Electrode for batteries, and battery

Abstract

Provided are: an electrode capable of enhancing battery productivity; and a battery having the electrode and excellent in productivity.　This electrode for batteries is characterized by having a porous collector and an active material layer provided on one surface or both surfaces of the porous collector, and is also characterized in that the porous collector holds particles (A) having an average particle diameter of 7 μm or less in voids thereof, the active material layer contains active material particles (B), and the average particle diameter of the entire active material particles (B) is 10 μm or more. This battery is characterized by having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and is also characterized in that the positive electrode and / or the negative electrode are / is said electrode for batteries.

Description

Battery electrodes and batteries

[0001] The present invention relates to an electrode that can improve the productivity of batteries, and to a battery that has the electrode and has excellent productivity.

[0002] Primary and secondary batteries used as power sources for various devices are generally of a type in which a wound electrode body, in which a positive electrode and a negative electrode are stacked with a separator between them and wound in a spiral shape, is housed in a cylindrical metal container, or of a flat type known as a coin or button shape in which a laminated electrode body, in which a positive electrode and a negative electrode are stacked with a separator between them, is housed in a flat metal container.

[0003] However, in recent years, there has been a need for applications that are difficult to apply using the above-mentioned metal containers, such as thin electronic devices, and in order to meet such demands, sheet-type batteries using laminate film exteriors have also been developed.

[0004] One known type of battery is a so-called printed battery, which is constructed by applying a conductive paste to the surface of a substrate (such as a plastic film) that constitutes the exterior body, using this as a current collector, and then forming a layer containing an active material (active material layer) on the conductive paste coating to form an electrode. However, it is difficult to reduce the resistance of such electrodes, which results in problems such as increased internal resistance of the printed battery and reduced load characteristics.

[0005] On the other hand, Patent Document 1 discloses that by constructing a battery using a positive electrode having a porous carbon sheet and a positive electrode active material layer containing a positive electrode active material held in the pores of the carbon sheet, it is possible to improve the load characteristics even in a sheet-like form. Patent Document 1 also discloses that a preferable embodiment of the positive electrode of the battery is to cover the separator-side surface of the porous carbon sheet with the positive electrode active material layer.

[0006] International Publication No. 2022 / 030611

[0007] However, the inventors' investigations have revealed that the positive electrode of the battery described in Patent Document 1 is prone to warping and cracking in the positive electrode active material layer covering the surface of the porous carbon sheet. If cracks occur in the positive electrode active material layer, active material particles may fall off from the positive electrode active material layer within the battery, causing a decrease in capacity or a short circuit. Batteries with such problems cannot be used commercially, reducing battery productivity. Furthermore, warping of the positive electrode also reduces battery productivity.

[0008] Therefore, in batteries having electrodes with the same configuration as the positive electrode described in Patent Document 1, there is a need to develop a technology that can suppress the occurrence of the above problems and increase productivity.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode that can increase the productivity of batteries, and a battery that includes the electrode and has excellent productivity.

[0010] The battery electrode of the present invention comprises a porous current collector and an active material layer on one or both sides of the porous current collector, wherein the porous current collector holds particles (A) having an average particle diameter of 7 μm or less within its pores, and the active material layer contains active material particles (B), and the average particle diameter of the entire active material particles (B) is 10 μm or more.

[0011] The battery of the present invention has a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and is characterized in that at least one of the positive electrode and the negative electrode is the battery electrode of the present invention.

[0012] According to the present invention, it is possible to provide an electrode that can increase the productivity of batteries, and a battery that includes the electrode and has excellent productivity.

[0013] 1 is a plan view schematically showing an example of a battery of the present invention; FIG. 2 is a cross-sectional view taken along line II in FIG. 1; FIG. 3 is a cross-sectional view schematically showing a positive electrode produced in Example 1; FIG. 4 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Example 1; FIG. 5 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Example 2; FIG. 6 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Example 3; FIG. 7 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Comparative Example 1; FIG. 8 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Comparative Example 2; FIG. 9 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Comparative Example 3; FIG. 10 is a photograph taken using a microscope of the surface of the positive electrode used in the battery of Comparative Example 4.

[0014] <Battery electrode> The battery electrode of the present invention (hereinafter sometimes simply referred to as "electrode") has a porous current collector and an active material layer containing active material particles on one or both sides of the porous current collector. The porous current collector holds particles (A) having an average particle size of 7 μm or less in its pores. The active material layer also contains active material particles (B), and the active material particles (B) as a whole have an average particle size of 10 μm or more.

[0015] For example, when a positive electrode is fabricated by forming an active material layer on the surface of a porous current collector through a process of coating and drying a composition containing active material particles and a solvent (dispersion medium), in the coating film formed by coating the porous current collector with the composition, the active material particles exert a force tending to aggregate with each other due to van der Waals forces acting between the active material particles and liquid bridging forces of the solvent. Then, when the coating film is dried to remove the solvent, the force of aggregation between the active material particles becomes strong, causing cracks in the active material layer and warping of the positive electrode.

[0016] As a result of extensive research, the present inventors have found that the van der Waals forces and liquid bridging forces can be reduced by increasing the particle size of the active material particles contained in the active material layer to a certain extent, and that the strength of the porous current collector can be increased by retaining particles with a relatively small particle size in the voids of the porous current collector, thereby improving the shape retention of the electrode.

[0017] Based on the above findings, the electrode of the present invention has particles (A) having an average particle size of a specific value or less held in the pores of a porous current collector, and active material particles (B) contained in an active material layer formed on one or both surfaces of the porous current collector have an average particle size of a specific value or more overall, thereby making it possible to suppress warping of the electrode and cracking of the active material layer. Therefore, in a battery using the electrode of the present invention (battery of the present invention), it is possible to suppress capacity reduction and short circuit occurrence during production, and further to reduce the complexity of production due to electrode warping, thereby enabling productivity to be increased.

[0018] The "active material layer" in the electrode of the present invention refers to a layer formed on one or both sides of the outer surface (surface portion) of the porous current collector, and even if a layer that holds active material particles is formed in the voids of the porous current collector, this layer is not included in the "active material layer."

[0019] The electrode of the present invention can be used in batteries having an electrolyte solution consisting of an aqueous solution with water as the solvent (such as alkaline batteries (alkaline primary batteries, alkaline secondary batteries), and manganese batteries), and can also be used in batteries having a nonaqueous electrolyte using a nonaqueous solvent as the electrolyte (nonaqueous electrolyte batteries (nonaqueous electrolyte primary batteries, nonaqueous electrolyte secondary batteries)). The electrode of the present invention can be used as the positive electrode and / or negative electrode of these batteries.

[0020] When the electrode is a positive electrode of an alkaline battery, examples of the active material particles (B) contained in the active material layer include particles of silver oxide (silver (I) oxide, silver (II) oxide, etc.), manganese oxide such as manganese dioxide, nickel oxyhydroxide, composite oxide of silver with cobalt, nickel or bismuth, etc. When the electrode is a positive electrode of a manganese battery, particles of manganese oxide such as manganese dioxide are used as the active material particles (B) contained in the active material layer.

[0021] When the electrode is a positive electrode of a non-aqueous electrolyte battery, the active material particles (B) contained in the active material layer may be selected from the group consisting of manganese dioxide; vanadium oxide, niobium oxide, titanium oxide, and sulfides such as iron disulfide; graphite fluoride; ｘ Mn ３ O ６ (0<x<2), Li ｘ MnO ２ Lithium-containing manganese oxides such as (0<x<1), Li ｘ Ti ５／３ O ４ (4 / 3≦x<7 / 3), LiMn ２ O ４ or a spinel-structured composite oxide in which some of the elements are replaced with other elements, Li １＋ｘ M １ O ２ (-0.1<x<0.1, M １ Lithium-containing composite oxides having a layered structure represented by the following: Co, Ni, Mn, Al, Mg, etc.; LiM ２ P.O. ４ (M ２ and various lithium-containing composite oxides such as olivine-type compounds represented by the formula (I): Co, Ni, Mn, Fe, etc.;

[0022] The layered lithium-containing composite oxide may be LiCoO ２ Lithium cobalt oxide and LiNi １－ａ Co ａ－ｂ Al ｂ O ２ (0.1≦a≦0.3, 0.01≦b≦0.2), as well as oxides containing at least Co, Ni and Mn (LiMn １／３ Ni １／３ Co １／３ O２ , LiMn ５／１２ Ni ５／１２ Co １／６ O ２ , LiNi ３／５ Mn １／５ Co １／５ O ２ etc.) can be exemplified.

[0023] When the electrode is a negative electrode of an alkaline battery (primary battery or secondary battery) or a manganese battery, for example, zinc-based particles (zinc particles and zinc alloy particles are collectively referred to as such) are used as the active material particles (B) contained in the active material layer.

[0024] Examples of alloy components of the zinc alloy particles include indium (e.g., a content of 0.005 to 0.05% by mass), bismuth (e.g., a content of 0.005 to 0.25% by mass, preferably 0.01% or more, and preferably 0.05% or less), and aluminum (e.g., a content of 0.001 to 0.15% by mass).

[0025] In addition, in consideration of reducing the environmental load when disposing of batteries, it is preferable that the zinc-based particles used in the negative electrode have low contents of mercury, cadmium, lead, and chromium, and it is more preferable that the specific contents are, on a mass basis, mercury: 0.1% or less, cadmium: 0.01% or less, lead: 0.1% or less, and chromium: 0.1% or less.

[0026] When the electrode is a negative electrode of a non-aqueous electrolyte primary battery, examples of the active material particles (B) contained in the active material layer include particles of metallic lithium, lithium alloys (lithium-aluminum alloys), and the like.

[0027] When the electrode is a negative electrode of a nonaqueous electrolyte secondary battery, examples of the active material particles (B) contained in the active material layer include particles of metallic lithium, lithium alloys (lithium-aluminum alloys), and the like, as well as particles of carbon materials such as graphite, pyrolytic carbons, cokes, glassy carbon, fired bodies of organic polymer compounds, mesophase carbon microbeads, carbon fibers, and activated carbon; alloys containing elements capable of alloying with lithium, such as Si and Sn; and oxides of Si and Sn.

[0028] The active material layer may contain only one type of the active material particles (B) exemplified above, or may contain two or more types.

[0029] The average particle diameter of the active material particles (B) contained in the active material layer is 10 μm or more, preferably 40 μm or more, from the viewpoint of suppressing cracking of the active material layer and warping of the electrode. However, if the size of the active material particles (B) is too large, there is a risk of deterioration in battery characteristics. Therefore, from the viewpoint of being able to construct a battery with better characteristics, the average particle diameter of the active material particles (B) contained in the active material layer is preferably 100 μm or less, more preferably 50 μm or less.

[0030] The average particle diameter of the active material particles (B) and the particles (A) held in the pores of the porous current collector referred to in this specification is the 50% diameter value (D) in the volume-based integrated fraction when the integrated volume is calculated from particles with small particle sizes using a laser scattering particle size distribution analyzer (for example, "LA-920" manufactured by Horiba, Ltd.). ５０ ) means

[0031] The active material layer may contain only the active material particles (B), or may contain other components in addition to the active material particles (B). Such components include a conductive additive, a binder, etc. That is, the active material layer can be formed from a mixture containing the active material particles (B) together with a conductive additive and / or a binder, etc.

[0032] Examples of the conductive additive that can be used include carbon materials such as natural graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon fibers, as well as conductive fibers such as metal fibers, carbon fluoride, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives. When the active material layer is formed using a mixture containing a conductive additive, the content of the conductive additive in the active material layer is preferably 5 to 15% by mass.

[0033] In addition, the binder may be a water-insoluble resin such as an acrylic resin (such as polyacrylic ester), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or styrene butadiene rubber (SBR), or a water-soluble resin such as polyacrylate (such as sodium polyacrylate or ammonium polyacrylate), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), or poly-N-vinylacetamide (PNVA).

[0034] When an active material layer is formed using a binder-containing mixture, if the amount of binder in the active material layer is too large, the resistance of the electrode may increase. Therefore, from the viewpoint of minimizing the resistance of the electrode and constructing a battery with better characteristics, the content of the binder in the active material layer is preferably 20% by mass or less, more preferably 10% by mass or less. Note that, although increasing the amount of binder in the active material layer makes the active material layer less likely to crack, the electrode of the present invention can effectively suppress the occurrence of cracks even if the amount of binder in the active material layer is reduced as described above. Furthermore, when an active material layer is formed using a binder-containing mixture, from the viewpoint of better ensuring the effects of using the binder (the effect of improving the formability and shape retention of the active material layer), the content of the binder in the active material layer is preferably 5% by mass or more.

[0035] Furthermore, when the active material layer is formed using a mixture containing the active material particles (B) together with a conductive additive and / or a binder, the content of the active material particles (B) in the active material layer is preferably 70 to 90 mass %.

[0036] The electrode may have an active material layer on one side or on both sides of a porous current collector, depending on the configuration of the electrode body (an electrode body having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode) of the battery, for example.

[0037] The thickness of the active material layer (thickness per side of the porous current collector; the same applies hereinafter) is preferably 30 μm or more, more preferably 50 μm or more, from the viewpoint of increasing the capacity of a battery using the electrode, for example. While cracks in the active material layer are unlikely to occur if the active material layer is relatively thin, they are relatively likely to occur if the thickness is 30 μm or more. However, the electrode of the present invention can effectively suppress the occurrence of cracks even when it has such a thick active material layer. Furthermore, if the active material layer is too thick, there is a risk that the proportion of active material particles (B) that are less likely to participate in the battery reaction will increase. Therefore, from the viewpoint of increasing the utilization rate of the active material particles (B), the thickness is preferably 500 μm or less, more preferably 300 μm or less.

[0038] The porous current collector of the electrode is a conductive porous material. Specific examples of the porous current collector include a conductive porous sheet (e.g., a nonwoven sheet made of fibers of the metal) made of a metal such as stainless steel, titanium, or nickel; a porous carbon sheet; and the like. For example, when the battery electrolyte is an aqueous solution having a pH of 12 or less, particularly an acidic aqueous solution, using a metallic porous current collector may cause corrosion depending on the material. However, when a porous carbon sheet is used as the porous current collector, such concerns are eliminated, allowing for a wider variety of battery configurations to be adopted. Therefore, it is more preferable to use a porous carbon sheet as the porous current collector.

[0039] As the porous carbon sheet, for example, a porous sheet made of fibrous carbon such as carbon paper, carbon cloth, or carbon felt can be preferably used. These sheets may have a single-layer structure, a multi-layer structure in which carbon papers, carbon cloths, or carbon felts are laminated together, or a multi-layer structure in which two or more of carbon paper, carbon cloth, and carbon felt are laminated together. Also, a porous sheet made of expanded graphite can be used as the porous carbon sheet.

[0040] The fiber diameter of the fibrous carbon constituting the sheet is preferably 2 to 30 μm, taking into consideration electrical conductivity and the like.

[0041] The thickness of the porous current collector is preferably 0.5 mm or less from the viewpoint of increasing the energy density of the battery that the electrode is used in. The lower limit of the thickness of the porous current collector is usually 0.05 mm, taking into consideration ease of handling and availability, and ensuring sufficient battery reaction and current collecting function at the electrode.

[0042] The porous current collector holds the particles (A) in its pores, and from the viewpoint of being able to hold the particles well and ensuring sufficient strength, it is preferable that the porosity be 50% or more and 95% or less.

[0043] The porous current collector may be selected from commercially available products that satisfy the above physical property values.

[0044] The porous current collector holds particles (A) with an average particle size of 7 μm or less within its pores. The action of these particles (A) increases the strength of the porous current collector, improving its shape retention, and, together with the effect of adjusting the particle size of the active material particles (B) contained in the active material layer, effectively suppresses warping of the electrode.

[0045] The particles (A) held in the pores of the porous current collector have an average particle size of 7 μm or less, preferably 5 μm or less, and more preferably 3 μm or less, from the viewpoint of improving the shape retention of the porous current collector by increasing the filling ability of the pores. In addition, taking into consideration the handleability of the particles (A) held in the pores of the porous current collector, the average particle size is preferably 0.1 μm or more, and more preferably 1 μm or more.

[0046] The particles (A) held in the pores of the porous current collector are preferably active material particles (a) or particles that are stable in the battery and do not cause unnecessary side reactions.

[0047] Among the particles (A) held in the pores of the porous current collector, the active material particles (a) include particles made of the same material as the active material related to the various active material particles exemplified above as the active material particles (B) that can be contained in the active material layer.

[0048] Specific examples of the particles (A) held in the pores of the porous current collector other than the active material particles (a) include particles of an oxide of at least one element selected from Si, Zr, Ti, Al, Mg, and Ca. Specific examples of the oxide include Al ２ O ３ , TiO ２ , SiO ２ , ZrO ２ , MgO, CaO, AlOOH, Al(OH) ３ Examples include:

[0049] The particles (A) to be held in the pores of the porous current collector may be one of the above-mentioned examples, or two or more of them may be used in combination. However, it is more preferable to use active material particles (a) because this can further increase the capacity of the battery in which the electrode is used.

[0050] The pores of the porous current collector may hold only the particles (A), or may hold a binder together with the particles (A). When a binder is also held in the pores of the porous current collector, the same binders as those exemplified above as those that can be contained in the active material layer can be used as the binder.

[0051] The amount of particles (A) held in the pores of the porous current collector is determined based on the amount of particles (A) held in the pores of the porous current collector per 1 cm of the porous current collector, from the viewpoint of better ensuring the effect of the use. ２ The upper limit of the amount of particles (A) held in the pores of the porous current collector is not particularly limited, but it is usually set to 1 mg or more, more preferably 10 mg or more, per 1 cm of the porous current collector. ２ Each dose is 100 mg or less.

[0052] Furthermore, when a binder is also retained in the pores of the porous current collector, if the amount is large, there is a risk of the resistance of the electrode increasing. Therefore, it is preferable that the amount of binder in the pores of the porous current collector is small. For example, when the amount of particles (A) retained in the pores of the porous current collector is 100 parts by mass, the amount of binder is preferably 10 parts by mass or less, and may be 0 parts by mass (no binder retained). Note that when using a binder to improve the retention of particles (A) in the pores of the porous current collector, from the viewpoint of ensuring the effect well, it is preferable that the amount of binder is 5 parts by mass or more when the amount of particles (A) retained in the pores of the porous current collector is 100 parts by mass.

[0053] Furthermore, the pores of the porous current collector may contain any of the various conductive additives listed above as examples of those that can be contained in the active material layer.

[0054] The electrode can be produced, for example, by a production method including the following steps (1) and (2).

[0055] Step (1): A composition (paste, slurry, etc.) in which particles (A) to be retained in the pores of the porous current collector are dispersed in a solvent is applied to the porous current collector, and the composition is allowed to penetrate into the pores.

[0056] The solvent for the composition can be water, an aqueous organic solvent such as ethanol, or a non-aqueous organic solvent such as N-methyl-2-pyrrolidone (NMP). In addition, when a binder or a conductive additive is to be held in the pores of the porous current collector together with the particles, the binder or the conductive additive is also added to the composition.

[0057] In addition, when a porous carbon sheet is used as the porous current collector, the porous carbon sheet is usually water-repellent, and therefore, if the composition using water as a solvent is used, it may be difficult for the composition to penetrate into the pores of the porous carbon sheet even when applied to the porous carbon sheet.

[0058] Therefore, when a porous carbon sheet is used as the porous current collector and the composition contains water as the solvent, it is preferable to further add a surfactant to the composition to increase its affinity with the porous carbon sheet, thereby enabling the composition to penetrate more effectively into the pores of the porous carbon sheet. Also, when the composition is prepared using a solvent other than water (an organic solvent), a surfactant may be added to further increase the penetration into the pores of the porous carbon sheet.

[0059] The surfactant to be blended in the composition to enhance the affinity with the porous carbon sheet may be any of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants, and examples thereof include fluorine-based surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, sulfonates of higher fatty acid esters, perfluoroalkylcarboxylic acids, perfluoroalkylsulfonic acids, and oxyethylene perfluoroalkyl ethers.

[0060] The amount of surfactant in the composition is preferably 0.3% by mass or more from the viewpoint of increasing affinity with the porous carbon sheet and enabling better penetration into the pores. However, since the surfactant may remain in the pores of the carbon sheet and act as a resistance component, the amount is preferably small. Therefore, the amount of surfactant in the composition is preferably 5% by mass or less, for example.

[0061] The total content of all components in the composition excluding the solvent (including a surfactant, if blended) (hereinafter referred to as "solids concentration") is usually 20 to 80 mass %.

[0062] The method for applying the composition to the porous current collector is not particularly limited, and a known application device or a method of immersing the porous current collector in a bath of the composition can be used.

[0063] The porous current collector with the composition infiltrated into the pores may be subjected to the next step (2) as is, or may be subjected to the step (2) after being dried to remove the solvent from the composition.

[0064] Step (2): An active material layer-forming composition, in which the active material particles (B), and optionally a conductive additive and a binder, etc. are dispersed in a solvent, is applied to one or both surfaces of the porous current collector with the composition infiltrated into the pores, and dried to form an active material layer.

[0065] The solvent for the active material layer-forming composition can be the same as the solvent for the composition that is to be penetrated into the pores of the porous current collector as exemplified above. Note that, as with the above composition, a surfactant may be blended into the active material layer-forming composition, but since the active material layer-forming composition is not to be penetrated into the pores of the porous current collector, it is not necessary to blend a surfactant even when a porous carbon sheet is used as the porous current collector.

[0066] There are no particular restrictions on the method for applying the active material layer-forming composition to the porous current collector, and methods using known application devices can be used. In addition, for example, when a step of removing the solvent in the composition that has penetrated into the voids of the porous current collector by drying is provided between steps (1) and (2) as described above, a method of immersing the porous current collector in a bath of the active material layer-forming composition can also be used.

[0067] The electrode on which the active material layer has been formed by drying in step (2) may be subjected to a pressing treatment.

[0068] The electrode can be provided with an electrode terminal for connecting to an external device. The electrode terminal may be formed by attaching a terminal portion made of a different material to a part of the porous current collector, but it is preferable to use a part of the porous current collector as the electrode terminal. That is, when cutting the porous current collector, it is possible to form a shape having a main body portion that holds the active material layer and a terminal portion that constitutes the electrode terminal, and to manufacture the electrode by holding the active material layer, etc., only on the main body portion. Forming the electrode terminal in this way can improve the productivity of the electrode, thereby making it possible to further increase the productivity of batteries that use the electrode.

[0069] The battery of the present invention has a positive electrode, a negative electrode, and a separator interposed therebetween, and at least one of the positive electrode and the negative electrode is the electrode of the present invention. The battery is usually formed by interposing a separator between the positive electrode and the negative electrode to form an electrode assembly, and housing this electrode assembly and an electrolyte in an exterior body.

[0070] (Electrodes) In a battery, either one of the positive electrode or the negative electrode may be the electrode of the present invention, and the other may be an electrode other than the electrode of the present invention, or both the positive electrode and the negative electrode may be the electrodes of the present invention.

[0071] When a battery has the electrode of the present invention only in the positive electrode, the negative electrode may be a negative electrode having a foil-shaped current collector instead of a porous current collector, and having on one or both sides thereof an active material layer (negative electrode mixture layer) of the same configuration as the active material layer of the electrode of the present invention; a negative electrode having a foil-shaped current collector instead of a porous current collector, and having on one or both sides thereof an active material layer (negative electrode mixture layer) of the same configuration as the active material layer of the electrode of the present invention except that the particle size of the active material particles is different; a negative electrode constituted by a metallic lithium foil or a lithium alloy foil (such as a lithium-aluminum alloy foil), or by attaching such a foil to a current collector; a negative electrode constituted by a zinc-based sheet (zinc sheet or zinc alloy sheet) having the same composition as the zinc-based particles exemplified above as the negative electrode active material; and the like.

[0072] When a battery has the electrode of the present invention only in the negative electrode, the positive electrode can be a positive electrode having a foil-shaped current collector instead of a porous current collector, and having an active material layer (positive electrode mixture layer) on one or both sides of the foil-shaped current collector, which has the same configuration as the active material layer in the electrode of the present invention except that the particle diameter of the active material particles is different; or the like.

[0073] (Separator) A separator interposed between the positive electrode and the negative electrode is preferably made of a nonwoven fabric. Examples of nonwoven fabrics constituting the separator include nonwoven fabrics primarily made of vinylon and rayon, vinylon-rayon nonwoven fabrics (vinylon-rayon mixed paper), polyamide nonwoven fabrics, polyolefin-rayon nonwoven fabrics, and polyolefin (polyethylene, polypropylene, ethylene-propylene copolymer, polymethylpentene, etc.) nonwoven fabrics. Also usable are vinylon paper, vinylon-linter pulp paper, vinylon-mercerized pulp paper, cellophane graft film, and microporous polyolefin films (microporous polyethylene film, microporous polypropylene film, etc.). These separators may have their surfaces hydrophilized to improve wettability with the electrolyte (electrolytic solution).

[0074] The thickness of the separator is, for example, preferably 10 to 500 μm, and in the case of a microporous film, preferably 10 to 50 μm, and in the case of a nonwoven fabric, preferably 20 to 500 μm, more preferably 50 to 500 μm.

[0075] When a porous separator is used, the porosity is preferably 40 to 90% by volume.

[0076] The porosity P (%) of the separator as used herein can be calculated by finding the sum for each component i using the following formula (1) from the thickness of the separator, the mass per area, and the density of the constituent components.

[0077] P = {1-(m / t) / (Σa ｉ ・ρ ｉ ) x 100 (1)

[0078] Here, in the formula (1), a ｉ : Ratio of component i when the total mass is 1, ρ ｉ : density of component i (g / cm ３ ), m: mass per unit area of ​​separator (g / cm ２), t: thickness of the separator (cm). The mass per unit area of ​​the separator, m, was determined by measuring the mass of a 20 cm square separator cut out with an electronic balance, and dividing the mass by 1 cm ２ The thickness t of the separator was measured at 10 randomly selected points using a micrometer and averaged.

[0079] (Electrolyte) When the battery is an alkaline battery or a manganese battery, an aqueous solution in which an electrolyte salt is dissolved is used as the electrolyte.

[0080] When the battery is an alkaline battery, an alkaline electrolyte is used as the electrolyte. Examples of alkaline electrolytes that can be used include an alkaline aqueous solution of an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, or lithium hydroxide, and an alkaline electrolyte to which zinc oxide has been added. The concentration of the alkali metal hydroxide in the alkaline electrolyte is preferably 28 to 38 mass % in the case of potassium hydroxide, for example, and if zinc oxide is used, the concentration is preferably 1.0 to 4.0 mass %.

[0081] When the battery is a manganese battery, the electrolyte is an aqueous solution having a pH in the range of 3 to 12. In order to prevent corrosion of the negative electrode active material, the pH of the aqueous solution is preferably 4 or higher, and more preferably 5 or higher. Examples of the electrolyte salt include chlorides such as sodium chloride, potassium chloride, magnesium chloride, calcium chloride, ammonium chloride, and zinc chloride; hydroxides of alkali metals and alkaline earth metals (sodium hydroxide, potassium hydroxide, magnesium hydroxide, etc.), acetates (sodium acetate, potassium acetate, magnesium acetate, etc.), nitrates (sodium nitrate, potassium nitrate, magnesium nitrate, etc.), sulfates (sodium sulfate, potassium sulfate, magnesium sulfate, etc.), phosphates (sodium phosphate, potassium phosphate, magnesium phosphate, etc.), borates (sodium borate, potassium borate, magnesium borate, etc.), citrates (sodium citrate, potassium citrate, magnesium citrate, etc.), glutamate (sodium glutamate, potassium glutamate, magnesium glutamate, etc.); bicarbonates of alkali metals (sodium bicarbonate, potassium bicarbonate, etc.); percarbonates of alkali metals (sodium percarbonate, potassium percarbonate, etc.); compounds containing halogens such as fluorides; and polycarboxylic acids. The electrolyte may contain one or more of these electrolyte salts. Among these, it is preferable to use an aqueous solution of zinc chloride as the electrolyte, and the concentration of zinc chloride is preferably 10 to 40% by mass.

[0082] Furthermore, when a zinc-based sheet is used for the negative electrode, corrosion from the aqueous electrolyte may cause the negative electrode to break, resulting in problems such as insufficient capacity. However, by incorporating a thickener into the aqueous electrolyte, preferably in a gel form (gel electrolyte), such problems can be prevented. Examples of thickeners that can be incorporated into the electrolyte include cellulose derivatives such as carboxymethyl cellulose (CMC) and carboxyethyl cellulose (CEC); polyalkylene glycols such as polyethylene glycol (PEG) (preferably with a molecular weight of 1,000 or more, more preferably 10,000 or more); polyvinylpyrrolidone; polyvinyl acetate; starch; guar gum; xanthan gum; sodium alginate; hyaluronic acid; gelatin; polyacrylic acid; and various other synthetic or natural polymers. Furthermore, when using thickeners among the above examples that have a functional group consisting of a carboxyl group or a salt thereof (such as -COOH or -COONa) in the molecule, it is also preferable to incorporate a polyvalent metal salt that acts as a gelation promoter into the electrolyte. The blending amount of the thickener in the electrolyte is preferably 0.1 to 5% by mass. When a gelation accelerator is used, the ratio of the gelation accelerator is preferably 1 to 30% by mass when the ratio of the thickener is 100% by mass.

[0083] When the battery is a non-aqueous electrolyte battery, a solution (non-aqueous electrolyte) in which a lithium salt is dissolved in a non-aqueous solvent is used as the electrolyte. In this case, the lithium salt is LiClO ４ , LiPF ６ , LiBF ４ , LiAsF ６ , LiSbF ６ Inorganic lithium salts such as LiCF ３ SO ３ , LiCF ３ CO ２ , Li ２ C ２ F ４ (SO ３ ) ２ , LiN(CF ３ SO ２ ) ２ , LiC(CF ３ SO２ ) ３ , LiC ｎ F ２ｎ＋１ SO ３ (n≧2), LiN(RfOSO ２ ) ２ [wherein Rf is a fluoroalkyl group]; and the like.

[0084] In addition, non-aqueous solvents for non-aqueous electrolytes include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile, and methoxypropionitrile; sulfites such as ethylene glycol sulfite; and the like. These may be used alone or in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and a chain carbonate. Furthermore, for the purpose of improving properties such as safety, charge / discharge cycle properties, and high-temperature storage properties, additives such as vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene may be added to these nonaqueous electrolyte solutions as appropriate.

[0085] The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

[0086] The aqueous electrolyte solution or the non-aqueous electrolyte solution may be made into a gel (gel electrolyte) by using a gelling agent such as a known polymer.

[0087] <Configuration of Battery, etc.> Figures 1 and 2 are diagrams showing a schematic representation of an example of a battery of the present invention. Figure 1 is a plan view of the battery, and Figure 2 is a cross-sectional view taken along line II of Figure 1.

[0088] The battery 1 shown in Figures 1 and 2 is an example of a sheet-like battery that contains an electrode assembly, in which a positive electrode 10 and a negative electrode 20 are stacked with a separator 30 interposed between them, and an electrolyte (not shown), inside a laminate film exterior body 40 made of two metal laminate films, and the laminate film exterior body 40 is sealed at its outer periphery by heat-sealing the upper and lower metal laminate films.

[0089] In FIG. 2, in order to avoid complicating the drawing, the layers constituting the laminate film exterior body 40 and the layers of the positive electrode 10 and the negative electrode 20 are not shown separately.

[0090] The positive electrode 10 is connected to a positive electrode terminal 11 within the battery 1, and although not shown, the negative electrode 20 is also connected to a negative electrode terminal 21 within the battery 1. One end of each of the positive electrode terminal 11 and the negative electrode terminal 21 is drawn out to the outside of the laminate film exterior body 40 so that they can be connected to external devices, etc.

[0091] The shape of the battery of the present invention is not particularly limited, and various shapes are possible, such as a flat shape (including a coin shape and a button shape), a cylindrical shape (cylindrical shape, or rectangular shape (rectangular cylindrical shape)), etc., in addition to the sheet shape (laminated shape) shown in Figures 1 and 2. Furthermore, as the exterior body (battery case) that houses the negative electrode, positive electrode, separator, and electrolyte, a resin film can be used, or a combination of a metal can (exterior can) with an opening and a lid (sealed can) can be used.

[0092] Examples of resin films that form the exterior body include nylon films (such as nylon 66 films) and polyester films (such as polyethylene terephthalate (PET) films).

[0093] In order to facilitate sealing by heat welding, the sheet-like outer packaging body made of a resin film may be laminated with a heat-sealable resin layer on the resin layer, and examples of the heat-sealable resin that constitutes the heat-sealable resin layer include modified polyolefin films (such as modified polyolefin ionomer films), polypropylene and copolymers thereof, etc. The thickness of the heat-sealable resin layer is preferably 20 to 200 μm.

[0094] A metal layer may be laminated on the resin film. The metal layer may 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.

[0095] It is also 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 have a single-layer structure in which it itself also serves as a water vapor barrier layer, or a multilayer structure in which it has multiple electrically insulating resin film layers, at least one of which serves as a water vapor barrier layer, or a multilayer structure in which an electrically insulating water vapor barrier layer is provided on the surface of a base layer made of a resin film.

[0096] Among such resin films, those in which a water vapor barrier layer made of at least an inorganic oxide is formed on the surface of a base layer made of a resin film are preferably used.

[0097] Examples of inorganic oxides constituting the water vapor barrier layer include aluminum oxide and silicon oxide. Note that a water vapor barrier layer made of silicon oxide tends to have a higher function of suppressing the permeation of moisture in the electrolyte solution in the battery than a water vapor barrier layer made of aluminum oxide. Therefore, it is more preferable to use silicon oxide as the inorganic oxide constituting the water vapor barrier layer.

[0098] The water vapor barrier layer made of an inorganic oxide can be formed on the surface of the substrate layer by, for example, a vapor deposition method. The thickness of the water vapor barrier layer is preferably 10 to 300 nm.

[0099] Examples of the substrate layer of the resin film having a water vapor barrier layer include the above-mentioned nylon film and polyester film, as well as polyolefin film, polyimide film, polycarbonate film, etc. The thickness of the substrate layer is preferably 5 to 100 μm.

[0100] 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 surface opposite to the substrate layer).

[0101] Furthermore, in the case of a resin film having a water vapor barrier layer and a substrate layer, the above-mentioned heat-sealable resin layer may be further laminated thereon.

[0102] The thickness of the entire sheet-like outer casing is preferably 10 μm or more from the viewpoint of providing sufficient strength to the sheet-like battery, and is preferably 200 μm or less from the viewpoint of preventing an increase in the thickness of the sheet-like battery and a decrease in energy density.

[0103] A sheet-type (laminated) battery can be fabricated by stacking two sheet-type exterior bodies or by folding one sheet-type exterior body and pasting and sealing the periphery.Flat or cylindrical batteries can also be fabricated by crimping the exterior can and the sealing can with a gasket or by welding the exterior can and the sealing can together.

[0104] When using an exterior body that is crimp-sealed, polypropylene (PP), nylon, etc. can be used as the material for the gasket interposed between the exterior can and the sealed can. In addition, if a particularly high level of heat resistance is required in relation to the use of the battery, heat-resistant resins with a melting point or thermal decomposition temperature of 200°C or higher, such as fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used. Furthermore, if the battery is used in an application that requires heat resistance, a glass hermetic seal can also be used for sealing.

[0105] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0106] Example 1 <Positive Electrode> 80.8 parts by mass of electrolytic manganese dioxide ["HH-PA" (average particle size 44 μm), active material particles (B) manufactured by Tosoh Corporation], 9.2 parts by mass of acetylene black (conductive additive), 6.0 parts by mass of ammonium polyacrylate (binder), and 4.0 parts by mass of zinc oxide were added and dispersed in a mixed solvent of water and ethanol at a mass ratio of 90:10 so that the total proportion of all components excluding the solvent (hereinafter referred to as "solids concentration") was 70% by mass, thereby preparing a positive electrode active material layer-forming composition (i).

[0107] The same electrolytic manganese dioxide as used in the positive electrode active material layer-forming composition (i) was pulverized to obtain particles having an average particle size of 2.1 μm [active material particles (a)]. These particles were used instead of the electrolytic manganese dioxide having an average particle size of 44 μm, and the solid content was changed to 60 mass %. A composition (ii) for infiltrating into the pores of porous carbon paper (porous current collector) was prepared in the same manner as the active material layer-forming composition (i).

[0108] Composition (ii) was applied to a porous carbon paper (thickness: 150 μm, porosity: 75%, air permeability (Gurley): 70 seconds / 100 ml) in an amount of 15 mg / cm after drying.２ The carbon paper was then stripe-coated and dried to obtain carbon paper (thickness: 200 μm) in which the particles, conductive additive, and binder in composition (ii) were retained in the pores of the porous carbon paper. Subsequently, composition (i) for forming a positive electrode active material layer was applied to the surface of the carbon paper on which composition (ii) was applied, in an amount of 17 mg / cm after drying. ２ The composition (i) for forming a positive electrode active material layer was also applied to the back side of the carbon paper on which the positive electrode active material layer was formed in a stripe coating amount of 17 mg / cm after drying. ２ The carbon paper was then coated in stripes and dried to form a 50 μm thick positive electrode active material layer on the other side. In this way, carbon paper was obtained having a region where both sides were covered with the positive electrode active material layer (hereinafter referred to as "region A") and a region where the positive electrode active material layer was not formed and only the porous carbon paper was present (hereinafter referred to as "region B"). This was then punched out into a shape having a main body for holding the positive electrode active material, consisting of region A measuring 15 mm × 15 mm, and a positive electrode terminal, consisting of region B measuring 5 mm × 10 mm. This resulted in a positive electrode having the cross-sectional structure shown in FIG. 3, a theoretical capacity of 27.4 mAh, and a thickness of region A of 300 μm.

[0109] FIG. 3 is a cross-sectional view schematically showing the positive electrode produced in Example 1. As shown in FIG. 3, the positive electrode 10 has positive electrode active material layers 10a, 10a on both sides of a porous carbon paper (porous current collector) 10b (in all Examples and Comparative Examples described below, the cross-sectional structure of the positive electrode is the same as that of Example 1).

[0110] <Negative Electrode> An electrolytic zinc foil (thickness: 0.1 mm) made of a zinc alloy containing 0.05 mass % Bi as an additive element and no In was punched into a shape having a main body measuring 15 mm × 15 mm and a negative electrode terminal measuring 5 mm × 10 mm to prepare a negative electrode.

[0111] <Electrolyte> An aqueous solution (pH=4.7) in which lithium chloride (concentration: 30% by mass) was dissolved was used as the electrolyte.

[0112] <Separator> The separator is a PP nonwoven film (thickness: 200 μm, basis weight: 48 g / m ２ ) was used.

[0113] <Sheet-like outer packaging> A sheet-like outer packaging was prepared using two 25 mm x 30 mm aluminum laminate films (thickness: 65 μm) having a polyethylene terephthalate film on the outer surface of an aluminum foil and a PP film as a heat-sealable resin layer on the inner surface.

[0114] <Battery Assembly> The positive electrode, the separator, and the negative electrode were stacked in this order on one aluminum laminate film, and then the other aluminum laminate film was placed on top of it. Next, the three peripheral sides of the two aluminum laminate films were heat-sealed to each other to form a bag-like shape, and 0.1 ml of the electrolyte solution was poured through the opening, and the opening was then heat-sealed to produce a sheet-like battery.

[0115] Example 2 A positive electrode having a theoretical capacity of 27.4 mAh and a positive electrode active material layer thickness of 50 μm per side of the carbon paper (thickness of region A: 300 μm) was prepared in the same manner as in Example 1, except that the positive electrode active material used in the positive electrode active material layer-forming composition (i) was changed to electrolytic manganese dioxide “HMR-AF” (average particle diameter: 21 μm) manufactured by Tosoh Corporation. A sheet-like battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

[0116] Example 3 The amount of the composition (i) for forming a positive electrode active material layer applied to both sides of the porous carbon paper coated with the composition (ii) was adjusted so that the applied amount after drying on both sides was 34 mg / cm ２ A positive electrode having a theoretical capacity of 46.5 mAh and a positive electrode active material layer thickness of 100 μm per side of the carbon paper (the thickness of region A was 400 μm) was produced in the same manner as in Example 1, except for changing the composition so that:

[0117] Comparative Example 1 A positive electrode having a theoretical capacity of 27.4 mAh and a positive electrode active material layer thickness of 50 μm per side of the carbon paper (thickness of region A: 300 μm) was prepared in the same manner as in Example 1, except that the positive electrode active material used in the positive electrode active material layer-forming composition (i) was changed to electrolytic manganese dioxide “EDM” (average particle diameter: 7.4 μm) manufactured by Mitsui Mining & Smelting Co., Ltd. A sheet-like battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

[0118] Comparative Example 2 A positive electrode having a theoretical capacity of 27.4 mAh and a positive electrode active material layer thickness of 50 μm per side of the carbon paper (thickness of region A: 300 μm) was prepared in the same manner as in Example 1, except that the positive electrode active material used in the positive electrode active material layer-forming composition (i) was changed to electrolytic manganese dioxide "FMH" (average particle diameter: 2.8 μm) manufactured by Tosoh Corporation. A sheet-like battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

[0119] Comparative Example 3 A positive electrode having a theoretical capacity of 27.4 mAh and a positive electrode active material layer thickness of 50 μm per side of the carbon paper (the thickness of region A was 300 μm) was produced in the same manner as in Example 1, except that composition (ii) was used instead of composition (i) for forming a positive electrode active material layer when forming a positive electrode active material on the surface of porous carbon paper. A sheet-like battery was produced in the same manner as in Example 1, except that this positive electrode was used.

[0120] Comparative Example 4 A positive electrode having a theoretical capacity of 46.5 mAh and a positive electrode active material layer thickness of 100 μm per side of the carbon paper (the thickness of region A was 400 μm) was produced in the same manner as in Example 1, except that composition (ii) was used instead of the composition for forming a positive electrode active material layer when forming a positive electrode active material on the surface of porous carbon paper. A sheet-like battery was produced in the same manner as in Example 1, except that this positive electrode was used.

[0121] The sheet-type batteries of Example 3 and Comparative Example 4 were discharged at a constant current of 1 mA at a temperature of 20°C, and pulse discharge tests were conducted every 3.6 hours to evaluate the discharge characteristics. The pulse discharge conditions were a pulse width of 10 msec, a pulse interval of 3 sec, and a pulse current value of 50 mA, and 10 pulse discharges were performed, and the closed circuit voltage (CCV) was measured. The results are shown in Table 1.

[0122] In addition, the sheet-like batteries of the Examples and Comparative Examples (batteries different from those subjected to the pulse discharge test) were disassembled, and the surface of the positive electrode was observed using a microscope ("VHX-7000" manufactured by Keyence Corporation), and the surface condition of the positive electrode active material layer was evaluated according to the following criteria.

[0123] <Evaluation criteria for cracks on the surface of the positive electrode active material layer> ○: Cracking on the surface of the positive electrode active material layer is well suppressed. △: A few small cracks are observed on the surface of the positive electrode active material layer. ×: Many large cracks are observed on the surface of the positive electrode active material layer.

[0124] These results, together with the average particle diameter of the positive electrode active material particles [active material particles (B)] contained in the positive electrode active material layer and the average particle diameter of the positive electrode active material particles [active material particles (a)] held in the pores of the porous carbon paper, are shown in Table 2. Photographs taken during this observation are also shown in Figures 4 to 10.

[0125]

[0126]

[0127] As shown in Table 1, the discharge characteristics of the sheet-type battery of Example 3 and the sheet-type battery of Comparative Example 4, which used positive electrodes with the same theoretical capacity, were almost equivalent. However, in the positive electrode used in the battery of Comparative Example 4 shown in FIG. 10, many large cracks were observed on the surface of the positive electrode active material layer, whereas in the positive electrode used in the battery of Example 3 shown in FIG. 6, cracks on the surface of the positive electrode active material layer were well suppressed.

[0128] 4 and 5, the positive electrodes used in the batteries of Examples 1 and 2 were able to effectively suppress cracking on the surface of the positive electrode active material layer, similar to the positive electrode used in the battery of Example 3. In contrast, in the positive electrodes used in the batteries of Comparative Examples 1 to 3, in which the average particle size of the positive electrode active material particles contained in the positive electrode active material layer was small, a few small cracks were observed on the surface of the positive electrode active material layer, as shown in Table 2 and Figures 7 to 9, or, similar to the positive electrode used in the battery of Comparative Example 4, many large cracks were observed on the surface of the positive electrode active material layer.

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

[0130] The battery of the present invention can be used in the same applications as those in which various known primary batteries and secondary batteries are used, and the battery electrode of the present invention can be used to constitute the battery of the present invention.

[0131] REFERENCE SIGNS LIST 1 sheet-shaped battery 10 positive electrode 10a positive electrode active material layer 10b carbon paper (porous current collector) 11 positive electrode terminal 20 negative electrode 21 negative electrode terminal 30 separator 40 sheet-shaped exterior body

Claims

1. A battery electrode having a porous current collector and an active material layer on one or both sides of the porous current collector, wherein the porous current collector holds particles (A) having an average particle size of 7 μm or less within its pores, and the active material layer contains active material particles (B), and the average particle size of the entire active material particles (B) is 10 μm or more.

2. The battery electrode according to claim 1, wherein the particles (A) have an average particle size of 5 μm or less.

3. The battery electrode according to claim 1, wherein the porous current collector holds active material particles (a) as the particles (A).

4. The battery electrode according to claim 1, wherein the active material layer contains a binder, the content of which is 20 mass % or less.

5. The battery electrode according to claim 1, wherein the thickness of the active material layer is 30 μm or more.

6. A battery having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the negative electrode is a battery electrode according to any one of claims 1 to 5.

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