Elementary Decomposition Mechanisms of Lithium Hexafluorophosphate in Battery Electrolytes and Interphases

: Electrolyte decomposition constitutes an outstanding challenge to long-life Li-ion batteries (LIBs) as well as emergent energy storage technologies, contributing to protection via solid electrolyte interphase (SEI) formation and irreversible capacity loss over a battery’s life. Major strides have been made to understand the breakdown of common LIB solvents; however, salt decomposition mechanisms remain elusive. In this work, we use density functional theory to explain the decomposition of lithium hexafluorophosphate (LiPF 6 ) salt under SEI formation conditions. Our results suggest that LiPF 6 forms POF 3 primarily through rapid chemical reactions with Li 2 CO 3 , while hydrolysis should be kinetically limited at moderate temperatures. We further identify selectivity in the proposed autocatalysis of POF 3 , finding that POF 3 preferentially reacts with highly anionic oxygens. These results provide a means of interphase design in LIBs, indicating that LiPF 6 reactivity may be controlled by varying the abundance or distribution of inorganic carbonate species or by limiting the transport of PF 6 − through the SEI.