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

The thermal decomposition of lithium-ion battery electrolytes 1.0 M LiPF 6 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 (CO 2), ethylene (CH 2CH 2), dialkylethers (R 2O), alkyl fluorides (RF), phosphorus oxyfiuoride (OPF3), fluorophosphates [OPF 2OR, OPF(OR) 2], fluorophosporic acids [OPF 2OH, OPF(OH) 2], and oligoethylene oxides. The mechanism of decomposition is similar in all LiPF 6/carbonate electrolytes. Trace protic impurities lead to generation of OPF 2OR, which autocatalytically decomposes LiPF 6 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 [OPF 2(OCH 2CH 2) nF]. © 2005 The Electrochemical Society. All rights reserved.