High performance of low-temperature electrolyte for lithium-ion batteries using mixed additives

Abstract

The BA with low melting point mixed with EC with high dielectric constant is used as solvents, and the LBF with large ionic mobility mixed with LPF, is used as mixed lithium salts. The BA+EC+LBF+LPF mixed additives improves the solubility, conductivity and melting point of the electrolyte, and also effectively improves the composition, thickness and uniformity of the CEI film, which together increased the capacity and voltage platform of the batteries at low temperatures. • BA with low melting point mixed with EC with high dielectric constant is used as solvents. • LBF with large ionic mobility mixed with LPF, is used as mixed lithium salts. • The LBF + BA + EC improves the solubility, conductivity and melting point of the electrolyte. • The LBF + BA + EC improves the composition, thickness and uniformity of the CEI film. • Behaviors of batteries at different low temperatures are greatly improved. In this work, the solvent and lithium salt are modified simultaneously to improve the low temperature performance of the electrolyte. The butyl acrylate (BA) with low melting point and high dielectric constant is combined with the ethylene carbonate (EC) with high dielectric constant and excellent film-forming property, which used as mixed additives. On the other hand, the LiBF 4 with small ion size and large ion mobility is chose to mixed with LiPF 6 with best comprehensive performance, which are used as mixed lithium salts. The BA + EC + LBF mixed additives improves the solubility, conductivity and melting point of the electrolyte, and effectively improves the composition, thickness and uniformity of the CEI film, which together increased the capacity and voltage platform of the batteries at low temperatures. The discharge capacities of BA16%+EC10%+0.3 M LBF battery at −10, −20, −30 and −40 °C are 173.1, 156.0, 147.0, and 119.3 mAh/g respectively, which are much higher than the batteries with the electrolyte without adding additives (122.0, 107.8, 95.7, and 74.3 mAh/g respectively). Furthermore, BA + EC + LBF can form a porous and thin LiF CEI film on the cathode surface, which is very favorable for transport of Li + , further improve the behaviors of the batteries at different low temperatures. Even in the case of charging and discharging at −40 °C, its discharge capacity can be stably maintained at 85 mAh/g. The BA + EC + LBF mixed additives used in this work as an effective strategy to improve the comprehensive behaviors of the battery at low temperatures, which would provide a new insight to design high performance of low temperature electrolyte.