Triethylbutylammonium bis(trifluoromethanesulphonyl)imide ionic liquid as an effective electrolyte additive for Li-ion batteries

Ionic liquids are promising additives for Li-ion batteries owing to its desirable physicochemical properties. Triethylbutylammonium bis(trifluoromethanesulphonyl)imide ([N2224][Tf2N]) ionic liquid was synthesized and their physical and electrochemical properties were investigated. Among several quaternary ammonium ionic liquids, [N2224][Tf2N] exhibited higher conductivity (1.31 mS cm−1), better thermal and electrochemical stabilities, and wide electrochemical window, i.e., more than 5.9 V. Standard solution was prepared by dissolving lithium bis(trifluoromethanesulphonyl)imide (LiTf2N) in ethylene carbonates/dimethyl carbonate (1:1, by weight). The conductivity for the electrolyte containing [N2224][Tf2N] and the mixed electrolyte without additives at 25 °C are 10.24 and 8.79 mS cm−1, respectively. LiFePO4 half-cell containing 0.6 mol L−1 LiTf2N-based organic electrolyte with [N2224][Tf2N] showed relatively high initial discharge capacity and coulombic efficiency at first cycle. It is found that the mix [N2224][Tf2N] electrolyte exhibits relatively high-rate capacity. The capacity retention of half-cell containing [N2224][Tf2N] is 2 % more than without additive at 0.2 C. However, the rate capacity retention of the half-cell with mix [N2224][Tf2N] electrolyte is above 10 % more than without additive at 0.5 C. The results showed that [N2224][Tf2N] was an effective electrolyte additive in LiFePO4 half-cell.