Superconcentrated Electrolytes to Create New Interfacial Chemistry in Non-aqueous and Aqueous Rechargeable Batteries

A non-aqueous electrolyte solution for lithium-ion batteries has been optimized at around 1 mol dm−3 salt concentration based upon ionic conductivity. Recently, however, superconcentrated solutions (e.g., over 3 mol dm−3) are emerging as a new class of liquid electrolyte that develops unique interfacial chemistry on battery electrodes. In this article, we discuss the origin of the unique interfacial chemistry from the viewpoint of their peculiar liquid structure, and highlight advanced rechargeable batteries based on the new electrolyte design. Superconcentrated (highly concentrated) solutions are emerging as a new class of liquid electrolytes. They can form a unique anion-derived passivation film on battery electrodes, which is in clear contrast to solvent-derived passivation generally observed in conventional dilute electrolytes. This unique passivation chemistry will bring several breakthroughs in non-aqueous and aqueous rechargeable batteries.