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An article to understand the production process of lithium-ion flexible pack batteries

lithium battery

Lithium-ion battery is a kind of secondary rechargeable battery, which mainly relies on lithium ions moving between the positive and negative electrodes to work. In the process of charging and discharging, Li+ is embedded and de-embedded between the two electrodes: when charging, Li+ is de-embedded from the positive electrode and embedded in the negative electrode through the electrolyte, and the negative electrode is in the state of lithium-rich; and the opposite is true when discharging.best lithium ion battery machine company According to the shape, the common batteries in the new energy vehicle market are divided into three categories: square aluminum shell batteries, soft pack batteries and cylindrical batteries.

Soft pack lithium-ion batteries refer to batteries with aluminum-plastic film as the outer packaging. Compared with square aluminum shell batteries and cylindrical batteries, soft pack batteries in the event of safety hazards generally first flatulence, or from breaking the seal to release energy, not easy to explode, and thus higher safety performance; at the same time, the same capacity of soft pack batteries than the square aluminum shell is lighter,equipment for lithium battery assembly with a higher energy density. In addition, the shape of the soft pack battery can be customized according to the customer's needs, the design is more flexible, and more advantageous in the development of new models of batteries. Of course, the soft pack battery also has disadvantages, most of the current aluminum-plastic film relies on imports, and the production process is complex, the degree of automation of the production line is not as high as the square aluminum shell, production efficiency is low. In recent years, with the continuous improvement of lithium-ion battery production process and equipment improvements, the production efficiency of soft pack batteries is also improving.

Soft pack batteries are mainly composed of positive and negative electrodes, electrolyte, diaphragm and shell. The parts protruding from both ends of the battery are the battery lugs. The distribution of lithium ion battery lugs includes single-ended lugs and double-ended lugs. The structure of soft pack lithium ion battery is not difficult to find, including positive electrode, negative electrode, and diaphragm. In addition, soft pack batteries also need electrolyte as a channel for ion transportation.

The production process of lithium-ion battery is more complex, take Wanxiang one, two, three as an example, it mainly includes: screeding, coating, milling, punching, stacking, encapsulation, liquid injection, and chemicalization into several processes.

Homogenization: The pole piece of lithium-ion battery is the most important part of the core, homogenization refers to the lithium-ion positive and negative pole piece of the coated slurry preparation process, slurry preparation needs to be mixed with positive and negative materials, conductive agents and binders, the slurry prepared by the need for uniformity and stability. Different lithium battery manufacturers have their own homogenization process formula, the homogenization process of the charging order, charging ratio and mixing process have a great impact on the homogenization effect. After the end of the homogenization of the slurry solid content, viscosity, fineness and other tests to ensure that the performance of the slurry to meet the requirements. Coating: The prepared positive and negative electrode slurry needs to be coated on aluminum foil or copper foil and dried, this process is called coating. Coating process is the core process of lithium-ion battery manufacturing, which largely determines the performance of lithium-ion battery. The coated rolls should have a flat surface, uniform color, no exposed foil, particles, scratches, wrinkles and so on. Laminating: The coated pole piece also needs to be laminating, laminating is through the friction generated between the roll and the pole piece to pull the pole piece into the rotating roll, the battery pole piece is deformed by the pressure and densification. The lamination of the pole piece is the process of compaction of the material on the positive and negative plates, the purpose of which is to increase the compaction density of the positive pole or negative pole material. Appropriate compaction density can increase the discharge capacity of the battery, reduce internal resistance, reduce polarization loss, extend the cycle life of the battery, and improve the utilization rate of the lithium-ion battery. However, too large or too small compaction density is not conducive to the embedding or dislodging of lithium ions. Therefore, when the battery pole piece is rolled, the rolling force should not be too large or too small, and should be in line with the characteristics of the pole piece material.

Slitting and punching: Due to capacity and efficiency requirements, the pole rolls in production are relatively large, and the pole rolls after rolling need to be cut to the required size of the pole piece, and this process is the process of slitting and punching.

Stacking: After slitting, the pole pieces need to be stacked in the order of negative, diaphragm, positive, diaphragm, negative, diaphragm, positive, diaphragm, negative, this process is called stacking, and the stacked pole pieces are called cores. The stacking method mainly includes Z-shaped stacking and swinging stacking. Some manufacturers in this process process design using the winding process, compared to the winding process, the disadvantage of the stacking process is that the alignment accuracy of the pole piece to achieve the requirements of a high, and at present? Stacking machine efficiency level is low, the degree of automation specialization is low. However, the battery performance of the stacking process is more favorable than the winding process. With the new energy automobile industry continues to expand and economic development, taking into account the battery in the security, production line collective efficiency and other issues, stacked sheet process is still the trend of long-term development.

Encapsulation: the stacked battery cells also need to go through the pole lug welding, the welded battery cells placed in the aluminum-plastic film after punching the pit and top, side sealing and other processes, that is, encapsulation. The encapsulated core is shown in Figure 3. In addition to the body of the core, the aluminum composite film is still left, this part is called the gas bag, this is because the core in the process of formation will produce a large amount of gas, this part of the gas will be removed along with the gas bag in the degas process.

Liquid injection: Liquid injection is the process of injecting electrolyte into the encapsulated battery cell. The role of the electrolyte is to provide a carrier for the transmission of ions in the battery. Adding specific additives to the electrolyte can improve the performance of lithium-ion batteries in terms of safety or high and low temperatures. Chemical formation: After liquid injection, the battery still needs to be charged under low current, which is equivalent to the activation process of lithium-ion battery. During the first charging process, SEI film will be formed on the surface of negative electrode, and the performance of SEI film directly determines the multiplication rate and self-discharge performance of lithium-ion batteries, therefore, the quality of the battery is directly determined by the quality of the formation process. The formation process will produce a large number of gases, these gases will affect the performance of the battery, so the formation of the battery also needs to be degassed, that is, Degas process. In order to ensure the consistency of battery performance, lithium-ion batteries also need to be divided into capacity, internal resistance, self-discharge and other tests, the different performance of the battery for grouping.

The above process is the preparation process of single battery. The same group of single batteries is assembled according to a certain series-parallel connection, which can be used in electric vehicles, energy storage and other fields.