JPH07282802A - Positive electrode mixture for cylindrical alkaline battery - Google Patents

Abstract

PURPOSE:To provide a positive electrode mixture for a cylindrical alkaline battery where moldability is excellent and an electrolyte absorption property cannot be deteriorated. CONSTITUTION:Graphite having an average particle diameter of 5-30mum as a conductive assistant is mixed with manganese dioxide of a positive electrode active material, to be thus formed into a hollow and cylindrical shape. 0.5-2% with respect to manganese dioxide, of finely powdery graphite having a particle shape of a scale, an average particle diameter of 2-3mum and a distribution width of 0-5mum is added into the resultant positive electrode mixture other than the above-stated graphite. Consequently, calcium stearate or zinc stearate as a lubricant becomes unnecessary. The finely powdery graphite prevents peeling-off or a crack on the surface of the positive electrode mixture with excellent moldability. Furthermore, it is possible to improve an electrolyte absorption property of the positive electrode mixture and enhance the performance of a battery.

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 used for a tubular alkaline battery.

[0002]

2. Description of the Related Art Conventionally, as a positive electrode mixture for a cylindrical alkaline battery, manganese dioxide, which is a positive electrode active material, is mixed with phosphorous graphite as a conductive auxiliary agent or carbon such as artificial graphite and compression granulated. A product obtained by pressure-molding a granular mixture into a hollow cylinder is widely used.

In order to increase the amount of the positive electrode active material, it is desirable that the carbon content be small (for example, 3 to 8%).
This increases the friction between the positive electrode mixture surface and the mold surface,
There is a problem that the surface of the positive electrode mixture is easily peeled off or cracked during the pressure molding, and the moldability of the mixture is extremely deteriorated.
In order to prevent these disadvantages, it is known to add calcium stearate or zinc stearate as a lubricant. (Japanese Patent Publication No. 5-48578)

[0004]

However, by adding the above-mentioned calcium stearate or zinc stearate, the lubricity of the positive electrode mixture can be improved and peeling or cracking of the mixture surface can be prevented. Is water-repellent, it lowers the electrolyte solution absorbability of the positive electrode mixture. In particular, in so-called unblended batteries, in which mercury, which was added for the purpose of preventing corrosion of zinc as the negative electrode mixture, was abolished, the contact efficiency of zinc deteriorates and the reaction efficiency decreases, so the amount of electrolyte solution is higher than that of the conventional one. Therefore, the decrease in the liquid absorption property of the positive electrode mixture due to the lubricant as described above has an adverse effect on the discharge performance of the battery.

An object of the present invention is to eliminate the above-mentioned inconvenience, to provide a positive electrode mixture for a cylindrical alkaline battery which has good moldability and does not deteriorate the liquid absorbing property of the electrolytic solution.

[0006]

[Means for Solving the Problems] In a positive electrode mixture for a tubular alkaline battery, which is formed by mixing manganese dioxide as a positive electrode active material with graphite having an average particle diameter of 5 to 30 μm as a conductive auxiliary agent to form a hollow cylindrical battery, In addition to the graphite, the positive electrode mixture has a scaly particle shape, an average particle diameter of 2 to 3 μm, and a distribution width of 0.
Fine powder graphite of ˜5 μm was added to the manganese dioxide in an amount of 0.5 to 2%.

[0007]

[Operation] When a positive electrode mixture for a tubular alkaline battery is pressure-molded into a hollow cylinder, the particle shape is scaly as a substitute for calcium stearate or zinc stearate, and the average particle diameter is 2 to 3 μm. When 0.5 to 2% of scaly fine powder graphite having a distribution width of 0 to 5 μm is added, peeling and cracking of the surface of the positive electrode mixture can be prevented, and moldability is improved. Further, the electrolyte absorbing property of the positive electrode mixture is also improved.

[0008]

EXAMPLES As a positive electrode mixture generally used in a cylindrical alkaline battery, a mixture of manganese dioxide, which is a positive electrode active material, and a carbon material is widely used. This carbon material serves as a conductive auxiliary agent that effectively transports electrons to the manganese dioxide particles dispersed in the positive electrode mixture, and is an effective material for press-molding the positive electrode mixture into a hollow cylinder. But also.

The conditions that the carbon material used as the conductivity aid should have are (1) excellent conductivity, (2) excellent electrolyte retention, and (3) combined These conditions are met by the excellent moldability of the agent, and graphite particles are used as a conductive auxiliary agent for alkaline batteries, and natural graphite (scaly graphite, scaly graphite, etc.) Alternatively, there is artificial graphite (carbon black type, etc.).

[0010] In particular, scaly graphite is used as a lubricant in forming a positive electrode mixture because it has a weak bond between carbon sheets and is easily peeled off or slippery and has excellent lubricity. The graphite added as a has an average particle size of 5 to 30.
It is said that the content is at least 10% or more for molding when a lubricant such as calcium stearate or zinc stearate is not added in μm.

However, it is preferable to add such a carbon material (graphite) in a large amount because the content of the positive electrode active material in the mixture decreases and the battery discharge capacity decreases.

On the other hand, as in the present invention, by adding a small amount of finely divided graphite in place of calcium stearate, zinc stearate or the like, the moldability is good and the electrolyte absorbability is also good. The mixture can be obtained with a small amount of added graphite. The details will be described below based on the test results.

Table 1 shows the compounding ratio of the additives when forming the positive electrode mixture. Assembling 100 LR6 type alkaline batteries each with 6 examples of the positive electrode material, moldability, electrolyte solution absorption and discharge characteristics. Was compared with the conventional product. The results are shown in Table 2.

As shown in Table 1, the positive electrode mixture battery used in the comparative experiment was as follows: Graphite A (average particle diameter 10 μm) was added to the mixture in an amount of 7.5% and calcium stearate was added in an amount of 0.5%. Product: 7.5% of graphite A alone (Example 1): 7.5% of graphite A and 0.3% of graphite B (average particle size 3 μm) (Example 2), : 7.5% of graphite A and 0.5% of graphite B (Example 3): 7.5% of graphite A and 1.5% of graphite B (Example 4), graphite A 7.5% and graphite B 2.5
% (Example 5): 7.5% of graphite B alone (Example 6), of which 7 is an example of the positive electrode mixture according to the present invention.

[0015]

[Table 1]

The comparison items shown in Table 2 were carried out in the following manner.

For the number of defective moldings, the number of cracks and cracks on the surface of the positive electrode mixture was visually counted. For the mixture strength, the strength in the radial direction of the mixture was measured using a push-pull meter.

The amount of liquid absorbed is determined by inserting the molded mixture into a positive electrode can and inserting a separator into which a 40% KOH aqueous solution of 2 c is added.
After injecting c and allowing it to stand still for 40 minutes, the accumulated KOH aqueous solution was sucked out, and the value obtained by subtracting this sucked-out amount from the injected amount was taken as the liquid-absorbed amount of the mixture.

Continuous discharge is a load resistance of 2Ω and a final voltage of 0.
The discharge duration when continuously discharged to 9 V was measured.

As a result of the comparative test, as shown in Table 2, (Example 1) could not be molded. This is because calcium stearate as a lubricant is not added. or,
In Example 2, graphite B was added as a lubricant, but the moldability was extremely poor. This is because the addition amount of graphite B is insufficient.

In (Example 3), (Example 4) and (Example 5), the addition amount of the graphite B of the present invention was set to 0.5 to 2.0%, which are conventional products. It is clear that it has a better mixture strength, liquid absorption, and discharge performance, and that it has no problem with moldability.

On the other hand, when only graphite B is added as in (Example 6), the liquid absorbency is improved but the mixture strength is extremely deteriorated. Thus, when 100% of fine powder graphite such as graphite B is used, the molding density is lowered and the strength of the molding mixture is reduced, which is not preferable in terms of battery assembly and battery performance.

[0023]

[Table 2]

[0024]

EFFECTS OF THE INVENTION When a positive electrode mixture for a tubular alkaline battery is pressure-molded into a hollow cylinder, it has a flaky particle shape and a scaly material with an average particle diameter of 2 to 3 μm and a distribution width of 0 to 5 μm. Since 0.5 to 2% of fine powder graphite is added, calcium stearate or zinc stearate as a lubricant is not required, and the fine powder graphite prevents peeling or cracking of the surface of the positive electrode mixture, and moldability Will be good. Further, the electrolyte absorbing property of the positive electrode mixture is also improved, and the battery performance is improved.

Front page continuation (72) Inventor Masatake Nishio 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd.

Claims (1)

[Claims] 1. A positive electrode material mixture for a tubular alkaline battery, which is formed by mixing manganese dioxide, which is a positive electrode active material, with graphite having an average particle size of 5 to 30 μm as a conductive additive to form a hollow cylindrical battery. Separately, 0.5 to 2% of fine powder graphite having a scaly particle shape and an average particle diameter of 2 to 3 μm and a distribution width of 0 to 5 μm is added to the manganese dioxide, which is a cylindrical alkali. Positive electrode mixture for batteries.