A non-aqueous electrolyte solution for lithium-ion batteries has been optimized at around 1mol 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.