Toward a Reversible Mn4+/Mn2+ Redox Reaction and Dendrite-Free Zn Anode in Near-Neutral Aqueous Zn/MnO2 Batteries via Salt Anion Chemistry
© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Rechargeable aqueous Zn/MnO2 batteries are very attractive large-scale energy storage technologies, but still suffer from limited cycle life and low capacity. Here the novel adoption of a near-neutral acetate-based electrolyte (pH ≈ 6) is presented to promote the two-electron Mn4+/Mn2+ redox reaction and simultaneously enable a stable Zn anode. The acetate anion triggers a highly reversible MnO2/Mn2+ reaction, which ensures high capacity and avoids the issue of structural collapse of MnO2. Meanwhile, the anode-friendly electrolyte enables a dendrite-free Zn anode with outstanding stability and high plating/stripping Coulombic efficiency (99.8%). Hence, a high capacity of 556 mA h g−1, a lifetime of 4000 cycles without decay, and excellent rate capability up to 70 mA cm−2 are demonstated in this new near-neutral aqueous Zn/MnO2 battery by simply manipulating the salt anion in the electrolyte. The acetate anion not only modifies the surface properties of MnO2 cathode but also creates a highly compatible environment for the Zn anode. This work provides a new opportunity for developing high-performance Zn/MnO2 and other aqueous batteries based on the salt anion chemistry.