First, the composition of the electrode:
1, the positive electrode composition:
a, lithium cobalt oxide: positive electrode active material, lithium ion source, providing lithium source for the battery.
b. Conductive agent: Improve the conductivity of the positive electrode sheet and compensate the electronic conductivity of the positive electrode active material.
The liquid absorption of the electrolyte of the positive electrode sheet is increased, the reaction interface is increased, and the polarization is reduced.
c. PVDF binder: Lithium cobaltate, a conductive agent and an aluminum foil or an aluminum mesh are bonded together.
d. Positive lead: Made of aluminum foil or aluminum strip.
2, the composition of the negative electrode:
a, graphite: negative electrode active material, which constitutes the main substance of the negative electrode reaction; mainly divided into two major categories of natural graphite and artificial graphite.
b. Conductive agent: Improve the conductivity of the negative electrode sheet and compensate for the electronic conductivity of the negative electrode active material.
Improve reaction depth and utilization. Prevent the generation of dendrites. The liquid absorption capacity of the conductive material is utilized to increase the reaction interface and reduce polarization. (Can be selected according to the graphite particle size distribution plus or not).
c. Additives: reduce irreversible reactions, improve adhesion, increase slurry viscosity, and prevent slurry precipitation.
d. Aqueous binder: Bonding graphite, conductive agent, additive and copper foil or copper mesh together.
e, negative lead: made of copper foil or nickel strip.
Second, the purpose of ingredients:
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.
With (a), positive dosing principle 1, physical and chemical properties of raw materials.
(1) Lithium cobaltate: 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 weakly alkaline, PH value is about 8.
(2) Conductive agent: non-polar substance, grape chain, water content 3-6%, oil absorption value ~300, particle size is generally 2-5 μm; mainly common carbon black, superconducting carbon black, graphite emulsion Etc., in the case of high-volume applications, superconducting carbon black and graphite emulsion are generally selected; usually neutral.
(3) PVDF (polyvinylidene fluoride) binder: non-polar substances, chains, molecular weight ranging from 300,000 to 3,000,000; molecular weight decreases after water absorption, viscosity is deteriorated.
(4) NMP (N-methylpyrrolidone): a weakly polar liquid used to dissolve/swell PVDF and to dilute the slurry.
2. Pretreatment of raw materials
(1) Lithium cobaltate: dehydrated. Generally, it is baked at 120 °C for 2 hours.
(2) Conductive agent: dehydration. Generally, it is baked at 200 °C for 2 hours.
(3) Adhesive: Dehydrated. Generally, it is baked at a normal pressure of 120-140 ° C for about 2 hours, 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.
3. Mixing of raw materials:
Material principle:
(1) Dissolution of the binder (according to the standard concentration) and heat treatment.
(2) Lithium cobaltate and conductive agent ball milling: The powder is initially mixed, and lithium cobaltate and conductive agent are bonded together to improve agglomeration and conductivity. 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.
4. 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 will start to compete for the solid surface; if the solid and gas are 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, 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 paddle 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 is beneficial to the gas discharge of the material gap and the surface, and the difficulty of liquid adsorption is reduced; 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.
5. Dilute. The slurry is adjusted to a suitable concentration to facilitate coating.
(B), the principle of negative electrode 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) Aqueous binder (SBR: styrene butadiene rubber): a small molecule linear chain emulsion that is highly soluble in water and polar solvents.
(3) Anti-precipitation agent (CMC: carboxymethyl cellulose): a polymer compound, easily soluble in water and a polar solvent.
(4) Isopropanol: 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; 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 during 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.
(6) The principle of dispersion and dispersion are the same as those in the positive electrode batching, which are discussed in detail in (3) and 4, and will not be explained in detail here.
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 adding, in order 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.
V. General:
With the increasingly transparent battery process, lithium-ion battery manufacturers are increasingly classifying ingredients as core secrets, because the selection, processing and rational matching of materials contain too many technicians' efforts, the same materials, and some manufacturers use It is particularly smooth, and some manufacturers are in trouble; some manufacturers can make high-end batteries with medium-grade materials, while some manufacturers use ** materials to make batteries that are unbearable; the basic knowledge of ingredients can make everyone's ingredients More understanding, less detours; but the level is limited, it is inevitable that there are omissions, I hope that everyone will criticize and correct. We also hope that everyone will seriously study in the work, exchange sincerely, boldly innovate, unite and jointly promote the improvement of the production level of lithium-ion batteries in China.
1, the positive electrode composition:
a, lithium cobalt oxide: positive electrode active material, lithium ion source, providing lithium source for the battery.
b. Conductive agent: Improve the conductivity of the positive electrode sheet and compensate the electronic conductivity of the positive electrode active material.
The liquid absorption of the electrolyte of the positive electrode sheet is increased, the reaction interface is increased, and the polarization is reduced.
c. PVDF binder: Lithium cobaltate, a conductive agent and an aluminum foil or an aluminum mesh are bonded together.
d. Positive lead: Made of aluminum foil or aluminum strip.
2, the composition of the negative electrode:
a, graphite: negative electrode active material, which constitutes the main substance of the negative electrode reaction; mainly divided into two major categories of natural graphite and artificial graphite.
b. Conductive agent: Improve the conductivity of the negative electrode sheet and compensate for the electronic conductivity of the negative electrode active material.
Improve reaction depth and utilization. Prevent the generation of dendrites. The liquid absorption capacity of the conductive material is utilized to increase the reaction interface and reduce polarization. (Can be selected according to the graphite particle size distribution plus or not).
c. Additives: reduce irreversible reactions, improve adhesion, increase slurry viscosity, and prevent slurry precipitation.
d. Aqueous binder: Bonding graphite, conductive agent, additive and copper foil or copper mesh together.
e, negative lead: made of copper foil or nickel strip.
Second, the purpose of ingredients:
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.
With (a), positive dosing principle 1, physical and chemical properties of raw materials.
(1) Lithium cobaltate: 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 weakly alkaline, PH value is about 8.
(2) Conductive agent: non-polar substance, grape chain, water content 3-6%, oil absorption value ~300, particle size is generally 2-5 μm; mainly common carbon black, superconducting carbon black, graphite emulsion Etc., in the case of high-volume applications, superconducting carbon black and graphite emulsion are generally selected; usually neutral.
(3) PVDF (polyvinylidene fluoride) binder: non-polar substances, chains, molecular weight ranging from 300,000 to 3,000,000; molecular weight decreases after water absorption, viscosity is deteriorated.
(4) NMP (N-methylpyrrolidone): a weakly polar liquid used to dissolve/swell PVDF and to dilute the slurry.
2. Pretreatment of raw materials
(1) Lithium cobaltate: dehydrated. Generally, it is baked at 120 °C for 2 hours.
(2) Conductive agent: dehydration. Generally, it is baked at 200 °C for 2 hours.
(3) Adhesive: Dehydrated. Generally, it is baked at a normal pressure of 120-140 ° C for about 2 hours, 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.
3. Mixing of raw materials:
Material principle:
(1) Dissolution of the binder (according to the standard concentration) and heat treatment.
(2) Lithium cobaltate and conductive agent ball milling: The powder is initially mixed, and lithium cobaltate and conductive agent are bonded together to improve agglomeration and conductivity. 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.
4. 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 will start to compete for the solid surface; if the solid and gas are 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, 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 paddle 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 is beneficial to the gas discharge of the material gap and the surface, and the difficulty of liquid adsorption is reduced; 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.
5. Dilute. The slurry is adjusted to a suitable concentration to facilitate coating.
(B), the principle of negative electrode 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) Aqueous binder (SBR: styrene butadiene rubber): a small molecule linear chain emulsion that is highly soluble in water and polar solvents.
(3) Anti-precipitation agent (CMC: carboxymethyl cellulose): a polymer compound, easily soluble in water and a polar solvent.
(4) Isopropanol: 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; 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 during 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.
(6) The principle of dispersion and dispersion are the same as those in the positive electrode batching, which are discussed in detail in (3) and 4, and will not be explained in detail here.
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 adding, in order 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.
V. General:
With the increasingly transparent battery process, lithium-ion battery manufacturers are increasingly classifying ingredients as core secrets, because the selection, processing and rational matching of materials contain too many technicians' efforts, the same materials, and some manufacturers use It is particularly smooth, and some manufacturers are in trouble; some manufacturers can make high-end batteries with medium-grade materials, while some manufacturers use ** materials to make batteries that are unbearable; the basic knowledge of ingredients can make everyone's ingredients More understanding, less detours; but the level is limited, it is inevitable that there are omissions, I hope that everyone will criticize and correct. We also hope that everyone will seriously study in the work, exchange sincerely, boldly innovate, unite and jointly promote the improvement of the production level of lithium-ion batteries in China.
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