Cross-layer failure induced by accumulated self-healing damage in multilayer metallized films

Metallized film capacitors have become key energy storage components in new energy power systems, electric vehicles, and pulsed power equipment due to their high power density and self-healing capability. However, the demand for higher power density and miniaturization poses challenges to their reliability. Moreover, research on single-layer metallized film self-healing may overlook interlayer failure mechanisms and cascading effects. We report a cross-layer failure induced by accumulated self-healing damage in multilayer metallized films. After applying 1.8 times the rated voltage for 5 h, the short-circuit failed core was dissected layer-by-layer and reconstructed by micro-CT. The short circuit originated from a multilayer through-cavity extending across metallized film layers, surrounded by dense self-healing zones. Inner-layer cavities pierced more layers but stayed compact; outer-layer cavities pierced fewer layers but spread wider. Further analysis suggests that interlayer cavities and connected demetallized regions formed by accumulated self-healing may weaken the restriction on discharge expansion and hinder the local pressure buildup required for rapid arc extinction, thereby prolonging the arcing duration. Continuous heat input induces interlayer cascade breakdown through thermal activation effects, ultimately melting the multilayer dielectric and metal electrodes. This study reveals that three-dimensional cumulative damage is the key triggering condition for the transition from progressive degradation to sudden short circuit, which provides a reference for design optimization and performance improvement of metallized film capacitors.