What are the main points of Lipo 6000mah coated pole piece drying?

With the reduction of the manufacturing cost of Lipo 6000mah and the improvement of product performance, Lipo 6000mah has been used more and more in people's lives. This puts forward higher requirements for the product performance of Lipo 6000mah, and also puts forward higher requirements for the manufacturing process of Lipo 6000mah.

One of the core processes of Lipo 6000mah is the preparation of pole pieces. After the positive and negative pole pieces are prepared, the electrolyte is injected into the battery through winding or lamination processes, and it becomes a usable battery after being activated by packaging, charging and discharging.
Among them, the battery pole piece is a composite material with a sandwich structure, which is mainly composed of two-sided porous coatings composed of active material particles, binders and conductive agents, and a metal current collector foil sandwiched in the middle.

After the preparation of positive and negative electrode slurry is completed, it is coated on aluminum foil and copper foil through a coating process. Next, let’s explore the drying knowledge of Lipo 6000mah coated pole piece with professional Lipo 6000mah manufacturer Chinahobbyline. I will introduce the Lipo 6000mah pole piece coating process, pole piece drying technology, drying process parameters and pole piece defects in detail.

1 Lipo 6000mah pole piece coating process

For the coating process of the Lipo 6000mah pole piece, drying of the Lipo 6000mah pole piece after coating is one of the main energy consumption units and is also the focus of research. The residual solvent in the drying process of Lipo 6000mah pole piece has a great influence on the stability, capacity and cycle life of the subsequent processing of Lipo 6000mah pole piece.

The process not only affects the manufacturing cost of the battery, but also indirectly determines the level of manufacturing technology and the safety of the battery. Due to the lack of in-depth research on the coating and drying process of Lipo 6000mah pole pieces, it is generally difficult to qualitatively improve the drying efficiency at present.

2 Lipo 6000mah pole piece drying technology

The immediate purpose of drying is to facilitate efficient and rapid removal of solvent from the coating slurry. There are many drying methods for Lipo 6000mah pole pieces. The common drying methods mainly include hot air drying (convection hot air drying, double-sided air supply floating drying, circulating hot air impact drying), superheated water vapor drying, far-infrared radiation drying and microwave drying.

Each method has its own advantages and disadvantages, and has its application, which mainly depends on the setting of the respective process parameters and the control requirements for the residual amount of solvent.

1) Hot air drying

The conventional hot-air drying method is the earliest widely used method, and the equipment is simple and easy to operate. The heat in hot-air drying comes from electrical energy or steam heat. The particle size of the active material in Lipo 6000mah pole piece slurry is nano-scale, and the characteristic diameter of the particle pores is about tens of nanometers when dried, which has the characteristics of capillary porous media.

Therefore, when the coating slurry is dried, the solvent removal method has a great influence on the uniform distribution of the electrode active material.
Lipo 6000mah pole piece drying process
Generally, double-sided air supply floating drying is used to dry the sheet on both sides, which has high drying efficiency and excellent drying effect. , and increase the difficulty of the foil strip, easy to break the belt and cause downtime. On this basis, the developed circulating hot air impingement drying has high working efficiency.

This method sprays hot air onto the surface of the coating slurry at a high speed, which weakens the unevenness of the coating surface and improves the thickness consistency of the coating layer. In practice, the drying process is adjusted by adjusting the air volume and air temperature in sections, which requires large investment and complicated maintenance.

2) Infrared drying

Different from hot air drying, infrared drying can remove capillary moisture and surface residual moisture in Lipo 6000mah electrode coating, which is especially suitable for high-energy electrode coatings with large thickness. Infrared radiation drying mainly uses infrared rays to evaporate the solvent, the drying process is simple, the heat is concentrated, and the drying speed is fast.
It is usually combined with convection drying to form a hybrid drying system. Due to the difference in coating thickness, the non-uniformity of infrared drying temperature has not been completely resolved, and the slurry drying efficiency for non-aqueous solvents is insufficient.

3) Microwave drying

The microwave drying technology promotes the removal of moisture from the Lipo 6000mah pole piece through microwave dielectric heating. The microwave is volume heating, and the free water inside the Lipo 6000mah pole piece is first vaporized during drying, forming a high evaporation pressure gradient and accelerating the internal water migration. Microwave mixing and drying can greatly improve the drying efficiency, and the damage to the coating is small during drying, but it is easy to cause bulging and frying of Lipo 6000mah pole pieces.

Microwave drying equipment
In practice, various battery manufacturers often do not use a certain drying method alone, but combine drying technologies such as infrared and microwave on the basis of hot air drying to improve drying efficiency. Although infrared drying can make up for the shortcomings of microwave-assisted technology, the uniformity of infrared rays is poor, resulting in inconsistent drying rates of Lipo 6000mah pole pieces and reducing the capacity consistency of cells.

3 Drying process parameters and Lipo 6000mah pole piece defects

At present, the main drying method is still hot air drying. During drying, the hot air speed, air temperature, coating thickness, slurry characteristics and drying equipment structure all affect. The good drying process ensures the uniform coating of the slurry fluid, improves the consistency of the power battery, ensures the good dispersion of the active material, and forms an electrolyte channel to increase the charge-discharge rate of the active material.

Poor drying may cause various defects such as agglomeration, pinholes, uneven thickness, scratches, and tailing of the coating layer. Improper operation of the drying process will directly cause the performance of the power battery to decline, and the consistency of each batch of Lipo 6000mah pole pieces will deteriorate, which will seriously affect the yield of the assembly process section and the cycle life of the module.

The overall drying time of the coating layer is short, mainly considering the influence of hot air temperature, wind speed and slurry solid content (solvent content).

1) Hot air temperature

In the initial stage, the temperature to be used for different solvents is different. For example, the water-based solvent is not easy to dry at low temperature, and the temperature is low, and the maintenance time of the constant speed section is longer. Generally, when the hot air temperature of water-based slurry is 90℃, the drying rate of Lipo 6000mah pole piece is faster and the drying defect is less.
The study found that when the drying temperature is lower, the distribution of the binder is more uniform, and the bonding between the current collector and the active material is stronger.

The high drying temperature not only tends to cause local enrichment of the binder, but also has poor surface flatness, which reduces the yield of the winding process. This is because the excessive temperature will harden the surface of the Lipo 6000mah pole piece, resulting in cracking and wrinkling of the Lipo 6000mah pole piece. During the drying process, the coating solvent evaporated continuously and the viscosity increased rapidly, but the migration rate of the surface solvent was higher than that near the foil end. Due to drastic changes in surface tension, honeycomb networks, thick edge defects or agglomeration of binder/solid particles are prone to occur.
aggregate formation defect

2) Hot air speed

Excessive air flow speed during hot air drying will lead to uneven coating, which directly affects the performance of the power battery. Therefore, the air flow speed should be controlled at different stages. Generally, slurries with lower viscosity are more sensitive than those with higher viscosity. In order to reduce the flow and damage of the coating layer, it is necessary to use low air speed for drying.
If the air speed of the oven is too large, the coating layer is prone to bubbles. This is because there is a lot of dust accumulated in the air ducts in and out of the coating oven, and increasing the air volume (wind speed) is easy to roll up the accumulated dust, which is scattered on the surface of the wet coating and produces a large number of air bubbles. The speckle defect is the formation of pattern-like speckles, which is mainly caused by the unstable flow rate of hot air.
Pit bubbles appear in Lipo 6000mah pole piece

3) Coating thickness

The thickness of the coating layer is mainly determined by the design parameters of the battery's charge-discharge and capacity characteristics. The coating is thicker, the capacity is larger but the charge-discharge rate is limited. The coating is thin, the battery charge and discharge rate is large and the capacity is correspondingly limited, and the coating dries quickly, and the coating defects are relatively few.
It is generally believed that a thicker coating layer is conducive to the release of drying stress, the coating adhesion is better, and the coating is thinner, and the segregation of inactive materials such as binders is weaker.

The interface analysis of the active material after drying shows that the current collector resistance is mainly affected by the uneven dispersion of the conductive agent, while the coating thickness is not significantly affected. If the coating thickness is not properly controlled, it is easy to cause defects such as wrinkles and streaks.
Stripe defect of Lipo 6000mah pole piece

4) Slurry properties

The influence of the slurry is mainly reflected in the content and type of the solvent, as well as the dispersion and adhesion characteristics of the active substance. The drying of Lipo 6000mah pole piece is greatly affected by the coating process, requiring uniform coating without obvious particles.

When drying, the relative dryness of hot air is generally reduced by partial return air in the front section to avoid excessive removal of the surface solvent, while the latter section requires that the temperature can be appropriately increased to improve drying efficiency and reduce solvent residues. In the early stage of drying, the fluidity of the slurry is large, the characteristics of the solvent affect the drying process, and the particle rearrangement process of the active substance occurs during the dispersion process.

The solvent content in the later stage of drying is low, and the coating layer basically loses its fluidity. The dispersibility of active substances and the binder are the main factors affecting the later drying.
Usually the dispersibility of the binder is affected by the drying rate, and the agglomeration is obvious if the operation is improper, which may be due to the enrichment of the binder caused by the evaporation of a large amount of solvent.
Summarize
Lipo 6000mah pole piece drying involves the transport of multiphase materials at different scales, with complex physical processes and diversified drying processes. The aggregation mode of the coating binder during the drying process is greatly affected by the drying process, and the microporous channels formed by the active material agglomerates have different transport processes at different scales. In practice, the performance of coating slurry, coating method, and subsequent manufacturing processes such as rolling need to be comprehensively considered.

The research on the relationship between the drying process of Lipo 6000mah pole piece and the cost and quality of Lipo 6000mah pole piece is still insufficient, and there is a lack of detailed research on special drying equipment for Lipo 6000mah production. It is necessary to continuously accumulate coating and drying process data and experience. This in turn optimizes the coating drying method.
The above is the whole content of lithium battery pole piece drying brought to you by CNHL, a lithium battery company. I hope that the introduction of the above content can help you better understand lithium batteries. For more information on lithium batteries, please refer to the following:
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