Enhancing high-temperature energy storage in all-organic composites through the polyfluorine effect

The extensive utilization of electrostatic capacitors across diverse sectors and extreme environments necessitates materials with high breakdown strength (E_b), substantial energy storage density (U_e) and exceptional toughness at high temperatures. Herein, all-organic composite films fluorinated-polyimide/polyvinylidenefluoride-hexafluoropropylene (F-PI/PVDF-HFP) were synthesized via in-situ compounding and multilayer casting. Experimental and theoretical calculations reveal that doping F-atoms in PI reduces dielectric loss and broadens the bandgap, while the introduction of the ferroelectric polymer PVDF-HFP enhances the high-temperature toughness and insulation of the composites through the polyfluorine effect, effectively suppressing carrier transport and preventing premature thermal/electrical breakdown. Consequently, the F-PI/PVDF-HFP achieves exceptional high-temperature energy storage performance (E_b ∼ 500 MV/m, U_e ∼ 5.2 J/cm³, η ∼ 80 %) alongside robust toughness at 120 °C, surpassing most polymer dielectrics even at 150 °C (U_e ∼ 2.91 J/cm³, η ∼ 75 %@423 MV/m). This investigation unveils novel strategy leveraging the polyfluorine effect to advance the high-temperature energy storage performance and processing characteristics of PI-based dielectrics.