When I coated copper foil with anode slurry, the surface seemed uneven, and tiny grains were seen. like the following image. I can't understand why. I tried to solve this problem (for example by increasing the time of mixing), but the methods didn't work.
Thanks for any suggestion
Please provide information about your materials (anode, binder with mw, solvent) and how do you prepare the slurry?
An-Giang Nguyen
The active material is a metal oxide, the binder is CMC (600,000 MW) and SBR (PH 6-7), and the solvent is deionized water. First of all, we prepare the CMC solution and then add Active Material and mix, and finally we add SBR.
Have you tried this without SBR, or with a higher binder loading (you don't mention the proportion)? The bumps seem like agglomerates, rather than gas bubbles, so I would suggest the mixing type isn't effective, and just mixing longer won't solve this. It might be as simple as the energy of mixing isn't adequate to break up the agglomerates of active material, but it could also be a more complex problem with the binder/metal oxide association. This might sound strange, but have you tried resting the slurry for a day (or 3) before spreading? I have found this to increase binder/active material association in some cases.
Thanks for your suggestions, Anne Sawhney
I didn't try without SBR because I thought SBR is essential to increase the adhesion of the slurry to the copper foil.
The proportion is 80,10,10; active material, carbon black, CMC/SBR (5/5). As you said these are agglomerations. And I think this was for inappropriate mixing of SBR. With proper mixing, the agglomerations didn't appear.
I also let the slurry rest overnight before adding SBR.
That's a lot of carbon black. The carbon black might also cause agglomerates, since it has such a high surface area.
When I experience problems like this, I usually take a reductive approach; trying to mix just 2 components of the slurry together, then another 2, continuing until I figure out what combination is causing agglomeration. Do you know if the same agglomeration occurs if your slurry only contains active material and CMC? If you have enough material, this is worth doing; it will also give you a control without carbon black that could be useful. It will also tell you if you actually need the SBR for adhesion, or if that's just complicating your protocol.
There isn't a short cut to optimizing the mixing; each slurry might respond differently. If you can't try another mixing apparatus/speed, I would suggest adding one component at a time, spreading periodically to assess, and mixing until your spread is smooth. For what it's worth, my most difficult aqueous slurry only homogenized when I left it slow-mixing continuously for 4-5 days, though I still had to degas it afterward.
Best of luck!
Anne Sawhney
I will try your suggestions. Could you explain please a little more about the degassing process?
Please refer to another thread on the subject of degassing: https://www.researchgate.net/post/How_to_degasing_the_slurry_of_LIB_electrodes
The proportion of carbon black to binders in this formulation appears insufficient, thus I recommend increasing the cmc and sbr percentage and decreasing the conductive additive in order to improve deagglomeration due to the increased repulsive force of cmc. The relationship between cmc and sbr and the order of addition to slurry is an important point to consider. Moreover, the ratio between the two specified binders would undoubtedly influence dispersion based on their effect on active material surface absorption.
the link to an article that is helpful: https://doi.org/10.1016/j.jcis.2022.06.006
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