO-NWs/rGO is attributed to two effects during the repeated discharge/charge cycling: a gradual evolution in morphology and crystal structure of electrode materials and the transformation of CoO onto the surface of rGO sheets. While the initial porous structure and the wire-shaped morphology of CoO NWs may help to alleviate the strains/stresses induced by the volume change associated with cycling, they do not seem to be the primary attributes to the observed performance enhancement. The implication of this finding is very important to the rational design of high-performance electrode materials: the equilibrium structure and morphology of electrode materials under repeated cycling conditions are far more important than the initial structure and morphology in designing nanostructured electrodes with desired performance and durability.