JPH0810596B2 - Metal oxide / hydrogen battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a so-called metal oxide / hydrogen secondary battery using a metal oxide as a positive electrode active material and hydrogen as a negative electrode active material.

(Prior Art) Currently, in a metal oxide / hydrogen battery, a type in which a hydrogen negative electrode is composed of a hydrogen storage alloy is drawing attention.
The reason is that this battery system originally has a high energy density, is advantageous in volumetric efficiency, can operate safely, and is excellent in characteristics and reliability.

As a hydrogen storage alloy used for the hydrogen negative electrode of this type of battery, LaNi5 has been frequently used. Also, La, C
An alloy of Ni with a misch metal (hereinafter referred to as Mm) that is a mixture of lanthanum-based elements such as e, Pr, Nd, and Sm, that is,
MmNi _{5 is} also widely used. In addition, alloys of rare earth elements such as LaCo ₅ and SmCo ₅ with Co are often used.

When such a hydrogen storage alloy is used, the internal pressure of the battery is certainly lower than the internal pressure (50 kg / cm ² or less) of a battery not using the hydrogen storage alloy. However, the value is still 2-5kg / at room temperature.
The value is about cm ² , which is higher than the internal pressure (0 to 1 kg / cm ² ) of a nickel-cadmium battery, for example.

When the internal pressure of the battery is higher than the atmospheric pressure, along with the fact that the structure of the battery container needs to be robust to some extent, the following inconvenient situation is characteristically caused. The first problem is that the molecular size of hydrogen molecules in the battery is small,
Therefore, it is unavoidable that the battery gradually leaks from the battery container, and the safety is significantly impaired. The second problem is that as a result of the first phenomenon, hydrogen stored in the hydrogen negative electrode is released and the battery capacity is It causes a decrease and causes self-discharge.

Under such circumstances, it has been proposed to use a hydrogen storage alloy having a low equilibrium plateau pressure for the hydrogen negative electrode, and various alloys have been studied.

For example, with regard to LaNi ₅ and MmNi ₅ , the equilibrium plateau pressures at room temperature are high at about 3 atm and 15 atm, respectively, so batteries using these as negative electrode materials suffer from the above-mentioned inconvenience of reduced safety and self-discharge. Occurs.

On the other hand, even if the equilibrium plateau pressure is low, the battery having the hydrogen storage alloy having a small amount of hydrogen that can be stored as the negative electrode material has the following problems. Firstly, because the hydrogen storage capacity is small, the battery capacity that can be charged is small. Secondly, because the charging capacity is small, the battery tends to be overcharged, and as a result, gaseous hydrogen is easily generated. is there. Hydrogen generation during overcharging raises the internal pressure of the battery, thus impairing the safety of the battery.

Considering the above points, it can be said that it is desirable to use a hydrogen storage alloy having a low equilibrium plateau pressure and a large hydrogen storage amount as the material of the hydrogen negative electrode.

For example, the known hydrogen storage alloys LaCo ₅ , LaNi _1.5 Co _3.5
The equilibrium plateau pressure near room temperature is as low as 0.1 atm and 0.2 atm, respectively, however, the amount of hydrogen that can be stored at 3 atm or less is only about 60% of LaNi ₅ (HHVan Mal, K, HJBu
schow and FAKuijpers, J. Less-Comon Metals, 32 ,
289 (1973)). Therefore, a battery using these as a negative electrode material has a problem that it has a small capacity and is likely to be overcharged.

In addition, there are reports that it has already been used as a material for hydrogen storage alloy electrodes (JJGWillems, Philps
J. Res, 39 , 1 (1984)) and Mm-Ni-Co alloys further lower the equilibrium plateau pressure compared to the previous La-Ni-Mm alloys and Mm-Ni-Mn alloys. Although it is possible to do so, this type of alloy has a problem that a sufficient hydrogen storage capacity cannot be obtained.

As described above, the hydrogen storage alloy as the negative electrode material of the metal oxide / hydrogen battery is required to have characteristics that the hydrogen storage amount is large and the equilibrium plateau pressure is low. However, even when using a hydrogen storage alloy that has both of these characteristics,
In actual battery systems, the following disadvantages often occur.
First of all, the electrode of the metal oxide / hydrogen secondary battery is
Long life characteristics that the capacity does not decrease even after repeating sufficient discharge in the electrolytic solution are required, but when the hydrogen storage alloy is chemically unstable with respect to charge and discharge in an alkaline aqueous solution,
There is a problem that the life of the battery will be exhausted by repeated charge and discharge. Second, the theoretical capacity of the hydrogen storage alloy electrode can be calculated from the hydrogen storage capacity of the alloy, but even if an alloy with a large hydrogen storage capacity is used, only a small electric capacity that is less than the theoretical capacity is often measured. is there.

Regarding the first problem, for example, MmNi _4.5 Mn _0.5 or MnNi
_{In the} case of an electrode using a negative electrode material such as a _4.2 Mn _0.8 alloy, which has been widely used in the past, the initial charge was 100% of the charging capacity.
Can be discharged, but 80 in about 100 charge / discharge cycles
%, The capacity will be reduced to 50% after about 150 times. This is considered to be due to the fact that the hydrogen storage alloy, which is the negative electrode material, is not chemically stable with respect to the charge / discharge cycle in the electrolytic solution, and such a chemical stability is required for extending the life. Sex is also required. Such scientific stability of the electrode is obtained, for example, when a hydrogen storage alloy containing a small amount of Al as a component is used as the material, and the electrode has a long life (JP-A-61-2269). Further, it is said that the hydrogen storage alloy has corrosion resistance because a closed oxide layer is formed on the surface due to the inclusion of elements such as Al, Cr and Si.
60-89066).

A second problem is that when the hydrogen-absorbing alloy powder is molded into an electrode using a polymer binder, alloy particles that are not electrically connected due to incomplete contact between the alloy powder particles are generated. It is due to that. That is, the particles of the hydrogen storage alloy, to which current does not flow during charging / discharging, do not store and release hydrogen and do not contribute to the capacity of the electrode at all, so that the capacity of the electrode becomes smaller than the theoretical capacity. Conventionally, there is an example (Japanese Patent Publication No. 57-30273) in which acetylene black is mixed into a hydrogen storage alloy powder to reduce electric resistance, but a metal oxide / hydrogen battery solved by focusing on such a problem. There is no.

As described above, for the negative electrode of the metal oxide / hydrogen battery, use a hydrogen storage alloy that has a large hydrogen storage capacity, a low equilibrium plateau pressure, and is scientifically stable against charge / discharge in an electrolytic solution, It is required that the alloy particles and the alloy particles be in good electrical contact with each other, but no hydrogen storage alloy electrode satisfying all of them has been obtained so far.
Therefore, it has all the characteristics of large capacity required for metal oxide / hydrogen batteries, increased internal pressure, reduced risk of hydrogen leakage, excellent stability, low self-discharge, and long life. I couldn't make the battery.

(Problems to be Solved by the Invention) The present invention solves the problem of preventing the risk of hydrogen leakage and rupture and ending the life in a short time, and further, the capacity of the electrode is smaller than the expected capacity. It solves the problem. That is, an object of the present invention is to provide a metal oxide / hydrogen battery which is excellent in safety, has less self-discharge, has a large capacity, and has a long life.

[Structure of the Invention] (Means for Solving the Problems) As a result of repeated research on the battery negative electrode using a hydrogen storage alloy as a material, the present inventors have found that a hydrogen storage alloy powder having an appropriate composition and an appropriate size. It was found that the above-mentioned problems can be solved by using an electrode containing both of the conductive powder of 1.

That is, the metal oxide / hydrogen battery of the present invention comprises a positive electrode, an alkaline electrolyte, and a negative electrode mainly composed of a rare earth-based hydrogen storage alloy containing at least two kinds of rare earth elements including cerium (Ce). A metal oxide / hydrogen battery provided, wherein the Ce content is 0.1% by weight or more and 10% by weight or less with respect to the total amount of the rare earth elements, and a conductive powder having an average particle size of 10 μm or less is included as a negative electrode auxiliary material It is characterized by

Particularly preferred hydrogen storage alloys for use in the present invention are those represented by the following formula MNi _x Co _y Mn _z Al _w (I) (wherein M is at least two rare earth elements (including yttrium) containing Ce). The ones shown are: And Ni, Co, M which is a component other than the rare earth element component M
When all of n and Al are contained in appropriate amounts, that is, x, y, z, w in the composition formula are 3.5 <x ≦ 4.4 ………… 0.05 <y ≦ 1.2 ……… 0.05 <z ≦ 1.2 ……… 0.05 <w ≦ 0.6 ……… 4.7 ≦ x + y + z + w ≦ 5.4 ……… If all the relations are satisfied, good hydrogen storage capacity, low equilibrium plateau pressure, and good chemical stability in the electrolyte can get. x, y, z, w are determined within the range of the formula by considering the action of each component described later. The composition of the alloy according to the present invention does not exclude inevitable impurities that enter during the production thereof. Examples of the inevitable impurities include Fe, Cu, Sn and the like.

The conductive powder may be metal powder such as Cu, Ni, Fe and Al, carbon powder such as activated carbon, graphite, acetylene black, Ketjen black, or a mixture thereof or activated carbon. The metal fine particles may be supported on the. Especially when such noble metal particles such as Pt are supported as such metal particles. In addition to the effect of increasing the capacity by ensuring electrical contact between the hydrogen-absorbing alloy particles described above and improving the charging / discharging characteristics at large current due to a decrease in electrical resistance, an effect of further preventing an increase in cell internal pressure Will also be noticeable. In a battery that uses a metal oxide for the positive electrode and a hydrogen storage alloy for the negative electrode, normally when overcharged,
Oxygen gas is generated from the positive electrode at the end of charging. Since this oxygen gas reacts with hydrogen on the surface of the negative electrode to become water, the internal pressure decreases if discharged or left for a long time in an open circuit state. Since the noble metal particles accelerate the chemical reaction of the oxygen and hydrogen to be combined with each other to form water, the oxygen does not become a gas state and the internal pressure does not rise even during charging. In addition, when the noble metal particles are contained even if oxygen gas is generated during extreme overcharging, the cell internal pressure reaches a low level and the internal pressure drops rapidly during discharge or when left alone, which is excellent in safety. . As the noble metal, Pt is the most excellent because of its catalytic ability, and then Ph, Ru, etc., and Ag, Au, etc. are suitable next.

The noble metal oxide / hydrogen battery of the present invention can be manufactured by the following method.

As the positive electrode made of a metal oxide, for example, a nickel oxide (NiOOH) electrode obtained by impregnating and forming an active material such as nickel hydroxide (Ni (OH) ₂ ) in a sintered body of metal nickel is used. You can

The hydrogen storage alloy, which is the material of the hydrogen negative electrode, can be obtained as a uniform solution by mixing a predetermined amount of each component element powder determined from the target composition and melting the mixed powder in, for example, a vacuum arc melting furnace. Further, the powder body can be easily prepared by crushing the solid solution or subjecting it to an activation treatment such as placing it in a hydrogen atmosphere at a pressure of atmospheric pressure or higher at room temperature. The hydrogen storage alloy powder prepared in this manner may be in a state of releasing hydrogen or may be in a state of partially storing hydrogen when the battery negative electrode is produced. The hydrogen storage alloy powder, a conductive powder such as activated carbon, and a binder such as tetrafluoroethylene are mixed and then kneaded to form a sheet, and the sheet and the current collector or the lead are bonded by, for example, pressure bonding. The hydrogen negative electrode of the battery can be manufactured by, for example,

Insulate the positive electrode and negative electrode thus obtained with a separator made of nylon or polypropylene, and use KOH or NaOH.
The metal oxide / hydrogen battery according to the present invention is constructed by immersing the electrolyte in an electrolytic solution containing an alkaline aqueous solution such as.

(Function) As M, which is a rare earth component of the hydrogen storage alloy according to the present invention, Ce and one or more other rare earth elements prepared in a predetermined ratio may be used in advance, but they should be inexpensively available. Therefore, it is desirable to use a mixture of rare earth elements obtained by partially removing Ce from ordinary misch metal. If the Ce amount is 0.1 to 10% by weight with respect to M, it has a sufficiently large hydrogen storage amount as a battery negative electrode material and a sufficiently low equilibrium plateau pressure, and is more preferably 0.1 to 8% by weight. If the amount of Ce exceeds 12% by weight, or
If it is less than 0.1% by weight, the life characteristics will deteriorate.
In particular, when the content is 0.1% by weight or more and 8% by weight or less, a long life is achieved. This Ce can be easily removed because it can be the only tetravalent oxide in the rare earth elements. Further, in the amount of metal components other than rare earth elements of the hydrogen storage alloy in the above formula (I) shown as a preferable composition, the amount of Ni is x ≦ 3.5.
Hydrogen storage capacity decreases, and equilibrium plateau pressure rises at 4.4 <x, causing a problem. Co is a component that has the effect of lowering the equilibrium plateau pressure. When the Co content is 1.2 <y, the hydrogen storage capacity decreases, while when the amount is very small, that is, y ≦ 0.05, the effect of including Co is effective. The problem of not being produced arises. Mn has a function of lowering the equilibrium plateau pressure while maintaining the hydrogen storage amount, and the amount is 0.05 <
z ≦ 1.2 is suitable. When the amount of Mn becomes 1.2 <z and becomes excessive, the hydrogen storage amount decreases, while when the amount of Mn is very small, that is, when z ≦ 0.05, the effect due to the inclusion of Mn cannot be sufficiently obtained. When both Co and Mn are contained, the effect is superior to that of only one of Co and Mn. When Co is included and Mn is not included, the equilibrium plateau pressure decreases, but the phenomenon of hydrogen storage amount remarkably occurs. Conversely, when Mn is included and Co is not included, the equilibrium plateau pressure is insufficiently decreased. Al is a component that acts to keep the alloy chemically stable in the electrolytic solution, and contributes to extending the battery life. The amount is preferably 0.05 <w ≦ 0.6, and when 0.6 <w, the hydrogen storage amount decreases and the capacity of the electrode decreases, and when w ≦ 0.05, the chemical stabilization action is insufficient and the battery life is extended. Absent.
Further, regarding the total amount of components other than the rare earth element in the above formula, in an alloy having a composition outside the range of the formula, a hydrogen storage capacity is greatly distorted from the structure of a typical hydrogen storage alloy LaNi ₅ type. The amount is reduced, which is not preferable.
The composition of the alloy described above does not exclude inevitable impurities that enter during the production thereof. Depending on the origin of the raw material ore, Fe is often contained as an impurity, and it is possible for impurities to be mixed from the furnace or vessel.

The conductive powder according to the present invention needs to have an average particle size of 10 μm or less. The average particle size used in the present invention is the powder
It was calculated by using the value measured by magnifying with SEM. When the hydrogen storage alloy is activated by hydrogen to form a powder, the particle size is about 2 to 70 μm, and the average particle size is
20 to 30 μm. Even when mechanically pulverized, when the battery is charged and discharged after forming the electrode, particles having an average particle size similar to that of hydrogen atomization are obtained. Therefore, in order to secure electrical contact between the hydrogen storage alloy particles having such a size, the average particle diameter of the conductive particles coexisting in the negative electrode needs to be 10 μm or less. As a result, the hydrogen-absorbing alloy particles are in good electrical contact with each other, and as a result, there is no separate alloy particle that does not occlude or release hydrogen during charge / discharge of the electrode, resulting in an electrode with a large capacity, which is used as the negative electrode metal. Oxide / hydrogen batteries will also have a large capacity. These conductive particles
If it exceeds 10 μm, the size becomes equal to or larger than the hydrogen storage alloy particles, and if the content of the conductive powder is small, isolated hydrogen storage alloy particles exist and the electric capacity of the electrode becomes insufficient. However, when the number is large, electrical contact is secured, but the amount of hydrogen storage alloy particles that can be contained volumetrically in the electrode decreases, resulting in a decrease in the capacity of the electrode. Therefore, the average particle size
The size of the conductive powder is limited because the effect of ensuring electrical contact between alloy particles of 20 to 30 μm is sufficiently exerted and the total volume occupied in the electrode is prevented from becoming excessive, and the average size of the conductive powder is limited. A particle size of 10 μm or less is suitable.

As the conductive powder, carbon powder such as metal powder or activated carbon,
Alternatively, a powdery catalyst or the like is suitable, but a carbon powder or a catalyst powder having a carbon powder as a carrier is particularly preferable because of its low specific gravity. This is because the inclusion of metal powder having a large specific gravity causes an increase in the weight of the electrode, but in the case of activated carbon powder or the like, the increase in weight due to the inclusion is slight and can be almost ignored. The content of the conductive powder varies depending on the type and particle size of the conductive powder, but in the case of carbon powder, the above-mentioned effect can be obtained at 0.05 to 10% by weight or less of the electrode weight. Especially average particle size 0.005
In the case of a fine carbon powder of ˜1 μm, a content of 5% by weight or less is preferable because a sufficient effect can be obtained. It should be noted that the inclusion of such a conductive powder also has the effect of lowering the electrical resistance, and simultaneously improves the charge / discharge characteristics of the electrode due to the large current.

(Example) Hereinafter, the present invention will be described in more detail based on examples.

Example 1 (1) Formation of Negative Electrode Powders of metal elements M, Ni, Co, Mn, and Al were mixed in predetermined amounts, and the obtained mixed powder was melted in a vacuum arc melting furnace to have a composition of MNi _4.2. A uniform solid solution of an alloy that becomes Co _0.2 Mn _0.3 Al _0.3 was obtained. As M, a mixture of rare earth elements obtained by removing a part of Ce from commercially available misch metal was used. The analysis values of the composition of M are La: 45.10 wt%, Nd: 37.01 wt%, Pr: 12.07 wt%, Ce: 4.
The content was 60% by weight, Sm: 1.06% by weight, Eu: 0.06% by weight, Dy: 0.05% by weight, Tb: 0.03% by weight, Lu: 0.02% by weight. This solid solution was crushed to a diameter of about 5 mm, then placed in a container connected to a vacuum pump and a hydrogen cylinder, kept at a vacuum of 10 ^-3 Torr or less at room temperature for 1 hour, then hydrogen was introduced, and the pressure was adjusted to about
It was pulverized by keeping it at room temperature for 1 to several hours under a hydrogen atmosphere of 10 kg / cm ² . The alloy powder was taken out of the container again after being degassed at room temperature to 60 ° C. for 1 hour or more and 10 ⁻³ Torr or less. The average particle size of the obtained alloy powder is about
It was 25 μm.

This alloy powder, commercially available acetylene black powder with an average particle size of 0.03 μm and tetrafluoroethylene powder as a binder were mixed in a weight ratio of 95.5: 0.5: 4 and then kneaded to form a 0.5 mm thick sheet. Formed. When the sheet was magnified and observed by SEM, the binder became fibrous and retained the hydrogen-absorbing alloy particles, and carbon particles were connected to the gaps.

The obtained two sheets were pressure-bonded from both sides of one nickel net to be integrated to form an electrode having a thickness of 0.7 mm, which was used as a negative electrode.

(2) Formation of Positive Electrode A porous nickel sintered body Ni (OH) ₂ was impregnated and subjected to chemical conversion treatment to form a NiOOH electrode, which was used as a positive electrode.

(3) Manufacture of Battery The battery shown in FIG. 1 was manufactured by using the above negative electrode, positive electrode, and polypropylene nonwoven fabric having a thickness of 0.3 mm as a separator, and using 8 mol / KOH aqueous solution as an electrolytic solution.

In FIG. 1, 1 is a negative electrode, 2 is a separator, and 3 is a positive electrode. Reference numerals 4 and 5 respectively denote a negative electrode terminal and a positive electrode terminal, which are taken out to the outside electrically independently of the battery container 6. 7 is an electrolytic solution. The negative electrode 1 according to the present invention was wrapped in a U shape with the separator 2, and the positive electrode 3 was arranged from both sides of the negative electrode 1 and they were brought into close contact with each other by the acrylic holder 8. The capacity of the positive electrode was set to be sufficiently larger than the capacity of the negative electrode, and the following measurements were performed under the condition that the battery performance was governed by the characteristics of the negative electrode. Also, in order to measure the negative electrode potential, Cd / Cd (OH)
_{2 The} reference electrode 11 was put in the system, and the lead 12 was taken out.

(4) Battery characteristics The discharge characteristics at the 20th cycle when this battery was repeatedly charged and discharged at a current density of 0.17 A per gram of hydrogen storage alloy are shown by the curve A in the characteristic diagram of FIG. In FIG. 2, the horizontal axis represents the discharge capacity per 1 g of the alloy, and the vertical axis represents the negative electrode potential based on the reference electrode. As is clear from the curve A in FIG. 2, the battery of this example has a large capacity of about 0.27 Ahg ^-1 .

After measuring the above-mentioned discharge characteristics, a life test was conducted in which the charge and discharge cycles were repeated at a charge capacity of 0.17 Ahg ^-1 and a discharge capacity of 90% or more was shown up to 1000 cycles.

Example 2 A battery similar to that of Example 1 was manufactured except that the conductive powder in the negative electrode was a carbon powder carrying 10% by weight of Pt.
The same measurement was performed. In this embodiment, the average particle size is 0.03 μm
The commercially available acetylene black powder of Pt was impregnated with Pt from a chloroplatinic acid solution, evaporated to dryness, and then reduced with hydrogen at a high temperature to prepare a Pt-supported powder. The discharge characteristic of this battery is shown by curve B in FIG. Also in this example, a large capacity was shown as in Example 1. Also, as with Example 1, the life characteristics showed a discharge capacity of 90% or more with respect to a charge capacity of 0.17 Ahg ^-1 up to 1000 cycles.

Comparative Example 1 A battery similar to that of Example 1 was manufactured except that the negative electrode contained no conductive powder. However, MNi _4.2 Co _0.2 Mn _0.3 Al
The weight ratio of _0.3 alloy powder and tetrafluoroethylene is 96: 4
And

The discharge characteristics were measured with the same current density and charge capacity as in Examples 1 and 2, but in this comparative example as shown by the curve C in FIG.
Only a capacity of 0.21 Ahg ^-1 was obtained. After the discharge characteristics were measured, the charge and discharge cycles were repeated at a charge capacity of 0.17 Ahg ^{-1 and} the capacity was 90% (0.153 Ahg ^-1 ) or less after 660 cycles.

Comparative Example 2 A battery in which the composition of the hydrogen storage alloy as the negative electrode material was NmNi4.2Mn0.8 and no conductive material was contained was manufactured in the same manner as in Example 1. The analytical value of the composition of Mm is La: 26.31% by weight, Nb: 14.3
The content was 4% by weight, Pr: 15.37% by weight, Ce: 43.30% by weight, Sm: 0.65% by weight. The weight ratio of alloy powder and tetraluorotylene is
It was 96: 4.

The discharge characteristics were measured with the same current density and charge capacity as in Examples 1 and 2, but as shown by the curve D in FIG. 2, in this comparative example, only a capacity of about 0.20 Ahg ^-1 was obtained. Also, 0.17Ahg
About 10 were repeated charging and discharging cycle in the charging capacity of ^-1
Only 0% of discharge capacity (0.153 Ahg ^-1 ) was obtained at 0 cycles.

The difference in the life characteristics of the batteries of Examples 1 and 2 and Comparative Example 1 using the alloys of the same composition is that Comparative Example containing no conductive powder even if the amount of alloy contained in the negative electrode was the same. In No. 1, the current density does not flow in the isolated hydrogen storage alloy powder, so that the current density for the hydrogen storage alloy powder that is effectively used is larger than that in Examples 1 and 2.

[Effects of the Invention] The metal oxide / hydrogen battery according to the present invention is a battery having a large theoretical capacity, preventing the risk of internal pressure rise, reducing self-discharge and hydrogen leakage, and having a long life. The electrical contact between the alloy particles is more reliably maintained, and the capacity of the electrode is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a battery according to the present invention, and FIG. 2 is a characteristic diagram showing discharge characteristics of a battery according to the present invention and a battery of a comparative example. 1 ... Negative electrode, 2 ... Separator, 3 ... Positive electrode, 4 ... Negative electrode terminal, 5 ... Positive electrode terminal, 6 ... Battery container, 7 ...
Electrolyte, 8 ... Holder, 9 ... Insulation gasket, 10 ...
… O-ring, 11 …… reference electrode, 12 …… reference electrode terminal

Claims (5)

[Claims] 1. A metal oxide / hydrogen battery comprising a positive electrode, an alkaline electrolyte, and a load containing a rare earth-based hydrogen storage alloy containing at least two rare earth elements containing cerium as a main material. The content of cerium in the negative electrode is 0.1% by weight or more and 10% by weight or less with respect to the total amount of the rare earth elements, and the average particle diameter of 10 μm is used as a secondary material of the negative electrode.
Metal oxide characterized by containing the following conductive powder
Hydrogen battery. 2. A rare earth-based hydrogen storage alloy, which is the main material of the negative electrode, is MNi _x Co _y Mn _z Al _w (where M is at least two or more rare earth elements containing cerium; x, y, z, w are respectively It represents the atomic ratio of M to 1 gram atom, and represents a number satisfying the relationship of 3.5 <x ≦ 4.4, 0.05 <y ≦ 1.2, 0.05 <z ≦ 1.2, 0.05 <w ≦ 0.6, 4.7 ≦ x + y + z + w ≦ 5.4. The metal oxide / hydrogen battery according to claim 1, which is a hydrogen storage alloy represented by: 3. The metal according to claim 1, wherein the content of cerium is 0.1% by weight or more and 8% by weight or less based on the total amount of rare earth elements. Oxide / hydrogen battery. 4. The metal oxide / hydrogen battery according to claim 1, wherein the conductive powder is carbon powder. 5. The conductive powder has an average particle size of 0.005 μm or more and 1 μm.
The metal oxide / hydrogen battery according to claim 4, characterized in that the carbon powder is m or less.