Tuning Fillers via Multidimensional Synergistic Optimization for High-Temperature Capacitive Energy Storage

High-temperature performance is crucial for dielectric capacitors, especially in military and aerospace applications, as they offer superior charge–discharge rates and power density compared to supercapacitors and batteries. However, the stability of polymers based on commercial dielectric capacitors under extreme environmental conditions (i.e., ≥100 °C) presents significant challenges. Herein, with polyimide (PI) as the matrix, a middle layer is produced that is rich in zero-dimensional nanoparticles, BaTiO3 (0DBTO@PI), to enhance dielectric polarization. The upper and lower layers integrate two-dimensional laminated Al2O3 (2DAO@PI) as thermal conductive and insulating layers to improve heat dissipation and electrical insulation. The composites combine polarization enhancement and thermal management to synergistically improve high-temperature capacitive energy storage. As a result, the designed composite capacitors maintain good performance at temperatures > 150 °C. Even at 200 °C, it retains 2.36 J cm−3 (a 203% increase over pure PI), demonstrating unprecedented stability under extreme temperatures. Layer-specific functionalization provides a new and significant paradigm for designing high-temperature polymer-based energy storage films.