Exploring the Manufacturing Process Details of 18650 Lithium Battery Cells.

Exploring the Manufacturing Process Details of 18650 Lithium Battery Cells.

The production and manufacturing process of lithium batteries can be easily handled by professionals in the field of new energy. But can a simple process express the various difficulties of lithium battery manufacturing technology? Below are the key points of process control for lithium batteries.

1. Firstly, it is necessary to confirm and bake the incoming materials. Generally, conductive agents need to be baked at ≈ 120 ℃ for 8 hours, bonding agents PVDF need to be baked at ≈ 80 ℃ for 8 hours, and active materials (LFP, NCM, etc.) need to be baked and dried depending on the status and process of the incoming materials. The current workshop requires a temperature of ≤ 40 ℃ and humidity of ≤ 25% RH.

2. After drying, (wet process) it is necessary to prepare PVDF gel solution (solute PVDF, solution NMP) in advance. The quality of PVDF adhesive solution has a crucial impact on the internal resistance and electrical performance of batteries. The factors that affect gluing include temperature and stirring speed. The higher the temperature, the yellowing of the adhesive solution, which affects its adhesion; Mixing at too high a speed can easily damage the adhesive, and the specific speed depends on the size of the dispersing disk. Generally, the linear speed of the dispersing disk is 10-15 m/s (which is highly dependent on the equipment). At this point, it is required to turn on the circulating water for the mixing tank, with a temperature of ≤ 30℃.

3. The next step is to prepare the positive electrode slurry. At this time, it is necessary to pay attention to the order of feeding (slowly mix the active substance and conductive agent first, and then add the gel solution), feeding time, and feeding ratio, and strictly follow the process. Secondly, it is necessary to strictly control the equipment's revolution and rotation speed (generally the dispersion line speed should be above 17m/s, depending on the equipment performance, which varies greatly from manufacturer to manufacturer), as well as the vacuum degree and temperature of the stirring. At this stage, it is necessary to regularly check the particle size and viscosity of the slurry, which are closely related to the solid content, material properties, feeding sequence, and process technology (not described here, welcome to discuss). At this time, the conventional process requires a temperature of ≤ 30 ℃ and humidity of ≤ 25% RH, vacuum degree ≤ -0.085MPa.

4. After the slurry is prepared, it needs to be transferred to the transfer tank or coating workshop. When transferring the slurry, it needs to be sieved to filter out large particles, sediment, and remove ferromagnetic substances. There is a risk of battery self discharge or short circuit due to the influence of large particles on coating until the end; Excessive ferromagnetic material in the slurry can lead to defects such as excessive self discharge of the battery. The process requirements at this time are temperature: ≤ 40 ℃, humidity: ≤ 25% RH, sieve mesh ≤ 100 mesh, particle size ≤ 15um (parameters for reference only).

Negative electrode ingredients (the negative electrode is composed of active material, conductive agent, adhesive, and dispersant)
1. The conventional negative electrode system is a water-based mixing process (using deionized water as the solvent), so there is no need for drying of the incoming materials. This process requires the conductivity of deionized water to be ≤ 1us/cm. Workshop requirement temperature: ≤ 40 ℃, humidity: ≤ 25% RH.

2. After confirming the incoming materials, prepare the adhesive solution (composed of CMC and water) first. At this time, graphite C and conductive agent are poured into the mixer for dry mixing. It is recommended not to evacuate, but to turn on the circulating water (due to severe heat generation caused by particle squeezing and friction during dry mixing), with a low speed of 15-20 rpm and an interval of approximately 15 minutes for 2-3 scraping cycles. Next, pour the glue solution into the mixer and start vacuuming (≤ -0.09mpa). Scrape the material twice at a low speed of 15-20 rpm, then adjust the speed (low speed of 35 rpm, high speed of 1200-1500 rpm) and run for 15-60 minutes (depending on the wet process of each manufacturer). Finally, pour the SBR into the mixer. It is recommended to stir quickly and slowly at this time (SBR belongs to long-chain polymers, and if the speed is too high, the molecular chains may break and lose their activity if left too long). It is recommended to stir at a low speed of 35-40rpm and a high speed of 1200-1800rpm for 10-20 minutes.

3. Finally, measure the viscosity (2000-4000 mPa. s), particle size (35um ≤), and solid content (40-70%), and vacuum screen (≤ 100 mesh). The specific process values may vary depending on the material properties, mixing process, and other factors. Workshop requirement temperature: ≤ 30 ℃, humidity: ≤ 25% RH.