Thermal Safety of Lithium-Ion Batteries With Ionic Liquid ([Bmim]TF2N)-Based Binary Electrolytes

Large-scaleapplicationof lithium-ion batteries has been hampered by thermal safety issues associated with organic electrolytes based on carbonates. The development of flame-resistant or noncombustible electrolytes is therefore essential. Recently, researchers have shown increasing interest in novel ionic liquid-based electrolytes. However, pure ionic liquids are unsuitable as electrolyte solvents. 1-Butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Bmim]TF 2 N) is a favorable candidate for binary electrolytes owing to its higher conductivity and lower viscosity. Herein, a series of experiments was conducted on binary electrolytes composed of [Bmim]TF 2 N and carbonate-based electrolytes (1 M LiPF 6 in EC/DMC/EMC, 1:1:1 v/v/v). The results revealed that the [Bmim]TF 2 N binary electrolyte outperformed the carbonate electrolyte.The [Bmim]TF 2 N-containing electrolytes exhibited higher total ionic conductivity than the carbonate-based electrolyte under the tested conditions. The binary electrolytes exhibited 6.61% and 11.63% greater flame-retardant efficiencies than the carbonate electrolytes when the [Bmim]TF 2 N concentrations were 20% ([Bmim]TF 2 N-20%) and 40% ([Bmim]TF 2 N-40%), respectively. After 100 cycles, LiFePO 4 batteries employing [Bmim]TF 2 N-20% and [Bmim]TF 2 N-40% delivered capacities of 141.8 and 141.4 mAh g −1 , respectively, with corresponding capacity retention rates that were 3.52% and 4.4% higher than those of the carbonate batteries (132.5 mAh g −1 ). Furthermore, among all the electrolytes tested, the [Bmim]TF 2 N-20% binary electrolyte exhibited the highest charge/discharge capacity under high-rate cycling conditions.