Revisiting the properties of lithium chloride as “water-in-salt” electrolyte for pouch cell electrochemical capacitors

Abstract

The search for alternative electrolytes is extremely topical in recent years with the “water-in-salt” electrolyte especially, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) coming to the fore in the context of high-voltage electrolytes. However, “water-in-LiTFSI” exhibits ultra-high cost and low ionic transport when compared with the aqueous lithium- halide, -nitrate as well as -sulphate salts. This work rediscovered the properties of a “water-in-salt” made from a superconcentrated 20 m (equivalent to 14.28 M) lithium chloride electrolyte. The electrolyte was tested using various carbon-based materials as a model system, and the finding was then expanded to a pouch cell supercapacitor. It is found that the use of superconcentrated LiCl could enhance the potential window of the supercapacitor in both half-cell electrodes (approximately of 3.0 V), and pouch-cell devices (1.4 V evaluated at 100 mV s⁻¹). This work shows the fundamental insight into the physical and electrochemical properties of LiCl for possible alternative use as a cheap “water-in-salt” electrolyte in energy storage apart from LiTFSI.