Hi,
I am using zview software to fit EIS data (26650 Li-ion cell) to equivalent circuit. I am using warburg element (short) to represent diffusion. they contain 3 parameters W-R, W-T and W-P (see pic). Does anyone know what they mean ? Is W-R representing diffusion resistance ?
The warburg impedance is a constan phase componet that model a change of phase that cannot be explained by resistances or capacitors .Physicaly, in fuel cells is usually related with difussion-reaction realitons and the microstrute of the electrode, that is how ard is for the reactives arrive to the electrosde once qthey are close. I think that would happepen someting simmilar in Li-ion cell .
https://ocw.mit.edu/courses/chemical-engineering/10-626-electrochemical-energy-systems-spring-2014/lecture-notes/MIT10_626S14_S11lec20.pdf
In your case, this impedance has hardly no effect (errors biger than 100%) so you can simpliy your model to reduce error in the other parameters
Hello Praveen,
I took a screenshot from Zview help. All those parameters are, of course, related with Warburg impedance equation. Ws-R are the diffusion impedance, indeed. Ws-P is a exponencial factor; the number 0.5 means the Warburg diffusion. Ws-T means "diffusion interpretation" and has an equation: L2/D, being L the diffusion layer thickness and D the diffusion coefficient. If you calculate the dimensions, Ws-T has units of s (seconds), considering L2 as cm2 and D as cm2 s-1, meaning the time for diffusion your system.
Well, now I think the mystery was solved.
@Othon Thank you so much. I also saw it in zview help. But didn't understand. Now I got it.
Hello Praveen,
I have the same problem with these parameters. However, I am using warburg element (open) to represent a diffusion-controlled reaction. I you have clear the information that these parameters give us, could you please explain me? I ask you about: Wo-R, Wo-T, Wo-P.
Thank you in advance!
@Victor: Othon has clearly explained about the Warburg parameters. Its the same for both short and open warburg.
Othon S. Campos How can we find the effective diffusion length? Is it approximately equal to cathode thickness?
Dear Mohammad Alipour ,
The calculation of the thickness of the diffusion layer is kinda difficult. There are some approximations by finite length elements (lots of PDEs if you like it), but there are other approaches, such as:
- Calculate the square root of the product between diffusion coefficent and the diffusion time;
- Applying the brownian motion to estimate the diffusion thickness.
Remeber that our diffusion studies in electrochemistry goes on very limited conditions, such as diluted solutions, unidirectional diffusion, "semi-infinite" diffusion, et caterva.
Hope it helps!
Thank you so much dear Othon S. Campos . It seems that finding the diffusion coefficient from CV data is much easier than finding it from EIS data.
Othon S. Campos Sir please can you tell me what are the generally acceptable values for Wo-R, Wo-T, Wo-P while fitting EIS data. Also tell me about the acceptable values for CPE elements.
Hello Deepak Rase ,
Those values are experimental ones, and I really don't know which are the "acceptable" values for your electrochemical system because impedance results depends upon your system. Careful electrohcemical investigation in non-DC techniques, like voltammetry, potentiometry etc, are important to asses the conditions of impedance experiment and interpretations.
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