Synergistic modification of BN and TiO2 on polyethersulfone multilayered dielectrics for enhanced elevated-temperature energy storage performance

Abstract

The development of high-power electronic devices demands dielectric composites with excellent breakdown strength and high relative permittivity, reliable performance at elevated temperatures, and high thermal conductivity. Polyethersulfone (PESU) is a promising dielectric material owing to its outstanding breakdown strength and thermal stability, but it suffers from a relatively low dielectric constant. To address this, the present study investigated modification strategies by incorporating boron nitride (BN) and titanium dioxide (TiO₂) into the PESU matrix, coupled with an optimized multilayer structural design. Composite dielectric films of 5 wt% TiO₂-PESU (5TP), 5 wt% BN-PESU (5BP), and 2.5 wt% BN + 2.5 wt% TiO₂-PESU (2.5BTP) and a hot-pressed five-layer structured film were fabricated via solution casting, and their dielectric, energy storage, and thermal properties were systematically evaluated, especially at elevated temperatures. Experimental results show that appropriate filler loading enhances composite performance. At 50 °C, the 5BP composite achieved an energy storage density of 4.38 J cm⁻³ and a charge–discharge efficiency of 89.6% at 420 kV mm⁻¹. Notably, the five-layer film integrated the advantages of single fillers, delivering a higher energy storage density of 6.53 J cm⁻³ and a charge–discharge efficiency of 86.9% at 380 kV mm⁻¹. Through comprehensive experiments and analysis, this work reveals the mechanism for optimizing the performance of modified PESU-based composites, providing a valuable reference for developing high-performance, stable thin-film capacitor dielectrics for high-temperature applications.