Optimization of drying scheme for polyetherimide film to achieve ultra-high breakdown strength and enhanced energy storage performance

As one of potential candidates for fabricating high-power dielectric polymer capacitors, polyetherimide (PEI) has been paid much attention. However, energy storage performance of PEI films, especially discharge energy density, has demonstrated notable discrepancies among various studies. The reported maximum discharge energy densities of PEI are still below 7 J∙cm⁻³, and are closely related to the drying procedures. In this work, PEI films were meticulously synthesized via the solution casting method, with focusing on optimizing the drying procedures to enhance their energy storage performance. The PEI films were pre-dried at various temperatures for different durations. The different drying procedures do not cause change in chemical bonds of PEI. The optimized protocol involves a precise pre-drying step at 80 °C for 8 h in vacuum, seamlessly followed by further drying at 200 °C for 12 h. Pure PEI prepared via the optimized drying procedure exhibits the lowest glass transition temperature of 215.69 °C, exceptional breakdown strength of 678 MV∙m⁻¹, and astounding discharge energy density of 8.48J∙cm⁻³, surpassing the majority of previously reported values. The work not only presents an effective simple method for developing high-performance pure PEI films, but also provides some guidance to enhance energy storage performance of polymer materials.