Enhancing the high electric field resistance and energy storage capacity of polymer dielectrics has been a long-standing challenge for the iterations of power equipment. Synergistic inhibition of carrier injection and transport is vital to energy storage performance improvement. Herein, promising polymer polyetherimide (PEI) was employed as a matrix and wider bandgap boron nitride nanosheets (BNNSs) were used as a reinforcing filler. Utilizing high-throughput stochastic breakdown simulations with the distribution characteristics of BNNSs as parameters, a series of topological gradient structures with the potential to enhance performance were obtained, thereby shortening the experimental cycle. Changing the BNNS distribution of symmetric/asymmetric and positive/inverse gradients, as well as the total and gradient contents of BNNSs, means that the position and condition of the surface barrier layer and central hinder layer change, which influences the energy storage performance of the polymer at room temperature and high temperature. Remarkably, the asymmetric gradient structure composite dielectrics exhibited excellent performances. Among them, the PEI-based composite dielectric with 2 vol% BNNS asymmetric inverse gradient distribution (gradient content of 1 vol%) achieved energy densities of 8.26 and 4.78 J cm⁻³ at room temperature and 150 °C, respectively. The asymmetric gradient structure design strategy holds great promise for optimizing the energy storage capacity of polymer dielectric capacitors.

As the power industry continues to advance rapidly, large-scale generators are evolving toward higher voltage levels and greater capacity. The heat accumulation associated with high voltage and large capacity accelerates the aging of the main insulation. It is necessary to enhance the thermal conductivity (λ) and dielectric properties of existing main insulation materials. This work focuses on investigating the effects of varying addition levels of two different-sized BN particles on the λ and dielectric properties of the mica tape composite dielectric. The experimental findings demonstrate a progressive enhancement in the λ of the mica tape corresponding to the incremental addition of h-BN concentration. When the doping concentration reaches 20 wt.%, the λ of the two h-BN-doped mica tape (h-BN/MT) reaches a maximum of 0.382 W/(m·K), 0.4 W/(m·K), respectively, which enhances the λ of the contrasting pure mica tape (0.199 W/(m·K)) by 91.95% and 101.01%, respectively. In terms of electrical insulation properties, both sizes of h-BN/MT perform well, with breakdown strength above 32 kV/mm. Furthermore, the second-order thermal conductivity model of mica tape doped with different sizes of h-BN was constructed by combining the Halpin–Tsai model with the Series model, which allows the calculation of λ of mica tape composites doped with different sizes of h-BN. This work provides a novel structural design approach for preparing mica tape composite dielectric that simultaneously exhibits high λ and high insulation properties.