A slightly modified GITT protocol was designed here to compare the GITT, ICI and EIS at the same SoC, which is schematically shown in Figure . A constant current of 20 mA g -1 (corresponding to C/10, where C is here defined as 200 mA g -1 for NMC811) was applied for 10 minutes, which was followed by a 1-hour rest. During the first minute of the rest, potential was recorded every 0.1 second for the ICI analysis. After the rest, an EIS measurement was performed from 20 kHz to 10 mHz with an amplitude of 10 mV. Another 10-minute rest followed the EIS measurement before the next current pulse. The modified GITT protocol was applied between 3.0 and 4.3 V for two cycles. In the second discharge, the cutoff was lowered to 2.0 and 2.5 V for cell 1 and 2, respectively. For both GITT and ICI analysis, the electrode volume and area were approximated by the volume and surface area of the NMC particles stated above. The impedance spectra, where a Warburg element is present, were fitted to the equivalent circuit model in Figure by a modified Levenberg-Marquardt algorithm provided by the "minpack.lm" package in the R-programming language. ) and a rest period (I = 0) of the modified GITT program used in this work for the comparison of the results from the GITT, ICI method and EIS.