High voltage aqueous based energy storage with “Water-in-LiNO3” electrolyte

Abstract

Electrochemical energy storage devices have gained considerable attention recently, with “water-in-salt” electrolytes emerging as a leading contender for use in lithium-ion batteries, and supercapacitors. Herein, the lithium nitrate (LiNO3) was then introduced as an inexpensive “water-in-salt” electrolyte (explored from low to super-concentrated conditions) for fabricating the coin cell supercapacitors instead of conventional lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The transition of electrolyte properties from “salt-in-water” to “water-in-salt” e.g., viscosity, ionic conductivity, density, pH, wettability, and surface tension are demonstrated. Specifically, the 20 m LiNO3 exhibits a significantly lower viscosity (4.99 ± 0.05 cP) that is approximately 6.4 times lower than the 21 m LiTFSI (32 cP). Moreover, the LiNO3 also provides high ionic conductivity (100.6 ± 0.12 mS cm−1), which is 12.6 times higher than the LiTFSI (8 mS cm−1). The fabrication of the supercapacitor using these electrolytes in the coin cell level was then discussed, highlighted on the electrode composition and current collector-which to the best of our knowledge. The use of highly concentrated LiNO3 in conjunction with an appropriate current collector and electrode composition represents an important step forward in the development of practical supercapacitors. The as-fabricated carbon-based supercapacitor using 20 m LiNO3 exhibits a broad electrochemical stability window range of up to 2.2 V with exceptional rate capability and remarkable cyclic stability. Thus, this work will establish practical aspects of the LiNO3 as a “water-in-salt” electrolyte instead of using high-cost LiTFSI. The successful implementation of these simple techniques provides a promising path toward commercializing next-generation energy storage devices.