Toward a Reversible Mn 4+ /Mn 2+ Redox Reaction and Dendrite‐Free Zn Anode in Near‐Neutral Aqueous Zn/MnO 2 Batteries via Salt Anion Chemistry

Rechargeable aqueous Zn/MnO 2 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 Mn 4+ /Mn 2+ redox reaction and simultaneously enable a stable Zn anode. The acetate anion triggers a highly reversible MnO 2 /Mn 2+ reaction, which ensures high capacity and avoids the issue of structural collapse of MnO 2 . 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/MnO 2 battery by simply manipulating the salt anion in the electrolyte. The acetate anion not only modifies the surface properties of MnO 2 cathode but also creates a highly compatible environment for the Zn anode. This work provides a new opportunity for developing high‐performance Zn/MnO 2 and other aqueous batteries based on the salt anion chemistry.