This work establishes the theoretical foundation and experimental validation for the application of the ICI method as an efficient alternative to GITT. Provided that 1) the diffusion process under investigation exhibits the semi-infinite diffusion behavior within the maximum time allowed for the current interruption and that 2) the pseudo-OCP slope is a good approximation of the true OCP slope, the ICI method can yield the diffusion coefficient with a much shorter experimental time. In the case of our validation experiment with NMC811, more than 90% of the time required for a typical GITT experiment can be saved. Moreover, the internal resistance and diffusion resistance coefficient (or equivalently, the Warburg coefficient) determined by the ICI method are also verified by EIS for NMC811. The efficient determination of diffusivity and resistance unlocks new applications which GITT and EIS are deemed too time-or resource-consuming, such as online cell parameterization for adaptive charging protocol and simultaneous observation of operando spectro-/diffractometry and electrochemical impedance/resistance. When exemplified by a combination of operando XRD and the ICI method, the rapid decrease of the Li-ion diffusion coefficient above 4.2 V over cycling could be correlated to the increasing irreversibility of the contraction and elongation of the c lattice parameter of the NMC structure. To our knowledge, it is the first report of concurrent characterization of the crystal structure and the Li + diffusion coefficient.