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

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 10⁵ 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.