The synergy of molecular architecture and thermal management for high-performance polyimide based dielectric capacitors

Polymer-based dielectrics are struggling with high-temperature energy storage applications because of a sharp increase in conductive losses and a high risk of dielectric breakdown. In this work, a dual strategy combining molecular-scale optimization of imide groups in the polyimide (PI) matrix with microstructural engineering using aligned boron nitride nanosheets (BNNSs) is proposed. Firstly, leakage current and inherent breakdown failure of dielectrics are significantly reduced by precisely controlling the imidization of the polymer matrix. Moreover, the effective thermal pathways to dissipate Joule heat of the dielectric at high temperature are constructed by the vertically aligned BNNSs. This synergistic strategy prompts a significant enhancement of energy storage performance. Importantly, even at an elevated temperature of 200 °C, the nanocomposites maintain excellent energy storage performance, achieving an energy density (U_e) of 4.5 J cm⁻³ with charge-discharge efficiency (η) of 90%, along with stable operation. Particularly, the low working field indicates its enhanced operational safety and lower energy consumption compared to the state-of-the-art dielectric capacitors. The proposed approach for constructing heat dissipation paths can be easily extended to other dielectrics to improve the high-temperature energy storage performance, enabling broader applications in electronics and energy storage devices.