Low-Content 2D Al2O3 Nanosheets for Concurrent Electrical Insulation and Thermal Management Toward High-Temperature Dielectric Energy Storage

Dielectric capacitors for pulsed power require stable operation at elevated temperatures, but commercial biaxially oriented polypropylene (BOPP) shows sharp performance degradation above ~105°C. Polyetherimide (PEI) is a promising polymer with high glass transition temperature, yet its low dielectric constant and poor thermal management limit high-temperature energy storage. Here, low-loading 2D Al 2 O 3 nanosheets (AO NSs) are introduced into PEI to simultaneously regulate charge transport and heat dissipation while avoiding the high-loading drawbacks of conventional 0D/1D ceramic fillers. The optimal 0.6 wt.% AO/PEI composite exhibits a high breakdown strength of 571.2 MV·m −1 at 25°C and retains 540.7 MV·m −1 at 100°C and 513.6 MV·m −1 at 150°C. Consequently, a maximum recoverable energy density of 7.9 J·cm −3 ( η > 90%) is achieved at 25°C, and 5.5 J·cm −3 ( η > 80%) at 150°C. Experiments combined with electric-treeing and temperature-distribution simulations verify suppressed field concentration and reduced heat accumulation, enabling stable performance over 10 4 cycles. These results demonstrate that low-content two-dimensional fillers provide an effective strategy for high-temperature dielectric energy storage. Highlights Low-content AO NSs enhance electrical and thermal properties in composites. The 0.6 wt.% AO/PEI composite shows high dielectric strength and stability at elevated temperatures. AO NSs suppress electric-field concentration and heat accumulation. Achieves 7.9 J·cm −3 energy density at 25°C and 5.5 J·cm −3 at 150°C.