Regulation of Breathing CuO Nanoarray Electrodes for Enhanced Electrochemical Sodium Storage

Cupric oxide (CuO) represents an attractive anode material for sodium-ion batteries owing to its large capacity (674 mAh g(-1)) associated with multiple electron transfer. However, the substantial volume swelling and shrinking (approximate to 170%) upon Na uptake and release, which mimics an electrode breathing process, disturbs the structural integrity, leading to poor electrochemical durability and low Coulombic efficiency. Here, a structural strategy to regulate the breathing of CuO nanoarray electrodes during Na cycling using an atomic layer deposition of cohesive TiO2 thin films is presented. CuO nanoarrays are electrochemically grown on 3D Cu foam and directly used as anodes for sodium storage. The regulated CuO electrode arrays enable a large reversible capacity (592 mAh g(-1)), a high cycle efficiency (approximate to 100%), and an excellent cycling stability (82% over 1000 cycles), which are some of the best sodium storage performance values reported for CuO systems. Electrochemical impedance and microscopic examination reveal that the enhanced performance is a direct outcome of the efficient regulation of the breathing of CuO nanowires by TiO2 layer.