We here demonstrate mathematically that the ICI method can render the diffusion coefficient based on Fick's second law and requires much less experimental time than GITT. The theoretical derivations of GITT and ICI are elaborated and compared. Three-electrode cells of NMC811 are then tested following a protocol that enables the direct comparison of GITT, ICI and EIS. Finally, the combination of operando XRD and the ICI method is demonstrated to directly correlate the structural evolution to the Li-ion mobility. This example manifests not only the efficiency of the ICI method in probing the transport properties, but also its compatibility with operando techniques. Moreover, it also indicates the potential of the ICI method as a tool for state of heath estimation of Li-ion batteries.