Main content:
Lithium-ion batteries can be classified into pouch, prismatic and cylindrical batteries according to the packaging method and shape. From the perspective of the internal molding process, pouch and prismatic batteries can be wound or stacked, and cylindrical batteries such as 18650 battery, 21700 battery, 4680 battery, etc. have curvatures everywhere, so they can only be wound.
The development time of the winding process is relatively longer, the process is mature, the cost is low, and the yield rate is high. However, comparing stacking battery vs winding, with the promotion and development of electric vehicles, the stacking process has become a rising star due to its advantages such as high volume utilization, stable structure, small internal resistance, and long cycle life.
1. Production process for stacking battery vs winding
Winding and stacking are the core links in the assembly process of lithium battery middle cells. Winding is a production process that rolls pole pieces, diaphragms, termination tapes, etc. that match in size after slitting into pole cores.
Different from stacking battery vs winding, stacking battery is a production process in which pole pieces and separators are alternately stacked together to finally complete the multi-layer laminated pole core.
From the perspective of battery shape, pouch batteries can only use stacking technology. The prismatic battery can use either the stacking process or the winding process, and the current mainstream is the winding process. Cylindrical batteries can only use winding technology.
2. Comparing process of stacking battery vs winding
|
Stacking |
Winding |
|
|
Energy density |
Higher. Higher space utilization. |
Lower. There is a C angle, and the larger the capacity, the lower the utilization rate. |
|
Structural stability |
Higher. The internal structure is uniform and the reaction rate is relatively low. |
Lower. There is a C angle, which leads to uneven rate of internal reaction of charging and discharging. |
|
Fast charging adaptation |
Better. The multi-pole plates are connected in parallel, the internal resistance is low, and the charge and discharge of large current can be completed in a short time, and the rate performance of the battery is high. |
Poor. During the charge and discharge process, the degradation rate of the active material at the high temperature position is accelerated, and the other positions are rapidly attenuated. |
|
Safety |
The risk is low. Stress distribution is more consistent, which keeps the interface flat and more stable. |
Lower. Potential problems such as powder shedding, burrs, pole piece expansion, and separator stretching are easy to occur at the bend. |
|
Cycle life |
Longer. Low internal resistance, relieve battery heating during fast charging, improve battery chemical system stability and prolong service life. |
Shorter. It is easy to deform in the later stage, which in turn affects the cycle life of the battery. |
|
Productivity |
Large-capacity batteries are generally low, mainly 6-8PPM. |
Higher, generally at 12-13PPM. |
|
Yield |
Low, the glitch problem is prominent. |
Higher automation, higher yield rate, higher number of pole pieces. |
|
Process maturity |
Low, the number of pole pieces is large, and the investment in equipment is large. |
Higher, fewer pole pieces, mature equipment and low investment cost. |
3. Advantages of stacking battery over winding battery
Higher battery energy density
There is a curvature at the corner of the winding, and the space utilization rate is lower than that of the stacking. The stacking battery can make full use of the corner space of the battery, so the energy density of the cell formed by the stacking is higher under the same volume of the cell design. Compared stacking battery vs winding battery, the energy density of stacking structures can be increased by about 5%.
More stable internal structure
Comparing stacking battery vs winding battery, the stacking battery does not have the problem of uneven internal stress at the corners. During the repeated use of the battery, the expansion force of each layer is similar, so the stacking battery can maintain a flat interface.
During the use of the wound battery, with the insertion of lithium ions, both the cathode and anode will expand, and due to the inconsistent internal stress of the inner and outer layers at the corner of the winding, wavy deformation will occur. This deformation will lead to the deterioration of the interface of the battery, uneven current distribution, and accelerate the instability of the internal structure of the battery.
Higher safety
The stacking battery is evenly stressed, there is no bending problem at both ends, and the battery safety is higher. However, compared stacking battery vs winding, after the pole pieces at both ends of the winding are bent, the coating material will be greatly bent and deformed, and the "C angle" bends are prone to powder drop and burr problems. In severe cases, it will cause an internal short circuit of the battery and cause thermal runaway.
Longer cycle life
The number of lugs of stacking batteries is twice that of winding, and the more the number of tabs, the shorter the electron transmission distance and the smaller the resistance.
It is well known that when the voltage and time are constant, the larger the resistance, the less heat generated, and the smaller the resistance, the smaller the heat generated, so the service life of stacking batteries is relatively longer than winding batteries to compare stacking battery vs winding battery.
4. Disadvantages of stacking battery over winding battery
The efficiency of the equipment is low, and the floor space of the stacking machine is larger than that of the winding machine.
High equipment investment
From the perspective of a single production line, a production line needs 10 winding machines. According to the price of 3-3.5 million RMB/set, the cost of a winding machine under a production line is about 30-35 RMB. The number of stacking machines required for a production line is related to the number of cells.
Low yield rate
The winding battery is easy to cut and has a high pass rate. Each battery cell only needs to cut the positive and negative electrodes once, which is less difficult. However, compared stacking battery vs winding, each battery has dozens of small pieces in stacking cutting, and each small piece has four cut surfaces, which is prone to defective products.
Difficult to control
There are only two pole pieces for winding a battery, and the winding spot welding is easy, and each battery only needs two spot welding, which is easy to control. However, different from stacking battery vs winding, the number of stacking pole pieces is large, and it is easy to have false welding. All the pole pieces must be spot welded to one solder joint, which is difficult to operate.
The winding process is to roll the slitted cathode and anode and the separator together by controlling the speed, tension, relative position, etc. of the pole pieces. The characteristics of the process make it only possible to prepare lithium batteries with regular shapes.
Compared stacking battery vs winding, the stacking process is to alternately stack the cathode and anode and the separator through the sheet feeding mechanism to form stacked cores, which can produce regular-shaped or special-shaped lithium batteries with higher flexibility.
5. Conclusion
The internal resistance of the winding battery is large, and the internal resistance can be greatly reduced through structural improvement. For example, the full tab structure can achieve a level of internal resistance similar to that of the stacking structure, but it requires higher equipment capabilities and quality control.
Different from stacking battery vs winding, the stacking battery has a flat structure, low internal resistance, and high space utilization. It shines in the field of power batteries. Some of top 10 lithium battery companies in the world represented by LG and BYD stick to the stacking route.
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