In this study, dimension control and nanostructure design were applied in developing electrode materials for superior Na-ion storage. Firstly, hierarchical Co3O4nanorods with increased number of interfaces between individual nanocrystallites were prepared for enhancing pseudocapacitance assisted Na-ions storage. When evaluated as anode materials for Sodium ion batteries, Co3O4nanorods exhibited excellentelectrochemical performance with specific capacities of 644 mAh/g at 25 mA/g and 225 mAh/g at 1 A/g. These values are significantly better than those of high surface area Co3O4nanoparticles. This can be ascribed to the synergistic effect of conversion reaction and interfaces induced pseudocapacitance for the superior Na-ions storage. Moreover, crevices generated between adjacent nanoparticles can facilitate faster Na-ion diffusion, and accommodate volume changes during conversion reaction, leading to an enhanced rate stability compared to nanoparticles electrode. Post-cycling microscopic analysis demonstrated excellent structural stability of the hierarchical nanorods after extended charge-discharge cycles.
Secondly, CoO nanoparticles anchored on three-dimensional reduced graphene oxides (RGO) (CoO@3D-RGO) were prepared through facile hydrothermal method and subsequently heat-treatment. Ultrafine CoO nanoparticles are well deposited on the surface of 3D-RGO networks, which effectively reduce the stacking of RGO sheets and maintain a high active surface area. When tested as Na-ion battery anode material, CoO@3D-RGO electrode delivered a high specific capacity of 401 mAh/g at 25 mA/g, and 149 mAh/g at 1 A/g. The improved electrochemical performance is ascribed to the 3D morphology, large accessible area, rapid ion transport ability, and low charge transfer resistance of the CoO@3D-RGO. Na-ion storage mechanism consists of both conversion and pseudocapacitance mechanism.Post-cycling microscopic studies confirmed the retention of 3D morphology during long-term charge-discharge cycles.