402030 polymer battery

The principle, formula and process flow of 402030 polymer battery

402030 polymer battery are a type of secondary battery (rechargeable battery), which mainly relies on the reciprocating insertion and deintercalation of Li+ between two electrodes. With the continuous development of downstream industries such as energy vehicles, the production scale of 402030 polymer battery is constantly expanding.

This topic is divided into two parts, the first part focuses on the principle, formula and process flow of 402030 polymer battery. The second part explains the manufacturing and function of lithium batteries. This article is the first part of this topic.

1. Working principle

1. Positive electrode structure

LiCoO2+conductive agent+adhesive (PVDF)+current collector (aluminum foil)

2. Negative electrode structure

Graphite+conductive agent+thickener (CMC)+binder (SBR)+current collector (copper foil)

What you should know about lithium-ion <atarget=_blankhref='http://www.dghoppt.cn/product-list-13.html'><b>battery</b></a> principles and processes (Part 1)

3. Working principle

3.1 Charging process

A power source charges the battery. At this time, the electrons e on the positive electrode run to the negative electrode through the external circuit, and the positive lithium ions Li+ "jump" from the positive electrode into the electrolyte, "climb" through the winding holes on the separator, "swim" to the negative electrode, and combine with the electrons that have already run over. At this moment:

The reaction on the positive electrode is:

The reaction on the negative electrode is:

3.2 Battery discharge process

There are constant current discharge and constant resistance discharge. Constant current discharge is actually adding a variable resistor that can change with the voltage in the external circuit. The essence of constant resistance discharge is to add a resistor to the positive and negative electrodes of the battery to allow electrons to pass through. It can be seen that as long as the electrons on the negative electrode cannot run from the negative electrode to the positive electrode, the battery will not discharge. Electrons and Li+ move together, in the same direction but different paths. During discharge, electrons run from the negative electrode to the positive electrode through the electronic conductor, and lithium ions Li+ "jump" from the negative electrode into the electrolyte, "climb" through the winding holes on the separator, "swim" to the positive electrode, and combine with the electrons that have already run over.

3.3 Charge and discharge characteristics

The positive electrode of the battery cell uses LiCoO2, LiNiO2, and LiMn2O2. Among them, LiCoO2 is a crystal with a very stable layer structure. However, when x Li ions are removed from LiCoO2, its structure may change, but whether it changes depends on the size of x.

After research, it was found that when x>0.5, the structure of Li1-xCoO2 is extremely unstable, and the crystal collapse will occur, which is manifested externally as the collapse of the battery cell. Therefore, the battery cell should control the x value in Li1-xCoO2 by limiting the charging voltage during use. Generally, if the charging voltage is not greater than 4.2V, then x is less than 0.5, and the crystal form of Li1-xCoO2 is still stable.

The negative electrode C6 itself has its own characteristics. After the first formation, the Li in the positive electrode LiCoO2 is charged into the negative electrode C6, and when discharged, the Li returns to the positive electrode LiCoO2. However, after the formation, a part of the Li must remain in the center of the negative electrode C6 to ensure the normal embedding of Li in the next charge and discharge, otherwise the voltage of the battery cell is very short. In order to ensure that a part of the Li remains in the negative electrode C6, it is generally achieved by limiting the lower limit voltage of discharge: the upper limit voltage of safe charging is ≤4.2V, and the lower limit voltage of discharge is ≥2.5V.

The principle of the memory effect is crystallization, which almost never occurs in lithium batteries. However, the capacity of 402030 polymer battery will still decrease after multiple charge and discharge, and the reasons are complicated and diverse. It is mainly the change of the positive and negative electrode materials themselves. From the molecular level, the hole structure that accommodates lithium ions on the positive and negative electrodes will gradually collapse and block; from a chemical point of view, it is the active passivation of the positive and negative electrode materials, and the side reaction will generate other stable compounds. Physically, the positive electrode material will gradually fall off, which will eventually reduce the number of lithium ions that can move freely in the battery during the charging and discharging process.

Overcharging and overdischarging will cause permanent damage to the positive and negative electrodes of 402030 polymer battery. From a molecular level, it can be intuitively understood that overdischarging will cause excessive release of lithium ions from the negative electrode carbon, causing its layer structure to collapse, and overcharging will force too many lithium ions into the negative electrode carbon structure, making some of the lithium ions no longer released.

Unsuitable temperature will trigger other chemical reactions inside the lithium-ion battery to generate compounds that we do not want to see, so a protective temperature control barrier or electrolyte additive is set between the positive and negative electrodes of many 402030 polymer battery. When the battery temperature rises to a certain level, the pores of the composite membrane are closed or the electrolyte is denatured, the internal resistance of the battery increases until the circuit is broken, and the battery no longer heats up, ensuring that the battery charging temperature is normal.

2. Lithium battery formula and process flow

1. Positive and negative electrode formula

1.1 Positive electrode formula: LiCoO2+conductive agent+adhesive agent+current collector (aluminum foil)

LiCoO2(10μm):96.0%

Conductive agent (CarbonECP) 2.0%

Adhesive agent (PVDF761) 2.0%

NMP (adding adhesiveness): weight ratio of solid matter is about 810:1496

a) Positive electrode viscosity control 6000cps (temperature 25 rotor 3);

b) NMP weight must be properly adjusted to meet viscosity requirements;

c) Pay special attention to the effects of temperature and humidity on viscosity

Positive electrode active material:

Lithium cobalt oxide: Positive electrode active material, lithium ion source, lithium source for battery improvement. Non-polar substance, irregular shape, particle size D50 is generally 6-8μm, water content ≤0.2%, generally alkaline, pH value is about 10-11.

Lithium manganate: non-polar substance, irregular shape, particle size D50 is generally 5-7μm, water content ≤0.2%, generally weakly alkaline, pH value is about 8.

Conductive agent: chain-like substance, water content <1%, particle size is generally 1-5μm. Generally, superconducting carbon black with excellent conductivity is used, such as Ketjen Carbon ECP and ECP600JD. Its functions: improve the conductivity of positive electrode materials, compensate for the electronic conductivity of positive electrode active materials; improve the liquid absorption of electrolyte of positive electrode sheets, increase reaction interface, and reduce polarization.

PVDF adhesive: non-polar substance, chain-like substance, molecular weight ranges from 300,000 to 3,000,000; molecular weight decreases after water absorption, and viscosity becomes worse. Used to bond lithium cobalt oxide, conductive agent and aluminum foil or aluminum mesh together. Common brands such as Kynar761.

NMP: weakly polar liquid, used to dissolve/swell PVDF, and also used to dilute slurry.

Current collector (positive electrode lead): Made of aluminum foil or aluminum tape.

1.2 Negative electrode formula: graphite + conductive agent + thickener (CMC) + binder (SBR) + current collector (copper foil)

Negative electrode material (graphite): 94.5%

Conductive agent (CarbonECP): 1.0% (Ketjen superconducting carbon black)

Binder (SBR): 2.25% (SBR = styrene-butadiene rubber latex)

Thickener (CMC): 2.25% (CMC = sodium carboxymethyl cellulose)

The weight ratio of water: solid matter is 1600:1417.5

a) Negative electrode viscosity control 5000-6000cps (temperature 25 rotor 3)

b) The water weight needs to be properly adjusted to meet the viscosity requirements;

c) Pay special attention to the effect of temperature and humidity on viscosity

2. Positive and negative mixing

Graphite: Negative active material, the main substance that constitutes the negative electrode reaction; mainly divided into two categories: natural graphite and artificial graphite. Non-polar substances are easily contaminated by non-polar substances and easily dispersed in non-polar substances; they are not easy to absorb water and are not easy to disperse in water. Contaminated graphite is easy to reassemble after dispersing in water. The general particle size D50 is about 20μm. The particle shapes are diverse and mostly irregular, mainly spherical, flaky, fibrous, etc.

Conductive agent: Its functions are:

a) Improve the conductivity of the negative electrode sheet and compensate for the electronic conductivity of the negative electrode active material.

b) Improve the reaction depth and utilization rate.

c) Prevent the occurrence of dendrites.

d) Use the liquid absorption capacity of conductive materials to improve the reaction interface and reduce polarization. (You can choose to add or not according to the distribution of graphite particle size).

Additives: Reduce irreversible reaction, improve adhesion, improve slurry viscosity, and prevent slurry deposition.

Thickener/anti-deposition agent (CMC): polymer compound, easily soluble in water and polar solvents.

Isopropyl alcohol: a weak polar substance, which can reduce the polarity of the binder solution and improve the compatibility of graphite and the binder solution after addition; it has a strong defoaming effect; it is easy to catalyze the network crosslinking of the binder and improve the bonding strength.

Ethanol: a weak polar substance, which can reduce the polarity of the binder solution and improve the compatibility of graphite and the binder solution after addition; it has a strong defoaming effect; it is easy to catalyze the linear crosslinking of the binder and improve the bonding strength (the effects of isopropyl alcohol and ethanol are essentially the same. When mass production is carried out, the cost factor can be considered and then which one to add can be selected).

Water-based binder (SBR): Bond graphite, conductive agent, additives and copper foil or copper mesh together. Small molecule linear chain emulsion, very soluble in water and polar solvents.

Deionized water (or distilled water): diluent, add as needed to change the fluidity of the slurry.

Negative lead: made of copper foil or nickel strip.

2.1 Positive electrode mixture:

2.1.1 Pretreatment of materials

1) Lithium cobalt oxide: dehydration. Generally, it is baked at 120°C and normal pressure for about 2 hours.

2) Conductive agent: dehydration. Generally, it is baked at 200°C and normal pressure for about 2 hours.

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

4) NMP: dehydration. Use dry molecular sieve for dehydration or use special material collection facilities for direct use.

2.1.2 Material ball milling:

1) After 4 hours, sieve and separate the ball mill;

2) Pour LiCoO2 and CarbonECP into the material barrel, add grinding balls (dry material: grinding balls = 1:1), and ball mill on the roller bottle and the speed is controlled at more than 60rmp

2.1.3 Material blending:

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

2) Ball milling of lithium cobalt oxide and conductive agent: make the powder initially mixed, lithium cobalt oxide and conductive agent bond together, improve the aggregation effect and conductivity. After being prepared into slurry, it will not be dispersed in the binder alone. The ball milling time is generally about 2 hours. To avoid mixing impurities, agate balls are generally used as ball milling mesons.

2.1.4 Dispersion and wetting of dry powder:

Principle: Solid powder is placed in the air. As time goes by, it will absorb part of the air 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 is stronger than the adsorption force between the liquid, the liquid cannot wet the solid; if the adsorption force between the solid and the liquid is stronger than the adsorption force between the gas, the liquid can wet the solid and squeeze out the gas.

When the wet angle is ≤90°, the solid is wetted. When the wet angle is >90°, the solid is not wetted.

All members of the positive electrode material can be wetted by the binder solution, so the dispersion of the positive electrode powder is relatively easy.

The influence of dispersion method on dispersion:

1) Static method (long time, poor effect, but does not damage the original structure of the material);

2) Mixing method: self-rotation or self-rotation plus revolution (short time, good effect, but may damage the structure of individual materials).

The influence of mixing paddle on dispersion speed: Mixing paddles generally include snake-shaped, butterfly-shaped, spherical, paddle-shaped, gear-shaped, etc. Generally, snake-shaped, butterfly-shaped, and paddle-shaped mixing paddles are used to deal with the initial stage of materials or ingredients with high dispersion difficulty; spherical and gear-shaped paddles are used for the state with low dispersion difficulty and have good effect.

The influence of mixing speed on dispersion speed. Generally speaking, the higher the mixing speed, the faster the dispersion speed, but the greater the damage to the material structure and the equipment.

The influence of concentration on dispersion speed. Generally speaking, the lower the slurry concentration, the faster the dispersion speed, but too thin will lead to material waste and aggravated slurry deposition.

The influence of concentration on bonding strength. The higher the concentration, the greater the flexibility and bonding strength; the lower the concentration, the lower the bonding strength.

The effect of vacuum on dispersion speed. High vacuum is conducive to the discharge of gas from material gaps and surfaces, reducing the difficulty of liquid adsorption; the difficulty of uniform dispersion of materials will be greatly reduced when the material is completely weightless or gravity is reduced.

The effect of temperature on dispersion speed. At a suitable temperature, the slurry has good fluidity and is easy to disperse. Too hot slurry is prone to crusting, and too cold slurry will greatly reduce its fluidity.

Dilution: Adjust the slurry to a suitable concentration for easy coating.

2.1.5 Operation steps

a) Pour NMP into the power mixer (100L) to 80°C, weigh PVDF and add it, and start the machine; parameter setting: speed 25±2 rpm, stirring for 115-125 minutes;

b) Turn on the cooling system, add the ground positive electrode dry material evenly in four times, each time for 28-32 minutes, add NMP according to the material requirements for the third addition, and add NMP after the fourth addition; power mixer parameter setting: speed 20±2 rpm

c) 30±2 minutes after the fourth addition, high-speed stirring is carried out for 480±10 minutes; power mixer parameter setting: revolution 30±2 rpm, autorotation 25±2 rpm;

d) Vacuum mixing: Connect the power mixer to vacuum, maintain the vacuum degree at -0.09Mpa, and mix for 30±2 minutes; Power mixer parameter settings: revolution 10±2 minutes, autorotation 8±2 rpm

e) Take 250-300 ml of slurry and use a viscometer to measure the viscosity; test conditions: rotor number 5, speed 12 or 30rpm, temperature range 25°C;

f) Take the positive electrode material out of the power mixer for colloid milling and sieving, and label it on the stainless steel basin at the same time. After handing over to the operator of the slurry pulling equipment, it can flow into the slurry pulling process.

2.1.6 Precautions

a) Finish, clean up the equipment and working environment;

b) When operating the machine, pay attention to safety to avoid head injuries.

2.2 Negative electrode mixing

2.2.1 Pretreatment of materials:

1) Graphite:

A. Mix to homogenize the materials and improve consistency.

B. Bake at 300~400°C under normal pressure to remove surface oily substances, improve compatibility with water-based adhesives, and round the edges and corners of graphite surface (some materials are not allowed to be baked to maintain surface characteristics, otherwise the performance will decrease).

2) Water-based adhesive: Proper dilution to improve dispersion.

2.2.2 Blending, wetting and dispersion:

1) Graphite and adhesive solution have different polarities and are not easy to disperse.

2) Graphite can be initially moistened with alcohol-water solution and then mixed with adhesive solution.

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

4) The dispersion process is to reduce the distance between polar and non-polar substances and increase potential energy or surface energy, so it is an endothermic reaction, and the overall temperature decreases during mixing. If conditions permit, the mixing temperature should be appropriately increased,It makes it easier to absorb heat, improves fluidity, and reduces the difficulty of dispersion.

5) If the mixing process includes a vacuum degassing process, the gas can be removed, and solid-liquid adsorption can be promoted, which will have a better effect.

6) The dispersion principle and dispersion method are the same as those in the positive electrode ingredients

2.2.3 Dilution:

Adjust the slurry to a suitable concentration for easy coating.

2.2.4 Material ball milling

1) Pour the negative electrode and Ketjenblack ECP into the material barrel and add them to the ball mill (dry material: grinding ball = 1:1.2) and perform ball milling on the roller bottle, and the speed is controlled at more than 60rmp;

2) After 4 hours, sieve and separate the ball mill;

2.2.5 Operation steps

1) Heat the purified water to 80°C and pour it into the power mixer (2L)

2) Add CMC and stir for 60±2 minutes; Power mixer parameter setting: revolution is 25±2 minutes, rotation is 15±2 rpm;

3) Add SBR and deionized water and stir for 60±2 minutes;

Power mixer parameter setting: revolution is 30±2 minutes, rotation is 20±2 rpm;

4) Add the negative electrode dry material in four evenly distributed times, and add purified water at the same time, each time for 28-32 minutes; Power mixer parameters Settings: Revolution is 20±2 rpm, rotation is 15±2 rpm;

5) After the fourth feeding, high-speed mixing is performed for 480±10 minutes after 30±2 minutes;

Power mixer parameter settings: Revolution is 30±2 rpm, rotation is 25±2 rpm;

6) Vacuum mixing: Connect the power mixer to vacuum, maintain the vacuum degree at -0.09 to 0.10Mpa, and mix for 30±2 minutes;

Power mixer parameter settings: Revolution is 10±2 minutes, rotation is 8±2 rpm

7) Take 500 ml of slurry and measure the viscosity with a viscometer;

Test conditions: rotor number 5, speed 30rpm, temperature range 25°C;

8) Take the negative electrode material out of the power mixer for grinding and sieving, and label it on the stainless steel basin. After handing over to the slurry pulling equipment operator, it can flow into the slurry pulling process.

2.2.6 Precautions

1) After the work is completed, clean up the equipment and working environment;

2) When operating the machine, pay attention to safety to avoid head injuries.

Precautions for batching:

Avoid mixing with other impurities;

Avoid slurry splashing;

The concentration (solid content) of the slurry should be adjusted gradually from high to low to avoid troublesome addition;

Pay attention to scraping the edges and bottom during the intermittent mixing process to ensure uniform dispersion;

The slurry should not be placed for a long time to avoid sedimentation or uniformity reduction;

The materials to be baked must be sealed and cooled before they can be added to avoid changes in the properties of the component materials;

The length of the mixing time is mainly based on the equipment function and the amount of materials added;

The use of the mixing paddle is replaced according to the difficulty of slurry dispersion. If it cannot be replaced, the speed can be adjusted from slow to fast to avoid damage to the equipment;

Sieve the slurry before discharging to remove large particles to prevent the formation of broken belts during coating;

Strengthen the training of batching personnel to ensure that they have professional knowledge to avoid major disasters;

The key to batching is uniform dispersion. Master this core and other methods can be adjusted by yourself.

The above is the principle, formula and process flow of 402030 polymer battery. If you want to learn 402030 polymer battery in full, please pay attention to the next article of this topic.

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