Ultrahigh polar phase content PVDF-based composite films with ultralow filler loading for high-energy-density flexible capacitors

Flexible polymer dielectric capacitors are essential in the modern electrical field and have received extensive attention due to their ultrahigh power density. Polyvinylidene fluoride (PVDF) has a high dielectric permittivity and is considered one of the most promising dielectric materials. However, its low breakdown strength (< 350 MV/m) and low discharge efficiency (< 50 %) severely limit its practical applications. In this study, a new type of flexible polymer dielectric film was prepared by hot pressing and melting blending of ultralow content of modified sulfonated aromatic polyamide (f-PPTA) and PVDF. f-PPTA is obtained by ionic interaction between sulfonated aramid backbone and octadecyl polyoxyethylene ether (PEGO). The two amphiphilic segments in PEGO can reduce the melt viscosity of the composite system, which is beneficial to preparing composite films by melting. In addition, a large number of hydrogen bonds are formed between the hydroxyl groups in the PEGO segment and PVDF, which induces the formation of 98 % ultrahigh content polar phase. Consequently, when the electric field strength is 528 MV/m, the composite film obtains a high energy-storage density of 17 J/cm³ and maintains a charge and discharge efficiency of 65%. This method develops a new way to obtain PVDF-based composite films with ultrahigh polar phase content and is expected to develop in the direction of continuous melt film formation.