JPS6355858A - Enclosed type alkaline storage battery - Google Patents

Abstract

PURPOSE:To reduce the oxygen gas generated by a positive electrode at the surface of a negative electrode, and to restrict the rise of the inner pressure of the battery, by furnishing an oxygen catalyst layer which consists of a conductive whisker over the surface of the negative electrode contacting to the positive electrode side. CONSTITUTION:A metallic oxide positive electrode 5, a negative electrode 4 which consists of a hydrogen absorption alloy 2 or a hydrate, a separator 6, and an alkaline electrolyte are furnished, and over the surface of the negative electrode 4 contacting to the positive electrode 5 side, is furnished an oxygen catalyst layer 3 which consists of a conductive whisker. The conductive whisker consists of a potassium titanate, over which a small amount of catalyst is included to give the catalystic function to the negative electrode 4. By exercising the control of the oxidation by the oxygen gas of the hydrogen absorption alloy 2, and the oxygen absorption or oxygen reducing reaction over the surface of the negative electrode 4 efficiently, the rise of the battery inner pressure is restricted, the charge and discharge cycle is extended, and the cost of the battery can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sealed alkaline storage battery that uses a hydrogen storage alloy or hydride as a negative electrode and a metal oxide as a positive electrode, and particularly relates to improvements in the negative electrode.

Conventional technology Conventionally, in sealed metal oxide-hydrogen storage batteries that use this type of hydrogen storage alloy or hydride as the negative electrode, oxygen gas generated at the positive electrode reacts with hydrogen stored in the negative electrode to turn it into water. A method of maintaining a sealed state has been devised. In this case, the oxygen gas needs to undergo a reduction reaction or ionization reaction on the surface of the negative electrode to turn it into water, but the surface of the hydrogen storage alloy particles is oxidized by the oxygen gas generated at the positive electrode, and the oxygen gas is efficiently converted into water. The rate of return will be slower.

Therefore, if the reaction that consumes oxygen gas lags behind the reaction that generates oxygen gas, oxygen gas will accumulate in the battery and the internal pressure of the battery will increase. This phenomenon becomes noticeable during rapid charging.

Problems to be Solved by the Invention In such a conventional configuration, when a sealed metal oxide-hydrogen storage battery enters an overcharge region, oxygen gas is generated from the positive electrode. Oxidation of the surface of the hydrogen storage alloy by this oxygen gas cannot be completely suppressed.

Therefore, the rate at which oxygen gas is generated from the positive electrode is greater than the rate at which it is absorbed on the surface of the negative electrode, and there is a problem in that excessive oxygen gas is accumulated within the battery, leading to an increase in the internal pressure of the battery and deterioration of its integrity.

The present invention solves these problems by suppressing the oxidation of the hydrogen storage alloy constituting the negative electrode by oxygen gas and efficiently performing oxygen absorption or oxygen reduction reaction on the negative electrode surface, thereby reducing the internal pressure of the battery. The purpose is to suppress the increase in battery life, extend charge/discharge cycles, and reduce battery costs.

Means for solving the problem In order to solve this problem, the present invention comprises a metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or a hydride, a separator and an alkaline electrolyte, which are in contact with the positive electrode side. An oxygen catalyst layer made of conductive whiskers is provided on the surface of the negative electrode, and the conductive whiskers are made of potassium titanate (K2O-
Furthermore, a small amount of catalyst is supported on the surface, and the negative electrode has a melting medium function and an oxidation suppressing function.

Function: With this structure, the oxygen gas generated from the positive electrode during overcharging does not come into direct contact with the hydrogen storage alloy that stores hydrogen, and the oxygen gas that reaches the surface of the negative electrode is transferred to the conductive whiskers or catalyst-supported conductive whiskers. is ionized by a reduction reaction in an oxygen catalyst layer consisting of Furthermore, since the previous reaction occurs preferentially before the oxygen gas reaches near the particles of the hydrogen storage alloy, the oxidation reaction of the hydrogen storage alloy is directly suppressed. Therefore, during overcharging, the oxygen gas generated from the positive electrode can be reduced and consumed on the negative electrode surface, which suppresses the rise in battery internal pressure, prevents oxidation of the hydrogen storage alloy, and extends the battery cycle life. That will happen.

The details will be explained below using examples.

Example Commercially available Mm (Mitshu Metal) 1. La, Ni, G.

Samples consisting of were weighed and mixed to a constant composition ratio, and heated and melted using an arc melting method. - For example, the alloy composition is Mmo, 5Lao, 5Ni5, 5C0
15 and used as a hydrogen storage alloy for negative electrode. This hydrogen storage alloy is made into a fine powder of 387 zm or less using a ball mill, etc., and thoroughly kneaded with an appropriate amount of polyvinyl alcohol resin aqueous solution.This paste-like alloy is cut into a certain size and filled into a foamed nickel porous body. Corrosion-resistant conductive whiskers are applied to both sides in a paste state along with a binder such as a fluororesin dispersion, and then pressurized and dried to form an oxygen catalyst layer, and the lead plate is attached to the negative electrode. did. Further, if necessary, the alloy can be used as a hydride. In this example, fibrous potassium titanate (K2O・n
Ti02) was used.

The average length of the fibers is 10 to 20 μm, and the average diameter is 0.2 to ○, 571 m. The structure and cross section of this negative electrode are shown in FIG. In FIG. 1A, a hydrogen storage alloy 2 is built into the pores of a foamed nickel porous body 1 which also serves as a current collector, and an oxygen catalyst layer 3 is formed on both surfaces thereof to constitute a negative electrode 4. B represents the cross section of the negative electrode 4.

Figure 2 shows the structure of the AA-sized sealed alkaline storage battery used in the test, in which the negative electrode was constructed using hydrogen storage alloy powder 15p, and the foamed nickel positive electrode manufactured by a known method was combined with a separator interposed therebetween. Shown below. In FIG. 2, a negative electrode plate 4 made of a hydrogen storage alloy and a nickel oxide positive electrode 6 are spirally wound with a separator 6 in between, and inserted into a case γ which also serves as a negative electrode terminal. Note that the insulating plates 8 and 9 are torn off above and below the electrode group, and the sealing plate 11 with the safety valve 10 is
The opening of case 7 is sealed. Reference numeral 12 denotes a cap-shaped positive terminal connected to the positive electrode gate 13 via the sealing plate 11. In addition, in order to suppress hydrogen generation from the negative electrode during charging, the negative electrode capacity was made larger than the positive electrode capacity, and a positive electrode rule was adopted. 0.0 as battery charging/discharging conditions.
Charging for 5 hours at 2G (current 400m) (150m)
% charge) and discharged at 0.2 G (current 400 m). The test temperature was 20°C in all cases, and the internal pressure of the battery was measured when the battery was overcharged to 150%. In particular, the behavior of the battery internal pressure after 10 cycles was compared. Here, as a conventional battery, a battery is constructed using a negative electrode without an oxygen catalyst layer. On the other hand, as a battery of the present invention, a battery B is one in which fine fibrous potassium titanate is formed as an oxygen catalyst and a conductive whisker on the surface of a hydrogen storage alloy negative electrode. Furthermore, a battery C was obtained in which an oxidation catalyst layer in which about 0.1 wt % of palladium catalyst was supported on the surface of conductive whiskers was formed on the surface of the hydrogen storage alloy negative electrode. Further, FIG. 3 shows the internal pressure of the conventional battery and the batteries B and C of the present invention during charging. As can be seen from Figure 3, the internal pressure of conventional batteries begins to rise before the charging rate reaches 100%.
Moreover, when the charging rate reaches 150ch, the battery internal pressure becomes ekq/ci.
reach up to. From a practical safety point of view, the internal pressure of the battery is 5.
kq/c! Since it is said that the following is preferable, this value poses a problem from a safety perspective. The reason for this phenomenon is that hydrogen gas is generated from the negative electrode before the charging rate reaches 100%, and oxygen gas generated from the positive electrode during charging cannot be completely absorbed by the negative electrode. Gas is gradually accumulating inside the battery and the internal pressure of the battery is rising.

That is, it is considered that the hydrogen storage function and oxygen catalyst function are insufficient on the surface of the negative electrode.

On the other hand, the increase in the internal pressure of batteries B and C of the present invention occurs from around 100% charging rate, and even when the charging rate reaches 150%, the internal pressure of battery B is 2.6 kg/(14, and battery C is 2.6 kg/(14). 1.5kg1~.This means that almost no hydrogen gas is generated from the negative electrode until the charging rate approaches 100%, and even during overcharging, the oxygen gas generated from the positive electrode is almost completely absorbed by the catalytic action of the negative electrode surface. Because hydrogen and oxygen gas are absorbed into the battery, there is little accumulation of hydrogen and oxygen gas within the battery, and the rise in battery internal pressure is kept low.

These conductive whiskers, which act as oxygen catalysts, have a fiber length of 210 to 20 μm and a diameter of 20.2 to 0.5 μm, and are very fine fibers, so they have a large surface area and have a large surface area. A value smaller than the resistance (1Ω・α) (0
, 1~o, 5Ω・(7)), the resistance on the surface of the negative electrode is small, it is active against oxygen gas, and has the effect of converting oxygen gas at a high rate. It is thought that there are. This can be understood from the fact that the effect is further enhanced when a catalyst is supported on the surface of the conductive whiskers.

On the other hand, when a cycle life test was conducted on these batteries, the conventional battery capacity decreased by more than 30 times the initial capacity after 100 charge/discharge cycles.

In this battery, the internal pressure of the battery rose too much, causing the safety valve to operate, and a phenomenon of liquid leakage from the safety valve was observed.The decrease in capacity mainly occurred due to an increase in internal resistance due to a decrease in electrolyte, but due to oxygen gas. It is also possible that the negative electrode capacity decreases due to oxidation of the hydrogen storage alloy. When we disassembled the battery that had been cycled 100 times and examined the negative electrode capacity, it was approximately 3% compared to the initial capacity.
It has been confirmed that there is a capacity drop of about 0%.

On the other hand, batteries B and C of the present invention have a charge/discharge cycle of 10
Even in the 0th cycle, the capacity remained almost unchanged from the initial capacity. No leakage phenomenon from the safety valve was observed. 100 just in case
After the battery had been cycled twice, the battery was disassembled and the capacity of the negative electrode was examined, but it was found that the capacity had decreased by only a few inches compared to the initial capacity. From this, it can be seen that the battery of the present invention has a function of suppressing oxidation due to oxygen gas in addition to the action of an oxygen catalyst, and is effective in extending the life of the negative electrode.

The conductive whiskers used here are characterized by being an oxide with conductivity, such as potassium titanate (K2O・nTio, ), which is an extremely stable material both chemically and physically. It is. In this way, conductive whiskers are stable against oxygen gas, and after adsorbing and retaining oxygen gas on the surface of the conductive whisker before it comes into direct contact with the hydrogen storage alloy, the conductive whisker is then reduced to the surface of the hydrogen storage alloy. It is thought to prevent oxidation.

Since conductive whiskers are in the form of fine fibers, when fibrous fluororesin is used as a binder, the individual fibers are intertwined and maintain mechanical strength, as well as maintain tightness with hydrogen-absorbing alloy particles. It can also improve the strength of the electrode plate itself. It is difficult to homogeneously manufacture fl fibers having a length of less than 5 μm, resulting in high costs. Therefore, the thickness is preferably 5 μm or more because it can be manufactured at low cost. Further, if the thickness is 40 μm or more, there is a possibility of a slight short circuit through the separator, so a range of 5 to 40 μm is optimal. On the other hand, a diameter of 0.1 μm or less is still difficult in terms of manufacturing process and is not practical due to high costs to ensure quality. A thickness of 0.1 μm or more is practical because it can be manufactured at low cost. However, when the thickness is 1 μm or more, the surface area becomes small, so that the oxygen catalytic effect decreases. Therefore, in consideration of oxygen catalytic action and cost reduction, a range of 0.1 to 1 μm is optimal.

Although a palladium catalyst was used on the surface of the conductive whiskers here, other noble metal catalysts or metal oxide catalysts may be used. Further, although potassium titanate is used as an example of the oxygen catalyst layer, conductive whiskers having other compositions may be used, and they may be mixed with other inorganic or metal powders.

Effects of the Invention As described above, according to the present invention, a sealed alkaline storage battery with low pressure increase inside the battery during overcharging, excellent safety, long charge/discharge cycle life, low cost, and stable quality can be obtained. You can get the effect of being able to

[Brief explanation of drawings]

Figures 1A and B are side views and cross-sectional views showing the structure of the negative electrode according to the present invention, Figure 2 is a cross-sectional view showing the structure of a sealed alkaline storage battery used in an example of the present invention, and Figure 3 is a cross-sectional view showing the structure of the negative electrode according to the present invention. FIG. 2 is a diagram showing changes in battery internal pressure with respect to charging rates of sealed alkaline storage batteries using negative electrodes and conventional negative electrodes. 1... Foamed nickel porous body, 2...
Hydrogen storage alloy, 3...Oxygen catalyst layer, 4...
...Negative electrode plate. Name of agent: Patent attorney Toshio Nakao and one other person
Foamed nickel now jL body 2-0-hydrogen chew,? y: Kaikin/Mokubeika first 3-acid rice
Mr. b 1 4-Negative food Bad Figure 1 A B Figure 2 Positive jt Dimensions

Claims (3)

[Claims] (1) comprising a metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or hydride, a separator and an alkaline electrolyte,
A sealed alkaline storage battery characterized in that an oxygen catalyst layer made of conductive whiskers is provided on the surface of the negative electrode in contact with the positive electrode side. (2) The conductive whiskers forming the oxygen catalyst layer are made of potassium titanate (K_2O・nTiO_2), and their average length and diameter are 6 to 40 μm and 0.1 to 1 μm, respectively.
A sealed alkaline storage battery according to claim 1. (3) The sealed alkaline storage battery according to claim 1, wherein a catalyst is supported on the surface of the conductive whiskers forming the oxygen catalyst layer.