The difference between wound lithium-ion batteries and laminated lithium-ion batteries
Lithium-ion batteries are divided into wound lithium-ion batteries and laminated lithium-ion batteries due to different processing methods. They have different principles and the same performance. So what is the difference between the lithium-ion batteries produced by these two methods? Which is better compared to laminated lithium-ion batteries?
Winding Lithium-Ion Batteries:
A battery composed of cells that are formed by winding together is called a wound battery. The wound battery is also called a battery core, and the battery industry insiders call it a rolled core.
Laminated Lithium Ion Batteries:
Generally, the Z-shaped lamination method is used for processing and production. The working principle of the laminated battery is the same as that of the traditional lithium-ion battery for electric vehicles.
Comparison of wound lithium-ion batteries and laminated lithium-ion batteries:
1. Comparison of battery discharge platforms:
The discharge platform for wound lithium-ion batteries is slightly lower. Due to the high internal resistance and large polarization, a part of the voltage is consumed by the internal polarization of the battery, so the discharge platform is slightly lower.
Laminated Li-ion battery discharge platform is high. Lower internal resistance and less polarization, so the discharge plateau will be higher than the wound cell and closer to the material‘s self-discharge plateau.
For many electrical equipment with high discharge cut-off voltage, laminated battery with high discharge platform is undoubtedly the preferred choice.
2. Battery capacity density comparison:
The capacity density of wound lithium-ion batteries is slightly lower. Due to the thickness of the tabs, the circular shape on both sides of the cell, and the thickness of the two-layer diaphragm at the end, the internal space is not fully utilized, and the volumetric capacity is therefore slightly lower.
Laminated lithium-ion batteries have higher capacity density. The internal space of the battery is fully utilized, so compared with the winding process, the volumetric specific capacity is higher.
The difference in battery capacity is only reflected in the two types of batteries that are thicker (insufficient utilization of the space on the side of the winding will be magnified) and thin (the thickness of the coiled tab will be magnified by occupying the thickness space in vain). For regular-sized batteries, the difference is there, but not particularly noticeable.
3. Battery energy density comparison:
The energy density of wound lithium-ion batteries is slightly lower. Due to the lower volume specific capacity and the lower discharge platform, the energy density is also not as good as that of the stacked process battery.
Laminated lithium-ion batteries have high energy density. The discharge platform and volumetric specific capacity are higher than those of the winding process battery, so the energy density is correspondingly higher.
For details, please refer to the enlargement platform and capacity density. In general, laminations are dominant.
4. Comparison of the applicable thickness of the battery:
The application range of wound lithium-ion batteries is narrow. Regarding ultra-thin batteries, the thickness of the tabs occupies an excessively large proportion of the space, which will affect the battery capacity. Regarding the ultra-thick battery, not only the pole piece is too long to control, but the space on both sides of the battery cannot be fully utilized, and the battery capacity will also be reduced.
Laminated lithium-ion batteries have a wide range of applications. Whether it is an ultra-thin battery or an ultra-thick battery, the lamination process can be competent.
Winding batteries have no advantage in ultra-thin and ultra-thick batteries, but at the same time, it should be noted that ultra-thin batteries are not widely used for the time being. Ultra-thick batteries can be realized by stacking two thinner batteries in parallel (however, it must be reduced by a certain amount.) capacity).
5. Battery thickness control comparison:
The thickness of wound lithium-ion batteries is difficult to control. Due to the uneven internal structure of the cell, the tabs, the end of the diaphragm, and both sides of the cell are prone to over-thickness.
The thickness of the laminated lithium-ion battery is easy to control. The internal structure of the cell is consistent, and the thickness of each part of the battery is correspondingly consistent, so it is easy to control its thickness.
Since the thickness of the wound lithium-ion battery is difficult to control, it is necessary to leave some margin in the thickness when designing, thereby reducing the design capacity of the battery.
6. Comparison of battery thickness deformation:
The wound lithium-ion battery is easily deformed. Due to the non-uniform internal structure, the degree and rate of internal reaction of the battery cells during charging and discharging are not uniform. Therefore, for thicker wound batteries, there is a possibility of deformation after high-rate charge and discharge or after repeated cycles.
Laminated lithium-ion batteries are not easily deformed. The internal structure is uniform, the reaction rate is relatively consistent, and even thick cells are not easily deformed.
This is also one of the reasons why wound batteries are not suitable for large thicknesses.
7. Battery shape comparison:
The wound lithium-ion battery has a single shape; it can only be used as a rectangular battery. Laminated Li-ion batteries are flexible in size. The size of each pole piece can be designed according to the size of the battery, so that the battery can be made into any shape.
Flexible size is an obvious advantage of the lamination process, but as far as the market is concerned, it seems that the demand for special-shaped cells is not very large.
8. Comparison of battery suitable fields:
The wound lithium-ion battery is only a conventional battery. Laminated lithium-ion batteries are used as high-rate batteries, special-shaped batteries, and power lithium batteries.
Because the lamination process has better rate performance and more choices of appearance and shape, the scope of application is also wider than that of wound batteries.
9. Battery coating comparison:
Coating requirements for wound lithium-ion batteries are high. For each pole piece, the coating film density of each part should not be significantly different, and the film density should be strictly controlled.
Laminated Li-ion battery coating requirements are low. Since the positive and negative electrodes are divided into many small pieces, the influence caused by the poor density of the coating film can be eliminated by dividing the small pieces before lamination.
Due to the improvement of the current process, it is not difficult to control the film density of the long pole piece of the wound battery within a range with little error, and it is very cumbersome to weigh and classify each small piece of the laminated battery. The point has little effect on the two.
10. Slitting:
The wound lithium-ion battery is easy to cut and has a high pass rate. As long as the positive and negative electrodes are cut once for each cell, the difficulty is small and the probability of defective products is low.
Laminated lithium-ion batteries are cumbersome to cut and have a low pass rate. Each battery has dozens of small pieces, and each small piece has four sections. The slicing process is prone to poor punching. Therefore, for a single battery, the probability of pole section and burr is greatly increased.
Although it is possible to strictly check the small pole pieces of the laminated battery through the screening after slitting, who has the time to check one by one when there are hundreds of thousands of small pole pieces?
11. Battery pole piece elasticity:
The coiled lithium-ion battery pole piece must have a certain elasticity. To prevent breakage and material loss at the bend.
Laminated lithium-ion battery pole pieces can be inelastic.
As long as there is no obvious problem with the coating of the pole piece ingredients, generally the pole piece can meet this condition.
12. Battery spot welding:
Easy spot welding of wound lithium-ion batteries. Each battery only needs to be spot welded in two places, which is easy to control.
Laminated lithium-ion batteries are prone to virtual welding. All pole pieces are spot welded to a single spot, which is difficult to operate and easy to solder.
It is not difficult to control the virtual welding in small batch production, but it is difficult to monitor and effectively solve the virtual welding in large batch production.
13. Battery production control:
Production control of wound lithium-ion batteries is relatively simple. One battery has two pole pieces for easy control.
The production control of laminated lithium-ion batteries is cumbersome. Each battery has dozens of pole pieces, and it is difficult to detect, transport, and count.
For a small-scale factory, the output of tens of thousands per day means millions of laminated pole pieces per day! If the output is hundreds of thousands, it may even be close to tens of millions of small pole pieces! The difficulty of turnover and monitoring in the production process can be imagined.
14. Operator requirements:
The wound lithium-ion battery has low operator requirements. It is difficult to complete the winding proficiently, but it is not difficult to complete the winding qualified. Once you understand the process and control the alignment of the pole pieces, you can get started.
Laminated lithium-ion batteries are demanding on operators. The lamination operation is difficult, and the too long and too wide design of the negative electrode sheet to the positive electrode sheet is generally not too large, so the operator needs to have a certain operation basis.
15. Battery entry threshold:
The barrier to entry for wound lithium-ion batteries is low. Manual winding is easy to operate, and manual operation can be considered when funds are insufficient, which saves the funds for purchasing large-scale automatic equipment and lowers the entry threshold.
Laminated lithium-ion batteries have high barriers to entry. The automation equipment is not yet mature, and the manual operation of the lamination process is cumbersome, resulting in an increase in labor costs, thus raising the entry threshold for lamination process batteries.
Lithium battery mid-stage process:
In the manufacturing process of lithium-ion batteries, the main process in the middle section is to complete the forming of the battery. The important technological processes include film production, pole piece winding, die cutting, cell winding forming and lamination forming, etc. Currently, the competition among domestic equipment manufacturers is relatively fierce. An area of ????accounting for about 30% of the value of lithium-ion battery production lines.
At present, the battery cell manufacturing process of power lithium-ion battery mainly includes two types: winding and lamination. The corresponding battery structure is mainly cylindrical, square, and soft pack. Cylindrical and square batteries are mainly produced by winding process. Soft pack battery The lamination process is mainly used. The cylinder is mainly represented by 18650 and 26650. The difference between the square and the soft package is that the outer shell is made of hard aluminum shell and aluminum-plastic film. Among them, the soft package is mainly based on the lamination process, and the aluminum shell is based on the winding process.
It is understood that the soft-package structure is mainly for the mid-to-high-end digital market, and the profit rate per unit product is higher. Under the same output conditions, the relative profit is higher than that of aluminum shell batteries. Because aluminum shell batteries are easy to form scale effects, and the product qualification rate and cost are easy to control, both currently have considerable profits in their respective market fields, and it is difficult for them to be completely replaced in the foreseeable future.
Because the winding process can realize high-speed production of cells through the rotation speed, and the lamination technology can improve the speed is limited, so the domestic power lithium-ion battery mainly adopts the winding process, so the shipment volume of the winding machine is currently more than Stacker.
The corresponding front process of winding and lamination production is the production and die-cutting of pole pieces. Production includes pole piece/pole lug welding after slitting, pole piece dust removal, sticking protective tape, pole lug wrapping and winding or cutting to length, wherein the winding pole piece is used for subsequent automatic winding, The cut-to-length pole piece is used for subsequent semi-automatic winding; the die-cut pole piece is to wind and punch the slitted pole piece for the subsequent lamination process.
To sum up, the wound lithium-ion battery is more suitable for rapid mass production, so the occupancy rate is higher, and the laminated lithium-ion battery has higher discharge performance and shape plasticity, and is irreplaceable in some special fields. The combination of technological lithium-ion batteries can better meet the needs of more users, and both wound lithium-ion batteries and laminated lithium-ion batteries have their own application areas. We don’t have to worry about which process is better. Only the more suitable is the most stable and best to use.
