Wenjing Ji

High dielectric constant ceramics fillers are widely used as fillers in polymer matrix to prepare high performance dielectric composites. Homogeneous filler distribution in these composites films is found to be quite difficult to achieve balance between high dielectric constant and high breakdown strength. Herein, multilayer structured composites films containing nickelous hydroxide (Ni(OH)₂) as fillers, with different multilayered structures were designed and prepared, including 2–5 layers structure with various filler distribution. The effects of multilayer structure on the dielectric performance are explored by keeping the overall filler content constant. Combined with computer simulation, it is suggested that the variation in filler distribution in these films can effectively redistribute electric field intensity. Meanwhile, the dielectric constant and breakdown strength of the overall composites can be adjusted by changing the volume ratio between high filler content layer and low filler content layer. It is noted that at least 1/3 of the overall film volume should be occupied by a high breakdown strength layer to keep rather high overall breakdown strength. Moreover, high dielectric constant layer should be the outer layers to achieve overall high dielectric constant. Among all the layered structures investigated, the maximum energy density of 6.03 J/cm³ is obtained for film with a 3-layer nonsequential arrangement structure, which is 68% higher than single layer film with identical composition. This study provides some reference value for the preparation of multilayered dielectric polymer composites films for energy storage applications. GRAPHICAL ABSTRACT

This study demonstrates a one-step and environmental friendly method to fabricate graphene/nickelous hydroxide (GO/Ni(OH)₂) hybrid filler via hydrothermal strategy for dielectric polymer composites based on PVDF. Ni(OH)₂ nanosheets are grown uniformly on the surface of GO sheets, such hybrid filler can bring a number of advantages for resulted composites: 1. Ni(OH)₂ could reduce the dielectric constant contrast between graphene and PVDF; 2. The special structure of such hybrid filler could lead to enhanced breakdown strength; 3. Strong interfacial interaction between filler and matrix could be achieved due to the hydroxyl groups on the surface of such hybrid filler. As a result, 1.25 wt% of such hybrid filler leads to dielectric constant of 12.05 at 103 Hz for the final composites, which is higher than neat PVDF (≈9.6). While the tanô is limited at 0.011 which is much lower than GO based composites. And the breakdown strength is 254 kV mm^-1, an enhancement of 20.9% over neat PVDF. More importantly, an energy density of 3.89 J cm^-3 can be achieved, with an enhancement of 2.6 times over GO/PVDF (1.47 J cm^-3) and 1.57 times over neat PVDF (2.47 J cm^-3). Furthermore, this study provides a one-step environmental friendly method for the fabrication of functional filler for various functional polymer nanocomposites.

A 3D flower-like porous NiO@polypyrrole composite is prepared to investigate the role of PPy coating for high-performance supercapacitors.