Ni(OH)2 as an novel shell layer material for core-shell dielectric filler based on barium titanate and their dielectric polymer composites in P(VDF-HFP) matrix

Dielectric capacitors with high dielectric constant and energy density are of great importance for electronic devices. Barium titanate(BaTiO 3 ) have been widely explored for polymer-based dielectric composites owning to its ultrahigh dielectric constant and commercial availability. However, due to the large difference of dielectric constant between BaTiO 3 and polymer matrix , the interface becomes fragile under electric field, which is not conducive for the improvement in breakdown strength and energy storage density . Herein, a flower like barium titanate/nickel hydroxide(BTO/Ni(OH) 2 ) core-shell structured filler has been fabricated to provide a novel approach to modify the interface between BTO and P(VDF-HFP) matrix for dielectric polymer composites . Ni(OH) 2 nanoflakes have grown in-situ on the surface of hydroxylated BaTiO 3 particles to form the flower like core-shell assemblies via hydrothermal reaction . Then, these synthetic BTO/Ni(OH) 2 particles with specific flower-like core-shell structure can be uniformly dispersed in P(VDF-HFP) without any additional surface modification due to their surface –OH groups. Meanwhile, Ni(OH) 2 shell triggered beta phase of P(VDF-HFP) near core-shell filler based on the interfacial interaction between Ni(OH) 2 and P(VDF-HFP). Thus, the intensity of the local electric field can be gradually reduced due to the formation of a dielectric constant gradient. Besides, these Ni(OH) 2 nanoflakes shell are able to cut down the local electric field and prevent the growth of electrical trees on the surface of BaTiO 3 during breakdown process. When the composite filler content is 10 wt%, the dielectric constant and breakdown strength increases to 14.8 and 330 kV/mm from 11 to 260 kV/mm, respectively. And the calculated energy density is 7.13 J/cm 3 , which is 1.5 times that of 10 wt% BTO/P(VDF-HFP) composite film . This study provides a novel shell material Ni(OH) 2 for the preparation of BTO core-shell structure filler, which has good compatibility with polymer substrates .