CN110534741B - Rapid preparation method and application of few-layer MXenes - Google Patents

Abstract

The invention discloses a rapid preparation method and application of a few-layer MXenes, wherein in the preparation method, a few-layer MXenes material is prepared by stripping a plurality of layers of MXenes liquid phase to obtain a few-layer MXenes solution with good dispersibility; by introducing electrolyte solution, destroying the electrostatic balance of MXenes solution with the aid of cation-assisted electrostatic coagulation (such as NH)⁴⁺) Standing or centrifuging at low speed or filtering to obtain sol, precipitate or filter cake as small-layer MXenes material; and then, the macro preparation of the MXenes powder with few layers can be realized through freeze drying and subsequent annealing treatment. The preparation method has the advantages that the technological process is simple, the prepared few-layer MXenes has the advantages of thin layer number, large sheet diameter, good dispersibility, no agglomeration and caking phenomenon, and good electrochemical performance, and is suitable for large-scale development and application of lithium ion batteries or sodium ion batteries.

Description

Rapid preparation method and application of few-layer MXenes

Technical Field

The invention relates to the technical field of nano materials, in particular to a rapid preparation method and application of few-layer MXenes.

Background

MXenes materials are generally prepared by corroding 'A' in MAX phase materials, wherein metal bonds, ionic bonds and covalent bonds coexist in MAX phase crystals, M is a transition group metal element, A is mainly a third main group element and a fourth main group element, X is carbon and/or nitrogen, M and X are mainly connected in the form of covalent bonds and ionic bonds, and the bonding strength between M and X is very high; the M and A elements and A elements are connected by metal bonds, so the chemical bonds are relatively weak. Therefore, only an appropriate method is selectedSelectively etching A layer of atoms in MAX phase to obtain MXenes material with two-dimensional morphology, directly etching MAX to obtain multiple layers of MXenes, and stripping to obtain MXenes with less layers (about 10 layers or less, no more than 20 layers) with chemical formula of M_n+1X_nT_xWherein M is a metal element such as Sc, Ti, V, Cr, Zr, Nb, Mo, Hf or Ta, X is C, N or CN, n is generally 1 to 3, and T is_xRefers to some uncertain groups (such as O, OH and F) adsorbed on the surface, and T can be omitted_xDirectly using M_n+1X_nIs represented by, i.e. M_n+1X_nT_xAnd M_n+1X_nThe representation method of (2) is alternative. The rich chemical element composition and the unique layered structure endow MXenes materials with a plurality of unexpected properties, and Mxenes have excellent conductivity (10 conductivity)⁵S/m), the conductivity reaches partial metal level; the mechanical property is good (better tensile strength and flexibility), the flexibility is easy to form a film and the film is directly used, and the forming process of subsequent preparation is avoided; the interlayer distance is large and flexible and adjustable, the MXenes interlayer distance obtained by etching and ultrasonic treatment is about 1nm, Van der Waals force exists between layers, the interlayer distance is flexible and adjustable without damaging the layered structure, the surface functional groups of the MXenes endow the MXenes with hydrophilicity and surface structure adjustability, the conductivity of the MXenes is not obviously influenced, the properties and the structure of the MXenes are reasonably utilized, and energy storage materials and devices with excellent performance can be prepared.

Chinese patent with the publication number of CN106495210B discloses a method for preparing MXenes colloid by mixing H₂SO₄Solution with NH₄HF₂And (2) mixing, namely etching the MAX raw material by using hydrofluoric acid generated in the mixing process, wherein the generated ammonium sulfate has heat absorptivity, so that the intensity of the reaction is reduced, and the danger of directly using HF acid is avoided, but the prepared MXenes material has thicker layer, the bonding layer spacing is about 1nm, the layer number is estimated to be about 5000 layers, and the advantages of the MXenes two-dimensional material cannot be fully exerted. The Chinese patent with application number of 201810359588.8 discloses a preparation method of three-dimensional MXenes, which is characterized in that MXenes are dispersed in a solvent to obtain super-high-performance MXenesThe multiple layers of MXenes are peeled into a few layers by sound dispersion, MXenes powder is prepared in a freeze drying mode subsequently, and due to the fact that a large amount of water is contained in the solution, the freeze drying process is slow (about 2 days are needed for freeze drying 5ml of water in a centrifugal tube by a conventional freeze dryer), and time and labor are wasted in the whole preparation process.

In addition, many documents and patents are reported about MXenes-based composite materials, and the conductive advantage of MXenes materials is exerted, and MXenes is prevented from agglomerating by introducing other material systems, for example, chinese patent application No. 201810939968.9 discloses a preparation method of core-shell structure nano silicon-MXenes composite negative electrode materials, chinese patent application No. 201810088813.9 discloses a preparation method of MXenes-Co composite materials, and the preparation of composite materials widens the application of MXenes, but the introduction of other materials limits the exertion of unique properties of MXenes to some extent, such as Ti₃C₂T_xThe interlayer spacing of MXenes is about 1nm, which is far larger than that of graphene and C₃N₄，MoS₂The interlayer spacing of other materials, the introduction of graphene with small interlayer spacing and the like can prevent the agglomeration of MXenes, but the introduction of graphene with small interlayer spacing is not a good choice for MXenes, and how to rapidly prepare small-layer MXenes materials in a large batch (the number of layers is about 10 and below, and is not more than 20) is still a more critical challenge problem so far.

Disclosure of Invention

In order to solve the problems, the conventional method can produce MXenes with too many layers, or when the number of the layers is reduced, the collection of MXenes has certain difficulties: (1) during suction filtration, the film forming densification is easy, so that the suction filtration cannot be continuously carried out; (2) due to the fact that the density is light, and the electrostatic repulsion effect between electronegative MXenes sheet layers is added, the MXenes sheet is very stable in aqueous solution and cannot be collected through conventional centrifugation, even if the MXenes sheet is centrifuged at a high speed, few layers of MXenes materials cannot be centrifuged, and the MXenes sheet layers in a powder state with good dispersibility cannot be obtained due to the fact that serious agglomeration is prone to occurring in the conventional suction filtration and high-speed centrifugation collection mode, and the advantages of the two-dimensional layered MXenes materials cannot be played. The invention provides rapid preparation and application of a few-layer MXenes, and the method provided by the invention can effectively solve the agglomeration problem of MXenes and rapidly prepare the few-layer MXenes material in a large batch.

In order to achieve the purpose, the invention provides the following technical scheme:

a rapid preparation method of few-layer MXenes comprises the following steps:

(1) taking MAX raw materials, and treating in etching solution to obtain a multilayer MXenes material;

(2) treating the MXenes material obtained in the step (1) in organic molecules or a surfactant;

(3) centrifuging the MXenes material obtained in the step (2), washing and precipitating, stripping, removing the precipitate, and collecting supernatant to obtain a small-layer MXenes solution;

(4) adding an electrolyte solution containing ammonium ions into the MXenes solution obtained in the step (3), performing electrostatic coagulation, standing or low-speed centrifugation or suction filtration, and obtaining sol, precipitate or filter cake which is the low-layer MXenes material;

(5) and (4) freeze-drying and annealing the material obtained in the step (4) to obtain MXenes material powder with few layers.

Further, the MXenes material in step (1) is Ti₄C₃、Ti₄N₃、Ti₃C₂、Ti₂C、Mo₂C、Hf₃C₂、V₃C₂、V₂C、V₂N、Nb₄C₃、Nb₃C₂、Nb₂C、Cr₃C₂、Ta₂C、Ta₄C₃、(Ti_0.5Nb_0.5) C, one or more combinations thereof.

Further, the etching solution in the step (1) is HF, LiF and HCl, NaF and H₂SO₄And one or more of other mixed liquid containing F salt and acid.

Further, the organic molecule in step (2) is one or more of tetramethylammonium hydroxide, tetrabutylammonium hydroxide, hydrazine hydrate, N-methylpyrrolidone, dimethyl sulfoxide, N-methylformamide and ethanol.

Further, the surfactant in step (2) is one or more of dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, octadecyl trimethyl ammonium chloride, polyvinyl pyrrolidone, and F127.

Further, the stripping treatment in the step (3) is one or a combination of mechanical shaking, ultrasound and cell crushing, and the solvent adopted by the MXenes solution is one or a combination of water, ethanol and acetone.

Further, the electrolyte solution in step (4) is a salt containing ammonium ions, and is one or more of ammonium bicarbonate, ammonia water, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium chloride and ammonium fluoride.

Further, the annealing temperature in the step (5) is 70-700 ℃.

The few-layer MXenes prepared by the method can be used as a negative electrode material of a lithium ion battery or a sodium ion battery.

In the technical scheme, the low-speed centrifugation generally means that the rotating speed does not exceed 6000 r/min; particularly, in the step (4), after the treatment by the method of the present invention, the sample can be centrifuged in the step, and the situation that the low speed centrifugation cannot be performed in the conventional method does not occur, but the rotation speed is not too high, and when the rotation speed is higher than 10000r/min, the agglomeration phenomenon occurs, and the few-layer MXenes powder with good dispersibility cannot be obtained, which is specifically referred to embodiment example 2 and fig. 12. The suction filtration is a common suction filtration mode, the introduced ammonium ions and MXenes lamella are porous in the electrostatic coagulation process, the densification phenomenon of MXenes in the conventional suction filtration method is avoided (the suction filtration process cannot be carried out due to densification), and the suction filtration process can be continuously carried out after the MXenes are porous.

The invention has the beneficial effects that:

by etching and stripping, the aqueous solution material of the MXenes in a small layer is electronegative, i.e. the MXenes material adsorbs negatively charged groups (OH) on the inner and outer surfaces^-,F^-Etc.) which is a property of the MXenes material itself. Compared with the traditional method for preparing MXenes materials, the method provided by the invention has the advantages that the cations (such as NH) in the electrolyte solution are led into the electrolyte solution skillfully by introducing the electrolyte solution such as ammonium salt⁴⁺) The MXenes solution is adsorbed on the surface of the MXenes material through electrostatic adsorption, the electrostatic balance of the MXenes solution is effectively destroyed, electrostatic coagulation occurs, and after standing for a period of time or low-speed centrifugation or suction filtration, small-volume MXenes sol, or MXenes precipitation after low-speed centrifugation, or filter cake after suction filtration is freeze-dried and annealed, namely ammonium salt can be converted into ammonia gas to be volatilized, and then small-layer MXenes material powder is obtained. The whole experimental process has the advantages of mild reaction, safety, low cost, short time, simple equipment and the like, greatly reduces the solution needing freeze drying in the freeze drying process due to the electrostatic coagulation effect, greatly shortens the experimental process, and has good application prospect in industrial mass production. The few-layer Mxenes sheet layer prepared by the invention has a good three-dimensional reticular sheet layer structure, when the small-layer Mxenes sheet layer is observed by a scanning electron microscope, the small-layer Mxenes sheet layer is of a sheet layer structure from 300 times to 70000 times in magnification, and is free of agglomeration, the thickness of the layer is below 10nm (the bonding layer interval is 1nm, and the estimated layer number is about 10 layers) through preliminary judgment, and atomic force microscope tests show that the thickness of some sheet layer MXenes materials is about 2-3nm (the layer number is about 2-3 layers), which fully indicates that cation assistance (such as NH (ammonia) is adopted for assistance⁴⁺) The feasibility of massively preparing the small-layer MXenes material by utilizing the electrostatic coagulation effect is utilized, and the small-layer MXenes material prepared by the method has wide application prospect in the energy storage fields of lithium batteries, electrochemical super capacitors and the like.

Drawings

FIG. 1 is Ti in example 1₃AlC₂Raw material and etched multilayer Ti₃C₂T_xXRD pattern of MXenes;

FIG. 2 shows Ti in example 1₃AlC₂Raw material and etched multilayer Ti₃C₂T_xA Raman spectrum of MXenes;

FIG. 3 is a multilayer Ti prepared in example 1₃C₂T_xMXenes scanning electron microscopeA photo;

FIG. 4 shows a few Ti layers in example 2₃C₂T_xAdding MXenes solution into ammonium bicarbonate solution, stirring uniformly, taking out 20ml, placing in a small glass bottle, and taking a picture of a real object with dynamic change of solution layering phenomenon in the static process;

FIG. 5 shows a few Ti layers in example 2₃C₂T_xAdding the MXenes solution into the ammonium bicarbonate solution, uniformly stirring, and standing the solution for 30 minutes to obtain a picture of a real object;

FIG. 6 shows a few Ti layers in example 2₃C₂T_xPhotograph of the MXenes solution after freeze-drying;

FIG. 7 shows a few Ti layers in example 2₃C₂T_xLow magnification scanning electron micrographs of MXenes powder;

FIG. 8 shows a few Ti layers in example 2₃C₂T_xHigh-magnification scanning electron microscope photographs of MXenes powder;

FIG. 9 shows a few Ti layers in example 2₃C₂T_xMXenes powder atomic force microscope photograph and thickness analysis data;

FIG. 10 shows a few layers V in example 3₂CT_xScanning electron microscope photographs of MXenes powder with low and high multiples;

FIG. 11 shows a few Ti layers in example 4₂CT_xScanning electron microscope pictures and element distribution analysis of MXenes powder;

FIG. 12 is a graph showing Ti in comparative example 2₃C₂T_xMXenes scanning electron microscope photograph;

FIG. 13 shows a few Ti layers in application example 1₃C₂T_xMaterial picture and scanning electron microscope photo of MXenes electrode film

FIG. 14 shows a few Ti layers in application example 2₃C₂T_xThe electrochemical cycle performance of the MXenes sheet;

FIG. 15 is a view showing the application of a multilayer Ti in comparative example 1₃C₂T_xThe electrochemical cycle performance of the MXenes electrode slice;

Detailed Description

The present invention will be further described with reference to the following specific examples and application examples. It should be understood that these examples are for illustrative purposes only and are not to be construed as limiting the invention in any way. Further, it should be understood that various changes or modifications can be made by those skilled in the art after reading the contents of the present invention, and those equivalents also fall within the scope of the invention defined by the appended claims.

Example 1

Making 10g of Ti with purity of more than 98%₃AlC₂Adding the ceramic powder into 100ml of 40 wt% HF solution, and stirring for 48 hours at normal temperature; then centrifugally washing with deionized water until the pH value is about 7, freeze-drying the centrifuged precipitate, then drying in vacuum to further remove the water in the material, wherein the drying temperature is 70 ℃, the drying time is 12h, grinding and collecting the dried material to obtain the Ti with the multilayer structure₃C₂T_xMXenes material.

(2) 1g of multi-layered Ti₃C₂T_xAdding MXenes material into 10ml of 25 wt% aqueous solution of tetramethylammonium hydroxide (TMAOH), stirring at normal temperature for 24h to allow organic molecule intercalation to enter MXenes layers, increasing interlayer spacing and reducing interlayer acting force by intercalation, and centrifuging to collect intercalated multilayer Ti₃C₂T_xPrecipitating MXenes materials, washing the precipitates with deionized water once, dispersing the collected precipitates in 50ml of deionized water, carrying out ultrasonic treatment for 30 minutes of ultrasonic treatment, centrifuging the precipitates for 10 minutes at 3500r/min, collecting the centrifuged supernatant, reserving the supernatant for subsequent use, dispersing the centrifuged precipitates in 50ml of deionized water again, centrifuging the precipitates for 30 minutes at 3500r/min for 10 minutes, collecting the centrifuged supernatant, reserving the supernatant for subsequent use, dispersing the centrifuged precipitates in 50ml of deionized water again, repeating the process until the total ultrasonic time reaches 4 hours, discarding the precipitates after the last centrifugation, collecting all the supernatants to obtain about 350ml of MXenes solution, and reserving the MXenes solution for subsequent use.

(3) Under the condition of stirring, 10ml of ammonia water with the concentration of 28% is dropwise added into 350ml of MXenes solution in the step (2), stirring is carried out for 30 minutes, standing is carried out, the precipitation of MXenes is obviously seen at the bottom of the beaker due to electrostatic coagulation, obvious layering occurs, the upper layer of aqueous solution is poured off, the lower layer of precipitate is collected, and the layered aqueous solution is poured off by repeating the process, namely standing, so that the water in the MXenes solution is reduced, and the time of the subsequent freeze drying process is favorably shortened.

(4) When the total volume of the MXenes solution is about 10ml, pre-freezing the MXenes solution in a refrigerator, freezing, freeze-drying, collecting powder, placing the powder in a crucible, and annealing in a tube furnace at the annealing temperature of 150 ℃ in an argon atmosphere for 6 hours.

(5) After annealing, the powder is ground and collected to obtain dry Ti with few layers₃C₂T_xMXenes material powder for subsequent use.

FIG. 1 shows that: this example consisted of the first Ti₃AlC₂Preparation of multilayer Ti from ceramic powder₃C₂T_xIn MXenes production process, raw material and multiple layers of Ti₃C₂T_xMXenes has obvious difference in XRD patterns, the (104) peak of 39 degrees of the raw material disappears, and 2 peaks belonging to Ti appear at 18.2 degrees and 27.6 degrees₃C₂(OH)₂The MXenes surface absorbs hydroxyl, and the (002) peak position moves to a small angle direction, namely from 9.9 degrees to 8.9 degrees.

FIG. 2 shows that the raw material Ti₃AlC₂Raman spectra of ceramic powder, 122,180,198 and 268cm^-1Corresponding to C-Ti-Al vibrations in the MAX phase, 580,630 and 660cm^-1Corresponding to C-Ti-C vibration in MAX phase, only 150,393 and 605cm are obtained after hydrofluoric acid etching^-1The 3 characteristic peaks correspond to Ti-C symmetric stretching vibration in MXenes. In combination with the scanning electron micrograph of FIG. 3, it was found that the starting material Ti was treated with HF acid₃AlC₂The ceramic powder produced a distinct multilayer structure, indicating that multilayer Ti was successfully produced₃C₂T_xMXenes powder.

Example 2

Making 10g of Ti with purity of more than 98%₃AlC₂Adding the ceramic powder into 100ml of 40 wt% HF solution, and stirring for 12 hours in a water bath kettle at 50 ℃; then centrifugally washing with deionized water until the pH value is about 7, freeze-drying the centrifuged precipitate, then drying in vacuum to further remove the water in the material, wherein the drying temperature is 70 ℃, the drying time is 12h, grinding and collecting the dried material to obtain the Ti with the multilayer structure₃C₂T_xMXenes material.

(2) 1g of multi-layered Ti₃C₂T_xAdding MXenes material into 10ml of 25 wt% tetrabutylammonium hydroxide (TBAOH) aqueous solution, stirring for 24h at normal temperature, allowing organic molecules to intercalate into MXenes layers, increasing interlayer spacing and weakening interlayer acting force through intercalation, centrifuging to collect multiple layers of MXenes material precipitate after intercalation, washing with deionized water once, dispersing the collected precipitate in 70ml of deionized water, performing ultrasonic treatment, centrifuging after 30 minutes of ultrasonic treatment, wherein the centrifugal rotating speed is 3500r/min, the centrifugal time is 10 minutes, collecting supernatant after centrifugation, reserving for subsequent use, injecting 70ml of deionized water into the precipitate after centrifugation, stirring the precipitate into solution, centrifuging after 30 minutes of ultrasonic treatment, wherein the centrifugal rotating speed is 3500r/min, the centrifugal time is 10 minutes, collecting supernatant after centrifugation, reserving for subsequent use, injecting 50ml of deionized water into the precipitate after centrifugation, the procedure was repeated until the total sonication time reached 4 hours, the pellet from the last centrifugation was discarded and all the supernatants previously collected, approximately 500ml of MXenes solution, were left for subsequent use.

(3) 3.2g ammonium bicarbonate is dissolved in 50ml deionized water, and after stirring for 30 minutes, uniform and transparent NH-containing solution can be obtained⁴⁺Aqueous ionic ammonium bicarbonate solution.

(4) Adding the solution prepared in the step (3) containing NH dropwise into 500ml of MXenes solution in the step (2) while stirring⁴⁺Aqueous ammonium bicarbonate solution of ions, straightAfter the addition is finished, stirring is continued for 30 minutes, then standing is carried out, the precipitation of MXenes at the bottom of the beaker is obviously seen due to electrostatic coagulation, obvious layering occurs, the upper-layer aqueous solution is poured out, the lower-layer solution is collected, the volume of the MXenes solution is obviously reduced, correspondingly, the concentration of the MXenes in the MXenes solution is increased, and the process of standing is repeated, and the upper-layer water is poured out until the total volume is about 20 ml.

(5) When the total volume of the MXenes solution is about 20ml, pre-freezing the MXenes solution in a refrigerator, freezing, freeze-drying, collecting powder, placing the powder in a crucible, and annealing in a tube furnace at the annealing temperature of 180 ℃ under the argon atmosphere for 6 hours.

(6) After annealing, the powder is ground and collected to obtain dry Ti with few layers₃C₂T_xMXenes powder for subsequent application.

FIG. 4 shows the introduction of the cation NH⁴⁺After ionization, a few Ti layers with electronegativity are adsorbed by cations₃C₂T_xThe surface of MXenes destroys the electrostatic balance (all electronegativity and mutual repulsion) maintained by the MXenes by mutual repulsion force action, electrostatic coagulation occurs, and in combination with figure 5, it can be seen that as the standing time is prolonged, the MXenes sheet layer is easy to settle, after standing for 30 minutes, the MXenes sheet layer is basically completely settled to generate obvious layering, and at the moment, the supernatant can be poured off, the water content of freeze drying is reduced, and the experiment period of freeze drying is shortened. FIG. 6 shows that a few layers of Ti₃C₂T_xMXenes sol, after freeze-drying, presents a fluffy net shape, the mass of the MXenes sol is 1.4g, if the amount of MAX etching is increased in the early stage, more centrifuge tubes are used at the same time, and NH is utilized⁴⁺The ion-assisted electrostatic coagulation method can realize the Ti with less layers₃C₂T_xThe macro preparation of MXenes.

FIG. 7 shows that a few layers of Ti₃C₂T_xMXenes powder, under low magnification scanning electron microscope, from 300 times magnification to 2000 times magnificationThe number of the particles is small, no obvious agglomeration phenomenon exists, and a very obvious lamellar structure can be seen by combining a high-power scanning electron microscope shown in figure 8, the thickness of the particles is below 10nm, and Ti is₃C₂T_xThe interlayer spacing of MXenes is about 1nm, and the obtained MXenes has the number of layers below 10 and the sheet diameter of about 5 um. The AFM photograph and thickness analysis data of FIG. 9 clearly show that a portion of the Ti is a few layers₃C₂T_xMXenes sheet thickness of 2-3nm, Ti is presumed₃C₂T_xThe layer number of MXenes is between 2 and 3 layers, the sheet diameter is about 3um, and the feasibility of rapidly and massively preparing the small-layer MXenes powder is fully demonstrated by combining the experimental phenomenon and the result of figures 4 to 9.

Example 3

V for making 10g purity more than 95%₂Adding AlC ceramic powder into 100ml of 40 wt% HF solution, and stirring for 40h in a water bath kettle at 55 ℃; then centrifugally washing with deionized water until the pH value is about 7, freeze-drying the centrifuged precipitate, then drying in vacuum to further remove the water in the material, wherein the drying temperature is 70 ℃, the drying time is 12h, grinding and collecting the dried material to obtain the V with the multilayer structure₂CT_xMXenes material.

(2) 0.5g of multilayered V₂CT_xMXenes material was added to 10ml of 25 wt% aqueous tetramethylammonium hydroxide solution, stirring for 24h at normal temperature to allow organic molecule intercalation to enter MXenes layers, increasing interlayer spacing and weakening interlayer acting force through intercalation, then centrifugally collecting the intercalated multilayer MXenes material precipitate, washing the precipitate once by using deionized water, dispersing the precipitate collected after washing in 50ml of deionized water, and (2) carrying out ultrasonic treatment, carrying out centrifugation after 30 minutes of ultrasonic treatment at a centrifugal rotation speed of 3500r/min for 10 minutes, collecting the centrifuged supernatant for subsequent use, injecting 50ml of deionized water into the centrifuged precipitate, stirring the precipitate into a solution, carrying out centrifugation after 30 minutes of ultrasonic treatment at a centrifugal rotation speed of 3500r/min for 10 minutes, collecting the centrifuged supernatant for subsequent use, and injecting 50ml of deionized water into the centrifuged precipitate.Water, repeating the above process until the total sonication time reaches 4 hours, discarding the pellet after the last centrifugation, and collecting all the above supernatants together at about 350ml V₂CT_xMXenes solution, and is reserved for subsequent use.

(3) 2g of ammonium carbonate is dissolved in 50ml of deionized water and stirred for 30 minutes to obtain uniform and transparent NH-containing solution⁴⁺An aqueous solution of ionic ammonium carbonate.

(4) 350ml of V in the above step (2) with stirring₂CT_xDropwise adding the solution prepared in the step (3) and containing NH into MXenes solution⁴⁺Aqueous ionic ammonium carbonate solution, stirring was continued for 30 minutes until the addition was complete.

(5) Centrifuging the MXenes solution in step (4) due to the use of NH⁴⁺Ions destroy the electronegativity of the MXenes solution, a few layers of MXenes materials can be easily centrifuged, the centrifugation speed is 2000r/min, the centrifugation time is 10 minutes, the centrifuged MXenes precipitates are collected, freeze drying is carried out, after freeze drying, powder is collected, the powder is placed in a crucible, annealing treatment is carried out in a tube furnace, the annealing temperature is 120 ℃, the annealing atmosphere is argon atmosphere, and the annealing time is 12 hours.

(6) After annealing, the powder is ground and collected to obtain dry V with few layers₂CT_xMXenes material powder for subsequent use.

FIG. 10 shows: v obtained in this example₂CT_xMXenes are three-dimensional reticular lamellar structures, show obvious lamellar layers from 400 times of magnification to 70000 times of magnification, have no agglomeration phenomenon, illustrate the method of the invention, are also suitable for preparing vanadium series MXenes materials, and further illustrate the universality of the invention.

Example 4

Measuring H₂SO₄50ml of the solution with a concentration of 8mol/L, to which 46g of NH was added with stirring₄HF₂Stirring evenly to prepare the mixture containing HF acid and (NH)₄)SO₄The etching solution of (1) is added into5g of Ti with a purity of more than 98 percent are added₂Stirring AlC ceramic powder for 40h at room temperature; then centrifugally washing with deionized water until the pH value of the supernatant>6, freeze-drying the centrifuged precipitate, then drying in vacuum to further remove the water in the material, wherein the drying temperature is 70 ℃, the drying time is 12h, grinding and collecting the dried material to obtain the Ti with the multilayer structure₂CT_xMXenes material.

(2) 0.5g of multi-layered Ti₂CT_xAdding MXenes material into 20ml of dimethyl sulfoxide organic solution, stirring for 24 hours at normal temperature to enable organic molecule intercalation to enter MXenes layers, centrifugally collecting multi-layer MXenes material precipitate after intercalation, washing the precipitate once by deionized water, dispersing the precipitate collected after washing into 50ml of deionized water, carrying out ultrasonic treatment, centrifuging after 30 minutes of ultrasonic treatment at the centrifugal rotation speed of 3500r/min for 10 minutes, collecting supernatant after centrifugation for later use, injecting 50ml of deionized water into the precipitate after centrifugation, stirring the precipitate into solution, centrifuging after 30 minutes in the same way, wherein the centrifugal rotation speed is 3500r/min for 10 minutes, collecting supernatant after centrifugation for later use, injecting 50ml of deionized water into the precipitate after centrifugation, repeating the processes until the total ultrasonic time reaches 4 hours, the supernatants were pooled and collected as approximately 350ml of MXenes solution for subsequent use, and the pellet after the last centrifugation was discarded.

(3) 3.2g ammonium bicarbonate is dissolved in 50ml deionized water, and after stirring for 30 minutes, uniform and transparent NH-containing solution can be obtained⁴⁺Aqueous ionic ammonium bicarbonate solution.

(4) Adding the solution prepared in the step (3) containing NH dropwise into 350ml of MXenes solution prepared in the step (2) while stirring⁴⁺Ionic ammonium bicarbonate aqueous solution, stirring was continued for 30 minutes until the addition was complete.

(5) Centrifuging the MXenes solution in step (4) due to the use of NH⁴⁺Ions destroy the electronegativity of the MXenes solution, a few layers of MXenes materials can be obtained by centrifugation at the centrifugal speed of 2000r/minThe time is 10 minutes, the centrifuged MXenes precipitate is collected, freeze-dried, and then the powder is collected, placed in a crucible, and annealed in a tube furnace at the annealing temperature of 120 ℃ under the argon atmosphere for 12 hours.

(6) After annealing, the powder is ground and collected to obtain dry Ti with few layers₂CT_xMXenes material powder for subsequent use.

FIG. 11 shows that: prepared Ti₂CT_xThe MXenes material has few layers, and the element distribution diagram shows that the distribution characteristic area of core elements Ti and C and Ti₂The C-sheets are identical.

Comparative example 1 was carried out

Similar to example 1, this comparative example obtained a few Ti layers₃C₂T_xThe amount of MXenes in water was about 350ml, and 50ml of MXenes in water was measured from a beaker and freeze-dried in a freezer.

It was found that the freeze-drying process required about 50h and was very time consuming if all the few Ti layers were to be freeze-dried₃C₂T_xCompared with MXenes aqueous solution, the time required by MXenes aqueous solution is about 400h, the invention greatly reduces the volume of the solution required to be freeze-dried by electrostatic coagulation, 350ml of solution is processed into about 10ml of solution, and the solution can be completely freeze-dried only within 10h, thereby greatly improving the efficiency.

Comparative example 2 was carried out

Similar to example 1, this comparative example obtained a few Ti layers₃C₂T_xCentrifuging MXenes aqueous solution at high speed of 12000r/min for 10 min, freeze drying, vacuum drying, and collecting Ti₃C₂T_xMXenes powder.

FIG. 12 shows Ti prepared in comparative example₃C₂T_xThe scanning electron microscope photo of MXenes shows that the MXenes agglomerate into blocks, no obvious lamella can be seen under a high-multiple scanning electron microscope, the agglomeration phenomenon is serious, and a large and thick lamella (as shown in the part d of the figure) is formed by a plurality of small layers of MXenes in partShown in the specification), the MXenes prepared by the method has serious agglomeration phenomenon, and the advantages of the MXenes two-dimensional layered material cannot be fully exerted in subsequent application.

Application example 1

In this application example, the small-layer MXenes material prepared in example 1 is used as a negative electrode material of a lithium ion battery, a negative electrode plate of the battery is prepared by a suction filtration film-forming method, a vacuum-filtered, vacuum-dried film is cut, sliced, assembled into a button lithium ion battery in a glove box, and then a relevant test of electrochemical performance is performed. The method comprises the following specific steps:

preparing a negative electrode: 350ml of Ti prepared in the above example 1 was added₃C₂T_xPreparing a film by adopting a vacuum filtration mode for the MXenes solution, saving a conductive agent and a binder which are required by the common battery pole piece, simplifying the preparation process of the pole piece, drying the pole piece for 10 hours at 70 ℃ under a vacuum condition after freeze drying, cutting the pole piece into electrode pieces with the diameter of 14mm after drying, and preparing a few layers of Ti₃C₂T_xThe MXenes material is a battery negative plate of the negative electrode material.

Assembling and testing the battery: in a glove box in argon atmosphere, the electrode sheet prepared above was used as a negative electrode, a lithium metal sheet was used as a counter electrode, and 1M LiPF₆The solution (DMC: EMC: FEC 1: 1: 1) was used as an electrolyte, Celgard 2300 was used as a separator, and a 2032 button-type lithium ion battery was assembled. The battery charging and discharging test is carried out on a Land battery test system by using a constant current charging and discharging mode, and the voltage test range is 0.01-3V.

FIG. 13 shows the material image and scanning electron micrograph of the membrane prepared by the present application, which is a clear lamellar without agglomeration.

Application example 2

This application example uses the less-layer Ti prepared in example 1 above₃C₂T_xMXenes material is used as the negative electrode material of the lithium ion battery, the negative electrode plate of the battery is prepared by adopting a coating method, the MXenes material is assembled into the button type lithium ion battery in a glove, and then the relevant test of the electrochemical performance is carried out. The method comprises the following specific steps:

preparing a negative electrode: mixing the above materialsFew-layer Ti prepared in example 1₃C₂T_xThe MXenes material is uniformly mixed with 5% of polyvinylidene fluoride (PVDF) binder and a conductive agent Super P according to the mass ratio of 8:1:1, the mixture is uniformly stirred to form slurry, the slurry is coated on a copper foil, the slurry is dried for 10 hours at 90 ℃ under the vacuum condition, the dried slurry is cut into electrode plates with the diameter of 14mm, and a few layers of Ti are prepared₃C₂T_xThe MXenes material is a battery negative plate of the negative electrode material.

Assembling and testing the battery: in a glove box in argon atmosphere, the electrode sheet prepared above was used as a negative electrode, a lithium metal sheet was used as a counter electrode, and 1M LiPF₆The solution (DMC: EMC: FEC 1: 1: 1) was used as an electrolyte, Celgard 2300 was used as a separator, and a 2032 button-type lithium ion battery was assembled. The battery charging and discharging test is carried out on a Land battery test system by using a constant current charging and discharging mode, and the voltage test range is 0.01-3V. FIG. 14 is a diagram of the cycle performance of the lithium ion battery prepared in the application example under the conditions of the current density of 500mA/g and the voltage range of 0.01-3V, and after 200 cycles, the specific capacity is about 380mAh/g, and the lithium ion battery has no capacity fading tendency.

Application comparative example 1

This comparative example used the multilayer Ti prepared in the step (1) of example 1 described above₃C₂T_xMXenes material is used as the negative electrode material of the lithium ion battery, the negative electrode plate of the battery is prepared by adopting a coating method, the MXenes material is assembled into the button type lithium ion battery in a glove, and then the relevant test of the electrochemical performance is carried out. The method comprises the following specific steps:

preparing a negative electrode: the multilayer Ti prepared in step (1) of example 1 above was used₃C₂T_xThe MXenes material is uniformly mixed with 5% of polyvinylidene fluoride (PVDF) binder and a conductive agent Super P according to the mass ratio of 8:1:1, the mixture is uniformly stirred to form slurry, the slurry is coated on a copper foil, the slurry is dried for 10 hours at 90 ℃ under the vacuum condition, the dried slurry is cut into electrode plates with the diameter of 14mm, and a few layers of Ti are prepared₃C₂T_xThe MXenes material is a battery negative plate of the negative electrode material.

Assembling and testing the battery: in a glove box under argon atmosphere,the electrode sheet prepared above was used as a negative electrode, a metal lithium sheet was used as a counter electrode, and 1M LiPF₆The solution (DMC: EMC: FEC 1: 1: 1) was used as an electrolyte, Celgard 2300 was used as a separator, and a 2032 button-type lithium ion battery was assembled. The battery charging and discharging test is carried out on a Land battery test system by using a constant current charging and discharging mode, and the voltage test range is 0.01-3V. As shown in fig. 15, which is a cycle performance diagram of the lithium ion battery prepared in the comparative example in the current density of 500mA/g and the voltage range of 0.01 to 3V, after 350 cycles, the specific capacity is about 150mAh/g, and the lithium ion battery has an obvious difference in electrochemical performance from the few-layer MXenes (the few-layer stable state, the specific capacity is about 380 mAh/g), it is fully demonstrated that the rapid preparation method of the few-layer MXenes provided by the invention has a wide application prospect in the field of electrochemical energy storage.

Claims (7)

1. A rapid preparation method of few-layer MXenes is characterized by comprising the following steps:

(1) taking MAX raw materials, and treating in etching solution to obtain a multilayer MXenes material;

(2) treating the MXenes material obtained in the step (1) in organic molecules or a surfactant;

(3) centrifuging, washing, precipitating and stripping the MXenes material obtained in the step (2), discarding the precipitate, and collecting the supernatant to obtain a small-layer MXenes solution;

(4) adding an electrolyte solution containing ammonium ions into the MXenes solution obtained in the step (3), performing electrostatic coagulation, standing or low-speed centrifugation or suction filtration, and obtaining sol, precipitate or filter cake which is the low-layer MXenes material; the electrolyte solution containing ammonium ions is one or a combination of ammonium bicarbonate, ammonia water, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium chloride and ammonium fluoride solution;

(5) and (4) carrying out freeze drying and annealing treatment on the material obtained in the step (4) to obtain the MXenes powder with few layers.

2. The method for rapidly preparing the few-layer MXenes according to claim 1,the MXenes material in the step (1) is Ti₄C₃、Ti₄N₃、Ti₃C₂、Ti₂C、Mo₂C、Hf₃C₂、V₃C₂、V₂C、V₂N、Nb₄C₃、Nb₃C₂、Nb₂C、Cr₃C₂、Ta₂C、Ta₄C₃、(Ti_0.5Nb_0.5) C, one or more combinations thereof.

3. The method as claimed in claim 1, wherein the etching solution in step (1) is HF, LiF and HCl, NaF and H₂SO₄And one or more of other mixed liquid containing F salt and acid.

4. The method for preparing MXenes rapidly as defined in claim 1 wherein the organic molecule in step (2) is one or more of tetramethylammonium hydroxide, tetrabutylammonium hydroxide, hydrazine hydrate, N-methylpyrrolidone, dimethyl sulfoxide, N-methylformamide, ethanol.

5. The method of claim 1, wherein the surfactant in step (2) is one or more selected from the group consisting of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, polyvinylpyrrolidone, and F127.

6. The method for rapidly preparing the few-layer MXenes of claim 1, wherein the stripping treatment in step (3) is one or more of mechanical shaking, ultrasound, and cell pulverization, and the solvent used for MXenes solution is one or more of water, ethanol, and acetone.

7. The method for rapidly preparing the few-layer MXenes according to claim 1, wherein the annealing temperature in the step (5) is 70-700 ℃.

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