JPH07107853B2 - Positive mix for cylindrical alkaline batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention relates to an improvement of a positive electrode mixture used in a tubular alkaline battery, and more particularly to a technique for improving moldability and battery performance.

<Background of the Invention> As a method for producing a positive electrode mixture used in a tubular alkaline battery, first, a small amount of a binder is added to a material of manganese dioxide or graphite, mixed, rolled into a sheet, and then pulverized to obtain an average particle size. A cylindrical positive electrode mixture is obtained by obtaining particles having a diameter of about 20 to 80 mesh and then molding in a mold.

At this time, conventionally, a small amount of a binder such as CMC is added and the mixture is made to have an appropriate particle size to improve the moldability.

By the way, a method for increasing the content of manganese dioxide, which is the main component in the positive electrode mixture, is desired as one means for increasing the capacity of the tubular alkaline battery. As one of measures for increasing the capacity, if the content of graphite is reduced, the content of manganese dioxide is relatively increased.

However, manganese dioxide itself has poor conductivity and poor formability, so a certain amount of graphite is indispensable.

Further, the presence of the binder lowers the content ratio of manganese dioxide and becomes an impediment factor to the improvement of the battery performance. Therefore, it is desirable to form the binder without addition if possible.

<< Problems to be Solved by the Invention >> When graphite having a large particle size is used as the graphite mixed in the positive electrode mixture, the moldability is improved, and the addition amount of the binder may be reduced or may be made non-added. Therefore, the amount of manganese dioxide can be increased accordingly.

Although this mechanism is not clearly understood, it is thought that the slippage of the mixture during molding is better than that with a small particle size, the compression density is increased, and the formability is improved.

In addition, it is considered that slipping works well even when the mold is released from the mold, and the friction is reduced, so that cracks and the like are less likely to occur.

However, when graphite with a large particle size is used, the surface area of each particle is small, so the conductivity is lower than when graphite with a small particle size is used, which affects battery performance and is limited. This will cause deterioration of battery performance in a large volume.

On the other hand, on the contrary, when graphite with a small particle size is used,
When molded into a tubular shape, the strength is insufficient, and cracking occurs when the mold is released from the mold, and when this is fitted in a positive electrode can, the mixture may peel off due to chipping or the like.

The present invention provides a positive electrode mixture for a tubular alkaline battery that overcomes the above problems, improves the moldability during molding, and improves the battery performance.

<< Means for Solving Problems >> In order to achieve the above-mentioned object, the present invention is more excellent in electroconductivity by fine granular graphite and formability by coarse granular graphite than in the case of using graphite having a conventional single particle size distribution. Focusing attention, we focused on the fact that by appropriately blending both and adding them to manganese dioxide, the weak points of both can be complemented and the overall performance can be improved.

The present invention has been made based on the above viewpoint, and has the following configuration.

That is, in the present invention, a manganese dioxide is used as a main agent, and graphite is dispersed and mixed into the manganese dioxide to form a cylindrical positive electrode mixture for an alkaline battery, wherein: the graphite is finely divided graphite having different particle size distributions and coarse particles. Of two types of graphite, and the average particle size of the fine graphite particles is 5 to 30 μ with scaly or artificial graphite, and the average particle size of the coarse graphite particles is 100 to 700 μ. The gist is to use flake-shaped or scaly graphite.

The preferable range of the compounding ratio of the particulate graphite having the above-mentioned shape to the manganese dioxide is 3 to 7% by weight, and the preferable range of the compounding ratio of the coarse-grained graphite having the above-mentioned shape is 1 to 5% by weight. The compounding ratio with respect to manganese is 4 to 12% by weight.

Also, the mixing ratio of fine-grain graphite and coarse-grain graphite is 60 to 40.
Or 90 to 10% by weight (hereinafter simply referred to as%).

And the compounding ratio of manganese dioxide to the entire graphite is
When the upper limit of 12% is exceeded, the absolute amount of manganese dioxide, which is the main ingredient, is insufficient as before, which affects battery performance. Conversely, when the lower limit of 4% is exceeded, In addition, the moldability at the time of press molding is lowered, and the battery performance is deteriorated as the conductivity is lowered.

Therefore, the addition amount within the above range is desirable, and more preferably within the range of 5 to 8% gives the best result.

Further, the mixing ratio of coarse-grained graphite to fine-grained graphite is
If the upper limit of 40% is exceeded, the moldability will be good, but if the conductivity is reduced below the lower limit of 10%, the conversely the moldability will decrease, and the molded article after molding will It tends to collapse, crack, or chip.

Therefore, it is necessary to set the content within the above range, and more preferably 70 to 30% or 90 to 10% gives the most preferable result.

The method for producing a mixture using the above two types of graphite is a method of mixing manganese dioxide within the above range in the same mixing step as in the conventional method, rolling and crushing this, and then adjusting the particle size to an appropriate value. If it is molded in the press molding process of (1), it will be molded into a cylindrical molding mixture.

In addition, at the time of blending, a small amount of a binder such as CMC may be added, but since sufficient shaping property is imparted by the shaping action of the coarse-grained graphite, the binder may be in a non-added state. The absolute amount of manganese dioxide, which is the main agent, can be increased.

After molding, fit this cylindrical positive electrode mixture into a positive electrode can, fill the inner circumference side with a negative electrode gel and a collector rod through a separator, and crimp the negative electrode terminal plate through a sealing gasket to form a cylindrical shape. Complete the alkaline battery.

The conventional graphite, which is compared with the graphite used in the present invention, has a single particle size distribution, and the average particle size is 15 to 25 μm.

<< Working >> The fine-grained graphite enhances conductivity and contributes to improved battery performance, while coarse-grained graphite contributes to improved moldability during press molding of the positive electrode mixture, and the amount of binder added. The amount of manganese dioxide can be decreased or the amount of manganese dioxide can be increased by that amount.

<< Examples >> Next, specific examples of the present invention will be described.

The present invention is not limited to the following embodiments, but can be variously modified within the range described above.

As shown in Table 1 below, the positive electrode mixture was prepared with the compounding ratio of graphite of various particle sizes to manganese dioxide.

In each example, the compounding ratio of graphite to manganese dioxide was adjusted to 7% by weight. Sample No. 1 has a conventional single particle size distribution, No. 2
Indicates fine particle graphite alone, and No. 7 indicates coarse granular graphite alone.

Therefore, the prototypes included in the scope of the present invention are Nos. 3 to 6
Up to.

However, the average particle size of graphite A is 7.5μ, the average particle size of graphite B is 420μ, the average particle size of graphite C is 20μ, and the strength and discharge performance of the molding mixture having the above composition are measured. The results are shown in Table 2.

As is clear from Table 2, the particulate graphite alone shown in the comparative example has excellent discharge performance, but the mixture strength is the lowest among the prototypes, and conversely when the coarse graphite alone is used. ,
The mixture strength is the highest, but the discharge performance is inferior. However, it was confirmed that the molding compound of the present invention containing both of them has higher strength and discharge performance than the conventional products.

<< Effects >> As described in detail in the above examples, in the present invention, it is possible to improve the moldability of the positive electrode mixture and the battery performance.

Claims (2)

[Claims] 1. A cylindrical positive electrode mixture for alkaline batteries, which comprises manganese dioxide as a main component and graphite dispersed therein, and molded into a cylindrical shape. And flake having an average particle size of 100 to 700 μ as the coarse-grained graphite, while using scaly or artificial graphite having an average particle size of 5 to 30 μ as the fine particle graphite. A positive electrode mixture for a cylindrical alkaline battery, which is characterized by using graphite in graphite or scale. 2. The compounding ratio of finely divided graphite to manganese dioxide is 3 to 7% by weight, and the compounding ratio of coarse-grained graphite is 1.
Claim 1 characterized in that it is ~ 5% by weight.
The positive electrode mixture for a cylindrical alkaline battery according to item.