Solid‐State Rechargeable Zn//NiCo and Zn–Air Batteries with Ultralong Lifetime and High Capacity: The Role of a Sodium Polyacrylate Hydrogel Electrolyte

Abstract Solid‐state aqueous energy conversion and storage are regarded as one of the most promising energy technologies for low‐cost and large‐scale applications without safety risk. However, current solid‐state aqueous batteries can only sustain tens to hundreds of charging–discharging cycles and deliver limited capacities, particularly in alkaline electrolytes. This has severely limited solid‐state energy technologies for large‐scale applications. Herein, it is reported that a sodium polyacrylate hydrogel electrolyte ensures an order of magnitude higher cycling stability than those of their state‐of‐the‐art counterparts and high capacities for the solid‐state Zn//NiCo and Zn–air batteries. The observed superb cell performance is attributed to a high ionic conductivity and water‐retaining capability intrinsically associated with the sodium polyacrylate hydrogel electrolyte, coupled with the acrylate‐ion‐facilitated formation of quasi‐solid electrolyte interface to eliminate zinc dendrites.