Acetate-based ‘oversaturated gel electrolyte’ enabling highly stable aqueous Zn-MnO2 battery

An aqueous Zn-MnO2 battery with high energy density and good cyclability has been successfully developed with use of an ‘oversaturated gel electrolyte’ (OSGE) prepared by cost-effective acetates and poly(acrylic acid) at 75°C. The electrochemical stability window of the OSGE was extended to 3.45 V at room temperature and was able to maintain this window in temperatures up to 80°C. The ionic conductivity of the OSGE was 3.74 × 10−3 S•cm−1 at room temperature. Molecular dynamics simulation was employed to investigate the contacted cation solvation sheath and could be used to account for the excellent stability of the acetate OSGE. On utilisation of the electrolyte, a high reversibility was demonstrated at room temperature, with 600-hour stripping/plating on Zn metal electrodes and no formation of dendrites. The Zn-MnO2 battery successfully operated for 2000 cycles under an over-charge working voltage (2.0 V). This study not only overcomes the limitation associated with the solubility of salts, but also provides a feasible route for developing a highly stable aqueous Zn-MnO2 battery.