First, the principle of mixing
By stirring the blades and the revolving frame to rotate each other, the mechanical suspension is generated and maintained, and the mass transfer between the liquid and solid phases is enhanced. Solid-liquid agitation is usually divided into the following parts: (1) suspension of solid particles; (2) resuspension of settled particles; (3) infiltration of suspended particles into liquid; (4) use between particles and between particles and paddles The force causes the particle agglomerates to disperse or control the particle size; (5) the mass transfer between the liquid and solid.
Second, the stirring effect
The compounding process actually mixes the various components in the slurry together in a standard ratio to prepare a slurry to facilitate uniform coating and ensure the consistency of the pole pieces. The ingredients generally comprise five processes, namely: pretreatment, blending, wetting, dispersion and flocculation of the raw materials.
Third, the slurry parameters
1, viscosity:
The resistance of a fluid to a flow is defined as the amount of shear stress required per 25 px 2 plane when the liquid is flowing at a rate of 25 px/s, called the kinematic viscosity, in Pa.s.
Viscosity is a property of fluids. When the fluid flows in the pipeline, there are three states of laminar flow, transitional flow, and turbulent flow. These three flow states are also present in the stirring equipment, and one of the main parameters determining these states is the viscosity of the fluid.
During the stirring process, it is generally considered that the viscosity is less than 5 Pa.s is a low viscosity fluid, such as: water, castor oil, sugar, jam, honey, lubricating oil, low viscosity emulsion, etc.; 5-50 Pas is a medium viscosity fluid For example: ink, toothpaste, etc.; 50-500 Pas are high viscosity fluids, such as chewing gum, plastisol, solid fuel, etc.; more than 500 Pas are extra high viscosity fluids such as: rubber mixtures, plastic melts, organic Silicon and so on.
2, particle size D50:
The size range of the particle size of 50% by volume of the particles in the slurry
3, solid content:
The percentage of solid matter in the slurry, the theoretical ratio of solid content is less than the solid content of the shipment
Fourth, the measure of mixed effects
A method for detecting the uniformity of mixing and mixing of a solid-liquid suspension system:
1, direct measurement
1) Viscosity method: sampling from different positions of the system, measuring the viscosity of the slurry with a viscometer; the smaller the deviation, the more uniform the mixing;
2) Particle method:
A, sampling from different positions of the system, using a particle size scraper to observe the particle size of the slurry; the closer the particle size is to the size of the raw material powder, the more uniform the mixing;
B, sampling from different positions of the system, using a laser diffraction particle size tester to observe the particle size of the slurry; the more normal the particle size distribution, the smaller the larger particles, the more uniform the mixing;
3) Specific gravity method: sampling from different positions of the system, measuring the density of the slurry, the smaller the deviation, the more uniform the mixing
2. Indirect measurement
1) Solid content method (macroscopic): Sampling from different positions of the system, after appropriate temperature and time baking, measuring the weight of the solid part, the smaller the deviation, the more uniform the mixing;
2) SEM/EPMA (microscopic): sample from different positions of the system, apply to the substrate, dry, and observe the particles or elements in the film after drying the slurry by SEM (electron microscope) / EPMA (electron probe) Distribution; (system solids are usually conductor materials)
Five, anode stirring process
Conductive carbon black: Used as a conductive agent. Function: Connecting large active material particles to make the conductivity good.
Copolymer latex — SBR (styrene butadiene rubber): used as a binder. Chemical name: Styrene-Butadiene copolymer latex (polystyrene butadiene latex), water-soluble latex, solid content 48~50%, PH 4~7, freezing point -5~0 °C, boiling point about 100 °C, storage temperature 5~ 35 ° C. SBR is an anionic polymer dispersion with good mechanical stability and operability, and has a high bond strength.
Sodium carboxymethyl cellulose (CMC) – (carboxymethyl cellulose sodium): used as a thickener and stabilizer. Appearance is white or yellowish floc fiber powder or white powder, odorless, tasteless, non-toxic; soluble in cold water or hot water, forming a gel, the solution is neutral or slightly alkaline, insoluble in ethanol, ether, An organic solvent such as isopropyl alcohol or acetone is soluble in a 60% aqueous solution of ethanol or acetone. It is hygroscopic, stable to light and heat, viscosity decreases with increasing temperature, the solution is stable at pH 2 to 10, PH is lower than 2, solids are precipitated, and pH is higher than 10. The color change temperature was 227 ° C, the carbonization temperature was 252 ° C, and the surface tension of the 2% aqueous solution was 71 nm/n.
The anode stirring and coating process is as follows:
Sixth, cathode stirring process
Conductive carbon black: Used as a conductive agent. Function: Connecting large active material particles to make the conductivity good.
NMP (N-methylpyrrolidone): used as a stirring solvent. Chemical name: N-Methyl-2-polyrrolidone, molecular formula: C5H9NO. N-methylpyrrolidone is a slightly ammonia-smelling liquid which is miscible with water in any proportion and is almost completely mixed with all solvents (ethanol, acetaldehyde, ketone, aromatic hydrocarbon, etc.). The boiling point of 204 ° C, a flash point of 95 ° C. NMP is a polar aprotic solvent with low toxicity, high boiling point, excellent solubility, selectivity and stability. Widely used in aromatics extraction; purification of acetylene, olefins, diolefins. The solvent used for the polymer and the medium for polymerization are currently used in our company for NMP-002-02, with a purity of >99.8%, a specific gravity of 1.025~1.040, and a water content of <0.005% (500ppm).
PVDF (polyvinylidene fluoride): used as a thickener and binder. White powdery crystalline polymer with a relative density of 1.75 to 1.78. It has extremely good UV resistance and weathering resistance, and its film is not hard and cracked after being placed outdoors for one or two decades. The dielectric properties of polyvinylidene fluoride are specific, the dielectric constant is as high as 6-8 (MHz~60Hz), and the dielectric loss tangent is also large, about 0.02~0.2, and the volume resistance is slightly lower, which is 2×1014ΩNaN. Its long-term use temperature is -40 ° C ~ +150 ° C, in this temperature range, the polymer has good mechanical properties. It has a glass transition temperature of -39 ° C, an embrittlement temperature of -62 ° C or less, a crystal melting point of about 170 ° C, and a thermal decomposition temperature of 316 ° C or more.
Cathode stirring and coating process:
7. Viscosity characteristics of the slurry
1. Curve of slurry viscosity with stirring time
As the stirring time is extended, the viscosity of the slurry tends to be a stable value without changing (it can be said that the slurry has been uniformly dispersed).
2. Curve of slurry viscosity with temperature
The higher the temperature, the lower the viscosity of the slurry, and the viscosity tends to a stable value when it reaches a certain temperature.
3. Curve of solid content of the transfer tank slurry with time
After the slurry is stirred, it is piped to the transfer tank for Coater coating. The transfer tank is stirred to rotate: 25Hz (740RPM), revolution: 35Hz (35RPM) to ensure that the parameters of the slurry are stable and will not change, including pulp. Material temperature, viscosity and solid content to ensure uniformity of slurry coating.
4, the viscosity of the slurry with time curve
Post time: Oct-28-2019