First Principles Study of Decomposition Reactions in the Electrolyte System Ethylene Carbonate and Lithium Hexafluorophosphate

Abstract

The decomposition mechanisms of electrolyte mixtures in lithium-ion batteries are still not completely understood, although the degradation of the electrolyte has a direct effect on the efficiency and lifetime of these devices. The main aim of this study is to investigate the decomposition reaction of ethylene carbonate and ${{\rm{LiPF}}}_{6},$ two common components of electrolyte mixtures for lithium-ion batteries. The main focus is the analysis of the reaction kinetics on the basis of the corresponding activation barriers using density functional theory. We show that this method provides reasonable molecular structures and qualitative trends, whereas coupled cluster calculations are required to provide more accurate energies. We furthermore investigate the influence of different conducting salts on the decomposition barrier of ethylene carbonate, finding that appropriate salts can raise the barrier and thus mitigate the decomposition reaction. In particular, the results suggest that substitution of ${{\rm{LiPF}}}_{6}$ by lithium bis(oxalato)borate could drastically inhibit the reaction. Furthermore, we study the potential decomposition of ${{{\rm{LiPF}}}_{6}}^{\,}$ to ${{\rm{PO}}}_{2}{{\rm{F}}}_{2}^{-},$ proposing an alternative route to the common hydrolysis reaction.