Super flexible graphene fibers (GFs) have great potential for yarn supercapacitors (YSCs) used in wearable devices. The performance of YSCs can be improved by increasing both the specific surface area and the hydrophilicity of GFs. Here, we report the continuous fabrication of hydrophilic GF by the wet spinning technique. The hydrothermal treatment of GF in KOH aqueous solution is the crucial step for the hydrophilicity improvement. The synthesized K-GF possesses a porous ruffle structure, excellent hydrophilicity, and good conductivity. The K-GF-based YSC shows good flexibility while folding from 0 to 180°and exhibits a capacitance of 145.6 mF/cm 2 at an energy density of 3.23 μW h/cm 2 and power density of 0.017 mW/cm 2 .

Flexible lithium sulfur batteries with high energy density and good mechanical flexibility are highly desirable. Here, we report a synergistic interface bonding enhancement strategy to construct flexible fibershaped composite cathodes, in which polypyrrole@sulfur (PPy@S) nanospheres are homogeneously implanted into the built-in cavity of self-assembled reduced graphene oxide fibers (rGOFs) by a facile microfluidic assembly method. In this architecture, sulfur nanospheres and lithium polysulfides are synergistically hosted by carbon and polymer interface, which work together to provide enhanced interface chemical bonding to endow the cathode with good adsorption ability, fast reaction kinetics, and excellent mechanical flexibility. Consequently, the PPy@S/rGOFs cathode shows enhanced electrochemical performance and high-rate capability. COMSOL Multiphysics simulations and density functional theory (DFT) calculations are conducted to elucidate the enhanced electrochemical performance. In addition, a flexible LiÀ S pouch cell is assembled and delivers a high areal capacity of 5.8 mAh cm À 2 at 0.2 A g À 1 . Our work offers a new strategy for preparation of advanced cathodes for flexible batteries.

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The intensive growth of smart portable devices has triggered a boom in the research of all-solid-state flexible supercapacitors. However, the unsatisfactory mechanical flexibility and limited energy density still hinder their practical application. Herein, a combination hydrothermal-assisted assemble strategy is proposed to design reduced graphene oxide fiber/MoS 2 nanosheet-assembled composite fabrics (rGOFF−MoS 2 ), where the MoS 2 nanosheets vertically grow on the surface of rGO fibers through C−O−Mo covalent bonds. The synthesized rGOFF−MoS 2 fabrics present an inter-linkage isotropy skeleton, a robust fusing node, an in situ vertical covalent bridge, an adequate pseudocapacitive reactivity, and a large electrochemical active surface (80.1 m 2 /g), resulting in fast interlaminar conductivity, great ionic migration and adsorption, and outstanding mechanical stability. The as-prepared flexible electrode displays a large capacitance of 330 F/g at 0.1 A/g (1330 mF/cm 2 at 1 mA/cm 2 ) and a high stability (95% capacitance retention after 10,000 cycles) in the H 2 SO 4 electrolyte. Additionally, the assembled solid-state flexible supercapacitor presents an energy density of 69.44 μW h/cm 2 (0.5 mW/cm 2 ) and an excellent mechanical flexibility, making the rGOFF−MoS 2 fabric a highly competitive candidate for practical applications in next-generation wearable/smart electronics.

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