JPS5920969A - Gas-diffusion electrode for cell - Google Patents

Abstract

PURPOSE:To provide a button-type air cell having higher average continuous voltage and larger net capacity, by employing a manganese oxide carrying a metal with catalytic activity and activated carbon as catalyzers so as to prevent deterioration in catalytic activity of the manganese oxide due to its hydrophilic property. CONSTITUTION:Preparing a solution of 200ml of water mixed with 300ml of methanol, 1.5g of polyvinyl alcohol is dissolved therein, 20ml of chloroplatinic acid solution containing 10mg/ml of platinum is added thereto, and 10g of a manganese oxide whose degree of oxidation being 1.6 is further added thereto, and the solution is suitably stirred at the temperature of 70 deg.C and left as it is for 3-5hr. The manganese oxide thus obtained has 20-30Angstrom of grain sizes of platinum grains uniformly distributed over and sticking to the surface thereof, the stuck amount being 1.8% by weight of the manganese oxide. The same is mixed with active carbon, and further mixed with dispersion of polytetrafluoroethylene which offers thereto binding effect and water repellency. The same is then applied to the nickel screen 3 and gets dried, and the gas-diffusion electrode is thus constructed thereby. The button-type air zinc cell using the electrode described above as its anode exhibits much better characteristics in the average comfinuous voltage and net capacity compared with conventional cells.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a gas diffusion electrode for a battery using oxygen as a positive electrode active material, such as an air battery.

Conventional configurations and their problems Various types of catalysts for gas diffusion electrodes have been proposed in the past. It has been proposed to use activated carbon in which noble metals such as platinum group elements and silver are precipitated, mixtures of activated carbon and manganese dioxide, and mixtures of activated carbon and porphyrin metal complexes. In general, platinum group elements, silver, etc. have a large catalytic effect, but in order to fully demonstrate their effects, the amount of addition is approximately 10 to 20% by weight, which is extremely inconvenient in terms of resources and cost. be. Furthermore, the use of large amounts of precious metals in button-type air batteries, which are attracting attention for use in hearing aids, is expensive, considering that rechargeable batteries are generally difficult to reproduce and reuse.

To solve this problem, various attempts have been made in the past to use cheap manganese oxides, such as manganese dioxide, as catalysts for air batteries, but although they are effective in increasing the initial open circuit voltage, they also increase the discharge voltage. It wasn't always enough. This is because manganese oxide discharges due to its own hydrophilic nature, or due to the electrolyte that permeates or diffuses during storage, an electrochemical reaction occurs between manganese oxide and activated carbon in the positive electrode catalyst, resulting in lower oxidation of manganese. The cause is that the catalytic ability of manganese oxide decreases due to the production of manganese oxides.

OBJECTS OF THE INVENTION It is an object of the present invention to solve the above-mentioned problem of reduced catalytic ability due to the hydrophilicity of manganese oxides, and further to significantly improve the catalytic ability.

Structure of the Invention The present invention is characterized in that a manganese oxide supporting a metal having catalytic ability and activated carbon are used as a catalyst.

Here, in order to support a metal on manganese oxide, a water-soluble polymer substance as a dispersant, such as polyvinyl alcohol, polyvinylpyrrolidone, or polyethylene oxide, is added to a solution of a metal salt having catalytic ability. Add manganese oxide and stir well, then add reducing agent, such as alcohol.

It is preferable to use a method in which formalin or the like is added to reduce the metal salt and deposit the metal on the surface of the manganese oxide.○ In particular, as the metal salt to be used, chlorides of the respective metals have high solubility and are effective. Further, when manganese oxide is expressed as MnO, the oxidation degree X is preferably 1.4 to 2.0. If the oxidation degree of manganese oxide is less than 1.4 or more than 2.0, it will be in an extremely unstable oxide state, and will decompose when it interacts with a reducing agent, etc., resulting in the formation of manganese oxide. It is difficult to maintain these characteristics.

DESCRIPTION OF EXAMPLES Below, the present invention will be explained in detail with reference to examples. Add 20 m 71 of a chloroplatinic acid solution containing the mixture, and further add 10 g of manganese oxide with an oxidation degree of 1.6, and leave it for 3 to 5 hours at a temperature of 70° C. with appropriate stirring.

Example 2 1.5 g of polyvinyl alcohol was dissolved in a solution of 300 ml of methanol mixed with 200 m7 of water, 20 ml of cobalt chloride solution containing 50 mi 7 ml of metal cobalt was added thereto, and the solution was further dissolved with an oxidation degree of 2 and ○. Add 109 manganese oxides and leave for 1 to 2 hours at a temperature of 70°C with appropriate stirring. Example 3 2.0 g of polyvinylpyrrolidone is dissolved in a solution of 30 ml of formalin and 600 ml of water, and the amount of metal lanthanum is dissolved in this solution. Add 20ml of lanthanum chloride solution containing 20mg/ml of manganese oxide with an oxidation degree of 1.8.
g and left to stand at a temperature of 60'C for 3 to 4 hours with appropriate stirring.

Platinum particles having a particle size of 20 to 30 were uniformly adhered to the surface of the manganese oxide obtained in Example 1, and the amount of adhesion was 1.8% by weight based on the manganese oxide. In Example 2, cobalt particles with a particle size of 10 to 30 were uniformly adhered, and the adhesion amount was 8.7% by weight, and in Example 3, cobalt particles with a particle size of 1
5 to 30 lanthanum particles adhere uniformly, and the amount of adhesion is 3
．． 6% by weight -)/ko.

Each manganese oxide obtained in Example 1.2.3,
Activated carbon and a binding agent and a water repellent spray were mixed therein, applied to a nickel screen, and dried to form gas diffusion electrodes A, B, and C, respectively. The compounding amounts of manganese oxide, activated carbon, and polytetrafluoroethylene are as follows:
The weight ratio was 9:5:4. In addition, as a comparative example, an electrode made of manganese oxide with a similar composition was
And so.

Using these electrodes as the positive electrode, configure the R44 size button-type zinc-air battery shown in the figure (battery capacity 420 mAh), and calculate the average maintaining voltage and actual capacity when constant current discharge of 2 mA, 5 mA, and 10 mA is performed. The comparison results are shown in the table below.

In the figure, 1 is a positive electrode container, inside which a catalyst layer 2 is coated on a nickel screen 3, a dried gas diffusion electrode 4, a water-repellent film 5, and a separator 6 are inserted. Negative electrode zinc 7 is filled in negative electrode container 8 . 9 is a gasket, 1o is a supporting paper for preventing liquid leakage, and 11 is an air supply hole provided at the bottom of the container 1.

As is clear from the above results, the battery using the gas diffusion electrode of the present invention has a higher average maintenance voltage and a larger actual capacity than the comparative example.

In the examples, platinum, cobalt, and lanthanum were used as catalyst metals supported on manganese oxide, but similar effects can be obtained by using ruthenium and zirconium, which are used as catalysts for this type of electrode.

Effects of the Invention In the present invention, as a result of supporting a metal having catalytic ability on manganese oxide, the active sites of the catalyst are increased, and the affinity of the manganese oxide to the electrolyte is weakened, so that it can be used as a positive electrode active material. Because it can strengthen its affinity with oxygen, it exhibits extremely excellent catalytic activity. Since manganese oxide itself still has catalytic ability, the amount of expensive noble metal catalyst added can be about 1% compared to the conventional method, and the same effect can be achieved, making it possible to form an electrode at a low cost.

[Brief explanation of the drawing]

The drawing is a cross-sectional side view of a main part of a zinc-air battery used in an example of the present invention. 1...Positive electrode container, 2...Catalyst layer, 3.
... Nickel screen, 4 ... Gas diffusion electrode, 5 ... Water repellent film O

Claims (3)

[Claims] (1) A gas diffusion electrode for batteries comprising a catalyst layer mainly consisting of manganese oxide supporting a metal with catalytic ability and activated carbon. (2) The gas diffusion electrode for a battery according to claim 1, wherein the manganese oxide has an oxidation degree X of 1.4 to 2.0 when expressed as MnOx. (3) The gas diffusion electrode according to claim 1, wherein the metal having catalytic ability is platinum, lanthanum, cobalt, ruthenium, or zirconium.