Battery

Abstract

The present invention provides a battery that uses a low-pH aqueous solution as the electrolyte while simultaneously suppressing the voltage drop that occurs as discharge progresses and ensuring good discharge characteristics. [Solution] The battery of the present invention has a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, all contained within an outer casing. The positive electrode contains silver oxide as a positive electrode active material, and the electrolyte is an aqueous solution with a pH of 3 to 12 and containing an alkali metal halide as an electrolyte salt.

Description

[Technical Field]

[0001] The present invention relates to a battery that has a low pH aqueous solution as the electrolyte, while being able to suppress the decrease in voltage as the discharge progresses and ensure good discharge characteristics. [Background technology]

[0002] While batteries using strongly alkaline aqueous solutions as electrolytes have been used for various purposes, in recent years, development has also been underway to develop batteries using low-pH aqueous solutions as electrolytes, taking into consideration safety when used as a power source for various body sensors such as body temperature patches, and convenience for general users when replacing and disposing of fully discharged batteries (Patent Documents 1 and 2, etc.). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056307 [Patent Document 2] International Publication No. 2022 / 030611 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, in batteries that use a strongly alkaline aqueous solution as the electrolyte, those that use silver oxide as the positive electrode active material are also known. Due to the properties of silver oxide, this type of battery has characteristics such as less voltage drop even when discharge has progressed to a certain extent. Taking advantage of these characteristics, it is applied to various uses, including power supply applications for equipment that require a relatively high lower voltage limit.

[0005] However, in batteries using silver oxide as the positive electrode active material, the performance tends to deteriorate when a low-pH aqueous solution, such as those described in Patent Documents 1 and 2, is used as the electrolyte. Therefore, there is a need to develop a technology to suppress this deterioration and ensure good performance.

[0006] The present invention has been made in view of the above circumstances, and its object is to provide a battery that has a low pH aqueous solution as the electrolyte, while being able to suppress the decrease in voltage as the discharge progresses and ensure good discharge characteristics. [Means for solving the problem]

[0007] The battery of the present invention has a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, all contained within an outer casing. The positive electrode contains silver oxide as a positive electrode active material, and the electrolyte is an aqueous solution with a pH of 3 to 12 and containing an alkali metal halide as an electrolyte salt. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a battery that has a low pH aqueous solution as the electrolyte, while suppressing the decrease in voltage as the discharge progresses and ensuring good discharge characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic plan view showing an example of the battery of the present invention. [Figure 2] This is a cross-sectional view taken along line II in Figure 1. [Figure 3] This diagram shows the relationship between the closed-circuit voltage and discharge capacity in the battery of the embodiment. [Modes for carrying out the invention]

[0010] The battery of the present invention uses silver oxide as the positive electrode active material and an aqueous solution with a pH of 3 to 12 as the electrolyte, but uses an alkali metal halide as the electrolyte salt of the electrolyte. By using such an electrolyte, it is possible to improve the discharge characteristics of the battery while suppressing the effect of using silver oxide as the positive electrode active material on the voltage drop suppression effect as discharge progresses.

[0011] (electrolyte) The electrolyte of a battery has a pH of 12 or less. In the case of electrolytes consisting of a highly alkaline aqueous solution with a high pH, ​​such as those used in alkaline batteries, there is a risk of skin irritation, and if the electrolyte leaks and comes into contact with the body, it may cause skin problems such as inflammation. Furthermore, there are concerns about the environmental burden when disposing of the battery. However, with an electrolyte with the pH described above, when applied to the power supply of medical and health equipment used in close contact with the body, even if it leaks from the casing (battery container) and comes into contact with the body, the effects can be minimized, and the environmental burden when disposing of the battery can also be reduced. In addition, the pH of the electrolyte is preferably 8 or less, more preferably 7 or less, and particularly preferably 6 or less, as this improves the discharge characteristics of the battery. Furthermore, the pH of the electrolyte is preferably 3 or more, and preferably 4 or more, in order to prevent corrosion of the negative electrode active material. The pH of the electrolyte can be adjusted by adjusting the concentration of the electrolyte salt used or by using alkali metal halides in combination with other electrolyte salts. Furthermore, by including weak acids such as carboxylic acids, carbonic acid, and phosphoric acid in the electrolyte, the pH of the electrolyte can be adjusted to a lower value.

[0012] The pH of the electrolyte as used herein is the value measured at 25°C using a known pH meter (such as the "LAQUA twin compact pH meter" manufactured by Horiba, Ltd., used in the examples described below).

[0013] Furthermore, alkali metal halides are used as the electrolyte salts in the electrolyte solution. Examples of alkali metal halides include alkali metal chlorides such as lithium chloride, potassium chloride, and sodium chloride; alkali metal bromides such as lithium bromide, potassium bromide, and sodium bromide; and alkali metal iodides such as lithium iodide, potassium iodide, and sodium iodide. The electrolyte solution may contain only one of these alkali metal halides, or it may contain two or more. Among these alkali metal halides, alkali metal chlorides are preferred, and lithium chloride or sodium chloride are more preferred.

[0014] In addition to alkali metal halides, other electrolyte salts can also be used as the electrolyte salt in the electrolyte solution. It is desirable that the electrolyte solution does not contain water-soluble hazardous substances (for example, compounds designated as "hazardous substances" in Appendix 2 of Japan's "Poisonous and Deleterious Substances Control Act" and Article 2 of the "Enforcement Order of the Poisonous and Deleterious Substances Control Act"), and it is preferable that other electrolyte salts used with alkali metal halides do not fall under the category of such hazardous substances.

[0015] Specific examples of other electrolyte salts used together with the alkali metal halide include ammonium chloride; hydroxides of alkaline earth metals (such as magnesium hydroxide, calcium hydroxide), acetates (such as sodium acetate, potassium acetate, magnesium acetate), nitrates (such as sodium nitrate, potassium nitrate, magnesium nitrate), sulfates (such as sodium sulfate, potassium sulfate, magnesium sulfate), phosphates (such as sodium phosphate, potassium phosphate, magnesium phosphate), borates (such as sodium borate, potassium borate, magnesium borate), citrates (such as sodium citrate, potassium citrate, magnesium citrate), glutamates (such as sodium glutamate, potassium glutamate, magnesium glutamate); bicarbonates of alkali metals (such as sodium bicarbonate, potassium bicarbonate); percarbonates of alkali metals (such as sodium percarbonate, potassium percarbonate); compounds containing halogens such as fluorides; polyvalent carboxylic acids; and the like.

[0016] The concentration of the electrolyte salt in the electrolytic solution (when a plurality of electrolyte salts are used, their total concentration) may be set within a range that can satisfy the ionic conductivity and pH required for the electrolytic solution, but usually it is 15 to 30% by mass.

[0017] In addition, when using other electrolyte salts together with the alkali metal halide as the electrolyte salt, from the viewpoint of ensuring a better effect of improving the battery characteristics by using the alkali metal halide, when the total amount of the electrolyte salts contained in the electrolytic solution is 100 parts by mass, the proportion of the alkali metal halide is preferably 50 parts by mass or more, more preferably 75 parts by mass or more, and even more preferably 90 parts by mass or more. Since the electrolytic solution may contain only the alkali metal halide as the electrolyte salt, the upper limit value of the proportion of the alkali metal halide when the total amount of the electrolyte salts contained in the electrolytic solution is 100 parts by mass is 100 parts by mass.

[0018] Also, in a battery having a negative electrode using a metal sheet (metal foil) that acts as a negative electrode active material as described later, when an aqueous electrolyte is used, there is a risk that the negative electrode may break due to corrosion by the electrolyte, and problems such as the capacity cannot be sufficiently drawn out may occur. However, when a thickening agent is added to the electrolyte and more preferably made into a gel state (gel electrolyte), in addition to avoiding the problem of fluctuations in the electrolyte composition, it is also possible to suppress unnecessary corrosion reactions of the negative electrode, as well as the accompanying gas generation and the occurrence of breakage of the negative electrode. Examples of thickening agents that can be added to the electrolyte include cellulose derivatives such as carboxymethyl cellulose (CMC) and carboxyethyl cellulose (CEC); polyalkylene oxides such as polyethylene oxide (PEO) (however, those with a molecular weight of 1000 or more are desirable, and those with a molecular weight of 10000 or more are more desirable); polyvinylpyrrolidone; polyvinyl acetate; starch; guar gum; xanthan gum; sodium alginate; hyaluronic acid; gelatin; polyacrylic acid; polymers or copolymers of acrylamide; and various synthetic polymers or natural polymers. Furthermore, when using those having a functional group (-COOH, -COONa, etc.) consisting of a carboxyl group or its salt in the molecule among the above-exemplified thickening agents, it is also preferable to add a polyvalent metal salt that acts as a gelation promoter to the electrolyte. The blending amount of the thickening agent in the electrolyte is preferably 0.1% by mass or more, more preferably 1% by mass or more, further preferably 3% by mass or more in order to enhance the above effects, and preferably 20% by mass or less, more preferably 15% by mass or less, further preferably 10% by mass or less in order to prevent deterioration of discharge characteristics. Also, when using a gelation promoter, in terms of mass ratio, when the ratio of the thickening agent is 100, the ratio of the gelation promoter is preferably 1 to 30.

[0019] Also, the electrolyte may be made into a gel state (gel electrolyte) using a gelling agent such as a known polymer.

[0020] (Positive electrode) For the positive electrode of the battery, a molded body obtained by pressure molding a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, etc., or a structure having a positive electrode mixture layer formed by applying a positive electrode mixture-containing composition, prepared by dispersing the positive electrode mixture in a solvent, to a current collector, can be used.

[0021] Silver oxide (silver-1 oxide, silver-2 oxide) is used as the positive electrode active material.

[0022] Silver oxide is preferably in granular form. Normally, silver oxide is supplied as a fine powder with a diameter of 0.1 to 5 μm, but if this silver oxide is granulated and used in granular form, the resistance will be lower than when used in fine powder form, thus improving the load characteristics of the battery.

[0023] When silver oxide is used in the form of a fine powder, a larger amount of conductive additive is needed to reduce resistance. However, carbon materials commonly used as conductive additives have a low bulk density, so adding too much of them makes it difficult to increase the amount of silver oxide, which is the positive electrode active material. In contrast, using granular silver oxide improves weighability and reduces variability, and also improves moldability by increasing the packing capacity when pressure molded. As a result, resistance is reduced and the characteristics of individual batteries are stabilized. Furthermore, the amount of carbonaceous material added as a conductive additive can be reduced, and the amount of silver oxide can be increased.

[0024] Furthermore, for example, silver oxide is easily reduced by reacting with carbonaceous materials as shown in the following equation, and tends to have a reduced discharge performance. 2Ag₂O + C → 4Ag + CO₂

[0025] However, by granulating silver oxide, the aforementioned reaction is suppressed, and as mentioned above, the amount of carbon material added can also be reduced, further suppressing the reduction reaction of silver oxide, resulting in better discharge characteristics (especially low-temperature heavy-load characteristics).

[0026] When granular silver oxide is used as the positive electrode active material, its particle size is preferably 50 μm or more, more preferably 75 μm or more, preferably 500 μm or less, and more preferably 300 μm or less, and its bulk density is preferably 1.5 g / cm³. 3 More preferably 1.8 g / cm³ 3 The above, preferably 3.5 g / cm³ 3 More preferably, 2.6 g / cm³ 3 The following applies. Compared to powdered silver oxide, this form of silver oxide has better fluidity, improved weighability and moldability as described above, reduced resistance and improved reactivity, resulting in superior battery load characteristics and more stable characteristics for each positive electrode (and consequently, battery) produced. The particle size of the granular silver oxide referred to here is the number-average particle diameter calculated by measuring the number of particles n and the diameter d of each particle by scattering laser light using a Honeywell Microtrac particle size analyzer "9320-X100". The bulk density of the granular silver oxide referred to here is the value obtained by placing a predetermined amount of granular silver oxide in a container and using a bulk density measuring device in accordance with the bulk density measurement method specified in Japanese Industrial Standard (JIS) R 1628.

[0027] Furthermore, other positive electrode active materials such as manganese oxide (manganese dioxide, etc.) can be used in addition to silver oxide. However, if the amount of positive electrode active materials other than silver oxide in the positive electrode active material is large, there is a risk that the effect of suppressing voltage drop when the battery discharges may decrease. Therefore, it is preferable that the silver oxide content in the total amount of positive electrode active material in the positive electrode is 10% by mass or more. Note that since the battery may contain only silver oxide as the positive electrode active material, the upper limit of the silver oxide content in the total amount of positive electrode active material in the positive electrode is 100% by mass.

[0028] Examples of conductive additives for the positive electrode include carbon materials such as graphite, Ketjenblack, and acetylene black, as well as oxides such as cobalt oxyhydroxide.

[0029] Examples of binders that can be used for the positive electrode include polytetrafluoroethylene, polyvinylidene fluoride, and styrene-butadiene rubber.

[0030] The composition of the positive electrode mixture is preferably such that the amount of positive electrode active material is 80 to 98% by mass, the content of the conductive additive is preferably 1.5 to 10% by mass, and the content of the binder is preferably 0.5 to 10% by mass.

[0031] In the case of a positive electrode mixture molded body, its thickness is preferably 0.15 to 4 mm. On the other hand, in the case of a positive electrode having a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (thickness per side of the current collector) is preferably 30 to 300 μm.

[0032] When a current collector is used for the positive electrode, examples of materials for the current collector include stainless steel such as SUS316, SUS430, and SUS444; aluminum; and aluminum alloys. Examples of its form include plain weave wire mesh, expanded metal, lath mesh, perforated 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.

[0033] (Negative electrode) The negative electrode of the battery uses an active material that is at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof.

[0034] Specific examples of such negative electrodes include metal sheets made of the aforementioned materials (zinc foil, zinc alloy foil, magnesium foil, magnesium alloy foil, aluminum foil, aluminum alloy foil). The thickness of the metal sheet is preferably 5 to 1000 μm.

[0035] Furthermore, metal particles composed of the aforementioned materials (zinc particles, zinc alloy particles, magnesium particles, magnesium alloy particles, aluminum particles, aluminum alloy particles) can also be used.

[0036] Examples of alloying components in zinc alloys include indium, bismuth, and aluminum, and one or more of these elements may be included.

[0037] The content of each alloying component in the zinc alloy is as follows, for example: The indium content is preferably 0.005% or more by mass, and also 0.1% or less, and preferably 0.04% or less. The bismuth content is preferably 0.002% or more by mass, and also 0.01% or more, and also 0.25% or less, and preferably 0.2% or less. The aluminum content is preferably 0.0001% or more by mass, and also 0.15% or less.

[0038] Zinc foil and zinc alloy foil can be either electrolytic foil or rolled foil. However, electrolytic foil is preferred because it is less likely to generate gas through reaction with the electrolyte in the battery, and electrolytic zinc alloy foil containing bismuth is more preferred. The preferred range for bismuth content in electrolytic zinc alloy foil is 0.02% to 0.1% by mass.

[0039] Furthermore, examples of alloying components for magnesium alloys include calcium, manganese, zinc, and aluminum, and the alloy may contain one or more of these elements.

[0040] The content of each alloying component in magnesium alloys is as follows, for example: The calcium content is, for example, 1% or more and 3% or less by mass. The manganese content is, for example, 0.1% or more and 0.5% or less by mass. The zinc content is, for example, 0.4% or more and 1% or less by mass. The aluminum content is, for example, 8% or more and 10% or less by mass.

[0041] Furthermore, examples of alloying components for aluminum alloys include zinc, tin, gallium, silicon, iron, magnesium, and manganese, and one or more of these elements may be included.

[0042] The content of each alloying component in aluminum alloys is, for example, as follows: The zinc content is, for example, 0.5% or more and 10% or less by mass. The tin content is, for example, 0.04% or more and 1.0% or less by mass. The gallium content is, for example, 0.003% or more and 1.0% or less by mass. The silicon content is, for example, 0.05% or less by mass. The iron content is, for example, 0.1% or less by mass. The magnesium content is, for example, 0.1% or more and 2.0% or less by mass. The manganese content is, for example, 0.01% or more and 0.5% or less by mass.

[0043] In the case of a negative electrode containing metal particles, the metal particles may be of a single type or of two or more types.

[0044] Furthermore, considering the reduction of environmental impact when disposing of batteries, it is preferable that the metal material used for the negative electrode has low content of mercury, cadmium, lead, and chromium. More preferably, the specific content is 0.1% or less by mass for mercury, 0.01% or less for cadmium, 0.1% or less for lead, and 0.1% or less for chromium.

[0045] As for the particle size of the zinc particles and zinc alloy particles, for example, it is preferable that the proportion of particles with a particle size of 75 μm or less is 50% by mass or less, more preferably 30% by mass or less, and that the proportion of particles with a particle size of 100 to 200 μm is 50% by mass or more, more preferably 90% by mass or more.

[0046] Furthermore, regarding the particle size of magnesium particles, magnesium alloy particles, aluminum particles, and aluminum alloy particles, for example, it is preferable that the proportion of particles with a particle size of 30 μm or less is 50% by mass or less, more preferably 30% by mass or less, and that the proportion of particles with a particle size of 50 to 200 μm is 50% by mass or more, more preferably 90% by mass or more.

[0047] In this specification, the particle size of metal particles is the particle size (D50) at a cumulative frequency of 50% based on volume, measured by dispersing these particles in a non-dissolving medium using a laser scattering particle size analyzer (e.g., Horiba LA-920).

[0048] In the case of a negative electrode containing the aforementioned metal particles, the mixture may include a gelling agent (such as sodium polyacrylate or carboxymethylcellulose) and a binder as needed when forming the mixture, and a negative electrode mixture (such as a gel-like negative electrode) can be used, which is formed by adding an electrolyte to this mixture. The amount of gelling agent in the negative electrode is preferably 0.5 to 1.5% by mass, and the amount of binder is preferably 0.5 to 3% by mass.

[0049] The electrolyte for the negative electrode containing metal particles can be the same as the one injected into the battery.

[0050] The content of metal particles in the negative electrode is preferably, for example, 60% by mass or more, more preferably 65% ​​by mass or more, and preferably 95% by mass or less, and more preferably 90% by mass or less.

[0051] The negative electrode containing metal particles preferably contains an indium compound. The indium compound in the negative electrode more effectively prevents the generation of hydrogen gas due to the corrosion reaction between the metal particles and the electrolyte.

[0052] Examples of the aforementioned indium compounds include indium oxide and indium hydroxide.

[0053] The amount of indium compound used in the negative electrode is preferably 0.003 to 1 in mass ratio per 100 metal particles.

[0054] Furthermore, a current collector may be used in the negative electrode containing a metal material, if necessary. Examples of current collectors for a negative electrode containing a metal material include metal meshes, foils, expanded metal, and perforated metal made of nickel, copper, stainless steel, etc.; carbon sheets and meshes; and so on. The thickness of the current collector of the negative electrode is preferably 10 μm to 300 μm.

[0055] Furthermore, the negative electrode current collector can be used with carbon paste applied to the surface that is intended to become the inner surface of the sheet-like outer casing, similar to the case of the positive electrode. The thickness of the carbon paste layer is preferably 50 to 200 μm.

[0056] For the negative electrode terminal portion used to connect the battery to the applicable device, for example, a foil (plate, sheet) or wire made of metal or carbon, as exemplified above as a possible component of the negative electrode current collector, can be used. When the negative electrode terminal portion is a foil (plate, sheet), its thickness is preferably 20 μm to 500 μm. When the negative electrode terminal portion is a wire, its diameter is preferably 50 μm to 1500 μm.

[0057] Furthermore, a portion of the current collector of the negative electrode can be used as a terminal. In addition, if the negative electrode is made of a metal sheet, the negative electrode having a main body portion and a terminal portion can be formed from a single metal sheet by cutting the metal sheet into a shape having a main body portion that functions as a negative electrode active material layer and a terminal portion.

[0058] (Separator) In a battery, a separator is interposed between the positive and negative electrodes. The separator can be made of nonwoven fabrics mainly composed of vinylon and rayon, vinylon-rayon nonwoven fabrics (vinylon-rayon blended paper), polyamide nonwoven fabrics, polyolefin-rayon nonwoven fabrics, vinylon paper, vinylon-linter pulp paper, vinylon-mercerized pulp paper, etc. Microporous films can also be used; microporous polyolefin films (such as microporous polyethylene films and microporous polypropylene films) are specific examples, and their surfaces may be hydrophilized to improve wettability with the aqueous electrolyte.

[0059] Alternatively, a separator may be made by stacking the microporous film, a cellophane film, and an absorbent layer (electrolyte-holding layer) such as vinylon-rayon blended paper. The thickness of the separator is preferably, for example, 10 to 500 μm, preferably 10 to 50 μm for the microporous film, and preferably 20 to 500 μm for the nonwoven fabric.

[0060] Furthermore, a separator can also be constructed using a laminate formed by layering a graft film, which is composed of a specific graft polymer, with a cellophane film.

[0061] The graft polymer constituting the graft film is, for example, a polymer in which (meth)acrylic acid or a derivative thereof is graft-polymerized onto a polyolefin (polyethylene, polypropylene, etc.) which is the main polymer; that is, a polymer in which side chains derived from (meth)acrylic acid or a derivative thereof are bonded to a main chain made of polyolefin. However, the graft polymer only needs to have the above-mentioned form and does not have to be produced by a method of graft polymerizing (meth)acrylic acid or its derivatives onto polyolefin.

[0062] The (meth)acrylic acid or its derivatives that constitute the graft polymer are represented by the following general formula (1). Note that of the following general formula (1), R 1 is H or CH3, and R2 This refers to hydrophilic substituents such as H or NH4, Na, K, Rb, and Cs.

[0063] [ka]

[0064] The aforementioned graft films and cellophane films are characterized by the fact that the polymers constituting these films themselves have the function of absorbing electrolytes and allowing ions to pass through.

[0065] The graft polymer constituting the graft film preferably has a graft rate of 160% or more, as defined by the following formula (2). Since there is a correlation between the graft rate of the graft polymer and the electrical resistance of the graft film, by using a graft polymer with a graft rate of the above value, the electrical resistance of the graft film can be controlled to a suitable value of 20 to 120 mΩ·in². The electrical resistance of the graft film is obtained by the AC voltage drop method (1 kHz). The film can be immersed in a 40% KOH (specific gravity: 1,400 ± 0.005) aqueous solution at an ambient temperature of 20 to 25°C and 25 ± 1°C, and the electrical resistance can be measured after 5 to 15 hours.

[0066] Graft rate (%) = 100 × (AB) / B (2)

[0067] In formula (2) above, A: mass of the graft polymer (g), and B: mass of the stem polymer in the graft polymer (g). Note that in formula (2), "B (mass of the stem polymer in the graft polymer)" can be determined by, for example, measuring the mass of the stem polymer used in the graft polymerization beforehand when the graft polymer is formed by graft polymerization of (meth)acrylic acid or its derivatives onto a polyolefin, which is the stem polymer. Furthermore, the grafting rate in the graft polymer may exceed 100% because the monomers used in the graft polymerization [(meth)acrylic acid or its derivatives] polymerize with each other, resulting in long-chain graft molecules. The upper limit of the grafting rate of the graft polymer defined in formula (2) is preferably 400%. Note that "(meth)acrylic acid" refers collectively to acrylic acid and methacrylic acid.

[0068] In the case of a separator composed of a laminate of a graft film and a cellophane film, the total thickness of the graft film and the cellophane film is preferably 30 μm or more, more preferably 40 μm or more, and preferably 70 μm or less, and more preferably 60 μm or less.

[0069] Furthermore, in the case of a separator composed of a laminate of graft film and cellophane film, the thickness of the graft film is preferably 15 μm or more, more preferably 25 μm or more, and preferably 30 μm or less.

[0070] Examples of laminates of graft film and cellophane film used to construct separators include those commercially available from GS Yuasa Membrane Corporation under the names "YG9132," "YG9122," and "YG2152."

[0071] (Battery type, etc.) There are no particular restrictions on the form of the battery; it can take any form, such as a flat type (including coin-shaped and button-shaped) having an outer casing (battery container) that is crimped and sealed with a gasket between the outer casing and a sealing plate; or the outer casing and sealing plate are welded together; a sheet type having a sheet-like outer casing made of resin film; or a cylindrical type (cylindrical, rectangular (square-tube)) having an outer casing (battery container) that is crimped and sealed with a gasket between the bottomed cylindrical outer casing and a sealing plate; or the outer casing and sealing plate are welded together.

[0072] When the battery is used as a power source for medical and health-related devices, such as patches that can be attached to the body, particularly patches that are attached to the surface of the skin to measure bodily conditions such as body temperature, pulse rate, and sweating, it is preferable to use a sheet-type battery having a sheet-like outer casing made of resin film.

[0073] The sheet-like outer covering is made of a resin film, and examples of such resin films include nylon film (such as nylon 66 film) and polyester film (such as polyethylene terephthalate (PET) film).

[0074] Generally, the sealing of a sheet-like exterior is performed by heat-sealing the end of the upper resin film of the sheet-like exterior to the end of the lower resin film. However, to facilitate this heat-sealing, a heat-sealable resin layer may be laminated onto the resin film as described above and used in the sheet-like exterior. Examples of heat-sealable resins constituting the heat-sealable resin layer include modified polyolefin films (such as modified polyolefin ionomer films), polypropylene and its copolymers, etc. The thickness of the heat-sealable resin layer is preferably 20 to 200 μm.

[0075] Furthermore, a metal layer may be laminated onto the resin film. The metal layer can be made of an aluminum film (aluminum foil, including aluminum alloy foil), a stainless steel film (stainless steel foil), or the like. The thickness of the metal layer is preferably 10 to 150 μm.

[0076] Furthermore, the resin film constituting the sheet-like exterior body may be a film in which the heat-sealable resin layer and the metal layer are laminated together.

[0077] Furthermore, it is preferable that the resin film constituting the sheet-like exterior body has an electrically insulating water vapor barrier layer. In this case, the electrically insulating resin film may be a single-layer structure in which the electrically insulating resin film itself also acts as the water vapor barrier layer, or it may be a multilayer structure having multiple layers of electrically insulating resin film in which at least one of the layers acts as the water vapor barrier layer, or it may be a multilayer structure having an electrically insulating water vapor barrier layer on the surface of a base layer made of resin film.

[0078] Among such resin films, those in which a water vapor barrier layer, composed of at least an inorganic oxide, is formed on the surface of a base layer made of resin film are preferably used.

[0079] Examples of inorganic oxides that constitute the water vapor barrier layer include aluminum oxide and silicon oxide. A water vapor barrier layer composed of silicon oxide tends to have a higher ability to suppress the permeation of moisture from the electrolyte in the battery compared to a water vapor barrier layer composed of aluminum oxide. Therefore, it is more preferable to use silicon oxide as the inorganic oxide that constitutes the water vapor barrier layer.

[0080] A water vapor barrier layer composed of inorganic oxides can be formed on the surface of a substrate layer, for example, by a vapor deposition method. The thickness of the water vapor barrier layer is preferably 10 to 300 nm.

[0081] In addition to the aforementioned nylon film and polyester film, the base layer of the resin film having a water vapor barrier layer can also be made of polyolefin film, polyimide film, polycarbonate film, etc. The thickness of the base layer is preferably 5 to 100 μm.

[0082] In the case of a resin film having a water vapor barrier layer and a substrate layer, a protective layer for protecting the water vapor barrier layer may be formed on the surface of the water vapor barrier layer (the side opposite to the substrate layer).

[0083] Furthermore, in the case of a resin film having a water vapor barrier layer and a base material layer, the aforementioned heat-sealable resin layer may be further laminated.

[0084] The overall thickness of the resin film is preferably 10 μm or more from the viewpoint of providing sufficient strength to the battery, and preferably 200 μm or less from the viewpoint of suppressing an increase in battery thickness and a decrease in energy density.

[0085] The water vapor permeability of the resin film constituting the sheet-like outer casing is 10 g / m². 2 It is preferable that the water vapor permeability is 24 hours or less. Furthermore, it is desirable that the resin film does not permeate water vapor as much as possible, that is, its water vapor permeability is preferably as low as possible, 0 g / m². 2 24 hours is also acceptable.

[0086] The water vapor transmission rate of resin films as used herein is a value measured in accordance with the JIS K 7129B method.

[0087] Furthermore, when using an outer casing with a crimped seal, the gasket material interposed between the outer casing and the sealing plate can be made of materials used in alkaline batteries, such as polypropylene or nylon.

[0088] Furthermore, to prevent elements such as iron that make up the outer casing from leaching out during charging, it is desirable to plate the inner surface of the outer casing with a corrosion-resistant metal such as tin, zinc, or indium.

[0089] Figures 1 and 2 schematically show an example of a battery. Figures 1 and 2 show an example where the battery comprises a negative electrode having a metal sheet and a sheet-like outer casing (in the case of a sheet-type battery). Figure 1 shows a plan view, and Figure 2 shows a cross-sectional view of line II of Figure 1.

[0090] As shown in Figure 2, in the battery 10, the positive electrode 20, the separator 40, the negative electrode 30, and the electrolyte (not shown) are housed within a sheet-like outer casing 50.

[0091] From the upper edge of the sheet-like outer casing 50 in the diagram, the terminal portion 21 of the positive electrode 20 and the terminal portion 31 of the negative electrode 30 protrude. As shown in Figure 2, the positive electrode terminal portion 21 is connected to the positive electrode 20 inside the battery 10, and although not shown, the negative electrode terminal portion 31 is also connected to the negative electrode 30 inside the battery 10. These terminal portions 21 and 31 are used as external terminals for electrically connecting the battery 10 to the application device.

[0092] In Figure 2, the sheet-like outer casing 50 (and the resin film that constitutes it) is shown as a single-layer structure, but as mentioned above, the resin film that constitutes the sheet-like outer casing can also be a multi-layer structure. Also, in Figure 2, the positive electrode 10 and the negative electrode 20 are shown as single-layer structures, but as mentioned above, the positive electrode and the negative electrode can also be a multi-layer structure, and furthermore, the negative electrode can contain metal particles such as zinc particles.

[0093] The shape of the sheet-like casing may be a polygon (triangle, quadrilateral, pentagon, hexagon, heptagon, octagon) in plan view, or it may be a circle or an ellipse in plan view. In the case of a sheet-like casing that is polygonal in plan view, the positive terminal and the negative terminal may be brought out from the same side, or they may be brought out from different sides.

[0094] When the battery is a sheet-shaped battery, its thickness (the length of a in Fig. 2) is not particularly limited and can be appropriately changed according to the use of the battery. Note that one of the advantages of a sheet-shaped battery is that it can be made thin. From this perspective, its thickness is preferably, for example, 1 mm or less. When the battery is a sheet-shaped air battery, it is particularly easy to provide such a thin one.

[0095] Also, there is no particular limitation on the lower limit value of the battery thickness, but in order to ensure a certain capacity, it is usually preferably 0.2 mm or more.

[0096] Since the electrolyte of the battery of the present invention is an aqueous solution and substantially does not contain heavy metal elements, the environmental load is small. Also, even if the electrolyte leaks due to breakage or the like and adheres to the body, problems are unlikely to occur. Therefore, the battery of the present invention is suitable as a power source for medical and health equipment such as patches that can be worn on the body, particularly patches that are worn on the surface of the skin and used to measure the body's conditions such as body temperature, pulse, and sweating amount. It can also be applied to the same uses as those where batteries using an aqueous solution such as conventional alkaline batteries as the electrolyte are employed.

Examples

[0097] Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. The pH of the electrolyte used in the batteries of each of the following examples and comparative examples is a value measured at 25°C using a "LAQUA twin compact pH meter" manufactured by Horiba, Ltd.

[0098] (Example 1) <Positive electrode> As the positive electrode active material, average particle size: 150 μm, bulk density: 2.4 g / cm 3A mixture containing 95% by mass of granular silver oxide and 5% by mass of graphite was pressure-molded, and the molded body was crushed and sieved to obtain a positive electrode mixture with an average particle size of 300 μm. A clay-like substance was prepared by mixing 75% by mass of the positive electrode mixture, 10% by mass of polytetrafluoroethylene, and 15% by mass of water. A positive electrode current collector was fabricated by punching out a stainless steel mesh (material: SUS304, mesh opening: 0.8 mm, wire diameter: 0.2 mm) into a shape having a body part measuring 15 mm x 15 mm and a positive electrode terminal measuring 5 mm x 12 mm. The positive electrode was fabricated by pressing the clay-like substance onto the body part of the current collector.

[0099] <Negative electrode> An electrolytic zinc alloy foil (thickness: 0.1 mm) made of a zinc alloy containing 0.05 mass% Bi as an additive element and no In was punched out into a shape having a main body measuring 15 mm x 15 mm and a negative electrode terminal measuring 5 mm x 12 mm to produce a negative electrode.

[0100] <Electrolyte> The electrolyte used was an aqueous solution (pH 4.82) in which lithium chloride was dissolved at a concentration of 20% by mass.

[0101] <Separator> For the separator, we used "YG2152" from GS Yuasa Membrane Co., Ltd. This separator consists of a 20 μm thick cellophane film and a 30 μm thick graft film laminated together. The graft film is composed of a graft copolymer having a polyethylene main chain grafted with acrylic acid. In addition, a 400 μm thick vinylon-rayon blended paper was used as the electrolyte retention layer. The separator and electrolyte retention layer were punched out into 21 mm x 21 mm squares for use.

[0102] <Sheet-like exterior material> A sheet-like outer casing was created using two 25mm x 30mm aluminum laminate films (thickness: 65μm) each, with a PET film on the outer surface of the aluminum foil and a polypropylene film as a heat-sealable resin layer on the inner surface.

[0103] <Battery assembly> On one aluminum laminate film, the positive electrode, the separator, the electrolyte holding layer, and the negative electrode were laminated in order, and then the other aluminum laminate film was placed on top. Next, the three sides of the two aluminum laminate films were heat-sealed together to form a bag, and then 0.06 ml of the electrolyte was injected through the opening into the positive electrode side and the negative electrode side, with the separator in between. Finally, the opening was heat-sealed to create a sheet-type battery with a theoretical capacity of 50 mA, similar in structure to that shown in Figures 1 and 2 (the sheet-type batteries in each of the examples and comparative examples described later also had a theoretical capacity of 50 mA).

[0104] Example 2 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 5.48) in which potassium chloride was dissolved at a concentration of 20% by mass.

[0105] Example 3 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 5.48) in which sodium chloride was dissolved at a concentration of 20% by mass.

[0106] Example 4 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 5.83) in which potassium bromide was dissolved at a concentration of 20% by mass.

[0107] Example 5 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 7.18) in which potassium iodide was dissolved at a concentration of 20% by mass.

[0108] Comparative Example 1 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 14.00) in which potassium hydroxide was dissolved at a concentration of 20% by mass.

[0109] Comparative Example 2 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 8.15) in which potassium acetate was dissolved at a concentration of 20% by mass.

[0110] Comparative Example 3 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 8.10) in which potassium bicarbonate was dissolved at a concentration of 20% by mass.

[0111] Comparative Example 4 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 10.98) in which sodium carbonate was dissolved at a concentration of 20% by mass.

[0112] Comparative Example 5 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 7.56) in which sodium formate was dissolved at a concentration of 20% by mass.

[0113] Comparative Example 6 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 4.89) in which zinc chloride was dissolved at a concentration of 20% by mass.

[0114] Comparative Example 7 A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution (pH 4.47) in which ammonium chloride was dissolved at a concentration of 20% by mass.

[0115] The open-circuit voltage (OCV) of the sheet-type batteries in the examples and comparative examples was measured at 25°C. These results are shown in Table 1.

[0116] [Table 1]

[0117] As shown in Table 1, the sheet-type batteries of Examples 1 to 5, which used an electrolyte solution containing an alkali metal halide as an electrolyte salt and having a pH of 3 to 12, exhibited OCV equivalent to or better than the battery of Comparative Example 1, which used a strongly alkaline aqueous solution containing potassium hydroxide as an electrolyte salt, and thus possessed excellent characteristics.

[0118] In contrast, the batteries of Comparative Examples 2 to 7 contained electrolyte salts other than alkali metal halides, and the electrolyte was an aqueous solution with a pH of 3 to 12. However, their OCV was lower and their performance was inferior to that of the batteries in the Examples.

[0119] Furthermore, for the sheet-type batteries of Examples 1 to 5, a fixed resistor of 3.9 kΩ was connected, and constant-resistance discharge was performed in an environment of 25°C. Figure 3 shows the relationship between the closed-circuit voltage (CCV) and discharge capacity of each battery obtained at this time.

[0120] As shown in Figure 3, the sheet-type batteries of Examples 1 to 5 were able to stably maintain their CCV even when a large amount of capacity was discharged (discharge progressed). In particular, the battery of Example 1, which had an electrolyte solution using lithium chloride as the electrolyte salt, and the battery of Example 3, which had an electrolyte solution using sodium chloride as the electrolyte salt, were able to stably maintain their CCV even when a considerable amount of capacity was discharged.

[0121] 10 batteries 20 positive electrode 21 Positive terminal section 30 negative electrode 31 Negative terminal section 40 Separators 50 Sheet-like exterior body

Claims

1. A battery having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, within its outer casing, The aforementioned positive electrode contains silver oxide as the positive electrode active material. The battery is characterized in that the electrolyte is an aqueous solution having a pH of 3 or more and 12 or less, and containing an alkali metal halide as an electrolyte salt.

2. The battery according to claim 1, which is a sheet-shaped battery having a sheet-shaped outer casing as the outer casing.

3. The battery according to claim 1, wherein when the total amount of electrolyte salt contained in the electrolyte is 100 parts by mass, the content of the alkali metal halide is 50 parts by mass or more.

4. The battery according to claim 1, wherein the electrolyte contains an alkali metal chloride as the alkali metal halide.

5. The battery according to claim 4, wherein the electrolyte contains lithium chloride or sodium chloride as the alkali metal chloride.

6. The battery according to claim 1, wherein the negative electrode is an active material of at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof.

7. The battery according to claim 6, wherein the negative electrode is composed of electrolytic zinc foil or electrolytic zinc alloy foil.

8. The battery according to claim 6, wherein the negative electrode contains a zinc alloy, the bismuth content of the zinc alloy is 0.01 to 0.25% by mass, and the indium content is 0.04% by mass or less.

Images