JP2005129309A - Positive electrode mixture of alkaline battery, and alkaline battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkaline battery having superior electric discharge performance using a positive electrode mixture without increasing an amount of addition of a binder, or without enhancing molding density excessively to secure sufficient molding strength. <P>SOLUTION: In the positive electrode mixture 16 of the alkaline battery molded into a circular solid by mixing a manganese dioxide, graphite, a water-soluble binder, and a potassium hydroxide aqueous solution, when the concentration of 3 wt% of the mixture is added to a 40% potassium hydroxide aqueous solution, the water-soluble binder showing a physical property in which the viscosity of its aqueous solution becomes 200 pa s or more is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive electrode mixture of an alkaline battery and an alkaline battery obtained by mixing manganese dioxide, graphite, a water-soluble binder, and an aqueous potassium hydroxide solution into a cyclic solid, and a cylinder such as LR6 (AA dry battery). This is particularly effective when applied to a type alkaline battery.

  For example, an alkaline battery such as LR6 is manufactured using a positive electrode mixture containing manganese dioxide as a main active material, an alkaline electrolyte composed of a high-concentration potassium hydroxide aqueous solution, and a negative electrode mixture containing gelled zinc as a main active material. The

  In this type of alkaline battery, a positive electrode mixture so-called positive electrode core formed into a cyclic solid is used. The positive electrode mixture is inserted into a bottomed cylindrical metal battery can. A cylindrical separator is disposed inside the inserted positive electrode mixture, and a gel-like negative electrode mixture is filled inside the separator to form an alkaline power generation element.

  The positive electrode mixture is inserted into the battery can in a press-fitted state. As a result, the battery can comes into close contact with the positive electrode mixture and serves as the positive electrode current collector and the positive electrode terminal. The opening of the battery can is sealed using a negative electrode terminal plate and a sealing gasket. A rod-shaped negative electrode current collector is erected and fixed by spot welding or the like inside the battery of the negative electrode terminal plate. This negative electrode current collector penetrates into the negative electrode mixture.

  The positive electrode mixture is prepared by mixing manganese dioxide, graphite, a water-soluble binder, and an aqueous potassium hydroxide solution, treating the mixture through processes such as compacting, crushing, and granulating, and then forming an annular (tubular) solid body. It can be obtained by molding. It is necessary to ensure sufficient molding strength (core strength) in the positive electrode mixture in order to prevent breakage such as cracks in the battery assembly process. In order to ensure this molding strength, the molding density of the molded body (positive electrode mixture) is increased or a binder is added (see Patent Document 1).

There are many kinds of binders such as PA (polyacrylic acid), CMC (carboxymethylcellulose), sodium polyacrylate, PTFE (polytetrafluoroethylene), PE (polyethylene), etc. Used a binder selected from the various materials. For example, Patent Document 1 discloses the use of a binder specified by a substance name such as PA or CMC.
JP-A-10-144304

  In the alkaline battery described above, when the molding density is increased in order to ensure the molding strength (positive electrode core strength) of the positive electrode mixture, the liquid absorbency of the electrolytic solution is deteriorated and the discharge performance is deteriorated. Further, when a large amount of binder is added to ensure the positive electrode core strength, the filling amount of the positive electrode active material is reduced and the discharge performance of the battery is deteriorated. Since the binder itself does not contribute to the reaction of the battery, the amount of the positive electrode active material is reduced by the amount added. However, there is a contradiction that if the amount of the binder added is small, the required positive electrode core strength cannot be ensured.

  In order to obtain the required positive electrode core strength, the molding density needs to be 3.1 g / cc or more. In order to obtain the required positive electrode core strength at a molding density lower than that, it is necessary to increase the amount of the binder added. However, as the amount of the binder added increases, the discharge performance deteriorates due to the reduction of the active material.

  When trying to obtain the required positive electrode core strength by increasing the molding density, the molding density must be at least higher than 3.3 g / cc. However, if the molding density is increased to that extent, this time, the deterioration of the discharge performance due to the decrease in the liquid absorbency of the electrolytic solution becomes obvious.

  The present invention has been made in view of the above contradictory problems, and its purpose is to ensure sufficient molding strength without increasing the amount of binder added and without excessively increasing the molding density. An object of the present invention is to provide a positive electrode mixture for alkaline batteries. Moreover, it is providing the alkaline battery excellent in discharge performance by using the positive mix.

  The means according to the present invention is a mixture of manganese dioxide, graphite, a water-soluble binder, and an aqueous potassium hydroxide solution, which is formed into a cyclic solid. It is characterized by using a water-soluble binder exhibiting physical properties such that the viscosity of the aqueous solution becomes 200 pa · s or more when added at a concentration of.

  In the above means, in order to optimize the present invention, it is desirable that the amount of the water-soluble binder added is 0.1 wt% to 0.3 wt% with respect to manganese dioxide as the positive electrode active material. Similarly, it is desirable that the molding density of the positive electrode mixture is 3.1 g / cc to 3.3 g / cc.

  The above means inserts a positive electrode mixture formed into a ring-shaped solid into a bottomed cylindrical metal battery can also serving as a positive electrode current collector and a positive electrode terminal in a press-fit state, and a separator is placed inside the positive electrode mixture. It is particularly effective when applied to an alkaline battery in which a power generation element is formed by placing and loading a gelled negative electrode mixture inside the separator.

  It is possible to provide a positive electrode mixture for an alkaline battery in which sufficient molding strength can be secured without increasing the amount of binder added and without excessively increasing the molding density. Moreover, the alkaline battery excellent in discharge performance can be provided by using the positive electrode mixture.

  FIG. 1 is a cross-sectional view showing an outline of an alkaline battery to which the technology of the present invention is applied. A battery 10 shown in the figure is an alkaline battery called LR6 (AA type dry battery), which has a cylindrical shape with a bottom and a metal battery can 11 serving as a positive electrode current collector and a positive electrode terminal, and a power generation element 15 including an alkaline electrolyte. A plate-shaped (or hat-shaped) metal negative electrode terminal plate 21, a rod-shaped metal negative electrode current collector 25, an electrically insulating resin sealing gasket 30, and the like.

  The power generation element 15 includes a positive electrode mixture 16 using manganese dioxide as a positive electrode active material (positive electrode active material), a separator 17 impregnated with an alkaline electrolyte, and a negative electrode mixture 18 using gelled zinc as a negative electrode active material. And formed. The positive electrode mixture 16 is formed into an annular (tubular) solid body and is inserted into the battery can 11 in a press-fitted state. A cylindrical separator 17 is disposed inside the positive electrode mixture 16, and a gel-like negative electrode mixture 18 is filled inside the separator 17. Electricity is generated by a discharge reaction between manganese dioxide in the positive electrode mixture 16 and zinc in the negative electrode mixture 18 in the presence of an alkaline electrolyte. A 40% aqueous potassium hydroxide solution is used as the alkaline electrolyte.

  The battery can 11 is a nickel-plated steel plate that is pressed into a bottomed cylindrical shape (deep drawing). A positive electrode mixture 16 is inserted into the battery can 11 in a press-fit state. Thereby, the battery can comes into close contact with the positive electrode mixture and serves as the positive electrode current collector and the positive electrode terminal. The negative electrode terminal plate 21 is dish-shaped (or hat-shaped), and a rod-shaped metal current collector 25 is erected and fixed by spot welding or the like on the inner side surface thereof, that is, the battery side surface. The current collector 25 is inserted into the negative electrode mixture 18.

  The gasket 30 is formed by molding an electrically insulating resin such as nylon in a substantially disk shape, and is interposed between the battery can 11 and the negative electrode terminal plate 21 in a pressurized state to seal the inside of the battery can 11. Stop. The opening of the battery can 11 is bent (curled) inward. By this bending process, the peripheral portion of the gasket 30 is sandwiched between the battery can 11 and the negative electrode terminal plate 21, and the battery can 11 is hermetically sealed.

  The positive electrode mixture 16 is formed by mixing manganese dioxide, graphite, a water-soluble binder, and an aqueous potassium hydroxide solution, treating the mixture in steps such as compacting, crushing, and granulating, and then molding the mixture into a circular solid. It is created by. In this case, as the binder, a water-soluble binder is used in which, when added to a 40% potassium hydroxide aqueous solution at a concentration of 3% by weight, the aqueous solution has a viscosity of 200 pa · s or more.

  For binders, if classified by substance (substance name), for example, PA (polyacrylic acid), CMC (carboxymethylcellulose), sodium polyacrylate, PTFE (polytetrafluoroethylene), PE (polyethylene), etc. There are different types. Conventional positive electrode mixtures have been produced using binders selected from the various substances. For example, a binder specified by a substance name such as PA or CMC has been used (for example, see the above-mentioned Patent Document 1).

  However, the binder specified by the substance name such as PA or CMC, even with the same substance name, depends on various factors such as the degree of polymerization of the polymer and the molecular size, for example, due to its physical properties, especially the viscosity characteristics shown under specific conditions. There are various types or grades. In other words, the binder has various physical factors that cannot be specified only by the substance name PA or CMC.

  The binder used in the present invention is not specified by a substance name that has been conventionally disclosed, but is a specific water-soluble binder that is limited by physical property factors that cannot be specified only by the substance name, in particular, by viscosity characteristics under specific conditions. That is, a water-soluble binder is used which exhibits physical properties such that when added to a 40% potassium hydroxide aqueous solution at a concentration of 3% by weight, the aqueous solution has a viscosity of 200 pa · s or more.

  The water-soluble binder having such physical property factors is used for the first time in the positive electrode mixture 16 for alkaline batteries of the present invention. By using a binder having this specific physical property, the amount of the binder added is increased. The positive electrode mixture for an alkaline battery having sufficient molding strength could be produced without excessively increasing the molding density. By using this positive electrode mixture 16, an alkaline battery with excellent discharge performance could be obtained.

  That is, by using a water-soluble binder exhibiting the above physical properties, even when the addition amount of the water-soluble binder is 0.1 wt% to 0.3 wt% with respect to manganese dioxide as the positive electrode active material, sufficient The molding strength could be secured. Further, by using a water-soluble binder in the above physical property range, sufficient molding strength (core strength) can be ensured even when the molding density of the positive electrode mixture is 3.1 g / cc to 3.3 g / cc. did it. Examples of the substance type of the water-soluble binder that can have the above physical property range include PA and / or CMC. That is, PA and / or CMC can be a water-soluble binder having the above physical property range by adjusting various conditions such as polymerization degree and molecular size. The method for providing the physical property range is not particularly limited in the present invention.

  Examples of the present invention will be described below.

First, two types of binders A and B were prepared. Binders A and B were classified according to the aqueous solution viscosity when the binder was added to a 40% potassium hydroxide aqueous solution at a concentration of 3% by weight.
FIG. 2 shows a change state of the aqueous solution viscosity with respect to an increase in the addition amount when a binder is added to a 40% aqueous potassium hydroxide solution. The viscosity was measured using a B-type rotational viscometer.
The binder of A, as indicated by the graph line A in the figure, had an aqueous solution viscosity greatly exceeding 200 Pa · s when the addition amount was 3% by weight. As shown by the graph line B in the figure, the binder of B had an aqueous solution viscosity of only 50 Pa · s and 100 Pa · s, even when the addition amount was increased to 3 wt%.

Next, a positive electrode mixture to which 0.1 wt% (wt%) of A binder was added (positive electrode core for LR6, the same applies hereinafter), a positive electrode mixture to which 0.2 wt% was added, and 0.3 wt% was added Each positive electrode mixture was prepared, and the relationship between the positive electrode core strength (kgf) and the molding density (g / cc) was examined for each positive electrode mixture.
Similarly, a positive electrode mixture to which 0.1 wt% (wt%) of B binder was added, a positive electrode mixture to which 0.2 wt% was added, and a positive electrode mixture to which 0.3 wt% was added were respectively prepared. The relationship between the positive electrode core strength (kgf) and the molding density (g / cc) was examined for each positive electrode mixture. In addition, all the addition amount of a binder is a weight ratio (%) with respect to manganese dioxide.

  FIG. 3 shows a graph in which the change state of the molding density (g / cc) with respect to the positive electrode core strength (kgf) is plotted for each positive electrode mixture. According to the figure, the group added with the binder A (binder A group) and the group added with the binder B (binder B group) have the same binder addition amount and molding density, but the molding strength is the same. It can be seen that the former (binder A group) significantly exceeds the latter (binder B group).

  The binder addition amount of 0.3% by weight is an upper limit at which the adverse effect on the discharge performance due to the reduction of the positive electrode active material does not manifest. Further, the molding density of 3.30 g / cc is an upper limit at which the adverse effect on the discharge performance due to the deterioration of the liquid absorbency of the electrolytic solution does not become apparent. Each of the positive electrode mixture of the binder A group is a positive electrode of the binder B group with a small amount of binder addition (0.1% by weight) and a low molding density (3.10 g / cc) which are sufficiently more than the upper limit. Molding strength (approximately 0) higher than the molding strength (approximately 0.80 kgf to approximately 0.85 kgf) obtained by the mixture at the upper limit addition amount (0.3 wt%) and the molding density (3.30 g / cc). .85 kgf to about 0.87 kgf).

  FIG. 4 shows the discharge performance of an alkaline battery (LR6 dry battery shown in FIG. 1) using the positive electrode mixture of the binder A group, with the binder addition amount (0.1 wt%, 0.2 wt%, 0.3 wt%). %, 0.4% by weight, 0.5% by weight) of the test results actually measured for each graph.

  In this discharge performance test, the discharge time under a constant resistance load (2Ω / 75Ω) was measured. The evaluation of the test results was performed by index display with the discharge time of an alkaline dry battery (LR6) using a positive electrode mixture in which the binder addition amount of A was 0.1% by weight as 100. In addition, about the positive electrode mixture without binder addition and the positive electrode mixture using the binder of B, since the positive electrode core intensity | strength was not enough, it broke in the process of inserting a positive electrode core in a battery can, and a battery was Could not be created.

  According to the test results shown in the figure, in 2Ω continuous discharge, there was no particular difference in the amount of binder added. However, in the 75Ω continuous discharge, it was recognized that the discharge performance tended to deteriorate as the amount of binder added increased. This is considered that the difference in the discharge capacity due to the added amount of the binder appeared. It can be said that a difference in discharge capacity due to the amount of active material tends to appear in the 75Ω continuous discharge.

  As described above, by using a water-soluble binder having specific physical properties, the addition amount of the water-soluble binder is in the range of 0.1 wt% to 0.3 wt% with respect to manganese dioxide as the positive electrode active material. However, the molding density of the positive electrode mixture is in the range of 3.1 g / cc to 3.3 g / cc, and sufficient positive electrode core strength can be ensured for each.

  It is possible to provide a positive electrode mixture for an alkaline battery in which sufficient molding strength can be secured without increasing the amount of binder added and without excessively increasing the molding density. Moreover, the alkaline battery excellent in discharge performance can be provided by using the positive electrode mixture.

It is sectional drawing which shows the structural outline | summary of the alkaline battery to which the technique of this invention is applied. It is a graph which shows the physical property regarding each viscosity about the binder used by this invention, and the binder used conventionally. It is a graph which shows the relationship of the shaping | molding strength with respect to binder addition amount and a shaping | molding density about the positive mix of this invention and the conventional positive mix. It is a graph which shows the result of having evaluated the discharge performance by the positive mix of this invention for every discharge condition and binder addition amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Alkaline battery 11 Battery can 15 Electric power generation element 16 Positive electrode mixture 17 Separator 18 Negative electrode mixture 21 Negative electrode terminal board 25 Negative electrode current collector 30 Sealing gasket

Claims (4)

  When a mixture of manganese dioxide, graphite, water-soluble binder, and aqueous potassium hydroxide is mixed into a cyclic solid and added to a 40% aqueous potassium hydroxide solution at a concentration of 3% by weight in a positive electrode mixture for an alkaline battery. And a positive electrode mixture for an alkaline battery, wherein a water-soluble binder having physical properties such that the viscosity of the aqueous solution is 200 pa · s or more is used.   2. The positive electrode mixture for an alkaline battery according to claim 1, wherein the water-soluble binder is added in an amount of 0.1 wt% to 0.3 wt% with respect to manganese dioxide as a positive electrode active material.   3. The positive electrode mixture for an alkaline battery according to claim 1, wherein the molding density of the positive electrode mixture is 3.1 g / cc to 3.3 g / cc. A positive electrode mixture formed into an annular solid is press-fitted into a bottomed cylindrical metal battery can also serving as a positive electrode current collector and a positive electrode terminal, and a separator is disposed inside the positive electrode mixture. An alkaline battery in which the positive electrode mixture according to any one of claims 1 to 3 is used in an alkaline battery in which a power generation element is formed by loading a gelled negative electrode mixture inside a separator.

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