Largely enhanced energy storage density of poly(vinylidene fluoride) nanocomposites based on surface hydroxylation of boron nitride nanosheets

Adding functional fillers is a simple but efficient way to improve the dielectric properties of polymer materials. However, the improvement of dielectric constant is usually accompanied by a decrease of breakdown strength (BDS), and vice versa, which results in only a limited increase of the energy storage density of polymer composites. In this work, boron nitride nanosheets (BNNSs), an insulator with high theoretical BDS (800 kV mm(-1)), were used to improve the dielectric properties of poly(vinylidene fluoride) (PVDF). To improve the dispersion of BNNSs and the interfacial interaction with the PVDF matrix, the grafting of hydroxyl groups onto the surface of BNNSs was first carried out to obtain surface modified BNNSs (OH-BNNSs). Interestingly, the surface hydroxylation of BNNSs could realize simultaneous enhancement both in BDS and dielectric constant. Therefore, a high energy storage density of 13.1 J cm(-3) has been achieved for PVDF/OH-BNNS nanocomposites with only 6 wt% filler content, which represents an impressive enhancement compared with neat PVDF (440%) or PVDF/BNNS (166%) nanocomposites. Moreover, decreased dielectric loss tangent, and improved thermal and mechanical properties of PVDF have also been achieved by adding OH-BNNSs. This research provides a new dimension of the surface modification of BNNSs and broadens their practical applications in the field of dielectric energy storage.