Zn ²⁺ Storage via Conversion Chemistry of α‐MnO ₂ in an Organic Electrolyte

Abstract

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//MnO 2 cells. Herein, we investigate the Zn 2+ storage behavior of α‐MnO 2 in 1 M zinc trifluoromethanesulfonate (Zn(OTf) 2 )/ N,N ‐dimethylformamide (DMF) electrolyte, which delivers negligible capacity due to sluggish Zn 2+ de‐solvation. Remarkably, introducing a small amount (2 vol%) of water into the DMF‐based electrolyte substantially improves Zn 2+ de‐solvation kinetics, thereby enhancing the storage performance of the α‐MnO 2 electrode without proton participation. We reveal that in this electrolyte, the α‐MnO 2 undergoes initial dissolution and ZnO formation during discharge, followed by a highly reversible conversion between Mn 2+  + ZnO and layered ZnMn 3 O 7 . Benefiting from the reversible Zn 2+ storage mechanism and suppressed Zn corrosion, the Zn//α‐MnO 2 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.