Bromide–acetate co-mediated high-power density rechargeable aqueous zinc–manganese dioxide batteries

Abstract

There is currently great interest in aqueous rechargeable Zn/MnO₂ batteries due to their advantages of low cost, high specific energy density, and environmental friendliness. However, the poor conductivity and low utilization of the MnO₂ cathode during the electrochemical reaction are the bottlenecks to achieving high power density and acceptable reversibility. Unlike most studies on the modification of MnO₂ cathodes, this work proposes a new bromide–acetate co-mediated multicomponent metal-ion aqueous electrolyte to realize a highly reversible and high-specific capacity two-electron transfer reaction between Mn²⁺ and MnO₂. In particular, extremely fast reaction kinetics is achieved due to the bromide modifier additive, which can incorporate into the solvation shells of the Zn²⁺ and Mn²⁺ aquo-complex and weaken their solvation effect. Therefore, not only are ultrahigh-rate performance (32C) and power density of 1770 W kg⁻¹ (based on MnO₂) realized, but also a long cycling stability of 2500 cycles (10C) is demonstrated. Raman spectroscopy, FTIR spectroscopy, and DFT calculation further reveal the co-mediation mechanism of bromide and acetate in the fast and reversible transformation between Mn²⁺ and MnO₂. This work accentuates the importance of the electrolyte in aqueous batteries and the great potential of high-performance Zn–MnO₂ batteries with low-cost bromide and acetate-based electrolyte for large-scale energy storage.