Achieving high energy efficiency of alkaline hybrid zinc battery by using the optimized Co–Mn spinel cathode

As a potential candidate in the future energy storage system, Zinc-air batteries (ZABs) are impeded by their insufficient discharge voltages and low charge-discharge efficiencies. Building the alkaline hybrid zinc batteries (AHZBs) combining ZAB and alkaline zinc/cobalt batteries (ZCB) at the battery level can supply an effective strategy to solve these problems. In this work, we fabricate a self-supported Mn–Co spinel electrode (named as MnCo2O4) with the porous nanofiber morphology by a facile hydrothermal method and assemble AHZB. Thanks to the large electrochemical active surface area and appropriate ratio of Co2+/Co3+, the as-prepared MnCo2O4 electrode shows both the high bifunctional oxygen catalytic activities for ZABs and metal ion redox properties for ZCBs. AHZB with the self-supported MnCo2O4 electrode possesses two voltage platforms in both charge and discharge processes due to the oxygen evolution/reduction reactions (OER/ORR) ZABs and metal ion redox reaction in ZCBs. Besides of the highly power density and excellent cyclic stability, the charge-discharge efficiency of our AHZB with the self-supported MnCo2O4 electrode can reach 86.2%, almost being the highest value in the recent works. Our work supplies a viable strategy for developing high-performance ZABs with improved discharge voltage and charge-discharge efficiency.