Enhanced high-temperature energy storage of a bilayer-structured dielectric composite through constructing MgO inorganic coating

Polymer dielectrics, as a crucial component for energy storage in film capacitors, exhibit significantly deteriorated capacitive performance at elevated temperatures owing to the sharp increase in leakage current density, which remains a great challenge for their application under harsh environments. Herein, we design a bilayer-structured composite dielectric with an inorganic coating, achieved via spraying two-dimensional (2D) MgO nanosheets with wide bandgap onto the surface of polyetherimide (PEI) film. Combining all experimental and simulated results, it is confirmed that the constructed MgO layer significantly increases the barrier height at the dielectric/electrode interface, reduces the leakage current density and suppresses the propagation of breakdown paths, therefore effectively enhancing the high-temperature energy storage performance of the designed bilayer PEI dielectric. Accordingly, the optimized bilayer dielectric delivers an excellent discharge energy density of 6.15 J/cm 3 with a charge-discharge efficiency of 80.0 % at 150 °C. Even at 200 °C, it can still achieve a high discharge energy density of 3.95 J/cm 3 with an efficiency of 76.2 %, and maintain outstanding operational reliability after repeating 100,000 charge-discharge cycles. This work provides a new insight for designing high-temperature PEI dielectric capable of operating under challenged environments and demonstrates great potential for scalable fabrication.