Polyimide dielectrics with cross-linked structure for high-temperature film capacitors

In order to balance the breakdown strength and dielectric loss of polymer dielectric materials, a series of cross-linked polyimide (XL-PI) films with outstanding dielectric properties and high temperature energy storage property are prepared by introducing the end-capping agent, i.e. norbornene dioic anhydride, in this work. The cross-linked structure between molecular chains restricts the polarized movement of polar groups and inhibits the directional migration of carriers, which greatly reduces the dielectric loss and improve the electrical insulation properties of cross-linked PI film, compared with pure PI film with linear molecular chains. The dielectric loss of XL-PI films is greatly reduced to 0.003–0.006. Simultaneously, the breakdown strength of the XL-PI sample is up to 545 kV/mm. And the dielectric loss and breakdown strength of the XL-PI samples are relatively stable in the temperature ranging from room temperature to 150 °C. The XL-PI film with 3 wt% norbornene dioic anhydride (XL-PI-3) shows the maximal energy storage density of 9.4 J/cm³ under 525 kV/mm at room temperature. Moreover, XL-PI-3 can maintain an energy storage density of 6.5 J/cm³ and an energy efficiency of 82% at 150 °C. This work provides a new idea to prepare PI dielectric film materials for high-temperature film capacitors.