Long-duration aqueous manganese metal anode by hydrogel solvation regulation

The key challenge of implementing aqueous manganese (Mn) metal batteries is severe water-related parasitic reactions, including the hydrogen evolution reaction and Mn corrosion. These issues originate largely from the high reactivity of solvated water around manganese ions (Mn²⁺). Herein, we design a hydrogel electrolyte that reconstitutes the Mn²⁺ solvation structure and establishes a hydration-regulated ion-migration environment. The incorporated 18-crown-6 macrocycles on polymer chains bind strongly to Mn²⁺, reducing its hydration number from 5.51 to 1.39 and forming a water-repelling, polymer-guided conduction pathway. Dynamic measurements demonstrate uniform Mn deposition and suppressed detrimental gas evolution. Consequently, Mn plating/stripping in this hydrogel becomes highly reversible, achieving an average Coulombic efficiency of 95% over 350 cycles (Mn||Cu cells) and low polarization of ∼24 millivolts for over 1800 hours (Mn||Mn cells). Moreover, pouch cells paired with a silver vanadium oxide (AgVO) cathode (N/P ratio of 4.63) retain 95.3% of the initial capacities after 200 cycles. This work demonstrates an effective solvation-regulation strategy via hydrogel design for durable Mn anodes in aqueous batteries.