CN111809272B

CN111809272B - Macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets and preparation method and application thereof

Info

Publication number: CN111809272B
Application number: CN202010457150.0A
Authority: CN
Inventors: 耿凤霞; 祝超
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2020-05-26
Filing date: 2020-05-26
Publication date: 2021-12-28
Anticipated expiration: 2040-05-26
Also published as: CN111809272A

Abstract

The invention discloses a macroscopic high-conductivity MXene ribbon fiber with orderly stacked nano-sheets and a preparation method and application thereof, and Ti is added₃AlC₂Putting the powder into HF solution, stirring and washing to obtain crystals; adding the crystals into a tetramethylammonium hydroxide aqueous solution, stirring, sequentially performing centrifugal treatment and washing, then re-dispersing in water, and performing ultrasonic treatment to obtain a titanium carbide aqueous solution; injecting the titanium carbide aqueous solution into a coagulating bath to obtain initial fibers; and (3) carrying out acid treatment and washing on the initial fiber to obtain the macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets. Based on Ti₃C₂The inherent metal conductivity and the oriented stacking structure of the nano sheets, and the prepared ribbon fiber has excellent conductivity (up to 2458S cm)^‑1). The research highlights the huge potential of MXene as a macroscopic assembly platform and expands the application of MXene materials in wearable electronic products.

Description

Macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets and preparation method and application thereof

Technical Field

The invention belongs to a flexible fibrous electrode technology, and particularly relates to a macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets, and a preparation method and application thereof.

Background

Based on recent explosive developments in miniaturization and wearable electronics, it has become increasingly important to develop flexible fibrous electrodes with high conductivity and reasonable electrochemical performance. Recently, two-dimensional nanoplatelets with thicknesses on the order of a few angstroms and lateral dimensions in the micrometer range have been proposed as ideal materials for constructing macroscopic fibrous electrodes. In particular, fibers having a nearly perfectly ordered arrangement of the nanosheet structure can maximize the performance utilization of the individual nanosheets. For example, graphene oxide nanoplatelets with a hydrophilic surface can be well dispersed in aqueous media, facilitating the production of continuous fibers using scalable wet spinning methods. In particular, by carefully controlling the stacking order of the nanosheets, the mechanical strength and electrical properties of the fiber can be greatly improved. To enhance the fiber electrochemical performance, mixed fiber electrodes have been prepared by depositing pseudocapacitive materials (e.g., manganese oxide, cobalt oxide, and ruthenium oxide) on graphene or other conductive fiber substrates. Alternatively, similar to the spinning process of graphene oxide, two-dimensional transition metal oxide nanoplates dispersed in an aqueous medium are directly assembled into a fibrous electrode. The nanosheets are sometimes composited 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 capability, but the overall rate capability is limited to a large extent by the inherently low electrical conductivity. Therefore, although there is an urgent need for conductive fibrous electrodes having excellent energy storage capacity, the development thereof is a difficult task.

Some pioneering experimental attempts have been reported for producing macroscopic MXene fibers, but most studies have had to incorporate components with fiber spinnability, such as reduced graphene oxide (rGO), conductive polymers PEDOT, etc. The formation of pure MXene fibers is largely limited by the size of the 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), where strong M-a bonds mean that MXene can only be generated by selective etching of the a layer using harsh chemical methods. In addition, the breaking of M-A bonds during etching can damage M-X bonds based on their similar bond energies. As a result, although the length of the parent MAX crystals is tens of microns, the MXenes obtained mostly exhibit only a limited lateral dimension, only a few hundred nanometers, creating additional grain boundaries, which constitute a significant obstacle to the construction of macroscopic MXene fibers. In particular, the small size of MXene is a disadvantage of aligning flakes in a macrostructure, which may require fine control of flake interface and synthesis parameters.

Disclosure of Invention

The invention aims to overcome the defect that pure MXene macroscopic fibers do not exist in the prior art, and discloses a macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets, a preparation method and application thereof. The MXene macroscopic fiber has potential application in the field of energy storage due to the unique physical and chemical properties. First, MXene has excellent metal conductivity given by a large number of free electrons in transition metal carbides or nitrides; secondly, the two-dimensional sheet morphology ensures high specific surface area, potentially providing high electric double layer capacitance; third, and most importantly, the redox reaction of a large number of surface groups, especially in an acidic environment, imparts additional pseudocapacitance to the MXene nanoplatelets. Thus, MXene has the potential to deliver good electrochemical performance without the aid of any auxiliary components.

The invention adopts the following technical scheme:

the preparation method of the macroscopic high-conductivity MXene ribbon fiber with the orderly stacked nanosheets comprises the following steps:

(1) mixing Ti₃AlC₂Putting the powder into HF solution, stirring and washing to obtain crystals; adding the crystals into a tetramethylammonium hydroxide aqueous solution, stirring, sequentially performing centrifugal treatment and washing, then re-dispersing in water, and performing ultrasonic treatment to obtain a titanium carbide aqueous solution;

(2) injecting the titanium carbide aqueous solution obtained in the step (1) into a coagulating bath to obtain initial fibers;

(3) and (3) carrying out acid treatment and washing on the initial fiber obtained in the step (2) to obtain the macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets.

And (3) assembling the macroscopic high-conductivity MXene ribbon fiber with the nanosheets stacked in order as a negative electrode with an electrolyte, a positive electrode and a diaphragm to obtain the high-performance flexible supercapacitor.

In the invention, in the 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, and the transverse dimension of the titanium carbide is 1-2.5 microns, preferably 1.6-2 microns. In the titanium carbide aqueous solution prepared by the method, the nano sheets have the characteristics of large size, uniform size distribution, high order of the nano sheets and the like, and are favorable for solution spinnability and preparation of continuous long fibers.

In the invention, in the step (2), the coagulation bath is a chitosan-acetic acid coagulation bath, preferably, the solvent in the chitosan-acetic acid coagulation bath is water, the concentration of chitosan is 0.6 wt%, and the concentration of acetic acid is 4 wt%; injecting with conventional injector, receiving with rotating disc, and preparing with existing technology to obtain Ti containing chitosan₃C₂And (3) initial fibers.

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

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

Ti of prior publication₃C₂The nanosheet solution is difficult to have spinnability, and Ti can be prepared only under the assistance of graphene or other spinnable binders₃C₂Composite fiber, and the present invention gives spinnable Ti₃C₂Preparing the solution to obtain pure MXene fibers by a wet spinning process and an acid treatment method; due to the pair of Ti₃C₂Preparation of solution and design of spinning parameters, pure Ti prepared₃C₂The fiber macroscopically presents a ribbon-shaped structure and has Ti in the microscopic interior₃C₂The structure of the ordered stacking of the nano-sheets is beneficial to maximizing the mechanical strength (30 MPa) of the fiber and minimizing the resistance between the nano-sheets (the conductivity is as high as 2458S cm)^-1) (ii) a The acid treated fiber of the invention enables the fiber to have an open two-dimensional ion transmission channel inside, and the fiber has high electrochemical performance (current density)Is 1A g^-1The hour capacity reaches 309F g^-1Current density of 10A g^-1When the capacity is 231F g^-1The capacity retention rate after 10000 cycles is 97.24%); pure Ti of the invention₃C₂The asymmetric super capacitor is assembled by matching the fibers with reduced graphene oxide fibers (rGO), and the assembled asymmetric capacitor has high volume energy density (58.4 mW h cm)^-3）。

Drawings

FIG. 1 is a schematic illustration of the preparation of a fiber and a structural drawing of the starting fiber and a pure titanium carbide fiber;

FIG. 2 is an atomic force microscope image of a titanium carbide nanosheet and nanosheet size distribution statistics, illustrating that the size of the nanosheet in a preferred solution is generally between 1.6-2.0 μm, and the size distribution range is narrow;

FIG. 3 is a polarization microscope image of titanium carbide solutions at different concentrations, illustrating the increasing order of the nanoplatelets in the solution as the concentration increases;

FIG. 4 is a graph and calculation of the spacing simulation of the nanoplates in solution, illustrating that the free volume of the nanoplates in solution is reduced and the constrained strength is increased and more ordered;

FIG. 5 is (c) optical microscope images of cross-section and top view of the original fiber at different stages, distance from the needle exit: i (1 cm), II (11 cm), III (21 cm), IV (31 cm), (d) photographs of continuous long macroscopic fibers;

FIG. 6 is thermogravimetric data of virgin fiber and pure titanium carbide film, from which it can be seen that the virgin fiber contains a small amount of flocculant chitosan;

FIG. 7 is XPS data for (a) virgin fiber and pure titanium carbide fiber having chitosan within the virgin fiber and no chitosan in the pure titanium carbide fiber obtained after acid treatment, indicating that chitosan was removed, and (b) infrared data for virgin fiber and pure titanium carbide fiber having chitosan therein, the virgin fiber having a characteristic absorption peak NH of chitosan₂The chitosan peak in the pure titanium carbide fiber obtained after acid treatment is not existed, which indicates that the chitosan is removed;

FIG. 8 shows the correlation between Ti and original Ti₃C₂Acid treated pure Ti compared to chitosan fibers₃C₂XRD pattern of fiber (a)

) (b) acid-treated pure Ti₃C₂Low power and (c) high magnification cross-section SEM images of fibers, (d) acid treated Ti₃C₂Cross-sectional HRTEM lattice images of fibers. Illustration is shown: a mode of FFT generation;

FIG. 9 is an elemental analysis under a transmission electron microscope after ultrathin sectioning of fibers;

FIG. 10 is a graph of the mechanical strength of the virgin fiber and the pure titanium carbide fiber; after acid treatment, chitosan is removed, so that the mechanical strength of the fiber is slightly reduced, but the fiber still has good mechanical strength;

FIG. 11 shows pure Ti wound on a glass rod₃C₂The pure titanium carbide fiber obtained by the photograph of the fiber and the SEM image of the tightly knotted fiber has good flexibility;

FIG. 12 shows the pure Ti as compared to other reported MXene-based fibers under the same test method₃C₂The conductivity of the fiber, the pure titanium carbide fiber obtained by the invention has high conductivity;

FIG. 13 is a comparison of the electrical resistance of the virgin fiber to that of a pure titanium carbide fiber, (a) the electrical resistance of a virgin fiber 11cm long, calculated to have an electrical conductivity of 767S cm^-1(b) the resistance of the pure titanium carbide fiber with the length of 11cm, and the calculated conductivity is 2458S cm^-1The resistance of the initial fiber and the pure titanium carbide fiber is in a linear relation with the change of the length, which shows that the fiber is uniform, (d) the resistance of the pure titanium carbide fiber under different bending angles shows that the resistance of the pure titanium carbide fiber is stable under bending;

FIG. 14 is a graph of the electrochemical performance of pure titanium carbide fibers in a three-electrode system. (a) Schematic of a 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 is shown: at different current densitiesNext, comparison of the capacity retention capability of the fiber optic super capacitor based on MXene. (e) 10. the method of the present invention⁴Cycle stability for each cycle. Illustration is shown: GCD curves for the first and last cycles;

FIG. 15 is a cross-sectional SEM image of pure titanium carbide fiber after cycling at 10A g-1 for 10000 cycles; the pure titanium carbide fiber has good working stability of the electrode;

FIG. 16 is a graph of the performance difference between the initial fiber and the acid treated pure titanium carbide fiber, where 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, and the pure titanium carbide fiber has a smaller ion diffusion resistance;

FIG. 17 is a graph of H calculated from impedance data⁺The diffusion coefficient of (d);

FIG. 18 shows GCD acid treated pure Ti of various lengths₃C₂Bending the fiber;

FIG. 19 is the electrochemical performance of an asymmetric fiber supercapacitor. (a) Schematic of a flexible asymmetric device. (b) Pure Ti₃C₂CV curves for fiber and rGO fiber at the same scan rate. (c) CV curves for asymmetric devices at different scan rates and (d) GCD curves at different current densities. (e) The volume energy density and the power density of the assembled asymmetric device are compared with those of other fiber super capacitors and fiber batteries. (f) A picture of blue LED logo fibers driven by three flexible devices connected in series, and (g) a picture of two series fibers woven into a glove to illuminate an electronic watch;

fig. 20 is an SEM surface view of (a) redox graphene fibers; (b) a cross-sectional view of a redox graphene fiber;

fig. 21 is a Cyclic Voltammogram (CV) of a redox graphene fiber at different sweep rates;

FIG. 22 is a diagram showing the operating range of the assembled device, with the operating voltage being 0-1.5V;

FIG. 23 shows the assembled device at a current density of 10A g^-110000 times of data are circularly worked, and the embedded graph is as follows: first and last constant current charge and discharge data before the device works circularly;

FIG. 24 is (a) titanium carbide nanoplates of the present invention with a coagulation bath of aqueous chitosan-acetic acid; the effect is as follows: can be made into continuous fiber with high mechanical strength; (b) according to the titanium carbide nanosheet, the coagulating bath is 5% calcium chloride water-isopropanol (volume ratio is 3: 1); the effect is as follows: short fibers can be obtained only, and the product is very brittle and almost has no strength; (c) small nano-sheets, wherein the coagulation bath is chitosan-acetic acid aqueous solution; the effect is as follows: short fiber with certain strength.

FIG. 25 is 10mg mL^-1The spinning effect of the titanium carbide solution in the chitosan-acetic acid solution can only obtain short fibers, but not continuous fibers.

Detailed Description

Materials: ti₃AlC₂Powders (98%, 325 mesh) were purchased from Shanghai cloth Han chemical engineering, Inc.; aqueous hydrofluoric acid (HF, 40%,>98%) and aqueous tetramethylammonium hydroxide (TMAOH, 25%) were purchased from J & K Scientific co., Ltd; hydrochloric acid (HCl, ≧ 98%) and sulfuric acid (H)₂SO₄≧ 98) from Alatin; chitosan (99%) and acetic acid (99.5%) were provided by the national pharmaceutical group chemical agents, ltd; polyvinyl alcohol (PVA, Mw = 1788) was purchased from alatin industries, shanghai, china; graphene Oxide (GO) was purchased from J & K Scientific, ltd.; the separator was purchased from Nippon Kodoshi Corporation (Nippon Kodoshi Co., Ltd.).

The three-electrode test method comprises the following steps: the electrochemical test was carried out in 1M sulfuric acid electrolyte with the electrode clamp holding the fibers directly as the working electrode, Ag/AgCl as the reference electrode, Pt as the counter electrode. (test equipment CHI660E electrochemical workstation);

and (3) testing two electrodes: performing electrochemical performance test on the fiber device by using a CHI660E electrochemical workstation, and directly testing the anode and the cathode of the fiber device by respectively connecting the electrochemical workstation;

and (3) conductivity test: measuring the resistance of the fiber with the length of 11cm by using an ohmmeter, then calculating the cross-sectional area of the fiber by using an SEM (scanning electron microscope), and calculating the conductivity by using a formula of sigma = L/RS;

and (3) calculating the mechanical strength: and calculating the sectional area of the fiber by adopting an SEM sectional internal diagram, and measuring the mechanical strength of the fiber by adopting an Instron 3365 universal material tensile instrument.

The preparation method of the macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets comprises the following steps:

(1) mixing Ti₃AlC₂Putting the powder into HF solution, stirring and washing to obtain crystals; adding the crystals into a tetramethylammonium hydroxide aqueous solution, stirring, sequentially performing centrifugal treatment and washing, then re-dispersing in water, and performing ultrasonic treatment to obtain a titanium carbide aqueous solution; preferably, after ultrasonic treatment, centrifugal treatment is carried out to obtain a titanium carbide aqueous solution;

And (4) assembling the macroscopic high-conductivity MXene ribbon fiber with the nanosheets orderly stacked in the step (3) as a negative electrode with an electrolyte, a positive electrode and a diaphragm to obtain the high-performance flexible supercapacitor.

The raw materials are all purchased from the market, and the related test methods are all conventional test methods in the field.

Example one

Preparing titanium carbide colloid aqueous solution: ti₃AlC₂The powder (1 g) was put into an HF solution (10 wt%, 30 mL), stirred for 10 minutes, then washed 3 times by centrifugation with distilled water, and then dried in a vacuum oven at 80 ℃ for 24 hours. The dried powder was placed in aqueous tetramethylammonium hydroxide (25 wt%, 10 mL) and stirred continuously for 24 hours; centrifuging the obtained suspension at 5000rpm for 10 min, taking the bottom precipitate, washing with deionized water and drying; then re-dispersing in deionized water, carrying out ultrasonic treatment at room temperature for 15 minutes, centrifuging at 3500rpm for 15 minutes, taking the upper suspension, centrifuging at 8000rpm for 15 minutes, and taking the lower suspension to obtain the titanium carbide colloid aqueous solution with the concentration of 20 mg/mL.

The aqueous solution of titanium carbide colloid was charged into a rotary nozzle (500 μm diameter nozzle)Gauge stainless steel spinning needle) into a plastic syringe and injected (40 mL h)^-1) In the coagulation bath, received by a rotating magnetic disk; the coagulation bath was an aqueous solution of chitosan containing 4 wt% acetic acid (0.6 wt% chitosan), the speed of the rotating magnetic disk was set at 560 rph, the distance from the nozzle to the center of the rotating magnetic disk: 6 cm; when the titanium carbide colloid water solution contacts with the coagulating bath, continuous initial fiber is formed immediately; after the initial fiber was allowed to stand in the coagulation bath for 15 minutes, it was washed with water and ethanol; then immersing the initial fiber into 1M sulfuric acid aqueous solution for 3 d; washing the acid-treated fiber with deionized water and ethanol for 5 times respectively, and drying under ambient conditions to obtain the macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets, namely pure Ti₃C₂A fiber.

The initial fiber was washed 5 times with deionized water and ethanol, respectively, and dried under ambient conditions to give Ti₃C₂Chitosan fibers, referred to as initial Ti, as comparative fibers₃C₂A fiber.

The invention will contain Ti₃C₂Tablet (20 mg mL)^-1) Is extruded from a needle (500 μm in diameter) through a syringe pump into a coagulation bath placed on a rotating disk, by wet spinning Ti in a coagulation bath of protonated chitosan₃C₂The solution and subsequent removal of the chitosan in acid produces macroscopically pure Ti₃C₂Fibers, as shown in fig. 1.

The prepared nanosheets have a transverse dimension of 1.6-2 [ mu ] m and an average thickness of about 1.6 nm (fig. 2), based on the repulsive force between the nanosheets, even when the concentration is increased to 20mg mL^-1The solutions also show high stability, based on > 10³The aspect ratio (width/thickness) of the nanosheet(s) was calculated to be 10.88mg mL of theoretical critical concentration for formation of a liquid crystal phase^-1However, the concentration of the compound is close to the critical concentration (20 mg mL)^-1) Polarization optical microscopy characterization of the doubled solution revealed no birefringence characteristic typical of liquid crystal phases (FIG. 3), 20mg mL^-1The average spacing between the nanoplatelets in the solution of (a) is estimated to be about 170 nm (fig. 4) for continuous fiber manufacturing.

Continuous fiber with good strength can be obtained by nano-sheet spinning with larger transverse dimension in the protonation chitosan coagulation bath, and Ti is used₃C₂The solution was injected into the coagulation bath through a narrow spinning nozzle (500 μm in diameter) at a certain speed, and flocculation occurred immediately, the cross section of which was the same as that of the injection needle, and the cylindrical fibers were gradually changed into ribbon-shaped fibers as the fibers were drawn from the outlet of the needle, as shown in FIG. 5c, and the morphology of the obtained cross-sectional view and the top view of the fibers was evolved, indicating that the abnormal formation of ribbon-shaped fibers was caused by the formation of a densely oriented stack of sheets, the cross-sectional area was calculated in four stages, and the gradually decreasing tendency was shown, and the prepared fiber object was shown in FIG. 5d, the fiber length was only dependent on the feed, the raw material was sufficiently long to spin continuous fibers sufficiently long, and the initial Ti was obtained by thermogravimetric data (TGA) analysis₃C₂Fibers and pure Ti₃C₂The difference in fibers, see fig. 6; chitosan between the nanosheets was completely removed by treatment in sulfuric acid, FIG. 7, resulting in a pure MXene fiber density of 3.26 g cm^-3Comparable to commercial carbon fibers.

Ti before and after the acid treatment was analyzed₃C₂Structural and morphological characteristics of the fibers. The X-ray powder diffraction (XRD) profile shown in figure 8a shows a reflection peak in the low angle regime of both samples, which means that regular lamellae of both structures are stacked. After acid treatment, the distance between the nano sheets is changed from original Ti₃C₂The distance between chitosan fibers, 1.43 nm, was reduced to 1.33 nm, clearly detectable with Ti₃C₂Diffraction (110) associated with in-plane features of the layer, indicating that after acid treatment, Ti₃C₂The main structure of the nano-sheet is well preserved. The morphology of the fibers obtained was characterized using Scanning Electron Microscopy (SEM), which showed a clear ribbon-like structure and regular sheet-to-sheet face stacking (fig. 8b and 8 c), validating the results of optical microscopy and XRD. Importantly, no large differences were found in cross-sectional observations of the virgin and acid treated fibers, indicating that the acid treatment did not cause structureDegrades and can successfully inherit the ordered stack structure. This structure can be observed more clearly in High Resolution Transmission Electron Microscope (HRTEM) images. In fig. 8d, the parallel stripes corresponding to the stacked layers can be clearly seen. The fringe distance was found to be 1.33 nm, consistent with XRD results. Performing a Fourier transform (FFT) mode showed well-aligned diffraction spots, further confirming Ti₃C₂Orderly stacking the nano sheets. The element Mapping results show that the Ti, C, O and S elements are uniformly distributed (FIG. 9).

Macroscopically pure Ti obtained as described above, based on the oriented stacked structure and the flexibility of the two-dimensional nanosheets₃C₂The tensile strength of the fibers reached 30MPa, see fig. 10, and the panels show that the pure titanium carbide fibers of the invention can be used to lift the key without interruption, so that the acid treatment does not cause significant deterioration in mechanical properties, based on the inheritance of the oriented sheet stack structure. These fibers have sufficient strength and flexibility to bend and knot on a phi 5 mm glass rod without any sign of breakage, as shown in fig. 11, and are therefore satisfactory for flexible energy storage devices. Furthermore, made of metal Ti₃C₂The two-dimensional open nanochannels between the lamellae and the electron channels provided by the lamellae facilitate rapid transport of ions and electrons. Measuring pure Ti₃C₂The conductivity of the fiber is 2458S cm^-1And is several orders of magnitude greater than the value for the MXene-based composite fiber, see fig. 12, with the upper right hand digit of the existing fiber being the reference number. The electrical conductivity values of the fibers vary little with the bending angle, due to their compact stacking structure and excellent mechanical flexibility, see fig. 13. Thus, Ti₃C₂The exceptionally highly oriented stack structure of the nanoplates can yield excellent ionic conductivity, rapid ionic diffusion within the crystal lattice and acceptable mechanical strength, which provides a solid foundation for the realization of flexible energy storage devices. Conductivity test method, measuring the resistance of a fiber 11cm long, then calculating the cross-sectional area of the fiber through an SEM sectional diagram, and calculating the cross-sectional area through the formula: conductivity σ = L/RS the conductivity was calculated.

In view of the above-discussed pure titanium carbide fiber orientation of the present inventionNanosheet stacking and high conductivity, first at 1M H₂SO₄The electrochemical performance of the obtained fibres was characterized in a standard three-electrode configuration in the electrolyte, where one end of the long fibres was directly clamped on the electrode as the working electrode, Ag/AgCl as the reference electrode, and the Pt sheet as the counter electrode (fig. 14 a). This arrangement is a harsh condition for the fiber electrode because the electrons at one end of the fiber electrode must travel a long distance to pass through the fiber before reaching the current collector. Acid-treated pure Ti₃C₂The Cyclic Voltammetry (CV) curves of the fiber at different scan rates over the potential range of-0.6 to 0.2V are shown in fig. 14 b. A current response showing a broad redox peak can be observed, clearly demonstrating the pseudocapacitive behaviour of the fibres; furthermore, even at 100 mV s^-1The CV curve also showed no significant distortion at the scan rate of (a), indicating its excellent rate performance. FIG. 14c shows a constant current charge-discharge (GCD) curve that deviates significantly from a perfect triangle, indicating Ti₃C₂Surface redox reaction of nanoplates, which is consistent with CV analysis results, even at 10A g^-1Also, there was no significant ohmic drop at the high current density indicated the high conductivity of the fiber electrode, the fiber was rated at 1A g^-1Has a current density of 309F g^-1（52.38 mF cm ^-1) The specific capacitance of (c). When the current density increased to 10A g^-1While, the capacitance remains at 231F g^-1（39.16 mF cm^-1) This indicates a capacity retention of 74.76%. In contrast, other MXene-based fiber supercapacitors showed lower retention of capacitance with increasing current density under the same test (fig. 14 d). Ti₃C₂The high rate performance of the fiber can be attributed to the rapid ion intercalation and de-intercalation based on the oriented stacking of the nanosheets, the rapid electron transfer and the Ti₃C₂Short path of ion transport in the layered structure. Further, acid-treated Ti₃C₂Fibrous electrode at 10A g^-1Also exhibits excellent cycling stability at current densities of 10, as shown in fig. 14e⁴After a long cycle of one cycle, the capacity retention was about 97.24%. In addition to this, the present invention is,there was no significant deformation, indicating the structural stability of the fibrous electrode prepared according to the invention (fig. 15).

Under the same measurement method, initial Ti₃C₂Replacement of pure Ti by fibers as electrodes₃C₂Fibres, at 10A g^-1Does not exhibit excellent cycling stability at current densities of 10 f⁴After one cycle, the capacity retention was about 91.38%.

FIG. 16A is a graph of electrochemical performance data (CV data) for virgin titanium carbide fibers versus pure titanium carbide fibers at 10 mV s^-1At sweep rates, the capacity of titanium carbide-chitosan fibers is significantly less than that of pure titanium carbide fibers. Electrochemical Impedance Spectroscopy (EIS) analysis was performed to gain insight into Ti₃C₂Charge transfer and ion transport properties of the fibers. Ti₃C₂The fiber electrode showed a shorter Warburg region at high frequency indicating a fast electron transfer rate, and a nearly perpendicular curve at low frequency indicating ideal capacitance characteristics (fig. 16). The excellent ion transport properties of the fibers were also analyzed from a kinetic perspective, with a diffusion coefficient estimated at 9.2X 10^-7 cm² s^-1With the original Ti₃C₂The value of chitosan fiber was 1.43X 10^-7 cm² s^-1(FIG. 17), confirming the designed Ti₃C₂The fibers have the structural advantages of an orderly stacked structure and prepreg channels. In order to highlight the Ti obtained₃C₂Excellent conductive network of fibers, also 2A g^-1The GCD curve of the fibers extending 5 times to 15 cm in length was tested as shown in fig. 18. Even at such lengths, no significant ohmic drop was observed, and the curves almost completely overlapped. All these results provide clear evidence that Ti was produced₃C₂The oriented stacking of the sheets provides excellent ion and electron transport properties between the fibrous electrodes and the layers, resulting in excellent overall electrochemical performance.

Example two

And (3) assembling the macroscopic high-conductivity MXene ribbon fiber with the sequentially stacked nanosheets as the negative electrode, the polyvinyl alcohol-sulfuric acid electrolyte and the positive electrode rGO fiber to obtain the high-performance flexible supercapacitor.

By adopting the method of the first embodiment, replacing the titanium carbide colloid aqueous solution with a commercial GO aqueous solution with a concentration of 10mg/mL (the thickness of GO sheet layer is about 1nm, and the transverse size is 3-5 mu m) to obtain GO initial fibers, immersing the GO initial fibers in a hydriodic acid (57 wt%) aqueous solution at 90 ℃ for 5 hours, and then washing to obtain rGO fibers serving as a positive electrode.

1g of PVA powder was dissolved in 10 mL of distilled water at 90 ℃ with stirring until a clear solution was obtained, and after adding 1g of sulfuric acid and stirring, the clear solution was cooled to room temperature, thereby obtaining a polyvinyl alcohol-sulfuric acid electrolyte.

And connecting the positive electrode and the negative electrode with a copper wire current collector respectively by using silver paste, then parallelly placing the positive electrode and the negative electrode into a heat-shrinkable tube, adding the existing polymer diaphragm and electrolyte, and heating, sealing and assembling the high-performance flexible supercapacitor.

Based on Ti₃C₂Excellent electrochemical performance of fiber electrode, acid-treated Ti using polyvinyl alcohol-sulfuric acid as electrolyte₃C₂The fibers are the negative electrodes, and the rGO fibers are the positive electrodes to assemble the asymmetric solid fiber supercapacitor, as shown in fig. 19 a. Ribbon-structured rGO fibers can also be obtained by wet spinning (fig. 20 is its SEM image) and exhibit typical capacitive properties (fig. 21), rGO fibers having a broad voltammetric response in the potential window of-0.1 to 0.9V, while acid-treated Ti₃C₂The potential window of the fiber was in the range of-0.6 to 0.2V (fig. 19 b). Therefore, the pair of electrodes can provide an effective voltage as high as 1.5V without polarization (fig. 22). As shown in fig. 19c and 19d, the CV and GCD curves of the asymmetric fiber supercapacitor exhibited curvature at similar voltages with ideal electrochemical behavior at different scan rates and current densities. Asymmetric fiber super capacitor at 5 mV s^-1May provide 88.67F g at a scan rate of^-1（256 F cm^-3) Can be compared to the value of a typical fiber supercapacitor. In addition, the asymmetric fiber super capacitor has the capacity retention rate of 92.4 percent and has long-term circulation stabilityQualitative (fig. 23). Fig. 19e gives a Ragone plot comparing volumetric energy and power density between different fiber supercapacitors and fiber batteries. The invention is at 1679 mW cm^-3Can provide 58.38 mW h cm^-3High bulk density of (2) at 17.63 mW h cm^-3Can provide about 7466 mW cm^-3High volumetric power density. These energy densities are comparable to typical asymmetric fiber optic supercapacitors, while the energy densities approach certain fiber optic batteries (table 1). Based on the excellent energy storage performance of asymmetric fiber supercapacitors, a practical application was established that uses three flexible devices in series to power a 3.5V blue Light Emitting Diode (LED) logo fiber or an electronic watch. The LED and electronic watch lit by the asymmetric fiber supercapacitor of the invention did not show significant dimming during bending of the device, demonstrating the mechanical strength and flexibility of the device of the invention (fig. 19f and 19 g).

TABLE 1 capacitor Performance

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comparative example

On the basis of the first embodiment, continuous macroscopic fibers cannot be obtained by using the existing small-size titanium carbide nanosheet aqueous solution, see fig. 24c, and the same spinning method.

Based on example one, continuous macroscopic fibers could not be obtained with the same spinning process using the existing inorganic ion coagulation bath (5 wt% calcium chloride water-isopropanol solution with a water to isopropanol volume ratio of 3: 1), see fig. 24 b.

On the basis of the first embodiment, the continuous macroscopic fiber cannot be obtained by the same spinning method by using 10mg/mL titanium carbide nanosheet aqueous solution, which is shown in FIG. 25.

On the basis of example one, a disc rotation speed of 400rph was used, and otherwise, continuous macroscopic fibers could not be obtained.

On the basis of the first embodiment, the macroscopically continuous Ti is obtained by adopting the existing large-size titanium carbide nanosheet aqueous solution (the transverse size is 3-4 microns) and the same spinning and acid soaking methods₃C₂The fibers were calculated for the same test at 1A g^-1Has a current density of 283F g^-1The specific capacitance of (c).

And (4) conclusion:

in the present invention, Ti is wet-spun in a coagulating bath of protonated chitosan₃C₂The solution is then treated with acid to remove the chitosan, and pure Ti with a band-shaped structure is successfully prepared₃C₂The fiber (width 1.1-1.3 mm, thickness 3-5 microns) has a highly oriented nanosheet stacking structure. Ti₃C₂Is a typical member of the MXene series, after which Ti is added₃C₂Used to refer to particular materials of such materials. In the process of treating chitosan by acid, the ordered stacking structure of the nanosheets is not damaged, and the mechanical property of the fiber is not damaged. Pure Ti is obtained₃C₂The belt presents three important advantages. First, the nanosheets in the fiber have a highly ordered stacked structure, meaning that the mechanical properties of each nanosheet are effectively integrated. Such pure Ti₃C₂The fibers can provide a tensile strength of 30.0 MPa sufficient for practical device applications. Secondly, each nanosheet is an excellent conductor, and the nanosheets are closely connected, helping to build a continuous conductive network and providing 2458S cm^-1Which is nearly two orders of magnitude greater than the conductivity of previously reported MXene-based composite fibers. Third, the ordered stack can form an open two-dimensional channel, which effectively reduces the ion transport obstruction even at higher current densities, thereby shortening the length of the ion diffusion path and facilitating the electrode reaction (231.0F g)^-1Or 39.2 mF cm^-1At a current density of 10A g^-1Under the conditions of (a). Based on the designed fiber Ti₃C₂The excellent electrochemistry action of electrode adopts the rGO fibre as the positive electrode material, has assembled asymmetric ultracapacitor system. At 1A g^-1Under the current density, the energy density reaches 58.4 m Wh cm^-3（20.0 W h Kg^-1) Corresponding to a volumetric power density of 1679.0 mW cm^-3（581.0 W Kg^-1). This work demonstrated acceptable processability of MXene and opened a new window for the application of MXene materials in future wearable electronics.

Claims

1. The preparation method of the MXene ribbon fiber with the orderly stacked nanosheets and the high macroscopic conductivity is characterized by comprising the following steps of:

(1) mixing Ti₃AlC₂Putting the powder into HF solution, stirring and washing to obtain crystals; adding the crystals into a tetramethylammonium hydroxide aqueous solution, stirring, sequentially performing centrifugal treatment and washing, then re-dispersing in water, and performing ultrasonic treatment to obtain a titanium carbide aqueous solution; 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 15-25 mg/mL; the transverse size of the titanium carbide is 1-2.5 microns;

(2) injecting the titanium carbide aqueous solution obtained in the step (1) into a coagulating bath to obtain initial fibers; the coagulating bath is chitosan-acetic acid coagulating bath; in the chitosan-acetic acid coagulation bath, the solvent is water, the concentration of chitosan is 0.6 wt%, and the concentration of acetic acid is 4 wt%;

(3) and (3) carrying out acid treatment and washing on the initial fiber obtained in the step (2) to obtain the macroscopic high-conductivity MXene ribbon fiber with the orderly stacked nanosheets, and soaking for 3 days in a 1M sulfuric acid solution after acid treatment.

2. Use of the macroscopic high-conductivity MXene ribbon fiber with orderly stacked nanosheets of claim 1 in the preparation of a high-performance flexible supercapacitor.