Decoupling of dielectric breakdown and charge transport in BOPP films under mechanical stress

Metalized biaxially oriented polypropylene (BOPP) film capacitors inevitably suffer from mechanical stress during manufacturing and service, yet the intrinsic correlation between structural evolution and charge dynamics remains unclear. Herein, we report a physical mechanism decoupling dielectric breakdown from steady-state charge transport in BOPP films under tensile stress. We demonstrate that prolonged stretching monotonically deteriorates dielectric constant and breakdown strength, which is driven by the continuous expansion of amorphous free volume and severe crystalline fragmentation. In contrast, the anomalous non-monotonic leakage current is governed by a stress-induced microstructural transition coupled with localized space-charge shielding. During the orientation-dominated stage, chain alignment optimizes lamellae and constructs shallow-trap percolation channels, facilitating carrier migration. Conversely, in the destruction-dominated stage, lamellar fragmentation generates abundant deep traps that disrupt transport networks. This study elucidates the nonlinear evolution of electromechanical coupling in insulating polymers, offering qualitative insights and conceptual boundaries for evaluating the reliability of film capacitors.