A detailed investigation of the thermal reactions of LiPF6 solution in organic carbonates using ARC and DSC

The thermal stability of 1 M LiPF6 solutions in mixtures of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in the temperature range of 40 to 350 degreesC was studied by accelerating rate calorimeters (ARC) and differential scanning calorimeters (DSC). Nuclear magnetic resonance (NMR) was used to analyze the condensed reaction products at different reaction stages. Studies by DSC and pressure measurements during ARC experiments with LiPF6 solutions detected a gas-releasing endothermic reaction starting at similar to170 degreesC, involving diethyl carbonate which occurs before a number of exothermic reactions, which follow as the temperature increases. Fluoride ions are released and react with the alkyl carbonate molecules both as bases and as nucleophiles. The bulk analysis by NMR shows that HO-CH2-CH2-OH, FCH2CH2-OH, F-CH2CH2-F, and polymer are major products. Gas analysis by NMR and Fourier transform infrared spectroscopy shows PF5, CO2, CH3F, CH3CH2F, and H2O as major gaseous products of the thermal reaction of these solutions. (C) 2003 The Electrochemical Society.