Hello everyone,

I'm trying to figure out how to calculate a diffusion coefficient of lithium ions into graphite. I have assembled a cell containing a graphite anode, lithium cathode and 1.0 M LiPF6 in 1:1 EC:DMC electrolyte. I have measured a PEIS, made an EEC and fitted the spectra using EC-Lab software from BioLogic. From there I have acquired a Warburg factor in Ω cm-1/2 and now I want to use an equation for calculating diffusion coefficient using the Warburg factor. I found two versions of one exact equation which only differ in one number. I guess they are both derived from a definition of Warburg impedance and there was made a mistake? I have enclosed an image of them.

These are the source materials:

https://www.biologic.net/documents/rde-diffusionv-electrochemistry-application-note-66/

http://www.electrochemsci.org/papers/vol7/7010345.pdf

And I also wonder what does the concentration (X or C in the equations) stand for. Should I use lithium concentration of an electrolyte or calculate concentration of lithium in solid phase of an anode? I would appreciate any help.