Utilizing an MgO insulation interlayer reduces electrical conduction and enhances the electric breakdown strength of PEI dielectric films, this facile but effective method significantly improves the high temperature capacitive performance.

Polymer dielectrics have the advantages of flexibility, good insulation, high power density, etc., which are widely used in the fields of pulsed power and power electronics. However, the conduction loss increases sharply at elevated temperature, which leads to the severely degraded energy storage performances and limits the polymer dielectric films to be used at elevated temperature. To address this issue, the SiO 2 layer is grown on both side of polyetherimide (PEI) films by magnetron sputtering technology, the SiO 2 /PEI/SiO 2 composite films with a sandwiched structure are successfully constructed. The results show that by growing a wide band gap SiO 2 layer between the PEI film and the metal electrode can improve the height of the potential barrier at the electrode/dielectric interface, thus effectively reducing the conduction loss. The maximum discharge energy density is 2.96 J cm −3 when the charge-discharge efficiency is above 90%, which outperforms the reported dielectric polymers and composites. In addition, combining with the cycling charging/discharging results, SiO 2 /PEI/SiO 2 composite films are demonstrated to have significant long-term reliability and excellent discharging capability at elevated temperature.

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