Method for preparing two-dimensional MXene material in seconds by high-energy shock fluorinated salt etching

Abstract

The application belongs to the technical field of two-dimensional materials, and relates to a method for preparing two-dimensional MXene materials through high-energy electric shock fluorinated salt etching in seconds, which comprises the following steps: 1) after grinding and mixing of a parent phase MAX powder and a fluorinated salt, the mixture is loaded into a quartz tube of a high-energy electric shock device, graphite electrodes are inserted into two ends of the quartz tube, and the material is compacted to be in close contact with the electrodes; 2) after completion of capacitor charging of the high-energy electric shock device, a discharge button is opened, high-energy electric shock is performed, the reaction is completed after flash phenomenon occurs, fluorinated salt is supplemented, and electric shock is repeated for 2-3 times; 3) the product after electric shock is ground and washed with acid, and after washing with deionized water until neutral, standing or centrifugal layering is performed, and the MXene two-dimensional material is obtained from the upper layer. Through high-energy electric shock, the reaction is completed in an instant, the comprehensive energy consumption is lower, and the etching efficiency is faster, and due to fast reaction time, high-temperature oxidation of the MXene can be effectively inhibited, and the application prospect is better.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional materials technology and relates to a method for preparing two-dimensional MXene materials in seconds by high-energy electrical shock etching of fluoride salts. Background Technology

[0002] MXene materials are obtained by selectively etching the A-layer elements of the parent MAX phase (where M represents transition metals such as titanium, niobium, and vanadium, A represents aluminum or silicon, and X represents carbon or nitrogen), followed by ion intercalation and stripping processes. MXene materials possess the high conductivity of transition metal carbides, and because their structure consists of transition metal atoms and carbon and nitrogen atoms arranged in a layered manner, they also have the advantages of diverse composition and tunable structure. This has led to the widespread application of MXene in various fields.

[0003] The most common type of MXene material (Ti3C2T) x Taking Ti3C2 as an example, the common method for obtaining it is through top-down etching of its parent material (Ti3AlC2). Hydrofluoric acid etching is the earliest method used to prepare Ti3C2. x The method for MXene materials has been used to this day, but hydrofluoric acid is highly corrosive, poses a significant environmental hazard, and can only produce multilayer MXene, making this method unsuitable for large-scale production. Subsequently, a method using fluoride salts to generate hydrogen fluoride in situ for etching MAX phases was introduced. Although the interlayer spacing can be expanded by using cation intercalation during the etching process, the etching efficiency is low, and there is still no good solution for many difficult-to-etch MAX phases. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for preparing two-dimensional MXene materials in seconds using high-energy electro-fluoride etching. Through high-energy electro-irradiation, free electrons break the weaker MA bonds in the MAX structure. Simultaneously, due to the internal resistance of the material, Joule heating is generated internally. The fluoride salt exists in a molten state at high temperature and corrodes the A atoms, thereby combining them into fluorides with lower melting points. This allows the A atoms to escape at high temperature and the MAX phase to transform into the MXene phase.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing two-dimensional MXene materials in seconds using high-energy electrical shock etching of fluoride salts, comprising the following steps:

[0007] 1) After grinding and mixing the parent phase MAX powder and fluoride salt, the mixture is loaded into the quartz tube of the high-energy electric shock device. Graphite electrodes are inserted into both ends of the quartz tube, and the material is compacted to make it in close contact with the electrodes.

[0008] 2) After the capacitor of the high-energy electric shock device is fully charged, turn on the discharge button to perform a high-energy electric shock. After a flash phenomenon occurs, the reaction ends. After replenishing the fluoride salt, repeat the electric shock 1 to 3 times.

[0009] 3) The product after electrolysis is ground and washed with acid. After washing with deionized water until neutral, it is allowed to stand or centrifuged to separate into layers. The upper layer is MXene two-dimensional material.

[0010] The MAX powder in the technical solution of this invention is selected from titanium aluminum carbide, vanadium aluminum carbide, niobium aluminum carbide, titanium silicon carbide or titanium tin carbide.

[0011] The fluoride salts described in this invention are selected from lithium fluoride, sodium fluoride, ammonium fluoride, or ammonium hydrofluoride. Under high-energy electric shock, a temperature of 3000K is generated within 0.1 seconds. Lithium fluoride has a melting point of 845℃, sodium fluoride 993℃, ammonium fluoride 98℃, and ammonium hydrofluoride 124℃; all of these can be melted instantly upon the generation of Joule heat. Al atoms have a boiling point of 2327℃, while lithium fluoride has a boiling point of 1537℃, making it easier for lithium fluoride to vaporize and escape. The free fluoride ions combine with the less vaporizable Al atoms to form new fluorides.

[0012] In the technical solution of this invention, the mass ratio of the parent phase MAX powder to the total amount of fluoride salt is 1:1 to 3.

[0013] In the technical solution of this invention, the electric shock energy corresponding to each 100mg of raw material is 50-800J.

[0014] It is worth noting that the high-energy electric shock device used in this invention is a device for regenerating lithium-ion battery electrode materials disclosed in application publication number CN 113258159 A. The dimensions of the quartz tube are adjusted as follows: diameter 4mm, wall thickness 2mm, and length 60mm. Through experiments, this device can be used to perform high-energy electric shock on the parent phase MAX material to obtain MXene two-dimensional material. The energy required for this reaction is calculated based on the energy required for the mass of reactants during high-energy electric shock, using the formula... The charging voltage and the number of capacitors can be set. The high-energy electric shock device can select n capacitors to adjust the reaction voltage in series or parallel. When the amount of reactant increases, a larger reactor can be selected for the reaction. Since high temperature can easily cause the MAX phase to decompose and change, in order to prevent the reactor from breaking due to instantaneous high temperature and the occurrence of uncontrollable side reactions, the energy should be controlled below 800J.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The environment in which instantaneous high-energy voltage alters chemical bonds

[0017] Whether using chemical etching or molten salt etching, the goal is to break the MA chemical bonds in the MAX phase, thereby achieving the subsequent separation of two-dimensional sheets. However, a high-voltage DC electric field can damage or even break the chemical bonds in the material. The destruction of MA metallic bonds can be controlled by adjusting the appropriate energy output.

[0018] 2. Rapid escape of A atoms assisted by molten fluorine salts

[0019] Choosing a fluoride salt with a low cation melting point allows the fluoride salt to melt at high temperatures, causing the cation to vaporize and volatilize. Meanwhile, the fluoride ions can combine with the atom (A) to form an ionic compound with a lower melting point than the A atom. Under Joule heating, substances with lower vaporization points are more likely to vaporize and escape, thus enabling the faster escape of the A atom in the MAX structure.

[0020] 3. Instantaneous high temperatures can trigger microscopic explosive reactions between layers.

[0021] In the instantaneous (second-level) reaction process, due to the drastic temperature changes, the cations and A atoms of the fluoride salt are more easily vaporized, and the expanding gas can further increase the interlayer distance. At the same time, molten fluorine can penetrate deeper into the interlayer, further corroding the interior of the MAX layered structure and providing more MXene yield.

[0022] 4. Instantaneous high-energy electrical shocks result in faster etching efficiency. Because the reaction is completed instantaneously and can be rapidly repeated, a large yield of MXene material can be obtained through repeated electrical shocks. Furthermore, the energy required for the shock is stored in a capacitor, requiring only an instantaneous high-energy current. Compared to currently common etching methods, this method has lower overall energy consumption and faster etching efficiency.

[0023] 5. This invention can match different MAX materials by adjusting the input energy. At the same time, the thorough mixing of fluoride salts and MAX phase materials can reduce the overall heat of chemical bond breaking by utilizing the corrosive effect of fluoride ions, effectively inhibiting the decomposition of MAX crystals. In addition, due to the fast reaction time, it can effectively inhibit the high-temperature oxidation of MXene, and has better application prospects. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the material manufacturing process of the present invention.

[0025] Figure 2 The images show SEM images of MAX after acid washing in Comparative Example 1 and MXene materials obtained by electrolysis once in Example 1.

[0026] Figure 3 These are TEM images and elemental distribution spectra of the MXene material obtained by two electric shocks in Example 2.

[0027] Figure 4 This is a TEM image of the material obtained in Example 3.

[0028] Figure 5 The X-ray diffraction patterns are of MAX after acid washing in Comparative Example 1 and MXene materials obtained by electrolysis in Examples 1-3.

[0029] Figure 6 This is an XPS image of the MXene material obtained by two electrical shocks in Example 2.

[0030] Figure 7 The MXene materials obtained by acid washing in Comparative Example 1 and by two electrolytic discharges in Example 2 were used as anode materials for lithium-ion batteries at 0.1 A g. -1 Electrochemical performance under cycling at current density.

[0031] Figure 8 This is the cyclic voltammogram (CV) of the lithium-ion battery anode prepared from the MXene material obtained by two electric shocks in Example 2.

[0032] Figure 9 This is the electrochemical impedance spectroscopy (EIS) of the lithium-ion battery anode prepared from the MXene material obtained by two electro-electrolysis experiments in Example 2.

[0033] Figure 10 The reaction process is shown in Example 4.

[0034] Figure 11 This is a SEM image of the MXene material obtained in Example 5.

[0035] Figure 12 This is a SEM image of the MXene material obtained in Example 6.

[0036] Figure 13 This is a photograph showing the volume expansion of the MXene material obtained in Example 6.

[0037] Figure 14 This is a SEM image of the MXene material obtained in Example 7.

[0038] Figure 15 This is a SEM image of the MXene material obtained in Example 8.

[0039] Figure 16 This is a SEM image of the MXene material obtained in Example 9.

[0040] Figure 17 This is the time required for the three MAX materials in Example 10 to achieve complete etching. Detailed Implementation

[0041] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0042] Comparative Example 1: Pickling Max

[0043] Lithium fluoride (100 mg) was added to dilute hydrochloric acid (20 ml, 9 mol / L) and mixed thoroughly in a plastic container. Aluminum carbide (Ti3AlC2) (100 mg) was then added and stirred at room temperature. The resulting solution was centrifuged and washed repeatedly until it approached neutral. The precipitate was then dispersed in an aqueous solution and ultrasonically dispersed for 30 min. Finally, it was freeze-dried to obtain the acid-washed MAX powder.

[0044] Example 1

[0045] According to such Figure 1 The diagram shows the material preparation process of this invention. 50 mg of aluminum titanate carbide and 50 mg of lithium fluoride are ground and mixed, then placed into a quartz tube. Conductive graphite rods are inserted into both ends to seal the tube, and the material is compacted using external force to ensure close contact with the electrodes. The quartz tube is placed in a reactor, and both ends are fixed with grooved copper rods. The input voltage is adjusted to 150V, and two capacitors (Hitachi HCGHA series 400V 5600UF 5600MFD 400VDC capacitors) are activated, with an electric shock energy of 126J. After the capacitors are fully charged, the discharge button is turned on, and an electric shock is performed once. A flash phenomenon occurs during the reaction, along with a lithium ion flame test. After the reaction is complete, the sample is removed and placed in dilute hydrochloric acid (20 ml, 1 mol / L) for ultrasonic dispersion and washing. It is then washed with deionized water until neutral. After standing and separating, the upper layer is MXene material (10 mg), and the lower layer is unetched MAX and multiple layers of MXene clay, existing in precipitate form.

[0046] Figure 2 The images show SEM images of MAX after acid washing in Comparative Example 1 and MXene materials obtained after one electrostatic discharge in Example 1. As can be seen from the images, MAX after acid washing still exhibits a layered structure. Figure 2 -a) indicates that no etching occurred; however, after electrical discharge, edge-etched MXene material can be obtained. Figure 2 -b).

[0047] Example 2

[0048] This embodiment is basically the same as Embodiment 1, except that: the voltage is kept the same at 150V, two capacitors are used, the electric shock energy is 126J, 50mg of fluoride salt is added after the first electric shock, and then another electric shock is performed. The upper layer yields MXene material (16mg).

[0049] Example 3

[0050] This embodiment is basically the same as Embodiment 1, except that: the voltage is kept the same at 150V, 5 capacitors are used, the electric shock energy is 315J, 50mg of fluoride salt is added after the first electric shock, followed by another electric shock, another 50mg of fluoride salt is added, and then another electric shock is performed. MXene material (12mg) is obtained in the upper layer.

[0051] Figure 3 These are TEM images and elemental distribution spectra of the MXene material obtained by two electrical discharges in Example 2. It can be seen that the MXene material obtained by electrical discharge has relatively complete layers.

[0052] Figure 4 This is a TEM image of the material obtained in Example 3. It can be seen that the obtained material exhibits agglomeration, and that graphene is partially loaded with titanium carbide.

[0053] Figure 5 The images show the X-ray diffraction patterns of MAX after acid washing in Comparative Example 1 and the MXene materials obtained by electro-electrolysis in Examples 1-3. It can be seen that MAX did not undergo etching behavior after acid washing; while after electro-electrolysis, obvious MXene (002) characteristic peaks appeared, and the proportion of titanium carbide increased with increasing electro-electrolysis energy.

[0054] Figure 6 The images show the XPS spectra of the MXene material obtained by two electrochemical discharges in Example 2, where (a) Ti 2p, (b) Al 2p, (c) C 1s, (d) O 1s, (e) F 1s, and (f) Cl 2p correspond to the fine elemental spectra. It can be seen that the MXene material obtained by electrochemical discharge possesses abundant fluorine-containing functional groups. Fluorine doping can improve the coulombic efficiency of MXene material when used as a negative electrode material, helping it to form a stable solid electrolyte interphase (SEI) film more quickly.

[0055] Take 50 mg each of MAX material obtained by acid washing in Comparative Example 1 and MXene material obtained by two electrolysis treatments in Example 2, and mix them with binder polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) in a ratio of 8:1:1. Prepare a slurry using N-methylpyrrolidone (NMP) as solvent, stir evenly, coat it onto copper foil, and place it in an oven at 80°C for 10 hours. After drying, cut it into circular active material electrodes with a diameter of 12 mm. Assemble a CR2032 button-type lithium-ion half-cell in an argon-filled glove box in the following order: negative electrode shell, active material electrode, separator, lithium sheet, gasket, and spring sheet, using lithium hexafluorophosphate (LiPF6) as electrolyte.

[0056] Figure 7The MXene materials obtained by acid washing in Comparative Example 1 and by two electrolytic discharges in Example 2 were used as anode materials for lithium-ion batteries at 0.1 A g. -1 Electrochemical performance under cycling at current density. It can be seen that the MXene material obtained by two electrochemical shocks has a higher initial capacity compared to the acid-washed MAX, and this capacity gradually increases with cycling time.

[0057] Figure 8 This is the cyclic voltammogram (CV) of the lithium-ion battery anode prepared from the MXene material obtained by two electro-electrolysis experiments in Example 2. It can be seen that the MXene material obtained by electro-electrolysis exhibits good pseudocapacitive storage behavior and has the ability to rapidly store charge.

[0058] Figure 9 This is the electrochemical impedance spectroscopy (EIS) spectrum of the lithium-ion battery anode prepared from the MXene material obtained by two electro-electrolysis experiments in Example 2. It can be seen that the MXene material obtained by electro-electrolysis exhibits good kinetics and low interfacial resistance.

[0059] Example 4

[0060] This embodiment is basically the same as embodiment 3, except that the charging voltage is 250V, the number of activated capacitors is 5, and the energy of the high-energy electric shock is 875J.

[0061] Figure 10 The reaction process is shown in Example 4. It can be seen that at this electric shock energy, a severe explosion occurs during the electric shock process; that is, the gas generated during the electric shock escapes, leading to an explosion. Therefore, the energy should be controlled below 800J.

[0062] Example 5

[0063] This embodiment is basically the same as Embodiment 2, except that the lithium fluoride material is replaced with ammonium fluoride (NH4F). The upper layer yields MXene material (15 mg).

[0064] Figure 11 The image shows a SEM image of the MXene material obtained in Example 5. It can be seen that even after changing the fluorine source material, MXene material with etched edges can still be obtained.

[0065] Example 6

[0066] This embodiment is basically the same as Embodiment 2, except that the lithium fluoride material is replaced with ammonium fluoride (NH4HF2). The upper layer yields MXene material (22 mg).

[0067] Figure 12This is a SEM image of the MXene material obtained in Example 6. It can be seen that even after changing the fluorine source material, MXene material with etched edges can still be obtained. (Comparison...) Figure 11 and Figure 12 It was found that, compared to lithium fluoride, MXene materials obtained by electrolysis using ammonium fluoride as the fluorine source have a larger interlayer spacing.

[0068] Figure 13 The image shows the volume expansion of the MXene material obtained in Example 6. This expansion is due to the presence of ammonium ions, which cause ammonia gas to impact the interlayer of the material during the electrostatic discharge.

[0069] Example 7

[0070] This embodiment is basically the same as Embodiment 2, except that the aluminum titanate carbide (Ti3AlC2) material is replaced with vanadium aluminum carbide (V4AlC3). The upper layer yields MXene material (9 mg).

[0071] Figure 14 This is a SEM image of the MXene material obtained in Example 7. It can be seen that even after replacing the parent phase MAX material, MXene material with etched edges can still be obtained.

[0072] Example 8

[0073] This embodiment is basically the same as Embodiment 2, except that the aluminum titanate carbide (Ti3AlC2) material is replaced with niobium aluminum carbide (Nb4AlC3). The upper layer yields MXene material (10 mg).

[0074] Figure 15 This is a SEM image of the MXene material obtained in Example 8. It can be seen that even after replacing the parent phase MAX material, MXene material with etched edges can still be obtained.

[0075] Example 9

[0076] This embodiment is basically the same as Embodiment 2, except that the aluminum titanate carbide (Ti3AlC2) material is replaced with aluminum titanate carbide nitrogen (Ti3AlCN). The upper layer yields MXene material (8 mg).

[0077] Figure 16 This is a SEM image of the MXene material obtained in Example 9. It can be seen that even after replacing the parent phase MAX material, MXene material with etched edges can still be obtained.

[0078] Example 10

[0079] Conventional aluminum carbide, aluminum carbide without fluoride salt electrolysis, and the lower precipitate after layering in Example 2 (aluminum carbide with fluoride salt electrolysis) were etched using HCl, HCl+LiF, and CuCl2 molten salt as etchants, respectively.

[0080] Figure 17 This refers to the time required for complete etching of the three MAX materials in Example 10. It can be observed that, compared to conventional aluminum carbide, both aluminum carbide without fluoride salt electrolysis and aluminum carbide with fluoride salt electrolysis exhibit rapid etching efficiency, proving that aluminum carbide with the remaining fluoride salt electrolysis can also achieve complete etching and shorten the etching time. Due to the presence of fluorine-containing functional groups, when using HCl as the etchant alone, aluminum carbide with fluoride salt electrolysis requires 15 hours to obtain a fully etched MXene material; when using HCl+LiF as the etchant, aluminum carbide with fluoride salt electrolysis requires only 10 hours to obtain a fully etched MXene material; and when using the molten salt method for etching, a fully etched MXene material is obtained in only 2 hours.

[0081] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for preparing two-dimensional MXene materials in seconds using high-energy electro-fluoride salt etching, characterized in that, Includes the following steps: 1) After grinding and mixing the parent phase MAX powder and fluoride salt, the mixture is loaded into the quartz tube of the high-energy electric shock device. Graphite electrodes are inserted into both ends of the quartz tube, and the material is compacted to make it in close contact with the electrodes. 2) After the capacitor of the high-energy electric shock device is fully charged, turn on the discharge button to perform a high-energy electric shock. The reaction ends after a flash phenomenon occurs. After replenishing the fluoride salt, repeat the electric shock 1 to 3 times. The electric shock energy corresponding to each 100 mg of raw material is 50 to 800 J. 3) The product after electrolysis is ground and washed with acid. After washing with deionized water until neutral, it is allowed to stand or centrifuged to separate into layers. The upper layer is MXene two-dimensional material.

2. The method according to claim 1, characterized in that, The parent phase MAX powder is selected from titanium aluminum carbide, vanadium aluminum carbide, niobium aluminum carbide, titanium silicon carbide or titanium tin carbide.

3. The method according to claim 1, characterized in that, The fluoride salt is selected from lithium fluoride, sodium fluoride, ammonium fluoride or ammonium hydrofluoride.

4. The method according to claim 1, characterized in that, The mass ratio of the parent phase MAX powder to the total amount of fluoride salt is 1:1~3.

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