1. Pretreatment of raw materials
(1) Lithium cobaltate: dehydrated. Generally, it is baked at a pressure of 120 oC for about 2 hours.
(2) Conductive agent: dehydration. Generally, it is baked at 200 °C for 2 hours or so.
(3) Adhesive: dehydrated. Generally, it is baked at 120-140 oC for 2 hours at normal pressure, and the baking temperature is determined by the molecular weight.
(4) NMP: dehydration. Use dry molecular sieve dehydration or use special reclaiming facilities for direct use.
2, the mixing of raw materials
(1) Dissolution of the binder (according to standard concentration) and heat treatment.
(2) Lithium cobaltate and conductive agent ball milling: the powder is initially mixed, and the lithium cobaltate and the conductive agent are bonded together to improve the agglomeration and conduction. After being formulated into a slurry, it is not separately distributed in the binder, and the ball milling time is generally about 2 hours; in order to avoid mixing impurities, an agate ball is usually used as a ball mill meson.
3. Dispersion and wetting of dry powder:
(1) Principle: The solid powder is placed in the air. As time passes, part of the air will be adsorbed on the surface of the solid. After the liquid binder is added, the liquid and the gas begin to compete for the solid surface; if the solid and gas adsorbed The liquid is stronger than the liquid, and the liquid cannot wet the solid; if the solid-liquid adsorption force is stronger than the gas's adsorption force, the liquid can wet the solid and extrude the gas. When the wetting angle is ≤ 90 degrees, the solid is wetted. When the wetting angle is ≤90 degrees, the solids are not wetted. All members of the positive electrode material can be wetted by the binder solution, so the positive powder dispersion is relatively easy.
(2) The effect of the dispersion method on dispersion:
A. The standing method (long time, poor effect, but does not damage the original structure of the material);
B, stirring method; rotation or rotation plus revolution (short time, good effect, but it may damage the structure of individual materials).
1. The influence of the stirring paddle on the dispersion speed. The agitating paddles generally include a serpentine shape, a butterfly shape, a spherical shape, a gear shape, and the like. Generally, the serpentine, butterfly, and paddle type agitating paddles are used to deal with the initial stage of materials or ingredients that are difficult to disperse; the spherical and gear shapes are used to disperse the less difficult state, and the effect is good.
2. The effect of stirring speed on the 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.
3. The effect of concentration on the dispersion speed. Generally, the smaller the slurry concentration, the faster the dispersion speed, but too thin will result in waste of material and aggravation of slurry precipitation.
4. The effect of concentration on bond strength. The higher the concentration, the greater the softening strength and the higher the bonding strength; the lower the concentration, the smaller the bonding strength.
5. The effect of vacuum on the dispersion speed. The high vacuum facilitates the gas discharge of the material gap and the surface, and reduces the difficulty of liquid adsorption; the difficulty of uniformly dispersing the material under the condition of complete weight loss or reduced gravity will be greatly reduced.
6. 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 crust, and the fluidity of too cold slurry will be greatly reduced.
7. Dilute. The slurry is adjusted to a suitable concentration to facilitate coating.