Coupled Bulk‐Interfacial Modulation Enables Suppressed Conduction Loss in High‐Temperature Polymer Capacitors

Polymer film capacitors are widely used in electronic devices and power systems, yet their energy storage performance (ESP) deteriorates significantly under harsh operating conditions. Here, we propose a synergistic strategy that integrates bulk physical crosslinking with interfacial plasma regulation to suppress conduction loss and enhance high‐temperature dielectric performance. 4‐cyanobenzaldehyde (4‐CZ) is incorporated into a polyetherimide (PEI) matrix to construct a noncovalent, electrostatically crosslinked network, which simultaneously constrains polymer chain dynamics and introduces charge‐transport barriers, thereby effectively inhibiting carrier migration. In parallel, plasma surface treatment further enhances interfacial trap density and suppresses charge injection. Owing to this synergistic regulation of bulk and interface, the optimized film delivers a discharge energy density ( U d ) of ∼7.6 J·cm −3 with an efficiency ( η ) of 91.8% at 150°C and 670 MV·m −1 , markedly outperforming pristine PEI. This work establishes a generalizable design strategy for high‐performance all‐organic polymer dielectrics toward high‐temperature energy storage applications.