Calorimetric studies of the thermal stability of electrolyte solutions based on alkyl carbonates and the effect of the contact with lithium

The thermal stability of different electrolytes - LiPF₆, LiPF₃(C₂F₅)₃ (LiFAP), LiFAP solutions containing 5% vinylene carbonate, and LiFAP solutions containing 1% Li bisalicylato borate - in a mixture of (2:1:2 v/v/v) EC, DEC and DMC is investigated. The results of a comprehensive study of the thermal behavior of these solutions in contact with Li metal and lithiated graphite electrodes (synthetic flakes) using both accelerating rate (ARC) and differential scanning (DSC) calorimetry, are reported herein. The surface films formed at room temperature on Li and lithiated graphite surfaces in all the solutions studied are not stable at elevated temperatures. The main exothermic reactions of the solution thermal decomposition in contact with Li metal occur at temperatures lower than the Li melting point (180 ^°C). The highest onset (at 165 ^°C) for the thermal decomposition in the presence of Li, was observed for solutions containing both LiFAP and VC. LiPF₆ solutions showed the lowest onset for thermal reaction (at 132 ^°C).