I am using equivalent circuits to fit 26650 LFP's current pulse measurements. We know that as temperature increases, the resistance decreases because of the ion's mobility. But at the same time, the capacitance of double layer increases. Does any one know the reason and any reference will be useful.
I would like to pay your attention to the paper: Double layer in ionic liquids: capacitance vs temperature given in the link: https://arxiv.org/pdf/1711.06854.pdf
You may find the answer of your question by reading it. It is so that the temperature dependence of the double layer capacitance depends on the dc voltage of the electrode.
Best wishes
Dear Praveen,
could you demonstrate, please, how did you measure this "capacitance" ?
Dear Prof. Ioannis,
By using equivalent circuit fitting (2RC ckt), I measure the capacitance of double layer. The other RC is used to represent diffusion.
Dear Praveen,
your naive model (for the 26650-LFP) drives you to the astonishing inquire about the unexpected positive[1] thermal coefficient (dC/dT>0) of this modelled "capacitance". As the temperature increases, the resistance normally decreases (dR/dT0).
So, try another (more reliable) model (for the 26650-LFP) to fit your data.
1. You say : "" ...But at the same time, the capacitance of double layer increases. ..."
Thank you Prof. But in general what is the rule for capacitance, if the temperature increases. Like for resistance we know that it decreases if the temperature increases.
I would approach that thinking on the viscosity of electrolyte. The lower the temperature, the high the viscosity. The the viscosity might be dumping the mobility of dissolved Li+X- salt ions.
I would like to pay your attention to the paper: Double layer in ionic liquids: capacitance vs temperature given in the link: https://arxiv.org/pdf/1711.06854.pdf
You may find the answer of your question by reading it. It is so that the temperature dependence of the double layer capacitance depends on the dc voltage of the electrode.
Best wishes
The DLC (Double Layer Capacitance) case in a Lithium ion battery is more complex, since we have NOT, only, one, but two, topologically different, DLCs,
e.g. one DLC per each interface, the 1)anode and the 2)cathode, electrodes.
The temperature coeff. of the each DLC is not the same and their Potential polarization peculiar stress demands:
1) a three electrodes' configuration e.g. an additional "//Li- metal", in a homemade (Li-ion-batt.) version,
as well as it demands,
2) a more reliable model (two different DLCs), dear Praveen Kumar Kuppusamy, include/add one more DLC, in your model.
Also, a viscosity based model, dear Mauro Francisco Pinheiro Da silva, does not help, since DLCs' charges are, nearly, immobile.
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