Hydrogel electrolyte design for long-lifespan aqueous zinc batteries to realize a 99% Coulombic efficiency at 90°C

Due to abundant water molecules in conventional aqueous electrolytes and hydrogels, the high activity of water molecules remains a fundamental barrier in zinc batteries (ZBs), especially when operating in aggressive environments (over 60°C). Herein, we design a hydrogel electrolyte via elaborate molecular engineering to optimize ion transport and electrochemical stability. Specifically, the Zn²⁺ transport can be efficiently expressed under a reduced water content condition with water-assisted functions and flexible polymer chains. Moreover, the decreased water content makes it possible to reduce water reactivity. The Zn||Zn and Zn||Ti batteries can stably and reversibly cycle (∼100% Coulombic efficiency) at room temperature and (∼99% Coulombic efficiency) at 90°C, respectively. The full batteries show remarkable cycling stability at room temperature and even at a challenging temperature of 90°C (∼100% Coulombic efficiency). This study offers an essential development in environment-adaptable aqueous batteries with highly stable and reversible performances.