After dividing and drying the battery electrodes, the next step is to make the battery cells. The production methods of battery cells can be divided into two types: stacked and wound. The stacking method involves cutting the positive and negative electrode plates and separators into specified sizes, then stacking the positive electrode plates, separators, and negative electrode plates into small cell units, and then stacking and paralleling the small cell units to form a large cell, as shown in Figure 1.

The winding method is a process in which the segmented electrode is fixed on the winding needle and the positive electrode, negative electrode, and diaphragm are rolled into a battery cell as the winding needle rotates, as shown in Figure 2. Here, parameters such as the size of the polarizer and the number of coils wound are determined based on the design capacity of the battery. Both methods have their own advantages and disadvantages. Below, we will compare them from three perspectives: battery electrochemical performance, safety performance, and processing technology.

1. Positive electrode feeding mechanism 2. Diaphragm unwinding mechanism 3. Negative electrode feeding mechanism 4. Rolling roller 5. Winding mechanism 6. Sealing and cutting mechanism
1、 Electrochemical performance of batteries
1. Different internal resistance of the battery
The battery cells produced by the stacked process have lower internal resistance, while the wound process has higher internal resistance. Because wound cells are usually single pole eared, while stacked cells can be seen as multi pole eared, greatly reducing their internal resistance. Different internal resistances result in different heat generation and capacity decay rates in the charging and discharging cycles of finished batteries. It is evident that the capacity decay of stacked batteries is slower.
2. Different battery life
As the charging and discharging cycle continues, heat is generated inside the battery, which in turn affects the temperature of the battery. For stacked batteries, the internal temperature distribution is relatively uniform, while for wound batteries, due to the only unidirectional heat transfer between the electrode and the separator, the temperature gradient distribution phenomenon is more severe, resulting in high internal temperature and low external temperature. Uneven temperature distribution leads to the deactivation of active substances at high temperature positions during the charging and discharging process of the battery, which prevents the function of lithium ion deintercalation and affects the rapid decay at other positions, thereby affecting the performance of the battery.
3. The internal stress of the battery cell is different
The two production methods result in the battery cells having different mechanical characteristics. The force area between the electrode and diaphragm of the stacked battery cell is consistent, with no obvious stress concentration points, and the battery will not experience sharp damage in any part during use. The edge of a coiled battery cell is where stress is concentrated. Based on the author's previous experience in battery disassembly and analysis, the bending of the electrode is more prone to micro short circuits, electrical breakdown, and lithium deposition. The stress concentration point is the primary location for battery deactivation, which also leads to a decrease in the cycle life of wound batteries.
4. Different battery rate performance
The stacked process is equivalent to parallel connection of multiple electrodes, making it easier to complete high current discharge in a short period of time, which is beneficial for the rate performance of the battery. The winding process, on the other hand, is exactly the opposite, with a single pole ear resulting in slightly poorer rate performance.
5. Different battery capacity densities
The capacity density of stacked batteries is higher because their internal space is more fully utilized. On the other hand, in a coiled battery, the two sides of the cell are circular and the last two layers of membranes occupied by the winding occupy a certain thickness, resulting in a lower capacity density.
2、 Comparison of battery safety
The safety of the two is also different, mainly analyzed from their internal resistance, stress, temperature distribution, etc. The safety of wound batteries with uneven temperature and high internal resistance is lower.
3、 Processing technology
1. The complexity of polar film production varies
The winding process is simpler to operate and easier to achieve industrial automation. Currently, most companies in the market adopt a winding form. However, the lamination process is very cumbersome, and the pass rate of electrode cutting is very low. For wound cells, only two blades are needed at the beginning and end, while for stacked cells, each pole requires four blades, making it difficult to maintain a high degree of consistency in the quality of the poles (cross-section, burrs, etc.), which can affect the final performance of the battery.
2. The complexity of battery cell production varies
The winding type battery cell operation is relatively simple, and can be quickly completed whether it is semi-automatic or fully automatic. The laminated process has a high degree of complexity, and manual operation is time-consuming and laborious. Automation is difficult to industrialize due to equipment issues.
In addition, in terms of quality control of battery cells, the wound type is easier to control, while the stacked type is difficult to achieve good consistency due to the cumbersome process steps.
In short, it is still necessary to choose a suitable process based on one's own conditions and battery requirements. After the process changes, significant changes need to be made to the cutting of the electrode and subsequent welding and assembly.