Regulation of Breathing CuO Nanoarray Electrodes for Enhanced Electrochemical Sodium Storage

Abstract 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 (≈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 TiO 2 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 (≈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 TiO 2 layer.