A Room‐Temperature Molten Hydrate Electrolyte for Rechargeable Zinc–Air Batteries

Aqueous Zn‐based batteries are attracting extensive interest because of their economic feasibility and potentially high energy density. However, poor rechargeability of Zn anode in conventional electrolytes resulting from dendrite formation and self‐corrosion hinders their practical implementation. Herein, a Zn molten hydrate composed of inorganic Zn salt and water is demonstrated as an advantageous electrolyte for solving these issues. In this electrolyte, dendrite‐free Zn deposition/dissolution reaction with a high Coulombic efficiency (≈99%) as well as long‐term stability, free from CO2 poisoning are realized. The resultant Zn–air cell exhibits a reversible capacity of 1000 mAh g(catalyst)−1 over 100 cycles at 30 °C. Combined with the intrinsic safety associated with aqueous chemistry and cost benefit of the raw material, the present Zn–air battery makes a strong candidate for large‐scale energy storage. Zinc molten hydrate electrolyte is demonstrated to be an advantageous electrolyte for Zn‐based battery applications. The high Zn concentration and reduced water activity not only promote dendrite‐free Zn plating/stripping at a high Coulombic efficiency but also effectively suppress self‐corrosion of Zn, enabling Zn–air batteries a long‐term cyclability.