Abstract
Lithium bis(fluorosulfonyl) imide (LiFSI) is regarded as an alternative to the classical LiPF6salt in today'sLiFePO4/graphite-based Li-ion batteries electrolyte owing to its slightly higher conductivity and lowerfluorine content. In an attempt to better evaluate the safety issues, here we report the comparative studyof the LiFSI and LiPF6based electrolyte/lithiated graphite interface thermal behavior. DSC measurementswith LiFSI-based electrolyte reveal a sharp exotherm with large heat release though at higher onsetand peak temperatures compared to LiPF6-based electrolyte. With the help of GC/MS,19F NMR and ESI-HRMS analyses, we assume that this highly energetic peak around 200◦C, which is dependant upon thelithium content, is mainly related to electrochemical reduction of FSI−anion. In a strategy to limit theprobability and damage of thermal runaway event, electrolyte additives such as vinylene carbonate (VC),fluoro ethylene carbonate (FEC), di-isocyanato hexane (DIH) and toluene di-isocyanate (TDI) have beeninvestigated and shown to significantly lower the energy associated with the exothermic phenomenon.