Tri-layer high-temperature all-organic films with superior energy-storage density and thermal stability

Ferroelectric polymer-based composites have gained increasing interest due to the benefits of high dielectric constants and discharge energy densities. However, they cannot be utilized in elevated-temperature environments owing to their poor temperature resistance and high energy loss. Herein, a tri-layer high-temperature all-organic film was elaborately studied, in which polycarbonate (PC) was used as the outer layer and different proportions of polymethyl methacrylate (PMMA) were blended with the ferroelectric polymer poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) as the intermediate layer. The results reveal that not only is the heat resistance of the composites improved, but also the outer layer with its wide bandgap inhibits carrier injection from the electrode and results in a low depolarization current and trap level density. The tri-layer all-organic composite with optimal PMMA content (40 wt%) has excellent energy-storage performance and thermal stability via prominently suppressing leakage current density and energy loss. As a result, at 120 °C and 300 MV m⁻¹, an extremely high discharge energy density of 9.23 J cm⁻³ and great charge-discharge efficiency of 80.9% are concurrently attained, far exceeding the commercial bench-mark biaxially oriented polypropylene (BOPP) (∼1.4 J cm⁻³) and the upper discharge energy density limits of representative ferroelectric polymer-based composites. Surprisingly, an exceptional discharge energy density of 8.63 J cm⁻³ can still be obtained at 140 °C. This contribution facilitates the high-temperature energy-storage applications of ferroelectric polymer-based dielectrics with a tri-layer configuration via effectively improving their energy-storage density and stability at high temperatures.