Method for preparing borophene by molten salt method and its application

Abstract

The present application provides a method for preparing borophene using a molten salt method, which comprises: mixing a boron source and a metal salt by ball milling for the first time to obtain a mixture A; adding a molten salt medium to the mixture A and continuing to ball mill for the second time to obtain a mixture B; compacting the mixture B and performing two-stage heating and heat preservation to obtain a borophene precursor; cooling the borophene precursor to room temperature and washing it with an acidic solution until it is neutral, and drying it to obtain borophene. The preparation method is simple in process, low in cost, green and safe, and the borophene obtained has good dispersibility, uniform size and high purity. The present application also provides an application of borophene obtained by the preparation method in the preparation of battery electrode materials and negative electrode modification.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of borophene materials, and in particular to a method for preparing borophene using a molten salt method and its application. Background Art

[0002] Borophene is another new type of two-dimensional material after graphene, molybdenum disulfide, two-dimensional layered metal carbon / nitride, and boron nitride. It has light weight, high conductivity, strong mechanical properties, high electrochemical activity, and excellent physical and chemical properties.

[0003] Currently, the main methods for preparing borophene include chemical vapor deposition, liquid-phase ultrasonic exfoliation, and electrochemical exfoliation. However, these methods suffer from long production cycles, toxic raw materials or intermediates, low product yields, and limitations in mass production. Borophene can also be produced through inert atmosphere thermal decomposition, oxidation / chemical etching, ion resin exchange, and solvent thermal nucleation and growth. While these methods offer shorter reaction times, they require demanding conditions and carry a high risk factor. Mechanical ball milling, on the other hand, requires the use of precious metal silver as a stabilizer, resulting in high costs, difficult-to-control product morphology, and low purity. Summary of the Invention

[0004] In view of this, the present application provides a method for preparing borophene using a molten salt process. This method uses a low-melting-point salt as the reaction medium, which allows the reactants to have a certain degree of fluidity in the molten salt phase during the synthesis process, accelerating the reaction rate and shortening the preparation time. Furthermore, this method is simple, safe, high-yield, and low-cost. The resulting borophene is of high purity and has good electrochemical properties.

[0005] The first aspect of the present application provides a method for preparing borophene using a molten salt method, comprising the following steps:

[0006] The boron source and the metal salt are subjected to a first ball milling to obtain a mixture A; wherein the oxidizing property of the metal cation in the metal salt is greater than the oxidizing property of the metal cation in the boron source;

[0007] Adding a molten salt medium to the mixture A and continuing to ball mill for a second time to obtain a mixture B;

[0008] The mixed material B is compacted and then heated and kept warm in two stages to obtain a boron olefin precursor;

[0009] The borophene precursor is cooled to room temperature, washed with an acidic solution until neutral, and dried to obtain borophene.

[0010] In an embodiment of the present application, the boron source includes one or more of aluminum diboride, magnesium diboride, chromium diboride, molybdenum boride, silicon boride and niobium boride; the metal salt includes one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, zinc chloride, zinc nitrate, zinc sulfate, zinc acetate, nickel chloride and cobalt chloride; the molten salt medium includes one or more of sodium chloride, potassium chloride, lithium chloride and calcium chloride.

[0011] In the embodiment of the present application, the molten salt medium includes sodium chloride and potassium chloride, and the mass ratio of the sodium chloride to potassium chloride is 1:1-10.

[0012] In the embodiment of the present application, the mass ratio of the boron source and metal salt added in the first ball milling to the molten salt medium added in the second ball milling is 1:(1-6):(20-60).

[0013] In the embodiment of the present application, the first ball milling further includes adding a molten salt medium, and the mass ratio of the molten salt medium added in the first ball milling to the boron source is 1-6:1.

[0014] In the embodiment of the present application, the first ball milling time is 5 min-30 min, and the rotation speed is 300 r / min-400 r / min; the second ball milling time is 10 min-30 min, and the rotation speed is 300 r / min-400 r / min.

[0015] In the embodiment of the present application, the heating time of the first stage of the two-stage heating and insulation is 60min-100min, the heating rate is 5℃ / min-10℃ / min, the insulation temperature is 300℃-500℃, and the insulation time is 60min-100min; the heating time of the second stage of heating and insulation is 60min-100min, the heating rate is 5℃ / min-8℃ / min, the insulation temperature is 600℃-700℃, and the insulation time is 120min-180min.

[0016] In an embodiment of the present application, the acidic solution includes any one of ammonium persulfate, dilute hydrochloric acid or dilute sulfuric acid; the molar concentration of the acidic solution is 0.5 mol / L-1 mol / L.

[0017] The second aspect of the present application provides a boron olefin produced by the method for producing boron olefin by the molten salt method provided in the first aspect of the present application.

[0018] The third aspect of the present application provides a method for preparing borophene using the molten salt method provided in the first aspect of the present application or the application of borophene provided in the second aspect of the present application in the preparation of battery electrode materials and negative electrode modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is a scanning electron microscope (SEM) photograph of borophene prepared in Example 1 of the present application;

[0020] Figure 2 The X-ray diffraction (XRD) patterns of borophene prepared in Example 1 of the present application and the raw material aluminum diboride;

[0021] Figure 3 The XRD patterns of borophene and aluminum diboride prepared in Example 2 of the present application are shown below:

[0022] Figure 4 This is an infrared spectrum (IR) photograph of borophene prepared in Example 1 of the present application;

[0023] Figure 5 A time-voltage curve diagram of a Na-Na symmetric battery provided in an application embodiment of the present application;

[0024] Figure 6 This is an SEM photograph of the surface of the Na negative electrode after modification with reduced graphene oxide / borophene film provided in an application example of the present application;

[0025] Figure 7 This is an SEM photograph of the surface of the Na negative electrode that has not been modified with reduced graphene oxide / borophene film, provided in an application example of the present application. DETAILED DESCRIPTION

[0026] The present application is further described in detail below in conjunction with preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0027] In this application, all professional terms have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this application.

[0028] Borophene is another new type of two-dimensional material after graphene, molybdenum disulfide, two-dimensional layered metal carbon / nitride, and boron nitride. It has light weight, high conductivity, strong mechanical properties, high electrochemical activity, and excellent physical and chemical properties.

[0029] Currently, the main methods for preparing borophene include chemical vapor deposition, liquid-phase ultrasonic exfoliation, and electrochemical exfoliation. However, these methods suffer from long production cycles, toxic raw materials or intermediates, low product yields, and limitations in mass production. Borophene can also be produced through inert atmosphere thermal decomposition, oxidation / chemical etching, ion resin exchange, and solvent thermal nucleation and growth. While these methods offer shorter reaction times, they require demanding reaction conditions and carry a high risk factor. Mechanical ball milling, on the other hand, requires the use of precious metal silver, resulting in high costs, difficult to control product morphology, and low purity.

[0030] To address the above issues, this application provides a molten salt method for preparing borophene. This method uses a low-melting-point metal salt as the reaction medium, which allows the reactants to have a certain degree of fluidity in the molten salt phase during the synthesis process, accelerating the reaction rate and shortening the preparation time. Furthermore, this method is simple, safe, high-yield, and low-cost. The resulting borophene is of high purity and has excellent electrochemical properties.

[0031] The present application provides a method for preparing borophene by a molten salt method, comprising the following steps:

[0032] S101, ball-milling the boron source and the metal salt for the first time to obtain a mixture A;

[0033] S102, adding a molten salt medium to the mixture A and continuing to ball mill for a second time to obtain a mixture B;

[0034] S103, compacting the mixed material B and then heating and keeping it in two stages to obtain a boron olefin precursor;

[0035] S104, cooling the borophene precursor to room temperature, washing it with an acidic solution until it becomes neutral, and drying it to obtain borophene.

[0036] In step S101, the boron source includes one or more of aluminum diboride, magnesium diboride, chromium diboride, molybdenum boride, silicon boride, and niobium boride; the metal salt includes one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, zinc chloride, zinc nitrate, zinc sulfate, zinc acetate, nickel chloride, and cobalt chloride, and the oxidizing property of the metal cation in the metal salt is greater than the oxidizing property of the metal cation in the boron source. In some embodiments of the present application, the boron source may be, for example, aluminum diboride, and the metal salt may be, for example, copper chloride. In other embodiments of the present application, the boron source may be, for example, magnesium diboride, and the metal salt may be, for example, zinc chloride. In embodiments of the present application, the boron source is a layered metal boride, and the oxidizing property of the metal cation in the metal salt is greater than the oxidizing property of the metal cation in the boron source. This ensures that a redox reaction occurs between the metal salt and the boron source, effectively removing the interlayer metal of the layered metal boride, leaving a boron layer, and thus obtaining borene. Furthermore, compared to other methods for preparing borophene using the same boron source and metal salt, the molten salt method produces borophene with controllable crystal morphology, better particle dispersion, and less agglomeration. Furthermore, the molten salt method, conducted under an inert atmosphere, avoids the extreme experimental conditions of the Hummer method and solvothermal methods, resulting in a safer experiment. This method effectively prevents contact between the boron source and water, which could lead to product hydrolysis, and localized heat, which could lead to product oxidation or further hydrolysis. This results in a higher purity of the borophene produced compared to other methods.

[0037] In an embodiment of the present application, the mass ratio of the boron source to the metal salt is 1:1-6. In some embodiments, the mass ratio of the boron source to the metal salt can be, for example, 1:1, 1:2, 1:3, 1:4, 1:5, or 1:6. In the present application, by regulating the ratio of the main reaction raw materials of the molten salt reaction within an appropriate range, the redox reaction can be made more sufficient and the impurities brought to the product borene by the incomplete reaction of the raw materials can be minimized, thereby improving the purity of the product.

[0038] In an embodiment of the present application, the molten salt medium includes one or more of sodium chloride, potassium chloride, lithium chloride, and calcium chloride. In an embodiment of the present application, the molten salt medium may be a single component or a combination of multiple molten salt media. In some embodiments of the present application, the molten salt medium is a combination of multiple molten salt media. Increasing the types of molten salt media and rationally selecting the combination of molten salt media can make the melting point of the resulting molten salt medium composition lower than the melting point of each single component in the composition, thereby further reducing the temperature of the molten salt reaction.

[0039] In some embodiments of the present application, step S101 further includes adding a molten salt medium during the first ball milling, and the mass ratio of the molten salt medium added during the first ball milling to the boron source is 1-6:1. In some embodiments of the present application, the mass ratio of the molten salt medium added during the first ball milling to the boron source can be 1:1, 2:1, 3:1, 4:1, 5:1, or 6:1. The present application can largely avoid the oxidation of borophene by adding a molten salt medium when mixing the boron source and the metal salt, reduce the generation of impurities such as B2O3, and thereby improve the purity of the obtained borophene.

[0040] In the embodiment of the present application, the time of the first ball milling is 5min-30min, and the rotation speed is 300r / min-400r / min. In some embodiments, the time of the first ball milling can be, for example, 5min, 10min, 15min, 20min, 25min, 30min; the rotation speed of the first ball milling can be, for example, 300r / min, 320r / min, 340r / min, 350r / min, 360r / min, 380r / min, 400r / min. The boron source and the metal salt are uniformly mixed by the first ball milling to obtain a mixture A, which is used as the main reactant of the redox reaction in the molten salt reaction.

[0041] The mass ratio of the molten salt medium to the boron source added in step S102 is 20-60: 1. In some embodiments of the present application, the mass ratio of the molten salt medium to the boron source added in step S102 can be 20: 1, 25: 1, 30: 1, 35: 1, 40: 1, 45: 1, 50: 1, 55: 1, or 60: 1. The present application controls the amount of the molten salt medium within a reasonable range so that the reactants, the boron source and the metal salt, maintain a certain fluidity in the molten salt medium, react fully, and improve the yield while minimizing impurities obtained due to incomplete reaction.

[0042] In some embodiments of the present application, the molten salt medium in step S102 includes sodium chloride and potassium chloride, and the mass ratio of sodium chloride to potassium chloride is 1:1-10. In some embodiments of the present application, the mass ratio of sodium chloride to potassium chloride can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10. Compared with the selection of conventional molten salt media, some embodiments of the present application select sodium chloride and potassium chloride as molten salt media and regulate the mass ratio of the two within a suitable range, which can reduce the reaction temperature and reduce the reaction cost while ensuring sufficient reaction. In other embodiments of the present application, the molten salt medium selects lithium chloride, sodium chloride and potassium chloride. Compared with the molten salt medium of a single system, increasing the type of molten salt medium can appropriately lower the melting point of the molten salt medium system, thereby making the reaction easier to carry out and the cost of the reaction lower.

[0043] In an embodiment of the present application, the time of the second ball milling is 10min-30min, and the rotation speed is 300r / min-400r / min. In some embodiments, the time of the second ball milling can be, for example, 10min, 15min, 20min, 25min, 30min; the rotation speed of the second ball milling can be, for example, 300r / min, 320r / min, 340r / min, 350r / min, 360r / min, 380r / min, 400r / min. The present application uses two-step ball milling to uniformly disperse the reactant mixture A in the molten salt medium, so that the reactants and the molten salt medium are in full contact, the subsequent molten salt reaction is more complete, and the dispersion and uniformity of the obtained product boron olefins are better. In some embodiments of the present application, the grinding balls for the first ball milling and the second ball milling can be, for example, ZrO2.

[0044] In step S103, in some embodiments, a compactor can be used for compaction, with a compaction pressure of 10 MPa to 30 MPa and a compaction time of 30 seconds to 60 seconds. In some embodiments of the present application, the compaction pressure can be, for example, 10 MPa, 15 MPa, 20 MPa, 25 MPa, or 30 MPa, and the compaction time can be, for example, 30 seconds, 40 seconds, 45 seconds, 50 seconds, or 60 seconds.

[0045] In the embodiment of the present application, after the mixture B is compacted, two-stage heating and heat preservation are performed. In some embodiments, the heating and heat preservation equipment may be, for example, a tubular furnace. Before heating and heat preservation, a protective gas is introduced into the heating equipment, and the ventilation time is 3 min-5 min. In some embodiments, the protective gas may be, for example, argon, and the ventilation time may be 3 min, 3.5 min, 4 min, 4.5 min, or 5 min. Carrying out a molten salt reaction under an atmosphere of protective gas can avoid the oxidation of the product borene to the greatest extent, suppress the generation of oxide impurities such as boron oxide, and thereby improve the purity of the product, and the inert protective gas can improve the safety of the experiment.

[0046] In the embodiment of the present application, the heating time of the first stage of the two-stage heating and insulation is 60min-100min, the heating rate is 5℃ / min-10℃ / min, the insulation temperature is 300℃-500℃, and the insulation time is 60min-100min. In some embodiments, the heating time of the first stage of heating and insulation can be, for example, 60min, 70min, 75min, 80min, 90min, 100min; the heating rate can be, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min; the insulation temperature can be, for example, 300℃, 350℃, 360℃, 400℃, 400℃, 420℃, 450℃, 480℃, 500℃; the insulation time can be, for example, 60min, 70min, 75min, 80min, 90min, 100min. The selection of parameters for the first stage of heating and insulation needs to be coordinated with the selection of the molten salt medium. The purpose of the first stage of heating and insulation is to melt the molten salt medium in the compacted mixture B into a low-temperature eutectic, provide a low-temperature, stable liquid phase environment for the molten salt reaction, and transform the solid-solid reaction into a more complete and faster solid-liquid reaction.

[0047] In the embodiment of the present application, the heating time of the second stage of the two-stage heating and heat preservation is 60min-100min, the heating rate is 5℃ / min-8℃ / min, the heat preservation temperature is 600℃-700℃, and the heat preservation time is 120min-180min. In some embodiments, the heating time of the second stage of heating and heat preservation can be, for example, 60min, 70min, 75min, 80min, 90min, 100min; the heating rate can be, for example, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min; the heat preservation temperature can be, for example, 600℃, 620℃, 640℃, 650℃, 660℃, 680℃, 700℃; the heat preservation time can be, for example, 120min, 125min, 130min, 135min, 140min, 150min, 160min, 170min, 175min, 180min. The purpose of the second heating and holding phase is to allow the reactants to fully undergo a redox reaction in the molten salt medium to produce the product, borophene. The boron source and metal salt in the liquid, low-temperature eutectic system allow for thorough mixing at the molecular and atomic scale. This significantly reduces the energy required for the reaction from a kinetic perspective, lowering the synthesis temperature and shortening the heating and holding times.

[0048] In step S104, after the borophene precursor is cooled to room temperature, the borophene precursor is washed with an acidic solution. In an embodiment of the present application, the acidic solution includes any one of ammonium persulfate, dilute hydrochloric acid or dilute sulfuric acid, and the molar concentration of the acidic solution is 0.5mol / L-1mol / L. In some embodiments, the molar concentration of the acidic solution can be, for example, 0.5mol / L, 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, or 1mol / L. The present application selects an acidic solution of appropriate concentration to wash borophene, which can remove metal elemental impurities such as copper or magnesium obtained through redox reactions on the surface of the borophene precursor, thereby improving the purity of the obtained borophene. In some embodiments of the present application, before washing the borophene precursor with an acidic solution, the borophene precursor can be washed to neutral with a detergent, and the detergent can be, for example, deionized water. In some embodiments, the acidic solution washing method can be, for example, ultrasonic oscillation followed by stirring, the ultrasonic oscillation power is 100W-300W, the ultrasonic oscillation time is 20min-40min, the stirring speed is 200r / min-400r / min, and the stirring time is 30min-120min. In some embodiments, the ultrasonic oscillation power can be, for example, 100W, 120W, 140W, 150W, 160W, 180W, 200W, 220W, 240W, 250W, 260W, 280W, 300W; the ultrasonic oscillation time can be, for example, 20min, 25min, 30min, 35min, 40min; the stirring speed can be, for example, 200r / min, 250r / min, 300r / min, 350r / min, 400r / min; and the stirring time can be, for example, 30min, 50min, 60min, 90min, 100min, 120min.

[0049] In an embodiment of the present application, the borophene precursor is washed with an acidic solution until it is neutral, and the washed sample is dried. In some embodiments of the present application, the drying process can be freeze drying, and the drying time is 24 hours to 48 hours. In some embodiments of the present application, the drying time can be, for example, 24 hours, 25 hours, 28 hours, 30 hours, 32 hours, 35 hours, 36 hours, 40 hours, 42 hours, 45 hours, or 48 hours.

[0050] The present application provides a method for preparing borophene using a molten salt process. Using one or more low-melting-point salts as the molten salt reaction medium, the molten salt phase can be generated under low-temperature conditions, providing a liquid phase environment. The boron source and metal salt have a certain solubility in the molten salt, allowing the reaction to proceed at the atomic scale, greatly accelerating the ion diffusion rate, thereby increasing the reaction rate while reducing the reaction conditions. This preparation method has the advantages of simple process, low synthesis temperature, process safety, high yield, and low cost. Furthermore, the borophene produced using this method has controllable crystal morphology, good particle dispersion, and high purity.

[0051] The present application also provides a boronene prepared by the method for preparing boronene by the molten salt method described above. The boronene prepared by the molten salt method provided above has the advantages of uniform chemical composition, good crystal morphology, and high phase purity. In addition, the surface of the boronene prepared by the molten salt method provided by the present application also includes a certain amount of hydroxyl (-OH), which is conducive to further modification of the surface functional groups on the basis of the prepared boronene while improving the ionic conductivity and electronic conductivity of the boronene.

[0052] The present application also provides a method for preparing borophene by the molten salt method as described above, or the application of the borophene prepared by the method in the preparation of battery electrode materials and negative electrode modification. The borophene prepared by the method for preparing borophene by the molten salt method provided by the present application is used in lithium / sodium ion batteries, and has excellent electrochemical performance and huge application potential. The borophene prepared by the molten salt method provided by the present application can be used as a negative electrode active material to prepare battery pole pieces, which can improve the capacity and cycle life of the battery, because the borophene electrode material has a typical two-dimensional atomic layer structure, and the boron atoms are small, which is conducive to adsorption and alloying, and is easy to form a stable conductive structure and interface, which is convenient for ion and electron transmission, and has good cyclicity and reversibility. The metal negative electrode is prone to produce dendrites on the surface of the metal negative electrode during the battery charge and discharge cycle. The pore structure of the diaphragm is large and uneven, which easily leads to uneven metal ion transmission, thereby inducing the growth of metal dendrites. The continuous growth of dendrites will cause the diaphragm between the positive and negative electrodes to be pierced, thereby seriously affecting the safety and stability of the battery. Therefore, this borophene is used to prepare a reduced graphene oxide / borophene membrane to modify the metal anode. Borophene and redox graphene exhibit a synergistic effect, improving the dispersibility of the borophene, resulting in a high conductivity and an overall conductive skeleton. On the one hand, due to the sodium affinity and spontaneous polarization effect of the reduced graphene oxide / borophene membrane, the reduced graphene oxide / borophene membrane-modified fiber-electrolyte interface can accelerate ion migration. On the other hand, the reduced graphene oxide / borophene membrane-modified separator-sodium anode interface can further homogenize ion transport, forming a uniform ion flux. The uniform deposition of sodium ions on the substrate facilitates a uniform distribution of the electric field, thereby inhibiting the rapid growth of sodium dendrites and enhancing transport kinetics. Furthermore, the three-dimensional reduced graphene oxide / borophene network structure improves the conductivity and wettability of the sodium anode, thereby reducing interfacial resistance and improving the problem of reduced electrochemical performance caused by dendrites on the anode surface. This beneficial modification of the battery anode results in a battery with improved cycle life and stability.

[0053] The present application is further described below with reference to several embodiments:

[0054] Example 1

[0055] Preparation of borophene: 0.3 g of aluminum diboride and 1.5 g of copper chloride were ball-milled for the first time, the ball-milling time was 30 min, and the speed was 300 r / min; 6.343 g of sodium chloride and 8.092 g of potassium chloride were added to the mixture obtained after ball milling, and the ball milling time was 10 min and the speed was 300 r / min; the mixture obtained after the two ball millings was pressed at a pressure of 30 MPa for 30 s using a tablet press, and then the sample was placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 5 min and then two The product was heated and kept warm in sections, first heated to 300°C for 100 minutes and then kept warm for 60 minutes. After the end of the heat preservation, it was continued to heat to 700°C for 100 minutes and then kept warm for 120 minutes. After the end of the heat preservation, it was cooled to room temperature. The obtained borophene precursor was added to 100 mL of 1 mol / L ammonium persulfate solution at room temperature, placed under 200 W ultrasonic power, ultrasonicated for 20 minutes, and then stirred at 200 r / min for 30 minutes. It was washed with deionized water three times until neutral. The washed sample was dried in a freeze dryer for 24 hours to obtain borophene.

[0056] Battery Preparation: 80 mg of boron nitride, 10 mg of conductive carbon black, and 10 mg of polyvinylidene fluoride were uniformly mixed and placed in a stir box. An appropriate amount of N-methylpyrrolidone was added dropwise, and the mixture was stirred in a blender for 15 minutes until it became viscous. The resulting paste was then knife-coated onto copper foil to a thickness of 100 μm. After drying in a vacuum oven at 80°C for 8 hours, the copper foil was punched into electrodes with a diameter of 14 mm. A lithium foil was used as the counter electrode and a glass fiber separator. After assembly, the electrolyte was injected into the resulting button cell.

[0057] Example 2

[0058] Preparation of borophene: 0.4593 g of magnesium diboride and 2.726 g of zinc chloride were ball-milled for the first time, the ball-milling time was 30 min, and the speed was 300 r / min; 4.593 g of sodium chloride and 4.593 g of potassium chloride were added to the mixture obtained after ball milling, and the ball milling time was 20 min and the speed was 300 r / min; the mixture obtained after the two ball millings was pressed at a pressure of 20 MPa for 60 s using a tablet press, and the sample was placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 5 min. Two-stage heating and insulation were carried out, first heating to 300°C for 60 minutes and then insulation for 60 minutes. After the insulation was completed, heating was continued to 550°C for 60 minutes and then insulation was carried out for 180 minutes. After the insulation was completed, the obtained borophene precursor was added to 100 mL of 0.5 mol / L ammonium persulfate solution at room temperature, placed under 180 W ultrasonic power, ultrasonicated for 20 minutes, and then stirred at 300 r / min for 30 minutes. After that, it was washed with deionized water three times until neutral, and the washed sample was dried in a freeze dryer for 48 hours to obtain borophene after drying.

[0059] Preparation of the battery: The borophene prepared in Example 2 was used as the active material, and the method was the same as that in Example 1.

[0060] Example 3

[0061] Preparation of borophene: 0.5 g of aluminum diboride and 1.5 g of copper chloride were ball-milled for the first time, the ball-milling time was 30 min, and the speed was 200 r / min; 6.343 g of sodium chloride and 8.092 g of potassium chloride were added to the mixture obtained after ball milling, and the ball milling time was 10 min and the speed was 400 r / min; the mixture obtained after the two ball millings was pressed at a pressure of 30 MPa for 30 s using a tablet press, and then the sample was placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 4.5 min before being heated. A two-stage heating and insulation method was adopted, first heating to 300°C for 100 minutes and then insulation for 60 minutes. After the insulation was completed, heating was continued to 600°C for 100 minutes and then insulation was completed for 120 minutes. After the insulation was completed, the obtained boron olefin precursor was added to 100 mL of 1 mol / L sulfuric acid solution at room temperature, placed under 180 W ultrasonic power, ultrasonicated for 30 minutes, and then stirred at 300 r / min for 60 minutes. After that, it was washed with deionized water three times until neutral. The washed sample was dried in a freeze dryer for 24 hours to obtain boron olefin.

[0062] Preparation of the battery: The boron olefins prepared in Example 3 were used as the active material, and the method was the same as that in Example 1.

[0063] Example 4

[0064] Preparation of borophene: 0.3 g of aluminum diboride and 1.5 g of copper nitrate were ball-milled for the first time, the ball-milling time was 40 min, and the speed was 300 r / min; 6.343 g of calcium chloride and 8.092 g of potassium chloride were added to the mixture obtained after ball milling, and the ball milling time was 20 min and the speed was 300 r / min; the mixture obtained after the two ball millings was pressed at a pressure of 20 MPa for 30 s using a tablet press, and then the sample was placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 4 min. Two-stage heating and insulation, first heating to 300°C for 100 minutes and then insulation for 60 minutes. After the insulation is completed, continue heating to 700°C for 100 minutes and then insulation for 120 minutes. After the insulation is completed, cool to room temperature; the obtained borophene precursor is added to 100mL of 1mol / L hydrochloric acid solution at room temperature, placed under 180W ultrasonic power, ultrasonicated for 30 minutes, and then stirred at 300r / min for 50 minutes, and then washed with deionized water three times until neutral. The washed sample is dried in a freeze dryer for 24 hours to obtain borophene after drying.

[0065] Preparation of the battery: The borophene prepared in Example 4 was used as the active material, and the method was the same as that in Example 1.

[0066] Example 5

[0067] Preparation of borophene: 0.3 g of aluminum diboride and 1.5 g of copper acetate were ball-milled for 30 min at a speed of 200 r / min. 6.343 g of lithium chloride, 6.343 g of potassium chloride, and 5.0 g of calcium chloride were added to the mixture obtained after ball milling and ball milled for 10 min at a speed of 400 r / min. The mixture obtained after the two ball millings was pressed at a pressure of 30 MPa for 30 s using a tablet press. The sample was then placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 3 mi. n and then perform two-stage heating and insulation, first heating to 300°C for 100 minutes and then insulation for 60 minutes. After the insulation is completed, continue heating to 700°C for 100 minutes and then insulation for 120 minutes. After the insulation is completed, cool to room temperature; the obtained borophene precursor is added to 100mL of 1mol / L sulfuric acid solution at room temperature, placed under 300W ultrasonic power, ultrasonicated for 30 minutes, and then stirred at 400r / min for 120 minutes, and then washed with deionized water three times until neutral, and the washed sample is dried in a freeze dryer for 24 hours to obtain borophene after drying.

[0068] Preparation of the battery: using the boron olefins prepared in Example 5 as the active material, the method is the same as that in Example 1.

[0069] Example 6

[0070] Preparation of borophene: 0.3 g of aluminum diboride and 1.6 g of copper sulfate were ball-milled for the first time, the ball-milling time was 30 min, and the speed was 200 r / min; 6.343 g of sodium chloride and 8.092 g of potassium chloride were added to the mixture obtained after ball milling, and the ball milling time was 10 min and the speed was 400 r / min; the mixture obtained after the two ball millings was pressed at a pressure of 20 MPa for 30 s using a tablet press, and then the sample was placed in a crucible, placed in a tube furnace, and argon protective gas was introduced for 5 min and then two The product was heated and kept warm in sections, first heated to 300°C for 100 minutes and then kept warm for 60 minutes. After the end of the heat preservation, it was continued to heat to 700°C for 100 minutes and then kept warm for 120 minutes. After the end of the heat preservation, it was cooled to room temperature. The obtained borophene precursor was added to 100 mL of 0.5 mol / L sulfuric acid solution at room temperature, placed under 200 W ultrasonic power, ultrasonicated for 30 minutes, and then stirred at 350 r / min for 100 minutes. It was washed with deionized water three times until neutral. The washed sample was dried in a freeze dryer for 24 hours to obtain borophene.

[0071] Preparation of the battery: The borophene prepared in Example 6 was used as the active material, and the method was the same as that in Example 1.

[0072] Comparative Example 1

[0073] Preparation of borophene: 0.3 g of aluminum diboride, 1.5 g of copper chloride, 6.343 g of sodium chloride and 8.092 g of potassium chloride were added to a ball mill and ball-milled for 30 min at a speed of 300 r / min. The mixture obtained after two ball millings was pressed at a pressure of 20 MPa for 30 s using a tablet press. The sample was then placed in a crucible and placed in a tubular furnace. Argon protective gas was introduced for 3 min and then two-stage heating and insulation was performed. First, it was heated to 300 ° C for 100 min and then kept warm for 60 min. After the insulation was completed, it was continued to be heated to 700 ° C for 100 min and kept warm for 120 min. After the insulation was completed, it was cooled to room temperature. The obtained borophene precursor was added to 100 mL of 1 mol / L sulfuric acid solution at room temperature and stirred at a speed of 300 r / min for 30 min. After that, it was washed with deionized water 3 times until neutral. The washed sample was dried in a freeze dryer for 24 h to obtain borophene after drying.

[0074] Preparation of the battery: The borophene prepared in Comparative Example 1 was used as the active material, and the method was the same as that in Example 1.

[0075] Comparative Example 2

[0076] Preparation of borophene: 0.3 g of aluminum diboride and 1.5 g of copper chloride were ball-milled for 30 min at a speed of 300 r / min, and for 10 min at a speed of 300 r / min. The mixture obtained after two ball millings was pressed with a tablet press at a pressure of 30 MPa for 60 s, and then the sample was loaded into a crucible and placed in a tubular furnace. After passing argon protective gas for 5 min, two-stage heating and insulation were performed, first heating to 300 ° C for 100 min and then insulation for 60 min. After the insulation was completed, the mixture was continued to be heated to 700 ° C for 100 min and then insulation for 120 min. After the insulation was completed, it was cooled to room temperature. The obtained borophene precursor was added to 100 mL of 1 mol / L hydrochloric acid solution at room temperature, placed under 180 W ultrasonic power, and ultrasonicated for 30 min. After washing with deionized water three times until neutral, the washed sample was dried in a freeze dryer for 24 h to obtain borophene after drying.

[0077] Preparation of the battery: The borophene prepared in Comparative Example 2 was used as the active material, and the method was the same as that in Example 1.

[0078] Comparative Example 3

[0079] Preparation of borophene: 0.4593 g of magnesium diboride and 2.726 g of zinc chloride were ball-milled for 30 min at a speed of 300 r / min. The mixture obtained after two ball millings was pressed at a pressure of 30 MPa for 60 s using a tablet press. The sample was then loaded into a crucible and placed in a tubular furnace. Argon protective gas was introduced for 5 min and then two-stage heating and insulation was performed. First, it was heated to 300°C for 60 min and then kept warm for 60 min. After the insulation was completed, it was continued to be heated to 550°C for 60 min and then kept warm for 180 min. After the insulation was completed, it was cooled to room temperature. The obtained borophene precursor was added to 100 mL of 1 mol / L ammonium persulfate solution at room temperature, placed under 180 W ultrasonic power, ultrasonicated for 20 min, and then stirred at 300 r / min for 30 min. After washing with deionized water three times until neutral, the washed sample was dried in a freeze dryer for 24 h to obtain borophene after drying.

[0080] Preparation of the battery: The boron olefins prepared in Comparative Example 3 were used as the active material, and the method was the same as that in Example 1.

[0081] Figure 1 This is an SEM photograph of the boron nitride prepared in Example 1 of the present application. It can be seen from the SEM photograph that the boron nitride prepared in Example 1 has good dispersibility and simple and consistent crystal morphology, and the particle size is in the range of 400nm-500nm.

[0082] The borophene and boron source obtained in Example 1 and Example 2 were characterized by X-ray diffractometer. Figure 2 The XRD patterns of borophene prepared in Example 1 of the present application and the raw material aluminum diboride; Figure 3 The XRD patterns of borophene and aluminum diboride prepared in Example 2 of the present application are as follows: Figure 2 and Figure 3 It can be seen that the characteristic diffraction peaks of aluminum diboride and magnesium diboride in the boron source prepared by the molten salt method of the present application disappear, and the diffraction peak intensity of borophene is relatively high, which indicates that the chemical composition of the prepared borophene is uniform and the purity is relatively high, and there is almost no generation of impurities such as aluminum diboride, magnesium diboride or boron oxide. Figure 4 That is, from the infrared spectrum (IR) photograph of the borophene obtained in Example 1 of the present application, it can be seen that the surface of the borophene obtained by the molten salt method provided in Example 1 also includes a certain amount of hydroxyl groups, which is conducive to further modification of the surface functional groups on the basis of the obtained borophene while improving the ionic conductivity and electronic conductivity of the borophene.

[0083] The battery performance test was performed on the batteries prepared in Examples 1-6 and Comparative Examples 1-3. The electrochemical window was 0.01V-3V. The measured results are shown in Table 1.

[0084] Table 1 Electrochemical performance test results of batteries prepared in Examples 1-6 and Comparative Examples 1-3

[0085]

[0086] As can be seen from Table 1, the lithium-ion batteries prepared in Examples 1-6 have a measured discharge capacity of more than 200 mA h / g at 25°C and 0.01V-3.0V, a cycle life of more than 500 cycles, a high coulombic efficiency, and excellent electrochemical performance, which are significantly better than the materials prepared under conditions such as no separate ball milling steps and no molten salt medium in Comparative Examples 1 to 3. Therefore, the boronene prepared by the method for preparing boronene by the molten salt method provided in this application has good electrochemical properties, and its application in lithium-ion batteries can improve the coulombic efficiency and cycle life of the battery.

[0087] In addition, the borene obtained in Example 3 was applied to a reduced graphene oxide / borene film. 20 mg of graphene oxide and 10 mg of the borene obtained in Example 3 were taken, ultrasonically dispersed for 30 min, and then filtered to form a film. 2 mL of hydrazine hydrate was added and reacted at 95 ° C for 12 h to obtain a reduced graphene oxide / borene film. Two sodium metal sheets were used as the positive and negative electrodes of a symmetrical battery, respectively. The reduced graphene oxide / borene film was cut into a size of 17 mm and attached to one side of the negative electrode of the battery. A glass fiber separator was placed between the positive and negative electrodes of the battery. 140 μl of electrolyte (the solvent was ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and the solute was 1 mol / L of sodium hexafluorophosphate) was injected and the battery was packaged to obtain a Na-Na symmetrical battery S1. In addition, a Na-Na symmetrical battery D1 was made, which was consistent with S1 except that the negative electrode did not have a reduced graphene oxide / borene film attached. The electrochemical performance of S1 and D1 was tested and the results were Figure 5 The time-voltage curve is shown in the figure. The symmetrical batteries S1 and D1 after cycling were disassembled and the Na negative electrodes obtained were characterized by scanning electron microscopy. The results are shown in the figure. Figure 6 and Figure 7 As shown. Figure 7 It can be seen that there are a lot of dendrites on the surface of the Na negative electrode that has not been modified by reduced graphene oxide / borophene film, while Figure 6 The surface of the Na negative electrode modified with reduced graphene oxide / borophene film is smoother and no dendrites are produced. Compared with the unmodified battery negative electrode, the growth of metallic sodium dendrites of the modified battery negative electrode is inhibited, thereby improving the cycle life and stability of the battery.

[0088] The preferred embodiments are described in detail above, but the present invention is not limited to the above-mentioned specific implementation methods. Under the guidance of this application, technicians in this field can also make various forms of specific changes without departing from the scope of protection of this application, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing borophene by a molten salt method, characterized in that: The following steps are involved: The boron source and the metal salt are subjected to a first ball milling to obtain a mixture A; wherein the oxidizing property of the metal cation in the metal salt is greater than the oxidizing property of the metal cation in the boron source; Adding a molten salt medium to the mixture A and continuing to ball mill for a second time to obtain a mixture B; The mixed material B is compacted and then heated and kept warm in two stages to obtain a boron olefin precursor; The borophene precursor is cooled to room temperature, washed with an acidic solution until neutral, and dried to obtain borophene.

2. The method for preparing borophene by the molten salt method according to claim 1, wherein: The boron source includes one or more of aluminum diboride, magnesium diboride, chromium diboride, molybdenum boride, silicon boride and niobium boride; the metal salt includes one or more of copper chloride, copper nitrate, copper sulfate, copper acetate, zinc chloride, zinc nitrate, zinc sulfate, zinc acetate, nickel chloride and cobalt chloride; the molten salt medium includes one or more of sodium chloride, potassium chloride, lithium chloride and calcium chloride.

3. The method for preparing borophene by the molten salt method according to claim 1, wherein: The molten salt medium includes sodium chloride and potassium chloride, and the mass ratio of the sodium chloride to potassium chloride is 1:1-10.

4. The method for preparing borophene by the molten salt method according to claim 1, wherein: The mass ratio of the boron source and metal salt added in the first ball milling to the molten salt medium added in the second ball milling is 1:(1-6):(20-60).

5. The method for preparing borophene by the molten salt method according to claim 1, wherein: The first ball milling further includes adding a molten salt medium, and the mass ratio of the molten salt medium added in the first ball milling to the boron source is 1-6:

1.

6. The method for preparing borophene by the molten salt method according to claim 1, wherein: The first ball milling process is performed for 5 min to 30 min at a rotation speed of 300 r / min to 400 r / min; the second ball milling process is performed for 10 min to 30 min at a rotation speed of 300 r / min to 400 r / min.

7. The method for preparing borophene by the molten salt method according to claim 1, wherein: The first stage of the two-stage heating and insulation has a heating time of 60 min-100 min, a heating rate of 5°C / min-10°C / min, a holding temperature of 300°C-500°C, and a holding time of 60 min-100 min; the second stage of the heating and insulation has a heating time of 60 min-100 min, a heating rate of 5°C / min-8°C / min, a holding temperature of 600°C-700°C, and a holding time of 120 min-180 min.

8. The method for preparing borophene by the molten salt method according to claim 1, wherein: The acidic solution includes any one of ammonium persulfate, dilute hydrochloric acid or dilute sulfuric acid; the molar concentration of the acidic solution is 0.5 mol / L-1 mol / L.

9. Borophene is prepared by the method for preparing borophene by the molten salt method according to any one of claims 1 to 8.

10. Use of the method for preparing borophene using a molten salt method according to any one of claims 1 to 8, or borophene obtained by the method for preparing borophene using a molten salt method according to any one of claims 1 to 8, in the preparation of battery electrode materials and negative electrode modification.

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