Bicontinuous Phase Network Formed by Anti‐Plasticization Enhances Energy Storage Performance in Polyetherimide Dielectric Film

Abstract Polymer dielectrics display high breakdown strength ( E b ) and larger power density, rendering them an indispensable component in electronic energy storage applications. Nevertheless, the discharged energy density ( U d ) of polymer dielectrics is limited by relatively low dielectric constant (ε r ) and sharply decreases in E b at elevated temperatures. The simultaneous improvement in both E b and ε r is highly desired, but the inverted relationship requires urgent resolution. Herein, the study introduces several plasticizers with low content into polyetherimide (PEI) matrix to fabricate composites. The formation of a bicontinuous phase network in polymer matrix is achieved through anti‐plasticization. Owing to the discrepancy in polarizability, the network can achieve an electric field redistribution and interface polarization. It is composed of a dielectric phase (bear a lower electric field) and an insulation phase (bear a higher electric field), resulting in a concomitant enhancement on both ε r and E b . A relatively high U d of 4.88 J cm −3 accompanied by η = 90% and charge‐discharge cycle stability up to 10 5 cycles at 150 °C are achieved in the composite content with 3 wt.% of butylsuccinic anhydride. This work presents a promising strategy for decoupling the inverse relationship and fabricating applicable high‐temperature polymer dielectrics through phase structure modulation.