Continuous Fabrication of Ti3C2Tx MXene-Based Braided Coaxial Zinc-Ion Hybrid Supercapacitors with Improved Performance

Abstract

Ti₃C₂T_x MXene-based coaxial zinc-ion hybrid fiber supercapacitors (FSCs) were fabricated with braided structure, which can be prepared continuously and present excellent flexibility and ultrastability. A sports watch driven by the watch belts which weaved uses the obtained zinc-ion hybrid FSC and LED arrays lighted by the FSCs under embedding into textiles, demonstrating the great potential application in smart wearable textiles. Zinc-ion hybrid fiber supercapacitors (FSCs) are promising energy storages for wearable electronics owing to their high energy density, good flexibility, and weavability. However, it is still a critical challenge to optimize the structure of the designed FSC to improve energy density and realize the continuous fabrication of super-long FSCs. Herein, we propose a braided coaxial zinc-ion hybrid FSC with several meters of Ti₃C₂T_x MXene cathode as core electrodes, and shell zinc fiber anode was braided on the surface of the Ti₃C₂T_x MXene fibers across the solid electrolytes. According to the simulated results using ANSYS Maxwell software, the braided structures revealed a higher capacitance compared to the spring-like structures. The resulting FSCs exhibited a high areal capacitance of 214 mF cm^-2, the energy density of 42.8 μWh cm^-2 at 5 mV s^-1, and excellent cycling stability with 83.58% capacity retention after 5000 cycles. The coaxial FSC was tied several kinds of knots, proving a shape-controllable fiber energy storage. Furthermore, the knitted FSC showed superior stability and weavability, which can be woven into watch belts or embedded into textiles to power smart watches and LED arrays for a few days.

Keywords: Coaxial structure; Fiber supercapacitor; MXene; Ti3C2Tx; Zinc-ion.

Fig. 1

Schematic diagram of the braided coaxial FSC. a Schematic illustration of the large-scale production of MXene and zinc-coated fibers and braided coaxial FSC. b SEM image of FSC. c Mapping image of zinc element on the surface of FSC. d Cross-sectional SEM image of a coaxial FSC

Fig. 2

a Structural diagram of winded coaxial FSC. b SEM image of winded coaxial FSC. c Comparison of area capacitance of braided and winded coaxial FSCs. d, g 3D models of two kinds of coaxial FSCs. e, h Simulated voltage distribution of braided and winded coaxial FSCs. f, i Simulated energy distribution of braided and winded coaxial FSCs

Fig. 3

Electrochemical performance of the braided coaxial FSC. a CV curves of 2 cm of the braided coaxial FSC at various scan rates. b Areal capacitance with respect to scan rates. c Areal capacitance with respect of cycle number at different current densities. d Galvanostatic charge–discharge curves at different current densities. e EIS curve of the FSC. f Comparisons of the energy and power densities with previously reported works. g Cycling performance and the corresponding coulombic efficiency of the fabricated FSC at 20 mA cm⁻²

Fig. 4

Bending, knotting, and twisting properties of fabricated FSC. a CV curves of coaxial FSC under bending (labeled with ∞) and bent with different curvatures diameter D. b Digital photographs of the FSCs with 2 cm powering electronic clocks at bending and knotting state. c A 12 LED array lightened by three SCs connected in series. d Capacitance retentions after twisting at increasing degrees up to 80 cycles

Fig. 5

Application of coaxial FSCs in textiles. a CV curves of a single FSC and the two FSCs connected in series and parallel. b Capacitance and energy of the coaxial FSCs with different lengths. c A 1.5 m length of coaxial FSC; photograph of a sports watch powered by a textile bracelet composed of two coaxial FSCs; the letters “CAS” consisting of 44 LED array lighted by six FSCs; a smart bracelet charged by four FSCs connected in series