MXene surface group modification method based on NaOH / NaI molten salt system

Abstract

The invention belongs to the field of lithium ion batteries, relates to a lithium ion battery electrode material, and particularly provides an MXene surface group modification method based on a NaOH / NaI molten salt system, which is used for realizing accurate regulation and control of MXene surface groups and modification of pure O groups and OH groups on the premise of not damaging an MXene structure. A NaOH / NaI molten salt system is adopted to modify an MXene surface group, an F group is replaced by an OH group to obtain OH group modified MXene, the OH group is further converted into an O group through high temperature, and pure O group modified MXene is obtained; moreover, the method is generally suitable for various MXenes, including single / double-metal MXenes, 21-phase MXenes, 32-phase MXenes, 43-phase MXenes and MXenes synthesized by other different methods; in addition, the method has the advantages of simple preparation process, low temperature, low cost and the like, and can be effectively applied to the fields of lithium ion batteries, supercapacitors and the like.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries and relates to lithium-ion battery electrode materials. The present invention specifically provides a method for modifying MXene pure oxygen and hydroxyl surface groups based on a NaOH / NaI molten salt system. Background Art

[0002] With the continuous growth of energy demand and the depletion of traditional fossil fuels, the development of renewable energy such as solar energy, wind energy, and tidal energy has been rapidly promoted to alleviate the energy crisis; however, the intermittent nature of these renewable energy sources means that they cannot provide a sustainable energy supply. Energy storage and conversion devices are the key to the effective utilization and promotion of renewable energy. Compared with supercapacitors used in portable electronic products and electric vehicles, lithium-ion batteries have higher energy density. In addition, lithium-ion batteries have high average output voltage, wide operating temperature range (-20℃~60℃), excellent cycle performance, fast charging and discharging, and charging efficiency of up to 100%. They are called green batteries and have broad application prospects in the future.

[0003] MXene is a type of two-dimensional transition metal carbide and / or nitride. Due to its two-dimensional structure, lithium-philic surface terminal, and excellent electrical conductivity, ionic conductivity, and mechanical properties, it has attracted extensive research in recent years. It is worth noting that through theoretical calculations, O-group MXene has the smallest energy barrier to lithium ions. Therefore, O-group MXene is expected to be used as an electrode of lithium-ion batteries to improve the capacity and cycle performance of lithium-ion batteries, thereby promoting the development of the lithium-ion battery field. On this basis, the present invention provides a method for modifying surface groups such as pure O groups and OH groups of MXene using a NaOH / NaI molten salt system. Summary of the invention

[0004] The purpose of the present invention is to provide a method for modifying pure oxygen and hydroxyl surface groups of MXene based on a NaOH / NaI molten salt system, so as to achieve precise control of MXene surface groups without destroying the MXene structure, and to achieve modification of pure O groups and OH groups. The present invention uses a NaOH / NaI molten salt system to modify the surface groups of MXene, replacing the F groups with OH groups to obtain OH group-modified MXene, and further converting the OH groups into O groups by high temperature to obtain pure O group-modified MXene; and the present invention is generally applicable to various MXenes, including single / bimetallic MXenes, 21-phase, 32-phase and 43-phase MXenes, and MXenes synthesized by other different methods.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for modifying MXene surface groups based on a NaOH / NaI molten salt system, characterized in that it comprises the following steps:

[0007] Step 1. Obtain MXene by etching the MAX phase;

[0008] Step 2. The MXene obtained in step 1 is centrifuged 5 to 6 times with deionized water until the pH value of the supernatant is equal to 6 to 7, and then dried at 60 to 80° C. under vacuum conditions to obtain MXene powder;

[0009] Step 3. Add the MXene powder obtained in step 2 to a NaOH / NaI mixed salt, and heat it at 220-260° C. for 30-60 min to obtain a multilayer MXene modified with an OH group; wherein the mass ratio of NaOH to NaI in the NaOH / NaI mixed salt is 0.7:1.5, and the mass ratio of MXene powder to NaOH / NaI mixed salt is 0.2:3.1;

[0010] Step 4. Repeatedly centrifuge the OH group-modified MXene obtained in step 3 using deionized water to obtain a cleaned OH group-modified multilayer MXene;

[0011] Step 5. Add deionized water to the OH group-modified multilayer MXene obtained in step 4 for ultrasonic treatment, and then perform repeated centrifugation to collect the supernatant to obtain the OH group-modified single-layer MXene.

[0012] A method for modifying MXene surface groups based on a NaOH / NaI molten salt system, characterized in that it comprises the following steps:

[0013] Step 1. Obtain MXene by etching the MAX phase;

[0014] Step 2. The MXene obtained in step 1 is centrifuged 5 to 6 times with deionized water until the pH value of the supernatant is equal to 6 to 7, and then dried at 60 to 80° C. under vacuum conditions to obtain MXene powder;

[0015] Step 3. Add the MXene powder obtained in step 2 to a NaOH / NaI mixed salt and heat it at 360-380°C for 30-60 min to obtain an O-group-modified multilayer MXene; wherein the mass ratio of NaOH to NaI in the NaOH / NaI mixed salt is 1.4:1.7, and the mass ratio of MXene powder to NaOH / NaI mixed salt is 0.2:2.2;

[0016] Step 4. Repeatedly centrifuge the OH group-modified MXene obtained in step 3 using deionized water to obtain a cleaned O group-modified multilayer MXene;

[0017] Step 5. Add deionized water to the O-group-modified multilayer MXene obtained in step 4 for ultrasonic treatment, and then perform repeated centrifugation to collect the supernatant to obtain the O-group-modified single-layer MXene.

[0018] Furthermore, in step 1 of the above two methods, the MXene includes but is not limited to Ti2C, Ti3C2, Mo2C, Mo2TiC2, Mo2Ti2C3, V2C, Nb4C3 or Ta4C3.

[0019] Furthermore, in step 1 of the above two methods, the specific process is:

[0020] To synthesize Ti2C, 1 g of Ti2AlC was added to 10 mL of 10 wt.% HF and stirred at room temperature for 8 h.

[0021] To synthesize Ti3C2, 1 g of Ti3AlC2 was added to 20 mL of an etchant containing 12 mL of 9 M HCl, 2 mL of 49 wt.% HF, and 6 mL of deionized water and stirred at room temperature for 24 h.

[0022] To synthesize Mo2C, 1 g of Mo2Ga2C was added to 10 mL of 48-50 wt.% HF and stirred at 55 °C for 100 h.

[0023] To synthesize Mo2TiC2, add 1 g of Mo2TiAlC2 to 10 mL of 48-50 wt.% HF and stir at 55 °C for 48 h;

[0024] To synthesize Mo2Ti2C3, 1 g of Mo2Ti2AlC3 was added to 10 mL of 48-50 wt.% HF and stirred at 55 °C for 96 h.

[0025] To synthesize Nb2C, 1 g of Nb2AlC was added to 10 ml of 48-50 wt.% HF and stirred at room temperature for 90 h.

[0026] To synthesize V2C, add 1 g of V2AlC to 10 ml of 48-50 wt.% HF and stir at room temperature for 90 h;

[0027] To synthesize Nb4C3, 1 g of Nb4AlC3 was added to 10 mL of 48-50 wt.% HF and stirred at room temperature for 96 h.

[0028] To synthesize Ta4C3, 1 g of Ta4AlC3 was added to 10 mL of 48-50 wt.% HF and stirred at room temperature for 72 h; the stirring speed during the above synthesis was set at 400 rpm.

[0029] Furthermore, in step 2 of the above two methods, the centrifugal speed is 3500-5000 rpm, and the single centrifugation time is 5-10 min.

[0030] Furthermore, in step 4 of the above two methods, the centrifugal speed is 3500-5000 rpm, the single centrifugation time is 5-10 min, and the number of centrifugation operations is 5-6 times.

[0031] Furthermore, in step 5 of the above two methods, the ultrasonic treatment time is 0.5h to 1h; the centrifugal speed is 3500 to 5000rpm, the single centrifugation time is 5 to 10min, and the number of centrifugal treatments is 3 to 4 times.

[0032] Based on the above technical solution, the beneficial effects of the present invention are:

[0033] The present invention provides a method for modifying pure oxygen and hydroxyl surface groups of MXene based on a NaOH / NaI molten salt system, which can achieve precise regulation of MXene surface groups without destroying the MXene structure, and achieve pure O group and OH group modification. Specifically:

[0034] 1. MXene modified with OH groups is obtained by treating MXene with a NaOH / NaI molten salt system. The F groups on the surface of MXene can be replaced with OH groups by treating MXene with a NaOH / NaI molten salt system. For example, the reaction formula is: Ti3C2(F)2+2NaOH=Ti3C2(OH)2+2NaF; further, the OH groups can be converted into O groups by high temperature to obtain O-group-modified MXene; further, different groups can be connected by substitution reactions, such as amino groups, organic groups, etc.

[0035] 2. The modification method proposed in the present invention is generally applicable to various MXenes, including single / bimetallic MXenes, 21-phase, 32-phase and 43-phase MXenes, and MXenes synthesized by other methods;

[0036] 3. The method of surface modification of MXene using the NaOH / NaI molten salt system in the present invention has the advantages of simple preparation process, low temperature, and low cost, and can be effectively applied to lithium-ion batteries, supercapacitors and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1is Ti3C2(OH) in Example 2 of the present invention x With Ti3C2O x Preparation flow chart of .

[0038] Figure 2 is Ti3C2(OH) in Example 2 of the present invention x With Ti3C2O x SEM image of .

[0039] Figure 3 is Ti3C2(OH) in Example 2 of the present invention x With Ti3C2O x XPS spectrum.

[0040] Figure 4 is Ti3C2(OH) in Example 2 of the present invention x With Ti3C2O x Battery performance diagram. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be noted that the following embodiments are only exemplary descriptions, and the present invention is not limited to these embodiments.

[0042] Example 1

[0043] A method for modifying MXene surface groups such as pure O and OH by using a NaOH / NaI molten salt system, wherein multilayer MXene is obtained by etching and peeling off a MAX phase, and the surface group type of the MXene treated by the NaOH / NaI molten salt system is replaced by OH from F, and the OH group is further converted into an O group by high temperature; the process of the modification method is as follows Figure 1 As shown, the specific steps are as follows:

[0044] Step 1: Add 1 g of Ti2AlC to 10 mL of 10 wt.% HF and stir at room temperature for 8 h at a stirring speed of 400 rpm to obtain Ti2C;

[0045] Step 2: The Ti2C obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Ti2C;

[0046] Step 3: Add 200 mg of multilayer Ti2C prepared in step 2 to a mixed salt (3.1 g) of NaOH / NaI (1.4 g:1.7 g), and heat at 260 °C in a tube furnace for 60 min to obtain Ti2C with OH groups;

[0047] Alternatively, 200 mg of multilayer Ti2C prepared in step 2 was added to a mixed salt (2.2 g) of NaOH / NaI (0.7 g:1.5 g), and heated at 360 °C for 30 min in a tube furnace to obtain Ti2C with O groups;

[0048] Step 4: The Ti2C with O or OH groups obtained in step 3 is centrifuged four times with deionized water at 3500 rpm, each centrifugation time is 5 min, and clean multilayer Ti2C with O or OH groups can be obtained;

[0049] Step 5: After adding water to the clean multilayer O or OH group Ti2C obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single layer of O or OH group Ti2C.

[0050] Example 2

[0051] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0052] Step 1: 1 g of Ti3AlC2 was added to 20 mL of an etchant containing 18 mL of 9 M HCl, 3 mL of 49 wt.% HF, and 9 mL of deionized water, and then stirred at room temperature for 24 h at a stirring speed of 400 rpm to obtain Ti3C2;

[0053] Step 2: The Ti3C2 obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Ti3C2;

[0054] Step 3: Add 200 mg of multilayer Ti3C2 prepared in step 2 to a mixed salt (3.1 g) of NaOH / NaI (1.4 g:1.7 g), and heat at 260 °C in a tube furnace for 60 min to obtain Ti3C2 with OH groups;

[0055] Alternatively, 200 mg of multilayer Ti3C2 prepared in step 2 was added to a mixed salt (2.2 g) of NaOH / NaI (0.7 g:1.5 g), and heated at 360 °C for 30 min in a tube furnace to obtain Ti3C2 with O groups;

[0056] Step 4: The Ti3C2 with O or OH groups obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, each centrifugation time is 5 minutes, and clean multilayer Ti3C2 with O or OH groups can be obtained;

[0057] Step 5: After adding water to the clean multilayer O or OH group Ti3C2 obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single layer of O or OH group Ti3C2.

[0058] Example 3

[0059] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0060] Step 1: Add 1 g of Mo2Ga2C to 10 mL of 48-50 wt.% HF, stir at 55°C for 100 h at a stirring speed of 400 rpm to obtain Mo2C;

[0061] Step 2: The Mo2C obtained in step 1 is centrifuged repeatedly with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Mo2C;

[0062] Step 3: Add 200 mg of multilayer Mo2C prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g) and heat at 260 °C in a tube furnace for 60 min to obtain Mo2C with OH groups;

[0063] Alternatively, 200 mg of multilayer Mo2C prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g) and heated at 360 °C for 30 min in a tube furnace to obtain Mo2C with O groups;

[0064] Step 4: The Mo2C with O or OH groups obtained in step 3 is centrifuged four times with deionized water at 3500 rpm, each centrifugation time is 5 min, and clean multilayer Mo2C with O or OH groups can be obtained;

[0065] Step 5: After adding water to the clean multilayer O or OH group Mo2C obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single layer of O or OH group Mo2C;

[0066] Example 4

[0067] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0068] Step 1: 1 g of Mo2TiAlC2 was added to 10 mL of 48-50 wt.% HF, and stirred at 55°C for 48 h at a stirring speed of 400 rpm to obtain Mo2TiC2;

[0069] Step 2: The Mo2TiC2 obtained in step 1 is centrifuged repeatedly with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Mo2TiC2;

[0070] Step 3: Add 200 mg of multilayer Mo2TiC2 prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g: 1.7 g), and heat at 260 °C in a tube furnace for 60 min to obtain Mo2TiC2 with OH groups;

[0071] Alternatively, 200 mg of multilayer Mo2TiC2 prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360°C for 30 min in a tube furnace to obtain Mo2TiC2 with O groups;

[0072] Step 4: The Mo2TiC2 with O or OH groups obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, each centrifugation time is 5 minutes, and clean multilayer Mo2TiC2 with O or OH groups can be obtained;

[0073] Step 5: After adding water to the clean multilayer O or OH-grouped Mo2TiC2 obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single-layer O or OH-grouped Mo2TiC2.

[0074] Example 5

[0075] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0076] Step 1: 1 g of Mo2Ti2AlC3 was added to 10 mL of 48-50 wt.% HF, stirred at 55°C for 96 h at a stirring speed of 400 rpm to obtain Mo2Ti2C3;

[0077] Step 2: The Mo2Ti2C3 obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Mo2Ti2C3;

[0078] Step 3: Add 200 mg of multilayer Mo2Ti2C3 prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g), and heat at 260°C for 60 min in a tube furnace to obtain Mo2Ti2C3 with OH groups;

[0079] Alternatively, 200 mg of multilayer Mo2Ti2C3 prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360°C for 30 min in a tube furnace to obtain Mo2Ti2C3 with O groups;

[0080] Step 4: The Mo2Ti2C3 with O or OH groups obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, and each centrifugation time is 5 minutes, so that clean multilayer Mo2Ti2C3 with O or OH groups can be obtained;

[0081] Step 5: After adding water to the clean multi-layer O or OH-grouped Mo2Ti2C3 obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain the single-layer O or OH-grouped Mo2Ti2C3.

[0082] Example 6

[0083] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0084] Step 1: 1 g Nb2AlC was added to 10 ml 48-50 wt.% HF and stirred at room temperature for 90 h at a stirring speed of 400 rpm to obtain Nb2C;

[0085] Step 2: The Nb2C obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Nb2C;

[0086] Step 3: Add 200 mg of multilayer Nb2C prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g), and heat at 260 °C in a tube furnace for 60 min to obtain Nb2C with OH groups;

[0087] Alternatively, 200 mg of multilayer Nb2C prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360°C for 30 min in a tube furnace to obtain Nb2C with O groups;

[0088] Step 4: The O or OH group Nb2C obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, each centrifugation time is 5 minutes, and clean O or OH group multilayer Nb2C can be obtained;

[0089] Step 5: After adding water to the clean multilayer O or OH group Nb2C obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single layer of O or OH group Nb2C.

[0090] Example 7

[0091] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0092] Step 1: 1 g of V2AlC was added to 10 ml of 48-50 wt.% HF, stirred at room temperature for 90 h at a stirring speed of 400 rpm to obtain V2C;

[0093] Step 2: The V2C obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer V2C;

[0094] Step 3: Add 200 mg of multilayer V2C prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g), and heat at 260°C in a tube furnace for 60 min to obtain V2C with OH groups;

[0095] Alternatively, 200 mg of multilayer V2C prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360° C. for 30 min in a tube furnace to obtain V2C with O groups;

[0096] Step 4: The V2C with O or OH groups obtained in step 3 is centrifuged four times with deionized water at 3500 rpm, each centrifugation time is 5 minutes, and clean multilayer V2C with O or OH groups can be obtained;

[0097] Step 5: After adding water to the clean multi-layer O or OH group V2C obtained in step 4 and ultrasonicating for 1 hour, repeatedly centrifuge at a speed of 3500 rpm for 5 minutes, and collect the supernatant to obtain a single layer of O or OH group V2C.

[0098] Example 8

[0099] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0100] Step 1: 1 g Nb4AlC3 was added to 10 mL of 48-50 wt.% HF, stirred at room temperature for 96 h at a stirring speed of 400 rpm to obtain Nb4C3;

[0101] Step 2: The Nb4C3 obtained in step 1 is repeatedly centrifuged with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Nb4C3;

[0102] Step 3: Add 200 mg of multilayer Nb4C3 prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g), and heat at 260°C for 60 min in a tube furnace to obtain Nb4C3 with OH groups;

[0103] Alternatively, 200 mg of multilayer Nb4C3 prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360°C for 30 min in a tube furnace to obtain Nb4C3 with O groups;

[0104] Step 4: The Nb4C3 with O or OH groups obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, each centrifugation time is 5 minutes, and clean multilayer Nb4C3 with O or OH groups can be obtained;

[0105] Step 5: After adding water to the clean multi-layer O or OH group Nb4C3 obtained in step 4 and ultrasonicating for 1 hour, the mixture is repeatedly centrifuged at 3500 rpm for 5 minutes, and the supernatant is collected to obtain a single-layer O or OH group Nb4C3.

[0106] Example 9

[0107] A method for modifying MXene with pure oxygen and hydroxyl surface groups using a NaOH / NaI molten salt system, the specific steps are as follows:

[0108] Step 1: 1 g Ta4AlC3 is selectively etched in 48-50 wt.% HF at room temperature for 72 h to obtain Ta4C3;

[0109] Step 2: The Ta4C3 obtained in step 1 is centrifuged repeatedly with deionized water at a speed of 3500 rpm for 5 minutes each time until the pH value of the supernatant is equal to 6, thereby obtaining multilayer Ta4C3;

[0110] Step 3: Add 200 mg of multilayer Ta4C3 prepared in step 2 to a mixed salt of NaOH / NaI (1.4 g:1.7 g), and heat at 260°C in a tube furnace for 60 min to obtain Ta4C3 with OH groups;

[0111] Alternatively, 200 mg of multilayer Ta4C3 prepared in step 2 was added to a mixed salt of NaOH / NaI (0.7 g:1.5 g), and heated at 360°C for 30 min in a tube furnace to obtain Ta4C3 with O groups;

[0112] Step 4: The Ta4C3 with O or OH groups obtained in step 3 is centrifuged four times with deionized water at a speed of 3500 rpm, each centrifugation time is 5 minutes, and clean multilayer Ta4C3 with O or OH groups can be obtained;

[0113] Step 5: After adding water to the clean multilayer O or OH group Ta4C3 obtained in step 4 and ultrasonicating for 1 hour, repeatedly centrifuge at a speed of 3500 rpm for 5 minutes, and collect the supernatant to obtain a single layer of O or OH group Ta4C3.

[0114] In terms of working principle:

[0115] In the present invention, the surface of MXene prepared by the F-containing solution has a large number of F groups. Through nucleophilic substitution, the NaOH / NaI molten salt system modifies the OH groups of MXene. The reaction formula is expressed as:

[0116] Ti3C2(F)2+2NaOH=Ti3C2(OH)2+2NaF

[0117] Furthermore, MXene with OH groups is converted into O groups at above 350°C, thereby obtaining MXene with pure O groups; MXene with OH groups and MXene with pure O groups can be prepared by controlling the reaction temperature and the ratio of molten salt.

[0118] Taking Example 2 as an example, the beneficial effects of the present invention are described in combination with SEM images, XPS spectra and battery performance graphs. Figure 2 , Figure 3 , Figure 4 As shown in the figure, Ti3C2T x 、Ti3C2O x The XRD patterns and SEM images of Ti3C2(OH)2 show the characteristics of a typical MXene material; after NaOH / NaI treatment, Ti3C2O x The 002 peak of XRD of Ti3C2(OH)2 moves to a smaller angle, which corresponds to an increase in the interlayer spacing of MXene. This is due to the insertion of Na ions in the molten system into the interlayer of MXene. Furthermore, the types and contents of surface groups of MXene were characterized by XPS and Raman techniques. Finally, the battery performance of O-group MXene was tested. Compared with pure MXene, the lithium ion storage capacity of O-group MXene was nearly doubled, and there was almost no capacity loss after 3000 cycles, which proved the good cycle performance of O-group MXene.

[0119] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for modifying MXene surface groups based on a NaOH / NaI molten salt system, characterized in that: The following steps are involved: Step 1. Obtain MXene by etching the MAX phase; Step 2. The MXene obtained in step 1 is centrifuged 5 to 6 times with deionized water until the pH value of the supernatant is equal to 6 to 7, and then dried at 60 to 80° C. under vacuum conditions to obtain MXene powder; Step 3. Add the MXene powder obtained in step 2 to a NaOH / NaI mixed salt, and heat it at 220-260° C. for 30-60 min to obtain a multilayer MXene modified with an OH group; wherein the mass ratio of NaOH to NaI in the NaOH / NaI mixed salt is 1.7:1.4, and the mass ratio of MXene powder to NaOH / NaI mixed salt is 0.2:3.1; Step 4. Repeatedly centrifuge the OH group-modified MXene obtained in step 3 using deionized water to obtain a cleaned OH group-modified multilayer MXene; Step 5. Add deionized water to the OH group-modified multilayer MXene obtained in step 4 for ultrasonic treatment, and then perform repeated centrifugation to collect the supernatant to obtain the OH group-modified single-layer MXene.

2. A method for modifying MXene surface groups based on a NaOH / NaI molten salt system, characterized in that: The following steps are involved: Step 1. Obtain MXene by etching the MAX phase; Step 2. The MXene obtained in step 1 is centrifuged 5 to 6 times with deionized water until the pH value of the supernatant is equal to 6 to 7, and then dried at 60 to 80° C. under vacuum conditions to obtain MXene powder; Step 3. Add the MXene powder obtained in step 2 to a NaOH / NaI mixed salt, and heat it at 360°C to 380°C for 30 to 60 minutes to obtain an O-group-modified multilayer MXene; wherein the mass ratio of NaOH to NaI in the NaOH / NaI mixed salt is 0.7:1.5, and the mass ratio of MXene powder to NaOH / NaI mixed salt is 0.2:2.2; Step 4. Repeatedly centrifuge the OH group-modified MXene obtained in step 3 using deionized water to obtain a cleaned O group-modified multilayer MXene; Step 5. Add deionized water to the O-group-modified multilayer MXene obtained in step 4 for ultrasonic treatment, and then perform repeated centrifugation to collect the supernatant to obtain the O-group-modified single-layer MXene.

3. The MXene surface group modification method based on the NaOH / NaI molten salt system according to claim 1 or 2, characterized in that: In step 1, the MXene includes but is not limited to Ti2C, Ti3C2, Mo2C, Mo2TiC2, Mo2Ti2C3, V2C, Nb4C3 or Ta4C3.

4. The MXene surface group modification method based on the NaOH / NaI molten salt system according to claim 1 or 2, characterized in that: The specific process of step 1 is: To synthesize Ti2C, 1 g of Ti2AlC was added to 10 mL of 10 wt.% HF and stirred at room temperature for 8 h. To synthesize Ti3C2, 1 g of Ti3AlC2 was added to 20 mL of an etchant containing 12 mL of 9 M HCl, 2 mL of 49 wt.% HF, and 6 mL of deionized water and stirred at room temperature for 24 h. To synthesize Mo2C, 1 g of Mo2Ga2C was added to 10 mL of 48-50 wt.% HF and stirred at 55 °C for 100 h. To synthesize Mo2TiC2, add 1 g of Mo2TiAlC2 to 10 mL of 48-50 wt.% HF and stir at 55 °C for 48 h; To synthesize Mo2Ti2C3, 1 g of Mo2Ti2AlC3 was added to 10 mL of 48-50 wt.% HF and stirred at 55 °C for 96 h. To synthesize Nb2C, 1 g of Nb2AlC was added to 10 ml of 48-50 wt.% HF and stirred at room temperature for 90 h. To synthesize V2C, add 1 g of V2AlC to 10 ml of 48-50 wt.% HF and stir at room temperature for 90 h; To synthesize Nb4C3, 1 g of Nb4AlC3 was added to 10 mL of 48-50 wt.% HF and stirred at room temperature for 96 h. To synthesize Ta4C3, add 1 g of Ta4AlC3 to 10 mL of 48-50 wt.% HF and stir at room temperature for 72 h; The stirring speed of the above synthesis was set to 400 rpm.

5. The MXene surface group modification method based on the NaOH / NaI molten salt system according to claim 1 or 2, characterized in that: In step 2, the centrifugal speed is 3500-5000 rpm, and the single centrifugation time is 5-10 min.

6. The MXene surface group modification method based on the NaOH / NaI molten salt system according to claim 1 or 2, characterized in that: In step 4, the centrifugal speed is 3500-5000 rpm, the single centrifugal time is 5-10 min, and the number of centrifugal operations is 5-6 times.

7. The MXene surface group modification method based on the NaOH / NaI molten salt system according to claim 1 or 2, characterized in that: In step 5, the ultrasonic treatment time is 0.5h to 1h; the centrifugal speed is 3500 to 5000rpm, the single centrifugal time is 5 to 10min, and the number of centrifugal treatments is 3 to 4 times.

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