High Electrochemical Capacity MnO 2 /Graphene Hybrid Fibers Based on Crystalline Regulatable MnO 2 for Wearable Supercapacitors.

Fiber-based supercapacitors (FSCs) exhibit desirable application potential and development prospects in wearable energy storage devices because of their flexibility and wearability. However, the low capacity in the unit volume and insufficient fiber strength hinder their further development in practical application. Herein, the MnO 2 nanomaterials with regulatable crystalline structure were synthesized by one-step hydrothermal strategy. The formation of the MnO 2 crystalline structure involved the "crimp-phase transition" process. Among them, the 2 × 2 tunnel type α-MnO 2 nanowires exhibited excellent electrochemical capacitance (43.8 F g -1 ), high rate performance (61%, 0.25 to 6 A g -1 ), and remarkable cyclic stability (99%), which can be attributed to their good symmetry in space and high shared vertices proportion. On this basis, the α-MnO 2 nanowires were coblended with GO to construct MnO 2 /rGO hybrid fibers by scalable continuous wet spinning and in situ acid reduction. Noteworthily, in MnO 2 /rGO hybrid fibers, the doping amount of MnO 2 nanowires as high as 50 wt % could be achieved, while the strength reached 11.73 MPa, which can be ascribed to the superior surface morphology of MnO 2 nanowires and the unique cement wall structure of hybrid fibers. Finally, the obtained hybrid fiber electrodes were assembled into symmetrical FSCs. Notably, the FSCs delivered remarkable volume specific capacitance (129.5 F cm -3 ) and impressive energy density (18 mWh cm -3 ) at 1.75 A cm -3 . In addition, the assembled all-solid-state FSCs indicated excellent deformability and application potential. This work offers some insight for promoting the continuous preparation of fiber electrodes, the development of FSCs, and practical application in wearable energy textile.