JPS58161256A - Processing method of manganese dioxide for cell - Google Patents

Abstract

PURPOSE:To improve the heavy load discharge characteristic by pressure compressing MnO2 added with auxiliary conductive agent thereby reducing the porous volume in a particle. CONSTITUTION:Auxiliary conductive agent of approximately 20-60wt% of entire auxliary conductive agent required for positive pole agent is added in MnO2, then pressure compressed to reduce the porous volume in MnO2 particle. Then the residual auxiliary conductive agent and binder are added to mold the positive pole agent. Since the pressure compressed MnO2 particle and the auxiliary conductive agent will contact sufficiently, the conductivity will be improved. Consequently the heavy load discharge characteristic at high current density in a cell employing said positive pole agent is improved.

Description

[Detailed description of the invention] Regarding the law.

Electrolytic manganese dioxide is often used as a positive electrode active material for dry batteries, but although electrolytic manganese dioxide exhibits excellent battery performance, it has the problem of being expensive.

Therefore, it has been proposed to heat-reduce low-cost natural manganese dioxide and then treat it with acid to obtain chemically treated manganese dioxide, which is lower in price than electrolytic manganese dioxide and exhibits superior battery performance.

However, since this manganese dioxide is obtained by heating and reducing natural manganese dioxide and treating it with acid, there are many large pores inside the particles, and the pore volume is much larger than that of electrolytic manganese dioxide. big.

Therefore, in order to produce a compact and chip-free positive electrode mixture molded body and to obtain good battery characteristics, it is necessary to wet the positive electrode mixture with a large amount of electrolyte, and as a result, the battery The amount of manganese dioxide filled into the battery is significantly smaller than that of electrolytic manganese dioxide, resulting in a problem of lower discharge capacity.

Therefore, the present inventors have solved the problem of absorbing too much electrolyte by reducing the volume of pores inside the particles by pressurizing the manganese dioxide, and have also proceeded further by reducing the volume of pores inside the particles by pressurizing the manganese dioxide. However, other manganese dioxides, such as electrolytic manganese dioxide, chemical manganese dioxide, and natural manganese dioxide, each exhibit unique battery characteristics that suit the usage conditions required for the battery by reducing the volume of pores inside the particles. He discovered that manganese dioxide could be obtained and filed a separate patent application for it.

By the way, due to the reduction in the volume of pores inside the particles due to the above-mentioned pressurized compression, the amount of electrolyte absorbed decreases and the amount of manganese dioxide filled into the battery increases, causing problems such as a longer discharge time during light load discharge. A distinctive effect is exhibited, but on the other hand, pressure compression causes manganese dioxide particles to stick, resulting in insufficient contact with the conductive additive, resulting in poor discharge characteristics in heavy load discharges with high current density. is not satisfactory either.

Therefore, the present inventors have conducted intensive research to improve such heavy load characteristics, and as a result, when compressing manganese dioxide under pressure to reduce the volume of pores inside the particles, the present inventors added a conductive additive to manganese dioxide. It was discovered that when manganese dioxide is added to the conductive additive, sufficient contact between the manganese dioxide and the conductive additive is maintained, the conductivity is improved, and the heavy load characteristics are improved, and the present invention has been completed.

The conductive additive added to the -C manganese dioxide during pressure compression may be the entire amount of the conductive additive required to be blended into the positive electrode mixture, but rather than adding the entire amount, It is preferable to add a portion and the rest at the time of preparing the mixture. The conductive additive added to manganese dioxide during pressurization is 20 to 60% (by weight, the same applies hereinafter) of the total conductive additive required in the positive electrode mixture.
is preferred. This is because if the amount of the conductive agent added during pressurization is less than the above range, sufficient contact with the conductive agent added later cannot be maintained, and conversely, if the amount is more than the above range, the chain structure may be deformed and electrolysis may occur. This is because the amount of the conductive auxiliary agent, which is not affected by a decrease in the liquid retaining ability, decreases, resulting in a decrease in discharge duration.

The conductive additive added to the manganese dioxide during pressurization may be the same as that added to the positive electrode mixture, such as acetylene black, phosphorous graphite, carbon black, etc.

For example, the pressure compression may be performed by supplying manganese dioxide into the gap between two rolls rotating in opposite directions and compressing the material using the rolls, or by using a press. The pressure during pressurization varies depending on the type of manganese dioxide used and how much pore volume of manganese dioxide is desired to be obtained, but when pressurizing with rolls, it is usually 1 to 2 t/(m), and usually 1 to 10 t/cm2 when compressing with a press.

Pressurized and compressed manganese dioxide is in the form of scales or flakes, so it is preferable to grind it into the original fine powder form for use as a positive electrode active material for batteries.

In the present invention, the intra-particle pore volume is measured by mercury intrusion method, and usually, the intra-particle pore volume of manganese dioxide before pressure compression is the sum of the pore diameters of 40 to 75,000x.
Electrolytic manganese dioxide is about 0.15 cm3/y, chemical manganese dioxide is about 0.55 cm3/y, chemically treated manganese dioxide is about 0.4 cm'/ys, natural manganese dioxide is about 0.88 cm3/9 The extent to which the intraparticle pore volume is reduced by pressure compression varies depending on the type of manganese dioxide used and the characteristics required for the battery, but chemical manganese dioxide, chemically treated manganese dioxide, etc. Generally, the goal is to reduce the intraparticle pore volume to the same level as electrolytic manganese dioxide.

Next, the present invention will be explained with reference to Examples.

Example 100 parts (parts by weight, the same shall apply hereinafter) of chemical manganese dioxide having an integrated internal pore volume of 0.55 Cm3/9 with a pore size of up to 40 A by the mercury intrusion method obtained from manganese ammonium carbamate through manganese carbonate. A mixture of 7 parts of acetylene black was supplied to a gap between two rolls rotating in opposite directions at 5 rpm, and the mixture was compressed under pressure by applying a load of 1.7 t/cm. After pressurizing and compressing, it was ground into the original fine powder form.

A part of this mixture was taken, manganese dioxide was separated, and the pore volume inside the particles was measured by mercury intrusion method.
The cumulative value was 0.25 cm3/p up to a pore diameter of 4°A.

A positive electrode mixture having the composition shown in Table 1 was prepared using manganese dioxide which had been pressurized and added with acetylene black as described above, and a SUM-1 type dry battery A was assembled, and the discharge duration of 2Ω continuous discharge was I looked into it. The results are shown in Table 2.

In the above dry battery A, the acetylene black added to manganese dioxide during pressure compression is the total acetylene black added to the positive electrode mixture (i.e., the amount added during pressure compression and the amount added during preparation of the positive electrode mixture). This corresponds to 48% of the total. The amount of acetylene black in Table 1 is the sum of the amount added during pressurization and the amount added during preparation of the mixture.

For comparison, a dry battery 13 in which the same chemical manganese dioxide as above was used as a positive electrode active material without being pressurized and compressed, and a positive electrode active material in which the same chemical manganese dioxide as above was pressurized and compressed without adding acetylene black. Table 2 shows the results of assembling the dry cell C used as the material and measuring the discharge duration in 20 consecutive discharges. Note that, like dry battery A, both dry batteries B and C are of the SLIM-1 type, and their positive electrode mixture compositions were determined from the viewpoint of maximizing discharge efficiency, and are as shown in Table 1.

Table 1 Positive electrode mixture composition As is clear from the results shown in Tables 1 and 2, when manganese dioxide that has not been compressed under pressure is used, dry electricity
As shown by B, a large amount of electrolyte must be added to obtain good discharge efficiency, resulting in a decrease in the amount of manganese dioxide filling and a decrease in discharge capacity. On the other hand, when pressurized compressed manganese dioxide is used, dry battery A,
As shown in C, a small amount of electrolyte is required, but in the case of dry cell C using pressure-compressed manganese dioxide without adding acetylene black, dry cell A using manganese dioxide treated by the method of the present invention The heavy load characteristics are inferior to that of .

Claims (1)

[Claims] 1. A method for treating manganese dioxide, which comprises adding a conductive additive to manganese dioxide before pressurizing and compressing the manganese dioxide to reduce the intraparticle pore volume.