Effect of Additives on Physicochemical and Electrochemical Properties of DES-Based Electrolyte for Energy Storage Applications

Deep eutectic solvents (DESs), due to their beneficial properties including high thermal stability, low toxicity, excellent biodegradability, and availability, are being increasingly used as electrolytes in energy storage applications. Lithium salts added to deep eutectic solvents (DESs) are being actively investigated as alternative electrolytes for lithium-ion batteries (LIBs). Physicochemical properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in ethaline DES (choline chloride/ethylene glycol in 1:2) are analyzed with formamide and benzonitrile as additives. Density, viscosity, and specific conductance were measured for the solutions containing LiTFSI in (DES + formamide) and LiTFSI in (DES + benzonitrile) over different LiTFSI molalities and temperatures. Using density data, apparent molar volume (Vϕ) and partial molar volume (Vϕ0) are calculated to analyze various solute–solvent interactions in the above systems. Molar conductivity (Λm) and limiting molar conductance (Λm°) are also calculated to analyze the structural behavior of LiTFSI in the above solvent systems. Fourier transform infrared (FT-IR) spectroscopic analysis has also been used to observe various structural changes and intermolecular interactions. Electrochemical stability was assessed by using cyclic voltammetry (CV) studies. The formamide-containing system exhibited a stability window of 2.11–2.29 V, while the benzonitrile system showed a window of 2.10–2.23 V across the tested LiTFSI concentrations.