Antioxidation method based on pH-responsive MXenes and application thereof

Abstract

The application discloses an anti-oxidation method based on pH response type MXenes and application thereof, and belongs to the technical field of two-dimensional nanomaterials, and specifically comprises the following steps: in a MXenes suspension, only by adding a metal ion-polyphenol organic compound complex and controlling the pH value to be 3-6, the anti-oxidation capping of MXenes is realized. On this basis, when application is needed, the MXenes maintaining the intrinsic characteristics can be separated out by adding an alkaline solution to adjust the pH value to be not less than 7. The whole process has low cost, avoids the problem that a reducing agent is difficult to remove, has strong universality, and enables the intrinsic characteristics of MXenes to be maintained for more than 3 years.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of two-dimensional nanomaterials, and particularly relates to an oxidation-resistant method based on pH-responsive MXenes and application thereof. BACKGROUND

[0002] MXenes refers to a new type of two-dimensional transition metal carbon / nitride graphene, and the basic chemical formula is M n+ 1X n T x (n = 1-3), M is a transition metal (one or a combination of Sc, Ti, Mo, etc.), X is C or N, and T represents a surface functional group (such as -OH, -F, -O, etc.). MXenes nanosheets have a large specific surface area and unique electronic, mechanical, optical and magnetic properties, and have good application prospects in energy storage, catalysis, electromagnetic shielding, optoelectronics, sensors, biological medicine and the like. However, the oxidation of MXenes during storage is a bottleneck problem, which limits its large-scale synthesis and practical application.

[0003] MXenes have a large number of defects and edges, and the exposure of a large number of high-activity transition metal M atoms leads to the thermodynamic metastability of MXenes. Therefore, MXenes are easily oxidized to generate transition metal M oxides and amorphous carbon, resulting in changes in material composition, structure collapse, and rapid deterioration of physical and chemical properties. Improving the oxidation resistance of MXenes is the basis for its large-scale synthesis and application.

[0004] At present, the methods for improving the oxidation resistance of MXenes mainly include two kinds: physical isolation of oxidants and reduction of oxidation kinetics. The physical isolation of oxidants includes but is not limited to: inert gas low-temperature preservation, organic solution preservation, surface coating, and addition of reducing agents. The reduction of oxidation kinetics includes but is not limited to: heat treatment of MXenes film under reducing or inert atmosphere to obtain a dense structure, and synthesis of MXenes in Lewis acid molten salt (>500 ℃). Although the above oxidation resistance methods can effectively prevent the oxidation of MXenes, the high energy consumption caused by low-temperature preservation and high-temperature heat treatment, the complex surface coating process, the high cost of organic solvents, and the difficulty in removing reducing agents limit the practical application of the above methods. The preparation and use of MXenes often occur in aqueous solutions, and preservation in aqueous solutions can effectively reduce the material preparation and use cost, which is conducive to the large-scale production and subsequent practical application of MXenes. How to improve the oxidation resistance of MXenes in aqueous solutions without damaging the intrinsic physical and chemical properties of MXenes is imminent. SUMMARY

[0005] In view of the above, the purpose of the present application is to provide a pH-responsive MXenes antioxidant method and its application, which can achieve low-cost and universal MXenes antioxidant and maintain the intrinsic properties of MXenes for a long time.

[0006] To achieve the above-mentioned purpose of the application, the embodiment provides a pH-responsive MXenes antioxidant method, which comprises the following steps:

[0007] A divalent or trivalent metal salt and a polyphenolic organic matter are dissolved in deionized water according to a molar ratio of 1:(0.8-1.3) or 1:(1.8-2.3), respectively, an acid solution same as the metal salt anion is added, and the pH is adjusted to 3-6; the metal salt solution and the polyphenolic organic matter solution are mixed and stirred to prepare a metal ion-polyphenolic organic matter complex solution;

[0008] The pH of a MXenes suspension is adjusted to the same value as that of the metal ion-polyphenolic organic matter complex solution by using an acid solution same as the metal salt anion, then the metal ion-polyphenolic organic matter complex is added and stirred uniformly, and a certain amount of polyphenolic organic matter is added, so that the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic matter in the obtained mixed solution is 1:(2-2.2) or 1:(3-3.2), and the antioxidant capping of MXenes is realized;

[0009] An alkaline solution is added to the mixed solution, and the pH is adjusted to not less than 7, then centrifugation and separation are performed to obtain MXenes maintaining the intrinsic properties.

[0010] The functional groups on the surface of MXenes can maintain the structural stability to a certain extent. The transition metal M atoms at the edges and surface defects are usually unstable due to incomplete bonding, and these high-activity M atoms are easy to nucleate and generate transition metal oxide particles when interacting with water and / or oxygen molecules. The present application first prepares an unsaturated coordination metal ion-polyphenolic organic matter complex, and uses metal ions to occupy the positions of transition metal M atoms at the edges and surface defects for capping. The polyphenolic organic matter added subsequently has two effects: 1) a part of the polyphenolic organic matter can act as an organic ligand, and when the solution pH reaches 7 and above, it can form a saturated coordination solid-state metal ion-polyphenolic organic matter complex with the unsaturated coordination metal ion-polyphenolic organic matter complex, and then be separated out; 2) meanwhile, another part of the polyphenolic organic matter acts as a reducing agent, which can effectively remove dissolved oxygen in the aqueous solution to avoid the oxidation of MXenes by dissolved oxygen in water.

[0011] When the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic compound is less than 1:2 or 1:3, adjusting the pH of the solution by adding alkali cannot make the metal ion-polyphenolic organic compound complex completely coordinate, which will result in part of the metal ion-polyphenolic organic compound complex not completely coordinated still existing in the MXenes solution. When the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic compound is greater than 1:2.2 or 1:3.2, although adjusting the pH of the solution by adding alkali can make the metal ion-polyphenolic organic compound complex change from incomplete coordination to complete coordination and be removed by centrifugation, but after centrifugation, part of the polyphenolic organic compound will still exist in the MXenes suspension, which will affect the intrinsic properties of MXenes in subsequent applications.

[0012] When the pH of the MXenes suspension is less than 3, MXenes are more easily oxidized under strong acid conditions, therefore, the pH of the MXenes suspension is limited to be greater than or equal to 3.

[0013] The intrinsic properties of MXenes include high electrical conductivity, controllable surface chemical properties and layered structure, and the rich surface functional groups and fast ion diffusion channels make MXenes exhibit high specific capacity and cycle stability in lithium ion batteries, and high power density and long cycle life in supercapacitors.

[0014] Preferably, when a divalent metal salt is used, the pH of the divalent metal salt solution and the polyphenolic organic compound solution is adjusted to 4-6.

[0015] Preferably, when a trivalent metal salt is used, the pH of the trivalent metal salt solution and the polyphenolic organic compound solution is adjusted to 5-6.

[0016] Preferably, the polyphenolic organic compound includes catechol or ellagic acid.

[0017] Preferably, the divalent or trivalent metal salt includes an iron salt, a cobalt salt or a nickel salt.

[0018] Preferably, the centrifugation conditions are: rotation speed less than 3500 rpm, time less than 1 h.

[0019] Preferably, the trivalent metal salt is an iron salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 5, and the molar ratio of the iron salt to catechol in the mixed solution is 1:3.05.

[0020] Preferably, the divalent metal salt is a nickel salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 4, and the molar ratio of the nickel salt to catechol in the mixed solution is 1:2.05.

[0021] The embodiment also provides application of MXenes in lithium batteries, and the MXenes maintaining intrinsic properties prepared by the method are prepared into flexible films and used as lithium ion battery electrodes.

[0022] The embodiment also provides application of MXenes in supercapacitors, and the MXenes maintaining intrinsic properties prepared by the method are prepared into flexible films and used as supercapacitor electrodes.

[0023] Compared with the prior art, the embodiment has at least the beneficial effects of:

[0024] In the MXenes antioxidation of the embodiment, only by adding metal ion-polyphenol organic complex and controlling the pH value to be 3-6, the antioxidation capping of the MXenes can be realized. On this basis, when application is needed, the MXenes maintaining intrinsic properties can be separated out by adding an alkaline solution to realize simple pH adjustment, the whole process has low cost, the problem of difficult removal of a reducing agent is avoided, the universality is strong, and the intrinsic properties of the MXenes can be maintained for more than 3 years. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0026] Figure 1 is a flow chart of the pH-responsive MXenes antioxidation method provided by the embodiment;

[0027] Figure 2 shows three Ti3C2T x Comparison chart of Raman spectra of samples:

[0028] Figure 3 is a comparison chart of X-ray photoelectron spectroscopy (XPS) full spectra of three Ti3C2T x samples provided by the embodiment;

[0029] Figure 4 is a comparison chart of Ti 2p high-resolution XPS spectra of three Ti3C2T x samples provided by the embodiment;

[0030] Figure 5 is a scanning electron microscope (SEM) image of a Ti3C2T x original sample provided by the embodiment;

[0031] Figure 6 Ti3C2T x - SEM images of oxidized samples;

[0032] Figure 7 Ti3C2T x - SEM images of regenerated samples;

[0033] Figure 8 Ti3C2T x - Cross-sectional SEM images of original flexible film samples;

[0034] Figure 9 Ti3C2T x - Cross-sectional SEM images of regenerated flexible film samples;

[0035] Figure 10 Ti3C2T x - Electrochemical impedance spectroscopy of original samples;

[0036] Figure 11 Ti3C2T x - Electrochemical impedance spectroscopy of oxidized samples;

[0037] Figure 12 Ti3C2T x - Electrochemical impedance spectroscopy of regenerated samples;

[0038] Figure 13 Ti3C2T x Charge-discharge performance of flexible film samples as anode of lithium battery (lithium sheet as cathode);

[0039] Figure 14 Ti3C2T x - Charge-discharge performance of oxidized samples as anode of lithium battery (lithium sheet as cathode);

[0040] Figure 15 Ti3C2T x - Charge-discharge performance of regenerated flexible film samples as anode of lithium battery (lithium sheet as cathode);

[0041] Figure 16 Ti3C2T x - Cycle performance of original flexible film, Ti3C2T x - Oxidized and Ti3C2T x - Regenerated flexible film three samples as supercapacitor electrode;

[0042] Figure 17Ti3C2T is Ti3C2T obtained by regeneration after 3 years of oxidation of Ni- catechol provided by the embodiment x - SEM images of the regenerated samples;

[0043] Figure 18 Ti3C2T is Ti3C2T obtained by regeneration after 3 years of oxidation of Co- catechol provided by the embodiment x - SEM images of the regenerated samples. DETAILED DESCRIPTION

[0044] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the protection scope of the present application.

[0045] An oxidation-resistant method based on pH-responsive MXenes is provided in the embodiment, as shown in formula (I), comprising the following steps: Figure 1 as shown in formula (I), comprising the following steps:

[0046] Step 1, dissolve divalent or trivalent metal salt and polyphenolic organic matter in deionized water according to a molar ratio of 1:(0.8-1.3) or 1:(1.8-2.3) respectively, add acid solution with the same anion as the metal salt to adjust the pH to 3-6, mix and stir the above-mentioned metal salt solution and polyphenolic organic matter solution to prepare a metal ion-polyphenolic organic matter complex solution;

[0047] When a divalent metal salt is used, the pH of the divalent metal salt solution and the polyphenolic organic matter solution is adjusted to 4-6, and when a trivalent metal salt is used, the pH of the trivalent metal salt solution and the polyphenolic organic matter solution is adjusted to 5-6. The polyphenolic organic matter includes catechol or ellagic acid, etc., and the divalent or trivalent metal salt includes iron salt, cobalt salt or nickel salt.

[0048] Step 2, adjust the pH of the MXenes suspension to the same pH value as the metal ion-polyphenolic organic matter complex solution by using an acid solution with the same anion as the metal salt, then add the metal ion-polyphenolic organic matter complex, stir uniformly, and then add a certain amount of polyphenolic organic matter, so that the molar ratio of divalent or trivalent metal salt to polyphenolic organic matter in the obtained mixed solution is 1:(2-2.2) or 1:(3-3.2), achieving oxidation-resistant capping of MXenes;

[0049] Step 3, add an alkaline solution to the mixed solution and adjust the pH to not less than 7, then centrifuge and separate to obtain MXenes maintaining the intrinsic properties.

[0050] Based on the above-mentioned oxidation-resistant method of MXenes, Ti3C2T xThe following specific examples illustrate a typical representative of MXenes, detailing a pH-responsive MXenes antioxidant method and its corresponding performance. Among them, layered Ti3C2T... x Ti3AlC2 was prepared by etching with LiF and HCl solution.

[0051] Example 1

[0052] The trivalent metal salt is Fe(NO3)3, the polyphenolic organic compound is catechol, the acid solution is HNO3, and the alkaline solution is NaOH solution. Therefore, the corresponding MXenes antioxidant methods are:

[0053] First, Fe(NO3)3 and catechol were dissolved separately in deionized water at a molar ratio of 1:2. A certain amount of HNO3 was added to adjust the pH of the solution to 5. The two were then mixed and stirred to prepare the Fe-catechol complex. Then, HNO3 was used to react Ti3C2T x After adjusting the pH of the suspension to 5, the above-mentioned Fe-catechol complex was added and stirred until homogeneous. Then, a certain amount of catechol was added, and stirring was continued until homogeneous, so that the molar ratio of Fe(NO3)3 to catechol in the resulting mixed solution was 1:3.05. Finally, NaOH solution was added to the mixed solution and the pH was adjusted to 7. After centrifugation at 3500 rpm for 10 min, the upper layer was Ti3C2T. x The suspension contained a Fe-catechol complex in the lower layer, from which Ti3C2T, maintaining its intrinsic properties, was isolated. x .

[0054] Freshly prepared Ti3C2T x Marked as Ti3C2T x -Pristine Ti3C2T naturally oxidized in aqueous solution for 3 years x Marked as Ti3C2T x -Oxidation, after 3 years of antioxidant protection with Fe-catechol organic complex, followed by pH adjustment to remove the complex and regenerate Ti3C2T x Marked as Ti3C2T x -Regeneration, collectively referred to as three samples.

[0055] Through three samples, as Figure 2 As shown in the Raman spectrum comparison diagram, the oxidized Ti3C2T x All Ti in the mixture is oxidized to TiO2, while Ti3C2T protected by the Fe-catechol organic complex is oxidized to TiO2. x It retains its functional groups and chemical state, and no TiO2 is formed. Through the analysis of three samples... Figure 3 As shown in the XPS full spectrum comparison, the oxidized Ti3C2Tx The oxygen content increased significantly, much higher than that in the original Ti3C2T x Further, as shown in Figure 4 , the analysis of Ti 2p element in each sample, the newly prepared and regenerated Ti3C2T x There is only a small amount of Ti (iv). After the natural oxidation of the water environment for 3 years, all Ti in Ti3C2T x has been oxidized to TiO2.

[0056] Further, three samples were also characterized by SEM. As shown in Figure 5 , the original Ti3C2T x prepared has a typical two-dimensional layered structure. As shown in Figure 6 , the oxidized Ti3C2T x shows a nanoscale shuttle structure. As shown in Figure 7 , the Ti3C2T x protected by Fe- catechol complex can still restore the typical two-dimensional layered structure after removing the Fe- catechol complex.

[0057] Further, the newly prepared and regenerated Ti3C2T x were filtered into films, and the cross sections of the films were characterized by SEM, as shown in Figure 8 and Figure 9 respectively. Through the cross-sectional SEM of the two samples, it can be seen that both materials can be well filtered into films and have good layered structure. The oxidized Ti3C2T x has all generated TiO2, and cannot be filtered into a film. Therefore, the cross-sectional SEM of the Ti3C2T x -oxidized film is not given here.

[0058] Further, the impedance spectra of Ti3C2T x -original, Ti3C2T x -oxidized and Ti3C2T x -regenerated were measured, as shown in Figure 10 , Figure 11 , Figure 12 respectively. Through the impedance spectrum, the charge transfer resistance of Ti3C2T x -original, Ti3C2T x -oxidized and Ti3C2T x -regenerated is 50 Ω, 154000 Ω and 70 Ω respectively. The original Ti3C2T x itself has excellent conductivity, which is reflected in the impedance spectrum as a small charge transfer resistance. Ti3C2T xTi3C2T x -raw and Ti3C2T x -raw, the higher the charge transport resistance of Ti3C2T x -raw, the higher the degree of oxidation of the material. It can be seen that the regenerated Ti3C2T x -raw under the protection of Fe- catechol is almost not oxidized. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

[0059] Application Example 1

[0060] Ti3C2T x -raw and Ti3C2T x -raw were extracted into flexible films, and Ti3C2T x -oxidized was mixed with a binder and a conductive agent and then coated on a copper foil to prepare an electrode. The flexible films and the copper foil as a current collector were used as an electrode of a lithium ion battery (lithium sheet as a negative electrode) to test the lithium storage performance. It can be seen from Figure 13 Figure 14 Figure 15 that Ti3C2T x -raw and Ti3C2T x -raw have excellent rate performance, and the charge and discharge specific capacity changes little when the charge current increases from 1 A / g to 5 A / g, and the coulombic efficiency of the material changes little during the entire rate performance test. Then, the rate performance of Ti3C2T x -oxidized is poor, and the charge and discharge specific capacity decreases rapidly with the increase of the charge current, which is related to the sharp increase of the charge transport resistance of the material after oxidation.

[0061] Application Example 2

[0062] Ti3C2T x -raw and Ti3C2T x -raw were extracted into flexible films, and Ti3C2T x -oxidized was mixed with a binder and a conductive agent and then coated on a nickel foam to prepare an electrode. The flexible films and the electrode with the nickel foam as a carrier and a current collector were used as an electrode of a supercapacitor to test the cyclic performance of the samples at a scan rate of 100 mV / s. The results are shown in Figure 16 It can be seen that the charge and discharge specific capacity of Ti3C2T x -raw and Ti3C2T​​​​x - The capacity retention rates of the regenerated samples were 98.5% and 98.0%, respectively. And Ti3C2T x The capacity retention of the oxidized sample decreased from 100% to 67.0%. These results indicate that the capacity retention of Ti3C2T under Fe-catechol protection is significantly reduced. x After removing Fe-catechol, Ti3C2T can still be maintained. x The intrinsic properties. And Ti3C2T without Fe-catechol protection. x Severe oxidation caused its capacity retention rate to drop sharply.

[0063] Example 2

[0064] The corresponding MXenes antioxidant methods are: NiCl2 for divalent metal salts, catechol for polyphenolic organic compounds, HCl for acidic solutions, and KOH for alkaline solutions.

[0065] First, NiCl2 and catechol were dissolved separately in deionized water at a molar ratio of 1:1. A certain amount of HCl was added to adjust the pH of the solution to 4, and the mixture was stirred to prepare the Ni-catechol complex. Then, Ti3C2T was treated with HCl. x After adjusting the pH of the suspension to 4, the above-mentioned Ni-catechol complex was added and stirred until homogeneous. Then, a certain amount of catechol was added, and stirring was continued until homogeneous, so that the molar ratio of NiCl2 to catechol in the resulting mixed solution was 1:2.05. Finally, KOH solution was added to the mixed solution and the pH was adjusted to 7. After centrifugation at 3500 rpm for 10 min, the upper layer was Ti3C2T. x The suspension contained a Ni-catechol complex in the lower layer, from which Ti3C2T, maintaining its intrinsic properties, was isolated. x .

[0066] Ti3C2T after 3 years of end-capping with Ni-catechol complex for antioxidant effects x - The regenerated sample was characterized to obtain, for example... Figure 17 The SEM image shown is analyzed. Figure 17 It can be seen that the Ni-catechol complex has a positive effect on Ti3C2T x It also has effective antioxidant properties.

[0067] Example 3

[0068] For divalent metal salts, CoSO4 is chosen; for polyphenolic organic compounds, catechol is chosen; for acidic solutions, H2SO4 is chosen; and for alkaline solutions, NaOH solution is chosen. Therefore, the corresponding MXenes antioxidant methods are:

[0069] First, CoSO4 and catechol were dissolved separately in deionized water at a molar ratio of 1:1. H2SO4 was added to adjust the pH of the solutions to 4.5. The two solutions were then mixed and stirred to prepare the Co-catechol complex. Then, H2SO4 was used to react Ti3C2T... x After adjusting the pH of the suspension to 4.5, the above-mentioned Co-catechol complex was added and stirred until homogeneous. Then, a certain amount of catechol was added, and stirring was continued until homogeneous, so that the molar ratio of CoSO4 to catechol in the resulting mixed solution was 1:2.1. Finally, NaOH solution was added to the mixed solution and the pH was adjusted to 7. After centrifugation at 3500 rpm for 10 min, the upper layer was Ti3C2T. x The suspension contained a Co-catechol complex in the lower layer, from which Ti3C2T, maintaining its intrinsic properties, was isolated. x .

[0070] Ti3C2T after 3 years of antioxidant treatment with Co-catechol complex end-capping x - The regenerated sample was characterized to obtain, for example... Figure 18 The SEM image shown is analyzed. Figure 18 It can be seen that the Co-catechol complex has a positive effect on Ti3C2T x It also has effective antioxidant properties.

[0071] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An anti-oxidation method based on pH-responsive MXenes, characterized in that, The method comprises the following steps: a divalent or trivalent metal salt and a polyphenolic organic compound are dissolved in deionized water at a molar ratio of 1:(0.8-1.3) or 1:(1.8-2.3), respectively, an acid solution same as the anion of the metal salt is added to adjust the pH to 3-6, and the metal salt solution and the polyphenolic organic compound solution are mixed and stirred to prepare an unsaturated coordination metal ion-polyphenolic organic compound complex solution; a suspension of MXenes is adjusted to the same pH as the metal ion-polyphenolic organic compound complex solution by using an acid solution same as the anion of the metal salt, then the metal ion-polyphenolic organic compound complex is added and stirred uniformly, a certain amount of polyphenolic organic compound is added, so that the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic compound in the obtained mixed solution is 1:(2-2.2) or 1:(3-3.2), and the oxidation resistance of the MXenes is realized; and an alkaline solution is added to the mixed solution to adjust the pH to not less than 7, and then centrifugation and separation are performed to obtain the MXenes maintaining the intrinsic properties; wherein the polyphenolic organic compound comprises catechol or ellagic acid; the divalent or trivalent metal salt comprises an iron salt, a cobalt salt or a nickel salt.

2. The pH-responsive MXenes-based antioxidation method according to claim 1, wherein, When a divalent metal salt is used, the pH of the divalent metal salt solution and the polyphenolic organic compound solution is adjusted to 4-6.

3. The pH-responsive MXenes-based antioxidation method according to claim 1, wherein, When a trivalent metal salt is used, the pH of the trivalent metal salt solution and the polyphenolic organic compound solution is adjusted to 5-6.

4. The pH-responsive MXenes-based antioxidation method according to claim 1, wherein, The centrifugation condition is that the rotation speed is less than 3500 rpm and the time is less than 1 h.

5. The pH-responsive MXenes-based antioxidation method according to claim 1, wherein, the trivalent metal salt is an iron salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 5, and the molar ratio of the iron salt to catechol in the mixed solution is 1:3.

05.

6. The pH-responsive MXenes-based antioxidation method according to claim 1, wherein, the divalent metal salt is a nickel salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 4, and the molar ratio of the nickel salt to catechol in the mixed solution is 1:2.

05.

7. Use of MXenes in lithium batteries, characterized in that, The MXenes maintaining the intrinsic properties prepared by the method of any one of claims 1-6 are prepared into a flexible film and used as an electrode of a lithium ion battery.

8. Use of MXenes in supercapacitors, characterized in that, The MXenes maintaining the intrinsic properties prepared by the method of any one of claims 1-6 are prepared into a flexible film and used as an electrode of a supercapacitor.

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