Thermal Stability of Ionic Liquids as an Electrolyte for Lithium-Ion Batteries

We have examined the thermal stability of several ionic liquids contacted with a charged cathode material Li0.5CoO2 by DSC and TG as the easy model-method to estimate the safety of ionic liquids as an electrolyte. From the results of DSC, it was found that the thermal stability depended on the type of ionic liquid, especially the chemical structure of the anion. The introduction of F atom to anion improved the thermal stability, but C=O groups in anion reduced the stability. For EMI·BF4 with Li0.5CoO2, DSC profile showed the exothermic peak from 200 degree C to 300 degree C and TG profile showed the weight loss in the same temperature area, though neither exothermic peak nor weight loss was observed up to 350 degree C for sole EMI·BF4. From the analysis of generated gas, the main gas was CO2 in the area of exothermic heat.