Optimization of high-temperature energy storage properties of polyetherimide-based nanocomposite films via BST@CdS core-shell structure

Flexible dielectric composites stand as a promising candidate in high-power energy storage technology, but their practical application is hindered by low energy storage density (Ue), efficiency (η), and poor thermal stability at elevated temperatures. Herein, core-shell nanoparticles using barium strontium titanate coated with cadmium sulfide (BST@CdS) are designed and incorporated into polyetherimide (PEI) matrices as fillers to fabricate nanocomposite films. The CdS on the surface of BST nanoparticles, with its moderate dielectric constant, alleviates electric field mismatch between BST nanoparticles and PEI, while also introducing additional interfacial polarization. Additionally, the electron traps formed at the CdS/PEI interface can capture free and injected electrons. These features concurrently lead to an enhanced dielectric constant, reduced dielectric loss, and suppressed leakage current density, thereby boosting the energy storage performance of nanocomposite films. Accordingly, the optimized PEI/BST@CdS nanocomposite boasts an outstanding Ue of 9.4 J cm-3 and an η of 93.9% at 600 kV mm-1 and 25 °C. Remarkably, even at 150 °C, it still achieves superior energy storage performance with a Ue of 4.4 J cm-3 and an η of 90.7% at 400 kV mm-1. This study presents a viable approach for fabricating high-performance dielectric energy storage capacitors.