I am trying to fabricate a full cell with commercial LiMNC cathode (4.5 V vs Lithium) and graphite anode (made in house) in a CR-2025 type coin cell. For the fabrication I am taking cathode loading to be almost double of the anode loading (active material) and also using commercial electrolyte (1M LiPF6 in EC:DEC). However, the OCV of my final cells shows less than 20 mv in all cases. What can be the possible problem and solution?
I think that there should be problem with the construction. I assume that it is a coin cell. I have constructed more than 100 cells for my work 1/5 of the cells failed. Momentary short circuit is one of the main reasons.
1.Make sure the thickness of the setup altogether (electrodes, spacers, O-ring, separator) is not beyond the threshold thickness of the coin cell setup. Which coin cell are you using (MTI, Hohsen...)?
2. The pressing pressure, lithium thickness, number of separators also play a role.
3. Make sure that the electrodes are at the centre and also dismantle the cell carefully so that you can find whether it has any problem with the alignment.
Make half cell to check whether there is any problem with the electrodes.
Thanks a lot for your answer sir. I have already optimised them separately in half cells. I am using MTI crimping equipment and coin cell components from hohsen. I am using only a single celgard separator. Hence no utilisation of Li foil. Yes I think alignment of electrodes might be a problem. But will that not show any OCV at all?. Can you please tell me stepwise how do you go about fabricating in your case?
Since you are experienced, I think it will be really helpful for a lot of beginners like me to learn it properly.
Thanks a lot.
Hello Sai,
Go through this publication I have sent you the link. This will help you.
Also do fabrication of the coin cell inside an Ar glove-box, as the electrolytes are moisture sensitive. Furthermore LiPF6 is photosensitive.
Article Construction and Testing of Coin Cells of Lithium Ion Batteries
Hi Dumindu,
Thanks for the link. And yes, I do fabricate the cells in glove box. Actually I have already optimized all the parameters for anodic and cathodic half cells separately. Anyways, I will go through the literature.
the ocv in your case is correct since ncm and graphite did not have been charged. the ocv of two materials in half cell is around 3 v.
Hi Chunhui,
Thanks for your answer. I think what you are telling is more logical. I will try and charge the cells first and see. This is because, no matter how carefully I perform all the other parts (the electrodes, cell fabrication etc.) the ocv is always around 20 mv.
Thank you.
Hi Sai
I think your problem can be related to the connection between your electrodes' current collectors and the cell's current collectors.
following question may be helpful.
1. is there any spring in your coin cell to press electrodes to the top and bottom of cell?
2. is the thickness of prepared electrode enough to contact cells collectors?
3. Did you test your half cells in a coin cell like this one or you did it in another cell?
and finally
4.Did you test your prepared cells in charge and discharge performance? because your cells assembled in a fully discharge state and at first your cells have to show low potential in OCV.
Regards
Thanks a lot, Hossein.
I think the problem was with the last one.
Now after charging it, I am able to get good capacity. Thanks a lot for ypur response.
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