The key technologies of the lithium battery pack winding process are as follows:

Tension control: Tension control during the winding process is of vital importance. Insufficient tension can cause the battery cells to loosen, and the electrode plates are prone to movement during the transportation of the battery cells. Excessive tension will cause the battery cells to become tight, resulting in wrinkles on the electrode plates and thus affecting the battery's performance. Tension control is usually achieved through a tension control system, which dynamically regulates the tension applied to the electrode sheets and separators during the winding process to ensure the tightness and consistency of the battery cells.

Winding equipment and precision: Modern winding machines typically use circular, elliptical and flat rhombic winding pins. Circular coiled pins, which were also used in square batteries in the early days, would cause more severe folding of the tabs. Meanwhile, the long and short shafts of the flat rhombic coiled pins have a significant difference in size, resulting in obvious changes in the tension of the electrode sheets and separators. Therefore, it is necessary to drive the motor to wind at variable speeds, and the process is difficult to control.

Alignment control: During the winding process, a CCD detector is used to monitor the alignment in real time to ensure a uniform and tight fit between the electrode sheet and the separator and reasonable coverage. For instance, the CCD detector can measure the distance between the positive and negative electrodes, as well as the distance between the positive and negative electrodes and the separator, promptly identify deviations, and automatically alarm to remove defective products if any abnormalities occur.

Winding speed and accuracy: The linear speed of the current winding machine has developed from the existing 2-3 m/s to 4-5 m/s, and the alignment accuracy of the winding electrode sheets has been improved from the existing ±0.3mm to ±(0.1-0.2mm). High-precision winding can enhance battery capacity and performance.

Needle winding design and optimization: The design of the needle winding directly affects the winding quality and the quality of the battery cells. Square batteries commonly use plate-type wound pins, which are composed of two metal sheets of the same size, upper and lower. The effective winding part is rectangular, with a tiny gap left between the two layers of metal sheets, allowing them to pass through and hold the separator. Cylindrical cells are flattened to form square cells. The width of the inner layer of the cell is slightly greater than half of the circumference of the circular wound pins. The internal tension of this flattened cell is large. The thickness was not easy to control and was later replaced by sheet needle rolls.

Winding direction and alignment control: The winding direction and the overturning difference of the electrode sheets (the outer negative electrode being longer than the positive electrode and the inner negative electrode being longer than the positive electrode) affect the battery performance. If the direction of the electrode sheet overturning difference is not properly controlled, it may cause the negative electrode sheet to not fully cover the positive electrode sheet. During the charging process of the battery cell, the lithium ions released from the positive electrode cannot find the corresponding graphite to embed in the lattice, forming dendrites. These dendrites can Pierce the separator, causing an internal short circuit and posing a safety hazard.

Winding environment and safety: The environmental humidity during the winding process should be controlled below 1%RH, and the dust content should be controlled below 100,000/ft³ to prevent dust from mixing into battery products and causing potential hazards such as short circuits. During the winding process, it is also necessary to be equipped with non-metallic foreign substances, such as stainless steel like Fe, Cu, Zn, Al, Sn, etc., to prevent metallic foreign substances from mixing into the positive electrode. After charging, the potential of the positive electrode will rise, and the dissolved metallic foreign substances at the high potential will precipitate and accumulate on the surface of the negative electrode, forming dendrites that can Pierce the separator and cause a short circuit.

Process parameter control: Winding tension, winding speed, winding needle circumference, negative electrode cutter life, and the number of empty rotations of the diaphragm at the beginning and end of the winding are all key parameters that affect the winding quality. If the winding tension is too small, the battery cells will be loose. If the winding tension is too large, the battery cells will be tightly clamped, causing wrinkles on the electrode sheets. Winding speed affects winding efficiency and equipment thermal isolation measures. The circumference of the winding needle affects the size of the battery cell, thereby influencing the battery capacity. The lifespan of the negative electrode cutter is mainly related to customer requirements. Even if there are burrs at the cutting position, since the negative electrode at the beginning and end of the wound battery cell wraps around the positive electrode, the part that overlaps after the burrs Pierce the separator is still the negative electrode. However, generally, the adjustment of the number of turns at the beginning of the wound needs to be verified for its impact on the core extraction and the thickness of the battery cell. The number of turns at the end of the wound is mainly related to the assembly and welding method.

Development trend: With the advancement of technology, the linear speed of the winding process is increasing from the current 2-3 m/s to 4-5 m/s, and the alignment of the winding electrode sheets is improving from ±0.3mm to ± 0.1mm, enhancing the winding efficiency. The winding process is developing towards the linear speed of needle winding. The linear speed of winding electrode sheets has increased from the current 2-3m/s to 4-5m/s. The winding alignment degree has been increased from ±0.3mm to ±(0.1mm), with higher precision.

Equipment and technology improvement: With the increasing requirements for winding quality, winding equipment has begun to adopt variable tension profiling closed-loop control. Through variable tension profiling closed-loop control, tension fluctuations are reduced. Variable tension profiling closed-loop control regulates tension by adjusting the feeding speed of the speed-regulating mechanical CAM and other methods.