Bioinspired, compositionally graded cellulose-based dielectrics with Schottky-engineered interfaces for high-performance and sustainable energy storage

Inspired by the hierarchical structure of the feathers of black swans at the Shaanxi University of Science and Technology (SUST), we developed compositionally graded cellulose-based composite films incorporating BCZT ceramic fillers with varying compositions into a cellulose/P(VDF-HFP) blend film (C8/PH2) for high-performance and sustainable dielectric capacitors. Three configurations-single-layer, down-graded trilayer (C8/PH2-BCZT-dg), and up-graded trilayer (C8/PH2-BCZT-ug)-were fabricated and systematically evaluated. The C8/PH2-BCZT-dg film achieved the highest recoverable energy storage density (W_rec = 38.73 J cm^-3) and efficiency (η = 79.39%), attributed to the stable Schottky emission conduction across its interfaces, as revealed by current-voltage fitting and band-diagram analysis. In contrast, the C8/PH2-BCZT-ug film structure exhibited a conduction-mechanism transition to Ohmic contact, leading to reduced breakdown strength. Finite element simulations confirmed the experimental breakdown trends and highlighted the role of internal potential distribution. The C8/PH2-BCZT-dg film also demonstrated excellent frequency stability (10 Hz-10 kHz), cycling durability (10⁶ cycles), and high-power performance, with rapid energy release (t_0.9 = 41.97 ns) and a discharge energy density of 21.07 J cm^-3 at 5.0 MV cm^-1. Furthermore, combustion testing revealed the superior fire resistance of the film, underscoring its safety for long-term operations. These results establish hydrogen-bond-engineered, compositionally graded cellulose composites as promising eco-friendly alternatives to petroleum-based dielectric materials for advanced energy-storage applications.