Electrochemical Impedance Spectroscopy Study of LiFePO 4 /Li during Discharging Process

Electrochemical impedance spectroscopy (EIS) study has been applied to investigate the electrochemical properties of LiFePO4/Li half-cell at initial state (before and after charge/discharge process), and a certain dept of discharge (DoD). The impedance spectra were collected over the frequency range from 42 Hz to 5 MHz. The EIS spectra of LiFePO4/Li half-cell show the appearance of semicircles in which the diameter increased with DoD. An equivalent circuit was constructed to each spectrum in order to elucidate to electrochemical properties changes of LiFePO4/Li half-cell battery as function of DoD. The information of bulk and interfacial resistances are obtained by modeling with the equivalent circuits according with the Nyquist plots of each spectrum. The experiment results show the increase in the resistance of LiFePO4/Li half-cell with the DoD.