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

Abstract

The thermal decomposition of lithium-ion battery electrolytes 1.0 M Li P F 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 ( C O 2 ) , ethylene ( C H 2 C H 2 ) , dialkylethers ( R 2 O ) , alkyl fluorides (RF), phosphorus oxyfluoride ( O P F 3 ) , fluorophosphates [ O P F 2 OR , O P F ( OR ) 2 ] , fluorophosporic acids [ O P F 2 O H , O P F ( O H ) 2 ] , and oligoethylene oxides. The mechanism of decomposition is similar in all Li P F 6 /carbonate electrolytes. Trace protic impurities lead to generation of O P F 2 OR , which autocatalytically decomposes Li P F 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 [ O P F 2 ( O C H 2 C H 2 ) n F ] .