Hi Artur,

thanks for your input. For battery electrodes, the Warburg impedance has been shown to provide information about the solid-state diffusion of Li+ in the host electrodes. It has also been associated with ionic diffusion in porous media, as in the case of supercapacitors.

In addition to that, the typical Warburg signature is not visible in a fresh, non-cycled graphite half-cell - or at least it does not dominate the low-frequency response -, when a purely capacitive, blocking behavior is often observed. However, it becomes very distinct when the cell achieve the lithiation potentials. In this case, I would re-frame my question as: what are the dominant phenomena contributing to a Warburg-like behavior in fully delithiated graphite half-cells which were not present in the fresh cell?

My initial guess is that the observed response could be attributed to Li+ permeation through the SEI layer (not present in a fresh cell), but I am not sure if this process can be related to a Warburg impedance.

Cointercalation plays an important role for electrochemical intercalation of lithium into graphite[1]. So, apart the (normal) intercalated Li+ ions into graphite (having a HIGH diffusion coefficient D1) there is a small number (Ns