Significant Enhancement in Dielectric Properties of Polyimide Alloys Through a Two-Phase Interlocking Structure

High temperature dielectric polymers are the favored materials for energy storage devices under harsh-environment, e.g., electronic devices and power systems. It is widely acknowledged that the energy storage capabilities of dielectric polymers are markedly deteriorated at elevated temperature because of the exponential increased leakage current. Herein, all-organic dielectric polymer alloys with two-phase continuous hard-soft structure have been firstly investigated via blending high glass transition temperature (T_g) fluorinated polyimide (FPI) and high bandgap aliphatic polyimide (API). The large energy band difference between FPI and API is conducive to trap energy and greatly inhibits conduction loss. In addition, the hard and soft molecular chains with two-phase interlocking structures are more closely arranged, bringing torturous pathways for charge carriers and reducing free volume, which enhances the breakdown strength. FPI/API alloy with high T_g (296 °C) and concurrent large bandgap delivers an ultrahigh discharge energy density of 6.6 J cm⁻³ at 150 °C and 3.02 J cm⁻³ at 200 °C with 90% discharge efficiency, significantly surpassing those reported dielectrics. Moreover, the FPI/API alloy exhibits remarkable cyclability and dielectric stability up to 10000 charge-discharge cycles even at elevated temperatures. This work provides an unprecedented opportunity on structure design of dielectric polymers to achieve high-temperature energy storage capacitors.