Enhanced energy storage density with improved self-healing property by biaxial orientation of 2D nanosheet composite polypropylene film

Dielectric materials with enhanced energy storage performances are urgently demanded owing to the development of advanced capacitor equipment. However, low energy density and weak self-healing capabilities of current dielectric materials still limit the practical applications. Here, a biaxially oriented (polypropylene/two-dimensional (2D) Al₂O₃ nanosheets/grafted polypropylene) nanocomposite was proposed. The biaxial orientation enabled the directional arrangement of nanosheets in the polymer matrix. The oriented 2D nanosheets played a dominate role in the restriction of charge transportation and the tradeoff of energy consumption during breakdown and self-healing. Therefore, on one hand, the discharge energy density reached a considerable value of 9.64 J/cm³. On the other hand, the self-healing area of the metalized films was a 36% smaller than that of biaxially oriented polypropylene (BOPP) at the comparable self-healing energy, which was related to the long-term reliability of capacitor. The further experiments and simulations indicated that the oriented γ-A₂O₃ nanosheets (AONs) arrangement suppressed electric field distortion and hindered the charge transportation, which greatly enhanced the breakdown strength and ultimately improved the energy storage performance. This strategy presented a potential solution for improving the energy storage performance of capacitor films, which is suitable for current industrial production.