Thermal Decomposition of LiPF[sub 6]-Based Electrolytes for Lithium-Ion Batteries

TLDR

The authors examined LiPF6‑based electrolytes containing DEC, EC, EC/DMC, and EC/DMC/DEC using multinuclear NMR, GC‑MS, and SEC, and found that trace protic impurities generate species that autocatalytically decompose and carbonate the mixture. Thermal decomposition of these carbonate electrolytes produces CO₂, ethylene, dialkyl ethers, alkyl fluorides, phosphorus oxyfluoride, fluorophosphates, fluorophosphoric acids, and oligoethylene oxides, with a similar mechanism across all solvents; DEC promotes ethylene formation while EC generates capped oligothylene oxides.

Abstract

The thermal decomposition of lithium-ion battery electrolytes in one or more carbonate solvents has been investigated. Electrolytes containing diethyl carbonate (DEC), ethylene carbonate (EC), a 1:1 mixture of EC/dimethyl carbonate (DMC), and a 1:1:1 mixture EC/DMC/DEC have been investigated by multinuclear nuclear magnetic spectroscopy, gas chromatography with mass selective detection, and size exclusion chromatography. Thermal decomposition affords products including: carbon dioxide , ethylene , dialkylethers , alkyl fluorides (RF), phosphorus oxyfluoride , fluorophosphates , fluorophosporic acids , and oligoethylene oxides. The mechanism of decomposition is similar in all /carbonate electrolytes. Trace protic impurities lead to generation of , which autocatalytically decomposes and carbonates. The presence of DEC leads to the generation of ethylene, while the presnce of EC leads to the generation of capped oligothylene oxides .