Breaking the energy density barrier in polymer film capacitors via molecular and interfacial design

Dielectric capacitors are indispensable in modern electric systems, including smart grids and hybrid electric vehicles. However, their inherently low energy density limits further device miniaturization and integration. In this study, we present a comprehensive tripartite strategy to overcome this challenge. First, a series of thiourea-based polymers with tailored main-chain architectures are synthesized to optimize free volume and charge distribution in the polymer matrix. Second, nanofillers are incorporated to modulate band structure, achieving an electrical rectification effect that generates high-density interfacial carrier traps in the interface region—effectively suppressing electric field distortion. A rationally designed sandwich structure further homogenizes the electric field distribution, significantly improving dielectric breakdown strength. As a result, the polymer composites display markedly improved energy storage capabilities. The optimized sandwich-structured films achieve a remarkable discharged energy density of 7.33 J/cm³ at 660 MV/m with 90.0 % efficiency at room temperature, and 6.29 J/cm³ at 620 MV/m with 89.1 % efficiency at 150 °C. This work offers an effective strategy for developing high-performance polymer dielectrics with excellent energy storage performance under both ambient and high-temperature conditions.