Besides raw materials, impurities introduced during the production process, such as process control and equipment wear, can reduce battery safety performance. This article will start from the process and analyze the key points to pay attention to at each step in order to improve the stability and subsequent safety performance of the battery cell remanufacturing process.
1. Homogenization
Slurry dispersion is the first step in lithium-ion battery manufacturing. As shown in the diagram, the tanks, stirring rods, and transport pipes of the homogenizing equipment are all made of metal, which can introduce metal impurities. Furthermore, long-term operation of the equipment can lead to wear and tear. Therefore, lithium battery manufacturers must clean the tanks before homogenization, regularly maintain the stirring equipment, clean the pipes promptly, and continuously monitor the performance of the batteries after homogenization. They must also establish their own internal cleaning standards to produce qualified lithium-ion batteries. It should also be noted that since many companies cannot guarantee that a homogenizing line only produces one type of battery, the pipes must be thoroughly cleaned when switching raw materials to prevent mixing of different batches of powder, which could lead to unnecessary performance and safety losses later. Of course, the frequency of cleaning and the standards after cleaning require long-term experimentation, as the requirements vary for different equipment and materials. I won't elaborate further here.
2. Coating
Regarding coating, cleaning each roller and repairing it after wear are quite important. This can prevent the introduction of impurities. Moreover, with the increasing popularity of double-sided coating equipment, coating speeds are getting faster and faster, and the length of coating equipment is also getting longer. Therefore, timely detection of problems will greatly improve battery safety.
3. Compaction
Similar to coating, as energy density increases, the compaction density of materials also increases. Therefore, cleaning and maintaining the rollers is the best way to prevent the introduction of impurities.
4. Slicing
For highly automated lithium-ion battery manufacturing companies, the positive and negative electrodes produced after slurry coating are quite wide, so they generally need to be slit. This slitting is typically done using a metal slitting blade to cut the wide strip into narrow strips to accommodate subsequent processes. This introduces a critical parameter: burrs. Burrs are directly related to safety; excessively large burrs can directly cause a short circuit in the battery. Therefore, burr control is a top priority among the parameters that every lithium-ion battery manufacturing company must control. How to control it? On the one hand, it depends on the precision of the equipment, the slitting process, and the requirements for lateral and longitudinal burrs; on the other hand, it depends on the maintenance of the slitting blade. Each company has its own control standards and inspection rules, which will not be elaborated upon here.
5. Laser cutting
The main purpose of this process is to use a laser to cut the tab part from the foil. Similar to slitting, the key control points are the level of burr control after laser cutting and whether dust and impurities can be cleaned and removed in a timely manner after laser cutting. This also depends on the level of automation of the equipment and a series of advanced online monitoring systems.
6. Winding/Laying
Regarding winding, the alignment of the winding, the degree to which the negative electrode covers the positive electrode, and the degree of burrs on the positive electrode, negative electrode, and separator after final cutting are the key control points;
