On the thermal stability of LiPF6

The results of a comprehensive study of the thermal stability of the salt LiPF6, using both accelerating rate (ARC) and differential scanning (DSC) calorimetry, are presented. Pressure monitoring during ARC experiments permits also the study of endothermic processes. The origins of apparently inconsistent results and conflicting interpretations in previous reports in the literature are explicated. In a confined volume, LiPF6(s) melts reversibly at 467 K with a heat of melting of 2.0 ± 0.2 kJ mol−1. Reversible decomposition to PF5(g) and LiF(s) commences with melting, but the autogenic development of PF5(g) pressure makes the temperature profile of decomposition a function of volume and sample size. The heat of this reaction at constant volume, ΔUr, as determined by a variety of methods is in the range 60 ± 5 kJ mol−1, and is approximately temperature independent in range 490-580 K.