JP3407989B2 - Metal hydride electrode - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal hydride electrode containing a hydrogen storage alloy as a main component, and more particularly to a metal hydride electrode for a sealed nickel-hydrogen alkaline storage battery.

[0002]

2. Description of the Related Art Nickel-hydrogen alkaline storage batteries are drawing attention because they are lighter in weight and higher in capacity and higher in energy density than nickel-cadmium storage batteries or lead storage batteries which have been conventionally used. This sealed nickel-hydrogen alkaline storage battery is generally manufactured as follows. First, the metal hydrogen storage electrode constituting the negative electrode of this battery is made of polytetrafluoroethylene (PTFE) as disclosed in JP-A-61-66366.
A binder is prepared by kneading a binder such as polyethylene oxide or the like and a hydrogen storage alloy powder to prepare a paste, and the paste is applied to both surfaces of a core body such as punching metal or expanded metal and dried. Further, a nickel-hydrogen alkaline storage battery having such a hydride electrode as a negative electrode, the metal hydride electrode and the sintered nickel positive electrode are spirally wound with a separator interposed therebetween,
It is manufactured by accommodating this in a battery outer can and further injecting an alkaline electrolyte to seal the outer can.

The sealed nickel-hydrogen alkaline storage battery manufactured in this manner is constructed so that the negative electrode capacity is larger than the positive electrode capacity in order to prevent hydrogen gas from being generated from the negative electrode at the end of battery charging. is there. Therefore, when the battery is charged, the positive electrode is overcharged before the negative electrode is fully charged. However, when the positive electrode is overcharged, oxygen gas is emitted from the positive electrode by the reaction shown in the following reaction formula (1). Occur. 4OH ⁻ → 2H ₂ O + O ₂ + 4e ⁻ (1) However, the oxygen gas generated in this positive electrode passes through the separator and moves to the negative electrode, and the following reaction occurs on the surface of the negative electrode hydrogen storage alloy in a charged state. It is absorbed by reacting with hydrogen to produce water according to the reaction represented by the formula (2). In this way, the oxygen gas generated in the positive electrode is consumed and absorbed in the negative electrode, so that the battery internal pressure does not increase in principle even in a sealed battery. 4MH + O ₂ → 4M + 2H ₂ O (2) However, when the oxygen gas consumption capacity of the negative electrode is small and the reaction of the above reaction formula (2) is not performed smoothly, the oxygen gas generated at the positive electrode is Since it is not completely consumed by the negative electrode, oxygen gas is gradually accumulated in the battery and the battery internal pressure rises. The increase in the battery internal pressure causes the battery safety valve to operate, causing gas to be released and the electrolyte to leak outside the battery.

Even if the negative electrode has a high oxygen gas absorption capacity to some extent, when the storage battery is overcharged with a large current, a large amount of oxygen gas is generated in the positive electrode, so that the negative electrode completely consumes this oxygen gas. At the same time, the oxygen gas also oxidizes the hydrogen storage alloy itself, so that the hydrogen storage alloy deteriorates and the hydrogen storage / release capacity decreases. That is, the generation of a large amount of oxygen gas causes a decrease in the charge / discharge cycle life of the battery.
Therefore, conventionally, the following means have been taken for the purpose of reducing the generation of oxygen gas from the positive electrode and smoothly promoting the consumption of oxygen gas at the negative electrode.

A) A method of properly controlling the charge amount. When a nickel-hydrogen alkaline storage battery is charged, the battery voltage gradually rises and reaches a peak just before full charge. If charging is continued even after this, the battery will be in an overcharged state, but the battery voltage will drop at the stage from full charge to overcharge. Therefore, it is possible to avoid overcharging the storage battery by detecting the voltage drop (−ΔV) that occurs immediately after the full charge and stopping the charging when the −ΔV is detected. Therefore, for this type of storage battery,
Conventionally, a method has been adopted in which a peak voltage value at the end of charging is stored and charging is performed using a charger that can automatically stop charging when the charging voltage drops by a constant value (-ΔV). .

However, in the conventional nickel-hydrogen alkaline storage battery, the change amount (-ΔV) of the battery charge potential that occurs during the process from full charge to overcharge is small. Therefore, -ΔV
There is a problem in that it cannot be detected reliably and quickly. −
If ΔV cannot be detected quickly and reliably, after the battery is fully charged, there is a time lag before the charging is stopped, and overcharging progresses during this time lag. Therefore, a large amount of oxygen gas is generated from the positive electrode.

(B) A method of enhancing the oxygen gas consumption capacity of the negative electrode by adding a metal to the negative electrode. This method is disclosed in Japanese Patent Application Laid-Open Nos. 2-239566 and 5
This is a technique proposed in Japanese Patent Laid-Open No. 41210, Japanese Patent Laid-Open No. 3-27466, and the like. Of these, JP-A-2-239
Japanese Unexamined Patent Publication (Kokai) No. 5-41210 discloses a method of adding a metal oxide such as CuO to the inside of a negative electrode made of a hydrogen storage alloy.
A method of adding an oxide, hydroxide or salt of at least one metal selected from silver or thallium is described. According to these techniques, the metal added to the negative electrode promotes the oxygen gas consumption reaction of the negative electrode and also increases -ΔV to some extent. Therefore, the charge / discharge cycle life of the battery can be improved. However, this technique adds a metal that does not have the ability to store and release hydrogen to the negative electrode, and therefore reduces the energy density of the negative electrode by the amount of the metal added. Therefore, in order to avoid a decrease in the energy density of the negative electrode, it is necessary to minimize the amount of metal added by maximizing the oxygen gas absorption promoting effect of the metal. Therefore, the above-mentioned publications (JP-A-2-239566 and JP-A-5-4).
In the technique described in Japanese Patent No. 1210), the effect of promoting the absorption of oxygen gas by the metal cannot be sufficiently obtained, so that the energy density of the negative electrode must be reduced to some extent.

On the other hand, in Japanese Laid-Open Patent Publication No. 3-274664, in view of the above problems, in order to improve the oxygen gas consumption capacity, a metal having a hydrogen storage alloy as a negative electrode material is formed on the surface of a metal. A technique for providing a mixed layer of powder and carbon powder is proposed. However, even in this technique, the effect of promoting absorption of oxygen gas by metal and the effect of increasing the amount of voltage drop after full charge cannot be sufficiently obtained.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and further increased the oxygen gas consumption capacity of the metal hydride electrode and further increased the voltage drop amount after full charge. An object is to provide a metal hydride electrode and thus improve the cycle life of a nickel-hydrogen alkaline storage battery.

[0010]

In order to achieve the above object, the invention according to claim 1 is characterized in that the surface of a base electrode using a hydrogen storage alloy as a negative electrode material is oxidized more noble than the operating voltage of the hydrogen storage alloy. It is characterized in that an additive comprising a metal oxide and / or hydroxide having a reduction potential and a conductive powder are provided.

According to a second aspect of the present invention, in the metal hydride electrode according to the first aspect, the conductive powder is carbon powder. The invention according to claim 3 is the metal hydride electrode according to claim 2, wherein the carbon powder is
It is characterized in that at least one is selected from the group consisting of acetylene black, carbon black, Ketjen black, and activated carbon.

According to a fourth aspect of the present invention, in the metal hydride electrode according to the first to third aspects, the additive is
It is characterized in that it is a metal compound selected from at least one selected from the group consisting of cuprous oxide, cupric oxide, copper hydroxide, silver (I) oxide, silver (II) oxide, and bismuth oxide. Claim 5
According to the invention, in the metal hydride electrode according to any one of claims 1 to 4, the additive disposed on the surface of the metal hydride electrode is 0.5% by weight or more with respect to the hydrogen storage alloy. It is characterized in that it is not more than 4% by weight.

[0013]

According to the above-mentioned constitution of the invention, as a result of the conductive powder and the additive acting as follows, the above object can be achieved. The conductive powder acts to increase the reaction surface area of the metal oxide and / or hydroxide additive. Further, the conductive powder functions as crystal nuclei of metal crystals and also improves conductivity between particles of the additive and the hydrogen storage alloy. In addition, the additive acts to widen the difference between the battery charging voltage at the time of full charge and that at the time of overcharge. These actions will be described in detail below.

.. Additives composed of metal oxides and / or hydroxides disposed on the electrode surface are more easily dissolved in an alkaline electrolyte than metal elements, so that after the battery is assembled, the metal ions can be promptly dissolved in the alkaline electrolyte as metal ions. Dissolve in. The metal ions dissolved in the alkaline electrolyte are deposited on the electrode surface again when the battery is charged, but since the conductive powder such as carbon powder is dispersed on the electrode surface, The powder increases the surface area of the negative electrode and acts as a precipitation nucleus for metal crystals. Therefore, the metal ions in the electrolytic solution can be smoothly deposited on the entire electrode surface centering on the deposition nuclei. That is, the deposition is not biased to a specific location on the electrode surface, and the metal crystal particles dispersed and deposited on the electrode surface in this manner are fine and have a large specific surface area. Has a large reaction area. Therefore, the oxygen gas generated at the positive electrode is efficiently adsorbed or combined with this metal,
The oxygen gas consumption reaction of the negative electrode is promoted.

It should be noted that the promotion of oxygen gas consumption is promoted by the reaction between the metal itself which is reduced at the time of charging and is deposited on the surface of the negative electrode, and oxygen.
It is considered that both of the above and the reaction with hydrogen on the surface of the hydrogen storage alloy contribute. In this case, the metal is
It is considered that oxygen gas is temporarily retained on the surface of the negative electrode by adsorbing or forming a compound and smoothly reacts with hydrogen on the surface of the hydrogen storage alloy.

.. An additive made of a metal oxide and / or hydroxide having a redox potential nobler than the operating potential of the hydrogen storage alloy can increase −ΔV according to the principle described later, and in a battery having a large −ΔV, , -ΔV detection control method enables proper battery charging. As a result, overcharging can be prevented, so that the reduction in cycle life due to the generation of a large amount of oxygen gas can be prevented.

.. Here, the mechanism by which the additive can increase -ΔV will be described. First, the potential of each reaction relating to the nickel-hydrogen alkaline storage battery using the metal hydride electrode of the present invention will be described. FIG. 6 is a diagram showing reaction potentials of respective battery constituent components of the nickel-hydrogen alkaline storage battery according to the present invention. In FIG. 6, the reaction formula is the reaction at the positive electrode, the reaction formula is the reaction by the hydrogen storage alloy at the metal hydride electrode (negative electrode), the reaction formula is the oxygen generation at the positive electrode, and the reaction formula is ... The oxidation reactions of the added additive metals (silver, copper, bismuth) are shown. The number on the left side of each reaction formula is 25
The standard electrode potential of each reaction in ° C is shown. Also,
The vertical direction of the figure shows the order of magnitude of the reaction potential. The higher the reaction formula is, the higher the potential of the reaction is, and the more noble the reaction formula is. , Shows that the reaction potential is low and base. The theoretical battery voltage of the nickel-hydrogen alkaline storage battery during normal charging / discharging is the potential of the reaction formula (+0.
52 V), the reaction potential (−0.8
28V). However, this is not always the case because an overvoltage is actually applied by charging and discharging.

Next, the reason why -ΔV occurs when the nickel-hydrogen alkaline storage battery is overcharged and the reason why -ΔV becomes large in the hydride electrode of the present invention will be explained.
The reaction in which oxygen gas is consumed at the negative electrode is an exothermic reaction. Therefore, even in a conventional negative electrode in which an additive made of a metal compound is not disposed in the negative electrode, the battery temperature rises when an oxygen gas consumption reaction occurs, and the reaction potential of the reaction formula in the positive electrode is Shift to (minus side). In addition to this, in the metal hydride electrode of the present invention, since a metal more noble than a hydrogen storage alloy such as silver, copper or bismuth, or a metal oxide or hydroxide metal thereof is present on the electrode surface (negative electrode), The reaction of the reaction formula ··· occurs at the negative electrode,
Since the potential of the reaction of this reaction formula ... Is nobler than the potential of the reaction of the reaction formula, the potential of the negative electrode is shifted to the noble side (plus side) by the reaction of the reaction formula. Also, the more often this reaction formula ... Is performed, the potential of the negative electrode shifts to the noble side (plus side), and the reaction of the reaction formula. As the battery temperature rises, the reaction potential of the above reaction formula becomes even more negative (minus side).
Shift to. That is, the added metal compound acts to further reduce the potential difference between the positive electrode and the negative electrode during overcharge. Further, the conductive powder provided on the electrode surface is
The conductivity between the metal and the negative electrode core is improved, and the reaction of the reaction formulas, and .functions.
Thus, as a result of the action of each element, according to the present invention,
The potential difference between the positive electrode and the negative electrode can be effectively reduced,
As a result, −ΔV can be increased.

The components of the present invention will be further described.
The conductive powder is preferably composed of fine particles having conductivity, and examples of such powder include carbon powder. Among the carbon powders, acetylene black, carbon black, Ketjen black, and activated carbon are particularly preferable. Since these carbon powders have excellent conductivity and fine particles, they act as crystal nuclei during the electrodeposition of metal ions dissolved in an alkaline electrolyte, and can precipitate metal crystals with a large specific surface area. This is because it has favorable properties.

Further, as the additive composed of the oxide and / or hydroxide of the metal, cuprous oxide, cupric oxide,
It is preferable to use at least one metal compound selected from the group consisting of copper hydroxide, silver (I) oxide, silver (II) oxide, and bismuth oxide. Because these metals have a suitable reaction potential for increasing −ΔV, and the oxides or hydroxides of these metals are more easily dissolved in the alkaline electrolyte than the metal element itself. This is because a large amount is deposited on the conductive powder.

Further, the content of the additive is preferably in the range of 0.5 to 5.4% by weight based on the hydrogen storage alloy, and more preferably 0.8 to 5.0% by weight based on the hydrogen storage alloy.
It is good to say This is because a sufficient charge / discharge cycle life can be secured within this range.

[0022]

EXAMPLES The present invention will be described in detail based on examples. [Example 1] In Example 1, a hydrogen storage electrode having acetylene black and cuprous oxide on the surface of the electrode was prepared, and a cylindrical sealed nickel-hydrogen alkaline storage battery was manufactured using this hydrogen storage electrode. Was produced. The manufacturing method is as follows. (Production of Metal Hydride Electrode) Commercially available Mm (Misch metal: mixture of rare earth elements), nickel, cobalt, aluminum, and manganese are used in an element ratio of 1.0: 3.4:
After weighing so as to have a ratio of 0.8: 0.2: 0.6, it is melted in a high frequency induction furnace in an argon gas atmosphere,
Further, this molten metal is cooled to form a compositional formula Mm _1.0 Ni _3.4 Co.
A hydrogen storage alloy ingot represented by _0.8 Al _0.2 Mn _{0. 6} were prepared. Next, this hydrogen storage alloy ingot was crushed to 150 μm or less in an inert gas atmosphere to obtain a hydrogen storage alloy powder.

Then, P is added to the above alloy powder as a binder.
5 wt% of TFE powder was added to the weight of the hydrogen storage alloy and kneaded to prepare a paste. This paste was applied to both sides of a current collector made of punching metal, dried and rolled to form a base electrode. Furthermore, 3% by weight of acetylene black and 7.5% by weight of cuprous oxide powder relative to the total weight of the slurry were added to 3% of polyvinyl alcohol.
1. A slurry for placement is prepared by mixing with an aqueous solution (dispersion medium), and the slurry is screen-printed on the surface of the base electrode by 1% by weight of acetylene black with respect to the hydrogen storage alloy of the electrode and 2. Coating and drying were repeated several times so that the amount of cuprous oxide was 5% by weight, and rolling was performed again.
In this way, a metal hydride electrode having acetylene black and cuprous oxide on the electrode surface was prepared.

Hereinafter, this electrode is referred to as an electrode a of the present invention. (Preparation of Storage Battery) The electrode a of the present invention and a known sintered nickel electrode were wound around a separator made of a non-woven fabric to prepare an electrode group. Insert this electrode group into the outer can,
A 30 wt% potassium hydroxide aqueous solution as an electrolytic solution was poured into the outer can, and then the outer can was closed to prepare a cylindrical sealed nickel-hydrogen alkaline storage battery having a theoretical capacity of 1000 mAh.

The storage battery thus manufactured is hereinafter referred to as Battery A of the present invention. [Examples 2 to 6] In Examples 2 to 6, acetylene black was used as the carbon powder, and cupric oxide, copper hydroxide, silver (I) oxide, silver (II) oxide, and bismuth oxide were used as additives, respectively. Metal hydride electrodes b, c, d, e and f were produced, and further sealed nickel-hydrogen alkaline storage batteries B, C, D, E and F were produced using these metal hydride electrodes. The manufacturing method of the electrode and the storage battery is the same as that of the first embodiment, and these batteries are the battery A of the present invention of the first embodiment.
Is different only in the metal compound (additive) arranged on the electrode surface.

[Examples 7-9] In Examples 7-9, cuprous oxide was used as the metal compound, and activated carbon (g), carbon black (h) and Ketjen black (i) were used as carbon powder. The metal hydride electrodes g, h, and i are used respectively.
Was prepared, and nickel-hydrogen alkaline storage batteries G, H, and I were prepared using these electrodes.

These batteries are the batteries A of Example 1.
The only difference is the type of carbon powder provided on the electrode surface. (Comparative Example 1) In Comparative Example 1, a metal hydride k in which neither carbon powder nor metal additive is provided on both the electrode surface and the inner surface.
And nickel-containing the electrode as a negative electrode.
A hydrogen alkaline storage battery K was produced. The method of manufacturing the electrodes and the like is the same as in the first embodiment.

The electrode k is the same as the base electrode of the first embodiment and has neither carbon powder nor metal. (Comparative Example 2) In Comparative Example 2, a metal hydride electrode 1 was prepared in which only 1% by weight of acetylene black with respect to the hydrogen storage alloy was provided on the surface of the base electrode of Example 1, and this electrode 1 was used as a negative electrode. Then, in the same manner as in Example 1, a nickel-hydrogen alkaline storage battery L was produced.

(Comparative Example 3) In Comparative Example 3, a metal hydride in which 1% by weight of acetylene black and 2.5% by weight of metallic copper were arranged on the surface of the base electrode of Example 1 with respect to the hydrogen storage alloy. A nickel-hydrogen alkaline storage battery M was produced in the same manner as in Example 1 except that the electrode m was produced and the electrode m was used as the negative electrode.

Comparative Example 4 In Comparative Example 4, a metal hydride electrode n having cuprous oxide added inside the electrode was prepared, and a storage battery N using this electrode n was prepared. A characteristic part in manufacturing the electrode n (a part different from the method described in the first embodiment) will be described. In the preparation of the metal hydride electrode of Example 1, an appropriate amount of water was added to the hydrogen storage alloy powder, 2.5 wt% cuprous oxide powder, and 5 wt% PTFE powder to knead to prepare a paste. The cuprous oxide was added to the inside of the electrode by a method in which the paste containing the cuprous oxide powder was applied to both surfaces of a collector made of punching metal.

The electrode n is the same as the electrode k of Comparative Example 1 except that the cuprous oxide powder is added inside the electrode. (Comparative Example 5) In Comparative Example 5, a metal hydride electrode o having cuprous oxide (metal additive) disposed on the electrode surface was prepared, and a nickel-hydrogen alkaline storage battery O was prepared using this electrode o as a negative electrode. did. This electrode o is the same as the electrode a of Example 1 except that carbon powder (acetylene black) is not provided on the electrode surface. That is, only 2.5% by weight of cuprous oxide is present on the surface of the base electrode.
It is provided by polyvinyl alcohol (PVA).

Comparative Example 6 In Comparative Example 6, a metal hydride electrode in which 1% by weight of acetylene black and 2.5% by weight of silver were arranged on the surface of the base electrode of Example 1 with respect to the hydrogen storage alloy. A nickel-hydrogen alkaline storage battery P was produced in the same manner as in Example 1 except that the electrode p was used as the negative electrode while producing p.

(Comparative Example 7) In Comparative Example 7, a metal hydride electrode in which 1% by weight of acetylene black and 2.5% by weight of bismuth with respect to the hydrogen storage alloy were provided on the surface of the base electrode of Example 1. A nickel-hydrogen alkaline storage battery Q was produced in the same manner as in Example 1 except that the electrode q was used as the negative electrode while producing q. Table 1 shows a list of the various storage batteries prepared above.

[0034]

[Table 1] [Experiment 1] Regarding the battery A of the present invention and the comparative batteries K, L, M, N, and O of the above-mentioned examples, the charging current was 100 at room temperature.
The battery was charged at 0 mA, and the relationship between the charged amount and the battery internal pressure was investigated. The result is shown in FIG. The charge amount% in FIG. 1 is
The theoretical battery capacity (1000 mAh) is shown as 100%.

As can be seen from FIG. 1, the internal pressure of the battery during overcharging is higher from the comparative battery K (no arrangement) ≧ comparative battery L (only acetylene black on the negative electrode surface)> comparative battery M (acetylene black on the negative electrode surface). + Copper) ≧ comparative battery N
(Only cuprous oxide inside negative electrode) >> Comparative battery O (only cuprous oxide on negative electrode surface) >> Battery A of the present invention (acetylene black + cuprous oxide on negative electrode surface) in that order. From this result, the following can be understood. That is, even if only acetylene black is provided on the negative electrode, the effect of suppressing the battery internal pressure is small. On the other hand, when copper or cuprous oxide is provided in the negative electrode, increase in the battery internal pressure can be suppressed considerably. In this case, cuprous oxide has a greater effect of disposition than metallic copper, and it is more effective to dispose it on the surface of the negative electrode rather than inside the negative electrode. Furthermore, when both acetylene black and cuprous oxide are provided on the surface of the negative electrode, the most excellent effect of suppressing the battery internal pressure can be obtained.

When both acetylene black and cuprous oxide are provided (Battery A of the present invention), the best results are obtained for the following two reasons. Since copper or cuprous oxide disposed on the negative electrode has a redox potential that is nobler than the operating voltage of the hydrogen storage alloy, it dissolves in the alkaline electrolyte during discharge and reprecipitates on the negative electrode surface during charging. It functions to capture oxygen gas in the circulation of dissolution (discharge) and precipitation (charge) and consume it in the hydrogen storage alloy. Here, when the copper disposed on the electrode surface is cuprous oxide, Since copper is more easily dissolved in the alkaline electrolyte than metallic copper, the utilization rate of the cuprous oxide provided is high. In addition, when an appropriate amount of acetylene black (powdered) is provided on the surface of the negative electrode, this acetylene black has conductivity and is fine particles, so that it increases the negative electrode surface area, and at the same time, it is electrolyzed during charging. It functions as a nucleus that allows the copper ions in the liquid to deposit smoothly. Therefore, fine copper crystals are deposited on the entire surface of the negative electrode with acetylene black as crystal nuclei. Since fine copper crystals have a large specific surface area and a large reaction area with oxygen gas, they can efficiently react with oxygen gas generated in the battery. In other words, when acetylene black is provided on the surface of the negative electrode (invention battery A), oxygen generated in the battery is higher than that when acetylene black is not provided (for example, comparative battery O). Gas can be consumed efficiently. Therefore, the rise in the battery internal pressure can be suppressed.

Although only the results of metallic copper and cuprous oxide are shown in FIG. 1, in copper, silver and bismuth, the oxide or hydroxide of the metal element is more alkaline than the metal element itself. Since they are easily dissolved in the liquid, similar results can be obtained with these. Further, other carbon powders such as carbon black, Ketjen black, and activated carbon are fine particles having conductivity like acetylene black. Therefore, in the combination of these metal oxides and these carbon powders, Also, like the combination of acetylene black and cuprous oxide,
Good results are obtained.

[Experiment 2] The battery (A,
And K, L, M, N, O) are charged at a charging current of 1000 mA at 0 ° C., and the time (detection time) from when the charging voltage shows a maximum value to −ΔV shows 10 mV is measured. did. The results are shown in Table 2 and the relationship between the charged amount (% of the theoretical capacity) and the battery voltage (V) of the present invention battery A and the comparative battery K are shown in FIG.

[0039]

[Table 2] The graph of FIG. 2 shows a charging voltage characteristic in which the battery voltage rises with the progress of charging, reaches a peak immediately before full charge, and then the battery voltage slightly drops when reaching an overcharged state. Further, it is understood that the battery A of the present invention has a larger voltage drop amount (-ΔV) at the stage from full charge to overcharge than the comparative battery K. Looking at the magnitude of such a voltage drop amount for each battery (Table 2), from the shorter detection time of -ΔV, the present invention battery A <Comparative battery O <Comparative battery N <
Comparative battery M <Comparative battery L <Comparative battery K.

From these results, when both acetylene black and cuprous oxide were provided on the surface of the negative electrode (invention battery A), only acetylene black (comparative battery L) and cuprous oxide (comparative battery N) were used. , O), when acetylene black and copper were provided together (comparative battery M), and when neither was provided (comparative battery K), the value was significantly reduced by -ΔV (charging voltage showed the maximum value). Amount of voltage drop from
It turns out that can be increased.

[Experiment 3] The batteries (A,
And K, L, M, N, O), a charge / discharge cycle test is performed under the following conditions, the discharge capacity is measured for each cycle, and the battery weight after the end of discharge in each cycle is measured. The relationship between the number of cycles and the battery capacity and the relationship between the number of charge / discharge cycles and the amount of decrease in the battery weight were investigated.

Charging condition : -Charging is performed at 1000 mAh using a charger capable of stopping charging when ΔV is 10 mV, and the battery is stopped for 1 hour after charging is stopped. Discharge conditions : Discharge at 1000 mAh, discharge end voltage is 1
The discharge is stopped when the voltage reaches V, and then the battery is stopped for 1 hour. FIG. 3 shows the relationship between the number of charge / discharge cycles and the battery capacity (% of the theoretical capacity), and FIG. 4 shows the relationship between the number of charge / discharge cycles and the amount of decrease in battery weight (mg).

As can be seen from the results of FIG. 3, from the longest cycle life of the battery, the battery of the present invention was A> comparative battery O> comparative battery N> comparative battery M> comparative battery L> comparative battery K. Further, from FIG. 4, the order of the number of charge / discharge cycles in which the weight reduction of each battery was recognized was similar to the result of the above battery cycle life. Here, the decrease in the battery weight occurs because the battery contents such as the electrolytic solution are discharged from the battery together with the gas from the battery safety valve portion due to the increase in the battery internal pressure. Therefore, the result of FIG. Means that the oxygen gas was smoothly consumed compared to the comparative batteries K to O, and the leakage of the electrolytic solution due to the increase in the battery internal pressure was small. From the correspondence between the results of FIG. 4 and the results of FIG. 3, it is found that suppressing the increase in the battery internal pressure improves the battery cycle life, and that both acetylene black and cuprous oxide are provided on the negative electrode surface. In, it is understood that the battery cycle life is remarkably improved. These results also match the results of Experiments 1 and 2 above.

[Experiment 4] In Experiment 4, the battery A of the present invention,
B, C, D, E, F, G, H, I and comparative batteries K, L,
For M, N, O, P, and Q, a charge / discharge cycle was performed under the same conditions as in Experiment 3, and the discharge capacity was 500 mAh.
The number of cycles until the following was measured. The number of cycles was used as the battery cycle life.

The results of the experiment are listed in Table 3 together with the results of Experiment 3.

[0046]

[Table 3] The following can be seen from Table 3. First, a comparative battery K containing neither carbon powder nor additive, a comparative battery L containing only acetylene black, a comparative battery N containing no carbon powder but only cuprous oxide (internally). Addition) or O
(Disposed on the surface) had a cycle life of less than 1200 times. Further, the comparative batteries M, P, and Q each having acetylene black as the carbon powder and copper, silver, or bismuth as the additive all had a cycle life of less than 1300 times. On the other hand, the present invention batteries A, B, C, D, E,
Each of F, G, H, and I had a cycle life of 1300 times or more.

Further, from the comparison between the batteries D and E of the present invention and the comparative battery P, the comparison between the battery F of the present invention and the comparative battery Q, and the comparison of the batteries A, B and C of the present invention and the comparative battery M, It has been clarified that the charge / discharge cycle life is improved when the metal element itself is used as an additive rather than when it is used in the form of a metal oxide or hydroxide. From the above, it has been proved that the charge / discharge cycle life is remarkably improved when the metal hydride electrode in which both the conductive powder and the additive made of the metal compound are provided on the surface of the electrode is used.

[Experiment 5] In Experiment 5, in the combination of acetylene black as the conductive powder and cuprous oxide as the additive, the acetylene black disposition amount was set to 1% by weight based on the hydrogen storage alloy, and The suitable amount of the additive to be added was investigated by a method of changing the amount of the additive from 0 to 10% by weight. Regarding the experimental method, batteries were prepared in the same manner as in Example 1 except that the amount of cuprous oxide was changed, and charge / discharge cycles were performed using these batteries under the same conditions as in Experiment 4. Then, the cycle life was measured.

The results are shown in FIG. From FIG. 5, the weight% of cuprous oxide to the hydrogen storage alloy is 0 to 1, and 5 to
It can be seen that in No. 10, the charging / discharging cycle life is substantially linearly increased or decreased, and the charging / discharging cycle life is 1200 times or more in the range of 0.5% by weight to 5.4% by weight. From this result, the additive to the hydrogen storage alloy is
0.5 wt% to 5.4 wt% is preferable, 0.8 wt%
It can be seen that the range of up to 5.0% by weight is more preferable.

[0050]

As described above, according to the present invention, it is possible to provide a hydride electrode having an excellent ability to absorb oxygen gas generated during overcharge and a large -ΔV. Therefore, in a nickel-hydrogen alkaline storage battery using such an electrode in the negative electrode, the oxygen gas generated in the positive electrode is smoothly consumed and absorbed in the negative electrode.
No electrolyte leakage due to the increase in battery internal pressure occurs.
Further, since the battery can be properly charged, a situation in which a large amount of oxygen gas is generated from the positive electrode due to overcharge does not occur. Therefore, a nickel-hydrogen alkaline storage battery battery having excellent charge / discharge cycle life can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a battery charge amount and a battery internal pressure.

FIG. 2 is a diagram showing a relationship between a charge amount (%) and a battery voltage (V).

FIG. 3 is a diagram showing the relationship between the number of charge / discharge cycles and the battery capacity (%).

FIG. 4 Number of charge / discharge cycles and battery weight reduction amount (mg)
It is a figure which shows the relationship of.

FIG. 5 is a diagram showing the relationship between the amount (%) of cuprous oxide added to a hydrogen storage alloy and the charge / discharge cycle life.

FIG. 6 is a view of nickel using the metal hydride electrode of the present invention.
It is a figure which shows the electric potential of each reaction in a hydrogen alkaline storage battery.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-41210 (JP, A) JP-A-3-274664 (JP, A) JP-A-63-195960 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 4/62 H01M 4/24

Claims (5)

(57) [Claims] 1. An additive comprising a metal oxide and / or hydroxide having a redox potential nobler than the operating voltage of the hydrogen storage alloy, on the surface of a base electrode having a hydrogen storage alloy as a negative electrode material. , A conductive powder, and a metal hydride electrode. 2. The metal hydride electrode according to claim 1, wherein the conductive powder is carbon powder. 3. The carbon powder is acetylene black,
The metal hydride electrode according to claim 2, wherein at least one selected from the group consisting of carbon black, Ketjen black, and activated carbon. 4. The metal compound selected from the group consisting of cuprous oxide, cupric oxide, copper hydroxide, silver (I) oxide, silver (II) oxide, and bismuth oxide. The metal hydride electrode according to claim 1, wherein the electrode is a metal hydride electrode. 5. The additive disposed on the surface of the metal hydride electrode is 0.5 wt% or more with respect to the hydrogen storage alloy,
The metal hydride electrode according to any one of claims 1 to 4, which is 5.4% by weight or less.