Hi,
I have a question about NMP usage in preparing cathodes for Li-ion batteries. I searched the internet and found that many people mention the ratio between active materials, carbon, and binder (PAA/PVDF), which are then dissolved in a "proper amount" of NMP. Different NMP amounts significantly affect the viscosity of the prepared cathode and the final electrode. I'm wondering if there is any standard NMP amount or concentration of solids in NMP for cathode manufacturing in Li-ion batteries. Thank you.
You can find some info or articles about optimizing the solid loading percent for cathode slurry preparation. Based on that, you can calculate the amount of NMP solvent.
In industry, they may prefer as low as possible amount of NMP or toward solvent-free dry electrode technology.
It is a very difficult task. The amount of NMP depends on physical characteristics of your electrode material, carbon...there isn't a right amount, you should proceed step by step, adding drop by drop the NMP and observing the slurry to reach the "right" viscosity. You should have experience for this work. In the papers it is not specified because it could be a subjective value
Marcella Bini
I don't think it is a subjective value. We can deal with severl parameters to optimize the amount of NMP such as viscosity, solid-liquid ratio, rheology... Of course, it will depend on the active material, conductive carbon type
Marcella Bini An-Giang Nguyen Thank you so much for the reply. I understand that the preparation of cathode ink should have certain parameters to ensure the quality of the final product. However, in the literature, people only provide the important ratios between the active materials, carbon, and binder. Since the solvent, whether it is water or NMP, evaporates in the final cathode, I could not find any clear information about the amount or solid-liquid ratio in the literature. Therefore, I am curious if there are any established methods or experiences for this step. I apologize for asking this question, as it may seem trivial.
Yun Gan
At the lab scale, some are making the slurry manually. Therefore, experience is more important and it may not be mentioned in the reports. However, you can find several articles on the optimization of that process.
Article Effects of the Mixing Sequence on Making Lithium Ion Battery...
Article The effect of solid content on the rheological properties an...
An example of our recipe is 0.105 g of active material (in such case a ferrite), 0.03 g of carbon, 0.015g of CMC (carboxylmethyl cellulose) and 0.6 ml of water. But, as I told you, the amount of water mainly depend on the viscosity of the slurry that you want to obtain. This is the reason why you do not find clear recipes
Marcella Bini Thank you so much for the information. I realize that viscosity is an important factor in determining the quality of the final product. However, I am still unsure about how to judge the quality of the cathode ink after it is prepared but before it is cast. As a beginner in this field, I have no experience, so please forgive my continuous questions.
Yun Gan
You should practice more and then you may have a feeling how good the slurry will be. If you're using a mortar and pestle to prepare the slurry, you can estimate its homogeneity and viscosity by observing its texture and consistency. Additionally, after casting the slurry onto a substrate, you can check its quality and uniformity before drying. After drying, the electrode should be checked again. You may use tweezers to scratch it and confirm how well it is stuck together.
The last step is to check its cyclability and compare it with other available data.
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