Electrolyte Engineering Toward High-Voltage Aqueous Energy Storage Devices

Abstract

Aqueous electrochemical energy storage (EES) devices are highly safe, environmentally benign, and inexpensive, but their operating voltage and energy density must be increased if they are to efficiently power multifunctional electronics, new-energy cars as well as to be used in smart grids. This Minireview summarizes the key breakthroughs and progress in expanding the electrochemical stability window (ESW) of aqueous EES devices over the past five years. After briefly introducing the electrode engineering ways to widen ESW, we focus on four ground-breaking electrolyte engineering strategies and classify them into two kinds from the perspective of salts and exotic solutes/solvents. The widening degree toward ESW of these emerging electrolytes is compared and the universal fundamental mechanism relating to the interactions between limited water molecules and high-concentration salts (or large amounts of exotic solutes/solvents) is elucidated. Key challenges and perspectives for high-ESW electrolytes as well as recent advances in low-cost and other metal ion (sodium, potassium, zinc, etc.)-based electrolytes for expanding ESW are also outlined.