Optimizing Ply Pattern and Composition of Layered Composites based on Cyanate Ester, Carbon Nanotube, and Boron Nitride: Toward Ultralow Dielectric Loss and High Energy Storage

High dielectric loss and low breakdown strength have been two bottlenecks restricting applications of conductor/polymer composites for high energy storage. Herein, three kinds of layered composites, named BC, BCB, and CBC, were fabricated through stacking up hexagonal boron nitride (hBN)/cyanate ester (CE) (B layer) on carbon nanotube (CNT)/CE with 0.4 wt % CNTs (C layer). The effects of ply pattern and composition on dielectric properties, breakdown strength, and energy density of composites were investigated and also compared with those of single-layer 0.4CNT/CE composite containing 0.4 wt % of CNTs. Results show that three kinds of layered composites have significantly reduced dielectric loss and improved breakdown strength and energy density. Especially, for the CBC composite with 20 wt % hBN in B layer (C20BC), its dielectric constant is as high as 323 (100 Hz) and retains a value larger than 270 (1–10<sup>3</sup> Hz), it is the highest value reported so far among multilayered composites based on conductor/polymer and insulating layers; moreover, its breakdown strength and energy density are about 1.5 and 25 times of that of 0.4CNT/CE composite, respectively. Note that C20BC composite has very low dielectric loss (0.049 at 100 Hz) or much less at increased frequencies (>100 Hz), only about 2.6 × 10<sup>–3</sup> times of that at 100 Hz of 0.4CNT/CE composite. The origin behind these attractive properties was intensively discussed.