Fabrication of multilayer alternating polymer-based dielectric composites with superior energy storage performance via layer-by-layer spraying assembly

Polymer-based dielectric composites are pivotal for advanced pulsed power and power electronics, yet synergistically enhancing dielectric constant and breakdown strength remains a formidable challenge. Herein, we report a controllable layer-by-layer spray assembly strategy to fabricate ordered multilayer polyetherimide (PEI)-based composites with alternating high-dielectric and high-insulation layers. Homologous carboxylated PEI (CPEI) was designed and covalently grafted onto boron nitride nanosheets (BNNS) and barium strontium titanate (BST) fillers, ensuring exceptional interfacial compatibility. This enabled the precise deposition of CPEI@BNNS/PEI and CPEI@BST/PEI layers, yielding 3-, 5-, and 7-layer films. The 7-layer film achieved a high dielectric constant of 7.43 at 1 kHz, a remarkable breakdown strength of 731.2 kV·mm⁻¹, and a record discharge energy density of 20.87 J·cm⁻³ – 4.91 times that of pure PEI – while maintaining >90% charge-discharge efficiency. Comprehensive characterization and simulations revealed that the alternating multilayer structure creates deep-level interface traps that effectively suppress space charge migration, homogenize the internal electric field, and block electrical tree propagation. This work provides a facile and scalable pathway for the design and fabrication of high-performance ultrathin dielectric films.