1.Mixing
1.1.Slurry stirring is the process of adding active materials, conductive carbon black, dispersants,
binders, additives, and other components to a mixing equipment in a certain proportion and
order. Under the mechanical actions such as agitation, kneading, and shearing generated by the
equipment, these components are mixed together to form a uniform, stable solid-liquid
suspension system suitable for coating.
Goal: Achieve uniformity and consistency at both macro and micro levels
1.2.Goal: Wettability, dispersion, and stabilization are the three key indicators of good slurry
1.3.Good wettability can reduce the difficulty of dispersion and improve mixing efficiency.
1.4.Mechanical stirring dispersion refers to the process of causing strong turbulent motion of the liquid flow through intense mechanical stirring, which leads to the breakup and suspension of particle aggregations.
1.5.The spatial hindrance effect of the dispersant adsorbed on the surface of the particles generates a strong repulsive force between the particles.
The cathode and anode slurries utilize polymeric materials (PVDF/CMC) to provide steric repulsion, maintaining the stable suspension of particles.
2.Mixing equipment
universities mainly use magnetic mixing and ultrasonic dispersion. Advantages: Less material usage. Problem: Poor dispersion effect.
Commercial mixing primarily uses planetary mixing. Advantages: excellent dispersion effects. Problem: requires a larger amount of material.
magnetic mixing simple dispersion disk planetary mixing
3.Mixing device
The mixing tank has both revolution and rotation (dispersion disk)
The tank is equipped with a circulating cooling water system to control the temperature of the entire slurry.
The tank has a vacuum pump to remove air bubbles.
4.Mixing Process
The mixing process is similar to the positive electrode, except for the final step add SBR (binder).
The left figure shows the general mixing process (revolution speed~20rpm)
5.Preparation of PVDF glue solution
5.1.Mainstream CMC gel solution
5.2.The process of formula improvement based on actual needs, incorporating new binders such as PAN, PAA, etc.
6.Slurry dispersion
Control the temperature of the slurry during the entire mixing process, and a vacuum pumping step is performed before shipment to ensure that the slurry coating is free of bubbles (similar to the preparation of cathode slurry)
add SP,disperse for 10min add SP,disperse for 2h
add active material, disperse for 2h adjust viscosity, then sieve
7.CMC and Surface Wetting
1)Due to the hydrophobic nature of the graphite surface, when graphite powder is added to water, it floats on the surface and does not wet properly. Therefore, it is necessary to add CMC (carboxymethylcellulose sodium) to improve the surface condition, allowing the graphite to wet and disperse in the water.
2)Some surfaces of secondary agglomerated graphite are difficult to wet completely. In such cases, kneading and mixing are needed to improve the wetting condition of the surfaces. (Detailed discussion will be share next time.)
