Dear Researchers,
I have been working with LiNi₀.₅Mn₁.₅O₄ (LNMO) cathode material for lithium-ion batteries, primarily assembling coin cells using LNMO as the cathode and graphite as the anode.
These LNMO/graphite coin cells have shown excellent performance with highly reproducible results. I have been using LP30 electrolyte (1M LiPF₆ in EC:DMC, 1:1 by weight) and GF/A glass fiber sheets as separators.
However, upon transitioning to pouch cell fabrication using the same LP30 electrolyte and Celgard as the separator, I’ve encountered several technical challenges:
Although many publications report successful LNMO/graphite pouch cells using Celgard, I haven’t been able to replicate those results. I suspect the poor wettability of Celgard might be a factor, so I extended the wetting time to two days and increased the cell stack pressure, but these adjustments haven’t resolved the issues.
I would greatly appreciate insights or suggestions from researchers with experience in pouch cell assembly and LNMO-based systems. I’m open to discussing potential causes and possible solutions.
Best regards, Umair
Dear Umair Nisar
I understand how frustrating it can be to encounter unexpected hurdles when transitioning from coin cells to pouch cells. The shift certainly introduces new variables, and it’s great that you’re proactively identifying possible causes.
Regarding wettability and electrolyte uptake, your observation about Celgard’s lower porosity compared to glass fiber is spot on. If you haven’t already, pre-conditioning the separator in the electrolyte before assembly might help improve wettability. Additionally, ensuring precise electrode alignment and uniform pressure across the pouch cell is crucial—misalignment or uneven compression can easily lead to inconsistent results.
Electrolyte volume and distribution are also key factors. Larger cells often require careful attention to both the amount and even spread of electrolyte. You might consider adjusting the volume or the method of introduction to ensure thorough wetting. It’s also worth exploring whether subtle interactions between your LP30 electrolyte and the Celgard separator could be affecting performance, as these may not have been apparent with glass fiber in coin cells.
If you continue to see issues, experimenting with alternative separators that more closely mimic the properties of glass fiber could be beneficial. I’d be interested to hear how things progress or if you notice any new patterns. Wishing you the best of luck with your research—please keep me posted!
Best regards,
Kaushik
An EIS test[1] will help to diagnose this issue, dear Umair Nisar .
1. Vdc=OCV, and Vac=
Hi Umair, I agree with Kaushik and Ioannis. One of the issues could be related to the wettability of the Celgard separator. Different types of Celgard have different wettability. Are you using Celgard 2400?
Instead of using a glass fiber separator in the pouch cell, I recommend testing the Celgard separator in a coin cell. Compare the OCV and EIS with the glass fiber one, and do the cycling. If everything is comparable, the issue might be related to pouch cell fabrication, which is indeed a bit more difficult to make consistent compared to coin cell fabrication.
Wish you all the best.
Vishnu Surendran thank you for sharing your insights. I am using Celgard 2325.
Furthermore, I have tested Celgard in coin cells and encountered similar issues as with pouch cells, which suggests that the problem may stem from the wetting behavior of Celgard.
I am planning some further experiments to understand and resolve this problem, I will update you if that works.
Dear Umair Nisar ,
consider a big number of coin cells you made. Usually, not all (coin cells) show such an excellent performance (and highly reproducible results) of the selected (as the excellent) coin cells. A pouch cell[1] can be considered (area scaling) as a big number of (bad/good) coin cells (in parallel electrical connection).
So, a (much bigger area) pouch cell EIS (based, actually, on the specific Zampl.) could be 'compared' with a big number of (a random number of bad/good set of) coin cells[2,3].
1. Partial Quot. from Umair Nisar : " ... However, upon transitioning to pouch cell fabrication using the same LP30 electrolyte and Celgard as the separator, I’ve encountered several technical challenges:
Poor Reproducibility: The pouch cells exhibit inconsistent capacity during formation cycles and much lower than the coin-cells.
Low Open-Circuit Voltage: While coin cells typically show an OCV of 0.3–0.5 V, the pouch cells display significantly lower values.
Cycling Stability: The cycling performance of pouch cells is notably poor compared to coin cells. ..."
2. Deciphering the Nature of an Overlooked Rate-Limiting Interphase in High-Voltage LiNi0.5Mn1.5O4 Cathodes: A Combined Electrochemical Impedance, Scanning Electron Microscopy and Secondary Ion Mass Spectrometry Study
https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/batt.202300352
3. Probing of Internal Short Circuit in Lithium-Ion Pouch Cells by Electrochemical Impedance Spectroscopy under Mechanical Abusive Conditions
https://r.search.yahoo.com/_ylt=AwrFaLPlY25oCAIAtrdXNyoA;_ylu=Y29sbwNiZjEEcG9zAzQEdnRpZAMEc2VjA3Ny/RV=2/RE=1753274598/RO=10/RU=https%3a%2f%2fiopscience.iop.org%2farticle%2f10.1149%2f1945-7111%2fabd452%2fpdf/RK=2/RS=DnALoYD6FhgZwKvIRAVEKy1bTs0-
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