JPS5822868B2 - nickel zinc alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nickel-zinc alkaline storage battery having an auxiliary electrode for hydrogen gas absorption.

[Technical background of the invention and its problems]

Conventionally, in nickel-zinc alkaline storage batteries, hydrogen and oxygen gases are generated due to reactions during charging and discharging, overcharging, self-discharge of electrode active materials, etc. This causes an increase in battery internal pressure, expansion of the battery can, and leakage of electrolyte. This caused problems such as leakage, making it difficult to seal the battery.

Two methods have been used to deal with these gas emissions.

One is to consider battery components. In other words, gas generation can be prevented by adjusting the composition of the electrode active material, adding compounds that increase the overvoltage for gas generation, adjusting the electrolyte composition or liquid volume, or appropriately selecting the balance between the anode and anode capacity. This is an attempt to do so.

The other is an attempt to reduce the generated gas back into the electrolyte.

The former method has not yielded sufficiently satisfactory results to date.

In sealed alkaline storage batteries, such as nickel-cadmium batteries, a mechanism is generally used in which the anode capacity is set so that oxygen gas is generated first from the anode during charging, and this oxygen gas is absorbed by the cadmium cathode.

Also, nickel-zinc alkaline batteries can absorb oxygen gas using a similar oxygen gas absorption mechanism, but zinc originally
Unlike cadmium, the solution deposition potential is extremely base, and hydrogen gas generation cannot be avoided even if the zinc electrode is brought into a partial discharge state.

For this reason, various additives with high hydrogen-generating vortex-generating overvoltage have been investigated, but satisfactorily results have not been obtained.

Also, since the deposited zinc is active, it self-dissolves (self-discharges) and generates hydrogen gas.

Hydrogen gas generated by these factors accumulates during charging and discharging, resulting in an increase in battery internal pressure.

Therefore, another method is to chemically combine oxygen gas and hydrogen gas at a ratio of 1:2 using a catalyst and return the generated gas to water without accumulating it in the battery.
Alternatively, since oxygen gas is absorbed by zinc electrodes and tends to be insufficient due to the binding ratio, there is a method to introduce oxygen gas from the air into the battery space and efficiently return hydrogen gas to water using a catalyst, or Alternatively, a method has been used in which hydrogen gas is returned to water using a gas diffusion electrode with an auxiliary electrode that has the function of electrochemically ionizing it, and modified methods that mix the methods described above have also been attempted. ing.

However, attempts to suppress gas generation within the battery in nickel-zinc alkaline storage batteries have not yielded satisfactory results.

Currently, methods are being explored to return the generated gas to water using a catalyst or auxiliary electrode.

However, to date, no efficient and long-life catalyst or auxiliary electrode has been developed.

The problem with the catalyst is that the water produced by the reaction of 2H2+0□→2H20 remains on the catalyst without being removed from the catalyst, and the active sites of the reaction are covered with water, gradually losing its gas absorption ability.

Furthermore, since the reaction between oxygen and hydrogen is accompanied by significant heat generation, if heat dissipation is insufficient, the operating temperature of the catalyst will rise significantly, causing various problems within the battery.

The method of electrochemical ionization using an auxiliary electrode is usually the same as the gas diffusion electrode in an oxygen-hydrogen fuel cell, and consists of gas phase, liquid phase (electrolyte), conductor (ionization catalyst).
In order to efficiently create a three-phase zone in which
Efforts have been made to increase the number of active sites for the reaction by using a porous catalyst phase.

However, when hydrogen gas is absorbed by anode connection using an alkaline electrolyte, H2+20H-+2H20+
Water is produced by the electrochemical reaction of 2e, but since this water is not removed efficiently, the three-phase zone is covered with water molecules, and as a result, the absorption capacity gradually decreases.

Therefore, there are drawbacks such as a short time for gas absorption of the auxiliary electrode, that is, a short absorption life.

[Purpose of the invention]

Among the gases generated in a nickel-zinc alkaline storage battery, the present invention allows oxygen gas to be absorbed by the zinc cathode, while hydrogen gas is efficiently and continuously absorbed by the auxiliary electrode to accelerate the reaction rate on the auxiliary electrode. The object of the present invention is to provide a long-life nickel-zinc alkaline storage battery in which the rate of water removal is greater than the rate of water production.

[Summary of the invention]

The present invention provides an anode having a nickel compound as an active material, a cathode having a larger discharge capacity than the anode and having a zinc compound as a main component, an auxiliary electrode for absorbing hydrogen gas which has been subjected to waterproof treatment, the anode and the anode. A resistor and a switching element are electrically connected between the auxiliary electrode and the resistor has a resistance of 7.5<K<75 with respect to battery capacity C (Ah).
0 (However, K is battery capacity 1(c) x resistance value R of resistor
)), and the operating voltage of the switching element is 0.7■ or more.

That is, the present invention is characterized in that a nickel-zinc storage battery is waterproofed and a specific resistor and switching element are provided between the auxiliary electrode for hydrogen absorption and the anode.

Note that the specific switching element used in the present invention is, for example, one that becomes non-conductive at an applied voltage of 0.7V or less when the operating voltage is 0.7V compared to an applied voltage of 0.7V or more. In practice, a silicon diode, a germanium diode, an oxide voltage nonlinear resistor (commonly known as a varistor), etc. can be used.

By using such a switching element, it becomes possible to effectively suppress an increase in battery internal pressure.

In other words, by using a switching element such as a silicon diode, the voltage difference between the anode and the auxiliary electrode is approximately 0.7 V.
In the case of
).

Therefore, if the voltage difference between the anode and the auxiliary electrode is 0.7 .mu. or more, a hydrogen absorption reaction will occur regardless of charging/discharging or open circuit.

Then, when the hydrogen gas pressure inside the battery decreases due to hydrogen gas absorption, the voltage difference between the anode and the auxiliary electrode becomes 0.7 V or less, and the current flowing to the auxiliary electrode becomes zero.

That is, the effect of inserting the switching element can be explained as follows.

If the connection is made without a switching element, the potential of the auxiliary electrode will remain at a negative potential until it becomes the same as the anode potential at the end of charging, so the auxiliary electrode will reach the oxygen gas generation potential and generate oxygen gas. This significantly reduces the charging efficiency of the nickel anode and causes it to lose its effectiveness as an auxiliary electrode.

Therefore, as mentioned above, when an auxiliary electrode is connected to the anode through a switching element such as a silicon diode and a resistor, the auxiliary electrode is divided into a base voltage of about 0.7 V with respect to the anode, and the oxygen gas from the auxiliary electrode is Occurrence is prevented.

Next, the effect of inserting a specific resistor used in the present invention will be explained as follows.

In other words, the auxiliary electrode and the positive electrode form a battery, so to speak.

The resistor and switching element therefore form the external circuit of this battery.

Therefore, inserting a resistor having a large resistance value has the effect of slowing down the reaction rate of this battery reaction, that is, the rate of water production at the absorption electrode, and suppressing rapid leakage of generated water from the auxiliary electrode.

That is, the present invention focuses on the fact that an increase in battery capacity leads to an increase in the reaction area, that is, an increase in the amount of gas generated, and at this time, it is necessary to improve the gas absorption rate at the auxiliary electrode for hydrogen gas absorption. As will be described later, it has been found that when the product K of the battery capacity and the resistance value is in the range of 7.5 to 750, gas absorption can be carried out efficiently without increasing the internal pressure of the battery.

〔Effect of the invention〕

With the above configuration, among the gases generated in the nickel-zinc alkaline storage battery, oxygen gas is absorbed by the zinc cathode, hydrogen gas is efficiently and continuously absorbed by the auxiliary electrode,
By adjusting the reaction rate on the auxiliary electrode, the water removal rate is greater than the water production rate, and a long-life nickel-zinc battery can be obtained without increasing the battery internal pressure.

[Embodiments of the invention]

The present invention will be explained in detail below using examples.

The nickel-zinc alkaline storage battery according to the present invention has a cathode 1 mainly composed of a zinc compound, as shown in FIG.
and a sintered anode 2 whose main component is a nickel compound.
A separator 3 interposed between these negative and anode 1 and 2
The electrode body 5 is inserted in a spiral shape into a cylindrical container 6 which also serves as a cathode terminal, and an alkaline electrolyte is injected into the container 6. .

The cathode 1 is electrically connected to the container 6 via a cathode lead 7, and the anode 2 is electrically connected to an anode terminal 10 provided in the center of a lid 9 that closes the opening of the container 6 via an anode lead 8. It is connected to the.

In the upper space of the electrode body 5, an auxiliary electrode 11 for absorbing hydrogen gas is placed on an auxiliary electrode electrolyte holder 12, and a resistor 13 and a switching element are disposed between the auxiliary electrode 11 and the anode 12. A silicon diode 20 is electrically connected thereto.

The auxiliary electrode 11 for hydrogen gas absorption is formed of a porous nickel sintered body, impregnated with a mixture of platinum and tungsten carbide, and bound with polytetrafluoroethylene for waterproofing. It is.

Note that the electrode body 5 was constructed in the size of an AA-sized battery with a charging capacity of 1.5 Ah.

The auxiliary electrode 11 for hydrogen gas absorption has an apparent surface area of 5 crA.
, 0.3712J thick, impregnated with a mixture of platinum and tungsten carbide, and bound with polytetrafluoroethylene to make it waterproof.

The resistor 13 is a carbon resistor, and its resistance value can limit the gas pressure within the battery.

The nickel-zinc storage battery constructed in this manner causes changes in the internal pressure of the battery as shown in FIG.

That is, when the hydrogen gas absorption auxiliary electrode 11 is not used (
When the abrasive auxiliary electrode 11 is directly connected to the anode via the silicon diode b (b) and the resistance value is 50 (C),
50, Q(d).

For the cases of 100, Q(e), 500, and Q(f), each battery was charged and discharged at a charging current of 300 mA and a discharging current of 600 mA at intervals of 2 hours. This shows the pressure change inside the battery.

As is clear from FIG. 2, by interposing a resistor and a silicon diode between the auxiliary electrode and the anode, it is possible to more effectively suppress the increase in battery internal pressure.

Also, as shown in Figure 2, the resistance value of the inserted resistor is 5.
Below 0, the rate of water production on the auxiliary pole exceeds the rate of water removal there, and the three-phase zone is gradually covered with water, reducing the absorption capacity.

On the other hand, when the resistance is about 50Ω, the rate of water removal exceeds the rate of water production, the hydrogen absorption ability is maintained, and a good absorption effect is exhibited.

However, when the resistance value is further increased to 500Ω, the water production rate, that is, the hydrogen absorption rate itself decreases, and therefore no significant effect is exhibited in suppressing the pressure rise.

Therefore, the resistance value R effective for gas absorption of the resistor connected in series with the silicon diode is preferably the battery capacity 1.
At 5Ah, 5Ω<R<500Ω, and the battery capacity C(Ah
), it exhibits excellent effects in the range of 7.5<K<750 (K=CR').

When the data of the above embodiment (corresponding to FIG. 2) is expressed in terms of the relationship between the battery internal pressure and the value, it is shown as in FIG. 3.

In other words, it is clear that when the value is 7.5 or less or 750 or more, the internal pressure increases significantly.

Further, it can be appropriately selected depending on the type and amount of the catalyst used in the auxiliary electrode for hydrogen gas absorption, the type and shape of the carrier, the amount of waterproofing agent treated, and the method of treatment.

For example, an absorption rod (0.5-20 crrt) treated with platinum (0.05-5 η/cnY) is coated with polytetrafluoroethylene (0.1-10η/cnY) as a waterproofing agent.
), the resistance value is particularly effective for batteries with a capacity of 1.5 Ah (5 to 500 Ω), that is, 7.5 < K < 750. ~20μ/cd) It is also possible to use an auxiliary electrode.

In addition to the above catalyst, palladium, palladium-silver alloy, sodium tungsten bronze N ax WO3 (o<x
<1) Spinel, e.g. NiFe2O4+CoF
At least one selected from e.g. 204 or a mixture thereof is also effective in absorbing hydrogen gas.

In particular, it is desirable to use catalysts other than platinum-based, or mixtures of platinum-based and other catalysts, from the viewpoint of inexpensive absorption rods.

All of the above-mentioned embodiments dealt with the case where the battery capacity C was 1.5Ah, but for example, the capacity of a D-type battery is 3.5Ah. Since it is OAh, the resistor connected between the anode and the auxiliary electrode may have a resistance value in the range of 2.5Ω to 250Ω.

However, even if the connection relationship between the switching element and the resistor is changed, the effect obtained will not change.

The above-mentioned auxiliary electrode is made of 3, which is active in the electrode reaction of hydrogen gas.
The auxiliary electrode may be placed on the side surface of the battery container or at the bottom of the electrode body, as long as the phase band is efficiently created and the battery capacity is not impaired.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a diagram showing the characteristics of each battery regarding battery internal pressure with respect to charge/discharge cycles, and FIG. 3 is a diagram showing the relationship between the value of the present invention and battery internal pressure. The curve diagram shown. 1... Cathode, 2... Anode, 11... Auxiliary electrode, 13
...Resistor, 20...Silicon diode.

Claims (1)

[Scope of Claims] 1. An anode containing a nickel compound as an active material, a cathode containing a zinc compound as a main component and having a larger discharge capacity than the anode, and an auxiliary electrode for absorbing hydrogen gas subjected to waterproof treatment;
A resistor and a switch electrically connected between the anode and the auxiliary electrode. the resistor has a battery capacity C (Ah
), the relationship is 7.5 (K (750 (however, K is battery capacity C x resistance value R of the resistor), and the operating voltage of the switching element is 0.7 V or more. A nickel-zinc alkaline storage battery characterized by: 2. A nickel-zinc alkaline storage battery according to claim 1, characterized in that a silicon diode is used as a switching element.