High Transparent Cellulose Acetate Composite Films toward Energy Storage Achieved by Tailoring the Dispersion of Carbonized Polymer Dots and Barium Titanate in the Sandwich Structure

Green energy sustainability has emerged as one of the most critical issues facing our planet. Dielectric films based on green, sustainable, and environmentally friendly polymers are considered to be one of the ways to develop green energy, attracting much interest of researchers recently. One of the great challenges is achieving high breakdown strength and energy storage density and simultaneously maintaining high transparency. Here, a series of sandwich-structured composite films with cellulose acetate (CA) as the substrate material and carbonized polymer dots (CPDs) and barium titanate (BT) as fillers were fabricated. The CPDs and BT were separately dispersed in different layers to construct the heterogeneous structure. The findings reveal that there is a robust interaction between CPDs and CA molecular chains through hydrogen bonding. This interaction, in conjunction with the unique Coulomb-blockade effect of CPDs, effectively restricts the generation of the leakage current and enhances the breakdown strength of the films. The introduction of polydopamine (PDA)-coated BT (PBT) increases the dielectric constant of the composite films. Specifically, the composite film with 0.1 wt % CPDs in the upper and lower layers and 3 wt % PBT in the middle layer exhibits a discharge energy density (Ud) of 4.33 J/cm3 at 500 MV/m with an ultrahigh efficiency (η) of 91.88%, and simultaneously, the transparency was maintained at 75.21%. This work provides an alternative for developing the next generation of eco-friendly dielectric films.