Degradation of lithium-ion battery (LIB) was evaluated by using liquid chromatography-quadruple time of flight mass spectroscopy (LC-QToF/MS). Lab-made LIBs were degraded by storing at their states of charge of 50% at 25 or 60°C for three months. The degradation of the LIB was accelerated at 60°C compared with that at 25°C. The electrochemical impedance spectroscopy analysis suggested that the remarkable degradation occurred for solid electrolyte interphase (SEI): it was implied that on one hand, the composition of the SEI for the LIB degraded at 25°C did not vary, on the other hand, that at 60°C varied. For LC-QToF/MS analysis, although decomposed products derived from the electrolyte solution were detected from the electrolyte in the LIB degraded at both 25 and 60°C, those decomposed products were almost the same. Whereas, the difference between decomposed products at 25 and 60°C was confirmed for the interphases between electrodes and electrolyte. The characteristic decomposed products at 60°C was a product with more than C35 and more than 500m/z of mass number. This product should be one of the reason of capacity degradation due to the internal resistance increase. Thus, a possibility of LC-QToF/MS was demonstrated.
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