Grafting p -Aminobenzonitrile for Enhanced High-Temperature Energy Storage Performance of Poly(ether imide)

The combination of high power density, fast charge–discharge rates, excellent breakdown strength (Eb), and intrinsic self-healing properties makes polymer dielectrics attractive for use as electrostatic capacitors. Nevertheless, operation under high temperatures and high electric fields induces a marked increase in conduction loss. This increased loss, in turn, causes the deterioration of both Eb and energy storage density (Ue), consequently restricting the practical application of these materials. This research proposed a molecular-level modification strategy in which p-aminobenzonitrile (pABN) was successfully grafted onto the side chains of poly(ether imide) (PEI). This approach constructs an effective energy barrier on the molecular scale, thereby hindering charge carrier transport and enhancing energy storage performance. At 150 °C, with a pABN grafting mass percentage of 0.25%, the electric field strength required to maintain 90% charge–discharge efficiency (η) increases to 420 MV/m, and the Ue reaches 2.83 J/cm3. Furthermore, the composite dielectric demonstrates outstanding charge–discharge characteristics and maintains stable energy storage efficiency over 50,000 cycles. This work establishes a molecular-level grafting strategy for developing energy storage devices suitable for high-temperature environments.