Dual-crosslinked polyimide dielectric films containing Cu elements for high-temperature film capacitors

Organic polymers are widely used in film capacitors as they contain excellent flexibility, outstanding electrical insulating performance, fast charge-discharge rate, higher power density, etc. However, most of the commercially used polymer films suffer from poor heat resistance and low energy density, thus limiting their applications. To solve this problem, an effective method was adopted to prepare high-temperature resistant polyimide (PI) dielectric films in this work. A dual-crosslinked PI composite films containing Cu elements were fabricated by amine crosslinking agent and coordination of Cu2+ with the N element in imidazole unit. The dielectric constant of the film increased from 4.00 to 4.88 at 1 kHz, and the breakdown strength of the films increased from 437 MV/m to 460 MV/m at room temperature. The discharge energy density (Ud) also reached the maximum of 3.12 J/cm3 at 150 °C, and the charge-discharge efficiency (η) was 69.4% when the feeding content of Cu2+ of 20% mol. It is worth mentioning that the form of coordination bond making Cu2+ occupies the position of the lone pair electron, which effectively improved the hydrophobicity of PI composite films.