Pure-phase MBene nanosheet as well as preparation method and application thereof

Abstract

The invention discloses a pure-phase MBene nanosheet as well as a preparation method and application thereof, a large-range nanosheet-shaped MBene is prepared by adopting a specific molar ratio, and MBene with good nanosheets is preferably selected. After the proportion of the precursor raw materials is determined, the reaction temperature is regulated and tested to obtain the optimal temperature for preparing the pure-phase MBene nanosheet, and the optimal conditions for preparing MnB and FeB nanosheets are determined by a similar method. By selecting a proper heating rate, the construction of the pure-phase MBene nanosheet is realized, and the problem of traditional hydrofluoric acid etching is solved. Meanwhile, the method is simple in process, environmentally friendly, high in repeatability and suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage, and particularly relates to a pure-phase MBene nanosheet, a preparation method thereof, and an application thereof. Background Art

[0002] With the urgent global demand for clean energy and the continuous enhancement of environmental protection awareness, there is a need for efficient, inexpensive, and sustainable energy storage to fully utilize renewable energy (Saher et al., Nature, 2024, 636, 622). The research and development of new energy storage technologies have become crucial. Alkali metal ion batteries, as important energy storage carriers, play a core role in achieving efficient energy storage and conversion. Among them, lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs) have attracted much attention. LIBs have been widely used in many fields such as automobiles, electronic products, and medical applications due to their relatively high open-circuit voltage, energy density, and low environmental pollution (Kong et al., Nature Communications, 2025, 16, 1). Therefore, the development of new anode materials with stable structures, moderate working voltages, and the ability to meet the rapid shuttling of alkali metal ions has become the key to promoting the development of alkali metal batteries. Among the numerous studied inorganic layered anode materials, MXene materials have stood out. They not only have characteristics such as a large specific surface area, many active sites, and atomic layer thickness, but also have the advantage of good metallic conductivity. Such materials have a high elastic modulus and high carrier mobility, and have good application prospects in conductive materials and functional enhanced composite materials. Boride MBene, as a layered material similar to MXene, shows important application potential in the energy storage field due to its unique layered structure and outstanding theoretical specific capacity characteristics of boron elements, and is a promising anode material for alkali metal ion batteries.

[0003] Currently, the traditional method for preparing boride MBene is mainly hydrofluoric acid etching. Although this method can prepare monolayer molybdenum boride-based MBene materials, it has significant safety hazards, and fluorine-containing by-products are extremely likely to cause environmental pollution, which seriously hinders the large-scale preparation and practical application of the materials. At the same time, the existing preparation process also has problems such as complex preparation processes, high costs, and unstable product quality. Therefore, developing a safe, environmentally friendly, efficient, and cost-controllable method for preparing layered MBene and effectively applying it to alkali metal ion batteries is of great significance for breaking through the current bottleneck of energy storage technology and promoting the development of the energy field. Summary of the Invention

[0004] The present invention discloses a method for preparing pure-phase MBene nanosheets with simple process and strong repeatability, and their applications, aiming to solve the problems of easy oxidation due to high hydrophilicity of MBene and poor dispersibility in organic solvents.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing pure-phase MBene nanosheets, comprising the following steps: mixing a ternary transition metal boride MAB with a chloride salt uniformly, heating to a temperature T at a specific heating rate under the protection of an inert atmosphere in a tubular furnace, keeping the temperature at T for a certain time to deintercalate A, and then cooling to room temperature to obtain MB powder, centrifuging, washing, and drying to prepare pure-phase MBene nanosheets.

[0006] Due to the structure of the nanosheets, the small size and large specific surface area are beneficial to better insertion and extraction of alkali metal ions, showing more excellent electrochemical performance.

[0007] In some embodiments, the ternary transition metal boride MAB phase material is one of MoAlB, Mn2AlB2, and Fe2AlB2.

[0008] Furthermore, the chloride salt is ZnCl2; the molar ratio of MAB to the chloride salt is 1:(2 - 3).

[0009] Furthermore, the temperature T for deintercalating A is 500 - 700 °C, the heating rate is 2 - 5 °C / min, and the holding time is 2 - 5 h.

[0010] Furthermore, the washing is sequentially performed with water and absolute ethanol.

[0011] The pure-phase MBene nanosheets prepared by the above method.

[0012] The application of the above pure-phase MBene nanosheets in alkali metal batteries. The alkali metal batteries refer to lithium, sodium, and potassium batteries, and the pure-phase MBene nanosheets are used as active substances and coated on the current collector as the negative electrode of the battery.

[0013] Furthermore, the pure-phase MBene nanosheets, conductive agent, and binder are mixed uniformly in a ratio of (6 - 8):(1 - 3):1, an appropriate amount of NMP or water is added, and ground until there are no obvious particles in the slurry. Then, it is uniformly coated on a copper foil with a mold and dried to obtain a MBene nanosheet negative electrode sheet. The loading amount of MBene nanosheets on the electrode is 0.5 - 1 mg cm −2 , the conductive agent is superP, acetylene black, or Ketjen black, and the binder is PVDF or CMC.

[0014] Advantages of the present invention: The present invention synthesizes pure-phase nanosheet MBene using boron-based precursors of different ternary transition metal borides MAB and ZnCl2 as raw materials. The raw materials are inexpensive, the synthesis is simple, safe, environmentally friendly, and the morphology is controllable, making it suitable for large-scale preparation and application. The prepared MBene has good application prospects in catalysis and electrochemical energy storage, such as anode materials for batteries. Description of the Drawings

[0015] Figure 1 XRD and SEM images of the MnB nanosheets prepared in Example 1; Figure 2 XRD and SEM images of the FeB nanosheets prepared in Example 2; Figure 3 Electrochemical performance images of the MnB nanosheets prepared in Example 3 in alkali metal ion batteries; Figure 4 XRD images of the materials prepared at different temperatures in Comparative Example 1; Figure 5 SEM images of the materials prepared at different temperatures in Comparative Example 1; Figure 6 XRD images of the materials prepared at different temperatures in Comparative Example 2; Figure 7 SEM images of the materials prepared at different temperatures in Comparative Example 2. Detailed Description of the Invention

[0016] The following will comprehensively and clearly elaborate on the synthesis of MBene nanosheets in combination with specific examples and drawings. It should be clear that the following examples are only a part of the present technology, not all of it, and do not constitute any limitation to the present invention. If no specific conditions are particularly emphasized in the examples, they are all carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments used, if the manufacturer is not indicated, they are all conventional products that can be purchased on the market.

[0017] Example 1 In this example, a method for preparing MnB MBene by molten salt etching of MAB materials includes the following steps First step: Grind 1 g of Mn2AlB2 (6.3 mmol) and 1.72 g of ZnCl2 (12.6 mmol) in a mortar until evenly mixed for about 20 min.

[0018] Second step: Pour the powder obtained in the previous step into a ceramic crucible, transfer it to a tube furnace, and under an argon atmosphere, gradually heat it to 700 °C at a uniform rate in 2.5 h, hold for 4 h, and wait for it to naturally cool to room temperature to obtain MnB MBene powder.

[0019] Step 3: Centrifuge the powder obtained in the previous step, wash it three times successively with water and absolute ethanol, and dry it at room temperature to obtain layered MnB MBene nanosheets.

[0020] The SEM and XRD diagrams are shown in Figure 1 , It can be seen from the SEM and XRD diagrams of layered MnB MBene that MnB MBene with high purity and crystallinity has been successfully synthesized in Example 1. Further analysis reveals that the size of the synthesized MnB MBene is between 100 and 500 nanometers, with a large specific surface area (>500 m 2 g -1 ), which has important applications in alkali metal ion batteries including lithium, sodium, and potassium ion batteries.

[0021] Example 2 In this example, a method for preparing FeB MBene by molten salt etching of MAB materials includes the following steps Step 1: Grind 1 g of Fe2AlB2 (6.3 mmol) and 1.70 g of ZnCl2 (12.6 mmol) in a mortar until evenly mixed for about 20 min.

[0022] Step 2: Pour the powder obtained in the previous step into a ceramic crucible, transfer it to a tube furnace, and heat it to 500 °C at a heating rate of 2 °C / min -1 in an argon atmosphere, hold for 4 h, and wait for it to naturally cool to room temperature to obtain FeB MBene powder.

[0023] Step 3: Centrifuge the powder obtained in the previous step, wash it three times successively with water and absolute ethanol, and dry it at room temperature to obtain layered FeB MBene nanosheets.

[0024] The SEM and XRD diagrams are shown in Figure 2 , It can be seen from the SEM and XRD diagrams of layered FeB MBene that FeB MBene with high purity has been successfully synthesized in Example 2. Further analysis reveals that the size of the synthesized FeB MBene is between 100 and 500 nanometers, and it has a large specific surface area (>500 m 2 g -1 ) due to its nanosheet structure, which has important applications in alkali metal ion batteries including lithium, sodium, and potassium ion batteries.

[0025] Example 3 In this example, electrochemical tests are carried out on the MnB MBene prepared in Example 1 in an alkali metal battery, including the following steps: Using the MnB prepared in Example 1 as the working electrode, the electrochemical performance of the nanosheet MnB MBene as the anode material for lithium-ion batteries was tested. The MnB MBene material, acetylene black, and CMC2200 were mixed evenly in deionized water at a mass ratio of 7:2:1, and wet-milled until the slurry was delicate and had no obvious granularity. The slurry was coated on the copper foil with a suitable viscosity, ensuring that the slurry on the copper foil was evenly coated. It was dried in a vacuum oven at 60 °C for 12 h and cut into pole pieces with a diameter of 14 mm. The loading amount of MnB on the copper foil was 0.5 - 1 mg / cm 2 Using metallic lithium as the anode, a Celgard 2500 separator with a diameter of 16 mm was used, and the electrolyte 1.0 M LiPF6 in EC: DMC: DEC = 1:1:1 vol% was used. A CR2025 type button half-cell was assembled in a glove box to test the electrochemical cycling performance of the assembled button battery.

[0026] Using the MnB prepared in Example 1 as the working electrode, the electrochemical performance of the nanosheet MnB MBene as the anode material for sodium-ion batteries was tested. The MnB MBene material, Ketjen black, and CMC2200 were mixed evenly in deionized water at a mass ratio of 7:2:1, and wet-milled until the slurry was delicate and had no obvious granularity. The slurry was coated on the copper foil with a suitable viscosity, and the loading amount was approximately 1 mg cm -2 It was dried in a vacuum oven at 60 °C for 12 h and cut into pole pieces with a diameter of 14 mm. Using metallic sodium as the anode, a Celgard 2500 separator with a diameter of 16 mm and a glass fiber separator (GF / F) were used, and the electrolyte 1.0 M NaPF6 in DIGLYME: DME = 1:1 vol% was used. A CR2032 type battery case was selected to assemble the battery in a glove box. The electrochemical cycling performance of the assembled button battery was tested.

[0027] Using the MnB prepared in Example 1 as the working electrode, the electrochemical performance of the nanosheet MnB MBene as the anode material for potassium-ion batteries was tested. The MnB MBene material, super P, and CMC2200 were mixed evenly in deionized water at a mass ratio of 6:3:1, and wet-milled until the slurry was delicate and had no obvious granularity. The slurry was coated on the copper foil with a suitable viscosity. It was dried in a vacuum oven at 60 °C for 12 h and cut into pole pieces with a diameter of 14 mm. The loading amount of MnB on the copper foil was 0.5 - 1 mg / cm 2Using metallic potassium as the negative electrode, a Celgard 2500 separator with a diameter of 16 mm and a glass fiber separator (GF / F) were employed. Electrolyte 3.0 M KFSI in DME was used, and a CR2032 type battery case was selected to assemble the battery in a glove box. The electrochemical cycling performance of the assembled button battery was tested.

[0028] The specific results are shown in Figure 3 , and the results show that in lithium-ion batteries, at a current density of 100 mA g -1 , the first-cycle charge capacity of the MnB MBene electrode was 979.1 mAh g -1 , the discharge capacity was 741.5 mAh g -1 , the first-cycle Coulombic efficiency was as high as 75.73%, and the capacity remained at 761.7 mAh g after 100 cycles -1 . In sodium-ion batteries, at a current density of 100 mA g -1 , the first-cycle charge capacity of the MnB MBene electrode was 607.8 mAh g -1 , the discharge capacity was 491.0 mAh g -1 , the first-cycle Coulombic efficiency was as high as 80.78%, and the capacity remained at 332.4 mAh g after 100 cycles -1 . In potassium-ion batteries, at a current density of 100 mA g -1 , the first-cycle charge capacity of the MnB MBene electrode was 542.1 mAh g -1 , the discharge capacity was 420.8 mAh g -1 , the first-cycle Coulombic efficiency was as high as 77.63%. The capacity remained at 232.8 mAh g after 100 cycles -1 . As the negative electrode of alkali metal ion batteries, MnB MBene exhibits excellent electrochemical performance.

[0029] Comparative Example 1 In the preparation method of MnB in this comparative example, in the second step of Example 1, the temperature was raised to 500 °C and 600 °C at a heating rate of 2 °C min -1 , and held for 4 h, and then allowed to cool naturally to room temperature to obtain the product. The XRD is as Figure 4 shown, and the SEM is as Figure 5 shown. It can be seen from Figure 4 that at 500 °C and 600 °C, Al ions have not been completely removed from Mn2AlB2, and pure-phase MnB has not been prepared. As the temperature increases, the characteristic peaks of Mn2AlB2 gradually shift towards MnB. At 700 °C, pure-phase MnB was successfully prepared with a relatively high crystallinity. And from Figure 5It can be seen from the SEM that the nanosheets formed at 500 °C and 600 °C are uneven and irregular in morphology, which is not conducive to the insertion of alkali metal ions.

[0030] Comparative Example 2 In the preparation method of FeB in this comparative example, in the second step of Example 2, the temperature was raised to 600 °C and 700 °C at a heating rate of 2 °C / min -1 , held for 4 h, and allowed to cool naturally to room temperature to obtain the product. The XRD is as Figure 6 shown, and the SEM is as Figure 7 shown. It can be seen from Figure 6 that as the temperature increases, for FeB, the characteristic peaks between 27° and 38° gradually weaken and the crystallinity becomes worse. And from Figure 7 the SEM, it can be seen that the FeB at 600 °C is in the shape of nanorods, and the FeB at 700 °C is in the morphology of nanoparticles. Although both are of nanoscale size, the morphology is uneven and the voids are small, which is not conducive to the insertion of alkali metal ions, and the surface active sites are not rich enough, which is not conducive to the electrochemical reaction.

[0031] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of pure-phase MBene nanosheets, characterized in that, The process is as follows: Mix the ternary transition metal boride MAB phase material evenly with the chloride salt, heat it to T at a specific heating rate under the protection of an inert atmosphere in a tubular furnace, hold it at temperature T for a certain time to deintercalate A, and then cool it to room temperature to obtain MB powder. After centrifugal washing and drying, pure phase MBene nanosheets are prepared.

2. The preparation method of the pure-phase MBene nanosheets according to claim 1, wherein, The ternary transition metal boride MAB phase material is one of MoAlB, Mn2AlB2, and Fe2AlB2.

3. The preparation method of the pure-phase MBene nanosheets according to claim 1, wherein, The chloride salt is ZnCl2.

4. The preparation method of the pure-phase MBene nanosheets according to claim 1, wherein, The molar ratio of MAB to the chloride salt is 1:(2 - 3).

5. The preparation method of the pure-phase MBene nanosheets according to claim 1, wherein, The temperature T for deintercalating A is 500 - 700 °C, the heating rate is 2 - 5 °C / min, and the holding time is 2 - 5 h.

6. The method for the pure-phase MBene nanosheets according to claim 1, wherein The washing is carried out by washing successively with water and anhydrous ethanol.

7. Pure phase MBene nanosheets prepared by the method according to any one of claims 1 - 6.

8. Application of the pure phase MBene nanosheets according to claim 7 in alkali metal batteries.

9. The application according to claim 8, characterized in that The alkali metal battery refers to lithium, sodium, and potassium batteries. The pure phase MBene nanosheets are coated on the current collector as the active material to serve as the negative electrode of the battery.

10. The application according to claim 8, characterized in that, Mix the pure-phase MBene nanosheets, conductive agent, and binder evenly in a ratio of (6-8):(1-3):1, add an appropriate amount of NMP or water, and grind until there are no obvious particles in the slurry. Then uniformly coat it on the copper foil using a mold and dry it to obtain the MBene nanosheet negative electrode sheet. The loading amount of MBene nanosheets on the electrode is 0.5-1 mg cm −2 , where the conductive agent is super P, acetylene black, or Ketjen black, and the binder is PVDF or CMC.

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