With the large use of lithium batteries as power sources in mobile phones, digital products, notebook computers, drones, aircraft models, power tools, military, new energy vehicles, portable energy storage, medical equipment, etc., the domestic lithium battery industry has achieved rapid development. As an important part of the manufacture of lithium batteries, the stacking and winding technology has received extensive attention in the academic and commercial circles.
At present, China’s lithium battery manufacturers are mainly concentrated in the coastal areas of Guangdong Province. Among them, GREPOW battery is also one of the best, today we will share the winding and stacking technology and its characteristics.
About stacking and winding
What Is Winding Technology？
Winding technology: such as a cylindrical battery, the technology is to stack the raw materials in the order of the negative electrode, the separator, the positive electrode, and the separator, and directly roll into a cylindrical shape by a winding method, and then placed in a metal casing;
What Is Stacking Technology？
Stacking technology: for example, a soft-clad battery, relying on a “stack”, such as a “z”-shaped stacking, first cutting the positive and negative materials into rectangular pieces of the same size, and then stacking them on the diaphragm, respectively. The Z” shape runs through it, separating the two poles, and finally wrapping the aluminum-plastic packaging;
|Item||Winding technology||Stacking technology|
|Higher internal resistance||Lower internal resistance|
|Normally, there is only a single tab for both the positive and negative electrodes.||It is equivalent to a plurality of small pole pieces connected in parallel, which reduces the internal resistance.|
|Low rate discharge capacity||High rate discharge capacity|
|It is difficult for a single-pole to fully discharge at large currents.||The multi-pole parallel connection makes it easier to discharge large currents in a short time.|
|Low discharge platform||High discharge platform|
|Due to the high internal polarization and high polarization, a part of the voltage is consumed in the internal polarization of the battery, so the discharge platform is slightly lower.||The lower internal resistance is less polarized, so the discharge platform will be higher than the wound battery and closer to the material’s self-discharge platform.|
|Low capacity density||High capacity density|
|Due to the thickness of the tabs, the circular shape on both sides of the cell, and the two layers of the closed film to occupy the thickness in vain, the internal space is not fully utilized, and the volume-specific capacity is thus slightly lower.||The internal space of the battery is fully utilized, and thus the volumetric specific capacity is higher than that of the winding process.|
|Low energy density||High energy density|
|Due to the low volumetric capacity and the low discharge platform, the energy density is not as good as the stacking technology battery.||The discharge platform and volume-specific capacity are higher than the winding technology battery, so the energy density is also relatively high.|
Scope of application
|Narrow application||Wide range of application|
|For ultra-thin batteries, the thickness of the tabs takes up too much space and affects the battery capacity.||Whether it’s an ultra-thin battery or an ultra-thick battery, the stacking technology can do the job.|
|Applicable to narrow thickness, the thickness is difficult to control||Thickness is easy to control and not easy to deform|
|For the ultra-thin battery, the thickness of the tabs takes up too much space and affects the battery capacity. For ultra-thick batteries, not only are the coils too long to be controlled, but the space on both sides of the battery cannot be fully utilized, and the battery capacity is also reduced. Moreover, the thickness is difficult to control. Because the internal structure of the cell is not uniform, the ends of the ear, the end of the diaphragm, and both sides of the cell are easy to be thick.||The internal structure of the battery core is the same, and the thickness of each part of the battery is also consistent, so it is easy to control the thickness. At the same time, the internal structure is uniform and the reaction rate is relatively uniform, even if the thick cell is not easily deformed.|
|The battery has a single shape, is easily deformed, and can only be made into a conventional battery.||Flexible size, suitable for high-rate batteries, shaped batteries, power batteries, etc.|
|Since the internal structure is not uniform, the degree of reaction inside the cell and the rate are not uniform during charging and discharging; therefore, for a thick wound battery, there is a possibility of deformation after charging or discharging at a large rate or after a plurality of cycles. Moreover, it can only be used to grow square batteries.||Each pole piece size can be designed according to the size of the battery so that the battery can be made into any shape. such as the following: Curved Battery, Round Batteries, Triangle Battery, Hexagon Battery, Ultra Narrow Battery, C Shape Battery, D Shape Battery, Polygonal Battery|
The advantages of “stacking”
1. After working for a period of time, the positive and negative pole pieces will have a certain degree of expansion. The battery of the winding method is at the corner. Due to the different degrees of internal and external expansion, wave deformation will occur, which makes the internal structure of the battery unstable. In severe cases, breakage may occur, causing an accident;
2. The battery of the stacking piece, each layer will only expand up and down, the internal structure is still flat, and it is safer in comparison. In the safety tests such as vibration, extrusion, water immersion, and acupuncture, the battery exceeds the national standard. In addition, the stacking method is because each of the positive and negative electrodes is isolated from each other so that each pole piece is provided with one tab and then welded together to form a final positive and negative electrode;
3. But the winding method in order to reduce the process, only a few layers to install a polar ear, the total is usually only half of the former, however, the polar ear acts as a wire for the battery, because the stacking method has more polar ears, its The cross-section is also larger than the winding method, and the resistance is also reduced so that the battery generates less heat during operation and is less prone to expansion.
4. Because of the rectangle battery currently used in electric vehicles, but the square-shell battery is bulky, the winding method will inevitably form a curvature at the four corners, creating a gap in the square shell, and the stacking method can make full use of the space, as much as possible With a square shell, the energy density will be about 5 percent higher than the former.
Is the battery cell made by stacking or winding better?
For consumer batteries, efficiency is increased compared to battery capacity and performance, so customers have a need for winding processes. However, for the power battery, considering the future of the battery is bigger and stronger, the industry generally believes that the stacking technology can give full play to the advantages of large-scale batteries, which have advantages over the winding in terms of safety, energy density, and process control. Therefore, in the field of power batteries, stacking technology is an application trend in the long-term development of soft pack batteries. At the same time, it can better control the cell yield, and the most important thing is to pursue high energy density, so stacking technology is the best choice in the future.
GREPOW’s decoding of key technologies for lithium battery stacking is the future for China’s lithium battery manufacturing industry.
Perhaps, the choice of no right or wrong, winding, and stacking is still determined by the market.