Flexible zinc-ion hybrid supercapacitors with high energy density and long cycling life enabled by the microfluidic assembly of MXene composite fibers

Abstract

Fiber-type zinc-ion hybrid supercapacitors (ZIHSCs) with a wide voltage window, high energy density and long cycle life have attracted significant attention in the flexible energy storage field. In this study, well-aligned and porous MXene fibers were precisely fabricated via the microfluidic-assisted wet spinning technology. MnO₂ nanoparticles were uniformly deposited on these MXene fibers via an in situ growth method to construct MXene/MnO₂ composite fibers, which alleviated the aggregation of MnO₂ nanoparticles and offered enhanced electric conductivity. The optimized MXene/MnO₂ composite fibers were utilized as symmetric supercapacitor electrode materials, and the specific capacitance in a PVA/H₂SO₄ electrolyte was as high as 1392.0 mF cm⁻² at 0.8 mA cm⁻². Flexible ZIHSCs were assembled using the MXene/MnO₂ composite fibers as a battery-type cathode and reduced graphene oxide/MXene (rGO/MXene) composite fibers as the anode in an aqueous ZnSO₄ electrolyte. The designed flexible ZIHSCs could effectively mitigate zinc dendrite formation, extend the voltage window from −0.1 to 1.5 V, and exhibit a high areal capacitance of 1356 mF cm⁻² and energy density of 120.5 µW h cm⁻². The flexible quasi-solid-state ZIHSCs in a PVA/ZnCl₂–MnSO₄ gel electrolyte maintained nearly 100% capacity retention after 10 000 cycles, demonstrating outstanding long-term cycling stability and promise for practical application. This study provides new insights for developing high-performance flexible zinc-ion hybrid supercapacitors and advancing their practical implementation in wearable devices and smart textiles.