Dynamic Mechanics of Micro-Crack Growth in Electrolyte-Swollen Polyolefin Separators
Electrolyte solvent plasticization lowers polyolefin yield stress, driving sub-critical micro-crack propagation under cyclic stack pressure.
Cell Winding Tension
Meaning
Manufacturing tension control governs the force applied to electrode sheets and separator membranes as they are wound around a central mandrel. Maintaining correct cell winding tension prevents structural defects such as telescoping, wrinkling or core buckling in the jellyroll. This parameter is measured in Newtons or as a percentage of web tensile strength, and it is controlled dynamically throughout the winding cycle.
It ceases to apply once the jellyroll is inserted into the cell can and the mandrel is removed.
Mechanical Stress
Excessive tension during the winding process can stretch the separator beyond its elastic limit. When the separator is deformed by high cell winding tension, its porosity decreases, which increases the internal resistance of the battery. This degradation leads to localized heating during cell operation.
Process Optimization
Gradual reduction of tension as the winding diameter increases is necessary to maintain a uniform radial pressure profile. Automated tension systems adjust the brake torque of the supply spindles in real time. This compensation maintains the integrity of the layers.
Defect Prevention
Insufficient tension creates loose gaps between the anode and cathode, which extends the lithium-ion diffusion distance. Poor layer contact can cause non-uniform current density and accelerate lithium plating. Correctly balanced tension guarantees long-term electrochemical stability.