Carbon-coated ZnO mat passivation by atomic-layer-deposited HfO₂ as an anode material for lithium-ion batteries

ZnO has had little consideration as an anode material in lithium-ion batteries compared with other transition-metal oxides due to its inherent poor electrical conductivity and large volume expansion upon cycling and pulverization of ZnO-based electrodes. A logical design and facile synthesis of ZnO with well-controlled particle sizes and a specific morphology is essential to improving the performance of ZnO in lithium-ion batteries. In this paper, a simple approach is reported that uses a cation surfactant and a chelating agent to synthesize three-dimensional hierarchical nanostructured carbon-coated ZnO mats, in which the ZnO mats are composed of stacked individual ZnO nanowires and form well-defined nanoporous structures with high surface areas. In order to improve the performance of lithium-ion batteries, HfO₂ is deposited on the carbon-coated ZnO mat electrode via atomic layer deposition. Lithium-ion battery devices based on the carbon-coated ZnO mat passivation by atomic layer deposited HfO₂ exhibit an excellent initial discharge and charge capacities of 2684.01 and 963.21mAhg^-1, respectively, at a current density of 100mAg^-1 in the voltage range of 0.01-3V. They also exhibit cycle stability after 125 cycles with a capacity of 740mAhg^-1 and a remarkable rate capability.