Copper Collector Generated Cu+/Cu2+ Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

Although Zn-Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn-air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn-air and Zn-Cu/Zn-Ni, in which CuXO@NiFe-LDH and Co-N-C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging-discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm-2), an outstanding energy density (940 Wh kg-1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu-O-Cu ↔ Cu-O and Ni-O ↔ Ni-O-O-H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery.