Basic knowledge of lithium batteries (2)
(二), the principle of negative dosing (roughly the same principle as the positive dosing)
1. Physical and chemical properties of raw materials.
(1) Graphite: Non-polar substance, easily contaminated by non-polar substances, easy to disperse in non-polar substances; not easy to absorb water, and not easy to disperse in water. Contaminated graphite, after being dispersed in water, is easy to re-agglomerate. The general particle diameter D50 is about 20 μm. The particles are various in shape and irregular, and are mainly spherical, flaky, fibrous, and the like.
(2) Waterborne binder (SBR): a small molecule linear chain emulsion that is highly soluble in water and polar solvents.
(3) Anti-precipitation agent (CMC): a polymer compound that is easily soluble in water and polar solvents.
(4) Isopropanol: a weakly polar substance, which reduces the polarity of the binder solution and improves the compatibility of the graphite and the binder; it has a strong defoaming effect; The cross-linking chain improves the bond strength.
Ethanol: a weakly polar substance, which reduces the polarity of the binder solution and improves the compatibility of the graphite and the binder solution; has a strong defoaming effect; easily catalyzes the linear crosslinking of the binder and improves the viscosity. The strength of the knot (the effect of isopropanol and ethanol is essentially the same, and the cost factor can be considered in mass production and then which one to add).
(5) Deionized water (or distilled water): A diluent is added as needed to change the fluidity of the slurry.
2. Pretreatment of raw materials:
(1) Graphite: A, mixed to homogenize the raw materials and improve consistency. B, 300 ~ 400 ° C atmospheric pressure baking, remove surface oily substances, improve the compatibility with water-based adhesives, round the surface of the graphite edge (some materials to maintain surface characteristics, do not allow baking, otherwise the efficiency is reduced).
(2) Aqueous binder: Dilute properly to improve dispersibility.
3. Blending, wetting and dispersing:
(1) Graphite and binder solution have different polarities and are not easily dispersed.
(2) The graphite may be initially wetted with an aqueous alcohol solution and then mixed with the binder solution.
(3) The stirring concentration should be appropriately lowered to improve the dispersibility.
(4) The dispersion process is to reduce the distance between polar and non-polar substances and increase the potential energy or surface energy. Therefore, for the endothermic reaction, the overall temperature decreases when stirring. If the conditions permit, the stirring temperature should be raised appropriately to make the heat absorption easier, while improving the fluidity and reducing the difficulty of dispersion.
(5) The stirring process, such as adding a vacuum degassing process, removes the gas and promotes solid-liquid adsorption, and the effect is better.
4. Dilute. The slurry is adjusted to a suitable concentration to facilitate coating.
Fourth, the ingredients note:
1. Prevent mixing of other impurities;
2. Prevent slurry splashing;
3. The concentration of the slurry (solid content) should be gradually adjusted from high to low to avoid adding trouble;
4. Pay attention to scraping and scraping the bottom during the mixing process to ensure uniform dispersion;
5, the slurry should not be left for a long time to avoid precipitation or uniformity reduction;
6. The materials to be baked must be sealed and cooled before they can be added to avoid changes in the properties of the components.
7. The length of the mixing time is mainly based on equipment performance and material addition; the use of the stirring paddle is replaced by the difficulty of slurry dispersion. If the replacement cannot be replaced, the rotation speed can be adjusted from slow to fast to avoid damage to the equipment;
8. The slurry is sieved before discharge to remove large particles to prevent breakage during coating;
9. Strengthen the training of the ingredients to ensure that they have the expertise to avoid a major disaster;
10, the key to the ingredients is to spread evenly, master the center, other methods can be adjusted.