Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-10-25
2003-08-05
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C420S900000, C148S538000
Reexamination Certificate
active
06602639
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hydrogen storage alloy reversibly capable of storing and emitting hydrogen and having electric conductivity, a process for producing the hydrogen storage alloy, a hydrogen storage alloy electrode, a process for producing the hydrogen storage alloy electrode, and a battery.
DESCRIPTION OF THE RELATED ART
Conventionally, a hydrogen storage alloy has been known which shows the general formula of AB
5
. A representative form of this hydrogen storage exhibits the hydrogen storage alloy showing a formula of MmNi
5
in which “A” sites in the general formula of AB
5
take “Mm”, and “B” sites take Ni. “Mm” means misch metal. In the above-mentioned hydrogen storage alloy showing the formula of MmNi
5
, a part of Ni is replaced by Mn, Co, Al, etc. to improve characteristic properties. Especially, the hydrogen storage alloy having the formula of MmNi
3.55
Al
0.30
CO
0.75
Mn
0.4
is provided.
Also, Japanese Unexamined Patent Publication (KOKAI) 8-315,813 discloses hydrogen storage alloy which has a parent phase having a crystal structure of CaCu
5
(=AB
5
) type, and a second phase having Ni and/or Co. According to this parent phase, when a ratio of the number of atoms of Mm ( misch metal ) is set at 1, (Ni+Co+Mn+Al) is set at 4.5-5.5 in a ratio of the number of atoms, in order to increase the degree of activation. This publication discloses that the second phase has the composition Mo (Ni—Co)
3
.
Also, Japanese Unexamined Patent Publication (KOKAI) No.7-286,225 discloses another hydrogen storage alloy. This hydrogen storage alloy has a hydrogen storage alloy phase having a crystal structure of CaCu
5
, and a second phase which is mainly composed of chemical elements not including Mm (misch metal) and which is distributed in a insular shape. In this publication, when Mm is misch metal, the hydrogen storage alloy phase has the general formula of MmNi
x
M
y
. Also, this publication discloses the hydrogen storage alloy phase having the formula expressed as 5.0≦(x+y)≦5.5. In general hydrogen storage alloy, since stress is caused by expansion in storing hydrogen storage and by contraction in emitting hydrogen, the hydrogen storage alloy is micronized. However, the second phase, not including Mm and being dispersed in a insular shape, can decrease the stress to suppress the micronization of the alloy.
Japanese Unexamined Patent Publication (KOKAI) 8-315,813 discloses a hydrogen storage, alloy electrode for an alkaline storage battery. In this publication, the parent phase of this alloy has the general formula of Mm—(Ni—Co—Mn—Al)
X
, in which “X” is expressed as 4.5≦x≦5.5. This parent phase has the crystal structure of CaCu
5
, and it has a spherical shape or a particle shape exhibiting a chicken egg shape. In this alloy, the second phases are produced at particle surfaces of the hydrogen storage alloy to has a catalytic ability for storing and emitting hydrogen. The second phase is composed of intermetallic compound having a high-melting point and including Ni and/or Co.
Japanese Unexamined Patent Publication (KOKAI) 4-168,240 discloses another hydrogen storage alloy having the formula of ABx. According to this hydrogen storage alloy, the “A” site in the formula of ABx shows lantern or misch metal, and the “B” site shows at least one from the group of nickel, cobalt, aluminum, manganese, chromium, copper, and zirconium. Then, the range of “X” is set in the formula of 5.5≦x≦6.5. This alloy can suppress micronization thereof caused by storing and emitting hydrogen. Japanese Unexamined Patent Publication (KOKAI) 4-168,240 discloses MmNi
3
Co
2
Al
0.5
Mn
0.5
as the hydrogen storage alloy exhibiting the formula of Mm—(Ni—Al—Co—Mn). However, when a ratio of the number of atoms of Mm is 1, a ratio of the number of atoms of Ni is as small as 3. As a result, it is insufficient to generate an electrically conductive network having good conductivity.
In industry, the battery with a negative electrode composed of hydrogen storage alloy has been provided. Generally, when this battery is used in room temperature, the ratio between internal resistance of the positive electrode and internal resistance of the negative electrode does not indicate a large difference. This shows fundamentally the following:
(internal resistance of positive electrode:internal resistance of negative electrode)=1:1
On the other hand, when the battery is used in low-temperatures, the internal resistance of negative electrode tends to relatively increase. Especially, when temperature is near 0° C., the internal resistance of the negative electrode composed of hydrogen storage alloy considerably increases. This shows fundamentally the following: (internal resistance of positie electrode:internal resistance of negative electrode )=1.3 (3-3.5).
When the battery is used in low-temperatures, the negative electrode shows a relative increasing rate in the internal resistance to restrict a battery reaction. Also, when the battery is charged at a high speed, since an exothermic reaction is generated by the internal resistance, the high-speed charging is restricted in the battery. Therefore, for ensuring the high-speed charging, it is preferable that internal resistance is low in the electrode and in the battery. In each of the hydrogen storage alloys concerning the above-mentioned publications, the second phase, showing good conductivity and including Ni, does not form a conductive network state sufficiently. Therefore, each of the above-mentioned hydrogen storage alloys is insufficient in forming an electric conductive route composed of the second phase.
Concerning Japanese Unexamined Patent Publication 4-168,240, the conductive route composed of the second phase is also insufficient.
The present invention has been developed in view of the above-mentioned circumstances. It is therefore an object of the present invention to provide hydrogen storage alloy, a process for producing the hydrogen storage alloy, a hydrogen storage alloy electrode, a process for producing the hydrogen storage alloy electrode, and a battery; which can improve electrical conductivity to decrease internal resistance and to increase power in low-temperatures and which can improve high-speed charging.
DISCLOSURE OF THE INVENTION
(Invention of Hydrogen Storage Alloy)
{circle around (1)} Hydrogen storage alloy according to a first aspect comprises: (1) a main composition expressed by the formula of Mm—(Ni—Al—Co—Mn); (2) a ratio of the number of atoms expressed by the formula of (Ni—Al—Co—Mn) is exhibited as 5.5<(Ni+Al+Co+Mn)≦9, and 3.5≦Ni, when Mm is set at 1 in a ratio of the number of atoms; and (3) an internal structure having a hydrogen storage alloy phase expressed by the general formula of AB
5
, and a second phase existing in the hydrogen storage alloy phase.
“Mm” means misch metal. The misch metal means an aggregate of rare earth elements such as Ce and La.
According to the hydrogen storage alloy concerning the first aspect, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) is 5.5 or less, the second phase showing good conductivity decreases relatively, a conductive network composed of the second phase is not sufficiently formed, and the internal resistance of the hydrogen storage alloy increases; therefore, not obtaining an effect that power is improved.
Meanwhile, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) exceeds 9, the conductive network composed of the second phase increases excessively, the hydrogen storage alloy phase decreases relatively; therefore, not obtaining a sufficient ability in storing and emitting hydrogen. Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) can be chosen on occasion. In the hydrogen storage alloy concerning the first aspect, the lower limit of the total quantity of (Ni+Al+Co+Mn) can be, for example, 5.6, 5.7, 5.8, 6.0, 6.2
Burns Doane , Swecker, Mathis LLP
Ryan Patrick
Toyota Jidosha & Kabushiki Kaisha
Tsang-Foster Susy
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