A high-purity vanadium-based hydrogen storage alloy with low aluminum content and its preparation method

Abstract

This invention relates to the field of hydrogen storage alloy materials, specifically to a high-purity vanadium-based hydrogen storage alloy with low aluminum content and its preparation method. The method involves effectively removing oxygen impurities from industrial raw materials by adding rare earth elements during the preparation of the vanadium-based hydrogen storage alloy, and further removing impurities such as Al and O from the alloy by combining vacuum electron beam melting. This one-step melting process yields a high-purity vanadium-based hydrogen storage alloy with high hydrogen storage content.

Description

Technical Field

[0001] This invention relates to the field of hydrogen storage alloy materials, specifically to a high-purity vanadium-based hydrogen storage alloy with low aluminum content and its preparation method. Background Technology

[0002] Vanadium-based solid solution hydrogen storage alloys, due to their body-centered cubic (BCC) structure and high theoretical hydrogen storage capacity (up to 3.8 wt%), can achieve efficient and reversible hydrogen absorption and desorption at room temperature, making them highly promising solid-state hydrogen storage materials. However, their commercial application faces two major bottlenecks: firstly, the high cost of metallic vanadium raw materials; and secondly, the susceptibility of the alloy's cycle stability and hydrogen storage capacity to severe influence from impurities in the raw materials. To reduce costs, industrially, lower-priced intermediate alloys such as ferrovanadium (VFe) and vanadium-aluminum (VAl) are commonly used to replace high-purity vanadium. However, these industrial vanadium sources inevitably introduce impurities such as aluminum (Al), silicon (Si), and oxygen (O) during the smelting process. Among these, the impact of aluminum impurities is particularly prominent: studies have shown that aluminum solid solution in the BCC matrix leads to lattice contraction, altering the alloy's electronic structure, thereby significantly increasing the hydrogen absorption / desorption plateau pressure, amplifying the hysteresis effect, and reducing reversible hydrogen storage capacity. Simultaneously, aluminum readily segregates with elements such as oxygen, inducing the precipitation of brittle second phases such as titanium-rich phases, disrupting the matrix compositional homogeneity, accelerating capacity decay and material pulverization during repeated hydrogen absorption / desorption cycles, and severely impairing the alloy's cycle life. Therefore, developing a high-purity vanadium-based hydrogen storage alloy preparation technology that can precisely control aluminum content while ensuring high hydrogen storage capacity and long-term cycle stability is crucial for accelerating the commercial application of this material.

[0003] To address the problem that vanadium-based hydrogen storage alloys introduce impurities such as aluminum due to the use of low-cost industrial vanadium sources, leading to lattice distortion, reduced hydrogen storage capacity, and deteriorated cycle life, there is an urgent need to provide a method that combines targeted purification of rare earth elements with electron beam vacuum refining to develop a preparation technology for vanadium-based hydrogen storage alloys with low aluminum content and high purity. Summary of the Invention

[0004] This invention discloses a method for preparing a high-purity vanadium-based hydrogen storage alloy with low aluminum content. The method includes preparing the high-purity vanadium-based hydrogen storage alloy by vacuum electron beam melting furnace, and the specific steps are as follows:

[0005] 1) Weigh out the industrial vanadium raw material, add rare earth metal and metal M, and mix;

[0006] The industrial vanadium raw material is selected from any one or more combinations of the following groups: industrial VFe alloy, industrial VAl alloy, industrial metallic V, and industrial MoVAl alloy.

[0007] The rare earth metal is selected from any one or a combination of two or more elements in the following group: cerium metal, yttrium metal, and lanthanum metal; through the targeted addition technology of rare earth elements, oxygen impurities in industrial raw materials can be effectively removed by generating rare earth oxide slag, resulting in a high-performance hydrogen storage alloy with low oxygen content.

[0008] The metal M is selected from any one or more elements from the group consisting of: Ti, Cr, Fe, Mn, Co, Ni, and Mo.

[0009] The mass of the rare earth metal is 0.5-10 wt% of the industrial vanadium raw material.

[0010] The purity of the rare earth metal is 99.5% to 99.95%, meaning that the mass content of rare earth elements is 99.5% to 99.95%.

[0011] The purity of the metal M is 99~99.95%, that is, the mass content of metal M is 99~99.95%; the amount of M is determined according to the general chemical formula of the target product.

[0012] 2) The target alloy, with the general chemical formula V, is melted using a vacuum electron beam furnace. x M 1-x Place the mixed raw materials from step 1) into the crucible of the vacuum electron beam furnace, close the furnace door, and evacuate the furnace to ensure the vacuum level in the melting chamber is ≤5.0×10⁻⁶. -3 Pa; then high-purity argon gas is introduced at a pressure of 0.05~1 MPa, and then evacuated to a vacuum of ≤2.0×10 Pa. -3 Pa, repeat the argon purging-vacuuming operation 2-3 times to thoroughly remove air and moisture from the furnace;

[0013] 3) Maintain the vacuum level in the furnace and lance, start the electron gun, and use a gradual power increase control mode for melting. Gradually increase the lance power until all the mixed raw materials are melted, while maintaining a lance vacuum level ≤ 5.0 × 10⁻⁶. -3 Pa, furnace vacuum degree ≤5.0×10 -2 Pa;

[0014] The power of the gun body is 35-75 kW, with 45-65 kW being the preferred power.

[0015] The melting time is 5-60 min, preferably 5-25 min;

[0016] The electron beam uses a linear scanning method; vacuum electron beam melting can control the changes in the alloy composition and the removal rate of impurities such as Al and O by adjusting parameters such as the vacuum degree of the gun, the power of the gun, and the melting time.

[0017] 4) After melting is completed, the electron beam is turned off and the furnace is cooled to room temperature under vacuum for ≥4 hours to obtain vanadium-based hydrogen storage alloy ingots.

[0018] This also includes repeating steps 2) to 4) of the vanadium-based hydrogen storage alloy ingot.

[0019] 5) Grind the vanadium-based hydrogen storage alloy ingot obtained in step 4) to remove surface impurities and obtain the finished vanadium-based hydrogen storage alloy.

[0020] Secondly, the present invention also provides a high-purity vanadium-based hydrogen storage alloy with low aluminum content, wherein the hydrogen storage alloy has the general chemical formula V0. x M 1-x M is selected from any combination of one or more elements from the following group: Ti, Cr, Fe, Mn, Co, Ni, Mo; wherein 40≤x≤95.

[0021] in,

[0022] This invention has at least the following beneficial effects:

[0023] 1) This invention uses vacuum electron beam melting, which can effectively remove Al and O impurity elements introduced from industrial vanadium raw materials. The impurity content in the vanadium-based hydrogen storage alloy prepared is significantly reduced, the main phase has high purity, and the precipitation of brittle second phases such as titanium-rich phase is effectively suppressed, thereby improving the reversible hydrogen storage capacity of the alloy.

[0024] 2) The vacuum electron beam melting method used in this invention can control the changes in alloy composition and impurity removal rate by adjusting parameters such as the vacuum degree of the gun body, the power of the gun body, and the melting time, so as to prepare a finished vanadium-based hydrogen storage alloy with Al content <0.01 wt% and O content as low as 0.01 wt%.

[0025] 3) The rare earth element targeted addition technology disclosed in this invention can further remove lattice oxygen impurities dissolved in industrial raw materials and alloys by generating rare earth oxide slag, thereby obtaining a high-performance hydrogen storage alloy with low oxygen content.

[0026] 4) This invention discloses a novel preparation technology using industrial vanadium as raw material, which combines vacuum electron beam melting with rare earth element deoxygenation and slag formation to obtain a vanadium-based hydrogen storage alloy with a reversible hydrogen storage capacity of 2.37 wt% (at 25°C). The hydrogen storage performance is comparable to that of alloys prepared from high-purity metallic vanadium raw materials (vanadium mass content in the raw materials ≥99.95%).

[0027] 5) The vacuum electron beam melting method used in this invention does not require pretreatment of industrial raw materials to remove impurities. It can obtain high-purity vanadium-based hydrogen storage alloys with low Al and O content in one step, realizing effective control and improvement of the alloy's comprehensive performance. The process route is clear and highly operable, providing a practical and feasible technical solution for accelerating the low-cost and high-performance commercialization of vanadium-based hydrogen storage alloys. Attached Figure Description

[0028] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0029] Figure 1 The hydrogen absorption kinetics curve of the VTiCr alloy in Example 1 at 25°C;

[0030] Figure 2 The PCT curves of the VTiCr alloy in Example 1 at 10°C, 25°C, 40°C, and 60°C are shown.

[0031] Figure 3 The hydrogen absorption kinetics curve of the VTiCr alloy in Example 2 at 25°C;

[0032] Figure 4 The PCT curves of the VTiCr alloy in Example 2 at 10°C, 25°C, 40°C, and 60°C are shown.

[0033] Figure 5 The PCT hydrogen absorption and desorption curves of the VTiCr alloys in Examples 1 and 2, and Comparative Examples 1 and 2, at 25°C are shown.

[0034] Figure 6 The XRD patterns of the VTiCr alloys in Examples 1 and 2, and Comparative Examples 1 and 2 are shown.

[0035] Figure 7 The images are SEM images of the VTiCr alloys in Examples 1 and 2, and Comparative Examples 1 and 2. Specific implementation methods

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in Embodiment 1 of this invention will be described in more detail below with reference to the accompanying drawings. The described embodiments are only some, not all, of the embodiments of this invention. Any other embodiments obtained by those skilled in the art through similar improvements and adjustments based on the content of this invention without inventive effort are considered to be within the scope of protection of this invention.

[0037] The specific implementation method is as follows:

[0038] In high-purity vanadium-based hydrogen storage alloys, aluminum solid solution in the body-centered cubic (BCC) matrix leads to lattice contraction, altering the alloy's electronic structure. This significantly increases the hydrogen absorption / desorption plateau pressure, amplifies the hysteresis effect, and reduces the reversible hydrogen storage capacity, making the impact of aluminum impurities particularly pronounced. Secondly, aluminum synergistically segregates with elements such as oxygen, inducing the precipitation of brittle second phases like titanium-rich phases. This disrupts the matrix composition homogeneity, accelerating capacity decay and material pulverization during repeated hydrogen absorption / desorption cycles, severely impairing the alloy's cycle life. The presence of silicon in the alloy causes lattice constant contraction in the BCC main phase, reducing the number and space of interstitial hydrogen storage sites, thus drastically reducing the alloy's reversible hydrogen storage capacity. Furthermore, rare earth elements have a strong binding effect with oxygen, effectively removing oxygen impurities from the alloy and generating cerium oxide or cerium aluminum oxide that floats on the alloy surface, thereby removing aluminum and oxygen impurities. Therefore, we consider introducing rare earth elements to purify the impurities in the alloy.

[0039] Example 1:

[0040] 1) Using a vacuum electron beam melting furnace to prepare chemical formula V 85 Ti5Cr 10 Vanadium-based hydrogen storage alloys (based on chemical formula V) 85 Ti5Cr 10 The molar ratio of Ti and Cr is used to determine the mass of Ti and Cr. Industrial vanadium with a V mass fraction of 95% is used as raw material, denoted as 95V raw material. 1701.61 g of 95V raw material is weighed, with a block size of about 2*2 cm. Then, 94.05 g of bulk titanium with a purity of 99% (i.e., a mass fraction of 99%), 204.33 g of bulk chromium with a purity of 99.5% (i.e., a mass fraction of 99.5%), and 136.13 g of bulk cerium with a purity of 99.5% (i.e., a mass fraction of 99.5%) are weighed (the mass of cerium used is 8 wt% of the mass of 95V raw material). All the blocks are kept to a size of about 2*2 cm. The above raw materials are mixed together.

[0041] Table 1 Raw Material Composition Table

[0042]

[0043] 2) Vacuum electron beam refining: Place the mixed metal raw materials into the crucible of the vacuum electron beam refining furnace, close the furnace door, and evacuate the furnace to a vacuum level of 2.0 × 10⁻⁶. -3 Below Pa; then high-purity argon gas was introduced at a pressure of 0.2 MPa, and then evacuated to a vacuum of 2.0 × 10⁻⁶ MPa. -3 For pressure below Pa, repeat the argon flushing-vacuuming operation 3 times to thoroughly remove air and moisture from the furnace;

[0044] 3) The vacuum degree of the gun body is ≤5.0×10 -3Pa, furnace vacuum degree ≤5.0×10 -2 When Pa, start the electron gun and gradually increase the power of the electron gun to 50 kW. After all the metal raw materials have melted, continue to hold the temperature for 15 min.

[0045] 4) After melting is completed, the electron beam is turned off and the furnace is cooled to room temperature under vacuum for 6 hours to obtain vanadium-based hydrogen storage alloy ingots.

[0046] To ensure the uniformity of the alloy composition, the vanadium-based hydrogen storage alloy ingot obtained in the above steps is flipped over, and steps 2) to 4) are repeated for a second melting, in which the electron gun power is increased to 60 kW. After all the metal raw materials are melted, the temperature is held for 10 min. Other processes and parameters are the same as in steps 2) to 4).

[0047] 5) Grind the obtained alloy ingot to remove surface impurities to obtain the finished vanadium-based hydrogen storage alloy.

[0048] The kinetic properties of the resulting vanadium-based hydrogen storage alloy are as follows: Figure 1 As shown, the alloy can be activated by two kinetic processes, with a maximum hydrogen storage capacity of 3.86 wt%. Figure 2 The PCT curves of the alloy at different temperatures are shown. At 25°C, the maximum hydrogen absorption capacity of the alloy is 3.85 wt%, the residual hydrogen content up to 0.001 MPa is 1.48 wt%, and the reversible hydrogen storage capacity can reach 2.37 wt%.

[0049] Figure 6 XRD analysis showed that the alloy was mainly composed of BCC phase, containing a small amount of CeO2 phase. The CeO2 phase and... Figure 7 The white bright spots in the SEM image correspond to this. ICP analysis of the obtained vanadium-based hydrogen storage alloy sample showed that the Al content was less than 0.01 wt% and the O content was 0.22 wt%, which is significantly lower than the 0.85 wt% (Al content) and 1.36 wt% (O content) in the 95V raw material. This indicates that the Al and O impurities can be effectively removed by vacuum electron beam melting and the introduction of rare earth elements.

[0050] Example 2:

[0051] The mass of cerium metal was adjusted to 68.06 g (the mass of cerium metal used was 4 wt% of the mass of 95V raw material), and the remaining steps were the same as in Example 1 to obtain a vanadium-based hydrogen storage alloy.

[0052] The XRD structure of the prepared vanadium-based hydrogen storage alloy also shows a BCC single phase, such as... Figure 6 As shown, the kinetic curve of the alloy is as follows: Figure 3 As shown, the alloy was basically activated after two cycles, with a maximum hydrogen storage capacity of 3.83 wt%. Figure 4 The PCT curves of the alloy at different temperatures are shown. At 10°C, the maximum hydrogen storage capacity of the alloy is 3.86 wt%, the residual hydrogen content at 0.001 MPa is 1.51 wt%, and the reversible hydrogen storage capacity is 2.35 wt%. At 25°C, the maximum hydrogen storage capacity of the alloy is 3.78 wt%, the residual hydrogen content at 0.001 MPa is 1.49 wt%, and the reversible hydrogen storage capacity is 2.29 wt%. ICP analysis showed that the Al content in the alloy sample was less than 0.01 wt%, and the O content was 0.43 wt%.

[0053] Comparative Example 1:

[0054] V is melted using a vacuum electric arc furnace 85 Ti5Cr 10 Hydrogen storage alloy.

[0055] First, the 95V raw material is pre-refined and impurity removed using an electric arc furnace. Specifically, the 95V raw material is mixed with 4 wt% Ce metal and placed in the crucible of the electric arc furnace, then evacuated to a vacuum level below 5 × 10⁻⁶. -3 After Pa, high-purity argon gas is introduced as a protective atmosphere for melting. The power supply current is gradually increased to 270 A. After the raw material is completely melted, it is kept at the temperature for 10 min. After the holding time is completed, it is cooled to obtain the pretreated 95 vanadium raw material ingot.

[0056] Repeat the above steps to remelt the obtained pretreated 95 vanadium raw material ingot to improve the uniformity of the composition. During the smelting process, metallic cerium reacts with impurities such as oxides and oxygen in the 95V raw material to form a low-density slag phase. After smelting and cooling, the surface slag is removed, and the surface of the pretreated 95 vanadium raw material ingot is polished to obtain a pre-purified vanadium ingot.

[0057] Using the above pre-purified vanadium ingots as a new vanadium source, V 85 Ti5Cr 10 The hydrogen storage alloy is smelted using a vacuum electric arc furnace, and 1 wt% rare earth Ce is added during the smelting process to further remove residual lattice oxygen impurities in the raw materials and alloy.

[0058] The PCT curve of the obtained alloy at 25°C is as follows: Figure 5As shown, the plateau pressure of the alloy is significantly higher than that of Examples 1 and 2. This is due to the higher Al and O content in the alloy. The reversible hydrogen storage capacity of the alloy at a hydrogen release pressure of 0.01 MPa is 2.34 wt%. ICP analysis shows that the Al content in the alloy is 0.36 wt% and the O content is 0.51 wt%, which is lower than that in the 95V raw material. However, this method failed to effectively remove the Al impurity content. The alloy obtained by vacuum electron beam melting in Example 1 has a lower Al content (<0.01 wt%) and O content (0.22 wt%), indicating that vacuum electron beam melting is a more effective alloy preparation method for removing Al and O impurities from the raw material.

[0059] Comparative Example 2:

[0060] High-purity vanadium (vanadium mass fraction ≥ 99.95%) was used to replace the pre-purified vanadium ingot in Comparative Example 1, and V was prepared by vacuum arc furnace melting. 85 Ti5Cr 10 A hydrogen storage alloy was developed, with 1 wt% rare earth element Ce added during the smelting process. The resulting alloy's PCT curve at 25°C is shown below. Figure 5 As shown, the reversible hydrogen storage capacity of the alloy under a hydrogen release pressure of 0.01 MPa is 2.38 wt%. ICP analysis shows that the alloy contains 0.028 wt% Al and <0.01 wt% O. The low Al and O content is due to the low impurity content in the high-purity raw materials.

[0061] As can be seen from the above examples and comparative examples, by introducing rare earth elements and using vacuum electron beam melting, the lowest Al content (<0.01 wt%) and O content can be obtained, and no pretreatment of raw materials is required. The target alloy can be obtained through one-step melting, and the resulting alloy has hydrogen storage performance comparable to that of alloys prepared from pure metallic vanadium raw materials.

[0062] Example 3:

[0063] The holding time in step 3 of Example 1 was adjusted to 10 min, and the remaining steps were the same as in Example 1. Alloy preparation was carried out, and the Al content in the obtained alloy was 0.14 wt% and the O content was 0.28 wt%, indicating that the removal effect of Al and O impurities in the alloy can be optimized by adjusting the melting time.

[0064] Table 2 Comparison of Al, O, Si and main phase contents in each embodiment and comparative example

[0065]

Claims

1. A method for preparing a high-purity vanadium-based hydrogen storage alloy with low aluminum content, comprising the following steps: 1) Weigh out industrial vanadium raw material and metal M, and add rare earth metals to them, then mix them. The industrial vanadium raw material is selected from any one or more combinations of the following groups: industrial VFe alloy, industrial VAl alloy, industrial metallic V, and industrial MoVAl alloy. The rare earth metal is selected from any one or a combination of two or more elements from the group consisting of: cerium, yttrium, and lanthanum. The metal M is selected from any one or more elements from the following group: Ti, Cr, Fe, Mn, Co, Ni, Mo; 2) The target alloy is melted in a vacuum electron beam furnace. The raw materials mixed in step 1) are placed in the vacuum electron beam furnace for melting and vacuum operation is performed to remove air and moisture from the furnace. 3) Maintain the vacuum level of the furnace body and the gun body, start the electron gun, use the linear scanning method for the electron beam, and gradually increase the power control mode for melting, gradually increasing the gun body power until all the mixed raw materials are melted; in, Gun body vacuum degree ≤ 5.0 × 10 -3 Pa; and / or Furnace vacuum degree ≤ 5.0 × 10 -2 Pa; and / or The power of the gun body is 35-75 kW; and / or Melting time is 5-60 min; 4) After melting is completed, the electron beam is turned off and the furnace is cooled to room temperature under vacuum to obtain vanadium-based hydrogen storage alloy ingots; 5) Grind the vanadium-based hydrogen storage alloy ingot obtained in step 4) to remove surface impurities and obtain the finished vanadium-based hydrogen storage alloy.

2. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, The mass of the rare earth metal is 0.5-10 wt% of the industrial vanadium raw material; and / or The amounts of metal M and vanadium constitute the target alloy chemical formula V. x M 1-x , where 40≤x≤95.

3. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, The purity of the rare earth metal is 99.5% to 99.95%; and / or The purity of the metal M is 99~99.95%.

4. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, Step 2) Vacuuming operation includes: first, evacuating the melting chamber to a vacuum level ≤ 5.0 × 10⁻⁶. -3 Pa; then high-purity argon gas was introduced to bring the pressure to 0.05~1 MPa, and then the vacuum was evacuated again to ≤2.0×10 Pa. -3 Pa; and / or The vacuuming operation is repeated 2 to 3 times.

5. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, Step 3) The gun power is 45-65 kW; and / or Melting time is 5-25 min.

6. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, Before step 5), the process also includes repeating steps 2) to 4) on the vanadium-based hydrogen storage alloy ingot.

7. The method for preparing a low-aluminum-content, high-purity vanadium-based hydrogen storage alloy according to claim 1, wherein, Step 4) Cooling time ≥ 4 h.

8. A low-aluminum-content, high-purity vanadium-based hydrogen storage alloy obtained by the preparation method according to any one of claims 1-7, wherein, The hydrogen storage alloy is a vanadium-based hydrogen storage alloy with the general chemical formula V. x M 1-x M is selected from any combination of two or more elements from the following group: Ti, Cr, Fe, Mn, Co, Ni, Mo; 40≤x≤95.

9. The application of the low-aluminum-content, high-purity vanadium-based hydrogen storage alloy of claim 8 in the preparation of hydrogen storage materials.

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