JPH097601A - Positive electrode mixed agent for alkaline battery - Google Patents

Abstract

PURPOSE: To satisfy both of a molding property and a discharging property in an positive electrode mixed agent of an alkaline battery. CONSTITUTION: In a positive electrode mixed agent for an alkaline battery in which manganese dioxide is adopted as an active material and mixed with carbon used as a conductive agent, expanding graphite is used as carbon, thereby enhancing a molding property in the case of molding a positive electrode mixed agent. As a result, a binder used is reduced, thereby being able to enhance a discharging property as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode mixture for alkaline batteries, which has good moldability and excellent discharge characteristics.

[0002]

2. Description of the Related Art A positive electrode mixture for a conventional alkaline manganese battery is formed by mixing electrolytic manganese dioxide as an active material with carbon such as phosphorous graphite or graphite as a conductive agent and an appropriate binder to form a granular form. The one manufactured by high-pressure molding using a die including a die, upper and lower punches, a core rod, and the like was used. As the above-mentioned granular material,
A high density product made by compression granulation is used. As a result, the molding density of the mixture is improved and the amount of the positive electrode active material in the battery is increased. Therefore, there is an advantage that the discharge capacity is correspondingly increased and the battery discharge performance is improved.

The role of carbon in such a positive electrode mixture is to enhance the conductivity between particles of the positive electrode active material such as manganese dioxide and to improve the conductivity between the positive electrode mixture and the positive electrode can. Thereby, the internal resistance of the battery can be reduced and the short-circuit current can be increased. By the way, in order to increase the amount of active material in the mixture, it is better to reduce carbon as a conductive agent as much as possible, and it is better to use less binder, but if carbon is reduced too much, internal resistance increases, The basic performance of the battery will not be satisfied.

As described above, phosphorus-like graphite or graphite has been used as carbon, but its content is 10% by weight with respect to the total amount of manganese dioxide and carbon.
I had to do more than that. As a method for improving this, a metal salt of stearic acid as a crystallization agent is added in an amount of 0.2 to 0.
It is also practiced to reduce the carbon content to 3 to 8% by weight by adding 6% by weight or adding Teflon.

[0005]

However, when the carbon content is reduced in this way, the friction between the surface of the positive electrode mixture and the surface of the mold increases during high pressure molding with the mold,
There is a problem that the ratio of the mixture to be cracked or the surface is peeled off becomes extremely large, and the mixture moldability is extremely deteriorated. Further, even if a small amount of a binder is added to reduce the carbon content, there is a problem that the water repellency of the surface of the mixture or the surface of manganese dioxide is hindered and the discharge characteristics are deteriorated.

The present invention has been made to solve the above problems, and reduces the frictional resistance between the surface of the positive electrode mixture and the surface of the mold to reduce cracks when the mixture is taken out of the mold and to discharge the battery. The purpose is also to improve the characteristics.

[0007]

The above object can be achieved by using expanded graphite for a part or all of carbon as a conductive agent. That is, according to the present invention, in a positive electrode mixture for an alkaline battery obtained by mixing manganese dioxide as an active material with carbon as a conductive agent, expanded graphite is used for a part or all of carbon as a conductive agent. Characterize.

The expanded graphite used in the present invention is obtained by inserting sulfuric acid or nitric acid or the like into the layers of natural graphite and rapidly heating it, and the graphite layers are greatly expanded to expand. It is in the state of being.

[0009]

In the present invention, expanded graphite is used as a part or all of the graphite contained as a conductive agent in the positive electrode mixture,
The lubricating action and the binding action between the positive electrode active material particles can be enhanced, and as a result, the amount of the binding agent can be considerably reduced or even reduced to zero in some cases. Therefore, it is not necessary to reduce the amount of manganese dioxide which is the active material, so that the discharge characteristics are not deteriorated. That is, the positive electrode mixture of the present invention can satisfy both moldability and dischargeability by using expanded graphite as a conductive agent.

[0010]

An embodiment of the present invention will be described with reference to the drawings.
The positive electrode mixture for the LR6 type battery shown in FIG. 3 was prepared with the seven types of formulations shown in Table 1 below.

[0011]

[Table 1]

[0012] Each of the above-mentioned compounds is granulated by dry compression granulation, and as shown in FIGS. 1B to 1D, a die 2, an upper punch 3, a lower punch 4 and a core rod 5 are used. And pressure-molded to obtain a positive electrode mixture 1 shown in (A). Insert a plurality of molded positive electrode mixture 1 into the positive electrode can 6 as shown in FIG.
Next, the battery of FIG. 3 was made. In FIG. 3, 7 is a positive electrode terminal, 8 is an outer label, 9 is a current collecting rod, 10 is a negative electrode acting substance, 11 is a separator and an electrolytic solution, and 12 is a negative electrode terminal.

First, when pressure molding is carried out by the method shown in FIG.
The number of cracks, surface peeling, cracks, etc. when the pellet-shaped mixture was taken out from the mold was examined. The incidence is shown in Table 2 below.

[0014]

[Table 2]

For each lot, a battery (FIG. 3) was prepared using a normally produced product, and 10 Ω covt. (Voltage: 0.9
V) was continuously discharged. Five lots were inspected for each lot, and the average value was calculated. The results are shown in Table 3 below.

[0016]

[Table 3]

As is clear from the above results, in the case of the positive electrode mixture using expanded graphite, the amount of graphite and the amount of binder in the mixture are reduced to increase the manganese dioxide content%, and discharge It can be seen that the moldability is good even when the characteristics are improved.

[0018]

As described above, since the positive electrode mixture of the present invention uses expanded graphite as carbon as a conductive agent, it can be formed at the time of taking out a formed body from a mold during mixture formation. It has the effect of reducing body cracking. Therefore, the amount of the binder of the positive electrode mixture component can be reduced, and it is not necessary to reduce the amount of manganese dioxide as the active material, so that the discharge characteristics are not impaired.

[Brief description of drawings]

FIG. 1A is a diagram sequentially illustrating a positive electrode mixture molded body obtained in an example of the present invention, and (B) to (D) a positive electrode mixture molding step in the example of the present invention.

FIG. 2A is a diagram illustrating a step of inserting the molded positive electrode mixture into a battery in the example of the present invention, and FIG. 2B is a diagram showing a state in which the molded positive electrode mixture is inserted into the battery.

FIG. 3 is a view for explaining the structure of an alkaline battery loaded with the positive electrode mixture of the present invention.

[Explanation of symbols]

1 ... Positive electrode mixture, 2 ... Die, 3 ... Upper punch, 4 ... Lower punch, 5 ... Core rod, 6 ... Positive electrode can, 7 ... Positive electrode terminal, 8 ...
Exterior label, 9 ... collector rod, 10 ... Negative acting substance, 11 ...
Separator and electrolytic solution, 12 ... Negative electrode terminal.

Claims (2)

[Claims] 1. In a positive electrode mixture for an alkaline battery, which comprises manganese dioxide as an active material and carbon mixed as a conductive agent, expanded graphite is used for a part or all of carbon as a conductive agent. A characteristic positive electrode mixture for alkaline batteries. 2. The positive electrode mixture for an alkaline battery according to claim 1, wherein the amount of carbon is 3 to 8% by weight based on the total amount of manganese dioxide and carbon.