Improving Extreme Temperature and Charge Rate Performance in Li-Ion Batteries through Addition of Fluorinated Electrolyte Additives

Abstract

Despite advances in Li-ion battery electrolytes, commercial electrolytes continue to include organic solvents that are unable to withstand many of the arduous conditions demanded by the industry today, such as extreme temperatures and charge rates. The stability limits of these solvents damper the advancement of Li-ion batteries needed to sustain automotive electrification and other industrial applications. Further efforts are needed to enable electrolyte formulations to withstand the operational demands of Li-ion batteries in the market today.Koura has developed a series of fluorinated materials for use in lithium-ion electrolytes that demonstrate improved stability and safety over conventional commercial electrolytes. In a recently completed study, the impact of Koura’s fluorinated solvents on performance in 4.3V Gr/NMC811 was examined, with a particular focus on benefits seen on extreme temperature and rate performance. Testing included cycling and rate performance across a range of temperatures from -20 °C to 45 °C and cycling conditions from C/2 to 4C. It has been found that these materials exhibit improved performance in low temperature testing, as well as reduced gassing and increased performance in high-temperature and fast charge cycling. To investigate the mechanisms responsible for the observed improvements, comprehensive post-test analysis has been conducted, including gas identification and quantification via gas chromatography, bulk electrolyte composition analysis via NMR spectroscopy, and surface layer characterization via XPS and SEM. Bulk properties of the materials and electrolytes are correlated to performance benefits where appropriate.This presentation will summarize Koura’s efforts to fill a major gap in the demands of the battery industry today through the development of fluorinated electrolyte materials. Specifically, we will present data highlighting the performance of fluorinated compounds on improving battery performance under strenuous conditions with respect to both temperature and cycling rate. Results from post-test analyses will be discussed highlighting the mechanisms underlying the observed performance improvements.