Polymer dots enabling ultrahigh capacitive energy storage in cellulose-based all-organic nanocomposites

Abstract

Dielectric capacitors represent a promising alternative to conventional electrochemical counterparts for applications in high-voltage networks, integrated circuits, and portable flexible electronics. Currently, most practical dielectric polymers are derived from petroleum-based sources, whereas environmentally sustainable biomass dielectric materials remain largely underexplored. We report a class of cyanoethyl cellulose (CEC)-based nanocomposites enhanced with polyethyleneimine-based polymer dots (PEPDs), which simultaneously elevate both the dielectric constant (ε_r) and breakdown strength (E_b). The wide-band-gap PEPDs with abundant amino groups form hydrogen bonds with the CEC backbone, ensuring uniform dispersion and creating continuous polar interfacial regions that substantially improve ε_r. In parallel, the high electron affinity of the polymer matrix, together with deep-level traps introduced by the wide-band-gap PEPDs, effectively suppresses charge migration and reduces conductive loss, leading to a notable enhancement in E_b. As a result, the optimized composite achieves a remarkable discharged energy density (U_d) of 35.2 J cm⁻³ at 700 MV m⁻¹, outperforming current dielectric biomass materials. This work establishes a promising pathway for the development of cellulose-based nanocomposites toward next-generation high-energy-density dielectric capacitors.