A LiAlH4-based composite hydrogen storage material and solid phase preparation method thereof

Abstract

The present invention discloses a LiAlH4-based composite hydrogen storage material and a solid-phase preparation method thereof. The method first prepares a lithium aluminum alloy by smelting in an inert atmosphere, then prepares a LiAl alloy by low-temperature freezing ball milling under liquid nitrogen cooling conditions, refines the grains and particle size of the lithium aluminum alloy, and finally obtains a coordinated aluminum-based composite hydrogen storage material by ball milling through a hydrogenation reaction in a hydrogen atmosphere. The present invention adopts a solid-phase preparation method, and can prepare LiAlH4 without using a catalyst, while avoiding the use of an organic solvent, eliminating the subsequent solvent removal process, and directly preparing LiAlH4 without passing through an intermediate phase Li3AlH6. The prepared LiAlH4-based composite hydrogen storage material does not contain Li3AlH6, has a low hydrogen release temperature, and a fast hydrogen release rate, and can realize the large-scale preparation and application of LiAlH4.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen storage material preparation, and specifically relates to a LiAlH4-based composite hydrogen storage material and a solid phase preparation method thereof. Background Art

[0002] As a new type of solid-state hydrogen storage material, coordinated aluminum hydride has broad application prospects in the fields of portable energy storage, new energy vehicles, fuel cell vehicles, hydrogen purification, and chemical and pharmaceutical fields due to its high mass hydrogen storage density, low hydrogen desorption temperature and high safety.

[0003] Since 1997, et al. reported that Ti-based catalysts can improve the hydrogen storage performance of NaAlH4, enabling it to achieve a reversible hydrogen storage capacity of more than 4wt% under relatively mild conditions. Due to their high mass hydrogen storage density and low hydrogen desorption temperature, coordinated aluminum-based hydrides such as NaAlH4, LiAlH4, and Mg(AlH4)4 have attracted widespread interest among researchers. Lithium is the metal with the lowest density. As a metal cation, LiAlH4 has a high mass hydrogen storage density (10.5wt%). At the same time, LiAlH4 itself has unstable thermodynamic properties and a low hydrogen desorption temperature (180-220℃), making it an ideal choice as a solid hydrogen storage material. By adding Ti-based catalysts, the decomposition products of NaAlH4, NaH and Al, can directly and reversibly absorb hydrogen back to NaAlH4 under certain temperature and certain hydrogen pressure conditions. Unlike NaAlH4, the first decomposition of LiAlH4 is an exothermic reaction, and it can slowly and spontaneously decompose under normal temperature and pressure difference. Theoretical calculations show that the products LiH and Al need extremely high hydrogen pressure (>10 5 bar). Limited by its own thermodynamic properties, the current industrial production and laboratory preparation of LiAlH4 is generally carried out in an organic solvent (tetrahydrofuran, dimethyl ether, etc.) environment, using LiH and AlCl3 or NaAlH4 and LiCl to perform ion exchange to first obtain a complex of LiAlH4 and solvent molecules, and then obtain pure LiAlH4 by heating and dynamic vacuum desolventization. This method has the following problems: 1. A large amount of solvent is required, and the reaction rate is slow; 2. The process is complicated, involving operations such as reaction + filtration + desolventization; 3. Inert products such as LiCl and NaCl are difficult to remove; 4. The product of the desolventization process will decompose. The above problems have seriously hindered the commercial application of LiAlH4.

[0004] Y. Kojima et al. added 5wt% TiCl3 as a catalyst to LiH and Al powder, and produced a very small amount of LiAlH4 and some Li3AlH6 after ball milling for 24 hours under 1MPa hydrogen pressure. The obtained composite hydrogen storage material consists of two aluminum-based hydrides LiAlH4, Li3AlH6 and unconverted LiH / Al. TPD results show that when heated to 327℃, the total hydrogen release of LiAlH4 and Li3AlH6 is only 0.8wt% [Y. Kojima et al. "Direct formation of LiAlH4 by amechanochemical reaction" Journal of Alloys and Compounds 441 (2007): 189–191]. The problems are: the need to add a catalyst, which increases the cost of raw materials; the prepared product contains some by-products Li3AlH6, and the hydrogen release is low, which is difficult to put into practical application.

[0005] At present, there is no report on the preparation of LiAlH4 by gas-solid reaction using LiAl alloy as reactant. This is because the synthesis of LiAlH4 by LiAl hydrogenation reaction is subject to both thermodynamic and kinetic limitations, and requires coordinated optimization of thermodynamics and kinetics. It can be seen that it is extremely challenging to directly prepare LiAlH4 by hydrogenation of the dehydrogenation product LiH and Al through solid-gas reaction. The realization of this synthetic route has great practical significance for the study of the reversible hydrogen absorption and dehydrogenation characteristics of LiAlH4 and the promotion of the practical application of coordinated aluminum hydride hydrogen storage materials. Summary of the invention

[0006] The present invention provides a LiAlH4-based composite hydrogen storage material and a solid phase preparation method thereof, aiming to overcome the problems in the prior art that a catalyst needs to be added, the prepared product contains some Li3AlH6, and the hydrogen release amount is low.

[0007] To achieve the purpose of the present invention, the present invention provides a technical solution: a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0008] Step 1: Smelting metal Li and Al in an inert atmosphere to obtain a LiAl alloy ingot, grinding off the oxide layer on the surface of the ingot in an inert gas glove box, and crushing the alloy ingot into blocks for standby use;

[0009] Step 2, preparing LiAl alloy by cryogenic ball milling;

[0010] Step 3: In a hydrogen atmosphere, the LiAl alloy is ball-milled by a hydrogenation reaction to prepare a LiAlH4-based composite hydrogen storage material.

[0011] Preferably, the atomic ratio of lithium to aluminum is 0.8 - 1.2:1.

[0012] Preferably, after step 1, ribbon preparation is carried out: the prepared alloy block is placed in a high-vacuum induction melting and spinning machine, and an amorphous / nanocrystalline ribbon of LiAl alloy is prepared by melt spinning quenching.

[0013] Preferably, after step 2, wet ball milling is carried out: LiAl is wet ball milled with the assistance of a solvent.

[0014] Preferably, in step 1, the metal further includes an Al-M master alloy, M is one of Ti, Ni, V, Zr, Zn, Y, Cu, Ga, Sn, Ge, Si, and the atomic ratio of Li, Al to M is 0.8 - 1:0.8 - 1:0 - 0.2, and the obtained alloy is (LiAl) 1-x M x (x = 0.01 - 0.2).

[0015] Preferably, in step 1, an induction melting furnace is used for melting. The crucible material used in the induction melting furnace is high-purity boron nitride or stainless steel. The induction melting vacuum degree is < E-4 Pa, and the inert gas is argon or helium. Melting is carried out 3 - 5 times to ensure the uniformity of the alloy.

[0016] Preferably, for the above melt spinning quenching, a high-purity boron nitride nozzle or a stainless steel nozzle is used. The rotation speed of the cooling copper roll for melt spinning quenching is 1000 - 6000 revolutions per minute, the spray casting gas pressure is 0.1 - 1 MPa, and the slit-copper roll spacing is 1 - 3 mm.

[0017] Preferably, in step 2, under the condition of liquid nitrogen cooling, the temperature of cryogenic ball milling is -196 °C. Vibration ball milling is used for cryogenic ball milling, the ball-to-material ratio is 5 - 500:1, the rotation speed of cryogenic ball milling is 100 - 1800 revolutions per minute, the cryogenic ball milling time is 10 - 1800 minutes, and the grinding beads used are hard alloy steel grinding beads; in step 3, planetary ball milling is used for hydrogenation reaction ball milling, the ball-to-material ratio is 40 - 200:1, the ball milling rotation speed is 100 - 600 revolutions per minute, and the ball milling time is 4 - 40 hours.

[0018] Preferably, in step 3, the pressure of H2 gas is 1 - 150 bar.

[0019] A LiAlH4-based composite hydrogen storage material prepared by the above solid-phase preparation method.

[0020] Compared with the existing preparation technology, the present invention has the following beneficial effects:

[0021] 1. The present invention uses lithium aluminum alloy as a reactant, and combines the lithium source and the aluminum source into one phase. On the one hand, it avoids the long-range diffusion of elements between the two solid phases when LiH+Al is used as the lithium source and the aluminum source, and reduces the reaction energy barrier; on the other hand, the reaction paths of lithium aluminum alloy and LiH+Al absorbing hydrogen to LiAlH4 are different, which regulates the thermodynamic and kinetic behaviors of preparing LiAlH4. This method ensures that lithium and aluminum are evenly dispersed, and reduces the grain size and particle size of the alloy by freezing ball milling, so that lithium, aluminum and hydrogen do not need long-range diffusion to combine. Nanocrystalline grains and highly active surface interfaces promote the alloy to absorb hydrogen across the intermediate phase Li3AlH6 in the absence of a catalyst, and directly generate LiAlH4, so that the prepared composite material contains only aluminum-based hydride LiAlH4 and byproduct LiH / Al, the LiAlH4 content accounts for a higher proportion, and the hydrogen release temperature of the composite is lower.

[0022] 2. The present invention refines the particle and grain size of lithium aluminum alloy, promotes the kinetic behavior of hydrogen absorption reaction, and the active surface interface between the particle grains promotes the dissociation of hydrogen molecules and the penetration and diffusion of active hydrogen, so that LiAlH4 can be prepared without using a catalyst. Without using a catalyst, the preparation process can be greatly simplified. At the same time, the prepared LiAlH4-based composite hydrogen storage material still maintains good low-temperature hydrogen release performance and improves the overall mass hydrogen storage density of the composite system.

[0023] 3. The present invention adopts a solid-gas reaction preparation method, which avoids the use of a large amount of organic solvents and eliminates the subsequent solvent removal process. The present invention directly prepares the LiAlH4-based composite hydrogen storage material by ball milling. The hydrogen storage material only contains aluminum-based hydride LiAlH4 and incompletely converted LiH / Al, and does not contain the intermediate phase Li3AlH6.

[0024] 4. The preparation process of the present invention is easy to operate. With lithium aluminum alloy as the reactant, the lithium aluminum in the prepared lithium aluminum alloy is dispersed at the atomic level. The grain size of the alloy is reduced to the nanoscale by low-temperature freezing ball milling, and high defects and strain density and more grain boundaries are obtained, thereby increasing the difference in thermodynamic enthalpy change between the product and the reactant. At the same time, the preparation process is optional. The catalytic phase can be further introduced into the alloy grain boundary in situ by melt quenching, and the particle size of the alloy can be reduced by wet ball milling. While the alloy effectively dissociates hydrogen, excellent hydrogen transmission and diffusion capabilities are obtained, greatly improving the kinetic characteristics of the reaction. The dehydrogenation temperature of the prepared composite hydrogen storage material can be further reduced to room temperature. Therefore, the present invention synergistically regulates the thermodynamic and kinetic properties of the hydrogenation reaction of the alloy through nano-scale dispersion of alloy elements, nano-sizing of grains / particles, introduction of a large number of defects, and in-situ catalysis, and successfully prepares LiAlH4-based composite hydrogen storage materials through solid-phase reaction, and the prepared composite system does not contain Li3AlH6. No catalyst is used, the cost is low, the LiAlH4 conversion rate is high, the hydrogen release temperature of the composite system is low, the energy consumption is low, the safety is high, and it is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The XRD pattern of the LiAl alloy prepared in Example 1 of the present invention;

[0026] Figure 2 This is a SEM image of the LiAl alloy powder after cryo-ball milling prepared in Example 1 of the present invention;

[0027] Figure 3 The temperature-dependent hydrogen release curves of the products of Example 1 and Comparative Example 1 of the present invention;

[0028] Figure 4 This is the solid-state Al NMR spectrum of the product of Example 1 of the present invention;

[0029] Figure 5 This is a SEM image of the LiAl alloy prepared in Example 2 of the present invention;

[0030] Figure 6 The XRD diagrams of the products of Examples 2, 4 and Comparative Example 2 of the present invention are shown below;

[0031] Figure 7 The temperature-dependent hydrogen release curves of the products of Example 2 and Comparative Example 2 of the present invention;

[0032] Figure 8 The temperature-dependent hydrogen release curves of the products of Examples 3 and 5 of the present invention;

[0033] Fig. 9 These are SEM images of the LiAl alloys prepared in Example 4 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0035] Unless otherwise specified, all operations such as weighing, grinding, drying, and storage of materials in the following examples were carried out in an argon atmosphere glove box.

[0036] The design idea of ​​the present invention is: adopting the method of smelting + grain / particle refinement + hydrogenation reaction ball milling, first, preparing lithium aluminum alloy by induction melting or resistance melting, then refining the grain / particle size of the alloy by melt rapid quenching, cryo-ball milling and / or wet ball milling technology, introducing a large number of defects and amorphous phases, and finally preparing aluminum-based composite hydrogen storage material by hydrogenation reaction ball milling.

[0037] According to analysis, at high temperature (>400℃), the third step decomposition reaction of pure LiAlH4 is: LiH+Al→LiAl+1 / 2H2, generating LiAl alloy and hydrogen. LiAl crystal belongs to NaTl structure, which is composed of two interlaced diamond sublattices, and each atom has tetrahedral T d Lithium-aluminum alloys are excellent fast ion conductors. The diffusion coefficient of lithium atoms at room temperature is relatively high, about 10 -7 According to theoretical calculations of the electronic structure of LiAl alloys, the Li-Al bond is dominated by covalent bonds, some of which are ionic bonds, Al-Al is a metallic bond, and Li-Li pairs are not bonded. This special structure allows the Li and Al elements to be evenly dispersed at the atomic level, and the V Li Anti-structure lithium atom Li in vacancies and aluminum substructures Al The uniform dispersion of Li and Al elements at the atomic level in a ratio of 1:1 and good Li ion migration have inherent advantages for the synthesis of LiAlH4 with a lithium-aluminum atomic ratio of 1:1.

[0038] Embodiment 1, a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0039] Step 1. In an argon glove box, metallic lithium and aluminum are measured at an atomic ratio of 1:1. 6.95 g of metallic lithium sheet is weighed and placed in a stainless steel crucible of an induction melting furnace. The sheet is heated to 300°C and kept warm for 2 hours to melt the lithium sheet into a whole. After the furnace is cooled, 26.98 g of aluminum particles are added, and the temperature is raised to 750°C again. The temperature is kept warm for 2 hours and the furnace is cooled. In order to ensure the uniform distribution of LiAl alloy elements, the crucible is repeatedly inverted and melted 3 times to obtain a LiAl alloy ingot.

[0040] In an argon atmosphere glove box, the oxide layer on the surface of the ingot was polished off, and the alloy ingot was broken into blocks for later use.

[0041] Step 2: Take 1 g of the above LiAl alloy, grind it into powder using a mortar in a glove box, and place it in a frozen ball mill. Under liquid nitrogen cooling conditions, the temperature of the frozen ball mill is -196°C, and 100 g of carbide steel grinding beads are added at a ball-to-material ratio of 100:1. The ball mill is sealed in the glove box and transferred out of the glove box.

[0042] The freezing ball milling jar was fixed on a vibrating freezing ball mill, and the freezing ball milling parameters were set as follows: pre-freezing for 20 minutes, 12 cycles, 5 minutes of ball milling each time, 2 minutes of rest, and 1800 rpm. After the ball milling was completed, the room temperature was restored, and the powder was transferred to a glove box after drying to obtain the frozen ball milled LiAl alloy powder.

[0043] Step 3: Take 1g of the frozen ball-milled LiAl alloy in a stainless steel ball mill, add 100g of hard-core alloy steel ball mill beads at a ball-to-material ratio of 100:1, seal the ball mill in a glove box, and transfer it out of the glove box. Evacuate the ball mill, flush it with high-purity hydrogen three times, and fill it with 5MPa hydrogen.

[0044] The ball mill jar filled with hydrogen was placed on a planetary ball mill for ball milling. The ball milling parameters were: alternating forward and reverse operation, a speed of 400 rpm, 10 min of rotation, 5 min of rest, and after 10 h of ball milling, the scraped material was removed to obtain the prepared LiAlH4-based composite hydrogen storage material sample, which included a large amount of the target product LiAlH4 and some by-products LiH and Al.

[0045] Figure 1 The XRD patterns of the prepared cast LiAl alloy and the LiAl alloy after cryo-milling are shown below. It can be found that the cast lithium-aluminum alloy is consistent with the literature reports, and there is no residual reactant metal lithium and aluminum, which proves that lithium-aluminum alloy phase is generated according to the stoichiometric ratio and has good crystallinity. After cryo-milling at -196℃ for 60 minutes, the grains of the lithium-aluminum alloy are refined and amorphized to a certain extent, the diffraction peak intensity decreases, the peak width becomes wider, and the grain size calculated by the Scherrer formula reaches 10.9nm.

[0046] Figure 2 The SEM images of the cast lithium aluminum alloy after grinding and the lithium aluminum alloy after cryo-ball milling are compared. The particle size of the cast alloy is about ten microns. After cryo-ball milling, the particle size is reduced to less than 10 microns.

[0047] Figure 3The graph is a comparison of the hydrogen release curves of the cast lithium aluminum alloy and the cryo-milled lithium aluminum alloy after hydrogenation reaction ball milling in comparative example 1. It can be seen that due to the large particle and grain size of the cast alloy, no LiAlH4 and Li3AlH6 are generated after hydrogenation, while the cryo-milled sample begins to decompose and release hydrogen at about 85°C, and releases a total of 0.6wt% hydrogen when the temperature is raised to 300°C.

[0048] Figure 4 The solid-state Al NMR spectrum of the sample treated by cryo-ball milling and hydrogenated ball milling for 10 hours. The chemical shift is 112.3ppm, which is consistent with the chemical shift of AlH4 reported in the literature, proving that LiAlH4 is successfully prepared in this embodiment, and there is no chemical shift front of AlH6 at -34ppm, proving that the preparation method of LiAl alloy absorbs hydrogen without passing through the intermediate phase LiAlH6, and directly generates LiAlH4. The LiAlH4-based composite hydrogen storage material sample prepared in this embodiment contains only LiAlH4 and LiH / Al, and does not contain the intermediate phase Li3AlH6. In the absence of a catalyst, the conversion rate of LiAlH4 is improved and the dehydrogenation temperature of the composite system is reduced. This embodiment proves that the present invention has made significant progress.

[0049] Embodiment 2, a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0050] Step 1. In an argon glove box, weigh 9g of aluminum particles and 1g of titanium particles in a mass ratio of 9:1, place them in a quartz crucible to prepare an Al-Ti master alloy, evacuate the charged vacuum induction melting furnace to 10E-4Pa, fill with argon for protection, heat and melt for 3min, and repeatedly melt for 5 times after cooling to ensure the uniformity of the alloy to obtain an Al-Ti master alloy.

[0051] Preparation of 5wt% titanium-doped LiAl alloy: Weigh 4g of the Al-Ti master alloy prepared above, 1.55g of lithium sheet, and 2.45g of aluminum particles, and put them into a high-purity boron nitride crucible. Evacuate the vacuum induction melting furnace after loading to 10E-4Pa, fill it with argon protection, heat and melt it for 1min, and then repeatedly melt it 3 times after cooling to ensure the uniformity of the alloy, and obtain a titanium-doped LiAl alloy ingot, which is recorded as 5Ti-AC.

[0052] In an argon atmosphere glove box, the oxide layer on the surface of the ingot was polished off, and the alloy ingot was broken into blocks for later use.

[0053] Compared with Example 1, this embodiment adds a thin strip preparation step: the titanium-doped LiAl alloy prepared above is placed in a high-purity boron nitride nozzle and placed in a transfer bin. The transfer bin is placed in a vacuum induction melting belt-spinning machine, and after the hatch is closed and sealed, it is evacuated to 10E-4Pa and filled with argon to normal pressure. After using the belt-spinning machine gloves to open the transfer bin for loading, adjust the slit-copper roller spacing to 1mm. After installing the belt-spinning machine glove sealing plate, heat and melt it and keep it for 30s to perform the belt-spinning operation. The belt-spinning parameters are: copper roller speed 2000RPM, spray casting pressure 0.5MPa. Use the transfer bin to collect the LiAl alloy thin strip after rapid quenching and transfer it to the glove box, recorded as 5Ti-MS.

[0054] Step 2: Take 2 g of the above-mentioned LiAl alloy ribbon, grind it into powder using a mortar in a glove box, place it in a frozen ball mill, and under liquid nitrogen cooling conditions, the temperature of the frozen ball mill is -196°C. Add 40 g of carbide steel grinding beads at a ball-to-material ratio of 20:1, seal the ball mill in the glove box, and transfer it out of the glove box.

[0055] The freezing ball milling jar was fixed on the vibrating freezing ball mill, and the freezing ball milling parameters were set as follows: pre-freezing for 10 minutes, 3 cycles, each ball milling for 5 minutes, rest for 2 minutes, and 900 rpm. After the ball milling was completed, the room temperature was restored, and the powder was transferred to a glove box after drying to obtain the frozen ball milled LiAl alloy powder.

[0056] Step 3: Take 1g of the frozen ball-milled LiAl alloy in a stainless steel ball mill, add 100g of hard-core alloy steel ball mill beads at a ball-to-material ratio of 100:1, seal the ball mill in a glove box, and transfer it out of the glove box. Evacuate the ball mill, flush it with high-purity hydrogen three times, and fill it with 2MPa hydrogen.

[0057] The ball mill jar filled with hydrogen is placed on a planetary ball mill for ball milling. The ball milling parameters are: alternating forward and reverse operation, a speed of 400 rpm, 10 minutes of rotation, 5 minutes of rest, and the ball mill jar is removed after 8 hours of ball milling. After scraping the material in the glove box, reseal, evacuate, inflate, and ball mill, and repeat this process 3 times. After a total of 24 hours of ball milling, the ball mill jar is removed and scraped to obtain a titanium-catalyzed LiAlH4-based composite hydrogen storage material sample, which is recorded as LiAl-5Ti. It includes a large amount of the target product LiAlH4, some by-products LiH / Al, and a small amount of titanium-containing catalyst.

[0058] Figure 5 The SEM comparison of the prepared cast titanium-doped LiAl alloy and the alloy after rapid quenching. It can be seen that the cast alloy is a uniform LiAl phase, and no grain boundaries are observed, indicating that the metal titanium is not well dispersed in the matrix of the LiAl alloy. Figure 6The XRD results of the alloy show that after melting and rapid quenching, the alloy phase TiAl3 precipitates at the grain boundaries, constructs an in-situ conductive and hydrogen-conducting network, and the grain boundaries are obvious, indicating that the element titanium is evenly distributed.

[0059] Figure 7 The temperature-dependent hydrogen release diagrams of titanium-doped LiAl alloy, magnesium-doped LiAl alloy and cast lithium aluminum alloy after hydrogenation ball milling under the same conditions as in this embodiment are compared. It can be seen that compared with pure cast lithium aluminum alloy, after adding magnesium, due to the catalytic effect of metal aluminum, MgH2 starts to release hydrogen at about 210°C. Due to the lack of d-orbital electrons, metal magnesium has no effect on the hydrogenation of LiAl alloy to LiAlH4, while the catalytic effect of transition metal titanium is obvious. The conductive hydrogen-conducting network after rapid quenching has a significant effect on improving the hydrogen absorption and desorption performance of LiAl alloy. Hydrogen release starts at 66°C and 0.6wt% hydrogen is released at 300°C, indicating that LiAlH4 is successfully prepared in this embodiment.

[0060] Embodiment 3, a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0061] Step 1: The steps for preparing Al-Ti master alloy are the same as those in Example 2.

[0062] To prepare 2wt% titanium-doped LiAl alloy, 1.5g of the Al-Ti master alloy prepared above, 1.49g of lithium flakes, and 4.51g of aluminum particles were weighed and placed in a high-purity boron nitride crucible. The vacuum induction melting furnace after loading was evacuated to 10E-4Pa, filled with argon for protection, heated and melted for 1min, and then repeatedly melted for 3 times after cooling to ensure the uniformity of the alloy.

[0063] Place the titanium-doped LiAl alloy prepared above into a high-purity boron nitride nozzle and into a transfer bin. Place the transfer bin into a vacuum induction melting belt-spinning machine, evacuate the bin to 10E-4Pa, fill it with argon to normal pressure, use the belt-spinning machine gloves to open the transfer bin for loading, and adjust the distance between the nozzle and the copper roller to 1mm. After installing the belt-spinning machine glove sealing plate, heat and melt it and keep it for 30s to perform the belt-spinning operation. The belt-spinning parameters are: copper roller speed 4000RPM, spray casting pressure 0.7MPa. Use the transfer bin to collect the LiAl alloy strip after rapid quenching and transfer it to the glove box for storage.

[0064] Step 2: Take 1 g of the above-mentioned LiAl alloy ribbon, grind it into powder using a mortar in a glove box, and place it in a frozen ball mill. Under liquid nitrogen cooling conditions, the temperature of the frozen ball mill is -196°C, and 100 g of hard-core alloy steel ball mill beads are added at a ball-to-material ratio of 100:1. The ball mill is sealed in the glove box and transferred out of the glove box.

[0065] The freezing ball milling jar was fixed on a vibrating freezing ball mill, and the freezing ball milling parameters were set as follows: pre-freezing for 15 minutes, 6 cycles, 5 minutes of ball milling each time, 2 minutes of rest, and 1200 rpm. After the ball milling was completed, the room temperature was restored, and the powder was transferred to a glove box after drying to obtain the frozen ball milled LiAl alloy powder.

[0066] Compared with Example 2, this example adds a wet ball milling step: weigh 2 g of the powder after the above-mentioned frozen ball milling treatment and place it in a ball mill, add 80 g of stainless steel grinding balls at a ball-to-material ratio of 40:1, add 4 ml of anhydrous tetrahydrofuran, seal it in a glove box, and transfer it out of the glove box.

[0067] The ball mill was filled with 0.5 MPa of high-purity argon as protective gas, and the ball mill was placed on a planetary ball mill for 10 hours. The ball milling parameters were: forward and reverse alternation, working for 20 minutes, stopping for 5 minutes, and a speed of 200 RPM.

[0068] The ball mill jar after the ball milling in the previous step was opened in the argon glove box, and the prepared paste sample was pre-dried at 60°C for 30 minutes using an intelligent temperature-controlled heating table, and then the grinding balls and powder were separated using a 200-mesh screen. The obtained powder was then placed in a tube furnace in the glove box for further drying. Drying parameters: dynamic vacuum, heating to 120°C, and heat preservation for 6 hours.

[0069] Step 3: Take 1g of the dried LiAl alloy in a stainless steel ball mill, add 150g of hard alloy steel grinding beads and hard core alloy steel ball milling beads at a ball-to-material ratio of 150:1, seal the ball mill in a glove box, and transfer it out of the glove box. Evacuate the ball mill, flush it with high-purity hydrogen for 3 times, and fill it with 5MPa hydrogen.

[0070] The sealed ball mill jar is placed on a planetary ball mill for ball milling. The ball milling parameters are: alternating forward and reverse operation, a speed of 400 rpm, 10 minutes of rotation, 5 minutes of rest, and the ball mill jar is removed after 10 hours of ball milling. After scraping the material in the glove box, reseal, vacuumize, inflate, and ball mill, and repeat this process 3 times. After a total of 30 hours of ball milling, the ball mill jar is removed and scraped to obtain a titanium-catalyzed LiAlH4-based composite hydrogen storage material sample, which is recorded as LiAl-2Ti. It includes a large amount of the target product LiAlH4, some by-products LiH / Al, and a small amount of titanium-containing catalyst.

[0071] Figure 8The hydrogen release curve of the sample after rapid quenching of 2wt% titanium-doped LiAl alloy, freezing ball milling and wet milling to reduce the particle grain size, and then hydrogenation reaction ball milling is shown. It can be proved that when the particles and grains are simultaneously refined to micro-nano, under high hydrogen pressure (5MPa), the forward conversion rate of LiAl alloy is improved. After ball milling for 30h, the sample begins to decompose and release hydrogen at about 72℃, and releases 1.3wt% hydrogen when the temperature is raised to 300℃, which proves that the LiAlH4 generated in this embodiment is more than that in Example 2.

[0072] Embodiment 4, a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0073] Step 1: The step of preparing Al-Ni master alloy is the same as the step of preparing Al-Ti master alloy in Example 2, except that the single substance Ti is replaced with a single substance Ni block.

[0074] To prepare 5 wt% nickel-doped LiAl alloy, 4 g of the Al-Ni master alloy prepared above, 1.55 g of lithium flakes, and 2.45 g of aluminum particles were weighed and placed in a high-purity boron nitride crucible. Other steps were the same as in Example 2.

[0075] Step 2 and step 3 are the same as in Example 2, with the same parameters.

[0076] The prepared nickel-catalyzed LiAlH4-based composite hydrogen storage material sample includes a large amount of target product LiAlH4, some by-products LiH / Al and a small amount of nickel-containing catalyst.

[0077] Fig. 9 This is the SEM image of the prepared nickel-doped LiAl after rapid quenching. Figure 6 From the XRD spectrum of the alloy, it can be judged that after the metal nickel is melted and rapidly quenched, the alloy phase NiAl3 is precipitated at the grain boundaries, and an electrically conductive and hydrogen conductive network is constructed in situ. The grain boundaries are obvious, indicating that the element Ni is evenly distributed.

[0078] By analyzing hydrogen release with temperature, the sample starts to release hydrogen at 85°C and releases 0.6wt% hydrogen at 300°C, indicating that LiAlH4 is successfully prepared. Compared with the LiAl alloy doped with titanium in Example 2, under the same preparation conditions, the catalytic effects of element Ti and element Ni on LiAl alloy are similar, and the hydrogen release temperature of the Ti-doped sample is about 20°C lower than that of the Ni-doped sample. The conductive hydrogen network constructed after rapid quenching has a significant effect on improving the hydrogen absorption and desorption performance of the LiAl alloy.

[0079] Embodiment 5, a solid phase preparation method of a LiAlH4-based composite hydrogen storage material, comprising the following steps:

[0080] Step 1 Preparation of Al-Mg master alloy is the same as the preparation of Al-Ti master alloy in Example 3, except that elemental Ti is replaced with elemental Mg particles, and 2 wt% of Mg is added to compensate for the loss caused by volatilization. The quartz crucible is replaced with a high-purity boron nitride crucible, and the other preparation parameters and conditions are the same as in Example 3.

[0081] To prepare 2 wt% Mg-doped LiAl alloy, 1.5 g of the Al-Mg master alloy prepared above, 1.49 g of lithium flakes, and 4.51 g of aluminum particles were weighed and placed in a high-purity boron nitride crucible. Other steps were the same as those in Example 3.

[0082] Step 2 and step 3 are the same as in the embodiment, and the parameters are the same.

[0083] A magnesium-doped LiAlH4-based composite hydrogen storage material sample was prepared, which was denoted as LiAl-2Mg, including a large amount of target product LiAlH4, some by-products LiH / Al and a small amount of MgH2.

[0084] The corresponding temperature-dependent hydrogen release diagram is Figure 8 As shown in the figure, after particle refinement and hydrogenation ball milling, the magnesium-doped LiAl alloy prepared using the parameters of this embodiment begins to release hydrogen at about 103°C and releases 0.98wt% hydrogen at 300°C, indicating that LiAlH4 was successfully prepared.

[0085] Comparative Example 1

[0086] As a comparison, after omitting the cryo-milling step, the effect of directly preparing LiAlH4 from the cast lithium aluminum alloy without grain refinement was compared.

[0087] The preparation process is compared with Example 1, except for step 2, and the other steps are the same as Example 1.

[0088] The prepared products are all by-products LiH / Al, without LiAlH4.

[0089] The temperature-dependent hydrogen release data is Figure 4 It is given that due to the lack of sufficient defects and highly active surfaces and interfaces in large-particle and large-grain lithium-aluminum alloys, hydrogen is difficult to dissociate and diffuse quickly, and hydrogenation inside the alloy is difficult, so LiAlH4 cannot be prepared from the cast alloy.

[0090] Comparative Example 2

[0091] As a comparison, it is proved that the in-situ introduction of transition metal elements has a promoting effect on the preparation of LiAlH4 from LiAl alloy. However, the introduction of elements without d orbitals, such as magnesium, has no obvious catalytic effect on the hydrogenation of the alloy and only serves to refine the grains.

[0092] Step 1 Preparation of Al-Mg master alloy is similar to the preparation of Al-Ti master alloy in Example 2, except that elemental Ti is replaced with elemental Mg particles, and 2 wt% of Mg is added to compensate for the loss caused by volatilization. The quartz crucible is replaced with a high-purity boron nitride crucible, and the other preparation parameters and conditions are the same as in Example 2.

[0093] The preparation steps for preparing 5wt% Mg-doped LiAl alloy are the same as those in Example 2, and the parameters are the same. 4g of the Al-Mg master alloy prepared above, 1.55g of lithium flakes, and 2.45g of aluminum particles are weighed and placed in a high-purity boron nitride crucible. The other steps are the same as those in Example 2.

[0094] The steps and parameters for preparing 5 wt % Mg-doped LiAl alloy amorphous ribbon are the same as those in Example 2.

[0095] Step 2 and Step 3 are the same as those in Example 2, with the same parameters.

[0096] Magnesium-doped LiAl alloy strip was prepared and recorded as 5Mg-MS.

[0097] A magnesium-doped composite hydrogen storage material sample was prepared, which was named LiAl-5Mg, and included byproducts LiH / Al and some MgH2, but no LiAlH4.

[0098] SEM images of the prepared magnesium-doped rapid-quenching alloy Fig. 9 The corresponding XRD Figure 6 The corresponding temperature-dependent hydrogen release diagram is given in Figure 5 It can be seen that after rapid quenching of the magnesium-doped LiAl alloy prepared using the parameters of this embodiment, there is no Mg-Al alloy phase in the XRD, and the grains are indeed refined in the SEM image. However, since the introduced magnesium lacks d-orbital electrons, the improvement effect on the hydrogen absorption kinetics of the LiAl alloy is not obvious. After hydrogenation ball milling with the parameters of this embodiment, no LiAlH4 is generated in the sample.

[0099] Based on the analysis of the above embodiments, transition metal element doping has a significant effect on improving the kinetics of hydrogen absorption and desorption of LiAl alloys. The hydrogen conduction network of the conduction band constructed in situ by rapid quenching, combined with the particle refinement to the nanoscale, can significantly reduce the dehydrogenation temperature of the prepared LiAlH4 composite hydrogen storage material, and can improve the alloy hydrogenation kinetics under the same conditions (hydrogenation ball milling hydrogen pressure, ball milling time, etc.), and improve the conversion rate of element LiAl to LiAlH4. Element modification is unnecessary for the conversion of lithium aluminum alloy to LiAlH4. Through grain particles, nano-scale strategy and hydrogenation ball milling technology, pure lithium aluminum alloy can be directly converted into LiAlH4 through solid-gas reaction without relying on any external catalyst.

[0100] Among the above embodiments, Embodiment 3 is the best embodiment.

[0101] It should be understood that the above description is for illustration and not for limitation. By reading the above description, all embodiments and all applications beyond the examples provided will be apparent to those skilled in the art.

Claims

1. A solid phase preparation method of LiAlH4-based composite hydrogen storage material, characterized in that: The following steps are involved: Step 1: smelting metal Li and Al in an inert atmosphere to obtain a LiAl alloy ingot, grinding off the oxide layer on the surface of the ingot in an inert gas glove box, and smashing the alloy ingot into blocks for standby use, wherein the atomic ratio of lithium to aluminum in the smelted metal is 0.8-1.2:1; Step 2: preparing LiAl alloy by cryogenic ball milling under liquid nitrogen cooling conditions; Step 3: In a hydrogen atmosphere, the LiAl alloy is ball-milled by a hydrogenation reaction to prepare a LiAlH4-based composite hydrogen storage material.

2. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 1, characterized in that: After the step 1, a thin strip is prepared: the prepared alloy block is placed in a high vacuum induction melting strip spinning machine, and a LiAl alloy amorphous / nanocrystalline thin strip is prepared by rapid quenching of the melt.

3. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 2, characterized in that: After the step 2, wet ball milling is performed, and the wet ball milling of LiAl is assisted by a solvent.

4. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 3, characterized in that: In the step 1, the metal also includes an Al-M master alloy, M is one of Ti\Ni\V\Zr\Zn\Y\Cu\Ga\Sn\Ge\Si, the atomic ratio of Li, Al and M is 0.8~1:0.8~1:0~0.2, and the obtained alloy is (LiAl)1-xMx, wherein x=0.01~0.

2.

5. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 4, characterized in that: In the step 1, an induction melting furnace is used for melting. The crucible used in the induction melting furnace is made of high-purity boron nitride or stainless steel. The inert gas is argon or helium. Melting is performed 3-5 times to ensure uniform alloy.

6. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 5, characterized in that: The melt rapid quenching uses a high-purity boron nitride nozzle or a stainless steel nozzle, the melt rapid quenching cooling copper roller speed is 1000-6000 rpm, the spraying gas pressure is 0.1-1 MPa, and the gap between the slit and the copper roller is 1-3 mm.

7. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 6, characterized in that: In the step 2, the temperature of the frozen ball mill is -196 ° C, the frozen ball mill adopts a vibrating ball mill, the ball-to-material ratio is 5-500:1, the frozen ball mill speed is 100-1800 rpm, the frozen ball mill time is 10-1800 minutes, and the grinding beads used are carbide steel grinding beads; In the step 3, the hydrogenation reaction is ball-milled using a planetary ball mill, with a ball-to-material ratio of 40-200:1, a ball milling speed of 100-600 rpm, and a ball milling time of 4-40 hours.

8. The solid phase preparation method of a LiAlH4-based composite hydrogen storage material according to claim 7, characterized in that: In step 3, the pressure of H2 gas is 1-150 bar.

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