Achieving high-concentration Cl− ions in non-aqueous electrolytes for high-energy-density Li-Cl2 batteries

Abstract

Chlorine-based electrochemical energy storage is a promising candidate for sustainable battery technology. The anionic redox reaction of Cl^0/−1 is of interest due to its superior redox potential (1.36 V vs. standard hydrogen electrode [SHE]), capacity (756 mAh g⁻¹), high power, and low cost. Although Cl chemistry has been used in aqueous batteries for a long time, its deployment in organic lithium batteries has been significantly impeded due to the insolubility of Cl⁻ ions (<0.1 M). Scarce oxidizable Cl⁻ blocks redox reactions and the inevitable lithium chloride (LiCl) film passivates electrodes on discharge. We report a eutectic effect to improve the Cl⁻ solubility in organic electrolytes (2 M or higher) by mixing a series of N-/P-centered chloride salts with lithium bis(trifluoromethanesulfonyl)imide at specific ratios. Based on an optimized Cl⁻ concentration, a Li-Cl<inf>2</inf> cell using I as a chemical fixation can achieve a three-electron transfer with a specific capacity of 702 mAh g⁻¹ and an energy density of 1,116 Wh kg⁻¹.