JP3113891B2 - Metal hydride storage battery - 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 storage battery using a hydrogen storage alloy as a negative electrode, nickel hydroxide or manganese dioxide as a main active material of a positive electrode, and an aqueous alkaline solution as an electrolyte. .

[0002]

2. Description of the Related Art A hydrogen storage alloy is used for a hydrogen storage electrode which is a negative electrode of a metal hydride storage battery. This hydrogen storage alloy replaces component elements such as the intermetallic compounds LaNi ₅ and ZrNi _{2 with} other various metal elements, and when used in an alkaline storage battery, has a charge / discharge cycle life characteristic, equilibrium hydrogen pressure, hydrogen Various characteristics such as the amount of occlusion and release are improved.

[0003] The positive electrode of this battery includes a sintering method used in conventional nickel-cadmium batteries and the like,
A foamed metal nickel hydroxide electrode, manganese dioxide, silver oxide, or the like is used.

Further, an alkaline aqueous solution mainly composed of potassium hydroxide, sodium hydroxide or the like is used as an electrolyte for this battery.

[0005]

When an alkaline storage battery using a hydrogen storage alloy as a negative electrode is left in a charged state, self-discharge accompanied by the generation of hydrogen from the hydrogen storage alloy occurs. There is a problem that it is larger than an alkaline storage battery using cadmium, and it has been desired to solve this problem.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a metal hydride storage battery in which a negative electrode is mainly composed of a hydrogen storage alloy and has an alkaline electrolyte. Concentration of naphthalene, iodide, cyanide, selenide, selenium dioxide, selenite, selenate, selenate, tellurium oxide, telluric acid,
Provided is a metal hydride storage battery containing at least one selected from tellurous acid, tellurite, tellurite, sulfide, sulfur dioxide, carbon monoxide, carbon disulfide, or thiourea.

[0007]

According to the present invention, by employing the above structure, the release of hydrogen from the hydrogen storage alloy is suppressed, and the self-discharge of the metal hydride storage battery is suppressed.

[0008] This operation will be described while discussing the self-discharge mechanism peculiar to this storage battery.

The main reason why the self-discharge rate is higher when the hydrogen storage alloy is used for the negative electrode than when cadmium is used for the negative electrode is considered as follows.

The mechanism of the self-discharge accompanied by the generation of hydrogen in the alkaline electrolyte is considered as follows.

That is, the first factor that determines the rate of self-discharge accompanying the generation of hydrogen at a metal electrode or a hydrogen storage electrode in an alkaline electrolyte is determined by the equilibrium potential of the electrode and the partial pressure of hydrogen on the surface of the electrode. There is a relationship with the equilibrium potential of the electrode reaction of hydrogen, and the second factor is the rate of the hydrogen generation reaction of the electrode or the rate of disappearance of hydrogen.

First, according to the first factor, the equilibrium potential of the hydrogen electrode reaction on the electrode surface can be obtained by the Nernst equation. If the equilibrium potential of the electrode is lower than the equilibrium potential of the hydrogen electrode reaction, If the self-discharge reaction accompanied by the generation of hydrogen gas occurs spontaneously, and the equilibrium potential of the electrode is higher than the equilibrium potential of the hydrogen electrode reaction, the self-discharge reaction accompanied by the generation of hydrogen gas does not occur spontaneously. This is determined by the principles of thermodynamics.

Next, the self-discharge rate when the equilibrium potential of the electrode is lower than the equilibrium potential of the hydrogen electrode reaction is determined by the rate of the hydrogen generation reaction on the electrode and the rate of disappearance of released hydrogen. .

Here, there are the following facts about self-discharge involving hydrogen generation of the hydrogen storage electrode and the cadmium electrode in the alkaline storage battery.

That is, at 25 ° C., the equilibrium potential of cadmium in the alkaline electrolyte is -0.809 V with respect to the standard hydrogen electrode potential, so that the equilibrium potential of the hydrogen electrode reaction becomes equal to the equilibrium potential of the cadmium electrode. Is
It can be calculated from the Nernst equation that the partial pressure of hydrogen is about 0.2 atm. Therefore, if the hydrogen partial pressure is lower than about 0.2 atm, the equilibrium potential of the cadmium electrode becomes lower than the equilibrium potential of the hydrogen electrode reaction, and self-discharge of the cadmium electrode accompanied by hydrogen generation should occur. is there.

Further, the equilibrium potential of the hydrogen storage electrode can be obtained by the Nernst equation using the equilibrium hydrogen pressure corresponding to the amount of hydrogen stored. When the hydrogen partial pressure is lower than the equilibrium hydrogen pressure of the hydrogen storage alloy, Then, self-discharge of the hydrogen storage electrode accompanied by hydrogen generation should occur.

When the battery is an open system, the hydrogen in the battery diffuses into the atmosphere and is lost. When the battery is a closed system, the hydrogen in the battery is charged (ie, the state of the oxidant). ) Is oxidized and consumed by the positive electrode active material. Therefore, the partial pressure of the hydrogen gas in the battery during standing is lower than the hydrogen partial pressure corresponding to the equilibrium potential of the hydrogen electrode reaction equal to the equilibrium potential of the negative electrode, regardless of whether the battery is open or closed. The temperature should always drop, and self-discharge of the negative electrode accompanied by generation of hydrogen gas should proceed. In this case, in the sealed battery, the hydrogen released by the self-discharge from the negative electrode reduces the charge product of the positive electrode, so that the positive electrode and the negative electrode self-discharge at the same rate. On the other hand, in the case of an open-type battery, the self-discharge rate of the negative electrode is higher than that of the positive electrode because hydrogen released to the atmosphere among the hydrogen released due to the self-discharge of the negative electrode does not reduce the charge product of the positive electrode. Become.

Although this is expected thermodynamically, in an actual battery, the equilibrium hydrogen pressure of the hydrogen storage electrode is lower than 0.2 atm, and the equilibrium potential of the hydrogen storage electrode is lower than the equilibrium potential of the cadmium electrode. Even when the cadmium electrode is noble, the self-discharge rate of the hydrogen storage electrode is significantly higher than that of the cadmium electrode, and the cadmium electrode hardly causes self-discharge accompanied by generation of hydrogen.

As described above, the main cause of the remarkable difference in the self-discharge rate accompanying the hydrogen generation between the hydrogen storage electrode and the cadmium electrode is that the hydrogen overvoltage of cadmium is extremely high,
On the other hand, the hydrogen overpotential of the hydrogen storage alloy is extremely low.

That is, since the hydrogen storage alloy has a remarkably low hydrogen overvoltage, the hydrogen generation reaction easily occurs when the hydrogen partial pressure becomes lower than the equilibrium hydrogen pressure of the hydrogen storage electrode.

Therefore, according to the present invention, in a metal hydride storage battery mainly composed of a hydrogen storage alloy and having an alkaline electrolyte, the electrolyte contains a naphthalene, iodide, cyanide, selenide, and a concentration of 0.00001 M or more. Selenium oxide, selenous acid, selenic acid, selenite, selenate, tellurium oxide, telluric acid, tellurite, tellurite, tellurite, sulfide, sulfur dioxide, carbon monoxide,
At least one selected from carbon disulfide and thiourea is contained.

These additives act as catalyst poisons for the hydrogen generation reaction. Therefore, even when a hydrogen storage alloy having a low hydrogen overvoltage and easily generating hydrogen is used, if these catalyst poisons are present, the rate of hydrogen generation from the negative electrode decreases, and the rate of self-discharge decreases.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by way of preferred embodiments.

A metal hydride storage battery having a negative electrode mainly composed of a hydrogen storage alloy and having an alkaline electrolyte was manufactured as follows.

As the negative electrode plate, five paste type plates were used. This electrode was manufactured as follows.

The composition of the hydrogen storage alloy is LmNi in atomic ratio.
The constituent elements were melted in a vacuum in a high-frequency induction furnace in a metal state so as to obtain _3.8 Co _0.7 Al _0.5 , cast, and then pulverized. Here, Lm is a lanthanum-rich misch metal which is a mixture of rare earth metals containing about 90% by weight of La. This alloy powder was dispersed in an aqueous solution of polyvinyl alcohol which functions as a thickener and a binder to form a paste. The paste was applied to both surfaces of a nickel-plated iron punching metal, dried, pressed, and cut to produce a hydrogen storage electrode.

The weight of the hydrogen storage alloy contained in the five negative electrodes of one battery is about 5.3 g.

As the positive electrode, four known sintered nickel hydroxide electrodes were used.

The total weight of nickel hydroxide contained in the four positive nickel hydroxide electrodes was 3.9 per cell.
g. Therefore, assuming that nickel hydroxide follows a one-electron reaction, the theoretical capacity of one battery positive electrode is about 1.
1 Ah. To this electrode was added 0.04 grams of cobalt hydroxide per gram of nickel hydroxide.

The battery for the test was prepared by alternately laminating these negative electrodes and positive electrodes through a separator provided with hydrophilicity by sulfonating non-woven polystyrene made of a fiber of a mixture of polypropylene and polystyrene. The plate group was housed in a rectangular sealed metal battery case and manufactured.

The electrolyte used in the conventional battery A is 20 g / l.
Using a 6 M aqueous KOH solution in which LiOH was dissolved, the batteries B, C, D, E, F, G, H, I, J, K, L,
M, N, O, P, Q, R, S, and T were each added to this aqueous alkali solution at a concentration of 0.00005 M naphthalene,
Potassium iodide, potassium cyanide, zinc selenide, 2
Selenium oxide, selenous acid, selenic acid, sodium selenite, sodium selenite, tellurium oxide, telluric acid,
Tellurous acid, potassium tellurite, potassium tellurite,
Potassium sulfide, sulfur dioxide, carbon dioxide, carbon dioxide,
And the thing which melt | dissolved thiourea was used for electrolyte solution.

These batteries were charged and discharged under the condition that they were charged at a 10-hour rate current for 15 hours based on the theoretical capacity of the positive electrode and discharged at a 5-hour rate current until the terminal voltage became 1 V. . Next, at a current of 10 hour rate, 15
Under the condition that the battery was charged for 5 hours and discharged at a current of 5 hours until the terminal voltage became 1 V, the discharge capacity before leaving was measured. The battery is charged for 15 hours at a current rate of 10 hours,
The discharge capacity after standing was measured under the condition that the battery was discharged at a current rate of 5 hours until the terminal voltage became 1 V after standing for 5 days. Leaving these batteries after charging / discharging and charging were all 25
Performed at an ambient temperature of ° C.

In this test, the capacity retention after standing was defined as the discharge capacity after standing relative to the discharging capacity before standing, and the value of the capacity retention of each battery obtained in the above test is shown in Table 1. Show.

[0034]

[Table 1] From Table 1, the batteries B, C, D, E, F, G, H,
The capacity retention of I, J, K, L, M, N, O, P, Q, R, S, and T is significantly higher than that of the conventional battery A, and therefore, the self-discharge rate is significantly lower. Is clear.

In the above embodiment, the case where the concentration of additives in the electrolytic solution of the battery of the present invention is 0.00005 M has been described. However, when the concentration of these additives is 0.00001 M or more, the same applies. It was confirmed that self-discharge was suppressed.

Further, in the above embodiment, the case where a compound with potassium is used as iodide, cyanide and sulfide is described. However, iodide ion, cyanide ion and sulfide are used as catalyst poisons. Since it is a compound ion, a similar effect can be obtained by using a compound such as sodium in addition to the compound with potassium. Also, in the case of zinc selenide, since selenide ions have the function and effect of the present invention, the same function and effect can be obtained with selenide of other elements than zinc. In the case of sodium selenate, sodium selenite, potassium tellurite, and potassium tellurite, selenate ion, selenite ion, tellurite ion, and tellurite ion respectively show the effect of the present invention. Therefore, not only a salt with a specific alkali metal but also a salt with another cation has the same effect.

In the above embodiment, the case where a specific composition was used as the hydrogen storage alloy for the negative electrode was described. However, in an alkaline storage battery, among the hydrogen storage alloys, those containing nickel were the hydrogen storage alloys. Acting as an electrode, the nickel on the surface of these alloys catalyzes the reaction of hydrogen. Since the catalyst poison used in the battery of the present invention acts on the catalytic activity of the nickel component to suppress self-discharge, the function and effect of the present invention is merely the alloy of the battery of the above embodiment. Instead, the same operation and effect as those of the above embodiment can be obtained also in the case where the constituent metals of the hydrogen storage alloy such as LaNi ₅ , ZrNi ₂ , TiNi, and Ti ₂ Ni are replaced with other elements.

In the above embodiment, the case where a sintered nickel hydroxide electrode is used for the positive electrode has been described.
Similar effects can be obtained when a foamed metal nickel hydroxide electrode, manganese dioxide electrode, or silver oxide electrode is used as the positive electrode.

In the above embodiment, the sealed type battery is described. However, in the case of the open type battery, the self-discharge of the negative electrode accompanying the generation of hydrogen is similarly effectively suppressed.

[0040]

As described above, the metal hydride storage battery of the present invention has an effect that the self-discharge rate is low.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/24-10/30 H01M 10/34

Claims (1)

(57) [Claims] 1. A metal hydride storage battery having a negative electrode mainly composed of a hydrogen storage alloy and having an alkaline electrolyte, wherein the electrolyte contains naphthalene, iodide, cyanide, selenide, and selenium dioxide having a concentration of 0.00001M or more. , Selenite, selenite, selenite, selenate, tellurium trioxide, telluric acid, tellurite, tellurite, tellurite, sulfide, sulfur dioxide, carbon monoxide, disulfide A metal hydride storage battery containing at least one selected from carbon and thiourea.