JP3992289B2 - Low Co hydrogen storage alloy - Google Patents

Description

The present invention relates to an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, and in particular, the content ratio of cobalt in the alloy is extremely small, and particularly to the life characteristics required for electric vehicles and hybrid electric vehicle applications. The present invention relates to an excellent low Co hydrogen storage alloy.

  A hydrogen storage alloy is an alloy that reacts with hydrogen to form a metal hydride and can reversibly store and release a large amount of hydrogen near room temperature. Therefore, it can be used for nickel / hydrogen mounted in hybrid electric vehicles and digital still cameras. Practical application has been studied in various fields such as batteries and fuel cells.

As the hydrogen storage alloy, various alloys such as an AB ₅ type alloy typified by LaNi ₅ , an AB ₂ type alloy typified by ZrV _0.4 Ni _1.5 , and other AB type alloys and A ₂ B type alloys are known. Many of them have a high affinity with hydrogen and have an element group (Ca, Mg, rare earth elements, Ti, Zr, V, Nb, Pt, Pd, etc.) that plays a role in increasing the hydrogen storage capacity, and the affinity with hydrogen. Although it is relatively low and has a small amount of occlusion, it is composed of a combination with element groups (Ni, Mn, Cr, Fe, etc.) that promote the hydrogenation reaction and lower the reaction temperature.

Our research group uses an AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure, more specifically, a rare earth-based mixture Mm (Misch metal) at the A site, and Ni, Al, B at the B site. Research has been conducted focusing on an Mm-Ni-Mn-Al-Co alloy using four elements of Mn and Co. This type of Mm-Ni-Mn-Al-Co alloy can form a negative electrode with a relatively inexpensive material compared to other alloy compositions, has a long cycle life, and increases internal pressure due to generated gas during overcharge. Features such as the ability to construct a few sealed nickel-metal hydride storage batteries.

  By the way, in the constituent elements of the Mm-Ni-Mn-Al-Co alloy, Co is an important element that suppresses the pulverization of the alloy and exhibits an effect in improving the life characteristics. In general, Co (molar ratio of 0.6 to 1.0) is blended. However, Co is a very expensive metal, and it is an important solution to reduce Co in consideration of future expansion of use of hydrogen storage alloys. On the other hand, since reducing the Co leads to a decrease in output characteristics and life characteristics, reducing Co while maintaining output characteristics and life characteristics has been one of the research subjects. Especially in the development of power sources for electric vehicles (EV: Electric Vehicle) and hybrid electric vehicles (HEV: Hybrid Electric Vehicle; vehicles that use two power sources: an electric motor and an internal combustion engine), while reducing the Co life Maintaining properties at a high level has been an essential task.

  In view of this problem, various proposals for maintaining battery characteristics while reducing the amount of Co have been disclosed.

  For example, Patent Document 1 (Japanese Patent Laid-Open No. 9-213319) proposes changing the composition of an Mm—Ni—Mn—Al—Co-based alloy and adding a small amount of one element thereto.

Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-294373) describes a method for providing a hydrogen storage alloy for a negative electrode for a secondary battery that is less expensive than conventional alloys with a large amount of Co and can be considered for recyclability. A hydrogen storage alloy having the composition of (1) and having a substantially single phase and an average major axis of crystals of 30 to 160 μm, or 5 μm to less than 30 μm has been proposed.
RNi _X Co _y M _Z (1) (R: rare earth element, M: Mg, Al, Mn, etc. 3.7 ≦ x ≦ 5.3, 0.1 ≦ y ≦ 0.5, 0.1 ≦ z ≦ 1.0, 5.1 ≦ x + y + z ≦ 5.5)

The research group to which the present inventor belongs, for example, in Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-18176), is excellent in hydrogen storage characteristics while reducing the content ratio of cobalt, and has excellent pulverization characteristics and good initial characteristics and output characteristics. As a hydrogen storage alloy having durability and storage stability, the general formula MmNi _a Mn _b Co _c Cu _d (where Mm is Misch metal, 3.7 ≦ a ≦ 4.2, 0 .3 <b ≦ 0.6, 0.2 ≦ c ≦ 0.4, 0 <d ≦ 0.4, 5.00 ≦ a + b + c + d ≦ 5.35) and hydrogen having a CaCu ₅ type crystal structure A storage alloy is proposed.

Further, in Patent Document 4 (Japanese Patent Laid-Open No. 2001-40442), the content of cobalt is reduced, and at the same time, the hydrogen storage characteristics are excellent, and the pulverization characteristics, good initial characteristics and output characteristics, and durability and as the hydrogen storage alloy having a high reliability for storage stability, the general formula _{MmNi a Mn b Al c Co d} X e ( wherein, Mm is the mischmetal, X is Fe and / or Cu, 3.7 ≦ a ≦ 4. 2, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.4, 0.2 ≦ d ≦ 0.4, 0 ≦ e ≦ 0.4, 5.00 ≦ a + b + c + d + e ≦ 5.20, where b = c = not 0, also 0 <b ≦ 0.3 and 0 <for c ≦ 0.4, the hydrogen storage having CaCu ₅ type crystal structure represented by b + c <0.5), An alloy is proposed.

Moreover, in patent document 5 (Unexamined-Japanese-Patent No. 2001-348636), manufacturing cost is reduced by making the content rate of cobalt extremely small, and it is excellent in the pulverization characteristic and the hydrogen occlusion characteristic, and the favorable output characteristic and storage characteristic As a hydrogen storage alloy having general formula MmNi _a Mn _b Al _c Co _d (where Mm is Misch metal, 4.1 <a ≦ 4.3, 0.4 <b ≦ 0.6, 0.2 ≦ c) ≦ 0.4, 0.1 ≦ d ≦ 0.4, 5.2 ≦ a + b + c + d ≦ 5.45) or general formula MmNi _a Mn _b Al _c Co _d X _e (where Mm is Misch metal, X is Cu And / or Fe, 4.1 <a ≦ 4.3, 0.4 <b ≦ 0.6, 0.2 ≦ c ≦ 0.4, 0.1 ≦ d ≦ 0.4, 0 <e ≦ 0 CaCu ₅ type crystal structure represented by .1,5.2 ≦ a + b + c + d + e ≦ 5.45) A AB ₅ type hydrogen storage alloy having proposes a hydrogen-absorbing alloy, wherein a lattice length of c axis is not less than 406.2Pm.

Furthermore, in Patent Document 6 (JP 2005-133193), the general formula _{MmNi a Mn b Al c Co d} ( wherein, Mm is the mischmetal, 3.7 ≦ a ≦ 4.7,0.3 ≦ b ≦ 0.65, 0.2 ≦ c ≦ 0.5, 0 <d ≦ 0.15, 4.9 ≦ a + b + c + d ≦ 5.5), a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure. Thus, a low Co hydrogen storage alloy for use in a battery charged / discharged in the central region of the charge / discharge depth is proposed, characterized in that the amount of corrosion required in the following test A is 600 μmol or less.

JP-A-9-213319 JP 2002-294373 A JP2001-18176 JP2001-40442 JP 2001-348636 A JP-A-2005-133193

  The present invention is a low-Co hydrogen that can further improve the life characteristics even when Co is further reduced, with research centered on applications for batteries mounted in next-generation electric vehicles and hybrid electric vehicles. It is intended to provide a storage alloy.

The present inventors have in view of the above problems have conducted extensive research, in the composition of the alloy represented by the general formula _{MmNi a Mn b Al c Co d} , reduce the composition ratio of Co (molar ratio) to 0.35 or less Even in this case, it has been found that the life characteristics (also referred to as durability) can be maintained at a high level by adjusting the a-axis length, c-axis length, and standard deviation of the a-axis length of the crystal lattice. The present invention has been conceived based on the above. As for the general formula _{MmNi a Mn b Al c Co d} Fe e composition of the alloy represented by the found that similar results, in which conceived the present invention based on this finding.

That is, the present invention has the general formula _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 0 <d ≦ 0.35,0 ≦ e ≦ 0.11,5.20 ≦ a + b + c + d + e ≦ 5 a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure which may be represented by .50), obtained by refinement of lattice constant with X-ray diffraction measurement, a crystalline lattice of the CaCu ₅ type crystal structure Low Co hydrogen, characterized in that the axial length is 499.0 pm or more, the c-axis length is 405.0 pm or more, and the standard deviation of the a-axis length is less than 2.0 × 10 ⁻² pm Propose a storage alloy.

A low-Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by the above-described predetermined composition formula, wherein the crystal lattice has an a-axis length of 499.0 pm or more and a c-axis length of 405.0 pm If the standard deviation of the a-axis length is less than 2.0 × 10 ⁻² pm within the above range, even if the Co content is reduced to a lower level than before, the life characteristics are further enhanced. Can be maintained at a level. Specifically, sufficiently high life characteristics can be obtained even when used for electric vehicles and hybrid electric vehicles (specifically, negative electrode active materials for batteries mounted on electric vehicles and hybrid electric vehicles). .

It is the figure plotted in the coordinate which consists of a horizontal axis | shaft: Standard deviation of a-axis length, and a vertical axis | shaft: Micronization index | exponent based on the measurement result about the hydrogen storage alloy obtained in the Example and the comparative example. It is the figure explaining the peak position used when refine | purifying a lattice constant using the X-ray-diffraction chart of the hydrogen storage alloy obtained in Example 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

  In this specification, “X to Y” (X and Y are arbitrary numbers) means “X or more and Y or less” unless otherwise specified, “preferably larger than X, Y It includes the meaning of “smaller”.

The hydrogen storage alloy of the present embodiment (hereinafter referred to as “the present hydrogen storage alloy”) can be represented by the general formula MmNi _a Mn _b Al _c Co _d or the general formula MmNi _a Mn _b Al _c Co _d F _e CaCa ₅ type. It is a low Co hydrogen storage alloy having a crystal structure.

(ABx)
In the present hydrogen storage alloy, the ratio of the total number of moles of elements constituting the B site to the total number of moles of elements constituting the A site in the ABx composition a + b + c + d or a + b + c + d + e (this ratio is also referred to as ABx or a + b + c + d (+ e)). ) Is 5.20 ≦ ABx ≦ 5.50. It consists of non-stoichiometric composition of B site rich, and if it is ABx in this range, it will contribute to the reduction of battery life and pulverization characteristics and suppress the deterioration of hydrogen storage characteristics and output characteristics. be able to. From such a viewpoint, ABx is more preferably 5.25 or more, and more preferably 5.45 or less.

(A-axis length / c-axis length)
In this hydrogen storage alloy, from the viewpoint of improving output characteristics (particularly pulse discharge characteristics), activity (activity), and life characteristics, it is important that the a-axis length is 499.0 pm or more, and in particular, 503.0 pm or less. Is preferred. In particular, it is more preferably 499.7 pm or more, and more preferably 502.7 pm or less. On the other hand, it is important that the c-axis length is 405.0 pm or more, and it is particularly preferable that the c-axis length is 408.0 pm or less. Of these, 405.6 pm or more is particularly preferable, and 407.4 pm or less is more preferable. For example, when the a-axis length is 499.7 pm to 501.2 pm and the c-axis length is 405.6 pm to 406.2 pm, it is a particularly preferable example.

  In view of improving output characteristics (particularly pulse discharge characteristics), activity (activity) and life characteristics, it is preferable to set the a-axis length and the c-axis length within the above ranges. The test results shown in the paragraphs [0038]-[0062] of the present invention are supported by the present invention.

Furthermore, it has been found that the preferred a-axis length and c-axis length differ depending on the level of ABx.
That is, for a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by the general formula MmNi _a Mn _b Al _c Co _d ,
(A) In the composition of 5.25 ≦ ABx <5.30, the a-axis length is preferably 500.5 pm or more and 502.7 pm or less, and the c-axis length is preferably 405.6 pm or more and 406.9 pm or less. .
(B) In the composition of 5.30 ≦ ABx <5.35, the a-axis length is preferably 500.0 pm or more and 502.4 pm or less, and the c-axis length is preferably 405.9 pm or more and 407.2 pm or less. .
(C) In the composition of 5.35 ≦ ABx <5.40, the a-axis length is preferably 499.8 pm or more and 502.3 pm or less, and the c-axis length is preferably 406.0 pm or more and 407.3 pm or less. .
(D) In the composition of 5.40 ≦ ABx <5.45, the a-axis length is preferably 499.7 pm or more and 502.3 pm or less, and the c-axis length is preferably 406.1 pm or more and 407.4 pm or less. .
In the composition of 5.20 ≦ ABx <5.25, the a-axis length is preferably 500.7 pm or more and 502.8 pm or less, and the c-axis length is preferably 405.5 pm or more and 406.9 pm or less. Has been confirmed.

In addition, regarding a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by the general formula MmNi _a Mn _b Al _c Co _d Fe _e ,
(E) In the composition of 5.25 ≦ ABx <5.30, the a-axis length is preferably 500.5 pm or more and 503.0 pm or less, and the c-axis length is preferably 405.6 pm or more and 407.9 pm or less. .
(F) In the composition of 5.30 ≦ ABx <5.35, the a-axis length is preferably 500.0 pm or more and 502.8 pmpm or less, and the c-axis length is preferably 405.6 pm or more and 408.2 pm or less. .
(G) In the composition of 5.35 ≦ ABx <5.40, the a-axis length is preferably 499.8 pm or more and 502.8 pm or less, and the c-axis length is preferably 405.6 pm or more and 408.3 pm or less. .
(H) In the composition of 5.40 ≦ ABx <5.45, the a-axis length is preferably 499.7 pm or more and 502.6 pm or less, and the c-axis length is preferably 405.7 pm or more and 408.4 pm or less. .
In the composition of 5.20 ≦ ABx <5.25, the a-axis length is preferably 500.7 pm or more and 503.1 pm or less, and the c-axis length is preferably 405.5 pm or more and 407.9 pm or less. Has been confirmed.

By controlling the a-axis length and the c-axis length within the above ranges according to the respective ranges of ABx, it is possible to provide life characteristics required for a hybrid electric vehicle or the like. The life characteristics in this case include, for example, the following measurement method, that is, the hydrogen storage alloy is pulverized and sieved to adjust the particle size within a range of 20 to 53 μm to obtain a hydrogen storage alloy powder. The average particle size of the hydrogen storage alloy powder (; Pre-cycle particle size, D ₅₀ ) was measured with a particle size distribution measuring device, and 2 g of this hydrogen storage alloy powder was weighed and placed in a sample holder for a PCT device, and the surface was washed twice with a hydrogen pressure of 1.75 MPa. Then, activation was performed twice by introducing a hydrogen pressure of 3 MPa, and then hydrogen was occluded by introducing 3 MPa of hydrogen gas into 2.0 g of hydrogen storage alloy powder by a PCT apparatus, and the temperature was increased to 45 ° C. When the average particle size of the hydrogen storage alloy powder after 50 cycles test (; particle size after cycle, D ₅₀ ) was measured with a particle size distribution analyzer, It can be set as the hydrogen storage alloy with the life characteristic in which the ratio of the particle size after the cycle with respect to the particle size before the cycle (micronization residual ratio (%)) is 50% or more.

  In order to maintain the high durability required for the use of the hybrid electric vehicle, the pulverization residual ratio (%) after 50 cycles needs to be 50% or more. As described above, by controlling the a-axis length and the c-axis length for each range of ABx, the Co composition ratio (molar ratio) is 0.35 or less, which is inexpensive, and as described above, the next-generation hybrid electric It is possible to provide a hydrogen storage alloy that satisfies the high durability required for a negative electrode active material for automobile batteries.

  As described above, the preferred a-axis length and c-axis length are different depending on the level of ABx, and the characteristics required for the use of the hybrid electric vehicle can thereby be obtained. Paragraph [0022] of Japanese Patent Application No. 2005-31782 ]-[0024], which is supported by the test results shown in paragraphs [0038]-[0062], which are also incorporated in the present invention and used as part of the technical idea of the present invention. Is.

(composition)
Regarding the composition ratio of Ni, Mn, Al, and Co or Ni, Mn, Al, Co, and Fe, as described above, 5.20 ≦ a + b + c + d (+ e) ≦ 5.50, and preferably 5.25 ≦. Although it may be adjusted as appropriate within the range of a + b + c + d (+ e) or a + b + c + d (+ e) ≦ 5.45, the present invention has a predetermined range regarding the ratio of Co and Fe, that is, 0 <d ≦ 0.35, 0 The condition is that ≦ e ≦ 0.11.

  If a + b + c + d (+ e), that is, ABx is specified in such a range, and the Co amount and Fe amount are specified, the standard deviation of the a-axis length, c-axis length, and a-axis length is adjusted to a predetermined range. Although the fixed effect in this invention, especially the effect which raises a pulverization residual rate can be acquired, it is still more preferable to adjust each amount of Ni, Mn, and Al from a viewpoint further shown below. At this time, as an example of the procedure for determining the composition ratio, the composition ratio (molar ratio) of Co and Fe is determined, the composition ratio (molar ratio) of Ni is adjusted, and then the ratio of Mn, Al, and ABx are adjusted. A method of adjusting the standard deviation of the a-axis length, the c-axis length, and the a-axis length of the crystal lattice can be exemplified by adjusting the manufacturing conditions.

  In the present invention, it is important that the ratio (d) of Co is 0 <d ≦ 0.35, preferably 0 <d ≦ 0.32, more preferably 0.10 ≦ d ≦ 0.32, Adjustment is made within the range of 0.10 ≦ d ≦ 0.28. The present invention is characterized in that the amount of Co can be reduced in this way.

  Fe is not an essential alloy element, but the addition of an appropriate amount of Fe can suppress pulverization, that is, improve the life characteristics. In the present invention, it is important that the ratio (e) of Fe is 0 ≦ e ≦ 0.11, preferably 0.001 <e ≦ 0.11, more preferably 0.002 <e ≦ 0.11. It is better to adjust within the range. If it is in the range of 0 ≦ e ≦ 0.11, there will be little influence of reducing the activity.

  The ratio (a) of Ni is adjusted within the range of 4.0 ≦ a ≦ 4.7, preferably 4.1 ≦ a ≦ 4.6, and more preferably 4.2 ≦ a ≦ 4.5. Good. If it is within the range of 4.0 ≦ a ≦ 4.7, the output characteristics can be easily maintained, and the pulverization characteristics and the life characteristics are not particularly deteriorated.

  The ratio (b) of Mn is preferably adjusted within the range of 0.30 ≦ b ≦ 0.65. If the ratio of Mn is in the range of 0.30 ≦ b ≦ 0.65, it is possible to easily maintain the pulverization residual rate.

  The proportion (c) of Al is preferably adjusted within the range of 0.20 ≦ c ≦ 0.50. If it is in the range of 0.20 ≦ c ≦ 0.50, it can be suppressed that the plateau pressure becomes higher than necessary and the energy efficiency of charge / discharge is deteriorated, and further, the decrease of the hydrogen storage amount is suppressed. You can also.

  In the above composition, “Mm” may be a rare earth-based mixture (Misch metal) containing at least La and Ce. Normal Mm contains rare earths such as Pr, Nd, and Sm in addition to La and Ce. For example, a rare earth mixture containing Ce (40 to 50%), La (20 to 40%), Pr, and Nd as main constituent elements can be given. The La content in Mm is generally 15 to 30% by weight, particularly 18 to 30% by weight, based on the hydrogen metal alloy.

  This hydrogen storage alloy may contain any impurity of Ti, Mo, W, Si, Ca, Pb, Cd, and Mg as long as it is about 0.05% by weight or less.

(Standard deviation of a-axis length)
It is important for this low Co hydrogen storage alloy that the standard deviation of the a-axis length obtained when the lattice constant is further refined by X-ray diffraction measurement is less than 2.0 × 10 ⁻² pm, among them is preferably at 1.8 × 10 ^-2 pm or less, 0.5 × among them 10 ^-2 pm~1.8 × 10 ^-2 pm, especially 0.7 × 10 ^-2 pm~1 among them. More preferred is 8 × 10 ⁻² pm.

That is, as proved in the test described later, the tendency of the pulverization residual rate after the 500 cycle test changes with the standard deviation of the a-axis length being 2.0 × 10 ⁻² pm as a boundary, and the standard of the a-axis length By making the deviation less than 2.0 × 10 ⁻² pm, preferably less than 2.0 × 10 ⁻² pm, the residual pulverization rate after 500 cycles, in other words, high life characteristics (durability) is exceptional. Can be increased.

(Production method of low Co hydrogen storage alloy)
Production method of the present hydrogen storage alloy, for example, the general formula _{MmNi a Mn b Al c Co d} (4.0 ≦ a ≦ 4.7,0.3 ≦ b ≦ 0.65,0.2 ≦ c ≦ 0. 5,0 <d ≦ 0.35,5.2 ≦ a + b + c + d ≦ 5.5) or the general formula _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 4.0 ≦ a ≦ 4. 7, 0.3 ≦ b ≦ 0.65, 0.2 ≦ c ≦ 0.5, 0 <d ≦ 0.35, 0 <e ≦ 0.11, 5.2 ≦ a + b + c + d + e ≦ 5.5) Each hydrogen storage alloy raw material is weighed and mixed so that the alloy composition of And cast at a casting temperature of 1350 to 1550 ° C., cooled at a predetermined cooling rate (a predetermined amount of cooling water), The present hydrogen storage alloy can be obtained by heat-treating at 1040 to 1080 ° C. for 3 to 6 hours in an inert gas atmosphere, for example, argon gas, and then rapidly cooling at a predetermined temperature decrease rate.

  At this time, it has been confirmed that the temperature drop rate after the heat treatment is one of the important factors for controlling the standard deviation of the a-axis length. That is, the standard deviation of the a-axis length can be adjusted by adjusting the temperature and time of the heat treatment and changing the temperature lowering rate after the heat treatment. As a preferred example, it is preferable to rapidly cool the heat treatment temperature (maintenance temperature) to 15 to 25 ° C./min, particularly about 20 to 25 ° C./min to about 500 ° C., and then naturally cool. Although this principle could not be clarified, it is possible to suppress the recrystallization of the hydrogen storage alloy and possibly adjust the standard deviation of the a-axis length by adjusting the temperature drop rate after heat treatment. Can be considered. However, it is possible to adjust the standard deviation of the a-axis length by adjusting the composition of the hydrogen storage alloy, and there is a possibility that the standard deviation of the a-axis length can be adjusted by other means.

  The above production method is an example of the production method of the present hydrogen storage alloy, and is not limited thereto.

  For example, the a-axis length and c-axis length of the crystal lattice are adjusted within a predetermined range by appropriately selecting and controlling the casting conditions (casting method, casting temperature, cooling rate, etc.) and heat treatment conditions according to the alloy composition. can do.

  In addition to heat treatment, it is also considered effective to control the particle size of the alloy powder by classifying the alloy before heat treatment, as disclosed in, for example, JP-A-2002-212601.

  As for the casting method, the mold casting method is a preferable example. For example, it can be manufactured by a twin roll method (specifically, see paragraphs [0013] to [0016] of JP-A No. 2004-131825) and other casting methods. is there.

(Use of low Co hydrogen storage alloy)
The obtained hydrogen storage alloy (ingot) is roughly pulverized and finely pulverized into a hydrogen alloy powder of the required particle size, and the surface of the alloy is coated with a metal material or a polymer resin as necessary, or an acidic aqueous solution or alkaline It can be used as a negative electrode active material for various batteries by appropriately performing a surface treatment such as treating the surface with an aqueous solution.

  The negative electrode for a battery can be prepared by mixing a negative electrode active material with a binder, a conductive auxiliary agent, and the like by a known method and molding the negative electrode active material.

  The hydrogen storage alloy negative electrode thus obtained can be used not only for secondary batteries but also for primary batteries (including fuel cells). For example, a nickel-MH (Metal Hydride) secondary battery can be composed of a positive electrode using nickel hydroxide as an active material, an electrolytic solution made of an alkaline aqueous solution, and a separator. It can be suitably used for power supply applications such as electric tools, electric vehicles, hybrid electric vehicles, and fuel cells (including hybrid fuel cells used in combination with other batteries such as lithium batteries). “Hybrid electric vehicle” means a vehicle that uses two power sources, an electric motor and an internal combustion engine. In this case, “internal combustion engine” includes not only a gasoline engine but also a diesel engine and other engines. included.

  It can also be used for hydrogen storage alloys used in heat pumps, storage of natural energy such as solar and wind power, hydrogen storage, and actuators.

  The low Co hydrogen storage alloy of the present invention is not a battery that is charged / discharged between the limit areas of the charge / discharge depth like a battery of an electric tool or a digital camera, but a charge / discharge depth such as a battery for an electric vehicle or a hybrid electric vehicle. When used as a negative electrode active material for a battery that is charged / discharged in the central region of the battery, in order to demonstrate performance with excellent life characteristics (cycle characteristics), Particularly preferred as the negative electrode active material.

  In a hybrid electric vehicle, the battery is controlled not to be fully charged and completely discharged, and is always maintained in a state where energy can be taken in and out.

  Here, the “battery charged / discharged in the central region of the charge / discharge depth” means a battery mainly charged / discharged in the hydrogen storage amount region that is less than the limit region of the charge / discharge depth. Batteries having a very limited width such as SOC: 40% to 100%, particularly 60% to 85%, more preferably 70% to 85%, and 55% to 65% are preferable. Can include batteries mounted on automobiles such as electric vehicles and hybrid electric vehicles.

  Hereinafter, the present invention will be specifically described based on examples.

Example 1
A hydrogen storage alloy having a composition of Mm (La 23%) Ni _4.29 Mn _0.50 Al _0.30 Co _0.20 (Mm is a misch metal mixture of rare earth metals including La, Ce, Nd and Pr, a + b + c + d = 5.29) is obtained. In addition, each raw material is weighed so that the weight ratio is Mm: 31.9%, Ni: 57.3%, Mn: 6.3%, Al: 1.8%, Co: 2.7%. Mixed. This mixture is put in a crucible and fixed in a high-frequency melting furnace, and the atmosphere in the furnace is reduced to 10 ⁻⁴ to 10 ⁻⁵ Torr, and then heated and melted to 1450 ° C. in an argon gas atmosphere. The alloy lump was poured into.

  The obtained alloy lump is placed in a stainless steel container and set in a vacuum heat treatment apparatus (manufactured by Nisshin Giken). After heat treatment at 1060 ° C. for 3 hours in an argon gas atmosphere, it is placed outside the vacuum heat treatment apparatus. Cooling water was circulated through the cooled water pipe and cooled to 500 ° C. at a rate of temperature decrease of 20 ° C./min. Thereafter, the circulation of the cooling water was turned off to naturally cool to room temperature.

  The obtained alloy is roughly crushed using a jaw crusher (Fuji Paudal: model 1021-B), and further pulverized to a particle size (-500 μm) passing through a 500 μm sieve by a horizontal brown crusher (Yoshida Seisakusho). Went.

(Examples 2-17 and Comparative Examples 1-8)
In Examples 2 to 17 and Comparative Examples 1 to 8, the raw materials were adjusted so as to have the compositions shown in Table 1, cooled to 500 ° C. after the heat treatment at the annealing temperature decrease rate shown in Table 1, and the other points of Example 1 It produced similarly.

[Characteristics and physical property evaluation]
The physical properties of the hydrogen storage alloys obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

<Measurement of micronization 500 cycles>
20 g of hydrogen storage alloy powder of −500 μm (particles passing through a sieve of 500 μmφ) obtained in Examples and Comparative Examples was pulverized for 1 minute with a cyclomill ((Type 1033-200) manufactured by Yoshida Seisakusho Co., Ltd.). A hydrogen storage alloy powder (sample) of −45 μm (particles passing through a 45 μmφ sieve mesh) was obtained by classification with a 45 μm sieve.

  4 g of the obtained sample was put into a sample holder for a PCT apparatus and connected to a PCT characteristic measuring apparatus (manufactured by Suzuki Shokan Co., Ltd.). Moreover, the remaining samples were used as samples before 500 cycles.

The following operation was carried out before turning the cycle.
(1) Alloy adhesion moisture treatment: In a mantle heater (250 ° C.), a hydrogen pressure of 1.7 MPa is introduced in a state where the sample holder for the PCT apparatus is heated and left for 10 minutes. Conducted once.
(2) Alloy activation treatment (treatment for causing the hydrogen storage characteristics of the alloy to appear): The sample holder for the PCT apparatus was taken out from the mantle heater, and a hydrogen pressure of 3 MPa was introduced and held for 10 minutes. Thereafter, vacuuming was performed for 10 minutes while the sample holder for the PCT apparatus was heated in a mantle heater (250 ° C.). This series of operations was performed twice.

The sample holder for the PCT device was taken out from the mantle heater, moved to a 45 ° C. constant temperature bath, evacuated for 30 minutes, and then subjected to a hydrogen storage / release cycle under the following conditions.
(Introduction pressure) 1.1 MPa
(Occlusion time) 300 sec
(Release time) 420 sec
(Number of cycles) 500 cycles

  After completing 500 cycles, evacuation was performed for 30 minutes, and then the sample was taken out from the sample holder for the PCT device to obtain a sample after 500 cycles.

The average particle diameter (D50) of the hydrogen storage alloy powder before and after 500 cycles was measured under the following condition settings using a microtrack (manufactured by Nikkiso Co., Ltd., HRA9320-X100). %).
(Formula) .. Micronized residual ratio (%) = (After cycle D50 (μm) / Before cycle D50 (μm)) × 100
(Transp): Reflect
(Sphere): No
(Ref Inx): 1.51
(Flow): 60 ml / sec

<PCT measurement>
20 g of hydrogen-absorbing alloy powder of −500 μm (particles passing through a sieve of 500 μmφ) obtained in Examples and Comparative Examples was pulverized for 1 minute with a cyclomill ((Type 1033-200) manufactured by Yoshida Seisakusho Co., Ltd.) A hydrogen storage alloy powder (sample) of −45 μm (particles passing through a 45 μmφ sieve mesh) was obtained by classification with a 45 μm sieve.

  4 g of the obtained sample was put into a sample holder for a PCT apparatus and connected to a PCT characteristic measuring apparatus (manufactured by Suzuki Shokan Co., Ltd.).

The following operation was performed before the PCT measurement.
(1) Alloy adhesion moisture treatment: In a mantle heater (250 ° C.), a hydrogen pressure of 1.7 MPa is introduced in a state where the sample holder for the PCT apparatus is heated and left for 10 minutes. Conducted once.
(2) Alloy activation treatment (treatment for causing the hydrogen storage characteristics of the alloy to appear): The sample holder for the PCT apparatus was taken out from the mantle heater, and a hydrogen pressure of 3 MPa was introduced and held for 10 minutes. Thereafter, vacuuming was performed for 10 minutes while the sample holder for the PCT apparatus was heated in a mantle heater (250 ° C.). This series of operations was performed twice.

  For the PCT measurement, the sample holder for the PCT device is taken out from the mantle heater, the holder is moved into a constant temperature bath set at 45 ° C., vacuuming is performed for 30 minutes, and then the PCT measurement is performed until the occlusion end pressure is 1.7 MPa. went. From the obtained PCT curve at 45 ° C., the equilibrium hydrogen pressure when H / M = 0.5 is determined as “P0.5”, and the hydrogen storage amount when the equilibrium hydrogen pressure is 0.5 MPa is expressed as “(H / M) 0.5 ".

<Measurement of a-axis length, c-axis length, a-axis standard deviation>
20 g of hydrogen storage alloy powder of −500 μm (particles passing through a sieve of 500 μmφ) obtained in Examples and Comparative Examples was pulverized for 1 minute with a cyclomill (manufactured by Yoshida Seisakusho Co., Ltd .: Model 1033-200), and the opening was 20 μm. The hydrogen storage alloy powder of −20 μm (particles passing through a 20 μmφ screen) was obtained. An X-ray diffraction sample was prepared by mixing 10 parts by weight of Si powder as an internal standard with respect to 100 parts by weight of the hydrogen storage alloy powder thus obtained.

  Fill the glass sample holder with the above sample and use RINT-2200V (manufactured by Rigaku Co., Ltd.), measure under the following conditions, perform the specified refinement, and standard of a-axis length, c-axis length and a-axis Deviation was determined.

  The refinement at this time is performed using the application software (software name: refinement of the lattice constant) attached to the RINT-2200V, and the angle is corrected from the added Si by the internal standard method, and the lattice constant is obtained by the least square method. Was refined. As a precaution, detailed setting conditions at the time of analysis are shown below.

(Smoothing)
-Smoothing method: Weighted average-Number of smoothing points: 15
・ Harmonic: 128
(Background removal)
・ Background removal method: Straight line in contact with both ends ・ Low angle side average score: 3
・ High angle side average score: 3
(Kα2 removal)
Intensity ratio (Kα2 / Kα1): 0.500
(Peak search method)
・ Peak top method (weight function)
Sin (2θ) × sin (2θ) × r (θ) × r (θ)
(Systematic error correction function)
・ Sin (2θ) × sin (2θ) × (1 / sin (θ) + 1 / θ)

(Tube) CuKα line (Tube voltage) 40 kV
(Tube current) 40 mA
(Diverging slit) 1 deg.
(Scattering slit) 1 deg
(Light receiving slit) 0.3mm
(Goniometer) RINT2000 vertical goniometer (attachment) ASC-43 (vertical)
(Slit) Fully automatic wide-angle goniometer slit (Monochromator) Fully automatic monochromator (Counter) Scintillation counter (Start angle) 20 °
(End angle) 90 °
(Step width) 0.010 °
(Scanning speed) 2 ° / min
(Scanning axis) 2θ / θ
(Measurement method) Continuous (spin speed) 30

In addition, the peaks used when refining the lattice constant are as follows (see FIG. 2).
• Peak indexed with Miller index (001) near 22 ° • Peak indexed with Miller index (101) near 30 ° • Indexed with Miller index (110) near 36 ° • Peak indexed with Miller index (200) near 42 ° • Peak indexed with Miller index (111) near 43 ° • Indexed with Miller index (002) near 45 ° • Peak indexed by Miller index (112) near 59 ° • Peak indexed by Miller index (211) near 61 ° • Indexed by Miller index (202) near 63 ° • Peak indexed with Miller index (300) near 65 ° • Peak indexed with Miller index (301) near 69 °

As a precaution, the Si peak used to refine the lattice constant as an internal standard is also shown below (see FIG. 2).
• Peak indexed with Miller index (111) near 28 ° • Peak indexed with Miller index (220) near 47 ° • Indexed with Miller index (311) near 56 ° Peak ・ Peak indexed by Miller index (422) near 88 °

  In Table 1 of the basic application claiming priority, the annealing temperature drop rate of Comparative Example 1-4 was described as 20 (° C./min), but this is an error and correctly 10 (° C./min). )Met.

In FIG. 1, based on the measurement results for the hydrogen storage alloys obtained in Examples and Comparative Examples, the horizontal axis: standard deviation of a-axis length, the vertical axis: pulverization index (Comparative Example 4 (standard deviation of a-axis length) : 2.0 × 10 ⁻² ) was defined as 100) and plotted (in the example, chromal, in the comparative example, kurosankaku), and an approximate straight line by the least square method was shown.

From the result of FIG. 1, the tendency of the pulverization residual rate clearly changes with the standard deviation σ (× 10 ⁻² pm) being 2.0, and the standard deviation σ (× 10 ⁻² pm) is 2 It has been found that the smaller the ratio is less than 0.0, preferably lower than 2.0, the higher the pulverization residual rate.

  Such a tendency is a new feature that was not found in the evaluation test after 50 cycles. By controlling the standard deviation of the a-axis length in this way, the life characteristics of the hydrogen storage alloy can be further improved. .

  Although it has not been proved why a new feature has emerged in the evaluation test after 500 cycles, it is possible that cracking of the hydrogen storage alloy can be sufficiently advanced by turning 500 cycles, and the particle size Can approach the crystallite size and reach the saturated state of cracking, so it can be assumed that a new correlation has appeared between the characteristics in crystallinity and the high-cycle micronization.

Claims (12)

(Wherein, Mm is the mischmetal, 0 <d ≦ 0.35,0 ≦ e ≦ 0.11,5.20 ≦ a + b + c + d + e ≦ 5.50) formula _{MmNi a Mn b Al c Co d} Fe e be represented by A low Co hydrogen storage alloy having a CaCu ₅ type crystal structure,
The a-axis length of the crystal lattice of the CaCu ₅ type crystal structure obtained by refining the lattice constant using the following 11 peaks together with the X-ray diffraction measurement is 499.0 pm or more, and the c-axis A low Co hydrogen storage alloy characterized by having a length of 405.0 pm or more and a standard deviation of a-axis length of less than 2.0 × 10 ⁻² pm.
・ Peak indexed by Miller index (001) near 22 °
・ Peak indexed by Miller index (101) near 30 °
・ Peak indexed by Miller index (110) near 36 °
・ Peak indexed by Miller index (200) around 42 °
・ Peak indexed by Miller index (111) near 43 °
・ Peak indexed by Miller index (002) around 45 °
・ Peak indexed by Miller index (112) near 59 °
・ Peak indexed by Miller index (211) around 61 °
・ Peak indexed by Miller index (202) around 63 °
・ Peak indexed by Miller index (300) around 65 °
・ Peak indexed by Miller index (301) around 69 ° In the above general formula, a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by 0 <d ≦ 0.32, 0.001 <e ≦ 0.11, 5.25 ≦ a + b + c + d + e ≦ 5.45 The low Co hydrogen storage alloy according to claim 1, wherein a standard deviation of a-axis length is 1.8 × 10 ^-2 pm or less. In the above general formula, a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be represented by 0 <d ≦ 0.32, 0.001 <e ≦ 0.11, 5.25 ≦ a + b + c + d + e ≦ 5.45 there are, low Co hydrogen storage alloy of claim 1, wherein the standard deviation of a-axis length is ^{0.5 × 10 -2 pm~1.8 × 10 -2} pm. In the above general formula, a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be expressed by 0.10 ≦ d ≦ 0.32, 0 ≦ e ≦ 0.02, 5.20 ≦ a + b + c + d + e ≦ 5.38 there are, low Co hydrogen storage alloy of claim 1, wherein the standard deviation of a-axis length is ^{0.7 × 10 -2 pm~1.8 × 10 -2} pm.   5. The low Co hydrogen storage according to claim 1, wherein 4.0 ≦ a ≦ 4.7, 0.30 ≦ b ≦ 0.65, and 0.20 ≦ c ≦ 0.50 in the general formula. alloy.   4. The low Co hydrogen storage according to claim 1, wherein 4.1 ≦ a ≦ 4.6, 0.30 ≦ b ≦ 0.65, and 0.20 ≦ c ≦ 0.50 in the general formula. alloy.   5. The low Co hydrogen storage according to claim 1, wherein 4.11 ≦ a ≦ 4.46, 0.38 ≦ b ≦ 0.51, and 0.29 ≦ c ≦ 0.34 in the general formula. alloy. General formula MmNi _a Mn _b Al _c Co _d Fe _e (Wherein, Mm is misch metal, 0 <d ≦ 0.35, 0 ≦ e ≦ 0.11, 5.20 ≦ a + b + c + d + e ≦ 5.50) Each hydrogen storage alloy raw material is weighed. And mixing them to form a molten metal, which is poured into a mold, cast at a casting temperature of 1350 to 1550 ° C., cooled, and then 1040 to 1080 ° C. in an inert gas atmosphere for 3 to 6 hours. The low Co hydrogen storage alloy according to any one of claims 1 to 7, which is obtained by a method for producing a low Co hydrogen storage alloy, wherein the low Co hydrogen storage alloy is cooled at a temperature lowering rate of 15 to 25 ° C / min. The low Co hydrogen storage alloy according to any one of claims 1 to 8, wherein the low Co hydrogen storage alloy is used as a negative electrode active material for a battery that requires 500 cycles . The low Co hydrogen storage alloy according to any one of claims 1 to 9 , wherein the low Co hydrogen storage alloy is used as a negative electrode active material of a battery mounted on an electric vehicle or a hybrid vehicle. A battery comprising the low Co hydrogen storage alloy according to any one of claims 1 to 10 as a negative electrode active material. General formula MmNi _a Mn _b Al _c Co _d Fe _e (Wherein, Mm is misch metal, 0 <d ≦ 0.35, 0 ≦ e ≦ 0.11, 5.20 ≦ a + b + c + d + e ≦ 5.50) Each hydrogen storage alloy raw material is weighed. And mixing them to form a molten metal, which is poured into a mold, cast at a casting temperature of 1350 to 1550 ° C., cooled, and then 1040 to 1080 ° C. in an inert gas atmosphere for 3 to 6 hours. A method for producing a low Co hydrogen storage alloy, characterized by cooling at a temperature lowering rate of 15 to 25 ° C./min after the heat treatment.

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