Other valuable information provided by the ICI method is the internal resistance (R), as shown in Figure . R values derived from the iR-drop in the GITT and ICI method are compared with the sum of R0, R1 and R2 from EIS (Figure ). The results from ICI and EIS are almost identical across the whole range of SoC. The GITT with 5-40 s interval yields similar R values during discharge but larger values upon charging. The results from the GITT with 50-150 s interval are scattered compared to the other methods. Nonetheless, all four methods confirm the high internal resistance below 3.7 V, which changes the linear region of E-√𝑡 plots, as discussed above. The internal resistance has been reported to be an important indicator for ageing of NMC811 and utilized for detecting Li-plating in commercial Li-ion cells. The convenience of the ICI method is further illustrated by the results in Figure , which show the change in Li-ion diffusion coefficient and internal resistance over more than 50 cycles. In the upper two panels, a clear decrease in the Li-ion diffusion coefficient can be observed above 4.2 V. The rate of decrease is higher in the first 10 cycles than in the following cycles. This SoC range, 4.2-4.3 V, corresponds to the drastic shrinkage of the c lattice parameter of the rhombohedral (R3 R m) unit cell, which has also been reported in several operando XRD studies of NMC811. On the other hand, the internal resistance increases more uniformly in all SoC above 3.7 V and the rate is faster in the initial cycles. + derived by the ICI method in cycle 6, 15, 25, 35 and 55. Note that the electrode potential here is obtained while cycling, not the OCP. Only values with E ≥ 3.7 V, where the ICI method is applicable as discussed above, are shown.