WO2021237862A1 - Macroscopic high-conductivity mxene ribbon-like fibers with ordered stacking of nanosheets, and flexible capacitor - Google Patents

Abstract

Disclosed are macroscopic high-conductivity MXene ribbon-like fibers with ordered stacking of nanosheets, and a flexible capacitor. A Ti₃AlC₂ powder is charged into an HF solution, stirred and washed to obtain a crystal; the crystal is then added to a tetramethyl ammonium hydroxide aqueous solution, and after stirring, same is sequentially subjected to a centrifugal treatment, washing and then to redispersion in water, and an ultrasonic treatment is carried out to obtain a titanium carbide aqueous solution; the titanium carbide aqueous solution is injected to a coagulation bath to obtain initial fibers; the initial fibers are subjected to an acid treatment and washing to obtain macroscopic high-conductivity MXene ribbon-like fibers with ordered stacking of nanosheets; and the ribbon-like fibers, which act as a negative electrode, are assembled with a separator, an electrolyte, and a positive electrode to obtain a flexible capacitor based on the macroscopic high-conductivity MXene ribbon-like fibers. On the basis of the intrinsic metal conductivity and oriented stacked structure of Ti₃C₂ nanosheets, the prepared ribbon-like fibers have excellent conductivity (up to 2458 S cm^-1). This study highlights the great potential of MXene as a macroscopic assembly platform and expands the application of MXene materials in wearable electronic products.

Description

Macroscopically highly conductive MXene ribbon fibers and flexible capacitors with orderly stacking of nanosheets Technical field

The invention belongs to flexible fibrous electrode technology, and specifically relates to macroscopically highly conductive MXene ribbon fibers with orderly stacked nanosheets and a flexible capacitor based on the macroscopically highly conductive MXene ribbon fibers.

Background technique

Based on the recent explosive development of miniaturization and wearable electronic devices, the development of flexible fibrous electrodes with high electrical conductivity and reasonable electrochemical performance has become increasingly important. Recently, two-dimensional nanosheets with a thickness on the order of several angstroms and a lateral dimension in the micrometer range have been proposed as ideal materials for constructing macroscopic fiber electrodes. In particular, fibers with a nearly perfectly ordered nanosheet structure can maximize the performance utilization of a single nanosheet. For example, graphene oxide nanosheets with a hydrophilic surface can be well dispersed in an aqueous medium, thereby helping to prepare continuous fibers using a scalable wet spinning method. In particular, by finely controlling the stacking order of nanosheets, the mechanical strength and electrical properties of the fiber can be greatly improved. In order to enhance the electrochemical performance of fibers, hybrid fiber electrodes have been prepared by depositing pseudocapacitive materials (such as manganese oxide, cobalt oxide, and ruthenium oxide) on graphene or other conductive fiber substrates. Or, similar to the spinning process of graphene oxide, two-dimensional transition metal oxide nanosheets dispersed in an aqueous medium are directly assembled into fiber electrodes. Sometimes nanosheets are combined with graphene as a current collector. It should be noted that fibers containing large amounts of electrochemically active materials can generally provide enhanced energy storage capabilities, but the overall rate performance is largely limited by the inherent low conductivity. Therefore, although there is an urgent need for a conductive fibrous electrode with excellent energy storage capabilities, its development is an arduous task.

Some groundbreaking experimental attempts have been reported for the production of macroscopic MXene fibers, but most studies have to incorporate components with fiber spinnability, such as reduced graphene oxide (rGO), conductive polymer PEDOT, etc. The formation of pure MXene fibers is largely limited by the size of MXene and the choice of a suitable coagulation bath. Unlike graphite and other layered structures (which hold the layers together by van der Waals forces), the strong MA bond This means that only by using harsh chemical methods to selectively etch the A layer can MXene be produced. In addition, the breaking of the M-A bond during etching can damage the M-X bond based on their similar bond energies. As a result, although the length of the parent MAX crystals is tens of micrometers, most of the obtained MXenes only show limited lateral dimensions, only a few hundred nanometers, resulting in additional grain boundaries, which are important for the construction of macroscopic MXene fibers. obstacle. In particular, the small size of MXene is a disadvantage of aligning the flakes in a macrostructure, which may require fine control of the flake interface and synthesis parameters.

technical problem

In order to solve the defect that there is no pure MXene macro fiber in the prior art, the present invention discloses an orderly stacked macroscopic high-conductivity MXene ribbon fiber with nanosheets and a preparation method and application thereof. The prepared pure MXene macro fiber has excellent mechanical properties, Electrical conductivity is a pioneering research work. The invention called MXene macro-fiber has potential applications in the field of energy storage due to its unique physical and chemical properties. First, a large number of free electrons in transition metal carbides or nitrides give MXene excellent metal conductivity; secondly, the two-dimensional flake shape ensures a high specific surface area, potentially providing a high electric double layer capacitance; third and most important Yes, the redox reaction of a large number of surface groups, especially in an acidic environment, gives MXene nanosheets additional pseudocapacitance. Therefore, MXene has the potential to deliver excellent electrochemical properties without the help of any auxiliary components.

Technical solutions

The present invention adopts the following technical solutions.

The preparation method of the macroscopically high-conductivity MXene ribbon-shaped fiber in which the nanosheets are stacked in an orderly manner includes the following steps.

(1) Put the Ti ₃ AlC ₂ powder into the HF solution, stir and wash to obtain crystals; then add the crystals into the tetramethylammonium hydroxide aqueous solution, and then go through centrifugal treatment and washing after stirring, and then re-disperse in water and ultrasonic treatment , Get an aqueous solution of titanium carbide.

(2) Inject the titanium carbide aqueous solution of step (1) into the coagulation bath to obtain initial fibers.

(3) The initial fibers of step (2) are acid-treated and washed to obtain macroscopic highly conductive MXene ribbon fibers with orderly stacked nanosheets.

The macroscopic high-conductivity MXene ribbon fibers, which are stacked in an orderly manner, are used as the negative electrode, and are assembled with the electrolyte, the positive electrode, and the separator to obtain a high-performance flexible supercapacitor.

In the present invention, in step (1), the concentration of the HF solution is 8-12 wt%; the concentration of the tetramethylammonium hydroxide aqueous solution is 22-28 wt%; the concentration of the titanium carbide aqueous solution is 10-30 mg/mL, The lateral dimension of titanium carbide is 1 to 2.5 microns, preferably 1.6 to 2 microns. In the titanium carbide aqueous solution prepared by the invention, the nanosheets have the characteristics of large size, uniform size distribution, and high orderliness of the nanosheets, which are beneficial to solution spinnability and the preparation of continuous long fibers.

In the present invention, in step (2), the coagulation bath is a chitosan-acetic acid coagulation bath. Preferably, in the chitosan-acetic acid coagulation bath, the solvent is water, the chitosan concentration is 0.6 wt%, and the acetic acid concentration is 4 wt%; conventional syringes are used for injection, and rotating disks are used for receiving. The specific preparation process is based on the prior art to obtain Ti ₃ C ₂ initial fibers containing chitosan.

In the present invention, in step (3), the acid treatment is immersion in a sulfuric acid solution, such as immersion in a 1M sulfuric acid aqueous solution for 3 days, and the washing is alcohol washing, such as ethanol washing.

In the present invention, in step (4), the electrolyte is polyvinyl alcohol-sulfuric acid as the electrolyte, the positive electrode is rGO fiber, and the electrolyte and the positive electrode are existing products; the specific method for assembling the supercapacitor is the prior art.

The currently disclosed Ti ₃ C ₂ nanosheet solution is difficult to have spinnability, and it needs to be assisted by graphene or other spinnable binders to prepare Ti ₃ C ₂ composite fibers, and the present invention achieves spinnability. The Ti ₃ C ₂ solution and the pure MXene fiber were prepared by wet spinning process and acid treatment method; due to _{the preparation of Ti 3} C ₂ solution and the design of spinning parameters, the prepared pure Ti ₃ C ₂ fiber macroscopically It presents a ribbon-like structure with a _{highly ordered stack of Ti 3} C ₂ nanosheets in the microscopic interior. This orderly stacked structure of nanosheets is conducive to maximizing the mechanical strength of the fiber (30 Mpa) and minimizing nanosheets and nanosheets (Conductivity is as high as 2458 S cm ^-1 ); the acid-treated fiber of the present invention makes the fiber have an open two-dimensional ion transport channel inside, and the fiber has high electrochemical performance (the current density is 1 A g ^-1 when the capacity When the current density reaches 309 F g ^-1 and the current density is 10 A g ^-1 , the capacity is 231 F g ^-1 , and the capacity retention rate after 10,000 cycles is 97.24%); the pure Ti ₃ C ₂ fiber of the present invention and reduced graphene oxide Fiber (rGO) matched and assembled asymmetric supercapacitors, and the assembled asymmetric capacitors have a high volumetric energy density (58.4 mW h cm ^-3 ).

Description of the drawings

Figure 1 is a schematic diagram of fiber preparation and a structural diagram of the initial fiber and pure titanium carbide fiber.

Figure 2 is an atomic force microscope image of the titanium carbide nanosheets and the statistics of the size distribution of the nanosheets, indicating that the size of the nanosheets in the optimized solution is generally between 1.6-2.0 μm and the size distribution range is narrow.

Figure 3 is a polarized light microscope image of a titanium carbide solution at different concentrations, indicating that as the concentration increases, the order of the nanosheets in the solution increases.

FIG. 4 is a simulation diagram and calculation of the distance between the nanosheets in the solution, which shows that the free volume of the nanosheets in the solution of the present invention is reduced, and the restrained force becomes larger and more orderly.

Figure 5 is (a) the schematic diagram of the wet spinning equipment and the structure of the obtained fiber, (b) _{the typical atomic force microscope (AFM) image of the Ti 3} C ₂ thin plate, (c) the cross-section and top view of the original fiber at different stages Optical microscope image, distance from the needle exit: I (1 cm), II (11 cm), III (21 cm), IV (31 cm), (d) photos of continuous long macroscopic fibers.

Figure 6 shows the thermogravimetric data of the initial fiber and pure titanium carbide film. It can be seen from the data graph that the initial fiber contains a small amount of flocculant chitosan.

Figure 7 is (a) XPS data of the initial fiber and pure titanium carbide fiber. The initial fiber contains chitosan. The pure titanium carbide fiber obtained after acid treatment has no chitosan, indicating that the chitosan has been removed; (b) ) Infrared data of the initial fiber and pure titanium carbide fiber, the initial fiber contains the characteristic absorption peak NH ₂ of chitosan, and the peak of chitosan in the pure titanium carbide fiber obtained after acid treatment is gone, indicating that chitosan Was removed.

8 is the original Ti ₃ C ₂ - compared to the chitosan fibers, the fibers of pure Ti ₃ C ₂ XRD pattern of acid-treated, (b) the purified Ti ₃ C ₂ acid-treated fibers and low magnification (c ) High-magnification cross-sectional SEM image, (d) HRTEM lattice image of the cross-section of the _{acid-treated Ti 3} C _{2 fiber.} Illustration: FFT generated mode.

Figure 9 shows the element analysis under the transmission electron microscope after fiber ultrathin sectioning.

Figure 10 shows the mechanical strength of the initial fiber and pure titanium carbide fiber; after acid treatment, the chitosan is removed, resulting in a slight decrease in the mechanical strength of the fiber, but it still has good mechanical strength.

_{Figure 11 is a photograph of pure Ti 3} C ₂ fibers wound on a glass rod and an SEM image of tightly knotted fibers. The obtained pure titanium carbide fiber has good flexibility.

_{Figure 12 shows the electrical conductivity of the pure Ti 3} C ₂ fiber compared with other reported MXene-based fibers under the same test method. The pure titanium carbide fiber obtained in the present invention has a high electrical conductivity.

Figure 13 shows the resistance comparison between the initial fiber and the pure titanium carbide fiber, (a) the resistance of the 11 cm long initial fiber, the calculated conductivity is 767 S cm ^-1 , (b) the resistance of the 11 cm long pure titanium carbide fiber, The calculated electrical conductivity is 2458 S cm ^-1 , (c) the resistance of the initial fiber and pure titanium carbide fiber varies with length, showing a linear relationship, indicating that the fiber is uniform, (d) pure titanium carbide fiber is bent at different angles The resistance below shows that the resistance of pure titanium carbide fiber is stable under bending.

Figure 14 shows the electrochemical performance of pure pure titanium carbide fibers in a three-electrode system. (A) Schematic diagram of three-electrode setup. (B) CV curves recorded at different scan rates. (C) GCD curves recorded at different current densities. (D) Specific capacitance and corresponding length capacitance at different scan rates. Illustration: Comparison of the capacitance retention capacity of MXene-based optical fiber supercapacitors at different current densities. (E) Cycle stability of ^{10 4 cycles.} Illustration: GCD curve of the first and last cycle.

Figure 15 is a cross-sectional SEM image of pure titanium carbide fiber after 10,000 cycles at 10 A g ^{-1; pure titanium carbide fiber has good electrode working stability.}

Figure 16 shows the performance difference between the initial fiber and the pure titanium carbide fiber after acid treatment. A is the electrochemical performance data of the initial titanium carbide fiber and the pure titanium carbide fiber, and B is the electrochemical impedance data. The pure titanium carbide fiber has a smaller value Ion diffusion resistance.

Figure 17 shows the ^{H +} diffusion coefficient calculated from impedance data.

Figure 18 shows that GCD bends _{acid-treated pure Ti 3} C _{2 fibers of different lengths.}

Figure 19 shows the electrochemical performance of asymmetric fiber supercapacitors. (A) Schematic diagram of flexible asymmetric equipment. (B) _{CV curves of pure Ti 3} C ₂ fiber and rGO fiber at the same scanning rate. (C) CV curves of asymmetric devices at different scanning speeds and (d) GCD curves at different current densities. (E) The volumetric energy density and power density of the assembled asymmetric device are compared with other fiber supercapacitors and fiber batteries. (F) A photo of the blue LED logo fiber driven by three flexible devices connected in series, and (g) a photo of two tandem fibers woven into gloves to illuminate an electronic watch.

Figure 20 is (a) the SEM surface image of the redox graphene fiber; (b) the cross-sectional view of the redox graphene fiber.

Figure 21 shows the cyclic voltammetry (CV) curves of redox graphene fibers at different scanning speeds.

Figure 22 shows the working range of the assembled device, the working voltage is 0-1.5 V.

Figure 23 shows the data of 10,000 cycles of the assembled device at a current density of 10 A g ^-1 . The inset figure shows the data of the first and last constant current charge and discharge before the device is cycled.

Figure 24 shows (a) the titanium carbide nanosheets of the present invention, the coagulation bath is chitosan-acetic acid aqueous solution; the effect: can form continuous fibers with high mechanical strength; (b) the titanium carbide nanosheets of the present invention, the coagulation bath is 5% chlorine Calcium water-isopropanol (volume ratio 3:1); effect: only short fibers can be obtained and are very brittle, almost without strength; (c) small nano-sheets, coagulation bath is chitosan-acetic acid aqueous solution; effect: Short fibers have a certain strength.

Figure 25 shows the spinning effect of a 10 mg mL ^-1 titanium carbide solution in a chitosan-acetic acid solution. Only short fibers can be obtained, not continuous fibers.

Embodiments of the present invention

Material: Ti ₃ AlC ₂ powder (98%, 325 mesh) was purchased from Shanghai Buhan Chemical Technology Co., Ltd.; hydrofluoric acid aqueous solution (HF, 40%,> 98%) and tetramethylammonium hydroxide aqueous solution (TMAOH, 25 %) purchased from J&K Scientific Co., Ltd;. Hydrochloric acid (HCl, ≥98%) and sulfuric acid (H ₂ SO ₄ , ≥98) were purchased from Aladdin; Chitosan (99%) and acetic acid (99.5%) were purchased from Aladdin Provided by Sinopharm Chemical Reagent Co., Ltd.; Polyvinyl alcohol (PVA, Mw = 1788) was purchased from Aladdin Industrial Co., Ltd. (Shanghai, China); Graphene oxide (GO) was purchased from J&K Scientific, Ltd.; Diaphragm was purchased from Nippon Kodoshi Corporation ( Japan High Paper Industry Co., Ltd.).

Three-electrode test method: the electrode clamps the fiber directly as the working electrode, Ag/AgCl as the reference electrode, and Pt as the counter electrode. The electrochemical test is carried out in 1M sulfuric acid electrolyte. (Test equipment CHI660E electrochemical workstation).

Two-electrode test: CHI660E electrochemical workstation is used to test its electrochemical performance. The positive and negative electrodes of the fiber device are respectively connected to the electrochemical workstation for direct testing.

Conductivity test: Use an ohmmeter to measure the resistance of the 11 cm-long fiber, then calculate the cross-sectional area of the fiber by SEM, and calculate the conductivity by the formula σ=L/RS.

Mechanical strength calculation: The fiber cross-sectional area is calculated by using the inner image of the SEM cross-section, and the mechanical strength of the fiber is measured by the Instron 3365 universal material extensometer.

The preparation method of the macroscopically highly conductive MXene ribbon fiber with orderly stacked nanosheets of the present invention is as follows.

(1) Put the Ti ₃ AlC ₂ powder into the HF solution, stir and wash to obtain crystals; then add the crystals into the tetramethylammonium hydroxide aqueous solution, and then go through centrifugal treatment and washing after stirring, and then re-disperse in water and ultrasonic treatment , The titanium carbide aqueous solution is obtained; preferably, the centrifugal treatment is performed after the ultrasonic treatment to obtain the titanium carbide aqueous solution.

(2) Inject the titanium carbide aqueous solution of step (1) into the coagulation bath to obtain initial fibers.

(3) The initial fibers of step (2) are acid-treated and washed to obtain macroscopic highly conductive MXene ribbon fibers with orderly stacked nanosheets.

Take the macroscopically highly conductive MXene ribbon fibers of step (3) that are stacked in an orderly manner as the negative electrode, and are assembled with the electrolyte, the positive electrode, and the separator to obtain a high-performance flexible supercapacitor.

The raw materials of the present invention are all commercially available, and the test methods involved are all conventional test methods in the field.

Example 1 Preparation of titanium carbide colloidal aqueous solution: Ti ₃ AlC ₂ powder (1g) was put into HF solution (10 wt%, 30 mL), stirred for 10 minutes, centrifuged with distilled water and washed 3 times, and then placed in a vacuum oven at 80°C Dry for 24 hours. Place the dried powder in an aqueous solution of tetramethylammonium hydroxide (25 wt%, 10 mL) and continue stirring for 24 hours; the resulting suspension is centrifuged at 5000 rpm for 10 minutes, and the bottom sediment is washed with deionized water and dried; then Re-disperse in deionized water, sonicate for 15 minutes at room temperature, centrifuge at 3500 rpm for 15 minutes, take the upper suspension and centrifuge at 8000 rpm for 15 minutes, and remove the lower suspension to obtain a titanium carbide colloidal aqueous solution with a concentration of 20 mg/mL.

Put the titanium carbide colloidal aqueous solution into a plastic syringe with a rotating nozzle (a conventional stainless steel spinning needle with a diameter of 500 μm), and inject it (40 mL h ^-1 ) into the coagulation bath, which is received by the rotating disk; the coagulation bath contains 4 wt% acetic acid aqueous solution of chitosan (chitosan 0.6 wt%), the speed of the spinning disk is set to 560 rph, the distance from the nozzle to the center of the spinning disk: 6 cm; when the titanium carbide colloidal aqueous solution is in contact with the coagulation bath, immediately A continuous initial fiber is formed; the initial fiber is allowed to stand in the coagulation bath for 15 minutes, and then washed with water and ethanol; then the initial fiber is immersed in a 1 M sulfuric acid aqueous solution for 3 d; the acid-treated fiber is separated with deionized water and ethanol Washed for 5 times and dried under ambient conditions to obtain macroscopically highly conductive MXene ribbon fibers with orderly stacking of nanosheets, called pure Ti ₃ C ₂ fibers.

The initial fiber was washed with deionized water and ethanol for 5 times, and dried under ambient conditions to obtain Ti ₃ C ₂ -chitosan fiber, which was used as a comparative fiber and was called the initial Ti ₃ C ₂ fiber.

In the present invention, a solution containing Ti ₃ C ₂ tablets (20 mg mL ^-1 ) is extruded from a needle (with a diameter of 500 μm) through a syringe pump into a coagulation bath placed on a turntable, through the coagulation of protonated chitosan Wet-spin Ti ₃ C ₂ solution in a bath and then remove chitosan in acid to prepare macroscopic pure Ti ₃ C ₂ fibers, as shown in Figure 1.

The lateral size of the prepared nanosheets is 1.6-2 µm, and the average thickness is about 1.6 nm (Figure 2). Based on the repulsive force between the nanosheets, the solution shows high stability ^{even when the concentration is increased to 20 mg mL -1} Based on ^{the aspect ratio (width/thickness) of nanosheets> 10 3} , the theoretical critical concentration of liquid crystal phase is calculated to be 10.88 mg mL ^-1 , but it is twice as close to the critical concentration (20 mg mL ^-1) The polarized optical microscopy characterization of the solution did not reveal the typical birefringence characteristics of the liquid crystal phase (Figure 3). ^{The average spacing between the nanoplatelets in the 20 mg mL -1} solution is estimated to be about 170 nm (Figure 4). Continuous fiber manufacturing.

Spinning larger transverse size nanosheets in a protonated chitosan coagulation bath can obtain continuous fibers with good strength. The Ti ₃ C ₂ solution is passed through a narrow spinning nozzle (diameter 500 µm) at a certain speed When injected into the coagulation bath, flocculation occurred immediately, and its cross section was the same as that of the injection needle. When the fiber was pulled out from the needle outlet, the cylindrical fiber gradually transformed into a ribbon fiber, as shown in Figure 5c. The morphological evolution of the cross-sectional view and the top view showed that the abnormal formation of ribbon-like fibers was caused by the formation of densely oriented sheet stacks. The cross-sectional area of the four stages was calculated and showed a gradually decreasing trend. The actual fiber is shown in Figure 5d. The fiber length only depends on the feed. There are enough raw materials to spin a long enough continuous fiber. Through the analysis of thermogravimetric data (TGA), the initial Ti ₃ C ₂ fiber and the pure Ti ₃ C ₂ fiber can be obtained. The difference is shown in Figure 6; the chitosan between the nanosheets can be completely removed by treatment in sulfuric acid. In Figure 7, the density of the pure MXene fiber obtained is 3.26 g cm ^-3 , which is equivalent to commercial carbon fiber.

The structure and morphological characteristics of _{Ti 3} C ₂ fibers before and after acid treatment were analyzed. The X-ray powder diffraction (XRD) curve shown in Figure 8a shows reflection peaks in the low-angle state of the two samples, which means that the two structures are regularly stacked. After the acid treatment, the spacing between the nanosheets from the original Ti ₃ C ₂ - chitosan fiber spacing is reduced to 1.43 nm 1.33 nm, clearly detected characteristics associated with the inner surface of the Ti ₃ C ₂ diffraction layer (110 ), which shows that the main structure of _{Ti 3} C _{2 nanosheets is well preserved after acid treatment.} The morphology of the obtained fibers was characterized using a scanning electron microscope (SEM), and the results showed a clear ribbon structure and regular sheet-to-sheet face stacking (Figures 8b and 8c), verifying the results of optical microscopy and XRD. It is important to note that in the cross-sectional observation of the original fiber and the acid-treated fiber, no big difference was found, which indicates that the acid treatment does not cause structural deterioration and can successfully inherit the orderly stacked structure. This structure can be observed more clearly in high-resolution transmission electron microscope (HRTEM) images. In Figure 8d, the parallel stripes corresponding to the stacked layers can be clearly seen. The fringe distance was measured to be 1.33 nm, which was consistent with the XRD results. The Fourier transform (FFT) mode showed well-aligned diffraction spots, further confirming the orderly stacking _{of Ti 3} C _{2 nanosheets.} The element Mapping results show that Ti, C, O and S elements are uniformly distributed (Figure 9).

Based on the oriented stacked structure and the flexibility of the two-dimensional nanosheets, _{the tensile strength of the macroscopically pure Ti 3} C ₂ fiber obtained above reaches 30 MPa, as shown in Figure 10. The small picture shows the pure titanium carbide fiber of the present invention that can lift the key And continuously, therefore, based on the inheritance of the oriented sheet stack structure, the acid treatment does not cause significant deterioration in mechanical properties. As shown in Figure 11, these fibers have sufficient strength and flexibility to be bent and knotted on a Φ5 mm glass rod without any signs of breakage, so they are satisfactory for flexible energy storage devices. In addition, the two-dimensional open nanochannels between the flakes and the electron channels provided by the metal Ti ₃ C _{2 flakes facilitate the rapid transmission of ions and electrons.} The measured electrical conductivity of the pure Ti ₃ C ₂ fiber is 2458 S cm ^-1 , which is several orders of magnitude larger than that of the MXene-based composite fiber, as shown in Figure 12. The number in the upper right corner of the existing fiber is the reference number. Due to its compact stacked structure and excellent mechanical flexibility, the electrical conductivity value of the fiber changes little with the bending angle, as shown in Figure 13. Therefore, _{the abnormally highly oriented stack structure of Ti 3} C ₂ nanosheets can produce excellent ion conductivity, rapid ion diffusion in the crystal lattice and acceptable mechanical strength, which provides a solid foundation for the realization of flexible energy storage devices. The electrical conductivity test method is to measure the electrical resistance of the 11cm-long fiber, and then calculate the cross-sectional area of the fiber through the SEM cross-sectional view. The electrical conductivity is calculated by the formula: electrical conductivity σ=L/RS.

Taking into account the oriented nanosheet stacking and high conductivity of the pure titanium carbide fibers of the present invention discussed above, the electrochemical properties of the obtained fibers were first characterized in a standard three-electrode configuration _{in a 1 MH 2} SO _{4 electrolyte, in which one end of the long fiber was directly} Clamp it on the electrode as the working electrode, Ag/AgCl as the reference electrode, and the Pt sheet as the counter electrode (Figure 14a). This arrangement is a harsh condition for the optical fiber electrode, because the electrons at one end of the optical fiber electrode must pass a long distance before passing through the optical fiber before reaching the current collector. The cyclic voltammetry (CV) curves of the acid-treated pure Ti ₃ C ₂ fiber in the potential range of -0.6 to 0.2 V at different scan rates are shown in Figure 14b. A current response showing a broad redox peak can be observed, which clearly proves the pseudocapacitance behavior of the fiber; in addition, even at ^{a scan rate of 100 mV s -1} , the CV curve does not show obvious distortion, indicating its superiority The rate performance. Figure 14c shows the constant current charge and discharge (GCD) curve, which clearly deviates from the perfect triangle, indicating _{the surface oxidation-reduction reaction of Ti 3} C ₂ nanosheets, which is consistent with the CV analysis results, even at a high of ^{10 A g -1} There is no obvious ohmic drop under the current density, indicating the high conductivity of the fiber electrode. The fiber has a specific capacitance of ^{309 F g -1} (52.38 mF cm ^-1 ) at a current density of ^{1 A g -1.} When the current density increases to 10 A g ^-1 , the capacitance remains at 231 F g ^-1 (39.16 mF cm ^-1 ), which means that the capacitance retention rate is 74.76%. On the contrary, under the same test, other MXene-based fiber supercapacitors showed lower capacitance retention as the current density increased (Figure 14d). The high rate performance of Ti ₃ C ₂ fibers can be attributed to the fast ion insertion and deintercalation based on the oriented stacking of nanosheets, fast electron transfer, and the short path of ion transport in the _{Ti 3} C _{2 layered structure.} Further, Ti ₃ C ₂ acid treated fiber electrodes at a current density of 10 A g ^-1 also exhibit excellent cycling stability, as shown in FIG. 14e, after a long-term cycle ¹⁰⁴ cycles, the capacitance retention rate About 97.24%. In addition, there is no obvious deformation, indicating the structural stability of the fiber electrode prepared by the present invention (Figure 15).

Under the same measurement method, the initial Ti ₃ C ₂ fiber used as the electrode to replace the pure Ti ₃ C ₂ fiber did not exhibit excellent cycle stability at a current density of 10 A g ^{-1 . After 10 4} cycles, the capacitance The retention rate is about 91.38%.

Figure 16A shows the electrochemical performance data (CV data) of the initial titanium carbide fiber and pure titanium carbide fiber. At a ^{sweep speed of 10 mV s -1} , the capacity of the titanium carbide-chitosan fiber is significantly smaller than that of the pure titanium carbide fiber. Electrochemical impedance spectroscopy (EIS) analysis was performed to gain insight into the charge transfer and ion transport characteristics of _{Ti 3} C _{2 fibers.} The Ti ₃ C ₂ fiber electrode shows a shorter Warburg area at high frequency, indicating a fast electron transfer rate, while at low frequency, it shows an almost vertical curve, indicating ideal capacitance characteristics (Figure 16). The excellent ion transport performance of the fiber was also analyzed from the perspective of kinetics. The diffusion coefficient is estimated to be 9.2×10 ^-7 cm ² s ^-1 , which is 1.43×10 ^-7 cm ² compared to the original Ti ₃ C _{2 chitosan fiber.} s ^-1 (Figure 17), confirming that the designed Ti ₃ C ₂ fiber has the advantages of an orderly stacked structure and a prepreg channel. In order to highlight the excellent conductive network of _{the obtained Ti 3} C ₂ fiber, the GCD curve of the fiber with a length extension of 5 times to 15 cm was ^{also tested at a current density of 2 A g -1, as shown in FIG. 18.} Even at such a length, no significant ohmic drop is observed, and the curves almost completely overlap. All these results provide clear evidence that the prepared _{fiber electrode with the oriented stack of Ti 3} C ₂ flakes provides excellent ion and electron transport performance between the layers, resulting in excellent overall electrochemical performance.

Embodiment 2 Take the macroscopically highly conductive MXene ribbon fibers with orderly stacked nanosheets of Embodiment 1 as the negative electrode, and assemble it with the polyvinyl alcohol-sulfuric acid electrolyte and the positive rGO fiber to obtain a high-performance flexible supercapacitor.

Using the method of Example 1, the titanium carbide colloidal aqueous solution was replaced with a commercially available GO aqueous solution with a concentration of 10 mg/mL (the thickness of the GO sheet was about 1 nm, and the lateral size was 3 to 5 µm) to obtain the initial GO fibers, which were then immersed in In hydroiodic acid (57wt%) aqueous solution at 90°C for 5 hours, then washed with water to obtain rGO fiber as a positive electrode.

Under stirring, 1 g of PVA powder was dissolved in 10 mL of distilled water at 90°C until a clear solution was obtained. After 1 g of sulfuric acid was added and stirred, the clear solution was cooled to room temperature to obtain a polyvinyl alcohol-sulfuric acid electrolyte.

The positive and negative electrodes are respectively connected with silver paste and copper wire current collectors and then placed in a heat shrinkable tube in parallel, added with the existing polymer separator and polyvinyl alcohol-sulfuric acid electrolyte, heated and sealed to form a high-performance flexible supercapacitor; the specific assembly method is as follows: current technology.

Excellent electrochemical properties of Ti ₃ C ₂ based fiber electrodes, polyvinyl alcohol - sulfuric acid as an electrolyte, an acid-treated Ti ₃ C ₂ is a negative fibers, the fibers are assembled RGO asymmetric supercapacitor solid fibrous cathode as Shown in 19a. The ribbon-like structure of rGO fiber can also be obtained by wet spinning (Figure 20 is the SEM image), and exhibits typical capacitance characteristics (Figure 21). The rGO fiber has a wide volt-ampere voltage in the potential window of -0.1 to 0.9 V. In response, the potential window of the acid-treated Ti ₃ C ₂ fiber was in the range of -0.6 to 0.2 V (Figure 19b). Therefore, the electrode pair can provide an effective voltage of up to 1.5 V without polarization (Figure 22). As shown in Figures 19c and 19d, the CV and GCD curves of asymmetric fiber supercapacitors exhibit curvatures at similar voltages, and have ideal electrochemical behaviors at different scan rates and current densities. The asymmetric fiber supercapacitor ^{can provide a capacitance of 88.67 F g -1} (256 F cm ^-3 ) at a scan rate of ^{5 mV s -1} , which is comparable to the value of a typical fiber supercapacitor. In addition, the asymmetric fiber supercapacitor has a capacitance retention rate of 92.4% and has long-term cycle stability (Figure 23). Figure 19e shows a Ragone chart comparing the volumetric energy and power density between different fiber supercapacitors and fiber batteries. The invention can provide a high volume density of 58.38 mW h cm ^-3 at 1679 mW cm ^-3 , and can provide a high volume power density of about 7466 mW cm ^{-3 at 17.63 mW h cm -3.} These energy densities are comparable to existing typical asymmetric optical fiber supercapacitors, but the energy density is close to existing optical fiber batteries. Based on the excellent energy storage performance of asymmetric fiber supercapacitors, a practical application was established, which uses three series-connected flexible devices to power 3.5 V blue light-emitting diode (LED) logo fiber or electronic watch. The LEDs and electronic watches lit by the asymmetric fiber supercapacitor of the present invention did not show obvious dimming during the bending of the device, which proved the mechanical strength and flexibility of the device of the present invention (Figures 19f and 19g).

Comparative Example On the basis of Example 1, the existing small-size titanium carbide nanosheet aqueous solution is used, as shown in Fig. 24c. The same spinning method cannot obtain continuous macroscopic fibers.

On the basis of Example 1, the existing inorganic ion coagulation bath (5wt% calcium chloride water-isopropanol solution, in which the volume ratio of water to isopropanol is 3:1), see Figure 24b, the same spinning Method, it is impossible to obtain continuous macroscopic fibers.

On the basis of Example 1, using a 10 mg/mL titanium carbide nanosheet aqueous solution and the same spinning method, continuous macroscopic fibers could not be obtained, as shown in Figure 25.

On the basis of the first embodiment, the disk rotation speed of 400 rph is adopted, and the rest is the same, and continuous macroscopic fibers cannot be obtained.

On the basis of Example 1, using the existing large-size titanium carbide nanosheet aqueous solution (lateral size 3-4 microns), the same spinning and acid soaking methods, the macro-continuous Ti ₃ C ₂ fiber obtained through the same test It is calculated that the fiber has a specific capacitance of ^{283 F g -1} at a current density of ^{1 A g -1.}

Conclusion: In the present invention, by wet spinning a solution of Ti ₃ C ₂ in the coagulation bath protonated chitosan in the chitosan in an acid is then removed, the ribbon structure successfully pure Ti ₃ C ₂ fibers (width 1.1 Preparation of ~1.3mm, thickness 3~5 microns), with highly oriented nanosheet stack structure. Ti ₃ C ₂ is a typical member of the MXene series, after which Ti ₃ C _{2 is} used to refer to specific materials of this type of material. During the acid treatment of chitosan, the orderly stacked structure of the nanosheets was not destroyed, and there was no damage to the mechanical properties of the fibers. The obtained pure Ti ₃ C ₂ tape exhibits three important advantages. First, the nanosheets in the fiber have a highly ordered stacked structure, which means that the mechanical properties of each nanosheet are effectively integrated. This pure Ti ₃ C ₂ fiber can provide a tensile strength of 30.0 MPa, which is sufficient for practical equipment applications. Secondly, each nanosheet is an excellent conductor, and the nanosheets are tightly connected to help build a continuous conductive network and provide a conductivity of 2458 S cm ^-1 , which is higher than the conductivity of the previously reported MXene-based composite fiber. The rate is nearly two orders of magnitude higher. Third, orderly stacking can form an open two-dimensional channel. Even at a higher current density, it can effectively reduce ion transport barriers, thereby shortening the length of the ion diffusion path and promoting the electrode reaction (231.0 F g ^-1 or 39.2 mF cm ^-1 , at a current density of 10 A g ^-1 ). Based on the excellent electrochemical behavior of the designed fiber Ti ₃ C ₂ electrode, an asymmetric supercapacitor was assembled using rGO fiber as the cathode material. At a ^{current density of 1A g -1} , the energy density reaches 58.4 m Wh cm ^-3 (20.0 W h Kg ^-1 ), and the corresponding volumetric power density is 1679.0 mW cm ^-3 (581.0 W Kg ^-1 ). This work proved the acceptable processability of MXene and opened a new window for the application of MXene materials in wearable electronic products in the future.

Claims (10)

1. The macroscopic high-conductivity MXene ribbon fiber in which the nanosheets are stacked in an orderly manner is characterized in that the preparation method of the macroscopic high-conductivity MXene ribbon-shaped fiber in which the nanosheets are stacked in an orderly manner comprises the following steps:

   (1) Put the Ti ₃ AlC ₂ powder into the HF solution, stir and wash to obtain crystals; then add the crystals into the tetramethylammonium hydroxide aqueous solution, and then go through centrifugal treatment and washing after stirring, and then re-disperse in water and ultrasonic treatment , To obtain an aqueous solution of titanium carbide;

   (2) Inject the titanium carbide aqueous solution of step (1) into the coagulation bath to obtain initial fibers;

   (3) The initial fibers of step (2) are acid-treated and washed to obtain macroscopic highly conductive MXene ribbon fibers with orderly stacked nanosheets.
2. The orderly stacked macroscopic highly conductive MXene ribbon fibers of nanosheets according to claim 1, wherein in step (1), the concentration of the HF solution is 8-12 wt%; The concentration is 22-28 wt%; the concentration of the titanium carbide aqueous solution is 10-30 mg/mL.
3. The orderly stacked macroscopic highly conductive MXene ribbon fiber of nanosheets according to claim 2, wherein the concentration of the titanium carbide aqueous solution is 15-25 mg/mL.
4. The orderly stacked macroscopic highly conductive MXene ribbon fibers of nanosheets according to claim 1, wherein in step (2), the coagulation bath is a chitosan-acetic acid coagulation bath.
5. The orderly stacked macroscopic highly conductive MXene ribbon fibers of nanosheets according to claim 4, wherein in the chitosan-acetic acid coagulation bath, the solvent is water, the chitosan concentration is 0.6 wt%, and the acetic acid concentration is 4 wt%.
6. The orderly stacked macroscopic highly conductive MXene ribbon fibers of nanosheets according to claim 1, wherein in step (3), the acid treatment is immersion in a sulfuric acid solution.
7. The orderly stacked macroscopic highly conductive MXene ribbon fiber of nanosheets according to claim 6, characterized in that the acid treatment is immersed in 1M sulfuric acid aqueous solution for 3 days.
8. The flexible capacitor based on the macroscopic high conductivity MXene ribbon fiber is characterized in that the preparation method of the flexible capacitor based on the macroscopic high conductivity MXene ribbon fiber includes the following steps:

   (1) Put the Ti ₃ AlC ₂ powder into the HF solution, stir and wash to obtain crystals; then add the crystals into the tetramethylammonium hydroxide aqueous solution, and then go through centrifugal treatment and washing after stirring, and then re-disperse in water and ultrasonic treatment , To obtain an aqueous solution of titanium carbide;

   (2) Inject the titanium carbide aqueous solution of step (1) into the coagulation bath to obtain as-spun fibers;

   (3) The as-spun fiber of step (2) is acid-treated and washed to obtain macroscopic high-conductivity MXene ribbon fibers with orderly stacked nanosheets;

   (4) Take the macroscopically highly conductive MXene ribbon fibers of step (3) that are stacked in an orderly manner as the negative electrode, and assemble it with the separator, the electrolyte, and the positive electrode to obtain a flexible capacitor based on the macroscopically highly conductive MXene ribbon fiber.
9. The flexible capacitor based on macroscopically highly conductive MXene ribbon fibers according to claim 8, wherein the lateral dimension of the titanium carbide in the titanium carbide aqueous solution is 1 to 2.5 microns.
10. The application of the macroscopically highly conductive MXene ribbon fibers in the orderly stacking of nanosheets in the preparation of high-performance flexible supercapacitors; the application of the flexible capacitor based on the macroscopically highly conductive MXene ribbon fibers of claim 8 in the preparation of flexible Application in electronic equipment.