Synergistic Enhancement of Corona Resistance in Polyimide Films via Co-doping with SiO2 and BN Nanoparticles

Polyimide has become the main material for wire enamel in new energy vehicle drive motors because of its good insulation and high temperature resistance, but its corona resistance has to be further improved. In this paper, SiO2 and BN were selected as inorganic nano-fillers, and the composites were prepared by incorporating SiO2 and BN into the polyimide matrix with a mass fraction of 10% using in situ polymerization. The electrical properties and electrical dendrite growth of pure PI, 10% SiO2/PI, and 10% BN/10% SiO2/PI were investigated. The results showed that the composite 10%BN/10%SiO2/PI doped with both BN and SiO2 had the longest corona resistance time, which could be attributed to the high insulating property of the inorganic particles themselves to extend the breakdown path of the local electric field, and the high thermal conductivity of the BN to transfer the heat quickly to avoid aging due to heat accumulation. However, the addition of inorganic particles makes the breakdown strength of the composites lower, which may be due to the agglomeration of inorganic particles.