Polyimide Films Impregnated with Epoxy Resin Demonstrating Superior Self-Healing Properties for Thermally Stable Energy Storage Capacitors

Metallized polymer films (MPFs) with superior self-healing properties are extremely attractive for application in energy storage capacitors. Self-healing behaviors allow MPFs to keep insulating between the local electrical breakdown region and the electrode, thereby reserving long-term operational viability of the capacitors. Polyimide (PI) is a type of well-developed polymer material with excellent mechanical and thermal stabilities, but it is deficient in intrinsic self-healing capabilities. This work reports a facile surface engineering strategy to endow metalized PI films with self-healing capabilities. By simple immersion of bare PI films in the solution of epoxy resin (ER) accompanied by curing of ER, PI films impregnated with ER (P–E films) not only show enhanced dielectric characteristics but also obtain excellent self-healing abilities upon multiple cycles of electrical breakdowns, even at a high temperature. For example, in comparison to bare PI films, PI films impregnated in ER solution with a solid content of 1 wt % (P–1%E) display improved initial Weibull breakdown strength (α_b1 of 353.0 versus 310.9 kV/mm), maximum discharging energy density (U_d of 2.1836 versus 0.8254 J/cm³), and charging/discharging efficiency (η of 95.72 versus 55.19%) at 150 °C. After 5 breakdown cycles, P–1%E films could maintain a much higher breakdown strength (α_b5 of 338.1 versus 21.3 kV/mm). When subjected to a constant electrical strength of 350 kV/mm at 150 °C, P–1%E films show merely <6% decline in both U_d and η values after 5 breakdown cycles. On the contrary, bare PI films would undergo dramatic performance decay after 1 or 2 breakdowns under similar conditions. In view of their outstanding self-healing properties at a high temperature, P–E films can serve as a promising candidate to fabricate thermally stable MPF capacitors for long-term operation.