The impedance spectrum of prismatic commercial Li-ion batteries is measured at various states of charge before and after the charge-discharge cycles and storage. The measured impedance is interpreted with a previously proposed equivalent circuit made up of anode and cathode in which the cathode component is composed of two particle size factors. The values corresponding to the characteristics of both electrodes are obtained by a fitting technique. The obtained values suggest that the capacity fade of the Li-ion battery due to the cycles is mainly caused by the increase of interfacial resistance of the cathode and a decrease in the anode capacity. These results suggest the validity of the equivalent circuit to interpret the causes of capacity fade.
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