Mn-based spinels evolved from layered manganese dioxides at mild temperature for the robust flexible quasi-solid-state zinc-air batteries

Flexible quasi-solid-state zinc-air batteries (ZABs) with outstanding power density, charge-discharge efficiency and robustness are extremely desired for wearable electronic devices. Therefore, it is urgent to develop superior bifunctional oxygen catalysts and robust solid-state electrolytes. Mn-based spinels (MMn2O4) attract great attention due to their high abundance, low toxicity and well-balanced activity-stability performances. However, the Mn-based spinels are generally synthesized at high temperature, which usually causes large particle size, low surface area and insufficient active sites, being detrimental to their oxygen catalytic activities. To solve this issue, we firstly develop a two-step mild-temperature method to synthesize the Mn-based spinels by the evolution from layered birnessite-type MnO2. The optimized Mn-based spinel with the nominal composition of CoMn1.5Ni0.5O4 (CMN-231H) demonstrates the remarkable oxygen catalytic activities with the half-wave potential (E-1/2) for oxygen reduction reaction (ORR) and potential at 10 mA cm(-2) (E-j=10) for oxygen evolution reaction (OER) of 0.780 V and 1.643 V, respectively, and the bifunctional oxygen catalytic activity of CMN-231H surpasses most reported spinels. Meanwhile, cellulose is introduced into polyacrylamide gel electrolyte to obtain the novel solid-state electrolyte (PAMC), demonstrating high ionic conductivity, water retention capability and excellent tensile property. Combining the CMN-321H and PAMC, the fabricated flexible quasi-solid-state ZABs show high power density, charge-discharge reversibility, cycling stability as well as robustness under severe working conditions. Our work supplies an effective way to synthesize Mn-based spinels under mild conditions and provides a promising approach for the development of quasi-solid-state flexible ZABs with high power density and strong robustness.