High-temperature energy storage with a new tri-layers polymer composites via hybrid assembly engineering

Dielectric film capacitors are fundamental components in advanced electrical fields such as smart grids and hybrid electric vehicle. The commercial film capacitors made by biaxially oriented polypropylene (BOPP) have high energy efficiency, but low energy density of only 2.0-3.0 J/cm³, while the inferior thermal stability restricts their high temperature applications. In this work, hybrid assembly engineering is proposed to design composite films with a new polymer of poly(acrylonitrile butadiene styrene) (ABS) as the matrix, boron nitride nanosheets (BNNS) and Na_0.5Bi_0.5TiO₃-Sr_0.7Bi_0.2TiO₃ (NBT-SBT) as two different fillers to improve high-temperature performance. The optimized composites SBS (NBT-SBT/ABS composites layer in the outside and BNNS/ABS composites layer in the middle) exhibit excellent high temperature energy storage characteristics, and its underlying mechanism is also understood by phase-field simulations. In particular, the maximum energy density at 120 °C can reach 15.0 J/cm³ at 575 MV/m, which is 8 times that of BOPP, while the efficiency is maintained at 89 %, far exceeding the performance of BOPP (<70 % at 120 °C). Together with their excellent cycling reliability (10⁶ cycles) and thermal stability, this strategy shows a great potential for high-temperature and high-power energy storage capacitors.