Battery

Abstract

To provide a battery that has an aqueous electrolyte and has excellent discharge characteristics at low temperatures.SOLUTION: A battery according to the present invention includes a negative electrode having at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof as an active material, and an aqueous electrolyte solution, and the electrolyte solution is an aqueous solution containing an electrolyte salt, which is a salt of a weak acid and a strong base and has a solubility of 100 g or more in 100 g of water at 0°C, at a concentration of 10 mass% or more. It is preferable that the electrolyte solution further contains a salt of a strong acid and a weak base.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a battery having an aqueous electrolyte and excellent discharge characteristics at low temperatures. [Background technology]

[0002] Batteries using aqueous electrolytes, such as air batteries and alkaline batteries, have been widely used for a long time, but in recent years, their use as power sources for various body sensors, such as body temperature patches, has been increasing.

[0003] In this type of battery, various improvements have been made in light of these application developments. For example, from the perspective of minimizing the environmental impact when users dispose of batteries after replacement, attempts have been made to ensure good performance while keeping the pH low by using an aqueous solution containing a salt of a strong acid and a weak base as the electrolyte (Patent Documents 1 and 2, etc.). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2018 / 056307 [Patent Document 2] International Publication No. 2020 / 162591 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in aqueous electrolyte batteries used for the aforementioned applications, in addition to environmental considerations during disposal, safety should also be considered in case the electrolyte leaks from the battery due to some trouble and comes into contact with the body. For example, it is desirable that the electrolyte does not contain heavy metal elements. However, batteries using electrolytes containing salts of strong acids and weak bases that do not contain heavy metal elements have problems such as significantly impaired discharge characteristics at low temperatures (for example, around -40°C), and there is still room for improvement in this respect.

[0006] The present invention has been made in view of the above circumstances, and its purpose is to provide a battery having an aqueous electrolyte and excellent discharge characteristics at low temperatures. [Means for solving the problem]

[0007] The battery of the present invention comprises a negative electrode having at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof as an active material, and an aqueous electrolyte, wherein the electrolyte is an aqueous solution containing an electrolyte salt at a concentration of 10% by mass or more, which is a salt of a weak acid and a strong base and has a solubility of 100 g or more in 100 g of water at 0°C. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a battery having an aqueous electrolyte and excellent discharge characteristics at low temperatures. [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 graph shows the evaluation results of the discharge characteristics of the batteries in the examples and comparative examples at room temperature. [Figure 4] This graph shows the evaluation results of the discharge characteristics of the batteries in the examples and comparative examples at low temperatures. [Figure 5] This graph shows the relationship between the discharge characteristics of the battery in the example at low temperatures and the electrolyte salt concentration in the electrolyte solution. [Figure 6] This graph shows the evaluation results of the discharge characteristics of the battery in the example at low temperatures. [Modes for carrying out the invention]

[0010] A battery using an aqueous solution containing a salt of a strong acid and a weak base, such as ammonium chloride, as an electrolyte salt as an electrolyte has an electrolyte with a low pH and good discharge characteristics. However, even in such a battery, sufficient discharge characteristics cannot be ensured in a low-temperature environment of 0 °C or lower, for example, about -40 °C.

[0011] On the other hand, in a manganese battery using manganese oxide for the positive electrode, etc., an aqueous solution containing zinc chloride as an electrolyte salt is used as the electrolyte. In such a battery, it can be discharged well even in a low-temperature environment of about -40 °C. However, since zinc chloride contains zinc, which is a heavy metal element, there is room for improvement in terms of safety when the electrolyte leaks and adheres to the body, etc.

[0012] When an aqueous solution containing a salt of a strong acid and a weak base as an electrolyte salt is placed in a low-temperature environment as described above, the electrolyte salt often precipitates or the aqueous solution freezes, so it is considered that the function as the electrolyte of the battery cannot be maintained. In contrast, in an aqueous solution containing zinc chloride as an electrolyte salt, such a phenomenon does not occur. Therefore, in the present invention, an aqueous solution containing an electrolyte salt not containing a heavy metal element and capable of maintaining the characteristics as the electrolyte of the battery even in a low-temperature environment is used as the electrolyte. As a result, although the discharge characteristics at low temperatures are inferior to those of a battery composed of an aqueous solution containing zinc chloride as an electrolyte salt, it is possible to enhance safety while ensuring practical characteristics.

[0013] The battery of the present invention can adopt various battery modes [alkaline batteries (alkaline primary batteries, alkaline secondary batteries), manganese batteries, air batteries, etc.] having an aqueous electrolyte, that is, an electrolyte composed of an aqueous solution using water as a solvent.

[0014] (Aqueous electrolyte) The battery of the present invention has an aqueous solution containing, as an aqueous electrolyte, an electrolyte salt that is a salt of a weak acid and a strong base (a salt formed from a weak acid and a strong base) and has a solubility of 100 g or more in 100 g of water at 0 °C at a concentration of 10% by mass or more.

[0015] Examples of weak acids that form salts with strong bases include carboxylic acids such as formic acid, acetic acid, and propionic acid, as well as phosphoric acid. Examples of strong bases that form salts with weak acids include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; and alkaline earth metal hydroxides such as calcium hydroxide and barium hydroxide. Since weak acids and strong bases generally do not contain heavy metal elements, the salts formed from them also do not contain heavy metal elements. Therefore, by using an aqueous solution containing a salt of a weak acid and a strong base as the electrolyte, a battery can be made that is highly safe even if the electrolyte leaks and comes into contact with the body.

[0016] For use in aqueous electrolytes, any salt formed from such a weak acid and strong base that has a solubility of 100 g or more in 100 g of water at 0°C is acceptable, but acetate salts such as potassium acetate and formate salts such as potassium formate are preferred.

[0017] The concentration of the salt of a weak acid and a strong base in the aqueous solution used in the aqueous electrolyte is preferably 10% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more, from the viewpoint of ensuring good discharge characteristics of the battery at low temperatures. Furthermore, while the electromotive force of the battery tends to increase as the pH of the aqueous solution used in the aqueous electrolyte decreases, the pH tends to shift towards higher as the concentration of the salt of the weak acid and a strong base increases. Also, if the concentration of the salt of the weak acid and a strong base becomes too high, there is a risk that the ionic conductivity of the aqueous solution will decrease. Therefore, from the viewpoint of further improving the characteristics of the battery, the concentration of the salt of a weak acid and a strong base in the aqueous solution used in the aqueous electrolyte is preferably 60% by mass or less, more preferably 50% by mass or less, and particularly preferably 40% by mass or less.

[0018] The aqueous solution used in the water-based electrolyte preferably contains not only a salt of a weak acid and a strong base, but also a salt of a strong acid and a weak base. Batteries using an aqueous solution containing a salt of a weak acid and a strong base as the electrolyte have better discharge characteristics at low temperatures compared to batteries using an aqueous solution containing a salt of a strong acid and a weak base, but their discharge characteristics at room temperature (e.g., 25°C) are inferior. However, when a salt of a strong acid and a weak base is used in combination with a salt of a weak acid and a strong base in the electrolyte, it is possible to further improve the discharge characteristics of the battery at both low temperatures and room temperature.

[0019] From the viewpoint of further improving the discharge characteristics of the battery, the concentration of the salt of a strong acid and a weak base in the aqueous electrolyte is preferably 3% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more. Furthermore, in order to prevent the salt of the strong acid and a weak base from precipitation on the electrode surface and hindering the discharge reaction when the battery temperature drops, the concentration of the salt of the strong acid and a weak base in the aqueous electrolyte is preferably 40% by mass or less, and more preferably 30% by mass or less.

[0020] In the case of an air battery, a problem of fluctuation in the electrolyte composition is likely to occur due to the evaporation of water in the aqueous electrolyte and its dissipation through the air vents. Therefore, from the viewpoint of avoiding such problems, a water-soluble high-boiling point solvent with a boiling point of 150°C or higher (preferably 320°C or lower) can be used together with water as the solvent for the aqueous electrolyte, or a thickening agent can be added to the aqueous electrolyte consisting of an aqueous solution [more preferably in the form of a gel (gel-like electrolyte)].

[0021] Examples of the aforementioned water-soluble high-boiling point solvents include polyhydric alcohols such as ethylene glycol (boiling point 197°C), propylene glycol (boiling point 188°C), and glycerin (boiling point 290°C); and polyalkylene glycols such as polyethylene glycol (PEG; for example, with a boiling point of 230°C) (preferably those with a molecular weight of 600 or less). When using a water-soluble high-boiling point solvent, its proportion in the total solvent is preferably 3 to 30% by mass.

[0022] Furthermore, in batteries having a negative electrode made of a metal sheet (metal foil) that acts as a negative electrode active material as described later, when an aqueous electrolyte consisting of an aqueous solution is used, there is a risk that the negative electrode may break due to corrosion by the aqueous electrolyte, and problems such as not being able to fully extract the capacity may occur. However, if a thickening agent is added to the aqueous electrolyte, and more preferably a gel (gel-like electrolyte), in addition to avoiding the aforementioned problem of fluctuations in the electrolyte composition, it is also possible to suppress unnecessary corrosion reactions of the negative electrode, as well as the resulting gas generation and the occurrence of negative electrode breakage. Examples of thickeners that can be incorporated into aqueous electrolytes include cellulose derivatives such as carboxymethylcellulose (CMC) and carboxyethylcellulose (CEC); polyalkylene oxides such as polyethylene oxide (PEO) (however, those with a molecular weight of 1000 or more are preferable, and those with a molecular weight of 10000 or more are more preferable); polyvinylpyrrolidone; polyvinyl acetate; starch; guar gum; xanthan gum; sodium alginate; hyaluronic acid; gelatin; polyacrylic acid; polymers or copolymers of acrylamide; and various other synthetic or natural polymers. Furthermore, when using one of the thickeners mentioned above that has a functional group consisting of a carboxyl group or a salt thereof (-COOH, -COONa, etc.) in its molecule, it is also preferable to incorporate a polyvalent metal salt that acts as a gelling accelerator into the aqueous electrolyte. In an aqueous electrolyte, the amount of thickener added is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, in order to enhance the aforementioned effect. To prevent a decrease in discharge characteristics, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. Furthermore, when a gelling accelerator is used, it is preferable that the proportion of the gelling accelerator is 1 to 30 by mass, with the proportion of the thickener being 100.

[0023] Furthermore, the aqueous electrolyte may be made into a gel (gel-like electrolyte) using a gelling agent such as a known polymer.

[0024] The pH of the aqueous electrolyte can be as high as 12 or higher, for example, 14 or higher, when the battery is an alkaline battery, but it is preferable to keep it below 12 from the viewpoint of reducing the environmental burden during disposal. Furthermore, to improve the discharge characteristics of the battery, the pH of the aqueous electrolyte is more preferably 8 or lower, even more preferably 7 or lower, and most preferably 6 or lower. In addition, to prevent corrosion of the negative electrode active material, the pH of the aqueous electrolyte is preferably 3 or higher, and more preferably 4 or higher. The pH of the aqueous electrolyte can be adjusted by adjusting the concentration of the salt of a weak acid and a strong base, or by using a salt of a strong acid and a weak base in combination. Furthermore, the pH of the aqueous electrolyte can be adjusted to a lower value by including a weak acid such as a carboxylic acid, carbonic acid, or phosphoric acid in the electrolyte.

[0025] (Negative electrode) The negative electrode uses at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof as the active material.

[0026] 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.

[0027] 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.

[0028] Examples of alloying components in zinc alloys include indium, bismuth, and aluminum, and one or more of these elements may be included.

[0029] The content of each alloying component in zinc alloys is as follows, for example: The indium content is, for example, 0.005% or more and 0.1% or less by mass. The bismuth content is, for example, 0.002% or more and 0.2% or less by mass. The aluminum content is, for example, 0.0001% or more and 0.15% or less by mass.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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).

[0040] 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.

[0041] The electrolyte for the negative electrode containing metal particles can be the same as the one injected into the battery.

[0042] 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.

[0043] 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.

[0044] Examples of the aforementioned indium compounds include indium oxide and indium hydroxide.

[0045] The amount of indium compound used in the negative electrode is preferably 0.003 to 1 per 100 metal particles by mass ratio.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] (positive electrode) In the case of alkaline or manganese batteries, the positive electrode can be of a structure in which a positive electrode mixture layer containing a positive electrode active material, a conductive additive, and a binder is present on one or both sides of the current collector.

[0051] Suitable positive electrode active materials for alkaline batteries include silver oxide (silverous oxide, silicic oxide, etc.); manganese oxides such as manganese dioxide; nickel oxyhydroxide; and composite oxides of silver with cobalt, nickel, or bismuth. For manganese batteries, manganese oxides such as manganese dioxide are used as the positive electrode active material. The conductive additives used in the positive electrode mixture layer include, for example, carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; carbon fibers; conductive fibers such as metal fibers; fluorinated carbon; metal powders such as copper and nickel; and organic conductive materials such as polyphenylene derivatives.

[0052] Examples of binders for the positive electrode mixture layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), CMC, and polyvinylpyrrolidone (PVP).

[0053] The composition of the positive electrode mixture layer 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. Furthermore, the thickness of the positive electrode mixture layer (thickness per side of the current collector) is preferably 30 to 300 μm.

[0054] A positive electrode having a positive electrode mixture layer can be manufactured, for example, by dispersing a positive electrode active material, a conductive additive, and a binder in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing composition (slurry, paste, etc.) (the binder may be dissolved in the solvent), applying this to a current collector and drying it, and then, if necessary, performing a pressing process such as calendering.

[0055] Furthermore, in the case of an air battery, the positive electrode (air electrode) can have a catalyst layer, for example, a structure in which a catalyst layer and a current collector are stacked.

[0056] The catalyst layer can contain catalysts, binders, and other materials.

[0057] Examples of catalysts for the catalyst layer include phthalocyanine metal complexes; silver, platinum group metals or their alloys; transition metals; platinum / metal oxides such as Pt / IrO2; and La 1-x Ca x Examples include perovskite oxides such as CoO3; carbides such as WC; nitrides such as Mn4N; manganese oxides such as manganese dioxide; and carbon [graphite, carbon black (acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc.), charcoal, activated carbon, etc.], and one or more of these are used.

[0058] Furthermore, it is preferable that the catalyst layer contains 1% by mass or less of heavy metals. Depending on its form, batteries can be easily destroyed by tearing them apart by hand when discarded, but in the case of a positive electrode having a catalyst layer with a low heavy metal content as described above, it is possible to create a battery that has a low environmental impact even when discarded without special treatment.

[0059] The heavy metal content in the catalyst layer as defined herein can be measured by X-ray fluorescence analysis. For example, it can be measured using a Rigaku X-ray fluorescence analyzer "ZSX100e" with an excitation source of Rh 50kV and an analysis area of ​​φ10mm.

[0060] Therefore, it is recommended that the catalyst for the catalyst layer not contain heavy metals, and it is even more preferable to use the various types of carbon mentioned above.

[0061] Furthermore, from the perspective of further increasing the reactivity of the positive electrode, the specific surface area of ​​the carbon used as a catalyst should be 200 m². 2 It is preferable that it be 300m or more per gram. 2 It is more preferable that it be 1 / g or more, and 500m 2It is even more preferable that the specific surface area is 1 / g or more. The specific surface area of ​​carbon as used herein is a value determined by the BET method in accordance with Japanese Industrial Standard (JIS) K 6217, and can be measured, for example, using a specific surface area measuring device that uses the nitrogen adsorption method (Mountech's "Macsorb HM modele-1201"). The upper limit of the specific surface area of ​​carbon is typically 2000 mm². 2 It is approximately / g

[0062] The catalyst content in the catalyst layer is preferably 20 to 70% by mass.

[0063] Examples of binders for the catalyst layer include fluororesin binders such as copolymers of PVDF, PTFE, vinylidene fluoride, and tetrafluoroethylene copolymers [e.g., vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), vinylidene fluoride-chlorotrifluoroethylene copolymer (PVDF-CTFE), vinylidene fluoride-tetrafluoroethylene copolymer (PVDF-TFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer (PVDF-HFP-TFE)]. Among these, polymers or copolymers of tetrafluoroethylene (PTFE) are preferred, with PTFE being more preferred. The binder content in the catalyst layer is preferably 3 to 50% by mass.

[0064] In the case of a positive electrode having a catalyst layer, for example, it can be manufactured by mixing the catalyst, binder, etc. with water, rolling it with a roll, and pressing it into close contact with the current collector. Alternatively, it can be manufactured by dispersing the catalyst and, if necessary, the binder, etc., in water or an organic solvent to prepare a catalyst layer forming composition (slurry, paste, etc.), applying it to the surface of the current collector, drying it, and then, if necessary, performing a pressing process such as calendering.

[0065] Furthermore, it is also possible to use a porous carbon sheet composed of fibrous carbon, such as carbon paper, carbon cloth, or carbon felt, as the catalyst layer. The carbon sheet can also be used as a current collector for the positive electrode, as described later, or it can serve both purposes.

[0066] Current collectors for positive electrodes having a positive electrode mixture layer or a positive electrode having a catalyst layer can be made of, for example, metal meshes, foils, expanded metal, or perforated metal such as titanium, nickel, stainless steel, or copper; or carbon meshes or sheets. When a current collector with voids is used, the components of the positive electrode mixture layer or catalyst layer may be held in the voids of the current collector, thereby integrating the positive electrode mixture layer or catalyst layer with the current collector. The thickness of the current collector for the positive electrode is preferably 10 μm or more and 300 μm or less.

[0067] Furthermore, if the battery has a sheet-like outer casing made of a resin film, a portion of the resin film can be used as the current collector for the positive electrode. In this case, for example, carbon paste can be applied to the surface of the resin film that is intended to become the inner surface of the sheet-like outer casing to form the current collector, or the metal layer of a resin film having a metal layer can be used as the current collector, and a positive electrode mixture layer or a catalyst layer can be formed on the surface of this current collector in the same manner as described above to form the positive electrode. The thickness of the carbon paste layer is preferably 30 to 300 μm.

[0068] The positive electrode typically has a terminal portion for connecting to the application device. The terminal portion of the positive electrode can be formed by connecting aluminum foil (plate) or wire, nickel foil (plate) or wire, etc., to the positive electrode current collector via a lead body, or by directly connecting to the positive electrode current collector. When the terminal portion of the positive electrode is foil (plate), its thickness is preferably 50 μm to 500 μm. When the terminal portion of the positive electrode is wire, its diameter is preferably 100 μm to 1500 μm. Alternatively, a portion of the current collector may be exposed to the outside to form the terminal portion of the positive electrode.

[0069] (Separator) In a battery, a separator is placed between the positive and negative electrodes. For alkaline, manganese, and air batteries, the separator can be made of nonwoven fabric mainly composed of vinylon and rayon, vinylon-rayon nonwoven fabric (vinylon-rayon blended paper), polyamide nonwoven fabric, polyolefin-rayon nonwoven fabric, vinylon paper, vinylon-linter pulp paper, vinylon-mercerized pulp paper, etc. Microporous films can also be used, with microporous polyolefin films (such as microporous polyethylene films and microporous polypropylene films) being specific examples. To improve wettability with aqueous electrolytes, their surfaces may be treated to be hydrophilic.

[0070] 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.

[0071] (Battery type, etc.) There are no particular restrictions on the form of the battery; it can be any form, such as a flat type (including coin type and button type) with a battery case in which the outer casing and sealing plate are crimped and sealed via a gasket, or the outer casing and sealing plate are welded together; a sheet type with a sheet-like outer casing made of resin film; or a cylindrical type (cylindrical, rectangular (square-tube)) with a battery case in which the bottomed cylindrical outer casing and sealing plate are crimped and sealed via a gasket, 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 preferably less than 24 hours. The resin film preferably does not transmit water vapor as much as possible, that is, its water vapor transmission rate is preferably as small as possible, and 0 g / m 2 · It may be 24 hours.

[0086] The water vapor transmission rate of the resin film referred to in this specification is a value measured according to the JIS K 7129B method.

[0087] When the battery is an air battery, it is preferable that the resin film constituting the sheet-like exterior body has a certain degree of oxygen permeability. Since the air battery supplies air (oxygen) to the positive electrode for discharging, air holes for introducing oxygen into the battery are formed in the sheet-like exterior body. When the resin film constituting the sheet-like exterior body has oxygen permeability, oxygen can be introduced into the battery through the exterior body from locations other than the air holes of the sheet-like exterior body. As a result, oxygen can be supplied more uniformly over the entire positive electrode, improving the discharge characteristics of the battery and increasing its discharge time. Also, it becomes possible to realize a sheet-like air battery without air holes in the sheet-like exterior body.

[0088] Specifically, the oxygen permeability of the resin film constituting the sheet-like exterior body when the battery is an air battery is preferably 0.02 cm 3 / m 2 ·24h·MPa or more, and more preferably 0.2 cm 3 / m 2 ·24h·MPa or more. However, when the battery is an air battery, if the resin film constituting the sheet-like exterior body permeates too much oxygen, self-discharge may occur and the capacity may be impaired. Therefore, the oxygen permeability of the resin film is preferably 100 cm 3 / m 2 ·24h·MPa or less, and more preferably 50 cm 3 / m 2 ·24h·MPa or less.

[0089] On the other hand, in the case of batteries other than air batteries, there are no particular restrictions on the oxygen permeability of the resin film constituting the sheet-like outer casing. However, from the viewpoint of improving the battery's storage capacity, it is preferable that the film does not permeate oxygen very well. Specifically, the oxygen permeability of the resin film is 10 cm². 3 / m 2 It is preferable that the pressure be 24h·MPa or less.

[0090] The oxygen permeability of resin films as used herein is the value measured in accordance with the JIS K 7126-2 method.

[0091] 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.

[0092] 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.

[0093] In the case of an air battery, a water-repellent film is usually placed between the positive electrode and the outer casing. This water-repellent film is made of a material that is water-repellent but also permeable to air. Specific examples of such water-repellent films include films made of fluororesins such as PTFE; polyolefins such as polypropylene and polyethylene; and other resins. The thickness of the water-repellent film is preferably 50 to 250 μm.

[0094] Furthermore, if the battery is an air battery, an air diffusion membrane may be placed between the outer casing and the water-repellent film to supply air taken into the outer casing to the positive electrode. The air diffusion membrane can be made of a nonwoven fabric composed of resins such as cellulose, polyvinyl alcohol, polypropylene, or nylon. The thickness of the air diffusion membrane is preferably 100 to 250 μm.

[0095] 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.

[0096] As shown in Figure 2, in the battery 10, the positive electrode 20, the separator 40, the negative electrode 30, and the aqueous electrolyte (not shown) are housed within a sheet-like outer casing 50.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] When the battery is a sheet-type battery, there are no particular restrictions on its thickness (length a in Figure 2), and it can be changed as appropriate depending on the battery's application. One of the advantages of a sheet-type battery is that it can be made thin, and from this viewpoint, its thickness is preferably, for example, 1 mm or less. When the battery is a sheet-type air battery, it is particularly easy to provide such a thin design.

[0101] Furthermore, there are no specific restrictions on the minimum thickness of the battery, but in order to ensure a certain capacity, it is generally preferable to set it at 0.2 mm or more.

[0102] The battery of the present invention has an aqueous electrolyte and is substantially free of heavy metal elements, resulting in a low environmental impact. Furthermore, even if the electrolyte leaks due to damage and comes into contact with the body, it is unlikely to cause problems. Therefore, the battery of the present invention is suitable as a power source for medical and health-related devices, such as patches that can be worn on the body, particularly patches worn on the surface of the skin to measure bodily conditions such as body temperature, pulse rate, and sweating. It can also be applied to the same applications as conventional batteries with aqueous electrolytes, such as air batteries and alkaline batteries. [Examples]

[0103] The present invention will be described in detail below based on the following examples. However, the following examples are not intended to limit the present invention.

[0104] The pH values ​​for the aqueous solutions used as electrolytes in the sheet-type batteries of each example and comparative example were all measured at 25°C using a "LAQUA twin compact pH meter" manufactured by Horiba, Ltd.

[0105] (Example 1) <Positive electrode> A positive electrode mixture-containing composition was prepared by mixing 87.5 parts by mass of electrolytic manganese dioxide [Tosoh Corporation's "SP-A" (average particle size 0.5 μm)], 10 parts by mass of graphite [Nippon Graphite Co., Ltd.'s "SP-20" (average particle size 30 μm)], 2.5 parts by mass of ammonium polyacrylate, and 150 parts by mass of water.

[0106] On porous carbon paper [thickness: 0.15 mm, porosity: 75%, air permeability (Gurley): 70 seconds / 100 ml], the cathode mixture-containing composition was applied at a coating amount of 18 mg / cm² after drying. 2 By applying a stripe coating in this manner and drying it, a carbon paper was obtained having regions that hold positive electrode active material (positive electrode mixture) in the voids and whose surface is covered with a layer containing positive electrode active material (positive electrode mixture layer) [hereinafter referred to as "region A"], and regions that do not hold positive electrode active material in the voids and whose surface is covered with only carbon paper [hereinafter referred to as "region B"]. This was punched out into a shape having a main body portion that holds positive electrode active material, consisting of region A measuring 30 mm x 30 mm, and a positive electrode terminal consisting of region B measuring 10 mm x 20 mm, thereby fabricating a positive electrode with a thickness of 0.2 mm and a theoretical capacity of 30 mAh.

[0107] <Negative electrode> An electrolytic zinc alloy foil (thickness: 0.03 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 of 30 mm x 30 mm and a negative electrode terminal of 10 mm x 20 mm to produce a negative electrode.

[0108] <Electrolyte> The electrolyte used was an aqueous solution (pH=8.27) prepared by dissolving potassium acetate (solubility of 216 g per 100 g of water at 0°C) at a concentration of 20% by mass.

[0109] <Separator> The separator is made of polypropylene nonwoven fabric film with a hydrophilic surface treatment (thickness: 50 μm, basis weight: 12 g / m²). 2 ) was used.

[0110] <Sheet-like exterior material> A sheet-like outer casing was created using two 50mm x 50mm aluminum laminate films (thickness: 65μm) each, each having 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.

[0111] <Battery assembly> The positive electrode, the separator, and the negative electrode were sequentially laminated on one aluminum laminate film, 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 0.1 ml of the electrolyte was injected through the opening. Finally, the opening was heat-sealed to create a sheet-like battery with the same structure as shown in Figures 1 and 2.

[0112] (Examples 2-6) Sheet-type batteries of Examples 2 to 6 were prepared in the same manner as in Example 1, except that the electrolyte was changed to aqueous solutions of potassium acetate dissolved at concentrations of 15% by mass, 25% by mass, 30% by mass, 40% by mass, and 50% by mass, respectively (pH=8.10, pH=8.46, pH=8.65, pH=9.11, and pH=9.72, respectively).

[0113] (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=8.72) in which potassium formate (solubility of 280 g in 100 g of water at 0°C) was dissolved at a concentration of 25% by mass.

[0114] (Example 8) A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution of potassium acetate (concentration: 20% by mass) and ammonium chloride (solubility in 100g of water at 0°C: 29.4g, concentration: 5% by mass).

[0115] (Example 9) A sheet-type battery was prepared in the same manner as in Example 1, except that the electrolyte was changed to an aqueous solution of potassium acetate (concentration: 20% by mass) and ammonium chloride (concentration: 10% by mass).

[0116] (Example 10) 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=7.32) containing potassium acetate (concentration: 20% by mass) and ammonium chloride (concentration: 15% by mass).

[0117] (Example 11) 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=7.88) containing potassium acetate (concentration: 30% by mass) and ammonium chloride (concentration: 5% by mass).

[0118] (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=5.01) in which ammonium chloride was dissolved at a concentration of 25% by mass.

[0119] (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=4.85) in which zinc chloride was dissolved at a concentration of 25% by mass.

[0120] (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 of sodium acetate (solubility of 36.2 g in 100 g of water at 0°C) dissolved at a concentration of 25% by mass.

[0121] (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 of sodium formate (solubility of 43.9 g in 100 g of water at 0°C) at a concentration of 25% by mass.

[0122] Table 1 shows the composition of the electrolyte used in the sheet-type batteries of the examples and comparative examples. In the pH column, "―" is written for values ​​for which no measurement was available. The pH of the electrolyte used in the batteries of Example 8 and Example 9 is between the pH of the electrolyte of the battery in Example 1 (8.27) and the pH of the electrolyte of the battery in Example 10 (7.32), suggesting that the pH decreases in the order of Example 1 > Example 8 > Example 9 > Example 10.

[0123] [Table 1]

[0124] For the sheet-type batteries of Examples 1, 3, 7, Comparative Example 1, Comparative Example 3, and Comparative Example 4, pulse discharge tests were performed under the following conditions in a room temperature (25°C) environment and a low temperature (-40°C) environment to evaluate the discharge characteristics at room temperature and low temperature.

[0125] The pulse discharge conditions were set to a pulse width of 10 msec and a pulse interval of 3 sec. The pulse current values ​​were set to 10 mA, 30 mA, and 50 mA at room temperature, and 0.5 mA, 1 mA, and 2 mA at low temperatures. Fifty pulse discharges were performed under each current value condition, and the closed-circuit voltage (CCV) was measured. The evaluation results of the discharge characteristics at room temperature are shown in Figure 3, and the evaluation results of the discharge characteristics at low temperatures are shown in Figure 4.

[0126] Furthermore, for the sheet-type batteries of Examples 1-7 and Comparative Examples 1-4, pulse discharge tests were performed under the same low-temperature environment as described above, with the pulse current value set to 1 mA, and the CCV of each battery was measured.

[0127] Table 2 shows the measurement results for batteries in Examples 3, 7, and Comparative Examples 1-4, which all have the same electrolyte salt concentration of 25% by mass, as low-temperature discharge characteristics. Furthermore, Figure 5 shows the change in CCV with respect to changes in potassium acetate concentration in the electrolyte, based on the measurement results of Examples 1-6.

[0128] [Table 2]

[0129] As shown in Figure 3, the battery of Comparative Example 1, which used an aqueous solution containing a salt of a strong acid and a weak base (ammonium chloride) that does not contain heavy metal elements as the electrolyte, and the sheet-type batteries of Comparative Examples 3 and 4, which used an aqueous solution containing an electrolyte salt (sodium acetate and sodium formate) that is a salt of a weak acid and a strong base and has a solubility of less than 100 g in 100 g of water at 0°C as the electrolyte, exhibited excellent discharge characteristics at room temperature. Furthermore, the sheet-type batteries of Examples 3 and 7, which used an aqueous solution containing an electrolyte salt (potassium acetate and potassium formate) that is a salt of a weak acid and a strong base and has a solubility of 100 g or more in 100 g of water at 0°C as the electrolyte, were also found to be batteries with similarly excellent discharge characteristics at room temperature, although their voltage was slightly lower than the aforementioned batteries.

[0130] On the other hand, as shown in Table 1 and Figure 4, the sheet-type batteries of Example 3 and Example 7 showed reduced discharge characteristics at low temperatures compared to the battery of Comparative Example 2, which used an aqueous solution containing zinc chloride as the electrolyte. However, they showed significantly improved discharge characteristics at low temperatures compared to the batteries of Comparative Examples 1, 3, and 4.

[0131] Furthermore, the results shown in Figure 5 generally correlated with the change in ionic conductivity of the electrolyte containing potassium acetate, which showed the highest value at room temperature at a concentration of approximately 40% by mass. These results indicate that the concentration of the salt of a weak acid and a strong base in the battery electrolyte should be 10% by mass or higher (ionic conductivity of the electrolyte of 80 mS / cm or higher at room temperature).

[0132] Next, for the sheet-type batteries of Examples 8 to 11, pulse discharge tests were performed in a low-temperature environment at current values ​​of 0.5 mA, 1 mA, and 2 mA, as described above, and the CCV was measured to evaluate the discharge characteristics at low temperatures. The results, along with those of Example 1, are shown in Figure 6.

[0133] The batteries of Examples 8 to 11, which contained potassium acetate (a salt of a weak acid and a strong base) along with ammonium chloride (a salt of a strong acid and a weak base) and whose electrolyte pH was lower than that of the battery in Example 1, were able to improve the discharge characteristics at low temperatures compared to the battery in Example 1, which used an aqueous solution containing only a salt of a weak acid and a strong base as the electrolyte.

[0134] As is clear from the above results, by using an aqueous solution containing an electrolyte salt that is a salt of a weak acid and a strong base, and whose solubility in 100g of water at 0°C is 100g or more, at a concentration of 10% by mass or more as the electrolyte, it is possible to construct a battery that is highly safe and has excellent discharge characteristics at low temperatures. [Explanation of Symbols]

[0135] 10 batteries 20 positive electrode 21 Positive terminal 30 negative electrode 31 Negative terminal section 40 Separators 50 Sheet-like exterior body

Claims

1. A battery comprising a negative electrode having at least one metal selected from the group consisting of zinc, aluminum, magnesium, and alloys thereof as an active material, and an aqueous electrolyte, A battery characterized in that the electrolyte is an aqueous solution containing an electrolyte salt at a concentration of 10% by mass or more, which is a salt of a weak acid and a strong base and has a solubility of 100 g or more in 100 g of water at 0°C.

2. The battery according to claim 1, wherein the salt of the weak acid and the strong base is a salt of a carboxylic acid.

3. The battery according to claim 1, wherein the electrolyte further contains a salt of a strong acid and a weak base.

4. The battery according to claim 1, wherein the pH of the electrolyte is 8 or less.

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