As I was preparing the electrode for lithium ion battery, I tried taking 70% active material (70mg) ,20%(20mg) pvdf binder (20mg/20ml) ,10%(10mg) carbon black as conducting additive. I kept it for dissolution for 8-10hours but still proper dissolution isn't done.
The ratio between solid and liquid for slurry casting majorly depends on the thickness of the film you want to cast, higher solid content leads to higher viscosity and you will be able to cast thicker film. Usually, the solid content will below 50 wt%. However, for your case, the solid content is ~100/120, way to high, so you'd better add more NMP and this could be the reason for your non-dissolving problem. If this is just your first several trails, I suggest you to start with low solid concentration, such as 20 wt%, then during mixing, gradually evaporate the extra NMP, monitor the viscosity of the slurry, find the best ratio for your casting. If you still want to keep a low solvent concentration, you'd better mix PVDF/NMP first, in a heated atmosphere, to obtain a clear solution.
Here's a good literature for you to read: Adv. Energy Mater. 2016, 1600655
As Chunhui Chen; also, what is the (initial) form of your pvdf (binder) ?
So, your PVDF in pellet (or granule) form is heated in NMP ?
The resulting solution is quite clear ?
Usually you would mix the PVDF in the solid part of the electrode (with Graphite and carbon black) so it better if it is in powder (granule) form, since this would allow it to mix everywhere. Then NMP is used after you have already mixed the solid part of the system.
Dr.Ioannis Samaras , you are right we have PVDF in the form of small granual .So it wouldn't mix with active material and conductive additive. So I mixed 100mg in 100ml NMP in order to make 1mg/1ml solution & yes, resulting solution is quit clear.
Like Panpan stated, first dissolve the PVDF in NMP to get a solution usually 5wt% before measuring equivalent weight of the PVDF according to its ratio in the active material:carbon:PVDF mixture.
For my electrode slurry, I used 10 ml of NMP and 200mg of PVDF pellet and i tried shaking them to help mix them because it was in a test tube. I then left it in a sonicator for 30mins. You can try this as well.
Pallets are very tricky to dissolve, should use powder form of pvdf
Your solution might be viscous because the binder content is 20%. usually 10 or less works better. Li-ion electrodes typically don't need such high binder content. You could try lowering binder amount along with the suggestions from other answers in this thread.
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