Lithium-ion hopping weakens thermal stability of LiPF6 carbonate electrolytes
Kee Sung Han, Mal‐Soon Lee, Namhyung Kim, Daiwon Choi, Sujong Chae, Jaegeon Ryu, GiovanniMaria Piccini, Roger Rousseau, Edwin C. Thomsen
Abstract
Lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes are widely used in commercial lithium-ion batteries (LIBs), but their thermal instability limits the cycle life and safety of LIBs at elevated temperatures. Few studies have yielded insight into the initial PF6− decomposition reaction that promotes thermal instability of LiPF6-based electrolytes. Here, we find that lithium-ion hopping assisted by the overall reorientational motion of propylene carbonate molecules facilitates PF6− decomposition at elevated temperatures in 1 M LiPF6/propylene carbonate electrolyte. Further, we demonstrate that urea additives, by preventing lithium-ion hopping, suppress the initial LiPF6 decomposition reaction and enhance the thermal stability of the electrolyte. LIB cell tests with LiNi0.6Mn0.2Co0.2O2||Li4Ti5O12 show improved LIB performance at elevated temperatures with the thermally stabilized electrolyte. This study provides key insights into the design of thermally stable LiPF6-based carbonate electrolytes for improving the cycle life, calendar life, and safety of LIBs in elevated-temperature applications.