Enhancement of dielectric breakdown strength and energy storage of all-polymer films by surface flattening

All-organic dielectric films with the significant advantage of easy processing are highly desired in electronic and electric industry. As dielectric energy storage materials, improvement of their dielectric permittivity and electric breakdown strength is a long-standing work. Polytetrafluoroethylene (PTFE) films possess excellent high temperature properties but their electric breakdown strength is largely dependent on the surface flattness. Especially, interconnecting fiber structure tends to form during calcination when an ultrathin film is fabricated through a coating process. Herein, the surface of the PTFE films was flattened with epoxy resin. A high electric breakdown strength of 555 kV/mm, which is 134% of the pure PTFE film, and an improved dielectric permittivity of 2.3 have been achieved for the PTFE film immersed in 0.5 wt% epoxy solution at room temperature. It displays a discharged energy density of 3.58 J/cm³ (2.2 times of the pure PTFE film) with 98% discharge efficiency. The achieved high electric breakdown strength is owing to the reduced local electric field at the interface between film surface and electrode according to the simulation results. Besides, it also achieved a high discharged energy density of 1.93 J/ cm³ at 150 °C with 99% efficiency. Therefore, using organic to flatten the surface of polymer films has proved significantly effective in improving the dielectric energy storage performance.