Scalable in-situ surface-coated polymer dielectrics with significantly enhanced high-temperature breakdown strength

Wide bandgap inorganic layers exhibit the effect to improve the insulating properties as charge barrier layers between the electrode and polymer dielectrics. However, their influence mechanisms on the high-temperature breakdown behavior still need to be further revealed. Herein, the in-situ grown strontium oxide (SrO) layers were coated on the surfaces of polyimide (PI) film to conduct this research. Compared with neat PI, the breakdown strength and discharge energy density (efficiency >90%) of the coated film was significantly elevated up 45% and 1000% at 200 °C, respectively. The experimental results show that SrO greatly reduces the entropy of surface molecular conformations and increases the energy level of localized states of PI film. The SrO coating effectively improves the injection barrier and interface trap levels simultaneously, undertakes a higher electric field, and hinders the destruction of PI film's surface molecules by high-energy electrons, thus reducing the conduction loss and constraining the generation and development of electrical trees at high fields. This work not only provides a comprehensive insight into the in-situ oxide coating on the insulating properties in polymer dielectrics but also offers a paradigm for developing scalable dielectric materials with high breakdown strength used in harsh-condition electrification.