Historical development and novel concepts on electrolytes for aqueous rechargeable batteries

Abstract

In battery systems, aqueous electrolytes are superior in ionic conductivity, interfacial wettability, safety and environmentally benign compared to organic liquids, polymers, inorganic solid-state and ionic liquid electrolytes. However, their narrow electrochemical stability window, electrode dissolution/side reactions and temperature-variation instability result in a low energy density, undesirable cyclic lifespan and limited working temperature window in aqueous rechargeable batteries. Herein, the historical development of aqueous electrolytes in various types of batteries, ranging from monovalent-ion batteries, multivalent-ion batteries, metal–air batteries, metal–chalcogen batteries, and hybrid batteries to redox flow batteries is summarized through the representative pioneering works. Meanwhile, the strategies of electrolyte additive, pH-management, salt-concentrated electrolyte, gelling, solvent hybridizing, interface tuning and beyond concentrated electrolyte to mitigate the challenges associated with aqueous electrolytes are reviewed and discussed in detail. All these new electrolyte concepts mutually stabilize aqueous rechargeable batteries and improve their corresponding energy density in a broad temperature range, ushering in a promising aqueous energy storage era.