Effects of Electrolyte Mediation and MXene Size in Fiber-Shaped Supercapacitors

Flexible and pliable fiber electrodes with decent electrical conductivity and high capacitance density are crucial to fiber-shaped supercapacitors (FSCs) whose real-world applications include electronic textiles, miniaturized energy storage devices, and so on. Herein, we report a hybrid fiber structure made of reduced graphene oxide (rGO) and MXene, both of which are highly conductive two-dimensional (2D) materials, assembled into fibers via the scalable wet-spinning technique. By incorporation of 60 wt % MXene, the hybrid fibers can reach a balanced performance with conductivity up to 743.1 S cm–1, meanwhile maintaining decent flexibility. To improve ion accessibility to inner pores within the fibers, nonvolatile electrolyte (H2SO4) was preincorporated in between MXene and rGO layers. In addition, the size effect of MXene sheets on the overall performance of hybrid fibers was studied, favoring larger size of MXene in general. With these effective strategies, our optimal FSCs provide outstanding energy density (ca. 12 μWh cm–2 and 9.85 mWh cm–3) at a high power density (ca. 8.8 mW cm–2 and 7.1 W cm–3), showing great promise where high volumetric output is desired.