PVDF-based high-energy-storage dielectrics by introducing insulating layer on the surface of metal-organic frameworks

In this paper, UiO-66 nanoparticles were synthesized through the hydrothermal synthesis technique. Subsequently, a series of metal-organic framework/polyvinylidene fluoride (MOF/PVDF) composite films were produced via a solution-casting approach. The dielectric properties of UiO-66/PVDF (U/P) composite are improved with the addition of UiO-66. The dielectric constant ( ɛ r ) of 20 wt% U/P composite film at 10 2 Hz is 11.20, 1.44 times that of pure PVDF film ( ɛ r = 7.78). However, the breakdown strength ( E b ) was only 95 kV mm −1 . To solve the problem of sharp decline in E b , TiO 2 with a wide band gap was introduced to form an insulating layer on the surface of UiO-66. This reduces the difference in electrical properties between the filler and PVDF, hinders the formation of the conductive path within the composite, reduces leakage current, and increases E b . Compared with the U/P composite, the ɛ r and E b of TiO 2 @UiO-66/PVDF (T@U/P) composite film are increased, and the dielectric loss (tan δ ) and leakage current density ( J ) are decreased. The energy storage density ( U e ) of 10 wt% T@U/P composite film is 4.51 J cm −3 and the charge and discharge efficiency ( η ) is 84.61% at 150 kV mm −1 . These results indicate that the dielectric properties of UiO-66 can be significantly enhanced by using titanium dioxide as an insulating layer. Highlights By introducing UiO-66, the ɛ r of PVDF material is improved. Modifying UiO-66 with TiO 2 can improve its breakdown strength significantly. The U e of the T@U/P-10 composite modified with UiO-66 is 4.51 J cm −3 .