Atomic-level structure engineering of metal oxides for high-rate oxygen intercalation pseudocapacitance.

Atomic-level structure engineering can substantially change the chemical and physical properties of materials. However, the effects of structure engineering on the capacitive properties of electrode materials at the atomic scale are poorly understood. Fast transport of ions and electrons to all active sites of electrode materials remains a grand challenge. Here, we report the radical modification of the pseudocapacitive properties of an oxide material, Zn x Co1- x O, via atomic-level structure engineering, which changes its dominant charge storage mechanism from surface redox reactions to ion intercalation into bulk material. Fast ion and electron transports are simultaneously achieved in this mixed oxide, increasing its capacity almost to the theoretical limit. The resultant Zn x Co1- x O exhibits high-rate performance with capacitance up to 450 F g-1 at a scan rate of 1 V s-1 , competing with the state-of-the-art transition metal carbides. A symmetric device assembled with Zn x Co1- x O achieves an energy density of 67.3 watt-hour kg-1 at a power density of 1.67 kW kg-1 , which is the highest value ever reported for symmetric pseudocapacitors. Our finding suggests that the rational design of electrode materials at the atomic scale opens a new opportunity for achieving high power/energy density electrode materials for advanced energy storage devices.