Enhanced Energy Density and Charge–Discharge Efficiency of the Bilayer Film over a Broad Temperature Range

Recently, multilayer polymer dielectrics have emerged as key focal points, capitalizing on the synergies of diverse materials, particularly in the realm of high-temperature energy storage. To enhance energy storage further, we developed a layered polymer material through the hot-pressing method. This material comprises a poly(ether imide) (PEI) and polyimide (PI) blend film (referred to as PP) as the first layer, and a blend film of poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) [P(VDF-TrFE-CFE)], poly(methyl methacrylate) (PMMA), and poly(vinylidene fluoride–chlorotrifluoroethylene) [P(VDF-CTFE)] (referred to as PAC) as the second layer. The PAC layer offers a high Ud value, while the PP layer contributes high η and heat resistance. The resulting bilayer composites exhibit a notable energy density (∼10 J/cm3) with high efficiency (>70%) at 500 MV/m and ambient temperature, as confirmed by the finite-element methods. Furthermore, the film demonstrates remarkable electric breakdown strength, consistently 200 MV/m at 120 °C. Notably, the bilayer film exhibits outstanding cyclic stability with excellent fatigue resistance (5 × 104 cycles at 200 MV/m). Our research presents a promising organic polymer composite film for achieving high-performance energy storage capabilities.