High Discharge Energy Density and Efficiency in Newly Designed PVDF@SiO2-PVDF Composites for Energy Capacitors

The fabrication of a core-shell structure is an effective method of obtaining a composite film with a high energy density. Herein, we prepared a new type of composite film with high energy density and energy efficiency by using silica-coated core-shells on poly(vinylidene fluoride) (PVDF) particles that comprised a high proportion of polar phases rather than inorganics with high dielectric constants. We prepared PVDF particles with a high proportion of the beta-phase using emulsion polymerization. Subsequently, we prepared PVDF@SiO2 core-shell particles by coating silica using the sol-gel method. The resultant PVDF@SiO2-PVDF exhibited a low reduction in the dielectric constant because of the lower amount of silica than that in other dense silica particles, which was verified through dielectric constant measurements and theoretical calculations. In addition, when the PVDF@SiO2 particle contained 40 wt % silica, a high breakdown strength of 598.95 MV/m was confirmed. Therefore, we verified that the PVDF@SiO2-PVDF composite film has a high discharge energy density of 12.051 J/cm(3) when the PVDF@SiO2 is 40 wt %. In addition, the domain size is limited by the silica shell, resulting in a high energy efficiency of 88.22%, which indicated a potential for the utilization of the composite film in energy storage devices. These results offer a novel strategy for the development of polymer-based capacitors with high energy densities and efficiencies.