JP2013114978A - Alkaline dry cell and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline dry cell in which collapse of a positive electrode pellet is little even after storage, excellent discharge performance is ensured, and deformation is suppressed even if a thin battery case is used.SOLUTION: The alkaline dry cell includes a bottomed cylindrical battery case, a hollow cylindrical positive electrode in contact with the inner surface of the case and containing manganese dioxide powder and graphite powder, a negative electrode disposed in the hollow section of the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. The battery case has a thickness of 0.1 mm or more and less than 0.18 mm, and the ratio of the number of cross-sectional areas where crack is not observed to the number of all cross-sectional areas obtained when the cross-sectional image of the positive electrode perpendicular to the central axis of the battery case is captured along the central axis at an interval of 0.4 mm is 91-97%.

Description

  The present invention relates to an alkaline battery and a method for producing the same, and more particularly to improvement of a positive electrode used in an alkaline battery.

Alkaline batteries are inexpensive batteries that are used in a wide current range, and are widely used as power sources for electronic devices such as portable devices. For this reason, various studies have been conducted to improve the discharge performance.
In addition, alkaline batteries have excellent discharge performance even after being stored for a long period of time, and are therefore used as an emergency power source during natural disasters such as typhoons and earthquakes. In such applications, further improvement in storage performance is desirable. As one of the performance deterioration factors during storage of the alkaline battery, an increase in the resistance component in the battery can be considered.

In order to suppress the deterioration of the discharge performance after storage due to the increase in resistance, a conductive film is formed on the inner wall of the battery case or the surface of the positive electrode to improve the electronic conductivity between the positive electrode and the battery case as the positive electrode current collector. Various improvements have been made, such as enhancement.
On the other hand, with respect to means for improving battery performance by improving the positive electrode itself, for example, Patent Document 1 proposes forming a relatively large number of cracks in the positive electrode in order to improve the initial high-rate discharge performance. Patent Document 2 proposes to control the porosity of the positive electrode.

JP 2009-266661 A JP 2003-536230 A

  However, the techniques of Patent Document 1 and Patent Document 2 are insufficient to improve battery performance after storage. Specifically, in Patent Document 1, since cracks are used as an electrolyte transfer path, positive cracks are generated actively by applying a relatively large pressure to the positive electrode pellets after the positive electrode pellets are placed in the battery case. I am letting. However, when there are too many cracks, when the formed positive electrode absorbs the electrolytic solution in the battery, the positive electrode easily expands (that is, the positive electrode easily loosens), and the positive electrode collapses from the inside with the crack as a starting point. Therefore, the discharge path is cut off locally, and the discharge performance is degraded. In addition, from the viewpoint of weight reduction, use of a thin battery case has also been studied, but when a thin battery case is used, the case may be deformed if the pressure applied to the positive electrode pellet is too large.

  Also in Patent Document 2, in order to fix the positive electrode pellet in the battery case, the positive electrode pellet is pressurized after being accommodated in the battery case. When the positive electrode is fixed in the battery case by pressurization, cracks are generated in the positive electrode due to the stress. When the battery in a cracked state is stored, the positive electrode is more likely to collapse as in Patent Document 1.

  When the positive electrode collapses, the discharge path is cut off because a gap that is not filled with the electrolytic solution is formed and the moving path of the electrolytic solution is interrupted. In particular, the decrease in discharge performance after storage is significant.

  Therefore, in order to solve the above-described conventional problems, the present invention prevents the loosening of the positive electrode inside the battery, and thus has an excellent discharge performance even after the battery is stored, and a thin battery case. An object of the present invention is to provide a cylindrical alkaline dry battery in which deformation is suppressed even when using.

  One aspect of the present invention includes a bottomed cylindrical battery case, a hollow cylindrical positive electrode that is in contact with the inner surface of the battery case and includes manganese dioxide powder and graphite powder, a negative electrode disposed in a hollow portion of the positive electrode, and a positive electrode Of the positive electrode perpendicular to the central axis of the battery case, the battery case having a thickness of 0.1 mm or more and less than 0.18 mm. When cross-sectional images are taken at intervals of 0.4 mm along the central axis, the ratio of the number of cross-sectional images in which no cracks are observed to the number of all cross-sectional images obtained is 91% or more and 97% or less. The present invention relates to an alkaline battery.

Another aspect of the present invention includes (1) a step of preparing a bottomed cylindrical battery case, and (2) a step of obtaining a positive electrode mixture containing manganese dioxide powder, graphite powder, and an alkaline electrolyte, (3) A hollow cylindrical shape having an outer diameter in which the positive electrode mixture is pressure-molded, the density of manganese dioxide is 2.55 to 2.80 g / cm ³ , and the clearance from the battery case is 0.1 mm or less (4) Insert the positive electrode pellet into the battery case, and insert a cylindrical insertion pin having a diameter smaller by 0.05 to 0.1 mm than the inner diameter of the positive electrode pellet into the hollow portion of the positive electrode pellet. And, further, a step of applying a pressure of 5 to 30 MPa to the positive electrode pellet from above to obtain a hollow cylindrical positive electrode in close contact with the battery case, and (5) arranging the separator in the hollow portion of the positive electrode, Alkaline in the case And a step of injecting a solution, (6) a step of filling a negative electrode through a separator in a hollow portion of the positive electrode, and (7) a step of sealing the battery case with a sealing unit. .

  According to the present invention, it is possible to provide an alkaline dry battery that has little collapse of the positive electrode even after storage, is excellent in discharge performance, and is suppressed in deformation even when a thin battery case is used.

It is a front view which makes some cross sections the cylindrical alkaline dry battery which concerns on one Embodiment of this invention. It is a cross-sectional view of the cylindrical alkaline battery of FIG. It is a schematic longitudinal cross-sectional view which shows an example of the process (3) in the manufacturing method of the alkaline dry battery of this invention. It is a schematic longitudinal cross-sectional view which shows an example of the process (4) in the manufacturing method of the alkaline dry battery of this invention.

  The alkaline dry battery of the present invention is arranged between a bottomed cylindrical battery case, a hollow cylindrical positive electrode in contact with the inner surface of the battery case, a negative electrode disposed in the hollow part of the positive electrode, and the positive electrode and the negative electrode. A separator and an alkaline electrolyte. The battery case is a thin case having a thickness of 0.1 mm or more and less than 0.18 mm. The positive electrode contains manganese dioxide powder and graphite powder.

  In general, in an alkaline battery, a hollow cylindrical positive electrode pellet is accommodated in a bottomed cylindrical battery case, and then the positive electrode pellet is pressurized from above using a predetermined jig, so that the inner surface of the battery case is Fix in close contact. At this time, in the positive electrode obtained, a plurality of cracks are formed along the axial direction of the positive electrode. Here, the crack means a linear void having a width substantially larger than the particle diameter of the manganese dioxide powder and smaller than about 0.5 mm in the cross section.

  If such a fine crack exists, the electrolytic solution can move in the crack, and thus it has been considered that it is advantageous in suppressing a decrease in discharge performance. However, it has been found that when there are too many cracks, when the positive electrode absorbs the electrolytic solution during battery assembly, the positive electrode easily expands, and the positive electrode easily collapses from the inside starting from the crack. When the inside of the positive electrode collapses, the voids may increase excessively and voids that are not filled with the electrolytic solution may be formed. Therefore, the discharge performance is degraded. Particularly, after the battery is stored, such a collapse of the positive electrode tends to be remarkable.

  Therefore, in the present invention, the ratio of cracks formed in the positive electrode is controlled within an appropriate range. Specifically, when a cross-sectional image of the positive electrode perpendicular to the central axis of the battery case is taken at intervals of 0.4 mm along the central axis, cracks are generated with respect to the number of all cross-sectional images obtained. The ratio of the number of cross-sectional images that are not observed is controlled to 91% or more and 97% or less.

  Therefore, it is possible to prevent the positive electrode from loosening and collapsing due to the permeation of the electrolytic solution, while ensuring the movement path of the electrolytic solution in the positive electrode. When the battery is discharged after storage, the collapse of the positive electrode is usually noticeable. However, in the battery of the present invention, such a collapse of the positive electrode can be effectively suppressed. As a result, it can suppress that the utilization factor of a positive electrode falls, and can maintain the discharge performance of a battery after a preservation | save.

  In addition, when the positive electrode pellet is pressed in the battery case and brought into intimate contact with the inner surface, when a thin battery case having a thickness of 0.1 mm or more and less than 0.18 mm is used, the case is deformed, resulting in product defects. There is a case. In the present invention, as described above, when the crack ratio is controlled within a specific range, the pressure applied to the battery case is also appropriately adjusted. Therefore, even when a thin battery case is used, the deformation can be suppressed. Since a thin battery case can be used, it is easy to reduce the weight of the battery and reduce the material required for the battery case, which is advantageous in terms of cost.

  Hereinafter, an embodiment of the alkaline dry battery of the present invention will be described with reference to FIG. FIG. 1 is a front view of a cross section of a horizontal half of an alkaline battery according to an embodiment of the present invention.

  As shown in FIG. 1, the alkaline battery includes a hollow cylindrical positive electrode 2, a negative electrode 3 disposed in the hollow portion of the positive electrode 2, a separator 4 disposed therebetween, and an alkaline electrolyte (not shown). These are housed in a bottomed cylindrical battery case 1 made of a nickel-plated steel plate. A conductive film (not shown) containing graphite is formed on the smooth inner surface of the battery case 1, and the battery case 1 also serves as a positive electrode terminal.

  The positive electrode 2 is disposed in contact with the inner surface of the battery case 1, and the gelled negative electrode 3 is filled in the hollow portion of the positive electrode 2 via the separator 4. The separator 4 has a bottomed cylindrical shape and is arranged on the inner surface of the hollow portion of the positive electrode 2 to separate the positive electrode 2 and the negative electrode 3 from each other and to separate the negative electrode 3 and the battery case 1 from each other. The positive electrode 2 may include, for example, manganese dioxide as a positive electrode active material and graphite powder as a conductive material, and a mixture of these and an alkaline electrolyte. The negative electrode 3 contains zinc or zinc alloy powder as a negative electrode active material, an alkaline electrolyte, and a gelling agent.

  The opening of the battery case 1 is sealed by a sealing unit 9. The sealing unit 9 includes a negative electrode terminal plate 7, a nail-like negative electrode current collector 6 extending from the center of the inner surface thereof, and a gasket 5 disposed from the periphery of the negative electrode terminal plate 7 toward the negative electrode current collector 6. . The negative electrode current collector 6 has a nail-like shape having a head portion and a body portion, and the body portion is inserted into a through hole provided in the central cylinder portion of the gasket 5, so that the negative electrode current collector 6 The head is welded to the flat portion at the center of the negative terminal plate 7. The body of the negative electrode current collector 6 is inserted into the negative electrode 3. The opening end portion of the battery case 1 is caulked to the flange portion of the peripheral edge portion of the negative electrode terminal plate 7 via the outer peripheral end portion of the gasket 5. The outer surface of the battery case 1 is covered with an exterior label 8.

FIG. 2 shows a cross-sectional view of the cylindrical alkaline dry battery of FIG. 1, that is, a cross-sectional view perpendicular to the axial direction of the cylindrical alkaline dry battery. In addition, the cross-sectional view of FIG. 2 is a schematic diagram for clearly showing the state of cracks in the positive electrode of the cylindrical alkaline dry battery.
As described above, in an alkaline dry battery, a hollow cylindrical positive electrode pellet is accommodated in a bottomed cylindrical battery case and then fixed in the battery case by pressurization. At this time, even in the alkaline dry battery of the present invention, the crack 10 is formed in the positive electrode 2 along the axial direction of the positive electrode 2.

  The crack 10 generated inside the positive electrode 2 can be observed by, for example, a cross-sectional image taken by X-ray CT. Specifically, a cross-sectional image is taken by X-ray CT perpendicular to the central axis of the cylindrical battery case 1 in the range where the positive electrode 2 exists. This cross-sectional image is taken at intervals of 0.4 mm along the central axis of the cylindrical battery case 1. In the case of an AA alkaline battery, since the length of the positive electrode in the direction along the central axis of the cylindrical battery case is about 42 mm, about 105 cross sections are photographed.

  In a cross-sectional image of X-ray CT imaging, if there is a crack in the positive electrode region, the crack is a portion where the positive electrode mixture does not exist, and therefore has a lower luminance than the surrounding positive electrode. As shown in FIG. looks like. Therefore, the presence of the crack 10 can be confirmed by visual observation. Further, the luminance can be measured, and the presence or absence of cracks can be determined based on the difference. Note that the presence / absence of a crack is determined based on a cross-sectional image of a battery in an undischarged state.

  For example, the brightness of the crack should be expressed with reference to the brightness of the positive electrode mixture after drawing a line segment with a length of about 0.6 mm across the crack and measuring the brightness distribution on the line. Can do. That is, the maximum luminance value (positive electrode mixture portion) X and the minimum luminance value (crack portion) Y on the line segment crossing the crack are calculated, and the luminance of the crack is (Y / X) × 100 [%]. Can be represented.

  In the present invention, the ratio of the number of cross-sectional images in which no cracks are observed to the number of all cross-sectional images obtained when the cross-sectional images of the positive electrode are taken at a predetermined interval is controlled within the range of 91 to 97%. To do. As described above, by causing cracks to exist in an appropriate ratio in the positive electrode, it is possible to facilitate movement of the electrolytic solution in the positive electrode while suppressing loosening and collapse of the positive electrode in the battery. Note that the smaller the luminance of the crack, the larger the crack itself, and the greater the function as the electrolyte diffusion path.

In the present invention, when the luminance is measured for a predetermined region of the cross-sectional image of the positive electrode as described above, it is determined that a crack is present when there is a portion having a luminance of 98% or less of the maximum luminance value.
The crack is measured at any stage from assembling the battery to mounting it on the equipment and before starting the discharge. If it is such a stage, you may measure at any time, for example, you may measure within one year or half a year from the assembly of a battery.

Hereinafter, the details of the alkaline battery will be described.
(Positive electrode)
The positive electrode includes manganese dioxide powder as a positive electrode active material and graphite powder as a conductive agent.
As manganese dioxide, electrolytic manganese dioxide is preferably used. In addition, industrially produced electrolytic manganese dioxide usually contains a small amount of impurities (such as ash), and its manganese dioxide purity is 90% or more. Examples of the crystal structure of manganese dioxide include α-type, β-type, γ-type, δ-type, ε-type, η-type, λ-type, and ramsdellite-type.

  The average particle diameter (D50) of the manganese dioxide powder is, for example, 30 to 60 μm, preferably 35 to 50 μm. When the average particle diameter is in such a range, the manganese dioxide particles in the positive electrode are not too dense, and the positive electrode is easily impregnated with the electrolyte (water), and cracks having an appropriate number and size are easily formed. The average particle size in this range is relatively larger than that of the prior art and can reduce the labor of grinding, which is advantageous in terms of cost.

As graphite for the conductive agent, natural graphite, artificial graphite, or the like can be used.
The average particle diameter (D50) of the graphite powder is, for example, 8 to 25 μm, preferably 8 to 18 μm. When the average particle size is in such a range, the graphite particles in the positive electrode are not too dense, and the positive electrode is easy to be impregnated with an electrolytic solution (water), and it is easy to form cracks of an appropriate number and size, which is advantageous. is there. Further, the average particle diameter in this range is relatively larger than that of the conventional one, and the labor of grinding can be reduced, which is advantageous in terms of cost.

  In the present specification, the average particle diameter (D50) is a median diameter in a volume-based particle size distribution. The average particle diameter can be determined using, for example, a laser diffraction / scattering particle distribution measuring device (LA-920) manufactured by Horiba, Ltd.

  From the viewpoint of the strength of the positive electrode and the utilization factor of the positive electrode, the content of the graphite powder in the positive electrode is, for example, 3 to 10 parts by mass, preferably 5 to 9 parts by mass, per 100 parts by mass in total of the manganese dioxide powder and the graphite powder. More preferably, it is 6-8 parts by mass. When the content of the graphite powder is in such a range, the binding property in the positive electrode can be more effectively ensured, and cracking of the positive electrode pellet can be more effectively suppressed. Further, even when the positive electrode pellet is pressure-molded in the battery case, it is easy to control the crack ratio within an appropriate range. Since it is possible to more effectively suppress the decrease in conductivity and to ensure the filling amount of the positive electrode active material, it is advantageous in suppressing the decrease in discharge performance.

  When the positive electrode expands with moisture, the adhesiveness with the battery case becomes good. Therefore, the positive electrode preferably contains moisture. Moisture can be added to the positive electrode, for example, by using an alkaline electrolyte in the production process of the positive electrode or by injecting an alkaline electrolyte into the battery case when assembling an alkaline dry battery. The positive electrode is preferably composed of a mixture of manganese dioxide powder, graphite powder and alkaline electrolyte.

  The water content in the positive electrode is, for example, 5 to 10 parts by mass, preferably 6 to 9 parts by mass, and more preferably 7 to 9 parts by mass per 100 parts by mass of manganese dioxide. When the water content in the positive electrode is within such a range, the positive electrode is likely to expand sufficiently, easily improve adhesion to the battery case, and is advantageous for suppressing an increase in internal resistance and leakage of the battery. . In addition, the water content in the positive electrode is measured at an arbitrary stage from the time when the battery is assembled to the time when the battery is mounted on the equipment and before the discharge is started. If it is such a stage, you may measure at any time, for example, you may measure within one year or half a year from the assembly of a battery.

  The positive electrode may further contain a binder as necessary. As the binder, for example, a polyolefin such as polyethylene or a resin such as a fluororesin such as polytetrafluoroethylene can be used. These resins can be used in the form of a powder.

  The content of the binder is, for example, 0.1 to 0.5 parts by mass, preferably 0.1 to 0.3 parts by mass, per 100 parts by mass in total of the manganese dioxide powder and the graphite powder. When the content of the binder is in such a range, it is advantageous because an appropriate binding property can be obtained and voids are easily formed in the positive electrode. In the present invention, a positive electrode pellet having an appropriate active material density and strength can be obtained without particularly using a binder. Therefore, even when a binder is used, the amount used is small as described above. can do. It is also preferable not to use a binder.

  The positive electrode is, for example, manganese dioxide powder, graphite powder, and if necessary, a positive electrode mixture containing an alkaline electrolyte and / or a binder is pressure-molded into pellets, and the obtained positive electrode pellets are placed in the battery case. After being accommodated in the battery case, it is obtained by secondary pressurization using a predetermined jig so as to be in close contact with the inner surface of the battery case. The positive electrode mixture may be once formed into flakes or granules, classified as necessary, and then pressed into pellets. Details of the method for manufacturing the positive electrode will be described later.

(Negative electrode)
The negative electrode contains zinc or zinc alloy powder as a negative electrode active material, an alkaline electrolyte, and a gelling agent. The negative electrode has a gel-like form.
The zinc alloy preferably contains at least one selected from the group consisting of indium, bismuth and aluminum from the viewpoint of corrosion resistance.
From the viewpoint of the filling property of the negative electrode and the diffusibility of the alkaline electrolyte in the negative electrode, the average particle size (D50) of the zinc or zinc alloy powder is, for example, 100 to 200 μm, preferably 110 to 160 μm.

  As the gelling agent, known gelling agents used in the field of alkaline primary batteries are used without particular limitation, and for example, a thickener and / or a water-absorbing polymer can be used. Examples of such a gelling agent include polyacrylic acid and sodium polyacrylate.

The amount of gelling agent added is, for example, 0.5 to 2 parts by mass, preferably 0.8 to 1.5 parts by mass, per 100 parts by mass of zinc or zinc alloy powder.
Content of zinc or zinc alloy powder is 170-220 mass parts with respect to 100 mass parts of alkaline electrolyte, Preferably it is 170-210 mass parts.

(Negative electrode current collector)
The material of the negative electrode current collector inserted into the gelled negative electrode preferably contains copper, and may be made of an alloy containing copper and zinc such as brass, for example. The negative electrode current collector may be subjected to a plating treatment such as tin plating, if necessary.

(Separator)
Examples of the material of the separator include cellulose and polyvinyl alcohol. The cellulose may be regenerated cellulose.
The separator may be a non-woven fabric mainly using fibers of the above materials, or may be a microporous film such as cellophane. You may use a nonwoven fabric and a microporous film together.

  As a separator, it is preferable to use a nonwoven fabric. Examples of such non-woven fabrics include non-woven fabrics mainly composed of cellulose fibers and polyvinyl alcohol fibers, and non-woven fabrics mainly composed of rayon fibers and polyvinyl alcohol fibers.

The thickness of the separator is, for example, 180 to 320 μm, preferably 200 to 300 μm, from the viewpoint of cushioning properties.
Although FIG. 1 shows a cylindrical separator with a bottom, the separator is not limited to this, and a separator having a known shape used in the field of alkaline dry batteries can be used. For example, a cylindrical separator and a bottom paper (or bottom separator) may be used in combination.

(Alkaline electrolyte)
In an alkaline battery, an alkaline electrolyte is contained in a positive electrode, a negative electrode, and a separator. As the alkaline electrolyte, for example, an alkaline aqueous solution containing potassium hydroxide and / or sodium hydroxide is used. The concentration of alkali in the alkaline electrolyte is preferably 30 to 38% by mass.
The alkaline aqueous solution may further contain zinc oxide. The concentration of zinc oxide in the alkaline electrolyte is preferably 1 to 3% by mass.

(Battery case)
For example, a bottomed cylindrical metal case is used as the battery case. For example, a nickel-plated steel plate is used for the metal case. In order to improve the adhesion between the positive electrode and the battery case, it is preferable to form a conductive film containing a conductive carbon material on the inner surface of the metal case.

The conductive coating can be formed by applying a coating containing a conductive carbon material to the inner surface of the metal case and drying.
Examples of the conductive carbon material include graphite such as natural graphite and artificial graphite, and carbon black. These materials may be used alone or in combination of two or more.

In addition to the conductive carbon material, the conductive film may further contain a polymer component such as polyvinyl butyral (PVB).
The thickness of the conductive coating is, for example, 1 to 20 μm, preferably 5 to 15 μm.

Moreover, in order to suppress that the iron which is a base material of a battery case corrodes after storage and contact resistance with a positive electrode pellet increases, it is preferable to make a titanium compound exist in the battery case inner surface. Specifically, a conductive film is formed after a titanium compound is applied to the battery case, or mixed with a coating material for the conductive film, or applied to the surface after forming the conductive film. Examples of the titanium compound include hydroxides and oxides such as TiO (OH) ₂ and TiO ₂ .

  In the present invention, when the positive electrode pellet is pressed in the battery case, the stress applied to the battery case can be reduced. Therefore, even if a thin battery case is used, the deformation can be effectively suppressed. The thickness of the thin battery case is, for example, 0.1 mm or more and less than 0.18 mm, preferably 0.1 to 0.17 mm, and more preferably 0.1 to 0.15 mm. If the thickness of the battery case is less than 0.1 mm, the strength of the battery case itself will be too low, and when an impact is applied due to transportation of the battery case in the battery assembly process, dropping of the battery after assembly, etc. The battery case is deformed. When the battery case is deformed, the clearance between the battery case and the positive electrode pellet is increased, and the internal resistance of the battery is easily increased. When the thickness of the battery case is 0.18 mm or more, expansion after storage is suppressed on the outer diameter side (battery case side) of the positive electrode. As a result, cracks tend to become larger toward the inner diameter side or the open side (sealing portion side) of the positive electrode, and the discharge performance after storage tends to deteriorate.

(Alkaline battery manufacturing method)
The method for producing the alkaline dry battery of the present invention comprises:
(1) preparing a bottomed cylindrical battery case;
(2) obtaining a positive electrode mixture comprising manganese dioxide powder, graphite powder, and an alkaline electrolyte;
(3) A hollow cylindrical shape having an outer diameter in which the positive electrode mixture is pressure-molded, the density of manganese dioxide is 2.55 to 2.80 g / cm ³ , and the clearance from the battery case is 0.1 mm or less Obtaining a positive electrode pellet of
(4) The positive electrode pellet is inserted into the battery case, and a cylindrical insertion pin having a diameter 0.05 to 0.1 mm smaller than the inner diameter of the positive electrode pellet is arranged in the hollow portion of the positive electrode pellet. Applying a pressure of 5 to 30 MPa from above to obtain a hollow cylindrical positive electrode in close contact with the battery case;
(5) After placing the separator in the hollow part of the positive electrode, injecting an alkaline electrolyte into the battery case;
(6) filling the negative electrode through a separator in the hollow part of the positive electrode;
(7) sealing the battery case with a sealing unit;
including.

  According to the above method, as described above, all the cross sections obtained when the cross-sectional images of the positive electrode perpendicular to the central axis of the battery case are taken at intervals of 0.4 mm along the central axis. A positive electrode in which the ratio of the number of cross-sectional images in which no cracks are observed to the number of images is 91% or more and 97% or less is efficiently obtained.

By such a manufacturing method, an alkaline dry battery including a positive electrode in which the crack ratio is controlled to an appropriate range as described above can be obtained easily and reliably.
Below, the detail of each process of the manufacturing method of an alkaline dry battery is demonstrated.
(Process (1))
In the step (1), for example, a bottomed cylindrical battery case of a desired size formed of a nickel-plated steel plate is prepared.
On the inner surface of the battery case, if necessary, a film containing the above-described conductive carbon material may be formed, or a titanium compound may be present.

(Process (2))
In the step (2), a positive electrode mixture is prepared by mixing manganese dioxide powder as a positive electrode active material, graphite powder as a conductive material, and an alkaline electrolyte at a predetermined mass ratio. When the positive electrode includes a binder, the binder can also be mixed at this stage. In the subsequent step (3), a positive electrode pellet having a relatively high manganese dioxide density is obtained, and the positive electrode pellet has a sufficient strength. Therefore, a smaller amount of binder than in the prior art may be used, which is advantageous in terms of cost.
The mixing can be performed by a conventional method, for example, by uniformly stirring the raw material mixture with a mixer or the like.

  The obtained positive electrode mixture may be granulated into flakes or granules, and the particle size may be adjusted by sizing or classifying if necessary. In a preferred method, the positive electrode mixture is sized to a constant particle size and used in a granular form. The average particle diameter (D50) of the granular positive electrode mixture (hereinafter also referred to as a granular mixture) is, for example, 0.4 to 0.7 mm.

(Process (3))
In step (3), using the positive electrode mixture obtained in step (2), a hollow cylindrical positive electrode pellet accommodated in a battery case is prepared.
An example of the step (3) will be described with reference to FIG. FIG. 3 is a schematic longitudinal sectional view showing an example of step (3) in the method for producing an alkaline battery of the present invention.

As shown in FIG. 3, using a hollow cylindrical die (die 11), the granular mixture obtained in the step (2) is pressure-molded as follows to produce a positive electrode pellet.
Specifically, the center pin 13 is disposed in the hollow portion of the hollow cylindrical die 11 so that the center pin 13 is located at the center of the hollow portion of the die 11. A hollow cylindrical lower molding punch 14a is inserted into the gap between the die 11 and the center pin 13 with the center pin 13 being passed through the hollow portion.

  While the lower molding punch 14a is moved downward from a predetermined position, the granular mixture 12 is filled in the gap between the die 11 and the center pin 13 with the upper surface of the lower molding punch 14a as the bottom. Next, a cylindrical upper molding punch 14b having a recess that can be inserted along the inner wall of the hollow portion of the die 11 and can accommodate the upper end portion of the center pin 13 at the center of the bottom surface, and an upper end portion of the center pin 13 in the recess portion. Is inserted from above into the hollow portion of the die 11 so as to accommodate the. Then, with the lower molding punch 14b fixed, pressure is applied to the upper molding punch 14b from above to press the bottom surface of the upper molding punch 14b against the filled granular mixture 12 and press molding. In this way, a hollow cylindrical positive electrode pellet is obtained.

  In order to reliably fill the granular mixture 12, the lower molding punch 14a is lowered slightly below a predetermined position, and then a part of the granular mixture 12 is filled in the gap between the die 11 and the center pin 13. The lower molding punch 14a may be slightly raised, and the lowering and raising of the lower molding punch 14a may be repeated as appropriate. Further, the lower molding punch 14a may be raised until the upper surface of the filled granular mixture 12 is located near the upper surface of the die 11, and the upper surface of the granular mixture 12 may be adjusted along the upper surface of the die 11 with a spatula or the like. .

The density of manganese dioxide in the positive electrode pellet is, for example, 2.55 to 2.8 g / cm ³ , preferably 2.6 to 2.75 g / cm ³ . The density in such a range is relatively high compared to the conventional case, and the positive electrode pellet has sufficient strength. Therefore, collapse of the positive electrode pellet can be effectively suppressed even when the positive electrode pellet is conveyed or pressure-formed in a subsequent process. In addition, the density of manganese dioxide can be adjusted by adjusting the pressure (pressing force of the upper forming punch) applied when the positive electrode pellet is formed.

  The size of the positive electrode pellet can be appropriately determined according to the size of the alkaline battery. In the next step, the size of the positive electrode pellet may be adjusted according to the number of positive electrode pellets to be inserted into the battery case.

(Process (4))
In the step (4), the positive electrode pellet obtained in the step (3) is inserted into a battery case and subjected to pressure molding using a specific jig to produce a hollow cylindrical positive electrode. By this step (4), the ratio of cracks formed in the positive electrode is adjusted.

  An example of the step (4) will be described with reference to FIG. FIG. 4 is a schematic longitudinal sectional view showing an example of step (4) in the method for producing an alkaline dry battery of the present invention.

  As shown in FIG. 4, the bottomed cylindrical battery case 1 is inserted into a hollow portion of a hollow cylindrical cartridge 21. At this time, a hollow cylindrical lower molding punch 24a is inserted into the lower portion of the hollow portion of the cartridge 21, and the bottom of the battery case 1 is disposed on the lower molding punch 24a. Next, two hollow cylindrical positive electrode pellets 15 are inserted into the battery case 1. At this time, the two positive electrode pellets 15 are stacked on the same axis so that the hollow portions of the pellets communicate with each other.

  Next, a cylindrical insertion pin 23 having a diameter 0.05 to 0.1 mm smaller than the inner diameter of the positive electrode pellet 15 is disposed in the hollow portion of the positive electrode pellet 15. On the positive electrode pellet 15, a hollow cylindrical upper molding punch 24 b is disposed in a state where the upper portion of the insertion pin 23 is inserted into the hollow portion. And it press-molds by pressing the positive electrode pellet 15 from the upper direction with the upper shaping | molding punch 24b. As a result, a hollow cylindrical positive electrode in close contact with the inner surface of the battery case 1 can be formed. At this time, the pressure which presses the positive electrode pellet 15 is controlled in the range of 5-30 MPa.

In step (4), the hollow cylindrical positive electrode pellet is inserted into the hollow cylindrical battery case so that the central axis of the battery case and the central axis of the positive electrode pellet are substantially overlapped.
Next, a cylindrical insertion pin is inserted into the hollow part of the positive electrode pellet, and in this state, pressure is applied to the positive electrode pellet from above to obtain a positive electrode in close contact with the inner surface of the battery case. At this time, by adjusting the clearance between the outer diameter of the positive electrode pellet and the inner diameter of the battery case, the clearance between the inner diameter of the positive electrode pellet and the diameter of the insertion pin, and the amount of pressure applied to the positive electrode pellet, The ratio and state of cracks and the density of manganese dioxide can be easily adjusted.

  The clearance between the outer diameter of the positive electrode pellet and the inner diameter of the battery case is 0.1 mm or less, preferably 0.05 to 0.1 mm. The clearance between the inner diameter of the positive electrode pellet and the diameter of the insertion pin is 0.05 to 0.1 mm. By providing such a clearance, the positive electrode pellet pressed from above at the time of forming the positive electrode is deformed so as to fill the gap on the insertion pin side, and a sparse portion is formed inside. In the next step (5), when the electrolytic solution is injected into the battery case, the positive electrode expands and cracks are formed in the sparse part. In addition, when forming a conductive film on the inner surface of the battery case, the clearance between the outer diameter of the positive electrode pellet and the surface of the conductive film is controlled within the above range.

  When the clearance between the outer diameter of the positive electrode pellet and the inner diameter of the battery case exceeds 0.1 mm, the volume of the space between the positive electrode pellet and the battery case becomes too large, and when the positive electrode pellet is pressurized, The positive electrode pellet is deformed toward the battery case, and many sparse parts are easily formed. As a result, the ratio of cracks increases so that the discharge characteristics are impaired. Further, when the positive electrode absorbs the alkaline electrolyte and expands when the battery is assembled, it becomes difficult for the positive electrode and the inner surface of the battery case to come into contact with each other, and the internal resistance of the battery is likely to increase.

  If the clearance between the inner diameter of the positive electrode pellet and the diameter of the insertion pin is less than 0.05 mm, even if the positive electrode pellet is pressurized, it becomes difficult to form a sparse part, so the movement of the electrolyte is hindered and the discharge characteristics are degraded. To do. In addition, if the clearance between the inner diameter of the positive electrode pellet and the diameter of the insertion pin exceeds 0.1 mm, many sparse parts are likely to be formed when the positive electrode pellet is pressed, and the ratio of cracks increases so that Properties are impaired.

  The pressure at the time of pressurizing the positive electrode pellet is 5 to 30 MPa, preferably 5 to 20 MPa or 15 to 30 MPa. In the present invention, since the positive electrode can be formed even at such a pressure, not only can the ratio of cracks be controlled to an appropriate range, but also the conductive film formed on the inner surface of the battery case is peeled off and the conductivity is reduced. It can also be suppressed. In addition, since the stress applied to the battery case is small and deformation of the battery case can be suppressed, a thin battery case can be used. If the said pressure is less than 5 MPa, even if it pressurizes a positive electrode pellet, since a sparse part will become difficult to be formed, the movement of electrolyte solution will be prevented and discharge characteristics will fall. On the other hand, when the pressure exceeds 30 MPa, many sparse parts are likely to be formed during pressurization of the positive electrode pellet, the ratio of cracks is excessively increased, and the discharge characteristics are impaired.

(Process (5))
In step (5), a separator is disposed in the hollow portion of the positive electrode obtained in step (4), and an alkaline electrolyte is injected into the battery case.
When the alkaline electrolyte penetrates into the positive electrode, the positive electrode expands, and along with this expansion, cracks are formed in the sparse part formed in the positive electrode in step (4).

(Process (6))
In the step (6), the negative electrode is filled into the hollow part of the positive electrode via the separator. As described above, a gelled negative electrode is usually used as described above.
The gelled negative electrode can be prepared by mixing a negative electrode raw material, specifically, zinc or zinc alloy powder as a negative electrode active material, an alkaline electrolyte, and a gelling agent.

(Process (7))
In the step (7), an alkaline dry battery is obtained by sealing the opening of the battery case with a sealing unit.
The sealing unit includes a resin sealing member (gasket), a bottom plate (negative electrode terminal plate) that also serves as a negative electrode terminal, and a nail-like negative electrode current collector. The battery case is sealed by caulking the open end of the battery case that also serves as the positive electrode terminal to the peripheral edge of the negative electrode terminal plate of the sealing unit via a gasket. At this time, the negative electrode current collector having a nail-like shape with the head welded to the inner surface of the negative electrode terminal plate is inserted into a through-hole provided in the central portion of the gasket so that the gel negative electrode Inserted into.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

<< Examples 1-5 and Comparative Examples 1-5 >>
(1) Production of positive electrode pellets Electrolytic manganese dioxide powder (purity 92%, average particle size (D50): 40 μm) as a positive electrode active material, graphite powder (average particle size (D50): 10 μm) as a conductive material, and alkaline electrolysis As a liquid, an aqueous potassium hydroxide solution having a concentration of 35% by mass (including 2% by mass of zinc oxide) was used at a mass ratio of 93: 7: 1.3. All of these components were mixed by stirring uniformly with a mixer and then sized to a predetermined particle size. The obtained granular material was pressure-molded as described above using the same mold as in FIG. 3, and a hollow cylindrical positive electrode pellet (outer diameter: 13.4 mm, inner diameter: 9.05 mm, height: 21.20 mm, mass: 5.14 g, volume: 1.63 cm ³ ). The mass of manganese dioxide in the positive electrode pellet was 4.34 g from the purity of electrolytic manganese dioxide and the mass ratio of each component, and the density of manganese dioxide in the positive electrode pellet was 2.67 g / cm ³ .

(2) Production of Alkaline Dry Battery Using the positive electrode pellet obtained above, an AA alkaline battery shown in FIG. 1 was produced as follows.
A conductive film (thickness: 10 μm) is formed on the inner surface of a bottomed cylindrical battery case (outer diameter: 13.8 mm, inner diameter: 13.5 mm, height: 51.5 mm) made of nickel-plated steel sheet. 1 was obtained. After two positive electrode pellets 2 were inserted into the battery case 1, the positive electrode 2 in a state of being in close contact with the inner surface of the battery case 1 was formed in the battery case 1 using the same jig as in FIG. 4. . The conductive film contains graphite as a conductive material and PVB as a binder.

  After the separator 4 was disposed inside the positive electrode 2, an alkaline electrolyte was injected into the battery case 1. As the separator 4, a non-woven fabric having a thickness of 0.145 mm, which is mainly composed of polyvinyl alcohol fiber and rayon fiber, wound twice in a cylindrical shape so as to have a thickness of 0.29 mm was used.

  Next, the gelled negative electrode 3 was filled inside the separator 4. The gelled negative electrode 3 includes a zinc alloy powder (average particle size: 150 μm) as a negative electrode active material, a 35% by mass potassium hydroxide aqueous solution (including 2% by mass of zinc oxide) as an electrolytic solution, and a poly-acid as a gelling agent. What mixed sodium acrylate in the ratio of 182: 100: 2 of mass ratio was used. The zinc alloy powder contained 0.02% by weight of indium, 0.01% by weight of bismuth, and 0.005% by weight of aluminum.

And as shown in FIG. 1, the opening part of the battery case 1 was sealed with the sealing unit 9, and the exterior label 8 was coat | covered on the outer surface of the battery case 1, and the alkaline dry battery was produced.
In Examples 1-5 and Comparative Examples 1-5, the ratio of cracks in the positive electrode was changed by adjusting the conditions during pressure molding in the battery case as shown in Table 1.

Example 6
In step (1), the outer diameter of the positive electrode pellet is changed to 13.34 mm, the thickness of the battery case is changed to 0.18 mm, and the conditions at the time of pressure molding in the battery case are as shown in Table 1. An alkaline dry battery was produced in the same manner as in Example 1 except that the above was changed.

Example 7
In step (1), the outer diameter of the positive electrode pellet is changed to 13.50 mm, the thickness of the battery case is changed to 0.10 mm, and the conditions at the time of pressure molding in the battery case are as shown in Table 1. An alkaline dry battery was produced in the same manner as in Example 1 except that the above was changed.

<< Comparative Example 6 >>
In step (1), the outer diameter of the positive electrode pellet is changed to 13.30 mm, and the conditions at the time of pressure molding in the battery case are changed as shown in Table 1, and the same method as in Example 1 Thus, an alkaline battery was produced.

<< Comparative Example 7 >>
In step (1), the outer diameter of the positive electrode pellet is changed to 13.30 mm, the thickness of the battery case is changed to 0.20 mm, and the conditions during pressure molding in the battery case are as shown in Table 1. An alkaline dry battery was produced in the same manner as in Example 1 except that the above was changed.

The following evaluation was performed about the alkaline dry battery obtained by the Example and the comparative example.
(1) Crack inside the positive electrode An undischarged alkaline battery after one week has passed after assembly, with the negative electrode terminal side facing down so that the direction from the positive electrode terminal to the negative electrode terminal is the direction of gravity. CT photography of the cross section of the alkaline battery was carried out in a circle so as to be perpendicular to the direction of gravity (that is, the central axis of the cylindrical battery case) from the negative electrode terminal to the negative electrode terminal.

The brightness in the cross-sectional image was measured using the line profile software attached to the photographing apparatus. Specifically, in the photographed cross-sectional image, a line having a length of 0.5 to 0.7 mm is drawn in the positive electrode portion so as to cross the black stripe (crack) of the positive electrode portion, and the line Luminance was measured. Next, on the line, the brightness of the brightest part (maximum value of brightness) and the brightness of the darkest part (minimum value of brightness) are extracted, the difference is obtained, and the ratio to the maximum value of brightness is calculated as a percentage. did. The ratio of the luminance difference is expressed by the following formula.
(Luminance difference ratio) = (maximum luminance-minimum luminance) / (maximum luminance) × 100

  Furthermore, the percentage of the number of images in which the portion where the luminance difference ratio exceeds 2% is not observed with respect to the total number of images photographed in the range where the positive electrode exists is expressed as a percentage, and there is no crack in the positive electrode. It was used as an indicator.

In addition, CT imaging | photography of the alkaline battery cross section was performed on the following imaging conditions by the X-ray CT analysis method using the micro focus X-ray CT system SMX-225CT-SV by Shimadzu Corporation.
Image size: Vertical and horizontal 1024 [pixel] x 1024 [pixel]
X-ray tube voltage: 160 [kV]
X-ray tube current: 40 [μA]
I. I. Size (screen size): 9 inches I.
S. I. D (distance from the X-ray source to the screen): 322.49 [mm]
S. O. D. (Distance from X-ray source to battery): 18.72 [mm]

Table position (Z): 6.364 [mm]
Slice thickness: 0.4 [mm]
Number of views: 2400 [View]
Average number: 2 [times]
Scaling factor: 10
CT mode 1: 2D-CT
CT mode 2: Offset scan CT mode 3: Full scan FOV (XY): 14.163511 [mm]
Pixel equivalent length: 0.013832 [mm / pixel]
Slice pitch: 0.4 [mm]

(2) Discharge test The alkaline dry battery after one week from the assembly was discharged at 1500 mW for 2 seconds in a constant temperature environment of 20 ° C ± 2 ° C, and then discharged at 650 mW for 28 seconds. This was repeated 10 times continuously as one discharge cycle, and a total of 5 minutes of discharge was performed. Then, it was rested for 55 minutes. With this discharge and pause as one operation, it was continuously repeated until the battery voltage reached 1.05 V, and the number of discharge cycles was evaluated.
In addition, the same test as described above was also performed after storing the alkaline dry battery after one week from the assembly for 4 weeks (28 days) in a constant temperature environment of 60 ° C. ± 2 ° C.

(3) Moisture content of positive electrode The alkaline dry battery after one week from the assembly was disassembled, the negative electrode and the separator were removed, and then the positive electrode was taken out. The positive electrode was pulverized in a mortar and dried in a vacuum dryer at 80 ° C. for 3 hours. The weight loss due to this drying was measured, and based on this, the water content of the positive electrode per 100 parts by mass of manganese dioxide powder was determined. In the alkaline dry batteries of Examples and Comparative Examples, the water content of the positive electrode was 8 parts by weight per 100 parts by weight of manganese dioxide powder.

  The evaluation results of the above (1) and (2) are shown in Table 1 together with the molding conditions of the positive electrode pellets and the conditions during pressure molding in the battery case. In Table 1, the difference between the battery case inner diameter and the pellet outer diameter means the clearance between the surface of the conductive coating formed on the inner surface of the battery case and the outer diameter of the positive electrode pellet.

  As is clear from Table 1, in the batteries of Examples 1 to 5, not only the first time but also the number of discharges after storing for 4 weeks at 60 ° C. was very large compared to the batteries of Comparative Examples 1 to 6. Excellent discharge characteristics.

  In Comparative Examples 1 and 2, both the initial number of discharges and the number of discharges after storage were significantly reduced compared to the Examples. This is because in Comparative Examples 1 and 2, the ratio of the cracks in which the luminance difference formed in the positive electrode exceeds 2% is too small to sufficiently secure the movement path of the electrolyte, and sufficient discharge performance. This is probably due to the fact that

  In Comparative Examples 3 to 5, although the initial number of discharges was large, the number of discharges after storage was reduced to about half compared to the Examples. In Comparative Examples 3 to 5, since there are many cracks in the positive electrode, it is considered that the number of discharges can be increased by ensuring a certain amount of the electrolyte movement path. However, when the battery is stored at 60 ° C. for 4 weeks due to many cracks, the collapse of the positive electrode is promoted, voids not filled with the electrolyte solution are formed, and the graphite coating formed on the inner surface of the battery case It is considered that sufficient discharge performance could not be obtained because the film peeled off and the conductivity decreased.

  In Comparative Example 6, not only after storage, but also the initial discharge performance decreased. Moreover, in the comparative example 7, the discharge performance after a storage fell. This is because the cross-sectional area inside the battery case is small and the case strength itself is too large, so that the outer diameter side of the positive electrode is less likely to expand after storage, and the crack is biased toward the inner diameter side or the open side (sealing part side) of the pellet. This is thought to be due to the increase.

  Compared to the results of such comparative examples, in the examples, not only the first time but also after storage, high discharge performance was obtained because the existence ratio of cracks with a luminance difference exceeding 2% was in an appropriate range. This is thought to be due to the fact that control was possible. Moreover, when the deformation | transformation of the battery case was confirmed visually, a deformation | transformation was not confirmed at all in the alkaline dry battery of an Example.

  Since the alkaline dry battery of the present invention can exhibit stable discharge performance even after storage, it is suitably used as a power source for electronic devices such as portable devices.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Positive electrode 3 Negative electrode 4 Separator 5 Gasket 6 Negative electrode collector 7 Negative electrode terminal board 8 Exterior label 9 Sealing unit 10 Crack 11 Dies 12 Granular mixture 13 Center pin 14a Lower molding punch 14b Upper molding punch 15 Positive electrode pellet 21 Cartridge 23 Insertion Pin 24a Lower Molding Punch 24b Upper Molding Punch

Claims (10)

A bottomed cylindrical battery case;
A hollow cylindrical positive electrode containing manganese dioxide powder and graphite powder in contact with the inner surface of the battery case;
A negative electrode disposed in a hollow portion of the positive electrode;
A separator disposed between the positive electrode and the negative electrode;
An alkaline electrolyte,
The battery case has a thickness of 0.1 mm or more and less than 0.18 mm,
When cross-sectional images of the positive electrode perpendicular to the central axis of the battery case are taken at intervals of 0.4 mm along the central axis, no cracks are observed with respect to the number of all cross-sectional images obtained. An alkaline dry battery in which the ratio of the number of cross-sectional images is 91% or more and 97% or less.   The alkaline dry battery according to claim 1, wherein the manganese dioxide powder has an average particle size (D50) of 30 to 60 µm.   The alkaline dry battery according to claim 1 or 2, wherein the graphite powder has an average particle size (D50) of 8 to 25 µm.   The said positive electrode is an alkaline dry battery of any one of Claims 1-3 which consists of a mixture of the said manganese dioxide powder, the said graphite powder, and the said alkaline electrolyte.   The alkaline dry battery according to claim 4, wherein the water content in the positive electrode is 7 to 9 parts by mass per 100 parts by mass of the manganese dioxide powder.   The said positive electrode further contains the polyolefin powder as a binder with the content of 0.1-0.5 mass part per 100 mass parts in total of the said manganese dioxide powder and the said graphite powder. Alkaline batteries.   The alkaline dry battery according to claim 1, wherein a conductive film containing a conductive carbon material is formed on an inner surface of the battery case. (1) preparing a bottomed cylindrical battery case;
(2) obtaining a positive electrode mixture comprising manganese dioxide powder, graphite powder, and an alkaline electrolyte;
(3) The positive electrode mixture is pressure-molded, the manganese dioxide has a density of 2.55 to 2.8 g / cm ³ , and a hollow having an outer diameter with a clearance of 0.1 mm or less from the battery case Obtaining a cylindrical positive electrode pellet;
(4) The positive electrode pellet is inserted into the battery case, and a cylindrical insertion pin having a diameter 0.05 to 0.1 mm smaller than the inner diameter of the positive electrode pellet is arranged in the hollow portion of the positive electrode pellet, Applying a pressure of 5 to 30 MPa from above to the positive electrode pellet to obtain a hollow cylindrical positive electrode in close contact with the battery case;
(5) After placing the separator in the hollow portion of the positive electrode, injecting an alkaline electrolyte into the battery case;
(6) filling the negative electrode in the hollow part of the positive electrode through the separator;
(7) sealing the battery case with a sealing unit;
A method for producing an alkaline battery.   The manufacturing method of the alkaline dry battery of Claim 8 whose thickness of the said battery case is 0.1 mm or more and less than 0.18 mm.   10. The method for producing an alkaline dry battery according to claim 8, wherein in the positive electrode, the content of the graphite powder is 6 to 8 parts by mass per 100 parts by mass in total of the manganese dioxide powder and the graphite powder.

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