JP3965209B2 - 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 more specifically, the content ratio of cobalt in the alloy is extremely small, and yet the output characteristics and activity particularly required for applications such as electric vehicles and hybrid vehicles Further, the present invention relates to a low Co hydrogen storage alloy having life characteristics.

  A hydrogen storage alloy is an alloy that reacts with hydrogen to form a metal hydride, and reversibly stores and releases a large amount of hydrogen near room temperature. Therefore, a nickel-hydrogen battery installed in a hybrid vehicle or a digital still camera, Practical use is being studied in various fields such as 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 relatively low affinity for hydrogen with element groups (Ca, Mg, rare earth elements, Ti, Zr, V, Nb, Pt, Pd, etc.) that have a high affinity for hydrogen and a large amount of hydrogen storage. Although the amount of occlusion is small, it is composed of a combination with element groups (Ni, Mn, Cr, Fe, etc.) that have a fast hydrogenation reaction and lower the reaction temperature. Since the characteristics of all types of alloys vary greatly depending on the composition, various alloy compositions have been studied for the purpose of improving the maximum hydrogen storage capacity and effective hydrogen storage capacity (high capacity), extending the service life, and increasing output. ing.

Research group of the present inventors, AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure among these, specifically using Mm (misch metal) which is a mixture of rare earth in the A site, the B site Research has been conducted focusing on Mm-Ni-Mn-Al-Co alloys using four elements of Ni, Al, 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 preferable to reduce Co in consideration of the future expansion of the use of hydrogen storage alloys. However, if Co is reduced, output characteristics and life characteristics will be reduced. Further, one of the research subjects is to reduce Co while maintaining the life characteristics. Especially in the development of power supply for electric vehicles (EV: Electric Vehicle) and hybrid vehicles (HEV: hybrid electric vehicles: vehicles that use two power sources: an electric motor and an internal combustion engine), output characteristics while reducing Co Maintaining life characteristics at a high level was an essential issue.

  In view of this problem, various proposals for reducing the amount of Co and maintaining the battery characteristics are disclosed.

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

Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-294373) is intended to provide 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 a composition of the formula (1), substantially single phase, and having 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)

In addition, the research group to which the present inventor belongs also has, for example, Patent Document 3 (Japanese Patent Laid-Open No. 2001-18176), which reduces the cobalt content, and at the same time has excellent hydrogen storage characteristics, fine powder characteristics, and good initial characteristics. As a hydrogen storage alloy having excellent output characteristics and 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) of the CaCu ₅ type represented by crystalline A hydrogen storage alloy with a structure is proposed.

In Patent Document 4 (Japanese Patent Application 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, the good initial characteristics and the output characteristics are provided, and the durability is improved. As a hydrogen storage alloy having high reliability with respect to storage stability, the general formula MmNi _a Mn _b Al _c Co _d X _e (where Mm is misch metal, 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 = except when c = 0, also 0 <b ≦ 0.3, and if the 0 <c ≦ 0.4, the hydrogen having a CaCu ₅ type crystal structure represented by b + c <0.5) A storage alloy is proposed.

In Patent Document 5 (Japanese Patent Laid-Open No. 2001-348636), the production cost is reduced by extremely reducing the content ratio of cobalt, and the powder is excellent in pulverization characteristics and hydrogen storage characteristics, as well as good output characteristics and storage characteristics. As a hydrogen storage alloy having a general formula MmNi _a Mn _b Al _c Co _d (where Mm is a 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 the 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 ≦ 0.1,5.2 ≦ a + b + c + d + e ≦ 5.45) of the CaCu ₅ type represented by crystalline A AB ₅ type hydrogen storage alloy having a granulation proposes a hydrogen-absorbing alloy, wherein a lattice length of c axis is not less than 406.2Pm.

Patent Document 1: Japanese Patent Application Laid-Open No. 9-213319 Patent Document 2: Japanese Patent Application Laid-Open No. 2002-294373 Patent Document 3: Japanese Patent Application Laid-Open No. 2001-18176 Patent Document 4: Japanese Patent Application Laid-Open No. 2001-40442 Patent Document 5: Japanese Patent Application Laid-Open No. 2001-40442 2001-348636

  As described above, the research group to which the present inventor belongs has found that the life characteristics of the battery can be maintained by controlling the lattice length of the c-axis within a predetermined range even for a hydrogen storage alloy having a low Co composition. In order to further reduce Co and maintain output characteristics (especially pulse discharge characteristics), activity (activity), and life characteristics at a high level while further developing for next-generation electric vehicles and hybrid vehicles, The idea of “controlling the c-axis lattice length” has been found to be limited.

  Accordingly, the present invention is intended to provide a low Co hydrogen storage alloy that can achieve a high life characteristic even when the Co content is reduced to a lower level.

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} , were reduced the composition ratio of Co (molar ratio) to 0.35 or less Even in this case, the alloy composition was adjusted so that the composition ratio (molar ratio) of Ni having hydrogen catalytic ability was increased to 4.0 or more and the composition ratio (molar ratio) of Mn was within a predetermined range. Thus, the alloy composition and the production conditions are set so that both the a-axis length and the c-axis length of the crystal lattice are in a certain range and the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less. By adjusting, it has been found that the life characteristics (also referred to as durability) can be made high, and the present invention has been conceived based on such knowledge. As for the composition of the alloy represented by the general formula _{MmNi a Mn b Al c Co d} Fe e, it found that almost the same or more favorable results obtained with similar means, conceived the present invention based on this finding It is a thing.

The present invention has the general formula _{MmNi a Mn b Al c Co d} ( wherein, Mm is the mischmetal, 4.0 ≦ a ≦ 4.7,0.30 ≦ b ≦ 0.65,0.20 ≦ c ≦ 0 .50,0 <a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure which can be represented by d ≦ 0.35,5.2 ≦ a + b + c + d ≦ 5.5), the crystal of the CaCu ₅ type crystal structure The a-axis length of the lattice is 499.0 pm or more and the c-axis length is 405.0 pm or more. In the pressure-composition isotherm diagram (PCT curve) at 45 ° C., the hydrogen storage amount (H / M) 0 A low Co hydrogen storage alloy is proposed in which the equilibrium hydrogen pressure at .5 is 0.06 MPa or less.

Further, the present invention has the general formula _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 4.0 ≦ a ≦ 4.7,0.30 ≦ b ≦ 0.65,0.20 ≦ c ≦ 0.50, 0 <d ≦ 0.35, 0 <e ≦ 0.11, 5.2 ≦ a + b + c + d + e ≦ 5.5) Low Co hydrogen having a CaCu ₅ type crystal structure This is an occlusion alloy, wherein the crystal lattice of the CaCu ₅ type crystal structure has an a-axis length of 499.0 pm or more and a c-axis length of 405.0 pm or more, and a pressure-composition isotherm diagram (PCT) at 45 ° C. Curve), a low Co hydrogen storage alloy is proposed, characterized in that the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less.

A low Co hydrogen storage alloy having a CaCu ₅ type crystal structure that can be expressed by the above-described predetermined composition formula, wherein the crystal lattice has an a-axis length of 499 pm or more and a c-axis length of 405 pm or more. For a low Co hydrogen storage alloy, all of the output characteristics (especially pulse discharge characteristics), activity (activity), and life characteristics are at a high level even if the Co content is reduced to a lower level than before. can do. Specifically, the amount of Co can be reduced to the extent required for electric vehicles and hybrid vehicle applications (specifically, the negative electrode active material of batteries mounted on electric vehicles and hybrid vehicles), and life characteristics can be maintained. In addition, the activity can be improved to 80% or more.

  Further, in the pressure-composition isotherm diagram (PCT curve) at 45 ° C., if the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less, the life characteristics (durability) are further improved. It can be reliably maintained at a high level.

In the present invention, the “a-axis length and c-axis length of the crystal lattice” refers to an alloy powder prepared by crushing and classifying an ingot-shaped hydrogen storage alloy to -20 μm (particle diameter passing through a 20 μmφ sieve mesh). Using an X-ray diffractometer, measurement was performed with a CuKα ray at a scanning speed of 1 ° / min and an angle of 100-150 °, and the lattice constant was refined by an error function measurement method (wilson & pike method). The values of the a-axis length and c-axis length specified in the present invention include a variation of ± 0.1 pm. The peaks used for refinement are as follows.
・ Peak indexed by Miller index (303) around 100 ~ 104 °.
A peak indexed with the Miller index (321) near 105-106 °.
A peak indexed with the Miller index (402) around 106-107 °.
A peak indexed with the Miller index (411) around 110-114 °.
A peak indexed with the Miller index (313) around 116-118 °.
A peak indexed with the Miller index (412) around 126-129 °.
A peak indexed with the Miller index (501) near 129-132 °.
・ Peak indexed by Miller index (331) around 139-142 °.

It is the figure which plotted the samples 1-30 in the coordinate which a horizontal axis: a-axis length and a vertical axis | shaft: c-axis length.

It is the figure which divided the samples 1-30 by Mn ratio (molar ratio), and plotted the relationship between the ratio of Al (horizontal axis) and a-axis length (vertical axis) for each Mn ratio.

It is the figure which divided the samples 1-30 by Mn ratio (molar ratio), and plotted the relationship between the ratio of Al (horizontal axis) and c-axis length (vertical axis) for each Mn ratio.

Sample 26 (Ni _4.50 Mn _0.35 Al _0.35 Co _0.10 ) having a Mn ratio (molar ratio) of 0.35 was selected from Samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

Sample 9 (Ni _4.45 Mn _0.40 Al _0.35 Co _0.10 ) with a Mn ratio (molar ratio) of 0.40 was selected from Samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

Sample 14 (Ni _4.40 Mn _0.45 Al _0.35 Co _0.10 ) with a Mn ratio (molar ratio) of 0.45 was selected from Samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

Sample 22 (Ni _4.35 Mn _0.50 Al _0.35 Co _0.10 ) having a Mn ratio (molar ratio) of 0.50 was selected from samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

Sample 6 (Ni _4.30 Mn _0.55 Al _0.35 Co _0.10 ) having a Mn ratio (molar ratio) of 0.55 was selected from Samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

Sample 10 (Ni _4.25 Mn _0.60 Al _0.35 Co _0.10 ) having a Mn ratio (molar ratio) of 0.60 was selected from samples 1 to 30, and the Mm ratio (molar ratio) of this sample was changed to ABx5.20. It is the figure which produced the alloy of -5.40 and showed the relationship between ABx (horizontal axis) and a-axis length (vertical axis) of the obtained alloy.

It is the figure which showed the relationship between ABx (horizontal axis) and c-axis length (vertical axis) of the same alloy as FIG.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 4, and the pulverization residual rate (vertical axis) after 50 cycles.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 6, and the pulverization residual rate (vertical axis) after 50 cycles.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 8, and the pulverization residual rate (vertical axis) after 50 cycles.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 10, and the pulverization residual rate (vertical axis) after 50 cycles.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 12, and the pulverization residual rate (vertical axis) after 50 cycles.

It is the figure which showed the relationship between ABx (horizontal axis) of the same alloy as FIG. 14, and the pulverization residual rate (vertical axis) after 50 cycles.

A sample of 5.20 ≦ ABx (a + b + c + d) <5.25 is plotted in the coordinates consisting of the vertical axis: c-axis length and the horizontal axis: a-axis length, and the pulverization residual rate after 50 cycles is 50% or more. (However, the region is not shown in this figure because there is no pulverization residual rate after 50 cycles of 50% or more).

A sample of 5.25 ≦ ABx (a + b + c + d) <5.30 is plotted in the coordinate consisting of the vertical axis: c-axis length and the horizontal axis: a-axis length, and the pulverization residual rate after 50 cycles is 50% or more. It is the figure which showed the area | region which becomes.

A sample of 5.30 ≦ ABx (a + b + c + d) <5.35 is plotted in the coordinates consisting of the vertical axis: c-axis length and the horizontal axis: a-axis length, and the pulverization residual rate after 50 cycles is 50% or more. It is the figure which showed the area | region which becomes.

A sample of 5.35 ≦ ABx (a + b + c + d) <5.40 is plotted in the coordinate consisting of the vertical axis: c-axis length and the horizontal axis: a-axis length, and the pulverization residual rate after 50 cycles is 50% or more. It is the figure which showed the area | region which becomes.

A sample of 5.40 ≦ ABx (a + b + c + d) <5.45 is plotted in the coordinates consisting of the vertical axis: c-axis length and the horizontal axis: a-axis length, and the pulverization residual rate after 50 cycles is 50% or more. It is the figure which showed the area | region which becomes.

The vertical axis is a graph in which samples 1 to 37 are plotted in coordinates consisting of a pulverization residual rate after 200 cycles (relative value when the sample 27 is 100), and the horizontal axis: a plateau pressure (equilibrium hydrogen pressure). .

It is a longitudinal cross-sectional view for demonstrating the structure of the open type test cell produced by the test.

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, and “preferably larger than X, Y It includes the meaning of “smaller”.

The hydrogen storage alloy of the present invention has a general formula MmNi _a Mn _b Al _c Co _d (where Mm is Misch metal, 4.0 ≦ a ≦ 4.7, 0.30 ≦ b ≦ 0.65, 0.20). ≦ c ≦ 0.50, 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 (where Mm is Misch metal, 4.0 ≦ a ≦ 4.7, 0.30 ≦ b ≦ 0.65, 0.20 ≦ c ≦ 0.50, 0 <d ≦ 0.35, 0 <e ≦ 0.11, 5.2 ≦ a + b + c + d + e a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure which may be represented by ≦ 5.5), a-axis length of the crystal lattice of the CaCu ₅ type crystal structure is not less than 499.0Pm, and c-axis In the pressure-composition isotherm diagram (PCT curve) at 45 ° C. with a length in the range of 405.0 pm or more Wherein the hydrogen storage capacity (H / M) equilibrium hydrogen pressure at 0.5 (hereinafter also referred to as "plateau pressure") is less than 0.06 MPa, the low Co hydrogen ABx type having a CaCu ₅ type crystal structure It is an occlusion alloy.

  In the low Co hydrogen storage alloy of the present invention, 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 expressed as “ABx” or “ a + b + c + d (+ e) ”) is 5.2 ≦ ABx ≦ 5.5, and therefore, it has a B-site rich non-stoichiometric composition. If it is ABx of this range, it will become a cause which can suppress the fall of a battery life or a pulverization characteristic, and can also suppress the fall of a hydrogen storage characteristic and an output characteristic. From such a viewpoint, ABx is more preferably 5.25 or more, and more preferably 5.45 or less.

  In the low Co hydrogen storage alloy of the present invention, from the viewpoint of improving output characteristics (particularly pulse discharge characteristics), activity (activity), and life characteristics, the a-axis length is preferably 499.0 pm or more, and 503.0 pm It is preferable that: In particular, it is more preferably 499.7 pm or more, and more preferably 502.7 pm or less. On the other hand, the c-axis length is more preferably 405.0 pm or more, and more preferably 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 preferable example.

  The inventor further found that the preferred a-axis length and c-axis length differ depending on the level of ABx, and based on this finding, proposes a preferred a-axis length and c-axis length for each ABx range.

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 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. .

  By controlling the a-axis length and c-axis length within the above ranges depending on the range of ABx, the life characteristics required for a hybrid vehicle or the like, that is, the hydrogen storage alloy is pulverized and sieved to a particle size of 20 to 53 μm. The hydrogen storage alloy powder was adjusted to the range, and after measuring the average particle size (pre-cycle particle size, D50) of this hydrogen storage alloy powder with a particle size distribution measuring device, 2 g of this hydrogen storage alloy powder was weighed and PCT holder Then, the surface was washed twice with a hydrogen pressure of 1.75 MPa, and then activated twice by introducing 3 MPa of hydrogen. Next, with a PCT apparatus, 2.0 g of hydrogen storage alloy powder was added to 45 g. A cycle test is repeated 50 times at 50 ° C, and the average particle size (particle size after cycle, D50) of the hydrogen storage alloy powder after the 50 cycle test is measured. When measured by the apparatus, the ratio of the cycle after the particle size for the previous cycle granularity (micronized residual rate (%)) can be a hydrogen storage alloy having a life characteristic, showing more than 50%.

  However, if the sample to be measured (hydrogen storage alloy) is very fine in particle size or the surface of the alloy is heavily oxidized, accurate data may not be obtained under the above activation conditions. Therefore, in this case, it is preferable to increase the measurement accuracy by raising the time and temperature under the above activation conditions.

  In order to maintain the high durability required for the application of the hybrid 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, so it is inexpensive, and as described above, the next-generation hybrid vehicle It is possible to provide a hydrogen storage alloy that satisfies the high durability required for the negative electrode active material of a battery.

  Since such high durability can be obtained not only in hybrid vehicle applications but also in batteries used for other applications, the application is not limited to hybrid vehicles in terms of high durability.

  Regarding the composition ratio of Ni, Mn, Al and Co, or Ni, Mn, Al, Co and Fe, as described above, 5.2 ≦ a + b + c + d (+ e) ≦ 5.5, and preferably 5.25 ≦. It may be appropriately adjusted within the range of a + b + c + d (+ e) or a + b + c + d (+ e) ≦ 5.45, but considering the characteristics of the low Co hydrogen storage alloy of the present invention, the Co composition ratio (molar ratio) is low. Then, it is preferable to adjust the a-axis length and c-axis length of the crystal lattice and the equilibrium hydrogen pressure by adjusting the ratio of Ni, Mn, Al, Fe and ABx and adjusting the manufacturing conditions. Therefore, the composition ratio of each element is determined, for example, by first determining the composition ratio (molar ratio) of Co and Ni, and then changing the composition ratio of Mn, Al, and Fe so that the composition ratio of Mn falls within a predetermined range. It is preferable to determine the alloy composition so as to adjust the above.

  The Co ratio (d) is adjusted within the range of 0 <d ≦ 0.35, preferably 0 <d ≦ 0.3, and more preferably 0 <d ≦ 0.2. If it is in the range of 0 <d ≦ 0.35, the hydrogen occlusion characteristic and the pulverization characteristic are not deteriorated, and the cost reduction can be sufficiently enjoyed.

  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, sufficient output characteristics can be obtained, and the pulverization characteristics and life characteristics are not adversely affected.

  The ratio (b) of Mn is preferably adjusted within the range of 0.30 ≦ b ≦ 0.65. In the alloy of the present invention, the proportion of Mn is also an important factor, and if the proportion of Mn is not adjusted in the range of 0.30 ≦ b ≦ 0.65, the pulverization residual rate after 50 cycles will be 50% or more. It is difficult to secure. Further, in the pressure-composition isotherm diagram (PCT curve) at 45 ° C., from the viewpoint of setting the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 to 0.055 MPa or less, preferably 0.31 ≦ b ≦ 0.65 and 0.32 ≦ b ≦ 0.65 from the viewpoint of setting the equilibrium hydrogen pressure to 0.050 MPa or less, preferably 0.35 ≦ b ≦ 0.60, more preferably 0.35 ≦ b ≦ 0.55.

  The proportion (c) of Al is preferably adjusted within the range of 0.20 ≦ c ≦ 0.50. If it is in the range of 0.2 ≦ c ≦ 0.5, the plateau pressure becomes higher than necessary and the influence of deteriorating the energy efficiency of charge / discharge is small, and the influence of reducing the hydrogen storage amount is also small. Further, in the pressure-composition isotherm diagram (PCT curve) at 45 ° C., from the viewpoint of setting the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 to 0.055 MPa or less, preferably 0.21 ≦ c ≦ 0.50 and 0.22 ≦ c ≦ 0.50 from the viewpoint of setting the equilibrium hydrogen pressure to 0.050 MPa or less, preferably 0.30 ≦ c ≦ 0.50, and more preferably 0.30 ≦ c ≦ 0.45.

  The ratio (e) of Fe is adjusted within the range of 0 <e ≦ 0.11, preferably 0.001 <e ≦ 0.11, and more preferably 0.002 <e ≦ 0.11. If it is in the range of 0 <e ≦ 0.11, there will be little influence which reduces activity and it can improve the pulverization characteristic.

  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 content of La in Mm is preferably 10 to 90% by mass, particularly 10 to 85% by mass, particularly 15 to 30% by weight, and particularly preferably 18 to 30% by weight, based on the content in Mm.

  In addition, the hydrogen storage alloy of this invention may contain the impurity of the grade which does not affect the effect which this invention desires. For example, any impurity of Ti, Mo, W, Si, Ca, Pb, Cd, and Mg may be included as long as it is about 0.05% by weight or less.

  Among the low-Co hydrogen storage alloys that satisfy the above requirements, the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less in the pressure-composition isotherm diagram (PCT curve) at 45 ° C. In particular, those having a pressure of 0.055 MPa or less, particularly 0.050 MPa or less are preferred.

  Here, in the pressure-composition isotherm diagram (PCT curve) at 45 ° C., when the hydrogen storage amount (H / M) is 0.5, it means the approximate center of the state where the equilibrium hydrogen pressure is in the plateau region. It has a meaning as an index of the average value of the pressure in the plateau region.

  It has been confirmed that when the equilibrium hydrogen pressure is 0.06 MPa or less, the residual pulverization rate after repeating the absorption and release of hydrogen 200 times is remarkably increased, and the life characteristics (durability) are remarkably increased. Examining the relationship between the equilibrium hydrogen pressure and the pulverization characteristics, the equilibrium hydrogen pressure does not affect the pulverization characteristics in the storage / release cycle of about several tens of cycles, but the electric vehicle (EV) and the hybrid vehicle (HEV) When it is necessary to assume long-term cycle use as in the above, it is particularly important to maintain the life characteristic (durability) that the equilibrium hydrogen pressure is 0.06 MPa or less. Although such a mechanism has not been confirmed experimentally, hydrogen storage alloys cause expansion and contraction of the lattice volume as hydrogen is stored and released, which causes pulverization. Particularly when hydrogen is released, that is, when the lattice volume shrinks, it tends to cause fine powder. For this reason, it is considered that an alloy having a higher equilibrium hydrogen pressure and more readily releasing hydrogen has a higher lattice volume shrinkage rate, so that the alloy is more likely to be cracked, resulting in a decrease in pulverization characteristics.

  When the equilibrium hydrogen pressure is 0.055 MPa or less, and further 0.050 MPa or less, the life characteristics (durability) are of course improved, but not only in terms of suppression of hydrogen gas generation and reduction of self-discharge in a high temperature range. It becomes preferable.

  On the other hand, the lower limit of the equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is preferably 0.020 MPa or more, particularly 0.030 MPa or more, and particularly preferably 0.040 MPa or more.

The relationship between the equilibrium potential (20 ° C., 6 MKOH, 1 atm, mercury oxide electrode standard) of the hydrogen storage alloy negative electrode and the equilibrium hydrogen pressure is given by the following Nernst equation.
_{Eeq (H 2 O / H)} -Eeq (HgO / Hg) = - 0.9324-0.0291LogPH2

  As can be seen from this equation, if the equilibrium hydrogen pressure is too low, the equilibrium potential of the negative electrode will shift in a noble direction when used as the negative electrode of the battery, and the battery voltage will drop to obtain sufficient output characteristics. It may not be possible.

  When using a hydrogen storage alloy for EV and HEV applications, it is necessary to consider using several tens to hundreds of single cells connected in series. That is, a very slight voltage difference per single cell, which is not a problem in other applications, greatly affects the overall voltage in EV and HEV applications. Therefore, not only the upper limit of the equilibrium hydrogen pressure but also the pressure range of the equilibrium hydrogen pressure is important, and is 0.06 MPa to 0.02 MPa, preferably 0.06 MPa to 0.03 MPa, more preferably 0.06 MPa to 0.04 MPa. It is important to adjust to the range.

  In addition, although the measuring method of the plateau pressure was shown in the Example mentioned later, when the particle size of the sample (hydrogen storage alloy) to be measured was very fine or the oxidation of the alloy surface was intense, it was shown in the Example. Accurate data may not be obtained under the activation conditions of the measurement method. Therefore, in this case, it is preferable to increase the measurement accuracy by raising the activation time and temperature shown in the embodiment. In addition, when accurate data cannot be obtained even in such a manner, for example, as in the case of a negative electrode alloy obtained by disassembling a battery, pulverization proceeds, the oxidation of the alloy surface is intense, and other than the alloy components For those containing an additive (measurement sample), it is necessary to subtract the weight that was not involved in the PCT measurement due to those causes. As the method, 20 cycle capacity is calculated | required with the open type test cell shown in the Example, "20 cycle capacity (mAh / g)" = ((96500 (A * s) * [H / M]) / (3600 [S / h] × average atomic weight per hydrogen storage alloy (g))) × 1000 (mA / A) [H / M] is determined. Then, PCT data obtained by converting the alloy weight so as to match this [H / M] may be obtained, and the equilibrium hydrogen pressure at the [H / M] 0.5 may be obtained.

For example, in the case of LaNi ₅ , the average atomic weight per metal of the hydrogen storage alloy referred to here is “average atomic weight (g) per metal of the hydrogen storage alloy” = (138.9 + 58.7 × 5) / 6 = 72.1 (g).

An alloy immersed in an alkaline solution such as a negative electrode alloy obtained by disassembling a battery may have a plateau pressure as high as about 0.002 MPa.
In addition, the plateau pressure of the hydrogen storage alloy obtained by disassembling the used battery rarely increases by about 0.01 MPa from the pre-use plateau pressure, so the pre-use plateau pressure should be estimated from the used plateau pressure. Can do.

(Production method of low Co hydrogen storage alloy)
Method for producing a low-Co hydrogen storage alloys of the present invention is not particularly limited, 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 (where Mm is Misch metal) 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) After each hydrogen storage alloy raw material is weighed and mixed, the a-axis length and c-axis length of the crystal lattice are both within a predetermined range, and 45 ° C. And a production method such that the equilibrium hydrogen pressure of hydrogen storage amount (H / M) 0.5 in the pressure-composition isotherm diagram (PCT curve) in FIG. The hydrogen storage alloy may be manufactured by adjusting the manufacturing conditions.

  For example, the hydrogen storage alloy raw material may be weighed and mixed, and the mixture is melted and cast, followed by heat treatment to produce the hydrogen storage alloy. At this time, the casting conditions (casting method, casting temperature, cooling rate) may be used. The a-axis length and the c-axis length of the crystal lattice can be adjusted to a predetermined range by appropriately selecting and controlling manufacturing conditions such as heat treatment conditions according to the alloy composition. In many cases, the a-axis length and the c-axis length of the crystal lattice can be changed by increasing the cooling rate in casting, and the c-axis length of the crystal lattice is often increased by increasing the heat treatment temperature. Can be made. However, some alloy types grow the c-axis length even when the heat treatment temperature is low, so it is necessary to appropriately control the alloy type.

  Further, in order to adjust both the a-axis length and the c-axis length of the crystal lattice so as to fall within a predetermined range, it is one of important factors to grow the crystal uniformly. In order to homogenize crystals, in addition to heat treatment, it is also effective to classify the alloy before heat treatment and control the particle size of the alloy powder as disclosed in, for example, JP-A-2002-212601. It is thought that it is. Therefore, such means can also be adopted as one of means for adjusting the a-axis length and c-axis length of the crystal lattice to a desired range.

  In order to adjust the plateau pressure, the value of ABx, the substitution amount of Mn or Al, the cooling rate at the time of casting, the heat treatment (annealing) conditions, particularly the heat treatment temperature, etc. may be appropriately adjusted according to the alloy composition.

  In many cases, the plateau pressure can be lowered by increasing the value of ABx or increasing the substitution amount of Mn or Al, but the balance between these is important.

  Also, in the case of a general water-cooled mold, the cooling rate at the time of casting has a large temperature difference due to the high temperature of the molten metal, and thus has sufficiently exceeded the range of influence on the plateau pressure. I thought it would not affect the plateau pressure. However, as a result of actually increasing the cooling rate, it was found that it affects the plateau pressure.

  As the casting method, a mold casting method is preferable, but for example, a twin roll method (specifically, refer to paragraphs [0013] to [0016] of Japanese Patent Application No. 2002-299136) and other casting methods can be used.

  Here, an example of the manufacturing method by the casting method will be described.

  First, the hydrogen storage alloy raw material is weighed and mixed so as to have a desired alloy composition, and the hydrogen storage alloy raw material is melted into a molten metal using, for example, a high-frequency heating melting furnace by induction heating. This is poured into a mold, for example, a water-cooled mold, and a hydrogen storage alloy is cast at 1350 to 1550 ° C. and cooled at a predetermined cooling rate (a predetermined amount of cooling water). The casting temperature at this time shall be 1200-1450 degreeC. The casting temperature here is the temperature of the molten metal in the crucible at the start of casting (before pouring the mold), and the casting temperature is the temperature of the mold pouring port (temperature before the mold).

  Next, the obtained hydrogen storage alloy is heat-treated in an inert gas atmosphere, for example, argon gas. The heat treatment conditions are preferably 1040 to 1080 ° C. and 3 to 6 hours.

  As described above, the cooling rate during casting affects not only the a-axis length and the c-axis length of the crystal lattice of the hydrogen storage alloy, but also the plateau pressure. Further, if the cooling rate is too slow, the obtained hydrogen storage alloy cannot obtain sufficient life characteristics, and if the cooling rate is too fast, good initial activity cannot be obtained. Therefore, it is important to set an appropriate cooling rate in consideration of not only the a-axis length, c-axis length and plateau pressure of the hydrogen storage alloy crystal lattice, but also life characteristics and initial activity.

(Use of low Co hydrogen storage alloy)
The obtained hydrogen storage alloy (ingot) is roughly pulverized and finely pulverized to obtain a hydrogen storage alloy powder having the required particle size. If necessary, the surface of the alloy is coated with a metal material or a polymer resin, or an acid or alkali 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. However, since it is necessary, such processing is not always necessary.

  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 (MetalHydride) 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, and can be an electric vehicle, hybrid vehicle, fuel cell (lithium battery). In addition, a hybrid fuel cell used in combination with other batteries, etc.), various electric devices such as small or portable electric devices, power tools, and the like can be suitably used.

  In the present specification, the term “hybrid vehicle” means a vehicle that uses two power sources, that is, an electric motor and an internal combustion engine. In this case, the “internal combustion engine” includes not only a gasoline engine but also a diesel engine. Other engines are also included.

  Among them, the low Co hydrogen storage alloy of the present invention is charged / discharged between the limit areas of charge / discharge depth (H / M = 0 or about 0.1 to about 0.8) like batteries of electric tools and digital cameras. When used as a negative electrode active material for batteries that are charged / discharged in the central region of the charge / discharge depth, such as batteries for electric vehicles and hybrid vehicles, rather than used batteries, both initial activity and life characteristics (cycle characteristics) are significantly superior. In particular, the negative electrode active material for a battery that is charged / discharged in the central region of such a charge / discharge depth is preferable.

  Here, the “battery charged / discharged in the central region of the charge / discharge depth” means a hydrogen storage amount that is less than the limit region of the charge / discharge depth (H / M = 0 or about 0.1 to about 0.8). It means a battery that is charged and discharged in a region, for example, a battery having H / M = about 0.2 to about 0.7, especially about 0.4 to 0.6 as a main use region is preferable. Examples thereof include batteries mounted on automobiles such as electric vehicles and hybrid vehicles.

  Note that it is also possible to use it for hydrogen storage alloys used in heat pumps, storage of natural energy such as solar and wind power, hydrogen storage, and actuators.

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

[Preparation of sample]
Each hydrogen storage alloy raw material was weighed and mixed so as to have the alloy composition shown in Table 1, and the mixture was put in a crucible and fixed in a high-frequency melting furnace, and after being evacuated to 10 ^-4 Torr or less, argon was added. It was heated and dissolved in a gas atmosphere, poured into a water-cooled copper mold, cast at the casting temperature shown in Table 2, and cooled with the amount of cooling water shown in Table 2 to obtain an alloy. Furthermore, this alloy was heat-treated at 1060 ° C. for 6 hours in an argon atmosphere to obtain ingot-like hydrogen storage alloys (samples 1 to 37).

  Although it has been confirmed that the Ce content is within the range shown in Table 1, more detailed quantification has not been achieved. Further, impurities cannot be quantified.

[Characteristics and physical property evaluation]
With respect to Samples 1 to 37 obtained above, various physical property values and various characteristic values were measured by the methods shown below, and the results are shown in Table 2.

<A-axis length><c-axislength>
A hydrogen storage alloy (ingot) is crushed, sieved, and classified to -20 μm (particle diameter passing through a 20 μmφ sieve mesh), filled in a glass holder, and supplied to a powder X-ray diffractometer (XRD manufactured by RIGAKU). did. Measurement was performed at a scanning speed of 1 ° / min with CuKα ray at an angle of 100-150 °, and the lattice constant was refined by an error function measurement method (wilson & pike method), and the a-axis length (pm) and c-axis The length (pm) was calculated. The calculated a-axis length and c-axis length values have a variation of ± 0.1 pm.

The peaks used for refinement are as follows.
・ Peak indexed by Miller index (303) around 100 ~ 104 °.
A peak indexed with the Miller index (321) near 105-106 °.
A peak indexed with the Miller index (402) around 106-107 °.
A peak indexed with the Miller index (411) around 110-114 °.
A peak indexed with the Miller index (313) around 116-118 °.
A peak indexed with the Miller index (412) around 126-129 °.
A peak indexed with the Miller index (501) near 129-132 °.
・ Peak indexed by Miller index (331) around 139-142 °.

<PCT capacity (H / M)><plateau pressure (PH2 / MPa)>
A hydrogen storage alloy (ingot) is pulverized and sieved, and then classified into 300 μm to 500 μm (a particle diameter that does not pass through a 300 μmφ screen but passes through a 500 μm screen) is a PCT device (automatic Siebelz device (Suzuki) )), The hydrogen storage amount (H / M) at 0.5 MPa when the PCT curve was measured at 45 ° C., and the plateau pressure (H / M = 0.5, MPa when measured as such) )

  Specifically, the following operation was performed before the PCT measurement.

    (1) Alloy adhesion moisture treatment: In a mantle heater (250 ° C.), 1.75 MPa of hydrogen was introduced while the PCT holder was heated, and after standing for 10 minutes, a series of operations for evacuation was performed twice.

    (2) Alloy activation treatment: The PCT holder was taken out from the mantle heater, 3 MPa hydrogen was introduced, and held for 10 minutes. Thereafter, evacuation was performed for 10 minutes while the PCT holder was heated in a mantle heater (250 ° C.). This series of operations was performed twice.

  Then, the PCT holder was taken out from the mantle heater and moved to a 45 ° C. constant temperature bath, and then evacuation was performed for 30 minutes. Thereafter, the PCT measurement was performed up to an occlusion end pressure of 1.7 MPa. From the obtained pressure-composition isotherm diagram at 45 ° C., the amount of hydrogen occlusion when the pressure is 0.5 MPa is calculated as PCT capacity H / M (H / M: hydrogen atom H amount per M 1 metal atom), and The pressure (MPa) when H / M was 0.5 was determined as the Brato pressure.

<Micronized residual rate (200-D (% vs. sample 27)) (10-D (%)) (50-D (%))>
The hydrogen storage alloy (ingot) is pulverized and sieved to adjust the particle size within the range of 20 μm to 53 μm (the particle diameter does not pass through a 20 μmφ screen but passes through a 53 μm screen) to obtain a hydrogen storage alloy powder. . The average particle size (D50) of this hydrogen storage alloy powder was measured by a particle size distribution measuring device (Microtrack manufactured by JGC Corporation), and this was used as the particle size before cycle.

  Next, 2 g of the hydrogen storage alloy powder was weighed, a sample was put in a PCT holder, and the operations (1) and (2) performed before the PCT measurement were performed in the same manner as the PCT capacity (H / M) measurement. .

  After the activation treatment, the PCT device (automatic Siebelz device (manufactured by Suzuki Shokan)) was used to perform a cycle test in which hydrogen storage / release was repeated 10 times, 50 times, or 200 times to 2.0 g of the hydrogen storage alloy powder (temperature). Conditions: 45 ° C., introduction pressure: 1.1 MPa, occlusion time: 300 sec, discharge pressure: 0.0 MPa, discharge time: 420 sec). At this time, it was set so that hydrogen was automatically introduced up to 1.1 MPa when the introduction pressure became 80% or less due to occlusion of hydrogen.

Thereafter, the average particle size (D50) when the average particle size (D50) is collected and measured again is defined as the post-cycle particle size, and both average particle sizes (D50) are used, and after 10 cycles from the following formula, after 50 cycles Alternatively, the pulverization residual ratio (%) after 200 cycles was calculated.
Micronization residual rate (%) = (particle size after cycle / particle size before cycle) × 100

  In addition, about the micronization residual rate (%) after 200 cycles, it showed as a relative value when the value (%) of the sample 27 is set to 100. Since the samples 1 to 37 are divided into a sample group having a low pulverization residual rate and a sample group having a high pulverization residual rate, the relative value with respect to the sample 27, which is one of the sample groups having a low pulverization residual rate, is easy to understand. It is shown as.

<Production of electrode cell>
Hydrogen storage alloy powder (ingot) is pulverized and sieved to -45 μm (particle diameter passing through a 45 μmφ sieve mesh), together with nickel powder (conductive material) and polyethylene powder (binder) 4.12 g was mixed, and the obtained mixed powder was pressed to produce pellets having a diameter of 15 mm and a thickness of 1.8 mm, and then sintered by vacuum firing at 150 ° C. for 1 hour to produce pellet electrodes.

  This pellet electrode is used as a negative electrode, and is sandwiched by a positive electrode (sintered nickel hydroxide) with sufficient capacity through a separator (manufactured by Nippon Vilene) and immersed in an aqueous KOH solution having a specific gravity of 1.30 (see FIG. 28).

  Details are as follows.

The discharge capacity of the electrode cell was measured by the following test method according to JIS H7205.
1) 1 g of hydrogen storage alloy is mixed with 3 g of nickel powder as a conductive material and 0.12 g of polyethylene powder as a binder, and 1.24 g of the obtained powder (containing 0.3 g of hydrogen storage alloy) is expanded Ni It is pressure-molded onto a pellet type having a diameter of 15 mm and a thickness of 1.8 mm, and vacuum-baked at 150 ° C. for 1 hour to produce a pellet electrode. This pellet electrode is used as a negative electrode. A positive electrode (sintered nickel hydroxide) having a capacity of twice or more was sandwiched through a separator and immersed in a 30 wt% KOH aqueous solution to produce an open type test cell.
2) The open type test cell was connected to the charge / discharge device and placed in a thermostat with adjustable temperature. The test conditions need to be set appropriately according to the measurement items. For example, if the capacity is 20 cycle capacity, charge: 0.2 C × 6 hours (120% vs. calculated negative electrode capacity), discharge 0.2 C, 0. It was measured under conditions of 7V cut and temperature 20 ° C.

  In addition, said "calculated negative electrode capacity | capacitance" is the capacity | capacitance which converted H / M obtained by the measuring method of PCT (H / M) into the electrochemical capacity. For example, when H / M = 0.8, “calculated negative electrode capacity (mAh / g)” = ((96500 (A · s) × 0.8) / (3600 (s / h) × hydrogen storage alloy 1 metal) The average atomic weight per unit (g))) × 1000 (mA / A) can be converted.

<Initial capacity (1∞ / mAh / g)><20 cycle capacity (20∞ / mAh / g)>
The above open-type test cell was connected to a charge / discharge device (HOKUTO charge / discharge tester) and placed in a thermostat (YAMATO) with adjustable temperature. Charging to discharging is one cycle, charging from the first charging to the fourth charging, charging from the sixth charging to the sixteenth charging, charging from the eighteenth discharging to the twentyth cycle discharging: The test was performed under the conditions of 0.2 C × 6 hours, discharge 0.2 C, 0.7 V cut, and temperature 20 ° C. The discharge capacity (mAh / g) at the first cycle at this time was taken as the initial capacity, and used as an index representing the initial activity. The 20th cycle discharge capacity (mAh / g) was set to 20 cycle capacity. The conditions for cycles other than those described above are described in the “Activity” test item.

<Activity>
Charge from the 4th cycle discharge to the 6th cycle charge, from the 16th cycle discharge to the 18th cycle charge in the above test: 1C × 1 hour 12 minutes, discharge: 1C, 0.7V cut, temperature 0 ° C. Conducted under conditions. The discharge capacity (mAh / g) at the fifth cycle at this time was set as the 5-cycle capacity, and the discharge capacity (mAh / g) at the 17th cycle was set at the 17-cycle capacity.

Then, the activity (%) was calculated by the following formula.
Activity (%) = (5 cycle capacity / 17 cycle capacity) × 100

<0 ° C./21st cycle capacity (0 ° C., 1 C, Cap / mAh / g)><Pulse>
In the above cycle test, after measuring the 20 cycle capacity, the discharge capacity (mAh / g) of the 21st cycle, which was charged at 0 ° C. for 0.2 C × 6 hours and discharged at 1 C, 0.7 V cut, was the 21 cycle capacity. It was. The larger the capacity, the better the low temperature characteristics.

  Moreover, after measuring 21 cycle capacity | capacitance, it charged at 0 degreeC as it was for 0.2 C x 6 hours, and discharged for 0.2 C x 2.5 hours. Then, it was allowed to stand for 30 minutes until the potential was stabilized, and the voltage value (V) after 10 seconds when discharging at 2 C was used as a pulse. The higher the voltage, the better the output characteristics at low temperatures.

  FIG. 1 is a diagram in which the a-axis length and c-axis length of samples 1 to 30 are plotted in coordinates composed of a horizontal axis: a-axis length and a vertical axis: c-axis length.

  From the results of FIG. 1 and Table 2, it was found that if the a-axis length and the c-axis length are within a certain range, the activity, output characteristics, and life characteristics are all good. Among them, Samples 2, 17, 22 and 24 were evaluated to be particularly good in terms of activity, output characteristics, and life characteristics.

  Moreover, in the result of Table 2, when it looked at the samples 31-37 of the alloy composition containing iron (Fe), it turned out that a lifetime characteristic becomes favorable by containing iron (Fe). Furthermore, it was found that when the amount of cooling water is increased, that is, when the cooling rate is increased, the c-axis length increases and the life characteristics tend to increase.

  2 and 3 divide samples 1 to 30 by Mn ratio (molar ratio), and for each Mn ratio, Al ratio (horizontal axis) and a-axis length (vertical axis) or c-axis length (vertical axis) It is the graph which plotted the relationship of.

  4 to 21 and Tables 3 to 5 select and extract samples (Samples 6, 9, 10, 14, 22, and 26) having different Mn ratios (molar ratios) from Samples 1 to 30. Alloys of ABx5.2 to 5.4 were prepared by changing the Mm ratio (molar ratio) in the alloy composition of the prepared samples (the preparation conditions are the same as the extracted samples), and for each extracted sample, in other words, for each Mn ratio FIGS. 4 to 15 and Tables 3 and 4 show the relationship between ABx and a-axis length (vertical axis) or c-axis length (vertical axis). ABx and the residual pulverization rate after 50 cycles Are shown in FIG. 16 to FIG. 21 and Table 5.

  From this, it was found that there is a correlation between ABx and the a-axis length and c-axis length, and when ABx increases, the a-axis length decreases and the c-axis length tends to increase.

  In addition, FIGS. 22 to 26 and Tables 6 to 9 divide Samples 1 to 30 by ABx, show the relationship between the a-axis length and the c-axis length for each ABx, and further fine powder after 50 cycles. It is the graph which showed the area | region whose conversion rate is 50% or more.

  For example, in the case of FIG. 22, that is, in the case of 5.20 ≦ ABx <5.25, there was no sample in which the pulverization after 50 cycles exceeded 50%. On the other hand, in the case of FIGS. 23 to 26, for example, as shown in FIG. 23, the a-axis length is 500.5 pm or more and 502.7 pm or less, and the c-axis length is 405.6 pm or more and 406.9 pm or less. The sample within the range (frame in the figure) had a pulverization residual ratio after 50 cycles of 50% or more, and the sample outside the frame was less than 50%. The same was true for the other figures.

  Thus, by finely dividing the AB ratio (ABx) range and specifying the range of the a-axis length and c-axis length for each AB ratio (ABx) range, the pulverization residual rate after 50 cycles is 50%. It became clear that the low Co hydrogen storage alloy which becomes the above could be specified.

FIG. 27 is a graph showing the relationship between the plateau pressure (equilibrium hydrogen pressure) and the pulverization residual rate after 200 cycles for samples 1 to 37. From this, it was confirmed that the samples (samples 13, 26, and 27) in which the equilibrium hydrogen pressure exceeded 0.060 MPa had a remarkably low pulverization residual rate. Although the cause of the high plateau pressure (equilibrium hydrogen pressure) of samples 13, 26, and 27 is not certain, the main reason is that sample 13 has a small amount of substitution of Mn and Al, and sample 26 has a substitution amount of Mn. It is presumed that the main cause is that the amount of Al is small, and that the sample 27 is mainly caused by a small amount of Al substitution.

Claims (20)

General formula MmNi _a Mn _b Al _c Co _d (where Mm is Misch metal, 4.31 ≦ a ≦ 4.7, 0.30 ≦ b ≦ 0.65, 0.20 ≦ c ≦ 0.50, 0 <D ≦ 0.35, 5.2 ≦ a + b + c + d ≦ 5.5), which is a low Co hydrogen storage alloy having a CaCu ₅ type crystal structure,
The crystal lattice of the CaCu ₅ type crystal structure has an a-axis length of 499.0 pm or more and a c-axis length of 405.0 pm or more,
A low Co hydrogen storage alloy characterized in that, in a pressure-composition isotherm diagram (PCT curve) at 45 ° C., an equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less.   2. The low Co hydrogen storage alloy according to claim 1, wherein 4.35 ≦ a ≦ 4.7.   2. The equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 in a pressure-composition isotherm diagram (PCT curve) at 45 ° C. is 0.020 MPa to 0.06 MPa. 2. The low Co hydrogen storage alloy according to 2.   CaCu _Five The a-axis length of the crystal lattice of the type crystal structure is not less than 499.0 pm and not more than 503.0 pm, and the c-axis length is not less than 405.0 pm and not more than 408.0 pm. The low Co hydrogen storage alloy described in 1.   The low Co hydrogen storage alloy according to any one of claims 1 to 4, wherein a hydrogen storage amount (H / M) at 0.5 MPa is 0.803 or more and 0.861 or less. The alloy composition satisfies the condition of 5.25 ≦ a + b + c + d <5.30, the a-axis length of the crystal lattice is 500.5 pm or more and 502.7 pm or less, and the c-axis length is 405.6 pm or more and 406.9 pm or less. The low Co hydrogen storage alloy according to any one of claims 1 to 5, wherein The alloy composition satisfies the condition of 5.30 ≦ a + b + c + d <5.35, the a-axis length of the crystal lattice is 500.0 pm to 502.4 pm, and the c-axis length is 405.9 pm to 407.2 pm. The low Co hydrogen storage alloy according to any one of claims 1 to 5, wherein The alloy composition satisfies the condition of 5.35 ≦ a + b + c + d <5.40, the a-axis length of the crystal lattice is 499.8 pm or more and 502.3 pm or less, and the c-axis length is 406.0 pm or more and 407.3 pm or less. The low Co hydrogen storage alloy according to any one of claims 1 to 5, wherein The alloy composition satisfies the condition of 5.40 ≦ a + b + c + d <5.45, the a-axis length of the crystal lattice is 499.7 pm or more and 502.3 pm or less, and the c-axis length is 406.1 pm or more and 407.4 pm or less. The low Co hydrogen storage alloy according to any one of claims 1 to 5, wherein Formula _{MmNi a Mn b Al c Co d} Fe e ( wherein, Mm is the mischmetal, 4.35 ≦ a ≦ 4.7,0.30 ≦ b ≦ 0.65,0.20 ≦ c ≦ 0.50 0 <d ≦ 0.35, 0 <e ≦ 0.11, 5.2 ≦ a + b + c + d + e ≦ 5.5), and 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 is 499.0 pm or more, and the c-axis length is 405.0 pm or more,
A low Co hydrogen storage alloy characterized in that, in a pressure-composition isotherm diagram (PCT curve) at 45 ° C., an equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 is 0.06 MPa or less.   The pressure-composition isotherm diagram (PCT curve) at 45 ° C has an equilibrium hydrogen pressure at a hydrogen storage amount (H / M) of 0.5 of 0.020 MPa or more and 0.06 MPa or less. The low Co hydrogen storage alloy described.   CaCu _Five The a-axis length of the crystal lattice of the type crystal structure is 499.0 pm or more and 503.0 pm or less, and the c-axis length is 405.0 pm or more and 408.0 pm or less. The low-Co hydrogen storage alloy according to claim 10 or 11, characterized in that The low Co hydrogen storage alloy according to any one of claims 10 to 12, wherein a hydrogen storage amount (H / M) at 0.5 MPa is 0.803 or more and 0.849 or less . The alloy composition satisfies the condition of 5.25 ≦ a + b + c + d + e <5.30, the a-axis length of the crystal lattice is from 500.5 pm to 503.0 pm, and the c-axis length is from 405.6 pm to 407. The low Co hydrogen storage alloy according to claim 10, wherein the low Co hydrogen storage alloy is 9 pm or less. The alloy composition satisfies the condition of 5.30 ≦ a + b + c + d + e <5.35, the a-axis length of the crystal lattice is from 500.0 pm to 502.8 pm, and the c-axis length is from 405.6 pm to 408. The low Co hydrogen storage alloy according to claim 10, wherein the low Co hydrogen storage alloy is 2 pm or less. The alloy composition satisfies the condition of 5.35 ≦ a + b + c + d + e <5.40, the a-axis length of the crystal lattice is from 499.8 pm to 502.8 pm, and the c-axis length is from 405.6 pm to 408. The low Co hydrogen storage alloy according to claim 10, wherein the low Co hydrogen storage alloy is 3 pm or less. The alloy composition satisfies the condition of 5.40 ≦ a + b + c + d + e <5.45, the a-axis length of the crystal lattice is from 499.7 pm to 502.6 pm, and the c-axis length is from 405.7 pm to 408. The low Co hydrogen storage alloy according to claim 10, wherein the low Co hydrogen storage alloy is 4 pm or less. The hydrogen storage alloy is pulverized and sieved to adjust the particle size within a range of 20 μm to 53 μm to obtain a hydrogen storage alloy powder. The average particle size (; particle size before cycle, D50) of the hydrogen storage alloy powder is measured by a particle size distribution analyzer. After the measurement, 2 g of this hydrogen storage alloy powder was weighed and placed in a PCT holder, surface washed twice with a hydrogen pressure of 1.75 MPa, and then activated twice so as to introduce 3 MPa of hydrogen, Next, with a PCT apparatus, hydrogen gas of 3 MPa was introduced into 2.0 g of hydrogen storage alloy powder to store hydrogen, and a cycle test was repeated 50 times at 45 ° C., followed by 50 cycles of hydrogen storage and release. When the average particle size (particle size after cycle, D50) of the hydrogen storage alloy powder is measured with a particle size distribution measuring device, the pulverization residual rate obtained by the following formula is 50% or more. Low Co hydrogen storage alloy according to any one or claims 14 to 17 according to claim 6 to 9.
Micronization residual rate (%) = (particle size after cycle / particle size before cycle) × 100   The low Co hydrogen storage alloy according to claim 18, wherein the low Co hydrogen storage alloy is used as a negative electrode active material for a hybrid vehicle battery. A battery comprising a structure using the low Co hydrogen storage alloy according to any one of claims 1 to 19 as a negative electrode active material.

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