Comparison of lithium-ion batteries with two different structures: winding and stacking
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Winding Lithium-Ion Battery:
A battery composed of cells formed by winding electrode materials is called a winding battery. The winding battery is also known as a cell or winding cell in the battery industry.
Stacking Lithium-Ion Battery:
Power batteries are generally available in three forms: prismatic, pouch, and cylindrical. They often employ two different manufacturing processes: winding and stacking. The stacking battery refers specifically to lithium-ion batteries used in electric vehicles that utilize the stacking process.
The stacking battery operates on the same principle as traditional lithium-ion batteries used in electric vehicles. It consists of a positive electrode, negative electrode, separator, and electrolyte, utilizing the movement of lithium ions to generate electricity.
Which Is Better: Winding Lithium-Ion Battery or Stacking Lithium-Ion Battery?
1. Discharge Platform Comparison:
Winding Lithium-Ion Battery: The discharge platform of winding lithium-ion batteries is slightly lower. Due to higher internal resistance and larger polarization, a portion of the voltage is consumed within the battery due to polarization, resulting in a slightly lower discharge platform.
Stacking Lithium-Ion Battery: The discharge platform of stacking lithium-ion batteries is higher. With lower internal resistance and smaller polarization, the discharge platform of stacking batteries will be higher than that of winding batteries and closer to the material’s inherent discharge platform.
For many devices that require a higher cut-off voltage during discharge, the higher discharge platform of stacking lithium-ion batteries would be the preferred choice.
2. Capacity Density Comparison:
Winding Lithium-Ion Battery: The capacity density of winding lithium-ion batteries is slightly lower. Factors such as the thickness of tabs, the cylindrical cell, and the two layers of separator at the ends occupying space can result in the internal space not being fully utilized, leading to a slightly lower volumetric capacity.
Stacking Lithium-Ion Battery: stacking lithium-ion batteries have higher capacity density. The internal space of the battery is utilized more efficiently, resulting in a higher volumetric capacity compared to the winding battery.
The difference in capacity is more pronounced in batteries with thicker tabs (insufficient utilization of space at the winding side) and thinner tabs (space occupied by the winding tabs). However, for general standard-sized batteries, the difference exists but may not be particularly significant.
3. Energy Density Comparison:
Winding Lithium-Ion Battery: The energy density of winding lithium-ion batteries is slightly lower. This is due to the lower volumetric capacity and lower discharge platform compared to stacking batteries.
Stacking Lithium-Ion Battery: stacking lithium-ion batteries have higher energy density. The higher discharge platform and higher volumetric capacity contribute to a higher energy density compared to winding batteries.
In summary, considering both the discharge platform and capacity density, stacking batteries have an advantage in terms of energy density.
4. Thickness Suitability Comparison:
Winding Lithium-Ion Battery: winding batteries have a narrower range of suitability in terms of thickness. For ultra-thin batteries, the thickness of the tabs occupies a significant proportion of the space, which can impact the battery’s capacity. For ultra-thick batteries, it becomes challenging to control the winding of excessively long electrode strips, and the space on both sides of the battery cannot be fully utilized, resulting in reduced capacity.
Stacking Lithium-Ion Battery: stacking batteries have a wider range of suitability in terms of thickness. Whether it is for ultra-thin or ultra-thick batteries, the stacking process can accommodate such requirements.
Winding batteries do not have an advantage in terms of ultra-thin or ultra-thick batteries. However, it’s worth noting that ultra-thin batteries are not widely used at the moment. For ultra-thick batteries, it is possible to achieve the desired thickness by stacking and connecting two thinner batteries in parallel (although at the cost of reduced capacity).
5. Thickness Control Comparison:
Winding Lithium-Ion Battery: It is challenging to control the thickness of Winding batteries. Due to the non-uniform internal structure of the cell, areas such as the tabs, ends of the separator, and edges of the cell are prone to thickness variations, resulting in difficulties in thickness control.
Stacking Lithium-Ion Battery: Stacking batteries are easier to control in terms of thickness. The internal structure of the battery is consistent, and the thickness of different parts of the battery is correspondingly uniform, making it easier to control the overall thickness.
Due to the challenges in thickness control for Winding lithium-ion batteries, design considerations often require leaving some margin in the thickness, which can result in a reduction in the design capacity of the battery.
6. Thickness Deformation Comparison:
Winding Lithium-Ion Battery: Winding batteries are prone to deformation. Due to the non-uniform internal structure, the reaction degree and rate inside the cell during charging and discharging are uneven. Therefore, for thicker winding batteries, there is a possibility of deformation after high-rate charging or discharging cycles.
Stacking Lithium-Ion Battery: Stacking batteries are less prone to deformation. With a uniform internal structure and consistent reaction rates, even thick cells are less likely to deform.
This is also one of the reasons why winding batteries are not suitable for achieving very large thicknesses.
7. Shape Comparison:
Winding Lithium-Ion Battery: Winding batteries have two kinds of shape and are typically in the form of rectangular prisms. They are limited to this specific shape.
Stacking Lithium-Ion Battery: Stacking batteries offer more flexibility in terms of shape. The size of each electrode can be designed based on the desired battery dimensions, allowing for the creation of batteries in various shapes.
The flexibility in size is a clear advantage of stacking battery technology. However, in the current market, the demand for non-rectangular batteries appears to be relatively low.
8. Suitable Applications Comparison:
Winding Lithium-Ion Battery: Winding batteries are primarily used for conventional applications, where standard-shaped batteries are required.
Stacking Lithium-Ion Battery: Stacking batteries are suitable for high-rate applications, non-standard shapes, and power applications. Their superior rate performance and the ability to create batteries in various shapes make them more versatile in terms of application.
Due to the better rate capability and the wider range of options in terms of appearance and shape, stacking batteries have a broader range of applications compared to winding batteries.
Winding Lithium-Ion Battery: Slitting winding batteries is convenient and has a high yield rate. Each cell only requires one slitting（relative machine：slitting machine） operation for the positive and negative electrodes, which is relatively simple and has a low probability of producing defective products.
Stacking Lithium-Ion Battery: Slitting stacking batteries is more intricate and has a lower yield rate. Each battery consists of multiple small strips, and each strip has four cutting surfaces. The slitting process is prone to defects, such as uneven cuts or burrs, which significantly increases the probability of producing electrode fragments or burrs on individual batteries.
10. Battery Spot Welding:
Winding Lithium-Ion Battery: Spot welding wound batteries is relatively easy. Each battery only requires two spot welds, which makes it easier to control the welding （relative machine：welding machine）process.
Stacking Lithium-Ion Battery: Spot welding stacking batteries is more prone to pseudo soldering . All the electrode strips need to be spot welded to a single point, which can be challenging to perform and increases the risk of incomplete welds.
Controlling pseudo soldering is not difficult for small-scale production. However, in large-scale production, it becomes challenging to monitor and effectively address the issue of incomplete welds.