Electrochemical impedance analysis on positive electrode in lithium-ion battery with galvanostatic control

Knowledge of the electrochemical parameters of the components of lithium ion batteries (LIBs) during charge–discharge cycling is critical for improving battery performance. An in-situ electrochemical impedance spectroscopy (in-situ EIS) method, where galvanostatic-controlled EIS is used to analyze a battery, enables the simultaneous acquisition of impedance spectra and charge–discharge curves. In the present paper, the in-situ EIS was used to investigate LiCoO2 electrodes with different particle sizes. The semicircles in the instantaneous impedance spectra acquired during charge–discharge were smaller than those in the impedance spectrum corresponding to an equilibrium state. In addition, the charge transfer resistance Rct during the discharging process was larger than that during the charging process; thus, hysteresis, defined as a difference between the Rct during discharging and that during charging, was observed. The particle size in the active material and the charge/discharge rate affected the magnitude of the Rct hysteresis, indicating that the in-situ EIS is useful for investigating electrode materials capable of high-rate charge–discharge processes. •Galvanostatic controlled impedance method is powerful tool to evaluate electrodes.•Lithium ion batteries with different active material sizes were investigated.•The charge transfer resistance increased with increasing the particle size.•Mass transfer contributes to the discharge reaction.