The most detailed analysis of the production process of lithium battery

Lithium ion batteries manufacturing has closed connected process. As a whole, the lithium battery manufacturing process produce including battery assembly process and the final injection fluid, prefilled, formation and aging process. In these stages of process, each working procedure can be divided into several key processes. Each step has made great influence on the performance of the battery.

Phase, the plate manufacturing process can be subdivided into slurry preparation, slurry coating, plate rolling, plate cutting, extremely dry process. It is understood that in a battery assembly process, and according to the different types of batteries, roughly divided into winding, into the shell, the welding process, etc. At the end of the liquid phase and including injection liquid, exhaust, sealing, prefilled, into each process such as, aging.

Battery manufacturing process of each working procedure can cause certain waste, the waste of the reasons of employee mistakes, equipment, environmental reasons and so on, in order to ensure that the cost of the product rate is good enough, just try to ensure that every step of the products are qualified.

A, the meaning of coating

Pulp slurry making the finished coating is the next working procedure, main purpose of this procedure is to have good stability, good viscosity and liquid paste evenly coated on is negative set fluid. Plate coating to the lithium battery has the vital significance, mainly reflected in the following:

1, the battery capacity of the products is of great significance

In the coating process, if the sheet before, during and after the three sections of location is anode paste coating thickness is not consistent, is easy to cause the battery capacity is too low, too high, are more likely to be formed in the process of cell cycle analysis lithium battery life.

2, has important significance for the safety of the battery

To do 5 s job before coating to ensure no, dust and other particles, sundries in the process of coating with extremely, if mixed with sundry will cause the battery internal micro short circuit, serious when the battery lead to fire explosion.

3, consistency of battery performance is of great significance

Battery plant more taboo is a batch of battery, large capacity, circle life differences, so in the process of plate coating to ensure the parameters before and after the pole piece.

4, have important significance to the battery life-span

Large difference of pulp before and after coating, sheet was mixed with dust, the thickness of the sheet or so uneven, and so on, all the pros and cons of electrochemical properties related to the battery.

So, the process of slurry coating requirement is: under the condition of paste is good enough, the pole piece live behind the material before, during and density is consistent, without impurities mixed with coating process. The sheet was good or bad, of course, to determine the effect of the definition is not just in the coating, if serious pole piece appear off powder, no resistance to bending, the phenomenon such as pole in a white bubble, this is where the problem of the thick liquid material, need to return to the first step to solve.

Second, the coating way

It is understood that down roll coating equipment is mainly composed of unit, feeding unit, tension control system, coating head, oven and other parts. Coating can be divided into transfer coating, and extrusion coating and two kinds of type, both have its advantages and disadvantages.

1, transfer coating

Coating roller rotation driven pulp, by adjusting the blade clearance to adjust the size as follows, and use the back roll or roller rotation will paste is transferred to the substrate, according to the technological requirements, control the thickness of coating layer to meet the weight requirements, at the same time, by heating to remove solvent in flat out on the base material of slurry, the solid material well bond on the substrate. As shown in figure 1.

Comprehensive analytical lithium battery pole piece production process

Its advantage is the pulp viscosity requirements is not high, easily by adjusting the parameters of the coating, no plugging material and so on, the shortcoming in power battery poorly coating for accuracy and ensure consistency of pole piece. Pulp exposed to the air between the rollers, have some influence on the properties of the pulp.

2, the extrusion type coating

Feeding system to transfer coating for screw pump, then will power delivery to paste extrusion head, made by extrusion form will paste on the collection of fluid liquid film coating to move, after drying to form uniform texture coating, as shown. Its advantage is after coating sheet is very uniform and high precision, high coating edge roughness, closed operating system, not influenced by foreign bodies, suitable for mass production. Its shortcoming in the high accuracy and high maintenance requirements, paste viscosity range demand is high, transformation specifications need to replace the new gasket.

Comprehensive analytical lithium battery pole piece production process

Third, the questions needed to attention in coating

Reduce coating defects in the process of coating and improve the quality of coating and the yield, cost reduction is an important content of coating process need to study. Coating process of waste is mainly the initial tuning machine (related to engineer operation level), foil coated interrupt, mixed with foreign body, etc., with every stop, the waste will produce a certain distance.

Often appears the question is: in coated material pollution, coating process is not stable, the operation is not standard, drying program setting error, etc., these problems will often cause the following problems:

Point defects

Mainly comes from the slurry bubble and entering of foreign body. It is understood that bubbles can be from the mixing of deaeration not completely, the working process of the feeding in or coating process. Foreign body mainly comes from the operation mistakes or environmental problems.

Spray coating process, the pulp internal bubbles on the pole piece, after oven to dry, the bubble burst, white round spot on the sheet forming. Here live material coating is thinner, also most likely to cause in the process of battery charging and discharging micro short circuit. Pole in the presence of a foreign body, around the particles coating is low surface tension, liquid membrane into the surrounding FaSheZhuang migration, formation of point defects. Means to prevent such defects are: control the operating environment, optimization of pulp mixing, controlling coating speed, ensure base material is clean.

Thick edge defects

Sheet in rolling process, thick edge under more pressure, not only cause pole piece on the horizontal density is different, also can cause thick edge living particles are being crushed. Thick edge defects after pressing plate, there will be more severe warping phenomenon, in the process of subsequent cutting, winding will also have a big impact. Thick side live particles after being crushed, in the process of charging and discharging lithium ions and electrons transfer path becomes far, will cause the battery internal resistance increasing deepen, affect the service life of the battery and security.

At the same time, because of the thick plate edge inside the core winding form stress concentration point, analysis the easily happened lithium and micro short circuit, the battery performance is extremely unfavorable. Causes of webbing is driven by the surface tension of pulp slurry to plate edge, no coating in migration, formation of thick edge after drying.

Research found that coating speed had no significant effect on the edge width and height, with the edge gradient coating increases with increasing speed, reduce the clearance ratio (coating clearance/membrane layer thickness), can reduce the edge effect. Related clearance coating the research results show that by adjusting the coating clearance, pressure adjustment also can reduce the thick edge. Using the method of adding surfactants reduce the surface tension of slurry can also be a certain extent, reduce the happening of the thick edge.

Fourth, the future development trend of the coating process

Extrusion type coating with high precision, and the advantages of uniform coating, suitable for larger width coated is widely applied in the field of power battery, and it also gradually replace transfer type coating machine is suitable for pilot line. The future coating process will toward high device performance, high grain rate, online thickness control precision, improve the efficiency of drying, etc.

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