JPS5916274A - Button type alkaline manganese battery - Google Patents

Abstract

PURPOSE:To provide a button type alkaline manganese battery which assures stable storage perfomance, excellent sudden discharge characteristic and low discharge rate capacitance by selecting adequate specific surface area and a rate of addition of artificial graphite to be used as a positive conductive material. CONSTITUTION:A positive electrode in use includes an artificial graphite having the specific surface area of 8-12m<2>/g added in the rate of 4-6wt%. A positive electrode 1 molded with a depolarizing mix obtained by mixing manganese dioxide and graphite powder is placed closely in contact with a nickel clad iron reservoir 2. A translucent separator 4 made of cellophane is also placed closely in contact with the upper surface of positive electrode 1. A liquid containing material 5 on the negative side is composed of a nylon nonwoven fabric. A battery is also provided with a gelated negative electrode 6 formed by kneading hardening zinc powder, polyacryrlic acid soda of 100-200 meshes and electrolyte, a sealing plate 7 which is also used as a negative terminal and a nylon gasket 8.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an alkaline manganese battery, in particular a button type battery, which is a mixture of manganese dioxide and graphite powder as a conductive material. This improves intermittent rapid discharge characteristics and general low rate discharge capacity.

Conventional Structures and Problems Manganese dioxide is widely used as a positive electrode active material for batteries because it is inexpensive. Recently, as the current consumption of electronic devices has become smaller and smaller, button-type alkaline manganese batteries have come to be used in applications that previously used silver oxide batteries.

The alkaline manganese battery in this trench uses natural graphite as the positive electrode mixture at a rate of 10 to 15%. A mixture of mt% was press-molded and used. When the amount of graphite added is large like this,
Although the moldability of the mixture was improved, various damage occurred.

That is, in the case of natural graphite, the ash content containing heavy metals such as Fe, Cr, Mg, etc. as impurities was 1% by weight or more, and the specific surface area was 14 m2/y or more as measured by a normal measurement method using nitrogen adsorption. Therefore, when mixed with manganese dioxide and incorporated into a battery after molding, the contact surface with manganese dioxide particles increases and impurities promote self-discharge due to local battery action in the alkaline electrolyte. As a result, there was an inconvenience that the open circuit voltage decreased during storage. This phenomenon increases in proportion to the amount of graphite added. In addition, in the case of natural graphite, the ash content of impurities is reduced to 0.5
It is said that it is impossible to remove it to less than % by weight, and that reducing the specific surface area is problematic in terms of yield and process.

Recently, artificial graphite made from pitch coke and tar coke has been developed. This artificial graphite has a high purity with an ash content of 0.2% by weight or less, and its specific surface area can be adjusted relatively easily, so it is extremely suitable as a conductive material to be mixed with manganese dioxide.

In general, when the specific surface area of graphite powder added as a conductive material increases, it tends to be more uniformly dispersed in manganese dioxide and has better formability, but it also tends to contain adsorbed gases and moisture, which are volatile components, which can cause self-discharge. performance will deteriorate after storage. On the other hand, if the specific surface area is small, the dispersion of manganese dioxide tends to be uneven, resulting in poor moldability and low molding yield.

On the other hand, if the proportion of graphite powder added in the positive electrode is high, the voltage characteristics and rapid discharge characteristics will be excellent, but the discharge capacity at low rates will be small.

As described above, even when using high-purity artificial graphite as a conductive material, there are many points to be improved regarding the specific surface area addition ratio.

Purpose of the Invention The present invention provides a button-shaped alkali manganese which has stable storage performance, excellent rapid discharge characteristics, and large low rate discharge capacity by optimizing the specific surface area and addition ratio of artificial graphite used as a conductive material for the positive electrode. The purpose is to provide batteries.

Structure of the Invention The present invention utilizes artificial graphite having a specific surface area of 8 to 12 m"/g.
Description of Examples Using a Positive Electrode Added at a Ratio of ~6% by Weight First, comparative results regarding the formability of graphite having different specific surface areas will be shown.

Table 1 shows the height of the molded product when 2 ml of artificial graphite powder was placed in a cylinder with a cross-sectional area of 2 cTl and molded by applying a pressure of 100 Ky/t#f using a universal testing machine. Also,
10 parts of a mixture of 95 parts by weight of electrolytic manganese dioxide powder and 5 M parts of graphite powder were mixed in the same manner as above to make 10 o o
Table 2 shows a comparison of the heights of molded bodies when molded at a pressure of Ky/cnf.

Table 1 Table 2 As for the height of the above-mentioned molded bodies, the lower the height, the better the moldability, but if one with a specific surface area of 7 m2/y or less is used, the moldability clearly deteriorates.

Next, the relationship between the specific surface area of graphite and the open circuit voltage of the battery will be explained.

95 parts by weight of electrolytic manganese dioxide and ash. Using a mixture containing 5 parts by weight of artificial graphite of 2% by weight or less, 100 LR44 type button batteries as described below were prototyped.
After storage at 0C for 40 days, it was measured at 20C and the frequency distribution of open circuit voltage is shown in Table 3.

From Table 3, it is clear that when the specific surface area of graphite is 13 m'/y or more, the open circuit voltage is unsatisfactory.

Next, the results of comparing various performances of batteries will be explained.

FIG. 1 shows an LR44 type almanganese battery.

Reference numeral 1 denotes a positive electrode formed from a mixture of manganese dioxide and graphite powder, which is closely attached to a nickel-plated iron container 2. 3 is a positive electrode current collecting ring.

4 is a separator made of a bovine permeable membrane such as cellophane, which is in close contact with the upper surface of the positive electrode 1. 5 is a liquid-containing material on the negative electrode side, which is made of nylon nonwoven fabric. 6 is a gel-like negative electrode prepared by kneading frozen zinc powder, 100 to 200 meshes of sodium polyacrylate, and an electrolyte. 7 is a sealing plate that also serves as a negative electrode terminal, and 8 is a nylon gasket.

This battery has a diameter of 11-611a + a height of 5.4M,
The nominal capacity is 1oomAh. The electrolytic solution used was a 40% by weight aqueous solution of bulky potash in which ZnO was dissolved to near saturation.

Table 4 shows the purity (ash content) and specific surface area of the graphite used here.

Using each graphite, a mixture with a mixing ratio of 2 to 10% by weight with respect to manganese dioxide was prepared, and the above-mentioned battery was prototyped.

Table 4: After that, it was aged at 45C for about 1 hour to maintain a well-balanced electrolyte on the separator layer and the interface between the positive and negative electrodes, and to promote uniform hydration on the inner surface of the negative electrode sealing plate.

The battery prototyped in this way was subjected to intermittent rapid discharge (pulse discharge) with a 26Ω resistor as a load at -200℃, discharging for 2 seconds and resting for 1 second, until the battery voltage reached 0.
The time required to reach 75V was investigated. In addition, continuous discharge was performed with a resistance of 15Ω as a load, and the discharge operating voltage was 1.3.
The low rate discharge time until reaching ov was also investigated.

FIG. 2 shows the relationship between the graphite content of the positive electrode and the intermittent rapid discharge time at -20C. In this figure, all solid lines indicate the discharge time immediately after trial production, and dotted lines indicate the discharge time after storage at 60C for 4 days.

Furthermore, Table 5 shows the open circuit voltage and 15 shows the Ω continuous discharge time.

Table 6 shows the maximum value of intermittent sudden discharge time in the future. In this region, since the content of graphite is large, the theoretical filling capacity of the positive electrode is reduced, and in the case of low rate 15Ω load discharge, the discharge time is significantly shorter than the initial stage, and the deterioration after storage is also significant. This is caused by impurities (ash) in graphite, which accelerates the decrease in open circuit voltage.

On the other hand, artificial graphite B has a specific surface area of 11.3 m'/9 and an ash content as low as 0.1 s%, and the maximum value of the low-temperature rapid discharge time after storage is at an addition rate of 4 to 5% by weight. And considering the open circuit voltage and low rate discharge time, it is 4 to 6% by weight.
is the optimal range. In this way, since graphite B can be added at a small addition rate, the theoretical filling capacity of the positive electrode increases, the low rate discharge time becomes longer, and the open circuit voltage is the highest at 1.60V immediately after storage, resulting in a stable product with little deterioration even after storage. shows performance.

Even with the same artificial graphite, in the case of C, the specific surface area is 18.1 m'
/ y, the contact area increases when mixed with manganese dioxide, and as the specific surface increases, adsorbed gases and moisture, which are volatile components, inevitably increase, and these act as a type of impurity, causing self-destruction. Due to the acceleration of discharge,
The drop in open circuit voltage is greater than that of B, which is the same artificial graphite, and the low rate discharge time is also shorter.

Effects of the Invention As described above, according to the present invention, a high-capacity button-shaped alkaline manganese battery with stable storage performance and excellent electrical discharge characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional side view of a main part of a button-shaped battery according to an example, and FIG. 2 shows the relationship between various graphite content ratios in the positive electrode and intermittent rapid discharge time at low temperatures. 1...Positive electrode, 4...Separator, 5...
...Liquid-containing material, 6...Negative electrode. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1

Claims (1)

[Claims] A positive electrode containing manganese dioxide as an active material and graphite as a conductive material is provided, and the graphite has a specific surface area of 8 to 12 m''/9.
A button-type alkaline manganese battery which is made of artificial graphite and has a positive electrode graphite content of 4 to 6% by weight.