Ab Initio Calculations of Thermal Decomposition Mechanism of LiPF₆-Based Electrolytes for Lithium-Ion Batteries

Ab initio molecular orbital calculations were done to examine the thermal decomposition mechanism of LiPF6-based electrolyte such as LiPF6 dissolved into carbonate ester. We focused our study on LiPF6 decomposition (LiPF6 + H2O → LiF + POF3 + 2HF) and ethylene carbonate decomposition (EC + POF3 → CO2 + CH2FCH2OPF2O). Intrinsic reaction coordinate calculations showed that the latter reaction has a significantly high reaction barrier more than 3 eV. However, we found that it may be reduced by 0.97 eV by considering PF6− ion which acts as a kind of catalyst in the reaction. Although POF3 triggers EC ring opening reaction unless both Li+ and PF6− ions are considered in the model, it remains a spectator in the C-O bond breaking reaction of diethyl carbonate (DEC) by PF6−.