Co‐Solvent Electrolyte Engineering Enables Reversible and High‐Energy Aqueous Manganese Metal Batteries

Abstract Aqueous manganese‐metal batteries (MMBs) hold great promise for next‐generation energy storage due to the Mn anode's low redox potential, high theoretical capacity, and environmental compatibility. However, their practical application is hindered by poor cycling stability and limited cathode capacity in conventional MnSO 4 electrolytes. Here, a co‐solvent strategy using N, N‐dimethylformamide (DMF) in 3 m MnSO 4 (15 vol%, termed MnSO 4 ‐DMF15) is introduced to regulate Mn 2 ⁺ solvation structure and interfacial behavior. The tailored electrolyte expands the electrochemical window to 2.76 V, suppresses hydrogen evolution, and enables dendrite‐free Mn plating on Zn substrates with a low overpotential (43 mV), ultra‐long cycling life (>2300 h), and high Coulombic efficiency of 98.3%. Full cells assembled with commercial MnO 2 cathodes deliver a high capacity of 405 mAh g −1 and 76.7% retention over 600 cycles. Notably, MnSO 4 ‐DMF15 enables an in situ Mn 2 ⁺/MnO 2 deposition mechanism, achieving 0.48 mAh cm −2 capacity in cathode‐free cells. A soft‐packed pouch cell further demonstrates high capacity (350 mAh g −1 ), mechanical flexibility, and stable performance. This work presents a scalable electrolyte engineering strategy that unlocks high energy density, reversibility, and material efficiency in aqueous MMBs, paving the way for their application in flexible and sustainable energy storage.