With the rise of pure electric vehicles, power battery as its core component has attracted much attention. The battery we see in the car is actually a battery pack pack made of a combination of many battery cells.At present, the mainstream types of battery cells on the market include ternary and lithium iron phosphate, whose upstream covers positive and negative electrode materials, diaphragm, electrolyte, and the production equipment of the battery cells.
Take the manufacturing process of lithium iron phosphate core as an example, let us understand its production process:
1, the former process: first of all, the positive electrode materials (such as lithium iron phosphate active materials, graphene conductive agent, PVDF adhesive) and negative electrode materials (such as graphite carbon powder, non-carbon materials) are mixed and stirred, this process is called slurry mixing. Next, the positive electrode material is coated on aluminum foil and the negative electrode material is coated on copper foil to form the positive and negative electrode wafers, this step is called coating. After that, the pole piece is rolled, slit and die-cut.
2. Intermediate process: The positive and negative electrode sheets are separated by a diaphragm, and then wound or stacked into a core using a winding machine or a stacking machine, followed by encapsulation and liquid injection.
The picture above shows the winding process, in which the left side of the pole piece and the diaphragm are wound up by rotating the core in the process.
The picture above shows the stacking process, in which the positive pole piece, the diaphragm and the negative pole piece are stacked sequentially by sliding the processing core left and right above the lower slide.
3. Post-processing: Includes formation (i.e., the first charge to activate the battery), sorting (detecting the battery capacity through charging and discharging), and sorting (classifying the battery according to its capacity in order to optimize the consistency of the battery pack).
In the entire manufacturing process, the midstream winding and stacking processes are the most critical, and they represent two different technological solutions.
Stacking process has the following advantages in performance compared to winding process:
1. Stacking process can more fully utilize the battery edge space, and the energy density under the same volume is about 5% higher than the winding process.
2. Stacking process can avoid the expansion of positive and negative electrode plates during the use of the battery, ensuring a more uniform current distribution and a more stable internal structure.
3. In the cycling process, the internal stress distribution of the battery using the laminated process is more uniform, thus improving the safety of the battery.
In addition, compared with wound batteries, stacked cells have a larger number of lugs, lower internal resistance, and less heat production, so the battery cycle life is correspondingly increased by 10%.
Despite its disadvantages in terms of productivity, yield and investment costs, the blade stacking process is still undergoing rapid development. For example, BYD’s razor blade batteries and Hive Energy’s short razor batteries both use the stacked-chip process to achieve a flat and long battery design.