Optimization Strategies and Mechanisms of High-Concentration Electrolytes for Aqueous Rechargeable Batteries

Abstract

Aqueous batteries represent a significant research area due to their low cost and high safety advantages. However, aqueous electrolytes suffer from high side-reaction activity, narrow electrochemical windows, and insufficient interface stability and are frozen at low temperatures, thus hampering practical applications. This review focuses on high-concentration brine-based aqueous electrolyte optimization strategies to address the above problems. The solvation structure, hydrogen-bond network, and interfacial components are the key factors that are altered by the appropriate salts, solvent selection, and electrode interaction. A high concentration of brine decreases the free water content, inhibits the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and widens the electrochemical window. Additional salts and solvents in the electrolyte can further promote the formation of the solid electrolyte interphase (SEI) and the cathode electrolyte interphase (CEI) to reduce deleterious interfacial side reactions. At the same time, the synergistic effects between the cathodes/anodes and the electrolyte expand the electrochemical window, improve the interface stability, and enhance the electrochemical properties of aqueous batteries. In this review, we describe the optimization strategies and mechanisms to provide guidance to future research on high-concentration electrolytes (HCE) and the challenge of high-energy and wide-temperature-range applications.