Thermal decomposition of LiPF6-based electrolytes for lithium-ion batteries

The thermal decomposition of lithium-ion battery electrolytes 1.0 M LiPF6 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 (CO2), ethylene (CH2CH2), dialkylethers (R2O), alkyl fluorides (RF), phosphorus oxyfluoride (OPF3), fluorophosphates [OPF2OR, OPF(OR)(2)], fluorophosporic acids [OPF2OH, OPF(OH)(2)], and oligoethylene oxides. The mechanism of decomposition is similar in all LiPF6/carbonate electrolytes. Trace protic impurities lead to generation of OPF2OR, which autocatalytically decomposes LiPF6 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 [OPF2(OCH2CH2)(n)F]. (c) 2005 The Electrochemical Society.