Preparation method and application of defect-ordered hexagonal pore structure antioxidant MXene materials

Abstract

A preparation method and application of a defect-ordered hexagonal pore structure antioxidant MXene material, comprising mixing hexagonal pore MAX phase Ti3AlC2 with CuCl2 and NaCl, loading into alumina corundum squares, and covering with a NaCl salt bed boat, placing the mixture in a muffle furnace, and sintering at a constant temperature of 820°C for 3 hours in an air atmosphere; after washing to remove impurities, the mixture is filtered, vacuum dried, and ground to obtain a defect-ordered hexagonal pore structure antioxidant. The advantages are: a simple and reasonable process, and under the joint action of trace amounts of metal oxides on the surface of the MXene material, an effective barrier against attacks by oxygen and water molecules is constructed, significantly improving the antioxidant properties of the MXene material.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a defect-ordered hexagonal pore structure antioxidant MXene material. Background Art

[0002] MXene materials are predicted to be a new generation of new energy storage materials due to their two-dimensional structure similar to carbon materials, controllable layer structure, high specific surface area, rich controllable surface functional groups, excellent conductivity and good chemical stability, and have become an ideal alternative to carbon electrodes.

[0003] Currently, the most common etching method for MXene materials is the more intense hydrofluoric acid etching method, which takes a long time and poses certain hazards to the environment and human body. CN117945402A discloses "A method for preparing a multilayer hexagonal MXene material with carbon vacancy defects for aqueous potassium ion supercapacitors." This method places dehydrogenated titanium powder, pure aluminum powder, and modified spherical graphite powder into a vacuum hot-pressing sintering furnace. After hot-pressing and sintering in the vacuum hot-pressing furnace with argon as a protective atmosphere, the mixture is cooled with liquid nitrogen to obtain the MAX phase Ti3AlC2 with hexagonal carbon vacancies. Microwave-assisted etching is then used to prepare the hexagonal MXene, resulting in a multilayer hexagonal MXene negative electrode material. The advantages of this method are: the use of liquid-phase microwave-assisted etching promotes the delamination of the MXene material and increases the energy density of the Mene in electrochemistry. However, this method uses a liquid-phase etching environment, and the surface of the obtained MXene material is hydrophilic hydroxyl and oxygen functional groups. The MXene material is easily attacked by oxygen molecules and water molecules in a neutral aqueous electrolyte, resulting in oxidation, which in turn leads to structural destruction, causing a sharp drop in the specific surface area of ​​the MXene material, and further leading to a sharp attenuation of the specific capacity and a significant reduction in the rate performance, seriously affecting its long-cycle stability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a defect-ordered hexagonal pore structure antioxidant MXene material with strong oxidation resistance and small mass specific capacity decay over a long period of charge and discharge, and its application.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a defect-ordered hexagonal pore structure antioxidant MXene material, the specific steps of which are as follows:

[0007] (1) Preparation of MAX phase Ti3AlC2 with hexagonal pores

[0008] Dehydrogenated titanium powder, pure aluminum powder, and modified spherical graphite powder were hot-pressed and sintered for 4 hours in an argon atmosphere at a temperature of 1600°C and a head pressure of 20T in a vacuum hot-pressing furnace. After hot-pressing, the mixture was rapidly cooled with liquid nitrogen for 0.5 hours to obtain MAX phase Ti3AlC2 with hexagonal pores.

[0009] (2) Preparation of multilayer hexagonal pore MXene by molten salt coating in high-temperature air atmosphere

[0010] The hexagonal pore MAX phase Ti3AlC2 is mixed with CuCl2 and NaCl in a molar ratio of 1:3:6 and ground for 30 minutes to obtain a hexagonal pore MAX phase Ti3AlC2-CuCl2-NaCl mixed powder; a NaCl salt bed is laid on the bottom of the alumina corundum boat, and then the hexagonal pore MAX phase Ti3AlC2-CuCl2-NaCl mixed powder is placed in the alumina corundum boat laid with the NaCl salt bed, and then a layer of NaCl salt bed is covered on the hexagonal pore MAX phase Ti3AlC2-CuCl2-NaCl mixed powder, and the boat is placed in a muffle furnace and sintered at a constant temperature of 820°C for 3 hours in an air atmosphere; because the NaCl salt bed covering in an air atmosphere cannot completely isolate oxygen Gas, a small amount of Al2O3 can be generated during the sintering process; the sintered product is naturally cooled to room temperature, added with deionized water to dissolve and wash, remove the NaCl molten salt, filter, and retain the solid phase; then, FeCl3 solution strong oxidant is added according to the molar ratio of CuCl2 to FeCl3 of 3:4, filtered and washed with clean water, filtered, retained the solid phase, and removed the copper element generated during sintering; HCl solution is added according to the molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, filtered and retained the solid phase; after filtration, the solid phase is retained; finally, deionized water is added for washing and placed in an ultrasonic device for 1 hour to further remove impurity salts, filtered, vacuum dried and ground to obtain a defect-ordered hexagonal pore structure antioxidant MXene material (Defect-Ti3C2)

[0011] Furthermore, the molar ratio of the dehydrogenated titanium powder, the pure aluminum powder and the modified spherical graphite powder is 2.95:1.05:1.6.

[0012] Furthermore, the concentration of the FeCl3 solution is 1 mol / L.

[0013] Furthermore, the concentration of the HCl solution is 1 mol / L.

[0014] Furthermore, during hot pressing sintering, the sintering power is 50KW.

[0015] Furthermore, the diameter of the effective contact surface of the pressure head of the vacuum hot pressing sintering furnace is Φ90 mm.

[0016] Furthermore, the inflation pressure of the argon protective atmosphere is 0.03 MPa.

[0017] An application of the defect-ordered hexagonal pore structure antioxidant MXene material prepared by the above-mentioned preparation method in aqueous potassium ion symmetric supercapacitors.

[0018] Furthermore, the defect-ordered hexagonal pore structure antioxidant MXene material is used as an electrode material for an aqueous potassium ion symmetric supercapacitor; the preparation process of the aqueous potassium ion supercapacitor is as follows:

[0019] (1) Preparation of defective multilayer hexagonal pore MXene electrodes

[0020] The defect-ordered hexagonal pore structure antioxidant MXene material was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground for 1 hour. NMP was added dropwise to form a slurry, which was coated on an aluminum foil current collector and rolled flat. The slurry was then dried at 60°C for 24 hours and maintained at 20 MPa for 30 seconds using a press to obtain a defect-ordered hexagonal pore structure antioxidant MXene material electrode.

[0021] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0022] The defect-ordered hexagonal pore structure antioxidant MXene material electrode as the negative electrode, the separator, and the defect-ordered hexagonal pore structure antioxidant MXene material electrode as the positive electrode are sequentially loaded into the capacitor shell, encapsulated, and injected with electrolyte to obtain a defect-ordered hexagonal pore structure antioxidant MXene aqueous potassium ion symmetric supercapacitor.

[0023] The beneficial effects of the present invention are:

[0024] (1) Through molten salt coating etching in a high-temperature air atmosphere, the process parameters are precisely controlled to ensure that the multi-layer hexagonal pore structure of the MXene material is retained, providing a high-speed channel for ion transport, while significantly improving the energy density of the material, enabling it to exhibit excellent performance in energy storage applications.

[0025] (2) The present invention directly prepares the MAX phase Ti3AlC2 precursor by sintering at 1600°C and then rapidly cooling it for a short time. The precursor has regular hexagonal pores and loose interlayers, which makes subsequent etching easier, shortens the subsequent solid-phase etching time, and avoids the MXene material from being oxidized in large quantities during long-term high-temperature sintering with a small amount of air that is not completely isolated, thereby affecting the electrochemical properties of the material.

[0026] (3) In an air atmosphere, a hexagonal pore MAX phase Ti3AlC2 precursor was etched by high-temperature molten salt coating to prepare a multilayer hexagonal pore MXene material with a micro-oxidation protective layer. Cl end groups formed on the surface of the MXene material replaced the hydrophilic end groups etched by liquid-phase acid etching, reducing the aggressiveness of oxygen and water molecules. At the same time, the unsaturated coordination bonds formed by the defective structure repelled oxygen atoms. Under the joint action of trace amounts of metal oxides on the surface, a barrier was effectively constructed to resist the attack of oxygen and water molecules, significantly improving the antioxidant properties of the MXene material. The enhanced antioxidant properties effectively avoided the sharp decrease in specific surface area and specific capacity attenuation caused by oxidation of the MXene material. At the same time, this improvement also improved the rate performance and cycle stability of the material, enabling the MXene material to operate stably for a long time in aqueous symmetric supercapacitor energy storage devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : This is the XRD pattern of the MAX phase Ti3AlC2 precursor with hexagonal pores and the multi-layer defect-ordered hexagonal pore structure antioxidant MXene material under rapid cooling of the present invention (corresponding to Example 1);

[0028] Figure 2 1 is an SEM image of the hexagonal pore MAX phase Ti3AlC2 material of the present invention (corresponding to Example 1);

[0029] Figure 3 This is an SEM image of the multi-layer defect-ordered hexagonal pore structure antioxidant MXene material of the present invention (corresponding to Example 1);

[0030] Figure 4 This is a CV comparison chart of the first cycle and the 25,000 cycle of the multi-layer defect-ordered hexagonal pore structure antioxidant MXene aqueous potassium ion symmetric supercapacitor after 25,000 cycles of charge and discharge;

[0031] Figure 5 This is an SEM image of a conventional MAX without hexagonal pores that has not been rapidly cooled by liquid nitrogen according to the present invention (corresponding to Example 1);

[0032] Figure 6 This is a CV comparison chart of the first cycle and the 25,000-cycle charge-discharge cycle of a conventional MXene aqueous potassium ion symmetric supercapacitor without hexagonal pores that is not rapidly cooled by liquid nitrogen according to the present invention (corresponding to Example 1);

[0033] Figure 7 This is an SEM image of a multilayer MXene prepared by etching conventional MAX (without hexagonal pores) by a molten salt coating method under a high-temperature vacuum atmosphere according to the present invention (corresponding to Example 2);

[0034] Figure 8 This is a CV comparison chart of the first cycle and the 25,000 cycle of the aqueous potassium ion supercapacitor after 25,000 cycles of charge and discharge of the multilayer MXene prepared by etching conventional MAX by the molten salt coating method in a vacuum atmosphere of the present invention (corresponding to Example 2);

[0035] Figure 9 This is a CV comparison chart of the first cycle and the 25,000-cycle charge and discharge of a multilayer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor obtained by etching hexagonal pores MAX under a vacuum atmosphere according to the present invention (corresponding to Example 3);

[0036] Figure 10 This is a CV comparison chart of the first cycle and the 25,000-cycle charge and discharge of the aqueous potassium ion symmetric supercapacitor of the present invention (corresponding to Example 4) obtained by long-term etching of hexagonal carbon vacancies MAX;

[0037] Figure 11 This is a CV comparison chart of the first cycle and 25,000 cycles of the aqueous potassium ion symmetric supercapacitor after 25,000 cycles of charge and discharge of the multilayer hexagonal pore MXene obtained by microwave-assisted etching of hexagonal pore MAX in the present invention (corresponding to Example 5). DETAILED DESCRIPTION

[0038] Example 1

[0039] The first step is the preparation of defect-ordered MAX phase Ti3AlC2 with hexagonal holes

[0040] Dehydrogenated titanium powder, pure aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6, and the furnace temperature was 1600°C. The power of the vacuum hot pressing sintering furnace used was 50KW, the pressure of the pressure head was set to 20T, and the diameter of the effective contact surface of the pressure head was Φ90mm. Argon was used as the protective atmosphere in the furnace, and the inflation pressure was set to 0.03MPa. The temperature was raised to 1600°C according to the set heating plan and hot pressing sintering was carried out for 3 hours. After the hot pressing sintering was completed, it was transported to a liquid nitrogen device for rapid sintering. After cooling for 0.5h, a MAX phase Ti3AlC2 material with hexagonal holes was obtained; after rapid cooling with liquid nitrogen, the defect order was improved, and a hexagonal exfoliated MAX phase Ti3AlC2 appeared at the surface position with improved order, which fell off to form hexagonal holes; a hexagonal exfoliated MAX phase Ti3AlC2 appeared inside the material with improved order, and the internal hexagonal exfoliated MAX phase Ti3AlC2 would pry open the tightly layered MAX phase Ti3AlC2, transforming the tight interlayer structure into a loose layer structure, providing a favorable basis for subsequent etching.

[0041] The second step is to prepare the oxidation-resistant multilayer hexagonal pore MXene electrode material by molten salt coating in air atmosphere.

[0042] The prepared MAX phase Ti3AlC2 material with hexagonal pores was weighed and mixed with CuCl2 and NaCl in a molar ratio of 1:3:6, and manually ground in an agate mortar for 30 minutes; a layer of NaCl salt bed was laid on the bottom of the alumina corundum ark in advance, and then the ground mixed powder was placed on the NaCl salt bed, and then the NaCl salt bed was covered on the mixed powder again, and finally the alumina corundum ark containing the product was placed in a muffle furnace and sintered at a constant temperature of 820°C for 3 hours in an air atmosphere; since oxygen cannot be completely isolated, a small amount of Al2O3 will be generated. The sintered product was taken out, cooled naturally, and then deionized water was added. Dissolve and wash with water to remove molten salt, filter and retain the solid phase; then add a 1 mol / L FeCl3 solution as a strong oxidant according to the molar ratio of CuCl2 to FeCl3 of 3:4 to remove the generated copper element, filter and wash, filter and retain the solid phase; add a 1 mol / L HCl solution according to the molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, filter and retain the solid phase; finally, add deionized water to wash again and put it into an ultrasonic device for 1 hour to further remove impurity salts, and finally after filtration, vacuum drying and grinding, a MXene (DH-Ti3C2) with layered hexagonal holes is obtained. The X-ray diffraction pattern (XRD) of the rapidly cooled hexagonal hole MAX phase Ti3AlC2 and the multi-layer defect-ordered hexagonal hole structure antioxidant MXene material of Example 1 of the present invention is as follows Figure 1 As shown; the scanning electron microscope image (SEM) of the hexagonal hole MAX is as shown Figure 2 (a) and Figure 2 (b) as shown; Figure 2 (a) and Figure 2 (b) It can be seen from its microscopic morphology that the holes are regular hexagonal in shape; combined with Figure 1 and Figure 2 It can be seen that the material prepared after rapid cooling is a MAX phase Ti3AlC2 material with hexagonal pores. Figure 3 This is the SEM image of the multi-layer defect-ordered hexagonal pore structure antioxidant MXene material prepared by the molten salt coating method in a high-temperature air atmosphere; Figure 3 It can be seen that the oxidation-resistant MXene material with a layered hexagonal pore structure prepared by etching at high temperature has the characteristics of uniform stratification and roughness; the surface roughness is caused by unsaturated coordination bonds and surface micro-oxidation; this improves the oxidation resistance of the multilayer hexagonal pore MXene; this lays a structural foundation for the multilayer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor to have high long-cycle stability and high energy density.

[0043] The third step is to assemble aqueous potassium ion symmetric supercapacitors

[0044] Defective multilayer hexagonal pore MXene materials were prepared as electrode materials and assembled into neutral aqueous potassium ion symmetric supercapacitors;

[0045] (1) Preparation of defective multilayer hexagonal pore MXene electrodes

[0046] The defective MXene (DH-Ti3C2) with layered hexagonal pores was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground into a small amount. NMP was added to form a slurry, which was then coated on a 40 mm × 30 mm aluminum foil current collector and rolled flat. The slurry was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, a press was used to maintain a pressure of 20 MPa for 30 seconds to obtain an electrode sheet of defect-ordered hexagonal pore structure and antioxidant MXene material.

[0047] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0048] The defect-ordered hexagonal pore structure antioxidant MXene material electrode sheets after cutting are used as the positive and negative electrodes, and the negative electrode, separator, and positive electrode are stacked, packaged, and injected in sequence to obtain a defect-ordered hexagonal pore structure antioxidant MXene aqueous potassium ion symmetric supercapacitor.

[0049] The CV comparison diagram of the first cycle and the 25,000 cycles of the multi-layer defect-ordered hexagonal pore structure antioxidant MXene aqueous potassium ion supercapacitor after 25,000 cycles of charge and discharge is shown in the figure below. Figure 4 shown by Figure 4 It can be seen that the mass specific capacity of the oxidation-resistant MXene aqueous potassium ion supercapacitor with multi-layer defect-ordered hexagonal pore structure is as high as 335.6Fg -1 Even after 25,000 cycles of charge and discharge testing, the mass specific capacity is still 324.8Fg -1 ; The long-cycle charging mass capacity retention rate of defective multilayer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor is as high as 96.8%; this provides a new strategy to solve the problem that in conventional aqueous potassium ion symmetric supercapacitors, the electrode material is easily oxidized in water during long cycles, resulting in structural destruction, and then the specific surface area decreases and the rate performance decays, leading to a sharp decline in stability under long-cycle cycles.

[0050] Comparative Example 1

[0051] The first step is the preparation of conventional MAX phase Ti3AlC2 (after hot pressing and sintering, without liquid nitrogen rapid cooling, to synthesize a conventional MAX phase Ti3AlC2 precursor without hexagonal pores;)

[0052] Dehydrogenated titanium powder, pure aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6 at a temperature of 1600°C. The vacuum hot pressing sintering furnace used had a power of 50KW, a pressure of 20T, and a diameter of Φ90mm for the effective contact surface of the pressure head. Argon was used as a protective atmosphere in the furnace, and the inflation pressure was set to 0.03MPa. The temperature was raised to 1600°C according to the set heating scheme and hot pressing sintering was carried out for 4 hours. The sintered product was removed and naturally cooled in the furnace to obtain MAX phase Ti3AlC2 material. Conventional Ti3AlC2 does not produce a large number of ordered defects and no hexagonal pores appear.

[0053] The second step is to use the molten salt coating method to etch conventional MAX in a high-temperature air atmosphere to prepare multilayer MXene (without hexagonal holes) electrode materials.

[0054] The prepared hexagonal-pore-free MAX phase Ti3AlC2 material was mixed with CuCl2 and NaCl in a molar ratio of 1:3:6 and manually ground in an agate mortar for 30 minutes. A NaCl salt bed was previously laid on the bottom of the alumina corundum ark to provide a molten pool environment and isolate it from air. The ground mixed powder was then placed in the NaCl salt bed, which was then covered with another layer of NaCl salt bed. Finally, the alumina corundum ark containing the product was placed in a muffle furnace; constant temperature sintering was carried out at 820°C for 3 hours in an air atmosphere; the sintered product was taken out, naturally cooled, and then deionized water was added to dissolve and wash it, filtered, and the solid phase was retained; then a strong oxidant of 1 mol / L FeCl3 solution was added according to the molar ratio of CuCl2 to FeCl3 of 3:4 to remove the generated copper element, filtered and washed, and the solid phase was retained, and a 1 mol / L HCl solution was added according to the molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, and the solid phase was retained by filtration; finally, deionized water was added again to wash it and it was placed in an ultrasonic device for 1 hour to further remove impurity salts; finally, after filtration, vacuum drying and grinding, MXene (D-Ti3C2) without hexagonal holes was obtained.

[0055] Comparative Example 1: The scanning electron microscope image (SEM) of the conventional MAX without ordered defect structure and hexagonal holes without liquid nitrogen rapid cooling is as follows: Figure 5 shown; from Figure 5 The microscopic morphology shows that MAX has a compact structure, but the exposed surface area is smaller than that of the MAX material with hexagonal holes in Example 1. Therefore, the specific surface area of ​​the corresponding etched MXene is also smaller, and the energy density of the prepared symmetric supercapacitor is also lower, but the oxidation resistance is improved and the long-cycle stability is improved;

[0056] The third step is to assemble aqueous potassium ion symmetric supercapacitors

[0057] Using multilayer MXene (without hexagonal pores) as the electrode material, a neutral aqueous potassium ion symmetric supercapacitor was assembled;

[0058] (1) Preparation of multilayer MXene (no hexagonal pores) electrode materials

[0059] After multilayer hexagonal pore MXene was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground for 1 hour, NMP was added dropwise to form a mixture. The prepared negative electrode mixture was coated on a cut 40mm×30mm aluminum foil current collector and rolled flat. The electrode sheet was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, it was pressed with a press at 20MPa for 30 seconds.

[0060] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0061] The cut MXene electrode sheets without hexagonal holes are used as positive and negative electrodes, and the negative electrode, separator, and positive electrode are stacked, packaged, and injected in this order to obtain a MXene aqueous potassium ion symmetric supercapacitor without hexagonal holes.

[0062] Comparative Example 1 is a parallel experiment of Example 1 after rapid cooling with liquid nitrogen. The CV comparison of the first cycle and the 25,000 cycle of the conventional MXene aqueous potassium ion symmetric supercapacitor without hexagonal pores constructed without defective ordering without rapid cooling with liquid nitrogen in Comparative Example 1 is shown in the figure. Figure 6 shown by Figure 6 It can be seen that relative to Example 1, the mass specific capacity of the MXene aqueous potassium ion supercapacitor without hexagonal holes in this comparative example is 286.5Fg -1 After 25,000 cycles of charge and discharge testing, the mass specific capacity is 254.7Fg -1 ; The long-cycle charging mass capacity retention rate of a conventional MXene aqueous potassium ion symmetric supercapacitor without hexagonal pores constructed by defect-free ordering without liquid nitrogen rapid cooling is only 88.9%.

[0063] Comparative Example 2

[0064] The first step is the preparation of conventional MAX phase Ti3AlC2 (after hot pressing and sintering, without liquid nitrogen rapid cooling, to synthesize a conventional MAX phase Ti3AlC2 precursor without hexagonal pores;)

[0065] Dehydrogenated titanium powder, pure aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6 at a temperature of 1600°C. The vacuum hot pressing sintering furnace used had a power of 50KW, a pressure of 20T, and a diameter of Φ90mm for the effective contact surface of the pressure head. Argon was used as a protective atmosphere in the furnace, and the inflation pressure was set to 0.03MPa. The temperature was raised to 1600°C according to the set heating scheme and hot pressing sintering was carried out for 4 hours. The sintered product was removed and naturally cooled in the furnace to obtain MAX phase Ti3AlC2 material. Conventional Ti3AlC2 does not produce a large number of ordered defects and no hexagonal pores appear.

[0066] The second step is to use the molten salt coating method under high temperature vacuum atmosphere to etch conventional MAX to prepare multilayer MXene (without hexagonal holes) electrode material (vacuum atmosphere etching)

[0067] The prepared MAX phase Ti3AlC2 material without hexagonal pores was weighed and mixed with CuCl2 and NaCl in a molar ratio of 1:3:6, and manually ground in an agate mortar for 30 minutes; a layer of NaCl salt bed was laid on the bottom of the alumina corundum ark in advance to provide a molten pool environment; then the ground mixed powder was placed on the NaCl salt bed, and then a layer of NaCl salt bed was covered on the mixed powder; finally, the alumina corundum ark containing the product was placed in a vacuum muffle furnace; argon was introduced as a protective gas, and constant temperature sintering was carried out at 820°C for 8 hours; the sintered product was taken out, cooled naturally, and deionized water was added. The process is as follows: dissolving and cleaning, filtering, and retaining the solid phase; then, a strong oxidizing agent of 1 mol / L FeCl3 solution is added according to a molar ratio of CuCl2 to FeCl3 of 3:4 to remove the generated copper element; after filtering and cleaning, filtering, retaining the solid phase, adding a 1 mol / L HCl solution according to a molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, filtering and retaining the solid phase; finally, adding deionized water to wash again and ultrasonicating in an ultrasonic device for 1 hour to further remove impurity salts; finally, after filtering, vacuum drying and grinding, MXene (Ti3C2) without hexagonal holes under vacuum is obtained;

[0068] Comparative Example 2: A scanning electron microscope image (SEM) of a conventional MXene obtained by etching a conventional MAX without ordered defects and hexagonal pores without rapid cooling by liquid nitrogen in a vacuum atmosphere is shown in FIG. Figure 7 shown; from Figure 7 The microscopic morphology shows that MXene has a bulk layered structure and a smooth surface. However, the exposed surface area is smaller than that of the MXene material with hexagonal pores in Example 1. Therefore, the energy density of the prepared symmetric supercapacitor is low, and the surface is not slightly oxidized when etched in a vacuum atmosphere, resulting in poor long-term cycle stability.

[0069] The third step is to assemble aqueous potassium ion symmetric supercapacitors

[0070] Using multilayer MXene (without hexagonal pores) under vacuum as the electrode material, a neutral aqueous potassium ion symmetric supercapacitor was assembled;

[0071] (1) Preparation of multilayer MXene (without hexagonal pores) electrode materials under vacuum

[0072] After multilayer MXene was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 under vacuum and ground for 1 hour, NMP was added dropwise to form a mixture. The prepared negative electrode mixture was coated on a cut 40mm×30mm aluminum foil current collector and rolled flat. The electrode sheet was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, it was pressed with a press at 20MPa for 30 seconds.

[0073] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0074] The cut MXene electrode sheet without hexagonal holes under vacuum is used as the positive electrode and the negative electrode, and the negative electrode, the diaphragm, and the positive electrode are stacked, packaged, and injected in order to obtain a MXene aqueous potassium ion symmetric supercapacitor without hexagonal holes under vacuum; Comparative Example 2 is a parallel experiment of Example 1 by etching under vacuum atmosphere without rapid cooling with liquid nitrogen. In this comparative example, the conventional MXene aqueous potassium ion symmetric supercapacitor obtained by etching under vacuum atmosphere without rapid cooling with liquid nitrogen and without ordered defects and hexagonal holes is shown in the CV comparison diagram of the first cycle and the 25,000 cycles after 25,000 cycles of charge and discharge. Figure 8 shown by Figure 8 It can be seen that relative to Example 1, the mass specific capacity of the MXene aqueous potassium ion symmetric supercapacitor without hexagonal holes under vacuum in this comparative example is 230.5Fg -1 After 25,000 cycles of charge and discharge testing, the mass specific capacity is 167.4Fg -1 In this comparative example, the conventional MXene aqueous potassium ion symmetric supercapacitor obtained by etching the conventional MAX without hexagonal pores without ordered defects in a vacuum atmosphere without rapid cooling by liquid nitrogen has a long-cycle charging mass specific capacity retention rate of only 72.6%.

[0075] Comparative Example 3

[0076] The first step is to use the molten salt coating method under high temperature vacuum atmosphere to etch the hexagonal pore MAX to prepare multi-layer hexagonal pore MXene electrode material (vacuum atmosphere etching)

[0077] The MAX phase Ti3AlC2 material with hexagonal pores prepared in Example 1 was weighed and mixed with CuCl2 and NaCl in a molar ratio of 1:3:6, and manually ground in an agate mortar for 30 minutes; a layer of NaCl salt bed was laid on the bottom of the alumina corundum boat in advance to provide a molten pool environment; then the ground mixed powder was placed on the NaCl salt bed, and then a layer of NaCl salt bed was covered on the mixed powder; finally, the alumina corundum boat containing the product was placed in a vacuum muffle furnace; argon was introduced as a protective gas, and constant temperature sintering was carried out at 820°C for 3 hours; the sintered product was taken out, cooled naturally, and deionized water was added. The product was dissolved in water for cleaning, filtered, and the solid phase was retained; then, a strong oxidant of 1 mol / L FeCl3 solution was added according to the molar ratio of CuCl2 to FeCl3 of 3:4 to remove the generated copper element; after filtration and cleaning, the product was filtered, the solid phase was retained, and a 1 mol / L HCl solution was added according to the molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, and the solid phase was retained after filtration; finally, deionized water was added for cleaning again and the product was ultrasonically ultrasonicated for 1 hour to further remove impurity salts; finally, after filtration, vacuum drying and grinding, a multi-layer hexagonal pore MXene (H-Ti3C2) under vacuum was obtained;

[0078] The second step is to assemble aqueous potassium ion symmetric supercapacitors

[0079] Using multilayer hexagonal pore MXene electrode materials under vacuum as electrode materials, a neutral aqueous potassium ion symmetric supercapacitor was assembled;

[0080] (1) Preparation of multilayer hexagonal pore MXene electrode materials under vacuum

[0081] After mixing and grinding multilayer hexagonal pore MXene with acetylene black and PVDF in a mass ratio of 8:1:1 under vacuum for 1 hour, NMP was added dropwise to form a mixture. The prepared negative electrode mixture was coated on a cut 40mm×30mm aluminum foil current collector and rolled flat. The electrode sheet was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, it was pressed with a press at a pressure of 20MPa for 30s.

[0082] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0083] The cut multi-layer hexagonal pore MXene electrode sheet under vacuum is used as the positive electrode and the negative electrode, and the negative electrode, the separator, and the positive electrode are stacked, packaged, and injected in sequence to obtain a multi-layer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor under vacuum; in this comparative example, the multi-layer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor obtained by etching the hexagonal pore MAX under vacuum atmosphere is shown in the CV comparison diagram of the first cycle and the 25,000 cycles after 25,000 cycles of charge and discharge. Figure 9shown by Figure 9 It can be seen that compared with Example 1, the mass specific capacity of the multi-layer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor under vacuum in this comparative example is 270.3Fg-1; after 25,000 cycles of long-cycle charge-discharge testing, the mass specific capacity is 186.2Fg-1. The long-cycle charge mass specific capacity retention rate of the aqueous potassium ion symmetric supercapacitor obtained by etching the hexagonal pore MAX in this comparative example is only 68.9%. The multi-layer hexagonal pore MXene obtained by etching the hexagonal pore MAX in a vacuum atmosphere in Comparative Example 3 has a higher specific capacity than Comparative Example 2, but its antioxidant performance after long-cycle testing is significantly reduced compared to Example 1.

[0084] Comparative Example 4

[0085] The first step is the preparation of defect-ordered MAX phase Ti3AlC2 with hexagonal carbon vacancies.

[0086] Dehydrogenated titanium powder, pure aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6 at a temperature of 1400°C. The power of the vacuum hot pressing sintering furnace used was 50KW, the pressure of the indenter was set to 10T, and the diameter of the effective contact surface of the indenter was Φ85mm. Argon was used as the protective atmosphere in the furnace, and the inflation pressure was set to 0.03MPa. The temperature was raised to 1400°C according to the set heating scheme and hot pressing sintering was carried out for 3 hours. After the hot pressing sintering was completed, the powder was transported to a liquid nitrogen device for rapid cooling for 2 hours to obtain the MAX phase Ti3AlC2 with hexagonal carbon vacancies.

[0087] The second step is to use the molten salt coating method in a long-term high-temperature air atmosphere to etch MAX with hexagonal carbon vacancies to prepare multi-layer hexagonal pore MXene electrode materials (long-term etching)

[0088] The prepared MAX phase Ti3AlC2 with hexagonal carbon vacancies was weighed and mixed with CuCl2 and NaCl in a molar ratio of 1:3:6, and manually ground in an agate mortar for 30 minutes; a layer of NaCl salt bed was laid on the bottom of the alumina corundum ark in advance to provide a molten pool environment; then the ground mixed powder was placed on the NaCl salt bed, and then a layer of NaCl salt bed was covered on the mixed powder; finally, the alumina corundum ark containing the product was placed in a muffle furnace and sintered at a constant temperature of 820°C for 3 hours in an air atmosphere. No yellow smoke was seen during solid phase etching, so the constant temperature etching was continued until yellow smoke appeared for 8 hours and then the etching was stopped; the sintered product was placed in a muffle furnace and sintered at a constant temperature of 820°C for 3 hours. The sample was taken out, cooled naturally, and then deionized water was added to dissolve and wash it, filtered, and the solid phase was retained; then a strong oxidant FeCl3 solution with a concentration of 1 mol / L was added according to the molar ratio of CuCl2 to FeCl3 of 3:4 to remove the generated copper element; after filtration and washing, 1 mol / L HCl solution was added according to the molar ratio of HCl to FeCl3 of 1:1 to remove metal impurities, and the solid phase was retained by filtration; finally, deionized water was added again to wash it and it was placed in an ultrasonic device for 1 hour to further remove impurity salts; finally, after filtration, vacuum drying and grinding, multi-layer hexagonal pore MXene (LH-Ti3C2) was obtained.

[0089] The third step is to assemble aqueous potassium ion symmetric supercapacitors

[0090] The MXene electrode material with multi-layer hexagonal holes etched for a long time is used as the electrode material to assemble a neutral aqueous potassium ion symmetric supercapacitor;

[0091] (1) Preparation of multilayer hexagonal pore MXene electrode materials by long-term etching

[0092] After long-time etched multilayer hexagonal pore MXene was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground for 1 hour, NMP was added to form a mixture. The prepared negative electrode mixture was coated on a cut 40mm×30mm aluminum foil current collector and rolled flat. The electrode sheet was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, it was pressed with a press at 20MPa for 30 seconds.

[0093] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0094] The multi-layer hexagonal pore MXene electrode sheets etched for a long time after cutting are used as the positive and negative electrodes, and the negative electrode, separator, and positive electrode are stacked, packaged, and injected in sequence to obtain a long-etched hexagonal pore MXene aqueous potassium ion symmetric supercapacitor; In this comparative example, the multi-layer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor obtained by long-term etching of hexagonal carbon vacancy MAX after 25,000 cycles of charge and discharge has a CV comparison diagram of the first cycle and the 25,000 cycles. Figure 10 shown by Figure 10 It can be seen that relative to Example 1, the mass specific capacity of the long-term etched multi-layer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor of this comparative example is 126.8Fg-1; after 25,000 cycles of long-cycle charge and discharge testing, the mass specific capacity is 64.5Fg-1; the long-cycle charging mass specific capacity retention rate of the aqueous potassium ion symmetric supercapacitor obtained by long-term etching of the multi-layer hexagonal pore MXene with hexagonal carbon vacancies MAX in this comparative example is only 50.9%. When the multi-layer hexagonal pore MXene obtained by etching the hexagonal carbon vacancy MAX for a long time in Comparative Example 4 was severely oxidized (the powder color turned white), resulting in its low specific capacity and poor cycle stability.

[0095] Comparative Example 5

[0096] The first step is the preparation of defect-ordered MAX phase Ti3AlC2 with hexagonal holes

[0097] Dehydrogenated titanium powder, pure aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6, and the furnace temperature was 1600°C. The vacuum hot pressing sintering furnace used had a power of 50KW, a pressure head set to 20T, and a diameter of the effective contact surface of the pressure head of Φ90mm. Argon was used as a protective atmosphere in the furnace, and the inflation pressure was set to 0.03MPa. The temperature was raised to 1600°C according to the set heating scheme and hot pressing sintered for 3h to obtain the MAX phase Ti with hexagonal pores. 3AlC2; after hot pressing and sintering, it is transported to a liquid nitrogen device for rapid cooling for 0.5h, the defect order is improved, and hexagonal exfoliated MAX phase Ti3AlC2 appears on the surface where the order is improved, and it falls off to form hexagonal holes; hexagonal exfoliated MAX phase Ti3AlC2 appears inside where the order is improved, and the internal hexagonal exfoliated MAX phase Ti3AlC2 will pry open the tightly layered MAX phase Ti3AlC2, transforming the tight interlayer structure into a loose layer structure, providing a favorable basis for subsequent etching.

[0098] The second step is to prepare multilayer hexagonal pore MXene electrode materials by microwave-assisted etching.

[0099] Weigh 2g of MAX phase Ti3AlC2 with hexagonal pores for later use, then draw 40mL of a mixture of ammonium fluoride and hydrochloric acid (the mass ratio of ammonium fluoride to hydrochloric acid is 1:7) and pour it into a polytetrafluoroethylene beaker. Under magnetic stirring, slowly add the hexagonal pore MAX phase Ti3AlC2 to the mixture of ammonium fluoride and hydrochloric acid; put it into a microwave reactor for microwave-assisted etching for 2h, with a microwave power of 300W, a frequency of 2.45GHz, and a pressure set to 1Gpa; then, place the reacted solution in an ultrasonic device and ultrasonically vibrate it at room temperature for 2h; take out the mixed solution after ultrasonic vibration and place it in a centrifuge, and perform solid-liquid separation at a high speed of 3000 rpm; add deionized water to the precipitate after centrifugation and wash until the pH value of the solution is equal to 6; filter the solution for solid-liquid separation; place the filtered powder in a vacuum drying oven and dry it for 6h; finally, grind and collect to obtain a multilayer hexagonal pore MXene (WH-Ti3C2) electrode material;

[0100] Step 3: Assemble aqueous potassium ion supercapacitors

[0101] The multilayer hexagonal pore MXene material obtained by microwave-assisted etching was used as the electrode material to assemble a neutral aqueous potassium ion symmetric supercapacitor;

[0102] (1) Preparation of multilayer hexagonal pore MXene electrode materials by microwave-assisted etching

[0103] The microwave-assisted etched multilayer hexagonal pore MXene was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground for 1 hour, and then NMP was added to form a mixture. The prepared negative electrode mixture was coated on a cut 40mm×30mm aluminum foil current collector and rolled flat. The electrode sheet was placed in a vacuum drying oven and dried at 60°C for 24 hours. After being taken out, it was pressed with a press at 20MPa for 30s.

[0104] (2) Assembly of aqueous potassium ion symmetric supercapacitors

[0105] The multilayer hexagonal pore MXene electrode sheets after microwave-assisted etching after slicing should be stacked, packaged, and injected in the order of negative electrode, diaphragm, and positive electrode to obtain a microwave-assisted etched hexagonal pore MXene aqueous potassium ion symmetric supercapacitor; the CV comparison diagram of the first cycle and 25,000 cycles of the multilayer hexagonal pore MXene aqueous potassium ion symmetric supercapacitor obtained by microwave-assisted etching hexagonal pore MAX in this comparative example after 25,000 cycles of charge and discharge is shown in the figure. Figure 11 shown by Figure 11As can be seen, compared to Example 1, the mass specific capacity of the aqueous potassium ion symmetric supercapacitor obtained by microwave-assisted etching of multi-layer hexagonal pore MXene in this comparative example is 304.9 Fg⁻¹; after 25,000 cycles of long-cycle charge-discharge testing, the mass specific capacity is 197.9 Fg⁻¹. The long-cycle charge mass specific capacity retention rate of the aqueous potassium ion symmetric supercapacitor obtained by microwave-assisted etching of hexagonal pore MAX in this comparative example is only 64.9%. The multi-layer hexagonal pore MXene obtained by microwave-assisted etching of hexagonal pore MAX in Comparative Example 5 has a higher specific capacity but insufficient antioxidant properties, which is due to the fact that the liquid phase etching does not provide a protective layer for the multi-layer hexagonal pore MXene.

[0106] The above are merely specific embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing an oxidation-resistant MXene material with a defect-ordered hexagonal pore structure, characterized by: The specific steps are as follows: (1) Preparation of MAX phase Ti3AlC2 with hexagonal pores Dehydrogenated titanium powder, pure aluminum powder, and modified spherical graphite powder were hot-pressed and sintered for 4 hours in an argon atmosphere at a temperature of 1600°C and a head pressure of 20T in a vacuum hot-pressing furnace. After hot-pressing, the mixture was rapidly cooled with liquid nitrogen for 0.5 hours to obtain MAX phase Ti3AlC2 with hexagonal pores. (2) Preparation of multilayer hexagonal pore MXene by molten salt coating in high-temperature air atmosphere The hexagonal pore MAX phase Ti3AlC2 was mixed with CuCl2 and NaCl in a molar ratio of 1:3:6 and ground for 30 min to obtain a hexagonal pore MAX phase Ti3AlC2-CuCl2-NaCl mixed powder; a NaCl salt bed was laid on the bottom of the alumina corundum boat, and then the hexagonal pore MAX phase Ti3AlC2-CuCl2-NaCl mixed powder was placed in the alumina corundum boat with the NaCl salt bed, and then the hexagonal pore MAX phase Ti3AlC2-CuCl2- A layer of NaCl salt bed is covered on the NaCl mixed powder, and the ark is placed in a muffle furnace and sintered at a constant temperature of 820°C for 3 hours in an air atmosphere; the sintered product is naturally cooled to room temperature, added with deionized water for dissolution and cleaning, filtered, and the solid phase is retained; then added to the FeCl3 solution according to the molar ratio of CuCl2 to FeCl3 of 3:4, filtered and washed with clean water, filtered, and the solid phase is retained; HCl solution is added according to the molar ratio of HCl to FeCl3 of 1:1 to remove impurities again, filtered and retained the solid phase; finally, deionized water is added for cleaning and placed in an ultrasonic device for ultrasonication for 1 hour, filtered, vacuum dried and ground to obtain a defect-ordered hexagonal pore structure antioxidant MXene material.

2. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: The molar ratio of the dehydrogenated titanium powder, the pure aluminum powder and the modified spherical graphite powder is 2.95:1.05:1.

6.

3. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: The concentration of the FeCl3 solution is 1 mol / L.

4. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: The concentration of the HCl solution is 1 mol / L.

5. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: During hot pressing sintering, the sintering power is 50KW.

6. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: The diameter of the effective contact surface of the vacuum hot pressing sintering furnace pressure head is Φ90mm.

7. The method for preparing the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 1, characterized in that: The filling pressure of the argon protective atmosphere is 0.03 MPa.

8. Use of the defect-ordered hexagonal pore structure antioxidant MXene material prepared by the preparation method according to claim 1 in an aqueous potassium ion symmetric supercapacitor.

9. Use of the defect-ordered hexagonal pore structure antioxidant MXene material according to claim 8 in an aqueous potassium ion symmetric supercapacitor, characterized in that: The defect-ordered hexagonal pore structure antioxidant MXene material is used as an electrode material for an aqueous potassium ion symmetric supercapacitor; The preparation process of aqueous potassium ion supercapacitors is as follows: (1) Preparation of defective multilayer hexagonal pore MXene electrodes The defect-ordered hexagonal pore structure antioxidant MXene material was mixed with acetylene black and PVDF in a mass ratio of 8:1:1 and ground for 1 hour. NMP was added dropwise to form a slurry, which was coated on an aluminum foil current collector and rolled flat. The slurry was then dried at 60°C for 24 hours and maintained at 20 MPa for 30 seconds using a press to obtain a defect-ordered hexagonal pore structure antioxidant MXene material electrode. (2) Assembly of aqueous potassium ion symmetric supercapacitors The defect-ordered hexagonal pore structure antioxidant MXene material electrode as the negative electrode, the separator, and the defect-ordered hexagonal pore structure antioxidant MXene material electrode as the positive electrode are sequentially loaded into the capacitor shell, encapsulated, and injected with electrolyte to obtain a defect-ordered hexagonal pore structure antioxidant MXene aqueous potassium ion symmetric supercapacitor.

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