Equivalent Series Resistance (ESR) and Internal Resistance (Ri) are two measures for the evaluation of a supercapacitors' resistance. The former is evaluated through the electrochemical impedance spectroscopy (EIS) and the latter, through the cyclic charge-discharge (CCD) experiment and the potential drop on current peak at the initiation of the discharge. Disregarding the obvious distinction in the method used for their measurement/evaluation, what is their difference (if any)?
Basically, the sources of the resistance in a supercapacitor are the same independent from the method used to measure and quantify them:
The intrinsic resistance of the electrolyte (R electrolyte), diffusion resistance of the electrolyte among and into the porous structure of the active material (R diff), contact resistance between the active material and the current collector (R cont) are the most well-known sources of the resistance.
On the other hand, ESR and Ri, to the best of my knowledge, are intended to measure the same things. So, as far as the global magnitude of the cell resistance is concerned (like in the case of power density estimation, where, the specific contributions of the different components to the global cell resistance are not important, but their summation instead) why should ESR and Ri be different? and if they are, what is the criterion for the use of either ESR or Ri ? There is no reliable agreement on this in the literature (some use ESR and some other the Ri).
is it if the system had R and C, one(ESR) is R, the other(Ri) is R+1/ωC?
not, in the moment that is used a model in EIS, it is because, we try to separate teh Resistance for diffusion, electrolyte, collectors, etc. And the Rint, or the ESR, it is a global measure of all the resistance
Hi Xingfei,
I think Hugo was also trying to respond you. If so, He is right and I will try to explain a bit more below.
The answer to your question is "No, that is not the case". Both ESR AND Ri are measures of the entire resistance of the cell/system. The electrochemical system is a complex combination of different components each behaving similar to an electrical component (eg., electrode double layer effect is similar to a capacitor and the electrolyte resistance is like a resistor). The overall resistance of the cell for the current flow (both electronic and ionic contributions) can be measured using different techniques such as EIS (from which the ESR can be calculated) or carghe-discharge (from which the Ri can be calculated).
The question intends to find out if theoretically and practically there is any difference between these two and if so, what is that and why it is so.
Moreover, this overall resistance is later used for the calculation of other performance properties of the system such as power density. We need to know which one has to be used there and why.
Hi Xingfei,
Yes, generally EIS is a more complicated method compared to the other technique and delicate elaborations are required to extract the data (eg., ESR) out of it. But about the precision and accuracy and reliability of the data (I mean in this case, for the overall resistance) I am not sure which one could be better.
hi
Is there a table that show supercapacitor's series resistance Corresponding to
supercapacitor capacitance ?
Hi Mostafa,
There is not such table. The capacitance of supercapacitors is mainly influenced by the type of the active material (pure double layer capacitor, pseudocapacitor, etc) and its specific surface area. Whereas, the resistance of supercapacitor is generally affected by the electrical / ionic conductivity of the cell components (electrode materials, electrical connections, electrolyte) and the contact resistance. Therefore, a high or low internal resistance could be observed for a supercapacitor, regardless of the magnitude of its capacitance.
So, what is the conclusion? I've been looking for answers lately as well and stumbled upon this discussion. Any leads would be appreciated.
Dear all,
In my best understanding, Equivalent Series Resistance and internal resistance is the same. Resistance calculated from EIS at high frequencies (>10kHz) is more appropriate. However, if you have "perfect" EDLC, only electrostatic process going on, then C/D is simpler, just need to use R=DV/DI, but not R=DV/I (huge mistake). Remember that to use R=DV/DI, which means R=Vdrop/2I in a symmetric devices and symmetric charge (I)/discharge(-I) currents. You must use the current change Delta I= I - (-I)= 2I
regards,
Hudson
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