JPS63121256A - Manganese dry cell - Google Patents

Abstract

PURPOSE:To increase the high-energy density by forming a thin film layer made of a carbon material on the surface of manganese dioxide grains used as a positive electrode material. CONSTITUTION:A thin film layer made of a carbon material is formed on the surface of manganese dioxide grains used as a positive electrode material. If the manganese dioxide quantity is made a fixed value and the packing density of the positive electrode black mix 1 is made the fixed value of the normal black mix reference, a volume gain is obtained for the deposition-processed manganese dioxide 1. That is, if the positive electrode electric capacity is made a fixed value, the deposition-processed manganese dioxide can output electric energy with a volume smaller than that of the normal black mix. Accordingly, the energy density for the unit volume is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in manganese dioxide, particularly the positive electrode active material of manganese dry batteries and alkaline manganese batteries.

BACKGROUND ART Conventionally, in this type of manganese dry battery and alkaline manganese battery, a mixture of electrolytic manganese dioxide powder as a positive electrode active material and carbon powder as a conductive material is usually used as a positive electrode mixture. The reason why a conductive material is necessary is that manganese dioxide alone exhibits a very low specific conductivity on the order of 10-4 to 10-3 s/cm. Therefore, in order to impart electronic conductivity to individual manganese dioxide particles and promote a sufficient reduction reaction, the specific conductivity of the positive electrode mixture must be 100 to 100.
It is necessary to make it on the order of 101 s/cm, and for that purpose, the carbon material as a conductive material has a weight ratio of 15 to 15 to the total mixture.
20 inches, 20 to 25 inches by volume is required.

By the way, what determines the positive electrode discharge capacity of a battery is the filling amount of the positive electrode mix, but as mentioned above, the ratio of carbon material to the mix volume needs to be at least 20 to 26 inches, so the battery's positive electrode discharge capacity is It is extremely difficult to further improve the discharge capacity or the energy density per volume.

This is because carbon materials generally have a large bulk density, and in order to reduce this as much as possible, conventional methods have been to make manganese dioxide heavier and to reduce the amount of conductive carbon material. We have been trying to improve the density.

However, in the method of using a carbon material as a conductive material, even if a slight improvement was observed, it would not lead to a substantial improvement in energy density unless the packing density of the carbon material was significantly improved.

One Problem to be Solved by the Invention In such conventional methods, even if manganese dioxide is made heavier, high energy density cannot be achieved unless the packing density of the carbon material is further increased.

Alternatively, this cannot be achieved unless the amount of conductive carbon material is drastically reduced.The reason why it is not possible to increase the manganese dioxide content in the positive electrode mixture is because the packing density of the conductive material is low and it is difficult to obtain sufficient electronic conductivity. This is because it is necessary to add a specified amount of carbon material, and there is a problem in that it is necessary to essentially improve these.

In order to solve this problem, the present invention forms a thin film layer of carbon material with high packing density per unit volume on the surface of manganese dioxide particles to provide a positive electrode mixture having excellent conductivity and high energy density. Means for solving the problem In order to solve this problem, the present invention provides a method for solving the problem by adding carbon material to the surface of manganese dioxide particles, which are the positive electrode active material of manganese dry batteries and alkaline manganese batteries. This method uses manganese dioxide formed into a thin film layer.

Effect With this configuration, in the positive electrode mixture, the manganese dioxide particles and the carbon material adhere extremely well, and the film thickness after formation is approximately 1.
5 μm, and the specific conductivity was on the order of 10° to 101 B/rm, showing good electronic conductivity. Furthermore, the volume ratio occupied by the conductive agent was 4 or less, indicating the possibility of increasing the amount of manganese dioxide filled. These advantages, such as excellent conductivity and low carbon material blending ratio, mean that the thin carbon material is more dense and the manganese dioxide and carbon material bond well. There is.

By using such a mixture, it is possible to increase the amount of manganese dioxide filled in conventional mixtures by about 18% by volume, and the energy density is also improved by a considerable amount. is now possible.

The present invention has been proposed based on such facts, and examples thereof will be described below.

Examples (Example 1) One method for forming a carbon material film on the surface of manganese dioxide is a vacuum evaporation method using arc discharge of a carbon rod. This type of vapor deposition method does not expose the sample to high temperatures, is not affected by binders, etc., and is a good method that hardly impairs the properties of manganese dioxide used in an aqueous solution system.

Place the pre-dried electrolytic manganese dioxide powder on a sample holder that can vibrate slightly in the Pel jar of a vacuum evaporation device, reduce the pressure using a rotary pump and a diffusion pump, and bring the pressure inside the Pel jar to B x 10-6 Torr.
Make it r. As the carbon rod, a rod with a diameter of 6 mm and a length of 100 mm manufactured by Tokai Carbon ■ was placed on the sample holder and used as an electrode for arc discharge. Before performing arc discharge, the sample holder is slightly vibrated to stir the manganese dioxide powder.

The conditions for arc discharge are a voltage of 50 to 60V.

The current was about 30 A, and arc discharge was performed for about 5 minutes.

The film thickness after the carbon material film was formed was measured separately using a stylus-type film thickness measuring device on a glass substrate placed in a Pelger at the same time.

Furthermore, the temperature inside the Pelger was repeatedly recorded by placing a thermocouple on the sample holder, and it was confirmed that the temperature was between 50°C and 80°C. The manganese dioxide obtained under these conditions was closely adhered to the carbon material, and the average film thickness was about 15 μm. Further, the electronic conductivity was 10° to 101 s/cm 2 which is the property of an actual manganese battery positive electrode mixture, and it has become possible to significantly improve the 1O-3 s/cm 2 which is the property of original manganese dioxide.

In addition, the crystallinity basically shows the crystal form of γ-M n O2, but the lattice spacing is 3.3, which is thought to be partly due to the carbon material.
Six peaks were seen in the X-ray diffraction diagram. Others, MnO
The X value shown for the engineering is 1.96, and the water content is 1.4 by weight.
He was in charge.

Next, the weight percentage of the carbon material relative to the vapor-deposited manganese dioxide obtained was determined to be about 8 parts, which obviously provides sufficient electronic conductivity. In addition, as a method for determining the ratio of carbon material to the volume of the mixture, a certain amount of each of the positive electrode mixture, which is made by mixing 10% carbon material with vapor-deposited manganese dioxide and untreated manganese dioxide, is placed in a diameter of 10 mm. The material was molded into pellets, and the thickness of the pellets was precisely measured and compared.

As a result, the ratio of conductive material is usually about 20% in the positive electrode mixture.
On the other hand, with vapor-deposited manganese dioxide, it was about 4
%, indicating that it is possible to increase the amount of manganese dioxide filled accordingly.

A model cell of a manganese dry battery shown in FIG. 1 was constructed by using the vapor-deposited manganese dioxide obtained as described above as a positive electrode, zinc as a negative electrode, and a neutral electrolyte mainly containing zinc chloride as an electrolyte. In Figure 0, which examines the utilization rate and energy density of manganese dioxide, 1 is the positive electrode mixture according to the present invention, that is, manganese dioxide subjected to vapor deposition treatment, and 02 is the positive electrode current collector, using a platinum plate. 3 is a separator, 4
uses a zinc plate as the negative electrode active material. 5 is a lead wire for positive and negative electrodes, 6 is a screw for fixing the cell, and 7.8 is a resin cell container. The discharge conditions are a current density of 9 mA.
/ad constant current continuous discharge test, and the ambient temperature was 20
"C. If the amount of manganese dioxide is constant and the filling density of the positive electrode mixture is a constant value based on the normal mixture, a volume gain will occur in the vapor-deposited manganese dioxide.

That is, when the positive electrode capacitance is kept constant, vapor-deposited manganese dioxide can output electrical energy with a smaller volume than a normal mixture. Therefore, the energy density per unit volume increases accordingly. The situation is shown in Figure 2.

A in FIG. 2 shows a comparison of utilization rates of manganese dioxide, and B shows a comparison of energy densities. In both figures, the time when a normal mixture is used is expressed as an index of 100. As is clear from the figure, there is no big difference between the normal mixture and vapor-deposited manganese dioxide in terms of utilization, but the latter is slightly better. This is thought to be because the adhesion between manganese dioxide and the carbon material is strong, and the contact resistance between the two is smaller than that of a normal mixture.

Also, in terms of energy density, vapor-deposited manganese dioxide is better, with an improvement of about 20 times compared to that of the ordinary mixture. This is thought to be largely due to the fact that the volume ratio of the conductive material is approximately the same as that of the normal mixture.

<Example 2> Next, a similar test was conducted using the model cell shown in Example 1 in an alkaline electrolyte saturated with zinc oxide.

Even when an alkaline electrolyte was used, the improvement in energy density due to the volume gain observed in a neutral electrolyte was revealed. Figures 3A and 3B, similar to Figure 2, show the utilization rate and energy density of manganese dioxide in comparison with conventional mixtures. It was found that the energy density was improved by about 18 times compared to the normal mixture.

From the above, it can be seen that using the vapor-deposited manganese dioxide according to the present invention: 1. In both neutral and alkaline electrolytes, the volume gain exceeded that of the normal mixture, indicating that this led to an improvement in energy density.

Effects of the Invention As described above, the use of manganese dioxide treated to form a film of carbon material according to the present invention provides the effect that a manganese dry battery or an alkaline manganese battery having a high energy density can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a model cell in an embodiment of the present invention;
Figures 2A and B are comparisons of the utilization rate and energy density of a normal mixture in a neutral electrolyte and the vapor-deposited manganese dioxide of the present invention. FIG. 3 is a diagram comparing the utilization rate and energy density of the vapor-deposited manganese dioxide and the vapor-deposited manganese dioxide of the present invention. 1... Positive electrode mixture, 3... Separator,
4... Negative electrode, 6... Lead wire, 7, 8
...Cell container. /-Z Gokusha 2- Positive electrode current collector 3- and parator 4-1 Negative 1i Fig. 2? I ff Figure 3 Oxide Maga, 201 [ 1cIo [ 8D [

Claims (1)

[Claims] A manganese dry battery characterized in that a thin film layer made of a carbon material is formed on the surface of manganese dioxide particles that are a positive electrode active material.