Fig. 4
a Nyquist plots of the CoO anode at voltage of 2.3 and 0.3 V vs. Li+/Li during the 2nd and the 100th discharging cycles. The inset shows the equivalent circuit model for this electrode. R ohm stands for series ohmic resistance. R sl and CPEsl represent surface layer resistance and capacitance, respectively. R ct and CPEdl represent the charge transfer resistance and double layer capacitance. Z w represents Warburg impedance. The lines in these figures are the fitted curves using this model. b Comparison of the individual real impedance, R ohm, R sl, and R ct obtained from the Nyquist plots