“Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries

TLDR

Aqueous electrolytes are limited to below 1.23 V to avoid degradation. The authors use extremely high‑concentration solutions that suppress hydrogen evolution and electrode oxidation, altering the Li solvation shell due to insufficient water to neutralize Li⁺. An aqueous Li bis(trifluoromethane sulfonyl)imide solution achieves a 3 V electrochemical window, enabling replacement of flammable organic electrolytes. Suo et al., Science, this issue p.

Abstract

A concentrated effort for battery safety Aqueous electrolytes are limited to run below 1.23 V to avoid degradation. Suo et al. smash through this limit with an aqueous salt solution containing lithium (Li) bis(trifluoromethane sulfonyl)imide to create an electrolyte that has an electrochemical window of 3 V (see the Perspective by Smith and Dunn). They used extremely high-concentration solutions, which suppressed hydrogen evolution and electrode oxidation. At these concentrations, the Li solvation shell changes because there simply is not enough water to neutralize the Li + charge. Thus, flammable organic electrolytes could potentially be replaced with a safer aqueous alternative. Science , this issue p. 938 ; see also p. 918