Engineering Oxygen-Vacancy Traps in Polymer-Based Composite Dielectrics for High-Performance Capacitive Energy Storage at 200 °C

Abstract

Leakage current at elevated temperature remains a critical challenge in polymer dielectrics for high-temperature capacitive energy storage. Introducing interfacial traps is an effective strategy to suppress leakage current, nevertheless, heavily relying on high doping ratios to achieve sufficient interfacial area. Herein, poly(m-phenylene isophthalamide) (PMIA)-based dielectric films reinforced with P25 TiO₂, a mixed-phase filler that generates abundant oxygen vacancies at inter-phase boundaries, is reported. These oxygen vacancies introduce additional energy states in the forbidden band of P25 TiO₂, capable of generating multiply-trapped sites even at low doping levels. At an ultra-low doping ratio of 0.3 wt.%, leakage current of composite films is reduced by two orders of magnitude, contributing to an enhanced breakdown strength of 611.2 MV m⁻¹ at 200 °C. This attains a maximum discharge energy density of 10.12 J cm⁻³ while retaining 6.86 J cm⁻³ at a charge–discharge efficiency over 90%. The oxygen-vacancy traps and ultra-fast charge transfer dynamics are experimentally and theoretically investigated using photoluminescence (PL), time-resolved photoluminescence (TRPL), femtosecond transient absorption spectroscopy (fs-TAS), and density functional theory (DFT) calculations. The work highlights the significance of engineering oxygen-vacancy traps for high-temperature capacitive energy storage, with P25 TiO₂ being a promising platform for future applications.