Electrode, battery, and manufacturing method for the electrode

Abstract

To provide an electrode constituting a battery capable of maintaining a high energy density without using a fluororesin as a binder.SOLUTION: An electrode includes: an electrode mixture layer including an electrode active material including manganese dioxide and aramid fibers. The content of the aramid fiber in the electrode mixture layer is 0.01% by mass or more and 0.3% by mass or less with respect to the electrode mixture layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode, a battery, and a method for manufacturing an electrode. [Background technology]

[0002] Lithium primary batteries, which use metallic lithium for the anode and manganese dioxide or graphite fluoride for the cathode, are widely used as 3V high-energy-density batteries, as the main power source for small electronic devices and as long-term backup power sources. Of these, lithium primary batteries using manganese dioxide are widely used because they are inexpensive and have excellent output characteristics over a wide temperature range.

[0003] A positive electrode using manganese dioxide is produced by kneading manganese dioxide, a conductive additive, and a binder, followed by molding. As the binder, a fluororesin such as PTFE (polytetrafluoroethylene) or PVdF (polyvinylidene fluoride) is used because of its high heat resistance and chemical resistance (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 044771 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-33373 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, from the viewpoint of reducing environmental impact, PFAS (perfluoroalkyl compounds and polyfluoroalkyl compounds) have been subject to regulation, and the above-mentioned fluororesins are also subject to regulation. Therefore, there is a demand for materials that can be used as binders to replace conventional fluororesins.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electrode for constituting a battery that can maintain a high energy density without using a fluororesin as a binder, a battery, and a method for manufacturing the electrode. [Means for solving the problem]

[0007] [1] An electrode comprising an electrode mixture layer containing an electrode active material containing manganese dioxide and aramid fibers, wherein the content of the aramid fibers in the electrode mixture layer is 0.01% by mass or more and 0.3% by mass or less with respect to the electrode mixture layer. [2] The electrode according to [1], wherein the electrode mixture layer further contains a polyalkylene oxide polymer having an aryl group in a side chain. [3] The electrode according to [2], wherein the polyalkylene oxide polymer is a copolymer of ethylene oxide, propylene oxide, and phenyl glycidyl ether. [4] A battery comprising the electrode according to any one of [1] to [3]. [5] The battery according to [4], wherein the battery is a lithium primary battery. [6] A method for manufacturing an electrode, comprising: a step of preparing an aqueous dispersion containing aramid fibers, a dispersant, and water; a step of mixing the aqueous dispersion with an electrode active material containing manganese dioxide to obtain an electrode mixture; and a step of removing the solvent in the electrode mixture to form an electrode mixture layer, wherein the dispersant contains a polyalkylene oxide-based polymer having an aryl group in a side chain. [7] The method for manufacturing an electrode according to [6], wherein the content of the aramid fiber in the electrode mixture layer is 0.01% by mass or more and 0.3% by mass or less with respect to the electrode mixture layer. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an electrode for constituting a battery that can maintain a high energy density without using a fluororesin as a binder, a battery, and a method for manufacturing the electrode. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is an electron microscope image of the aramid fibers used in the examples. [Figure 3] FIG. 3 is a photograph showing the results of a liquid absorption test of the positive electrode pellet. [Figure 4] 4A to 4G are graphs showing the results of measuring the impedance of the battery. [Figure 5] 5A and 5B are graphs showing the results of a battery discharge test. DETAILED DESCRIPTION OF THE INVENTION

[0010] As a result of extensive research, the present inventors have found that by using aramid fiber (preferably microfibrillated aramid fiber) as a binder for an electrode using manganese dioxide, the fibrous aramid can form a network structure in the electrode, thereby enabling even a small amount of the aramid to satisfactorily bind the electrode active material and conductive additive, thereby enabling the production of a battery having an energy density equal to or higher than that of conventional batteries, without using conventional fluororesins.

[0011] The electrode is fabricated by mixing an electrode active material, a conductive additive, a binder dispersion, and, if necessary, a diluent to prepare an electrode mixture, which is then pelletized or applied to a current collector. Conventionally, organic solvents such as NMP have been mainly used as the dispersion medium or diluent for the binder dispersion, but from the viewpoint of further reducing the environmental load, it is desirable to be able to use an aqueous medium.

[0012] As a result of further investigation, the present inventors have found that the aramid fibers can be more highly dispersed even in an aqueous medium by using, as a dispersant, preferably a polyalkylene oxide polymer having an aryl group in a side chain.

[0013] The reason for this is not clear, but is presumed to be as follows. The benzene rings contained in the aramid fibers form π bonds with aryl groups (e.g., phenyl groups) contained in the dispersant, thereby increasing the affinity between the aramid fibers and the dispersant and making the aramid fibers more easily dispersible in an aqueous medium. As a result, the aramid fibers are more easily dispersible in an electrode mixture containing an aqueous medium, so that even a smaller amount of the dispersant can sufficiently bind the electrode active material and the conductive additive.

[0014] Hereinafter, an example of an electrode according to the present embodiment will be described using an electrode used as a positive electrode of a lithium primary battery. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] 1. Electrode The electrode includes an electrode mixture layer.

[0016] 1-1. Electrode mixture layer The electrode mixture layer contains an electrode active material and aramid fibers. In the present embodiment, the electrode mixture layer preferably further contains a conductive assistant.

[0017] 1-1-1. Electrode active material The electrode active material includes manganese dioxide (MnO2). The electrode active material may further include other active materials as needed. Examples of other active materials include graphite-based active materials such as graphite fluoride, metal oxides such as MoO3, VO5, and Mn2O4, and metal sulfides such as TiS2 and MoS.

[0018] The average particle diameter of the electrode active material is not particularly limited, but is preferably, for example, 1 to 100 μm. By making the average particle diameter of the electrode active material 1 μm or more, moldability can be further improved. Furthermore, since the specific surface area of ​​the electrode active material is unlikely to become excessively large, the content of binders and conductive additives that bind the electrode active material particles together can be further reduced. Furthermore, since the electrode active material particles are more likely to become entangled with the microfibrillated aramid fibers, loss of the electrode active material can be further suppressed. On the other hand, by making the average particle diameter of the electrode active material 100 μm or less, the reaction area becomes larger, and thus the discharge capacity can be further increased.

[0019] The average particle size of the electrode active material can be measured by a laser diffraction / scattering method using a particle size distribution measuring device as the average particle size (median diameter) at which the mass-based integration is 50%.

[0020] 1-1-2.Conductive additives Examples of the conductive additive include graphites, carbon blacks, and carbon fibers.

[0021] The content of the conductive auxiliary agent is not particularly limited, but can be, for example, 5 to 30 parts by weight per 100 parts by weight of the electrode active material.

[0022] 1-1-3. Aramid fiber The aramid fibers may function as a binder.

[0023] The content of aramid fiber in the electrode mixture layer is 0.01 to 0.3% by mass relative to the electrode mixture layer. When the content of aramid fiber is 0.01% by mass or more, the aramid fiber sufficiently forms a mesh structure in the electrode mixture layer, allowing the electrode active material, conductive additive, etc. to be bound. On the other hand, when the content of aramid fiber is 0.3% by mass or less, the proportion of aramid fiber, which is an insulating component, is low, so the internal resistance value of the battery is unlikely to be excessively high. For these reasons, the discharge capacity of the battery can be further increased. From the same viewpoint, the content of aramid fiber is preferably 0.03 to 0.3% by mass.

[0024] Aramid fibers are fibers containing a polymer (aromatic polyamide) having a structure in which two or more aromatic rings are bonded via amide bonds. Examples of aromatic polyamides include polymers containing structural units represented by the following formula: [ka]

[0025] In the above formula, Ar 1 , Ar 2 represents an aromatic ring or a group in which two or more aromatic rings are bonded via a single bond or a linking group. Examples of the aromatic ring include aromatic hydrocarbon rings having 6 to 10 carbon atoms, such as a benzene ring and a naphthalene ring. Examples of linking groups include divalent hydrocarbon groups (e.g., linear or branched alkylene groups having 1 to 18 carbon atoms, and divalent alicyclic hydrocarbon groups having 3 to 18 carbon atoms), carbonyl groups (-CO-), ether bonds (-O-), ester bonds (-COO-), -NH-, and -SO2-. The aromatic ring may have a substituent. Examples of the substituent include a halogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a substituted or unsubstituted amino group, a sulfo group, etc. The aromatic ring may be condensed with an aromatic or non-aromatic heterocycle.

[0026] The aromatic polyamide can be obtained by reacting a halide of an aromatic dicarboxylic acid with an aromatic diamine.

[0027] Examples of aromatic dicarboxylic acids in the aromatic dicarboxylic acid halides include isophthalic acid, terephthalic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, etc. Among these, terephthalic acid is preferred.

[0028] Examples of aromatic diamine acids include p-phenylenediamine, m-phenylenediamine, 4,4'-diaminobiphenyl, 2,4-diaminodiphenylamine, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylamine, 4,4'-diaminodiphenyl sulfone, 2,4-diaminotoluene, 2,6-naphthalenediamine, 1,5-naphthalenediamine, etc. Among these, p-phenylenediamine is preferred.

[0029] The aromatic polyamide may be meta-type or para-type. For example, the para-type is preferred from the viewpoint of increasing mechanical strength and reducing the risk of breakage during kneading when preparing an electrode mixture. That is, a para-type aromatic polyamide obtained by reacting terephthalic acid with p-phenylenediamine is preferred.

[0030] The aramid fiber can be produced by spinning the aromatic polyamide into a fiber form by a known method. After the fiber is spun, it can be subjected to a crushing treatment or the like as needed. For example, it can be microfibrillated by applying a strong mechanical shear force using an ultra-high pressure homogenizer or the like.

[0031] The average fiber length (L) of the aramid fiber is not particularly limited, but is preferably 100 to 1000 μm, for example. When the average fiber length of the aramid fiber is 100 μm or more, the aramid fiber is more likely to be entangled with particles of the electrode active material, conductive agent, etc., and is more likely to exhibit binding performance. When the average fiber length of the aramid fiber is 1000 μm or less, the dispersibility of the aramid fiber in the electrode mixture can be further improved, and the moldability can be further improved.

[0032] The average fiber diameter (D) of the aramid fiber is not particularly limited, but is preferably, for example, 0.01 to 0.5 μm. When the average fiber diameter of the aramid fiber is 0.01 μm or more, the mechanical strength of the aramid fiber can be further increased. When the average fiber diameter of the aramid fiber is 0.5 μm or less, an increase in the internal resistance of the battery can be further suppressed. For example, L / D is preferably 1000 to 3000.

[0033] The average fiber length (L) and average fiber diameter (D) of the aramid fiber can be measured by the following method. An electron microscope image of the aramid fiber is taken using an electron microscope (SEM, TEM). From the obtained electron microscope image, the fiber length and thickness (diameter) of 100 randomly selected fibers are measured, and the average fiber length and average fiber diameter are calculated by arithmetically averaging these values.

[0034] 1-1-4. Dispersants It is preferable that the electrode mixture layer further contains a dispersant for dispersing the aramid fibers, which can further increase the dispersibility of the aramid fibers in the electrode mixture, and therefore, even if the content of the aramid fibers in the electrode mixture layer is reduced, good binding performance is likely to be obtained.

[0035] The type of dispersant is not particularly limited as long as it can disperse aramid fibers well in an aqueous medium. Examples of the dispersant include polyalkylene oxide polymers. Among them, polyalkylene oxide polymers having aryl groups in their side chains are preferred from the viewpoint of further improving the dispersibility of aramid fibers.

[0036] The polyoxyalkylene polymer having an aryl group in the side chain is a polymer containing a structural unit a derived from an alkylene oxide having an aryl group, and is preferably a polymer containing a structural unit a derived from an alkylene oxide having an aryl group and a structural unit b derived from an alkylene oxide not having an aryl group.

[0037] The structural unit a derived from an alkylene oxide having an aryl group easily interacts with aramid fibers. On the other hand, the structural unit b derived from an alkylene oxide without an aryl group easily forms hydrogen bonds with water molecules. As a result, in the binder dispersion used to prepare the electrode mixture, the aramid fibers can be more easily dispersed in the aqueous medium via the dispersant.

[0038] The polymer can be obtained by copolymerizing an alkylene oxide having an aryl group with an alkylene oxide not having an aryl group by a known method or a method similar thereto. Each alkylene oxide may be used alone or in combination.

[0039] The alkylene oxide having an aryl group is represented by, for example, the following formula: [ka]

[0040] In the above formula, Z is a single bond or a linking group. The linking group may contain an alkylene chain, an ether bond, an ester bond, or an imide bond. Ar is an aryl group. Examples of the aryl group include a phenyl group, a naphthyl group, and a phthalimide group, and a phenyl group is preferred. The aryl group may further have a substituent such as a halogen atom or an alkyl group.

[0041] Examples of alkylene oxides having an aryl group include the following: Among these, phenyl glycidyl ether is preferred. [ka]

[0042] The alkylene oxide not having an aryl group is preferably an alkylene oxide having 1 to 4 carbon atoms, more preferably an alkylene oxide having 2 or 3 carbon atoms. Of these, ethylene oxide and propylene oxide are preferred. These alkylene oxides may further have a substituent other than an aryl group (for example, an alkyl group, an alkoxy group, or an unsaturated aliphatic hydrocarbon group (such as an allyl group)).

[0043] Preferred examples of the polymer include copolymers of phenyl glycidyl ether, ethylene oxide and propylene oxide.

[0044] In the polymer, the content of the structural unit a relative to the total amount of the structural units a and b is not particularly limited, but is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and even more preferably 0.5 to 10% by mass. When the content of the structural unit a is 0.01% by mass or more, the structural unit a is more likely to interact with the aramid fiber. On the other hand, when the content of the structural unit a is 50% by mass or less, the content of the structural unit b increases, making it easier to enhance affinity with the aqueous medium. In other words, by keeping the content of the structural unit a within the above range, the dispersibility of the aramid fiber in the aqueous medium can be further improved. The total amount of the structural unit a and the structural unit b is preferably 90% by mass or more, more preferably 95% by mass or more, and may even be 100% by mass, relative to the total amount of all structural units in the polymer.

[0045] The weight-average molecular weight of the dispersant is not particularly limited, but from the viewpoint of dispersibility, a larger weight-average molecular weight is preferable, for example, 1,000 or more, preferably 5,000 or more, and more preferably 10,000 or more. On the other hand, from the viewpoint of further suppressing excessive viscosity increase when preparing an electrode mixture, a smaller weight-average molecular weight is preferable, for example, 500,000 or less, preferably 200,000 or less. The weight-average molecular weight can be measured in polystyrene equivalent terms by the GPC method.

[0046] The content of the dispersant in the electrode mixture layer is not particularly limited, but is preferably 0.01 Preferably, the content of the dispersant in the electrode mixture layer is 0.01% by mass or more. When the content of the polymer is 0.01% by mass or more, the dispersibility of the aramid fibers in the electrode mixture is further improved, so that even if the amount of aramid fibers is reduced, higher binding performance can be obtained. When the content of the polymer is 0.5% by mass or less, an increase in the internal resistance of the battery can be further suppressed. From the same viewpoint, the content of the dispersant in the electrode mixture layer is more preferably 0.04 to 0.5% by mass.

[0047] 1-1-5. Other ingredients The electrode mixture layer may further contain other components in addition to those mentioned above, as necessary, such as a neutralizing agent such as LiOH, a thickener, and the like.

[0048] 1-2.Other The electrode may be composed of an electrode mixture layer, or may further include a current collector that holds the electrode mixture layer. For example, when producing an electrode for a wound battery or a stacked battery, the electrode preferably further includes a current collector. Examples of materials for the current collector include stainless steel and aluminum.

[0049] 2. Electrode manufacturing method The electrode can be manufactured through the steps of 1) preparing an aqueous dispersion of aramid fibers, 2) mixing the aqueous dispersion with an electrode active material to obtain an electrode mixture, and 3) removing the solvent from the electrode mixture to obtain an electrode including an electrode mixture layer. Each step will be described below.

[0050] Step 1) First, an aqueous dispersion containing aramid fibers, a dispersant, and water is prepared. The aramid fibers and the dispersant are as described above.

[0051] The content of the aramid fibers in the aqueous dispersion is not particularly limited, but can be, for example, 0.02 to 0.1% by mass.

[0052] The content of the dispersant in the aqueous dispersion may be such that the content of the dispersant relative to the electrode mixture layer falls within the above-mentioned range. For example, the content of the dispersant in the aqueous dispersion is preferably 0.001 to 10% by mass, more preferably 0.002 to 0.5% by mass, relative to the aqueous dispersion. This allows the aramid fibers to be more satisfactorily dispersed in the aqueous dispersion.

[0053] The dispersion method is not particularly limited, but can be carried out using a homodisper or the like.

[0054] Step 2) Next, the electrode active material and the aqueous dispersion of aramid fibers are mixed to obtain an electrode mixture. In the present embodiment, the electrode active material, the conductive assistant, and the aqueous dispersion of aramid fibers are mixed, and a diluent is further added as necessary to obtain an electrode mixture.

[0055] The diluent may be water or a hydrophilic organic solvent (collectively referred to as an aqueous medium). Examples of the hydrophilic organic solvent include ether-based solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, etc.

[0056] The mixing method is not particularly limited, and may be wet or dry. For example, when preparing a pellet-shaped electrode, dry mixing is preferred. Dry mixing can be performed using, for example, a planetary mixer.

[0057] The electrode active material, the conductive additive, and the aqueous dispersion of aramid fibers may be mixed simultaneously or sequentially. From the viewpoint of making it easier to disperse the aramid fibers, it is preferable to dry-mix the electrode active material and the conductive additive, and then further add and mix the aqueous dispersion of aramid fibers. The aqueous dispersion of aramid fibers may be added in one batch or in multiple batches.

[0058] Furthermore, after the materials (active material and conductive material) are kneaded by dry kneading until they are dispersed, a mixed solution prepared by mixing liquid materials (aramid fiber dispersion and diluent) may be added in several portions. By preparing a mixed solution prepared by mixing liquid materials in advance, it is possible to further suppress, for example, granulation of materials caused by the prior addition of other water and poor dispersion of aramid fibers within the granulated materials. It is also possible to further suppress the cross-linked structure of the aramid fibers from being dissolved by water added later.

[0059] Step 3) Next, the solvent in the obtained electrode mixture is removed to obtain an electrode including an electrode mixture layer. For example, when producing an electrode for a coin-type battery as described below, the electrode mixture may be formed into a pellet while removing the solvent in the electrode mixture.

[0060] The molding method is not particularly limited, but for example, the electrode mixture can be placed in a mold and pressed into a pellet shape. From the viewpoint of evaporating and drying the solvent in the electrode mixture, a heat treatment may be further performed as necessary.

[0061] When producing an electrode for a wound battery or a stacked battery, the electrode can also be obtained by applying or immersing a current collector in an electrode mixture and then drying it. In this case, the electrode mixture can be obtained by, for example, mixing (wet mixing) an electrode active material, aramid fibers, and a conductive additive in a diluent.

[0062] 3.Battery FIG. 1 is a schematic cross-sectional view showing an example of the configuration of a battery according to one embodiment of the present invention.

[0063] As shown in FIG. 1, the battery 10 according to this embodiment is a so-called coin-type lithium primary battery, and includes a coin-type container 11, and housed therein are a disk-shaped positive electrode 12, a disk-shaped negative electrode 13, a separator 14, and an electrolyte (not shown).

[0064] (Container 11) The container 11 has a positive electrode can 11A, a negative electrode cup 11B, and a gasket 15. A storage space for storing a positive electrode 12, a negative electrode 13, a separator 14, and an electrolyte is formed between the positive electrode can 11A and the negative electrode cup 11B.

[0065] The positive electrode can 11A has a bottom and a sidewall that rises from the periphery of the bottom toward the negative electrode cup 11B. The positive electrode can 11A accommodates the positive electrode 12 and functions as a current collector for the positive electrode 12.

[0066] The material of the positive electrode can 11A may be a material known in the field of lithium primary batteries, such as stainless steel (SUS316, SUS430, SUS444, etc.). The inner surface of the positive electrode can 11A may be plated or the like.

[0067] The negative electrode cup 11B has a top and a sidewall that rises from the periphery of the top toward the positive electrode can 11A. The tip of the sidewall is folded back outward. The negative electrode cup 11B houses the negative electrode 13 and functions as a current collector for the negative electrode 13.

[0068] The material of the negative electrode cup 11B may be a material known in the field of lithium primary batteries, such as iron, titanium, or stainless steel (SUS316, SUS430, SUS444, etc.). The inner surface of the negative electrode cup 11B may be plated or the like.

[0069] The peripheral edges of the positive electrode can 11A and the negative electrode cup 11B are crimped via a gasket 15. This seals the storage space within the container 11.

[0070] The material of the gasket 15 is not particularly limited, but from the viewpoint of sealing properties, for example, polypropylene, polybutylene terephthalate, polyphenylene sulfide, etc. are preferable.

[0071] (positive electrode 12) The positive electrode 12 is the electrode described above.

[0072] (Negative electrode 13) The negative electrode 13 contains a plate-shaped lithium metal or lithium alloy. Examples of lithium alloys include lithium-aluminum (Li-Al) alloy, lithium-magnesium (Li-Mg) alloy, lithium-tin (Li-Sn) alloy, lithium-zinc (Li-Zn) alloy, lithium-antimony (Li-Sb) alloy, lithium-silicon (Si) alloy, and lithium-nickel-silicon (Li-Ni-Si) alloy. The content of metal elements other than lithium contained in the lithium alloy may be, for example, 0.1% by mass or more and 5% by mass or less.

[0073] Alternatively, a lithium alloy layer may be formed by disposing a metal that can be alloyed with lithium on the surface of the negative electrode 13. For example, an aluminum foil may be disposed on the surface of the lithium metal that is the negative electrode 13, so that a lithium alloy layer may be formed.

[0074] (Separator 14) The separator 14 is disposed between the positive electrode 12 and the negative electrode 13 to electrically insulate them. The separator 14 can be a microporous film or nonwoven fabric made of an olefin-based resin such as polyethylene or polypropylene.

[0075] (electrolyte) An electrolytic solution (not shown) is filled in the internal space of the container 11. As a result, the positive electrode 12, the negative electrode 13, and the separator 14 are immersed in the electrolytic solution. In this embodiment, the electrolytic solution is a non-aqueous electrolytic solution and contains a non-aqueous solvent and an electrolyte.

[0076] The type of non-aqueous solvent is not particularly limited, and examples thereof include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC), ethers such as 1,2-dimethoxyethane (DME), and lactones such as γ-butyrolactone. These may be used alone or in combination of two or more. For example, from the viewpoint of achieving a better balance between dielectric constant and viscosity, a cyclic carbonate and a chain carbonate may be used in combination.

[0077] The electrolyte is a lithium salt, examples of which include lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium trifluoromethanesulfonate (LiCFSO), LiN(CFSO), LiN(CFS0), LiN(CFSO)(CFS0), and the like.

[0078] The concentration of the electrolyte in the electrolytic solution is not particularly limited, but may be, for example, 0.1 to 5 mol %, and preferably 0.25 to 3.5 mol %. The concentration of the electrolyte means the total concentration of dissociated and undissociated electrolytes.

[0079] (action) The battery 10 according to the above embodiment includes the above electrode as the positive electrode 12. In such a positive electrode 12, the aramid fiber can satisfactorily bind the positive electrode active material manganese dioxide and the conductive additive, even in small amounts. This makes it possible to obtain a battery that can maintain a high energy density without using a conventional fluororesin as a binder.

[0080] 2. Battery manufacturing method The battery 10 can be manufactured, for example, through 1) a step of preparing the positive electrode 12 and 2) a step of assembling the battery 10 using the prepared positive electrode 12.

[0081] 1) Preparation of the positive electrode The positive electrode 12 can be prepared by the electrode manufacturing method described above.

[0082] 2) Battery assembly process A battery is assembled using the prepared positive electrode 12. The assembly procedure is not particularly limited, but can be carried out, for example, by the following procedure.

[0083] First, the negative electrode 13 is placed in the negative electrode cup 11B, and the positive electrode 11 is placed in the positive electrode can 11A. Next, a gasket 15 is placed around the periphery of the negative electrode 13, and after an electrolyte is poured into the negative electrode cup 11B, the negative electrode cup 11B and the positive electrode can 11A are crimped together via the gasket 15 so that the negative electrode 13 and the positive electrode 12 face each other with the separator 14 interposed between them. This completes the battery 10.

[0084] 3. Variations In the above embodiment, a coin-type battery has been described as an example of a lithium primary battery, but the present invention is not limited to this. For example, the battery may be a wound (spiral) battery in which a positive electrode, a negative electrode, and a separator are stacked and wound, and then sealed in a can or the like together with an electrolyte, or a stacked (laminated) battery in which a sheet-like product in which a positive electrode, a negative electrode, and a separator are stacked is sealed in a relatively flexible exterior body together with an electrolyte. [Example]

[0085] The present invention will be described below with reference to examples, which should not be construed as limiting the scope of the present invention.

[0086] 1. Preparation of Aramid Fiber Aqueous Dispersion 1-1. Aramid fiber Tiara KY400S (microfibrillated para-aramid fiber) manufactured by Daicel Miraize Co., Ltd. was prepared.

[0087] (thermal analysis measurement) Thermal analysis was performed under the following conditions, and the appearance was observed at 10°C intervals. (Measurement conditions) Measuring device: Rigaku Corporation TG-DTA8122 Heating rate: 10℃ / min Upper limit of temperature rise: 400℃ Atmosphere: Air, 100mL / min As a result, thermal analysis measurements showed no combustion reaction at 400°C, and no change in the shape of the material was observed.

[0088] (Scanning electron microscope observation, measurement of average fiber diameter and average fiber length) When the shape of the aramid fiber was observed under a scanning electron microscope at 5000x magnification, it was confirmed that the fiber was in a microfibrillated form, as shown in Figure 2. The average fiber diameter (D) and average fiber length (L) of the aramid fibers were measured by the following method. One hundred fibers were randomly selected from the image obtained by the above-mentioned scanning electron microscope observation, and their fiber diameters and fiber lengths were measured and their arithmetic means were calculated. As a result, the average fiber diameter (D) was 0.2 to 0.3 μm, the average fiber length (L) was 400 to 600 μm, and the L / D ratio was approximately 2000.

[0089] 1-2. Dispersants Dispersant 1 was prepared as CP-B1 (ethylene oxide (EO)-propylene oxide (PO)-phenyl glycidyl ether (PGE) copolymer, copolymerization ratio EO:PO:PGE = 98:1:1 (mass ratio), weight-average molecular weight approximately 100,000) manufactured by Meisei Chemical Industry Co., Ltd.

[0090] 1-3. Preparation of aqueous dispersion of aramid fiber 100 parts by mass of water, 0.0375 parts by mass of aramid fiber, and 0.15 parts by mass of the dispersant 1 were placed in a container, and stirred using a homodisper until the dispersant was dissolved in the water. Next, the aramid fibers were added to the resulting solution, and the mixture was further stirred with a homodisper until dispersed, thereby preparing an aqueous dispersion of aramid fibers (aramid fiber concentration: 0.04% by mass).

[0091] 2. Preparation and evaluation of positive electrode pellets (Preparation of Positive Electrode Pellet 1) First, manganese dioxide (MnO2, average particle size 35 μm) as a positive electrode active material and carbon black as a conductive additive were dry mixed using a planetary mixer so that the mass ratio of MnO2:carbon black was 93:4. After confirming that the aramid fibers were uniformly dispersed, the aqueous dispersion of the aramid fibers was added as a binder solution in three portions so that the content of the aramid fibers in the resulting electrode mixture layer would be the value shown in Table 1, and the mixture was dry-mixed using a planetary mixer. Next, pure water was added as a diluent to this, and the solid content was adjusted to 77% by mass to obtain a mixture. The obtained mixture was placed in a mold and pressed at a pressure of 2.5 kN for 120 seconds to form a pellet, thereby producing a positive electrode pellet 1 having a diameter of 6 mm (6 mm).

[0092] (Preparation of positive electrode pellets 2 to 6) Positive electrode pellets 2 to 6 were obtained in the same manner as in the positive electrode 1, except that the amount of the aramid fiber aqueous dispersion added was adjusted to change the aramid fiber content.

[0093] (Preparation of Positive Electrode Pellet 7) Positive electrode pellet 7 was produced in the same manner as in Example 1, except that an aqueous dispersion of PTFE (emulsion polymerization product) was used as the binder solution instead of the aqueous dispersion of aramid fiber, and the PTFE content in the resulting electrode mixture layer was adjusted to the value shown in Table 1.

[0094] (liquid absorption test) (1) Preparation of electrolyte A mixed solvent was prepared by mixing propylene carbonate (PC), ethylene carbonate (EC), and 1,2-dimethoxyethane (DME) in a volume ratio of PC:EC:DME = 10.5:10.5:79. LiCF3SO3 was dissolved in this mixed solvent to a concentration of 0.63 M to prepare a nonaqueous electrolyte solution.

[0095] (2) Liquid absorption test 10 μL of the electrolyte solution prepared above was dropped onto the prepared positive electrode pellet. The change in the appearance of the positive electrode pellet was then visually observed and evaluated according to the following criteria. ◎: The pellet shape is well maintained (almost no active material falls off) and the electrolyte is absorbed sufficiently. ○: Maintains the pellet shape (with little loss of active material, etc.) and absorbs electrolyte sufficiently ×: The electrolyte is not absorbed and most of it remains on the surface

[0096] The compositions and evaluation results of positive electrode pellets 1 to 7 are shown in Table 1. The results of the liquid absorption test of the positive electrode pellets are shown in Figure 3. The liquid absorption test was carried out only on positive electrode pellets 1, 2 and 7. [Table 1]

[0097] As shown in Table 1 and Figure 3, it can be seen that positive electrode pellet 7 (comparative example) does not absorb the electrolyte, with most of it remaining on the surface. In contrast, positive electrode pellets 1 and 2 (examples) show little or no active material falling off, and they sufficiently absorb the electrolyte. In particular, positive electrode pellet 2 has a more sufficient network of aramid fibers, so there is no active material falling off at all, and the pellet shape can be better maintained.

[0098] These findings show that aramid fibers function well as a binder even in small amounts.

[0099] 3. Battery Fabrication and Evaluation [Creating Battery 1] (Preparation of negative electrode) A disk-shaped metallic lithium anode was pressed into the SUS negative electrode cup. After pressing, the metallic lithium had a thickness of 0.4 mm and a diameter of 8 mm.

[0100] (Preparation of Electrolyte) A mixed solvent was prepared by mixing propylene carbonate (PC), ethylene carbonate (EC), and 1,2-dimethoxyethane (DME) in a volume ratio of PC:EC:DME = 10.5:10.5:79. LiCF3SO3 was dissolved in this mixed solvent to a concentration of 0.63 M to prepare a nonaqueous electrolyte solution.

[0101] (Battery construction) First, a paper separator was placed on the metallic lithium on the negative electrode cup, and the above-prepared electrolyte solution was dropped onto this separator. Next, the positive electrode pellet 1 prepared above was placed on the separator and allowed to absorb the electrolyte. Thereafter, a stainless steel positive electrode can was placed on the positive electrode pellet 1. This positive electrode can and negative electrode cup were crimped and sealed with an insulating gasket interposed therebetween to prepare a lithium primary battery having an outer diameter of 20 mm and a thickness of 25 mm.

[0102] [Preparation of batteries 2 to 7] Batteries 2 to 7 were fabricated in the same manner as Battery 1, except that the type of positive electrode pellet was changed to the positive electrode pellet shown in Table 2.

[0103] [evaluation] (Impedance measurement) The AC internal resistance of the produced battery was measured in the range of 65535 Hz to 0.1 Hz by the AC impedance method.

[0104] (Discharge test) The fabricated battery was discharged at a constant current of 0.01 C to a discharge voltage of 1.5 V. The discharge test was carried out at 23°C.

[0105] The evaluation results of batteries 1 to 7 are shown in Table 2. Graphs showing the results of measuring the impedance of the battery are shown in FIGS. 4A to 4G, and graphs showing the results of the discharge test of the battery are shown in FIGS. 5A and 5B.

[0106] [Table 2]

[0107] 4A to 4G, Batteries 1 to 5 have smaller AC internal resistance (the sum of the solution resistance (Rs) and the charge transfer resistance (Rc)), particularly the charge transfer resistance (Rc), than Batteries 6 and 7. This indicates that the electron transfer resistance in the positive electrode mixture layer is small, and the interface resistance of the positive electrode is small.

[0108] Furthermore, as shown in Figures 5A and 5B, Battery 6, in which the aramid fiber content in the electrode mixture layer is 0.5 mass %, has a lower discharge capacity than Conventional Battery 7, while Batteries 1 to 5, in which the aramid fiber content in the electrode mixture layer is 0.3 mass % or less, exhibit a discharge capacity equal to or higher than that of Conventional Battery 7.

[0109] These findings show that by setting the content of aramid fibers in the electrode mixture layer to 0.3 mass % or less, a discharge capacity equal to or greater than that of conventional batteries can be obtained without using a fluororesin as a binder.

[0110] 4. Study of dispersants (reference experiment) 4-1. Dispersants Dispersant 1: Ethylene oxide-propylene oxide-phenyl glycidyl ether copolymer Dispersant 2: PEO (polyethylene oxide) Dispersant 3: PEG (polyethylene glycol)

[0111] 4-2. Aramid fiber dispersion test 1% by mass of a dispersant was added to pure water filled in a glass bottle, and dissolved using a homodisper. Next, 0.5% by mass of the aramid fibers were added to the resulting solution, and the mixture was stirred and dispersed using a homodisper.

[0112] (dispersibility) The dispersibility of the resulting dispersion (immediately after preparation) was visually observed. Those with no settling or separation and excellent dispersibility were judged as ⊚, and those with little settling or separation and good dispersibility were judged as ◯.

[0113] (Changes over time) The resulting dispersion was stored at 25°C for 7 days, and the presence or absence of separation or sedimentation was checked every day. Those that showed no sedimentation or separation even after 3 days were judged as ⊚, and those that showed some sedimentation or separation before 3 days but were not problematic were judged as ◯. The results are shown in Table 3. [Table 3]

[0114] The dispersibility of all the aqueous dispersions immediately after preparation was good. In particular, the aqueous dispersion using Dispersant 1 maintained a better dispersed state even after 3 days of stirring than the aqueous dispersions using Dispersants 2 and 3, and no agglomerates of aramid fibers were observed.

[0115] From these findings, it can be seen that dispersant 1 (ethylene oxide-propylene oxide-phenyl glycidyl ether copolymer) is particularly effective as a dispersant for aramid fibers. [Industrial Applicability]

[0116] According to the present invention, it is possible to provide an electrode for constituting a battery that can maintain a high energy density without using a fluororesin as a binder, a battery, and a method for manufacturing the electrode. [Explanation of symbols]

[0117] 10 batteries 11 Container 11A positive electrode can 11B Negative electrode cup 12 Positive electrode 13 Negative electrode 14 Separator 15 Gasket

Claims

1. An electrode, an electrode mixture layer including an electrode active material including manganese dioxide and aramid fibers; The content of the aramid fiber in the electrode mixture layer is 0.01% by mass or more and 0.3% by mass or less with respect to the electrode mixture layer. electrode.

2. the electrode mixture layer further contains a polyalkylene oxide polymer having an aryl group in a side chain; 10. The electrode of claim 1.

3. The polyalkylene oxide polymer is a copolymer of ethylene oxide, propylene oxide, and phenyl glycidyl ether.

3. The electrode of claim 2.

4. The electrode according to any one of claims 1 to 3, battery.

5. The battery is a lithium primary battery. The battery of claim 4.

6. preparing an aqueous dispersion containing aramid fibers, a dispersant, and water; a step of mixing the aqueous dispersion with an electrode active material containing manganese dioxide to obtain an electrode mixture; a step of removing the solvent in the electrode mixture to form an electrode mixture layer; Including, The dispersant contains a polyalkylene oxide polymer having an aryl group in a side chain. Electrode manufacturing method.

7. The content of the aramid fiber in the electrode mixture layer is 0.01% by mass or more and 0.3% by mass or less with respect to the electrode mixture layer. The method for manufacturing the electrode according to claim 6 .

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