Thermal Decomposition of LiPFsub 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.