Concentrated Battery Electrolytes: Developing New Functions by Manipulating the Coordination States

The basic formula of Li-ion battery electrolytes (i.e., LiPF6 and ethylene carbonate) has remained unchanged ever since commercialization in the early 1990s. However, toward advanced batteries with higher energy density and higher safety, a new electrolyte design that leads to better functions is required. Recently, various new functions have been discovered for highly concentrated electrolytes (over 3 mol dm−3 (M) vs. standard 1 M), which arises from their unique coordination states of ions and solvent molecules. Based on this achievement, the coordination states are increasingly recognized as key to further functionalizing battery electrolytes. This account introduces an electrolyte design based on the coordination states and provides future visions on rechargeable batteries that will be realized thereby.