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 TiO 2 , 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 TiO 2 , 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 TiO 2 being a promising platform for future applications.