Polyimide-Based Composite Films with Largely Enhanced Energy Storage Performances toward High-Temperature Electrostatic Capacitor Applications

The next generation of high-energy-density electrostatic capacitors operable under elevated temperatures is urgently demanded to cope with the development of advanced high-power electronic systems. However, the inherent characteristics of the existing polymer dielectrics, such as poor heat dissipation, narrow band gaps, and high conduction loss, limit their energy density at high temperatures and result in a major hindrance to their applications under harsh conditions. Herein, a class of sandwich-structured dielectric polymer nanocomposites based on high-permittivity barium titanate nanoparticles (BT NPs) and heat-resistant hexagonal boron nitride nanosheets (BNNSs) are reported. In contrast to the traditional single-layer designs, the sandwich-structured configuration could elegantly combine the complementary functionalities of multicomponents in a synergistic fashion. Accordingly, functionalized with BT NPs in the outer layers offering superior permittivity and BNNSs in the central layer impeding the charge injection from electrodes, the properly designed sandwich-structured polymer composite films achieve a superior discharge energy density (Ud) of 11.5 J cm–3 accompanied by an efficiency (η) of 86.2% at room temperature, which is a 570% enhancement of neat polyimide (PI ∼2.00 J cm–3) and 960% over biaxially oriented polypropylene (∼1.2 J cm–3). Particularly, the composite films exhibit high-temperature performances with Ud ∼ 4.072 J cm–3 and η ∼ 83.3% at 150 °C. The remarkable Ud and η obtained in this work proved the feasibility of the layered polymer nanocomposite film in high-temperature electrostatic capacitors.