A method for the preparation of carbon-rich-defect mxenes materials for use in magnesium-carbon dioxide batteries

Abstract

The application discloses a preparation method of carbon-defect-rich MXenes material for a magnesium-carbon dioxide battery, which comprises the following steps: introducing potassium ions and a hydrogen source into a MXenes base material, so that potassium hydrogen compounds are formed on the surface and between the layers of the MXenes; through high-temperature heat treatment, carbon on the surface of the MXenes material is removed and reacts with the potassium hydrogen compounds to form potassium hydrogen carbon compounds; finally, hydrofluoric acid is used to remove the potassium hydrogen carbon compounds, so that carbon defects are formed on the surface of the MXenes material, and the carbon-defect-rich MXenes material is obtained. The preparation method is simple, and the process is easy to control. The carbon-defect-rich MXenes material prepared by the method is used as a positive electrode catalyst in the magnesium-carbon dioxide battery, so that the battery has good cycle stability and high coulomb efficiency.

Description

Technical Field

[0001] This invention belongs to the field of novel inorganic functional materials and relates to a method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries. Background Technology

[0002] Metal-carbon dioxide batteries possess the dual functions of CO2 utilization and electrical energy storage. Among various metal-carbon dioxide batteries, the Mg-CO2 battery exhibits the highest thermodynamic equilibrium potential (2.80 V) and the largest theoretical specific energy (1880 Wh·kg⁻¹). -1 This makes Mg-CO2 batteries a potentially revolutionary energy storage technology. However, the development of Mg-CO2 batteries is still limited by slow reaction kinetics. The slow reaction kinetics of the active material CO2 leads to irreversible reactions and battery failure, necessitating the development of efficient catalysts to accelerate the conversion reaction kinetics during discharge and charging. Two-dimensional materials, especially two-dimensional layered MXene materials, as a novel material, possess excellent metallic conductivity and abundant surface functional groups, making them highly efficient catalyst materials for Mg-CO2 batteries. Therefore, the preparation of low-cost, safe, and environmentally friendly carbon-deficient MXene-modified catalyst materials through simple methods is of great significance for magnesium-carbon dioxide batteries.

[0003] Currently prepared Mg-CO2 battery catalyst materials have certain defects. For example, patent CN119029421A discloses an amine-containing electrolyte for realizing a rechargeable magnesium carbon dioxide battery, its preparation method, and its application. However, when the electrolyte prepared therein is applied to a Mg-CO2 battery, although at 100 mA·g... -1 It can be circulated for 400 hours, but the electrolyte is prone to decomposition, resulting in excessively high overpotential.

[0004] The paper "Angew. Chem. Int. Ed. 2024, 63" describes a method to optimize CO2 utilization through chemical means and improve magnesium ion transport at the electrode interface through material design, thereby significantly enhancing the overall performance of Mg-CO2 batteries. This battery achieves a performance of 200 mA·g -1 It can withstand 70 cycles, exhibiting excellent cycle stability. While the PDA-mediated reversible magnesium anode interface electrolyte promotes the reversible deposition / dissolution of magnesium ions, it is also more prone to side reactions with the electrolyte. These excessive side reactions lead to uneven local current density, resulting in irregular deposition layers on the magnesium anode surface, ultimately affecting battery performance.

[0005] Patent CN110010862A discloses a magnesium secondary battery cathode material MXene Ti3C2 / TiS2 and its preparation method. It uses two-dimensional material MXene Ti3C2 as a substrate, with layered TiS2 loaded within the MXene Ti3C2 sheets. The resulting material, used as a magnesium battery cathode material, exhibits relatively low capacity decay in electrochemical performance testing, but the maximum tested current density is only 200 mA·g. -1 This indicates that at high current density (500 mA·g) -1 The catalytic effect is poor under certain conditions.

[0006] Therefore, the main problem with magnesium-carbon dioxide batteries is:

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

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

[0009] (3) The catalyst is prone to more side reactions with the electrolyte during the reaction, which will form irregular deposits on the surface of the material. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention aims to provide a method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries. The method involves introducing potassium ions and a hydrogen source onto an MXenes substrate, causing potassium hydride compounds to form on the MXenes surface and between layers. High-temperature heat treatment then removes carbon from the MXenes surface, reacting it with the potassium hydride compounds to form potassium-hydrocarbon compounds. Finally, hydrofluoric acid is used to remove the potassium-hydrocarbon compounds, resulting in carbon defects on the MXenes surface, thus obtaining carbon-defect-rich MXenes materials. This invention offers a simple preparation method with easily controlled processes. The resulting carbon-defect-rich MXenes materials, when used as cathode catalysts in magnesium-carbon dioxide batteries, contribute to good cycle stability and high coulombic efficiency.

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

[0012] A method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries comprises the following steps in sequence:

[0013] S1. Preparation of MAX powder: Weigh M powder, A powder and carbon powder according to the stoichiometric ratio, add them to a planetary ball mill and ball mill for 10-24 h, with a ball-to-material ratio of (5-10):1 and a rotation speed of 150-300 r / min. Then, load the powder into a graphite mold and place it in a hot press sintering furnace for sintering 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 obtained 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℃ for 24-48 h, then centrifuge at 500-600 rpm for 2-5 min, wash with deionized water 3-6 times, and dry at 60-80℃ for 24-48 h to obtain MXenes powder;

[0015] S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: Mix potassium salt with other molten salts evenly, heat to 400-600℃, add MXenes powder and CaH2 prepared in step S2, react at 600-1000℃ for 3-12h, cool to room temperature after the reaction is completed, wash with deionized water 3-6 times, filter and dry to obtain MXenes material containing potassium hydrogen carbon compounds.

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

[0017] As a limitation of the preparation method of the present invention, in step S1, the MAX powder is one or more of Ti3AlC2, Ti2AlC, V2AlC, V4AlC3, MoTiAlC2, Nb4AlC3, Nb2AlC, and Ti3SiC2.

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

[0019] As a third limitation of the preparation method of the present invention, 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.

[0020] As a fourth limitation of the preparation method of the present invention, in step S3, the mass ratio of the potassium salt to other molten salts, MXenes powder, and CaH2 is 1:2:1:0.5.

[0021] In this invention, potassium salt is mixed with other molten salts. During this process, due to the change in interionic interactions, a eutectic mixture is formed. The melting point of the eutectic mixture is lower than that of each pure component. The lower melting point allows the magnesium-carbon dioxide battery to operate at a relatively low temperature, thereby improving the battery's cycle stability and coulombic efficiency.

[0022] The mass ratio of potassium salt to other molten salts, MXenes powder, and CaH2 is crucial, directly affecting the formation of carbon defects on the surface of MXenes materials, and consequently influencing the cycle stability and coulombic efficiency of magnesium-carbon dioxide batteries. Specifically: when the mass ratio of potassium salt to other molten salts, MXenes powder, and CaH2 is 1:2:1:0.5, ideal carbon defects are formed, which helps enhance the conductivity and reactivity of MXenes materials, thereby improving the overall performance and cycle stability of magnesium-carbon dioxide batteries. If the molar ratio is greater than this, it will lead to excessive formation of carbon defects or inhibit the stable structure of MXenes, causing non-uniformity and decreased stability of material properties, thus shortening the cycle life and reducing the coulombic efficiency of magnesium-carbon dioxide batteries. If the molar ratio is less than this, it will limit the formation of carbon defects, leading to reduced surface activity and poor conductivity of MXenes materials, resulting in low charge-discharge efficiency and slowed 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℃ and the 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 compound to hydrofluoric acid is (1-2):(1-3) g / mol.

[0025] In this invention, the molar ratio of MXenes material containing potassium hydroxide 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 hydrofluoric acid, modifying and etching the material surface to a certain extent, thus 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, thus maintaining its unique two-dimensional layered structure. If the molar ratio is greater than this, the concentration of hydrofluoric acid in the system will be too high, the reaction rate will be accelerated and too violent, resulting in excessive destruction of the interlayer structure of the MXenes material, increased interlayer spacing, and even collapse of the layered structure. At the same time, the potassium hydroxide on the surface of the material will be excessively eroded, changing the original chemical composition and properties of the material. If the molar ratio is less than this, the amount of hydrofluoric acid will be insufficient to react fully with the MXenes material containing potassium hydroxide, and the excess potassium hydroxide on the surface of the material cannot be effectively removed, resulting in low purity of the material, insufficient exposure of active sites, and thus affecting the reactivity and performance of the material in subsequent applications.

[0026] The potassium-hydrogen-carbon compound formed during the preparation process of this invention has a strong interionic coordination with the surface functional groups of MXenes, making it difficult to decompose. Fluoride ions introduced by hydrofluoric acid can effectively attack the bonding sites. The strong chemical reaction between the two allows for the selective destruction of the hydrocarbon structure without affecting the basic structure and properties of MXenes, thus maintaining the integrity of MXenes. Hydrocarbons contain positively charged carbon atoms, which fluoride ions readily attack and react with. Simultaneously, the CH and CC bonds in hydrocarbons have relatively low bond energies, while the metal-carbon (MC) bonds in MXenes have high bond energies and good stability. Furthermore, the surface functional groups of MXenes can shield and weakly bond fluoride ions, and their layered structure also hinders the intrusion of fluoride ions. In addition, by controlling the reaction temperature, time, and hydrofluoric acid concentration, fluoride ions can preferentially react with hydrocarbons, avoiding excessive destruction of MXenes.

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

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

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

[0030] In the preparation process of this 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 MXenes. The presence of potassium-hydrogen-carbon compounds disrupts the originally relatively stable atomic arrangement structure of MXenes. The subsequent high-temperature heat treatment process provides sufficient energy for the chemical reaction. At high temperatures, the potassium-hydrogen-carbon compounds react with carbon atoms in MXenes. During the removal of carbon from the MXenes surface, potassium ions participate in the formation of new chemical bonds, recombine with carbon and hydrogen elements to form potassium hydrocarbons. This process significantly changes the crystal structure of MXenes, with the removal of carbon leading to vacancies and distortions in the crystal lattice. Finally, the product comes into contact with hydrofluoric acid, which contains HF covalent bonds. Due to the high electronegativity and small ionic radius of fluoride ions in hydrofluoric acid, the HF bonds have a certain polarity. Therefore, when reacting with transition metal atoms on the surface of MXenes, the HF bonds are easily broken, releasing highly reactive fluoride ions, which then replace some groups in the potassium hydrocarbons to form metal-fluorine bonds. After the formation of metal-fluorine bonds, the strong electronegativity of fluorine leads to high and stable bond energies, altering the chemical environment of the MXenes surface and weakening the interaction between potassium hydrocarbons and the MXenes surface. Simultaneously, the metal-fluorine bonds impart a negative charge to the MXenes surface, generating electrostatic repulsion, thus causing potassium hydrocarbons to separate from the MXenes surface. Due to the significant differences in chemical properties and size between fluoride ions and the substituted groups, the substitution process induces localized stress changes in the MXenes structure. These stress changes lead to the breakage of some chemical bonds, resulting in carbon defects. This increases the number and types of defects, ultimately yielding MXenes materials rich in carbon defects.

[0031] The MXenes material prepared by this invention exhibits regular carbon defects. These defects increase the specific surface area and surface active sites of the material, enhancing its adsorption capacity for carbon dioxide molecules. Furthermore, carbon defects introduce additional electronic states near the Fermi level, increasing the likelihood of electron transitions and thus affecting the material's conductivity and electron transport properties. During discharge, magnesium (Mg) acts as the negative electrode, exhibiting strong reducing properties and readily losing electrons to undergo oxidation. The electrode reaction is: Mg - 2e⁻ - =Mg 2+ The generated magnesium ions enter the electrolyte solution and reside at the carbon defect active sites of the MXenes material. The activated CO2 molecules then react with the magnesium ions (Mg2+) that migrate from the electrolyte. 2+The reaction occurs, producing magnesium oxide (MgO) and carbon (C), and the overall reaction can be represented as 2Mg + CO2 = 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 influence of an applied electric field, electrons flow from the MXenes electrode to the magnesium electrode, while magnesium ions migrate from the MXenes electrode to the magnesium electrode. At this point, the magnesium oxide and carbon deposited on the MXenes electrode surface need to be converted back into carbon dioxide and magnesium. The carbon defect-rich MXenes material 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 defects can lower the reaction energy barriers for magnesium oxide decomposition and carbon oxidation, making these reactions more likely to occur.

[0032] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they 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 this 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 this invention can maintain its structural integrity, is not prone to aggregation, and is safe and environmentally friendly;

[0036] 3. The carbon-defect-rich MXenes material prepared by this invention exhibits excellent cycling performance when used in magnesium-carbon dioxide batteries, reaching 500 mA·g. -1 Under high current, it can stably cycle 150 times;

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

[0038] This invention is applicable to the preparation of MXenes materials rich in carbon defects.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

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

[0041] Figure 2The carbon-defect-rich MXenes material prepared in Example 1 of this invention was used as a cathode catalyst in a Mg-CO2 battery at 200 mA·g -1 The following is a graph showing the cyclic performance.

[0042] Figure 3 The image shows the XRD pattern of the carbon-defective MXenes material prepared in Example 2 of this invention.

[0043] Figure 4 The carbon-defect-rich MXenes material prepared in Example 2 of this invention was used as a cathode catalyst in a Mg-CO2 battery at 200 mA·g -1 The following is a graph showing the cyclic performance.

[0044] Figure 5 The carbon-defect-rich MXenes material prepared in Example 3 of this invention was used as a cathode catalyst in a Mg-CO2 battery at 200 mA·g -1 The following is a graph showing the cyclic performance.

[0045] Figure 6 The carbon-defect-rich MXenes material prepared in Example 4 of this invention was used as a cathode catalyst in a Mg-CO2 battery at 200 mA·g -1 The following is a graph showing the cyclic performance.

[0046] Figure 7 The graph shows the cycling performance of the carbon-defective MXenes material prepared in Example 4 of this invention as a positive electrode catalyst for Mg-CO2 batteries at different current densities. Detailed Implementation

[0047] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0049] Example 1

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

[0051] S1. Preparation of MAX powder: Weigh Ti powder, Al powder and carbon powder according to the stoichiometric ratio, add them to a planetary ball mill at a ball-to-material ratio of 5:1, and ball mill at 150 r / min for 10 h. Then, load the powder into a graphite mold and place it in a hot press sintering furnace. Under the protection of argon atmosphere, heat the powder from room temperature to 1300℃ at a heating rate of 5℃ / min, hold it at 1 h, and pressurize it at 20 MPa to obtain Ti2AlC powder.

[0052] S2. Preparation of MXenes powder: Weigh 1 g of Ti2AlC powder and add it to a mixed solution of 5 mol HCl and 0.5 g LiF. Stir the mixture at 40 °C for 24 h, then centrifuge at 500 rpm for 2 min, wash with deionized water 3 times, and dry at 60 °C for 24 h to obtain the product Ti2C, i.e., MXenes powder.

[0053] S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: 1 g KCl and 2 g LiF were mixed evenly and heated to 400℃. 1 g of MXenes powder prepared in step S2 and 0.5 g CaH2 were added to the mixture and reacted at 600℃ for 3 h. After the reaction was completed, the mixture was cooled to room temperature, washed 3 times with deionized water, filtered, and then dried at 70℃ for 8 h to obtain MXenes material containing potassium hydrogen carbon compounds.

[0054] S4. Preparation of carbon-defect-rich MXenes material: 1 g of the MXenes material containing potassium hydrogen carbon compounds prepared in step S3 was placed in a tube furnace and heated from room temperature to 500℃ at a heating rate of 5℃ / min under argon gas protection. The temperature was held for 12 h and then cooled to room temperature. 1 mol of hydrofluoric acid was added and reacted at 35℃ for 24 h. The mixture was washed three times with deionized water to obtain carbon-defect-rich MXenes material with a carbon defect concentration of 0.1%.

[0055] The carbon-defect-rich MXenes material prepared in this embodiment was subjected to transmission scanning electron microscopy (TEM) testing, such as... Figure 1 As shown in the figure, the defects in the material are regular elliptical in shape, and the defect dispersion is extremely uniform.

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

[0057] Example 2

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

[0059] S1. Preparation of MAX powder: Weigh Ti powder, Al powder and carbon powder according to stoichiometric ratio, add them to a planetary ball mill at a ball-to-material ratio of 8:1, and ball mill at 200 r / min for 15 h. Then, load the powder into a graphite mold and place it in a hot press sintering furnace. Under the protection of argon atmosphere, heat the powder from room temperature to 1350℃ at a heating rate of 8℃ / min, hold it at 1.5 h, and pressurize it at 30 MPa to obtain Ti3AlC2 powder.

[0060] S2. Preparation of MXenes powder: Weigh 1.05 g Ti3AlC2 powder and add it to a mixed solution consisting of 6 mol HCl and 0.6 g LiF. Stir the mixture at 45℃ for 32 h, then centrifuge at 550 rpm for 3 min, wash with deionized water 4 times, and dry at 65℃ for 30 h to obtain the product Ti3C2, i.e., MXenes powder.

[0061] S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: 0.5 g K2CO3 and 1 g LiCl were mixed evenly and heated to 500℃. 0.5 g of MXenes powder prepared in step S2 and 0.25 g CaH2 were added to the mixture and reacted at 800℃ for 6 h. After the reaction was completed, the mixture was cooled to room temperature, washed 4 times with deionized water, filtered, and then dried at 75℃ for 9 h to obtain MXenes material containing potassium hydrogen carbon compounds.

[0062] S4. Preparation of carbon-defect-rich MXenes material: 1.2 g of the MXenes material containing potassium hydrogen carbon compounds prepared in step S3 was placed in a tube furnace and heated from room temperature to 800℃ at a heating rate of 6℃ / min under argon gas protection. The temperature was held for 18 h, cooled to room temperature, and then 1.5 mol of hydrofluoric acid was added and reacted at 45℃ for 20 h. The mixture was washed 4 times with deionized water to obtain carbon-defect-rich MXenes material with a carbon defect concentration of 5%.

[0063] The carbon-defect-rich MXenes material prepared in this embodiment was subjected to XRD testing, such as... Figure 3 As shown in the figure, the standard peak of Ti3C2 corresponding to the carbon-defective MXenes can be seen, indicating that the carbon defects introduced during the preparation process did not change the crystal phase of MXenes. This shows that despite the presence of defects, the material still maintains its original structural stability.

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

[0065] Example 3

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

[0067] S1. Preparation of MAX powder: Weigh V powder, Al powder and carbon powder according to the stoichiometric ratio, add them to a planetary ball mill at a ball-to-material ratio of 10:1, and ball mill at 300 r / min for 24 h. Then, load the powder into a graphite mold and place it in a hot press sintering furnace. Under the protection of argon atmosphere, heat the powder from room temperature to 1400℃ at a heating rate of 10℃ / min, hold it at that temperature for 2 h, and pressurize it at 50 MPa to obtain V2AlC powder.

[0068] S2. Preparation of MXenes powder: Weigh 1.1 g of V2AlC powder and add it to a mixed solution consisting of 8 mol HCl and 0.8 g LiF. Stir the mixture at 50 °C for 48 h, then centrifuge at 550 rpm for 4 min, wash with deionized water 5 times, and dry at 70 °C for 36 h to obtain product V2C, i.e., MXenes powder.

[0069] S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: 1.4 g KHCO3 and 2.8 g Li2CO3 were mixed evenly and heated to 600℃. 1.4 g of MXenes powder prepared in step S2 and 0.7 g CaH2 were added to the mixture and reacted at 1000℃ for 12 h. After the reaction was completed, the mixture was cooled to room temperature, washed 5 times with deionized water, filtered, and then dried at 75 ℃ for 10 h to obtain MXenes material containing potassium hydrogen carbon compounds.

[0070] S4. Preparation of carbon-defect-rich MXenes material: 1.5 g of the MXenes material containing potassium hydrogen carbon compounds prepared in step S3 was placed in a tube furnace and heated from room temperature to 1000℃ at a heating rate of 8℃ / min under argon gas protection. The temperature was held for 24 h, cooled to room temperature, and then 2.5 mol of hydrofluoric acid was added and reacted at 55℃ for 12 h. The mixture was washed 5 times with deionized water to obtain carbon-defect-rich MXenes material with a carbon defect concentration of 10%.

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

[0072] Example 4

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

[0074] S1. Preparation of MAX powder: Weigh Ti powder, Al powder and carbon powder according to stoichiometric ratio, add them to a planetary ball mill at a ball-to-material ratio of 8:1, and ball mill at 200 r / min for 5 h. Then, load the powder into a graphite mold and place it in a hot press sintering furnace. Under the protection of argon atmosphere, heat the powder from room temperature to 1350℃ at a heating rate of 8℃ / min, hold it at 1.5 h, and pressurize it at 30 MPa to obtain Ti3AlC2 powder.

[0075] S2. Preparation of MXenes powder: Weigh 1.05 g Ti3AlC2 powder and add it to a mixed solution of 10 mol HCl and 1 g LiF. Stir the mixture at 40 °C for 48 h, then centrifuge at 600 rpm for 5 min, wash with deionized water 6 times, and dry at 80 °C for 48 h to obtain the product Ti3C2, i.e., MXenes powder.

[0076] S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: 2 g K2CO3 and 4 g LiCl were mixed evenly and heated to 400℃. 2 g of MXenes powder prepared in step S2 and 1 g CaH2 were added to the mixture and reacted at 1000℃ for 3 h. After the reaction was completed, the mixture was cooled to room temperature, washed 6 times with deionized water, filtered, and then dried at 80℃ for 12 h to obtain MXenes material containing potassium hydrogen carbon compounds.

[0077] S4. Preparation of carbon-defect-rich MXenes material: 2 g of the MXenes material containing potassium hydrogen carbon compounds prepared in step S3 was placed in a tube furnace and heated from room temperature to 800℃ at a heating rate of 10℃ / min under argon gas protection. The temperature was held for 18 h, cooled to room temperature, and then 3 mol of hydrofluoric acid was added and reacted at 45℃ for 24 h. The mixture was washed 6 times with deionized water to obtain carbon-defect-rich MXenes material with a carbon defect concentration of 5%.

[0078] The carbon-defect-rich MXenes material prepared in this embodiment was used as a cathode catalyst in a magnesium-carbon dioxide battery, and its cycle performance was tested. Figure 6 As shown, the results indicate that at 200 mA·g -1 Under a given current, it can cycle 200 times. Furthermore, from... Figure 7 As can be seen from this, under high current density (500 mA·g), -1 It can still cycle 150 times, which shows its excellent cycle stability. It also confirms that MXenes materials rich in carbon defects have good catalytic activity and conductivity, and can provide high battery capacity.

[0079] Comparative Example

[0080] To investigate the effects of different parameters or preparation methods on the performance of the product of this invention, the following comparative experiments were conducted. Different catalyst materials were prepared in the following comparative examples:

[0081] Comparative Example 1

[0082] This comparative example prepares an MXenes material. The preparation process is similar to that of Example 1, except that steps S3 and S4 are not performed.

[0083] Comparative Example 2

[0084] This comparative example prepares an MXenes material containing potassium hydrogen carbon compounds. The preparation process is similar to that of Example 1, except that step S4 is omitted.

[0085] Comparative Example 3

[0086] This comparative example prepares a carbon-defect-rich MXenes material. The preparation process is similar to that of Example 1, except that in step S3, the mass ratio of KCl to LiF, MXenes powder, and CaH2 is 2:1:2:1.

[0087] Comparative Example 4

[0088] This comparative example prepares a carbon-defect-rich MXenes material. 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] This comparative example prepares a carbon-defect-rich MXenes material. 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. 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, and the gas pressure was set to 0.03 MPa. The temperature was increased from room temperature to 1400℃ at a heating rate of 5℃ / min for 3 hours. After the hot pressing sintering was completed, the material was transported to a liquid nitrogen device for rapid cooling for 2 hours. A large number of ordered carbon vacancies were generated inside the obtained MXA material.

[0092] Comparative Example 6

[0093] This comparative example prepares an MXenes material. 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 instead:

[0094] Group A: Use hydrochloric acid;

[0095] Group B: Use sulfuric acid;

[0096] Group C: Use nitric acid;

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

[0098] Group E: Use 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 their coulombic efficiency was tested. The specific test results are as follows:

[0101]

[0102] As shown in the table above, when the catalyst materials prepared in Examples 1-4 are applied to magnesium-carbon dioxide batteries, the coulombic efficiency of the magnesium-carbon dioxide batteries is higher than that of Comparative Examples 1-6, and is all above 90%. This indicates that the various steps of the technical solution of this invention are closely related and mutually influential, jointly determining the morphological characteristics and performance of the product. Furthermore, the mass ratio of potassium salt to other molten salts, MXenes powder, and CaH2, as well as the amount of hydrofluoric acid, all affect performance. In addition, in Comparative Example 6, the AF group reacted with different strong acids with the generated potassium-carbon compound, and the results were all inferior to those with hydrofluoric acid. This is because: although the hydrochloric acid, sulfuric acid, nitric acid, and aqua regia used in the AD group are also relatively strong acids, they lack fluorine and cannot create defects on the MXenes surface, thus resulting in lower coulombic efficiency; while the fluorosulfonic acid and fluoroantimony acid used in the E and F groups mainly ionize H+ in solution. + and SO3F - / SbF6 - Its ionic radius is greater than that of F - The large electronegativity of fluoride ions results in extremely low reactivity, unlike hydrofluoric acid which provides enough reactive fluoride ions to effectively attack the structure of potassium hydrocarbons. Consequently, it is also unable to form defects on the MXenes surface, leading to relatively low coulombic efficiency.

[0103] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within 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 these steps in sequence: S1. Preparation of MAX powder: Weigh M powder, A powder and carbon powder according to the stoichiometric ratio, add them to 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, load the powder into a graphite mold and place it in a hot-press sintering furnace for sintering under vacuum or inert gas protection to obtain MAX powder; the MAX powder is one or more of Ti3AlC2, Ti2AlC, V2AlC, V4AlC3, MoTiAlC2, Nb4AlC3, Nb2AlC, and Ti3SiC2. S2. Preparation of MXenes powder: Weigh 1-1.1 g of the MAX powder obtained 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℃ for 24-48 h, then centrifuge at 500-600 rpm for 2-5 min, wash with deionized water 3-6 times, and dry at 60-80℃ for 24-48 h to obtain MXenes powder; S3. Preparation of MXenes material containing potassium hydrogen carbon compounds: Mix potassium salt with other molten salts evenly, wherein the other molten salts are one or more of LiF, LiCl, Li2CO3, and CaCl2, heat to 400-600℃, add MXenes powder and CaH2 prepared in step S2, wherein the mass ratio of potassium salt to other molten salts, MXenes powder and CaH2 is 1:2:1:0.5, react at 600-1000℃ for 3-12 h, after the reaction is completed, cool to room temperature, wash with deionized water 3-6 times, filter and dry to obtain MXenes material containing potassium hydrogen carbon compounds; S4. Preparation of carbon-defect-rich MXenes material: The MXenes material containing potassium hydrogen carbon compounds prepared in step S3 is placed in a tube furnace and sintered under argon gas protection. After cooling to room temperature, hydrofluoric acid is added and reacted at 35-55℃ for 12-24 h. The mixture is washed 3-6 times with deionized water to obtain carbon-defect-rich MXenes material. The mass molar ratio of the MXenes material containing potassium hydrogen carbon compounds to hydrofluoric acid is (1-2):(1-3) g / mol.

2. The method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries according to claim 1, characterized in that, In step S1, the heating rate during sintering is 5-10℃ / min, the temperature is 1300-1400℃, the holding time is 1-2 h, and the pressure is 20-50 MPa.

3. The method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries according to claim 1, characterized in that, In step S3, the potassium salt is one or more of KCl, K2CO3, KHCO3, and K2C2O4.

4. The method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries according to claim 1, characterized in that, In step S3, the drying temperature is 70-80 ℃ and the time is 8-12 h.

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

6. A method for preparing carbon-defect-rich MXenes materials for magnesium-carbon dioxide batteries according to any one of claims 1-5, characterized in that, In step S4, the carbon defect concentration of the carbon defect-rich MXenes material is 0.1-10%.

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