How much do you know about the lithium battery homogenization process with the participation of NMP solvent?

We’ve been talking about NMP solvents lately. So, how much do you know about the homogenization process of lithium batteries that NMP solvent participates in? Today, let’s find out together.

The significance of the lithium battery homogenization process is to obtain stable chemical effects; when the homogenization process is in place, the probability of lithium battery fire and explosion will be relatively reduced. And this homogenization process is exactly the process of batching, stirring, coating and other processes involving NMP solvent.

If you have been paying attention to our articles, you will know that in the previous articles, we also talked about lithium battery ingredients, stirring, coating and other processes. The dry-process positive and negative ingredients in the lithium battery preparation process can be divided into stages such as mixing → wetting → dispersion → stabilization. Among them, the wet stage generally requires a slower rotation speed; while the dispersion stage often requires a certain shear force, and requires high-speed rotation, the linear speed should reach more than 20m/s.

What kind of operation is called mixing? In theory, mixing materials in any state uniformly can be called mixing. But in the lithium battery industry, the operation of mixing solid materials, or adding a small amount of liquid to solid materials, is called mixing. If the solid and liquid materials are mixed, or the gaseous and liquid materials are mixed, it is called stirring.

The stirring in the lithium battery preparation process is simply the process of making the material tend to homogenize. Because the raw materials are all chemicals involved in the production of lithium batteries , these materials not only have strong physical effects, but also have certain chemical effects during the actual stirring process.

Stirring, that is, the form of mixing of various materials, is mainly divided into dispersive mixing and distributive mixing.

Dispersion mixing refers to the process in which the liquid or solid particles are continuously broken during the mixing process, not only the size will continue to be decreased, but the position will be also changed;

Distributed mixing refers to the rearrangement of the position of the dispersed phase (dispersed substances) in the multi-component continuous phase (referring to the substances that disperse other substances in the dispersion system) to achieve uniform distribution; Disperse-phase particles only change in position relative to each other, but not in particle size (referring to the average size of crumbs or ore grains in a rock or sediment).

For lithium battery slurry with high viscosity and high solid content, the actual mixing is a comprehensive process of dispersive mixing and distributive mixing.

After this process, the active material, conductive agent, binder, etc. are uniformly dispersed in the NMP solvent according to a certain mass ratio to form a stable slurry with a certain viscosity. This slurry is used to smear on the pole piece.

The requirements of the pole piece for the ideal slurry:

(i) Active substances, the particles are fine, uniformly dispersed, without agglomeration; the conductive agent particles form a thin layer, disperse into a conductive network, and interlock on the current collector to the greatest extent, connecting the active matter particles;

(ii) The particles of the active substances are preferably small to ensure a high current density of the battery.

It looks complicated, but the lithium battery itself is created by a very complex process. As the “small transparency” in the raw materials of lithium batteries, NMP solvent, as the solvent of the binder PVDF, participates in the dispersion of the slurry during the preparation of lithium batteries. In order to maintain smooth performance of the battery, it is necessary to apply the NMP solvent evenly on the metal substrate (pole piece) of the battery at an average speed.

Today, we will temporarily understand the ingredient mixing process in the homogenization process of lithium batteries. In the next article, we will continue to understand other contents of the homogenization process of lithium batteries.