Dear Colleagues,
I am confused with identifying each regions on the Li-ion battery's Nyquist-plot and I would like to ask for clarification.
- My assumption is that the region 1. represents the Li-ion diffusion in the electrolyte mainly in the bulk.
- Then, by frequency increase, there is a transition into the double-layer region 2. because there is not enough time to make the Li-ions fully move towards the electrode and hence, the mass transport is going to be formed near the active particles.
- Later on, the straight line in region 3. can be linked to the Li-ion solid diffusion in the active particle and through the SEI layer.
- The region 4. can be addressed as a contribution of the current collector and the type of the electrode material.
What do you think? Am I right?
Dear Bence Csomos
Go through the following book, you ill get an idea.
https://www.wiley.com/en-us/Impedance+Spectroscopy%3A+Theory%2C+Experiment%2C+and+Applications%2C+3rd+Edition-p-9781119074083
region 1, which is a straight line at the low frequency, represents the double layer capacitance at the electrode-electrolyte interface. The bend near the start of this line (between region 1 and region 2) is the electrolyte diffusion resistance. The semicircle appears due to the resistances at the interface. If there is only electrode-current collector interface, then only one semicircle will appear, similar to that in supercapacitor electrodes. If there is an additional interface due to the SEI layer, then another semicircle will appear. The starting point of the Nyquist plot at x-axis is the ESR, the series resistance of the cell, which comes from all the intrinsic resistance of the cell components, such as electrolyte, current collector, electrode materials, binders etc. the region in the -ve x-axis is called induction region, which does not have much relevance in electrochemical energy storage.
Thank you for your answer.
I am wondering how the double-layer effect can be related to the frequency range between 0,1 Hz - 0,01 Hz. As far as I know, the double-layer effect can be only detected around in few seconds of periodic time. The semi-circle on my figure is between 0,8 Hz and 25Hz. That is why I would address the Region 2 (big semi-circle) for double-layer effect and Region 3 (the small and short semi-circle) as the electrode-current collector's resistance. SEI can be neglected since I am using a quite new battery.
Since the kinetic limiting factor is the diffusion in the solid active material, I would address the tail (Region 1) for diffusion in the solid and in the electrolyte within the electrode.
A have made an extended EIS down to 1 mHz and the tail continues with a little bend at the same way like on my previous figure.
- Badges
- Science topic
- Similar topics
- Engineering
- Electrical Engineering
- Electrodes