Alkaline batteries

Abstract

This alkaline battery comprises a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode each include an electrolyte solution. The positive electrode includes electrolytic manganese dioxide, sodium, and zinc, wherein the electric potential of the electrolytic manganese dioxide is 300-340 mV, inclusive, relative to a mercury oxide reference electrode. The content of sodium in the positive electrode is 800-3000 mass ppm, inclusive, and the content of zinc in the positive electrode is 2400-4600 mass ppm, inclusive.

Description

[Technical field]

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

[0002] Alkaline dry batteries (alkaline manganese dry batteries) are widely used because they have a larger capacity and can extract a larger current than manganese dry batteries.

[0003] Patent Document 1 proposes an alkaline battery including a positive electrode containing electrolytic manganese dioxide, a negative electrode containing zinc or a zinc alloy, a separator disposed between the positive electrode and the negative electrode, and an alkaline electrolyte, in which the positive electrode contains 0.1 to 0.7 parts by weight of sodium per 100 parts by weight of electrolytic manganese dioxide and 0.005 to 0.05 parts by weight of silicon per 100 parts by weight of electrolytic manganese dioxide.

[0004] Patent Document 2 proposes a battery containing, as a positive electrode active material, electrolytic manganese dioxide having an average mesopore diameter of 6.5 nm or more and 10 nm or less and an alkaline potential of 290 mV or more and 350 mV or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-287672 A [Patent Document 2] International Publication No. 2020 / 110951 Brochure Summary of the Invention

[0006] When high-potential electrolytic manganese dioxide is used as the positive electrode active material, high-load discharge performance is improved. However, needle-shaped crystals of zinc oxide are precipitated on the positive electrode during medium-load discharge. The growth of these needle-shaped crystals can damage the separator, causing an internal short circuit.

[0007] One aspect of the present disclosure relates to an alkaline dry battery including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode each contain an electrolyte, the positive electrode contains electrolytic manganese dioxide, sodium, and zinc, the potential of the electrolytic manganese dioxide is 300 mV or more and 340 mV or less versus a mercury oxide reference electrode, the sodium content in the positive electrode is 800 ppm by mass or more and 3000 ppm by mass or less, and the zinc content in the positive electrode is 2400 ppm by mass or more and 4600 ppm by mass or less.

[0008] According to the present disclosure, in an alkaline dry battery, it is possible to improve the high-load discharge performance while suppressing the occurrence of an internal short circuit during medium-load discharge. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an apparatus for measuring the potential of electrolytic manganese dioxide in the positive electrode of an alkaline dry battery in one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a partially sectional front view of an alkaline dry battery according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram showing evaluation results of an alkaline dry battery according to one embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram showing evaluation results of an alkaline dry battery according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram showing evaluation results of an alkaline dry battery according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram showing evaluation results of an alkaline dry battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An alkaline dry battery according to an embodiment of the present disclosure includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode contains electrolytic manganese dioxide (hereinafter also referred to as EMD), sodium (Na), and zinc (Zn). The potential of the EMD is 300 mV or more and 340 mV or less with respect to a reference electrode of mercury oxide (Hg / HgO), the Na content in the positive electrode is 800 mass ppm or more and 3000 mass ppm or less, and the Zn content in the positive electrode is 2400 mass ppm or more and 4600 mass ppm or less.

[0011] The positive electrode and the negative electrode each contain an electrolyte. That is, an alkaline dry battery contains an electrolyte in the positive electrode, an electrolyte in the negative electrode, and other electrolytes (for example, electrolytes impregnated in the separator). Here, the electrolyte in the positive electrode is the electrolyte remaining in the positive electrode after the electrolyte attached to the surface has been removed. The electrolyte attached to the surface is the electrolyte that can be separated from the positive electrode by natural falling using the method described below.

[0012] The potential of EMD means the potential of EMD relative to a mercury oxide (Hg / HgO) reference electrode in a KOH aqueous solution (KOH content: 40% by mass) at 20±1° C.

[0013] The potential of an EMD can be measured, for example, as follows: Figure 1 is a schematic diagram of an apparatus 101 for measuring the potential of an EMD.

[0014] (1) Disassemble an unused battery, remove the positive electrode, dry it, and crush it in a mortar or the like to obtain a powder sample (positive electrode powder). The powder sample may be EMD powder.

[0015] (2) 2 g of powder sample 51 (cathode powder or EMD powder) and 20 ml of 40 mass % KOH aqueous solution are added to a centrifuge tube 102 to obtain a sample liquid (dispersion liquid of powder sample). The sample liquid is stirred and then allowed to stand at 20° C. for 24 hours.

[0016] (3) Thereafter, the sample liquid is centrifuged to cause the powder sample 51 to settle at the bottom of the centrifuge tube 102 .

[0017] (4) In the sample liquid (20±1°C) after centrifugation, a platinum electrode 104 is brought into contact with the precipitate of the powder sample 51, and a reference electrode 103 (Hg / HgO) is placed in the supernatant liquid 52 (40% by mass KOH aqueous solution). The platinum electrode 104 and the reference electrode 103 are connected to the plus side 103a and the minus side 103b of a digital voltmeter 103, respectively. The potential difference (voltage) measured at this time is taken as the potential of the EMD with respect to the reference electrode 103.

[0018] The Na content (ppm by mass) in the positive electrode means the ratio (parts per million) of the mass of Na contained in the positive electrode to the mass of the entire positive electrode. The Zn content (ppm by mass) in the positive electrode means the ratio (parts per million) of the mass of Zn contained in the positive electrode to the mass of the entire positive electrode. The Na content and Zn content in the positive electrode are the amounts of Na and Zn, respectively, contained in the positive electrode of an unused alkaline battery one week or more after its manufacture.

[0019] Using EMD with a high potential of 300 mV or more as the positive electrode active material improves high-load discharge performance. However, if the potential of the EMD exceeds 340 mV, the open circuit voltage (OCV) of the battery may not satisfy the International Electrotechnical Commission (IEC) standard (IEC60086-2 Ed.14 2021).

[0020] Even when an EMD having a high potential of 300 mV or more is used, the deposition of needle-like crystals of zinc oxide on the positive electrode during medium load discharge can be suppressed by reducing the Na content and Zn content in the positive electrode to within the above ranges. The occurrence of an internal short circuit caused by the deposition of the needle-like crystals can be suppressed. The potential of the EMD may be 320 mV or more. However, if the potential of the EMD exceeds 340 mV, it may be difficult to suppress the deposition of needle-like crystals of zinc oxide even if the amount of Na and the amount of Zn in the positive electrode are reduced.

[0021] When the Na content in the positive electrode is 3000 ppm by mass or less, the deposition of ZnO on the positive electrode during discharge is sufficiently suppressed, and when the Zn content in the positive electrode is 4600 ppm by mass or less, the amount of ZnO deposition on the positive electrode during discharge can be sufficiently reduced.

[0022] When the Na content in the positive electrode is 800 ppm by mass or more, the pH of the positive electrode increases moderately, and corrosion of the battery components such as the case is suppressed. In addition, from the viewpoint that a predetermined amount of a neutralizing agent containing Na is used during the production of EMD described below and a gelling agent containing Na is used during the preparation of the negative electrode, the positive electrode may contain 800 ppm by mass or more of Na.

[0023] In order to suppress dissolution of the negative electrode active material containing Zn, a certain amount of zinc oxide is added to the electrolyte, and from the viewpoint of retaining such an electrolyte containing zinc oxide in the positive electrode, the positive electrode may contain Zn in an amount of 2400 mass ppm or more.

[0024] The Na contained in the positive electrode comes from a Na-containing neutralizing agent (e.g., sodium hydroxide) used in the neutralization process during EMD production, a Na-containing gelling agent (e.g., sodium polyacrylate) used when making the negative electrode, etc. The Na content in the positive electrode can be adjusted by changing the concentration or amount of the neutralizing agent used, the amount of the Na-containing gelling agent added when making the negative electrode, etc.

[0025] The Zn contained in the positive electrode is mainly derived from zinc oxide contained in the electrolyte used to impregnate the separator (for filling the case) and to make the negative electrode during the manufacturing process of alkaline dry batteries. The Zn content in the positive electrode can be adjusted by changing the zinc oxide content in these electrolytes.

[0026] The Na content in the positive electrode is preferably 2300 ppm by mass or more and 2900 ppm by mass or less. From the viewpoint of easily suppressing dissolution of the negative electrode active material, the Zn content in the positive electrode is preferably 3500 ppm by mass or more and 4500 ppm by mass or less.

[0027] The Na content (ppm by mass) and Zn content (ppm by mass) in the positive electrode can be determined as follows.

[0028] (i) Disassemble an alkaline dry battery (an unused battery that has been manufactured for more than one week), remove the positive electrode, place the positive electrode on a paper sheet (filter paper), and allow the electrolyte adhering to the surface of the positive electrode to naturally fall for five minutes to remove the electrolyte adhering to the surface of the positive electrode. The electrolyte that naturally falls at this time is absorbed by the filter paper and is not included in the electrolyte held by the positive electrode (electrolyte in the positive electrode).

[0029] (ii) The positive electrode is dissolved in hydrochloric acid to obtain a measurement sample. Specifically, 10 mL of hydrochloric acid is added to 1 g of the positive electrode and heated for 2 hours, after which the insoluble matter is removed by filtration, and ion-exchanged water is added to make the volume 100 mL to obtain a measurement sample. The amount of Na and Zn in the measurement sample is measured by inductively coupled plasma (ICP) atomic emission spectroscopy. The Na content and Zn content in the positive electrode are calculated based on the measured value. Note that the measurement sample is diluted 10 times with ion-exchanged water before use. An ICP-OES analyzer (manufactured by Thermo Fishier Scientific, device name "iCAP 7400") can be used as the analysis device.

[0030] The Na content (ppm by mass) in the EMD used in the preparation of the positive electrode can also be determined in the same manner as in (ii) above.

[0031] The positive electrode holds an electrolyte. The electrolyte is an aqueous solution of potassium hydroxide (KOH) containing zinc oxide. The electrolyte held by the positive electrode (the electrolyte contained in the positive electrode) is synonymous with the electrolyte in the positive electrode. The content of the electrolyte in the positive electrode may be 10% by mass or more and 13% by mass or less, or may be 10.7% by mass or more and 12.6% by mass or less. In this case, it is easy to adjust the Na content and Zn content in the positive electrode to within the above range while maintaining the excellent discharge performance of the battery. The content (mass%) of the electrolyte in the positive electrode means the ratio (percentage) of the mass of the electrolyte contained in the positive electrode to the mass of the entire positive electrode.

[0032] Most of the Na and Zn in the positive electrode are contained in the electrolyte held by the positive electrode. The Na content and Zn content in the positive electrode may be adjusted by changing the content of the electrolyte in the positive electrode. The content of the electrolyte in the positive electrode can be adjusted, for example, by changing the density of the positive electrode, the content of graphite in the positive electrode, etc. Graphite is usually included in the positive electrode as a conductive agent and is used in combination with EMD. The higher the graphite content and the higher the density of the positive electrode, the more difficult it is for the positive electrode to retain the electrolyte. The density of the positive electrode means the density of the positive electrode pellet before the electrolyte impregnated in the separator penetrates into the positive electrode pellet that is in close contact with the inner surface of the case.

[0033] The content of the electrolyte in the positive electrode can be determined as follows.

[0034] The electrolyte content is calculated from the moisture, K, and Zn content in the positive electrode. The moisture, K, and Zn in the positive electrode are derived from the water, KOH, and ZnO in the electrolyte, respectively. Specifically, first, a positive electrode from which the electrolyte adhering to the surface is removed is obtained in the same manner as in (i) above. Then, 10 g of the positive electrode is taken, held at 140°C for 15 minutes to remove the moisture, and the amount of moisture M (g) is calculated as the reduction from 10 g. The moisture content (mass%) in the positive electrode is calculated as (M / 10) x 100. Separately, the K content (mass%) and Zn content (mass%) in the positive electrode are calculated in the same manner as in (ii) above, and the obtained values ​​are converted into the KOH content (mass%) and ZnO content (mass%), respectively. The obtained water content, KOH content, and ZnO content are summed up, and this is calculated as the electrolyte content (mass%) in the positive electrode.

[0035] The alkaline dry battery according to the present embodiment will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following embodiment. In addition, appropriate modifications are possible within the scope of the effects of the present disclosure. Furthermore, combination with other embodiments is also possible.

[0036] FIG. 2 is a front view of a lateral half cross-section of an alkaline dry battery according to an embodiment of the present disclosure.

[0037] As shown in FIG. 2, an alkaline dry battery includes a power generating element including a hollow cylindrical positive electrode 2, a gelled negative electrode 3 disposed in the hollow portion of the positive electrode 2, a separator 4 disposed between them, and an electrolyte 10. The electrolyte 10 is an alkaline electrolyte. The power generating element is housed in a cylindrical metal case 1 with a bottom that also serves as a positive electrode terminal. For the case 1, for example, a nickel-plated steel plate is used. The positive electrode 2 is disposed in contact with the inner wall of the case 1. To increase the adhesion between the positive electrode 2 and the case 1, the inner surface of the case 1 is preferably coated with a carbon film.

[0038] The cylindrical separator 4 with a bottom is composed of a cylindrical separator 4a and a bottom paper 4b. The separator 4a is arranged along the inner surface of the hollow part of the positive electrode 2, and separates the positive electrode 2 from the negative electrode 3. Therefore, the separator arranged between the positive electrode and the negative electrode means the cylindrical separator 4a. The bottom paper 4b is arranged at the bottom of the hollow part of the positive electrode 2, and separates the negative electrode 3 from the case 1.

[0039] The opening of the case 1 is sealed by a sealing unit 9. The sealing unit 9 includes a resin gasket 5, a negative electrode terminal plate 7 that also serves as a negative electrode terminal, and a negative electrode current collector 6. The gasket 5 has an annular thin wall portion 5a. When the internal pressure of the battery exceeds a predetermined value, the thin wall portion 5a breaks and gas is released to the outside of the battery. The negative electrode current collector 6 is inserted into the negative electrode 3. The material of the negative electrode current collector 6 is, for example, an alloy containing copper and zinc, such as brass. The negative electrode current collector 6 may be plated with tin or the like as necessary. The negative electrode current collector 6 has a nail-like shape having a head and a body, and the body is inserted into a through hole provided in a central cylindrical portion of the gasket 5, and 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 open end of case 1 is crimped onto a flange portion on the periphery of negative electrode terminal plate 7 via the outer peripheral end of gasket 5. The outer surface of case 1 is covered with exterior label 8.

[0040] The positive electrode 2 contains EMD, which is a positive electrode active material, and an electrolyte. The EMD is used in the form of a powder. From the viewpoint of ensuring the filling property of the positive electrode and the diffusibility of the electrolyte in the positive electrode, the average particle size of the EMD is, for example, 30 μm or more and 60 μm or less. From the viewpoint of moldability and suppression of expansion of the positive electrode, the BET specific surface area of ​​the EMD is, for example, 20 m 2 / g or more, 50m 2 / g or less.

[0041] In this specification, the average particle size is the median diameter (D50) in the particle size distribution based on volume. The average particle size is determined, for example, by using a laser diffraction and / or scattering type particle size distribution measuring device. The BET specific surface area is the surface area measured and calculated using the BET formula, which is a theoretical formula for multilayer adsorption. The BET specific surface area can be measured, for example, by using a specific surface area measuring device using the nitrogen adsorption method.

[0042] The positive electrode 2 may contain a conductive agent in addition to the EMD and the electrolyte. Examples of the conductive agent include carbon black such as acetylene black, and conductive carbon materials such as graphite. As the graphite, natural graphite, artificial graphite, etc. can be used. The conductive agent may be in a fibrous form, etc., but is preferably in a powder form. The average particle size of the conductive agent can be selected, for example, from a range of 5 nm or more and 50 μm or less. When the conductive agent is carbon black, the average particle size of the conductive agent is preferably 5 nm or more and 40 nm or less, and when the conductive agent is graphite, the average particle size of the conductive agent is preferably 3 μm or more and 50 μm or less.

[0043] The graphite content in the positive electrode mixture may be 3 parts by mass or more and 8 parts by mass or less, and preferably 4 parts by mass or more and 7 parts by mass or less, per 100 parts by mass of the total of EMD and graphite. When the graphite content is 7% by mass or less, the filling amount of EMD is easily ensured, and good medium-load discharge performance is easily obtained.

[0044] The positive electrode 2 can be obtained, for example, by pressure molding a positive electrode mixture containing a positive electrode active material, a conductive agent, and an alkaline electrolyte into a pellet shape. The positive electrode mixture may be once formed into a flake or granule shape, classified as necessary, and then pressure molded into a pellet shape. After being housed in a case, the pellet may be secondarily pressed using a predetermined tool so as to adhere closely to the inner wall of the case. The average density of the EMD in the positive electrode pellet is, for example, 2.78 g / cm 3 More than 3.08g / cm 3 The density of the positive electrode pellet is 3.2 g / cm 3 More than 3.6g / cm 3 The positive electrode (positive electrode mixture) may further contain other components (for example, polytetrafluoroethylene) as necessary.

[0045] The negative electrode 3 has a gel-like form. That is, the negative electrode 3 contains a gelling agent in addition to the negative electrode active material and the electrolyte. The negative electrode active material contains zinc or a zinc alloy. From the viewpoint of corrosion resistance, the zinc alloy preferably contains at least one selected from the group consisting of indium, bismuth, and aluminum. The electrolyte for preparing the negative electrode can be the same as the electrolyte for impregnating the separator.

[0046] The negative electrode active material is usually used in the form of a powder. From the viewpoint of the packing property of the negative electrode and the diffusibility of the alkaline electrolyte in the negative electrode, the average particle size of the negative electrode active material powder is, for example, 80 μm or more and 200 μm or less, preferably 100 μm or more and 150 μm or less.

[0047] As the gelling agent, a known gelling agent used in the field of alkaline dry batteries can be used without any particular limitation, and for example, a water-absorbing polymer can be used. Examples of such gelling agents include polyacrylic acid and sodium polyacrylate. The Na content in the positive electrode can be adjusted by changing the content of the gelling agent containing Na (for example, sodium polyacrylate) in the negative electrode. The amount of the gelling agent added can be 0.5 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the negative electrode active material. In the amount of the gelling agent added within the above range, the Na content in the positive electrode can be adjusted by changing the compounding ratio of polyacrylic acid and sodium polyacrylate.

[0048] For example, a nonwoven fabric or a microporous film is used for the separator 4. Examples of the material for the separator include cellulose and polyvinyl alcohol. For example, the nonwoven fabric is made mainly of fibers of these materials. For the microporous film, cellophane or the like is used. The thickness of the separator may be 150 μm or more and 300 μm or less, or 180 μm or more and 300 μm or less. The separator may be formed by stacking multiple sheets (such as nonwoven fabric) so that the thickness falls within the above range.

[0049] In Fig. 2, the bottomed cylindrical separator 4 is composed of a cylindrical separator 4a and a bottom paper 4b, but is not limited thereto. A bottomed cylindrical integral body may also be used as the separator, and separators of known shapes used in the field of alkaline dry batteries may be used.

[0050] The electrolyte contained in the battery (in the positive electrode, negative electrode, and separator) is an aqueous potassium hydroxide solution (alkaline electrolyte). The content of potassium hydroxide in the electrolyte is, for example, 30% by mass or more and 50% by mass or less. The electrolyte further contains zinc oxide. The content of zinc oxide in the electrolyte is, for example, 1% by mass or more and 5% by mass or less. The contents (mass%) of potassium hydroxide and zinc oxide in the electrolyte respectively refer to the ratio (percentage) of the mass of potassium hydroxide and zinc oxide contained in the electrolyte relative to the total mass of the electrolyte.

[0051] [Example] The present disclosure will be specifically described below based on examples and comparative examples, but the present disclosure is not limited to the following examples. Figures 3 to 6 show evaluation results of an alkaline dry battery according to one embodiment of the present disclosure.

[0052] Examples 1 to 21 and Comparative Examples 1 to 8 An AA cylindrical alkaline battery (LR6) as shown in FIG. 2 was fabricated by the following procedure.

[0053] [Preparation of positive electrode] A mixture was obtained by adding 0.2 parts by mass of polytetrafluoroethylene as an additive to a total of 100 parts by mass of the positive electrode active material powder (average particle size 35 μm) and graphite powder (average particle size 8 μm). 2 parts by mass of the electrolyte were added to 100.2 parts by mass of the mixture, thoroughly stirred, and then compression-molded into flakes to obtain a positive electrode mixture. A KOH aqueous solution containing ZnO was used as the electrolyte. The KOH content and ZnO content in the electrolyte were 40% by mass and 2% by mass, respectively.

[0054] As the positive electrode active material, EMD was used, the potential and Na content of which are shown in Figs. 3 to 5. The potential of the EMD and the Na content of the EMD were determined by the method described above. The potential of the EMD in Figs. 3 to 5 indicates the potential with respect to a reference electrode 103 of mercury oxide (Hg / HgO). The content of graphite in the positive electrode (positive electrode mixture) was set to the value shown in Figs. 3 to 5. The content of graphite in the positive electrode in Figs. 3 to 5 indicates the amount (parts by mass) per 100 parts by mass of the total of EMD and graphite.

[0055] The flake-like positive electrode mixture was crushed into granules, which were then classified using a 10 to 100 mesh sieve. A predetermined amount of the granules obtained was then pressure-molded into a predetermined hollow cylindrical shape with an inner diameter of 8.9 mm and an outer diameter of 13.65 mm to produce two positive electrode pellets.

[0056] [Preparation of negative electrode] 100 parts by mass of the negative electrode active material, 50 parts by mass of the electrolyte, and a gelling agent were mixed together to obtain a gelled negative electrode 3. The negative electrode active material used was zinc alloy powder (average particle size 130 μm) containing 0.02% by mass of indium, 0.01% by mass of bismuth, and 0.005% by mass of aluminum.

[0057] The electrolyte used was a KOH aqueous solution containing ZnO. The KOH content in the electrolyte was 33 mass %. The ZnO content in the electrolyte was the value shown in Figures 3 to 5.

[0058] A mixture of cross-linked branched polyacrylic acid and highly cross-linked chain sodium polyacrylate (Na polyacrylate) was used as the gelling agent. The content of the gelling agent in the negative electrode was the value shown in Figures 3 to 5. Note that the content of the gelling agent in the negative electrode in Figures 3 to 5 is the amount (parts by mass) per 100 parts by mass of the negative electrode active material, and the value in parentheses indicates the mass ratio (Na polyacrylate:polyacrylic acid).

[0059] [Assembling alkaline batteries] Case 1 was prepared, in which the inside of a bottomed cylindrical case (outer diameter 14.0 mm, height 49.9 mm) made of nickel-plated steel sheet was covered with a carbon coating. Two positive electrode pellets were inserted vertically into case 1, and then pressure was applied to form positive electrode 2 in close contact with the inner wall of case 1. The density of the positive electrode (positive electrode pellets) in close contact with the inner surface of the case was the value shown in Figures 3 to 5.

[0060] A cylindrical separator 4 with a bottom was placed inside the positive electrode 2, and a predetermined amount of electrolyte was poured into the case 1 and absorbed into the separator 4. The separator 4 was composed of a cylindrical separator 4a and a bottom paper 4b. The cylindrical separator 4a had a thickness of 200 μm and was composed of a nonwoven fabric sheet with a thickness of 100 μm rolled twice. The electrolyte for impregnating the separator (for injecting the electrolyte into the case) was the same as the electrolyte for preparing the negative electrode. This was left for a predetermined time in this state, and the electrolyte was allowed to permeate from the separator 4 to the positive electrode 2. After that, 6.6 g of a gelled negative electrode 3 was filled inside the separator 4.

[0061] A sealing unit 9 consisting of a gasket 5, a negative electrode terminal plate 7, and a negative electrode current collector 6 was placed in the opening of the case 1. At this time, the body of the negative electrode current collector 6 was inserted into the negative electrode 3. The opening end of the case 1 was crimped to the peripheral edge of the negative electrode terminal plate 7 via the gasket 5, and the opening of the case 1 was sealed. The outer surface of the case 1 was covered with an exterior label 8. In this manner, an alkaline dry battery was produced. In Figs. 3 to 5, A1 to A21 are the batteries of Examples 1 to 21, and B1 to B8 are the batteries of Comparative Examples 1 to 8.

[0062] The Na content, Zn content, and electrolyte content in the positive electrode, which were determined by the methods described above, were the values ​​shown in FIGS.

[0063] The following evaluation 1 was carried out for each of the batteries of the Examples and Comparative Examples.

[0064] [Evaluation 1: Occurrence rate of abnormal discharge during medium load discharge] A single battery was connected in series to a 3.9 Ω resistor, and the battery was discharged for one hour at a load of 3.9 Ω in an environment of 20±2°C, and this step was repeated once a day. The discharge time (accumulated time of one-hour discharge) until the closed circuit voltage of the battery reached 0.9 V was then measured. If the discharge time was less than eight hours, it was determined to be an abnormal discharge. Note that this abnormal discharge occurs when needle-shaped crystals of ZnO precipitate on the positive electrode during discharge, causing an internal short circuit.

[0065] The discharge time of each of the five batteries was measured, the number of batteries that experienced abnormal discharge was counted, and the ratio of the number of batteries that experienced abnormal discharge out of the five was calculated as the abnormal discharge occurrence rate. The evaluation results are shown in Figures 3 to 5.

[0066] 3, the Na content and Zn content in the positive electrode were reduced to 3000 mass ppm or less and 4600 mass ppm or less, respectively, by appropriately adjusting the graphite content in the positive electrode and / or the density of the positive electrode (positive electrode pellets) In the batteries A1 to A4, the abnormal discharge occurrence rate during medium load discharge was 0%.

[0067] In the batteries A5 to A12 in Fig. 4, the content of sodium polyacrylate in the negative electrode and / or the content of ZnO in the electrolyte for impregnating the separator and for preparing the negative electrode were appropriately adjusted. As a result, the Na content and Zn content in the positive electrode were reduced to 3000 mass ppm or less and 4600 mass ppm or less, respectively. In the batteries A5 to A12, the abnormal discharge occurrence rate during medium load discharge was 0%.

[0068] In the batteries A13 to A21 in FIG. 5, the Na content in the EMD was appropriately adjusted. Furthermore, the content of sodium polyacrylate in the negative electrode and / or the ZnO content in the electrolyte for impregnating the separator and for preparing the negative electrode were appropriately adjusted as necessary. As a result, the Na content and the Zn content in the positive electrode were reduced to 3000 mass ppm or less and 4600 mass ppm or less, respectively. In the batteries A13 to A20, the abnormal discharge occurrence rate during medium load discharge was 0%. In the battery A21, the abnormal discharge occurrence rate during medium load discharge was reduced to 20%.

[0069] On the other hand, in the batteries B1 to B8, the Na content and / or Zn content in the positive electrode was high, and the incidence of abnormal discharge during medium-load discharge increased to 40% or more.

[0070] In the batteries A13 to A15, A17 to A21, and B7 to B8, the EMD was washed to adjust the Na content in the EMD. Specifically, 300 g of EMD was washed with 1.8 L of a 25°C washing solution (NaOH aqueous solution, pure water, or dilute sulfuric acid) for a predetermined time, the washing solution was removed by filtration, and hot air at 100°C was blown for 20 minutes to dry the EMD. In the battery B8, a NaOH aqueous solution (concentration 16.2 mmol / L) was used as the washing solution, and the washing time was 1 hour. In the batteries A13 to A14, pure water was used as the washing solution, and the washing time was 20 minutes. In the battery A15, a NaOH aqueous solution (concentration 12.2 mmol / L) was used as the washing solution, and the washing time was 1 hour. In the batteries A17 to A18 and B7, dilute sulfuric acid (concentration 50 mmol / L) was used as the washing solution, and the washing time was 1 hour. For the batteries A19 to A21, pure water was used as the cleaning solution, and the cleaning time was 10 minutes.

[0071] Comparative Example 9 Battery C1 of Comparative Example 9 was produced in the same manner as battery B1 of Comparative Example 1, except that EMD having a potential of 280 mV was used.

[0072] Comparative Example 10 Battery C2 of Comparative Example 9 was produced in the same manner as battery A1 of Example 1, except that EMD having a potential of 280 mV was used.

[0073] The batteries C1 and C2 were subjected to the above-mentioned Evaluation 1 as well as the following Evaluation 2.

[0074] The following evaluation 2 was also carried out for the batteries A1, B1, B3, and B5.

[0075] [Evaluation 2: High-load discharge performance] In an environment of 20±2°C, a pulse discharge was performed 10 times by alternating between discharging at 1.5 W for 2 seconds and discharging at 0.65 W for 28 seconds, followed by a rest period of 55 minutes. The discharge time (accumulated pulse discharge time) until the closed circuit voltage of the battery reached 1.05 V was measured.

[0076] The evaluation results of batteries C1 and C2 are shown in Fig. 4 together with the evaluation results of batteries A1, B1, B3, and B5. Note that the discharge time during high-load discharge in Fig. 4 is expressed as an index relative to the discharge time of battery C1 of Comparative Example 9, which is set to 100.

[0077] In the batteries C1 and C2, the EMD potential was less than 300 mV, and no abnormal discharge occurred during medium-load discharge, but the high-load discharge performance decreased.

[0078] In batteries B1, B3, and B5, the EMD potential was 300 mV or higher, and the high-load discharge performance was improved. However, because the Na content and / or Zn content in the positive electrode was high, the occurrence rate of abnormal discharge during medium-load discharge increased to 40% or more.

[0079] In Battery A1, the EMD potential was 300 mV or more, and the high-load discharge performance was improved. In addition, in Battery A1, the EMD potential was 300 mV or more, but the Na content and Zn content in the positive electrode were 3000 mass ppm or less and 4600 mass ppm or less, respectively, so no abnormal discharge occurred during medium-load discharge. [Industrial Applicability]

[0080] The alkaline dry battery according to the present disclosure is suitable for use as a power source for, for example, portable audio devices, electronic games, lights, and the like. [Explanation of symbols]

[0081] 1 case 2 Positive electrode 3 Negative electrode 4. Cylindrical separator with bottom 4a Cylindrical separator 4b bottom paper 5 Gasket 5a Thin wall part 6 Negative electrode current collector 7 Negative terminal plate 8 Exterior Label 9. Sealing unit 10 Electrolyte 104 Reference electrode

Claims

1. A positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the positive electrode and the negative electrode each contain an electrolyte; The positive electrode contains electrolytic manganese dioxide, sodium, and zinc, The potential of the electrolytic manganese dioxide is 300 mV or more and 340 mV or less with respect to a mercury oxide reference electrode; The content of the sodium in the positive electrode is 800 ppm by mass or more and 3000 ppm by mass or less, The content of the zinc in the positive electrode is 2400 ppm by mass or more and 4600 ppm by mass or less.

2. 2. The alkaline dry battery according to claim 1, wherein the content of the sodium in the positive electrode is 2300 ppm by mass or more and 2900 ppm by mass or less.

3. 3. The alkaline dry battery according to claim 1, wherein the positive electrode contains the electrolyte in an amount of 10% by mass or more and 13% by mass or less.

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