Superior dielectric energy storage performance at elevated temperatures enabled by precisely tailored MgO NPLs distribution in tri-layer polymer composites

Polymer film capacitors are essential components in modern electronics due to their superior performance. However, their limited high-temperature stability hinders applications in demanding fields like electric vehicles and aerospace. While nanofiller doping has been extensively explored to enhance high-temperature performance, the inherent filler aggregation driven by van der Waals forces, hydrogen bonding, and electrostatic interactions remains a critical yet overlooked challenge, leading to heterogeneous dielectric response, compromised breakdown strength, and mechanical deterioration. Wide-bandgap magnesium oxide nanoplates (MgO NPLs) are synthesized via hydrothermal method and incorporated as fillers at ultralow loading into promising polyetherimide (PEI) matrix, followed by fabrication of tri-layer films through combined solution-casting and hot-pressing. An innovative concept of precisely tailoring filler distribution in polymer matrix has been proposed for the first time to effectively prevent nanofiller aggregation and charge accumulation, achieving uniform electric field distribution while minimizing interfacial dielectric mismatch and local field distortion. Consequently, the tri-layer composite dielectric maintains exceptional energy storage characteristics even under extreme high-temperature conditions. The maximum discharge energy density (U_d) reaches 7.82 J/cm³ with an efficiency (η) of 87.47 % at 150 ℃. Remarkably, at 200 ℃, the composite delivers an impressive U_d of 4.17 J/cm³ with η above 90 %, representing a tenfold improvement over pristine PEI and surpassing currently available commercial polymer dielectrics, newly developed synthetic polymers, and polymer composites. The proposed strategy of precisely tailoring the filler distribution demonstrates universal applicability across various polymer systems and diverse nanofillers, establishing a new paradigm for developing high-temperature-stable polymer dielectrics.