Magnesium-carbon dioxide battery positive electrode material and preparation method thereof

Abstract

The invention discloses a magnesium-carbon dioxide battery positive electrode material and a preparation method thereof, the chemical composition general formula of the magnesium-carbon dioxide battery positive electrode material is Mo4 / 3R2a / 3B2-VR ', VR' represents vacancy of R ', R is one or more of Lu, Dy, Er, Ho and Tb, R' is Y or Sc, and a is greater than or equal to 0.1 and less than or equal to 0.9; the preparation method comprises the following steps: calcining the material to obtain Mo4 / 3R '2 / 3-2a / 3R2a / 3AlB2, adding an etching agent, and selectively etching transition metal (Y or Sc) and Al to obtain a ternary transition metal boride, namely the positive electrode material of the magnesium-carbon dioxide metal battery. The preparation method is simple, the process is easy to control, and the prepared positive electrode material of the magnesium-carbon dioxide metal battery not only has excellent catalytic performance, but also shows low overpotential and long cycle life, and can efficiently and stably absorb and utilize carbon dioxide.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium batteries and relates to a magnesium-carbon dioxide battery positive electrode material and a preparation method thereof. Background Art

[0002] With the growing global demand for clean energy and the intensification of climate change issues, traditional energy storage technologies such as lithium-ion batteries are facing challenges such as limited resources. Metal-CO2 batteries are considered to be a new type of electrochemical energy storage technology that combines the functions of clean energy storage and greenhouse gas utilization. They use metals (such as lithium, sodium, magnesium, aluminum, etc.) as electrodes and carbon dioxide as active substances. Energy storage and release are achieved through the electrochemical reaction of metals and carbon dioxide. Its working principle is based on the oxidation of the metal negative electrode and the reduction reaction of carbon dioxide. Considering the safety hazards and poor stability of highly active alkali metals, magnesium has attracted widespread attention because of its more stable characteristics. It has a relatively low redox potential (2.38V) and a higher theoretical capacity (3833mAh / cm 3 ). Although this technology has the advantages of high energy density, abundant resources and environmental protection, it still faces technical challenges such as slow reaction kinetics, insufficient electrolyte stability and limited cycle life. The above problems can be effectively solved by optimizing electrode materials, electrolytes and battery design.

[0003] Two-dimensional transition metal boride (MBene) is an important member of two-dimensional (2D) nanomaterials. MBene materials have the advantages of large specific surface area, multiple active sites, and high conductivity, and are widely used in magnesium-carbon dioxide batteries. 4 / 3 B 2 Although it has abundant surface vacancies, these defects usually lead to a decrease in its key properties such as conductivity and thermal stability. In addition, in the process of preparing this highly defective MBene, the second transition metal on the surface is etched away, resulting in the inability to use the combination of two transition metals to regulate material properties, thus limiting its wide application.

[0004] For example, the document "Science 2021, 373, 801-805" discloses a single-layer two-dimensional molybdenum boride with a chemical formula of Mo 4 / 3 B 2-x T z (where T z is a surface termination group), through (Mo 2 / 3 Y 1 / 3 ) 2 AB 2 and(Mo 2 / 3 Sc 1 / 3 ) 2 AB 2The two-dimensional molybdenum boride sheet was prepared by selective etching in a hydrofluoric acid aqueous solution. However, the large number of defects on the surface greatly affected its stability. The single Mo-B chemical bond lacked efficient catalytic performance and was difficult to directly use as a Mg-CO 2 Battery positive electrode material.

[0005] The document "Angewandte Chemie International Edition 2022, 134(17):e202200181" discloses a Mg-CO 2 Battery. This battery uses CO 2 With water as the gas component and CNT as the cathode, the cycle life is only 50 cycles at 200 mA / g. 2 The battery converts the decomposition products into MgCO, which is easier to adsorb and decompose. 3 ·3H 2 O, but the CNT catalytic performance as cathode is poor, resulting in Mg-CO 2 The battery is not performing as expected.

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

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

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

[0009] Third, there is a lack of relevant research on transition metal-doped two-dimensional layered molybdenum boride materials, and the bimetallic MBene catalysts that have been studied in Mg-CO 2 There is less performance research in the battery field.

[0010] Therefore, the above problems can be effectively avoided by designing and discovering new MAB phases and synthesizing bimetallic MBene with certain vacancies. Summary of the invention

[0011] In view of the above technical problems, the present invention aims to provide a positive electrode material for a magnesium-carbon dioxide metal battery and a preparation method thereof, wherein the chemical composition general formula is Mo 4 / 3 R 2a / 3 B 2- -V R’ , where V R’Represents the vacancy of R', R is one or more of Lu, Dy, Er, Ho, Tb, R' is Y or Sc, 0.1≤a≤0.9; Mo is obtained by calcination 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AB 2 , then an etchant is added to selectively etch away the transition metal (Y or Sc) and Al to obtain a ternary transition metal boride, i.e., a positive electrode material for a magnesium-carbon dioxide metal battery. The preparation method of the present invention is simple, the process is easy to control, and the prepared positive electrode material for a magnesium-carbon dioxide metal battery not only has excellent catalytic performance, but also exhibits a low overpotential and a long cycle life, and can efficiently and stably absorb and utilize carbon dioxide.

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

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

[0014] The present invention also provides a method for preparing a positive electrode material for a magnesium-carbon dioxide battery, which is carried out in the following steps in sequence:

[0015] S1. Preparation of Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AB 2

[0016] Mo, Al, R, R' and B were weighed according to the stoichiometric ratio, and ball-milled in a ball mill. Then, they were calcined in an ultra-fast high-temperature furnace, and ground into 300-400 meshes using a mortar to obtain Mo. 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AB 2 powder;

[0017] S2. Preparation of intermediate products

[0018] Will Mo 4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AB 2The powder is mixed evenly with HCl, HF and water, stirred at 30-45°C for 720-1440 minutes, filtered and washed, mixed with tetramethylammonium hydroxide, and stirred at a speed of 50-400 r / min for 30 minutes, and then deionized water is added thereto, filtered and washed until the pH is 7, to obtain an intermediate product;

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

[0020] 40 mL of deionized water was added to the intermediate product and centrifuged. The upper layer of liquid was filtered and freeze-dried to obtain Mo 4 / 3 R 2a / 3 B 2 -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 hours.

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

[0023] In the present invention, the calcination process is crucial and affects the purity and particle size of the product. When the calcination temperature is 1100-1800°C and the calcination time is 10-600s, the purity of the sintered product is high (>85%) and the particle size is moderate; when the calcination temperature is less than 1100°C, the target product cannot be obtained by reaction, and when the calcination temperature is greater than 1800°C, the target product will be partially decomposed; and when the calcination time is less than 10s, the raw materials cannot fully react, and the calcination time is greater than 600s, which 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 AB 2 The molar ratio between powder and 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 AB 2 The molar ratio of powder to tetramethylammonium hydroxide is 1:5.

[0026] In the present invention, the presence of tetramethylammonium hydroxide can be used as an intercalation agent to achieve the delamination of the transition metal boride after etching.4 / 3 R' 2 / 3-2a / 3 R 2a / 3 AB 2 The molar ratio of 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 intercalation agent will result in inadequate separation and inability to obtain a monolayer transition metal boride; when the molar ratio is greater than 1:5, an excess of intercalation agent causes the solution to be too dilute and the product is difficult to collect.

[0027] As a fifth limitation of the preparation method of the present invention, in step S3, the rotation speed during the centrifugation 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°C and the time is 48-96h.

[0029] The magnesium-carbon dioxide battery positive electrode material prepared by the present invention is a two-dimensional transition metal boride (MBene). The layered transition metal boride (MAB) is obtained by sintering in an ultrafast high-temperature furnace, and then the etchant selectively etches away R' and Al according to the difference in the strength of the chemical bonds between Mo, Al, R and R' and the boron element, thereby obtaining the two-dimensional transition metal boride. Experimental studies have found that since the Mo-B bond is stronger than the Y / Sc-B bond and the Mo-Y / Sc bond, among which the Mo-Y / Sc bond is the weakest, it is difficult to retain the surface Y / Sc atoms during the etching process. In compounds where the Y / Sc position is R=Lu, Dy, Er, Ho, and Tb, the strength of the Mo-R bond is similar to that of the Mo-B bond, and the significant enhancement of the Mo-R bond helps to retain the 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 etched Al and Y / Sc, while the difficultly etched Mo and R, thereby obtaining the target two-dimensional transition metal boride. The etched R' leaves vacancies on the surface of the material. The presence of vacancies will significantly change the electronic properties of the surface, thereby affecting the adsorption behavior of the reaction intermediates. At the same time, the synergistic effect of vacancies and neighboring atoms will form unique active sites, which will reduce the energy barrier and facilitate the adsorption and decomposition of reactants on the surface of the positive electrode material. The thermal stability of the two-dimensional layered molybdenum boride is improved by reducing the surface vacancies, and some vacancies are retained, thereby effectively improving the Mg-CO 2 The adsorption and decomposition of the reactants in the battery make it as Mg-CO 2The positive electrode material of the battery absorbs and utilizes carbon dioxide efficiently and stably. In addition, the chemical bonds formed between transition metals (Lu, Dy, Er, Ho, Tb) and boron provide catalytic active sites for the reaction. Transition metals and boron can transfer charge, thereby changing the electronic structure of the active site. This charge transfer can optimize the adsorption energy of reactants on the catalyst surface, thereby reducing the reaction energy barrier. At the same time, because boron atoms have empty p orbitals, they can interact with the d orbitals of transition metals. This interaction can also enhance the catalytic activity of transition metals.

[0030] The two-dimensional transition metal boride prepared by the present invention is a ternary compound. During the discharge process, CO 2 The molecules are reduced to magnesium oxalate (MgC 2 O 4 ) or magnesium carbonate hydrate (such as MgCO 3 ·5H 2 O), the cathode catalyst can effectively promote CO 2 Reduction of MgC 2 O 4 or MgCO 3 ·5H 2 O, compared with the traditional MgCO 3 The product effectively improves the reaction kinetics of the battery, thereby improving the overpotential and cycle performance of the magnesium-carbon dioxide battery.

[0031] 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.

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

[0033] 1. The magnesium-carbon dioxide positive electrode material prepared by the present invention is a transition metal-doped two-dimensional layered molybdenum boride material having an ultra-thin two-dimensional sheet structure;

[0034] 2. The magnesium-carbon dioxide cathode material prepared by the present invention has a large number of surface vacancies, thereby reducing the reaction energy barrier, facilitating the adsorption and decomposition of water molecules or intermediate reactants, and optimizing the reaction kinetics;

[0035] 3. When the magnesium-carbon dioxide positive electrode material prepared by the present invention is used in a magnesium-carbon dioxide battery, the magnesium-carbon dioxide battery has an extremely low overpotential, a high discharge capacity and a long cycle life.

[0036] The invention is suitable for preparing positive electrode materials of magnesium-carbon dioxide batteries.

[0037] 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

[0038] Figure 1 [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 X-ray diffraction pattern of

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

[0040] Figure 3 The Mo prepared in step S1 of Example 3 of the present invention 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 Energy dispersive X-ray spectra of powders;

[0041] Figure 4 The Mo prepared in Example 3 of the present invention 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 Scanning electron microscope image of

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

[0043] Figure 6 This is a test diagram of the cycle performance of the magnesium-carbon dioxide battery positive electrode material prepared in Example 1 of the present invention and Comparative Examples 1-5 when used in a magnesium-carbon dioxide battery. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] Example 1

[0047] This example prepares [(Mo 2 / 3 (Er 1 / 12 Ho 1 / 12 )] 2 B 2 -V Y , its preparation process and steps are as follows:

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

[0049] Mo, Y, Er, Ho, Al and B were weighed according to the stoichiometric ratio and placed in a ball mill. They were ball milled at 300 rpm for 4 h, then placed in an ultra-fast high-temperature furnace, calcined at 1800 °C for 10 s, and ground into 300 mesh using a mortar to obtain [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 powder;

[0050] S2. Preparation of intermediate products

[0051] 0.5 mol [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 The powder was mixed evenly with 9 mol HCl, 1.5 mol HF and 4.5 mol water, stirred at 30°C for 720 min, filtered and washed, mixed with 2.5 mol tetramethylammonium hydroxide, and stirred at a speed of 50 r / min for 30 min, deionized water was added, filtered and washed until the pH was 7, and the liquid was removed to obtain an intermediate product;

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

[0053] 40 mL of deionized water was added to the intermediate product and centrifuged at 2000 r / min for 5 min. The upper layer of liquid was filtered and freeze-dried at -80 °C for 48 h to obtain [(Mo 2 / 3 (Er 1 / 12 Ho 1 / 12 )] 2 B 2 -V Y .

[0054] Figure 1 The [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 The X-ray diffraction pattern of the product is [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 phase and part of the impurity phase MoB, synthesized [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 The characteristic peaks of the material are in good agreement with the theoretically predicted characteristic peaks of the crystal, and no impurity peaks of Er or Ho appear, indicating that [(Mo 2 / 3 (Y 1 / 6 Er 1 / 12 Ho 1 / 12 )] 2 AB 2 .

[0055] Example 2

[0056] In this example, Mo was prepared 4 / 3 Er 3 / 5 B 2 -V Y , its preparation process and steps are as follows:

[0057] S1. Preparation of Mo 4 / 3 Y 1 / 15 Er 3 / 5 AB 2

[0058] Mo, Y, Er, Al and B were weighed according to the stoichiometric ratio and placed in a ball mill. They were ball milled at 350 rpm for 6 h, then placed in an ultra-fast high-temperature furnace, calcined at 1300 °C for 500 s, and ground to 350 mesh using a mortar to obtain Mo.4 / 3 Y 1 / 15 Er 3 / 5 AB 2 powder;

[0059] S2. Preparation of intermediate products

[0060] 0.25 mol Mo 4 / 3 Y 1 / 15 Er 3 / 5 AB 2 The powder was mixed evenly with 4.5 mol HCl, 0.75 mol HF and 2.25 mol water, stirred at 40°C for 1080 min, filtered and washed, mixed with 1.25 mol tetramethylammonium hydroxide, stirred at 200 r / min for 30 min, and then deionized water was added, filtered and washed until the pH was 7, and the liquid was removed to obtain an intermediate product;

[0061] S3. Preparation of Mo 4 / 3 Er 3 / 5 B 2 -V Y

[0062] 40 mL of deionized water was added to the intermediate product and centrifuged at 3000 r / min for 10 min. The upper layer of liquid was filtered and freeze-dried at -80 °C for 72 h to obtain Mo 4 / 3 Er 3 / 5 B 2 -V Y .

[0063] Figure 2 The Mo prepared in step S1 of this embodiment 4 / 3 Y 1 / 15 Er 3 / 5 AB 2 The scanning electron microscope image of the powder shows that its morphology presents an obvious layered structure.

[0064] Example 3

[0065] In this example, Mo was prepared 4 / 3 Ho 1 / 15 B 2 -V Y , its preparation process and steps are as follows:

[0066] S1. Preparation of Mo 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2

[0067] Mo, Y, Ho, Al and B were weighed according to the stoichiometric ratio and placed in a ball mill. They were ball milled at 400 rpm for 8 h, then placed in an ultra-fast high-temperature furnace, calcined at 1100 °C for 600 s, and ground into 400 mesh using a mortar to obtain Mo. 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 powder;

[0068] S2. Preparation of intermediate products

[0069] 0.5 molMo 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 The powder was mixed evenly with 9 mol HCl, 1.5 mol HF and 4.5 mol water, stirred at 45°C for 1440 min, filtered and washed, mixed with 2.5 mol tetramethylammonium hydroxide, and stirred at 400 r / min for 30 min, then deionized water was added, filtered and washed until the pH was 7, and the liquid was removed to obtain an intermediate product;

[0070] S3. Preparation of Mo 4 / 3 Ho 1 / 15 B 2 -V Y

[0071] 40 mL of deionized water was added to the intermediate product and centrifuged at 3500 r / min for 15 min. The upper layer of liquid was filtered and freeze-dried at -80 °C for 96 h to obtain Mo 4 / 3 Ho 1 / 15 B 2 -V Y .

[0072] Figure 3 The Mo prepared in step S1 of this embodiment 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 Energy dispersive X-ray spectrum of the powder. It can be seen from the figure that the elements Mo, Y, Ho, Al, B and other elements in the product are evenly distributed on the particles, indicating that Mo was successfully prepared. 4 / 3 Y 3 / 5 Ho 1 / 15 AB 2 The Mo prepared in this embodiment is uniformly dissolved in the powder. 4 / 3 Ho 1 / 15 B 2 -V YScanning electron microscopy analysis showed that Figure 4 As shown in the figure, we can see that Mo 4 / 3 Ho 1 / 15 B 2 -V Y It presents an ultra-thin two-dimensional structure.

[0073] Example 4

[0074] This example prepares (Mo 2 / 3 Dy 1 / 6 ) 2 B 2 -V Sc , its preparation process and steps are as follows:

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

[0076] Mo, Y, Ho, Al and B were weighed according to the stoichiometric ratio and placed in a ball mill. They were ball milled at 400 rpm for 8 h, then placed in an ultra-fast high-temperature furnace, calcined at 1800 °C for 600 s, and ground to 400 mesh in a mortar to obtain [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 powder;

[0077] S2. Preparation of intermediate products

[0078] 0.5 mol [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 The powder was mixed evenly with 9 mol HCl, 1.5 mol HF and 4.5 mol water, stirred at 40°C for 1080 min, filtered and washed, mixed with 2.5 mol tetramethylammonium hydroxide, stirred at 400 r / min for 30 min, deionized water was added, filtered and washed until the pH was 7, and the liquid was removed to obtain an intermediate product;

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

[0080] 40 mL of deionized water was added to the intermediate product and centrifuged at 3500 r / min for 15 min. The upper layer of liquid was filtered and freeze-dried at -80 ° C for 96 h to obtain (Mo 2 / 3 Dy 1 / 6 ) 2 B 2 -V Sc .

[0081] Figure 5 The [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 The X-ray diffraction pattern of the product is [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 phase and part of the impurity phase MoB, synthesized [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 The characteristic peaks of the material are in good agreement with the characteristic peaks of the crystal predicted by theory, and no impurity peaks appear, indicating that [(Mo 2 / 3 (Sc 1 / 6 Dy 1 / 6 )] 2 AB 2 .

[0082] Comparative Example

[0083] In order to explore the influence of different parameters or different preparation raw materials in the preparation process of the present invention on the performance of the product of the present invention, the following comparative experiments were carried out. Different magnesium-carbon dioxide battery positive electrode materials were prepared in the following comparative examples, as follows:

[0084] Comparative Example 1

[0085] In this comparative example, a magnesium-carbon dioxide battery positive electrode material is prepared according to the preparation method in the document "Science 2021, 373, 801-805", and the specific preparation method is as follows:

[0086] S1. Preparation of Mo 4 / 3 Y 2 / 3 AB 2

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

[0088] S2. Preparation of intermediate products

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

[0090] S3. Preparation of Mo 4 / 3 B 2

[0091] 40 mL of deionized water was added to the intermediate product and centrifuged at 3500 r / min for 15 min. The upper layer of liquid was filtered and freeze-dried at -80 °C for 72 h to obtain Mo 4 / 3 B 2 .

[0092] Comparative Example 2

[0093] In this comparative example, a magnesium-carbon dioxide positive electrode material is prepared. The preparation process is similar to that of Example 1, except that in step S1, Cr is used instead of Mo element.

[0094] Comparative Example 3

[0095] In this comparative example, a magnesium-carbon dioxide positive electrode material is prepared. The preparation process is similar to that of Example 1, except that in step S1, Er element is used instead of Y element.

[0096] Comparative Example 4

[0097] In this comparative example, a magnesium-carbon dioxide positive electrode material is prepared. The preparation process is similar to that of Example 1, except that in step S1, the calcination temperature is 1000° C., and the other parameters are the same as those of Example 1.

[0098] Comparative Example 5

[0099] In this comparative example, a magnesium-carbon dioxide positive electrode material is prepared. 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 )] 2 AB 2 The molar ratio of powder to tetramethylammonium hydroxide is 1:3.

[0100] In order to verify the electrochemical performance of the magnesium-carbon dioxide positive electrode material prepared by the present invention in magnesium-carbon dioxide batteries, the positive electrode 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, and then 2.5 mL of N-methylpyrrolidone solvent was added and ground for 0.5 h, then coated on carbon paper, dried at 60 ° C for 10 h, and used in magnesium-carbon dioxide batteries with the assistance of water. 2 CO of O 2 The gas is introduced into the battery device through a specific conduit and then led out through another outlet to keep the gas flowing. The specific test results are shown in the following table:

[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 6 It can be seen that the battery cycle number of Example 1 is the highest, reaching 102 cycles, showing excellent cycle performance, and the lower overpotential (ΔV≈0.09) shows the excellent catalytic performance of the positive electrode material. The battery cycle numbers of Comparative Examples 1 to 5 are all low, with the highest being only 52 cycles and the lowest being 28 cycles, showing poor cycle performance. The higher overpotential (ΔV) indicates that these samples have poorer catalytic performance in magnesium-carbon dioxide batteries than the positive electrode materials prepared by the present invention.

[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 magnesium-carbon dioxide battery positive electrode material, characterized in that: Its chemical composition formula is Mo 4 / 3 R 2a / 3 B2-V R’ , where V R’ Represents the vacancy of R', R is one or more of Lu, Dy, Er, Ho, Tb, R' is Y or Sc, 0.1≤a≤0.

9.

2. The method for preparing a magnesium-carbon dioxide battery positive electrode material according to claim 1, characterized in that: Follow the steps below in order: 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 the stoichiometric ratio, and ball-milled in a ball mill. Then, they were calcined in an ultra-fast high-temperature furnace, and ground into 300-400 meshes using a mortar 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 evenly with HCl, HF and water, stirred at 30-45°C for 720-1440 minutes, filtered and washed, mixed with tetramethylammonium hydroxide, and stirred at a speed of 50-400 r / min for 30 minutes, and then deionized water is added thereto, filtered and washed until the pH is 7, to obtain an intermediate product; S3. Preparation of Mo 4 / 3 R 2a / 3 B2-V R’ 40 mL of deionized water was added to the intermediate product and centrifuged. The upper layer of liquid was filtered and freeze-dried to obtain Mo 4 / 3R 2a / 3 B2-V R’ .

3. The method for preparing a magnesium-carbon dioxide battery positive electrode material according to claim 2, characterized in that: In step S1, the ball milling speed is 300-400 rpm and the time is 4-8 hours.

4. The method for preparing a magnesium-carbon dioxide battery positive electrode material according to claim 2, characterized in that: In step S1, the calcination temperature is 1100-1800°C and the time is 10-600s.

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

9.

6. The method for preparing a magnesium-carbon dioxide battery positive electrode material according to claim 2, 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 positive electrode material according to claim 2, characterized in that: In step S3, the rotation speed during the centrifugation is 2000-3500 r / min, and the time is 5-15 min.

8. The method for preparing a positive electrode material for a magnesium-carbon dioxide battery according to claim 2, characterized in that: In step S3, the freeze-drying temperature is -80°C and the time is 48-96 hours.

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