JPH11204112A - Nickel hydrogen battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To gradually gel an aluminum oxide in an electrolyte, for restraining reduction of a positive electrode, and prevent the lowering of a discharge capacity by using a hydrogen storage alloy for a negative electrode, a nickel oxide for a positive electrode, and an alkali aqueous solution for an electrolyte, and adding an aluminum oxide to the negative electrode. SOLUTION: As an active substance of a negative electrode, a hydrogen storage alloy capable of absorbing and discharging hydrogen is employed, a nickel oxide is employed as a positive electrode, and a nickel hydrogen battery is provided with an alkali aqueous solution which is an electrolyte. An aluminum oxide is added to this negative electrode as a gel generation component makes contact with the electrolyte and is gradually gelled. This alumina gel adsorbs part of hydrogen and a segregation component discharged from a positive electrode during battery discharge, without inhibiting a conductive cobalt compound formation a nickel hydroxide that is a regular battery reaction. Thereby, Ni(OH)2 of a positive electrode component is reduced, self-discharge is prevented, a battery life is extended without lowering a discharge capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for reversibly storing and storing hydrogen.
The present invention relates to a nickel-hydrogen alkaline storage battery in which a hydrogen storage alloy or a hydrogen storage alloy made of a hydride to be released is used as a negative electrode and a nickel electrode made of nickel hydroxide is used as a positive electrode.

[0002]

2. Description of the Related Art Conventionally, a sealed nickel-metal hydride battery using a hydrogen storage alloy capable of storing and releasing a large amount of electrochemically hydrogen for a negative electrode, a nickel oxide for a positive electrode, and an alkaline aqueous solution as an electrolyte. Is known as a light-weight and high-capacity storage battery. The negative electrode of this nickel-metal hydride battery is mainly composed of a hydrogen storage alloy capable of storing and releasing hydrogen as an active material. In the manufacture of this hydrogen storage alloy electrode, first,
A mixture of a hydrogen storage alloy powder, a thickener such as polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), and a nickel powder as a binder used to prevent the hydrogen storage alloy powder from falling off the electrode. Get what you do. The mixture is slurried, applied to a porous conductive plate, dried, roll-formed, and then heat-treated in a vacuum or inert gas.

[0003] The nickel-metal hydride battery has a problem in terms of life. This is because the hydrogen occluded in the hydrogen storage alloy electrode at the time of discharge is electrochemically released into the alkaline electrolyte, and part of the hydrogen becomes free dissolved hydrogen and diffuses in the alkaline electrolyte to the nickel electrode. Then, an operation of reducing the active material Ni (OH) ₂ is performed. In other words, a phenomenon occurs in which the nickel electrode, which is the positive electrode, causes self-discharge and lowers the potential, and if the battery is left in a discharged state, the battery voltage further decreases even after the battery capacity becomes zero, and finally, Is the positive electrode active material N
It will reach the reduction potential of i (OH) ₂ . In such a state, the battery capacity cannot be restored to the rated capacity even if a new charge is performed, and the life of the battery is shortened.

Japanese Patent Application Laid-Open No. Hei 9-171837 discloses a technique of adding an aluminum compound to a battery as a technique capable of suppressing a decrease in open voltage at the time of discharging. This technology uses nickel electrodes in batteries,
An aluminum compound which gels upon contact with the alkaline electrolyte is added to any of the hydrogen storage alloy electrode, the separator, and the alkaline electrolyte. The aluminum compound contacts the electrolytic solution to form an alumina gel, and acts to adsorb a part of hydrogen and a component eluted from the alloy.

[0005]

However, in the above technique, the gelation of aluminum starts immediately after the electrolyte is injected, and the formation of a conductive cobalt compound on nickel hydroxide, which is a normal battery reaction, is hindered. Has a new problem that the polarization of the metal becomes large and the discharge capacity decreases.

[0006]

In order to solve the above-mentioned problems, the present invention employs aluminum oxide as an aluminum compound which gels upon contact with an alkaline electrolyte, and uses the same as hydrogen constituting a negative electrode of a nickel-metal hydride battery. It is added to the storage alloy electrode.

[0007]

According to the present invention, by adopting such a configuration,
In order to solve the above-mentioned problem, the electrochemical operation of this nickel-metal hydride battery can be explained as follows. First, since the battery of the present invention is also basically a nickel-metal hydride battery, in the negative electrode which is a hydrogen storage alloy electrode,
A reaction as shown in Chemical formula 1 is performed. Here, M indicates a hydrogen storage alloy, and MH indicates a hydrogen storage alloy in a state where hydrogen is stored.

[0008]

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On the other hand, the nickel electrode serving as the other positive electrode performs a well-known reaction operation as shown in Chemical formula 2.

[0010]

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However, since aluminum oxide is added to the negative electrode of the present invention, this aluminum oxide exists as a gel in the presence of an alkaline electrolyte. Because this gel has excellent adsorption capacity,
Part of the hydrogen released from the hydrogen storage alloy electrode during discharging of the battery and components that are eluted from the electrode and are segregated without being alloyed are adsorbed by the gelled aluminum oxide. By acting in this way, it is possible to prevent the nickel electrode from being reduced by dissolved hydrogen and prevent segregated components from being deposited on the nickel electrode, and to reduce the open voltage during discharge, that is, various factors that cause the decrease in the potential of the nickel electrode. Can be removed. In this respect, the present invention has basically the same function as that of the above-mentioned Japanese Patent Application Laid-Open No. 9-171837. However, the present invention employs aluminum oxide in particular as an aluminum compound, which constitutes a negative electrode of a nickel-metal hydride battery. Is characterized in that it is added in such a form as to be gradually dissolved in the electrolyte solution in the hydrogen storage alloy electrode. The aluminum oxide of the present invention does not gel immediately upon contact with an alkaline electrolyte, and is added to the negative electrode, a hydrogen storage alloy electrode, to maintain the high conductivity of the nickel electrode, A long-life nickel-metal hydride battery can be realized without deteriorating characteristics and utilization.

The present invention has a technical significance in that aluminum oxide is employed as an aluminum compound which gels upon contact with an alkaline electrolyte and is added to a hydrogen storage alloy electrode constituting a negative electrode of a nickel-metal hydride battery. However, the reaction rate at which this aluminum oxide gels and dissolves in the electrolytic solution is slow, and as a result, a hydrogen storage electrode that gels at an appropriate rate can be obtained.

[0013]

An embodiment of the present invention will be described in detail. Commercially available powders of misch metal, nickel, cobalt, manganese, and aluminum are weighed and mixed so as to have a predetermined alloy composition ratio according to the purpose, heated and melted by an arc melting method, and then cooled to form a hydrogen storage alloy lump. Get. This alloy lump is mechanically pulverized to a powder of 150 mesh or less, and a quantity of 2 parts by weight of polyvinylidene powder, 10 parts by weight of nickel powder (conductive material), and 3 parts by weight of aluminum oxide with respect to 100 parts by weight of this alloy powder. The mixed powder is added to 20 parts by weight of a 1% carboxymethylcellulose (thickening agent) aqueous solution, and then stirred to prepare an alloy powder slurry. This alloy powder slurry is punched with a punching nickel sheet having an aperture ratio of 38% ( Thickness
0.07mm, opening diameter 1.5mm)
Rolling at a pressure of 0 ton / cm ² produces a hydrogen storage alloy electrode having a total thickness of 0.37 mm.

The above-mentioned hydrogen storage alloy electrode is used as a negative electrode, a nickel electrode is used as a positive electrode, and a nylon separator is interposed between the electrodes to form a laminated wound and wound electrode group. It is stored in a bottomed cylindrical can made of iron, and it is filled with an aqueous solution of KOH, NaOH and LiOH having a specific gravity of 1.33, and sealed with AA size, rated capacity of 1200 m.
Ah battery was assembled. The nickel electrode was manufactured by filling a foamed nickel substrate with an active material paste containing nickel hydroxide as a main component, followed by drying and rolling.

In order to confirm the effects of the present invention, three types of comparative samples were prepared and comparative experiments were performed. [Comparative Example Battery 1] A battery assembled in the same manner as in the Example except that aluminum oxide was not added to the negative electrode for simple comparison. [Comparative Example Battery 2] 100 g of activated alumina powder was put into 1 liter of water and stirred to prepare an activated alumina suspension.
After the separator was immersed in this suspension, it was taken out and dried to deposit 0.06 g of activated alumina. Battery assembled using this separator. [Comparative Example Battery 3] A hydrogen storage alloy powder and a 5% by weight aluminum oxide powder were filled in a ball mill, argon gas was sealed therein, and the mixture was stirred at room temperature at a rotation speed of 80 rpm for 20 hours to perform mechanical alloying. And a battery assembled using the hydrogen storage alloy subjected to this mechanical alloying treatment.

Each of these batteries was subjected to an activation treatment by repeating charging and discharging at 0.2 C (1/5 of the rated current) three times. Table 1 shows the third discharge capacity. Table 1 also shows the discharge capacity when the discharge current was 1 C (rated current) and 3 C (three times the rated current). First, in each case, the discharge current is larger than the discharge capacities of the other comparative examples, indicating favorable characteristics as a battery.

[0017]

[Table 1]

Further, a life test was performed using these batteries. As a result, the discharge capacity retention rate was 500 cycles, and the battery of the present invention was 96% of the first cycle. On the other hand, Comparative Example Battery 1 was 88%, Comparative Example Battery 2 was 92%,
The battery of Comparative Example 3 was 91%. The internal resistance at this time was 20 mΩ (battery of the present invention), 35 mΩ (comparative battery 1), 27 mΩ (comparative battery 2), and 28 mΩ (comparative battery 3).
It can be seen that the battery of the present invention has an extremely long life.

The difference between the present invention and Comparative Example 1 is that only aluminum oxide was not added to the hydrogen storage alloy electrode of the negative electrode. However, when charge and discharge were repeated 500 cycles, the discharge capacity reached 88%. It falls down, and each stage is different from the 96% maintenance of the present invention. This is because the nickel electrode is reduced by dissolved hydrogen, segregated components are deposited on the nickel electrode, and the nickel electrode swells with the progress of the cycle. It is considered that the capacity gradually decreases due to the gradual increase in the resistance.On the other hand, in the case of the present invention, after about 50 to 200 cycles, the aluminum oxide gels and moves to the nickel electrode side. It is considered that the high capacity is maintained even after 500 cycles in order to exhibit the effect of suppressing the swelling of the nickel electrode.

Comparative Example 2 is similar to the present invention in that aluminum oxide coexists in the battery together with the electrolytic solution. However, this is one in which activated alumina is adhered to the separator, and the electrolytic solution is injected. It is understood that the gelation of aluminum starts immediately afterwards, and the formation of a conductive cobalt compound on nickel hydroxide, which is a normal battery reaction, is inhibited, the polarization of the battery increases, and the discharge capacity decreases.

Comparative Example 3 is further similar to the present invention, in which aluminum oxide is contained in the negative electrode of the hydrogen storage alloy, but its initial characteristics are not preferable as shown in Table 1. It is considered that since the film is formed by performing a mechanical alloying treatment with the hydrogen storage alloy, a local battery action occurs between the alloy and the metal, and the metal oxide is more easily dissolved. When aluminum complex which dissolves generated at this time is moved to the nickel electrode side, to inhibit the production of complex ion (HC _{O O 2),} further inhibition decreases the conductivity of the nickel electrode also a generation of a conductive C _O compound And the discharge capacity is reduced. On the other hand, in the present invention, the aluminum oxide does not dissolve immediately after the injection, and the generation of the conductive C 2 _O compound is not suppressed, so that the initial characteristics are not impaired. Thus, according to the above embodiment, when aluminum oxide is added to the hydrogen storage alloy electrode in a form that is gradually dissolved in the electrolyte, the battery capacity does not decrease at the initial stage, and the high-rate discharge characteristics are good, In addition, there is an advantage that the life is long.

[0022]

As is clear from the performance test of the above embodiment, the nickel-metal hydride battery of the hydrogen storage alloy electrode according to the present invention gradually gelated without aluminum oxide being dissolved and gelled immediately after injection. Progresses, without impairing the initial characteristics, and by gradually gelling the aluminum oxide, it is possible to prevent the nickel electrode from being reduced by dissolved hydrogen and the segregated components from being deposited on the nickel electrode,
Various factors that cause a decrease in open voltage during discharge, that is, a decrease in the potential of the nickel electrode can be eliminated, and furthermore, an effect of suppressing swelling of the nickel electrode is exerted, so that it has a long life and extremely high performance.

Claims (1)

[Claims] 1. A nickel-metal hydride battery using a hydrogen storage alloy for a negative electrode, a nickel oxide for a positive electrode, and an alkaline aqueous solution as an electrolyte, wherein aluminum oxide is added to the negative electrode.