A lithium-containing rare earth magnesium nickel hydrogen storage alloy and a preparation method thereof

Abstract

The present application relates to hydrogen storage alloy technical field, provide a kind of lithium-containing rare earth magnesium nickel hydrogen storage alloy and its preparation method, the hydrogen storage alloy composition general formula is R 1‑a Mg a Ni x Al y N z , matrix phase is the superlattice structure with hexagonal system and / or rhombic system, there is second phase in alloy cross section EPMA image with strip distribution, its radial length is 10-100 μm, axial width is 5-20 μm, the area proportion in cross section is 10-30%. Alloy is prepared by using conventional induction melting method and after heat treatment, Li element addition uses AlLi, MgLi, MgAlLi intermediate alloy as raw material. When Li addition amount is 0.1wt.%-0.5wt.%, alloy has good low-temperature discharge performance, the maximum discharge capacity can reach more than 280 mAh / g at-30 DEG C, while having higher capacity and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage alloys, and more particularly to a lithium-containing rare earth magnesium-nickel hydrogen storage alloy and its preparation method. Background Technology

[0002] Due to my country's vast territory and wide latitudinal span, there is a significant temperature difference between the north and south. Northern my country experiences cold winters, and in low-temperature environments, the discharge capacity of secondary batteries drops sharply, severely hindering the popularization and development of new energy electric vehicles. Therefore, nickel-metal hydride batteries, which serve as auxiliary power for new energy vehicles, need to possess high energy density while also exhibiting high rate capability and stable cycling over a wide temperature range. The key to achieving this is improving the performance of the negative electrode hydrogen storage alloy.

[0003] In hydrogen storage alloy materials, rare-earth AB5-type alloys are currently widely used in nickel-metal hydride (NiMH) rechargeable batteries, but their theoretical discharge capacity is relatively low, only about 340 mAh / g. Superlattice-type rare-earth hydrogen storage alloys, with their crystal structure formed by stacking [A2B4] and [AB5] subunits along the c-axis, combine the high capacity of AB2-type alloys with the advantages of easy activation and good high-current discharge capability of AB5-type alloys. They represent a new generation of materials that can replace traditional AB5-type alloys as the negative electrode in NiMH rechargeable batteries. AB5 alloys with added Mg... 3～4 Rare-earth magnesium-nickel alloys have a theoretical capacity exceeding 400 mAh / g and exhibit excellent activation characteristics. In recent years, they have gradually begun to be applied in nickel-metal hydride (NiMH) batteries, becoming a new research hotspot. To meet the application requirements of NiMH batteries, it is urgent to improve the low-temperature discharge performance of rare-earth magnesium-nickel hydrogen storage materials.

[0004] Lithium has the highest charge density among alkali and alkaline earth metals, thus exhibiting the strongest polarization intensity and readily polarizing other atoms or ions, thereby affecting the phase structure and hydrogen absorption / desorption performance of hydrogen storage alloys. Adding lithium to rare-earth magnesium-nickel based hydrogen storage materials may help improve the low-temperature discharge performance of the alloy. Patent document 1 (CN 104480425 B) discloses a lithium-doped vanadium-based alloy with high hydrogen storage capacity and its preparation method. This method utilizes Li element implantation onto the surface of the vanadium-based hydrogen storage alloy, resulting in a significant catalytic effect and accelerating the hydrogen absorption / desorption reaction. However, in this technology, since the Li element only exists in the surface layer of the alloy particles, its impact on the hydrogen absorption / desorption reaction is limited, and it does not address improving low-temperature discharge performance.

[0005] Existing technical literature

[0006] Patent Document 1: CN 104480425 B Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a lithium-containing rare-earth magnesium-nickel hydrogen storage alloy and its preparation method, which improves the low-temperature discharge capacity and enhances the low-temperature discharge capability of the alloy by introducing trace amounts of lithium into the rare-earth magnesium-nickel alloy during the preparation process.

[0008] In one embodiment, the present invention provides a lithium-containing rare-earth magnesium-nickel hydrogen storage alloy. The matrix phase of the rare-earth magnesium-nickel hydrogen storage alloy is a superlattice structure having a hexagonal crystal system belonging to space group P63 / mmc and / or a rhombic crystal system belonging to space group R-3m. The alloy cross-section EPMA image shows a striped distribution of a second phase with a radial length of 10–100 μm, an axial width of 5–20 μm, and an area ratio of 10–30% in the cross-section. Preferably, the radial length is 10–90 μm, the axial width is 5–15 μm, and the area ratio in the cross-section is 15–30%.

[0009] Furthermore, the general formula for the rare earth magnesium-nickel hydrogen storage alloy is R. 1-a Mg a Ni x Al y N z Wherein, 0.05≤a≤0.28, 0≤y≤0.5, 0≤z≤0.5, 3.2≤x+y+z≤3.8; R is at least one rare earth element selected from Y and Sc; N is at least one element selected from Co, Fe, Mn, V, Cr, Zn, Sn, Cu, Si, and B; the mass percentage of Li in the alloy is 0.1%≤Li≤0.5%. The main function of Mg is to improve the structural stability of the alloy. If its content is too low, hydrogen-induced amorphization or disproportionation will easily occur during the charging and discharging process of the alloy, while if its content is too high, other phases with poor structural stability will easily be generated. Therefore, in the general formula composition, the Mg component is 0.05≤a≤0.28. In addition, Mg is easily oxidized in alkaline electrolyte, which accelerates the corrosion of the alloy. The mass percentage of Li is preferably 0.1% to 0.4%.

[0010] Furthermore, the hexagonal crystal system in the superlattice matrix phase of the rare-earth magnesium-nickel hydrogen storage alloy includes 2H-type (R,Mg)2(Ni,Al,N,Li)7 phase and 2H-type (R,Mg)5(Ni,Al,N,Li) phase. 19 One or two of the phases; the rhombic crystal system includes the 3R-type (R,Mg)2(Ni,Al,N,Li)7 phase and the 3R-type (R,Mg)5(Ni,Al,N,Li) phase. 19 One or two of the phases. In the alloy, x+y+z between 3.2 and 3.8 can ensure that the alloy matrix contains 2H-type (R,Mg)2(Ni,Al,N,Li)7 phase and 2H-type (R,Mg)5(Ni,Al,N,Li) phase.19 Phase, 3R type (R, Mg) 2 (Ni, Al, N, Li) 7 phase, 3R type (R, Mg) 5 (Ni, Al, N, Li) 19 One or more of the ones you like.

[0011] Furthermore, the second phase of the hydrogen storage alloy is mainly (R,Mg)(Ni,Al,N,Li)5 phase, with the element atomic ratio between the (R,Mg) side and the (Ni,Al,N,Li) side being between 1:4 and 1:5.

[0012] In another embodiment, the present invention also provides a method for preparing the lithium-containing rare-earth magnesium-nickel hydrogen storage alloy, comprising the following steps:

[0013] (1) The metal raw materials and lithium elements, which are used as raw materials for alloys, are added according to the above-mentioned general formula for rare earth magnesium-nickel hydrogen storage alloys to obtain alloy raw materials.

[0014] (2) Induction melting process: The alloy raw materials are melted in an inert atmosphere using conventional induction melting methods to obtain alloy ingots;

[0015] (3) Annealing process: The alloy ingot is sealed in an inert atmosphere and annealed and cooled in a stainless steel tank to reduce the remaining space volume after the alloy ingot is placed, so as to reduce the volatilization of Mg, Li, etc., and obtain lithium-containing rare earth magnesium nickel hydrogen storage alloy.

[0016] Furthermore, considering that Li has a low melting point and high volatility, a lithium-containing master alloy is used as the raw material in order to make it easier for Li to melt into the alloy.

[0017] Preferably, the lithium-containing master alloy is at least one of AlLi, MgLi, or MgAlLi, wherein the mass percentage of Li is 5% to 15%, and the mass percentage of Li is preferably 7% to 12%.

[0018] Furthermore, considering the volatility of Mg and Li, the amount of Mg and Li added in this invention is equivalent to 150% to 180% of the theoretical content calculated according to the alloy composition.

[0019] Furthermore, the annealing process includes heating from room temperature to 600°C at a heating rate of 5–10°C / min, then further heating to 930–980°C at a heating rate of 1–2°C / min, holding at that temperature for 5–12 hours, and finally performing a cooling treatment, which can be quenching or natural cooling, preferably quenching. The holding temperature of the heat treatment is positively correlated with the value of x+y+z in the general formula for hydrogen storage alloys.

[0020] Furthermore, the inert atmosphere is helium or argon, preferably helium, which can better suppress the volatilization of elements.

[0021] Furthermore, in addition to the preparation method described above, the lithium-containing rare earth magnesium-nickel hydrogen storage alloy of the present invention can also be prepared using other commonly used preparation methods for hydrogen storage alloys in the field.

[0022] Advantages of the present invention

[0023] This invention introduces trace amounts of lithium into rare-earth magnesium-nickel alloys during the preparation process using AlLi, MgLi, or MgAlLi master alloys as raw materials. This increases the content of the striped second phase in the alloy, which is beneficial for increasing the phase interface and improving the diffusion rate of hydrogen between different phase interfaces, thereby improving the hydrogen absorption and desorption kinetics of the alloy and increasing the discharge capacity at low temperatures. Simultaneously, with the increase of lithium content, the hydrogen absorption and desorption plateau voltage of the alloy increases, further enhancing the low-temperature discharge capability of the alloy. In the lithium-containing rare-earth magnesium-nickel hydrogen storage alloy of this invention, when the Li addition amount is 0.1wt.% to 0.5wt.%, the alloy exhibits good low-temperature discharge performance, with a maximum discharge capacity of over 280mAh / g at -30℃, while also possessing high capacity and cycle stability. Attached Figure Description

[0024] Figure 1 This is the electron probe microanalysis (EPMA) spectrum of the cross section of Example 1 at 200x magnification;

[0025] Figure 2 This is the electron probe microanalysis (EPMA) spectrum of the cross section of Example 1 at 500x magnification;

[0026] Figure 3 This is the electron probe microanalysis (EPMA) spectrum of the cross section of Comparative Example 1 at 500x magnification;

[0027] Figure 4 This is the electron probe microanalysis (EPMA) spectrum of the cross section in Example 6 at 500x magnification.

[0028] Figure 5 These are the XRD patterns of Example 1 and Comparative Example 1;

[0029] Figure 6 These are the discharge curves of Example 1 and Comparative Example 1 at -30°C. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that the various installation methods and technical terms mentioned in this invention are all well-known technical terms in the relevant technical field, and therefore will not be explained further.

[0032] In the preparation of lithium-containing rare-earth magnesium-nickel hydrogen storage alloys, when calculating the required amount of metal raw materials for each element according to the chemical composition ratio, the volatilization loss of different elements during the smelting process should be considered. The amount of material used should be increased appropriately according to the different types of elements. In particular, since lithium has a very low melting point and strong volatility, in order to make lithium easier to melt into the alloy, Li is introduced as a raw material using MgLi, AlLi or MgAlLi alloy, wherein the content of Li is 5wt.% to 15wt.%. Considering the volatility of Mg and Li, the amount of Mg and Li added is equivalent to 150% to 180% of the theoretical content calculated according to the alloy composition.

[0033] Example 1

[0034] As shown in Table 1, the lithium-containing rare-earth magnesium-nickel hydrogen storage alloy prepared in this embodiment has a chemical composition of La. 0.72 Nd 0.10 Mg 0.18 Ni 3.40 Al 0.15 Its Li content is 0.2 wt.%, and its preparation method is as follows:

[0035] (1) Batching process: Calculate the required metal raw materials for the corresponding elements according to the alloy chemical composition ratio designed in Table 1. The Li element is made from MgLi and AlLi alloys. The Li content in the MgLi alloy is 7 wt.% and the Li content in the AlLi alloy is 10 wt.%. Other elements are added as elemental metals. The MgLi content is 160% in excess based on the Mg content.

[0036] (2) Induction melting process: The prepared alloy raw materials are melted in an induction furnace under vacuum and helium atmosphere protection to prepare alloy ingots.

[0037] (3) Annealing process: The prepared alloy ingot is sealed in a stainless steel tank under an argon atmosphere for annealing. The annealing process first raises the temperature from room temperature to 600°C at a heating rate of 5°C / min, and then continues to raise the temperature to the heat treatment temperature at a heating rate of 1°C / min, holding it at that temperature for a certain time. The heat treatment temperature and holding time are detailed in Table 1. Finally, the annealed alloy is removed and quenched to obtain the target alloy.

[0038] Example 2

[0039] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.72 Nd 0.10 Mg 0.18 Ni 3.40 Al 0.15 Its Li content is 0.1 wt.%, and its preparation process is the same as in Example 1.

[0040] Example 3

[0041] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.72 Nd 0.10 Mg 0.18 Ni 3.40 Al 0.15 Its Li content is 0.05 wt.%, and its preparation process is the same as in Example 1.

[0042] Example 4

[0043] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium, and the chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.55 Y 0.20 Mg 0.25 Ni 3.00 Al 0.15 Co 0.05 Its Li content is 0.3 wt.%, and its preparation process is the same as in Example 1.

[0044] Example 5

[0045] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium, and the chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.55 Y 0.20 Mg 0.25 Ni 3.00 Al 0.15 Co 0.05 Its Li content is 0.4 wt.%, and its preparation process is the same as in Example 1.

[0046] Example 6

[0047] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.55 Y 0.20 Mg 0.25 Ni 3.00 Al 0.15 Co 0.05 Its Li content is 0.5 wt.%, and its preparation process is the same as in Example 1.

[0048] Example 7

[0049] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.55 Y 0.20 Mg 0.25 Ni 3.00 Al 0.15 Co 0.05 Its Li content is 0.55wt%, and its preparation process is the same as in Example 1.

[0050] Example 8

[0051] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.75 Sm 0.10 Mg 0.15 Ni 3.70 Al 0.10 Its Li content is 0.12 wt.%, and its preparation process is the same as in Example 1.

[0052] Example 9

[0053] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment contains lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.75 Sm 0.10 Mg 0.15 Ni 3.70 Al 0.10 Its Li content is 0.25 wt.%, and its preparation process is the same as in Example 1.

[0054] Comparative Example 1

[0055] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment does not contain lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.72 Nd 0.10 Mg 0.18 Ni 3.40 Al0.15 The preparation process is the same as in Example 1, except that each element is added as a metallic element. Considering the volatility of Mg, the theoretical content of the ingredients is calculated to be 150% according to the alloy composition.

[0056] Comparative Example 2

[0057] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment does not contain lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.55 Y 0.20 Mg 0.25 Ni 3.00 Al 0.15 Co 0.05 The preparation process is the same as in Example 1, except that each element is added as a metallic element. Considering the volatility of Mg, the theoretical content of the ingredients is calculated to be 150% according to the alloy composition.

[0058] Comparative Example 3

[0059] As shown in Table 1, the rare earth magnesium-nickel hydrogen storage alloy prepared in this embodiment does not contain lithium. The chemical composition of the rare earth magnesium-nickel hydrogen storage alloy is La. 0.75 Sm 0.10 Mg 0.15 Ni 3.70 Al 0.10 The preparation process is the same as in Example 1, except that each element is added as a metallic element. Considering the volatility of Mg, the theoretical content of the ingredients is calculated to be 150% according to the alloy composition.

[0060] Table 1 Chemical composition and preparation process of hydrogen storage alloy

[0061]

[0062] The alloys obtained from the examples and comparative examples were crushed, ground, and sieved. Alloy powders of the corresponding particle size range and the remaining blocky alloy ingots were collected for EPMA, XRD, discharge performance and hydrogen storage performance testing.

[0063] Test Example 1: Electron Probe MA Test

[0064] The block alloy ingots of Examples 1-9 and Comparative Examples 1-3 were embedded in conductive hot-pressing inlay powder and cured under pressure. Then, they were coarsely ground and finely ground to a polished mirror surface using a wet grinding machine to obtain the cross section required for EPMA testing.

[0065] like Figures 1-3 As shown, Figure 1 and Figure 2 The images show the EPMA spectra of the alloy cross-section in Example 1 at magnifications of 200x and 500x, respectively. Figure 3The image shows the EPMA spectrum of the alloy cross-section of Comparative Example 1 at 500x magnification. The alloy of Example 1 contains 0.2 wt.% Li, while the alloy of Comparative Example 1 does not contain Li.

[0066] Depend on Figures 1-3 It can be seen that Example 1 containing 0.2 wt.% Li has a striped second phase with a radial length of about 10 to 70 μm and an axial width of about 5 to 10 μm. The area of ​​the second phase, as obtained by image processing software, accounts for about 18% of the total cross-sectional area. In contrast, Comparative Example 1, which does not contain Li, does not have a striped second phase, but only a small amount of irregular impurities. The area of ​​these impurities, as obtained by image processing software, accounts for only 3% of the total cross-sectional area.

[0067] Further analysis using energy dispersive spectroscopy (EDS) revealed the composition of phases with different contrast levels in Example 1. The light gray matrix phase region was identified as La. 0.71 Nd 0.10 Mg 0.19 Ni 3.33 Al 0.14 Its stoichiometric ratio B / A is 3.47, possibly a 2H or 3R type (La,Nd,Mg)2(Ni,Al)7 phase; the dark gray second phase region is composed of La. 0.80 Nd 0.15 Mg 0.04 Ni 4.03 Al 0.19 Its stoichiometric ratio B / A is 4.22, which may be a (La,Nd,Mg)(Ni,Al)5 phase.

[0068] like Figure 4 In the EPMA image of Example 6, a second phase with a striped distribution has a radial length of approximately 50–90 μm and an axial width of approximately 5–15 μm. Image processing software shows that the area of ​​the second phase accounts for approximately 28% of the total cross-sectional area.

[0069] Test Example 2: X-ray Powder Diffraction (XRD) Test

[0070] XRD analysis was performed on hydrogen storage alloy powder with a mesh size smaller than 400. The analysis used Cu Kα radiation at a power of 40 kV × 300 mA, employing a step scan mode with a step size of 0.02° and a dwell time of 1 s per step. The 2θ angle ranged from 20° to 80°. The XRD patterns of Example 1 and Comparative Example 1 obtained from the tests are shown below. Figure 5 As shown. Analysis of the diffraction peak positions and intensity characteristics in the XRD patterns revealed that the hydrogen storage alloy phase structure in Example 1 and Comparative Example 1 mainly consists of 2H-type (La,Nd,Mg)2(Ni,Al)7 and 2H-type (La,Nd,Mg)5(Ni,Al) phases. 19The (La,Nd,Mg)(Ni,Al)5 phase was compared with that of Comparative Example 1. The diffraction peak intensity of the (La,Nd,Mg)(Ni,Al)5 phase was higher in Example 1.

[0071] The XRD test results were refined using Rietveld to obtain the phase contents of the alloys in Example 1 and Comparative Example 1, as shown in Table 2:

[0072] Table 2 shows the phase content of the alloy obtained by Rietveld's refinement.

[0073]

[0074] From Table 2 and Figure 5 It can be seen that the superlattice 2H type (La,Nd,Mg)2(Ni,Al)7 phase has the highest content in Example 1, and the superlattice 2H type (La,Nd,Mg)5(Ni,Al) phase has the highest content. 19 The content of the (La,Nd,Mg)2(Ni,Al)7 phase was only about 6 wt.%, and because its composition was similar to that of the (La,Nd,Mg)2(Ni,Al)7 phase, it could not be clearly distinguished in EPMA, and both were considered matrix phases. The content of the (La,Nd,Mg)(Ni,Al)5 phase was about 20 wt.%, which was similar to the content of the phases with a striped regular distribution in the cross section of the EPMA spectrum, and was the second phase. In Comparative Example 1, the content of the (La,Nd,Mg)(Ni,Al)5 phase was 2.87 wt.%, and it was distributed as irregular dots in the EPMA spectrum.

[0075] The matrix phase structure composition of the examples and comparative examples as determined by XRD is detailed in Table 3. Among them, the 2H type belongs to the hexagonal crystal system P63 / mmc space group, and the 3R type belongs to the rhombic crystal system R-3m space group.

[0076] Test Example 3: Discharge Performance Test

[0077] The collected hydrogen storage alloy powder with a mesh size between 160 and 200 was used for discharge performance testing. The testing procedure is as follows:

[0078] Accurately weigh 200mg of hydrogen storage alloy powder and 800mg of carbonyl nickel powder, mix them evenly, and then cold press them at 16MPa for 10min to form an electrode sheet with a diameter of 16mm×1mm. Place the sheet in the middle of a folded nickel foam and cold press it to form a shape, then spot weld it to the nickel strip. The test device is a sandwich-type two-electrode test device. The negative electrode is the hydrogen storage alloy electrode, the auxiliary electrode is the [Ni(OH)2 / NiOOH] electrode, and the electrolyte is a 6mol / L KOH alkaline solution. The test temperature is controlled by a high and low temperature chamber. The test temperature is room temperature 25℃ and low temperature -30℃.

[0079] After the alloy electrode was left to stand in an open circuit for 24 hours to ensure sufficient wetting, it was charged at a constant current of 60 mA / g for 450 min at 25℃ and -30℃ respectively, left to stand for 10 min, and then discharged at a constant current of 60 mA / g with a cutoff potential of -1.0V and left to stand for 10 min. This cycle was repeated to achieve the maximum discharge capacity at different temperatures.

[0080] The test method for the cyclic stability of the alloy is as follows: At room temperature, charge at a constant current of 300 mA / g for 90 min, allow to stand for 10 min, then discharge at a constant current of 300 mA / g with a cutoff potential of -1.0 V, allow to stand for 10 min, and repeat this cycle. The ratio of the remaining discharge capacity to the maximum discharge capacity measured under these conditions after 200 charge-discharge cycles is S. 200 The results are detailed in Table 3.

[0081] As shown in Table 3, within the scope of this invention, the content of the (La,Nd,Mg)(Ni,Al)5 phase in alloys with different compositions without the addition of lithium is less than 5 wt.%, and the phases are randomly distributed in a dotted pattern. Comparing Examples 1-3 with Comparative Example 1, it can be seen that after adding Li, and with increasing Li content, the content of the striped second phase gradually increases, the alloy phase interface increases, and the low-temperature discharge capacity increases. The ratio of the low-temperature discharge capacity to the room-temperature discharge capacity increases from 69.6% in Comparative Example 1 without Li to a maximum of 78.6% in Example 1 with 0.2 wt.% Li (e.g., ...). Figure 6 That is, by Figure 6 The discharge curves of Example 1 and Comparative Example 1 at -30°C show that the discharge capacity of the hydrogen storage alloy containing 0.2% Li in Example 1 at -30°C is significantly higher than that of the hydrogen storage alloy without hydrogen in Comparative Example 1. This demonstrates that the rare-earth magnesium-nickel based hydrogen storage alloy with added hydrogen (within the scope of this invention) significantly improves low-temperature discharge performance.

[0082] In Example 3, when the Li content was less than 0.1 wt.%, the content of the second phase was low, and the improvement on low-temperature performance was not significant.

[0083] In Examples 4-7, as the Li content increased from 0.3 wt.% to 0.55 wt.%, the second phase accounted for 33% when the Li content was 0.55 wt.%. Due to the excessively high content of the second phase, the discharge capacity of the alloy at room temperature and low temperature decreased significantly, and the capacity retention rate after 200 cycles dropped to less than 70%, resulting in unsatisfactory electrochemical performance. Therefore, the preferred Li mass percentage content is 0.1% to 0.5%. Furthermore, as shown in Table 3, when the Li mass percentage content is within this range, the alloy exhibits excellent low-temperature discharge performance, and the maximum discharge capacity at -30°C can reach over 280 mAh / g.

[0084] Test Example 4: Hydrogen Storage Performance Test

[0085] The gaseous hydrogen storage performance of hydrogen storage alloys can be represented by the pressure-composition-temperature (PCT) characteristic curve of the alloy. The Siever method is used to measure the performance at 25°C. The test method is as follows: take about 2g of alloy powder with a particle size of less than 80 mesh, evacuate at 400°C for 1 to 2 hours, and after cooling to room temperature, charge hydrogen gas at 5MPa pressure at 25°C to absorb hydrogen. Then evacuate at 400°C for 1 hour. Repeat this cycle 2 to 3 times to fully activate the alloy. Then, perform PCT curve testing at room temperature.

[0086] The hydrogen desorption plateau pressure of the material can be obtained from the PCT curve. The results are shown in Table 3. The hydrogen desorption plateau pressure of the examples is higher than that of the comparative examples with the same composition. Therefore, the addition of trace amounts of lithium helps to improve the hydrogen desorption plateau pressure of the hydrogen storage alloy, thereby improving the discharge performance of the hydrogen storage alloy at low temperature.

[0087] Based on the test results of Examples 1 to 4, it can be seen that when lithium is not added, the alloys with different chemical compositions have a small amount of non-superlattice structure second phase and an irregular distribution. As the lithium content increases, the content of the striped second phase gradually increases, the alloy phase interface increases, the discharge capacity at low temperature is improved, and the hydrogen desorption plateau voltage of the alloy also gradually increases with the increase of lithium content. The increase of the plateau helps to improve the low-temperature hydrogen desorption performance.

[0088] For those skilled in the art, this invention is not limited to the details of the exemplary embodiments described above, and can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Any minor modifications, equivalent substitutions, and improvements made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

[0090]

Claims

1. A lithium-containing rare-earth magnesium-nickel hydrogen storage alloy, characterized in that, The general formula of the rare earth magnesium-nickel based hydrogen storage alloy is R 1-a Mg a Ni x Al y N z Wherein, 0.05≤a≤0.28, 0≤y≤0.5, 0≤z≤0.5, 3.2≤x+y+z≤3.8; R is at least one rare earth element selected from Y and Sc; N is at least one element selected from Co, Fe, Mn, V, Cr, Zn, Sn, Cu, Si, and B; the mass percentage of Li in the alloy is 0.1%≤Li≤0.5%. The matrix phase of the rare-earth magnesium-nickel based hydrogen storage alloy has a space group of P63 / mmc The hexagonal crystal system and / or belonging to space group 1 R-3m The superlattice structure of the rhombic crystal system has a second phase with a striped distribution in the EPMA image of the alloy cross section. The radial length is 10~100μm, the axial width is 5~20μm, and the area ratio in the cross section is 10~30%.

2. The lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to claim 1, characterized in that, The hexagonal crystal system in the superlattice matrix of the alloy includes 2H-type (R,Mg)2(Ni,Al,N,Li)7 phase and 2H-type (R,Mg)5(Ni,Al,N,Li) phase. 19 One or two of the phases; the rhombic crystal system includes the 3R-type (R,Mg)2(Ni,Al,N,Li)7 phase and the 3R-type (R,Mg)5(Ni,Al,N,Li) phase. 19 One or two of the choices.

3. The lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to claim 1, characterized in that, The second phase is a (R,Mg)(Ni,Al,N,Li)5 phase, wherein the atomic ratio of the elements on the (R,Mg) side and the (Ni,Al,N,Li) side is between 1:4 and 1:

5.

4. A method for preparing a lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to any one of claims 1 to 3, comprising the following steps: (1) Batching process: The metal raw materials of the corresponding elements and the Li element as the raw material of the alloy are added according to the chemical composition ratio of the above rare earth magnesium nickel hydrogen storage alloy to obtain alloy raw materials. (2) Induction melting process: The above alloy raw materials are melted in an induction furnace under vacuum and inert atmosphere protection to prepare alloy ingots. (3) Annealing process: The alloy ingot is sealed in an inert atmosphere in a stainless steel tank for annealing and cooling to obtain a lithium-containing rare earth magnesium-nickel hydrogen storage alloy. in, The induction melting process in step (2) introduces Li by using at least one intermediate alloy of AlLi, MgLi or MgAlLi as raw material, and the mass percentage of Li in the intermediate alloy is 5% to 15%.

5. The method for preparing the lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to claim 4, characterized in that, The inert atmosphere is helium or argon.

6. The method for preparing the lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to claim 4, characterized in that, The annealing process involves heating from room temperature to 600°C at a heating rate of 5–10°C / min, then continuing to heat to 930–980°C at a heating rate of 1–2°C / min, and holding at that temperature for 5–12 hours.

7. The method for preparing lithium-containing rare-earth magnesium-nickel hydrogen storage alloy according to claim 4, characterized in that, The cooling process is either quenching or natural cooling.

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