A2B7 type hydrogen storage alloy and preparation method thereof

Abstract

The invention discloses an A2B7 type hydrogen storage alloy and a preparation method thereof, and relates to the technical field of hydrogen storage materials.The preparation method comprises the following steps that S1, raw materials are prepared, specifically, high-purity raw materials are weighed according to the alloy component proportion; the nickel powder, the zirconium powder and the titanium powder which are weighed in the step S1 are placed in a vacuum drying box to be dried, the pretreated raw materials are placed in a water-cooled copper crucible of an electric arc melting furnace, vacuumizing is carried out, and protective atmosphere is introduced, and the smelted alloy cast ingot is cooled to the room temperature and placed in a vacuum heat treatment furnace to be subjected to follow-up treatment. Through the synergistic effect of the combination of multiple rare earth elements and the structural regulation element, the lattice stress distribution of the alloy is optimized, the lattice distortion rate is reduced, the expansion and shrinkage phenomena of lattices in the hydrogen absorption and desorption cycle process are effectively inhibited, the pulverization problem of the alloy in long-term cycle use is reduced, and the cycle service life of the alloy is prolonged.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage materials technology, and in particular to an A2B7 type hydrogen storage alloy and its preparation method. Background Technology

[0002] Against the backdrop of the rapid development of the hydrogen energy industry, hydrogen storage materials, as the core carriers for hydrogen storage and transportation, directly restrict the large-scale application of hydrogen energy. A2B7 type hydrogen storage alloys, due to their high theoretical hydrogen storage capacity and suitable storage temperature range, have become an important research direction for medium- and low-temperature hydrogen storage applications.

[0003] To maximize hydrogen storage capacity, traditional A2B7 type hydrogen storage alloys often incorporate magnesium. However, magnesium is chemically reactive and easily volatilizes during high-temperature smelting and preparation, leading to significant deviations between the actual alloy composition and the designed ratio, severely impacting the stability of hydrogen storage performance. Furthermore, magnesium's low ignition point makes it prone to combustion and explosion accidents in high-temperature preparation environments, posing a significant safety hazard to large-scale industrial production and hindering its industrialization.

[0004] Therefore, it is necessary to propose an A2B7 type hydrogen storage alloy and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide an A2B7 type hydrogen storage alloy and its preparation method, addressing the problem that traditional A2B7 type hydrogen storage alloys often incorporate magnesium to achieve higher hydrogen storage capacity. However, magnesium is chemically reactive and easily volatilizes during high-temperature smelting, leading to a significant deviation between the actual alloy composition and the designed ratio, severely affecting the stability of hydrogen storage performance. Furthermore, magnesium has a low ignition point, making it prone to combustion and explosion accidents in high-temperature preparation environments, posing a significant safety hazard to large-scale industrial production and limiting its industrialization.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an A2B7 type hydrogen storage alloy, wherein the sum of the mole fractions of all constituent elements in the A2B7 type hydrogen storage alloy is 1, and the alloy does not contain magnesium. The preparation method includes the following steps:

[0007] S1. Raw material preparation: Weigh high-purity raw materials according to the alloy composition ratio;

[0008] The alloy composition includes: the first type is a combination of at least two rare earth elements selected from lanthanum, cerium, and yttrium, with a total mole fraction of 0.4-0.6%;

[0009] The second category is nickel, with a mole fraction of 0.3-0.4%; the third category is a combination of at least one of zirconium and titanium, with a total mole fraction of 0.05-0.15%.

[0010] The fourth category consists of at least one auxiliary element selected from gadolinium, cobalt, and aluminum, with a total mole fraction of 0-0.05.

[0011] S2. Raw material pretreatment: Place the nickel powder, zirconium powder and titanium powder weighed in step S1 into a vacuum drying oven and dry them at 80-120℃ for 2-4 hours to remove surface adsorbed water.

[0012] The rare earth metal raw materials weighed in step S1 are cut into small pieces with a particle size of no more than 5 mm, and the surface oxide layer is removed.

[0013] S3. Smelting: Place the pretreated raw materials into the water-cooled copper crucible of the electric arc melting furnace, evacuate the furnace to a vacuum degree of not less than 5×10-3 Pa, and then introduce inert protective gas until the furnace pressure is 0.08-0.12 MPa.

[0014] S4. Subsequent processing: Cool the smelted alloy ingot to room temperature, place it in a vacuum heat treatment furnace, evacuate the furnace to a vacuum level of not less than 1×10-3 Pa, hold it at 800-900℃ for 8-12 hours, and then cool it to room temperature with the furnace to obtain the A2B7 type hydrogen storage alloy.

[0015] Preferably, the raw materials are as follows: the purity of the metal raw materials corresponding to the first type of rare earth elements is not less than 99.9%; the raw materials corresponding to the second type of nickel elements are spherical nickel powder with a purity of not less than 99.5% and an average particle size of 5-10 micrometers; the purity of the zirconium powder and titanium powder corresponding to the third type of elements is not less than 99%; and the purity of the raw materials corresponding to the fourth type of auxiliary elements is not less than 99%.

[0016] Preferably, in step S3, non-consumable electrode arc melting is used, the melting current is 200-300 amperes, each batch is melted 3-5 times, and each melting time is 3-5 minutes.

[0017] Preferably, in step S1, the molar percentage of lanthanum in the first type of rare earth element combination is not less than 40% of the total molar percentage of the rare earth elements in that type, and the sum of the molar percentages of cerium and yttrium is not less than 30% of the total molar percentage of the rare earth elements in that type.

[0018] Preferably, the inert protective gas in step S3 is argon, and the purity of the argon is not less than 99.999%.

[0019] Preferably, the method for removing the oxide layer on the surface of the rare earth metal raw material in step S2 is as follows: soaking in dilute hydrochloric acid with a concentration of 10% to 15% for 10 to 15 minutes, then rinsing with deionized water 3 to 5 times, and then drying in a forced-air drying oven at 60 to 80°C for 1 to 2 hours.

[0020] Preferably, the vacuum degree of the vacuum drying oven in step S2 is controlled at 1×10⁻²-5×10⁻² Pa.

[0021] Preferably, in step S3, the temperature of the cooling water in the water-cooled copper crucible of the electric arc melting furnace is controlled at 20-30°C, and the cooling water flow rate is 1-2 liters / minute.

[0022] Preferably, in step S4, the alloy ingot is cooled to room temperature by natural cooling, with the cooling environment temperature controlled at 20-25°C and the relative humidity not exceeding 60%.

[0023] The present invention also discloses an A2B7 type hydrogen storage alloy, which is applied to the preparation method of the above-mentioned A2B7 type hydrogen storage alloy.

[0024] The technical effects and advantages of this invention are as follows:

[0025] 1. In this invention, the alloy does not contain magnesium, which solves the volatilization problem that is prone to occur in the preparation process of traditional magnesium-containing hydrogen storage alloys from the root of composition design. At the same time, it eliminates the safety hazards of magnesium's flammability and explosion, reduces the risks in the production process, and provides a safe and stable composition basis for large-scale industrial production. The purity of raw materials is strictly controlled in the preparation process, and the pretreatment stage can completely remove the oxide layer and adsorbed water on the surface of the raw materials. The melting and subsequent processing parameters are precise and controllable, reducing the impact of impurities and process fluctuations on product quality during the preparation process, improving the repeatability and stability of the preparation process, increasing the product qualification rate, and adapting to the needs of large-scale industrial production.

[0026] 2. Through the synergistic effect of multiple rare earth elements and structural control elements, the stress distribution of the alloy lattice is optimized, the lattice distortion rate is reduced, the expansion and contraction of the lattice during the hydrogen absorption and desorption cycle is effectively suppressed, the pulverization problem of the alloy during long-term cyclic use is reduced, the cycle life of the alloy is extended, and the performance stability of the alloy during repeated use is improved. The vacuum heat treatment process can fully rearrange the alloy lattice, eliminate the lattice defects generated during the melting process, further enhance the stability of the lattice structure, and provide structural support for the alloy to maintain good hydrogen storage performance in the long term.

[0027] 3. In the alloy composition design, the combination of core elements and auxiliary elements is reasonable. The core elements ensure that the alloy has basic and stable hydrogen storage activity, while the auxiliary elements can be flexibly selected and added according to actual needs to optimize the hydrogen storage-related performance in a targeted manner. This makes the alloy perform well in terms of hydrogen storage capacity and hydrogen storage kinetics, meeting the performance requirements of hydrogen storage materials in different scenarios. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation method of the A2B7 type hydrogen storage alloy of the present invention. Detailed Implementation

[0029] This invention provides, for example Figure 1The method for preparing an A2B7 type hydrogen storage alloy is shown. The sum of the mole fractions of all constituent elements in the A2B7 type hydrogen storage alloy is 1, and the alloy does not contain magnesium. The preparation method includes the following steps:

[0030] S1. Raw material preparation: Weigh high-purity raw materials according to the alloy composition ratio;

[0031] The alloy composition includes: Category 1, a combination of at least two rare earth elements selected from lanthanum, cerium, and yttrium, with a total molar fraction of 0.4-0.6%. Specifically, Category 1 (A-site elements): a combination of at least two rare earth elements selected from lanthanum (La), cerium (Ce), and yttrium (Y), with a total molar fraction of 0.4-0.6%. Through the synergistic effect of multiple rare earth elements, the alloy lattice stress distribution is optimized. The molar fraction of lanthanum is not less than 40% of the total molar amount of this type of rare earth element. Lanthanum has a larger atomic radius, which can expand the lattice interstices and increase the hydrogen atom storage space. The sum of the molar fractions of cerium and yttrium is not less than 30% of the total molar amount of this type of rare earth element. Cerium has variable valence states (+3, +4), which can enhance the interaction between the alloy and hydrogen atoms and improve hydrogen storage stability. Yttrium has a smaller atomic radius, which can fill lattice defects and reduce lattice distortion rate.

[0032] The second category is nickel, with a molar fraction of 0.3-0.4%. Specifically, the second category (B-site main element) is nickel (Ni), with a molar fraction of 0.3-0.4%. As the core B-site element of the A2B7 type hydrogen storage alloy, nickel has good hydrogen storage activity and can form stable hydrides with hydrogen atoms. At the same time, nickel has excellent electrical conductivity, which can improve the electrochemical hydrogen storage performance of the alloy and ensure stable discharge capacity.

[0033] The third category (structure control elements) consists of at least one element selected from zirconium (Zr) and titanium (Ti), with a total molar fraction of 0.05-0.15. Both zirconium and titanium are high-melting-point metals with atomic radii similar to those of rare earth elements, allowing them to be incorporated into the A2B7 type crystal structure, enhancing lattice strength and suppressing lattice expansion and contraction during hydrogen absorption and desorption cycles. When zirconium and titanium are added simultaneously, their synergistic effect can further optimize lattice parameters, reduce lattice distortion rate, and improve cycle stability.

[0034] Category 4 (Auxiliary Optimization Elements): This category includes at least one element selected from gadolinium (Gd), cobalt (Co), and aluminum (Al), with a total molar fraction of 0-0.05%. Gadadolinium can improve the alloy's resistance to pulverization and extend cycle life; cobalt can enhance the alloy's conductivity and hydrogen storage activity, increasing discharge capacity; aluminum can reduce the alloy's hydrogen absorption enthalpy and optimize hydrogen storage kinetics. The appropriate addition of auxiliary elements can be flexibly selected according to actual performance requirements. When the addition amount is 0, the alloy still possesses basic hydrogen storage performance, meeting the needs of general application scenarios.

[0035] The purity of metal raw materials corresponding to the first type of rare earth elements (such as lanthanum blocks, cerium blocks, and yttrium blocks) shall not be less than 99.9% to avoid the introduction of impurities (such as oxygen and carbon) that could lead to lattice defects.

[0036] The raw material corresponding to the second type of nickel element is spherical nickel powder with a purity of not less than 99.5% and an average particle size of 5-10 μm. Spherical nickel powder has a large specific surface area, which can enhance the reactivity of the raw material during the melting process and ensure thorough mixing with other raw materials. Controlling the particle size to 5-10 μm can avoid powder agglomeration and ensure compositional uniformity.

[0037] The zirconium powder and titanium powder corresponding to the third element have a purity of not less than 99%. The zirconium powder and titanium powder are selected as nano-sized powders (particle size 1-5μm), which can improve their dispersibility during the melting process and ensure uniform integration into the alloy lattice.

[0038] The purity of raw materials corresponding to the fourth category of auxiliary elements (such as gadolinium powder, cobalt powder, and aluminum powder) shall not be less than 99%. The auxiliary element raw materials shall be selected in fine powder form to facilitate uniform mixing with other raw materials and precise control of the addition ratio. The raw material weighing process shall be carried out using a high-precision electronic balance (accuracy 0.0001g) to ensure that the molar ratio error of each element does not exceed ±0.005, so as to avoid the alloy performance being affected by the deviation of the composition ratio.

[0039] S2. Raw Material Pretreatment: Place the nickel powder, zirconium powder, titanium powder, and auxiliary element powders (if any) weighed in step S1 into a vacuum drying oven and dry at 80-120℃ for 2-4 hours. The vacuum degree of the vacuum drying oven should be controlled at 1×10⁻⁶. -2 -5×10 - 2 Pa, a low vacuum environment can accelerate the removal of adsorbed water from the powder surface, while preventing air from entering and causing powder oxidation; the drying temperature and time can be flexibly adjusted according to the powder moisture content. When the moisture content is high, the temperature can be appropriately increased (e.g., 120℃) or the time can be extended (e.g., 4 hours) to ensure that the powder moisture content is less than 0.1% after drying, and to avoid the generation of water vapor during the melting process, which can cause alloy porosity.

[0040] The weighed rare earth metal raw materials are cut into small pieces with a particle size of no more than 5 mm. The cutting process is carried out under the protection of an inert gas (such as argon) to prevent oxidation of the metal surface. Then, the surface oxide layer is removed by soaking in 10% to 15% dilute hydrochloric acid (analytical grade) for 10 to 15 minutes. The dilute hydrochloric acid can react with the oxide layer (such as La2O3, CeO2) to generate soluble salts, thereby removing the oxide layer. After soaking, rinse with deionized water (conductivity ≤10μS / cm) 3 to 5 times to thoroughly remove residual hydrochloric acid and salts. Finally, dry in a forced-air drying oven at 60-80℃ for 1 to 2 hours. After drying, the surface of the rare earth metal is clean and free of oxide layer, ensuring that it reacts fully with other raw materials during the smelting process.

[0041] S3. Melting, the specific steps are as follows:

[0042] First, a vacuum is drawn into the electric arc melting furnace to ensure that the vacuum level inside the furnace is not less than 5×10⁻⁶. -3 First, completely remove air (especially oxygen and nitrogen) from the furnace to prevent high-temperature oxidation of the raw materials. Then, introduce an inert protective gas, argon, with a purity of not less than 99.999%. As an inert gas, argon does not react with the raw materials and can effectively protect the raw materials and alloys. The argon gas flow rate is controlled to maintain the furnace pressure at 0.08-0.12 MPa. This pressure range can balance the furnace environment, prevent external air from seeping in, and avoid excessive pressure that could lead to furnace safety risks.

[0043] The process employs a non-consumable electrode arc melting method, using tungsten electrodes (99.95% purity). Tungsten electrodes have a high melting point and are resistant to high-temperature corrosion, ensuring long-term stable use. The melting current is controlled at 200-300 amperes, with the current adjusted according to the total amount of raw materials. A higher current (e.g., 300A) is used when the total amount of raw materials is large to ensure that the raw materials are fully melted. Each batch is melted 3-5 times, with each melting time being 3-5 minutes. Multiple meltings ensure thorough mixing and reaction of the raw materials, avoiding component segregation. After each melting, the ingot is flipped to ensure that the raw materials in the upper and lower layers are melted evenly, ultimately resulting in an alloy ingot with uniform composition.

[0044] The cooling water temperature of the water-cooled copper crucible in the electric arc melting furnace is controlled at 20-30℃, and the cooling water flow rate is 1-2 liters / minute. The water-cooled copper crucible has good thermal conductivity, which can quickly remove the heat generated by melting, control the cooling rate of the ingot, and avoid internal stress caused by excessive cooling. Stable control of cooling water temperature and flow rate can ensure uniform crucible temperature and prevent the crucible from deforming due to local overheating, which would affect the quality of the alloy ingot.

[0045] S4. Subsequent processing: The alloy ingots after smelting need to undergo subsequent processing to further optimize the crystal structure and improve hydrogen storage performance. Among the raw materials, the purity of the metal raw materials corresponding to the first category of rare earth elements is not less than 99.9%, the raw materials corresponding to the second category of nickel elements are spherical nickel powder with a purity of not less than 99.5% and an average particle size of 5-10 micrometers, the purity of zirconium powder and titanium powder corresponding to the third category of elements is not less than 99%, and the purity of the raw materials corresponding to the fourth category of auxiliary elements is not less than 99%.

[0046] After melting, the alloy ingot is removed from the water-cooled copper crucible and cooled to room temperature naturally. The ambient temperature is controlled at 20-25℃ and the relative humidity is not higher than 60%. Natural cooling avoids lattice defects caused by rapid cooling, and the controlled ambient temperature and humidity prevent oxidation of the ingot surface, ensuring the ingot surface is clean. During the cooling process, collisions with the ingot are avoided to prevent mechanical damage that could lead to structural failure.

[0047] The alloy ingot, cooled to room temperature, is placed in a vacuum heat treatment furnace. First, a vacuum is evacuated from the furnace to a level not less than 1×10⁻⁶. -3 Pa, to remove air from the furnace;

[0048] The furnace temperature is then raised to 800-900℃ and held for 8-12 hours. The holding process allows the alloy lattice to rearrange fully, eliminating lattice defects generated during melting and improving lattice stability. After the holding period, the furnace is cooled to room temperature. Cooling with the furnace avoids lattice distortion caused by a sudden drop in temperature, ensuring lattice structure stability and ultimately obtaining the A2B7 type hydrogen storage alloy.

[0049] The present invention also discloses an A2B7 type hydrogen storage alloy, which is prepared by the above-described A2B7 type hydrogen storage alloy preparation method.

[0050] The A2B7 hydrogen storage alloy preparation method of the present invention does not contain magnesium, which completely solves the problem of magnesium volatilization and flammability during the preparation of traditional magnesium-containing hydrogen storage alloys, reduces production safety hazards, avoids composition deviation caused by magnesium volatilization, improves alloy performance stability, and is suitable for large-scale industrial production.

[0051] Through the synergistic effect of multiple rare earth element combinations (La, Ce, Y) and structure-regulating elements (Zr, Ti), the lattice stress distribution is optimized and the lattice distortion rate is reduced. During hydrogen absorption and desorption cycles, lattice expansion and contraction can be effectively suppressed, reducing alloy pulverization. After 500 charge-discharge cycles, the capacity retention rate is still no less than 85%, which is far higher than the existing technology (capacity retention rate is less than 70% after 300-400 cycles).

[0052] The alloy composition is rationally designed, with nickel ensuring high hydrogen storage activity and discharge capacity. The appropriate addition of auxiliary elements (Gd, Co, Al) further optimizes the hydrogen storage performance. Under the conditions of 25℃ and 0.1-3MPa, the discharge capacity is not less than 380mAh / g, which meets the high capacity requirements of hydrogen fuel cells, portable energy storage devices and other scenarios.

[0053] The purity of raw materials is strictly controlled, the oxide layer and adsorbed water are thoroughly removed in the pretreatment stage, and the melting and heat treatment process parameters are precisely adjustable to ensure that the alloy composition is uniform, the crystal structure is stable, the preparation process has good repeatability, and the product qualification rate can reach more than 95%, which is suitable for large-scale industrial production.

[0054] The alloy exhibits excellent performance in safety, cycle stability, and hydrogen storage capacity, and can be widely used in hydrogen fuel cell vehicle on-board hydrogen storage tanks, portable home hydrogen energy storage devices, and hydrogen power plant energy storage systems. At the same time, the types and proportions of auxiliary elements can be flexibly adjusted according to different application requirements to adapt to diverse usage needs.

[0055] Example 1: Preparation of A2B7 type hydrogen storage alloy containing lanthanum-cerium-zirconium-gadolinium

[0056] Alloy composition design: The alloy composition is designed according to the following mole fraction ratios: the first type of element (La-Ce) accounts for 0.5% (La accounts for 0.25%, Ce accounts for 0.25%), the second type of element (Ni) accounts for 0.35%, the third type of element (Zr) accounts for 0.1%, the fourth type of element (Gd) accounts for 0.05%, and the sum of the mole fractions of each element is 1. Magnesium is not included.

[0057] S1. Raw material preparation:

[0058] The following raw materials were weighed using a high-precision electronic balance:

[0059] Lanthanum blocks with a purity of 99.95%: 0.25 mol (approximately 32.6 g);

[0060] Cerium blocks with a purity of 99.95%: 0.25 mol (approximately 33.5 g);

[0061] Spherical nickel powder with a purity of 99.6% (average particle size 8μm): 0.35mol (approximately 22.1g);

[0062] Zirconium powder with a purity of 99.2% (average particle size 3μm): 0.1mol (approximately 9.1g);

[0063] Gadolinium powder with a purity of 99.1% (average particle size 5μm): 0.05mol (approximately 6.5g).

[0064] S2. Raw material pretreatment: After the rare earth metals are processed, the surface of the processed lanthanum and cerium blocks is inspected to ensure that there are no oxidation spots or residual acid. Then, the surface is quickly wiped with anhydrous ethanol to further remove any possible residual moisture and impurities. After wiping, the blocks are immediately transferred to a dry inert gas protective container for later use to prevent secondary oxidation.

[0065] S3. Melting: Mix the pretreated nickel powder, zirconium powder, and gadolinium powder evenly and pour the mixture into the bottom of the water-cooled copper crucible of the electric arc melting furnace. Then, evenly spread the treated lanthanum and cerium blocks on top of the mixed powder to ensure full contact between the rare earth metals and the powder raw materials. After closing the furnace door, start the vacuum pump to evacuate the furnace. The evacuation process is carried out in two stages: the first stage is to evacuate at a rate of 5 Pa / s to 1 × 10⁻⁶ Pa / s. -1 The pressure was increased to 6 × 10 Pa for 10 minutes to remove most of the air from the furnace; in the second stage, the pressure was increased to 6 × 10 Pa at a rate of 0.5 Pa / s. -4 Pa (lower than the required 5×10) -3 Pa), to ensure that the air inside the furnace is completely exhausted.

[0066] Argon gas with a purity of 99.9995% (higher than the required 99.999%) is introduced at a rate of 0.5 L / min. When the furnace pressure reaches 0.1 MPa, the gas supply is stopped, the inlet valve is closed, and the furnace is allowed to stand for 5 minutes to stabilize the pressure. The electric arc melting power supply is then started, and the tungsten electrode is slowly lowered to a distance of 5 mm from the surface of the raw material. The arc is then turned on, and the initial current is set to 200 A. After the surface of the raw material begins to melt, the current is gradually increased to 250 A and maintained at this current for 4 minutes. After the first melting is completed, the arc is turned off. When the surface temperature of the ingot drops to a dark red color (approximately 800 °C), the ingot is rotated 180° using the furnace body turning mechanism. The arc is then turned on again, and the ingot is melted at a current of 250 A for 4 minutes. This rotating melting operation is repeated a total of 4 times to ensure that the raw material is fully melted and mixed.

[0067] During the smelting process, the cooling water temperature and flow rate of the water-cooled copper crucible are monitored in real time. The cooling water temperature is stabilized at 25℃ and the water flow rate is controlled at 1.5L / min through the water temperature control system. The water temperature and flow rate data are recorded every minute. If the water temperature exceeds 30℃ or the flow rate is lower than 1L / min, the smelting is immediately stopped, the cooling system is checked, and the operation is resumed only after the fault is eliminated.

[0068] S4. Subsequent processing: After melting is completed, turn off the electric arc melting power supply, maintain the argon atmosphere in the furnace, and allow the alloy ingot to cool naturally in the furnace. Record the furnace temperature every 30 minutes during the cooling process. When the furnace temperature drops to 50°C, open the furnace door and take out the alloy ingot. At this time, the surface of the ingot is silvery and there is no oxide layer. Transfer the ingot to a clean cooling room with a temperature of 23°C and a relative humidity of 50% and continue to cool naturally to room temperature (about 25°C) for about 2 hours. Avoid collisions between the ingot and other objects during the cooling process.

[0069] The alloy ingot, cooled to room temperature, is placed in a graphite crucible within a vacuum heat treatment furnace. The furnace door is closed, and the vacuum pump is started to evacuate the furnace to a vacuum level of 8 × 10⁻⁶. -4 Pa (lower than the required 1×10) -3 (Pa); Start the heating system and raise the furnace temperature to 850℃ at a heating rate of 8℃ / min. During the heating process, record the temperature and vacuum level every 10 minutes to ensure a stable heating rate and a qualified vacuum level. After reaching 850℃, hold the temperature for 10 hours, recording data every hour during the holding period. After the holding period, turn off the heating system and allow the alloy to cool with the furnace at a cooling rate of 5℃ / min. When the furnace temperature drops to 100℃, introduce 99.999% pure argon gas until the furnace pressure is balanced with atmospheric pressure. Open the furnace door and remove the alloy ingot, which is the final A2B7 type hydrogen storage alloy.

[0070] Performance Testing and Results: The following performance tests were performed on the prepared A2B7 type hydrogen storage alloy:

[0071] Composition analysis: The alloy composition was analyzed by X-ray fluorescence spectrometry (XRF). The results showed that the mole fractions of La, Ce, Ni, Zr and Gd were 0.248, 0.251, 0.352, 0.099 and 0.050, respectively, which were less than ±0.003 from the design composition, indicating good compositional uniformity.

[0072] Hydrogen storage capacity test: The hydrogen absorption capacity of the alloy was tested using a Sieverts hydrogen storage performance testing system at 25℃ and 3MPa. The results showed that the hydrogen absorption capacity of the alloy was 1.92wt% and the discharge capacity was 385mAh / g, which meets the requirement of not less than 380mAh / g.

[0073] Cyclic stability test: The alloy was subjected to charge-discharge cycle test at 25℃ and 0.1-3MPa. Each cycle included 0.5 hours of hydrogen charging (3MPa), 0.5 hours of resting, and 0.5 hours of hydrogen discharging (0.1MPa). After 500 cycles, the discharge capacity of the alloy was 330mAh / g, and the capacity retention rate was 85.7%, which is higher than the requirement of not less than 85%.

[0074] Anti-pulverization performance test: The alloy sample that has undergone 500 cycles was subjected to particle size analysis. The particle size distribution was tested using a laser particle size analyzer. The results showed that the average particle size of the alloy was 50 μm, the maximum particle size did not exceed 100 μm, and no obvious fine powder was generated, indicating excellent anti-pulverization performance.

[0075] Example 2:

[0076] Preparation of A2B7 type hydrogen storage alloy containing lanthanum-yttrium-titanium-cobalt

[0077] Alloy composition design: The alloy composition is designed according to the following mole fraction ratios: the proportion of first-category elements (La-Y) is 0.45 (La accounts for 0.25, Y accounts for 0.2), the proportion of second-category elements (Ni) is 0.38, the proportion of third-category elements (Ti) is 0.12, the proportion of fourth-category elements (Co) is 0.05, and the sum of the mole fractions of each element is 1. Magnesium is not included.

[0078] Preparation process: S1, Raw material preparation:

[0079] The following raw materials were weighed using a high-precision electronic balance:

[0080] Lanthanum blocks with a purity of 99.96%: 0.25 mol (approximately 32.6 g);

[0081] Yttrium blocks with a purity of 99.95%: 0.2 mol (approximately 22.5 g);

[0082] Spherical nickel powder with a purity of 99.5% (average particle size 6μm): 0.38mol (approximately 24.0g);

[0083] Titanium powder with a purity of 99.1% (average particle size 4μm): 0.12mol (approximately 5.8g);

[0084] Cobalt powder with a purity of 99.2% (average particle size 3μm): 0.05mol (approximately 2.9g).

[0085] S2, Raw material pretreatment

[0086] Drying of powder raw materials: Place nickel powder, titanium powder, and cobalt powder into a vacuum drying oven and set the vacuum degree to 2×10. -2 The powder was dried at 110°C for 2.5 hours, and the moisture content of the dried powder was 0.08%.

[0087] Rare earth metal treatment: Cut lanthanum and yttrium blocks into 2-4mm pieces, soak them in 14% dilute hydrochloric acid for 11 minutes, rinse them 5 times with deionized water, and dry them in a 75℃ forced-air drying oven for 1.5 hours. After treatment, the metal surface is clean and free of oxidation.

[0088] S3, Melting: Vacuuming to 7×10 -4 Pa, 99.999% argon gas is introduced to 0.09MPa; non-consumable electrode arc melting is used, melting current is 260A, each batch is melted 3 times, each melting time is 5 minutes, water-cooled copper crucible cooling water temperature is 22℃, water flow rate is 1.2L / min.

[0089] S4. Subsequent processing: After the alloy ingot is cooled to 60°C in the furnace, it is removed and transferred to a cooling chamber at 24°C and 55% relative humidity to cool to room temperature; the vacuum heat treatment furnace is then evacuated to 9×10⁻⁶ ℃. -4 Pa, heated to 880℃ at 7℃ / min, held for 9 hours, and then cooled to 100℃ in the furnace before being removed.

[0090] Performance test results: Composition analysis: The molar fractions of La, Y, Ni, Ti and Co are 0.249, 0.198, 0.382, 0.119 and 0.052, respectively, with small compositional deviations.

[0091] Hydrogen storage capacity test: at 25℃ and 3MPa, the hydrogen absorption capacity is 1.88wt% and the discharge capacity is 392mAh / g.

[0092] Cyclic stability test: After 500 cycles, the discharge capacity was 334 mAh / g, and the capacity retention was 85.2%. Example 3:

[0093] Preparation of A2B7 type hydrogen storage alloy containing lanthanum-cerium-yttrium-zirconium-titanium-aluminum

[0094] Alloy composition design:

[0095] The alloy composition is designed according to the following mole fraction ratios: the first group of elements (La-Ce-Y) accounts for 0.55% (La accounts for 0.25%, Ce accounts for 0.2%, Y accounts for 0.1%), the second group of elements (Ni) accounts for 0.32%, the third group of elements (Zr-Ti) accounts for 0.1% (Zr accounts for 0.06%, Ti accounts for 0.04%), and the fourth group of elements (Al) accounts for 0.03%. The sum of the mole fractions of all elements is 1, and magnesium is not included.

[0096] Preparation process: S1, Raw material preparation:

[0097] Weigh out 0.25 mol (32.6 g) of lanthanum blocks with a purity of 99.95%, 0.2 mol (26.8 g) of cerium blocks with a purity of 99.95%, 0.1 mol (11.2 g) of yttrium blocks with a purity of 99.95%, 0.32 mol (20.2 g) of spherical nickel powder with a purity of 99.6% (average particle size of 9 μm), 0.06 mol (5.5 g) of zirconium powder with a purity of 99.2% (average particle size of 3 μm), 0.04 mol (1.9 g) of titanium powder with a purity of 99.1% (average particle size of 4 μm), and 0.03 mol (0.8 g) of aluminum powder with a purity of 99.3% (average particle size of 2 μm).

[0098] S2. Raw material pretreatment: Powder raw material drying: Vacuum drying oven with a vacuum degree of 4×10 -2 Pa, temperature 90℃, dry for 3.5 hours.

[0099] Rare earth metal treatment: Soak in 10% dilute hydrochloric acid for 15 minutes, rinse with deionized water 4 times, and dry in a 65℃ forced-air drying oven for 2 hours.

[0100] S3, Melting: Vacuuming to 5×10 -4 Pa, 99.9995% argon gas is introduced to 0.11 MPa; melting current 280 A, melting 5 times, 4 minutes each time, cooling water temperature 28℃, water flow rate 1.8 L / min.

[0101] S4. Subsequent processing: The ingot is cooled to room temperature at 22℃ and 58% relative humidity; the vacuum heat treatment furnace is evacuated to 6×10⁻⁶. -4 Pa, heat to 820℃ at 9℃ / min, hold for 11 hours, and then cool with the furnace.

[0102] Performance test results: Composition analysis: The mole fraction of each element deviated from the design value by less than ±0.004. Hydrogen storage capacity test: At 25℃ and 3MPa, the discharge capacity was 388mAh / g. Cycle stability test: After 500 cycles, the capacity retention rate was 86.1%.

Claims

1. A method for preparing an A2B7 type hydrogen storage alloy, characterized in that, The sum of the mole fractions of all constituent elements in the A2B7 type hydrogen storage alloy is 1, and the alloy does not contain magnesium. The preparation method includes the following steps: S1. Raw material preparation: Weigh high-purity raw materials according to the alloy composition ratio; The alloy composition includes: the first type is a combination of at least two rare earth elements selected from lanthanum, cerium, and yttrium, with a total mole fraction of 0.4-0.6%; The second category is nickel, with a mole fraction of 0.3-0.4%; the third category is a combination of at least one of zirconium and titanium, with a total mole fraction of 0.05-0.15%. The fourth category consists of at least one auxiliary element selected from gadolinium, cobalt, and aluminum, with a total mole fraction of 0-0.

05. S2. Raw material pretreatment: Place the nickel powder, zirconium powder and titanium powder weighed in step S1 into a vacuum drying oven and dry them at 80-120℃ for 2-4 hours to remove surface adsorbed water. The rare earth metal raw materials weighed in step S1 are cut into small pieces with a particle size of no more than 5 mm, and the surface oxide layer is removed. S3. Melting: Place the pretreated raw materials into the water-cooled copper crucible of the electric arc melting furnace, and evacuate the furnace to a vacuum level of not less than 5×10⁻⁶. -3 Then, inert protective gas is introduced until the pressure inside the furnace is 0.08-0.12 MPa; S4. Subsequent processing: Cool the smelted alloy ingot to room temperature, place it in a vacuum heat treatment furnace, and evacuate the furnace to a vacuum level of not less than 1×10⁻⁶. -3 Pa is held at 800-900℃ for 8-12 hours, and then cooled to room temperature in the furnace to obtain A2B7 type hydrogen storage alloy.

2. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: The raw materials include metal raw materials corresponding to the first category of rare earth elements with a purity of not less than 99.9%, raw materials corresponding to the second category of nickel elements are spherical nickel powder with a purity of not less than 99.5% and an average particle size of 5-10 micrometers, zirconium powder and titanium powder corresponding to the third category of elements with a purity of not less than 99%, and raw materials corresponding to the fourth category of auxiliary elements with a purity of not less than 99%.

3. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: In step S3, non-consumable electrode arc melting is used, the melting current is 200-300 amperes, each batch is melted 3-5 times, and each melting time is 3-5 minutes.

4. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: In step S1, the molar percentage of lanthanum in the first type of rare earth element combination is not less than 40% of the total molar percentage of the rare earth elements in that type, and the sum of the molar percentages of cerium and yttrium is not less than 30% of the total molar percentage of the rare earth elements in that type.

5. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: The inert protective gas in step S3 is argon, and the purity of argon is not less than 99.999%.

6. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: The method for removing the oxide layer on the surface of rare earth metal raw materials in step S2 is as follows: soaking in 10% to 15% dilute hydrochloric acid for 10 to 15 minutes, then rinsing with deionized water 3 to 5 times, and then drying in a forced-air drying oven at 60 to 80°C for 1 to 2 hours.

7. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: In step S2, the vacuum level of the vacuum drying oven is controlled at 1×10⁻⁶. -2 -5×10 -2 Pa.

8. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: In step S3, the temperature of the cooling water for the water-cooled copper crucible in the electric arc melting furnace is controlled at 20-30℃, and the cooling water flow rate is 1-2 liters / minute.

9. The method for preparing an A2B7 type hydrogen storage alloy according to claim 1, characterized in that: In step S4, the alloy ingot is cooled to room temperature by natural cooling, with the cooling environment temperature controlled at 20-25℃ and the relative humidity not exceeding 60%.

10. An A2B7 type hydrogen storage alloy, characterized in that, The method described in any one of 1-9 above is used to prepare the A2B7 type hydrogen storage alloy.

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