Electrode manufacturing is a key procedure where the battery cathode and anode are made. And the first step of it is mixing. As its name suggests, electrode materials are measured and mixed in this step; active materials and solvents are mixed, producing slurries.
Since the anode active materials (anode materials) have a weak crystal structure, equipment that may apply strong shear stress (the stress applied parallel to a given surface) should be avoided. Therefore, a planetary mill, a machine that looks like the one used when kneading dough, takes the place.
*For the anode active materials, graphite is used here.
A binder (a substance that fastens materials) improves adhesion between the particles of the active materials as they are being mixed. It should be stable enough to maintain its adhesive quality even when contacted with electrolyte or an oxidation-reduction reaction occurs. Good binder materials have high adhesion strength, good solubility (in industrial solvents), electrochemical inertness, and resistance to most chemicals.
PVDF X NMP
Polyvinylidene fluoride (PVDF) is normally used for binders, often with N-Methyl-2-pyrrolidone (NMP) as a solvent. This combination creates high adhesion, helps dispersion of conductive additives, and offers stability in oxidation-reduction reactions. Recently, as researchers seek to further increase energy density, styrene-butadiene rubber (SBR) or carboxy methyl cellulose (CMC) are also employed as substitutes. The materials allow raising the proportion of active materials and cutting that of binders.
Active Materials and Conductive Additives
The proportions of active material particles of certain sizes (particle-size distribution) can affect the mixing process and the quality of the electrode. Oversized or undersized particles need to be removed since they can produce dust. Also, more point contacts in active materials can cause more holes that can shrink the battery capacity. Those holes can be plugged by adding conductive additives that improve the electrode conductivity.
In conclusion, the mixing process is to mix active electrode materials, binders, solvents, and conductive additives, producing an intermediate good, a slurry. For its part, LG Energy Solution announced introduction of Dreamline 2.0, a platform that would upgrade the mixing equipment in Ultium Cells plants, the joint venture of LG and General Motors, from the current 2,300-liter level to 3,000-liter level.
We have examined the mixing process, the first step of electrode manufacturing in making batteries. Next time, we will find out what happens to the slurry in the “coating” process, the second step of electrode manufacturing!