Nonlinear Conduction of Ultra-Low-Percolation Threshold CNT/Polyimide Composites under Electric Field Partitioning

Abstract Non-uniform electric fields in NEV insulation systems impose conflicting requirements on dielectric materials. Low-field regions require high insulation, while high-field regions demand efficient field regulation. Conventional linear dielectrics fail to satisfy both due to field-independent conductivity, resulting in weak regulation at low fields and severe field concentration at high fields. CNT polyimide composites with tunable nonlinear conduction are developed through matrix selection and interfacial engineering. PI-based systems are suitable for low-field insulation, whereas TPI-based systems exhibit superior high-field response. KH570 preserves the interfacial barrier and enables field-triggered conduction, leading to strong nonlinearity and effective suppression of field concentration. KH550 enhances interfacial bonding and improves breakdown strength while maintaining appreciable nonlinear conductivity, thereby achieving a better balance between electrical conduction and dielectric reliability. These results establish a clear material-application matching across different electric field regimes and provide a strategy for field-partitioned insulation design.