Toward a reversible Mn⁴⁺/Mn²⁺ redox reaction and dendrite-free Zn anode in near-neutral aqueous Zn/MnO₂ batteries via salt anion chemistry

Abstract

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.