Imidazolium-Based Dicationic Ionic Liquid Electrolyte: Strategy toward Safer Lithium-Ion Batteries

Ionic liquids have emerged as next-generation electrolytes; however, their ionic conductivity is hindered by relatively high viscosity, limiting electrochemical assessment of cells at medium-to-high temperature. A subtle change in the structure of the imidazolium cation with a suitable anion can effectively improve the diffusion process, ultimately increasing ionic conductivity and cyclability. Here, dicationic ionic liquid (DIL) [C 6 (mim) 2 ][TFSI] 2 has been synthesized and studied for lithium-ion batteries. The highest conductivity of 1.02 × 10 –3 S cm –1 at 30 °C and electrochemical stability window up to 5.3 V are far superior. A Li/LiFePO 4 cell with a DIL at a 0.1 C rate presented a capacity of 133 mAh g –1 at the 100th cycle with 98.8% of Coulombic efficiency. Even at a higher current rate, the cell retains the initial discharge capacity, suggesting superior reversibility and stabilization of the system. The cells show discharge capacities of about 113.3 and 73.6 mAh g –1 at 0.2 and 0.5 C rates, respectively. The DIL performance at room temperature proves that the mobility of clusters and formation of aggregates affects Li + ion coordination and diffusion. This diverse class of ionic-liquid-based materials has the potential for green and sustainable chemistry.