JPH0677450B2 - Sealed nickel-hydrogen battery - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed nickel-hydrogen storage battery using a hydrogen storage alloy for a negative electrode, and more particularly to improving gas absorption capacity on the surface of the hydrogen storage alloy negative electrode.

2. Description of the Related Art Conventionally, a nickel-based alloy using this type of hydrogen storage alloy
In order to seal the hydrogen storage battery, it is necessary to react oxygen gas generated from the positive electrode during overcharge with hydrogen stored in the negative electrode and return it to water. The oxygen gas absorption capacity of the hydrogen storage alloy negative electrode is expressed by the equations (1) and (2).

_{1 / 2O 2 + H 2 O} + 2e - → 2OH - ...... (1) MHx + 2OH - → MH x-2 + 2H 2 O + 2e - (2) That is, when a hydrogen storage alloy in the negative electrode, (1) an oxygen ion reaction Is the rate-determining factor, and in order to improve the gas absorption capacity of the nickel-hydrogen storage battery, the reaction of formula (1) needs to proceed rapidly. However, the hydrogen storage alloy negative electrode has a poor oxygen gas ionization ability, and if a sealed battery is constructed, the internal pressure of the battery tends to rise during overcharge. In order to solve this problem, a method of adding a noble metal catalyst such as platinum or palladium to the negative electrode has been proposed (JP-A-51-103424).

Problems to be Solved by the Invention In such a conventional configuration, the noble metal catalyst is very expensive, which is a major obstacle in terms of cost.

Further, when the continuous overcharge is performed without control, there is a problem that the battery internal pressure rises without being constant.

The present invention is to solve such problems, by improving the surface of the hydrogen storage alloy negative electrode, by an inexpensive and simple configuration, to improve the gas absorption capacity of the nickel-hydrogen storage battery,
Moreover, it is an object of the present invention to provide a sealed nickel-hydrogen storage battery in which the internal pressure of the battery does not rise even when continuously overcharged for a long time without control.

Means for Solving the Problems In order to solve the above problems, the present invention configures a sealed nickel-hydrogen storage battery by using a hydrogen storage alloy negative electrode in which a layer made of carbon powder is formed on the surface of a hydrogen storage alloy. It was done.

Action The present invention has the above-described structure to rapidly advance the ionization reaction of oxygen gas generated from the positive electrode during overcharge on the negative electrode surface.

EXAMPLES The present invention will be described below with reference to examples. Hydrogen storage alloy is Mm
A Ni _3.8 Mn _0.4 Al _0.3 Co _0.5 alloy was used. This alloy is a commercially available Mischmetal Mm (mixture of rare earth elements, such as Ce45
wt%, La30wt%, Nd5wt%, other rare earth elements 20wt%) and Ni,
Weigh each sample of Mn, Al, and Co to the specified composition ratio, put it in an arc melting furnace, put it in a vacuum state to 10 ^-4 to 10 ^-5 Torr, then arc discharge in an argon gas atmosphere and heat melting. And MmNi
_A hydrogen storage alloy of _3.8 Mn _0.4 Al _0.3 CoO _0.5 was obtained. Furthermore, in order to improve the homogeneity of this alloy,
Heat treatment was carried out at 1050 ° C. for 6 hours, and then the alloy was roughly pulverized and then powdered to 38 μm or less with a ball mill to obtain an alloy powder used for a negative electrode. These alloy powders were made into a paste with a 5 wt% aqueous solution of polyvinyl alcohol, filled into a foamed nickel porous body and dried. Next, attach this electrode to KO with a specific gravity of 1.30.
It was immersed in an H 2 aqueous solution at 45 ° C. for 12 hours, subjected to alkali treatment, washed with water, dried, and pressurized to give a negative electrode. The surface of the negative electrode is coated with Ketjen Black (made by EC-PX Lion Oil and Fats) or graphite (Nippon Graphite) dispersed in a 1.5 wt% polyvinyl alcohol aqueous solution to obtain various film thicknesses of Ketjen Black or graphite. The carbon powder layer of was formed. Further, in order to form a mixed layer of the fluororesin, a solution obtained by mixing an aqueous dispersion of the fluororesin and Ketjen black was applied to form a mixed layer of the Ketjen black and the fluororesin. The following table shows the hydrogen storage alloy negative electrodes used in the examples.

FIG. 1 is an electrode configuration diagram prepared for testing the characteristics of the negative electrode of the present invention. In FIG. 1, 1 is a negative electrode plate mainly composed of a hydrogen storage alloy, and 2 is a Ketching black layer, a graphite layer or a mixed layer of Ketjen black and a fluororesin, which is formed by coating on the surface thereof.

The negative electrode shown in FIG. 1 and a known nickel positive electrode were wound with a separator interposed therebetween to form an AA size sealed nickel-hydrogen storage battery. The specific gravity of the electrolyte is 1.30 KOH aqueous solution and LiO.
A solution obtained by dissolving H · H ₂ O at 40 g / l was used. Although not shown, the internal pressure of the battery was measured by making a hole having a hole diameter of 1 mm in the bottom of the battery case with a drill, attaching a pressure sensor here and fixing the battery to a fixing device. The charging condition when measuring the battery internal pressure was 1/3 cmA × 4.5H, and the charging condition when measuring the battery internal pressure during continuous overcharging was 1/3 cmA × 48H.

FIG. 2 shows the result of examining the relationship between the charging time and the battery internal pressure of the battery configured by using the negative electrodes A to G shown in the table. Second
As is clear from the figure, the electrode A of the conventional example in which the carbon layer of Ketjen Black is not provided has a charging rate of 1/3 cmA of 4.5.
After a time, a pressure of 10 Kg / cm ² is reached. On the other hand, the internal pressure of the battery constructed by using the electrodes C to F is 6 Kg / cm ² or less, and by providing a carbon layer made of Ketjen black on the negative electrode surface, the oxygen gas absorption capacity of the hydrogen storage alloy negative electrode can be improved. It can be seen that it is significantly improved. That is, the oxygen gas generated from the positive electrode is ionized (1 / 2O ₂ + H ₂ O +) on the surface of the negative electrode.
2e ^- → 2OH ^-) is although, by the carbon layer of the Ketjen black is present on the surface of the negative electrode, it is promoted oxygen ion reaction, the oxygen gas absorption ability is improved.

Further, it can be seen that the electrode G provided with the layer made of Ketjen black and the fluororesin has the same film thickness as the electrode D of Ketjen black alone, but the internal pressure of the battery is lowered. This is because the ionization reaction of oxygen gas is in the gas phase
It is a reaction at the three-phase interface between solid and liquid phases, and by mixing a water-repellent resin such as fluororesin with Ketjen Black, an appropriate three-phase interface is formed and the oxygen ionization reaction is promoted. Become. Therefore, the battery formed using the electrode G has a lower battery internal pressure than that of the electrode D.

Further, the battery using the electrode H having the graphite layer has a higher battery internal pressure than the battery using the electrode D. That is, unlike the Cd electrode and the Zn electrode used in the alkaline secondary battery, the OH ⁻ ion concentration decreases due to the generated H ₂ O, as is clear from the reaction formula. Therefore, there is a need for ionization of oxygen at low alkali concentrations, i.e. improved catalytic activity. Unlike graphite, Ketjen black is a fine carbon fine powder branched into a number of chains in a three-dimensional direction and has good electron conductivity, but has a catalytic action more than that. Therefore, the electrode D
The gas absorption capacity of the battery using is improved.

Although the one using the electrode B is more effective than the conventional example, the internal pressure of the battery is as high as 8 kg / cm ² . Further, when the thickness of the carbon layer is 200 μm or more, the volume of the negative electrode increases and the sealed battery cannot be constructed. Therefore, the film thickness is 2-200μ
A range of m is preferred.

Figure 3 shows the relationship between charging time and battery internal pressure when continuously overcharged at 1/3 cmA for 48 hours. In the case of using the electrode A of the conventional example, the internal pressure of the battery is not constant and becomes 20 kg / cm ² . The sealed nickel-metal hydride storage battery is equipped with a safety valve that operates at 10 kg / cm ² . Therefore, at an internal pressure of 10 Kg / cm ² or more, the safety valve will operate, causing liquid leakage or shortening the cycle life. With the electrode D of the present invention, the battery internal pressure was 5 kg / cm ² even after continuous overcharge for 48 hours.
Therefore, problems such as liquid leakage did not occur even after continuous overcharging.

Effects of the Invention As described above, according to the present invention, by using a hydrogen storage alloy negative electrode in which a thin layer made of carbon powder is formed on the surface of a hydrogen storage alloy, oxygen gas absorption capacity is improved, and continuous overcharge is performed. Even in the case, the present invention provides a sealed nickel-hydrogen storage battery in which the battery internal pressure does not rise. Further, since it uses carbon, which is extremely cheaper than the noble metal catalyst, it has great industrial value.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an electrode structure in the present invention, FIG. 2 is a characteristic view showing a battery internal pressure, and FIG. 3 is a characteristic view showing a battery internal pressure in continuous overcharge. 1 ... Electrode made of hydrogen storage alloy, 2 ... Thin layer made of carbon powder.

Claims (4)

[Claims] 1. A nickel positive electrode and a surface of a hydrogen storage alloy,
A sealed nickel-hydrogen storage battery using a hydrogen storage alloy negative electrode having a carbon powder layer formed thereon. 2. The sealed nickel-hydrogen storage battery according to claim 1, wherein the carbon powder is a fine powder that is branched into a myriad of chains in a three-dimensional direction. 3. A thin layer of carbon powder having a thickness of 2 μm to 20 μm.
The sealed nickel-hydrogen storage battery according to claim 1, which uses a hydrogen storage alloy negative electrode having a thickness of 0 μm. 4. The sealed nickel-hydrogen storage battery according to claim 1, wherein the thin layer of carbon powder is a mixed layer with a fluororesin.