JPH05121105A - Cobalt air secondary battery - Google Patents

Abstract

PURPOSE:To eliminate a configuration change of a negative electrode to realize a long service life by using porous cobalt for a negative electrode active material in an air cell and enabling charging without using an additive agent. CONSTITUTION:An electrolyte 4 is in contact with cobalt 1 and an air electrode 3 while interposing a separator 2, and takes in air from outside through an air hole 10. Oxygen is uniformly supplied to a whole surface 4 the air electrode 3 by means of a diffusion paper. A water-repellent film 5 prevents the electrolyte 4 from leaking to the outside of an air battery. The porous cobalt 1 is used for a negative electrode active material of an air cell to enlarge a contact surface with the electrolyte 4. The separator 2 is errosion-proof against the electrolyte 4. When a carbon material or a specified metallic material is used for the electrode 3, an alkaline solution having excellent ionic conductivity can be used for the electrolyte 4. Accordingly, the use of the cobalt 1 for the negative electrode active material enables charging as a single body and facilitates manufacturing. Therefore, an additive agent becomes unnecessary, a configuration change of a negative electrode is eliminated, and a long service life is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cobalt-air secondary battery, and more particularly to an air battery having a negative electrode made of a metal active material, a positive electrode made of an oxygen active material, and an electrolyte solution made of an alkaline aqueous solution, and having a charging function. Regarding air batteries.

[0002]

2. Description of the Related Art Air batteries use oxygen in the air as a positive electrode active material, and thus have a high energy density, and those using zinc as a negative electrode active material have already been put to practical use as primary batteries. There is. In order to make the best use of the feature of this high energy density, attempts have been made to make a secondary battery capable of charging an air battery. Charge and discharge of an air battery largely depend on the electrochemical properties of the metal used for the negative electrode active material, but there are many problems resulting from this, making it difficult to make a secondary battery. For example, in a zinc-air battery, the dissolution of the negative electrode due to discharge causes the deposition of dendrites (dendrites) during charging, which causes passivation and the like, leading to a deterioration in battery life characteristics. As measures against this, conventionally, the following means have been studied. For example, preparation of an insoluble negative electrode in which an additive is mixed with a negative electrode active material, or suppression of dendritic crystal growth by adding the additive to an electrolytic solution.

Also, for metals other than zinc, aluminum-air batteries using aluminum as the negative electrode active material are also under study. In this battery, Al (OH) ₃ generated by discharge
Since it is extremely difficult to reduce Al, the irregular charging method of replacing Al (OH) ₃ with new aluminum is adopted. Therefore, in this case, unlike a general secondary battery, its use is considerably limited.

[0004]

It is an object of the present invention to solve the above problems, that is, charging is possible without using additives,
It is to provide a long-life air battery.

[0005]

In order to solve the above problems, the cobalt secondary battery of the present invention is characterized by using cobalt as a negative electrode active material of an air battery.

In the conventional technology for forming a secondary battery of an air battery using zinc or the like as a negative electrode active material, an additive is used to suppress dissolution or morphological change of the negative electrode, which is a problem during charging. I've done it. On the other hand, the present invention is characterized in that cobalt is used as the negative electrode active material, which hardly causes dissolution and shape change even without such additives.

[0007]

EXAMPLE FIG. 1 is a diagram for explaining an example of a battery according to the present invention. The figure shows a schematic cross-sectional view of the battery of the present invention. 1 is cobalt, 2 is separator, 3 is air electrode, 4 is electrolyte, 5 is water repellent film, 6 is diffusion paper, and 7 is negative battery A case, 8 is a positive battery case, 9 is an insulator, and 10 is an air hole.

Here, the electrolytic solution 4 is in contact with the cobalt 1 and the air electrode 3 with the separator 2 interposed therebetween. Reference numeral 10 is an air hole through which outside air is taken. Also, diffusion paper 6
Is for uniformly supplying oxygen to the entire surface of the air electrode 3, and the water-repellent film 5 prevents the electrolytic solution from leaking out of the battery.

Next, the operating mechanism of the battery will be described. First, in discharging, when the positive electrode and the negative electrode are connected to an external load, the following rightward electrochemical reaction occurs inside the battery.

[0010]

[Formula 1]

[0011]

[Formula 2]

Here, the potential in parentheses is the standard electromotive force. From this, the theoretical open electromotive force of this battery is 1.13.
It becomes V. In reality, the negative electrode active material is porous cobalt, the positive electrode (catalyst electrode) is platinum, and the electrolyte is potassium hydroxide (1 mo
An open electromotive force of 0.88 V was obtained with the battery configuration using 1 / l). In charging, the above-mentioned leftward reaction occurs by applying a voltage from the outside, and the threshold value of the voltage actually required at this time was 1.3V to 1.4V. Next, the charge / discharge measurement by this battery system was performed as follows. First, the battery is completely discharged, and the following (a) to
This was repeated with (d) as one cycle.

(A) 1.6V constant voltage charging is carried out for 5 hours (not complete charging).

(B) Rest for 10 minutes.

(C) A constant current discharge of 3 mA, a voltage of 0 V
Continue until you descend.

(D) Rest for 10 minutes.

The measurement results are shown in FIG. Here, the shaded area is the voltage and the other is the current. This graph is drawn with the current delayed by 5 minutes with respect to the voltage. From the figure, it can be seen that about 80% of the amount of electricity at the time of charging is discharged by discharging. Further, in the cycle characteristics, 60% or more of the first discharge time was observed even after repeating 50 times of charge and discharge. Furthermore, there was almost no dissolution of cobalt in the electrolytic solution or change in the morphology.

From the above, it is clear that the present air battery sufficiently functions as a secondary battery. In this measurement, the cobalt electrode was obtained by compressing the cobalt powder to have a diameter of 2.4c.
m was formed into a disk shape having a thickness of 0.8 mm to make it porous. As a result, the electrolytic solution entered the inside of the cobalt electrode and the entire electrode was able to participate in the charge / discharge reaction. This shows the advantage of making the cobalt electrode porous. In addition, a constant current discharge of 2 mA was performed using this electrode, and a result of a battery capacity of 128 mAh was obtained.

In the above examples, the cobalt 1 used has a large contact area with the electrolytic solution 4 due to porosity or the like. . Further, the separator 2 may be any film-like cellophane, polyethylene, polyvinyl alcohol, ceramic or the like as long as it is not affected by the electrolytic solution. . The air electrode 3 can use a carbon material such as charcoal or carbon black, or a metal material such as platinum, gold, or porous nickel, and the electrolyte solution 4 can be KOH or N.
An alkaline solution having good ion conductivity such as aOH can be used. The water repellent film 5 has a property of repelling the electrolytic solution 4 such as porous polytetrafluoroethylene, and the diffusion paper 6 is cellulose or the like. Battery cases 7 and 8 are AB
There is no particular limitation as long as it is made of a material that is not affected by the electrolytic solution 4, such as S resin or fluororesin. Insulator 9 is synthetic rubber,
An elastic material such as a polymer having a large insulating property can be used. Further, the air holes 10 may be of any size as long as sufficient oxygen can be sent to the air electrode.

[0020]

As described above, in the present invention, a rechargeable air battery is realized by using cobalt as the negative electrode active material. In this case, there are the following excellent effects.

The negative electrode is made of only cobalt, and no additives such as an electrolytic solution are required. Therefore, the battery can be easily manufactured. The negative electrode has no change in shape and has a long life.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a cobalt secondary battery of the present invention.

FIG. 2 shows charge / discharge characteristics of an air battery using a cobalt electrode, which is used for explaining an example of the present invention.

[Explanation of symbols]

 1 Cobalt 2 Separator 3 Air electrode 4 Electrolyte 5 Water repellent film 6 Diffusion paper 7 Negative battery case 8 Positive battery case 9 Insulator 10 Air holes

Claims (2)

[Claims] 1. A cobalt-air secondary battery, wherein cobalt is used as a negative electrode active material of the air battery. 2. The cobalt-air secondary battery according to claim 1, wherein the cobalt is porous.