JPH0815077B2 - Sealed alkaline storage battery - Google Patents

Description

TECHNICAL FIELD The present invention uses an electrode made of an alloy or hydride that reversibly stores and releases hydrogen, that is, a hydrogen storage electrode as a negative electrode,
The present invention relates to a sealed alkaline storage battery having a metal oxide electrode as a positive electrode, and particularly to an improvement of a negative electrode.

2. Description of the Related Art Conventionally, in an alkaline storage battery using this type of hydrogen storage electrode as a negative electrode, the hydrogen storage alloy or hydride that constitutes the negative electrode is subdivided by repeated charge / discharge cycles, and cracks due to expansion are generated, resulting in electrode support The battery performance will be degraded due to reasons such as falling off. This phenomenon is particularly noticeable in open-type alkaline storage batteries. Therefore, an attempt has been proposed to solve the above problems by coating the surface of the hydrogen storage alloy particles with copper (Japanese Patent Laid-Open No. 50-11).
1546). That is, a negative electrode is proposed in which the surface of a hydrogen storage alloy or hydrogenated particles is coated with copper / nickel by electroless plating to provide a coating film to improve the mechanical strength and electrical conductivity of the electrode itself. ing. And the alkaline storage battery which combined this negative electrode and the metal oxide positive electrode through the separator is also considered.

Problems to be Solved by the Invention With such a conventional configuration, the mechanical strength and conductivity of the electrode itself are improved, and the battery performance is improved. On the other hand, since the metal coating the surface of the hydrogen storage alloy particles is inert to hydrogen, it is irrelevant to the energy storage capacity regulated by the hydrogen storage amount. Therefore, if the coated metal portion is large, the capacity per unit weight is reduced by that amount. Particularly in a sealed alkaline storage battery, the volume occupied by the positive electrode and the negative electrode in a given volume is fixed, so an increase in the volume occupied by the negative electrode leads to a decrease in the volume occupied by the positive electrode, and the battery capacity is regulated by the positive electrode capacity. Therefore, the discharge capacity is reduced. Therefore, it has been proposed to form a hydrogen storage alloy or hydride powder layer coated with the metal only on the surface of the negative electrode. In this configuration, the oxygen gas generated in the positive electrode needs to be converted into water by the reduction reaction on the surface of the negative electrode, but the reaction consumed by the generation of oxygen gas is delayed, and the oxygen gas accumulates in the battery to increase the internal pressure of the battery. In particular, this phenomenon remarkably appears at the time of rapid charging, and there is a problem that safety is deteriorated.

Therefore, the present invention solves such a problem, by promoting the oxidation prevention of the hydrogen storage alloy by oxygen gas and oxygen absorption or oxygen ionization on the negative electrode surface in a well-balanced manner even when the charging current is relatively large. The purpose is to suppress the rise in internal pressure of the battery and extend the life of charge / discharge cycles.

Means for Solving the Problems 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, and a copper on the surface of the negative electrode. , A hydrogen storage alloy partially covered with nickel or an alloy thereof in a porous manner, or a porous oxidation suppressing layer composed of hydride powder and carbon powder. More preferably, in the hydrogen storage alloy or hydride powder and carbon powder coated with the above-mentioned metal, a catalyst is supported on the particle surface of both or one of them.

The hydrogen storage alloy powder or hydride powder obtained by porously coating the surface of the hydrogen storage alloy or hydride particles with a conductive metal such as copper, nickel, or an alloy thereof is used as a binder such as a fluororesin. Together with carbon powder,
This porous mixture is formed only on the surface of the electrode substrate made of a hydrogen storage alloy or a hydride. With this configuration, the oxygen catalytic action and the oxidation inhibiting action on the surface of the negative electrode are given, and the discharge capacity per unit volume and weight is improved. It also has excellent high-rate charging characteristics. This is because the hydrogen storage alloy coated with the metal formed on the surface of the negative electrode also contributes to the discharge capacity. In addition, since the surface layer made of a mixture of hydrogen-occlusion alloy and carbon powder coated with metal is porous and has a large surface area, it promotes an oxygen catalyst and an oxidation suppressing action to suppress an increase in battery internal pressure and improve durability. be able to.

 The details will be described in the following examples.

Example A sample composed of commercially available Mm (Misch metal), La, Ni, and Co was weighed and mixed at a constant composition ratio, and heated and melted by an arc melting method. As an example, the alloy composition Mm
_0.5 La _0.5 Ni _3.5 Co _1.5 was used as the hydrogen storage alloy for the negative electrode. This alloy was crushed to 37 μm or less with a crusher, filled in a foam metal together with a binder, and then pressurized and dried to obtain a negative electrode sample a.
And Next, a sample of the same alloy powder was taken, and a copper coating film was formed porous on the surface of this sample by a known electroless plating method. The electroless plating conditions adopted at that time are as follows.

After electroless plating, it seems that a uniform copper coating film is formed on the surface of the hydrogen storage alloy particles, but many holes are present. Storage and release of hydrogen progress through this hole. 5% by weight of carbon powder, for example, carborafine, which is plant activated carbon, was mixed with the fluororesin dispersion medium with respect to the copper-coated hydrogen storage alloy powder. This paste-like mixture was applied to the surface of the negative electrode sample a manufactured previously, and then pressed and dried to form an integrated negative electrode sample b. Leads were attached to the negative electrode samples a and b to serve as electrodes. 15 g of the hydrogen storage alloy powder and 1.5 g of the mixture formed on the electrode surface were used. A well-known foamed nickel positive electrode is used to form a sealed alkaline storage battery having a nominal capacity of 2 Ah via a separator.
・ Set to B.

Next, a negative electrode sample was prepared in which about 0.1% by weight of the palladium catalyst was supported on the above-prepared copper-coated hydrogen storage alloy powder and carbon powder by a known supporting method. A similar battery using a negative electrode sample c in which a catalyst was supported only on a copper-coated hydrogen storage alloy powder, a negative electrode sample d in which a catalyst was supported only on carbon powder, and a negative electrode sample e in which a catalyst was supported on both of them was respectively C, D, Let E. FIG. 1 shows the structure of the negative electrode, and FIG. 2 shows a sealed alkaline storage battery. FIG. 1 shows a negative electrode plate 3 in which an oxidation suppressing layer 2 is formed on both surfaces of a substrate made of a hydrogen storage alloy 1. B represents a cross section of the negative electrode 3.

In FIG. 2, a negative electrode 3 made of a hydrogen storage alloy and a nickel positive electrode 4 are spirally wound via a separator 5 and inserted in a case 6 which also serves as a negative electrode terminal. Insulating plates 7 and 8 are applied on the upper and lower sides of the electrode plate group, and the opening of the case 6 is sealed by a sealing plate 10 having a safety valve 9. Reference numeral 11 denotes a cap-shaped positive electrode terminal which is connected to the positive electrode lead 12 via the sealing plate 10. 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 the positive electrode law was adopted. The battery was charged and discharged at 0.3C (600mA) for 5 hours (150% charge) and discharged at 0.1C (200mA). The temperature of the charge / discharge cycle test was set to 25 ° C, and the internal pressure of each battery was measured at 150% charge. The measurement of the cell internal pressure was compared with the initial value after 100 cycles. The measurement results are shown in Table 2 in comparison with the conventional battery A and the inventive batteries B, C, D and E. However, the safety valve is activated when the internal pressure reaches 10 kg / cm ² or more.

As can be seen from Table 2, the internal quality of Battery A is 5.0k in the initial stage.
It showed g / cm ² and reached to 10 kg / cm ² or more after 100 cycles, and the leakage phenomenon due to the safety valve operation was observed. Therefore, the decrease in discharge capacity due to the increase in internal resistance caused by the decrease in the electrolytic solution is remarkable. The discharge capacity after 50 cycles
It shows less than 1Ah and has decreased to less than 50% of the initial capacity.
On the other hand, the internal pressures of the batteries B, C, D, and E of the present invention initially show 1.5-3.0 kg / cm ² , and even after 100 cycles.
It rises only about 2.0-4.0kg / cm ² . Among these, the battery using the negative electrode carrying the catalyst has a small increase in the battery internal pressure. Therefore, the discharge capacity after 100 cycles is 2 Ah.
Holds all, and almost no decrease in capacity is observed. From this result, the battery of the present invention is compared with the conventional battery.
The internal pressure of the battery at 150% charge is very low, and the discharge capacity is hardly reduced. Therefore, a battery with high safety and long life can be obtained. In such high rate charging, the reason why the increase in battery internal pressure and the increase in capacity were obtained is because the oxygen catalyst works efficiently on the surface of the negative electrode plate to absorb the oxygen gas generated from the positive electrode. Oxidation of the surface of the hydrogen storage alloy due to gas is suppressed, and the hydrogen storage alloy coated with metal also contributes to the discharge capacity. Further, since it is in the state of a mixture with carbon powder, it is considered that the surface area of the oxidation suppressing layer is large and the oxygen catalyst is also very active, which accelerates the oxygen absorption rate.

By using a fluororesin when forming the oxygen-suppressing layer as in the present embodiment, both powders can be combined without reducing the activity of the oxygen catalyst. The hydrogen-occlusion alloy powder coated with metal, the carbon powder, and the fluororesin powder are independent of each other, and the fluororesin intervenes between the bonds of the two to strengthen the bond of both particles. Moreover, a great effect can be seen where the surface area is not reduced.

In this embodiment, a powder obtained by mechanically crushing a hydrogen storage alloy was used, but a hydride obtained by hydrogenating the hydrogen storage alloy and subdividing the hydrogen storage alloy may also be used. A negative electrode was prepared in the state of dehydrogenating the hydrogenated powder, and the same test method was used except that nickel was used as the metal coating film instead of copper, but almost the same performance as the negative electrode starting from the hydrogen storage alloy was obtained. Indicated. However, nickel has a harder coating film than copper, so it is necessary to increase the applied pressure a little.Because it is a slightly less porous material than copper, oxygen gas absorption is a little poor, and the battery internal pressure is relatively low.
It increased by about 0.5 kg / cm ² . Although this point was slightly different depending on the coated metal, other properties were almost the same. The same effect can be obtained by using an alloy.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a high-capacity sealed alkaline storage battery having high safety at high rate charging, long cycle life, and high capacity.

[Brief description of drawings]

1A and 1B are a side view and a cross-sectional view showing the structure of a negative electrode plate in the present invention, and FIG. 2 is a view showing the configuration of a sealed alkaline storage battery used in an embodiment of the present invention. 1 ... Anode plate, 2 ... Hydrogen storage alloy, hydride, 3 ...
Oxidation suppression layer.

Claims (2)

[Claims] 1. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or a hydride, a separator and an alkaline electrolyte, and the surface of the negative electrode is partially covered with copper, nickel or an alloy thereof in a porous form. A sealed alkaline storage battery, characterized in that it is provided with a porous oxidation suppressing layer made of a mixture of hydrogen storage alloy or hydride powder and carbon powder. 2. A hydrogen storage alloy coated with copper, nickel or an alloy thereof, or a mixture of hydride powder and carbon powder, wherein a catalyst is supported on the particle surface of both or one of them. The sealed alkaline storage battery according to the item.