Preparation method and application of a lightweight powder two-dimensional transition metal carbide

Abstract

The present invention discloses a preparation method and application of a light powder of two-dimensional transition metal carbides (MXenes). The light powder has the fluidity and mechanical plasticity common to powder materials, and at the same time, the typical apparent density is less than 100 mg cm-3. The light powder MXenes can also be referred to as expanded MXenes. The method includes: (1) etching a MAX ceramic phase material with a fluorine-containing etchant in a reaction system with high viscosity; (2) after the etching is completed, washing with a solvent to remove by-products and impurities in the reaction system, and vacuum drying to obtain a light powder MXenes material; (3) processing the prepared light powder MXenes material into a functional assembly material. Because of its controllable nanoporous structure inside, it can have very excellent properties and broad application prospects in the fields of electrochemical energy storage, electromagnetic interference shielding, pollutant adsorption, antistatic, etc.

Description

Technical Field

[0001] The present invention belongs to the fields of electromagnetic interference shielding, thermal conductive materials, conductive polymer composites, supercapacitors, etc. Specifically, the present invention relates to a preparation method and application of lightweight powder two-dimensional transition metal carbides (MXenes). Background Art

[0002] With the continuous growth of the demand for conductive / thermal conductive nanomaterials in human society, it has promoted the application of low-dimensional nanomaterials such as expanded graphite, graphene, and carbon nanotubes in the preparation of polymer composites, which have extremely broad application prospects in the fields of electromagnetic interference shielding, thermal conductive materials, conductive materials, and supercapacitors. Two-dimensional transition metal carbides (MXenes) materials were first synthesized in 2011. It has excellent metallic conductivity, good thermal conductivity, and processability, so it has good application prospects in electromagnetic interference shielding, conductive and thermal conductive materials, and electrochemical energy storage materials. However, during the process of powder processing, MXenes are difficult to be prepared into lightweight powder materials, so a relatively high addition amount is required to improve the conductivity and thermal conductivity of the composite material, which will have a greater adverse impact on maintaining the mechanical properties of the composite material itself. Therefore, developing a preparation method for lightweight powder MXenes with a high expansion ratio is particularly crucial for the preparation and application of its composite materials.

[0003] Generally, MXenes are obtained by etching MAX ceramic phase materials in a solution phase, where the Al atomic layer in the MAX ceramic phase material is etched away by hydrofluoric acid to produce MXene products. Currently, this etching reaction is usually carried out in an aqueous solution or an organic solvent. For example, in an etching system of lithium fluoride and hydrochloric acid, the MAX phase material is etched and converted into MXene, and Li + is inserted into the interlayer of MXene. During the subsequent impurity removal process, MXene can be swollen and peeled into single layers. Subsequently, drying the MXene nanomaterial dispersion can only obtain a densely packed thin film material or a fluffy porous foam, and cannot obtain a processable powder material. In addition, by etching in systems such as hydrofluoric acid and ammonium bifluoride aqueous solution, only a dense powder MXene product that does not swell and peel can be obtained, and its apparent density is usually above 300 mg cm -3 which also cannot meet the requirements for subsequent processing of composite materials. Summary of the Invention

[0004] To solve one of the technical problems in the related art, an object of the present invention is to provide a method for preparing lightweight powder two-dimensional transition metal carbides (MXenes). The lightweight powder MXenes prepared by this method are also known as expanded MXenes, which have a high expansion ratio and a low apparent density, and can improve the conductive / thermal conductivity of the composite as much as possible while reducing the filling volume fraction during the preparation of polymer composites, so that they can be applied in electromagnetic interference shielding, conductive / thermal materials, and electrochemical energy storage devices.

[0005] The method for preparing lightweight powder two-dimensional transition metal carbides (MXenes) provided by the present invention includes the following steps:

[0006] Etching the MAX ceramic phase material with a fluorine-containing etchant in a high-viscosity reaction system to achieve a high expansion ratio of the particles by slowing down the diffusion rate of hydrogen bubbles generated between the lamellae, and obtaining lightweight powder two-dimensional transition metal carbides (MXenes).

[0007] In the above method, the MAX ceramic phase material can be selected from at least one of Ti3AlC2, Ti3AlCN, Mo2TiAlC2, Ti2AlC, V2AlC, and the MAX ceramic phase material used generally has a particle size of 100 mesh to 800 mesh;

[0008] The high-viscosity reaction system refers to a polymer aqueous solution, a polymer melt, or a molten salt system with a zero-shear viscosity greater than 50 mPa·s;

[0009] Among them, the polymer aqueous solution can be selected from one or several of polyvinyl alcohol, sodium alginate, and sodium carboxymethyl cellulose aqueous solution, preferably polyvinyl alcohol aqueous solution, and the polyvinyl alcohol content is preferably 5 wt%;

[0010] The polymer melt can be polyethylene glycol, and the molecular weight of polyethylene glycol is preferably 800 - 2000;

[0011] The molten salt system is an ionic liquid or a eutectic system;

[0012] Among them, the ionic liquid can be selected from one or several of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; preferably 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium tetrafluoroborate;

[0013] The eutectic system can specifically be a system composed of choline chloride and sorbitol;

[0014] The mass ratio of the high-viscosity reaction system (disperse phase) to the MAX ceramic phase material can be 2:1 to 20:1, specifically 10:1 or 5:1;

[0015] The fluorine-containing etchant is selected from at least one of hydrogen fluoride, lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, ammonium bifluoride, and potassium bifluoride, among which ammonium bifluoride, potassium bifluoride, or hydrogen fluoride is preferred;

[0016] When lithium fluoride, sodium fluoride, potassium fluoride, or ammonium fluoride is used as the etchant, it needs to be blended with an acid to produce an active hydrogen fluoride etchant;

[0017] The mass ratio of the fluorine-containing etchant used to the MAX ceramic phase material can be 1:1 to 5:1, specifically 2:1, 1:1, 3:1, or 5:1.

[0018] The etching is carried out at room temperature to 100 °C, and the etching time can be 6 hours to 10 days;

[0019] The etching is carried out in an open system under stirring;

[0020] The above method may further include an operation of removing by-products and impurities in the reaction system by solvent washing after the etching process is completed, and vacuum drying to obtain a light powder MXenes material;

[0021] The solvent for washing can be one or several of water, ethanol, ethylene glycol, methanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone;

[0022] The washing can be carried out multiple times, and the total amount of the solvent used for washing is not less than 200 mL / g MXene;

[0023] The washing method can be centrifugal washing and / or filtration washing.

[0024] The above method may further include an operation of processing the obtained light powder MXenes material into a functional assembly material.

[0025] The processing method is selected from at least one of hydrostatic pressing, roll pressing, filtration, doctor blading, in-situ polymerization of polymer materials, melt spinning, extrusion molding, and centrifugal spraying methods.

[0026] The light powder MXenes prepared by the above method and the functional assembly (composite) material prepared by processing the light powder MXenes material also belong to the protection scope of the present invention.

[0027] The light powder MXenes has a high expansion ratio and a low apparent density (less than 100 mg cm -3 ).

[0028] The functional assembly material can specifically be a polymer composite material.

[0029] For the method of preparing lightweight powder MXenes of the present invention, the used MAX ceramic phase material is simple and easy to obtain; there are many economical choices for the reaction system, such as polyvinyl alcohol and polyethylene glycol, etc.; meanwhile, the post-treatment process is also relatively simple and compatible with industrial processes. The prepared lightweight powder MXenes can be used for the preparation of polymer composite materials, and thus can be applied in fields such as conductive / thermal conductive materials, electromagnetic interference shielding materials, and electrochemical energy storage devices. Among them, due to the high expansion ratio of the lightweight powder MXenes, the addition amount can be minimized, and the physical and chemical properties of the raw material matrix can be maintained to the greatest extent.

[0030] In addition, the method of preparing lightweight powder MXenes according to the above embodiments of the present invention may further have the following additional technical features:

[0031] In some embodiments of the present invention, the high-viscosity reaction system refers to a polymer aqueous solution, polymer melt or ionic liquid with a zero-shear viscosity greater than 50 mPa·s. Specifically, we found that systems such as polyvinyl alcohol aqueous solution, polyethylene glycol melt, and 1-butyl-3-methylimidazolium chloride can be selected. In these systems, a high expansion ratio of the particles is achieved by slowing down the diffusion rate of the hydrogen gas bubbles generated between the lamellae.

[0032] In some embodiments of the present invention, the fluorine-containing etchant is selected from at least one of hydrogen fluoride, lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, ammonium bifluoride, and potassium bifluoride; the fluoride ions in these etchants can combine with the Al atoms in the MAX ceramic phase to form stable complex ions, thereby promoting the etching reaction of the MAX ceramic phase.

[0033] In some embodiments of the present invention, the MAX ceramic phase material is selected from at least one of Ti3AlC2, Ti3AlCN, Mo2TiAlC2, Ti2AlC, and V2AlC. The present invention is applicable to a variety of MAX ceramic phase materials; the used MAX ceramic phase material generally has a particle size of 100 mesh to 800 mesh.

[0034] In some embodiments of the present invention, the etching reaction process is generally carried out at room temperature to 100 °C. The system requires sufficient mechanical stirring and is carried out in an open system. At the same time, attention should be paid to installing a gas absorption device to remove acidic components such as HF. The reaction time is generally 6 hours to 10 days.

[0035] In some embodiments of the present invention, the solvent for washing is selected from at least one of water, ethanol, ethylene glycol, methanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; the ratio of the amount of solvent used for washing (mL) to the mass (g) of the MAX ceramic phase raw material is generally 20 - 2000.

[0036] In some embodiments of the present invention, the method of solvent washing is selected from at least one of centrifugal washing and filtration washing; this step is mainly to remove impurities such as AlF6 3- and NH4F. The vacuum drying method includes direct vacuum drying and also freeze vacuum drying; this step is mainly to remove the solvent in the light powder MXenes to obtain a dry powder material that can be used for the next processing step.

[0037] In some embodiments of the present invention, the processing method is selected from at least one of hydrostatic pressure, roll pressing, filtration, doctor blading, in-situ polymerization of polymeric materials, melt spinning, extrusion molding, and centrifugal spraying. The polymer / MXenes composite material prepared in this step has certain application prospects in the fields of conductive / thermal conductive materials, electromagnetic interference shielding materials, and electrochemical energy storage devices.

[0038] In yet another aspect of the present invention, the present invention provides a method for preparing light powder MXenes. According to the embodiments of the present invention, the light powder MXenes is obtained by the above method for preparing light powder MXenes. Thus, the light powder MXenes material prepared by this method has a high expansion ratio (apparent density less than 100 mg cm -3 ) and the fluidity of the powder material, and can be applied to the preparation of polymer composites.

[0039] Starting from the analysis of the etching process of the MAX ceramic phase material, the present invention designs a high-viscosity system to etch the MAX ceramic phase material with a fluorine-containing etchant, and slows down the diffusion rate of hydrogen bubbles generated between the layers to achieve a high expansion ratio of the particles, thereby successfully preparing the light powder MXenes (apparent density less than 100 mg cm -3 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic process flow diagram of the method for preparing light powder MXenes of the present invention;

[0041] Figure 2 is a scanning electron microscope image of the light powder MXenes prepared in Example 1 of the present invention;

[0042] Figure 3It is the transmission electron microscopy image of the lightweight powder MXenes prepared in Example 1 of the present invention;

[0043] Figure 4 It is the X-ray diffraction analysis diagram of the lightweight powder MXenes prepared in Example 1 of the present invention;

[0044] Figure 5 It is the chemical structure analysis result of the lightweight powder MXenes prepared in Example 1 of the present invention;

[0045] Figure 6 It is the electrochemical energy storage performance result of the lightweight powder MXenes prepared in Example 1 of the present invention;

[0046] Figure 7 It is the apparent density comparison diagram of the lightweight powder MXenes obtained in Examples 1 to 9 of the present invention, where [C4mim]Cl / NH4HF2 represents the MXenes sample obtained in Example 1; [C4mim]BF4 / NH4HF2 represents the MXenes sample obtained in Example 3; PEG400 / NH4HF2 represents the MXenes sample obtained in Example 6; HF40 represents the MXene sample obtained by etching with traditional HF (40wt%); other samples are comparative samples, including EG: expanded graphite; GN: graphene nanoplate powder; and MXenes prepared by other methods.

[0047] Figure 8 It is the XRD diffraction pattern of the lightweight powder MXenes prepared in Example 6 of the present invention, Detailed implementation manners

[0048] The present invention will be further described in detail below in conjunction with the specific implementation manners. The provided examples are only for clarifying the present invention, rather than limiting the scope of the present invention. The following examples can be used as a guide for those of ordinary skill in the art to make further improvements and do not limit the present invention in any way.

[0049] The experimental methods in the following examples are all conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0050] In one aspect of the present invention, the present invention provides a method for preparing lightweight powder MXenes. According to an embodiment of the present invention, with reference to Figure 1 , the method includes:

[0051] S100: Mix the MAX ceramic phase material with a fluorine-containing etchant in a high-viscosity etching system. The MAX ceramic phase material is obtained from Jilin Yiyi Technology Co., Ltd., which is a high-purity MAX phase ceramic material, providing products with mesh sizes of 200, 300, 400, and 600. It can also be further ground and sieved as needed to obtain MAX ceramic phase powder raw materials with smaller sizes.

[0052] In this step, the MAX ceramic phase material is mixed with a fluorine-containing etchant in a high-viscosity etching system, and a certain temperature and reaction time are maintained to achieve the etching and volume expansion of the MAX ceramic phase material. Specifically, in this step, a suitable fluorine-containing etchant must be selected so that the Al atomic layer in the MAX ceramic phase material can be effectively etched. Generally speaking, an acidic fluorine-containing system can generally achieve this purpose. Therefore, fluorine-containing etchants such as ammonium bifluoride, potassium bifluoride, and hydrogen fluoride can be used. At the same time, etchants such as lithium fluoride, sodium fluoride, and ammonium fluoride can also be mixed with acids to produce active hydrogen fluoride etchants.

[0053] According to an embodiment of the present invention, the fluorine-containing etchant can be one or more of hydrogen fluoride, lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, ammonium bifluoride, and potassium bifluoride. Among them, ammonium bifluoride and hydrogen fluoride are preferably used as the fluorine-containing etchant. The mass ratio (g) of the etchant used to the mass (g) of the MAX ceramic phase raw material can be 1, 2, 3, or 5. The inventors found that when the amount of the etchant is too small, the etching reaction often cannot proceed completely, and the raw material MAX ceramic phase will exist in the product. When the amount of the etchant used is too large, the produced MXene product will also be transformed to form over-etched products such as NH4TiOF3. Specifically, the amount of the etchant used should be associated with the reaction temperature and time. For specific details, please refer to the specific examples given in the specification.

[0054] According to another embodiment of the present invention, the high-viscosity reaction system (zero-shear viscosity greater than 50 mPa·s) can be one of the following three systems: i) a molten salt system, mainly an ionic liquid and other eutectic mixture systems; ii) a polymer aqueous solution; iii) a polymer melt. The ionic liquid can be selected from one or more of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. Among them, 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium tetrafluoroborate are preferred. The polymer aqueous solution can be selected from one or more of polyvinyl alcohol, sodium alginate, and sodium carboxymethylcellulose aqueous solutions. Among them, a polyvinyl alcohol aqueous solution is preferred, and the polyvinyl alcohol content is preferably 5 wt%. The polymer melt can be polyethylene glycol, and the molecular weight of the polyethylene glycol is preferably 800 - 2000.

[0055] According to another embodiment of the present invention, the MAX ceramic phase material may be one or several of Ti3AlC2, Ti3AlCN, Mo2TiAlC2, Ti2AlC, V2AlC; among which, Ti3AlC2 and Ti3AlCN can achieve the best etching effect (complete etching). In addition, the particle size of the MAX ceramic phase material powder is preferably 400 mesh or above, because the particle size will significantly affect the kinetics of etching and the final completeness.

[0056] S200: Etch the mixture in S100 at a certain temperature.

[0057] In this process, the fluorine-containing etchant in the reaction system will etch the Al atomic layer in the MAX ceramic phase material, thereby generating H2 bubbles. The diffusion rate of these bubbles in the high-viscosity reaction medium can be reduced by one to two orders of magnitude, so that significant swelling behavior occurs between layers, and then MXene powder materials with a high expansion ratio are prepared. At the same time, it is easy to know that in this process, the MXene powder is peeled into a nanosheet structure by this mechanical peeling effect, and the separated nanosheet layers have a certain flexibility, thus showing a wrinkled structure (see Figure 2 ).

[0058] According to an embodiment of the present invention, the etching reaction is carried out in a polytetrafluoroethylene container, and a magnetic stir bar or a mechanical stirring rod can be used therein. The reaction conditions for the etching process are from room temperature to 100 °C, preferably 70 °C, at which the reaction rate, the completeness of the reaction and the singularity of the product can be taken into account. The reaction duration is from 6 hours to 10 days. According to the results of chemical and structural characterization, the inventors found that a better etching effect can be obtained only when the reaction is carried out for more than 36 h. Too long reaction time will produce over-etched products such as NH4TiOF3.

[0059] S300: Wash the product prepared in S200 with a solvent and dry it under vacuum to obtain light powder MXenes.

[0060] In this step, the aforementioned etching process can obtain MXene powder with a high expansion ratio, but it will also produce impurities or by-products such as AlF6 3- etc. Therefore, it is necessary to wash the product with a solvent to remove soluble impurities and the reaction system matrix / etchant, such as ionic liquids, polymers and other salts.

[0061] According to an embodiment of the present invention, the solvent for washing can be one or several of water, ethanol, ethylene glycol, methanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone; for an etching system miscible with water, such as 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, polyvinyl alcohol aqueous solution, polyethylene glycol high molecular melt, water can be used for the process of washing and removing impurities. For a reaction system immiscible with water, such as 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt, solvents such as ethanol and acetone should be selected for the initial washing, and then water is used to remove the salt impurities in the system.

[0062] According to another embodiment of the present invention, the washing methods include centrifugal washing and filtration washing. According to the experimental results of the inventors, these two methods can achieve similar impurity removal effects. The total amount of the solvent used for washing should be no less than 200 mL / g of MXene.

[0063] According to another embodiment of the present invention, the vacuum drying methods include freeze-drying and vacuum drying. Among them, in order to maintain the morphology of the lightweight powder MXene as much as possible, the freeze-drying method is preferably used. This is because during the ordinary drying process, the removal of water in the material will be accompanied by the generation of capillary force contraction, causing corresponding changes in the structure of the powder.

[0064] For the method for preparing lightweight powder MXenes according to the embodiments of the present invention, the research and understanding of the reaction system and material system used are relatively in-depth, and at the same time, the raw materials are simple and easy to obtain, which is suitable for large-scale industrial production processes. The inventors have proved that it is feasible to carry out large-scale preparation for the reaction system in the embodiments without affecting the quality of the product. The key points to be considered when expanding the reaction device are to control the heat transfer and mass transfer processes in the system, promote the uniform mixing of the materials and the timely discharge of the reaction product hydrogen to avoid corresponding safety hazards. The lightweight powder MXenes prepared by the present invention have the characteristics of high expansion rate and good exfoliation effect (the separated MXene sheets have nanoscale thickness and good flexibility), so they can be widely used in the preparation of polymer composites, such as enhancing the electrical conductivity, thermal conductivity and electromagnetic interference shielding performance of the composites. Due to the high expansion rate and exfoliated morphological characteristics of the lightweight powder MXenes, it can be expected to greatly reduce the volume fraction of the MXenes component in the composite while ensuring the performance of the composite, thus bringing the minimum impact on the performance of the original polymer matrix material. At the same time, the inventors also found that the lightweight powder MXenes can be directly processed into electrodes with multi-scale micro-nano structures, which have extremely excellent electrochemical energy storage performance and can be used to prepare high-energy density electrochemical capacitor devices.

[0065] In yet another aspect of the present invention, the present invention provides a method for preparing lightweight powder MXenes. According to an embodiment of the present invention, the lightweight powder MXenes is obtained by using the above-mentioned method for preparing lightweight powder MXenes. Thus, the lightweight powder MXenes prepared by this method, or also known as expanded MXenes, has a low apparent density (less than 100 mg cm -3 ), as well as the fluidity and plasticity of the powder. It should be noted that the features and advantages of the above-mentioned method for preparing lightweight powder MXenes also apply to lightweight powder MXenes, and will not be elaborated herein.

[0066] The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0067] In all the following embodiments, the MAX ceramic phase is a powder with a mesh size of 400, and the preparation is carried out in a 50 mL thick-walled polytetrafluoroethylene reaction kettle with magnetic stirring. All the chemical reagents used are of analytical purity or higher.

[0068] In all the following embodiments, the characterization and testing methods used are as follows:

[0069] 1) Scanning electron microscope: to observe the microscopic morphology of lightweight powder MXenes;

[0070] 2) Transmission electron microscope: to observe the microscopic morphology of lightweight powder MXenes nanosheets;

[0071] 3) X-ray diffractometer: to analyze the stacking structure of lightweight powder MXenes;

[0072] 4) X-ray photoelectron spectrometer: to analyze the chemical structure of lightweight powder MXenes;

[0073] 5) Electrochemical workstation: to study the electrochemical energy storage performance of lightweight powder MXenes.

[0074] In some of the following embodiments, the preparation method of the electrochemical capacitor electrode used is as follows:

[0075] A certain amount of lightweight powder MXenes is compressed in a tablet press mold under specific conditions of a pressure of 300 MPa for 1 minute, and then demolded. The self-supporting MXenes electrode material is pressed onto a stainless steel mesh current collector electrode under a pressure of 20 MPa for 30 seconds.

[0076] Example 1

[0077] Add 0.5 g of Ti3AlC2 MAX ceramic phase powder, 5.0 g of 1-butyl-3-methylimidazolium chloride, and 1.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Place the reaction device on a hot stage, control the temperature of the reaction system at 70 °C, and melt 1-butyl-3-methylimidazolium chloride under magnetic stirring at 200 r min -1 to complete the preliminary mixing of the reaction system. Then adjust the reaction speed to 500 r min -1 , and maintain the reaction temperature at 70 °C for 72 h. Inject 30 mL of deionized water into the reaction system to terminate the reaction, and then remove 1-butyl-3-methylimidazolium chloride, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system by centrifugal washing. The specific centrifugal washing parameters are 1 g of titanium carbide MXene product ~ 60 mL of deionized water (washed 5 times in total, and the actual amount of deionized water used is 300 mL / g MXene), centrifugal force 2,000 g, and washed 5 times in total. After washing and removing impurities, disperse the titanium carbide MXene product in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dry under vacuum to obtain a lightweight powder of titanium carbide MXene product.

[0078] Since the diffusion rate of hydrogen gas bubbles generated during the etching of the Al atomic layer is greatly reduced in the high-viscosity reaction system, the MXene powder material prepared therefrom has a large expansion ratio. Actual tests show that its apparent bulk density is 65 mg cm -3 . Observations by scanning electron microscopy ( Figure 2 ) show that the lightweight powder of titanium carbide MXene has a morphology similar to an unfolded book, with a nanosheet structure dozens of nanometers thick. Due to its thin thickness, it exhibits a certain flexibility. Ultrasonically disperse it in ethanol, and then observe it by transmission electron microscopy. It can be seen that the MXene nanosheets therein have a very complete lattice structure ( Figure 3 ), which proves that the structure of MXene is maintained throughout the etching process. The X-ray diffraction analysis pattern shows that the lightweight powder of titanium carbide MXene has an intercalated chemical structure ( Figure 4 ), and the characteristic interlayer spacing is about . Chemical analysis and characterization mainly based on X-ray photoelectron spectroscopy reveal the surface chemical characteristics of the lightweight powder of titanium carbide MXene ( Figure 5 ), where the surface functional groups can be divided into three types: -O, -F, and -OH, which follow a certain distribution, consistent with the literature (Wang, H.-W. et al., Resolving the Structure of Ti3C2T xMXenes obtained by HF etching reported in (Chem. Mater., 2016, 28, 349 - 359) have similar characteristics. In addition, the presence of Cl was not observed in the X-ray photoelectron spectroscopy characterization, indicating that Cl does not react onto the MXene nanosheets in a reaction system such as 1-butyl-3-methylimidazolium chloride. Electrochemical energy storage is a major application of titanium carbide MXene. In particular, titanium carbide MXene materials have unique advantages in terms of volumetric energy density and charge-discharge rate. Therefore, here we utilized the easy-to-process property of lightweight powder titanium carbide MXene and prepared a binder-free and conductive-filler-free pure titanium carbide MXene electrode by a simple mechanical static pressure method, and simultaneously explored its electrochemical energy storage behavior in 1 M sulfuric acid electrolyte ( Figure 6 ), and the results showed that it could still exhibit all its capacitance even at a high areal loading (~300 F g -1 ). Specifically, an electrochemical energy storage electrode with an areal specific capacitance of 11.4 F cm -2 could be obtained at an areal loading of 42 mg cm -2 .

[0079] In subsequent examples, the inventors explored different reaction ratios (Example 2), high-viscosity reaction systems (Example 3, 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid; Example 4, deep eutectic system; Example 5, polymer aqueous solution; Example 6, polymer melt), different MAX phase raw materials (Example 7), and large-scale preparation experiments (Example 8). The comparison of the apparent densities of some of the obtained lightweight powder MXene materials and the densities of MXene materials prepared by traditional methods (aqueous etching system, the method is the same as the literature Naguib, M. et al., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater., 2011, 23, 4248 - 4253) can be seen in detail in Figure 7 .

[0080] Example 2

[0081] Add 1.0 g of Ti3AlC2 MAX ceramic phase powder, 5.0 g of 1-butyl-3-methylimidazolium chloride, and 2.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Place the reaction device on a hot stage, control the temperature of the reaction system at 70 °C, and stir at 200 r min -1Under magnetic stirring, 1-butyl-3-methylimidazolium chloride was melted to complete the preliminary mixing of the reaction system. Then, the reaction speed was adjusted to 500 r min -1 , and the reaction was maintained at 70 °C for 72 h. 60 mL of deionized water was injected into the reaction system to terminate the reaction, and then 1-butyl-3-methylimidazolium chloride, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system were removed by centrifugal washing. The specific centrifugal washing parameters were 1 g of titanium carbide MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and impurity removal, the titanium carbide MXene product was dispersed in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dried under vacuum to obtain a lightweight powder of titanium carbide MXene product.

[0082] The apparent density of the MXene powder material prepared thus was 47 mg cm -3 , and it had a similar microscopic morphology to the lightweight powder MXene in Example 1.

[0083] Example 3

[0084] 0.5 g of Ti3AlC2 MAX ceramic phase powder, 5.0 g of 1-butyl-3-methylimidazolium tetrafluoroborate, and 1.0 g of ammonium bifluoride powder were added to a PTFE reaction vessel. The reaction device was placed on a hot stage, and the temperature of the reaction system was controlled at 50 °C. Under magnetic stirring at 200 r min -1 , the preliminary mixing of the reaction system was completed. Then, the reaction speed was adjusted to 500 r min -1 , and the reaction was maintained at 50 °C for 72 h. 30 mL of deionized water was injected into the reaction system to terminate the reaction, and then 1-butyl-3-methylimidazolium tetrafluoroborate, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system were removed by centrifugal washing. The specific centrifugal washing parameters were 1 g of titanium carbide MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and impurity removal, the titanium carbide MXene product was dispersed in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dried under vacuum to obtain a lightweight powder of titanium carbide MXene product.

[0085] The apparent density of the MXene powder material prepared thus was 58 mg cm -3 , and it had a similar microscopic morphology to the lightweight powder MXene in Example 1. It was assembled into a MXene electrode material by the method of static pressure, and the areal loading obtained by testing in 1 M sulfuric acid electrolyte was 42 mg cm -2 The areal specific capacitance at was 8.6 F cm -2 .

[0086] Example 4

[0087] Add 0.5 g of Ti3AlC2 MAX ceramic phase powder, 1.4 g of choline chloride, 3.6 g of sorbitol, and 1.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Place the reaction device on a hot stage, control the temperature of the reaction system at 85 °C, and complete the preliminary mixing of the reaction system under magnetic stirring at 200 r / min -1 Then adjust the reaction speed to 500 r / min -1 , and maintain the reaction temperature at 85 °C for 60 h. Inject 30 mL of deionized water into the reaction system to terminate the reaction, and then remove choline chloride, sorbitol, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system by centrifugal washing. The specific centrifugal washing parameters are 1 g of titanium carbide MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and removing impurities, disperse the titanium carbide MXene product in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dry under vacuum to obtain a lightweight powder of titanium carbide MXene product.

[0088] The apparent density of the MXene powder material prepared thus is 95 mg / cm -3 , and it has a similar microscopic morphology to the lightweight powder MXene in Example 1.

[0089] Example 5

[0090] Add 0.5 g of Ti3AlC2 MAX ceramic phase powder, 5.0 g of 10 wt% PVA (polyvinyl alcohol, type 1788) aqueous dispersion, and 1.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Control the temperature of the reaction system at 25 °C, and complete the preliminary mixing of the reaction system under magnetic stirring at 200 r / min -1 Then adjust the reaction speed to 500 r / min -1 , and maintain the reaction temperature at 25 °C for 72 h. Inject 30 mL of deionized water into the reaction system to terminate the reaction, and then remove PVA, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system by centrifugal washing. The specific centrifugal washing parameters are 1 g of titanium carbide MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and removing impurities, disperse the titanium carbide MXene product in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dry under vacuum to obtain a lightweight powder of titanium carbide MXene product.

[0091] The apparent density of the MXene powder material prepared thus is 96 mg / cm -3Meanwhile, it has a similar microscopic morphology to the light powder MXene in Example 1. It is assembled into an MXene electrode material by the method of static pressure, and the areal loading obtained by testing in 1 M sulfuric acid electrolyte is 42 mg cm -2 The areal specific capacitance at -2 is 7.5 F cm

[0092] Example 6

[0093] Add 0.5 g of Ti3AlC2 MAX ceramic phase powder, 5.0 g of PEG400 (polyethylene glycol, average molecular weight 400), and 1.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Place the reaction device on a hot stage, control the temperature of the reaction system at 70 °C, and under magnetic stirring at 200 r min -1 to complete the preliminary mixing of the reaction system. Then adjust the reaction speed to 500 r min -1 , maintain the reaction temperature at 70 °C and react for 72 h. Inject 30 mL of deionized water into the reaction system to terminate the reaction, and then remove PEG, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system by centrifugal washing. The specific centrifugal washing parameters are 1 g of titanium carbide MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and removing impurities, disperse the titanium carbide MXene product in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dry under vacuum to obtain a light powder titanium carbide MXene product.

[0094] The apparent density of the MXene powder material prepared thus is 88 mg cm -3 , meanwhile, it has a similar microscopic morphology to the light powder MXene in Example 1. It is assembled into an MXene electrode material by the method of static pressure, and the areal loading obtained by testing in 1 M sulfuric acid electrolyte is 42 mg cm -2 The areal specific capacitance at -2 is 9.4 F cm Figure 8 . At the same time, X-ray diffraction ( ) analysis shows that its interlayer spacing can reach about + , so it can be inferred that in addition to NH4

[0095] Example 7

[0096] Add 0.5 g of Ti3AlCN MAX ceramic phase powder, 5.0 g of 1-butyl-3-methylimidazolium chloride, and 1.0 g of ammonium bifluoride powder into a PTFE reaction vessel. Place the reaction device on a hot stage, control the temperature of the reaction system at 70 °C, and under magnetic stirring at 200 r min -1Under magnetic stirring, 1-butyl-3-methylimidazolium chloride was melted to complete the preliminary mixing of the reaction system. Then, the reaction speed was adjusted to 500 r / min -1 , and the reaction was maintained at 70 °C for 72 h. 30 mL of deionized water was injected into the reaction system to terminate the reaction, and then 1-butyl-3-methylimidazolium chloride, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system were removed by centrifugal washing. The specific centrifugal washing parameters were 1 g of titanium carbonitride MXene product ~ 60 mL of deionized water, a centrifugal force of 2,000 g, and a total of 5 washes. After washing and impurity removal, the titanium carbonitride MXene product was dispersed in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dried under vacuum to obtain a light powder titanium carbonitride MXene product.

[0097] The apparent density of the titanium carbonitride MXene powder material prepared thus was 76 mg / cm -3 , and it had a similar microscopic morphology to the light powder titanium carbide MXene in Example 1. It was assembled into a MXene electrode material by the method of static pressure, and the areal loading obtained by testing in a 1 M sulfuric acid electrolyte was 42 mg / cm -2 The areal specific capacitance at was 5.9 F / cm -2 , because the conductivity of titanium carbonitride MXene was significantly lower than that of titanium carbide MXene.

[0098] Example 8

[0099] 50.0 g of Ti3AlC2 MAX ceramic phase powder, 250.0 g of 1-butyl-3-methylimidazolium chloride, and 100.0 g of ammonium bifluoride powder were added to a 1000 mL PTFE reaction vessel. The reaction device was placed on a hot stage, and the temperature of the reaction system was controlled at 70 °C. Under mechanical stirring at 200 r / min -1 , 1-butyl-3-methylimidazolium chloride was melted to complete the preliminary mixing of the reaction system. Then, the reaction speed was adjusted to 500 r / min -1 , and the reaction was maintained at 70 °C for 72 h. 400 mL of deionized water was injected into the reaction system to terminate the reaction, and then 1-butyl-3-methylimidazolium chloride, unreacted ammonium bifluoride, and other by-products / impurities in the reaction system were removed by filtration washing. The specific filtration washing parameters were 1 g of titanium carbide MXene product ~ 100 mL of deionized water, and a total of 3 washes. After washing and impurity removal, the titanium carbide MXene product was dispersed in deionized water (1 g of MXene product ~ 30 mL of deionized water), and then freeze-dried under vacuum to obtain a light powder titanium carbide MXene product.

[0100] The apparent density of the prepared titanium carbide MXene powder material is 49 mg / cm -3 , and it has a similar microscopic morphology to the lightweight powder titanium carbide MXene in Example 1. It is assembled into an MXene electrode material by the method of static pressure, and the areal loading obtained by testing in 1 M sulfuric acid electrolyte is 42 mg / cm -2 , and the areal specific capacitance at this time is 10.8 F / cm -2 .

[0101] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0102] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A preparation method of lightweight powder two-dimensional transition metal carbides MXenes, comprising the following steps: Etching a MAX ceramic phase material with a fluorine-containing etchant in a high-viscosity reaction system to obtain lightweight powder two-dimensional transition metal carbides MXenes; The high-viscosity reaction system refers to a polymer aqueous solution, a polymer melt or a molten salt system with a zero-shear viscosity greater than 50 mPa s; The polymer aqueous solution is selected from one or more of polyvinyl alcohol, sodium alginate, and sodium carboxymethylcellulose aqueous solution; The polymer melt is polyethylene glycol; The molten salt system is an ionic liquid, and the ionic liquid is selected from one or more of 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; 2. The method according to claim 1, wherein: The MAX ceramic phase material is selected from at least one of Ti3AlC2, Ti3AlCN, Mo2TiAlC2, Ti2AlC, and V2AlC; The MAX ceramic phase material has a particle size of 100 mesh to 800 mesh.

3. The method according to claim 1 or 2, characterized in that: The mass ratio of the high-viscosity reaction system to the MAX ceramic phase material is 2:1 to 20:

1.

4. The method according to claim 1, characterized in that: The fluorine-containing etchant is selected from at least one of hydrogen fluoride, lithium fluoride, sodium fluoride, potassium fluoride, ammonium fluoride, ammonium bifluoride, and potassium bifluoride; The mass ratio of the used fluorine-containing etchant to the MAX ceramic phase material is 1:1 to 5:

1.

5. The method according to claim 1, wherein: The etching is carried out at room temperature to 100 °C, and the etching time is 6 hours to 10 days.

6. The method according to claim 1, characterized in that: The method further includes an operation of removing by-products and impurities in the reaction system by solvent washing after the etching process is completed, and vacuum drying to obtain a lightweight powder MXenes material; The solvent for washing is selected from one or more of water, ethanol, ethylene glycol, methanol, acetone, N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; The washing is carried out multiple times, and the total amount of the solvent used for washing is not less than 200 mL / g MXene.

7. The method according to claim 1, characterized in that: The method further includes an operation of processing the obtained lightweight powder MXenes material into a functional assembly material, wherein the processing method is selected from at least one of static pressure, roll pressing, filtration, doctor blading, in-situ polymerization of polymer materials, melt spinning, extrusion molding, and centrifugal spraying methods.

8. The light powder MXenes prepared by the method according to any one of claims 1-7, wherein the apparent density of the light powder MXenes is less than 100 mg cm ‒3 , and has a morphology similar to an unfolded book.

9. A functional assembly material prepared by processing the lightweight powder MXenes according to claim 8.

10. Use of the functional assembly material according to claim 9 in the fields of electrochemical energy storage, electromagnetic interference shielding, pollutant adsorption, and antistatic.

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