JPH05275108A - Battery - Google Patents

Abstract

PURPOSE:To provide a high performance secondary battery having a large discharge capacity by forming a solid electrolytic film as a positive electrode by use, of an air electrode, and using a hydrogen storage alloy having a high capacity and density as a negative electrode. CONSTITUTION:As a positive electrode is provided an air electrode 3 formed by pasting an ion exchange resin and applying it to a porous carbon fiber plate electrode. As a negative electrode, a negative electrode 1 consisting of a foamed nickel base (hydrogen storage alloy) having a large hydrogen storing quantity is used. As an electrolyte, a cation exchange film 2 mainly consisting of a chemically stable fluorine resin is used to extend the life. To integrate the air electrode 3 with the ion exchange film 2 for the purpose of high output and high density, the both are received in a battery can 8. Thus, a high performance secondary battery having a large capacity can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery, and more particularly to a primary or secondary battery formed by a reaction between hydrogen contained in a hydrogen storage alloy and oxygen in the air.

[0002]

2. Description of the Related Art High-performance batteries with high energy density and long life are used in small batteries for cordless equipment, batteries for electric vehicles,
In addition, even in the case of large-sized batteries for storing electric power, the need for them is increasing more and more in recent years. The hydrogen storage alloy is a material effective as a carrier for utilizing hydrogen, which is the element having the highest theoretical energy density, and is used for nickel-metal hydride batteries (Japanese Patent Laid-Open No. 63-6746).

An air battery that uses oxygen in the air as an active material is an effective method for increasing the energy density with a small amount of active material with a built-in battery. Air-zinc primary batteries have already been put to practical use, and air-zinc secondary batteries have been studied for electric vehicles (Japanese Patent Laid-Open No. 60-172173).

[0004]

The conventional nickel-metal hydride battery has a volume energy density (Wh / liter) higher than that of the existing nickel-cadmium battery by about 50% or more, while the weight energy density (Wh / l) is higher than that of the existing nickel-cadmium battery. Wh / kg) is
It was almost the same, and it was insufficient from the viewpoint of increasing the energy density. On the other hand, in the air-zinc secondary battery, although the energy density was high, the battery life was about 200 cycles. The cause is that the shape of the negative electrode changes remarkably with charge and discharge due to the uptake of carbon dioxide in the air, or the air electrode performance deteriorates.
In addition, the output density of the air electrode was low, which was not suitable for large-current discharge.

An object of the present invention is to provide a high performance battery which solves the problems of the conventional nickel-metal hydride battery and air battery.

[0006]

In order to solve the above-mentioned problems of the prior art, the features of the present invention are greatly improved by adding the following improvements which cannot be realized only by combining an existing air electrode with a metal hydride. The purpose is to achieve improvement in energy density. That is, an air electrode is used for the positive electrode, a solid film is used for the electrolyte at the same time, a hydrogen storage alloy having a high capacity density is used for the negative electrode, and a structure capable of ensuring an effective surface area capable of high output density is used to form a primary or secondary battery. I have configured it.

The problem inevitably caused when the positive electrode is changed to the air electrode to increase the energy density is the life of the air electrode, and in order to solve the problem, the electrolytic solution from the potassium hydroxide aqueous solution is excellent in chemical stability. It was converted to an ion exchange membrane having a fluororesin as a skeleton. As a result, deterioration of the electrolyte and performance deterioration of the air electrode due to permeation of the electrolyte into the air electrode can be suppressed.
The present invention can be constructed by using either a cation exchange membrane or an anion exchange membrane as the ion exchange membrane. The reactions of these batteries are as follows.

[0008]

[Chemical 1]

Comparing (1) and (2), the effect of carbon dioxide in the air can be neglected by using the cation exchange membrane, and the ingress and egress of water accompanying the electrode reaction is limited to the air electrode side. This is advantageous because it can be done. Further, in order to stably operate the ion exchange membrane as a low resistance electrolyte membrane, the membrane needs to be in a wet state, and means for supplying water to the membrane must be provided. However, even if the membrane is too wet, the air electrode becomes difficult to act as a gas electrode. Therefore, it is indispensable to provide a means for removing water generated by the reaction and keep the membrane in an appropriate wet state. The material of the film is preferably a material having a structure in which a strong acid group such as a sulfonic acid group or a strong base group such as an alkylammonium group is bonded to the skeleton of the fluororesin from the viewpoint of electrical conductivity.

By using a hydrogen storage alloy for the negative electrode, it is possible to eliminate the change in the form associated with charge and discharge, which can contribute to a longer life. However, since the electric capacity becomes small, a material having a high capacity density is required to make up for it. Conventionally,
The AB ₅ type alloy represented by LaNi ₅ which has been mainly used for nickel-metal hydride batteries has a hydrogen storage capacity of about 1.4 wt%, whereas the AB represented by ZrMn ₂ or its substitution product. _For type ₂ alloys, approximately 1.7 wt%
Further, it can be expected that the magnesium-based A ₂ B type alloy represented by Mg ₂ Ni or a substitution product thereof will increase to about 3 wt%. However, magnesium-based Mg ₂
With Ni alloys, the equilibrium pressure of the hydrogen storage reaction is too low at room temperature, so it is desirable to increase the equilibrium pressure by alloying.

The decrease in power density, which is a problem of using the positive electrode as an air electrode, can be solved by reducing the electric resistance and the reaction resistance by integrating the electrolyte ion exchange membrane and the electrode. The method of integration is as follows: An air electrode layer composed of an electrode catalyst, a conductive agent, a water repellent agent, etc. is thermocompression-bonded to the ion exchange membrane by hot pressing, or a catalytic metal is deposited on the surface of the ion exchange membrane by ion exchange. The method etc. can be applied.
Further, the technique of dispersing the ion exchange resin in the air electrode is effective in increasing the effective reaction surface area of the air electrode. Similarly, the inventors have found that coexistence of an ion exchange resin in the hydrogen storage alloy layer of the negative electrode is also effective in the battery having the structure of the present invention. As a method of coexisting the ion exchange resin in the electrode, a method of molding together with another electrode material at the time of manufacturing the electrode, a method of applying after the electrode molding, or a method of adding by impregnation or the like is suitable.

It is also effective to improve the reaction efficiency of the electrode by adding an electrode catalyst also to the hydrogen storage alloy side of the ion exchange membrane in order to make hydrogen atoms in and out of the hydrogen storage alloy smooth. The catalyst to be added needs to have a catalytic ability to accelerate the ionization reaction of hydrogen, and more specifically, platinum, nickel, palladium, etc. are preferable.

[0013]

The essential point of the operation of the present invention is to use the positive electrode as an air electrode and to use a hydrogen storage alloy having a larger hydrogen storage capacity for the negative electrode in order to increase the energy density, and to have excellent chemical stability as an electrolyte. This is because an ion exchange membrane having a fluororesin as a skeleton was used to extend the life, and in order to further increase the power density, the air electrode and the electrolyte membrane were integrated and the ion exchange resin was added to the electrode.

[0014]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a secondary battery of the present invention.
In the figure, 1 is a negative electrode mainly composed of a hydrogen storage alloy, 2 is a cation exchange membrane that is an electrolyte, 3 is an air electrode that is a positive electrode, 4 is an air chamber into which air is sent, 5 is an air inlet, and 6 is It is an air outlet. Reference numeral 7 is a thin tube that serves as a means for supplying water to the cation exchange membrane 2, and 8 is a battery container that houses a battery.

<Embodiment 1> Next, the embodiment of the present invention shown in FIG. 1 will be described. The negative electrode was prepared by filling a hydrogen-occlusion alloy crushed to a particle size of 100 μm or less on a foamed nickel substrate having a porosity of 95% as an aqueous slurry using polyvinyl alcohol as a binder. After drying, the thickness was adjusted by a roller press. The amount of polyvinyl alcohol added to the binder was 1 wt%. The alloy composition of the hydrogen storage alloy used ZrMn _{0. 5} C
_{r 0. 2 Co 0. 3} Ni 1. _0.

The air electrode is carbon black powder 20w
80 parts by weight of an electrode catalyst supporting t% of platinum and 20 parts by weight of polytetrafluoroethylene fine powder as a binder are added to a liquid ion exchange resin (A liter drich
Chemica liter, Nafion solution) was dried and then added so as to be 20 parts by weight in terms of the weight of the ion-exchange resin, and the paste was applied to a porous carbon fiber plate electrode support.

The negative electrode was impregnated with a liquid ion exchange resin at 1 mg / cm ^2, and a fluororesin-sulfonic acid type cation exchange membrane (Nafion 117 manufactured by Du Pont) as an electrolyte was superposed on the air electrode. ^They were integrated by thermocompression bonding under the conditions of ℃ and 200 kg / cm ² . The obtained integrated electrode was housed in the battery container shown in FIG. 1 to prepare a battery. Electrode Effective electrode area is 70 cm ² and the filling capacity of the battery is 4000 m
It is Ah. Water was supplied at a rate of 0.11 ml / min to the battery at room temperature at a rate of 0.11 ml / min, and air was flowed at 1 l / min for 2 hours at a current of 2 A and discharged at 4 A. The obtained discharge characteristics are shown in A of FIG. A discharge capacity of 3700 mAh was obtained.

[0019] <Example 2> hydrogen storage alloy LaNi _{4. 4}
Co _{0. 3} A liter _0. All ₃ except for using Example 1
2B shows the discharge characteristics of the battery manufactured and evaluated under the same conditions as described above. A discharge capacity of 3030 mAh was obtained.

<Comparative Example> As a comparative example, a conventional nickel-metal hydride battery was manufactured. The metal hydride electrode was prepared in the same manner as the negative electrode of the example. The nickel electrode is a normal sintered nickel electrode. A 31 wt% potassium hydroxide aqueous solution was used as the electrolytic solution. It was stored in an electrode container having the same size as that of the example, charged at a current of 1 A for 2.5 hours, discharged at 2 A, and evaluated for charge and discharge. The obtained results are shown in C of FIG. The discharge capacity was 1800 mAh. The example battery is a high energy density battery that provides a larger discharge capacity than the nickel-metal hydride battery of the prior art.

[0021]

According to the present invention, a high performance secondary battery having a significantly improved capacity density and energy density as compared with the prior art was obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the structure of a battery according to the present invention.

FIG. 2 is a discharge characteristic diagram of a battery according to the present invention and a battery according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydrogen storage alloy negative electrode, 2 ... Cation exchange membrane, 3 ... Air electrode, 4 ... Air chamber, 5 ... Air inlet, 6 ... Air outlet, 7 ... Water supply thin tube, 8 ... Battery container.

Claims (7)

[Claims] 1. A gas diffusion electrode in which oxygen in the air acts as an active material serves as a positive electrode, and an ion exchange membrane having a fluororesin skeleton serves as an electrolyte, and a hydrogen storage alloy capable of storing and releasing hydrogen as a negative electrode. A battery characterized by being a substance. 2. The battery according to claim 1, comprising a mechanism for supplying water to at least one of the positive electrode and the negative electrode. 3. The battery according to claim 1, wherein the electrolyte is a cation exchange membrane having a fluororesin as a skeleton. 4. The battery according to claim 1, wherein the electrolyte is an anion exchange membrane having a fluororesin as a skeleton. 5. The battery according to claim 1, 2, 3 or 4, wherein an ion exchange resin coexists in the hydrogen storage alloy layer of the negative electrode. 6. The method according to claim 1, 2, 3, 4 or 5.
A battery in which a platinum catalyst is present on the hydrogen storage alloy layer side of the ion exchange membrane. 7. claim in 2, 3, 4, 5 or 6, wherein the negative electrode of the AB ₅ type alloy hydrogen storage alloy represented by LaNi _5, AB ₂ represented by ZrMn ₂ or derivatives thereof Type alloy, or a battery made of at least one of magnesium-based A ₂ B type alloys represented by Mg ₂ Ni or a substitution product thereof.