Flat battery and its manufacturing method

Abstract

Provided are a flat battery that is excellent in productivity and a method for manufacturing the same.　This flat battery is characterized in that: a positive electrode, a negative electrode, a separator, and an electrolytic solution are sealed in a battery container having an outer can and a sealing can; the positive electrode is housed in the outer can; and a porous electrolytic solution absorber is inserted between the positive electrode and the inner bottom surface of the outer can. This method for manufacturing a flat battery is characterized by including, when manufacturing a flat battery in which a positive electrode, a negative electrode, a separator, and an electrolytic solution are sealed in a battery container having an outer can and a sealing can, a step for disposing an electrolytic solution absorber on the inner bottom surface of the outer can, a step for disposing the positive electrode on the electrolytic solution absorber and, after the step for disposing the electrolytic solution absorber and before or after the step for disposing the positive electrode, a step for injecting the electrolytic solution into the outer can, a porous body having a void ratio of 40-90% being used as the electrolytic solution absorber.

Description

[Technical Field]

[0001] The present invention relates to a flat battery with excellent productivity and a method for manufacturing the same. [Background technology]

[0002] In a flat battery in which a positive electrode, a negative electrode, a separator, and an electrolyte are sealed in a battery container composed of an outer can that serves as the positive electrode terminal and a sealed can that serves as the negative electrode terminal, a method is usually employed in which, when housing the positive electrode and electrolyte in the outer can, the electrolyte is first poured into the outer can and then the positive electrode and separator are placed inside the outer can, or the positive electrode is first placed inside the outer can, and then a separator is placed directly on the positive electrode or further on top of that, and then the electrolyte is poured in.

[0003] However, even when the positive electrode comes into contact with the electrolyte, the electrolyte does not immediately begin to be absorbed into the positive electrode, and therefore, in the former process, when the positive electrode is inserted into an outer can filled with the electrolyte, the level of the electrolyte rises according to the volume of the positive electrode. If the separator placed on the positive electrode could immediately absorb the rising electrolyte, the problem of the electrolyte overflowing from the outer can would not occur, but because it takes some time for the separator to absorb the electrolyte, if a large amount of electrolyte is poured into the outer can, the problem of the electrolyte leaking is more likely to occur.

[0004] On the other hand, in the latter process, the electrolyte solution dropped onto the positive electrode (or onto the separator) flows and flows into the gap between the side wall of the outer can and the positive electrode. However, since it takes time for the separator and the positive electrode to absorb the electrolyte, if the amount of electrolyte solution is large, the problem of electrolyte leakage is likely to occur.

[0005] On the other hand, there have been proposals for technologies to prevent leakage of electrolyte during the manufacturing of flat batteries. For example, Patent Documents 1 and 2 describe a method in which a recess is provided on the bottom side of the positive electrode can of the positive electrode mixture, so that dripped electrolyte is collected in the recess and leakage is prevented.

[0006] Patent Document 3 also describes a method in which a bag-shaped body is formed from an electrolyte solution holding material (separator) and a liquid-tight film, a positive electrode is sealed inside, the electrolyte solution is absorbed from the electrolyte solution holding material side, and the body is then incorporated into a battery container. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-154789 [Patent Document 2] Japanese Patent Publication No. 2020-119628 [Patent Document 3] Japanese Patent Application Publication No. 1-157058 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the methods of Patent Documents 1 and 2 reduce the capacity of the positive electrode, and there is also the possibility that air bubbles remain in the downwardly formed recesses, preventing the electrolyte from being collected.

[0009] Furthermore, the method of Patent Document 3 requires complicated steps, and the presence of a liquid-tight film between the positive electrode and the battery container makes it difficult to ensure electrical continuity.

[0010] For these reasons, it is necessary to develop technology that can increase the productivity of flat batteries by suppressing electrolyte leakage during manufacturing while also preventing deterioration of characteristics.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flat battery with excellent productivity and a method for manufacturing the same. [Means for solving the problem]

[0012] The flat battery of the present invention is characterized in that a positive electrode, a negative electrode, a separator, and an electrolyte are sealed in a battery container having an outer can and a sealed can, the positive electrode is housed in the outer can, and a porous electrolyte absorber is inserted between the positive electrode and the inner bottom surface of the outer can.

[0013] The method for producing a flat battery of the present invention is a method for producing a flat battery in which a positive electrode, a negative electrode, a separator, and an electrolyte are sealed in a battery container having an outer can and a sealing can, the method comprising the steps of: arranging an electrolyte absorber on the inner bottom surface of the outer can; arranging the positive electrode on the electrolyte absorber; and disposing the electrolyte in the outer can after the step of arranging the electrolyte absorber and before or after the step of arranging the positive electrode. can and a step of injecting the electrolyte solution into the electrolyte solution absorber, wherein a porous body having a porosity of 40 to 90% is used as the electrolyte solution absorber. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a flat battery with excellent productivity and a method for manufacturing the same. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a flat battery of the present invention. [Figure 2] FIG. 3 is a cross-sectional view schematically illustrating another example of a flat battery of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The flat battery of the present invention comprises a battery container having an outer can and a sealed can, and a positive electrode, a negative electrode, a separator, and an electrolyte sealed therein. The positive electrode is housed in the outer can, and a porous electrolyte absorber is inserted between the positive electrode and the inner bottom surface of the outer can.

[0017] FIG. 1 is a cross-sectional view showing a schematic diagram of an example of a flat battery of the present invention. In the flat battery 1 shown in FIG. 1, a sealable can 3 containing a negative electrode 5 is fitted into the opening of an outer can 2 containing a positive electrode 4 and a separator 6 via an annular gasket (resin gasket) 7 with an L-shaped cross section. The open end of the outer can 2 is tightened inward, causing the gasket 7 to abut against the sealable can 3, sealing the opening of the outer can 2 and creating a sealed structure inside the battery. That is, in the battery shown in FIG. 1, the space (sealed space) within the battery container consisting of the outer can 2, the sealable can 3, and the gasket 7 is filled with power generating elements including a positive electrode 4, a negative electrode 5, and a separator 6. Furthermore, an electrolyte (not shown) is poured into the space and held by the separator. The outer can 2 also serves as the positive electrode terminal, and the sealable can 3 also serves as the negative electrode terminal.

[0018] In the flat battery 1, a porous electrolyte absorber 8 is inserted between the positive electrode 4 and the inner bottom surface of the outer can 2.

[0019] In the flat battery of the present invention, an electrolyte absorber is placed on the inner bottom surface of the outer can during production, so that when electrolyte is subsequently injected into the outer can before or after the positive electrode is placed, the electrolyte absorber absorbs and retains a certain amount of electrolyte, thereby highly suppressing leakage of the electrolyte. Thus, the present invention makes it possible to increase the productivity of flat batteries.

[0020] The electrolyte absorber may be a porous sheet, such as a nonwoven fabric primarily made of vinylon and rayon, a vinylon-rayon nonwoven fabric (vinylon-rayon mixed paper), a polyamide nonwoven fabric, or a polyolefin-rayon nonwoven fabric; a porous sheet made of resin (including paper) such as vinylon paper, vinylon-linter pulp paper, or vinylon-mercerized pulp paper; or a porous carbon sheet. Examples of porous carbon sheets that can be used as the electrolyte absorber include carbon paper, carbon cloth, and carbon felt made of fibrous carbon, as well as molded sheets made of expanded graphite. The same material as the separator may also be used.

[0021] The electrolyte solution absorber preferably has a porosity of 40% or more, more preferably 60% or more, since this improves the function of absorbing and retaining the electrolyte solution. However, if the porosity of the electrolyte solution absorber is too high, the electrolyte solution retention function may be reduced, so the porosity is preferably 90% or less, more preferably 80% or less.

[0022] The porosity P (%) of the electrolyte solution absorber as used in this specification can be calculated by finding the sum for each component i using the following formula (1) from the thickness of the electrolyte solution absorber, the mass per area, and the density of the constituent components.

[0023] P = {1-(m / t) / (Σa i ρ i )}×100 (1)

[0024] Here, in the formula (1), a i : The ratio of component i when the total mass is 1, ρ i : Density of component i (g / cm 3 ), m: Mass per unit area of ​​the electrolyte absorber (g / cm 2 ), t: thickness of the electrolyte absorber (cm). The mass per unit area m of the electrolyte absorber was measured by cutting a 20 cm square of the electrolyte absorber using an electronic balance, and the mass was calculated by dividing the area by 1 cm 2 The thickness t of the electrolyte absorber was measured at 10 randomly selected points using a micrometer and averaged.

[0025] The average pore size of the electrolyte solution absorber is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 20 μm or more, from the viewpoint of enabling rapid absorption of the electrolyte solution.

[0026] However, if the pore size of the electrolyte absorber is too large, there is a risk that the electrolyte retention function may be reduced, so it is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less.

[0027] The average pore size of the electrolyte solution absorber as referred to in this specification is a value measured based on the bubble point method specified in JIS K 3832.

[0028] Furthermore, the thickness of the electrolyte absorber is preferably 30 μm or more, and more preferably 50 μm or more, from the viewpoint of being able to retain a relatively large amount of electrolyte.

[0029] However, if the electrolyte absorber is too thick, it may be necessary to reduce the amount of positive electrode or negative electrode in the battery, which may cause a decrease in capacity. Therefore, the thickness is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 150 μm or less, and particularly preferably 100 μm or less.

[0030] The area of ​​the electrolyte absorber in plan view is not particularly limited as long as it can absorb a sufficient amount of electrolyte to prevent leakage, but it is preferably 50% or more, more preferably 80% or more, and even more preferably 90% or more, of the area of ​​the inner bottom surface of the outer can (100%). The area of ​​the electrolyte absorber in plan view can also be the same as the area of ​​the inner bottom surface of the outer can (i.e., 100% of the area of ​​the inner bottom surface of the outer can (100%)). However, it is usually sufficient to set the ratio at about 95 to 99%.

[0031] In a flat battery, if a conductive material such as a porous carbon sheet is used as the electrolyte absorber, the positive electrode and the outer can are electrically connected via the electrolyte absorber, and the use of the electrolyte absorber does not impair current collection from the positive electrode. However, if an insulating electrolyte absorber such as a resin sheet is used, the contact area between the positive electrode and the inner bottom surface of the outer can is reduced, which may result in insufficient current collection from the positive electrode. Therefore, in a flat battery, it is preferable that the positive electrode and the side wall of the outer can are electrically connected. This allows for good current collection from the positive electrode, even if an insulating electrolyte absorber is used.

[0032] Conduction between the positive electrode and the side wall of the outer can may be achieved by, for example, bringing the side surface of the positive electrode into direct contact with the side wall of the outer can, as shown in FIG. 1, or may be achieved by, for example, holding the positive electrode on a metal pedestal and bringing this pedestal into contact with the side wall of the outer can.

[0033] A cross-sectional view schematically illustrating another example of a flat battery of the present invention is shown in Figure 2. In the flat battery, electrical continuity between the positive electrode and the outer can may be achieved by making the area of ​​the electrolyte absorber in a plan view smaller than the area of ​​the inner bottom surface of the outer can, and bringing the peripheral edge of the bottom surface of the positive electrode, which faces the inner bottom surface of the outer can, into contact with the inner bottom surface of the outer can, as shown in Figure 2.

[0034] The flat battery of the present invention can take the form of either a primary battery or secondary battery having a non-aqueous electrolyte, or a primary battery or secondary battery having an aqueous electrolyte.

[0035] In addition, when an aqueous electrolyte is used, some electrolyte absorbers such as porous carbon sheets are usually water-repellent, making it difficult for them to absorb the electrolyte, and the effects of the present invention may not be fully achieved. In such cases, hydrophilization treatment can be performed to improve the absorbency of the electrolyte absorber and prevent the above-mentioned problems.

[0036] The hydrophilization treatment can be carried out by, for example, a method of immersing a water-repellent porous sheet, such as a porous carbon sheet, for constituting an electrolyte solution absorber in a treatment solution containing a surfactant to adhere the surfactant to the surface of the carbon, a method of imparting functional groups to the surface of the carbon by treatment such as electrolytic oxidation or oxidation in an acidic solution, or a method of roughening the surface of the carbon by plasma treatment or the like.

[0037] Furthermore, since secondary batteries generally require a larger amount of electrolyte than primary batteries, leakage is more likely to occur during battery manufacturing. Therefore, the flat battery of the present invention has a more pronounced effect when used as a secondary battery.

[0038] The structure of a flat battery will be described in detail below, taking an alkaline battery, which is the main embodiment of the present invention, as an example.

[0039] When the flat battery is an alkaline battery, the positive electrode can be made of a compound that can be used as a positive electrode active material for alkaline primary batteries or alkaline secondary batteries, such as silver oxide or nickel oxyhydroxide. Examples of such a compound include a molded body of a positive electrode mixture that contains a conductive additive in addition to a positive electrode active material, and a structure in which a molded body of a positive electrode mixture is formed as a positive electrode mixture layer on one or both sides of a current collector.

[0040] When silver oxide is used as the active material of the positive electrode, AgO or Ag2O can be used.

[0041] Although the particle size of silver oxide is not particularly limited, the average particle size is preferably 10 μm or less, and more preferably 2 μm or less. In particular, when silver oxide of such a size is used to make an alkaline battery into a secondary battery, the utilization rate during charging is improved and a large charge capacity can be obtained even with a relatively low end-of-charge voltage, which further improves the charge-discharge cycle characteristics of the battery and also makes it possible to suppress swelling of the battery that can occur, for example, when the end-of-charge voltage is increased.

[0042] However, silver oxide with too small a particle size is difficult to manufacture and handle thereafter, so the average particle size of silver oxide is preferably 0.01 μm or more, and more preferably 0.03 μm or more.

[0043] The particle size of silver oxide and other particles (graphite particles, carbon black particles, insulating inorganic particles, and zinc particles for the negative electrode) referred to in this specification is a value measured by dispersing these particles in a medium that does not dissolve the particles using a laser scattering particle size distribution analyzer (for example, "LA-920" manufactured by Horiba, Ltd.).

[0044] Examples of the conductive additive for the positive electrode mixture include particles of a carbonaceous material such as carbon black particles, graphite particles, etc. It is more preferable to use a combination of carbon black particles and graphite particles as the conductive additive.

[0045] The use of carbon black particles facilitates the formation of a good conductive network within the compact of the positive electrode mixture, which increases the number of contact points with silver oxide particles, the positive electrode active material, compared to the use of graphite particles alone, thereby effectively reducing the electrical resistance within the compact of the positive electrode mixture. For example, when an alkaline battery is used as the secondary battery, this can improve the reaction efficiency of the positive electrode active material during charging.

[0046] On the other hand, when carbon black particles alone are used, it may be necessary to use a binder to improve the moldability of the positive electrode mixture compact depending on the thickness of the compact. However, when graphite particles are also used, the moldability of the positive electrode mixture compact is improved. Therefore, even when the positive electrode mixture compact is thin, for example, 0.4 mm or less, more preferably 0.3 mm or less, the moldability is good, and it becomes easy to prevent production defects without using a binder.

[0047] The graphite particles in the positive electrode mixture may be either particles of natural graphite (such as flake graphite) or particles of artificial graphite, and one or more of these may be used.

[0048] As described above, the graphite particles have the function of improving the moldability of the positive electrode mixture compact. From the viewpoint of better exerting this function, the graphite particles preferably have an average particle size of 1 μm or more, more preferably 2 μm or more, and from the viewpoint of improving electrical conductivity, the average particle size is preferably 7 μm or less, more preferably 5 μm or less.

[0049] Examples of carbon black particles for the positive electrode mixture include furnace black, channel black, acetylene black, thermal black, etc., and one or more of these can be used. Among these carbon black particles, acetylene black, which has high conductivity and few impurities, is preferably used.

[0050] When the alkaline battery is a secondary battery, if silver oxide is used as the positive electrode active material, it is preferable to further contain insulating inorganic particles in the positive electrode mixture, which can further improve the charge-discharge cycle characteristics of the battery.If insulating inorganic particles are used, the positive electrode mixture can further improve the charge-discharge cycle characteristics of the battery by further containing carbon black particles and graphite particles.

[0051] Examples of insulating inorganic particles for the positive electrode mixture include particles of an oxide of at least one element selected from Si, Zr, Ti, Al, Mg, and Ca. Specific examples of the oxide include Al2O3, TiO2, SiO2, ZrO2, MgO, CaO, AlOOH, and Al(OH)3. Particles that are insoluble or poorly soluble in alkaline electrolyte are preferred. These insulating inorganic particles may be used alone or in combination of two or more.

[0052] If the particle size of the insulating inorganic particles is too large, the effect of improving the charge-discharge cycle characteristics of the battery may be reduced. Therefore, from the viewpoint of further improving the charge-discharge cycle characteristics of the battery, the average particle size of the insulating inorganic particles is preferably 0.5 μm or less, and more preferably 0.3 μm or less.

[0053] Furthermore, if the particle size of the insulating inorganic particles is too small, the effect of improving the charging efficiency (initial capacity) of the battery may be reduced. Therefore, from the viewpoint of further improving the charging efficiency of the battery, the average particle size of the insulating inorganic particles is preferably 0.01 μm or more, and more preferably 0.05 μm or more.

[0054] When silver oxide is used as the positive electrode active material in order to ensure capacity, the composition of the positive electrode mixture preferably has a content of 60 mass % or more, more preferably 80 mass % or more, and particularly preferably 90 mass % or more, where the total solid content constituting the positive electrode mixture is 100 mass %.

[0055] Furthermore, the content of the conductive additive in the positive electrode mixture is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more, from the viewpoint of conductivity; on the other hand, in order to prevent a decrease in capacity and gas generation during charging, the content is preferably 8% by mass or less, more preferably 7% by mass or less, even more preferably 5% by mass or less, and particularly preferably 3% by mass or less.

[0056] When carbon black particles and graphite particles are contained in the positive electrode mixture, the content of the graphite particles is preferably 1% by mass or more, and more preferably 2% by mass or more, from the viewpoint of ensuring the effect of improving the charging efficiency and charge / discharge cycle characteristics of the battery by using the carbon black particles in combination. When carbon black particles and graphite particles are contained in the positive electrode mixture, the content of the graphite particles is preferably 7% by mass or less, and more preferably 4% by mass or less, from the viewpoint of preventing a decrease in the capacity of the battery due to an excessive decrease in the amount of positive electrode active material in the positive electrode mixture.

[0057] Furthermore, when carbon black particles and graphite particles are contained in the positive electrode mixture, the content of the carbon black particles is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more, from the viewpoint of ensuring the effect of improving the charging efficiency and charge / discharge cycle characteristics of the battery by using the carbon black particles in combination with the graphite particles. However, if the amount of carbon black particles in the positive electrode mixture is too large, there is a risk that the amount of swelling of the positive electrode will increase, for example, when the battery is stored at high temperatures. Therefore, from the viewpoint of suppressing swelling of the positive electrode during battery storage (particularly storage at high temperatures of about 60°C) and improving the storage characteristics of the battery, when carbon black particles and graphite particles are contained in the positive electrode mixture, the content of the carbon black particles is preferably 1.5% by mass or less, and more preferably 1% by mass or less.

[0058] Furthermore, when insulating inorganic particles are contained in the positive electrode mixture, the content thereof is preferably 0.1% by mass or more, and more preferably 3% by mass or more, from the viewpoint of satisfactorily ensuring the effects of their use (particularly the effect of improving the charge-discharge cycle characteristics of the battery). However, if the amount of insulating inorganic particles in the positive electrode mixture is too large, the loading amount of the positive electrode active material decreases, leading to a decrease in the battery capacity. In addition, depending on the type of insulating inorganic particles, the discharge capacity may suddenly decrease as the charge-discharge cycle progresses. Therefore, the content of insulating inorganic particles in the positive electrode mixture is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0059] As described above, the positive electrode mixture can be formed without using a binder, but a binder may be used when increased strength is required (for example, when graphite is not used as a conductive additive). Examples of binders for the positive electrode mixture include fluororesins such as polytetrafluoroethylene (PTFE). When a binder is used, the content of the binder in the positive electrode mixture is preferably 0.1 to 20 mass%.

[0060] In the case of a positive electrode consisting only of a compact of a positive electrode mixture, the positive electrode mixture can be produced by, for example, mixing a positive electrode active material, a conductive additive, and, if necessary, an alkaline electrolyte (the same alkaline electrolyte as that injected into a battery can be used), and then press-molding the mixture into a predetermined shape.

[0061] Furthermore, in the case of a positive electrode having a molded body of a positive electrode mixture (positive electrode mixture layer) and a current collector, for example, the positive electrode mixture-containing composition (slurry, paste, etc.) is prepared by dispersing a positive electrode active material, a conductive additive, etc. in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and this is applied to a current collector, dried, and, if necessary, subjected to a pressing process such as a calendaring process, thereby producing the positive electrode.

[0062] However, the positive electrode is not limited to those produced by the above methods, and may be produced by other methods.

[0063] When the positive electrode is made of only a molded body of the positive electrode mixture, its thickness is preferably 0.15 to 4 mm. On the other hand, when the positive electrode has a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (thickness per surface of the current collector) is preferably 30 to 300 μm.

[0064] When a current collector is used for the positive electrode, examples of the current collector include those made of stainless steel such as SUS316, SUS430, and SUS444; aluminum; and aluminum alloys. Examples of the current collector include plain woven wire mesh, expanded metal, lath mesh, punched metal, metal foam, and foil (plate). The thickness of the current collector is preferably, for example, 0.05 to 0.2 mm. It is also desirable to apply a paste-like conductive material such as carbon paste or silver paste to the surface of such a current collector.

[0065] When the flat battery is an alkaline battery, the negative electrode uses zinc particles, i.e., particles composed of pure zinc (including unavoidable impurities) or zinc alloy. In such a negative electrode, the zinc in the particles acts as the active material. Examples of alloy components of zinc alloy particles include indium, bismuth, and aluminum (the remainder being zinc and unavoidable impurities). The zinc particles in the negative electrode may be composed of only one type of particle with a single composition, or may contain two or more types of particles with different compositions.

[0066] However, it is preferable to use zinc particles that do not contain mercury as an alloying component. Batteries using such zinc particles can reduce environmental pollution caused by battery disposal. Also, for the same reason as in the case of mercury, it is preferable to use zinc particles that do not contain lead as an alloying component.

[0067] Regarding the particle size of the zinc particles, for example, the proportion of particles with a particle size of 75 μm or less in the total powder is preferably 50 mass% or less, more preferably 30 mass% or less, and the proportion of powder with a particle size of 100 to 200 μm is 50 mass% or more, more preferably 90 mass% or more.

[0068] The negative electrode may contain, for example, a gelling agent (sodium polyacrylate, carboxymethyl cellulose, etc.) added as needed in addition to the zinc particles, and an alkaline electrolyte may be added to this to form a negative electrode agent (gelled negative electrode). The amount of gelling agent in the negative electrode is preferably, for example, 0.5 to 1.5 mass %.

[0069] The negative electrode can also be a non-gelled negative electrode that is substantially free of the gelling agent described above. (Note that a non-gelled negative electrode may contain a gelling agent as long as it does not thicken the alkaline electrolyte near the zinc particles. Therefore, "substantially free of a gelling agent" means that the gelling agent may be present to a degree that does not affect the viscosity of the alkaline electrolyte.) In the case of a gelled negative electrode, the alkaline electrolyte is present near the zinc particles together with the gelling agent. However, the gelling agent thickens the alkaline electrolyte, inhibiting the movement of the alkaline electrolyte and, ultimately, the movement of ions in the electrolyte. This is thought to slow the reaction rate at the negative electrode, hindering the improvement of the load characteristics (especially heavy load characteristics) of the battery. In contrast, by making the negative electrode non-gelled and maintaining a high ion migration rate in the alkaline electrolyte without increasing the viscosity of the alkaline electrolyte near the zinc particles, the reaction rate at the negative electrode can be increased, thereby further improving the load characteristics (especially heavy load characteristics).

[0070] The alkaline electrolyte contained in the negative electrode can be the same as that injected into the battery.

[0071] The content of zinc particles in the negative electrode is, for example, preferably 60% by mass or more, more preferably 65% ​​by mass or more, and preferably 75% by mass or less, more preferably 70% by mass or less.

[0072] The negative electrode preferably contains an indium compound, which can more effectively prevent gas generation due to the corrosion reaction between zinc particles and the alkaline electrolyte.

[0073] Examples of the indium compound include indium oxide and indium hydroxide.

[0074] The amount of the indium compound used in the negative electrode is preferably 0.003 to 1 in terms of mass ratio to 100 zinc particles.

[0075] When the flat battery is an alkaline battery, the separator interposed between the positive and negative electrodes can be made of a nonwoven fabric primarily made of vinylon and rayon, a vinylon-rayon nonwoven fabric (vinylon-rayon mixed paper), a polyamide nonwoven fabric, a polyolefin-rayon nonwoven fabric, vinylon paper, vinylon-linter pulp paper, or vinylon-mercerized pulp paper. Alternatively, the separator can be made by stacking a hydrophilically treated microporous polyolefin film (such as a microporous polyethylene film or a microporous polypropylene film), a cellophane film, and a liquid-absorbing layer (electrolyte retention layer) such as a vinylon-rayon mixed paper. The thickness of the separator is preferably 20 to 500 μm.

[0076] Furthermore, when the flat battery is an alkaline secondary battery, it is preferable to dispose an anion conductive membrane between the positive electrode and the negative electrode, which has a polymer matrix and has dispersed therein particles of at least one metal compound selected from the group consisting of metal oxides, hydroxides, carbonates, sulfates, phosphates, borates, and silicates.

[0077] When the flat battery is an alkaline battery, the alkaline electrolyte used is preferably an aqueous solution of one or more alkali metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.), with potassium hydroxide being particularly preferred. For example, in the case of an aqueous potassium hydroxide solution, the concentration of potassium hydroxide is preferably 20% by mass or more, more preferably 30% by mass or more, and preferably 40% by mass or less, more preferably 38% by mass or less. By adjusting the concentration of the aqueous potassium hydroxide solution to such a value, an alkaline electrolyte with excellent conductivity can be obtained.

[0078] In addition to the above-mentioned components, various known additives may be added to the alkaline electrolyte as needed, as long as the effects of the present invention are not impaired. For example, zinc oxide may be added to prevent corrosion (oxidation) of zinc particles used in the negative electrode. Zinc oxide may also be added to the negative electrode.

[0079] Furthermore, when the flat battery is an alkaline secondary battery, one or more compounds selected from the group consisting of manganese compounds, tin compounds, and indium compounds can be dissolved in the alkaline electrolyte in order to improve the charge-discharge cycle characteristics.

[0080] Furthermore, when the flat battery is an alkaline secondary battery, it is preferable that at least one of the negative electrode, alkaline electrolyte, and separator contains a polyalkylene glycol or a calcium compound, which can suppress the growth of zinc dendrites at the negative electrode due to the action of the polyalkylene glycol or calcium compound, thereby improving the charge / discharge cycle characteristics and storage characteristics of the battery.

[0081] Furthermore, when the flat battery is an alkaline secondary battery, it is also preferable to contain tellurium or a compound thereof (such as tellurium dioxide) in any of the components within the battery, for example, at least one of the positive electrode, negative electrode, and separator, or in the alkaline electrolyte, thereby improving the charge / discharge cycle characteristics and load characteristics of the battery.

[0082] When the flat battery is an alkaline battery, the outer can and the sealing can can be made of iron or stainless steel plated with nickel, etc. It is desirable to plate the inner surface of the outer can with a corrosion-resistant metal such as gold to prevent elements such as iron constituting the outer can from eluting during charging.

[0083] Furthermore, it is preferable that a metal layer made of copper or a copper alloy such as brass is formed on the surface of the sealing can that comes into contact with the negative electrode, and it is more preferable that a tin layer is further formed on the surface of the metal layer.

[0084] Furthermore, when the flat battery is an alkaline battery, the gasket can be made of a resin such as polyamide (eg, nylon 66).

[0085] The shape of the flat battery in plan view may be circular or polygonal such as quadrilateral (square or rectangle), and in the case of a polygonal shape, the corners may be curved.

[0086] A flat battery can be manufactured, for example, by the following procedure. An electrolyte absorber is placed on the inner bottom surface of an outer can, and then an electrolyte is poured into the outer can before placing the positive electrode, or the positive electrode is placed in the outer can before pouring the electrolyte. This is then fitted with a sealable can containing a negative electrode and fitted with a gasket, with a separator sandwiched between the positive and negative electrodes, and the can is then crimped to seal the can, thereby manufacturing a flat battery. Note that when pouring the electrolyte into the outer can containing the positive electrode, a separator may be placed on the positive electrode. [Example]

[0087] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0088] Example 1 Silver oxide (I) (AgO) containing 3.7% (by mass) of Bi with an average particle diameter of 1.4 μm relative to the total amount of silver: 90.3 parts by mass, and graphite particles (BET specific surface area: 20 m 2 / g, average particle size: 3.7 μm): 3.8 parts by mass, and carbon black (BET specific surface area: 68 m 2 A positive electrode mixture substantially free of cadmium was prepared by mixing 1.9 parts by mass of acetylene black (average particle diameter: 35 nm, primary particles of which were 1.9 parts by mass), 1 part by mass of TiO particles (average particle diameter: 250 nm), and 3 parts by mass of polytetrafluoroethylene (PTFE).

[0089] This positive electrode mixture: 73 mg was filled into a mold, and the filling density was 5.7 g / cm 3 The mixture was pressure-molded into a disk shape with a diameter of 5.2 mm and a height of 0.6 mm to prepare a positive electrode mixture compact.

[0090] For the negative electrode active material, mercury-free zinc alloy particles, which contain 500 ppm In, 400 ppm Bi, and 10 ppm Al as additive elements and are commonly used in alkaline primary batteries, were used. The particle size of the zinc alloy particles determined by the above-mentioned method was the average particle diameter (D 50 ) was 120 μm, and the proportion of particles with a particle size of 75 μm or less was 25 mass % or less.

[0091] The zinc alloy particles and ZnO were mixed in a mass ratio of 97:3 to obtain a composition for forming a negative electrode (negative electrode composition). 18 mg of this composition was weighed out and used to prepare a negative electrode.

[0092] The alkaline electrolyte was a mixed solution of 35% by mass of potassium hydroxide and 3% by mass of zinc oxide, to which 1% by mass of lithium hydroxide, 1% by mass of polyethylene glycol, and 9.2% by mass of tellurium dioxide were added. The tellurium content in the electrolyte was 7.4% by mass.

[0093] 5 g of an aqueous dispersion of PTFE (solid content: 60% by mass), 2.5 g of an aqueous solution of sodium polyacrylate (concentration: 2% by mass), and 2.5 g of hydrotalcite particles (average particle diameter: 0.4 μm) were kneaded and rolled to prepare a membrane with a thickness of 100 μm, which was then punched out into a circle with a diameter of 5.6 mm to prepare an anion conductive membrane.

[0094] A separator was constructed by laminating a multilayer film, in which two graft films (thickness: 30 μm) composed of a graft copolymer having a structure in which acrylic acid is graft-copolymerized onto a polyethylene main chain, on either side of a cellophane film (thickness: 20 μm), and a vinylon-rayon blend paper (thickness: 100 μm). The resulting film was punched out into a circle with a diameter of 5.6 mm, and the anion-conductive membrane was then layered on top of the multilayer film.

[0095] A circular electrolyte absorber (5.5 mm in diameter, porosity: 65%, average pore size: 20 μm, thickness: 100 μm) made of vinylon-rayon nonwoven fabric was placed on the inner bottom surface of an outer can made of gold-plated steel plate. The positive electrode (positive electrode mixture compact) was then placed on top of the absorber, and 9 μL of alkaline electrolyte was then dripped onto it. This outer can was then fitted with a sealing can made of copper-stainless steel (SUS304)-nickel clad plate containing a negative electrode (negative electrode composition) and fitted with a nylon 66 annular gasket, with a separator sandwiched between the positive and negative electrodes. The can was then sealed by crimping to assemble a flat alkaline secondary battery with a diameter of 5.8 mm and a thickness of 2.7 mm, similar to the structure shown in Figure 1. The separator was positioned so that the anion-conductive membrane faced the negative electrode.

[0096] Comparative Example 1 A flat alkaline secondary battery was fabricated in the same manner as in Example 1, except that no electrolyte absorber was used.

[0097] The flat alkaline secondary batteries of Example 1 and Comparative Example 1 were evaluated as follows.

[0098] <Evaluation of leakage during manufacturing> Twenty flat alkaline secondary batteries of each of Example 1 and Comparative Example 1 were assembled, and the number of batteries that leaked was counted.

[0099] <Discharge characteristic evaluation> The batteries of Example 1 and Comparative Example 1 (which did not leak during assembly) were discharged at a current value of 1.0 mA until the voltage reached 1.0 V, and the discharge capacity was measured.

[0100] The results of the above evaluations are shown in Table 1.

[0101] [Table 1]

[0102] As shown in Table 1, the flat alkaline secondary battery of Comparative Example 1, which did not have an electrolyte solution absorber, experienced leakage during assembly in some cases, but the flat alkaline secondary battery of Example 1, due to the action of the electrolyte solution absorber, did not experience leakage during assembly and had good productivity.

[0103] In addition, the battery of Example 1 used an electrolyte absorber made of an insulating material, but by establishing electrical continuity between the positive electrode and the side wall of the outer can, it was possible to ensure a discharge capacity equivalent to that of the battery of Comparative Example 1, which did not have an electrolyte absorber.

[0104] Example 2 <Preparation of positive electrode> As a positive electrode active material, average particle diameter: 150 μm, bulk density: 2.4 g / cm 3 Granulated silver oxide: 94.3 parts by mass, BET specific surface area: 68 m 2 / g, primary particle average particle diameter: 35 nm acetylene black particles: 1.9 parts by mass, BET specific surface area: 20 m 2 3.8 parts by mass of graphite particles having an average particle diameter of 3.7 μm were mixed to prepare a mixture, and 91 mg of this mixture was press-molded into a disk shape to obtain a packing density of 5.35 g / cm. 3 A positive electrode mixture compact having a diameter of 6.4 mm was prepared.

[0105] <Carbon sheet hydrophilic treatment> A porous carbon sheet manufactured by FREUDENBERG (thickness: 140 μm, basis weight: 66 g / m) was used as the sheet to be inserted between the positive electrode and the inner bottom surface of the outer can. 2 The carbon sheet was punched out to a diameter of 6.4 mm, and then immersed in a treatment solution prepared by dispersing a fluorochemical surfactant "Surflon S-242 (trade name)" (manufactured by AGC Seimi Chemical Co., Ltd.) in water at a concentration of 1% by mass, and then taken out and dried at 60°C for 15 minutes to perform a hydrophilization treatment.

[0106] <Battery assembly> The negative electrode used mercury-free zinc particles with an average particle size of 120 μm, a ratio of particles with a particle size of 75 μm or less of 10 mass% or less, a ratio of particles with a particle size of 100 to 150 μm of 90 mass% or more, and containing 0.05 mass% (500 ppm) of In, 0.04 mass% (400 ppm) of Bi, and 0.001 mass% (10 ppm) of Al.

[0107] A gasket made of nylon 66 was attached to a sealing plate made of a copper-stainless steel-nickel three-layer clad plate, and 21 mg of the zinc particles was filled into the space inside. 12 μL of an alkaline electrolyte consisting of an aqueous solution in which potassium hydroxide and zinc oxide were dissolved at concentrations of 30.6% by mass and 4% by mass, respectively, was then poured in to form a negative electrode.

[0108] The carbon sheet was placed on the inner bottom of a 6.4 mm inner diameter outer can made of SUS430. After pouring 9 μL of the same alkaline electrolyte solution as above onto the carbon sheet, the positive electrode (a molded body of the positive electrode mixture) was placed on top. A laminated film (YG2152, manufactured by Yuasa Membrane Systems Co., Ltd.) consisting of a 20 μm thick cellophane film and a 30 μm thick graft film composed of a graft copolymer having a structure in which acrylic acid is graft copolymerized onto a polyethylene main chain, and a 100 μm thick vinylon-rayon blended paper were placed on top of the positive electrode. The electrolyte was allowed to be absorbed into the positive electrode and the blended paper, and the sealing plate and the outer can were sealed via the gasket to produce a button alkaline battery.

[0109] In the battery of Example 2, no leakage of the electrolyte was observed during assembly of the battery.

[0110] Example 3 A button-type alkaline battery was fabricated in the same manner as in Example 2, except that the carbon sheet of Example 2 punched to a diameter of 6.4 mm was used as is without being subjected to hydrophilization treatment.

[0111] In the battery of Example 3, leakage of the electrolyte was confirmed in 50% of the assembled batteries.

[0112] Example 4 Instead of the carbon sheet of Example 2, a thickness of 230 μm and a basis weight of 97 g / m 2 A button alkaline battery was fabricated in the same manner as in Example 2, except that a carbon sheet having an air permeability of 50 seconds / 100 ml was subjected to the same hydrophilization treatment as in Example 2.

[0113] In the battery of Example 4, no leakage of the electrolyte was observed during assembly of the battery.

[0114] Example 5 A button-type alkaline battery was fabricated in the same manner as in Example 2, except that a vinylon-rayon mixed paper having a thickness of 100 μm was used instead of the carbon sheet of Example 2.

[0115] In the battery of Example 5, no leakage of the electrolyte was observed during assembly of the battery.

[0116] Comparative Example 2 A button-type alkaline battery was produced in the same manner as in Example 2, except that no carbon sheet was placed on the inner bottom surface of the outer can.

[0117] In Comparative Example 2, leakage of the electrolyte was confirmed in all of the assembled batteries.

[0118] Comparative Example 3 A button-type alkaline battery was fabricated in the same manner as in Comparative Example 2, except that the amount of alkaline electrolyte injected into the exterior can was changed to 2.5 μL.

[0119] In the battery of Comparative Example 3, no leakage of the electrolyte was observed during assembly of the battery.

[0120] The following measurements were carried out on each of the produced batteries.

[0121] <Battery discharge capacity> The battery was discharged at a constant current of 0.05 mA at room temperature, and the discharge capacity until the battery voltage dropped to 1 V was determined.

[0122] <Battery load characteristics> The battery was discharged at a constant current of 20 mA at room temperature, and the battery voltage (closed circuit voltage) was measured 10 ms after the start of discharge to evaluate the load characteristics of the battery.

[0123] The measurement results are shown in Table 2.

[0124] [Table 2]

[0125] In the batteries of Examples 2 to 4, the porous carbon sheet placed on the inner bottom surface of the outer can functioned as an electrolyte absorber, and therefore, despite the large amount of electrolyte being poured into the outer can, the percentage of batteries that leaked was reduced compared to the battery of Comparative Example 2, in which nothing was placed on the inner bottom surface of the outer can. In addition, because the carbon sheet also functioned as a current collector, a battery with excellent load characteristics could be constructed, similar to the battery of Comparative Example 2, in which the positive electrode was in direct contact with the inner bottom surface of the outer can for electrical conduction.

[0126] In particular, in the batteries of Examples 1 and 3, which used hydrophilically treated carbon sheets, the liquid absorption of the carbon sheets was improved, and leakage of the electrolyte could be more effectively suppressed.

[0127] In contrast, in the battery of Example 5, the vinylon-rayon blend paper placed on the inner bottom surface of the outer can functioned as an electrolyte absorber and prevented leakage of the electrolyte, but the inner bottom surface of the outer can was insulated from the bottom surface of the positive electrode, resulting in a lower discharge capacity than the batteries of Examples 2 to 4. In all of the fabricated batteries, the positive electrode and the side wall of the outer can were in contact and electrically conductive, allowing discharge to occur without any problems at the start of discharge. However, when a volume change occurred in the positive electrode toward the end of discharge, it became difficult to ensure electrical continuity between the positive electrode and the side wall of the outer can, preventing some of the positive electrode active material from discharging, which is thought to be why the discharge capacity was reduced.

[0128] In the battery of Comparative Example 3, the amount of electrolyte injected into the outer can was reduced, which prevented leakage of the electrolyte, but the internal resistance of the battery increased and the load characteristics deteriorated.

[0129] The present invention can be implemented in other forms without departing from the spirit of the present invention. The embodiments disclosed in this application are merely examples, and the present invention is not limited to these embodiments. The scope of the present invention shall be interpreted in accordance with the appended claims rather than the description in the above specification, and all modifications within the scope of the claims are included in the scope of the claims. [Industrial Applicability]

[0130] The flat battery of the present invention can be used in applications where conventionally known primary batteries or secondary batteries are used, depending on the form in which it is used. [Explanation of symbols]

[0131] 1 Flat battery 2 outer can 3 Sealed cans 4 Positive electrode 5 negative electrode 6 Separator 7 Gasket 8 Electrolyte absorber

Claims

1. A flat battery in which a positive electrode, a negative electrode, a separator, and an electrolyte are sealed in a battery container having an outer can and a sealing can, the positive electrode is accommodated in the outer can, and a porous electrolyte absorber is inserted between the positive electrode and the inner bottom surface of the outer can; The flat battery is characterized in that the electrolyte absorber is made of a porous carbon sheet or resin.

2. 2. The flat battery according to claim 1, wherein the area of ​​the electrolyte absorber in a plan view is 50% or more of the area of ​​the inner bottom surface of the outer can.

3. 3. The flat battery according to claim 1, wherein the electrolyte absorber has a thickness of 30 [mu]m or more.

4. 4. The flat battery according to claim 1, wherein the electrolyte is an aqueous electrolyte.

5. 5. The flat battery according to claim 4, wherein the electrolyte absorber is subjected to a hydrophilic treatment.

6. 6. The flat battery according to claim 1, wherein the electrolyte absorber is a porous carbon sheet made of fibrous carbon.

7. 6. The flat battery according to claim 1, wherein the electrolyte absorber is a nonwoven fabric made of resin.

8. 8. The flat battery according to claim 1, wherein the positive electrode and the side wall of the outer can are electrically connected.

9. 9. The flat battery according to claim 8, wherein the positive electrode is in contact with the inner surface of the side wall of the outer can.

10. A method for manufacturing a flat battery in which a positive electrode, a negative electrode, a separator, and an electrolyte are sealed in a battery container having an outer can and a sealing can, comprising the steps of: a step of placing an electrolyte solution absorber on the inner bottom surface of the outer can; disposing the positive electrode on the electrolyte absorber; a step of injecting an electrolyte into the outer can after the step of arranging the electrolyte solution absorber and before or after the step of arranging the positive electrode, A method for manufacturing a flat battery, characterized in that the electrolyte absorber is a porous carbon sheet having a porosity of 40 to 90%, or a porous resin body having a porosity of 40 to 90%.

11. The method for manufacturing a flat battery according to claim 10, wherein the area of ​​the electrolyte absorber in a plan view is 50% or more of the area of ​​the inner bottom surface of the outer can.

12. The method for producing a flat battery according to claim 10 or 11, wherein the thickness of the electrolyte absorber is 30 to 500 μm.

13. A method for manufacturing a flat battery according to any one of claims 10 to 12, wherein a porous carbon sheet made of fibrous carbon is used as the electrolyte absorber.

14. A method for manufacturing a flat battery according to any one of claims 10 to 12, wherein a resin nonwoven fabric is used as the electrolyte absorber.

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