The quality of the fitting depends on your electrical circuit model. Therefore, we should first find an electrical circuit model that is suitable to your battery. In my view, there are two approaches. One is to use the distribution of relaxation time technique to identify how many RC do you need. A pertinent paper is Fourier transform distribution function of relaxation times; application and limitations by Dr Bernard A Boukamp. The other is to use a graphical method, which is much easier to handle, see my paper, Graphical analysis of electrochemical impedance spectroscopy data in Bode and Nyquist representations. The more fundamental approach is to abandon electrical circuit model and to use physical impedance models, e.g., An Analytical Three-Scale Impedance Model for Porous Electrode with Agglomerates in Lithium-Ion Batteries, or Theory of Impedance Response of Porous Electrodes: Simplifications, Inhomogeneities, Non-Stationarities and Applications. I will be happy to discuss you more. You can access me through email, [email protected].

Dear Praveen Kumar Kuppusamy,

try to use 4 (2e+, 2e-) electrodes in your next EIS measurements for the A123 26650 (LFP, 2.5 Ah) cells.

Thanks a lot for your suggestions