Lithium-ion hopping weakens thermal stability of LiPF6 carbonate electrolytes

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.