Asymmetrically wound structures and methods of making the same, electrodes, films, and electrochemical energy storage devices

Abstract

This invention discloses an asymmetric wound structure, its fabrication method, an electrode, a thin film, and an electrochemical energy storage device. The asymmetric wound structure is formed by rolling up two-dimensional MXene nanosheets, possessing hollow nanochannels extending along the axial direction. Along this axial direction, the wound structure has two distinct radial dimensions, defined as a first radial dimension R1 and a second radial dimension R2, where R1 > R2. The asymmetry between the first radial dimension R1 and the second radial dimension R2 enables the formation of a polarized electric field within the wound structure. This inherent polarized electric field, requiring no external power source, provides an intrinsic driving force for efficient ion transport, solving the problem of slow ion transport in electrodes.

Description

Technical Field

[0001] This invention belongs to the fields of new materials and electrochemistry, and in particular relates to asymmetric wound structures and their preparation methods, electrodes, thin films and electrochemical energy storage devices. Background Technology

[0002] Electrochemical capacitors (also known as supercapacitors) are considered strong candidates for next-generation energy storage devices due to their superior characteristics such as high power density, rapid charge and discharge capabilities, and long cycle life. Compared with traditional energy storage devices such as lithium-ion batteries, electrochemical capacitors can complete the charge and discharge process within seconds to minutes, and their power density can be tens or even hundreds of times that of traditional batteries, showing broad application prospects in fields such as electric vehicles, smart grids, and portable electronic devices.

[0003] MXene is a novel family of two-dimensional transition metal carbide / nitride / carbonitride materials, whose general formula can be represented as M n+1 X n T x In this model, M represents an early transition metal element (such as Ti, V, Nb, Mo, etc.), X represents carbon and / or nitrogen, and T represents a terminal group on the material surface (such as -OH, -O, -F, -Cl, etc.). MXene materials possess a unique layered structure, excellent metallic conductivity, abundant surface chemically active sites, and good hydrophilicity and mechanical flexibility, demonstrating enormous application potential in the field of electrochemical energy storage.

[0004] However, existing MXene electrode studies are mostly limited to low mass loading conditions (typically less than 20 mg cm⁻¹). -2 When fabricated into high-quality loaded thick-film electrodes, MXene materials often suffer from a significant decline in electrochemical performance due to the limited ion transport kinetics within the thick electrode. Specifically, as the electrode thickness increases, the diffusion path of ions from the electrolyte to the active sites inside the electrode lengthens, increasing diffusion resistance and leading to reduced electrode utilization, decreased specific capacity, and deteriorated rate performance. This problem severely limits the application of MXene materials in practical electrochemical energy storage devices. Summary of the Invention

[0005] To address the technical problem that the electrochemical performance of MXene materials is significantly reduced due to the limited ion transport kinetics in the electrode in the prior art, this invention provides an MXene material with an asymmetric rolled structure and its preparation method to improve ion transport performance and thus improve the performance of electrochemical energy storage devices. The first aspect of the present invention provides an asymmetric wound structure formed by rolling up two-dimensional material MXene nanosheets, having hollow nanochannels extending along the axial direction; along the axial direction, the wound structure has two different radial dimensions, defined as a first radial dimension R1 and a second radial dimension R2, wherein R1>R2, and the asymmetry between the first radial dimension R1 and the second radial dimension R2 can form a polarized electric field inside the wound structure.

[0006] In some embodiments, the second radial dimension R2 is 10 to 100 nm; preferably, it is 15 to 40 nm.

[0007] In some embodiments, the axial length of the above-described winding structure is 0.5 to 50 μm; preferably, it is 1 to 10 μm.

[0008] In some embodiments, the ratio of the first radial dimension R1 to the second radial dimension R2 is 1.05 to 5; preferably, it is 1.1 to 2.5.

[0009] In some embodiments, the asymmetric winding structure described above has enhanced transport performance for at least one cation.

[0010] In some embodiments, the cation is selected from H. + Li + Na + NH4 + Zn 2+ Mg 2+ Al 3+ .

[0011] In some embodiments, the strength of the aforementioned polarization electric field is greater than 10. 3 V / m; more preferably, greater than 10 4 V / m; In some implementations, the general formula for the above-mentioned MXene is M. n+1 X n T x M is selected from at least one of Ti, V, Nb, Mo, Ta, Cr, Zr, Hf, Sc, and Y; X is selected from C and / or N; and T represents a functional group. n The range is 1 to 4.

[0012] In some implementations, the MXene mentioned above is selected from: V2CT x Ti3C2T x Nb2CT x Mo2CT x Ti2CT x Ti4C3T x V4C3T xNb4C3T x At least one of them; In some embodiments, the specific surface area of ​​the asymmetric winding structure described above is 10 to 200 m². 2 g -1 ; In some embodiments, the conductivity of the asymmetric winding structure described above is greater than 4000 S cm. -1 Preferably, ≥8000 S cm -1 .

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned asymmetric winding structure, comprising the following steps: (1) Mix the MAX phase precursor with an etchant and perform a selective etching reaction to remove the A layer elements in the MAX phase and obtain a multilayer MXene material; (2) Mix the multilayer MXene material obtained in step (1) with the intercalating agent solution and perform intercalation stripping treatment to increase the interlayer spacing; (3) The product obtained in step (2) is separated and washed to remove residual intercalating agent; (4) Disperse the product obtained in step (3) in a dispersion medium and stir. (5) The dispersion obtained in step (4) is subjected to solid-liquid separation, and the precipitate is collected to obtain the asymmetric winding structure.

[0014] In some embodiments, the general formula for the aforementioned MAX phase precursor is M. n+1 AX n M is selected from at least one of Ti, V, Nb, Mo, Ta, Cr, Zr, Hf, Sc, and Y; A is selected from at least one of Al, Ga, Si, and Ge; and X is selected from C and / or N. n The range is 1 to 4.

[0015] In some embodiments, the MAX phase precursor described above has been mechanically crushed before step (1).

[0016] In some embodiments, after mechanical crushing, the particle size of the MAX phase precursor is 600 mesh to 1000 mesh; or, the particle size is 1 to 20 μm; preferably, 2 to 5 μm.

[0017] In some embodiments, the etchant is selected from at least one of hydrofluoric acid, a mixed solution of lithium fluoride and hydrochloric acid, a mixed solution of sodium fluoride and hydrochloric acid, and a mixed solution of ammonium fluoride and hydrochloric acid.

[0018] In some embodiments, the intercalating agent is selected from at least one of tetraalkylammonium hydroxide, tetraalkylammonium halide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0019] In some embodiments, the aforementioned tetraalkylammonium hydroxide is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0020] In some embodiments, the concentration of the intercalating agent solution is 10-50 wt.%; preferably, 20-30 wt.%.

[0021] In some embodiments, the stirring speed is >400 rpm; preferably, ≥600 rpm; and even more preferably, ≥800 rpm.

[0022] A third aspect of the present invention provides a thin film comprising the above-described asymmetric winding structure.

[0023] In some embodiments, the thickness of the above-mentioned film is greater than 5 μm; preferably, it is 10 to 1000 μm.

[0024] In some embodiments, the mass load of the asymmetric winding structure in the above-described film is ≥10 mg / cm². 2 Preferably, ≥25 mg / cm 2 More preferably, ≥35 mg / cm 2 More preferably, ≥50 mg / cm 2 .

[0025] In some embodiments, the thin film exhibits capacitance characteristics independent of its thickness.

[0026] In some embodiments, when the mass load is doubled, the mass specific capacitance of the above-mentioned film decreases by less than 5%.

[0027] A fourth aspect of the present invention provides a method for preparing the above-mentioned thin film, comprising the following steps: (1) The wound structure is dispersed in a dispersion medium to obtain a dispersion; (2) The dispersion obtained in step (1) is subjected to film formation treatment and dried to obtain a thin film; preferably, the film formation treatment is selected from at least one of vacuum filtration film formation, blade coating film formation, spray coating film formation and spin coating film formation.

[0028] In some embodiments, step (2) is followed by a crosslinking process: immersing the dried film in a crosslinking agent solution to carry out a crosslinking reaction.

[0029] In some embodiments, the crosslinking agent is selected from at least one of borates, aluminum salts, calcium salts, and zirconium salts.

[0030] In some embodiments, a binder is added to the dispersion.

[0031] A fifth aspect of the present invention provides an electrode comprising the above-described asymmetric winding structure or the above-described thin film. A sixth aspect of the present invention provides an electrochemical energy storage device comprising the electrodes described above.

[0032] In some embodiments, the electrochemical energy storage device is selected from at least one of electrochemical capacitors, supercapacitors, lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, magnesium-ion batteries, and aluminum-ion batteries.

[0033] The seventh aspect of the present invention provides an application of the above-described asymmetric winding structure or the above-described thin film in an electrochemical energy storage device.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) The asymmetric winding structure provided by this invention has a unique axially asymmetric hollow nanochannel structure, which spontaneously forms an electron concentration gradient inside the winding body, inducing a significant polarization electric field along the material axis. The intensity of this polarization electric field can reach 10. 3 V / m or higher, even reaching 10 4 The V / m order of magnitude significantly enhances ion transport dynamics. The inherent polarization electric field of this structure, which requires no external power source, provides the intrinsic driving force for efficient ion transport.

[0035] (2) The asymmetric winding structure material of the present invention affects H + Li + Na + Zn 2+ The conductivity of various ions is increased by about an order of magnitude, generally reaching 10. 2 μS or higher fundamentally solves the problem of slow ion transport in electrodes. It can be used as a general platform technology in energy storage devices such as supercapacitors and various metal-ion batteries, and has extremely high industrial value and commercial potential.

[0036] (3) The electrode using the material of this invention still exhibits excellent electrochemical performance, including high specific capacitance and capacitance retention, even under high mass loading. More notably, when the electrode mass loading increases from 25 mg / cm³, the electrochemical performance remains excellent. 2 Increased to 50 mg / cm 2 At this time, its capacitance per unit mass decay rate is extremely low (<5%), exhibiting unique thickness / load independent characteristics, achieving a balance between high energy density and high power density. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the asymmetric MXene winding structure of the present invention and the strong polarization electric field it generates.

[0038] Figure 2 This is an electric field distribution diagram of the asymmetric winding model of the present invention.

[0039] Figure 3 The asymmetric V2CT in Embodiment 1 of the present invention x The winding structure (a) and V2CT x Scanning electron microscopy (SEM) images of nanosheets (b) show numerous conical, tubular, and sheet-like morphologies.

[0040] Figure 4 For example, in Embodiment 1 of the present invention, (a) asymmetric V2CT x (a) Transmission electron microscopy (TEM) image of the coiled structure and (b) cross-sectional TEM image, showing the hollow nanochannels.

[0041] Figure 5 This is a schematic diagram of Kelvin probe force microscopy (KPFM) measurement of a single asymmetric MXene wound structure in Embodiment 1 of the present invention. (b) is a KPFM image of a single asymmetric MXene wound structure, and (c) is the corresponding line scan image.

[0042] Figure 6 The asymmetric V2CT in Embodiment 1 of the present invention x Rolled-up structure thin film (a) and V2CT x Optical photograph and cross-sectional SEM image of the nanosheet film (b).

[0043] Figure 7 The asymmetric V2CT in Embodiment 1 of the present invention x Small-angle X-ray scattering (SAXS) pattern (a) and N2 adsorption / desorption isotherm (b) of the wound-structured thin film.

[0044] Figure 8 The asymmetric V2CT in Embodiment 1 of the present invention x Wound structure and V2CT x Comparison of X-ray diffraction (XRD) curves of nanosheets.

[0045] Figure 9 The asymmetric V2CT in Embodiment 1 of the present invention x Rolled-up structure thin film (a) and V2CT x The current-voltage (IV) curves of the nanosheet thin film (b) in different electrolytes (including H2SO4, Li2SO4, Na2SO4, (NH4)2SO4, MgSO4, ZnSO4 and Al2(SO4)3).

[0046] Figure 10 The asymmetric V2CT in Embodiment 1 of the present invention xThe ionic conductivity of the wound thin film, as shown under the same conditions, is higher than that of ions (such as H+). + Li + Na + NH4 + Zn 2+ Mg 2+ Al 3+ The conductivity increased significantly to approximately 10. 2 μS, while V2CT x Nanosheet films are only about 10 1 μS.

[0047] Figure 11 This is a schematic diagram of the process flow for preparing a high-load, thick-layer asymmetric MXene rolled-up thin film electrode in Embodiment 3 of the present invention.

[0048] Figure 12 In Example 3 of the present invention, the mass loading was 25 mg cm⁻¹. -2 (a) 35 mg cm -2 (b) and 50mg cm -2 (c) Asymmetric V2CT x The photographs of the rolled-up thin films show thicknesses ranging from 194 to 400 micrometers.

[0049] Figure 13 The asymmetric V2CT in Embodiment 3 of the present invention x Rolled-up structure thin film (a) and V2CT x Top-view SEM image of the nanosheet film (c), showing asymmetric V2CT. x The wound structure film contains many randomly distributed wound structures. Asymmetric V2CT x Wound structure thin film (b) and V2CT x Cross-sectional SEM images of the nanosheet film (d) reveal a three-dimensional interconnected network structure that is significantly different from that of the thick MXene nanosheet film.

[0050] Figure 14 This is a schematic diagram of ion transport in the two-dimensional MXene nanosheet film (a) and the one-dimensional MXene rolled-up structure film (b) in Embodiment 3 of the present invention.

[0051] Figure 15 The asymmetric V2CT in Embodiment 3 of the present invention x Electrochemical performance of wound-structured thin films. Among them, (a) represents asymmetric V2CT. x The wound thin film was tested in 3 M H2SO4 electrolyte at scan rates ranging from 5 to 10000 mV s. -1(a) Cyclic voltammetry (CV) curves at different times. (b) Asymmetric V2CT. x Wound-wound thin films in the range of 5 to 10000 mV s -1 The mass-to-capacitance ratio at scan rate demonstrates excellent rate performance. (c) shows asymmetric V2CT. x The relationship between the peak anodic current and the scan rate of the wound thin film is shown in the range of 5 to 10000 mV / s. -1 Within the scan rate range, the dynamic parameter b ≈ 0.98. (d) is for asymmetric V2CT. x Wound-structured thin films at 1000 mV s -1 The measured cycle performance shows that it retains an excellent capacitance retention of 97% after 10,000 cycles. (e.g., for asymmetric V2CT) x Wound-wound thin films (e) and V2CT x Two-dimensional intensity color map of the DRT curve of the nanosheet thin film (f), showing asymmetric V2CT. x The wound structure film has a lower H + Diffusion resistance (R) diff ).

[0052] Figure 16 V2CT with different loads in Embodiment 3(a) of the present invention x Wound structure thin films and V2CT x Nanosheet thin films at 2 mV s -1 CV curves at scan rates. (b) Different loading amounts (25, 50 mg cm⁻¹) -2 V2CT with thicknesses (194, 400 μm) x Wound-structured thin films at 2 mV s -1 The mass-to-capacitance ratio exhibits unique thickness-independent capacitance characteristics. (c) Corresponding V2CT x Wound-wound thin films in the range of 2 to 100 mV s -1 The areal capacitance at scan rate was shown at a loading of 50 mg cm⁻¹. -2 The scan rate is 2 mV / s -1 At that time, the areal capacitance was as high as approximately 26 F cm. -2 (d) Asymmetric V2CT under different loads x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films exhibit lower charge transfer impedance. (e)V2CT x Comparison of areal capacitance between wound structure thin films and other reported electrode materials.

[0053] Figure 17In Example 4(a) of the present invention, the mass loading is 50 mg cm⁻¹ -2 Asymmetric V2CT x (a) Mass specific capacitance and areal specific capacitance of the wound structure thin film. (b) Mass loading of 50 mg cm⁻¹ -2 Asymmetric V2CT x The wound structure film at 5, 10 and 20 mA cm -2 Constant current charge-discharge (GCD) curves at current density.

[0054] Figure 18 In Example 4 of this invention, the mass loading is 50 mg cm⁻¹. -2 Asymmetric V2CT x Cyclic performance of the wound-structured thin film at 100 mA cm⁻¹ -2 After 5000 cycles at current density, the capacitance retention rate is 95.7%, demonstrating long-term stability.

[0055] Figure 19 The asymmetric V2CT in Embodiment 4 of the present invention x Rolled-up structure thin film (a) and V2CT x Nanosheet films (b) in 0.5 M Li₂SO₄ electrolyte, 5 to 1000 mV s -1 CV curves at scan rates. (c) Non-ideal V2CT x The wound-structured thin film was tested in 0.5 M Li₂SO₄ electrolyte at 5 to 1000 mV s⁻¹. -1 Mass capacitance at scan rate shows improvement over V2CT. x Nanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance.

[0056] Figure 20 The asymmetric V2CT in Embodiment 4 of the present invention x Wound structure thin film (a) and V2CT x Nanosheet thin films (b) in 0.5 M Na₂SO₄ electrolyte, 5 to 1000 mV s -1 CV curves at different scan rates. (c) Asymmetric V2CT x The wound-structured thin film was tested in 0.5 M Na₂SO₄ electrolyte at 5 to 1000 mV s. -1 Mass capacitance at scan rate shows improvement over V2CT. x Nanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT xThe EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance.

[0057] Figure 21 The asymmetric V2CT in Embodiment 4 of the present invention x Wound structure thin film (a) and V2CT x Nanosheet thin films (b) in 0.5 M (NH4)2SO4 electrolyte, 5 to 1000 mV s -1 CV curves at different scan rates. (c) Asymmetric V2CT x The wound-structured thin film was tested in 0.5 M (NH4)2SO4 electrolyte at 5 to 1000 mV s. -1 Mass capacitance at scan rate shows improvement over V2CT. x Nanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance.

[0058] Figure 22 The asymmetric V2CT in Embodiment 4 of the present invention x Wound structure thin film (a) and V2CT x Nanosheet thin films (b) in 1 M MgSO4 electrolyte, 5 to 1000 mV s -1 CV curves at different scan rates. (c) Asymmetric V2CT x Wound-structured thin films in 1 MMgSO4 electrolyte, 5 to 1000 mV s -1 Mass capacitance at scan rate shows improvement over V2CT. x Nanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance.

[0059] Figure 23 The asymmetric V2CT in Embodiment 4 of the present invention x Wound structure thin film (a) and V2CT x Nanosheet thin films (b) in 1 M ZnSO4 electrolyte, 5 to 1000 mV s -1 CV curves at different scan rates. (c) Asymmetric V2CT x The wound-structured thin film in 1 M ZnSO4 electrolyte, 5 to 1000 mV s -1 Mass capacitance at scan rate shows improvement over V2CT. xNanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance.

[0060] Figure 24 The asymmetric V2CT in Embodiment 4 of the present invention x Wound structure thin film (a) and V2CT x Nanosheet films (b) in 0.5 M Al2(SO4)3 electrolyte, 5 to 1000 mV s -1 CV curves at different scan rates. (c) Asymmetric V2CT x The wound-structured thin film was tested in 0.5 M Al2(SO4)3 electrolyte at 5 to 1000 mV s. -1 Mass capacitance at scan rate shows improvement over V2CT. x Nanosheet thin films exhibit superior capacitance performance. (d) Asymmetric V2CT x The EIS curves of the wound structure thin film show that it is superior to V2CT. x Nanosheet films have lower charge transfer impedance. Detailed Implementation

[0061] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0062] The MAX phase precursor used in the examples was purchased from Jinan Sanchuan New Material Technology Co., Ltd., with a purity of ≥99.9%; there were no specific restrictions on the source of other chemical reagents.

[0063] The technical concept of this invention lies in utilizing the asymmetric winding behavior of two-dimensional MXene nanosheets under specific conditions to construct an asymmetric hollow winding structure with different radial dimensions. This structure can spontaneously generate an electron concentration gradient along its axial direction, thereby inducing the formation of an embedded polarization electric field. This polarization electric field can significantly enhance the directional migration of ions, providing a fundamental solution to the long-standing technical problem of slow ion transport dynamics in high-load, thick electrodes.

[0064] This invention utilizes a specific processing technique to induce asymmetric winding of two-dimensional MXene nanosheets. The preparation method includes the following steps: (1) Pretreatment: A-layer elements (such as Al, Ga, etc.) are selectively etched away from the MAX phase precursor after particle size screening to obtain multilayer MXene material. The etchant can be selected from hydrofluoric acid, a mixed solution of fluoride salt and acid, etc.; preferably, the particle size of the MAX phase precursor is 600~1000 mesh, or the particle size is between 1~10 μm.

[0065] (2) Intercalation and stripping: The multilayer material is mixed with the intercalating agent solution, and mechanical stirring or shearing force is applied to allow the intercalating agent molecules to enter the interlayer space, increasing the interlayer spacing and creating conditions for subsequent winding. The intercalating agent can be selected from at least one of tetraalkylammonium hydroxide, tetraalkylammonium halide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; preferably, the tetraalkylammonium hydroxide is selected from tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), and tetrabutylammonium hydroxide (TBAOH). The process parameters such as the stirring speed and the concentration of the intercalating agent can be optimized according to the specific material.

[0066] (3) Ultrasonic treatment: The intercalated product is dispersed in a dispersion medium and stirred. The shear force generated during stirring provides the driving force for the winding of the two-dimensional nanosheets. The stirring speed, time and temperature can control the formation and uniformity of the winding structure. Preferably, the stirring speed is greater than 400 rpm; more preferably, ≥600 rpm; more preferably, ≥800 rpm; and most preferably, 600~800 rpm.

[0067] (4) Separation and purification: Collect the desired product by solid-liquid separation methods (such as centrifugation, filtration, etc.).

[0068] The asymmetric winding structure prepared by the above method has a unique geometric structure (such as...). Figure 1 (Illustration): The wound body is a hollow tubular structure with two different radial dimensions along its axial direction, defined as the first radial dimension R1 and the second radial dimension R2, where R1 > R2. This structural asymmetry forms the geometric basis for the subsequent generation of the polarization electric field. The radial dimension, axial length, and degree of asymmetry (R1 / R2 ratio) of the wound body can be controlled within a certain range. Due to the geometric asymmetry, an electron concentration gradient forms inside the wound body, thereby inducing a polarization electric field along its axial direction. (Asymmetric wound model electric field distribution diagram) Figure 2 Figure a) shows that the axial electric field increases as the radius decreases. This electric field strength is related to factors such as the asymmetry of the winding, the radial dimension, and the dielectric properties of the material, and its strength can typically reach 10. 3V / m or higher, even up to 10 5 V / m. This enhanced polarization electric field effectively promotes ion transport and significantly improves the ion conductivity of the material. The technical solution of the present invention is explained in detail below through specific embodiments: Example 1 This embodiment provides a V2CT x The asymmetric wound structure of MXene and its preparation method include the following steps: 1.1 Etching the MAX phase precursor to obtain multilayer MXene, the specific implementation steps include: (1) Mechanical crushing treatment of V2AlC MAX phase precursor. V2AlC powder was placed in a ball mill and ball-milled, and then sieved through a 1000-mesh sieve to obtain V2AlC particles with a particle size of 2~5 μm.

[0069] (2) The aluminum layer was selectively removed by in-situ hydrofluoric acid etching. The specific operation was as follows: 2 g NaF and 60 mL 12 M HCl were mixed in a 100 mL polytetrafluoroethylene-lined autoclave and stirred until homogeneous. 2.0 g of ball-milled and sieved V2AlC powder was slowly added while stirring. The autoclave was sealed and placed in an oven, where it was reacted at 95 °C for 4 days.

[0070] (3) After the reaction is complete, allow the autoclave to cool naturally to room temperature. Transfer the etching product to a centrifuge tube, wash repeatedly with deionized water, and centrifuge (5000 rpm) until the pH of the supernatant is close to 6. Collect the precipitate and vacuum dry it at 60°C for 12 hours to obtain multilayer V2CT. x MXene material.

[0071] 1.2 Fabrication of the asymmetric winding structure, the specific implementation steps include: (1) Take 0.5 g of the multilayer V2CT prepared above. x MXene material was added to 25 mL of a 25 wt.% tetrabutylammonium hydroxide (TBAOH) solution. The mixture was placed on a magnetic stirrer and mechanically stirred at 600 rpm for 30 minutes to perform intercalation and exfoliation treatment, thereby increasing the interlayer spacing.

[0072] (2) After stirring, transfer the mixture to a centrifuge tube and centrifuge at 10,000 rpm for 5 minutes to remove the supernatant. Wash the precipitate repeatedly with deionized water and centrifuge until the residual TBAOH intercalating agent is removed.

[0073] (3) The washed precipitate was redispersed in 60 mL of deionized water and ultrasonically treated for 1 hour (approximately 300 W power) in an ice-water bath below 10°C to further peel and wind the material. During the winding process, the small lateral dimensions of the MXene layer generated significant uneven bending strain, leading to asymmetric V2CT. x The formation of the wound structure.

[0074] (4) After ultrasonic treatment, the dispersion was centrifuged at 2500 rpm for 5 minutes to separate the solid and liquid components. The supernatant was collected to obtain V2CT. x A dispersion with an asymmetric wound structure.

[0075] 1.3 Morphological Characterization The morphology of the prepared product was characterized. SEM images ( Figure 3 As shown in (a), the obtained product exhibits a conical tubular morphology. TEM image ( Figure 4 Further investigation confirmed that the wound structure is an asymmetric hollow tubular structure with a large radius at one end and a small radius at the other, containing hollow nanochannels extending along the axial direction. Statistical measurements of multiple wound bodies showed that the second radial dimension R2 (smaller end radius) was 15–40 nm, the axial length of the wound body was 1–10 μm, and the ratio of the first radial dimension R1 to the second radial dimension R2 (R1 / R2) was 1.1–2.5. Selected area electron diffraction (SAED) patterns (not shown) revealed clear diffraction spots, indicating that the prepared wound structure has good crystallinity.

[0076] To characterize asymmetric V2CT x The distribution of the polarization electric field on the wound structure was measured using KPFM. Figure 5 (a) For example Figure 5 As shown in Figure b, a single asymmetric wound structure exhibits a linear potential distribution along the axial direction. Based on Faraday's law (E = Δφ / L, where Δφ is the potential difference along the length L of a single MXene wound structure), the asymmetric V2CT is calculated. x The axial polarization electric field of the wound structure is approximately 2.0 × 10⁻⁶. 4 V / m. In contrast, MXene nanosheets exhibit a relatively uniform potential distribution with no obvious polarization field (E≈0 V / m). Figure 5 (c) In the asymmetric MXene wound structure, this enhanced polarization electric field will effectively promote ion transport.

[0077] 1.4 Performance Testing To evaluate the ion transport performance of the asymmetric MXene wound structure, the V2CT prepared above was first... xAsymmetric wound structure dispersions were deposited into films via vacuum filtration and dried to obtain self-supporting films. In contrast, conventional V2CT was used... x Nanosheet dispersions were also used to prepare nanosheet films via vacuum filtration.

[0078] The obtained thin film exhibits a stacked network composed of randomly oriented MXene wound structures interconnected. Figure 6 (a). Furthermore, TEM and cross-sectional HRTEM revealed that the film possesses an abundant hollow channel structure with channel diameters ranging from approximately 20 to 100 nm. Figure 4 This is similar to V2CT, which has a layered stacked structure. x Nanosheet thin films ( Figure 6 The difference is significant in b). Small-angle X-ray scattering (SAXS) further confirmed this hollow structure in the range of q = 0.007–0.011 Å. -1 A broad peak appears at this point, corresponding to an interlayer spacing of approximately 57.1–89.8 nm. Figure 7 (a) Additionally, Brunauer-Emmett-Teller (BET) measurements indicate that the specific surface area of ​​the MXene wound-structured film is 47.5 m². 2 g -1 ( Figure 7 (b), far exceeding that of MXene nanosheet films (8.4 m). 2 g -1 This is mainly attributed to the abundant hollow channels in the MXene wound structure film.

[0079] XRD patterns ( Figure 8 The prepared asymmetric V2CT shows that... x The coiled structure exhibits a characteristic diffraction peak at 5.6°, corresponding to the (002) crystal plane. For comparison, V2CT... x The (002) peak of the nanosheet is located at 7.0°. The left shift of this peak position indicates that the interlayer spacing is significantly increased due to the intercalation process and the formation of the coiled structure.

[0080] Ion current-voltage (IV) measurements show that, compared to nanosheet films, V2CT... x Wound-structured thin films exhibit enhanced ion transport properties. Figure 9 ). With H + For example, asymmetric V2CT x The wound-structured thin film exhibited a high ionic conductivity of approximately 422.2 μS in 0.5 M H₂SO₄ solution, significantly higher than its control sample (approximately 29.9 μS). Figure 10 Moreover, this enhanced ionic conductivity phenomenon has also been observed in other cations. Under the influence of a polarized electric field, charged ions (including but not limited to H+) exhibit enhanced ionic conductivity.+ Li + Na + NH4 + Zn 2+ Mg 2+ Al 3+ The directional migration of ions (such as V2CT) in the wound structure is significantly promoted. Compared to two-dimensional nanosheets without a wound structure, the wound structure of this invention generally improves the conductivity of different ions by more than an order of magnitude. Furthermore, asymmetric V2CT... x The wound structure thin film also exhibits a significantly high electrical conductivity (σ), approximately 8333 S cm. -1 It is V2CT x Nanosheet thin film (115 S cm) -1 It is about 80 times more efficient than other methods, which is beneficial for efficient charge transfer in electrochemical processes.

[0081] Example 2 This embodiment is used to verify the universality of the technical solution of the present invention for different MXene materials. Based on the preparation method of Example 1, different types of MAX phase precursors were used to prepare corresponding asymmetric wound structures through corresponding etching and intercalation winding processes, as shown in the table below:

[0082] The product was displayed by SEM images, showing a conical tubular morphology, similar to the V2CT in Example 1. x The asymmetric wound structures are similar. KPFM was used to test the surface potential distribution of a single asymmetric wound structure (method as in Example 1). The test results show that asymmetric wound structures formed from different MXene materials can all generate significant axially polarized electric fields, with strengths around 10... 4 On the order of V / m.

[0083] Example 3 This embodiment provides electrochemical testing of the asymmetric MXene wound structure of the present invention and its application in the field of energy storage, more specifically, the asymmetric MXene wound structure is used as an electrode material in an electrochemical capacitor.

[0084] First, an asymmetric MXene wound structure is fabricated into a thin-film electrode. In this embodiment, a vacuum filtration method is used to prepare the thin film as the electrode sheet. Specific implementation steps include: taking the V2CT prepared in Example 1... x An asymmetric wound structure dispersion was mixed with a 1 mg / mL carboxymethyl cellulose (CMC) solution at a mass ratio of 9:1 and stirred at room temperature for 30 minutes to form a homogeneous suspension. The suspension was then vacuum filtered to obtain a self-supporting MXene film, which was vacuum dried for 12 hours to obtain a self-supporting V2CT.x An asymmetric wound thin film (which can be used as a thin-film electrode) is preferably 10-100 micrometers thick. In this embodiment, a thickness of approximately 15 μm and a mass loading of 2 mg cm⁻¹ were obtained. -2 Electrochemical performance was tested using thin-film electrodes.

[0085] In other embodiments, thin film electrodes can also be formed by other film-forming methods, such as: blade coating, spray coating, spin coating, etc.

[0086] For high-quality loaded thick films requiring improved mechanical strength and cycle stability, a crosslinking step is added after the fabrication of the MXene thin-film electrode. The resulting thick film, as an electrode material, preferably has a thickness of 100 to 1000 micrometers, more preferably between 200 and 500 micrometers; the preferred mass loading as an electrode material is ≥20 mg / cm³. -2 Preferably, ≥25 mg cm -2 More preferably, ≥35 mg cm -2 More preferably, ≥50 mg cm -2 The crosslinking agent can be at least one of the following: borate, aluminum salt, calcium salt, and zirconium salt.

[0087] One specific embodiment includes: immersing the obtained self-supporting MXene film into a pre-prepared sodium tetraborate solution, soaking for 12 hours at room temperature, rinsing several times with deionized water, and then vacuum drying the film at 90°C for 4 hours. During the heating process, borate ions undergo coordination crosslinking reactions with the hydroxyl groups on the MXene surface and the carboxyl groups of the CMC binder to form a three-dimensional network structure, resulting in a reinforced film. Figure 11 In this embodiment, different loading amounts (25, 35, 50 mg cm⁻¹) were obtained using this method. -2 Thick films. For example... Figure 12 As shown, the prepared thick film is black, with a smooth and flat surface, exhibiting a certain degree of flexibility, and a thickness ranging from 194 to 400 micrometers. Even at 50 mg / cm²... -2 Under high loads, the film remained intact, without cracking or peeling. This indicates that crosslinking treatment effectively improved the mechanical strength of the thick electrode. Figure 13 As shown, compared with thick MXene nanosheet films prepared by the same method, the prepared thick MXene rolled-up structure film exhibits a three-dimensional (3D) interconnected network structure, which helps to improve its wettability to the electrolyte and shorten the ion diffusion distance. Figure 14Contact angle tests showed that the contact angle of the asymmetric MXene wound structure thick electrode was 48°, while that of the conventional MXene nanosheet thick electrode was 72°. The smaller contact angle indicates that the thick electrode of this invention has better electrolyte wettability, thanks to its three-dimensional porous network structure, which facilitates rapid electrolyte penetration into the electrode interior.

[0088] Based on its excellent ion and electron transport properties, asymmetric V2CT x Wound-film structures offer promising electrode materials for electrochemical capacitors. First, using a three-electrode system in a 3 M H₂SO₄ electrolyte, asymmetric V₂CT was preliminarily evaluated by cyclic voltammetry (CV). x Electrochemical performance of a rolled-up thin film (15 μm thick). For example... Figure 15 As shown in Figure a, asymmetric V2CT x Wound-wound thin films at 5 to 2000 mV s - The distortion observed in the CV curve at the scan rate is negligible, indicating good high-rate performance. In contrast, the CV curve of the MXene nanosheet film deteriorates significantly with increasing scan rate. Specific capacitance calculations show that the asymmetric MXene rolled-up structure film exhibits good high-rate performance at 5 mV s⁻¹. -1 It exhibits 506 Fg at scan rate -1 High-quality specific capacitance ( Figure 15 (b) When the scan rate is increased to 2000 mV / s -1 At that time, its specific capacitance remained at 453.5 F g. -1 The capacitance retention rate is approximately 90%, significantly higher than that of MXene nanosheet films (247.4 F g). -1 (approximately 52%). Even at 5000 mV s -1 At ultra-high scan rates, the asymmetric MXene rolled-up thin film still exhibits approximately 80% capacitance retention (approximately 400 F g). - ¹), approximately twice that of MXene nanosheet films (approximately 41%), clearly demonstrates the superiority of our prepared V2CT. x The wound-structured thin film exhibits excellent rate performance. Furthermore, the asymmetric MXene wound-structured thin film demonstrates significant long-term cycling stability at 1000 mV s. -1 After 10,000 cycles, the capacitance retention rate is still approximately 97%. Figure 15 (d). To further understand the source of the excellent electrochemical performance of the asymmetric MXene rolled-up thin film, charge storage kinetics and relaxation time distribution (DRT) analyses were performed. Figure 15As shown in Figure c, the kinetic parameter b of the MXene rolled-up structure film, calculated through linear fitting, is approximately 0.98, exceeding that of the MXene nanosheet film (0.88), revealing the rapid charge storage kinetics of the asymmetric MXene rolled-up structure film. Furthermore, based on DRT analysis, compared to the MXene nanosheet film, the MXene rolled-up structure film exhibits a lower ion diffusion resistance (R0) during the electrochemical process. diff () Figure 15 (e, f) further demonstrates the rapid ion transport dynamics in asymmetric MXene wound structure films.

[0089] To further evaluate practical applicability, mass loadings (25, 35, and 50 mg cm⁻¹) were tested. -2 Electrochemical performance of asymmetric MXene rolled-up thick films was investigated. CV tests further demonstrated that with a mass loading of 25 mg / cm³, the electrochemical performance of the films was significantly improved. -2 A 194 μm thick MXene roll-to-roll film was tested at 2 mV s. -1 It exhibits approximately 500 F g at scan rates. -1 The high-quality specific capacitance is far higher than that of MXene nanosheet films with the same loading (approximately 270 F g). -1 , Figure 16 (a, b). Furthermore, when the scan rate increases from 2 mV / s... -1 Increased to 5, 10, 20, 50 and 100 mV s -1 At that time, MXene wound structure film (25 mg cm -2 The specific capacitances of the samples are approximately 539.1, 537.9, 485.0, 399.4, and 255.8 F / g, respectively. -1 It consistently outperforms MXene nanosheet films. Furthermore, when the mass loading increases from 25 mg / cm³, it shows superior performance. -2 Increase to 50 mg cm -2 When the thickness increases from 194 μm to 400 μm, the MXene rolled-up structure film at 2 mV s -1 It remains at approximately 510 F g. -1 High-quality specific capacitance with a decay rate of only about 4.9% ( Figure 16 (b) exhibits significant thickness-independent capacitance characteristics. This is mainly attributed to rapid ion transport and low charge transfer resistance ( Figure 16 (d). In contrast, under the same conditions, MXene nanosheet films exhibit severe performance degradation, with the specific capacitance decreasing to approximately 167 F g. -1(Attenuation rate approximately 36.1%). It is noteworthy that the areal capacitance of the thick MXene wound structure film is positively correlated with the mass loading, especially for a thickness of 400 μm (50 mg cm⁻¹). -2 The thin film, at 2 mV s -1 Approximately 26 F cm was achieved at the scan rate -2 The ultra-high areal capacitance is superior to most reported thick electrode capacitors. Figure 16 (e). Furthermore, constant current charge-discharge tests were conducted on a three-electrode system, and the results showed that: MXene wound structure thin film (50 mg cm⁻¹) -2 ) at 100mA cm -2 After 5000 cycles at current density, the capacitance retention rate is 95.7%. Figure 17 and 18 It exhibits long-term stability, clearly demonstrating its superior practicality in electrochemical capacitors.

[0090] Example 4 This embodiment presents an example of asymmetric V2CT. x The application and electrochemical performance testing of the wound-structured thin film as an electrode material in different cationic electrolyte systems were investigated. Using the 15-micrometer-thick film prepared in Example 3, the same three-electrode testing system and method were employed, except that the 3 M H₂SO₄ electrolyte was replaced with one of the following six different cationic sulfate electrolytes: (1) 0.5 M Li₂SO₄ aqueous solution (corresponding to Li + ) (2) 0.5 M Na2SO4 aqueous solution (corresponding to Na + ) (3) 0.5 M (NH4)2SO4 aqueous solution (corresponding to NH4) + ) (4) 1 M MgSO4 aqueous solution (corresponding to Mg 2+ ) (5) 1 M ZnSO4 aqueous solution (corresponding to Zn 2+ ) (6) 0.5 M Al2(SO4)3 aqueous solution (corresponding to Al 3+ ) The corresponding electrochemical test (CV and EIS) results ( Figures 19-23The results show that the asymmetric MXene rolled-up structure film of this invention maintains a high specific capacitance even at high scan rates, exhibiting superior rate performance. EIS testing indicates that the charge transfer resistance and ion diffusion impedance of the asymmetric MXene rolled-up structure film are significantly lower than those of the MXene nanosheet film. This demonstrates that the asymmetric MXene rolled-up structure film of this invention can effectively promote the transport of ions of different valence states. This demonstrates its application potential in various types of electrochemical energy storage devices (such as lithium-ion batteries, sodium-ion batteries, zinc-ion batteries, magnesium-ion batteries, aluminum-ion batteries, etc.).

[0091] Comparative Example 1 Following the preparation method of Example 1, but by changing the process parameters in the winding step: reducing the stirring speed to 400 rpm and the stirring time to 30 minutes, a symmetrical winding structure with basically consistent radial dimensions was formed (i.e., the radius ratio of the two ends of the winding body R1 / R2≈1.0). SEM observation confirmed that the obtained product was mainly a tubular structure with similar radii at both ends, without obvious asymmetric features.

[0092] The surface potential distribution of a single symmetrical wound structure was tested using the same KPFM method as in Example 1. The results show that the potential distribution along the axial direction of the symmetrical wound structure is uniform, and its axial polarization electric field intensity E ≈ 0 V / m.

[0093] Comparative Example 2 Following the preparation method of Example 1, but using MAX phase raw materials with particle sizes of 200 mesh and 400 mesh (without fine sieving), under the same conditions, the obtained products exhibited symmetrical coiled structures with essentially uniform radial dimensions (i.e., the radius ratio of the two ends of the coiled body R1 / R2≈1.0). SEM observation confirmed that the obtained products were mainly slender tubular structures with similar radii at both ends, without obvious asymmetric features.

[0094] The surface potential distribution of a single symmetrical wound structure was tested using the same KPFM method as in Example 1. The results show that the potential distribution along the axial direction of the symmetrical wound structure is uniform, and its axial polarization electric field intensity E ≈ 0 V / m.

[0095] As can be seen, the asymmetric winding structure of this invention, through a specific design of two different radial dimensions, induces an electron concentration gradient and a strong polarization electric field, which is a key technical feature for achieving an order-of-magnitude increase in ionic conductivity and excellent electrochemical performance. The technical effect of this invention relies on the core geometric feature of "asymmetry." Symmetrical winding structures cannot replace this invention, nor can they predict or derive the outstanding technical effects achieved by this invention.

[0096] Test Method Description All structural characterization, ion transport performance testing, and electrochemical performance testing in this application were performed according to the following methods.

[0097] (I) Material structure characterization Scanning electron microscopy (SEM): The morphology of the samples was observed using a JEOL-7500 field emission scanning electron microscope with an accelerating voltage of 5~15 kV. Cross-sectional samples were prepared by liquid nitrogen embrittlement.

[0098] Transmission electron microscopy (TEM) and selected area electron diffraction (SAED): The microstructure was observed using a JEOL NEM-2100F high-resolution transmission electron microscope with an accelerating voltage of 200 kV. Samples were prepared by adding a dispersion droplet onto a copper grid.

[0099] X-ray diffraction (XRD): Phase analysis was performed using a Rigaku D / MAX-2500 X-ray diffractometer with CuKα radiation (λ = 0.15406 nm), a scanning range of 5°–80°, and a scanning rate of 5° min. - ¹.

[0100] Kelvin probe force microscopy (KPFM): The surface potential distribution of the sample was measured using the KPFM mode of a Bruker Dimension Icon atomic force microscope. Tests were conducted at room temperature and under atmospheric conditions using a conductive probe (Pt / Ir coated). The polarization electric field intensity was calculated using the formula E = Δφ / L, where Δφ is the potential difference along the axis of the coil, and L is the axial length.

[0101] Small-angle X-ray scattering (SAXS): The test was conducted using a Xeuss 3.0HR SAXS system (Xenocs, France), with an X-ray wavelength λ = 0.154 nm, a sample-to-detector distance of 2.5 m, and a test duration of 30 minutes. The interlayer spacing was calculated using Bragg's formula d = 2π / q.

[0102] Nitrogen adsorption-desorption isotherms and specific surface area (BET): Measured using a Quantachrome Autosorb-iQ specific surface area analyzer at 77 K. Samples were degassed at 120 °C for 12 hours prior to testing. Specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method, and pore volume was calculated using the Barrett-Joyner-Halenda (BJH) method.

[0103] Conductivity testing: Measured at room temperature using an ST2253-SZ four-probe resistivity meter (Suzhou Jingge). The sample was cut into strips of 1 cm × 2 cm, and the test current range was 1 μA ~ 100 mA.

[0104] Contact angle test: The contact angle was measured at room temperature using a DSA100 contact angle meter (KRUSS, Germany). Approximately 5 μL of electrolyte (3 M H2SO4) was dropped onto the film surface, and the contact angle between the droplet and the surface was recorded.

[0105] (II) Ion transport performance test Ionic conductivity was measured using linear sweep voltammetry (LSV) on a CHI 760E electrochemical workstation. The test system was a three-electrode system: the prepared thin film (1 cm² area) was used as an example. 2 The working electrode is a graphite rod, the reference electrode is an Ag / AgCl electrode (saturated with KCl), and the counter electrode is a graphite rod. The scan rate is 50 mV / s. -1 The potential range is -0.2 V to 0.2 V. Ionic conductivity is calculated based on the slope of the IV curve using the formula G = I / V (μS), where I is the current (μA) and V is the voltage (V). The electrolytes used are: 0.5 M H₂SO₄, 0.5 M Li₂SO₄, 0.5 M Na₂SO₄, 0.5 M (NH₄)₂SO₄, 1 M MgSO₄, 1 M ZnSO₄, and 0.5 M Al₂(SO₄)₃. All electrolytes are prepared using deionized water, and the reagent purity is ≥99.9%.

[0106] (III) Electrochemical performance testing Three-electrode system: using the prepared thin film as the working electrode (area 1 cm²). 2 The Ag / AgCl electrode was used as the reference electrode (saturated KCl), and the graphite rod was used as the counter electrode. The electrolyte was 3 M H2SO4 or various neutral sulfate solutions, and the test was conducted at room temperature.

[0107] Cyclic voltammetry (CV) tests were performed on a CHI 760E electrochemical workstation with a potential window of -0.35 V to 0.25 V and a scan rate of 5 to 10000 mV s. -1 The specific capacitance is determined by the formula. C g = ∫ i dV / ( υ·m·ΔV ) Calculate, where i Current (A) ΔV For potential window (V). υ For scan rate (V s) -1 ), m is the electrode mass (g). Area capacitance ( C a ) by multiplying the specific capacitance by the mass load (g cm) -2 )calculate.

[0108] Constant current charge-discharge (GCD) test: conducted on the LAND CT2001A battery test system, with a current density of 1 ~ 100 mA cm⁻¹. -2 (or 1 ~ 20 Ag) -1 The potential window is the same as that for CV testing. The capacitance is calculated based on the discharge curve, and the cycle stability test is performed at a specified current density.

[0109] Electrochemical impedance spectroscopy (EIS) testing: performed on a CHI 760E electrochemical workstation, with a test frequency range of 100 kHz ~ 0.01 Hz, an AC amplitude of 10 mV, and the test was conducted at open circuit potential.

[0110] Relaxation Time Distribution (DRT) Analysis: EIS data was analyzed for DRT using an online platform (https: / / relaxis-drt.rhd-instruments.de / ), with Tikhonov regularization employed and regularization parameters determined using the L-curve method.

[0111] Dynamic analysis (b-value analysis): based on power law relationship i = a υ b Take the anode peak current at different scan rates and plot log( i ) - log( υ The curve is linearly fitted to obtain the b value.

[0112] Capacitor contribution rate analysis: According to the formula i ( V ) = k 1 υ + k 2 υ 0.5 In the range of 5 to 100 mV s -1 Within the scan rate range, the current values ​​at different potentials are fitted. k 1 υ The term represents the capacitance contribution. k 2 υ 0.5 The item represents the contribution to diffusion control.

[0113] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. An asymmetric winding structure, characterized in that, The asymmetric coiled structure is formed by coiling two-dimensional material MXene nanosheets and has hollow nanochannels extending along the axial direction. Along the axial direction, the coiled structure has two different radial dimensions, defined as a first radial dimension R1 and a second radial dimension R2, where R1 > R2. The asymmetry between the first radial dimension R1 and the second radial dimension R2 can form a polarized electric field inside the coiled structure.

2. The asymmetric winding structure as described in claim 1, characterized in that, The second radial dimension R2 is 10 to 100 nm; preferably, it is 15 to 40 nm. And / or, the length of the winding structure along the axial direction is 0.5 to 50 μm; preferably, it is 1 to 10 μm; And / or, the ratio of the first radial dimension R1 to the second radial dimension R2 is 1.05 to 5; preferably, it is 1.1 to 2.5; And / or, the asymmetric winding structure has enhanced transport properties for at least one cation; preferably, the cation is selected from H+. + Li + Na + NH4 + Zn 2+ Mg 2+ Al 3+ .

3. The asymmetric winding structure as described in claim 1 or 2, characterized in that, The intensity of the polarization electric field is greater than 10. 3 V / m; more preferably, greater than 10 4 V / m; And / or, the general formula of the MXene is M n+1 X n T x M is selected from at least one of Ti, V, Nb, Mo, Ta, Cr, Zr, Hf, Sc, and Y; X is selected from C and / or N; and T represents a functional group. n The values ​​are 1 to 4; preferably, the MXene is selected from: V2CT x Ti3C2T x Nb2CT x Mo2CT x Ti2CT x Ti4C3T x V4C3T x Nb4C3T x At least one of them; And / or, the specific surface area of ​​the asymmetric winding structure is 10 to 200 m². 2 g -1 ; And / or, the conductivity of the asymmetric winding structure is greater than 4000 S cm. -1 Preferably, ≥8000 S cm -1 .

4. A method for preparing an asymmetric winding structure as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Mix the MAX phase precursor with an etchant and perform a selective etching reaction to remove the A layer elements in the MAX phase and obtain a multilayer MXene material; (2) Mix the multilayer MXene material obtained in step (1) with the intercalating agent solution and perform intercalation stripping treatment to increase the interlayer spacing; (3) The product obtained in step (2) is separated and washed to remove residual intercalating agent; (4) Disperse the product obtained in step (3) in a dispersion medium and stir. (5) The dispersion obtained in step (4) is subjected to solid-liquid separation, and the precipitate is collected to obtain the asymmetric winding structure.

5. The preparation method according to claim 4, characterized in that, The general formula for the MAX phase precursor is M. n+1 AX n M is selected from at least one of Ti, V, Nb, Mo, Ta, Cr, Zr, Hf, Sc, and Y; A is selected from at least one of Al, Ga, Si, and Ge; and X is selected from C and / or N. n The range is 1 to 4; And / or, the MAX phase precursor is mechanically crushed before step (1); preferably, after mechanical crushing, the particle size of the MAX phase precursor is 600 mesh to 1000 mesh; or, the particle size is 1 to 20 μm; preferably, 2 to 5 μm; And / or, the etchant is selected from at least one of hydrofluoric acid, a mixed solution of lithium fluoride and hydrochloric acid, a mixed solution of sodium fluoride and hydrochloric acid, and a mixed solution of ammonium fluoride and hydrochloric acid; And / or, the intercalating agent is selected from at least one of tetraalkylammonium hydroxide, tetraalkylammonium halide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; preferably, the tetraalkylammonium hydroxide is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. And / or, the concentration of the intercalating agent solution is 10-50 wt.%; preferably, 20-30 wt.%. And / or, the stirring speed is >400 rpm; preferably, ≥600 rpm; more preferably, ≥800 rpm.

6. A thin film, characterized in that, It includes the asymmetric winding structure as described in any one of claims 1 to 5.

7. The thin film as claimed in claim 6, characterized in that, The thickness of the film is greater than 5 μm; preferably, it is 10 to 1000 μm. And / or, the mass load of the asymmetric winding structure in the film is ≥10 mg / cm². 2 Preferably, ≥25 mg / cm 2 More preferably, ≥35 mg / cm 2 More preferably, ≥50 mg / cm 2 ; And / or, the film exhibits capacitance characteristics independent of thickness; or, when the mass load is doubled, the specific capacitance of the film decreases by less than 5%.

8. A method for preparing a thin film as described in claim 6 or 7, characterized in that, Includes the following steps: (1) The wound structure is dispersed in a dispersion medium to obtain a dispersion; (2) The dispersion obtained in step (1) is subjected to film formation treatment and dried to obtain a thin film; preferably, the film formation treatment is selected from at least one of vacuum filtration film formation, blade coating film formation, spray coating film formation and spin coating film formation. Optionally, after step (2), a crosslinking treatment step is further included: immersing the dried film in a crosslinking agent solution to carry out a crosslinking reaction; preferably, the crosslinking agent is selected from at least one of borate, aluminum salt, calcium salt, and zirconium salt; Optionally, a binder is added to the dispersion.

9. An electrode, characterized in that, It comprises an asymmetric winding structure as described in any one of claims 1 to 5; or, a thin film as described in any one of claims 6 to 8.

10. An electrochemical energy storage device, characterized in that, It includes the electrode described in claim 9; preferably, the electrochemical energy storage device is selected from at least one of electrochemical capacitors, supercapacitors, lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, zinc-ion batteries, magnesium-ion batteries, and aluminum-ion batteries.

11. An asymmetric winding structure as described in any one of claims 1 to 5, or the application of a thin film as described in any one of claims 6 to 8 in an electrochemical energy storage device.

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