Synergistic enhancement of high-temperature energy storage performance in polypropylene composites via hierarchical BNNS@BTNC nanofillers

Polymer film capacitors confront critical challenges under harsh conditions of high temperatures and electric fields due to high conduction loss and degraded breakdown strength. Here, we report a novel polymer composite design: polypropylene (PP) reinforced with boron nitride nanosheet@barium titanate nanocrystal (BNNS@BTNC), achieving superior high-temperature energy storage performance. The optimized BNNS@BTNC/PP composite delivers a discharge energy density of 2.96 J/cm³ (5.9 times that of commercial high-temperature polymers, ~ 0.5 J/cm³) and maintains 92.4% efficiency under 550 MV/m and 120 °C. The wide-bandgap BNNS substrate is a physical barrier that inhibits electrical breakdown propagation paths. It captures charge carriers through deep traps, reducing leakage current and conduction loss. The BTNC uniformly distributed on high-aspect-ratio BNNS enhances interfacial polarization and phase compatibility. The oriented BNNS network significantly boosts in-plane thermal conductivity by 50%, effectively preventing thermal runaway. Finite element simulations validate the composite’s thermal stability, aligning with experimental results. Notably, the composite film maintains stable capacitive performance over extended charge–discharge cycles (50,000 cycles) in harsh environments (400 MV/m and 120 °C). These remarkable performances, combined with the scalable fabrication using commercially available raw materials, highlight the practical viability of the composite film for high-temperature capacitive energy storage applications.