Hello research community,
While going through EIS of aged cells, I found that the cells EIS data is different every time. For example, Cell A kept at storage for one day for testing at 50% SOC to prepare it for a characterization procedure such as EIS in my case. I repeat the same test to expect that the results will repeat itself, but it does not!
Does anyone have any explanation for the changing data when I repeat the tests?
Does anyone has an approach towards it?
Best Regards,
Moonmoon
Dear Moonmoon Pati ,
corrosion modifies your aged cells, even during (only for one day) storage; internal corrosion changes your Z-spectra.
We know, that the Z-spectra of the EIS measurements change at different points on the polarization curve (SOC) of non-aged cells, say a(ny) curve Z(SOC).
What is the value of the VDC-polarization[1] parameter, as well as the (small ?) value of the VAC-amplitude parameter, in your P-EIS[2] (for SOC:50%) ?
A hint: If G-EIS[2] (Galvanostatic-EIS mode) is available, also, then try it (the G-EIS mode) for your aged cells, suffering from possible corrosion issues e.g. a polarization's timeline having semantic modification and instabilities.
1. Powerpoint slide#08, "What is Electrochemical Impedance Spectroscopy? Example: Anodic corrosion of iron in sulfuric acid" in: C.Reece: An Introduction to Electrochemical Impedance Spectroscopy (EIS) https://www.jlab.org/conferences/tfsrf/Thursday/Th2_1-EIS%20intro%20Reece.pdf
2. EIS: Potentiostatic or Galvanostatic Mode? https://www.gamry.com/application-notes/EIS/eis-potentiostatic-galvanostatic-mode/
The case is quite commonly occurred, which may be derived from the instability of the electrode interfaces. My experience is that cycling the cells for 5-10 cycles to establish stable interfaces before EIS testing could be helpful to produce reproducible results.
Besides, if self-discharge occurs during the battery aging, the SOC of the battery would be changed, which therefore could result in some difference for the EIS.