The compounds deposited on a lithium transition metal oxide charged in a siloxane-based electrolyte were analyzed by Fourier transformation infrared (FT-IR) spectroscopy and thermal analysis. The decomposition of the siloxane-based electrolyte occurred at voltages above 4.2V, and the compounds that deposited on the cathode surface consisted of species from both the decomposed siloxane molecule and the electrolyte salt. Differential scanning calorimetry (DSC) profiles of the charged cathode revealed an exothermic peak at 130°C. The exothermic temperature corresponded to the onset of weight loss of the siloxane-based electrolyte, as revealed in the thermal gravimetry-differential thermal analysis (TG-DTA) diagram. The results indicated that the deposited compounds on the cathode surface and the siloxane-based electrolyte were decomposed at this temperature. Finally, two major exothermic peaks in the DSC profile for the siloxane-based electrolyte occurred at higher temperatures than those for carbonate-based electrolyte, and showed reduced heat flow. The present research suggests that the siloxane-based electrolyte can improve safety of a lithium battery.