Interface engineering of 2D dielectric nanosheets for boosting energy storage performance of polyvinylidene fluoride-based nanocomposites with high charge-discharge efficiency

Polyvinylidene fluoride (PVDF) film, with high energy density and excellent mechanical properties, has drawn attention as an energy storage device. However, conduction loss in PVDF under high electric fields hinders improvement in efficiency due to electrode-limited and bulk-limited conduction. Well-aligned multilayer interfaces of two-dimensional (2D) nanocoatings can block charge injection, reducing electrode-limited conduction loss in dielectric polymers. Thus, rational selection of 2D fillers is crucial for designing high-energy-density dielectric materials. This study explores 2D oxide nanosheets with varying dielectric constants and bandgaps, such as Ti_0.87O₂, Ca₂Nb₃O₁₀, and montmorillonite (MMT). Ca₂Nb₃O₁₀ nanosheets, with a higher dielectric constant and similar bandgap to Ti_0.87O₂, created a higher Schottky barrier (0.6 eV), resulting in a discharge energy density (U_d) of 26.4 J cm^-3 at 720 MV m^-1 in PVDF-Ca₂Nb₃O₁₀ film. The PVDF-MMT film, coated with MMT nanosheets featuring a lower dielectric constant yet a higher bandgap, achieves a similar U_d of 26.8 J cm^-3 at 720 MV m^-1, with efficiencies (η) above 80% for both films. The results indicate that the bandgap and dielectric constant of 2D nanosheets play a crucial role in determining PVDF composites' energy storage density and efficiency, necessitating a balance between these parameters. Furthermore, ultraviolet (UV) irradiation was introduced to induce trap centers and inhibit charge conduction and energy loss in PVDF-based composites under high electric fields. Consequently, the UV-treated PVDF-MMT composite film achieves a U_d of 29.1 J cm^-3 and an η of 78.3% at 750 MV m^-1. This work offers an effective strategy for developing high-energy density, high-efficiency PVDF-based polymer materials.