Surface energy-driven perpendicular gradient structure in flexible composite dielectrics for high-temperature capacitive energy storage

Flexible dielectrics are urgently needed in advanced electrical systems and modern power electronics. Nevertheless, conventional polymer dielectrics suffer from low discharged energy density and charge-discharge efficiency at elevated temperatures due to severe conduction loss. Here, we report a perpendicular gradient structured polymer composite dielectric with an inorganic hybrid crosslinking network of Si-O-Ti. Driven by surface energy difference, SiO2 accumulates on the film surface to block the charge injection, while bulk TiO2 boosts the dielectric constant. The hybrid crosslinking network of Si-O-Ti also enhances the thermal stability, mechanical modulus and insulation strength by reducing free volume. Ultimately, the obtained composite delivers a discharged energy density of 6.04 J/cm3 above 90% efficiency at 200 °C, exhibiting a 364.62% enhancement over the pristine polymer. This strategy effectively modulates surface and bulk properties, accordingly contributing to improving high-temperature capacitive energy storage performance. The authors design a perpendicular gradient structured polymer composite dielectric with an inorganic hybrid crosslinking network of Si-O-Ti. This unique architecture enables an energy density of 6.04 J/cm3 with an efficiency of 90% at 200 °C.