Preparation scheme of positive and negative electrode slurry for lithium ion battery

As the mainstream solution for automotive power batteries in recent years, lithium batteries have many production processes. There are various solutions in the equipment industry for each process, and new solutions are constantly entering with the development. The production of lithium batteries is divided into three stages: pole piece production, cell assembly, and formation testing. Among them, the production of the pole piece is divided into four steps: slurry preparation, coating, rolling, and slitting. This time, the editor will introduce the slurry preparation stage, and introduce several common slurry preparation methods and equipment in battery factories at present. Brief introduction to everyone.


In the manufacture of electrodes for lithium ion batteries, the positive electrode slurry is composed of a binder, a conductive agent, and a positive electrode material; the negative electrode slurry is composed of a binder, graphite carbon powder, and the like. The preparation of positive and negative slurries includes a series of technological processes such as mutual mixing, dissolution and dispersion between liquid and liquid, liquid and solid materials, and these processes are accompanied by changes in temperature, viscosity, and environment. In the positive and negative electrode slurries, the dispersion and uniformity of the granular active material directly affects the movement of lithium ions between the two poles of the battery, so the mixing and dispersion of the slurry of each pole piece material is very important in the production of lithium ion batteries. , The quality of slurry dispersion directly affects the quality of subsequent lithium-ion battery production and the performance of its products.

Double planetary mixer

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a How it works

When the planet carrier is rotating, it can drive the stirring shaft of the machine to revolve around the material barrel of the reaction kettle, and at the same time the stirring shaft of the double planet rotates at a high speed, which can promote the material to be strongly sheared and kneaded. So as to achieve the goal of fully emulsification, dispersion and mixing of materials, the mixing effect of this structure equipment is several times that of ordinary mixers. At the same time, a set of scrapers is set on the planetary carrier of the double planetary mixer to rotate with the planetary carrier. Through continuous and seamless scraping, the wall barrel has no residual battery slurry, which improves the mixing effect. The double planetary mixer is a vacuum-resistant machine that can be used for vacuuming, heating and cooling. It can meet the processing requirements of the wet mixing process of lithium battery slurry.

Advantage:

1. Low clearance. The gap between the slurry and the slurry, the slurry and the barrel wall, the slurry and the barrel bottom is low, and the precise gap between the stirring paddles and the stirring paddle and the inside of the stirring tank ensures that the stirring tank has no dead angle and has a high degree of kneading effect. Rapid mutual penetration and kneading.

2. High efficiency. The unique mixing, dispersing and stirring structure design greatly improves the production capacity of lithium battery production equipment and enables efficient production.

3. The material does not stick to the wall, and the discharge is clean.
The 360-degree design without dead angle ensures that the material is evenly mixed. The scraper on the planet carrier of the double planetary mixer can easily make the barrel wall free of stagnant material. At the same time, it is supplemented by a scraper-type stirring paddle, which can scrape the bottom of the bucket, avoid the dead angle of stirring, greatly improve the mixing effect of materials, and ensure the quality of the finished product.

4. High dispersion/shear and low noise. The linear speed of dispersion/emulsification parts can reach more than 23M/S, parts processing, professional tooling, high parts coordination, less wear, more stable operation and low noise; under full load operation, a low-noise working space is created.

5. Corrosion resistance and zero leakage. Anti-corrosion mechanical seal plus soft and static seal, planetary transmission box adopts fully-sealed structure, and the all-round sealing concept improves the sealing performance by 50% on the traditional basis; and the high degree of vacuum retention ensures zero pollution in the stirring process.

6. High strength. According to different mixing processes (dry mixing, wet mixing), after strict strength calculation, it is suitable for high-viscosity, high-solid content battery positive and negative slurries and binders.

7. High integration. The links of premixing, stirring, turnover and filtration are seamless and quick-release docking, and there is no contact with air. It can be fully controlled by PLC, and the speed, temperature, lifting and vacuum systems can be integrated on a panel for control.

shortcoming:

During the operation, the double planetary stirring will also encounter many problems:

1. Batch dispersion process, long mixing and dispersion time and large energy consumption.
2. The electrode powder material is added from the top of the planetary agitator, and the dust is easy to fly and float. More importantly, the powder is easily agglomerated when mixed with the liquid phase.
3. The material is easy to remain on the tank cover, tank wall and stirring paddle of the planetary agitator, and the cleaning operation is difficult.
4. Air is easy to remain in the dispersion mixing tank, and the generation of air bubbles affects the dispersion effect.
5. The batch process limits mass production, the production line occupies a large area, and the maintenance cost is high.

Battery slurry twin-screw stirring

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The screw type mixing system generally consists of measuring hopper, weighing and conveying system, storage tank, rubber making tank, transfer tank, feeder, high-speed mixer, booster pump, magnetic filter, high-speed homogenizer, auxiliary equipment and DCS central control system. The positive and negative raw materials (powder and liquid) of the lithium battery are automatically and continuously transported to the screw mixer online through a precise metering system, and the operations of mixing, dispersing, grinding, and vacuuming are completed in the screw mixer to form a slurry, and then The slurry is continuously output from the screw mixer into the next production process.

The twin-screw mixing automatic production line has the advantages of high production efficiency, closed production, low material and energy consumption, etc., and has also been recognized in the industry.

Advantage:

1. Strong production continuity. The continuous mixing process is based on a twin-screw extruder, and the basic operations such as continuous raw material feeding, pre-mixing and kneading, fine dispersion and degassing are concentrated in a single device. The continuous mixing process includes all liquid and solid components. Controllable continuous feeding material and the microscopic distribution of solid particles in the liquid phase.

2. Less capital investment in equipment. With high production efficiency, the continuous mixing process can replace multiple batch mixers with one operating line. Therefore, the investment required for mass production equipment can be significantly reduced.

3. Reduce operating costs by virtue of energy saving, high degree of automation and less human resources required.

4. Enhance the repeatability and controllability of product performance.

5. Online quality control to achieve more stable product quality. Fully automated operations for raw material feeding (powders and liquids), stirring, dispersing and venting increase formulation accuracy, improve process control and enhance traceability.

shortcoming:

1. It is difficult to ensure the accuracy of the weightless scale. Due to the large difference in the proportion of additives and raw materials, in the non-stacked feeding method, a higher-precision loss-in-weight scale should be used to ensure the accuracy of feeding measurement, and ensure that various particles can enter the equipment continuously and accurately according to the formula ratio. Only in this way can the uniformity of the mixture be improved, thereby improving the quality of the battery.

2. The consistency of the material is poor, and the twin-screw design should adopt a reasonable combination of screw design to ensure the continuity of material entry and the uniformity of mixing.

plow mixer
Plough mixer is composed of transmission parts, agitator, circular barrel and high-speed flying knife. When the plough of the mixer is running at high speed, in addition to axially dispersing the material, it can also drive the material to flow around the circular barrel. Effectively solve the problem of material stratification, and the high-speed flying knife in the middle assists in mixing and dispersing and deaggregating the agglomerated material. The materials can be uniformly mixed in a short time under the dual action of the plowshare and the flying knife.

Advantage:

1. The mixing speed is fast. The application of the core technology of the new concept coulter stirring mechanism, coupled with the discrete stirring of the high-speed rotating cutter head, according to the different formulations of the product, the mixing time of the main machine is 90-180s.

2. The mixing accuracy of the mixing host is high. The workability and uniformity of various materials are good, no segregation occurs during mixing, and the mixing ratio of stirring can be as high as 1:10000, which can meet the construction requirements to the greatest extent.

3. The unloading adopts pneumatic door opening, and the unique opening method enables the unloading to be completed within 10 seconds;

4. The flying knife is made of manganese steel and equipped with a hard-toothed gear reducer, which can be started at full load;

5. The wear of the plowshare and flying blade can be replaced, and the liquid spray function can be added on the basis of dry powder mixing to make the solid-liquid mixing effect better.

shortcoming:

1. Poor production continuity. If the loading amount is too much, the material in the coulter mixer will affect the mixing effect, prolong the mixing time, and increase the power consumption because there is not enough space for movement in the coulter mixer. The amount of material is too small to form enough resistance, which weakens the mixing effect and prolongs the mixing time.

2. It is easy to cause the accumulation of materials, and the residue is not easy to clean after use.

Different slurry preparation schemes are used in various enterprises in the industry, and there is no conclusion on which one is better. North China Innovation Energy is committed to the research and development of slurry preparation technology, creating an advanced slurry preparation system, and providing industry customers with better solutions. Excellent slurry preparation solution.