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Tension control is the core technology that affects the advanced degree of winding machine. During the entire winding process, in order to ensure the high consistency of the battery assembled from the cells, special attention should be paid to the tension control of the winding. The difference in tightness caused by tension fluctuations will cause uneven stretching deformation of the wound-out battery core, resulting in delamination or S-shaped wrinkles of the battery core material, which seriously affects the consistency of the product. The wrinkles caused by the uneven surface of the separator and electrode sheet will increase the internal resistance of the battery. Winding tension control is a high-speed dynamic balancing process. The winding machine has extremely high requirements in terms of electrical and software control. The servo control system is required to respond quickly, and the software programming also requires a unique level of experience. For the winding of prismatic lithium batteries, the linear speed of winding needs to be kept constant, and the angular velocity needs to be automatically adjusted. Therefore, the tension control of prismatic lithium battery winding has higher technical requirements. At present, leading domestic companies can control the tension fluctuation of cylindrical batteries below 5%, and the tension fluctuation of square batteries below 10%.
The automatic deviation correction technology and winding speed of the winding machine are also critical. The deviation correction system can ensure that the electrode sheet and the diaphragm are wound neatly during the battery winding process, and the relative position between the positive electrode/negative electrode/diaphragm is accurate, at present, the industry generally requires that the upper and lower deviations of the positive and negative electrode sheets or separators after rolling are less than 0.5mm, and exceeding this value will affect the battery deformation. At present, the cylindrical cells of domestic leading companies can reach a high-speed winding speed of more than 18 m/s. Prismatic cells need to ensure a constant linear speed, so winding at variable angular speeds is slower, and domestic leading companies can reach above 0.8 m/s.