I am working on Supercapacitor applications. I have done electrochemical impedance spectroscopy (EIS) using CH instrument and trying to plot equivalent circuit using ZView software. As I am new to this field, please help me to analyze the Nyquist plot and its equivalent circuit.
I have added the file having equivalent circuit and plot
Dear Madhuri,
before starting to obtain an equivalent circuit for ESI, it is best to already have a rough idea what you expect of your sample/device. As you mentioned, you are working on supercapacitors? I would therefore draw the different layers/components of my sample and think where there could be capacitances in the sample, resistances, or parasitic inductances. Typically, you could expect some form of geometric capacitance that depends on your film thickness, its geometry, and dielectric constant of the material (assuming it is a material sandwiched between electrodes). Then, you also might have pin-holes or other types of channels that could be expressed via a shunt resistor in parallel to your capacitor. A series resistor for losses at the contacts and a parasitic inductor for the connected cables could also be added. Start with a simple model and extend it if necessary, but think about what components to add and what the physical meaning of them could be.
Hope this helps, but without any more details about the type of sample, it is difficult to give more specific advice.
Best regards.
Hi, try to build a model using your CH instrument.
Extract values for series resistance Rs and charge transfer resistances Rct from your figures and build a model.
Dear Madhuri,
remeasure EIS-spectra using a 3-electrodes' configuration in order to look for your supercapacitor's WE (Working Electrode) properties[1], avoiding some hideous cell's complexities/contributions (from CE, electrolyte, etc.) in your Nyquist plot(.jpg).
A(ny) blind fitting[1] (ZView software), based on 'bad' EIS-spectra, might mislead your studies.
However, you can split your next fitting process in 3-spectral partial regimes, low[2], medium[3], and high[4] F, in order to build partial (sub)models naturally matching the WE-material's parts[1] of your initial supercapacitor.
1. A review of supercapacitor modeling, estimation, and applications: A control/management perspective https://www.sciencedirect.com/science/article/abs/pii/S1364032117309292
2. F-low: 10mHz, near to, 100Hz.
3. F-medium: 300Hz up to, about, 10kHz.
4. F-high: 10kHz to 1MHz; extend EIS-spectra up to 1MHz, in order to find, readily, the value of the ESR[1,5,6].
5. https://en.wikipedia.org/wiki/Equivalent_series_resistance
6. Supercapacitor ESR, Specification and Life Time https://passive-components.eu/supercapacitor-esr-specification-and-life-time/
I can recommend you the following book.
Book A. Lasia, Electrochemical Impedance Spectroscopy and its App...
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