Enhanced energy density of polymer dielectrics at high temperature by building a B–N coordinated supramolecular network

Electrostatic capacitors are considered the preferred candidates for high-power energy storage. The demand for electrostatic capacitors operating at high temperatures (>150 °C) has been driven by applications in electric vehicles, aerospace systems, etc. Herein, we propose a strategy of using a B–N coordination supramolecular network to construct crosslinked polymer dielectrics for improved energy storage performance at elevated temperatures and electric fields. Specifically, by incorporating 2,7-diboronic ester-9,9′-spirobifluorene (DBASBF) into the polyetherimide (PEI) matrix, B–N coordination bonds are formed between the nitrogen atoms in PEI and the boron atoms in DBASBF, leading to the formation of a supramolecular coordination network. Theoretical calculations and experimental results confirm that the formation of this supramolecular network effectively enhances mechanical robustness and suppresses charge migration. As a result, the fully organic PEI/DBASBF-0.5% composite dielectric achieves a discharged energy density of 4.52 J cm−3 at 200 °C with an energy efficiency exceeding 90%, which is increased by 139% compared with the PEI matrix and surpasses many of the currently reported polymer dielectrics. Moreover, the composite also exhibits outstanding flexibility, along with remarkable long-term reliability. This work offers a design paradigm for developing high-performance polymer dielectrics suitable for harsh environments.