Microstructures, electrical behavior and energy storage properties of Ag@shell/PVDF-based polymers: different effects between an organic polydopamine shell and inorganic zinc oxide shell

Two kinds of 1D core–shell nanorods silver@polydopamine (Ag@PDA) and silver@zinc oxide (Ag@ZnO) were successfully synthesized and doped into polyvinylidene fluoride (PVDF) to fabricate composites. The different surface modification effects between the organic PDA shell and inorganic ZnO shell on structure and dielectric properties of PVDF composites were investigated. Results indicated that the ZnO shell showed a crystalline structure, while the PDA shell is amorphous. Due to the difference in crystal structure of the coating shell, the Ag@ZnO/PVDF composites showed a better dielectric performance than the Ag@PDA/PVDF composites, while the Ag@PDA/PVDF showed excellent mechanical properties. The crystallized structure of ZnO not only promoted the crystal conversion of PVDF molecules, but also effectively limited the movement of charge carriers in composites. In the case of 10wt% fillers' content and before breakdown strength, the energy storage densities of Ag@PDA/PVDF and Ag@ZnO/PVDF composites are 79.53% and 209.2% higher than that of pure PVDF films, respectively. Moreover, the charge/discharge efficiency of Ag@ZnO/PVDF composite is also higher than that of pure PVDF and Ag@PDA/PVDF composite. When testing at 1800 kV/cm electrical strength, the energy storage density of Ag@ZnO/PVDF composite increases to 4.02 J/cm3.