Roll-to-roll fabricated polymer composites filled with subnanosheets exhibiting high energy density and cyclic stability at 200 °C

Polymers are key dielectric media for energy storage capacitors in power electronics for electric vehicles and solar panels, and there is an urgent need to enhance their discharged energy density (Ud) at high temperatures. Existing polymer–inorganic nanocomposites with high Ud cannot be produced by conventional roll-to-roll fabrication processes and exhibit compromised cyclic stability. In this study, we introduced phosphotungstic acid subnanosheets, a ‘reservoir’ for charges, into polymers to form a subnanocomposite. Even a low loading (0.2 wt%) of ultralarge, ultrathin, flexible subnanosheets was found to effectively strengthen polymers and hinder the propagation of breakdown paths. These subnanosheets can also trap charges through grafted surfactant molecules and polyoxometalate cluster backbones. An ultrahigh Ud of 7.2 J cm−3 with a charge–discharge efficiency of 90% and charge–discharge cycle stability up to 5 × 105 cycles at 200 °C were observed. Furthermore, a 100-metre-long roll of the subnanocomposite film was roll-to-roll fabricated on an industrial solution-casting production line. This work demonstrates the potential of this subnanocomposite strategy for the mass fabrication and application of high-performance polymer dielectrics.