Significant improvement of high-temperature energy storage of poly(4-methyl-1-pentene) films by cooperatively regulating the multiscale structures

Biaxially oriented polypropylene (BOPP) are the most popular dielectric materials that used in the film capacitors products, however, the maximum operating temperature of BOPP films is only 105 °C, which limits its application in the extreme high-temperature and high-field conditions. Thus, it is urgent to develop the new-typed dielectric films with excellent energy storage performance at elevated temperature for meeting the requirements of new energy vehicles and high-voltage-direct transmission engineering. Recently, non-polar polyolefin poly (4-methyl-1-pentene) (PMP) dielectrics with superior high-temperature endurance and exhibit great potential to replace BOPP. In this work, PMP films have been successfully fabricated by melt casting technique and achieved mass-production. To further improve the high-temperature energy storage performance of PMP dielectric films, we propose a cooperative modulation of the multiscale structures including molecular chains and surfaces. In detail, UV-irradiation grafting of trifluoroethyl methacrylate (TFEMA) onto PMP molecular chains creates “bulk-traps” through polar group effects, which can effectively trap electric charges and reduce conduction loss at high-temperature. Meanwhile, the AlN/PZT heterostructured inorganic barrier layers are deposited onto the surfaces of TFEMA-grafted-PMP films via magnetron sputtering technique. The energy band structure differences between AlN/metal electrodes and AlN/PZT interfaces were utilized to construct interface barriers, thereby suppressing charge injection from metal electrodes and reducing high-temperature conduction losses. The results demonstrate that the high-temperature energy storage performances of the films have been significantly improved by optimizing UV irradiation duration and inorganic barrier layer thickness. At 150 °C, a discharged energy density of 4.23 J/cm 3 with η maintained above 91 % has been achieved, while the films exhibit excellent cycling stability of charge-discharge performances.