A method and a reaction device for preparing nanofibrillar lithium borohydride

Abstract

The application discloses a method and a reaction device for preparing nanofibrillar lithium borohydride. The reaction device comprises a material tank with a valve and placed in a freeze-drying chamber, a condensing machine for adjusting the temperature of the material in the material tank to freeze-dry and normal-temperature dry the material, a vacuum pump connected with one end of the freeze-drying chamber for vacuumizing to form negative pressure in the freeze-drying chamber, and an inert gas supply device connected with the freeze-drying chamber for providing inert gas to the freeze-drying chamber. The method comprises the following steps: mixing a mixed solution containing lithium borohydride and a polar organic solvent with a refrigerant to obtain a solution, transferring the solution to a reaction kettle, filling hydrogen into the reaction kettle, freezing to condense the solution in the reaction kettle, and sequentially performing vacuumizing, low-temperature freeze-drying and vacuumizing normal-temperature drying on the material in the reaction kettle in a water-free and oxygen-free environment to remove the polar organic solvent and the refrigerant, so as to obtain nanofibrillar lithium borohydride.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanomaterial preparation, and particularly relates to a method and a reaction device for preparing nanofibrous lithium borohydride. BACKGROUND

[0002] Nanotechnology refers to the science and technology of studying and applying materials at the nanoscale. Nanomaterials generally refer to materials with unique physical and chemical properties at a size of 1 to 100 nanometers.

[0003] Hydrogen, as a clean energy, does not produce carbon dioxide when used, and is therefore considered an important choice to replace fossil fuels. However, the storage and transportation of hydrogen has been one of the main obstacles to its widespread application.

[0004] Traditional methods of hydrogen storage include high-pressure gaseous storage and cryogenic liquid storage, but both methods have high energy consumption, low storage density, and safety problems.

[0005] In order to solve these problems, researchers have turned to solid-state hydrogen storage materials, which can store hydrogen at high density at lower pressure and temperature. Metal hydrides, complex hydrides, and high specific surface area adsorbents such as carbon nanomaterials, zeolites, and metal-organic frameworks (MOFs) have been widely studied as alternative media.

[0006] Metal borohydride is considered one of the most promising high-capacity candidates, with a weight density of up to 18wt%, and reversible hydrogen storage capacity. However, its desorption temperature needs to exceed 300℃, and rehydrogenation requires 350℃ and 35MPa. Therefore, it is necessary to further improve the kinetics and thermodynamics of borohydride.

[0007] One of the effective strategies is to reduce the particle size to nanoscale. Nanomaterials have more significant kinetic regulation and can regulate thermodynamics of lithium borohydride due to its high specific surface area and unique quantum effect. Nanosizing of lithium borohydride can be realized by limiting it in porous structures through melt impregnation and solution impregnation methods, and the hydrogen absorption and desorption temperature of the lithium borohydride is significantly reduced. By using solvent evaporation strategy, lithium borohydride nanoparticles with a size of 10.6-147.4 nm are obtained, and the main peak of dehydrogenation stabilized by polymethyl methacrylate is reduced from 488℃ to 72℃. In order to maximize the reversible hydrogen storage capacity, people try to synthesize unsupported lithium borohydride nanoparticles. Lithium borohydride nanobelt with a width of 10-40 nm, hydrogen desorption starts at 60℃ [Y.P.Pang, Y.F.Liu, M.X.Gao, L.Z.Ouyang, J.W.Liu, H.Wang, M.Zhu, H.G.Pan, A mechanical-force-driven physical vapour deposition approach to fabricating complex hydride nanostructures, Nature Commun., 2014, 5, 3519.]. Currently, the yield of unsupported lithium borohydride nanoparticles synthesized in the laboratory is low, and there is a problem of solvent residue, which makes the dehydrogenation temperature of lithium borohydride cannot be effectively reduced.

[0008] The freeze-drying method for preparing nanometer powder has the advantages of regular powder shape, less hard agglomeration, small and uniform particle size, high chemical purity, good chemical uniformity, low sintering temperature, reliable and operable preparation method, and good repeatability. By freeze-drying method, it is expected to obtain unsupported nanofibrous lithium borohydride, further improve the thermodynamics and effective hydrogen storage capacity of lithium borohydride, and promote the application research of lithium borohydride hydrogen storage material. SUMMARY

[0009] The application provides a method and a reaction device for preparing nanofibrous lithium borohydride. The method is simple and easy to operate, and has a large yield, which can be applied to other hydrides. The nanofibrous lithium borohydride prepared by the method has a good uniformity.

[0010] [1] A reaction device for preparing nanofibrous lithium borohydride, comprising:

[0011] A material tank with a valve is placed in the freeze-drying chamber, and the material tank is filled with a material for forming nanofibrous lithium borohydride in the inner cavity of the tank body;

[0012] A condensing machine is used to adjust the temperature of the material in the material tank to freeze-dry and dry at room temperature.

[0013] A vacuum pump connected to the freeze-drying chamber for vacuumizing the freeze-drying chamber to form a negative pressure environment in the freeze-drying chamber;

[0014] An inert gas supply device connected to the freeze-drying chamber for supplying inert gas to the freeze-drying chamber.

[0015] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes a material tank, a valve, a condenser, a vacuum pump, an inert gas supply device, and a controller.

[0016] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes a valve for adjusting the flow of gas.

[0017] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes a material tank including a tank cover and a tank body.

[0018] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes a condenser located below the material tank.

[0019] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride further includes a controller and a temperature sensor.

[0020] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes a vacuum pump having another end connected to a tail gas treatment device.

[0021] In some embodiments, the reaction device for preparing nanofibrillar lithium borohydride includes an inert gas supply device in the form of a high-pressure inert gas cylinder.

[0022] In the present application, the inert gas can include at least one of nitrogen, a noble gas (e.g., argon, etc.), hydrogen, and a mixture of hydrogen and a noble gas.

[0023] [2] Use of the reaction device according to [1] in the preparation of nanofibrillar lithium borohydride.

[0024] [3] A method for preparing nanofibrillar lithium borohydride, comprising:

[0025] mixing a mixed solution containing lithium borohydride and a polar organic solvent with a refrigerant, transferring the obtained solution to a ventable reaction kettle, filling the reaction kettle with hydrogen, freezing the solution in the reaction kettle to form a solid, and then sequentially performing vacuum low-temperature freeze drying and vacuum normal-temperature drying on the materials in the reaction kettle in an anhydrous and oxygen-free environment to remove the polar organic solvent and the refrigerant, filling the reaction kettle with inert gas to normal pressure at the end of drying, and finally removing the nanofibrillar lithium borohydride from the reaction kettle in an inert atmosphere environment.

[0026] In some embodiments, the method for preparing nanofibrillar lithium borohydride, the polar organic solvent can include at least one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, hexylene oxide, and dimethoxyethane, and preferably includes diethyl ether. Lithium borohydride serves as a chain backbone, and the polar organic solvent forms a protective coordination with the metal in lithium borohydride to become a one-dimensional coordination polymer.

[0027] In some embodiments, the method for preparing nanofibrillar lithium borohydride, the refrigerant can include at least one of cyclohexane and n-hexane, and preferably includes cyclohexane.

[0028] In some embodiments, the method for preparing nanofibrillar lithium borohydride, the concentration of lithium borohydride in the mixed solution containing lithium borohydride and a polar organic solvent can be 0.02-2 mmol / mL, and preferably 0.18-0.2 mmol / mL.

[0029] In some embodiments, the method for preparing nanofibrillar lithium borohydride, the volume ratio of the polar organic solvent to the refrigerant can be 3:1-9, such as 3:1, 1:1, 1:3, etc., and preferably 1:3. When the volume ratio continues to decrease, lithium borohydride will precipitate from the clear solution and become a suspension.

[0030] In some embodiments, the method for preparing nanofibrillar lithium borohydride, 1-10 bar of hydrogen can be filled into the reaction kettle.

[0031] In some embodiments, the method for preparing nanofibrillar lithium borohydride, liquid nitrogen can be used for freezing to condense the solution in the reaction kettle into a solid. Cyclohexane has a melting point of 4-7°C, and solidifies into a solid at a low temperature under liquid nitrogen freezing.

[0032] In some embodiments, the method for preparing nanofibrous lithium borohydride, the temperature of the vacuum low-temperature freeze drying can be -80 to -40℃ (for example, -70℃, etc.), and the time can be 6 to 12 hours.

[0033] In some embodiments, the method for preparing nanofibrous lithium borohydride, the temperature of the vacuum normal-temperature drying can be 20 to 50℃, and the time can be 6 to 12 hours.

[0034] The cyclohexane is removed by direct sublimation under low temperature (for example, -67℃) and low pressure (vacuum) conditions, in which the cyclohexane directly changes from solid state to gaseous state. Since the temperature is very low during the sublimation process, the structure and properties of the nanomaterials are preserved. The time can be 6 to 12 hours. This stage is mainly to remove the remaining cyclohexane and ether molecules under normal temperature (for example, 20 to 30℃) and low pressure. The product after drying is a loose one-dimensional structure, and the time can be 6 to 12 hours.

[0035] In the present application, the inert gas can include at least one of nitrogen, a noble gas (for example, argon, etc.), hydrogen, and a mixed gas of hydrogen and a noble gas.

[0036] In the present application, the inert gas atmosphere can include at least one of a nitrogen gas atmosphere, a noble gas atmosphere, a hydrogen gas atmosphere, and a mixed gas atmosphere of hydrogen and a noble gas.

[0037] In some embodiments, the method for preparing nanofibrous lithium borohydride can use the reaction device of [1].

[0038] [4] The nanofibrous lithium borohydride prepared by the method of [3].

[0039] The diameter of the nanofibrous lithium borohydride of the present application is adjustable in the range of 5μm to 100nm.

[0040] [5] The application of the nanofibrous lithium borohydride of [4] in hydrogen absorption and release.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] The present application uses a physical method to control the nucleation and growth of lithium borohydride at low temperature, and can prepare nanofibrous lithium borohydride with high purity, and the diameter is adjustable in the range of 5μm to 100nm.

[0043] The yield is large, and it has good universality for complex metal coordination hydride.

[0044] The prepared lithium borohydride has high purity and small diameter, and has excellent hydrogen storage performance. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1A schematic diagram of a reaction device for preparing nanofibrous lithium borohydride according to the present application.

[0046] Figure 2 A schematic diagram of a reaction device for preparing nanofibrous lithium borohydride according to the present application. Figure 1 A schematic diagram of a reaction device for preparing nanofibrous lithium borohydride according to the present application.

[0047] Figure 3 A schematic diagram of a reaction device for preparing nanofibrous lithium borohydride according to the present application. Figure 1 A schematic diagram of a reaction device for preparing nanofibrous lithium borohydride according to the present application.

[0048] Figure 4 A transmission electron microscope photograph of the product in Example 1 of the present application.

[0049] Figure 5 X-ray diffraction patterns of lithium borohydride in Examples 1-4 of the present application.

[0050] Figure 6 Fourier transform infrared absorption spectra of lithium borohydride in Examples 1-4 and Comparative Example 1 of the present application.

[0051] Figure 7 Scanning electron microscope (SEM) photographs of the products in Example 1 (a, b), Example 2 (c, d), Example 3 (e, f) and Example 4 (g, h) of the present application.

[0052] Figure 8 Temperature programmed desorption spectra of lithium borohydride in Example 1, Example 2, Example 3 and Comparative Example 1 of the present application.

[0053] Figure 9 Optical photographs of lithium borohydride prepared in Example 1 (a), Example 2 (b), Example 3 (c) and Example 4 (d) of the present application. DETAILED DESCRIPTION

[0054] The present application will be further described in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are intended to illustrate the present application and are not intended to limit the scope of the present application. The operation methods in the following examples, if not otherwise specified, are usually carried out under conventional conditions, or under conditions recommended by the manufacturers.

[0055] The structural characteristics of the samples prepared in each example are characterized by X-ray diffraction patterns, Fourier transform infrared absorption spectra and energy dispersive spectra. Among them, the X-ray diffraction patterns are collected on a MiniFlex 600 X-ray diffractometer, the instrument is at 40 kV, 15 mA, and the XRD data is collected in the range of 10°-90° with a step size of 0.05°. The Fourier transform infrared absorption spectra are collected in transmission mode on a German Bruker Tensor 27 spectrometer, dry KBr and sample powder are mixed in a mass ratio of 200:1, and the applied pressure is 10 MPa.

[0056] The hydrogen desorption properties of the prepared samples were characterized by temperature programmed desorption spectra and volume hydrogen desorption curves. The temperature programmed desorption spectra were measured by a mass spectrometer and a self-made temperature control heating device, with argon gas as the carrier gas at a flow rate of 20 mL / min, and the temperature rising rate was 2 ℃ / min. The volume hydrogen desorption curves were measured by a self-made volume hydrogen desorption instrument, under vacuum conditions, with a temperature rising rate of 2 ℃ / min, and non-isothermal hydrogen desorption test was carried out.

[0057] For SEM measurement, the powder was dispersed on a conductive tape in the glove box and transferred to a Hitachi SU8010 scanning electron microscope under argon protection using a custom-made scanning stage, with a working voltage of 5 kV. Transmission electron microscope photos were taken on a Hitachi HT7700.

[0058] Referring to Figure 1 A reaction device for preparing nanofibrillar lithium borohydride includes a vacuum pump 1, an exhaust treatment device 2, a controller 3, a freeze-drying chamber 4, an inert gas supply device 6, a material tank 7, a condensing machine 8, and a temperature sensor 9.

[0059] The material tank 7 includes a sealingly fitted tank cover and a tank body. The material tank 7 is provided with a breather pipe in communication with the inner cavity of the tank body. The breather pipe is an elongated iron pipe, and a valve 10 is arranged on the breather pipe, and the valve 10 is away from the tank body of the material tank 7, so as to maintain the stability of the valve 10 in repeated cold and hot alternation and prevent the valve 10 from failing.

[0060] The material tank 7 is placed in the freeze-drying chamber 4, and the material tank 7 is provided with a material for forming nanofibrillar lithium borohydride in the inner cavity of the tank body.

[0061] The condensing machine 8 is located below the material tank 7 and is used to adjust the temperature of the material in the material tank 7 to freeze-dry and normal-temperature dry the material in the material tank 7.

[0062] The temperature sensor 9 is arranged on the material tank 7 and is used to monitor the temperature of the material tank 7.

[0063] The controller 3 is connected with the temperature sensor 9 and the condensing machine 8, and the controller 3 controls the operation and running of the condensing machine 8 according to the temperature of the material tank 7 monitored by the temperature sensor 9.

[0064] One end of the vacuum pump 1 is connected with the freeze-drying chamber 4 and is used to form a negative pressure environment in the freeze-drying chamber 4, and the other end of the vacuum pump 1 is connected with the exhaust treatment device 2.

[0065] The exhaust treatment device 2 is a filtering device, which is designed as a barrel with an open top, and is provided with activated carbon and alcohol inside, and is used to filter and absorb the organic gas extracted by the vacuum pump 1 in the drying process.

[0066] The inert gas supply device 6 is a high-pressure inert gas bottle, which is connected to the freeze-drying chamber 4 through a pressure reducing valve 5 and is used to provide inert gas to the freeze-drying chamber 4 .

[0067] Use the above Figure 1 The reaction apparatus shown is evacuated, see Figure 2 A sealed material tank 7 contains the material for forming nanofibrous lithium borohydride and is filled with hydrogen. Valve 10 is opened to protect the sample in tank 7 under hydrogen pressure. In the freeze-drying chamber 4, vacuum pump 1 is activated to initiate a vacuum operation, gradually reducing the hydrogen pressure above the sample until it reaches a negative pressure. Organic molecules contained in the material within the tank sublime while frozen, passing through vacuum pump 1 and into exhaust gas treatment unit 2. During this process, the sample is kept out of contact with air, achieving a low-temperature vacuum process under inert gas protection.

[0068] Use the above Figure 1 The reaction device shown is back-gassed, see Figure 3 , open the high-pressure inert gas cylinder and adjust the pressure reducing valve 5 to 0.1 MPa. The inert gas enters the material tank 7 above the sample. Turn off the vacuum pump 1. The pressure in the material tank 7 and the freeze-drying chamber 4 continues to rise until the freeze-drying chamber 4 reaches atmospheric pressure. At this time, the internal and external pressures are balanced. Quickly close the valve 10 of the material tank 7. The sample is transferred to the glove box under the protection of inert gas and removed.

[0069] The following examples 1 to 3 all adopt the above Figures 1 to 3 The reaction apparatus shown in the figure uses argon as the inert gas.

[0070] Example 1

[0071] Add 40 mg of lithium borohydride and 10 mL of ether to a flask and stir for 40 minutes. Transfer the lithium borohydride ether solution to a three-necked flask, add 30 mL of cyclohexane, and stir for 40 minutes. Transfer the solution to a vented reactor (i.e., material tank 7). Fill the reactor with 5 bar of high-purity hydrogen and place it in liquid nitrogen for 10 minutes. During the freezing process, the cyclohexane solution condenses into a solid. Move the reactor to condenser 8 and dry it at -70°C under vacuum for 12 hours. Turn off the refrigeration and continue drying under vacuum for 6 hours. Use a high-pressure argon cylinder to fill the freeze-drying chamber 4 with argon, and quickly close the reactor valve 10. Remove the resulting nanofibrous lithium borohydride (recorded as LiBH4-40-10 ether-30 cyclohexane) in an argon atmosphere glove box and store it.

[0072] The transmission electron microscope photo of the nanofiber-shaped lithium borohydride product of this example is as follows Figure 4 shown.

[0073] Example 2

[0074] The difference from Example 1 is only that the amount of diethyl ether is changed to 20 mL, the amount of cyclohexane is changed to 20 mL, and the rest is the same, to obtain the product nanofibrous lithium borohydride (which can be recorded as LiBH4-40-20 diethyl ether-20 cyclohexane).

[0075] Example 3

[0076] The difference from Example 1 is only that the amount of diethyl ether is changed to 30 mL, the amount of cyclohexane is changed to 10 mL, and the rest is the same, to obtain the product nanofibrous lithium borohydride (which can be recorded as LiBH4-40-30 diethyl ether-10 cyclohexane).

[0077] Example 4

[0078] The difference from Example 1 is only that the amount of diethyl ether is changed to 40 mL, the amount of cyclohexane is changed to 0 mL (i.e. no cyclohexane is added), and the rest is the same, to obtain the product lithium borohydride (which can be recorded as LiBH4-40-40 diethyl ether).

[0079] Comparative Example 1

[0080] Commercial lithium borohydride after ball milling is used as a comparative sample. Take 1 g of lithium borohydride and add it to a ball mill tank with a volume of 180 mL, the ball milling ratio is 120:1, the ball milling time is 12 h, the rotation speed is 500 revolutions / minute, and after ball milling, the original lithium borohydride sample is scraped out in an argon-filled glove box, which is recorded as ball-milled-LiBH4.

[0081] Figure 5 The X-ray diffraction test results are shown. The diffraction peaks of nanofibrous lithium borohydride coincide with the standard diffraction peaks of orthorhombic lithium borohydride; as the proportion of cyclohexane increases, the diffraction intensity gradually weakens.

[0082] Figure 6 The results of the Fourier transform infrared absorption test are shown. Commercial lithium borohydride and nanofibrous lithium borohydride detect characteristic B-H vibrations at 2380, 2291, 2221 and 1122 cm -1 .

[0083] Figure 7The following are scanning electron microscope photos of Examples 1-4. It can be seen that the lithium borohydride prepared in Example 1 is in the form of nanofibers, with an average width of about 100 nm and a length of more than 100 μm; the lithium borohydride prepared in Example 2 is in the form of nanofibers, with an average width of about 300 nm and a length of more than 100 μm; the lithium borohydride prepared in Example 3 is in the form of nanofibers, with an average width of about 5 μm and a length of about 40 μm; the lithium borohydride prepared in Example 4 is in the form of blocks, with a particle size of 100 μm. As the amount of cyclohexane added as the refrigerant decreases, the diameter of the lithium borohydride fibers continues to increase. When the amount of refrigerant added is zero, the lithium borohydride becomes blocky. The addition of the refrigerant not only reduces the size of the lithium borohydride, but also changes the morphology of the lithium borohydride into a nanofiber-like shape.

[0084] The hydrogen release and hydrogen absorption performances of lithium borohydride samples were tested in the temperature-dependent hydrogen release and temperature-dependent hydrogen absorption modes. The test conditions were vacuum (initial vacuum degree was 1×10 -3 Torr) from room temperature to 600 ° C at a rate of 2 ° C / min and heated to 350 ° C at a rate of 1 ° C / min under 100 bar H2 pressure and kept at this temperature for 6 hours. The degassing curve of the sample during the heating process was analyzed by mass spectrometry and fixed volume. The results are as follows Figure 8 . Figure 8 The graph is a comparison of the hydrogen release curves of the nanofiber lithium borohydride samples prepared in Example 1, Example 2, and Example 3 and the ball-milled lithium borohydride sample prepared in Comparative Example 1. As can be seen from the figure, Figure 8 The starting dehydrogenation temperatures of Example 1, Example 2, and Example 3 are 100°C, 150°C, and 200°C, respectively, and the peak temperatures of the first step dehydrogenation are 350°C, 400°C, and 425°C, respectively. Figure 8 The peak dehydrogenation temperature (433° C.) of the ball-milled lithium borohydride of Comparative Example 1 is shown to be reduced by 83° C., 33° C., and 8° C., respectively, which indicates that the nanofibers improve the dehydrogenation performance of lithium borohydride.

[0085] Figure 9 Shown are optical photographs of lithium borohydride prepared in Examples 1 to 4. It can be seen that as the amount of cyclohexane added decreases, the volume of the lithium borohydride product decreases, and the particle size of the product becomes larger and more compact.

[0086] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for producing nanofibrillar lithium borohydride, characterized by, The application relates to a preparation method of nanofibrillar lithium borohydride. The mixed solution containing lithium borohydride and a polar organic solvent is mixed with a refrigerant, the obtained solution is transferred into a ventilable reaction kettle, hydrogen is filled into the reaction kettle, the solution in the reaction kettle is frozen into a solid, and then the material in the reaction kettle is subjected to vacuum low-temperature freeze drying and vacuum normal-temperature drying in sequence in a water-free and oxygen-free environment, the polar organic solvent and the refrigerant are removed, inert gas is filled into the reaction kettle to normal pressure after the drying is completed, and finally the nanofibrillar lithium borohydride is obtained by taking out the material from the reaction kettle in an inert atmosphere environment.

2. The method of claim 1, wherein, The polar organic solvent comprises at least one of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, hexylene oxide and ethylene glycol dimethyl ether; The refrigerant comprises at least one of cyclohexane and n-hexane; The concentration of lithium borohydride in the mixed solution containing lithium borohydride and a polar organic solvent is 0.02-2 mmol / mL; The volume ratio of the polar organic solvent to the refrigerant is 3:1-9; 1-10 bar hydrogen is filled into the reaction kettle; The solution in the reaction kettle is frozen into a solid by using liquid nitrogen; The temperature of the vacuum low-temperature freeze drying is-80--40 DEG C, and the time is 6-12 hours; The temperature of the vacuum normal-temperature drying is 20-50 DEG C, and the time is 6-12 hours; The inert gas comprises at least one of nitrogen and a rare gas; The inert atmosphere environment comprises at least one of a nitrogen atmosphere environment and a rare gas atmosphere environment.

3. The method according to claim 1 or 2, characterized in that, The reaction device for preparing nanofibrillar lithium borohydride comprises: A material tank (7) placed in a freeze-drying chamber (4) and provided with a valve (10), the material tank (7) is provided with material for forming nanofibrillar lithium borohydride in the inner cavity of the tank body; the material tank (7) is the ventilable reaction kettle; A condensing machine (8) for adjusting the temperature of the material in the material tank (7) to freeze dry and dry at normal temperature; A vacuum pump (1) connected with one end of the freeze-drying chamber (4) and used for forming a negative pressure environment in the freeze-drying chamber (4); An inert gas supply device (6) connected with the freeze-drying chamber (4) and used for providing inert gas to the freeze-drying chamber (4).

4. The method of claim 3, wherein, The material tank (7) is provided with a ventilation pipe communicated with the inner cavity of the tank body, and the valve (10) is arranged on the ventilation pipe and away from the tank body of the material tank (7); The condensing machine (8) is located below the material tank (7); The reaction device further comprises a controller (3) and a temperature sensor (9); the temperature sensor (9) is arranged on the material tank (7) and used for monitoring the temperature of the material tank (7); the controller (3) is connected with the temperature sensor (9) and the condensing machine (8), and the controller (3) controls the working and operating conditions of the condensing machine (8) according to the temperature of the material tank (7) monitored by the temperature sensor (9); The other end of the vacuum pump (1) is connected with an exhaust treatment device (2); the exhaust treatment device (2) is a filtering device and is provided with activated carbon and alcohol and is used for filtering and absorbing the organic gas extracted by the vacuum pump (1) in the drying process. The inert gas supply device (6) is a high-pressure inert gas bottle connected to the freeze-drying chamber (4) through a pressure-reducing valve (5); the inert gas includes at least one of nitrogen and a rare gas.

5. The nanofibrous lithium borohydride prepared by the method according to any one of claims 1-4.

6. The nanofibrous lithium borohydride of claim 5, wherein, The diameter of the nanofibrous lithium borohydride is adjustable between 5 μm and 100 nm.

7. The nanofibrous lithium borohydride according to claim 5 or 6 for use in hydrogen absorption and desorption.

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