Alkaline dry battery

Abstract

This alkaline dry battery is provided with: a hollow cylindrical positive electrode disposed in a battery case; a gel-like negative electrode filled in the hollow part of the positive electrode and containing zinc powder; and a separator disposed between the positive electrode and the negative electrode. The total thickness of the separator is in the range of 160-300 [mu] m. The negative electrode contains a sulfate in an amount of 0.01-0.5 mass% relative to the mass of the negative electrode in terms of sulfate ions.

Description

Technical Field

[0001] The present disclosure relates to alkaline dry cell batteries. Background Art

[0002] Alkaline dry batteries (alkaline manganese dry batteries) are widely used because they have a larger capacity and can deliver higher currents than manganese dry batteries. Alkaline dry batteries typically consist of a positive electrode, a negative electrode, a separator positioned between the two electrodes, and an alkaline electrolyte. The positive electrode contains manganese dioxide as the positive electrode active material. Various proposals have been made to improve the characteristics of alkaline dry batteries.

[0003] Patent Document 1 discloses an alkaline battery comprising a gel-like negative electrode mixture and a sealing gasket having a boss portion, a plate-shaped intermediate partition formed around the boss portion, and a curved portion formed on the outer periphery of the intermediate partition portion, curved in a U-shape toward the positive electrode mixture. The negative electrode-side opening edge of the separator is spaced from the curved portion and abuts the inner side surface of the intermediate partition portion. The distance from the inner peripheral edge of the opening-side end surface of the positive electrode mixture closest to the opening to the sealing gasket along a virtual line parallel to the battery's central axis is 1.0 mm to 2.75 mm. The separator is formed from vinylon fibers, rayon fibers, polyvinyl alcohol fibers, and pulp. The separator is formed by winding a separator material having a liquid retention rate of 250% to 350% at least twice and at most five times, resulting in a thickness of 230 μm to 575 μm. The amount of zinc powder in the gelled negative electrode mixture is 2.00 g or more and 3.81 g or less. According to Patent Document 1, this configuration provides an alkaline battery having excellent impact resistance while having appropriate discharge performance.

[0004] Patent Document 2 proposes adding a calcium compound or a sulfuric acid compound to at least one of a positive electrode, a negative electrode containing zinc, and an electrolyte in an alkaline battery comprising a positive electrode, a negative electrode containing zinc, and an electrolyte to prevent a decrease in discharge voltage under heavy-load discharge conditions. According to Patent Document 2, sulfate ions migrate toward the negative electrode along with H₂O during discharge. Therefore, even under heavy-load discharge conditions, the electrolyte volume near the negative electrode remains sufficient, thereby suppressing a decrease in discharge voltage.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 5366490

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2001-297776 Summary of the Invention

[0009] To increase the battery's discharge capacity, one approach is to reduce the total thickness of the separator and, instead, increase the amount of positive or negative electrode mixture loaded. However, if the separator is thinner, zinc oxide will precipitate inside the separator during medium-load intermittent discharge, making internal short circuits more likely to occur.

[0010] One aspect of the present disclosure relates to an alkaline dry battery comprising: a hollow cylindrical positive electrode disposed within a battery case; a gel-like negative electrode containing zinc powder and filling the hollow portion of the positive electrode; and a separator disposed between the positive electrode and the negative electrode, wherein the separator has a total thickness in the range of 160 to 300 μm, and the negative electrode contains sulfate in an amount of 0.01 to 0.5% by mass relative to the mass of the negative electrode, calculated as sulfate ions.

[0011] According to the present disclosure, it is possible to suppress the occurrence of an internal short circuit during medium-load intermittent discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a partially exploded cross-sectional view showing an example of an alkaline dry battery according to an embodiment. DETAILED DESCRIPTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes exemplified, but other numerical values ​​and other materials may also be applied as long as the invention to which the present disclosure relates can be implemented. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be replaced by "above numerical value A and below numerical value B". In the following description, when a lower limit and an upper limit are exemplified for numerical values ​​of specific physical properties, conditions, etc., as long as the lower limit is not above the upper limit, any one of the exemplified lower limits can be arbitrarily combined with any one of the exemplified upper limits. When multiple materials are exemplified, one can be selected and used alone, or two or more can be used in combination.

[0014] Furthermore, the present disclosure includes combinations of matters described in two or more claimed technical solutions arbitrarily selected from the plurality of claimed technical solutions described in the attached claims. In other words, as long as no technical contradiction arises, matters described in two or more claimed technical solutions arbitrarily selected from the plurality of claimed technical solutions described in the attached claims may be combined.

[0015] (Alkaline dry cell batteries)

[0016] The alkaline dry battery of this embodiment comprises: a hollow cylindrical positive electrode disposed within a battery case; a gel-like negative electrode containing zinc powder, which fills the hollow portion of the positive electrode; and a separator disposed between the positive and negative electrodes. The zinc powder includes zinc alloy powder. The total thickness of the separator ranges from 160 to 300 μm. The negative electrode contains sulfate in an amount, calculated as sulfate ions, ranging from 0.01 to 0.5% by mass relative to the mass of the negative electrode.

[0017] By incorporating sulfate into the negative electrode, internal short circuits caused by the precipitation of zinc oxide under medium-load intermittent discharge conditions are suppressed. Therefore, by using a thin separator with a total thickness of 300 μm or less, an alkaline dry battery with excellent medium-load intermittent discharge characteristics can be achieved while maintaining a high discharge capacity.

[0018] It is believed that the precipitation of zinc oxide is caused by the OH group in the electrolyte in the negative electrode caused by discharge. - Ions are consumed, the pH of the electrolyte decreases, and the electrolyte tilts toward neutrality, which reduces the solubility of zinc ions dissolved in the electrolyte. In particular, under usage conditions such as medium loads of approximately 250 to 500 mA, where discharge is repeated intermittently for approximately one hour per day, the pH of the electrolyte decreases significantly in certain areas, making the electrolyte prone to becoming neutral. This can lead to internal short circuits caused by the precipitation of zinc oxide.

[0019] Sulfate added to the negative electrode is difficult to dissolve in the electrolyte of an undischarged alkaline dry cell due to its strong alkalinity. However, as the pH of the electrolyte in the negative electrode decreases with discharge, it becomes readily soluble, further lowering the pH of the electrolyte toward the acidic side. Meanwhile, zinc ions have the lowest solubility at neutral temperatures and readily dissolve in alkaline and acidic conditions. Therefore, sulfate dissolves during medium-load intermittent discharge, shifting the pH of the electrolyte from neutral to acidic, making zinc ions more soluble and suppressing the precipitation of zinc oxide.

[0020] It should be noted that under heavy load (eg, approximately 1 A) discharge conditions, alkaline dry batteries generally experience a drop in discharge voltage and reach the end of their life before the electrolyte reaches neutrality, and thus are less likely to experience internal short circuits due to zinc oxide precipitation.

[0021] If the content of sulfate contained in the negative electrode is 0.01% by mass or more in terms of sulfate ion conversion relative to the mass of the negative electrode, the effect of suppressing the internal short circuit caused by the precipitation of zinc oxide can be fully obtained. On the other hand, if the content of sulfate is excessive, the uneven distribution of sulfate inside the negative electrode becomes larger, so the uneven pH of the electrolyte inside the negative electrode becomes larger during discharge, sometimes promoting internal short circuit. From the aspect of suppressing the pH unevenness of the electrolyte, the content of sulfate can be 0.5% by mass or less in terms of sulfate ion conversion relative to the mass of the negative electrode. The content of sulfate can be 0.01% by mass or more and 0.5% by mass or less, preferably 0.05% by mass or more and 0.3% by mass or less, more preferably 0.08% by mass or more and 0.2% by mass or less.

[0022] Here, the content of sulfate converted into sulfate ions refers to the sulfate ions (SO4 2- The content of sulfate is determined by disassembling an undischarged alkaline dry cell, collecting at least a portion of the negative electrode (e.g., 80% or more) and measuring its mass. The collected negative electrode is then exposed to pure water to dissolve the sulfate, and ion chromatography is performed to determine the content of sulfate. 2- The amount of sulfate was quantified and the mass of the sulfate in the negative electrode was calculated, thereby determining the content of sulfate converted into sulfate ions.

[0023] When the content of sulfate is within the above range, if the total thickness of the separator is 160 μm or more, the internal short circuit caused by the precipitation of zinc oxide can be fully suppressed. On the other hand, the thicker the thickness of the separator, the easier it is to suppress the internal short circuit, but the filling volume of the active material is reduced and the discharge performance is reduced. If the total thickness of the separator is 300 μm or less, it is possible to achieve an alkaline dry battery with high discharge performance and suppressed internal short circuit even when used in medium load intermittent discharge. The total thickness of the separator is 160 μm or more and 300 μm or less, preferably 160 μm or more and 260 μm or less, more preferably 180 μm or more and 240 μm or less.

[0024] The desired total thickness of a separator can be achieved by stacking multiple separators of a given thickness, or by winding a single separator of a given thickness multiple times and stacking them. The total thickness of a separator is the average thickness of three angularly equivalent points on the cylindrical separator (three adjacent points separated by an angular interval of 120°). The total thickness of a separator refers to the thickness of the separator while it absorbs the electrolyte within the battery.

[0025] The total thickness T of the separator is determined by obtaining a cross-section of a manufactured alkaline dry cell using CT scanning and measuring the distance between the positive and negative electrodes. The distance from the tip of the positive terminal to the tip of the negative terminal is defined as the total height. The distance between the positive and negative electrodes in a cross-section measuring half the total height is measured at three angularly equivalent points (three adjacent points spaced 120° apart). The average value of these three points is defined as the total thickness T of the separator.

[0026] The total air permeability A of the separator is, for example, 0.1 to 3.0 cc / cm 2 ·s, more preferably 0.2 to 1.5 cc / cm 2 s range. Air permeability is measured as follows: After manufacturing, the alkaline dry cell is disassembled and removed. The separator is washed with a 34% by mass KOH aqueous solution, allowed to stand for one day under reduced pressure at 20°C and dried. The resulting separator is then measured using the Frazier air permeability tester method specified in JIS L1096:2010. When multiple separators of the same type are stacked, the total air permeability A can be calculated by dividing the air permeability of a single separator measured without stacking by the number of stacked separators. When different types of separators are stacked, the air permeability of the stacked separator is measured to determine the total air permeability A.

[0027] The cations that constitute the sulfate are not particularly limited as long as they do not interfere with the discharge reaction of the battery. The sulfate may be a salt of a metal cation and a sulfate ion. From the perspective of having a greater effect on lowering the pH after dissolution, the sulfate preferably comprises at least one selected from potassium sulfate, sodium sulfate, aluminum sulfate, potassium aluminum sulfate, calcium sulfate, zinc sulfate, and lithium sulfate, and preferably also comprises hydrates thereof.

[0028] The alkaline dry battery disclosed herein comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and may comprise other components as required. Examples of the components of the alkaline dry battery disclosed herein are described below.

[0029] (positive electrode)

[0030] The positive electrode contains manganese dioxide as the positive electrode active material. The positive electrode typically contains a positive electrode active material and a conductive material, and optionally, a binder. The positive electrode can be formed by pressurizing a positive electrode mixture into a cylindrical body (positive electrode pellets). The positive electrode mixture, for example, contains a positive electrode active material, a conductive material, an alkaline electrolyte, and optionally, a binder. The cylindrical body can also be pressurized after being housed in the housing body to ensure a tight fit with the inner wall of the housing body.

[0031] A preferred example of manganese dioxide as the positive electrode active material is electrolytic manganese dioxide, but natural manganese dioxide and chemical manganese dioxide can also be used. The crystal structure of manganese dioxide includes α-type, β-type, γ-type, δ-type, ε-type, η-type, λ-type, and ramsdellite-type.

[0032] The average particle size (D50) of the manganese dioxide powder may be, for example, in the range of 25 μm to 60 μm in order to easily ensure the filling property of the positive electrode and the diffusibility of the electrolyte in the positive electrode.

[0033] From the viewpoint of formability and suppression of positive electrode expansion, the BET specific surface area of ​​manganese dioxide can be, for example, 20 m 2 / g~50m 2 The BET specific surface area can be measured, for example, using a specific surface area measuring device based on a nitrogen adsorption method.

[0034] The conductive material can be a conductive carbon material. Examples of conductive carbon materials include carbon black (such as acetylene black) and graphite. Examples of graphite include natural graphite and artificial graphite. The conductive material can be a powdered conductive material. The average particle size (D50) of the conductive material can be in the range of 3 μm to 20 μm. The content of the conductive material in the positive electrode can be in the range of 3 to 10 parts by mass (e.g., 5 to 9 parts by mass) per 100 parts by mass of manganese dioxide.

[0035] To absorb hydrogen generated within the battery, a silver compound can be added to the positive electrode. Examples of silver compounds include silver oxide (Ag2O, AgO, Ag2O3, etc.) and silver-nickel composite oxide (AgNiO2).

[0036] (negative electrode)

[0037] The negative electrode contains zinc alloy powder as the negative electrode active material. From the perspective of corrosion resistance, the zinc alloy may contain at least one selected from indium, bismuth and aluminum. The indium content in the zinc alloy may be, for example, in the range of 0.01% by mass to 0.1% by mass. The bismuth content in the zinc alloy may be, for example, in the range of 0.003% by mass to 0.02% by mass. The aluminum content in the zinc alloy may be, for example, in the range of 0.001% by mass to 0.03% by mass. From the perspective of corrosion resistance, the content of elements other than zinc in the zinc alloy may be in the range of 0.025% by mass to 0.08% by mass.

[0038] From the perspective of negative electrode packing and electrolyte diffusibility within the negative electrode, the average particle size (D50) of the zinc alloy powder can be in the range of 100 μm to 200 μm (e.g., 110 μm to 160 μm). It should be noted that, in this specification, the average particle size refers to the median particle size (D50) at which the cumulative volume reaches 50% in a volume-based particle size distribution. The median particle size can be determined, for example, using a laser diffraction / scattering particle size distribution analyzer.

[0039] The negative electrode comprises zinc alloy powder, a gelling agent, a surfactant, a sulfate, and an electrolyte. The negative electrode can be formed by mixing the zinc alloy powder, gelling agent, surfactant, sulfate, and electrolyte. To ensure more uniform dispersion of additives (gelling agent, surfactant, etc.) in the negative electrode, it is preferred to pre-add the additives to the electrolyte used to prepare the negative electrode. The electrolyte (alkaline electrolyte) described below can be used.

[0040] In order to improve corrosion resistance, a compound containing a metal having a high hydrogen overvoltage, such as indium or bismuth, may be appropriately added to the negative electrode.

[0041] (Negative electrode current collector)

[0042] The alkaline dry battery disclosed herein may include a negative electrode current collector inserted into the negative electrode. The negative electrode current collector may be made of a metal (elemental metal or an alloy). The negative electrode current collector is preferably made of copper, or may be an alloy of copper and zinc (e.g., brass). The negative electrode current collector may be plated with tin or other plating as needed.

[0043] (diaphragm)

[0044] As the separator, non-woven fabrics mainly composed of fibers, microporous films made of resins, etc. can be used. Examples of fiber materials include cellulose and polyvinyl alcohol. Non-woven fabrics can be formed by mixing cellulose fibers with polyvinyl alcohol fibers, or by mixing rayon fibers with polyvinyl alcohol fibers. Examples of materials for microporous films include resins such as cellophane and polyolefins. The thickness (total thickness) of the separator is in the range of 160μm to 300μm. In the case of a thin separator, multiple separators can be stacked to adjust the thickness to the above-mentioned value.

[0045] (electrolyte)

[0046] As the electrolyte (alkaline electrolyte), for example, an alkaline aqueous solution containing potassium hydroxide can be used. The concentration of potassium hydroxide in the alkaline electrolyte is preferably in the range of 30 to 50% by mass (e.g., 30 to 40% by mass). The alkaline electrolyte may contain zinc oxide.

[0047] The alkaline electrolyte may contain a surfactant. The use of a surfactant can improve the dispersibility of the negative electrode active material particles. Examples of surfactants include those listed for the negative electrode. The surfactant content in the alkaline electrolyte is typically in the range of 0.001 to 0.5% by mass (e.g., 0.002 to 0.2% by mass).

[0048] (Battery casing)

[0049] The battery casing is not particularly limited; a casing corresponding to the shape of the battery can be used. The shape of the alkaline dry cell of this embodiment is not particularly limited; it can be cylindrical or coin-shaped (including button-shaped). The battery casing typically includes a battery shell, a negative terminal plate, and a gasket. The battery shell can be, for example, a metal shell with a bottom and a cylindrical shape. The metal shell can be, for example, a nickel-plated steel plate. To reduce the contact resistance between the positive electrode and the battery shell, the inner surface of the battery shell can be coated with a carbon film. The negative terminal plate can be formed of the same material as the metal shell, for example, a nickel-plated steel plate.

[0050] Examples of gasket materials include polyamide, polyethylene, polypropylene, polyphenylene ether, and polyphenylene oxide. From the perspective of corrosion resistance to alkaline electrolytes, preferred gasket materials include polyamide 6,6, polyamide 6,10, polyamide 6,12, and polypropylene. The gasket typically has a thin, annular portion.

[0051] An example embodiment of the present disclosure is described below in detail with reference to the accompanying drawings. The components of the alkaline dry cell described below can be applied to the components described above. Furthermore, the components of the alkaline dry cell described below can be modified based on the above description. Furthermore, the matters described below can also be applied to the above embodiment.

[0052] A partially exploded cross-sectional view of an alkaline dry cell 10 having an inside-outside structure according to an embodiment of the present disclosure is shown in FIG. Figure 1 The cylindrical alkaline dry battery 10 includes a battery case 1 , a positive electrode 2 disposed in the battery case 1 , a negative electrode (gel-like negative electrode) 3 , a separator 4 , and an electrolyte solution (not shown).

[0053] The battery case 1 is a bottomed cylindrical case that functions as the positive electrode terminal. The positive electrode 2 is a hollow cylindrical structure placed in contact with the inner wall of the battery case 1. The negative electrode 3 is placed within the hollow portion 2H of the positive electrode 2. The separator 4 is placed between the positive electrode 2 and the negative electrode 3. The negative electrode has the characteristics described above.

[0054] The separator 4 is composed of a cylindrical separator 4a and a backing paper 4b. The separator 4a is arranged along the inner surface of the hollow portion 2H of the positive electrode 2, separating the positive electrode 2 from the negative electrode 3. The backing paper 4b is arranged at the bottom of the hollow portion 2H of the positive electrode 2, separating the negative electrode 3 from the battery case 1.

[0055] The opening of the battery case 1 is sealed by a sealing unit 9. The sealing unit 9 includes a gasket 5, a negative electrode current collector 6, and a negative electrode terminal plate 7 that functions as a negative electrode terminal. The negative electrode current collector 6 has a nail shape with a head and a main body. The negative electrode current collector 6 includes, for example, copper, or an alloy including copper and zinc, such as brass. The negative electrode current collector 6 may also be subjected to a plating treatment such as tin plating as needed. The main body of the negative electrode current collector 6 is inserted into the through hole provided in the center of the gasket 5, and is inserted into the negative electrode 3. The head of the negative electrode current collector 6 is welded to the flat portion in the center of the negative electrode terminal plate 7. The gasket 5 has an annular thin-walled portion 5a.

[0056] The open end of the battery case 1 is crimped to the peripheral edge (flange) of the negative electrode terminal plate 7 via the peripheral edge of the gasket 5. The outer surface of the battery case 1 is covered with an outer packaging label 8. The battery case 1, gasket 5, and negative electrode terminal plate 7 constitute the battery outer shell. The positive electrode 2, negative electrode 3, separator 4, and alkaline electrolyte (not shown) are arranged within the battery outer shell.

[0057] The method of assembling the alkaline dry battery 10 is not particularly limited, and existing techniques can be applied as needed.

[0058] <Example>

[0059] The alkaline dry cell of the present disclosure is further described in detail through examples.

[0060] <Example 1>

[0061] (1) Preparation of electrolyte (alkaline electrolyte)

[0062] As the alkaline electrolyte, an alkaline aqueous solution containing potassium hydroxide (concentration: 33% by mass) and zinc oxide (concentration: 2% by mass) was prepared.

[0063] (2) Preparation of positive electrode

[0064] Manganese dioxide (positive electrode active material) and graphite (conductive material) were mixed to form a mixture. The mixture was mixed at a mass ratio of manganese dioxide to graphite of 100:6. Electrolytic manganese dioxide powder (average particle size (D50): 40 μm) was used for the manganese dioxide, and graphite powder (average particle size (D50): 8 μm) was used for the graphite.

[0065] The electrolyte was added to the mixture, stirred thoroughly, and then compressed into a sheet to obtain a positive electrode mixture. The mass ratio of the mixture to the electrolyte was set to 100:2. The electrolyte used was the same alkaline electrolyte prepared in (1) above.

[0066] Next, the flaky positive electrode mixture was crushed into pellets, which were then classified using a 10-100 mesh sieve to obtain granules. The resulting pellets were then press-molded into a hollow cylindrical shape (10.8 mm in height) to obtain positive electrode pellets (mass 2.9 g).

[0067] (3) Preparation of negative electrode

[0068] A gelled negative electrode was obtained by mixing zinc alloy powder, a surfactant, a gelling agent, a sulfate, and an electrolyte. The zinc alloy powder and materials other than the sulfate were mixed in a mass ratio of surfactant:gelling agent:electrolyte = 0.005:2.4:100. The electrolyte used was the same alkaline electrolyte prepared in (1) above. Potassium sulfate (K2SO4) was used as the sulfate, and the content thereof was 0.01% by mass in terms of sulfate ions relative to the entire negative electrode. The content of the zinc alloy powder and the sulfate relative to the entire negative electrode was 66% by mass. The negative electrode active material used was zinc alloy powder containing 0.02% by mass of indium, 0.01% by mass of bismuth, and 0.005% by mass of aluminum. The surfactant used was an anionic surfactant. The gelling agent used was a mixture of cross-linked polyacrylic acid and a partial sodium salt of cross-linked polyacrylic acid.

[0069] (4) Assembly of alkaline dry batteries

[0070] Using the above components, alkaline dry cell batteries were assembled by the following method. Figure 1 The battery assembly steps are explained.

[0071] First, a coating agent (product name: バニーハイト) manufactured by Nippon Kokuen Co., Ltd. is applied to the inner surface of a bottomed cylindrical shell made of nickel-plated steel sheet to form a carbon film with a thickness of about 10 μm, thereby obtaining a battery shell 1. Next, four positive electrode pellets are inserted longitudinally into the battery shell 1 and then pressurized to form a positive electrode 2 in a state of close contact with the inner wall of the battery shell 1. After a bottomed cylindrical separator 4 is arranged on the inner side of the positive electrode 2, the alkaline electrolyte prepared in the above (1) is injected and impregnated into the separator 4. The battery is left in this state for a predetermined time to allow the alkaline electrolyte to penetrate from the separator 4 to the positive electrode 2. Then, 6.4 g of the gel-like negative electrode 3 is filled inside the separator 4.

[0072] The separator 4 is formed using a cylindrical separator 4a and a backing paper 4b. The cylindrical separator 4a and the backing paper 4b are formed using a nonwoven fabric sheet mainly composed of a mixture of rayon fibers and polyvinyl alcohol fibers (mass ratio of 1:1).

[0073] The negative electrode current collector 6 is formed by stamping conventional brass into a nail shape and then tinning the surface. The head of the negative electrode current collector 6 is welded to the negative electrode terminal plate 7 made of nickel-plated steel. The main body of the negative electrode current collector 6 is then press-fitted into the central through-hole of the gasket 5, which is primarily composed of polyamide 6,10. This completes the sealing unit 9 consisting of the gasket 5, negative electrode current collector 6, and negative electrode terminal plate 7.

[0074] Next, the sealing unit 9 is placed in the opening of the battery case 1. At this point, the main body of the negative electrode current collector 6 is inserted into the negative electrode 3. Next, the open end of the battery case 1 is crimped onto the periphery of the negative electrode terminal plate 7 with the gasket 5 interposed therebetween, thereby sealing the opening of the battery case 1. Thus, the positive electrode 2, negative electrode 3, separator 4, and alkaline electrolyte (not shown) are placed in the battery case.

[0075] Next, the outer surface of the battery case 1 was covered with the outer label 8. In this way, the alkaline dry battery A1 of Example 1 was produced.

[0076] For battery A1, a cross section from the positive electrode terminal at the bottom of the battery case 1 to half the height of the negative electrode terminal plate 7 was obtained by CT scanning, and the total thickness of the separator was determined by the above method. The total thickness of the separator was 160 μm.

[0077] (5) Evaluation

[0078] The battery was connected to a 3.9Ω resistor via a switch. The switch was turned on with a duty cycle of 1 hour per day, and intermittent discharge was performed. Specifically, a cycle of 1 hour of discharge followed by a 23-hour rest period was repeated in an environment of 20±1°C. This discharge cycle was repeated until the battery voltage reached 0.8V.

[0079] For 10 alkaline dry cell batteries (N = 10), the total discharge time (i.e., the total period during which the switch was on) from the start of discharge to the point when the battery voltage dropped below 0.8 V was evaluated as the duration. If the duration was less than 8 hours, it was determined that an internal short circuit had occurred during discharge. The number of batteries with a duration of less than 8 hours, n, was determined.

[0080] <Examples 2 to 8, Comparative Examples 1 to 10>

[0081] Alkaline dry batteries A2 to A8 and B1 to B10 of Examples 2 to 8 and Comparative Examples 1 to 10 were produced and evaluated in the same manner as in Example 1 except that the thickness of the separator and / or the content of sulfate in the negative electrode were changed.

[0082] In Comparative Examples 1, 4, 7, and 10, alkaline dry batteries were produced without adding sulfate to the negative electrode, and batteries B1, B4, B7, and B10 were obtained, respectively.

[0083] For batteries A2 to A8 and B1 to B10, a cross section from the positive electrode terminal at the bottom of the battery case 1 to half the height of the negative electrode terminal plate 7 was obtained by CT scanning, and the total thickness of the separator was determined by the above method. The results are shown in Table 1.

[0084] Table 1 shows the evaluation results of the duration. For Batteries A1-A8 and B1-B10, the percentage of batteries with a duration of less than 8 hours, n / N, is shown as the internal short circuit occurrence rate. Table 1 also shows the total separator thickness and the sulfate content in the negative electrode for Batteries A1-A8 and B1-B10, along with the internal short circuit occurrence rate, n / N. The sulfate content represents the percentage of the mass of sulfate ions in the sulfate relative to the total mass of the negative electrode.

[0085] As shown in Table 1, in the case of a battery having a total separator thickness of 160 μm or greater and a sulfate content in the range of 0.01 to 0.5 mass % in terms of sulfate ions, internal short circuits were suppressed.

[0086] In battery B1, the total separator thickness was as thin as 150 μm, and no sulfate was added to the negative electrode, resulting in a high incidence of internal short circuits. In contrast, in batteries B2 and B3, the incidence of internal short circuits was reduced compared to battery B1 by adding sulfate to the negative electrode, but the effect of suppressing internal short circuits was not sufficient.

[0087] In Battery B5, the incidence of internal short circuits decreased compared to Battery B4, which did not have sulfate added. However, the sulfate content, as low as 0.005% by mass in terms of sulfate ions, was insufficient to fully suppress internal short circuits. On the other hand, in Battery B6, the sulfate content, as excessive as 0.7% by mass in terms of sulfate ions, increased the incidence of internal short circuits compared to Battery A4. This is believed to be because as the sulfate content increased, the distribution of sulfate within the negative electrode became more uneven, and the pH variation of the electrolyte within the negative electrode also increased, which in turn promoted internal short circuits.

[0088] In battery B10, the total separator thickness is 320 μm, which is sufficiently thick to suppress internal short circuits even without adding sulfate to the negative electrode. However, a thicker separator reduces the amount of negative electrode active material, which reduces the battery's discharge capacity. To achieve high discharge capacity and suppress internal short circuits, batteries A1 to A8 are preferred, with a total separator thickness of 160 to 300 μm and a sulfate content of 0.01 to 0.5% by mass, calculated as sulfate ions.

[0089]

Table 1

[0090]

[0091] <Examples 9 to 17>

[0092] In the preparation of the negative electrode (3) above, the sulfate added to the negative electrode was changed from potassium sulfate (K2SO4) in Example 1. Otherwise, the same procedures as in Example 1 were followed to prepare alkaline dry batteries A9 to A17 of Examples 9 to 17, and the same evaluations were performed.

[0093] Table 2 shows the evaluation results for batteries A9 to A17, along with the evaluation results for batteries A1, A5, and A7. For each battery, Table 2 shows the ratio n / N of batteries with a duration of less than 8 hours as the internal short circuit occurrence rate. Table 2 also shows the total thickness of the separator in each battery and the type of sulfate contained in the negative electrode, along with the internal short circuit occurrence rate n / N. The sulfate content of each battery shown in Table 2, calculated as sulfate ions, was 0.01% by mass relative to the total mass of the negative electrode.

[0094]

Table 2

[0095]

[0096] As shown in Table 2, in batteries A9 to A17, internal short circuits were suppressed regardless of the type of sulfate added to the negative electrode.

[0097] Industrial applicability

[0098] The present disclosure can be applied to alkaline dry batteries.

[0099] Description of Reference Numerals

[0100] 1: Battery housing

[0101] 2: Positive electrode

[0102] 2H: Hollow part

[0103] 3: Negative electrode

[0104] 4: Diaphragm

[0105] 4a: Cylindrical diaphragm

[0106] 4b: Bottom paper

[0107] 5: Padding

[0108] 5a: Thin-walled part

[0109] 6: Negative electrode collector

[0110] 7: Negative terminal plate

[0111] 8: Outer packaging label

[0112] 9: Sealing unit

[0113] 10: Alkaline dry batteries

Claims

1. An alkaline dry cell battery comprising: A hollow cylindrical positive electrode disposed in the battery case and having a hollow portion; a gel-like negative electrode filled in the hollow portion of the positive electrode and containing zinc powder; and a separator disposed between the positive electrode and the negative electrode, The total thickness of the separator is in the range of 160 μm to 300 μm. The negative electrode contains sulfate in an amount of 0.01% by mass to 0.5% by mass relative to the mass of the negative electrode, calculated as sulfate ions.

2. The alkaline dry battery according to claim 1, wherein The sulfate includes at least one selected from potassium sulfate, sodium sulfate, aluminum sulfate, potassium aluminum sulfate, calcium sulfate, zinc sulfate, lithium sulfate, and hydrates thereof.

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