Evaluating Polyolefin Separator Friction Limits in Lubricated Cell Stacks
Sufficient stack pre-load retention and ceramic coating friction prevent wetted polyolefin separator sliding and tab shear in lubricated cell stacks.
Separator Wrinkling
Meaning
Physical distortion of the porous polymer membrane appears as folds or creases that disrupt the uniform distance between electrodes. Manufacturing processes that involve uneven tension can cause separator wrinkling during cell assembly. This structural defect prevents uniform ion transport.
Deformation Mechanism
Excessive winding tension or mismatched thermal expansion during cell drying forces the thin separator film to buckle. Squeezing of the active material layers during the calendering or winding process can also create local friction that initiates separator wrinkling. Sourcing departments examine the winding parameter logs of cell manufacturers to ensure the tension control is highly calibrated.
Electrochemical Effect
Non-uniform contact between the separator and the electrode plates leads to a localized concentration of lithium ions. This uneven flux creates conditions favorable for the growth of lithium dendrites, which can penetrate the wrinkled membrane and cause an internal short circuit. Cells with this defect show higher rates of self-discharge and are prone to premature thermal failure.
Eliminating these hot spots is critical to ensure the safety of high-energy cells.
Process Control
Purchasing specifications mandate inline optical inspection and ultrasonic scanners to detect internal layer defects before the electrolyte is injected. Automated roll-to-roll handling systems with tension sensors minimize the risk of mechanical deformation of the delicate polymer film. Continuous monitoring of the web path reduces the occurrence of these defects during high-speed production runouts.