NiMH No.7 battery.Technical knowledge information on lithium battery ingredients

　　1. Composition of electrode:

　　1. Positive electrode composition:

　　a. Lithium cobalt oxide: positive active material, lithium ion source, which increases the lithium source for the battery.

　　b. Conductive agent: Improve the conductivity of the positive electrode, compensate for the electronic conductivity of the positive active material, increase the electrolyte absorption capacity of the positive electrode, increase the reaction interface, and reduce polarization.

　　c. PVDF adhesive: bond lithium cobalt oxide, conductive agent and aluminum foil or aluminum mesh together.

　　d. Positive lead: made of aluminum foil or aluminum strip.

　　2. Negative electrode composition:

　　a. Graphite: negative active* material, which constitutes the main material of the negative electrode reaction; it is mainly divided into two categories: natural graphite and artificial graphite.

　　b. Conductive agent: improves the conductivity of the negative electrode sheet and compensates for the electronic conductivity of the negative electrode active material.

　　Improve response depth and utilization. Prevent the formation of dendrites. Utilize the liquid absorption ability of conductive materials to improve the reaction interface and reduce polarization. (You can choose to add or not add according to the graphite particle size distribution).

　　c. Additives: Reduce irreversible reactions, improve adhesion, increase slurry viscosity, and prevent slurry precipitation.

　　d. Water-based adhesive: bond graphite, conductive agent, additives and copper foil or copper mesh together.

　　e. Negative lead: made of copper foil or nickel strip.

　　2. The purpose of lithium battery batching: The batching process is actually to mix the various components in the slurry together according to standard proportions and prepare the slurry to facilitate uniform coating and ensure the consistency of the pole pieces*. Ingredients generally include five processes, namely: pretreatment of raw materials, blending, soaking, dispersion and flocculation.

　　3. Lithium battery ingredients principle:

　　(1) Principle of positive electrode ingredients

　　1. Physical and chemical properties of raw materials.

　　(1) Lithium cobalt oxide: non-polar substance, irregular shape, particle size D50 is generally 6-8 μm, water content ≤0.2%, usually alkaline, PH value is about 10-11.

　　Lithium manganate: non-polar substance, irregular shape, particle size D50 is generally 5-7 μm, water content ≤0.2%, usually weak base*, pH value is about 8. (2) Conductive agent: non-polar substance, grape chain, water content 3-6%, oil absorption value ~300, particle size generally 2-5 μm; mainly ordinary carbon black, superconducting

　　Carbon black, graphite emulsion, etc., when used in large quantities, a combination of superconducting carbon black and graphite emulsion is generally selected; usually medium.

　　(3) PVDF adhesive: non-polar substance, chain substance, molecular weight ranging from 300,000 to 3,000,000; after absorbing water, the molecular weight decreases and the viscosity becomes worse.

　　(4) NMP: Weak polar liquid, used to dissolve/swell PVDF and dilute the slurry.

　　2. Pretreatment of raw materials

　　(1) Lithium cobalt oxide: dehydration. Generally, bake at 120°C for about 2 hours at normal pressure.

　　(2) Conductive agent: dehydration. Generally, bake at 200°C for about 2 hours at normal pressure.

　　(3) Binder: Dehydrated. Generally, it is baked at 120-140°C at normal pressure for about 2 hours. The baking temperature depends on the molecular weight.

　　(4) NMP: dehydration. Use dry molecular sieves to dehydrate or use special retrieval facilities for direct use.

　　3. Blending of raw materials:

　　(1) Dissolution of adhesive (according to standard concentration) and heat treatment.

　　(2) Ball milling of lithium cobalt oxide and conductive agent: The powder is initially mixed, and lithium cobalt oxide and conductive agent are bonded together to improve agglomeration and conductivity. After being formulated into a slurry, it will not be distributed alone in the binder. The ball milling time is generally about 2 hours; in order to avoid mixing in impurities, agate balls are usually used as ball milling mesons.

　　4. Dispersion and soaking of dry powder:

　　(1) Principle: Solid powder is placed in the air. As time goes by, part of the air will be adsorbed on the surface of the solid. After the liquid binder is added, the liquid and gas begin to compete for the solid surface; if the adsorption force between the solid and the gas If the adsorption force between the solid and the liquid is stronger than the adsorption force on the gas, the liquid can wet the solid and squeeze out the gas. When the wetting angle is ≤90 degrees, the solid is wetted. When the wetting angle is >90 degrees, the solid is not wetted. All components in the cathode material can be wetted by the binder solution, so the cathode powder is relatively easy to disperse.

　　(2) The impact of dispersion methods on dispersion:

　　A. 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 may damage the structure of individual materials).

　　1. The influence of stirring paddle on dispersion speed. Stirring paddles generally include snake-shaped, butterfly-shaped, spherical, paddle-shaped, gear-shaped, etc. Generally, serpentine-shaped, butterfly-shaped, and paddle-shaped stirring paddles are used to deal with the initial stage of dispersing materials or ingredients that are difficult to disperse; spherical and gear-shaped stirring paddles are used for states where dispersion is less difficult and have good effects.

　　2. 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 structure and equipment.

　　3. The effect of concentration on dispersion speed. Generally, the smaller the slurry concentration, the faster the dispersion speed, but too thin will lead to material waste and aggravation of slurry precipitation.

　　4. The effect of concentration on bonding strength. The greater the concentration, the greater the softening strength and the greater the bonding strength; the lower the concentration, the smaller the bonding strength.

　　5. The effect of vacuum degree on dispersion speed. High vacuum degree is conducive to the discharge of gas from gaps and surfaces of materials, reducing the difficulty of liquid adsorption; the difficulty of material dispersion evenly under complete weightlessness or reduced gravity will be greatly reduced.

　　6. The effect of temperature on dispersion speed. At the appropriate temperature, the slurry flows best and is easy to disperse. The slurry that is too hot will easily form a skin, and the flow rate of the slurry that is too cold will be greatly reduced.

　　5. Dilution. Adjust the slurry to the appropriate concentration for easy coating.

　　(2) The principle of negative electrode batching (roughly the same as the positive electrode batching principle)

　　1. Physical and chemical properties of raw materials.

　　(1) Graphite: It is a non-polar substance, easily contaminated by non-polar substances, and easily dispersed in non-polar substances; it is not easy to absorb water and is not easy to disperse in water. Contaminated graphite easily re-agglomerates after being dispersed in water. The general particle size D50 is about 20 μm. The shapes of particles are diverse and irregular, mainly spherical, flaky, fibrous, etc.

　　(2) Water-based binder (SBR): small molecular wire-chain emulsion, easily soluble in water and extremely strong solvents.

　　(3) Anti-sedimentation agent (CMC): a polymer compound, easily soluble in water and extremely strong solvents.

　　(4) Isopropyl alcohol: a weak polar substance. After adding it, it can reduce the polarity of the adhesive solution and improve the compatibility between graphite and the adhesive solution; it has a strong defoaming effect; it can easily catalyze the network cross-linking of the adhesive. chain to improve bonding strength.

　　Ethanol: a weakly polar substance. After adding it, it can reduce the polarity of the adhesive solution and improve the compatibility between graphite and the adhesive solution; it has a strong defoaming effect; it can easily catalyze the cross-linking of adhesive lines and improve the bonding strength. (The effect of isopropyl alcohol and ethanol is essentially the same. When producing large quantities, you can choose which one to add based on cost factors).

　　(5) Deionized water (or distilled water): diluent, add as appropriate to change the flow of the slurry.

　　2. Pretreatment of raw materials:

　　(1) Graphite:

　　A. Mix to homogenize the raw materials and improve consistency.

　　B. Bake at normal pressure at 300~400℃ to remove surface oil substances, improve compatibility with water adhesives, and round the edges of the graphite surface (some materials are not allowed to be baked in order to maintain surface characteristics, otherwise the efficiency will be reduced).

　　(2) Water adhesive: dilute appropriately to improve dispersion ability.

　　3. Blending, soaking and dispersing:

　　(1) Graphite is extremely different from the binder solution and is not easy to disperse.

　　(2) The graphite can be preliminarily wetted with an alcohol-aqueous solution, and then mixed with the binder solution.

　　(3) The stirring concentration should be appropriately reduced to improve dispersion.

　　(4) The dispersion process is to reduce the distance between polar substances and non-polar substances and increase potential energy or surface energy, so it is an endothermic reaction, and the overall temperature decreases during stirring. If conditions permit, the stirring temperature should be appropriately raised to make it easier to absorb heat, improve flow rate, and reduce the difficulty of dispersion.

　　(5) If a vacuum degassing process is added to the stirring process to eliminate gas and promote solid-liquid adsorption, the effect will be better.

　　(6) The dispersion principle and dispersion method are the same as those in the cathode ingredients,

　　It is discussed in detail in 3. (1) and 4 and will not be explained in detail here.

　　4. Dilution

　　Adjust the slurry to the appropriate concentration for easy coating.

　　4. Things to note when preparing ingredients for lithium batteries:

　　1. Prevent other impurities from being mixed in;

　　2. Prevent slurry from splashing;

　　3. The concentration (solid content) of the slurry should be gradually adjusted from high to low to avoid additional trouble;

　　4. During the intermittent mixing process, pay attention to scraping the edges and bottom to ensure even dispersion;

　　5. The slurry should not be left aside for a long time to avoid settling or even reduction;

　　6. The materials to be baked must be sealed and cooled before being added to avoid changes in the quality of the components;

　　7. The length of the mixing time is mainly based on the equipment capacity and the amount of material added; the use of the mixing paddle should be replaced based on the difficulty of slurry dispersion. If it cannot be replaced, the rotation speed can be adjusted from slow to fast to avoid damage to the equipment;

　　8. Screen the slurry before discharging to remove large particles to prevent strip breakage during coating;

　　9. Strengthen training for ingredients personnel to ensure that they master professional knowledge to avoid catastrophe; 10. The key to ingredients is to disperse them evenly and master the center. Other methods can be adjusted by yourself.

　　5. Summary:

　　As the battery manufacturing process becomes increasingly transparent, lithium-ion battery manufacturers increasingly list ingredients as core secrets, because the selection, processing and reasonable matching of materials involve the efforts of too many technical personnel. Some manufacturers use the same materials. It goes very smoothly, but some manufacturers are full of troubles; some manufacturers can use mid-range materials to make high-end batteries, but some manufacturers use the best materials to make batteries that are terrible. If there are any deficiencies in the above information, we will will be corrected promptly

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