A hydrogen storage alloy material with wide temperature range and a preparation method thereof

Abstract

The application discloses a wide-temperature-range hydrogen storage alloy material and a preparation method thereof. 0.65‑ 0.71 Zr 0.01‑0.02 Y 0.25‑0.28 Mg 0.03‑0.05 Ni 3.70‑ 3.80 Al 0.22‑0.25 The alloy is prepared through vacuum induction melting and partition annealing heat treatment in sequence, and the prepared hydrogen storage alloy has good wide-temperature-range performance, shows good environmental compatibility and can work efficiently under high-temperature / low-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of nickel-metal hydride battery technology, and in particular to a wide-temperature-range hydrogen storage alloy material and its preparation method. Background Technology

[0002] The booming development of new energy vehicles has placed higher demands on the battery market. In low-temperature environments, the drastic decrease in battery discharge capacity and performance directly impacts their usability. Taking lithium-ion batteries as an example, when the operating temperature drops from 20°C to 0°C, the battery capacity decreases by 20%. Poor low-temperature discharge performance severely restricts the popularization and development of new energy electric vehicles.

[0003] Nickel-metal hydride (NiMH) batteries are environmentally friendly and have broad application prospects in the field of new energy vehicles. The application of new energy electric vehicles places more stringent demands on the discharge performance of NiMH batteries. NiMH batteries must not only have good discharge performance at high temperatures but also operate normally at -40℃. Therefore, it is necessary to develop new wide-temperature-range NiMH batteries that can operate efficiently within a temperature range of -40℃ to 60℃, especially achieving normal charge and discharge under low-temperature conditions. Achieving this goal is closely related to the negative electrode material of NiMH batteries—hydrogen storage alloys. Current research on the low-temperature performance of NiMH batteries mainly focuses on AB5-type rare-earth hydrogen storage alloys. However, this type of alloy has a low electrochemical capacity, which is insufficient to meet the high-capacity requirements of the NiMH battery market. Therefore, it is necessary to develop superlattice rare-earth hydrogen storage alloys with higher room-temperature electrochemical discharge capacity and good discharge performance under both high and low temperature conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a wide-temperature-range hydrogen storage alloy material and its preparation method, wherein the molecular formula of the hydrogen storage material is La. 0.65-0.71 Zr 0.01-0.02 Y 0.25-0.28 Mg 0.03-0.05 Ni 3.70-3.80 Al 0.22-0.25 The alloy is prepared by induction melting and partitioned annealing heat treatment. By rationally designing the types and contents of elements, controlling the chemical composition of the alloy and strictly controlling the type and content of phase structure, the high-temperature / low-temperature discharge performance of the alloy is improved, enabling it to achieve wide-temperature-range operation.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A wide-temperature-range hydrogen storage alloy material with the general chemical formula: La 0.65-0.71 Zr 0.01-0.02 Y 0.25-0.28 Mg 0.03- 0.05 Ni3.70-3.80 Al 0.22-0.25 As a limitation of the present invention, the alloy is a multiphase alloy containing an AB5-type phase structure and also containing A5B. 19 Type 2 and / or AB4 type phase structure.

[0007] As a further limitation of the present invention, the content of the AB5 type phase structure in the alloy is 10-25 wt%.

[0008] In this invention, the alloy is a multiphase alloy containing an AB5-type phase structure and an A5B phase. 19 Type A5B and / or Type A4 superlattice alloys. In multiphase alloy structures, phase boundaries can provide channels for hydrogen diffusion, promoting alloy kinetic properties. Compared to Type AB3 and Type A2B7 structures, Type A5B... 19 Both the AB4 phase structure and the AB5 phase structure improve the kinetic performance and cycle stability of the alloy. The AB5 phase structure can also promote the kinetic performance of the alloy, but the capacity of the AB5 alloy is relatively low, which is not conducive to the electrochemical discharge capacity of the alloy. Therefore, the AB5 phase structure should be controlled within a certain range. The high / low temperature discharge performance can be adjusted and optimized by regulating the phase structure composition to obtain a wide temperature range hydrogen storage alloy.

[0009] This invention also provides a method for preparing a wide-temperature-range hydrogen storage alloy material, which is carried out sequentially according to the following preparation process:

[0010] (1) Vacuum induction melting:

[0011] According to the proportions of the hydrogen storage alloy, the elemental metals are mixed evenly and put into a vacuum induction melting furnace to melt, refine and cast the materials to obtain the as-cast hydrogen storage alloy. In this process, the first batch of materials is an element with a high melting point and the second batch of materials is the volatile element magnesium.

[0012] (2) Partial annealing heat treatment:

[0013] The as-cast hydrogen storage alloy was placed in an annealing furnace for secondary annealing heat treatment, which was carried out according to the following steps:

[0014] (S1) First heating stage: heat from room temperature to 600℃ and hold for 1 hour;

[0015] (S2) Second heating stage: Heat from 600℃ to 850℃ and hold for 1 hour;

[0016] (S3) Third heating stage: Heat from 850℃ to 990~1100℃ and hold for 10-18h;

[0017] (S4) Cooling stage: Cool to room temperature with the furnace.

[0018] As a limitation of the preparation method of the present invention, the heating rates of each heating stage are as follows:

[0019] The heating rate in the first heating stage is 4℃ / min, and the heating rate in the second heating stage is 2℃ / min.

[0020] The heating rate in the third heating stage is 2℃ / min.

[0021] The partitioned annealing heat treatment method of this invention can effectively promote the transformation of alloy crystal structure, reduce internal stress, refine grains, reduce lattice defects, and make the alloy microstructure uniform. The alloy provided by this invention contains Mg, an element with a low melting point. The first stage of heating is carried out at a relatively fast heating rate of 4℃ / min to 600℃ and held for 1 hour to reduce the volatilization of Mg and promote the uniform diffusion of Mg in the system to reach equilibrium. The second heating stage is carried out at a heating rate of 2℃ / min from the lower temperature of 600℃ to the higher temperature region. In this stage, the free enthalpy in the crystal increases, which increases the driving force for alloy crystallization. The A2B7 phase and the CaCu5 phase in the alloy form A5B through peritectic reaction. 19 During the heat treatment process, the grains continuously grow. When the heating rate is too fast, the nucleation rate exceeds the grain growth rate, resulting in more dislocations around the grains, stress concentration, and damage to the alloy's structural stability. Conversely, when the heating rate is too slow, the grain growth rate is very slow. The third heating stage involves heating from 850℃ to 990–1100℃ at a rate of 2℃ / min. This stage is A5B. 19 The suitable temperature range for grain growth in the AB4 and 3R type phase structures is as follows: below 990℃, the suitable temperature for peritectic reaction is not reached; while above 1100℃, low-melting-point elements easily transform into gases and precipitate from the alloy, leading to grain growth. Within this temperature range, the AB4 and 3R type phases exhibit suitable growth. 19 The Ce5Co type structure 19 The structure is transformed into a 2H type A5B. 19 Type Pr5Co 19 Additionally, Pr5Co 19 Further transformation leads to the formation of the AB4-type phase structure. If the holding time at this stage is too short, the peritectic reaction will be incomplete; if it is too long, recrystallization will occur, resulting in grain growth. During the cooling process, the alloy cools naturally, and grain growth is completed.

[0022] Under high-temperature conditions, the thermodynamic stability of metal hydrides decreases, some hydrides decompose, and the negative electrode capacity decreases. Furthermore, high temperatures exacerbate alloy oxidation and corrosion, leading to irreversible loss of the alloy's electrochemical discharge capacity. Under low-temperature conditions, the decrease in nickel-metal hydride battery discharge capacity is mainly due to the deterioration of the alloy electrode's kinetic properties, resulting in a decrease in the electrocatalytic ability and hydrogen diffusion rate of the hydrogen storage alloy negative electrode. Therefore, to improve the high-temperature and low-temperature discharge capabilities of nickel-metal hydride batteries, it is necessary to comprehensively consider the alloy's chemical composition and phase structure, improve the thermodynamic stability and corrosion / oxidation resistance of metal hydrides, and enhance the alloy electrode's kinetic properties.

[0023] Traditional La–Mg–Ni hydrogen storage alloys are susceptible to oxidation and corrosion. In the electrolyte, the alloy's constituent elements form La(OH)3, Mg(OH)2, and Ni(OH)2 products, reducing the active material in the alloy electrode and causing capacity loss. Furthermore, corrosion products on the alloy surface increase resistance and reduce charge transfer rate. Replacing La with rare earth elements with high electronegativity can improve the alloy's corrosion resistance. La has a relatively low electronegativity of 1.1, while Y and Zr have electronegativity of 1.2 and 1.4 respectively, both higher than La, which is beneficial for improving corrosion resistance and reducing the reduction of active material. On the other hand, replacing Ni on the boron side with Al can also improve corrosion resistance. Al can form dense Al(OH)3 on the alloy surface, improving the stability of surface oxides, enhancing corrosion resistance, and suppressing irreversible capacity loss of the alloy electrode. In addition, Al also helps improve the alloy's thermodynamic stability.

[0024] To improve the low-temperature discharge performance of alloys, the main focus is on enhancing surface charge transfer and bulk hydrogen diffusion. Additionally, it's necessary to appropriately reduce the thermodynamic stability of metal hydrides and increase the hydrogen desorption capacity of the alloy electrode under low-temperature conditions. This also requires a multi-element alloy composition design strategy. La has an atomic radius of 0.188 nm, while Y and Zr have atomic radii of 0.181 nm and 0.160 nm, respectively, both lower than La. After partially replacing La atoms with these elements, the cell volume of the alloy's phase structure decreases, the hydrogen absorption / desorption plateau pressure increases, and the stability of the metal hydrides decreases. On the other hand, Y and Zr elements also have varying degrees of influence on the alloy's kinetic properties. For example, Zr is beneficial for improving the alloy's kinetic properties and promoting discharge at low temperatures. Ni can catalyze electrochemical hydrogen absorption and desorption reactions, improving the alloy's kinetic properties. Single-phase A2B7 and A5B... 19 Taking type alloy as an example, A5B 19The higher Ni content on the B side of the alloy results in better kinetic properties, with superior high-rate discharge and low-temperature discharge performance compared to the A2B7 alloy. Therefore, the kinetic properties of alloys can be improved by preparing alloys with a high B / A stoichiometric ratio. This invention prepares multiphase alloys by matching alloy components and controlling the alloy phase structure, thereby improving the alloy's kinetic properties. This is because the increased number of phase interfaces when multiple phase structures coexist provides channels for hydrogen atom diffusion, thus increasing the hydrogen diffusion rate and enhancing kinetic performance. In summary, the multiphase alloys designed in this invention facilitate the preparation of wide-temperature-range hydrogen storage alloys, resulting in hydrogen storage alloy electrode materials with excellent high / low-temperature discharge performance.

[0025] This invention provides a multi-element alloy containing Y, Zr, and Al elements in addition to La, Mg, and Ni. In addition to strictly controlling the chemical composition of the alloy, the phase structure composition of the alloy is precisely controlled and the grains are refined through a secondary annealing heat treatment method. This enhances the uniformity of the alloy structure, improves the alloy's corrosion / oxidation resistance and kinetic properties, thereby improving the alloy's discharge capability at high / low temperatures and obtaining a wide-temperature-range hydrogen storage alloy.

[0026] The preparation process described above in this invention is a whole, and the various steps are interconnected and influence each other.

[0027] The beneficial effects achieved by adopting the above-mentioned technical solution of the present invention are as follows:

[0028] 1. The hydrogen storage alloy electrode material provided by this invention has good discharge performance under both high and low temperature environments.

[0029] 2. The hydrogen storage alloy provided by this invention has a reasonable elemental composition, which not only improves the high-temperature and low-temperature discharge performance of the hydrogen storage alloy electrode, but also features a simple preparation method, easy process control, and uniform microstructure, ensuring the hydrogen storage performance of the alloy. Furthermore, the alloy contains no high-valence Nd element, effectively controlling alloy costs and facilitating the industrial-scale application of the alloy described in this invention.

[0030] 3. After preparation by the method of the present invention, the specific phase structure composition is controlled, and a wide-temperature range hydrogen storage alloy with good high-temperature / low-temperature discharge performance and cycle stability is finally obtained. The alloy prepared by the present invention has a discharge capacity of more than 345 mAh / g at room temperature, a discharge capacity of 320 mAh / g at 60℃, a low-temperature discharge capacity of more than 190 mAh / g at -40℃, and a capacity retention rate of more than 88% after 100 1C charge / discharge cycles.

[0031] The following will describe the wide-temperature-range hydrogen storage alloy material of the present invention in detail with reference to the embodiments. However, the embodiments shall not be regarded as limiting the scope of protection of the present invention. Attached Figure Description

[0032] Figure 1 The XRD patterns of the hydrogen storage alloys prepared in Examples 1-4 are shown below.

[0033] Figure 2 The activation curves of the hydrogen storage alloys prepared in Examples 1-4 are shown.

[0034] Figure 3 The discharge curve of the hydrogen storage alloy prepared in Example 1 under high temperature conditions;

[0035] Figure 4 The discharge curves of the hydrogen storage alloys prepared in Examples 1-4 under low temperature conditions are shown.

[0036] Figure 5 The diagram shows the cycle life of the hydrogen storage alloys prepared in Examples 1-4. Detailed Implementation

[0037] Unless otherwise specified, all raw materials used in the following examples are commercially available, and all preparation and testing methods used are existing methods. The induction melting temperature in the following examples is 1000-1500℃, and the melting time is 0.1-0.5h.

[0038] Example 1

[0039] The wide-temperature-range hydrogen storage alloy material prepared in this embodiment has the chemical composition La. 0.65 Zr 0.02 Y 0.28 Mg 0.0 5Ni 3.80 Al 0.0.25 The preparation process is as follows:

[0040] (1) Batching: La, Zr, Y, Mg, Ni and Al metals with a purity greater than 99.99% are used as raw materials. The required metal raw materials for each element are calculated according to the alloy chemical composition ratio. Considering the volatilization loss of different elements during the smelting process, the amount of materials used is increased appropriately according to the different types of elements.

[0041] (2) Induction melting: Metal raw materials La, Zr, Y, Mg, Ni and Al are charged into an induction melting furnace for melting. Mg, as a volatile element, is added into the induction melting furnace in a secondary feeding manner. After casting and cooling, the as-cast alloy is obtained.

[0042] (3) Secondary annealing heat treatment: Take the as-cast alloy, place it in an annealing jar, seal it, and then put it into a vacuum tube furnace for annealing heat treatment:

[0043] (S1) First heating stage: heating from room temperature to 600℃ at a rate of 4℃ / min, and holding for 1 hour;

[0044] (S2) Second heating stage: heating from 600℃ to 850℃ at a heating rate of 2℃ / min, and holding for 1 hour;

[0045] (S3) Third heating stage: heating from 850℃ to 990℃ at a heating rate of 2℃ / min, and holding at this target temperature for 18h;

[0046] (S4) Cool to room temperature with the furnace.

[0047] The obtained hydrogen storage alloy was mechanically pulverized, ground, and sieved (400 mesh). The alloy powder was then subjected to X-ray diffraction (XRD) testing to analyze the positions and intensity characteristics of the diffraction peaks in the XRD pattern. Figure 1 As shown, the alloy phase structure was found to be Pr5Co. 19 (21.0wt%), Ce5Co 19 (54.0wt%), LaNi5 (25.0wt%).

[0048] Example 2

[0049] The wide-temperature-range hydrogen storage alloy electrode material prepared in this embodiment has a chemical composition of La. 0.68 Zr 0.01 Y 0.27 Mg 0.04 Ni 3.76 Al 0.24 The preparation process is as follows:

[0050] (1) Batching: La, Zr, Y, Mg, Ni and Al metals with a purity greater than 99.99% are used as raw materials. The required metal raw materials for each element are calculated according to the alloy chemical composition ratio. Considering the volatilization loss of different elements during the smelting process, the amount of materials used is increased appropriately according to the different types of elements.

[0051] (2) Induction melting: Metal raw materials La, Zr, Y, Mg, Ni and Al are charged into an induction melting furnace for melting. Mg, as a volatile element, is added into the induction melting furnace in a secondary feeding manner. After casting and cooling, the as-cast alloy is obtained.

[0052] (3) Secondary annealing heat treatment: Take the as-cast alloy, place it in an annealing jar, seal it, and then put it into a vacuum tube furnace for annealing heat treatment:

[0053] (S1) First heating stage: heating from room temperature to 600℃ at a rate of 4℃ / min, and holding for 1 hour;

[0054] (S2) Second heating stage: heating from 600℃ to 850℃ at a heating rate of 2℃ / min, and holding for 1 hour;

[0055] (S2) Third heating stage: heating from 850℃ to 1000℃ at a heating rate of 2℃ / min, and holding at this target temperature for 15h;

[0056] (S3) Cool to room temperature with the furnace.

[0057] The obtained hydrogen storage alloy was mechanically pulverized, ground, and sieved (400 mesh). The alloy powder was then subjected to X-ray diffraction (XRD) testing to analyze the positions and intensity characteristics of the diffraction peaks in the XRD pattern. Figure 1 As shown, the alloy phase structure was found to be Pr5Co. 19 (19.6wt%), Ce5Co 19 (60.4wt%), LaNi5 (20.0wt%).

[0058] Example 3

[0059] The wide-temperature-range hydrogen storage alloy electrode material prepared in this embodiment has a chemical composition of La. 0.70 Zr 0.01 Y 0.26 Mg 0.03 Ni 3.74 Al 0.23 The preparation process is as follows:

[0060] (1) Batching: La, Zr, Y, Mg, Ni and Al metals with a purity greater than 99.99% are used as raw materials. The required metal raw materials for each element are calculated according to the alloy chemical composition ratio. Considering the volatilization loss of different elements during the smelting process, the amount of materials used is increased appropriately according to the different types of elements.

[0061] (2) Induction melting: The metal raw materials La, Zr, Y, Mg, Ni and Al are charged into the induction melting furnace for melting. Mg, as a volatile element, is added into the induction melting furnace in a secondary feeding method. After casting and cooling, the as-cast alloy is obtained.

[0062] (3) Secondary annealing heat treatment: Take the as-cast alloy, place it in an annealing jar, seal it, and then put it into a vacuum tube furnace for annealing heat treatment:

[0063] (S1) First heating stage: heating from room temperature to 600℃ at a rate of 4℃ / min, and holding for 1 hour;

[0064] (S2) Second heating stage: heating from 600℃ to 850℃ at a heating rate of 2℃ / min, and holding for 1 hour;

[0065] (S3) Third heating stage: heating from 850℃ to 1050℃ at a heating rate of 2℃ / min, and holding at this target temperature for 12h;

[0066] (S3) Cool to room temperature with the furnace.

[0067] The obtained hydrogen storage alloy was mechanically pulverized, ground, and sieved (400 mesh). The alloy powder was then subjected to X-ray diffraction (XRD) testing to analyze the positions and intensity characteristics of the diffraction peaks in the XRD pattern. Figure 1 As shown, the alloy phase structure was found to be Pr5Co. 19 (40.6wt%), Ce5Co 19 (44.4wt%), LaNi5 (15.0wt%).

[0068] Example 4

[0069] The wide-temperature-range hydrogen storage alloy electrode material prepared in this embodiment has a chemical composition of La. 0.70 Zr 0.01 Y 0.25 Mg 0.04 Ni 3.70 Al 0.22 The preparation process is as follows:

[0070] (1) Batching: La, Zr, Y, Mg, Ni and Al metals with a purity greater than 99.99% are used as raw materials. The required metal raw materials for each element are calculated according to the alloy chemical composition ratio. Considering the volatilization loss of different elements during the smelting process, the amount of materials used is increased appropriately according to the different types of elements.

[0071] (2) Induction melting: The metal raw materials La, Zr, Y, Mg, Ni and Al are charged into the induction melting furnace for melting. Mg, as a volatile element, is added into the induction melting furnace in a secondary feeding method. After casting and cooling, the as-cast alloy is obtained.

[0072] (3) Secondary annealing heat treatment: Take the as-cast alloy, place it in an annealing jar, seal it, and then put it into a vacuum tube furnace for annealing heat treatment:

[0073] (S1) First heating stage: heating from room temperature to 600℃ at a rate of 4℃ / min, and holding for 1 hour;

[0074] (S2) Second heating stage: heating from 600℃ to 850℃ at a heating rate of 2℃ / min, and holding for 1 hour;

[0075] (S2) Third heating stage: heating from 850℃ to 1100℃ at a heating rate of 2℃ / min, and holding at this target temperature for 10h;

[0076] (S3) Cool to room temperature with the furnace.

[0077] The obtained hydrogen storage alloy was mechanically pulverized, ground, and sieved (400 mesh). The alloy powder was then subjected to X-ray diffraction (XRD) analysis. The positions and intensity characteristics of the diffraction peaks in the XRD pattern were analyzed. Figure 1 As shown, the alloy phase structure was found to be Pr5Co. 19 (10.6wt%), Ce5Co 19 (13.2wt%), AB4 (66.2wt%), LaNi5 (10.0wt%).

[0078] Performance testing

[0079] The hydrogen storage alloys prepared in Examples 1-4 were used as the negative electrode of a nickel-metal hydride battery half-cell, with nickel hydroxide as the positive electrode and KOH aqueous solution (6 mol / L) as the electrolyte. The electrochemical capacity, high-temperature discharge, and low-temperature discharge performance of the negative electrode were tested using a LAND battery tester.

[0080] The battery is activated at a charge / discharge current density of 0.2C, such as... Figure 2 As shown, the maximum discharge capacities of Examples 1-4 were 349.7, 354.0, 354.6, and 355.4 mAh / g, respectively, followed by high-temperature / low-temperature discharge performance and cycle stability tests. Figure 3 As shown, the alloy of Example 1 exhibits good discharge performance at a high temperature of 60°C, with a discharge capacity of 323 mAh / g.

[0081] like Figure 4 As shown, the alloys of Examples 1 to 4 have good low-temperature discharge performance at -40℃. The low-temperature discharge capacities of the alloys of Examples 1, 2, 3 and 4 are 208, 193, 213 and 198 mAh / g, respectively.

[0082] like Figure 5 As shown, after 100 cycles at a 1C charge-discharge current density, the alloy capacity retention rates of Examples 1, 2, 3, and 4 were 88.8%, 89.3%, 88.1%, and 90.6%, respectively.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wide-temperature-range hydrogen storage alloy material, characterized in that, The general chemical formula is: La 0.65-0.71 Zr 0.01-0.02 Y 0.25- 0.28 Mg 0.03-0.05 Ni 3.70-3.80 Al 0.22-0.25 ; The alloy is a multiphase alloy containing an AB5-type phase structure and also contains A5B phase. 19 The alloy contains AB5 phase structure and / or AB4 phase structure; the content of AB5 phase structure in the alloy is 10~25 wt%. The preparation method of the wide-temperature-range hydrogen storage alloy material is carried out in the following order: (1) Vacuum induction melting: According to the proportion of the hydrogen storage alloy, the metal elements are mixed evenly and put into a vacuum induction melting furnace to melt, refine and cast the materials to obtain the as-cast hydrogen storage alloy. In this process, the first batch of materials is an element with a high melting point and the second batch of materials is the volatile element magnesium. (2) Partial annealing heat treatment: The as-cast hydrogen storage alloy was placed in an annealing furnace for secondary annealing heat treatment, which was carried out according to the following steps: (S1) First heating stage: heat from room temperature to 600℃ and hold for 1 hour; (S2) Second heating stage: heat from 600℃ to 850℃ and hold for 1 hour; (S3) Third heating stage: heat up from 850℃ to 990~1100℃ and hold for 10-18 hours; (S4) Cooling stage: Cool to room temperature with the furnace.

2. The wide-temperature-range hydrogen storage alloy material according to claim 1, characterized in that, The heating rates for each heating stage are as follows: 4℃ / min for the first heating stage, 2℃ / min for the second heating stage, and 2℃ / min for the third heating stage.

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