Enhanced dielectric tunability and energy storage density of sandwich-structured Ba0.6Sr0.4TiO3/PVDF composites

• BST/PVDF composites with two different sandwich structure were fabricated. • High U e (10.54 J/cm 3 ) and T u (83.33%) were obtained in BST/PVDF-PVDF-BST/PVDF structure. • The BPB structure increases U e and T u by 100% and 40% than monolayer, respectively. • Finite element simulation indicated sandwich structure enhanced storage density. The regional distribution of fillers can change the distribution of electric field in the ceramic/polymer composites and further affect the dielectric properties. Here, Ba 0.6 Sr 0.4 TiO 3 /PVDF (BST/PVDF) monolayer and its two kinds of sandwich-structural composites, PVDF-BST/PVDF-PVDF (PBP) and BST/PVDF-PVDF-BST/PVDF (BPB), were fabricated using solution casting method combined hot pressing process. The results showed BPB structural composite possesses the best dielectric performances with a relative permittivity of 17.3, an energy density ( U e ) of 10.54 J/cm 3 which is 2 times of BST/PVDF monolayer composite with the same BST content, as well as a dielectric tunability of 83.33%. Finite element simulation further proves that sandwich structure, especially BPB structure, can reduce the occurrence of electrical breakdown in the composite, and improve the energy storage characteristics and dielectric tunability. This work gives new thinking for the development of energy storage thin-film composites.