Preparation method of MXenes material rich in carbon defects in magnesium-carbon dioxide battery

Abstract

The invention discloses a preparation method of a carbon-rich defect MXenes material for a magnesium-carbon dioxide battery, which comprises the following steps: introducing potassium ions and a hydrogen source on an MXenes substrate material to form a potassium-hydrogen compound on the surface and between layers of MXenes, and then performing high-temperature heat treatment to enable carbon on the surface of the MXenes material to fall off and react with the potassium-hydrogen compound to form a potassium-hydrogen-carbon compound, thereby obtaining the carbon-rich defect MXenes material for the magnesium-carbon dioxide battery. And finally, removing the potassium hydrogen carbon compound by using hydrofluoric acid, so that carbon defects are formed on the surface of the MXenes material, and the MXenes material rich in the carbon defects is obtained. The preparation method is simple, the process is easy to control, and the prepared MXenes material rich in carbon defects is applied to a magnesium-carbon dioxide battery as a positive electrode catalyst, so that the battery has good cycle stability and high coulombic efficiency.

Description

Technical Field

[0001] The invention belongs to the field of novel inorganic functional materials and relates to a method for preparing a carbon defect-rich MXenes material used in a magnesium-carbon dioxide battery. Background Art

[0002] As the threat of global greenhouse gas emissions intensifies, achieving carbon neutrality has become a major task that needs to be solved urgently. 2 The dual functions of utilization and electrical energy storage are considered to be one of the most promising emission reduction strategies. Among various metal-CO2 batteries, Mg-CO 2 The battery has the highest thermodynamic equilibrium potential (2.80V) and the largest theoretical specific energy (1880Wh·kg -1 ), making it a potentially transformative central energy storage technology. However, Mg-CO 2 The development of batteries is still limited by the slow reaction kinetics. 2 Slow reaction kinetics can lead to irreversible conversion reactions and battery failure. There is an urgent need to develop efficient catalysts to accelerate the conversion reaction kinetics during discharge and charge. Two-dimensional materials, especially two-dimensional layered MXene materials, as a new type of material, have excellent metallic conductivity and rich surface functional groups, making them a promising candidate for Mg-CO 2 Therefore, it is of great significance for magnesium-carbon dioxide batteries to prepare low-cost, safe and environmentally friendly carbon-defective MXene-modified catalyst materials through a simple method.

[0003] The currently prepared Mg-CO 2 Battery catalyst materials have certain defects. For example, patent CN119029421A discloses an amine-containing electrolyte for realizing a rechargeable magnesium-carbon dioxide battery and its preparation method and application. The prepared electrolyte is applied in Mg-CO 2 When the battery is in 100mA·g -1 When the battery is charged, it can cycle for 400 hours, but the electrolyte is easily decomposed, resulting in excessive overpotential.

[0004] Reference "Angew. Chem. Int. Ed." 2024, 63" Optimizing CO by chemical means 2 The utilization of magnesium ions and the improvement of the transport of magnesium ions at the electrode interface through material design can significantly improve the Mg-CO 2 The overall performance of the battery. The battery is 200mA·g -1, 70 cycles can be performed with excellent cycle stability. Although the PDA-mediated reversible magnesium anode interface electrolyte can promote the reversible deposition / dissolution of magnesium ions, it is also more prone to side reactions with the electrolyte. These excessive side reactions can lead to uneven local current density, thus forming an irregular deposition layer on the surface of the magnesium anode, which ultimately affects the performance of the battery.

[0005] Patent CN110010862A discloses a magnesium secondary battery positive electrode material MXene-Ti 3 C 2 / TiS 2 And its preparation method, which is based on two-dimensional material MXene-Ti 3 C 2 As the substrate, the layered structure of TiS 2 Loaded on MXene-Ti 3 C 2 The prepared material is used as the positive electrode material of magnesium battery. The electrochemical performance test shows that the capacity decay is relatively small, but the maximum current density of the test is only 200mA·g -1 , indicating that at high current density (500mA·g -1 ) has poor catalytic effect.

[0006] It can be seen that the main problems of magnesium-carbon dioxide batteries are:

[0007] (1) The catalyst effect is not ideal, with low activity and poor stability.

[0008] (2) The raw material cost is high and not suitable for large-scale production.

[0009] (3) The catalyst can easily undergo more side reactions with the electrolyte during the reaction, forming irregular deposits on the surface of the material. Summary of the invention

[0010] In view of the above technical problems, the present invention aims to provide a method for preparing a MXenes material rich in carbon defects for use in magnesium-carbon dioxide batteries, by introducing potassium ions and a hydrogen source onto a MXenes substrate material to form potassium hydrogen compounds on the surface and between layers of the MXenes, and then subjecting the carbon on the surface of the MXenes material to high-temperature heat treatment to fall off and react with the potassium hydrogen compound to form a potassium hydrogen carbon compound, and finally using hydrofluoric acid to remove the potassium hydrogen carbon compound to form carbon defects on the surface of the MXenes material, thereby obtaining a MXenes material rich in carbon defects. The preparation method of the present invention is simple, and the process is easy to control. The prepared MXenes material rich in carbon defects is used as a cathode catalyst in a magnesium-carbon dioxide battery, which can make the battery have good cycle stability and high coulombic efficiency

[0011] To achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery is carried out in the following order:

[0013] S1. Preparation of MAX powder: weigh M powder, A powder and carbon powder according to the stoichiometric ratio, add them into a planetary ball mill and ball mill for 10-24 hours, with a ball-to-material ratio of (5-10):1 and a rotation speed of 150-300 r / min. Then, the powder is loaded into a graphite mold, placed in a hot pressing sintering furnace, and sintered under vacuum or inert gas protection to obtain MAX powder;

[0014] S2. Preparation of MXenes powder: weigh 1-1.1 g of the MAX powder prepared in step S1, add it to a mixed solution consisting of 5-10 mol HCl and 0.5-1.0 g LiF, stir and react at 40-50 ° C for 24-48 hours, then centrifuge at 500-600 rpm for 2-5 minutes, wash with deionized water 3-6 times, and dry at 60-80 ° C for 24-48 hours to obtain MXenes powder;

[0015] S3, preparing MXenes materials containing potassium hydrogen carbon compounds: mixing potassium salt and other molten salts evenly, heating to 400-600°C, adding the MXenes powder prepared in step S2 and CaH 2 , react at 600-1000°C for 3-12h, cool to room temperature after the reaction, wash with deionized water 3-6 times, filter and dry to obtain MXenes material containing potassium hydrogen carbon compound;

[0016] S4. Preparation of MXenes material rich in carbon defects: The MXenes material containing potassium hydrogen carbon compound prepared in step S3 is placed in a tubular furnace, sintered under argon gas protection, cooled to room temperature, added with hydrofluoric acid and reacted at 35-55°C for 12-24h, and washed with deionized water for 3-6 times to obtain a MXenes material rich in carbon defects.

[0017] As a limitation of the preparation method of the present invention, in step S1, the MAX powder is Ti 3 AlC 2 、Ti 2 AlC、V 2 AlC、V 4 AlC 3 、MoTiAlC 2 , Nb 4 AlC 3 , Nb 2 AlC、Ti 3 SiC2 One or more of .

[0018] As another limitation of the preparation method of the present invention, in step S1, the heating rate during sintering is 5-10°C / min, the temperature is 1300-1400°C, the holding time is 1-2h, and the pressure is 20-50MPa.

[0019] As a third limitation of the preparation method of the present invention, in step S3, the potassium salt is KCl, K 2 CO 3 , KHCO 3 , K 2 C 2 O 4 One or more of; the other molten salt is LiF, LiCl, Li 2 CO 3 , CaCl 2 One or more of .

[0020] As a fourth limitation of the preparation method of the present invention, in step S3, the potassium salt is mixed with other molten salts, MXenes powder, CaH 2 The mass ratio between them is 1:2:1:0.5.

[0021] In the present invention, potassium salt is mixed with other molten salts. During this process, due to the change of the interaction between ions, a low eutectic mixture is formed. The melting point of the low eutectic mixture is lower than the melting points of each pure component. The lower melting point can make the magnesium-carbon dioxide battery operate at a relatively low temperature, thereby improving the cycle stability and coulombic efficiency of the battery.

[0022] Potassium salt and other molten salts, MXenes powder, CaH 2 The mass ratio between them is crucial, which will directly affect the formation of carbon defects on the surface of MXenes materials, and then affect the cycle stability and coulombic efficiency of magnesium-carbon dioxide batteries. Specifically: when potassium salt is mixed with other molten salts, MXenes powder, CaH 2 When the mass ratio between them is 1:2:1:0.5, ideal carbon defects will be formed, which will help enhance the conductivity and reactivity of MXenes materials, thereby improving the overall performance and cycle stability of magnesium-carbon dioxide batteries; if it is greater than this molar ratio, it will lead to excessive formation of carbon defects or inhibit the stable structure of MXenes, causing inhomogeneity and decreased stability of material performance, thereby shortening the cycle life and coulombic efficiency of magnesium-carbon dioxide batteries; less than this molar ratio will limit the formation of carbon defects, resulting in reduced surface activity and poor conductivity of MXenes materials, thereby leading to low charge and discharge efficiency and slower kinetic reaction rate of magnesium-carbon dioxide batteries.

[0023] As a fifth limitation of the preparation method of the present invention, in step S3, the drying temperature is 70-80° C. and the drying time is 8-12 h.

[0024] As a sixth limitation of the preparation method of the present invention, in step S4, the mass molar ratio of the MXenes material containing potassium hydrogen carbon compounds to hydrofluoric acid is (1-2): (1-3) g / mol.

[0025] In the present invention, the mass molar ratio of the MXenes material containing potassium hydrogen carbon compounds to hydrofluoric acid is extremely important. When the molar ratio is (1-2): (1-3) g / mol, some active sites on the surface of the MXenes material react moderately with the hydrofluoric acid, modifying and etching the surface of the material to a certain extent, optimizing the surface properties of the material, exposing more active groups that are beneficial to subsequent reactions, and the structure of the material remains basically stable, and its unique two-dimensional layered structure can be well maintained; if it is greater than this molar ratio, the concentration of hydrofluoric acid in the system will be too high, the reaction rate will be accelerated and too intense, resulting in excessive destruction of the interlayer structure of the MXenes material, increased interlayer spacing, and even collapse of the layered structure, and at the same time, the potassium hydrogen carbon compounds on the surface of the material will be excessively corroded, changing the original chemical composition and properties of the material; if it is less than this molar ratio, the amount of hydrofluoric acid will be insufficient to fully react with the MXenes material containing potassium hydrogen carbon compounds, and the excess potassium hydrogen carbon compounds on the surface of the material cannot be effectively removed, resulting in low purity of the material and insufficient exposure of active sites, thereby affecting the reactivity and performance of the material in subsequent applications.

[0026] The potassium hydrogen carbon compound formed in the preparation process of the present invention has a strong inter-ionic coordination effect with the surface functional groups in MXenes, and is not easy to decompose. The fluorine ions introduced by hydrofluoric acid can effectively attack the bonding site, and the strong chemical reaction between the two enables it to selectively destroy the structure of hydrocarbons without affecting the basic structure and performance of MXenes, thereby maintaining the integrity of MXenes. Hydrocarbons contain positively charged carbon atoms, and fluorine ions easily attack and react with positively charged carbon atoms. At the same time, the bond energy of CH and CC bonds in hydrocarbons is relatively low, while the metal-carbon (MC) bond energy in MXenes is high and has good stability. At the same time, the surface functional groups of MXenes can shield and weakly bond fluorine ions, and their layered structure also hinders the intrusion of fluorine ions. In addition, by controlling the reaction temperature, time, and hydrofluoric acid concentration, the fluorine ions can react with hydrocarbons first to avoid excessive damage to MXenes.

[0027] As the seventh limitation of the preparation method of the present invention, in step S4, the heating rate during sintering is 5-10°C / min, the temperature is 500-1000°C, and the insulation time is 12-24h.

[0028] The present invention is also limited in that, in step S4, the carbon defect concentration of the prepared carbon defect-rich MXenes material is 0.1-10%.

[0029] The present invention also provides an application of the carbon defect-rich MXenes material, and the prepared carbon defect-rich MXenes material is used in a magnesium-carbon dioxide battery.

[0030] In the preparation process of the present invention, potassium salt is mixed with other molten salts and then a hydrogen source is added to enable them to react with the MXenes precursor, thereby forming potassium hydrogen carbon compounds on the surface and between the layers of the MXenes. The presence of potassium hydrogen carbon compounds destroys the relatively stable atomic arrangement structure of MXenes; the high-temperature heat treatment process then provides sufficient energy for the chemical reaction, and the potassium hydrogen carbon compounds react with the carbon atoms in the MXenes at high temperatures. In the process of removing carbon from the surface of the MXenes, potassium ions participate in the formation of new chemical bonds, and recombine with carbon and hydrogen elements to form potassium hydrocarbons. This process causes a significant change in the crystal structure of MXenes, and the removal of carbon causes vacancies and distortions in the lattice; the final product is in contact with hydrofluoric acid, which contains HF covalent bonds. Since the fluoride ions in the hydrofluoric acid have high electronegativity and small ionic radius, the HF bonds have a certain polarity, so when reacting with the transition metal atoms on the surface of the MXenes, the HF bonds are easily broken, and fluoride ions with high reactivity are released, which replace some groups in the potassium hydrocarbons to form metal-fluorine bonds. After the metal-fluorine bond is formed, the electronegativity of fluorine is strong, resulting in high and stable bond energy, which changes the chemical environment of the MXenes surface and weakens the interaction between potassium hydrocarbons and the MXenes surface; at the same time, the metal-fluorine bond makes the MXenes surface negatively charged, resulting in electrostatic repulsion, thereby separating potassium hydrocarbons from the MXenes surface. Due to the large difference in chemical properties and size between fluoride ions and substituted groups, the substitution process will cause local stress changes in the MXenes structure. This stress change will cause some chemical bonds to break, thereby generating carbon defects, increasing the number and types of defects, and ultimately obtaining MXenes materials rich in carbon defects.

[0031] The MXenes material prepared by the present invention has regular carbon defects, which increase the specific surface area and surface active sites of the material and enhance the adsorption capacity of carbon dioxide molecules. On the other hand, carbon defects will cause additional electronic states to appear near the Fermi level, increasing the possibility of electron transition, thereby affecting the conductivity and electron transport properties of the material. During discharge, magnesium (Mg) as the negative electrode has strong reducibility and is easy to lose electrons and undergo oxidation reaction. The electrode reaction formula is: Mg-2e - =Mg 2+The generated magnesium ions enter the electrolyte solution and exist on the carbon defect active sites of the MXenes material. The activated CO 2 The magnesium ions (Mg 2+ ) reacts to generate magnesium oxide (MgO) and carbon (C). The overall reaction can be expressed as 2Mg+CO 2 =2MgO+C. In this process, the carbon defects in the MXene material promote electron transfer and chemical reactions, allowing the reaction to occur at a relatively low overpotential. During charging, under the action of an external electric field, electrons flow from the MXenes electrode to the magnesium electrode, and magnesium ions migrate from the MXenes electrode to the magnesium electrode. At this time, the magnesium oxide and carbon deposited on the surface of the MXenes electrode need to be converted back into carbon dioxide and magnesium. MXenes materials rich in carbon defects can provide active sites for this process, accelerating the decomposition of magnesium oxide and the oxidation of carbon. The special electronic structure at the carbon defect can reduce the reaction energy barrier of magnesium oxide decomposition and carbon oxidation, making these reactions easier to occur.

[0032] The above technical solution of the present invention is taken as a whole, and each step is closely related and influences each other, which jointly determine the morphological characteristics and performance of the product.

[0033] The above technical solution has the following advantages or beneficial effects:

[0034] 1. The carbon defect-rich MXenes material prepared by the present invention creates more active sites on the surface of the MXenes material, changes the surface chemical properties of the MXenes material, and thus improves the catalytic activity;

[0035] 2. The carbon defect-rich MXenes material prepared by the present invention can maintain its structural integrity, is not prone to agglomeration, and is safe and environmentally friendly;

[0036] 3. The carbon defect-rich MXenes material prepared by the present invention exhibits excellent cycle performance when used in magnesium-carbon dioxide batteries. -1 Under high current, it can stably cycle 150 times;

[0037] 4. The preparation method of the present invention is simple, the process is easy to control, and is suitable for large-scale industrial production.

[0038] The present invention is suitable for preparing MXenes materials rich in carbon defects.

[0039] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1This is a transmission scanning electron micrograph of the carbon defect-rich MXenes material prepared in Example 1 of the present invention;

[0041] Figure 2 The carbon defect-rich MXenes material prepared in Example 1 of the present invention is used as Mg-CO 2 Battery cathode catalyst at 200mA·g -1 Cycle performance diagram below;

[0042] Figure 3 This is the XRD pattern of the carbon defect-rich MXenes material prepared in Example 2 of the present invention;

[0043] Figure 4 The carbon defect-rich MXenes material prepared in Example 2 of the present invention is used as Mg-CO 2 Battery cathode catalyst at 200mA·g -1 Cycle performance diagram below;

[0044] Figure 5 The carbon defect-rich MXenes material prepared in Example 3 of the present invention is used as Mg-CO 2 Battery cathode catalyst at 200mA·g -1 Cycle performance diagram below;

[0045] Figure 6 The carbon defect-rich MXenes material prepared in Example 4 of the present invention is used as Mg-CO 2 Battery cathode catalyst at 200mA·g -1 Cycle performance diagram below;

[0046] Figure 7 The carbon defect-rich MXenes material prepared in Example 4 of the present invention is used as Mg-CO 2 Cycling performance diagram of battery cathode catalyst at different current densities. DETAILED DESCRIPTION

[0047] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0048] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0049] Example 1

[0050] This embodiment prepares a MXenes material rich in carbon defects for use in magnesium-carbon dioxide batteries, and the preparation process and steps are as follows:

[0051] S1. Preparation of MAX powder: Ti powder, Al powder and carbon powder were weighed according to the stoichiometric ratio, added into a planetary ball mill at a ball-to-material ratio of 5:1, and ball-milled at a speed of 150 r / min for 10 h. Then the powder was loaded into a graphite mold and placed in a hot pressing sintering furnace. Under the protection of argon atmosphere, the temperature was raised from room temperature to 1300°C at a heating rate of 5°C / min, and kept at this temperature for 1 h at a pressure of 20 MPa to obtain Ti 2 AlC powder;

[0052] S2. Preparation of MXenes powder: weigh 1gTi 2 AlC powder was added to a mixed solution of 5 mol HCl and 0.5 g LiF, stirred at 40 °C for 24 h, then centrifuged at 500 rpm for 2 min, washed three times with deionized water, and dried at 60 °C for 24 h to obtain the product Ti 2 C, i.e. MXenes powder;

[0053] S3, preparation of MXenes material containing potassium hydrogen carbon compound: 1g KCl and 2g LiF were mixed evenly, heated to 400°C, and 1g MXenes powder prepared in step S2 and 0.5g CaH 2 , react at 600°C for 3 hours, cool to room temperature after the reaction, wash with deionized water 3 times, filter, and then dry at 70°C for 8 hours to obtain MXenes materials containing potassium hydrogen carbon compounds;

[0054] S4. Preparation of MXenes material rich in carbon defects: Place 1 g of the MXenes material containing potassium hydrogen carbon compounds prepared in step S3 in a tubular furnace, and under the protection of argon gas, heat the temperature from room temperature to 500°C at a heating rate of 5°C / min, keep warm for 12 hours, cool to room temperature, add 1 mol of hydrofluoric acid and react at 35°C for 24 hours, wash with deionized water three times to obtain a MXenes material rich in carbon defects with a carbon defect concentration of 0.1%.

[0055] The carbon defect-rich MXenes material prepared in this example was tested by transmission scanning electron microscopy. Figure 1 As shown in the figure, it can be seen that the defects of the material are regular elliptical shapes and the defect dispersion is extremely uniform.

[0056] The carbon defect-rich MXenes material prepared in this example was used as a cathode catalyst in a magnesium-carbon dioxide battery, and its cycle performance was tested. Figure 2 As shown, the results show that at 200mA·g -1 Under the current of, it can circulate 95 times.

[0057] Example 2

[0058] This embodiment prepares a MXenes material rich in carbon defects for use in magnesium-carbon dioxide batteries, and the preparation process and steps are as follows:

[0059] S1. Preparation of MAX powder: Ti powder, Al powder and carbon powder were weighed according to the stoichiometric ratio, added into a planetary ball mill at a ball-to-material ratio of 8:1, and ball-milled at a speed of 200 r / min for 15 h. Then the powder was loaded into a graphite mold and placed in a hot pressing sintering furnace. Under the protection of argon atmosphere, the temperature was raised from room temperature to 1350°C at a heating rate of 8°C / min, and kept at this temperature for 1.5 h at a pressure of 30 MPa to obtain Ti 3 AlC 2 powder;

[0060] S2. Preparation of MXenes powder: weigh 1.05 g Ti 3 AlC 2 The powder was added to a mixed solution consisting of 6 mol HCl and 0.6 g LiF, stirred at 45 °C for 32 h, then centrifuged at 550 rpm for 3 min, washed 4 times with deionized water, and dried at 65 °C for 30 h to obtain the product Ti 3 C 2 , i.e. MXenes powder;

[0061] S3. Preparation of MXenes containing potassium hydrogen carbon compounds: 0.5 g K 2 CO 3 Mix well with 1 g LiCl, heat to 500 °C, add 0.5 g MXenes powder prepared in step S2 and 0.25 g CaH 2 , react at 800°C for 6 hours, cool to room temperature after the reaction, wash with deionized water 4 times, filter, and then dry at 75°C for 9 hours to obtain MXenes materials containing potassium hydrogen carbon compounds;

[0062] S4. Preparation of MXenes material rich in carbon defects: 1.2 g of the MXenes material containing potassium hydrogen carbon compound prepared in step S3 was placed in a tubular furnace. Under the protection of argon gas, the temperature was increased from room temperature to 800°C at a heating rate of 6°C / min, and the temperature was kept for 18 hours. After cooling to room temperature, 1.5 mol of hydrofluoric acid was added and reacted at 45°C for 20 hours. The material was washed with deionized water 4 times to obtain a MXenes material rich in carbon defects with a carbon defect concentration of 5%.

[0063] The MXenes material rich in carbon defects prepared in this example was subjected to XRD test. Figure 3 As shown in the figure, it can be seen that the Ti 3 C 2 The standard peaks of , indicating that the carbon defects introduced during the preparation process did not change the crystal phase of MXenes. This shows that despite the defects, the material still maintains its original structural stability.

[0064] The carbon defect-rich MXenes material prepared in this example was used as a cathode catalyst in a magnesium-carbon dioxide battery, and its cycle performance was tested. Figure 4 As shown, the results show that at 200mA·g -1 Under the current of , it can circulate 80 times.

[0065] Example 3

[0066] This embodiment prepares a MXenes material rich in carbon defects for use in magnesium-carbon dioxide batteries, and the preparation process and steps are as follows:

[0067] S1. Preparation of MAX powder: V powder, Al powder and carbon powder were weighed according to the stoichiometric ratio, added into a planetary ball mill at a ball-to-material ratio of 10:1, and ball-milled at a speed of 300 r / min for 24 h. Then the powder was loaded into a graphite mold and placed in a hot pressing sintering furnace. Under the protection of argon atmosphere, the temperature was raised from room temperature to 1400°C at a heating rate of 10°C / min, and kept at this temperature for 2 h at a pressure of 50 MPa to obtain V 2 AlC powder;

[0068] S2. Preparation of MXenes powder: weigh 1.1 g V 2 AlC powder was added to a mixed solution consisting of 8 mol HCl and 0.8 g LiF, stirred at 50 °C for 48 h, then centrifuged at 550 rpm for 4 min, washed 5 times with deionized water, and dried at 70 °C for 36 h to obtain product V 2 C, i.e. MXenes powder;

[0069] S3. Preparation of MXenes containing potassium hydrogen carbon compounds: 1.4 g KHCO 3 With 2.8 g Li 2 CO 3 Mix well, heat to 600 °C, add 1.4 g of MXenes powder prepared in step S2 and 0.7 g of CaH 2 , react at 1000°C for 12 hours, cool to room temperature after the reaction, wash with deionized water 5 times, filter, and then dry at 75°C for 10 hours to obtain MXenes materials containing potassium hydrogen carbon compounds;

[0070] S4. Preparation of MXenes material rich in carbon defects: 1.5 g of the MXenes material containing potassium hydrogen carbon compound prepared in step S3 was placed in a tubular furnace. Under the protection of argon gas, the temperature was increased from room temperature to 1000°C at a heating rate of 8°C / min, and the temperature was kept for 24 hours. After cooling to room temperature, 2.5 mol of hydrofluoric acid was added and reacted at 55°C for 12 hours. The material was washed with deionized water 5 times to obtain a MXenes material rich in carbon defects with a carbon defect concentration of 10%.

[0071] The carbon defect-rich MXenes material prepared in this example was used as a cathode catalyst in a magnesium-carbon dioxide battery, and its cycle performance was tested. Figure 5 As shown, the results show that at 200mA·g -1 Under the current of , it can circulate 150 times.

[0072] Example 4

[0073] This embodiment prepares a MXenes material rich in carbon defects for use in magnesium-carbon dioxide batteries, and the preparation process and steps are as follows:

[0074] S1. Preparation of MAX powder: Ti powder, Al powder and carbon powder were weighed according to the stoichiometric ratio, added into a planetary ball mill at a ball-to-material ratio of 8:1, and ball-milled at a speed of 200 r / min for 5 h. Then the powder was loaded into a graphite mold and placed in a hot pressing sintering furnace. Under the protection of argon atmosphere, the temperature was raised from room temperature to 1350°C at a heating rate of 8°C / min, and kept at this temperature for 1.5 h at a pressure of 30 MPa to obtain Ti 3 AlC 2 powder;

[0075] S2. Preparation of MXenes powder: weigh 1.05 g Ti 3 AlC 2The powder was added to a mixed solution consisting of 10 mol HCl and 1 g LiF, stirred at 40 °C for 48 h, then centrifuged at 600 rpm for 5 min, washed 6 times with deionized water, and dried at 80 °C for 48 h to obtain the product Ti 3 C 2 , i.e. MXenes powder;

[0076] S3. Preparation of MXenes containing potassium hydrogen carbon compounds: 2 g K 2 CO 3 Mix well with 4 g LiCl, heat to 400 °C, add 2 g MXenes powder prepared in step S2 and 1 g CaH 2 , react at 1000°C for 3 hours, cool to room temperature after the reaction, wash with deionized water 6 times, filter, and then dry at 80°C for 12 hours to obtain MXenes materials containing potassium hydrogen carbon compounds;

[0077] S4. Preparation of MXenes material rich in carbon defects: 2 g of the MXenes material containing potassium hydrogen carbon compound prepared in step S3 was placed in a tubular furnace. Under the protection of argon gas, the temperature was increased from room temperature to 800°C at a heating rate of 10°C / min, and the temperature was kept for 18 hours. After cooling to room temperature, 3 mol of hydrofluoric acid was added and reacted at 45°C for 24 hours. The material was washed with deionized water for 6 times to obtain a MXenes material rich in carbon defects with a carbon defect concentration of 5%.

[0078] The carbon defect-rich MXenes material prepared in this example was used as a cathode catalyst in a magnesium-carbon dioxide battery, and its cycle performance was tested. Figure 6 As shown, the results show that at 200mA·g -1 Under the current of , it can circulate 200 times. Figure 7 It can be seen that at high current density (500mA·g -1 ), it can still cycle 150 times, which shows its excellent cycle stability performance. At the same time, it proves that the MXenes material rich in carbon defects has good catalytic activity and conductivity, and can provide higher battery capacity.

[0079] Comparative Example

[0080] In order to explore the effects of different parameters or different preparation methods in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiments were conducted. Different catalyst materials were prepared in the following comparative examples, as follows:

[0081] Comparative Example 1

[0082] In this comparative example, a MXenes material is prepared. The preparation process is similar to that of Example 1, except that steps S3 and S4 are not performed.

[0083] Comparative Example 2

[0084] In this comparative example, a MXenes material having potassium hydrogen carbon compounds is prepared. The preparation process is similar to that of Example 1, except that step S4 is not performed.

[0085] Comparative Example 3

[0086] In this comparative example, a MXenes material rich in carbon defects is prepared. The preparation process is similar to that of Example 1, except that in step S3, the KCl is mixed with LiF, MXenes powder, and CaH 2 The mass ratio is 2:1:2:1.

[0087] Comparative Example 4

[0088] In this comparative example, a MXenes material rich in carbon defects is prepared. The preparation process is similar to that of Example 1, except that in step S4, the mass molar ratio of the MXenes material containing potassium hydrogen carbon compound to hydrofluoric acid is 1:5 g / mol.

[0089] Comparative Example 5

[0090] In this comparative example, a MXenes material rich in carbon defects is prepared. The preparation process is similar to that of Example 1, except that the preparation method of step S1 is different from that of Example 1, and the rest of the process is the same as that of Example 1. The specific preparation method of step S1 is as follows:

[0091] Titanium powder, aluminum powder and modified spherical graphite powder were placed in a vacuum hot pressing sintering furnace at a molar ratio of 2.95:1.05:1.6. Argon was used as the protective atmosphere in the furnace, the inflation pressure was set to 0.03 MPa, and the temperature was raised from room temperature to 1400°C at a heating rate of 5°C / min for hot pressing sintering for 3 hours. After the hot pressing sintering was completed, it was transported to a liquid nitrogen device for rapid cooling for 2 hours, and a large number of ordered carbon vacancies were generated inside the obtained MXA material.

[0092] Comparative Example 6

[0093] In this comparative example, a MXenes material is prepared. The preparation process is similar to that of Example 1, except that in step S4, hydrofluoric acid is not used, but the following strong acid is used:

[0094] Group A: using hydrochloric acid;

[0095] Group B: using sulfuric acid;

[0096] Group C: using nitric acid;

[0097] Group D: aqua regia (a mixture of hydrochloric acid and nitric acid in a volume ratio of 3:1) was used;

[0098] Group E: using fluorosulfonic acid;

[0099] Group F: Fluoroantimonic acid.

[0100] The catalyst materials prepared in Examples 1-4 and Comparative Examples 1-6 were used as positive electrode catalysts in magnesium-carbon dioxide batteries, and Coulomb efficiency tests were performed on them. The specific test results are as follows:

[0101]

[0102] It can be seen from the above table that when the catalyst materials prepared in Examples 1-4 are applied to magnesium-carbon dioxide batteries, the coulombic efficiency of magnesium-carbon dioxide batteries is higher than that of comparative examples 1-6, and is above 90%, indicating that the various steps of the technical solution of the present invention are closely related and influence each other, and jointly determine the morphology and performance of the product. At the same time, potassium salt and other molten salts, MXenes powder, CaH 2 The mass ratio between them and the amount of hydrofluoric acid used will affect the performance. In addition, in Comparative Example 6, the AF group used different strong acids to react with the generated potassium hydrogen carbon compound, and the results were not as good as hydrofluoric acid. This is because: although the hydrochloric acid, sulfuric acid, nitric acid, and aqua regia used in the AD group are also strong, they do not have fluorine elements and cannot cause defects on the surface of MXenes, so their coulomb efficiency is low; while the fluorosulfonic acid and fluoroantimonic acid used in the E and F groups mainly ionize H in the solution. + and SO 3 F - / SbF 6- , whose ionic radius is larger than F - The large electronegativity makes the fluoride ion extremely inactive and cannot provide sufficiently active fluoride ions like hydrofluoric acid to effectively attack the structure of potassium hydrocarbons. Finally, it cannot form defects on the surface of MXenes, resulting in a relatively low coulombic efficiency.

[0103] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries, characterized in that: Follow the steps below in order: S1. Preparation of MAX powder: weigh M powder, A powder and carbon powder according to the stoichiometric ratio, add them into a planetary ball mill and ball mill for 10-24 hours, with a ball-to-material ratio of (5-10):1 and a rotation speed of 150-300 r / min. Then, the powder is loaded into a graphite mold, placed in a hot pressing sintering furnace, and sintered under vacuum or inert gas protection to obtain MAX powder; S2. Preparation of MXenes powder: 1-1.1 g of the MAX powder prepared in step S1 was weighed, and added to a mixed solution consisting of 5-10 mol HCl and 0.5-1.0 g LiF, and stirred at 40-50° C. for 24-48 h, and then centrifuged at 500-600 rpm for 2-5 min, washed with deionized water for 3-6 times, and dried at 60-80° C. for 24-48 h to obtain MXenes powder; S3, preparing MXenes materials containing potassium hydrogen carbon compounds: mixing potassium salt and other molten salts evenly, heating to 400-600°C, adding the MXenes powder prepared in step S2 and CaH2 thereto, reacting at 600-1000°C for 3-12h, cooling to room temperature after the reaction, washing with deionized water for 3-6 times, filtering and drying to obtain MXenes materials containing potassium hydrogen carbon compounds; S4. Preparation of MXenes material rich in carbon defects: The MXenes material containing potassium hydrogen carbon compound prepared in step S3 is placed in a tubular furnace, sintered under argon gas protection, cooled to room temperature, added with hydrofluoric acid and reacted at 35-55°C for 12-24h, and washed with deionized water for 3-6 times to obtain a MXenes material rich in carbon defects.

2. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S1, the MAX powder is one or more of Ti3AlC2, Ti2AlC, V2AlC, V4AlC3, MoTiAlC2, Nb4AlC3, Nb2AlC, and Ti3SiC2.

3. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S1, the heating rate during sintering is 5-10°C / min, the temperature is 1300-1400°C, the insulation time is 1-2h, and the pressure is 20-50MPa.

4. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S3, the potassium salt is one or more of KCl, K2CO3, KHCO3, and K2C2O4; the other molten salt is one or more of LiF, LiCl, Li2CO3, and CaCl2.

5. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S3, the mass ratio of the potassium salt to other molten salts, MXenes powder, and CaH2 is 1:2:1:0.

5.

6. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S3, the drying temperature is 70-80°C and the drying time is 8-12 hours.

7. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S4, the mass molar ratio of the MXenes material containing potassium hydrogen carbon compound to hydrofluoric acid is (1-2): (1-3) g / mol.

8. The method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to claim 1, characterized in that: In step S4, the heating rate during sintering is 5-10°C / min, the temperature is 500-1000°C, and the holding time is 12-24h.

9. A method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to any one of claims 1 to 8, characterized in that: In step S4, the carbon defect concentration of the prepared carbon defect-rich MXenes material is 0.1-10%.

10. A method for preparing a carbon defect-rich MXenes material for a magnesium-carbon dioxide battery according to any one of claims 1 to 8, characterized in that: The prepared carbon-defect-rich MXenes materials are used in magnesium-carbon dioxide batteries.

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