In-plane aligned doping pattern in electrospun PEI/MBene nanocomposites for high-temperature capacitive energy storage

To achieve superior energy storage performance in dielectric polymer films, it is crucial to balance three key properties: high dielectric constant, high breakdown strength, and low dielectric loss. Here, we present the realization of ultrahigh efficiency and energy density in electrospun MBene/PEI composite films, achieved through an in-plane aligned doping pattern. The 1.0 wt% film exhibits a dielectric constant of 10.7 at 1 kHz while maintaining a low dielectric loss below 0.0074. Compared to the random doping pattern, the dielectric constant increases by 25.9%, and dielectric loss is suppressed by 40.3%. The uniform and non-connected dispersion of MBene fillers promotes a homogeneous electric field distribution and minimizes the risk of developing continuous leakage current paths. Therefore, the breakdown strength remains high at 494 kV mm^-1. Possessing ultrahigh dielectric constant, minimal dielectric loss, and well-preserved breakdown strength, the MBene/PEI film yields an energy density of 8.03 J cm^-3 at room temperature, and achieves 5.32 J cm^-3 at 150 °C, with an efficiency exceeding 90%. Additionally, this in-plane aligned doping pattern also enhances mechanical properties. This work provides a unique solution to mitigate side effects by utilizing conductive fillers, presenting a valuable strategy to fabricate dielectric films for high-performance energy storage.