Fig. 1. Typical processes in a lithium-ion battery electrode and their identification using electrochemical impedance spectroscopy measurements. The basic scheme showing the electrode structure in panel a was taken from ref. ⁷.

a Schematics showing the movement of electrons and mobile ions in a typical Li-ion insertion positive electrode. b Theoretical impedance response for an ideal case where each individual step shown in a can be seen as a separate feature. c Example of a practical EIS measurement where many of the predicted features are not seen due to overlap of time constants, very small values of impedance values for certain steps or other measurement artefacts. Most of the missing features can be retrieved using dedicated electrochemical experiments, as explained in the main text.