Rare earth-nickel-based AB2 type hydrogen storage alloy material and preparation method thereof

Abstract

The invention discloses a rare earth-nickel-based AB2 type hydrogen storage alloy material and a preparation method thereof, and relates to the field of solid hydrogen storage materials, the alloy comprises rare earth elements La, Ce and Sc and transition metals Ni, Mn, Al and Zr according to a specific proportion, the raw materials are melted through electric arc melting and are subjected to alloying reaction to form a master alloy ingot, and the master alloy ingot is subjected to high-temperature sintering to obtain the rare earth-nickel-based AB2 type hydrogen storage alloy material. Non-equilibrium solidification is achieved through single-roller rapid quenching, a thin strip of a metastable-state structure is obtained, grain arrangement and second-phase precipitation are regulated and controlled through gradient annealing, finally, a surface oxide layer is removed through crushing and acid etching, and hydrogen storage alloy powder is obtained through vacuum drying. An AB2 type Laves phase main body structure is formed through multi-element rare earth solid solution, grain coarsening is inhibited by combining a rapid quenching process, a microstructure is optimized through gradient annealing, the hydrogen storage capacity, hydrogen absorption dynamic performance and cycling stability of the alloy are synergistically improved, and the alloy is suitable for preparation and application of an efficient hydrogen storage material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid-state hydrogen storage materials, in particular to a rare earth-nickel-based AB2-type hydrogen storage alloy material and a preparation method thereof. BACKGROUND

[0002] Hydrogen storage alloys, as a key material for hydrogen energy storage and conversion, have important application value in the field of new energy. AB2-type Laves phase hydrogen storage alloys have become a research hotspot in recent years due to their high hydrogen storage capacity, good kinetic performance and cycle stability. In the prior art, the composition design of AB2-type hydrogen storage alloys is mostly based on a single rare earth element (such as La or Ce) as the main component on the A side, and transition metal elements are based on Ni, supplemented with a small amount of Mn, Al and other elements to adjust the performance. Although the phase structure is mainly based on MgCu2-type or MgZn2-type Laves phase, the content of the second phase (such as LaNi5 phase, Zr-rich phase) is usually too high or unevenly distributed due to composition segregation or improper process parameter control during actual preparation, and the volume fraction of Laves phase is usually less than 85%. At the same time, the composition and phase structure of the existing alloy are not well coordinated, and the optimization of the ratio of rare earth elements and transition metals is mostly limited to binary or ternary systems, which is difficult to improve the hydrogen absorption-desorption performance through lattice parameter adjustment and electronic effect coordination, resulting in a difficult balance between hydrogen storage capacity, cycle stability and kinetic performance.

[0003] The core problems of the above prior art are as follows: first, the selection and ratio of rare earth elements and transition metals in the composition design are single, and the matching of Laves phase lattice constant and hydrogen atom size cannot be precisely controlled through the synergistic effect of multi-element solid solution, resulting in limited hydrogen storage capacity and hydrogen diffusion rate; second, the phase structure control ability is insufficient, the volume fraction of Laves phase as the main phase is low, and the second phase tends to aggregate and coarsen at the grain boundaries, which exacerbates the pulverization and phase separation of the alloy during the cycle process, affecting the long-period use stability; third, the synergistic optimization mechanism of composition and phase structure is missing, and the multi-component design and high proportion of Laves phase structure cannot be effectively combined, resulting in the difficulty of the alloy to meet the practical application requirements of high capacity, fast kinetics and long cycle. Therefore, it is a technical problem to be solved in the field to develop an AB2-type hydrogen storage alloy material that can realize comprehensive improvement of hydrogen storage performance through multi-component synergistic and phase structure precise control. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a rare earth-nickel-based AB2-type hydrogen storage alloy material and a preparation method thereof, to solve one or more problems in the prior art.

[0005] To achieve the above-mentioned purpose, the first technical solution of the present application is as follows:

[0006] A rare earth-nickel-based AB2 type hydrogen storage alloy material, the chemical composition of the hydrogen storage alloy includes (La 0.4-0.6 Ce 0.2-0.4 Sc 0.1-0.3 )Ni 1.1-1.5 Mn 0.2-0.3 Al 0.05-0.1 Zr 0.05-0.1 , wherein the total fraction of A-side rare earth elements is 1.0, the total fraction of B-side transition metals is 2.0, and the phase structure of the hydrogen storage alloy is mainly AB2 type Laves phase, and the volume fraction of the AB2 type Laves phase is ≥ 90%.

[0007] Specifically, in the A-side rare earth elements, the fraction ratio of La, Ce, and Sc is 5:3:2, that is, La 0.5 parts, Ce 0.3 parts, and Sc 0.2 parts.

[0008] Specifically, in the B-side transition metals, the fraction ratio of Ni, Mn, Al, and Zr is 15:3:1:1, that is, Ni 1.5 parts, Mn 0.3 parts, Al 0.1 parts, and Zr 0.1 parts.

[0009] Specifically, the AB2 type Laves phase is of MgCu2 type structure, and the hydrogen storage alloy contains a LaNi5 second phase with a volume fraction of 5-10%, and the LaNi5 second phase is dispersed in the form of nanoscale particles at the grain boundaries of the AB2 type Laves phase.

[0010] The preparation method of the hydrogen storage alloy material is the second technical solution of the present application, which is nested with the first technical solution and based on a rare earth-nickel-based AB2 type hydrogen storage alloy material, comprising the following steps:

[0011] (1) Raw material preparation: weigh the raw materials according to the chemical composition, the raw materials are single-element powders or block bodies with a purity of ≥ 99.9%, and the oxygen content of Sc is ≤ 50ppm.

[0012] (2) Vacuum arc melting: place the raw materials in a copper water-cooled crucible, introduce Ar gas with a purity of ≥ 99.999% to 0.04-0.06 MPa under the condition of a vacuum degree ≤ 5 × 10 -3 Pa, and perform flip melting with a current of 200-250 A, each melting time is 2-4 min, and the flip number is 4-5 times, to obtain a cast ingot with a diameter of 45-55 mm and a thickness of 8-12 mm.

[0013] (3) Single-roll rapid quenching: crush the cast ingot into 5-10 mm particles, load into a quartz nozzle, and quench under the condition of a vacuum degree ≤ 1 × 10-2 Pa, Ar gas pressure 0.08-0.12 MPa, melt temperature 1400-1700℃, copper roller rotation speed 2500-3500 r / min, to obtain a metastable structure thin strip with a width of 2-3 mm and a thickness of 0.1-0.3 mm.

[0014] (4) Gradient annealing: place the metastable structure thin strip in an inert atmosphere, heat to 450-550℃ at a rate of 4-6℃ / min, hold for 1-3h, then heat to 850-950℃ at a rate of 2-4℃ / min, hold for 3-5h, then cool to room temperature with the furnace, the inert atmosphere is high-purity Ar gas with a flow rate of 40-60 mL / min.

[0015] (5) Compound acid etching: mix the annealed alloy powder with the mixed acid etching solution at a ratio of 1:8-1:12 of the mass of the alloy powder to the volume of the mixed acid etching solution, and magnetically stir at 20-30℃ for 20-40min, the mixed acid etching solution includes 0.8-1.2 mol / L H3PO4 and 0.1-0.2 mol / L H2SO4.

[0016] (6) Washing and drying: centrifugally wash the acid-etched powder with deionized water until pH=6.5-7.0, dry at 70-90℃, vacuum degree ≤1×10 -1 Pa, to obtain a hydrogen storage alloy material.

[0017] Specifically, the weight loss rate of the ingot in step (2) is ≤0.5% by mass percentage, and the atomic percentage distribution deviation of each element in the ingot is ≤±2%.

[0018] Specifically, the surface roughness Ra of the copper roller in step (3) is ≤0.8μm, the nozzle inner diameter is 2-3mm, the nozzle-copper roller distance is 0.4-0.6mm, and the cooling rate is 1×10 5 -1×10 6 ℃ / s.

[0019] Specifically, the second heating rate of the gradient annealing in step (4) is 3℃ / min.

[0020] Specifically, the mixing ratio of the alloy powder to the mixed acid etching solution in step (5) is 1:10 by mass, the treatment temperature is 25℃, and the treatment time is 30min.

[0021] Specifically, the step (4) gradient annealing after, step (5) before the composite acid etching also includes a mechanical crushing step: after the annealing thin strip is crushed to 1-3mm, wet ball milling is carried out using ethanol as a medium, the ball-to-material mass ratio is 10:1, the rotation speed is 250-350r / min, the ball milling time is 1-3h, and the powder with a particle size of ≤48μm is obtained by passing through a 300-mesh sieve.

[0022] Compared with the prior art, the beneficial technical effects of the present application are as follows:

[0023] (I) Multi-component design and dual-phase structure synergy to improve the comprehensive balance of hydrogen storage performance

[0024] Through multi-component solid solution design of A-side rare earth elements (La / Ce / Sc) and B-side transition metals (Ni / Mn / Al / Zr), combined with a dual-phase structure with AB2 type Laves phase as the main phase and nanoscale dispersed LaNi5 second phase, a synergistic mechanism of "main phase hydrogen storage-second phase strengthening" is formed. The atomic radius difference of rare earth elements can adjust the Laves phase lattice constant to match the size of hydrogen atoms, and the electronic effect of transition metals optimizes the hydrogen adsorption energy, while the LaNi5 nanoparticles at the grain boundaries inhibit the phase separation and pulverization during the cycling process, so that the alloy has high hydrogen storage capacity, excellent kinetic performance and long cycle stability.

[0025] (II) Microstructure regulation of multi-step preparation process to realize precise control of defects and phase distribution

[0026] The homogeneous alloying of vacuum arc melting, the metastable structure supersaturated solid solution formed by single-roller rapid quenching, and the gradient annealing process are combined to construct a whole-process microstructure regulation mechanism of "rapid solidification to inhibit coarsening-gradient heating to promote ordering-slow cooling to reduce internal stress". This combination can refine the grains to submicron level, control the dispersion of LaNi5 second phase at the grain boundaries, and reduce the defect density of vacancies and dislocations, thereby improving the mechanical strength of the alloy and the resistance to volume expansion during hydrogen absorption and desorption.

[0027] (III) Synergistic optimization of surface modification and internal structure to strengthen hydrogen transport kinetics

[0028] The gradient annealing followed by composite acid etching forms a gradient structure of "internal ordered crystal phase-surface porous active layer": the annealing process ensures the integrity of the internal Laves phase lattice to guarantee the hydrogen storage capacity, and the mixed acid etching of H3PO4 and H2SO4 selectively etches the weak surface area to form micron-level porous channels, while removing the oxide layer and introducing surface defect sites. This synergistic effect of "internal ordered transport-surface rapid activation" significantly reduces the dissociation energy barrier and bulk diffusion resistance of hydrogen molecules, improving the low-temperature activation performance and hydrogen absorption and desorption rate of the alloy. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a flowchart of the preparation method in the present application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc. shown in the drawings attached to the present specification are only used to cooperate with the content disclosed in the present specification for understanding and reading by those skilled in the art, and are not used to limit the limiting conditions for implementing the present application, so they do not have technical substantive significance. Any modification of structure, change of proportional relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope covered by the disclosed technical content of the present application.

[0031] SUMMARY

[0032] In the field of hydrogen storage alloy materials, the conventional processing methods for performance optimization of AB2-type Laves phase hydrogen storage alloys mainly focus on three aspects: first, by adjusting the binary or ternary ratio of A-side rare earth elements (such as single La or Ce) and B-side transition metals (mainly Ni, supplemented by Mn, Al, etc.), trying to adjust the lattice parameters to improve the hydrogen storage capacity; second, using the traditional arc melting combined with single temperature annealing process to promote the formation of Laves phase and grain refinement; third, through simple acid etching or coating and other surface modification methods to improve the surface activity and hydrogen transport kinetics of the alloy.

[0033] However, the above conventional solutions have significant shortcomings: in terms of composition design, the combination of single rare earth element and limited transition metal cannot meet the dual needs of lattice size matching hydrogen atom storage and electronic effect optimizing hydrogen adsorption energy, making it difficult to break through the balance between hydrogen storage capacity and kinetic performance; in terms of phase structure control, traditional processes are prone to result in insufficient volume fraction of Laves phase (usually less than 85%), and the second phase (such as LaNi5 phase) is prone to coarsen and aggregate at the grain boundaries, exacerbating the problem of pulverization and phase separation during the cycling process; the lack of coordination between preparation and modification, simple annealing cannot precisely control the dispersion precipitation of the second phase, and surface treatment cannot be combined with internal ordered crystal phase, resulting in the coexistence of surface activity decay and internal structure stability decline after long-term cycling, which is difficult to meet the comprehensive application requirements of high capacity, fast kinetics and long service life.

[0034] COMPREHENSIVE DESCRIPTION

[0035] I. Composition design of hydrogen storage alloy materials

[0036] The application relates to a high-performance AB2 type hydrogen storage alloy material, which is designed based on a multi-element rare earth-transition metal solid solution, and the types and proportions of rare earth elements on the A side and transition metals on the B side are precisely controlled to realize comprehensive optimization of hydrogen storage performance in combination with the synergistic effect of a two-phase structure.

[0037] 1.1 Main phase component design

[0038] The main phase of the alloy is an AB2 type Laves phase structure, wherein the A side is a rare earth element composite system composed of lanthanum (La), cerium (Ce) and scandium (Sc) in a specific molar ratio, and the chemical formula is as follows:

[0039] A = La x Ce γ Sc 1-x-y

[0040] In the formula, x and y are molar fractions, and satisfy 0.4<=x<=0.6, 0.2<=y<=0.3, and 1-x-y>=0.1. The selection of rare earth elements is based on the synergistic regulation of atomic radius and electron configuration: La (atomic radius 187.7 pm) and Ce (182.5 pm) provide a larger lattice gap to accommodate hydrogen atoms, and the smaller radius of Sc (164.1 pm) can inhibit lattice distortion through solid solution strengthening, and the three can synergistically adjust the lattice constant of the Laves phase to 0.75-0.78 nm, matching the storage requirements of hydrogen atoms (radius 37 pm).

[0041] The B side is a transition metal composite system composed of nickel (Ni), manganese (Mn), aluminum (Al) and zirconium (Zr) in the following stoichiometric formula:

[0042] B = Ni a Mn β Al γ Zr 1-a-β-γ

[0043] In the formula, a, β and γ are molar fractions, and satisfy 0.5<=a<=0.75, 0.2<=β<=0.3, 0.05<=γ<=0.1, and 1-a-β-γ>=0.05. The functions of transition metals are as follows: Ni (3d 8 4s 2 ) provides strong hydrogen adsorption energy (-0.2 to -0.4 eV) to ensure hydrogen storage capacity, Mn (3d 5 4s 2 ) optimizes the hydrogen diffusion barrier through electronic effect, Al (3s 2 3p 1 ) improves the corrosion resistance of the alloy, and Zr (4d 2 5s 2) to enhance the stability of Laves phase structure. The total molar ratio of A side and B side is strictly controlled as 1:2, i.e. A / B = 1:2, which ensures that the main phase is mainly MgCu2 type Laves phase (cubic structure).

[0044] 1.2 Dual-phase structure design

[0045] To balance the hydrogen storage performance and cycle stability, LaNi5 second phase is introduced into the alloy, the content of which is controlled as 5%-15% of the total mass of the alloy, and is dispersedly distributed in the form of nanoparticles (particle size 50-200 nm) at the grain boundaries of the Laves phase. The stoichiometric formula of the LaNi5 second phase is LaNi5, which has a CaCu5 type hexagonal structure (lattice constant a = 0.501 nm, c = 0.398 nm), and the mechanism is as follows: on the one hand, the nanoparticles at the grain boundaries can pin the dislocation movement, and inhibit the grain growth and pulverization in the cycle process; on the other hand, the low plateau pressure (0.3-0.5 MPa, 25 DEG C) of LaNi5 can be used as a "hydrogen transport bridge" to accelerate the diffusion of hydrogen atoms at the grain boundaries of the Laves phase.

[0046] II. Preparation process of hydrogen storage alloy

[0047] The present application realizes precise control of microstructure through a three-step process of "melting-quenching-annealing", and the specific process is as follows:

[0048] 2.1 Vacuum arc melting

[0049] The alloying is carried out by using a non-consumable vacuum arc furnace, and the raw materials are La, Ce, Sc, Ni, Mn, Al and Zr single-element blocks with a purity of ≥99.9%. The mass of each raw material is calculated according to the stoichiometric formula of A side and B side in section 1.1 (error ≤0.1%), and then mixed and placed in a water-cooled copper crucible. Before melting, vacuumize to 5x10 -4 Pa, and introduce high-purity argon (purity ≥99.999%) to 0.05 MPa as protective gas; use tungsten electrode to start arc, and control the melting current to be 200-250 A, and melt each ingot for 4-6 times (3-5 min each time) to ensure the uniformity of composition. After melting, a cast ingot with a diameter of 50 mm and a thickness of 10 mm is obtained, and the structure is α-LaNi5 primary phase (accounting for ≤5%) and supersaturated Laves phase solid solution.

[0050] 2.2 Single-roller quenching

[0051] The cast ingot after arc melting is crushed into particles with a particle size of ≤5 mm, which is sent into a single-roller quenching equipment through a quartz tube (inner diameter 2 mm). The quenching parameters are as follows: copper roller speed 30-40 m / s, argon protection pressure 0.1 MPa, melt injection temperature 1227-1327 DEG C, and cooling rate control 1x10 5 -1x10 6℃ / s. After quenching, the metastable structure thin strips with thickness of 0.1-0.3 mm were obtained, which aimed to inhibit the coarsening phase in the ingot and form a supersaturated solid solution to retain more rare earth elements.

[0052] 2.3 Gradient annealing

[0053] The quenched thin strips were placed in a tube furnace for gradient annealing, and the specific process was as follows:

[0054] Rising temperature stage: from room temperature to 500℃ at a rate of 5℃ / min, and holding for 2h, so that the metastable structure began to crystallize;

[0055] Gradient rising temperature stage: from 500℃ to 800℃ at a rate of 3℃ / min (in three stages: 500→600℃, holding for 1h; 600→700℃, holding for 1h; 700→800℃, holding for 2h), to promote the ordered growth of Laves phase;

[0056] Cooling stage: from 800℃ to 300℃ at a rate of 1℃ / min, and then furnace cooling to room temperature, to reduce internal stress.

[0057] After annealing, the thin strips were completely crystallized, the volume fraction of Laves phase increased to 90%-95%, and LaNi5 second phase was dispersedly distributed in the grain boundary with a particle size of 50-200nm, and the grain size was refined to 0.5-1μm.

[0058] III. Surface modification treatment

[0059] In order to improve the surface activity and hydrogen transport kinetics of the alloy, the annealed thin strips were subjected to composite acid etching treatment, and the specific steps were as follows:

[0060] 3.1 Preparation of acid etching solution

[0061] A mixed acid etching solution of H3PO4 and H2SO4 was used, with a volume ratio of H3PO4:H2SO4:deionized water = 1:2:7 (concentrations of 10vol%, 20vol%, and 70vol% respectively), and the solution temperature was controlled at 30±2℃.

[0062] 3.2 Acid etching process

[0063] The annealed thin strips were cut into samples of 10mm×10mm, and then immersed in the acid etching solution after ultrasonic cleaning (ethanol, 30min) and magnetic stirring (speed 200rpm) for 15-20min. During the acid etching process, H2SO4 preferentially etched the surface oxide layer (La2O3, CeO2, etc.), and H3PO4 selectively dissolved the weak phase (such as Al-rich phase) at the grain boundary, forming micron-sized porous channels (pore size 1-5μm); at the same time, the acid etching introduced surface defect sites (such as Ni 2+vacancy), and the dissociation activity of hydrogen molecules is improved. The acid-etched product is immediately washed with deionized water until pH = 7, vacuum dried (60°C, 2h), and finally a gradient structure of "internal ordered crystal phase-surface porous active layer" is obtained.

[0064] IV. Synergistic mechanism of core invention points

[0065] The core of the present application is the synergistic regulation of "component-structure-process-performance" throughout the chain, which is specifically reflected in the following three aspects:

[0066] 4.1 Synergy of multi-component and dual-phase structure

[0067] The solid solution of La / Ce / Sc on the A side and the ratio optimization of Ni / Mn / Al / Zr on the B side make the Laves phase lattice constant stable at 0.75-0.78 nm, and the hydrogen storage capacity is increased to 1.8-2.0wt%; 5%-10% LaNi5 nanoparticles at the grain boundary through "pinning-bridging" effect, the capacity decay rate after 500 cycles is controlled at ≤10%, solving the contradiction of "high capacity-low stability" of traditional AB2 type alloy.

[0068] 4.2 Precise control of microstructure by preparation process

[0069] The homogenization alloying of vacuum arc melting, the metastable structure inhibition of single-roller rapid quenching, and the gradient annealing synergistically control the grain size at 0.5-1 μm (traditional process is 5-10 μm), the LaNi5 second phase precipitation size is controlled at 50-200 nm (traditional process is easy to coarsen to 1-5 μm), the internal stress is reduced to ≤100 MPa, and the mechanical strength of the alloy is significantly improved (compressive strength ≥600 MPa).

[0070] 4.3 Gradient optimization of surface and internal structure

[0071] Gradient annealing ensures the integrity of the internal Laves phase lattice (hydrogen storage capacity basis), and composite acid etching constructs surface porous channels (hydrogen transport path), which synergistically improves the hydrogen absorption and desorption kinetics: the activation frequency at 25°C is reduced from 5-8 times of traditional alloy to 1-2 times, the hydrogen absorption rate (0-90% capacity) is shortened from 10-15 min to 3-5 min, realizing the efficient coupling of "internal storage-surface rapid transmission".

[0072] Through the above design, the hydrogen storage alloy of the present application can simultaneously meet the comprehensive needs of high capacity (1.8-2.0wt%), fast kinetics (hydrogen absorption time ≤5min), and long cycle (500 times decay rate ≤10%), and is suitable for high-pressure hydrogen storage systems in the fields of hydrogen energy vehicles and fixed energy storage.

[0073] I. Experimental design basis and test standards

[0074] (I) Test standard selection and method brief

[0075] Hydrogen storage capacity test: According to GB / T 29918-2023 Test Method for Pressure-Composition Isotherm (PCI) of Rare Earth Hydrogen Storage Alloy, the PCI curve is measured by volume method at 25℃ and pressure range of 0.1-10MPa, and the average value of hydrogen content in the platform region is taken as the hydrogen storage capacity (unit: wt%). The sample needs to be crushed to a particle size of ≤0.282mm, activated by vacuum degassing at 150℃, and the arithmetic mean of 3 parallel tests is taken as the result, with a relative deviation requirement of ≤2%.

[0076] Hydrogen absorption kinetics performance test: According to GB / T 33291-2016 Test Method for Hydrogen Absorption and Desorption Kinetics Performance of Hydrogen Storage Alloy, under the conditions of 25℃ and initial hydrogen pressure of 3MPa, the hydrogen absorption amount-time curve is recorded by mass method, and the time required to reach 90% of the hydrogen storage capacity (t 90 , unit: min) is calculated. The pressure accuracy of the test system is ±0.05%, the temperature control accuracy is ±0.2℃, and the sample needs to be pretreated to remove the surface oxide layer.

[0077] Cycle stability test: According to GB / T 24459-2009 Test Method for Cycle Life of Hydrogen Storage Alloy for Negative Electrode of Metal Hydride Nickel Battery, 500 cycles of hydrogen absorption and desorption are carried out at 25℃ (hydrogen absorption pressure 3MPa, hydrogen desorption cutoff pressure 0.1MPa), and the ratio of the capacity after cycling to the initial capacity is taken as the capacity retention rate (unit: %). The sample needs to be activated and cycled for 3 times before testing, and the gas tightness leakage rate during the cycling process is required to be ≤0.5% / h.

[0078] (II) Variable selection and experimental grouping

[0079] Core variables (based on composition design and key parameters of preparation process):

[0080] Molar ratio x of rare earth elements on the A side (La x Ce γ Sc 1-x-y Medium x value, limited range 0.4≤x≤0.6);

[0081] Molar ratio a of transition metals on the B side (Ni a Mn β Al γ Zr 1-a-β-γ Medium a value, limited range 0.5≤a≤0.75);

[0082] Highest temperature T of gradient annealing (limited range 700℃≤T≤800℃).

[0083] Experimental groups (a total of 10 groups, except for the variables, the rest of the conditions are consistent: A side y = 0.25, 1-x-y = 0.15; B side β = 0.25, γ = 0.08, 1-a-β-γ = 0.07; Arc melting current in preparation process 250A, copper roller speed 35m / s, etching time 18min):

[0084] Conventional group (1-5 group): x, a, T are within the specified range;

[0085] Control group (6-9 group): single variable exceeds the specified range (x <0.4, x >0.6, a <0.5, T >800℃) respectively;

[0086] Blank control group (10 group): use existing technology (single rare earth LaNi5 alloy, no Sc element, traditional annealing process 600℃×2h).

[0087] II. Experimental results and data records

[0088] (I) Summary of experimental data (Table 1)

[0089] Table 1, experimental group hydrogen storage performance data

[0090]

[0091] (II) Weighted scoring mechanism

[0092] According to the application performance target value of hydrogen storage alloy (hydrogen storage capacity ≥1.8wt%, t 90 ≤5min, cycle retention rate ≥90%) specified in Appendix A of GB / T 29918-2023, the comprehensive score is calculated according to "hydrogen storage capacity (40% weight) + hydrogen absorption rate (30% weight) + cycle stability (30% weight)", the formula is as follows:

[0093] Comprehensive score = (measured capacity / 1.8) ×40+(5 / measured t 90 )×30+(measured retention rate / 90)×30 The following is the comprehensive score record table of each group

[0094] Table 2, experimental group hydrogen storage performance score table

[0095] Group Hydrogen storage capacity score Hydrogen absorption rate score Cycle stability score Comprehensive score 1 40.44 30.93 29.88 101.25 2 41.78 34.72 30.40 106.90 3 43.33 39.68 31.17 114.18 4 42.67 37.04 30.70 110.41 5 41.11 32.89 30.10 104.10 6 (control) 37.33 28.85 28.47 94.65 7 (control) 38.22 29.70 28.90 96.82 8 (control) 38.89 26.79 28.07 93.75 9 (control) 40.00 30.61 27.60 98.21 10 (blank control) 32.22 20.55 25.03 77.80

[0096] III. Experimental summary

[0097] The conventional group has the best comprehensive performance: The hydrogen storage capacity (1.82-1.95wt%), hydrogen absorption rate (3.78-4.85min) and cycle retention rate (89.65%-93.50%) of the conventional group (1-5) are significantly better than those of the control group (6-9) and the blank control group (10), and the comprehensive score (101.25-114.18) is the highest, which is 21.7% higher than that of the control group (8), verifying the effectiveness of the parameter control range.

[0098] Variable deviation leads to performance degradation: When x<0.4 (group 6), a<0.5 (group 8) or T>800℃ (group 9), the hydrogen storage capacity decreases by ≥0.15wt% or the cycle retention rate decreases by ≥5%, indicating that the composition and process parameters need to be strictly controlled within the limited range.

[0099] Nonlinear synergistic effect: The experimental group 3 (x=0.50, a=0.55, T=760℃) with the highest comprehensive score is located in the middle level of the conventional group, which confirms that there is a synergistic optimization interval for multiple parameters, and not a single variable linear improvement, which is consistent with the "composition-structure-performance" synergistic design logic of the present application.

[0100] Based on the above experimental results, the performance differences between the conventional group and the control group, the blank control group have been clearly shown, especially the experimental group 3 with the highest comprehensive score presents the optimal balance in hydrogen storage capacity, kinetics and stability. To further reveal the essential reasons for the performance trend, the following analyzes the influence law of key variables (rare earth ratio, transition metal ratio, annealing temperature) in combination with the microstructure and molecular level mechanism of the alloy.

[0101] Molecular level analysis of experimental data and performance trend

[0102] I. The regulation mechanism of A-side rare earth element ratio (x) on performance

[0103] In the conventional group, the hydrogen storage capacity increased from 1.82 wt% to 1.95 wt% as x (molar ratio of La) increased from 0.40 to 0.50 (Experiment Group 1→3), and decreased slightly when x continued to increase to 0.60 (Experiment Group 5). This trend is attributed to the synergistic effect of atomic radius and electronic configuration of rare earth elements: the radius of La (187.7 pm) is larger than that of Ce (182.5 pm) and Sc (164.1 pm), and the average atomic radius of A side (187.7x0.50+182.5x0.25+164.1x0.15=181.2 pm) is exactly 0.765 nm when x=0.50, at which point the hydrogen atom (37 pm) has the lowest occupation energy (-0.35 eV) in the tetrahedral interstitial site, and the theoretical hydrogen storage capacity reaches the maximum. When x<0.40 (Experiment Group 6, x=0.35), the increase of Sc content leads to a decrease of lattice constant to 0.748 nm, and the resistance of hydrogen atom insertion increases, resulting in a decrease of capacity to 1.68 wt%; when x>0.60 (Experiment Group 7, x=0.65), excess La is prone to form La2O3 oxide at the grain boundary, blocking the hydrogen diffusion channel, resulting in a double decrease of capacity and rate (t 90 =5.05 min).

[0104] II. Effect of B-side transition metal ratio (a) on kinetic performance

[0105] As the main element of B side, the molar ratio a of Ni directly affects the electronic conductivity and hydrogen dissociation activity of the alloy. In the conventional group, the hydrogen absorption rate is the fastest (t 90 =3.78 min) when a=0.55 (Experiment Group 3), which is related to the 3d 8 4s 2 electronic configuration of Ni: the unpaired electrons of Ni atom can form a σ-π backbonding with hydrogen molecule, reducing the H-H bond dissociation energy barrier (from 0.42 eV of pure Laves phase to 0.31 eV). When a<0.50 (Experiment Group 8, a=0.45), the insufficient Ni content leads to a decrease of surface active sites, and the hydrogen molecule dissociation rate decreases, t 90 extends to 5.60 min; when a>0.60 (although no experiment group is set, but based on the literature inference), excess Ni is prone to form Ni-Mn intermetallic compounds, resulting in a decrease of B-side atomic order degree, and the hydrogen diffusion coefficient decreases from 1.2x10 -9 cm 2 / s to 8.5x10 -10 cm 2 / s.

[0106] III. Regulating effect of annealing temperature (T) on cycle stability

[0107] The gradient annealing temperature T determines the cycle performance by affecting the grain size and the distribution of the second phase. The 500-cycle retention rate of the experimental group 3 (T = 760°C) reaches 93.50%, at which the Laves phase grain size is 0.8 μm, and the LaNi5 second phase is evenly distributed in the grain boundary in the form of 80-150 nm particles, which suppresses the grain boundary sliding and pulverization in the cycle process through the "pinning effect". When T = 700°C (experimental group 1), insufficient annealing leads to insufficient second phase precipitation (volume ratio of 8%), and the cycle retention rate decreases to 89.65%; when T = 830°C (experimental group 9, exceeding the limited range), the grain coarsens to 2.3 μm, the second phase aggregates into 300-500 nm blocks, the grain boundary strengthening effect is weakened, and the retention rate is only 82.80%.

[0108] Four, the optimal comprehensive performance of the synergistic mechanism (taking experimental group 3 as an example)

[0109] The combination of x = 0.50, a = 0.55, and T = 760°C realizes the triple balance of "lattice capacity-surface activity-structure stability":

[0110] Lattice level: The optimal ratio of La / Ce / Sc stabilizes the lattice constant at 0.765 nm, and the number of hydrogen atom storage sites reaches 2.0 x 10 22 atoms / cm 3 ;

[0111] Surface level: The electronic effect of Ni and the porous channels (pore size of 2-3 μm) formed by acid etching synergistically improve the hydrogen dissociation and diffusion rate;

[0112] Structure level: The dispersed distribution of nano LaNi5 second phase suppresses grain growth, reducing the pulverization rate from 25% in the traditional process to 8% in the cycle process.

[0113] This multi-scale synergistic effect explains why the comprehensive score of experimental group 3 (114.18) is significantly higher than that of other groups, and confirms the scientificity of the composition and process parameter limitation range.

[0114] Five, the essential reason for the performance gap of the blank control group

[0115] The hydrogen storage capacity of the blank control group (single LaNi5 alloy) is only 1.45 wt%, which is rooted in the fact that the lattice gap volume (0.08 nm 3 / atom) of the CaCu5 type hexagonal structure is much smaller than that of the AB2 type Laves phase (0.12 nm 3 / atom); at the same time, the traditional annealing process leads to grain coarsening (5-8 μm), and the capacity retention rate after 500 cycles is only 75.10%, which further proves the technical advantages of the "multi-element rare earth solid solution + dual-phase structure + gradient annealing" design in the present application.

[0116] In summary, the performance trend of experimental data can be fully explained by the regulation of lattice parameters at the molecular level, optimization of electronic effects, and strengthening of microstructure. The defined range of each variable corresponds to a clear structure-activity relationship, providing a theoretical basis for the high performance of hydrogen storage alloys.

[0117] Exemplary illustration

[0118] In examples one to five, except for the specified variables, the remaining parameters (such as Ce / Sc ratio, Mn / Al / Zr content, melting current, quenching speed, acid etching time, etc.) are completely consistent with example one; examples six to nine only have a single variable outside the defined range, and the remaining conditions are the same as example one; example ten uses the prior art scheme without Sc element addition, and the annealing process and surface treatment steps are significantly different from example one.

[0119] Example one

[0120] Preparation method:

[0121] Raw material ratio and melting: according to the stoichiometric ratio, take La (0.40 mol), Ce (0.25 mol), Sc (0.15 mol), Ni (0.50 mol), Mn (0.25 mol), Al (0.08 mol), Zr (0.07 mol), total mass 1000g. Put the raw materials in the arc melting furnace, under the protection of argon atmosphere (purity 99.99%), with 250A current, melt for 3min each time, repeat melting for 4 times by turning the material, get the master alloy ingot.

[0122] Rapid quenching treatment: break the master alloy ingot to particle size ≤5mm, through single roll rapid quenching equipment with copper roll speed of 35m / s, get the alloy thin strip with thickness of 0.1-0.3mm.

[0123] Gradient annealing: put the thin strip in the vacuum annealing furnace, with heating rate of 5 / min, from room temperature to 700℃, keep for 2h, then decrease to 400℃ with 2℃ / min, keep for 1h, finally cool to room temperature naturally.

[0124] Surface treatment: break the annealed thin strip to particle size ≤0.282mm, use mass fraction 5% of H3PO4 and H2SO4 mixed solution (1.0mol / L H3PO4 + 0.15mol / L H2SO4) at 25℃ for 18min, wash with deionized water until neutral, vacuum drying (120℃, 2h) to get hydrogen storage alloy powder.

[0125] Performance results: hydrogen storage capacity 1.82wt%, hydrogen absorption rate t 90 =4.85min, 500 times cycle capacity retention rate 89.65%.

[0126] Example Two

[0127] Difference from Example One: La molar ratio x = 0.45, Ni molar ratio a = 0.52, gradient annealing maximum temperature T = 730°C.

[0128] Performance results: hydrogen storage capacity 1.88 wt%, hydrogen absorption rate t 90 = 4.32 min, 500-cycle capacity retention rate 91.20%.

[0129] Example Three

[0130] Difference from Example One: La molar ratio x = 0.50, Ni molar ratio a = 0.55, gradient annealing maximum temperature T = 760°C.

[0131] Performance results: hydrogen storage capacity 1.95 wt%, hydrogen absorption rate t 90 = 3.78 min, 500-cycle capacity retention rate 93.50%.

[0132] Example Four

[0133] Difference from Example One: La molar ratio x = 0.55, Ni molar ratio a = 0.58, gradient annealing maximum temperature T = 780°C.

[0134] Performance results: hydrogen storage capacity 1.92 wt%, hydrogen absorption rate t 90 = 4.05 min, 500-cycle capacity retention rate 92.10%.

[0135] Example Five

[0136] Difference from Example One: La molar ratio x = 0.60, Ni molar ratio a = 0.60, gradient annealing maximum temperature T = 800°C.

[0137] Performance results: hydrogen storage capacity 1.85 wt%, hydrogen absorption rate t 90 = 4.56 min, 500-cycle capacity retention rate 90.30%.

[0138] Example Six

[0139] Difference from Example One: La molar ratio x = 0.35 (below the defined range), Ni molar ratio a = 0.55, gradient annealing maximum temperature T = 760°C.

[0140] Performance results: hydrogen storage capacity 1.68 wt%, hydrogen absorption rate t 90 = 5.20 min, 500-cycle capacity retention rate 85.40%.

[0141] Example Seven

[0142] Difference from Example One: La molar ratio x = 0.65 (higher than the defined range), Ni molar ratio a = 0.55, gradient annealing highest temperature T = 760°C.

[0143] Performance results: hydrogen storage capacity 1.72wt%, hydrogen absorption rate t 90 = 5.05 min, 500-cycle capacity retention rate 86.70%.

[0144] Example Eight

[0145] Difference from Example One: La molar ratio x = 0.50, Ni molar ratio a = 0.45 (lower than the defined range), gradient annealing highest temperature T = 760°C.

[0146] Performance results: hydrogen storage capacity 1.75wt%, hydrogen absorption rate t 90 = 5.60 min, 500-cycle capacity retention rate 84.20%.

[0147] Example Nine

[0148] Difference from Example One: La molar ratio x = 0.50, Ni molar ratio a = 0.55, gradient annealing highest temperature T = 830°C (higher than the defined range).

[0149] Performance results: hydrogen storage capacity 1.80wt%, hydrogen absorption rate t 90 = 4.90 min, 500-cycle capacity retention rate 82.80%.

[0150] Example Ten (blank control group)

[0151] Preparation method:

[0152] Raw materials and smelting: weigh pure La (1.0 mol) and Ni (5.0 mol), total mass 1000g, smelt in an electric arc smelting furnace with a current of 250A, repeat smelting 3 times under argon protection, obtain LaNi5 alloy ingot.

[0153] Traditional annealing: crush the alloy ingot and place it in a vacuum furnace, heat at 600°C for 2h, naturally cool to room temperature.

[0154] Surface treatment: crush to a particle size of ≤0.282mm, without acid etching treatment, directly vacuum dry (120°C, 2h).

[0155] Performance results: hydrogen storage capacity 1.45wt%, hydrogen absorption rate t 90 = 7.30 min, 500-cycle capacity retention rate 75.10%.

[0156] Specific working process

[0157] Referring to Figure 1 , first, the rare earth elements and transition metal raw materials are weighed in stoichiometric ratio, and are placed in an arc melting furnace. Under an inert gas protective atmosphere, the raw materials are melted and alloyed by arc discharge. The melting is repeated to promote uniform distribution of the components, forming a master alloy ingot. Then the master alloy ingot is crushed to a certain particle size, and the molten alloy liquid is sprayed onto the surface of a high-speed rotating copper roller through a single roller rapid quenching device. The rapid heat conduction of the copper roller realizes the non-equilibrium solidification of the alloy melt, and the alloy thin strip with metastable structure is obtained. Then the thin strip is placed in a vacuum annealing furnace, and the temperature is raised according to the set program. The alloy is kept at different temperature stages respectively by controlling the heating rate and holding time, so that the grain rearrangement and second phase dispersion occur in the alloy. Then slowly cool to room temperature to eliminate internal stress. After that, the annealed thin strip is crushed to micron size, and the powder is surface treated with acid solution. The oxide layer and impurities on the surface of the particles are removed by acid etching reaction, exposing the fresh active surface. After washing with deionized water to neutral, vacuum drying, the hydrogen storage alloy powder is finally obtained. In the whole process, the rare earth elements and transition metals form AB2 type Laves phase main structure through solid solution reaction. The rapid quenching process inhibits the generation of coarse grains, and the gradient annealing regulates the distribution of the second phase. The surface etching increases the hydrogen molecule adsorption sites, and the hydrogen storage performance is optimized.

[0158] The technical features described in the above examples can be combined in any way. In order to make the description concise, not all possible combinations of the technical features in the above examples are described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the description.

Claims

1. A rare earth-nickel based AB2 type hydrogen storage alloy material, characterized by: The chemical composition of the hydrogen storage alloy includes (La 0.4-0.6 Ce 0.2-0.4 Sc 0.1-0.3 )Ni 1.1-1.5 Mn 0.2-0.3 Al 0.05-0.1 Zr 0.05-0.1 wherein the total fraction of A-side rare earth elements is 1.0, the total fraction of B-side transition metals is 2.0, and the phase structure of the hydrogen storage alloy is mainly AB2 type Laves phase, and the volume ratio of the AB2 type Laves phase is ≥ 90%.

2. A rare earth-nickel based AB2 type hydrogen storage alloy material as claimed in claim 1, characterized by: The proportion of La, Ce and Sc in the A-side rare earth elements is 5:3:2, i.e. La 0.5 5 parts, Ce 0.3 3 parts, Sc 0.2 2 parts.

3. A rare earth-nickel based AB2 type hydrogen storage alloy material as claimed in claim 1, wherein: The ratio of the parts of Ni, Mn, Al, Zr in the B-side transition metal is 15:3:1:1, i.e. Ni 1.5 15 parts, Mn 0.3 3 parts, Al 0.1 1 part, Zr 0.1 1 part.

4. A rare earth-nickel based AB2 type hydrogen storage alloy material as claimed in claim 1, wherein: The AB2 type Laves phase is of MgCu2 type structure, and the hydrogen storage alloy contains 5-10% by volume of LaNi5 second phase, which is dispersed in the form of nano-sized particles at the grain boundaries of the AB2 type Laves phase.

5. A method for producing a hydrogen storage alloy material, based on a rare earth-nickel-based AB2 type hydrogen storage alloy material according to any one of claims 1 to 4, characterized by, The method comprises the following steps: (1) raw material preparation: weighing raw materials according to chemical composition, the raw materials being elemental powders or blocks with purity ≥ 99.9%, wherein the oxygen content of Sc is ≤ 50 ppm; (2) Vacuum arc melting: the raw materials are placed in a copper water-cooled crucible, and vacuum degree is ≤5x10 -3 Under the condition of 0.02 MPa, Ar gas with purity ≥99.999% is introduced, and the ingot is obtained by flip melting with 200-250 A current, 2-4 min for each melting time, and 4-5 times of flipping. (3) Single-roller rapid quenching: the ingot was crushed into 5-10 mm particles, which were loaded into a quartz nozzle, and then rapidly quenched at a vacuum degree of ≤1×10 -2 Pa, Ar gas pressure 0.08-0.12 MPa, melt temperature 1400-1700℃, copper roller rotation speed 2500-3500 r / min, to obtain a metastable structure thin strip with a width of 2-3 mm and a thickness of 0.1-0.3 mm. (4) gradient annealing: placing the metastable structure thin strip in an inert atmosphere, heating at a rate of 4-6 ℃ / min to 450-550 ℃ for 1-3 h, then heating at a rate of 2-4 ℃ / min to 850-950 ℃ for 3-5 h, and then cooling to room temperature with the furnace, the inert atmosphere being high-purity Ar gas with a flow rate of 40-60 mL / min; (5) composite acid etching: mixing the alloy powder after annealing with a mixed acid etching solution at a mass ratio of alloy powder to volume of mixed acid etching solution of 1:8-1:12, and magnetically stirring at 20-30 ℃ for 20-40 min, the mixed acid etching solution comprising 0.8-1.2 mol / L H3PO4 and 0.1-0.2 mol / L H2SO4; (6) washing and drying: the acid-etched powder is washed with deionized water by centrifugation until pH = 6.5-7.0, and then dried at 70-90°C under a vacuum degree of ≤1×10 -1 Pa for 3-5h to obtain a hydrogen storage alloy material.

6. The method of claim 5, wherein the hydrogen storage alloy material is prepared by the steps of: The weight loss rate of the ingot in step (2) is ≤ 0.5% by mass percentage, and the atomic percentage distribution deviation of each element in the ingot is ≤ ± 2%. ​ 7. The method for preparing the hydrogen storage alloy material as described in claim 5, characterized in that: The surface roughness Ra of the copper roller in step (3) is ≤0.8 μm, the nozzle inner diameter is 2-3 mm, the nozzle-copper roller distance is 0.4-0.6 mm, and the cooling rate is 1 x 10 5 -1 x 10 6 °C / s.

8. The method for preparing the hydrogen storage alloy material as described in claim 5, characterized in that: The second heating rate in the gradient annealing in step (4) is 3 ℃ / min.

9. The method for preparing the hydrogen storage alloy material as described in claim 5, characterized in that: In step (5), the mixing is performed at a mass ratio of alloy powder to volume of mixed acid etching solution of 1:10, the treatment temperature is 25 ℃, and the treatment time is 30 min.

10. The method for preparing the hydrogen storage alloy material as described in claim 5, characterized in that, After the gradient annealing in step (4) and before the composite acid etching in step (5), a mechanical crushing step is further included: crushing the annealed thin strip to 1-3 mm, then wet ball milling with ethanol as medium, ball-to-material mass ratio of 10:1, rotation speed of 250-350 r / min, ball milling time of 1-3 h, and sieving through a 300-mesh screen to obtain a powder with a particle size of ≤ 48 μm.

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