Improved breakdown strength of Poly(vinylidene Fluoride)-based composites by using all ball-milled hexagonal boron nitride sheets without centrifugation

Hexagonal boron nitride (h-BN) is an ideal candidate to endow ferroelectric polymers with high energy density (Ue) due to its intrinsic high breakdown strength (E-b) of 800 kV/mm. Generally, it is believed that only boron nitride nanosheets (BNNSs) could remarkably improve E-b of composite. Nevertheless, low-yield and timeconsuming preparation procedures of BNNSs greatly limits the application of h-BN. To overcome this challenge, in this study, all ball-milled h-BN (B-BN) sheets were entirely used to enhance E-b of poly (vinylidene fluoride) (PVDF) without any further centrifugation. E-b of composites increased as ball-milling time increases at filler content of 8 wt%. Remarkably, PVDF with h-BN ball-milled for 16 h (B-16-BN) possesses an impressive Eb value of 506.8 kV/mm, which is 2.86 times that of neat PVDF (272.4 kV/mm) and even 1.33 times higher than that of PVDF/h-BN composites (380.6 kV/mm). E-b of PVDF/B-16-BN composites is close to that of PVDF/OHBNNSs composites at same filler content, suggesting that the centrifugation is not a necessary procedure. Besides, improved dielectric loss, calculated U-e, mechanical properties and in-plane thermal conductivity can also be achieved for PVDF/B-16-BN composites. These improved properties of PVDF/B16-BN composites indicate that the employment of B56-BN can avoid the weakness of low-yield and time-consuming preparation procedure of BNNSs and broaden its applications in the field of energy storage. Finally, the improved dispersion of OH-BN as well as synergy effect (f) on E-b between OH-BN and OH-BNNSs were discussed to better understand these improved properties of PVDF/B-16-BN composites.