Fluorinated Battery Electrolytes for Low Temperature Cycling

Lithium-ion batteries often see dramatic capacity losses when cycling at low temperatures, due to sluggish lithium transport within the bulk electrolyte and at the electrode-electrolyte interfaces. The development of new battery electrolytes with enhanced lithium-ion conductivity and improved interfacial transfer at low temperatures is needed to improve the overall stability and wide operating range performance of batteries. Koura has developed fluorinated materials for lithium-ion electrolytes with improved stability and safety properties, and in this study their efficacy in batteries under low temperature conditions is investigated and compared to conventional electrolytes. Fundamental transport properties such as lithium transference number, conductivity, and viscosity are reviewed. Cycling and rate performance across a range of temperatures from -20°C to 45°C are also investigated, and interfacial properties are assessed. By combining analyses of the bulk electrolyte properties, interfacial electrochemistry, and performance data at several temperatures, a comprehensive picture of the effect of electrolyte on low and wide temperature performance is developed. Experimental results show that several of Koura’s fluorinated materials can improve low temperature cycling performance, and key considerations in optimizing electrolyte properties and composition for low temperature performance are discussed.