Effect of 1,1,2,2‐Tetrafluoroethyl‐2,2,3,3‐Tetrafluoropropyl Ether (TTE) as a Diluent in Deep Eutectic Solvent Acetamide–LiFSI for Nonflammable and High Oxidative Stable Electrolyte

ABSTRACT

In this study, a small amount of 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) was used as a dilution agent in the deep eutectic solvent (DES) composed of acetamide and lithium bis(fluorosulfonyl)imide (LiFSI) to improve the electrolyte's nonflammability and oxidative stability. In this approach, TTE functions as a solvent modifier by effectively decreasing the viscosity of DES. The decrease in viscosity is advantageous as it helps enhance the overall flow and handling characteristics of the electrolyte. We optimized the weight ratio of % wt. TTE from 10% to 20% to observe the impact of TTE solvent on overall electrolyte characteristics. In particular, the viscosity of 10% wt. TTE was reduced by approximately half compared to pure DES (decreasing from 54.5 to 35.4 cP). The addition of TTE solvent improved ionic conductivity from 1.97 mS cm ⁻¹ (for DES A at 30°C) to 2.48 mS cm ⁻¹ for DES‐A1. It is important to note that TTE may also impact the stability and compatibility of the DES with other components. DES‐A1, with an optimal ratio of 10% wt. TTE demonstrated a high electrochemical stability window (5.1 V at a current density of 0.01 mA/cm ² ). As a result, the modified DES can be effectively used as an electrolyte in Li‐ion batteries, showing promising cyclability in half‐cell tests with LiFePO ₄ cathode (reached a relatively high initial capacity of 147 mAh g ⁻¹ ) and LiNi _0.2 Fe _0.8 PO ₄ cathode (82 mAh g ⁻¹ ) at 0.1 C (∼0.03 mA cm ⁻² ).