A magnesium-carbon dioxide battery cathode material and a preparation method thereof

Abstract

The application discloses a magnesium-carbon dioxide battery positive electrode material and a preparation method thereof, and a chemical composition general formula of the magnesium-carbon dioxide battery positive electrode material is Mo 4 / 3 R 2a / 3B2-V R’ , wherein V R’ represents a vacancy of R', R is one or more of Lu, Dy, Er, Ho and Tb, R' is Y or Sc, and 0.1<=a<=0.9; the material is obtained by calcination firstly to obtain Mo 4 / 3 R' 2 / 3‑2a / 3 R 2a / 3AlB2, then etching agent is added to selectively etch transition metals (Y or Sc) and Al, so that a ternary transition metal boride, i.e., a positive electrode material of a magnesium-carbon dioxide metal battery, is obtained. The preparation method is simple, and a process is easy to control. The positive electrode material of the magnesium-carbon dioxide metal battery prepared by the method has excellent catalytic performance, low overpotential and long cycle life, and can efficiently and stably absorb and utilize carbon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of magnesium battery technology, and relates to a magnesium-carbon dioxide battery cathode material and its preparation method. Background Technology

[0002] With the increasing global demand for clean energy and the intensification of climate change issues, traditional energy storage technologies such as lithium-ion batteries face challenges such as limited resources. Metal-carbon dioxide batteries are considered a novel electrochemical energy storage technology that combines clean energy storage with greenhouse gas utilization. They utilize metals (such as lithium, sodium, magnesium, and aluminum) as electrodes and carbon dioxide as the active material, achieving energy storage and release through the electrochemical reaction between the metal and carbon dioxide. Their working principle is based on the oxidation of the metal anode and the reduction of carbon dioxide. Considering the safety hazards and poor stability of highly reactive alkali metals, magnesium has received widespread attention due to its more stable properties. It possesses a relatively low redox potential (2.38V) and a high theoretical capacity (3833mAh / cm³). 3 Despite its advantages such as high energy density, abundant resources, and environmental friendliness, this technology still faces technical challenges, including slow reaction kinetics, insufficient electrolyte stability, and limited cycle life. These problems can be effectively solved by optimizing electrode materials, electrolytes, and battery design.

[0003] Two-dimensional transition metal borides (MBenes) are important members of two-dimensional (2D) nanomaterials. MBene materials possess advantages such as large specific surface area, numerous active sites, and high conductivity, and are widely used in magnesium-carbon dioxide batteries. Currently, synthesized Mo... 4 / 3 Although B2 has abundant surface vacancies, these defects usually lead to a decrease in its key properties such as electrical conductivity and thermal stability. Furthermore, in the process of preparing such highly defective MBene, etching removes the second transition metal on the surface, making it impossible to use the combination of the two transition metals to modulate the material properties, thus limiting its wide application.

[0004] For example, the literature "Science 2021, 373, 801-805" discloses a single-layer two-dimensional molybdenum boride with the chemical formula Mo. 4 / 3 B 2-x T z (where T) z It is a surface terminating group), through (Mo 2 / 3 Y 1 / 3 )2AlB2 and (Mo 2 / 3 Sc 1 / 3The study successfully prepared two-dimensional molybdenum boride sheets by selective etching of 2AlB2 in aqueous hydrofluoric acid. However, the numerous defects on the surface greatly affected its stability, and the single Mo-B chemical bond lacked efficient catalytic performance, making it difficult to use directly as a cathode material for Mg-CO2 batteries.

[0005] The paper “Angewandte Chemie International Edition 2022, 134(17):e202200181” discloses a Mg-CO2 battery. This battery uses CO2 and water as gas components and CNTs as the cathode, but its cycle life is only 50 cycles at 200 mA / g. Although this paper proposes a water-assisted Mg-CO2 battery that converts decomposition products into more easily adsorbed and decomposed MgCO3·3H2O, the poor catalytic performance of CNTs as the cathode leads to the unsatisfactory performance of the Mg-CO2 battery.

[0006] In summary, the main drawbacks of current magnesium-carbon dioxide batteries are:

[0007] First, current magnesium-carbon dioxide battery cathode catalysts are not effective, and the decomposition barrier of discharge products is relatively high, so new catalysts need to be explored.

[0008] Second, the magnesium-carbon dioxide battery cathode material (two-dimensional layered molybdenum boride) prepared by the current method has poor stability due to the presence of a large number of vacancies, and it is difficult to obtain high catalytic activity on the surface of a single element.

[0009] Third, there is currently a lack of research on two-dimensional layered molybdenum boride materials doped with transition metals, and there are few studies on the performance of bimetallic MBene catalysts in Mg-CO2 batteries.

[0010] Therefore, by designing and discovering new MAB phases, the synthesis of bimetallic MBene with certain vacancies can effectively avoid the above problems. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention aims to provide a positive electrode material for magnesium-carbon dioxide metal batteries and its preparation method, wherein the general chemical formula is Mo. 4 / 3 R 2a / 3 B 2- -V R’ , where V R’ The vacancy represents R', where R is one or more of Lu, Dy, Er, Ho, and Tb, and R' is Y or Sc, with 0.1 ≤ a ≤ 0.9; Mo is obtained by calcination. 4 / 3 R' 2 / 3-2a / 3 R 2a / 3AlB2 is prepared by adding an etchant to selectively etch away the transition metal (Y or Sc) and Al, yielding a ternary transition metal boride, which is the cathode material for magnesium-carbon dioxide metal batteries. This invention provides a simple preparation method with easy process control. The resulting magnesium-carbon dioxide metal battery cathode material not only exhibits excellent catalytic performance but also demonstrates low overpotential and long cycle life, enabling efficient and stable absorption and utilization of carbon dioxide.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A magnesium-carbon dioxide battery cathode material with the general chemical formula Mo 4 / 3 R 2a / 3 B2-V R’ , where V R’ Represents the vacancy of R', where R is one or more of Lu, Dy, Er, Ho, and Tb, and R' is Y or Sc, with 0.1 ≤ a ≤ 0.9.

[0014] This invention also provides a method for preparing a magnesium-carbon dioxide battery cathode material, which is carried out in the following order:

[0015] S1, Preparation of Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2

[0016] Mo, Al, R, R', and B were weighed according to stoichiometric ratios and ball-milled in a ball mill. After calcination in an ultra-high-speed furnace, the mixture was ground to 300-400 mesh using a mortar and pestle to obtain Mo. 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2 powder;

[0017] S2, Preparation of intermediate products

[0018] Will Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2 powder is mixed with HCl, HF and water until homogeneous. After stirring at 30-45℃ for 720-1440 min, the mixture is filtered and washed. It is then mixed with tetramethylammonium hydroxide and stirred at 50-400 r / min for 30 min. Deionized water is added and the mixture is filtered and washed until the pH reaches 7 to obtain the intermediate product.

[0019] S3, Preparation of Mo 4 / 3 R 2a / 3 B2-V R’

[0020] Add 40 mL of deionized water to the intermediate product and centrifuge. Filter the supernatant and freeze-dry to obtain Mo. 4 / 3 R 2a / 3 B2-V R’ .

[0021] As a limitation of the preparation method of the present invention, in step S1, the ball milling speed is 300-400 rpm and the time is 4-8 h.

[0022] As another limitation of the preparation method of the present invention, in step S1, the calcination temperature is 1100-1800℃ and the time is 10-600s.

[0023] In this invention, the calcination process is crucial, affecting the purity and particle size of the product. When the calcination temperature is 1100-1800℃ and the calcination time is 10-600s, the sintered product has high purity (>85%) and moderate particle size. When the calcination temperature is below 1100℃, the target product cannot be obtained through reaction, and when the calcination temperature is above 1800℃, the target product will partially decompose. Furthermore, when the calcination time is less than 10s, the raw materials cannot react sufficiently, and when the calcination time is greater than 600s, it will lead to uneven grain size.

[0024] As a third limitation of the preparation method of the present invention, in step S2, the Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 The molar ratio of AlB2 powder to HCl, HF, and water is 1:18:3:9.

[0025] As a fourth limitation of the preparation method of the present invention, in step S2, the Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 The molar ratio of AlB2 powder to tetramethylammonium hydroxide is 1:5.

[0026] In this invention, the presence of tetramethylammonium hydroxide can act as an intercalating agent to achieve layering of the etched transition metal boride. Its Mo... 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 The molar ratio of AlB2 powder to tetramethylammonium hydroxide is crucial. When the molar ratio is 1:5, a monolayer transition metal boride can be obtained. However, when the molar ratio is less than 1:5, insufficient intercalating agent will prevent complete separation and the monolayer transition metal boride cannot be obtained. When the molar ratio is greater than 1:5, excessive intercalating agent will result in an overly dilute solution, making it difficult to collect the product.

[0027] As a fifth limitation of the preparation method of the present invention, in step S3, the centrifugation speed is 2000-3500 r / min and the time is 5-15 min.

[0028] As a sixth limitation of the preparation method of the present invention, in step S3, the freeze-drying temperature is -80℃ and the time is 48-96h.

[0029] The magnesium-carbon dioxide battery cathode material prepared in this invention is a two-dimensional transition metal boride (MBene). Layered transition metal borides (MAB) are obtained by sintering in an ultrafast high-temperature furnace. Then, based on the differences in the chemical bond strength between Mo, Al, R, and R' with boron, an etchant selectively etches away R' and Al, yielding the two-dimensional transition metal boride. Experimental studies revealed that because the Mo-B bond is stronger than the Y / Sc-B and Mo-Y / Sc bonds, with the Mo-Y / Sc bond being the weakest, it is difficult to retain surface Y / Sc atoms during etching. In compounds where R = Lu, Dy, Er, Ho, Tb at the Y / Sc site, the strength of the Mo-R bond is similar to that of the Mo-B bond. The significant enhancement of the Mo-R bond helps to retain R atoms on the two-dimensional surface. By adjusting the etching temperature and time during the etching process, the etchant only etches away the easily etchable Al and Y / Sc, while struggling to etch Mo and R, thus obtaining the target two-dimensional transition metal boride. The etched R' leaves vacancies on the material surface. The presence of these vacancies significantly alters the surface's electronic properties, thus affecting the adsorption behavior of reaction intermediates. Simultaneously, the synergistic effect of vacancies with neighboring atoms forms unique active sites, lowering the energy barrier and facilitating the adsorption and decomposition of reactants on the cathode material surface. By reducing surface vacancies, the thermal stability of two-dimensional layered molybdenum boride is improved, while retaining some vacancies, effectively improving the adsorption and decomposition of reactants in Mg-CO2 batteries. This allows it to efficiently and stably absorb and utilize carbon dioxide as a cathode material in Mg-CO2 batteries. Furthermore, the chemical bonds formed between transition metals (Lu, Dy, Er, Ho, Tb) and boron provide catalytic active sites for the reaction. Charge transfer between transition metals and boron alters the electronic structure of the active sites. This charge transfer optimizes the adsorption energy of reactants on the catalyst surface, thereby lowering the reaction energy barrier. Simultaneously, because boron atoms have empty p orbitals, they can interact with the d orbitals of transition metals, which also enhances the catalytic activity of the transition metals.

[0030] The two-dimensional transition metal boride prepared by this invention is a ternary compound. During discharge, CO2 molecules are reduced to magnesium oxalate (MgC2O4) or magnesium carbonate hydrate (such as MgCO3·5H2O) on the surface of the positive electrode catalyst. This positive electrode catalyst can effectively promote the reduction of CO2 to generate MgC2O4 or MgCO3·5H2O. Compared with the traditional MgCO3 product, it effectively improves the reaction kinetics of the battery, thereby improving the overpotential and cycle performance of the magnesium-carbon dioxide battery.

[0031] 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.

[0032] The above technical solution has the following advantages or beneficial effects:

[0033] 1. The magnesium-carbon dioxide cathode material prepared by this invention is a two-dimensional layered molybdenum boride material doped with transition metals, which has an ultrathin two-dimensional sheet structure.

[0034] 2. The magnesium-carbon dioxide cathode material prepared by this invention has a large number of surface vacancies, thereby reducing the reaction energy barrier, which is beneficial to the adsorption and decomposition of water molecules or intermediate reactants, and optimizes the reaction kinetics.

[0035] 3. When the magnesium-carbon dioxide cathode material prepared by this invention is used in magnesium-carbon dioxide batteries, the magnesium-carbon dioxide batteries have extremely low overpotential, high discharge capacity, and long cycle life.

[0036] This invention is applicable to the preparation of magnesium-carbon dioxide battery cathode materials.

[0037] 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

[0038] Figure 1 The [(Mo] prepared in step S1 of Example 1 of this invention 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 X-ray diffraction pattern of 2AlB2;

[0039] Figure 2 The Mo prepared in step S1 of Example 2 of this invention 4 / 3 Y 1 / 15 Er 3 / 5 Scanning electron microscope image of AlB2;

[0040] Figure 3 The Mo prepared in step S1 of Example 3 of this invention 4 / 3 Y 3 / 5 Ho 1 / 15 Energy dispersive X-ray spectrum of AlB2 powder;

[0041] Figure 4 The Mo prepared in Example 3 of this invention 4 / 3 Y 3 / 5 Ho 1 / 15 Scanning electron microscope image of AlB2;

[0042] Figure 5The (Mo) prepared in Example 4 of this invention 2 / 3 Dy 1 / 6 )2B2-V Sc X-ray diffraction pattern;

[0043] Figure 6 The graphs show the cycle performance test results of the magnesium-carbon dioxide battery cathode materials prepared in Example 1 and Comparative Examples 1-5 of this invention when applied to magnesium-carbon dioxide batteries. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] Example 1

[0047] This embodiment prepares [(Mo 2 / 3 (Er 1 / 12 Ho 1 / 12 )]2B2-V Y The preparation process and steps are as follows:

[0048] S1, Preparation of [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )]2AlB2

[0049] Mo, Y, Er, Ho, Al, and B were weighed according to stoichiometric ratios and placed in a ball mill. The mixture was ball-milled at 300 rpm for 4 hours, then placed in an ultra-fast high-temperature furnace and calcined at 1800℃ for 10 seconds. Finally, it was ground to 300 mesh using a mortar and pestle to obtain [(Mo...]]. 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )]2AlB2 powder;

[0050] S2, Preparation of intermediate products

[0051] 0.5 mol [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12)]2AlB2 powder was mixed with 9 mol HCl, 1.5 mol HF and 4.5 mol water. After stirring at 30℃ for 720 min, the mixture was filtered and washed. It was then mixed with 2.5 mol tetramethylammonium hydroxide and stirred at 50 r / min for 30 min. Deionized water was added and the mixture was filtered and washed until the pH was 7. The liquid was removed to obtain the intermediate product.

[0052] S3, Preparation of [(Mo 2 / 3 (Er 1 / 12 Ho 1 / 12 )]2B2-V Y

[0053] Add 40 mL of deionized water to the intermediate product, centrifuge at 2000 r / min for 5 min, filter the supernatant, and freeze-dry at -80℃ for 48 h to obtain [(Mo 2 / 3 (Er 1 / 12 Ho 1 / 12 )]2B2-V Y .

[0054] Figure 1 The [(Mo] prepared in step S1 of this embodiment 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 The X-ray diffraction pattern of 2AlB2 shows that the product is [(Mo]2AlB2]. 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 The synthesized [(Mo)]2AlB2 phase and some impurity phase MoB, were obtained from the synthesis of [(Mo)]2AlB2 phase and some impurity phase MoB. 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 The characteristic peaks of the [(Mo)2AlB2 material match well with the theoretically predicted characteristic peaks of the crystal, and no Er or Ho impurity peaks appear, indicating that [(Mo)2AlB2]2AlB2 material has been successfully prepared. 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )]2AlB2.

[0055] Example 2

[0056] This embodiment prepares Mo 4 / 3 Er 3 / 5 B2-V Y The preparation process and steps are as follows:

[0057] S1, Preparation of Mo 4 / 3 Y 1 / 15 Er 3 / 5 AlB2

[0058] Mo, Y, Er, Al, and B were weighed according to stoichiometry and placed in a ball mill. The mixture was ball-milled at 350 rpm for 6 hours, then placed in an ultra-fast high-temperature furnace and calcined at 1300℃ for 500 seconds. Finally, it was ground to 350 mesh using a mortar and pestle to obtain Mo. 4 / 3Y 1 / 15 Er 3 / 5 AlB2 powder;

[0059] S2, Preparation of intermediate products

[0060] 0.25 mol Mo 4 / 3 Y 1 / 15 Er 3 / 5 AlB2 powder was mixed with 4.5 mol HCl, 0.75 mol HF and 2.25 mol water until homogeneous. After stirring at 40°C for 1080 min, the mixture was filtered and washed. It was then mixed with 1.25 mol tetramethylammonium hydroxide and stirred at 200 r / min for 30 min. Deionized water was then added, and the mixture was filtered and washed until the pH reached 7. The liquid was removed to obtain the intermediate product.

[0061] S3, Preparation of Mo 4 / 3 Er 3 / 5 B2-V Y

[0062] Add 40 mL of deionized water to the intermediate product, centrifuge at 3000 r / min for 10 min, filter the supernatant, and freeze-dry at -80℃ for 72 h to obtain Mo. 4 / 3 Er 3 / 5 B2-V Y .

[0063] Figure 2 The Mo prepared in step S1 of this embodiment 4 / 3 Y 1 / 15 Er 3 / 5 The scanning electron microscope image of AlB2 powder shows that its morphology exhibits a distinct layered structure.

[0064] Example 3

[0065] This embodiment prepares Mo 4 / 3 Ho 1 / 15 B2-V Y The preparation process and steps are as follows:

[0066] S1, Preparation of Mo 4 / 3 Y 3 / 5 Ho 1 / 15 AlB2

[0067] Mo, Y, Ho, Al, and B were weighed according to stoichiometry and placed in a ball mill. The mixture was ball-milled at 400 rpm for 8 hours, then placed in an ultra-fast high-temperature furnace and calcined at 1100℃ for 600 seconds. Finally, it was ground to 400 mesh using a mortar and pestle to obtain Mo. 4 / 3 Y 3 / 5Ho 1 / 15 AlB2 powder;

[0068] S2, Preparation of intermediate products

[0069] 0.5 mol Mo 4 / 3 Y 3 / 5 Ho 1 / 15 AlB2 powder was mixed with 9 mol HCl, 1.5 mol HF and 4.5 mol water until homogeneous. After stirring at 45°C for 1440 min, the mixture was filtered and washed. Then, 2.5 mol tetramethylammonium hydroxide was added and stirred at 400 r / min for 30 min. Deionized water was then added and the mixture was filtered and washed until the pH reached 7. The liquid was removed to obtain the intermediate product.

[0070] S3, Preparation of Mo 4 / 3 Ho 1 / 15 B2-V Y

[0071] Add 40 mL of deionized water to the intermediate product, centrifuge at 3500 r / min for 15 min, filter the supernatant, and freeze-dry at -80℃ for 96 h to obtain Mo. 4 / 3 Ho 1 / 15 B2-V Y .

[0072] Figure 3 The Mo prepared in step S1 of this embodiment 4 / 3 Y 3 / 5 Ho 1 / 15 The energy-dispersive X-ray diffraction (EDXRD) spectrum of AlB2 powder shows that elements such as Mo, Y, Ho, Al, and B are uniformly distributed on the particles, indicating successful preparation of Mo. 4 / 3Y 3 / 5 Ho 1 / 15 AlB2 powder, with the elements uniformly dissolved in the prepared powder. Furthermore, the Mo prepared in this embodiment... 4 / 3Ho 1 / 15 B2-V Y Scanning electron microscopy analysis was performed, and the results are as follows: Figure 4 As shown in the figure, Mo can be seen 4 / 3 Ho 1 / 15 B2-V Y It exhibits an ultra-thin two-dimensional structure.

[0073] Example 4

[0074] This embodiment prepares (Mo) 2 / 3 Dy 1 / 6 )2B2-V Sc The preparation process and steps are as follows:

[0075] S1, Preparation of [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )]2AlB2

[0076] Mo, Y, Ho, Al, and B were weighed according to stoichiometry and placed in a ball mill. The mixture was ball-milled at 400 rpm for 8 hours, then placed in an ultra-fast high-temperature furnace and calcined at 1800℃ for 600 seconds. Finally, it was ground to 400 mesh using a mortar and pestle to obtain [(Mo...]]. 2 / 3 (Sc 1 / 6 Dy 1 / 6 )]2AlB2 powder;

[0077] S2, Preparation of intermediate products

[0078] 0.5 mol [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )]2AlB2 powder was mixed with 9 mol HCl, 1.5 mol HF and 4.5 mol water. After stirring at 40℃ for 1080 min, the mixture was filtered and washed. It was then mixed with 2.5 mol tetramethylammonium hydroxide and stirred at 400 r / min for 30 min. Deionized water was then added and the mixture was filtered and washed until the pH reached 7. The liquid was removed to obtain the intermediate product.

[0079] S3, Preparation (Mo) 2 / 3 Dy 1 / 6 )2B2-V Sc

[0080] Add 40 mL of deionized water to the intermediate product, centrifuge at 3500 r / min for 15 min, filter the supernatant, and freeze-dry at -80℃ for 96 h to obtain (Mo 2 / 3 Dy 1 / 6 )2B2-V Sc .

[0081] Figure 5 The [(Mo] prepared in step S1 of this embodiment 2 / 3 (Sc 1 / 6 Dy 1 / 6 The X-ray diffraction pattern of 2AlB2 shows that the product is [(Mo]2AlB2]. 2 / 3 (Sc 1 / 6 Dy 1 / 6The synthesized [(Mo)]2AlB2 phase and some impurity phase MoB, were obtained from the synthesis of [(Mo)]2AlB2 phase and some impurity phase MoB. 2 / 3 (Sc 1 / 6 Dy 1 / 6 The characteristic peaks of the [(Mo)2AlB2 material match well with the theoretically predicted characteristic peaks of the crystal, and no impurity peaks appear, indicating that [(Mo)2AlB2]2AlB2 material has been successfully prepared. 2 / 3 (Sc 1 / 6 Dy 1 / 6 )]2AlB2.

[0082] Comparative Example

[0083] To investigate the effects of different parameters or raw materials on the performance of the product of this invention, the following comparative experiments were conducted. Different magnesium-carbon dioxide battery cathode materials were prepared in the following comparative examples:

[0084] Comparative Example 1

[0085] This comparative example prepares a magnesium-carbon dioxide battery cathode material according to the preparation method in the literature "Science 2021, 373, 801-805". The specific preparation method is as follows:

[0086] S1, Preparation of Mo 4 / 3 Y 2 / 3 AlB2

[0087] Mo, Y, Al, and B were weighed according to stoichiometric ratio and thoroughly mixed in an agate mortar. The mixture was then transferred to an alumina crucible, placed in a tube furnace, and calcined at 1400℃ for 480 min. The mixture was then ground to 200 mesh using a mortar to obtain Mo. 4 / 3 Y 2 / 3 AlB2 powder;

[0088] S2, Preparation of intermediate products

[0089] Will 2g Mo 4 / 3 Y 2 / 3 AlB2 powder was added to 20 mL of 40 wt% hydrofluoric acid aqueous solution and mixed thoroughly. The mixture was stirred at 30 °C for 210 min, then deionized water was added and centrifuged to remove residual acid and reaction products. 10 mL of tetramethylammonium hydroxide was added to a centrifuge tube, shaken for 2 min, and centrifuged at 6000 rpm for 2 min. Ethanol was added to the tube to wash away the remaining tetramethylammonium hydroxide. This process was repeated three times to obtain the intermediate product.

[0090] S3, Preparation of Mo 4 / 3 B2

[0091] Add 40 mL of deionized water to the intermediate product, centrifuge at 3500 r / min for 15 min, filter the supernatant, and freeze-dry at -80℃ for 72 h to obtain Mo. 4 / 3 B2.

[0092] Comparative Example 2

[0093] This comparative example prepares a magnesium-carbon dioxide cathode material. The preparation process is similar to that of Example 1, except that in step S1, Cr is used instead of Mo.

[0094] Comparative Example 3

[0095] This comparative example prepares a magnesium-carbon dioxide cathode material. The preparation process is similar to that of Example 1, except that in step S1, the element Y is not used, but the element Er is used.

[0096] Comparative Example 4

[0097] This comparative example prepares a magnesium-carbon dioxide cathode material. The preparation process is similar to that of Example 1, except that in step S1, the calcination temperature is 1000℃, and the other parameters are the same as those in Example 1.

[0098] Comparative Example 5

[0099] This comparative example prepares a magnesium-carbon dioxide cathode material. The preparation process is similar to that of Example 1, except that in step S1, [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 The molar ratio of AlB2 powder to tetramethylammonium hydroxide is 1:3.

[0100] To verify the electrochemical performance of the magnesium-carbon dioxide cathode material prepared in this invention in magnesium-carbon dioxide batteries, the cathode material powders prepared in Examples 1-4 and Comparative Examples 1-5 were mixed with KB and PVDF at a mass ratio of 6:5:1, respectively. Then, 2.5 mL of N-methylpyrrolidone solvent was added and the mixture was ground for 0.5 h. The mixture was then coated onto carbon paper and dried at 60 °C for 10 h. With the aid of moisture, the mixture was used in magnesium-carbon dioxide batteries. CO2 gas containing 1-10 vol% H2O was introduced into the battery device through a specific conduit and then exited through another outlet to maintain gas flow. Specific test results are shown in the table below.

[0101] serial number Number of cycles Example 1 102 Example 2 80 Example 3 70 Example 4 95 Comparative Example 1 42 Comparative Example 2 43 Comparative Example 3 52 Comparative Example 4 28 Comparative Example 5 32

[0102] In addition, from Figure 6As can be seen, the battery in Example 1 had the highest cycle count, reaching 102 cycles, demonstrating excellent cycle performance. Furthermore, the low overpotential (ΔV≈0.09) indicates the excellent catalytic performance of the cathode material. The batteries in Comparative Examples 1 to 5 all had lower cycle counts, ranging from a maximum of 52 cycles to a minimum of 28 cycles, exhibiting poorer cycle performance. The higher overpotential (ΔV) indicates that these samples showed inferior catalytic performance compared to the cathode material prepared in this invention in magnesium-carbon dioxide batteries.

[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 a magnesium-carbon dioxide battery cathode material, characterized in that, Follow these steps in sequence: S1, Preparation of Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2 Mo, Al, R, R', and B were weighed according to stoichiometric ratios and ball-milled in a ball mill. After calcination in an ultra-high-speed furnace, the mixture was ground to 300-400 mesh using a mortar and pestle to obtain Mo. 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2 powder; S2, Preparation of intermediate products Will Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AlB2 powder is mixed with HCl, HF and water until homogeneous. After stirring at 30-45℃ for 720-1440 min, the mixture is filtered and washed. It is then mixed with tetramethylammonium hydroxide and stirred at 50-400 r / min for 30 min. Deionized water is added, and the mixture is filtered and washed until the pH reaches 7 to obtain the intermediate product. S3, Preparation of Mo 4 / 3 R 2a / 3 B2-V R’ Add 40 mL of deionized water to the intermediate product and centrifuge. Filter the supernatant and freeze-dry to obtain Mo. 4 / 3R 2a / 3 B2-V R’ .

2. A magnesium-carbon dioxide battery cathode material, characterized in that, The material is prepared by the method described in claim 1, and its general chemical formula is Mo. 4 / 3 R 2a / 3 B2-V R’ , where V R’ Represents the vacancy of R', where R is one or more of Dy, Er, and Ho, and R' is either Y or Sc, 0.1 ≤ a ≤0.

9.

3. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S1, the ball milling speed is 300-400 rpm and the time is 4-8 h.

4. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S1, the calcination temperature is 1100-1800℃ and the time is 10-600 s.

5. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S2, the Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 The molar ratio of AlB2 powder to HCl, HF, and water is 1:18:3:

9.

6. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S2, the Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 The molar ratio of AlB2 powder to tetramethylammonium hydroxide is 1:

5.

7. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S3, the centrifugation speed is 2000-3500 r / min and the time is 5-15 min.

8. The method for preparing a magnesium-carbon dioxide battery cathode material according to claim 1, characterized in that, In step S3, the freeze-drying temperature is -80℃ and the time is 48-96 h.

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