Dear Dhevathi Kannan ,

the alternative G-EIS (Galvanostatic control for EIS measurements) mode might be better[1] for your (this) case study[2], in the freq. range [0.1Hz, 1MHz].

The main advantage of the G-EIS (over the common P-EIS) mode for this study is that the Z-specta are independent from any OCV possible modifications or errors in OCV fast reading(s) and VDC-preset values, during either

1) the rest time, or even, during

2) an EIS measurement time[3] (of a single Z-spectum).

1. We recommend galvanostatic control for EIS measurements on batteries with low internal resistances, and potentiostatic mode for high-impedance systems such as coatings or corrosion-resistant materials. https://www.gamry.com/application-notes/EIS/eis-potentiostatic-galvanostatic-mode/

2. 4.1.4. Current Control

Applied Current Range full scale per range

Applied Current Resolution 1/32,000 x full scale

Applied Current Accuracy +0.2% of range+0.2% of reading +/-200pA

Maximum Current Range/Resolution 1 A /60 uA

Minimum Current Range/Resolution 4 nA / 120 fA

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VersaSTAT 4 Hardware Manual https://www.ameteksi.com/-/media/ameteksi/download_links/documentations/supportcenter/princetonappliedresearch/productmanuals/versastat-4-manual.pdf?la=en

3. Mainly, the time (measurement time & rest time) during the initial measurement(s).

In principle it is needed some relaxation time. You could perform an EIS every 15 min or so and check if there are significant differences between 2 or even 3 runs. In my experience waiting 10 min could be sufficient, but it does not hurt to the test on you specific system to double check that your waiting time gives stable spectra.

Thank you for your answer. I performed EIS immediately after reaching the charge cut off voltage and then performed EIS every one hour for the next 4 hours and I performed EIS after 14 hours. Solution resistance for instantaneous EIS was higher than the long wait time. EIS with wait times between 1-4 hours did not show any significant difference. However, the voltages of the battery at the beginning of EIS with respect to the wait times are as follows - instantaneous cut off voltage 3.587 V, 1 hr = 3.529 V, 2 hr = 3.499 V, 3 hr= 3.523 V, 4 hr = 3.518 V, after 14 hrs rest = 3.508 V. I am not sure if this helps, or it is something to consider.

Dear Dhevathi Kannan

First of all, please tell us more about your system (anode, cathode, electrolyte etc.). Also, it would be very useful if you put labels on each nyquist plot in order to better understand the problem. Regarding your question, when a cell reaches equilibrium state, EIS plots should be exactly the same. I notice that the deviation of 1st and last EIS is more or less 2%. Please check the quality of measurements and your equipment. Also, check EIS measurement after 1 or 2 days to see any deviations.

Regards,

Ioannis Gkionis

Hi Ioannis Gkionis , I have updated the description and have added details of the voltage and the instrumentation in the description.I have attached the updated figure.

Depends on your goals. If you want to do a characterization for different SOC, I would recommend a rest time of 1h in your case. Important thing is to keep rest time equally spaced. Hope this helps. Regards, Hartmut