A long-life single-phase AB4 type rare earth hydrogen storage alloy and its preparation method

Abstract

The application discloses a long-life single-phase AB4 type rare earth hydrogen storage alloy and a preparation method thereof. 1‑a‑b‑c Mg a Y b Sm c Ni z‑x‑y Al x Mn y , wherein a, b, c, x, y and z represent molar ratios, 0.12<=a<=0.22, 0.05<=b<=0.10, 0.18<=a+b<=0.30, 0.16<=c<=0.22, 0.10<=x<=0.17, 0.02<=y<=0.05 and 0.15<=x+y<=0.19, and 3.76<=z<=4.02; the rare earth hydrogen storage alloy is subjected to induction smelting, high-temperature annealing, cooling recrystallization and recrystallization annealing processes, thereby forming a 100 wt.% 3R type AB4 phase superlattice structure, and the rare earth hydrogen storage alloy has excellent cycle stability, and a capacity retention rate is >=65% after 500 times of charge-discharge cycles.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage materials technology, and relates to a long-life single-phase AB4 type rare earth hydrogen storage alloy and its preparation method. Background Technology

[0002] The development and application of high-performance hydrogen storage materials has become a major national need. Among them, rare-earth magnesium-nickel based hydrogen storage alloys, due to their unique superlattice structure, possess significant advantages such as fast room-temperature hydrogen absorption and desorption kinetics, excellent activation performance, high theoretical capacity, and environmental friendliness, making them a next-generation anode material for nickel-metal hydride batteries. Rare-earth magnesium-nickel based alloys exhibit complex and diverse AB... n (n=3, 3.5, 3.8, and 4) type superlattice phase structures, each of which also exhibits H-type and R-type allotropic configurations. Previous studies have compared AB3-type and AB... 3.5 Type and AB 3.8 When studying single-phase alloys, it was found that as the n value increased, the hydrogen storage capacity of the alloy decreased slightly, but the cycle stability showed an upward trend (Journal of Power Sources 300 (2015) 77-86). However, recent studies have further indicated that AB4 type, compared to AB... 3.8 Magnesium-type alloys combine high capacity and structural stability, giving them a significant advantage in the development of long-life hydrogen storage materials (Journal of Magnesium and Alloys 9 (2021) 2039-2048).

[0003] One of the key technologies for achieving long-life superlattice alloys lies in precisely controlling the phase structure of the alloy through the fabrication process to obtain a single-phase structure. When multiple phases coexist within an alloy, the inconsistent expansion / contraction rates of the lattice volume during hydrogen absorption / desorption (charge / discharge) cause lattice mismatch stress, which can lead to intergranular cracking and pulverization of alloy particles during cycling, resulting in capacity decay. Therefore, obtaining a single-phase structure through heat treatment of the alloy ingot is crucial for improving the alloy's discharge capacity and cycle life.

[0004] However, superlattice alloys are prone to peritectic reactions during heat treatment. The formation energies between different superlattice phases are relatively small, and complex solid-state diffusion processes are involved. Therefore, phase decomposition or non-equilibrium phase transformations are highly likely to occur during heat treatment, leading to the formation of multiphase structures. How to effectively control the phase structure of superlattice hydrogen storage alloys has become a major challenge in this field in recent years and is urgently needed for industrial applications. This is especially true for the AB4 type phase structure with higher n values, which is a metastable or high-temperature stable phase with an extremely narrow stable composition range and temperature window. Traditional single-stage annealing heat treatment follows a thermodynamic path of heating-holding-cooling, which easily leads to the decomposition region of the AB4 phase or fails to provide the kinetic conditions for stable nucleation and growth, thus easily forming A5B. 19 The AB4 single-phase alloy may exhibit a multiphase mixed structure, including AB5, which could lead to crystal transformation of the AB4 phase. Currently, the thermodynamic formation conditions and evolution mechanisms of AB4 single-phase alloys are unclear, and mature single-phase preparation process parameters are lacking.

[0005] Furthermore, the electrochemical performance (especially cycle stability) of superlattice alloys exhibits a complex coupling relationship with phase purity and elemental composition. Fluctuations in alloy composition can significantly alter the process window for pure phase formation, further increasing the difficulty of material preparation. In summary, developing novel AB4-type rare-earth magnesium-nickel hydrogen storage alloys with optimized composition and stable structure, and breaking through their controllable single-phase preparation technology, are key technical challenges that urgently need to be addressed in the development of long-life superlattice structure hydrogen storage materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention aims to provide a long-life single-phase AB4 type rare-earth hydrogen storage alloy and its preparation method. The general chemical formula of the hydrogen storage alloy is: La 1-a-b-c Mg a Y b Sm c Ni z-x-y Al x Mn y In the formula, a, b, c, x, y, and z represent the atomic molar ratios, 0.12≤a≤0.22, 0.05≤b≤0.10, and 0.18≤a+b≤0.30, 0.16≤c≤0.22, 0.10≤x≤0.17, 0.02≤y≤0.05, and 0.15≤x+y≤0.19, 3.76≤z≤4.02. This rare earth hydrogen storage alloy, after induction melting, high-temperature annealing, cooling recrystallization, and recrystallization annealing processes, forms a 100 wt.% 3R-type AB4 phase superlattice structure, exhibiting excellent cycle stability, with a capacity retention rate of ≥65% after 500 charge-discharge cycles.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A long-life single-phase AB4 type rare earth hydrogen storage alloy, wherein the hydrogen storage alloy can be represented by its general chemical formula La. 1-a-b-c Mg a Y b Sm c Ni z-x-y Al x Mn y The formula represents the atomic molar ratio, where a, b, c, x, y, and z represent the atomic molar ratios, 0.12≤a≤0.22, 0.05≤b≤0.10, and 0.18≤a+b≤0.30, 0.16≤c≤0.22, 0.10≤x≤0.17, 0.02≤y≤0.05, and 0.15≤x+y≤0.19, 3.76≤z≤4.02.

[0008] As a limitation of the present invention, the crystal structure of the rare earth hydrogen storage alloy is an AB4 type superlattice structure with a space group of R-3m and a phase content of 100 wt.%.

[0009] The chemical composition range of the rare-earth hydrogen storage alloy of this invention is one of the keys to its long cycle life. In the alloy element composition of this invention, after an appropriate amount of rare-earth Sm element replaces La on the A side, it preferentially enters the [A2B4] subunit, effectively reducing its cell volume, thus making its size more compatible with the [AB5] subunit, enhancing the structural stability of the alloy, reducing micro-strain and internal stress during hydrogen absorption and desorption, and reducing the degree of pulverization. In addition, Y element needs to be added on the A side. Y has a smaller atomic radius than Sm, and its addition can further effectively reduce the instability of the [A2B4] sublattice in the superlattice structure, and produce a synergistic effect with Mg, jointly improving the alloy's anti-pulverization ability and cycle stability; at the same time, its addition also helps to enhance the thermodynamic stability of the AB4 type phase structure. This specific Y-Sm composition ratio significantly changes the phase transformation kinetics during alloy solidification, causing the precursor phase in the ingot to tend to transform into a stable phase under heat treatment within a specific temperature range of 1025~1030℃. Furthermore, the Al and Mn elements on the B side jointly regulate the cell volume of the superlattice structure, improve the matching degree of the [A2B4] and [AB5] subunit structures, reduce the deformation energy and stress during the hydrogen absorption and desorption process of the alloy, suppress alloy pulverization, and help extend the cycle life. Simultaneously, during charge and discharge, Sm and Y on the alloy surface are oxidized to form dense rare earth oxides or hydroxides, while Al is oxidized to an Al2O3 film. The resulting composite surface film effectively inhibits further oxidation and corrosion of the alloy substrate, thereby significantly improving the alloy's cycle life. Therefore, the rare earth hydrogen storage alloy prepared within the chemical composition range of this invention is a single-phase AB4 type superlattice structure alloy. This pure-phase rare earth hydrogen storage alloy exhibits excellent cycle life as an active material for the negative electrode of nickel-metal hydride batteries.

[0010] This invention also provides a method for preparing a long-life single-phase AB4 type rare earth hydrogen storage alloy, which is carried out in the following order: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. Prepare the target alloy using the induction melting method. The magnesium-containing intermetallic compound is added in a secondary feeding manner, and then the alloy ingot is obtained by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment to obtain a long-life single-phase AB4 type rare earth hydrogen storage alloy.

[0011] As a limitation of the preparation method of the present invention, in step S2, the recrystallization heat treatment process is carried out according to the following procedure: In the first stage, the temperature is first increased from room temperature to 600 ℃ at a heating rate of 4~5 ℃ / min, and then increased from 600 ℃ to 1025~1030 ℃ at a heating rate of 1 ℃ / min, and held for 10~12 h. In the second stage, the temperature is reduced to 600°C at a rate of 1°C / min, and argon gas is introduced to raise the pressure inside the furnace to 60~90 kPa. In the third stage, the temperature was increased from 600 ℃ to 1025~1030 ℃ at a heating rate of 1℃ / min, and held for 10~12 h. In the fourth stage, the furnace is cooled to room temperature.

[0012] The single-phase AB4-type superlattice structure formed by the rare-earth hydrogen storage alloy prepared by this invention is another key to its long cycle life. This invention addresses the current bottlenecks in the preparation technology of single-phase AB4-type superlattice hydrogen storage alloys by employing a recrystallization annealing method, namely high-temperature annealing, cooling recrystallization, and recrystallization annealing processes, precisely controlling the temperature curve and holding time to effectively stabilize the formation of the 3R-type AB4 phase superlattice structure, promoting the transformation of the alloy into a single-phase AB4-type superlattice structure, and solving its metastable transformation problem. Specifically: In the first stage, the temperature is rapidly increased from room temperature to 600 °C to reduce the volatilization of Mg and simultaneously allow Mg to diffuse into equilibrium within the system, providing a basis for compositional homogeneity for subsequent recrystallization. Then, a slow heating method is employed to ensure sufficient atomic diffusion and avoid incomplete phase transformation due to sudden temperature changes. Within the temperature range of 1025–1030 °C, a peritectic reaction is induced between the CaCu5-type phase and the MgCu4Sn-type phase dissociation products in the alloy ingot, transforming them into the 2H-type A5B. 19 Type A5B, 3R 19 Type 3 and AB4 phase.

[0013] The insulation temperature during this stage must be strictly controlled between 1025 and 1030 ℃. If it is below 1025 ℃, the phase change driving force will be insufficient, and the precursor phase A5B will... 19 The phase cannot fully participate in the peritectic reaction and leaves residues; if the temperature is above 1030℃, the structure will decompose into the AB5 type phase, and this decomposition cannot be eliminated in subsequent stages.

[0014] The second stage involves a slow cooling to 600 °C, a crucial process for lattice relaxation and pressure equilibrium. Unlike traditional single-stage annealing, this invention introduces a cooling step after high-temperature homogenization. This utilizes the low-temperature stage to eliminate thermal stress generated by the high-temperature treatment, inducing the initial formation of metastable phase nuclei. This allows the 3R-type AB4 phase to fully grow and stabilize, preventing phase decomposition due to excessive supercooling and the formation of a non-superlattice AB5 phase. Simultaneously, argon gas is added at this stage to 60-90 kPa. This effectively reduces the risk of oxidation, and the appropriate pressure further suppresses the volatilization of low-melting-point elements, preventing the AB4 phase from transforming into the AB5 phase.

[0015] In the third stage, the temperature is slowly increased from 600 ℃ to 1025~1030 ℃ and held within this temperature range. Based on the already formed 3R-type AB4 phase crystal nuclei, atoms are allowed to diffuse fully, achieving A5B. 19 The phase recrystallizes and undergoes a crystal form transformation to the AB4 phase.

[0016] This stage involves recrystallization heat treatment, and the temperature should not be lower than 1025℃ or higher than 1030℃. Below 1025℃, the driving force for atomic diffusion is insufficient to overcome the barrier to peritectic reaction, and the precursor phase A5B... 19 The transformation of the metastable AB4 phase into the stable phase will cause the metastable AB4 phase to transform into A5B. 19 The temperature range of 1025~1030℃ exceeds the thermodynamic stability limit of the AB4 phase in this composition system, causing the superlattice structure to irreversibly decompose into the AB5 phase. Therefore, maintaining a temperature range of 1025~1030℃ is the only path to achieve a single-phase AB4 type superlattice structure in the alloy of this invention.

[0017] Fourth stage: Slow cooling (furnace cooling) to completely solidify the AB4 phase structure and avoid secondary phase transformation.

[0018] The recrystallization heat treatment process of this invention is closely related to the elemental composition of the alloy and the crystal form of the desired AB4-type superlattice structure, and directly determines whether the final alloy is a pure phase structure, affecting the hydrogen absorption / desorption and charge / discharge cycle life of the rare earth hydrogen storage alloy. Furthermore, the heat treatment temperature of this invention needs to be matched with the holding time to ensure the complete peritectic reaction, allowing the alloy grains to grow fully and form a single-phase structure.

[0019] As another limitation of the preparation method of the present invention, the temperature during induction melting is 1400~1450℃, the time is 10~18 min, and the pressure is 60~70 kPa.

[0020] As a final limitation of the present invention, the nickel-metal hydride battery assembled using the hydrogen storage alloy prepared therefrom as the negative electrode active material of the nickel-metal hydride battery retains a capacity of ≥65% after 500 charge-discharge cycles at a current density of 360 mA / g.

[0021] The above-mentioned technical solution of the present invention is a whole in which each step is closely related and mutually influential, and together they determine the morphological characteristics and performance of the product.

[0022] The above technical solution has the following advantages or beneficial effects: 1. The long-life single-phase AB4 rare earth hydrogen storage alloy prepared by this invention has excellent cycle stability, and its capacity retention rate is ≥65% after 500 charge-discharge cycles when used as a negative electrode material for nickel-metal hydride batteries; 2. The long-life single-phase AB4 rare earth hydrogen storage alloy of the present invention is prepared by induction melting followed by a specific recrystallization heat treatment method. The method is simple, can effectively control the formation of the AB4 type crystal structure of the alloy, is easy to operate, and is suitable for industrial production.

[0023] This invention is applicable to the preparation of long-life single-phase AB4 type rare earth hydrogen storage alloys.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0025] Figure 1 The Rietveld full spectrum fitting spectrum of the long-life single-phase AB4 type rare earth hydrogen storage alloy prepared in Example 1 of this invention; Figure 2 The Rietveld full spectrum fitting spectrum of the long-life single-phase AB4 type rare earth hydrogen storage alloy prepared in Example 2 of the present invention; Figure 3 The Rietveld full spectrum fitting spectrum of the long-life single-phase AB4 type rare earth hydrogen storage alloy prepared in Example 3 of the present invention; Figure 4 The Rietveld full spectrum fitting spectrum of the long-life single-phase AB4 type rare earth hydrogen storage alloy prepared in Example 4 of this invention; Figure 5 Capacity retention curves of long-life single-phase AB4 rare earth hydrogen storage alloys prepared in Examples 1-4 of this invention as electrode materials; Figure 6The X-ray diffraction (XRD) spectra of the rare earth hydrogen storage alloys prepared in Comparative Example 1 and Example 1 of this invention are shown. Detailed Implementation

[0026] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified. Example 1

[0028] This embodiment prepares a La 0.58 Mg 0.18 Y 0.08 Sm 0.16 Ni 3.65 Al 0.17 Mn 0.02 The preparation process and steps of a long-life single-phase AB4 type rare earth hydrogen storage alloy are as follows: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. After evacuation, fill the furnace with argon gas to a pressure of 60 kPa and heat it to 1400 ℃ for melting. After the raw materials melt, add the magnesium-containing intermetallic compound into the melt through a secondary feeding method, continue melting for 18 min, and then obtain the alloy ingot by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment. First, the temperature is increased from room temperature to 600 ℃ at a heating rate of 5 ℃ / min, and then increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min, and held for 10 h. Then, the temperature is decreased to 600 ℃ at a cooling rate of 1 ℃ / min, and argon gas is introduced to increase the pressure in the furnace to 60 kPa. The temperature is then increased from 600 ℃ to 1030 ℃ at a heating rate of 1 ℃ / min, and held for 10 h. Finally, the furnace is cooled to room temperature. Example 2

[0029] This embodiment prepares a La 0.55 Mg 0.22 Y 0.05 Sm 0.18Ni 3.72 Al 0.14 Mn 0.04 The preparation process and steps of a long-life single-phase AB4 type rare earth hydrogen storage alloy are as follows: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. After evacuation, fill the furnace with argon gas to a pressure of 65 kPa and heat it to 1420 ℃ for melting. After the raw materials melt, add the magnesium-containing intermetallic compound into the melt through a secondary feeding method, continue melting for 15 min, and then obtain the alloy ingot by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment. First, the temperature is increased from room temperature to 600 ℃ at a heating rate of 4℃ / min, and then increased from 600 ℃ to 1030 ℃ at a heating rate of 1℃ / min, and held for 12 h. Then, the temperature is decreased to 600 ℃ at a cooling rate of 1℃ / min, and argon gas is introduced to increase the pressure in the furnace to 90 kPa. Then, the temperature is increased from 600 ℃ to 1025 ℃ at a heating rate of 1℃ / min, and held for 12 h. Finally, the furnace is cooled to room temperature. Example 3

[0030] This embodiment prepares a La 0.60 Mg 0.12 Y 0.06 Sm 0.22 Ni 3.61 Al 0.13 Mn 0.02 The preparation process and steps of a long-life single-phase AB4 type rare earth hydrogen storage alloy are as follows: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. After evacuation, fill the furnace with argon gas to a pressure of 70 kPa and heat it to 1450 ℃ for melting. After the raw materials melt, add the magnesium-containing intermetallic compound into the melt through a secondary feeding method, continue melting for 10 min, and then obtain the alloy ingot by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment. First, the temperature is increased from room temperature to 600 ℃ at a heating rate of 4.5 ℃ / min, and then increased from 600 ℃ to 1028 ℃ at a heating rate of 1 ℃ / min, and held for 11 h. Then, the temperature is decreased to 600 ℃ at a cooling rate of 1 ℃ / min, and argon gas is introduced to increase the pressure in the furnace to 80 kPa. The temperature is then increased from 600 ℃ to 1028 ℃ at a heating rate of 1 ℃ / min and held for 11 h. Finally, the furnace is cooled to room temperature. Example 4

[0031] This embodiment prepares a La 0.50 Mg 0.20 Y 0.10 Sm 0.20 Ni 3.87 Al 0.10 Mn 0.05 The preparation process and steps of a long-life single-phase AB4 type rare earth hydrogen storage alloy are as follows: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. After evacuation, fill the furnace with argon gas to a pressure of 60 kPa and heat it to 1400 ℃ for melting. After the raw materials melt, add the magnesium-containing intermetallic compound into the melt through a secondary feeding method, continue melting for 18 min, and then obtain the alloy ingot by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment. First, the temperature is increased from room temperature to 600 ℃ at a heating rate of 4 ℃ / min, and then increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min, and held for 12 h. Then, the temperature is decreased to 600 ℃ at a cooling rate of 1 ℃ / min, and argon gas is introduced to increase the pressure in the furnace to 80 kPa. The temperature is then increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min, and held for 10 h. Finally, the furnace is cooled to room temperature.

[0032] Examples 1-4: Structural and Performance Tests (a) Structural testing The rare earth hydrogen storage alloys obtained in Examples 1-4 were polished to remove the surface oxide layer. After mechanical crushing, grinding, and sieving, the powder passing through a 400-mesh sieve was subjected to X-ray diffraction (XRD) testing. The collected data were quantitatively analyzed using Rietveld full-spectrum fitting, and the results are as follows: Figures 1-4As shown in Table 1. The results show that the alloys prepared in Examples 1 to 4 are all AB4 type superlattice structures with space group R-3m, and are all single phases (phase content 100 wt.%), that is, single-phase 3R type AB4 superlattice structure alloys were successfully obtained.

[0033] (ii) Performance Testing The rare-earth hydrogen storage alloys obtained in Examples 1-4 were powdered. Powder with a particle size range of 200-400 mesh was mixed with carbonyl nickel powder at a mass ratio of 0.15 g:0.75 g, and cold-pressed into electrode sheets with a diameter of 10 mm under a pressure of 15 MPa. Using this electrode as the working electrode, sintered Ni(OH)₂ / NiOOH as the counter electrode, and 6 mol / L KOH solution as the electrolyte, a two-electrode test system was assembled. Testing was performed using a LAND CT3001A battery tester. First, activation was performed by charge-discharge at a current density of 72 mA / g, charging for 7 h, resting for 10 min, and then discharging to 1.0 V until the maximum discharge capacity was reached. Subsequently, cycle life testing was performed at a current density of 360 mA / g, charging for 1.1 h, resting for 5 min, and then discharging to 1.0 V. The discharge capacity within 500 cycles was recorded. The capacity retention rate of the alloy was defined as the ratio of the discharge capacity of a certain cycle to the maximum discharge capacity, and the cycle life was characterized by the capacity retention rate over 500 cycles. This invention uses the capacity retention rate over 500 cycles to characterize the cycle life of the alloy electrode, and the results are as follows: Figure 5 As shown in Table 1. Alloys 1-4, used as negative electrodes in nickel-metal hydride batteries, had maximum discharge capacities of 363 mAh / g, 368 mAh / g, 370 mAh / g, and 372 mAh / g, respectively, and capacity retention rates of 70.1%, 66.5%, 68.8%, and 65.7% after 500 cycles, respectively.

[0034] Table 1. Crystal structure and cycle capacity retention of alloys in Examples 1-4 In summary, the single-phase AB4 rare-earth hydrogen storage alloy prepared by this invention exhibits excellent long cycle life as both a negative electrode material for nickel-metal hydride batteries and a solid-state hydrogen storage material.

[0035] Comparative Example To investigate the effects of different element contents and different heat treatment processes on the performance of the product of this invention, the following comparative experiments were conducted, as detailed below: Comparative Example 1: Rare Earth Hydrogen Storage Alloys Prepared with Different Element Contents In this comparative example, a rare earth hydrogen storage alloy was prepared. The preparation method was similar to that of Example 1, except that the element content was different from that of Example 1. The remaining steps and parameters were the same as those of Example 1. The chemical formulas of each hydrogen storage alloy are as follows: Group A: La 0.60 Mg 0.26 Sm 0.16 Ni 3.65 Al 0.17 Mn 0.02 ; Group B: La 0.66 Mg 0.18 Y 0.08 Sm 0.10 Ni 3.65 Al 0.17 Mn 0.02 ; Group C: La 0.60 Mg 0.18 Y 0.08 Sm 0.16 Ni 3.57 Al 0.17 Mn 0.10 ; Group D: La 0.60 Mg 0.18 Y 0.08 Sm 0.16 Ni 3.77 Al 0.05 Mn 0.02 ; Group E: La 0.65 Mg 0.13 Y 0.10 Sm 0.12 Ni 3.60 Al 0.15 .

[0036] The alloys prepared in the above groups were subjected to structural testing and assembled into nickel-metal hydride batteries according to the methods of Examples 1 to 4. Their electrochemical performance was then tested, and the specific results are shown in Table 2 below.

[0037] Table 2 Crystal structure and electrochemical properties of each alloy in this comparative example As shown in Table 2, although the comparative example used the exact same preparation method and conditions as Example 1, and the types of elements used were also the same, when evaluating the cycle stability as a nickel-metal hydride battery anode material, it was found that deviations in composition not only caused changes in the alloy's microstructure but also led to a significant deterioration in its cycle life. For alloys in groups A to C, the absence of the key element Y, or the content of Sm and Mn exceeding the scope of this invention, significantly reduced the thermodynamic stability of the AB4 phase. During recrystallization heat treatment, the alloy is prone to phase decomposition, generating A5B. 19Impurities such as AB4 or AB5-type phases are present. The coexistence of multiple phases increases lattice mismatch stress and exacerbates particle pulverization during charge-discharge cycles, while simultaneously reducing corrosion resistance, resulting in a significant decrease in capacity retention. For group D (Al-deficient) alloys, although a single AB4 phase can still be formed under the conditions described in this invention, the severe Al deficiency greatly weakens the alloy's oxidation and corrosion resistance, leading to rapid loss of active materials during cycling. Therefore, despite high phase purity, its cycle life is far inferior to that of the compositionally optimized group A. Group E alloys used compositions reported in the literature but not within the scope of this invention's optimization. The results show that even using the method of this invention, this composition cannot yield a high-purity AB4 single phase, and its cycle stability is lower than that of the embodiments of this invention. This further confirms the necessity of the composition range determined in this invention for obtaining highly stable single-phase AB4 alloys and excellent cycle performance.

[0038] Comparative Example 2: Rare Earth Hydrogen Storage Alloys Prepared Using Different Heat Treatment Processes The recrystallization heat treatment conditions of this invention are a key control step for stably obtaining single-phase AB4 type rare earth hydrogen storage alloys. This comparative example, based on the alloy chemical composition and preparation method of Example 4, systematically investigates the effects of different heat treatment processes on the alloy microstructure and properties. The specific process conditions are as follows: Group A: A single annealing process was adopted. First, the temperature was increased from room temperature to 600 ℃ at a heating rate of 4 ℃ / min, and then increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min, and held for 12 h. Group B: A single annealing process was adopted. First, the temperature was increased from room temperature to 600 ℃ at a heating rate of 4 ℃ / min, and then increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min, and held for 35 h. Group C: A single annealing process was adopted. First, the temperature was increased from room temperature to 600 ℃ at a heating rate of 4 ℃ / min, and then increased from 600 ℃ to 1010 ℃ at a heating rate of 1 ℃ / min, and held for 12 h. Group d: A single annealing process was adopted. First, the temperature was increased from room temperature to 600 ℃ at a heating rate of 1℃ / min, and then increased from 600 ℃ to 1040 ℃ at a heating rate of 1℃ / min, and held for 12 h. Group e: The recrystallization heat treatment process was adopted. In the third stage, the temperature was increased from 600 ℃ to 1025 ℃ at a heating rate of 1 ℃ / min and held for 6 h. Group f: The recrystallization heat treatment process was adopted. In the third stage, the temperature was increased from 600 ℃ to 1030 ℃ at a heating rate of 1 ℃ / min and held for 18 h. Group g: The recrystallization heat treatment process was adopted. In the third stage, the temperature was increased from 600 ℃ to 1020 ℃ at a heating rate of 1 ℃ / min and held for 12 h. Group h: The recrystallization heat treatment process was adopted. In the third stage, the temperature was increased from 600 ℃ to 1040 ℃ at a heating rate of 1 ℃ / min and held for 10 h.

[0039] The alloy prepared above was subjected to phase structure testing, and the results are as follows: Figure 6 The results are shown in Table 3. The nickel-metal hydride batteries were assembled and their electrochemical performance was tested.

[0040] Table 3. Crystal structure and electrochemical properties of alloys obtained by different heat treatment processes in this comparative example. As shown in Table 3, to obtain a high-purity single-phase AB4 structure with excellent cycle life, the following three process conditions must be met simultaneously, and none can be omitted: 1) A recrystallization heat treatment (double annealing) process must be used: Even with extended holding time (e.g., in group b), a single annealing process (groups a-d) cannot obtain a pure AB4 phase, proving that the metastable phase requires a dynamic process of nucleation and stabilization before recrystallization, and single annealing cannot provide this necessary condition; 2) The secondary holding time must be controlled within the optimal range of 10-12 h: Too short a holding time (group e) will lead to incomplete phase transformation, while too long a time (group f) may cause abnormal grain growth or local decomposition. The optimal holding time range is conducive to obtaining a complete phase transformation and stable structure; 3) The secondary holding temperature must be precisely controlled within a narrow window of 1025-1030℃: If the temperature is below 1020℃ (group g), the reaction driving force is insufficient, making complete transformation difficult and leaving residual A5B. 19 When the temperature exceeds 1030 ℃ (group h), the AB4 phase will irreversibly decompose into the AB5 phase, resulting in a sharp drop in performance. The process provided in Example 4 of this invention simultaneously satisfies all the above conditions, thereby successfully achieving the stable preparation of a single-phase AB4 type superlattice structure and possessing excellent long cycle life.

[0041] Comparative Example 3: Performance Comparison with Existing Superlattice Single-Phase Alloys This comparative example uses methods described in existing literature and patent literature to prepare hydrogen storage alloys, as detailed below: AA: A La-type atom was prepared using the method described in the literature "Journal of the Electrochemical Society 170 (2023) 080504". 0.60 Sm 0.20 Mg 0.20 Ni 3.50 Al 0.20Hydrogen storage alloy, specifically the AB4 type alloy; BB: A La-type material was prepared using the method described in the literature "Scripta Materialia 285 (2025) 116508". 0.7 Ti 0.1 Mg 0.2 Ni 3.96 Hydrogen storage alloy, specifically the AB4 type alloy; CC: A La-based preparation was prepared using the method described in the literature "International Journal of Hydrogen Energy 48 (2023) 32849-32859". 0.65 Sm 0.12 Y 0.10 Mg 0.13 Ni 3.60 Al 0.15 Hydrogen storage alloy, specifically AB4 type alloy; DD: A La was prepared using the method described in Chinese Invention Patent CN202210858839.3. 0.5 Y 0.5 Ni 3.67 Mn 0.33 Hydrogen storage alloy, specifically the AB4 type alloy; The above alloys were subjected to structural characterization and electrochemical performance testing. The test results are shown in Table 4.

[0042] Table 4. Properties of the alloys prepared in this comparative example Analysis of the test results shows that although some progress has been made in the preparation of AB4-type hydrogen storage alloys, it is generally difficult to simultaneously achieve key performance indicators such as high phase purity, high discharge capacity, and long cycle life. The AA and BB groups, being multiphase mixed structures, exhibit significant limitations in long-term cycle stability. The CC group alloys in the literature have high capacity, but their 500-cycle retention rate (61.8%) is low. Although the DD group patented alloy is single-phase, its capacity is relatively low (345.6 mAh / g), and its cycle life is poor.

[0043] In summary, this invention discloses a universal, stable, and reproducible preparation method through the synergistic process of component design and recrystallization heat treatment. This method not only ensures the phase purity of AB4 phase to 100 wt.%, but also steadily improves the capacity retention rate of nickel-metal hydride batteries to a new high of ≥65% after 500 cycles. It achieves simultaneous optimization of phase purity and long cycle life, representing a substantial advancement in the technology of this field.

[0044] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A long-life single-phase AB4 type rare earth hydrogen storage alloy, characterized in that, The general chemical formula of the hydrogen storage alloy is: La 1-a-b-c Mg a Y b Sm c Ni z-x-y Al x Mn y The formula represents the atomic molar ratio, where a, b, c, x, y, and z represent the atomic molar ratios, 0.12≤a≤0.22, 0.05≤b≤0.10, and 0.18≤a+b≤0.30, 0.16≤c≤0.22, 0.10≤x≤0.17, 0.02≤y≤0.05, and 0.15≤x+y≤0.19, 3.76≤z≤4.

02.

2. The long-life single-phase AB4 type rare earth hydrogen storage alloy according to claim 1, characterized in that, The rare earth hydrogen storage alloy has an AB4 type superlattice structure with a space group of R-3m and a phase content of 100 wt.%.

3. The method for preparing a long-life single-phase AB4 type rare earth hydrogen storage alloy according to claim 1 or 2, characterized in that, Follow these steps in sequence: S1. Select elemental metals or intermetallic compound alloys as raw materials, and mix them according to the ratio of each element. Add an excess of metal raw materials during mixing to compensate for burn-off. Place the magnesium-containing intermetallic compound into the raw material bin, and place the other raw materials except the magnesium-containing intermetallic compound into the crucible of the vacuum induction melting furnace. Prepare the target alloy using the induction melting method. The magnesium-containing intermetallic compound is added in a secondary feeding manner, and then the alloy ingot is obtained by pouring and cooling. S2. The alloy ingot sealed in the annealing vessel is subjected to recrystallization heat treatment in a vacuum environment to obtain a long-life single-phase AB4 type rare earth hydrogen storage alloy.

4. The method for preparing a long-life single-phase AB4 type rare earth hydrogen storage alloy according to claim 3, characterized in that, In step S2, the recrystallization heat treatment process is carried out according to the following procedure: (a) In the first stage, the temperature was first increased from room temperature to 600 ℃ at a heating rate of 4~5 ℃ / min, and then increased from 600 ℃ to 1025~1030 ℃ at a heating rate of 1 ℃ / min, and held for 10~12 h. (b) In the second stage, the temperature is reduced to 600°C at a rate of 1°C / min, and argon gas is introduced to raise the pressure inside the furnace to 60~90 kPa; (c) In the third stage, the temperature was increased from 600 °C to 1025~1030 °C at a heating rate of 1 °C / min, and held for 10~12 h. (d) Fourth stage: Cool to room temperature with the furnace.

5. The method for preparing a long-life single-phase AB4 type rare earth hydrogen storage alloy according to claim 3, characterized in that, In step S1, the temperature during induction melting is 1400~1450℃, the time is 10~18 min, and the pressure is 60~70 kPa.

6. A method for preparing a long-life single-phase AB4 type rare earth hydrogen storage alloy according to any one of claims 3 to 5, characterized in that, The hydrogen storage alloy prepared in this manner, when used as the negative electrode active material in a nickel-metal hydride battery, exhibits a capacity retention rate of ≥65% after 500 charge-discharge cycles at a current density of 360 mA / g.

Images