JPH0462763A - Manufacture of metal hydride storage battery - Google Patents

Abstract

PURPOSE:To increase a discharge capacity by promoting activation of a negative electrode by means of low temperature charging. CONSTITUTION:This kind of battery consists of a nickel electrode for a positive electrode and hydrogen absorbing alloy for a negative electrode, but since the surface of the negative electrode is oxidized and extremely inactive immediately after the battery is assembled, any sutticient discharging characteristic cannot be obtained. Accordingly, charging and discharging activation is required. And since the hydrogen absorbing alloy has poor thermal conduction, a hydrogen equilibrium pressure rises with heat generation at the charging time and the charging efficiency falls. Therefore, the charging is carried out at a low temperature, so that the charging efficiency rises and the activation degree of the battery is increased.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a method for manufacturing a metal hydride storage battery having a negative electrode made of a water The present invention relates to an activation method.

(B) Prior Art Storage batteries that have been commonly used include alkaline storage batteries such as Ni-cadmium storage batteries, and lead storage batteries. In recent years, metal hydride storage batteries, which have a negative electrode equipped with a hydrogen storage electrode made of a hydrogen storage alloy, have attracted attention because they are lighter, have a higher capacity, and may have higher energy density than these batteries.

Examples of hydrogen storage alloys used in the negative electrode of this type of battery include JP-A-63-21750 and JP-A-62-24.
As shown in Publication No. 6259, etc., rare earth hydrogen storage alloys are described, and by improving the composition, it is possible to improve the corrosion resistance of the alloy during charging and discharging, and to suppress pulverization.

Furthermore, JP-A-61-39461 and JP-A-1-6
As seen in Publication No. 04371, an activation treatment is proposed in which the hydrogen storage alloy is allowed to absorb and release hydrogen in a gaseous state before the electrolyte is injected. Various studies have been made to activate the battery in the battery state.

After the metal hydride storage battery constructed in this way is assembled through processes such as liquid injection and sealing, it is usually electrochemically activated several times, that is, charged and discharged, and the negative electrode is activated. It has increased activity and has achieved performance that can withstand practical use.

However, even batteries manufactured in this manner have problems in that the discharge capacity during high rate discharge is small and the operating voltage is low. In addition, the overcharging characteristics were not sufficient, and weight loss was observed in some cases as the internal pressure of the battery increased.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above problems, and improves the high rate discharge characteristics and overcharge characteristics of a metal hydride storage battery equipped with a negative electrode made of a hydrogen storage alloy. This paper proposes preferred activation conditions during the production of this type of battery.

(d) Means for Solving the Problems The method for manufacturing a metal hydride storage battery of the present invention involves assembling and sealing a battery comprising a positive electrode, a negative electrode made of a hydrogen storage alloy, and an alkaline electrolyte, and then heating it at a low temperature. It is characterized by being activated by charging.

Further, as the temperature range, it is particularly preferable to perform charging at -20 to 20°C.

Among the above temperature ranges, the effect becomes remarkable in the range of -10 to 10°C.

(e) Effect The present inventor conducted various studies and found that by setting the ambient temperature during charging to a low temperature in the activation treatment step,
It was discovered that the activation of the negative electrode was significantly promoted, and the present invention was completed. That is, as is clear from the direct reaction with hydrogen gas, the hydrogen storage alloy undergoes an exothermic reaction during the hydrogenation reaction. Furthermore, since hydrogen storage alloys have poor thermal conductivity, heat generated during charging accumulates locally, which increases hydrogen equilibrium pressure and reduces charging efficiency. Therefore, by setting the ambient temperature during charging to a low temperature, it becomes possible to cool the battery and remove locally accumulated heat, thereby improving charging efficiency. Furthermore, this increases the depth of charge of the negative electrode, and increases the activity of the negative electrode, that is, the activity of the battery, based on the mechanism described below.

Further, this type of hydride storage battery uses, for example, a nickel electrode for the positive electrode and an electrode made of a hydrogen storage alloy for the negative electrode. The surface of the hydrogen storage alloy constituting the negative electrode immediately after assembly of this type of battery is oxidized during the manufacturing process, making it extremely inert and unable to provide sufficient discharge characteristics. Therefore, activation treatment by electrochemical charging and discharging is usually required. Through this activation treatment, the hydrogen storage alloy is pulverized and a clean, unoxidized metal surface is exposed. Since it is extremely active, the activity of the battery is improved, and the discharge rate characteristics and overcharge characteristics are improved.

When we investigated this mechanism, we found that the activity of the battery, that is, the activity of the negative electrode, depends on the depth of charging and discharging. Furthermore, it has been found that a negative electrode that has been deeply charged and discharged maintains high reactivity. In order to obtain such effects, there are known methods such as treating the hydrogen storage alloy with hydrogen gas during the battery assembly process, or charging and discharging the negative electrode in an alkaline aqueous solution before assembly. Since oxidation by oxygen gas in the atmosphere occurs in the post-process after this treatment, it is extremely difficult to maintain high activity.

Therefore, by charging the assembled battery at a low temperature, the depth of charge and discharge of the negative electrode can be increased. That is, when charging at a low temperature, the positive electrode becomes a higher-order oxide than when charging at room temperature, so the generation of oxygen gas is delayed. For example, in a nickel-cadmium battery, the activity of the negative electrode is high immediately after assembly, and even when charged at a low temperature as in the present invention, the activity of the negative electrode does not increase. However, as mentioned above, since the metal hydride storage battery is completely inactive immediately after assembly, the activation effect of the present invention can be obtained.

Furthermore, since the degree of activation is determined by the depth of charge of the negative electrode, the depth of charge of the negative electrode must be deepened at least once. That is, the charging depth of the negative electrode is determined by the consumption of oxygen gas generated from the positive electrode. If this oxygen gas generation is delayed, the depth of charge of the negative electrode becomes deeper by that time, and the clean and highly active metal surface due to the pulverization of the hydrogen storage alloy is exposed, increasing the reactivity of the negative electrode. Furthermore, since the present invention involves a reaction within a battery system, it is possible to maintain high activity permanently.

(f) Example Below, the comparison between the present invention and a comparative example will be mentioned and explained in detail.

As the hydrogen storage alloy constituting the negative electrode, 95 parts by weight of pulverized LaN1tCos, which is a rare earth hydrogen storage alloy, and 5 parts by weight of polytetrafluoroethylene (PTFE) dispersion as a binder. Add and mix uniformly to fiberize the PTFE. Water is added to this paste to form a paste, which is pasted on both sides of a nickel-plated punched metal current collector to obtain a negative electrode, which is a hydrogen storage alloy electrode.

As the positive electrode, a known sintered nickel electrode used for Niacel-Cadmium [7411, etc.] was used.

These positive and negative electrodes are wound together with an alkali-resistant separator to obtain a spiral 1. After inserting this electrode body into a battery can, an alkaline electrolyte is injected and the cap is sealed to give a nominal capacity of 1200 mAH. Assembled the battery.

The battery thus obtained was charged at 180 m and A for 16 hours, and the battery voltage reached 1.5 mA at 240 mA. Charge and discharge were repeated five times under the condition that the battery was discharged until it reached OV. Here, the ambient temperature during charging was variously varied from -40°C to 60°C, and discharging was performed at 25°C.

Using batteries activated under these conditions, each
The batteries were discharged at 400 mA and the discharge capacity and operating voltage were compared. The results are shown in Table 1 and FIG.

As is clear from Table 1 and Figure 1, the batteries A-G of the present invention, which were charged at low temperatures, have a higher discharge capacity and operating voltage than the comparative battery H-. Excellent rate discharge characteristics,
It can be seen that the activation of the negative electrode is progressing.

Further, it is understood that among the batteries A to G of the present invention, particularly batteries C to G, that is, batteries in which the ambient temperature during charging is -20°C to 20°C, exhibit excellent high rate discharge characteristics.

Furthermore, the internal pressure of the batteries A-K, that is, the overcharge characteristics when the batteries A-K were overcharged at 600 mA for 3 days was investigated.

The results are shown in FIG. As is clear from Figure 3,
Batteries A-G of the present invention, which were charged at low temperatures, were compared to comparative batteries H-
It can be seen that the internal pressure of the battery during overcharging is lower and the overcharging characteristics are excellent, the activity of the negative electrode is higher, and the consumption efficiency of oxygen gas is higher. In addition, batteries A-G of the present invention
Among these, especially batteries C-G, that is, the ambient temperature during charging is -2
It can be seen that the battery at 0°C to 20°C exhibits excellent overcharge characteristics.

From the results shown in FIGS. 1 to 3, it can be seen that the battery of the present invention in which the ambient temperature during charging was set at -10 to 10 DEG C. had extremely excellent discharge characteristics and overcharge characteristics.

(G) Effects of the Invention As detailed above, according to the method for manufacturing a metal hydride storage battery of the present invention, after the battery is assembled and sealed, it is charged and activated at a low temperature. The rate discharge characteristics and overcharge characteristics can be improved, and its industrial value is extremely large.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between charging temperature and battery discharge capacity.
Figure 2 is a diagram showing the relationship between charging temperature and battery operating voltage;
FIG. 3 is a diagram showing the relationship between charging temperature and battery internal pressure. A, B, C, D, E, F, G...Battery of the present invention, H, L
J, K... Comparison batteries.

Claims (1)

[Claims] (1) A method for producing a metal hydride storage battery, which comprises assembling and sealing a battery consisting of a positive electrode, a negative electrode made of a hydrogen storage alloy, and an alkaline electrolyte, and then charging and activating it at a low temperature. (2) The method for manufacturing a metal hydride storage battery according to claim (1), wherein the temperature range is -20°C to 20°C.