Annealing-Assisted Dip-Coating Synthesis of Ultrafine Fe₃O₄ Nanoparticles/Graphene on Carbon Cloth for Flexible Quasi-Solid-State Symmetric Supercapacitors

With the rapid development of science and technology, traditional supercapacitors have become increasingly difficult to support applications in various scenarios; therefore, the development of flexible solid-state supercapacitors is critical to meet future needs. In this work, we propose an efficient and controllable annealing-assisted dip-coating method to prepare ultrafine Fe3O4 nanoparticles/graphene on carbon cloth and use it directly as a supercapacitor electrode without any subsequent operations and extra additives. When tested in three-electrode systems, this electrode exhibits excellent electrochemical performance, such as considerable specific capacitance (406 F g–1 at 1 A g–1), high rate capability (retention of 56.9% when the current density is increased 20-fold from 1 to 20 A g–1), and prolonged cycle life (retention of 94.0% after 3200 consecutive cycles). Moreover, the assembled flexible quasi-solid-state symmetric supercapacitor has excellent flexibility (no obvious degradation in performance after being folded at 45, 90, 135, and 180°), high energy density of 19.2 W h kg–1 at 800.2 W kg–1, great power density of 8614.7 W kg–1 at 10.7 W h kg–1, and prominent cyclic stability (no decay after 4000 cycles at 1 A g–1). These results demonstrate the feasibility and superiority of this synthesis method, as well as its potential for practical applications.