Comparison of lithium battery stacking process and winding process

Process principle

1. Stacking process:

Cut the positive and negative electrodes into the required size, and then combine them with the separator to form a small battery cell. Then the small battery cells are stacked and connected in parallel to form a battery module.

2. Winding process:

The positive electrode, separator and negative electrode are wound in a certain order by a fixed winding needle, and extruded into a cylindrical, elliptical or square shape. Then, these wound electrodes are placed in a square or cylindrical metal shell. The size of the electrode and the number of windings are usually determined by the design capacity of the battery.

Differences in electrical properties

1. Internal resistance:

The internal resistance of the battery manufactured by the stacking process is low. This is because the stacking process uses multiple poles to be welded in parallel, which reduces the migration path of lithium ions. The low internal resistance can improve the heating of the battery cell during use, making the decay rate of the initial energy density of the battery cell slower. In contrast, the battery manufactured by the winding process has a higher internal resistance because it uses a single pole to output the current.

2. Cycle life:

The battery manufactured by the stacking process has better heat dissipation performance, and its internal structure supports a more uniform distribution of heat: while the battery manufactured by the winding process has a gradient change in internal structure and mechanics, and the heat dissipation direction is uneven, which is prone to temperature gradient distribution. This causes the battery manufactured by the winding process to have a faster capacity decay in long-term use, resulting in a shorter battery cycle.

3. Electrode sheet mechanical stress:

There are also differences in mechanical stress between the two processes. The electrode sheets manufactured by the stacking process have the same stress area and no obvious stress concentration point, and the electrode sheet material layer is not easily damaged during the charge and discharge process. The cells manufactured by the winding process produce stress concentration at the bends, which can easily lead to structural damage, short circuits and lithium metal precipitation of the battery under the stimulation of electrical signals, thus affecting the cycle life of the battery.

4. Battery rate performance:

Batteries manufactured by the stacking process have better rate performance than the winding process, and can complete high-current discharge faster in a short time. This is because the stacking process is equivalent to connecting multiple poles in parallel, increasing the current channel.

5. Energy density design differences:

The stacking process can better utilize the packaging space and increase the filling of effective materials, so the batteries manufactured by the stacking process can support higher energy density. However, the winding process fails to achieve a higher space utilization rate due to the curved circular structure of the electrode sheet and the space occupied by the Qiyan energy-adjustable membrane structure, resulting in a lower energy density.

Advantages of the process

1. Advantages of the stacking process:

High capacity density: The stacking process can better utilize the internal space, and compared with the winding process, the battery has a higher capacity under the same volume;

High energy density: The battery manufactured by the stacking process has a higher discharge platform and volume specific capacity, so it can have a higher energy density;

Flexible size: The stacking process can design the size of each electrode according to the size of the lithium battery, so it can be made into any shape.

2. Advantages of winding process:

Easy spot welding: The winding process only requires two points for each lithium battery, and the operation is relatively simple;

Simple production control: The winding process has two poles for one battery, which is easy to control;

Convenient slitting: Each battery cell only needs to be slid once for the positive and negative poles, with low difficulty coefficient and low quality inspection.

Disadvantages of the process

1. Disadvantages of the stacking process:

Easy to weld: Since it is necessary to weld multiple layers of positive or negative poles together, the operation is difficult and easy to weld;

Low equipment efficiency: At present, the efficiency of domestic stacking machines is usually 0.8 seconds/piece, which is a big gap compared with the 0.17 seconds/piece of imported stacking machines.

2. Disadvantages of the winding process: high internal resistance and large polarization:

Since the winding process has only a single positive and negative pole ear, part of the voltage will be consumed in the internal polarization process of the battery, resulting in poor charge and discharge rate performance of the battery;

Poor heat dissipation effect: The winding process is not easy to operate the thermal isolation measures between the cells. Improper handling can easily lead to local overheating, which in turn causes thermal runaway;

Battery thickness is difficult to control: Due to the uneven internal structure of the cell manufactured by the winding process, the thickness of the pole ear, the end of the diaphragm and both sides of the cell is prone to unevenness.