Zn2+ Storage via Conversion Chemistry of α-MnO2 in an Organic Electrolyte

Abstract

Aqueous zinc-manganese oxide batteries have attracted considerable attention for energy storage applications due to their low cost, high safety, and environmental friendliness. However, unavoidable proton-involved electrode reactions in mild aqueous electrolytes often lead to significant pH fluctuations and accelerated Zn corrosion, resulting in limited operational lifespans (typically less than 1000 h) for most reported Zn//MnO₂ cells. Herein, we investigate the Zn²⁺ storage behavior of α-MnO₂ in 1 M zinc trifluoromethanesulfonate (Zn(OTf)₂)/N,N-dimethylformamide (DMF) electrolyte, which delivers negligible capacity due to sluggish Zn²⁺ de-solvation. Remarkably, introducing a small amount (2 vol%) of water into the DMF-based electrolyte substantially improves Zn²⁺ de-solvation kinetics, thereby enhancing the storage performance of the α-MnO₂ electrode without proton participation. We reveal that in this electrolyte, the α-MnO₂ undergoes initial dissolution and ZnO formation during discharge, followed by a highly reversible conversion between Mn²⁺ + ZnO and layered ZnMn₃O₇. Benefiting from the reversible Zn²⁺ storage mechanism and suppressed Zn corrosion, the Zn//α-MnO₂ cell operates stably for 132 days at 0.1 A g^-1 and retains 87.1% of its capacity after 1200 cycles. This work offers a new proton-free conversion reaction pathway for constructing stable Zn-Mn batteries based on organic electrolytes.

Keywords: Conversion reaction; Electrochemistry; Electrolytes; Energy storage; Zinc manganese battery.