Widening the Operational Temperature Range of Lithium Batteries Using Flame-Retardant Sulfone-Based Highly Concentrated Electrolytes

Abstract

High-concentration Li salt/sulfone solutions have attracted attention as promising liquid electrolytes for Li batteries owing to their high oxidative stability, nonflammability, and high Li+ ion transference number (t Li+). Herein, we report the temperature-dependent electrolyte properties of a sulfone-based ternary mixture composed of LiN(SO2F)2, sulfolane, and dimethyl sulfone, which enables Li batteries to operate in a wide temperature range. At −20 °C, the rate capability of a Li/LiCoO2 cell with the sulfone-based electrolyte was comparable to that with a conventional carbonate-based electrolyte, even though the ionic conductivity of the electrolyte was significantly lower in the former case (0.11 versus 2.92 mS cm−1). This is because the former electrolyte has a higher t Li+ value, effectively suppressing the concentration overpotential during cell charging and discharging. Moreover, the vapor pressure was much lower for the sulfone-based electrolyte than for the carbonate-based one, and the Li/LiCoO2 cell with the former electrolyte was successfully operated at 60 °C. This study provides insights into the characteristics of high-concentration electrolytes that affect the temperature dependence of Li battery performance.