Hydrogen storage alloy and method for producing the same

Abstract

To provide a hydrogen storage alloy which enables cost reduction without significantly reducing hydrogen storage amount compared to conventional technologies.SOLUTION: There is provided a hydrogen storage alloy which comprises 15 to 30 mass% of La, 5 to 15 mass% of Ce, 0 to 0.05 mass% of Pr, 0.01 to 0.15 mass% of Nd, 0 to 0.05 mass% of Sm, 5 to 15 mass% of Co, 2 to 8 mass% of Mn, 0 to 0.05 mass% of Al, 0 mass% or more and less than 3.00 mass% of Fe, 0 mass% or more and less than 3.00 of Cu, 0 mass% or more and less than 3.00 mass% of P, 0 mass% or more and less than 3.00 mass of C and the remainder of Ni and inevitable impurities and satisfies the following expressions (1) and (2). 4.5<B / A<5.5 (1) and 0.10<[Fe]+[Cu]+[P]+[C]<3.00 (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydrogen storage alloys and methods for producing the same. [Background technology]

[0002] In order to build an energy supply society that uses hydrogen as a secondary energy, hydrogen storage methods are being developed. Possible hydrogen storage methods include storing hydrogen as high-pressure hydrogen or liquid hydrogen, or using organic hydrides or hydrogen storage alloys (MH). Among these, the storage method using MH, which has excellent safety and volumetric filling efficiency, is attracting attention.

[0003] MH is required to have a high hydrogen storage capacity. Generally, it is preferable for MH to have a low impurity content. For example, Patent Document 1 discloses that if the total amount of metallic impurities exceeds 1000 wtppm (i.e., exceeds 0.10 mass%), the hydrogen storage capacity of the hydrogen storage alloy significantly decreases. Specifically, in an example in which the total amount of metallic impurities was 0.10 mass% or less, the hydrogen storage capacity was 7.5 wt% or more, while in a comparative example in which the total amount of metallic impurities was more than 0.10 mass%, the hydrogen storage capacity was 3.0 wt% or less, which is a decrease to 40% or less. It also discloses that non-metallic impurities (S, C, N) particularly reduce hydrogen storage capacity, and therefore their respective contents should be 100 wtppm or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2011-21276 Summary of the Invention [Problem to be solved by the invention]

[0005] MHs can usually be produced using pure metals, etc. However, pure metals are expensive. Furthermore, in recent years, the cost of pure Ni and other materials has increased due to factors such as increased demand for stainless steel in the Pacific Rim region. To reduce costs, it is possible to produce MHs using recycled materials instead of pure metals. However, using recycled materials increases the amount of impurities, which may result in a significant decrease in the hydrogen storage capacity, as disclosed in Patent Document 1, for example.

[0006] The present invention has been made in view of the above circumstances, and one of its objectives is to provide a hydrogen storage alloy that can reduce costs without significantly reducing the hydrogen storage capacity compared to the prior art, and a method for manufacturing the same. [Means for solving the problem]

[0007] Aspect 1 of the present invention is La: 15~30% by mass, Ce: 5~15% by mass, Pr: 0~0.05% by mass, Nd: 0.01~0.15% by mass, Sm: 0~0.05% by mass, Co: 5~15% by mass, Mn: 2~8% by mass, Al: 0~0.05% by mass, Fe: 0% by mass or more and less than 3.00% by mass, Cu: 0% by mass or more and less than 3.00% by mass, P: 0% by mass or more and less than 3.00% by mass, C: 0% by mass or more and less than 3.00% by mass, and The balance is a hydrogen storage alloy consisting of Ni and unavoidable impurities and satisfying the following formulas (1) and (2). 4.5 0.10<[Fe]+[Cu]+[P]+[C]<3.00 (2) ​In formula (1), A is the total number of moles of La, Ce, Pr, Nd, and Sm contained in the hydrogen storage alloy, and B is the total number of moles of Ni, Co, Mn, and Al contained in the hydrogen storage alloy. In formula (2), [Fe], [Cu], [P] and [C] represent the contents of Fe, Cu, P and C, respectively, expressed in mass %.

[0008] Aspect 2 of the present invention is The hydrogen storage alloy according to aspect 1 satisfies the following formula (3): [P] + [C] ≥ 0.1 (3) In the formula (3), [P] and [C] represent the P and C contents, respectively, expressed in mass %.

[0009] Aspect 3 of the present invention is The method for producing a hydrogen storage alloy according to aspect 1 or 2 is characterized in that raw materials containing recycled materials are used.

[0010] A fourth aspect of the present invention is Aspect 4 is the method according to aspect 3, wherein the recycled material is a recycled material from a secondary battery.

[0011] A fifth aspect of the present invention is 5. The method according to claim 4, wherein the secondary battery is a lithium ion battery. [Effects of the Invention]

[0012] According to the embodiments of the present invention, it is possible to provide a hydrogen storage alloy and a method for producing the same that can reduce costs without significantly reducing the hydrogen storage capacity compared to the prior art. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 shows the results of measuring the hydrogen storage capacity of the hydrogen storage alloys of Test Nos. 1 to 4. [Figure 2]FIG. 2 shows the results of measuring the hydrogen absorption rate of the hydrogen storage alloys of Test Nos. 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have investigated from various angles to realize a hydrogen storage alloy that can reduce costs without significantly reducing the hydrogen storage capacity compared to conventional techniques. As a result, they have found that a specific composition (M A Ni B-x-y-z Co x Mn y Al z , M is a specific lanthanide such as La or Ce, 4.5

[0015] The following provides details of each requirement stipulated by the embodiment of the present invention.

[0016] The hydrogen storage alloy according to the embodiment of the present invention preferably contains 15 to 30 mass% La, 5 to 15 mass% Ce, 0 to 0.05 mass% Pr, 0.01 to 0.15 mass% Nd, 0 to 0.05 mass% Sm, 5 to 15 mass% Co, 2 to 8 mass% Mn, 0 to 0.05 mass% Al, 0 to less than 3.00 mass% Fe, 0 to less than 3.00 mass% Cu, 0 to less than 3.00 mass% P, 0 to less than 3.00 mass% C, with the balance being Ni and inevitable impurities. Furthermore, the hydrogen storage alloy according to the embodiment of the present invention satisfies the following formulas (1) and (2): ​4.5 0.10<[Fe]+[Cu]+[P]+[C]<3.00 (2) In formula (1), A is the total number of moles of La, Ce, Pr, Nd, and Sm contained in the hydrogen storage alloy, and B is the total number of moles of Ni, Co, Mn, and Al contained in the hydrogen storage alloy. In formula (2), [Fe], [Cu], [P] and [C] represent the contents of Fe, Cu, P and C, respectively, expressed in mass %. The alloy described above can reduce costs without significantly reducing the hydrogen storage capacity compared to conventional technologies. It can also maintain a predetermined hydrogen storage capacity without pulverization even after repeated hydrogen storage and desorption (e.g., 25 times). Furthermore, it can exhibit a hydrogen storage rate equivalent to that of conventional technologies.

[0017] [La: 15~30% by mass, Ce: 5~15% by mass, Pr: 0~0.05% by mass, Nd: 0.01~0.15% by mass, Sm: 0~0.05% by mass] In LaNi5-based hydrogen storage alloys, La can be substituted with Ce, Pr, Nd, and Sm in predetermined amounts. In the embodiments of the present invention, Ce, Pr, Nd, and Sm can be contained in addition to La within the above-mentioned ranges. Pr and Sm may be contained (i.e., greater than 0% by mass) or not (i.e., 0% by mass). This reduces the effects of specific impurities.

[0018] [Co: 5~15% by mass, Mn: 2~8% by mass, Al: 0~0.05% by mass] In the LaNi5-based hydrogen storage alloy, Ni can be substituted with Co, Mn, or Al in a predetermined amount. In the embodiment of the present invention, Co, Mn, and Al can be contained in addition to Ni within the above ranges. Al may be contained (i.e., greater than 0% by mass) or not (i.e., 0% by mass). This can reduce the influence of specific impurities.

[0019] [Fe: 0 mass% or more and less than 3.00 mass%]​ Fe may be an impurity that may be mixed in when recycled materials are used, etc. The Fe content is preferably greater than 0 mass%, more preferably greater than 0.01 mass%, and even more preferably greater than 0.10 mass%. On the other hand, the upper limit of the Fe content may be less than 3.00 mass%, or may be 2.00 mass% or less, or 1.00 mass% or less, so as to satisfy formula (2).

[0020] [Cu: 0% by mass or more and less than 3.00% by mass] Cu may be an impurity that may be mixed in when recycled materials are used, etc. The Cu content is preferably greater than 0 mass%, more preferably greater than 0.01 mass%, and even more preferably greater than 0.10 mass%. On the other hand, the upper limit of the Cu content may be less than 3.00 mass%, or may be 2.00 mass% or less, or 1.00 mass% or less, so as to satisfy formula (2).

[0021] [P: 0 mass% or more and less than 3.00 mass%] P may be an impurity that may be mixed in when recycled materials are used, etc. The P content is preferably greater than 0% by mass, more preferably greater than 0.01% by mass, and even more preferably greater than 0.10% by mass. On the other hand, the upper limit of the P content may be less than 3.00% by mass, or may be 2.00% by mass or less, or 1.00% by mass or less, so as to satisfy formula (2).

[0022] [C: 0 mass% or more and less than 3.00 mass%] C may be an impurity that may be mixed in when recycled materials are used, etc. The C content is preferably greater than 0% by mass, more preferably greater than 0.01% by mass, and even more preferably greater than 0.10% by mass. On the other hand, the upper limit of the C content may be less than 3.00% by mass, or may be 2.00% by mass or less, or 1.00% by mass or less, so as to satisfy formula (2).

[0023] The hydrogen storage alloy according to the embodiment of the present invention preferably contains the above-described component composition, with the balance being nickel and inevitable impurities in one embodiment of the present invention. Elements such as S that are introduced due to the conditions of raw materials, materials, manufacturing facilities, etc. are permitted as inevitable impurities. Note that, for example, Fe, Cu, P, and C are typically considered inevitable impurities, but some elements have composition ranges that are separately specified as described above. Therefore, in this specification, the term "unavoidable impurities" is used to refer to elements that do not have composition ranges that are separately specified.

[0024] [4.5 The hydrogen storage alloy according to the embodiment of the present invention must satisfy formula (1) as one of the requirements for reducing costs without significantly degrading hydrogen storage properties compared to conventional techniques. If B / A is 4.5 or less or 5.5 or more, there is a risk of significant degradation of hydrogen storage properties.

[0025] [0.10<[Fe]+[Cu]+[P]+[C]<3.00 ···(2)] The hydrogen storage alloy according to the embodiment of the present invention must satisfy formula (2) as one of the requirements for reducing costs without significantly degrading hydrogen storage properties compared to conventional techniques. The content of one or more elements selected from the group consisting of Fe, Cu, P, and C is greater than 0.10 mass% so as to satisfy the lower limit of formula (2). For example, the lower limit of formula (2) may be satisfied by including a predetermined amount of one, two, three, or all four elements selected from the group consisting of Fe, Cu, P, and C. For example, the content of one or more elements of Fe and Cu may be greater than 0.10 mass%. Below the lower limit of formula (2), for example, the use of recycled materials is significantly restricted, making it virtually impossible to achieve cost reductions compared to conventional techniques. On the other hand, above the upper limit of formula (2), hydrogen storage properties may be significantly degraded. ​Furthermore, conventional hydrogen storage alloys suffer from the problem of being pulverized by repeated expansion due to hydrogen absorption, and the resulting powder clogs filters in devices containing the alloy. By satisfying formula (2), the hydrogen storage alloy according to the embodiment of the present invention can reduce the amount of expansion due to hydrogen absorption and suppress pulverization.

[0026] Among Fe, Cu, P, and C, P and C in particular have relatively small atomic radii, which can adversely affect the absorption of hydrogen, which has a small atomic radius. Furthermore, P and other elements can be difficult to remove during the manufacturing process of the hydrogen storage alloy. The hydrogen storage alloy according to the embodiment of the present invention may contain a predetermined amount of P and / or C, which significantly reduces costs compared to conventional techniques. Specifically, the embodiment of the present invention achieves a significant cost reduction effect by satisfying the following formula (3): [P] + [C] ≥ 0.10 (3) The lower limit of formula (3) is more preferably greater than 0.10 mass%, even more preferably greater than 0.12 mass%, and even more preferably greater than 0.15 mass%. The upper limit of formula (3) may be, for example, less than 3.00 mass%, 2.00 mass% or less, or 1.00 mass% or less so as to satisfy formula (2).

[0027] The hydrogen storage alloy according to the embodiment of the present invention may have the above-described chemical composition, and its manufacturing method is not particularly limited and can be manufactured by a known method. In the manufacturing method of the hydrogen storage alloy according to the embodiment of the present invention, it is preferable to use raw materials containing recycled materials, from the viewpoints of cost reduction and global environmental conservation. More preferably, the recycled materials include secondary batteries, and even more preferably, lithium-ion batteries. These batteries may contain Fe, Cu, P, and C in addition to Ni, Co, Mn, Al, and other constituent elements of the embodiment of the present invention. For example, in a lithium-ion battery, the positive electrode material may contain Ni, Co, Mn, Fe, and / or P, the negative electrode material may contain C, the positive electrode current collector may contain Al, the negative electrode current collector may contain Cu, and the electrolyte salt may contain P. Therefore, recycled materials from these batteries are suitable for the manufacturing method according to the embodiment of the present invention. [Example]

[0028] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0029] After incineration and crushing of lithium-ion batteries, Co, Ni, and Mn were metallized in a reducing atmosphere, and then the metals and slag were separated and recovered, yielding a recycled alloy with the composition shown in Table 1. As shown in Table 1, while the above separation and recovery can remove, for example, Li, certain impurities according to an embodiment of the present invention (Fe, Cu, P, and C) cannot be completely removed, and some of them remained in the recycled alloy. In Table 1, "<0.01" indicates that the corresponding component was not present or was below the detection limit.

[0030] [Table 1]

[0031] Specified rare earth elements (La, Ce, Pr, Nd, and Sm) and pure metals (Ni, Co, and Mn) were mixed in specified proportions and melted in a general furnace such as a high-frequency induction furnace to obtain the hydrogen storage alloy of Test No. 1. The hydrogen storage alloys of Test Nos. 2 to 4 were obtained in the same manner as Test No. 1, except that approximately 10 mass%, approximately 15 mass%, and approximately 20 mass% of the pure metals were replaced with recycled alloys. Specifically, Test No. 2 was prepared by replacing approximately 10 mass% (approximately 5.43 mass parts Ni, approximately 0.94 mass parts Co, and approximately 0.44 mass parts Mn) of the pure metals of Test No. 1 (54.34 mass parts Ni, 9.41 mass parts Co, and 4.42 mass parts Mn) with approximately 6.81 mass parts recycled alloys. The component compositions of Test Nos. 1 to 4 are shown in Table 2. In Table 2, "<0.01" indicates that the corresponding component was not present or was below the detection limit. "-" indicates that the corresponding component was not analyzed because it was considered to be absent or below the detection limit. Furthermore, the contents of La to Sm in Test No. 1 were the same as the contents of La to Sm in Test Nos. 2 to 4, and Table 2 lists only the total contents of La to Sm in Test No. 1.

[0032] [Table 2]

[0033] The hydrogen storage alloys of Test Nos. 1 to 4 were subjected to the following hydrogen storage characteristic evaluation. 100 g of each alloy was sealed in a container, and hydrogen was absorbed into each alloy by introducing hydrogen at a rate of 1.5 NL / min under a gauge pressure of 0.9 MPaG at -10°C. Hydrogen was then released from each alloy at a gauge pressure of 0.0 MPaG at 80°C. This cycle was repeated 25 times.

[0034] Figure 1 shows the results of evaluating the hydrogen storage capacity versus the number of cycles. Compared to the conventional hydrogen storage alloy, Test No. 1, which contained a low amount of impurities, Test Nos. 2 to 4, which contained more than 0.10 mass% of total impurities (less than 3.00 mass%) of Fe, Cu, P, and C, showed a decrease in hydrogen storage capacity of less than 20%, meaning that the hydrogen storage capacity did not decrease significantly. Furthermore, all alloys were found to maintain their hydrogen storage capacity after 2 to 25 cycles without disintegrating, compared to the first cycle.

[0035] The results of the hydrogen absorption rate evaluation for the first cycle are shown in Figure 2. For all alloys, the amount of hydrogen absorption was nearly saturated in about 5 to 10 minutes, and it was found that the hydrogen absorption rate could be maintained even when the total impurity content of Fe, Cu, P, and C was more than 0.10 mass% (less than 3.00 mass%).

Claims

1. La: 15 to 30% by mass, Ce: 5 to 15% by mass, Pr: 0 to 0.05% by mass, Nd: 0.01 to 0.15% by mass, Sm: 0 to 0.05% by mass, Co: 5 to 15% by mass, Mn: 2 to 8% by mass, Al: 0 to 0.05% by mass, Fe: 0% by mass or more and less than 3.00% by mass, Cu: 0% by mass or more and less than 3.00% by mass, P: 0% by mass or more and 0.094% by mass or less, C: 0% by mass or more and 0.4% by mass or less, and The balance is Ni and unavoidable impurities, and the hydrogen storage alloy satisfies the following formulas (1), (2), and (3): 4.5<B / A<5.5...(1) 0.10<[Fe]+[Cu]+[P]+[C]<3.00...(2) [P]+[C]≧0.1...(3) In formula (1), A is the total number of moles of La, Ce, Pr, Nd, and Sm contained in the hydrogen storage alloy, and B is the total number of moles of Ni, Co, Mn, and Al contained in the hydrogen storage alloy. In formula (2), [Fe], [Cu], [P] and [C] represent the contents of Fe, Cu, P and C, respectively, expressed in mass %. In formula (3), [P] and [C] represent the P and C contents, respectively, expressed in mass %.

2. 2. The method for producing a hydrogen storage alloy according to claim 1, wherein raw materials containing recycled materials are used.

3. The manufacturing method according to claim 2 , wherein the recycled material is a recycled material from a secondary battery.

4. The method according to claim 3 , wherein the secondary battery is a lithium ion battery.

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