The dispersion of lithium-ion battery slurry in NMP solution should follow two principles!
Sep 28, 2022
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Last week, we have been discussing the homogenization technology of lithium-ion batteries, and found that NMP (full name: N-Methyl-2-Pyrrolidone/ 1-Methyl-2-Pyrrolidone) solvent everywhere. This is for sure, because the “small transparent” NMP solvent is one of the raw materials for preparing lithium-ion batteries. Today, we continue to discuss the homogenization process of lithium-ion batteries, and its slurry performance.
Performance of Li-ion Battery Slurry: Dispersibility + Stability
The dispersibility of lithium-ion batteries is judged by the solid content, viscosity and particle size distribution of the slurry;
The stability is judged by the 24-hour change in the solid content of the slurry (the mass ratio of the solid matter in the slurry to the slurry) and the 24-hour change in the viscosity of the slurry.
The dispersion of lithium-ion battery slurry is mainly to study the solid→liquid dispersion system, which is the dispersion of solid particle dispersed phase in liquid NMP (N-Methyl-2-Pyrrolidone/ 1-Methyl-2-Pyrrolidone) or deionized water continuous phase.
The dispersion of solid particle dispersed phase in NMP (N-Methyl-2-Pyrrolidone/ 1-Methyl-2-Pyrrolidone) solution or deionized water continuous phase should follow two principles:
Wet wetting principle (principle of near polarity): The particles must be wetted by the liquid medium to allow better immersion into the liquid phase.
Surface grabbing principle: The total surface grabbing particles must be a large number of particles that can be sufficiently isolated from each other so that direct contact and mutual support of the particles are prevented.
The dispersion of solid particles in the liquid phase (a homogeneous solution is also a phase) is the process of uniformly separating and dispersing solid particles in the liquid phase and forming a stable suspension. This process consists of 3 steps:
1. Infiltration of solid particles in the liquid phase;
2. The separation and dispersion of solid particle agglomerates under the action of mechanical force;
3. Stabilize the dispersed particles to prevent re-agglomeration.
The main parameters that affect the mixing and dispersion process:
1. The influence of stirring speed on dispersion speed. Generally speaking, the higher the stirring speed, the faster the dispersion speed, but the greater the damage to the material itself and the equipment.
2. The effect of concentration on dispersion speed and bonding strength.
Usually, the smaller the slurry concentration, the faster the dispersion speed, but too thin will lead to waste of material and aggravation of slurry precipitation.
The greater the concentration, the greater the kneading strength and the greater the bonding strength; the lower the concentration, the lower the bonding strength.
3. The effect of vacuum degree on the dispersion speed.
High vacuum is conducive to the discharge of gas from material gaps and surfaces, reducing the difficulty of liquid adsorption;
In the case of complete weightlessness or reduced gravity, the difficulty of uniform dispersion will be greatly reduced.
4. The effect of temperature on the dispersion speed.
At a suitable temperature, the slurry has good fluidity and is easy to disperse.
Too hot slurry is easy to form skin, too cold slurry will greatly reduce the fluidity.
Stablize
Dispersion stabilization refers to the process of shielding van der Waals (an electrical attraction) from primary particles or smaller aggregates under the action of electrostatic repulsion and steric repulsion, so that particles no longer aggregate.
Lithium-ion battery slurries are all suspension systems.
Suspensions flocculate over time at rest and stratify quickly due to gravity.
The purpose of dispersion is to deflocculate and prevent stratification within the validity period of the product, maintain the uniform distribution of suspended particles, and improve the stability of the product.
Flocculation is the process of reducing the number of particles through particle collisions under static (due to Brownian motion) or dynamic (under shear) conditions.
In the colloid system, if the stabilizer is not considered, the interaction between particles is mainly van der Waals attraction;
Coulombic forces (repulsion or attraction) that accompany charged particles.
The origins of these forces are quite different.
Derjaguin and Landau in the Soviet Union, Verwey and Overbeek in the Netherlands independently proposed the DLVO theory, which forms the basis of the classical theory of flocculation in lyophilic dispersion systems.
It expounds the stability of colloidal suspension system, which is mainly related to the relative distance of van der Waals attraction and Coulomb force between colloidal particles.
It expounds the stability of colloidal suspension system, which is mainly related to the relative distance of van der Waals attraction and Coulomb force between colloidal particles.
In this paper, we not only introduce the two principles to be followed for the dispersion of lithium-ion battery slurry in NMP solution, but also introduce several important parameters that affect the mixing and dispersion process; and introduce the stability of dispersion. What else do you want to know in the next article, please continue to discuss.
2.What are the lithium-ion battery homogenization processes and equipment involving NMP solvent?
3.ZESHENG team-#equipment #maintenance is carried out seriously every day!
