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) [C6(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/LiFePO4 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.