The cell winding process is the core link in lithium-ion battery manufacturing, and its key control directly affects the performance, safety and consistency of the battery. The following is an analysis of the key control elements of the process:
1.Material quality and consistency
- Cathode/ Anode: Coating uniformity, edge neatness (no burrs) and thickness tolerance should be strictly controlled. Uneven coating can lead to differences in internal resistance, and burrs can pierce the separator and cause short circuits.
- Separators: High tensile strength (to prevent overstretching and breakage) and uniform air permeability to ensure uniform electrolyte wetting. Material defects (e.g. micropores, impurities) increase the risk of short circuits.
- Incoming material inspection: Automated inspection equipment (e.g. CCD vision system) checks material dimensions, surface defects and physical properties to ensure batch consistency.
2.Winding alignment (layer matching)
- Alignment of battery electrode and Cathode: Cathode and Anode need to be completely separated by the separator, and the offset should be less than 0.5mm, using high-precision deskewing system (e.g. laser or photoelectric sensor) to adjust the position in real time.
- Needle design: The geometric accuracy of the needle (e.g. the shape of the needle for cylindrical/square battery cells) has a direct impact on the degree of alignment, and needs to be calibrated regularly to prevent wear and tear that can lead to deviation.
3.Tension Control
- Dynamic Tension Adjustment: The tension of the segments is set according to the material characteristics (e.g., brittleness of the battery electrode, ductility of the separator) to avoid over-tightening (breakage of the battery electrode) or over-loosening (interlayer gap). Usually the battery electrode tension range is 5-20N, and the separator tension is lower (3-10N).
- Closed-loop feedback system: using servo motors and tension sensors for real-time monitoring to ensure that the tension is stable during the winding process.
4.Equipment precision and stability
- Winding speed: too high a speed (such as > 1.5m / s) may lead to misalignment or tension fluctuations, the need to balance the efficiency and quality, the common speed range of 0.5-1.2m / s.
- Equipment rigidity: spindle concentricity, guide roller parallelism and other mechanical accuracy needs regular maintenance to avoid vibration or wear and tear caused by winding offset.
- Environmental control: temperature and humidity should be constant (e.g. 25±2℃℃, humidity ≤15%) to prevent the battery electrode from absorbing moisture or separator deformation.
5.Process monitoring and testing
- On-line inspection: Integrated vision system monitors battery electrode alignment, separator wrinkles and surface defects in real time.
- Post-winding inspection: Check battery cell appearance (no creases, bubbles), size (diameter/length tolerance ±0.1mm) and number of layers, use X-ray to detect internal structure alignment.
- Data traceability: Record winding parameters (tension, speed, number of turns, etc.) for quality traceability and process optimization.
6.Process parameter optimization
- Design of number of turns and layers: Optimize the winding structure according to the capacity and internal resistance requirements, e.g. increasing the number of layers can improve the energy density but may increase the internal resistance.
- Hot pressing (optional): Some processes add a hot pressing step after winding to eliminate inter-layer gaps and improve battery cell density.
7.Special structure differentiation control
- Cylindrical battery cell: pay attention to tension uniformity and roundness of the winding needle to avoid “J-shaped” winding defects.
- Prismatic battery cell: Strict control of battery electrode alignment is required to prevent insufficient coverage of the separator at the corners.
- Stacking process comparison: Winding process is more efficient but requires more uniformity, while stacking is more suitable for high thickness battery cells.
