Janus composite film comprising metal–organic framework/polyimide and BNNSs/polyimide as high energy storage dielectrics

In order to prepare polymer dielectric materials with high energy storage density, a series of polyimide (PI) based Janus composite films were prepared by metal–organic frameworks (MOFs) material (UiO-66) with high dielectric constant ( ɛ r ) and boron nitride nanosheets (BNNSs) with high breakdown strength ( E b ). As reported, the UiO-66 can significantly improve the ɛ r of the composites. The ɛ r of 20 wt% UiO-66/PI film is 10.51 at 10 3 Hz, which is 3.1 times that of pure PI film (3.39 at 10 3 Hz). However, the E b of 20 wt% UiO-66/PI is only 58 MV m −1 , which is only 16.51% of pure PI (352 MV m −1 ). The sharp decline in E b reduces the energy storage capacity of the composites. To solve this problem, first, BNNSs with an average diameter of 2 μm and a thickness of 1.36 nm (about 4–5 layer) were obtained by hydrothermal reflux stripping. BNNSs/PI//UiO-66/PI Janus composite films with double-layer structure were prepared by directly casting BNNSs/PI on the surface of UiO-66/PI. For 0.3 wt% BNNSs/PI//10 wt% UiO-66/PI, the calculated energy storage density ( U e ) is 5.75 J cm −3 at 140 MV m −1 , which is 3.57 times that of pure PI film (1.61 J cm −3 at 140 MV m −1 ). Meanwhile, the charge discharge efficiency is 82.55% (at 140 MV m −1 ). Highlights BNNSs prepared by hydrothermal reflux stripping have fewer layers. BNNSs/PI composites improve the E b of UiO-66/PI composites by Janus structure. The U e of BP-0.3//UP-10 composites with Janus structure was 5.75 J cm −3 .