JP2925589B2 - Alkaline manganese battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an alkaline manganese battery, and more particularly, to an improvement in a binder of a positive electrode mixture thereof.

[Conventional technology]

Conventionally, in order to improve the weighing property and moldability, the positive electrode mixture of alkaline manganese batteries has been prepared by wet-forming a positive electrode material consisting of manganese dioxide as a positive electrode active material, graphite powder as a conductive additive, and carbon black. The resulting mixture was extruded with an extrusion granulator having an extrusion hole having a diameter of 0.5 to 1.0 mm into granules, and the obtained granules were classified and adjusted to a predetermined particle size range. And then,
In order to prevent the granulated material from powdering, a water-soluble binder (binder) having a pasty property such as sodium polyacrylate or carboxymethylcellulose is added at the time of compounding the positive electrode material so as to increase the binding force between the positive electrode materials. (For example, JP-A-61-2266).

However, since the water-soluble binder absorbs the electrolyte in the battery, the molded positive electrode mixture absorbs the electrolyte and swells and softens, thereby increasing the internal resistance of the battery and deteriorating the discharge performance. A problem occurred. In other words, the positive electrode mixture swells due to the absorption of the electrolytic solution and softens, thereby reducing the degree of adhesion to the positive electrode can and the electron conductivity inside the positive electrode mixture due to a conductive auxiliary agent such as graphite powder or carbon black. The internal resistance increases, and the electrolyte solution is absorbed by the positive electrode mixture and moves to the positive electrode side, so that the electrolyte solution near zinc, which is the negative electrode active material, runs short and the discharge reaction on the negative electrode side is sufficiently performed. It does not progress, and the discharge performance is reduced, for example, the discharge duration is shortened. Such a decrease in the wet strength of the molded positive electrode mixture in the battery proceeds with the passage of time, and the decrease in the battery performance based on the decrease is particularly noticeable after storage.

Therefore, the present inventors previously used low molecular weight tetrafluoroethylene resin powder as a binder for the positive electrode mixture, and added this low molecular weight tetrafluoroethylene resin powder to the total weight of manganese dioxide and the conductive additive. By adding 0.3 to 3% by weight of the positive electrode mixture, it is possible to suppress an increase in internal resistance due to the absorption of the electrolyte of the positive electrode mixture and a decrease in the discharge performance due to the movement of the electrolyte toward the positive electrode mixture, and a patent application has already been made. (Japanese Patent Application No. 63-44958).

That is, a positive electrode active material such as manganese dioxide powder, graphite powder, a conductive auxiliary such as carbon black, and the above low molecular weight ethylene tetrafluoride resin powder are mixed with a small amount of potassium hydroxide (KO).
H) Aqueous solution or caustic soda (NaOH) aqueous solution and water are added and mixed. Is added to prevent corrosion), and the obtained positive electrode mixture is extruded with an extrusion granulator and granulated, and the moisture is dried and adjusted to an appropriate moisture value with good moldability and weighing property. , Filled into a molding die and molded into a desired shape such as a ring shape, inserted into a positive electrode can, and thereafter, when a battery is manufactured according to a conventional method, the low molecular weight ethylene tetrafluoride resin powder Is less absorbent than conventional aqueous binders such as sodium polyacrylate and carboxymethyl cellulose, so that the positive electrode mixture after molding requires electrolyte in the battery. Or reduces the degree of adhesion between the positive electrode can by swelling absorption above, there is no such thing as reduced electron conductivity in the positive electrode mixture. Therefore,
Since the electrolyte on the negative electrode side is not unnecessarily absorbed by the positive electrode mixture, a sufficient electrolyte solution is secured around zinc, which is the negative electrode active material, and the discharge reaction on the negative electrode side proceeds sufficiently, so that the discharge performance is improved. Is not reduced.

[Problems to be solved by the invention]

By using the low molecular weight tetrafluoroethylene resin powder as a binder for the positive electrode mixture as described above, the constituent materials of the positive electrode mixture are bound, powdering of the granulated material is prevented, and the positive electrode mixture after molding is also used. The low molecular weight ethylene tetrafluoride resin powder does not contribute to the discharge reaction, and the addition thereof reduces the filling amount of the positive electrode active material. As a result, the discharge capacity is reduced, and the conductive material has no conductivity, which causes a reduction in electron conductivity inside the positive electrode mixture.

Therefore, the present invention uses the low-molecular-weight ethylene tetrafluoride resin powder in a smaller amount to contribute to the improvement of the weighing property and moldability of the positive electrode mixture, and the positive electrode mixture after molding is used in the battery. It is an object of the present invention to provide an alkaline manganese battery that does not collapse.

[Means for solving the problem]

The present invention uses a low molecular weight ethylene tetrafluoride resin powder as a binder of the positive electrode mixture, and the low molecular weight tetrafluoroethylene resin powder is used in an amount of 0.3% by weight or more based on the total weight of manganese dioxide and the conductive additive. The positive electrode mixture mixed in powder form with less than 10% by weight is flaked with a roll, and this is crushed and granulated for use.
The above object has been achieved.

That is, Japanese Patent Application No. 63-44958 filed earlier by the present applicant.
In the invention of No. (hereinafter referred to as the "prior application invention"), granulation for improving the weighing property and moldability of the positive electrode mixture was examined by extrusion granulation using an extrusion granulator, and thus the preparation of the positive electrode mixture In doing so, a wet mixture in which water is added to the positive electrode material is used, so in order to prevent the granulated material from collapsing, the low molecular weight ethylene tetrafluoride resin powder is added to the total weight of manganese dioxide and the conductive additive. Although it was necessary to add 0.3% by weight or more, granulation was performed by forming the positive electrode mixture mixed in powder form into flakes with a roll, and then pulverizing the flakes. Even if the added amount is less than 0.3% by weight based on the total weight of manganese dioxide and the conductive additive, powdering of the granular material can be prevented.
In other words, when the positive electrode mixture is formed into flakes and granulated, the positive electrode mixture receives a large compressive force when passing through the roll gap, and becomes flakes. It becomes denser than the granulated material, and the granular material obtained by crushing it is also dense and does not easily powder, and also when molding using the positive electrode mixture, Since the positive electrode mixture can be highly filled in the mold, and the molded positive electrode mixture is also molded at a high density, the amount of the low molecular weight ethylene tetrafluoride resin powder is added to the total weight of manganese dioxide and the conductive additive. If the amount is less than 0.3% by weight, it is possible to prevent the molded positive electrode mixture from collapsing in the battery.

The low molecular weight tetrafluoroethylene resin powder used as a binder of the positive electrode mixture in the present invention is the same as in the case of the prior application, but the molecular weight is said to be in the range of tens of thousands to hundreds of thousands, Compared with ordinary tetrafluoroethylene resin, that is, high molecular weight tetrafluoroethylene resin having a molecular weight on the order of several millions, it has a lower molecular weight, is more flexible, and has the property that particles are bound by compression. . In addition, the low molecular weight ethylene tetrafluoride resin does not have reactivity with manganese dioxide, and therefore does not react with manganese dioxide to cause a voltage drop unlike a conventional water-soluble binder. Furthermore, since the low molecular weight tetrafluoroethylene resin has a small coefficient of friction and good lubricity,
Since the fluidity of the positive electrode mixture during molding is good and the variation in the filling amount in the molding die is small, the variation in battery performance is reduced. Although the method for producing such a low molecular weight ethylene tetrafluoroethylene resin and the detailed molecular weight range have not been disclosed at present, specific products include, for example, Lubron L-2 and Lubron manufactured by Daikin Industries, Ltd. L-5 (all are trade names) are commercially available.

Instead of such a low molecular weight ethylene tetrafluoride resin powder, for example, it is conceivable to use a dispersion-based tetrafluoroethylene resin as a binder as used in an organic electrolyte-based lithium battery, In the case of a dispersion-based tetrafluoroethylene resin, when it is brought into contact with a high-concentration alkaline solution, the tetrafluoroethylene resin aggregates and cannot be uniformly dispersed, and cannot be used in an alkaline battery at all.

In the present invention, the addition amount of the low-molecular-weight tetrafluoroethylene resin powder is set to 0.1% by weight or more and less than 0.3% by weight based on the total weight of manganese dioxide and the conductive additive. If the amount of the added ethylene resin powder is less than 0.1% by weight, the binding effect of the low molecular weight tetrafluoroethylene resin powder is small even if the particles are granulated through flakes, and the molded positive electrode mixture is not used in the battery. This is because there is a possibility that the film may be disintegrated and the adhesion to the positive electrode can decrease, or the electron conductivity in the positive electrode mixture may decrease and the internal resistance may increase. Further, the upper limit of the amount of the low molecular weight tetrafluoroethylene resin powder to be added is less than 0.3% by weight based on the total weight of the manganese dioxide and the conductive auxiliary agent. This is because a decrease in discharge capacity and an increase in internal resistance occur in accordance with an increase in the addition amount of the molecular weight tetrafluoroethylene resin powder.

〔Example〕

Next, the present invention will be described in more detail with reference to examples.

Example 1 80 parts by weight of manganese dioxide powder, 10 parts by weight of phosphorous graphite powder, 0.18 parts by weight of low molecular weight ethylene tetrafluoride resin powder and 5 parts by weight
Mix for 30 minutes, and then add
Parts by weight were added and mixed for another 10 minutes. The low molecular weight tetrafluoroethylene resin powder is Lubron L-2 (trade name) manufactured by Daikin Industries, Ltd., and the amount of the low molecular weight tetrafluoroethylene resin powder is based on the total weight of manganese dioxide and phosphorous graphite. On the other hand, it is 0.2% by weight.

The positive electrode mixture obtained as described above is compressed at a compression pressure of 1.5 t / c.
flakes between the two rolls prepared in
This flake was pulverized and classified to obtain a granular positive electrode mixture.

2.1 mg of the above positive electrode mixture was filled in a mold and pressed to form a molding density.
3.2 g / cm ² , 8.3 mm in inner diameter, 12.4 mm in outer diameter, 10 mm height, formed into a ring shape, insert four ring-shaped positive electrode mixture into the positive electrode can along its inner peripheral surface, Insert the core rod into the hollow part of the agent, lower the punch slidably mounted on the outer periphery of the core rod, press the positive electrode mixture from above, make it adhere to the inner peripheral surface of the positive electrode can, pull up the punch, and lift the core rod. After being pulled out, the opening of the positive electrode can is bent to form a groove near the opening end, and then a cup-shaped separator is inserted into the hollow portion of the positive electrode mixture, and the electrolytic solution and the negative electrode agent are injected into the hollow portion of the separator. After filling, an AA (LR6) alkaline manganese battery having the structure shown in FIG. 1 was manufactured according to a conventional method.

In FIG. 1, (1) is a positive electrode mixture, and the positive electrode mixture (1) is formed into a ring shape using manganese dioxide as a positive electrode active material and low molecular weight fluorinated ethylene resin powder as a binder as described above. Thereafter, four of the positive electrode cans are inserted into the positive electrode can (2) so as to be stacked, and pressed from above to make close contact with the inner peripheral surface of the positive electrode can (2). These are adhered to each other.
(3) is a separator, (4) is a negative electrode agent, and this negative electrode agent (4) is a gel formed by adding a soda salt of carboxymethylcellulose as a gelling agent to a calcined zinc powder and a high-concentration aqueous solution of potassium hydroxide. It is composed of a mixture with an alkaline electrolyte prepared as described above. (5) is a negative electrode current collector, (6) is an annular support, and (7) is a sealing body. (8) is a negative electrode connecting plate, (9) is a negative electrode terminal plate, (10) is an insulating ring, (1)
1) and (12) are heat-shrinkable resin tubes, (13) is a positive electrode terminal plate, (14) is a metal outer can, and (15) is an insulating ring.

The ring-shaped positive electrode mixture was placed horizontally, and when a load was applied from above to examine the load when the ring-shaped positive electrode mixture was broken, the load at the time of destruction was 560 g,
This positive electrode mixture did not collapse or break during battery assembly.

Comparative Example 1 80 parts by weight of manganese dioxide powder, 10 parts by weight of phosphorous graphite powder and 0.45 parts by weight of sodium polyacrylate powder were mixed for 5 minutes, then 2.5 parts by weight of a 35% by weight aqueous solution of potassium hydroxide and 13 parts by weight of ion-exchanged water Parts were added and mixed for another 10 minutes. The addition amount of this sodium polyacrylate is 0.5% by weight based on the total weight of manganese dioxide and phosphorous graphite.

The positive electrode mixture obtained as described above was extruded by an extrusion granulator, granulated, and dried to adjust the water content to 3% by weight.

AA-size alkali metal was used in the same manner as in Example 1 except that sodium polyacrylate was used as the binder, the wet mixture was performed, and the positive electrode mixture granulated by the extrusion granulator was used.
A manganese battery was manufactured.

The ring-shaped positive electrode mixture was horizontally arranged, and a load was applied when a load was applied from above to cause breakage of the ring-shaped positive electrode mixture. The load at the time of destruction was 600 g.

Comparative Example 2 AA-size alkaline manganese batteries were produced in the same manner as in Comparative Example 1, except that carboxymethyl cellulose was used as the binder instead of sodium polyacrylate in Comparative Example 1.

The ring-shaped positive electrode mixture was placed horizontally, and a load was applied when a load was applied from above to break the ring-shaped positive electrode mixture. The load at the time of destruction was 550 g.

Initially, the batteries of Example 1 and the batteries of Comparative Examples 1 and 2 were stored at 60 ° C for 20 days and after storage at 60 ° C for 40 days.
Short-circuit current at 10 ° C, continuous discharge duration up to 0.9 V at discharge resistance of 10Ω and intermittent discharge at -20 ° C and 2Ω (5 seconds discharge)
Table 1 shows the measurement results of the discharge time up to a final voltage of 0.9 V in the discharge.

As shown in Table 1, the battery of Example 1 using low-molecular-weight tetrafluoroethylene resin powder as a binder used the battery of Comparative Example 1 using sodium polyacrylate as a binder and carboxymethyl cellulose as a binder. Compared with the battery of Comparative Example 2, the short-circuit current was large (that is, the internal resistance was small), and particularly, the decrease in short-circuit current due to storage was small, and the decrease in discharge duration due to storage was also small. This is because, in the battery of Example 1, the low molecular weight ethylene tetrafluoride resin powder used as the binder has a low absorbability of the electrolytic solution, and therefore the positive electrode mixture does not absorb the electrolytic solution and swells. The decrease in the adhesion between the mixture and the positive electrode can and the decrease in electron conductivity inside the positive electrode mixture are small, and the positive electrode mixture does not absorb the electrolytic solution more than necessary. This is because a sufficient electrolytic solution was secured and the discharge reaction proceeded smoothly.

Further, as shown in Table 1, the battery of Example 1 has a longer discharge time in the intermittent discharge at −20 ° C. and 2Ω than the batteries of Comparative Examples 1 and 2. This is because in the battery of Comparative Example 1 using sodium polyacrylate as a binder and the battery of Comparative Example 2 using carboxymethyl cellulose as a binder,
As described above, the positive electrode mixture absorbs the electrolyte and swells to increase the internal resistance, and the electrolyte near the zinc becomes insufficient due to the electrolyte absorption of the positive electrode mixture, and the discharge reaction on the negative electrode side proceeds sufficiently. In addition to this, it is considered that this is due to the fact that the viscosity of the electrolyte increases due to the elution of the binder into the electrolyte, and the ionic conductivity in the electrolyte decreases.

Next, changes in short-circuit current and discharge duration with changes in the amount of low molecular weight ethylene tetrafluoride resin powder added will be described.

Examples 2-3 and Comparative Example 1 The addition amount of the low molecular weight ethylene tetrafluoride resin powder was 0.05% by weight, based on the total weight of manganese dioxide and phosphorous graphite.
AA-size alkaline manganese batteries were produced in the same manner as in Example 1 except that the amounts were changed to 10% by weight and 0.29% by weight.

Short-circuit current and discharge resistance of these batteries at 20 ° C
Table 2 shows the results of examining the discharge duration when the battery was continuously discharged to a final voltage of 0.9 V with Ω.

As shown in Table 2, the battery of Example 2 in which the addition amount of the low molecular weight tetrafluoroethylene resin powder was 0.10% by weight and the battery of Example 3 in which the addition amount of the low molecular weight tetrafluoroethylene resin powder was 0.29% by weight were used. The battery had a large short-circuit current (that is, a low internal resistance) and a long discharge duration, but the battery of Comparative Example 1 in which the amount of the low molecular weight tetrafluoroethylene resin powder added was 0.05% by weight had a short-circuit current of Smaller, shorter discharge duration. This is because in the battery of Comparative Example 1 in which the amount of the low molecular weight tetrafluoroethylene resin powder added was small, the binding effect of the low molecular weight tetrafluoroethylene resin powder was not sufficient, and the molded positive electrode mixture collapsed in the battery. This is considered to be because the adhesion to the positive electrode can was reduced, the electron conductivity inside the positive electrode mixture was reduced, and the internal resistance was increased.

Further, the ring-shaped positive electrode mixture of the batteries of Examples 2 to 3 and Comparative Example 1 was horizontally arranged, and a load was applied when a load was applied from above to break the ring-shaped positive electrode mixture. The results are shown in Table 3.

As shown in Table 3, the addition amount of the low molecular weight tetrafluoroethylene resin powder of the battery of Example 2 in which the addition amount of the low molecular weight tetrafluoroethylene resin powder was 0.10% by weight was 0.29% by weight. % Of the ring-shaped positive electrode mixture of the battery of Example 3 is:
Although the load at the time of breakage exceeded 500 g, the load at the time of breakage occurred in the ring-shaped positive electrode mixture of the battery of Comparative Example 1 in which the addition amount of the low molecular weight tetrafluoroethylene resin powder was 0.05% by weight. It was 420 g, indicating that the strength of the positive electrode mixture was low, and the positive electrode mixture collapsed in the battery, and the discharge performance was likely to be reduced.

〔The invention's effect〕

As described above, in the present invention, using a low molecular weight ethylene tetrafluoride resin powder as a binder of the positive electrode mixture,
By adding the above low molecular weight ethylene tetrafluoride resin powder to the total weight of manganese dioxide and the conductive additive in an amount of 0.1% by weight or more and less than 0.3% by weight, the swelling or collapse of the positive electrode mixture in the battery is prevented. As a result, an alkaline manganese battery having low internal resistance and good discharge performance could be provided.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an embodiment of the alkaline manganese battery of the present invention. 1 ... Positive electrode mixture, 3 ... Separator, 4 ... Negative electrode agent

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 4/08 H01M 4/62

Claims (1)

(57) [Claims] In an alkaline manganese battery using zinc as a negative electrode active material and manganese dioxide as a positive electrode active material, low molecular weight ethylene tetrafluoride resin powder is used as a binder for a positive electrode mixture using manganese dioxide as a positive electrode active material. Using the above low molecular weight ethylene tetrafluoride resin powder, add 0.1% by weight or more and less than 0.3% by weight with respect to the total weight of manganese dioxide and the conductive additive and mix the powdered positive electrode mixture into flakes with a roll. An alkaline manganese battery characterized in that it is granulated and used by grinding.