High\nElectrochemical Capacity MnO₂/Graphene\nHybrid Fibers Based on Crystalline Regulatable MnO₂ for\nWearable Supercapacitors

Abstract

Fiber-based\nsupercapacitors (FSCs) exhibit desirable application\npotential and development prospects in wearable energy storage devices\nbecause of their flexibility and wearability. However, the low capacity\nin the unit volume and insufficient fiber strength hinder their further\ndevelopment in practical application. Herein, the MnO₂ nanomaterials\nwith regulatable crystalline structure were synthesized by one-step\nhydrothermal strategy. The formation of the MnO₂ crystalline\nstructure involved the “crimp-phase transition” process.\nAmong them, the 2 × 2 tunnel type α-MnO₂ nanowires\nexhibited excellent electrochemical capacitance (43.8 F g^–1), high rate performance (61%, 0.25 to 6 A g^–1),\nand remarkable cyclic stability (99%), which can be attributed to\ntheir good symmetry in space and high shared vertices proportion.\nOn this basis, the α-MnO₂ nanowires were coblended\nwith GO to construct MnO₂/rGO hybrid fibers by scalable\ncontinuous wet spinning and in situ acid reduction. Noteworthily,\nin MnO₂/rGO hybrid fibers, the doping amount of MnO₂ nanowires as high as 50 wt % could be achieved, while the\nstrength reached 11.73 MPa, which can be ascribed to the superior\nsurface morphology of MnO₂ nanowires and the unique cement\nwall structure of hybrid fibers. Finally, the obtained hybrid fiber\nelectrodes were assembled into symmetrical FSCs. Notably, the FSCs\ndelivered remarkable volume specific capacitance (129.5 F cm^–3) and impressive energy density (18 mWh cm^–3)\nat 1.75 A cm^–3. In addition, the assembled all-solid-state\nFSCs indicated excellent deformability and application potential.\nThis work offers some insight for promoting the continuous preparation\nof fiber electrodes, the development of FSCs, and practical application\nin wearable energy textile.