Heterostructured n-ZnO@p-CuO nanosheets filled in a polymer matrix for enhanced electrostatic energy storage performance

Metallized film capacitors use plastic films as the dielectric spacer, and these polymer films generally have low dielectric constants. To boost the electrostatic energy storage density of a film capacitor, advanced high-k films with high electrical breakdown strength and low dielectric loss are highly desired. Herein, polymer nanocomposite films were made by filling ZnO@CuO nanosheets into poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)]. The n-type ZnO nanosheets are synthesized in an aqueous solution. Through a calcination process, thin layers of p-type CuO are coated over the ZnO nanosheets. Compared to pure P(VDF-HFP) and ZnO/P(VDF-HFP) films, the ZnO@CuO/P(VDF-HFP) films exhibit higher dielectric constant and higher breakdown strength. The optimal content of ZnO@CuO nanosheet in the polymer matrix is determined to be 3 wt%, which leads to a dielectric constant of 15.6 at 1 kHz and the highest energy density of 5.6 J cm^-3. The efficacy of ZnO@CuO nanosheets in enhancing the dielectric performance of the polymer nanocomposite is elucidated in detail. This research provides a scalable and low-cost strategy to produce polymer nanocomposite films with high capacitive energy storage performance.