Polymer dielectrics with excellent energy storage performance at high temperature are urgently needed in advanced applications, such as hybrid electric vehicles, smart grid and pulsed power sources. Polyetherimide (PEI), which is supposed to be the most promising candidate among polymer dielectric materials, displays a limitation for high‐temperature polymer dielectrics owing to the rapidly decreasing discharged energy density (Ud) and charge‐discharge efficiency (η). Herein, a novel PEI with cross‐linked networks was firstly prepared by utilising 2,4,6‐Triaminopyrimidine (TAP) as a cross‐linker. The results showed that the breakdown strength of the cross‐linked PEI (c‐PEI) with 2 wt% TAP increased to 399.4 MV/m, showing an increment of 23.3% in comparison with non‐cross‐linked PEI. Additionally, owing to the restrained polarisation loss and relaxation loss by cross‐linked networks, the dielectric loss of c‐PEI dielectric gradually decreased with the increasing content of TAP. Of particular significance was the c‐PEI dielectrics exhibiting improved Ud and η at high temperature. The maximum Ud of c‐PEI with 2 wt% TAP was 2.53 J/cm3 at 150°C, which was 24.8% higher than non‐cross‐linked PEI (2.11 J/cm3 at 150°C). This research provides an innovative strategy to achieve novel PEI dielectrics with improved Ud and η at high temperature.

This study reports that a novel high-temperature poly (m-phenyleneisophthalamide) (PMIA) composite with enhanced dielectric constant and thermal conductivity was prepared by filling with BaTiO3 nanowires–carbon nanotubes (BTCNs) fillers. Due to effective functionalization of BaTiO3 nanowires (BTNWs) and multi-wall carbon nanotubes (MWCNTs), the fabricated BTCNs fillers were homogeneously dispersed in PMIA matrix. The consequence displays that the dielectric constant of PMIA composite with 15 wt % BTNWs fillers increases to 27.6 at 103 Hz, which is about nine times higher than that of pure PMIA. Moreover, owing to the high thermal conductivity of MWCNTs, the thermal conductivity of PMIA with 15 wt% BTNWs fillers increases to 1.01 W/(mK). The enhanced thermal conductivity is beneficial for BTCNs/PMIA composite to dissipate the generated heat by dielectric loss. Considering these merits, this research would provide new methods and ideas for preparation of high-temperature dielectric polymer composites and reducing the internal thermal effect.