Surface engineering of 2D dielectric polymer films for scalable production of High-Energy-Density films

Film Capacitors with high-energy storage density, high-temperature stability and charge–discharge efficiency are highly desirable in advanced microelectronic and electrical power systems. Polymers have been widely adopted as the main dielectrics in film capacitors due to their low dielectric loss, high breakdown strength, flexibility, lightweight, low cost and ease of processing into a large area, defect-free and free-standing thin film. However, the low dielectric constant of dielectric polymers severely hinders the improvement in the energy storage density of dielectric polymer films. In the last two decades, numerous efforts have been made to improve the energy density of dielectric films through employing polymer nanodielectric composites (PNCs), all organic polymer composites (AOPCs), molecularly designed polymers (MDPs), multi-layered polymer composites (MPCs) and surface engineered polymers (SEPs). However, only surface engineered polymers stands out from other approaches in the improvement of energy density from a view of scalable, continuous and large-area treatment of thin polymer films, which is the most promising strategy to solve the urgent demand for high energy density in the film capacitor industry. Unlike prior reviews focusing on PNCs, AOPCs, MDPs and MPCs from a view of lab-scale production, this review focuses on recent achievements in surface engineering of two-dimensional (2D) dielectric polymer films on both lab and industry scale productions. The key factors that determine the energy storage performance of dielectric polymer films are discussed in detail. The conventional strategies to improve the energy storage performance of dielectric polymer films are briefly introduced. The challenges associated with scalable, continuous and large-area production of thin dielectric polymer films with high structural quality and uniform dielectric performance are then pointed out and emphasized. The categories of surface engineering strategy including radiation treatment, inorganic deposition and organic impregnation are subsequently introduced and the key factors and main principles for designing SEPs to improve the dielectric and energy storage performances of dielectric polymer films are discussed and summarized. Current attempts using SEPs to improve the energy storage performance of films are summarized in detail. Some key insights to the current progress on SEPs are subsequently stated. Future pathways for the improvements of dielectric and energy storage performances through surface engineering of 2D dielectric polymer films for both scientists and engineers are suggested.