Li-Ion Electrolytes Containing Ester Co-Solvents for Wide Operating Temperature Range

Abstract

As part of our continuing efforts to develop advanced electrolytes to improve the performance of lithium-ion cells, especially at low temperatures, we have identified a number of electrolyte co-solvents that can be incorporated into multi-component electrolyte formulations for enhanced performance, especially at very low temperatures (down to -70oC). In the current work, we investigated a number of ester co-solvents, namely methyl propionate (MP), ethyl propionate (EP), methyl butyrate (MB), ethyl butyrate (EB), propyl butyrate (PB), and butyl butyrate (BB), in multi-component electrolytes of the following composition: 1.0 M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + X (20:60:20 v/v %) [where X = ester co-solvent]. These electrolytes have been optimized to provide good low temperature performance (down to -60oC) while still offering reasonable high temperature resilience to produce the desired wide operating temperature systems (-60 to +60oC). This has primarily been achieved by fixing the EC-content at 20% and the ester co-solvent at 20%, in contrast to the previously developed systems.