Meaning
Internal mechanical deformation occurs when the multiple layers of a cylindrical cell shift sideways along their central axis because of loose winding tension or external physical forces. Systematic jellyroll axial telescoping disrupts the uniform alignment of electrodes and can lead to edge damage or the eventually rupture of the internal terminal connections inside the cell casing.
Alignment Disturbance
Occurrence typically begins during the handling phase if the cell experiences a sharp impact that causes the tightly wound core to slide relative to the outer housing. Any jellyroll axial telescoping causes the electrode edges to stick out from the center of the roll where they might come into direct contact with the steel header assembly or the base plate. This displacement creates a risk of internal short circuiting as the delicate edges of the current collectors are forced into spaces where the electrical insulation is not designed to operate.
Monitoring the physical position of the winding through x-ray inspection ensures that the stack remains perfectly centered after high speed assembly and welding.
Pressure Interaction
Movement is often exacerbated by the expansion and contraction of materials during intensive high current discharge cycles that change the diameter of the roll inside the can. If jellyroll axial telescoping remains uncorrected, the physical pressure on the copper and aluminum tabs increases which leads to metal fatigue and high resistance at the main power terminals. Advanced robotic winding machines avoid this by applying precise tension controls that ensure the friction between the layers is high enough to lock the stack in its target coordinates.
Detailed cross sectioning of failed units reveals if the slippage occurred uniformly or if only specific central layers moved which indicates a problem with the core pin removal process.
Geometric Boundary
Detection thresholds define how many millimeters of shift are acceptable before a cell is rejected as a significant safety risk during the end of line quality scan. Any instance of jellyroll axial telescoping serves as a failure signal for the winding station calibration and triggers an immediate pause in the assembly line to prevent the distribution of unstable hardware. Manufacturers use specific adhesive tapes or physical spacers at the top and bottom of the core to stop the winding from migrating even when subjected to road vibration.
Final cell safety relies on the core staying stationary to ensure the pathways for lithium ions remain uniform across the entire surface of the spirally wrapped electrode assembly.
