Aqueous electrolyte battery

Abstract

An aqueous electrolyte battery according to the present disclosure comprises: an aqueous electrolyte; a positive electrode mixture layer that contains a positive electrode material and a positive electrode binder; a negative electrode mixture layer that contains a negative electrode material and a negative electrode binder; a collector; and a separator that is disposed between the positive electrode mixture layer and the negative electrode mixture layer. At least one among the positive electrode binder and the negative electrode binder contains a wholly aromatic polyamide.

Description

Aqueous electrolyte battery

[0001] This disclosure relates to an aqueous electrolyte battery.

[0002] Conventionally, in the electrodes of aqueous electrolyte batteries (for example, alkaline secondary batteries such as nickel-metal hydride batteries, lead-acid batteries, etc.), polyvinyl alcohol (PVA) is sometimes used as a binder to bind the electrode active material to the current collector (for example, Patent Document 1 or Patent Document 2).

[0003] Patent Document 1: Japanese Patent Application Publication No. 6-295727 Patent Document 2: Japanese Patent Publication No. 6-82554

[0004] PVA binder partially dissolves in the aqueous electrolyte when used in aqueous electrolyte batteries for extended periods. Therefore, repeated charging and discharging may reduce the charge and discharge capacity of aqueous electrolyte batteries.

[0005] Conventional binders may not be able to firmly bond the active material to the metal foil. Therefore, metal foil could not be used as a current collector in aqueous electrolyte batteries, and porous metal materials had to be used instead.

[0006] However, using porous metal materials as current collectors in aqueous electrolyte batteries may limit cell design due to the bulkiness of the porous metal materials. In particular, if the aqueous electrolyte battery is a bipolar type with a high battery capacity per unit volume, the porous metal material will hinder the sealing of the aqueous electrolyte within the cell, causing the aqueous electrolyte to be shared among multiple cells and preventing the achievement of a bipolar structure.

[0007] The problem that one embodiment of this disclosure aims to solve is to provide an aqueous electrolyte battery in which the charge and discharge capacity of the aqueous electrolyte battery does not easily decrease due to repeated charging and discharging.

[0008] The specific means for achieving the objectives are as follows: <1> An aqueous electrolyte battery comprising: an aqueous electrolyte; a positive electrode mixture layer containing a positive electrode active material and a positive electrode binder; a negative electrode mixture layer containing a negative electrode active material and a negative electrode binder; a current collector; and a separator disposed between the positive electrode mixture layer and the negative electrode mixture layer, wherein at least one of the positive electrode binder and the negative electrode binder contains a fully aromatic polyamide. <2> The aqueous electrolyte battery according to <1>, wherein at least one of the positive electrode binder and the negative electrode binder contains the fully aromatic polyamide and polyvinyl alcohol. <3> The aqueous electrolyte battery according to <1> or <2>, wherein the mass ratio of the fully aromatic polyamide to the polyvinyl alcohol (fully aromatic polyamide: polyvinyl alcohol) is 1:99 to 99:1. <4> The aqueous electrolyte battery according to any one of <1> to <3>, wherein the fully aromatic polyamide is a meta-type fully aromatic polyamide. <5> The aqueous electrolyte battery according to any one of <1> to <4> above, wherein the current collector is a metal foil. <6> The aqueous electrolyte battery according to <5> above, comprising a plurality of bipolar electrodes, wherein the bipolar electrodes each have the metal foil, the positive electrode mixture layer disposed on one side of the metal foil, and the negative electrode mixture layer disposed on the other side of the metal foil.

[0009] According to this disclosure, an aqueous electrolyte battery is provided in which the charge and discharge capacity of the aqueous electrolyte battery does not easily decrease due to repeated charging and discharging.

[0010] Figure 1 is a cross-sectional view of an aqueous electrolyte battery according to an embodiment of this disclosure. Figure 2 is a scanning electron microscope (SEM) image of the surface of the electrode mixture layer in Reference Examples 1 to 3. Figure 3 is a photograph of the appearance of the electrodes in Reference Examples 1 and 3 before and after ultrasonic cleaning in an aqueous potassium hydroxide solution. Figure 4 is a photograph of the appearance of the electrodes in Reference Examples 1 to 3 at the time of dropping the aqueous potassium hydroxide solution onto the electrode mixture layer and 10 minutes after dropping. Figure 5 is a graph showing the relationship between the number of cycles and the percentage (%) relative to the peak value of the charge / discharge capacity in Example 1 and Comparative Example 1. Figure 6 is a graph showing the measured values ​​of charge / discharge capacity against the number of cycles in Examples 1 and 2 and Comparative Example 1.

[0011] The contents of this disclosure are described in detail below. The descriptions of the constituent elements described below may be based on representative embodiments of this disclosure, but this disclosure is not limited to such embodiments.

[0012] In this disclosure, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. In this disclosure, in numerical ranges described in stages within "Modes for Carrying Out the Invention," the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In this disclosure, in numerical ranges described within "Modes for Carrying Out the Invention," the upper or lower limit of that numerical range may be replaced with the values ​​shown in "Examples." In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the figures, the same or corresponding parts are denoted by the same reference numerals and described without repetition.

[0013] (1) Aqueous Electrolyte Battery The aqueous electrolyte battery of the present disclosure comprises an aqueous electrolyte, a positive electrode mixture layer containing a positive electrode active material and a positive electrode binder, a negative electrode mixture layer containing a negative electrode active material and a negative electrode binder, a current collector, and a separator disposed between the positive electrode mixture layer and the negative electrode mixture layer. At least one of the positive electrode binder and the negative electrode binder contains a fully aromatic polyamide.

[0014] "All-aromatic polyamide" refers to a polyamide whose main chain consists only of benzene rings and amide bonds. All-aromatic polyamides may also have small amounts of aliphatic monomers copolymerized into them. "Aqueous electrolyte" refers to an electrolyte whose main component is water. "Main component is water" means that the water content is 50% by mass or more, may be 80% by mass or more, may be 95% by mass or more, or may be 99% by mass or more, based on the total amount of the aqueous electrolyte. "Current collector" refers to a sheet-like material that collects electrons generated from the active material and supplies electrons to the active material.

[0015] Because the aqueous electrolyte battery disclosed herein has the above configuration, the charge and discharge capacity of the aqueous electrolyte battery is less likely to decrease due to repeated charging and discharging.

[0016] The types of aqueous electrolyte batteries are not particularly limited as long as they are secondary batteries using an aqueous electrolyte, and examples include nickel-metal hydride batteries, nickel-cadmium batteries, and lead-acid batteries. The configuration of the aqueous electrolyte battery disclosed herein may be a known battery configuration, except that at least one of the positive electrode binder and the negative electrode binder contains a fully aromatic polyamide.

[0017] The electrode configuration of an aqueous electrolyte battery is not particularly limited and may be monopolar or bipolar. In a monopolar structure, the aqueous electrolyte battery comprises a current collector (hereinafter also referred to as the "positive electrode current collector"), a positive electrode mixture layer laminated on at least one surface of the positive electrode current collector, a current collector (hereinafter also referred to as the "negative electrode current collector"), and a negative electrode mixture layer laminated on at least one surface of the negative electrode current collector. In a monopolar structure, the electrodes may be wound or laminated. In a bipolar structure, the aqueous electrolyte battery comprises bipolar electrodes. Details of the bipolar electrodes will be described later with reference to Figure 1. An aqueous electrolyte battery may contain one cell or multiple cells. When an aqueous electrolyte battery contains multiple cells, the multiple cells may be electrically connected in series or parallel.

[0018] (1.1) A cathode mixture layer aqueous electrolyte battery comprises a cathode mixture layer.

[0019] (1.1.1) Positive Electrode Binder The positive electrode mixture layer contains a positive electrode binder. The positive electrode binder binds the positive electrode active material to the current collector.

[0020] (1.1.1.1) The total aromatic polyamide cathode binder contains total aromatic polyamide if the anode binder does not contain total aromatic polyamide. The cathode binder may contain total aromatic polyamide or may not contain total aromatic polyamide if the anode binder contains total aromatic polyamide. The cathode binder may consist only of total aromatic polyamide.

[0021] All-aromatic polyamides are polymers that are poorly soluble in water but highly hydrophilic. All-aromatic polyamides do not dissolve in aqueous electrolytes and can effectively bond active materials to current collectors (especially metal foils).

[0022] The total aromatic polyamide may be a meta-type total aromatic polyamide or a para-type total aromatic polyamide. Examples of meta-type total aromatic polyamides include polymetaphenylene isophthalamide. Examples of para-type total aromatic polyamides include coplyparaphenylene 3,4'-oxydiphenylene terephthalamide and polyparaphenylene terephthalamide.

[0023] The all-aromatic polyamide is preferably a meta-type all-aromatic polyamide. Meta-type all-aromatic polyamides are readily soluble in solvents. Para-type all-aromatic polyamides are poorly soluble in solvents. The meta-type all-aromatic polyamide offers excellent handling properties.

[0024] All aromatic polyamides may be commercially available. Examples of commercially available products include Conex (registered trademark; meta-type), Technora (registered trademark; para-type), and Twaron (registered trademark; para-type), all manufactured by Teijin Limited.

[0025] (1.1.1.2) From the viewpoint of improving affinity with the electrolyte, it is preferable that the hydrophilic binder further contains a hydrophilic binder. "Hydrophilic binder" refers to a binder that has an affinity for water. When the positive electrode binder further contains a hydrophilic binder, the positive electrode mixture layer comes into contact with the aqueous electrolyte more easily than when the positive electrode binder does not contain a hydrophilic binder. As a result, the positive electrode active material in the positive electrode mixture layer contributes more easily to the battery reaction. In addition, the electrolyte penetrates into the electrode more easily during battery manufacturing. On the other hand, from the viewpoint of improving the charge and discharge capacity of the aqueous electrolyte battery, it is preferable that the hydrophilic binder content is low and the total aromatic polyamide content is high.

[0026] Examples of hydrophilic binders include polyvinyl alcohol (PVA), starch, latex (e.g., acrylic latex and acrylic copolymer latex), hemicellulose, carboxymethylcellulose (CMC), galactomannan, gelatin, and polyurethane dispersions. Hydrophilic binders may be used individually or in combination of two or more types.

[0027] The positive electrode binder preferably contains a fully aromatic polyamide and polyvinyl alcohol. This improves the charge and discharge capacity of the aqueous electrolyte battery and also enhances its affinity with the electrolyte.

[0028] If the positive electrode binder further contains a hydrophilic binder, the mass ratio of the total aromatic polyamide to the hydrophilic binder (total aromatic polyamide:hydrophilic binder) is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, and even more preferably 20:80 to 80:20.

[0029] If the positive electrode binder further contains polyvinyl alcohol, the mass ratio of the total aromatic polyamide to the polyvinyl alcohol (total aromatic polyamide:hydrophilic binder) is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, and even more preferably 20:80 to 80:20.

[0030] (1.1.2) Positive electrode active material The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material is appropriately selected according to the type of aqueous electrolyte battery.

[0031] Examples of positive electrode active materials for nickel-metal hydride batteries or nickel-cadmium batteries include nickel oxides (e.g., nickel oxyhydroxide) and nickel hydroxide. Examples of positive electrode active materials for lead-acid batteries include lead dioxide and lead sulfate. The positive electrode active material may be used alone or in combination of two or more types.

[0032] (1.1.3) Conductive Aid The positive electrode mixture layer may further contain a conductive aid. Examples of the conductive aid include carbon blacks (such as acetylene black and ketjen black), carbon fibers, metal fibers, metal powders, and organic conductive materials (such as polyphenylene derivatives).

[0033] (1.2) Negative Electrode Mixture Layer The aqueous electrolyte battery includes a negative electrode mixture layer.

[0034] (1.2.1) Negative Electrode Binder When the negative electrode binder does not contain wholly aromatic polyamide, the negative electrode mixture layer contains wholly aromatic polyamide. When the positive electrode binder contains wholly aromatic polyamide, the negative electrode binder may or may not contain wholly aromatic polyamide. The negative electrode binder may consist only of wholly aromatic polyamide.

[0035] (1.2.1.1) Wholly Aromatic Polyamide The wholly aromatic polyamide may be the same as those exemplified as the wholly aromatic polyamide in the positive electrode mixture layer. The wholly aromatic polyamide in the negative electrode binder may be the same as or different from the wholly aromatic polyamide in the positive electrode binder.

[0036] (1.2.1.2) Hydrophilic Binder It is preferable that the negative electrode binder further contains a hydrophilic binder. Examples of the hydrophilic binder include the same ones as those exemplified as the hydrophilic binder in the positive electrode mixture layer.

[0037] (1.2.2) Negative Electrode Active Material The negative electrode mixture layer contains a negative electrode active material. The negative electrode active material is appropriately selected according to the type of the aqueous electrolyte battery.

[0038] Examples of the negative electrode active material of a nickel-hydrogen battery include a hydrogen storage alloy containing hydrogen and a hydrogen compound. Examples of the negative electrode active material of a nickel-cadmium battery include a cadmium compound. Examples of the negative electrode active material of a lead storage battery include lead and lead sulfate. The negative electrode active material may be used alone or in combination of two or more kinds.

[0039] (1.2.3) Conductive Aid The negative electrode mixture layer may further contain a conductive aid. Examples of the conductive aid include the same ones as those exemplified as the conductive aid in the positive electrode mixture layer.

[0040] (1.3) Aqueous electrolyte The aqueous electrolyte battery includes an aqueous electrolyte. The aqueous electrolyte may be gelled as needed. The aqueous electrolyte may further contain a solute in addition to water. The solute is appropriately selected according to the type of the aqueous electrolyte battery.

[0041] As the solute of nickel-hydrogen batteries and nickel-cadmium batteries, examples include alkali metal hydroxides (such as nickel hydroxide, etc.). As the solute of lead-acid batteries, examples include sulfuric acid, etc. The solute may be used alone or in combination of two or more types.

[0042] (1.4) Separator The aqueous electrolyte battery includes a separator. The separator electrically insulates the positive electrode mixture layer and the negative electrode mixture layer, and provides an ion migration path between the positive electrode mixture layer and the negative electrode mixture layer. Examples of the separator include microporous membranes and non-woven fabrics, etc.

[0043] Examples of the microporous membrane include porous films and laminated films, etc. Examples of the material of the porous film include polyolefins (such as polyethylene, polypropylene, etc.). The laminated film may be a laminate of a porous film made of polyethylene and a porous film made of polypropylene. Examples of the fibers constituting the non-woven fabric include synthetic fibers (such as polyolefin fibers, polyester fibers, aramid fibers, etc.) and glass fibers, etc.

[0044] (1.5) Current collector The aqueous electrolyte battery includes a current collector.

[0045] The current collector is appropriately selected according to the electrode configuration of the aqueous electrolyte battery. Examples include metal foils and porous metal sheets, etc. "Metal foil" refers to a metal foil having no through holes. "Porous metal sheet" refers to a metal sheet having through holes.

[0046] When the electrode configuration of an aqueous electrolyte battery is monopolar, the current collector may be either metal foil or a porous metal sheet. When the electrode configuration of an aqueous electrolyte battery is bipolar, the current collector is preferably metal foil. In a bipolar structure, the current collector being metal foil allows the aqueous electrolyte to be more reliably sealed within the cell. This seals the aqueous electrolyte within the cell, enabling the realization of a bipolar structure. The material of the current collector is not particularly limited as long as it is metal, and may be appropriately selected depending on the type of aqueous electrolyte battery.

[0047] Examples of materials for the positive electrode current collector of nickel-metal hydride batteries and nickel-cadmium batteries include nickel. Examples of materials for the negative electrode current collector of nickel-metal hydride batteries and nickel-cadmium batteries include stainless steel, nickel, and nickel alloys. Examples of materials for the positive electrode current collector and negative electrode current collector of lead-acid batteries include lead and lead alloys (e.g., Pb-Sb alloys and Pb-Ca alloys).

[0048] (1.6) Enclosures Water-based electrolyte batteries usually have an enclosure. The enclosure houses the positive electrode mixture layer, the negative electrode mixture layer, the current collector, and the separator. Examples of enclosures include laminate film (e.g., aluminum sheet, etc.) and battery cans (e.g., cylindrical, prismatic, and coin-shaped, etc.).

[0049] (1.7) Bipolar electrode aqueous electrolyte battery preferably comprises a plurality of bipolar electrodes stacked along the stacking direction. The bipolar electrode comprises a metal foil, a positive electrode mixture layer disposed on one side of the metal foil, and a negative electrode mixture layer disposed on the other side of the metal foil. This improves the battery capacity per unit volume of the aqueous electrolyte battery.

[0050] A water-based electrolyte battery equipped with multiple bipolar electrodes has multiple cells. These multiple cells may be electrically connected in series.

[0051] In aqueous electrolyte batteries with multiple bipolar electrodes, metal foil is used as the current collector instead of a porous metal sheet. Therefore, the aqueous electrolyte is more securely sealed within the cell. In other words, the aqueous electrolyte is not shared among multiple cells, resulting in the realization of series connections within the bipolar structure.

[0052] Figure 1 is a cross-sectional view showing an example of an aqueous electrolyte battery of the present disclosure including bipolar electrodes. The aqueous electrolyte battery of this embodiment comprises a plurality of bipolar electrodes 10, a plurality of separators 20, an aqueous electrolyte 30, and an outer casing 40. The plurality of bipolar electrodes 10 are stacked along the stacking direction D. The bipolar electrode 10 has a metal foil 11, a positive electrode mixture layer 12 disposed on one side of the metal foil 11, and a negative electrode mixture layer 13 disposed on the other side of the metal foil 11. The separator 20 is disposed between the positive electrode mixture layer 12 and the negative electrode mixture layer 13. The aqueous electrolyte 30 is sealed inside the cell C. The outer casing 40 houses the plurality of bipolar electrodes 10, the plurality of separators 20, and the aqueous electrolyte 30. The plurality of cells C are electrically connected in series.

[0053] (1.8) Preferred Embodiments The aqueous electrolyte battery of the present disclosure is preferably satisfied with a first condition. The "first condition" means that at least one of the positive electrode binder and the negative electrode binder contains the all aromatic polyamide. When the aqueous electrolyte battery of the present disclosure satisfies the first condition, the charge-discharge capacity of the aqueous electrolyte battery is less likely to decrease with repeated charge-discharge than when the first condition is not satisfied.

[0054] The aqueous electrolyte battery of the present disclosure preferably satisfies a second condition. The "second condition" means that at least one of the positive electrode binder and the negative electrode binder contains the all-aromatic polyamide and polyvinyl alcohol. By satisfying the second condition, the aqueous electrolyte battery of the present disclosure can improve the cycle characteristics of the aqueous electrolyte battery and the affinity with the electrolyte compared to when the second condition is not satisfied.

[0055] The aqueous electrolyte battery of the present disclosure preferably satisfies a third condition. The "third condition" means that the mass ratio of the total aromatic polyamide to the polyvinyl alcohol (total aromatic polyamide:polyvinyl alcohol) is 1:99 to 99:1. By satisfying the third condition, the aqueous electrolyte battery of the present disclosure can achieve both strong bonding of the electrode active material and good access of the electrolyte to the electrode surface, compared to when the third condition is not satisfied.

[0056] The aqueous electrolyte battery of the present disclosure preferably satisfies the fourth condition. The "fourth condition" indicates that the all-aromatic polyamide is a meta-type all-aromatic polyamide. The aqueous electrolyte battery of the present disclosure that satisfies the fourth condition has better handling properties than the one that does not satisfy the fourth condition.

[0057] The aqueous electrolyte battery of the present disclosure preferably satisfies the fifth condition. The "fifth condition" indicates that the current collector is a metal foil. By satisfying the fifth condition, the aqueous electrolyte battery of the present disclosure not only facilitates electrode manufacturing through a simple coating process, but also enables the realization of a bipolar structure.

[0058] The aqueous electrolyte battery of the present disclosure preferably satisfies the sixth condition. The sixth condition indicates that the current collector comprises a plurality of bipolar electrodes. The bipolar electrode comprises the metal foil, the positive electrode mixture layer disposed on one side of the metal foil, and the negative electrode mixture layer disposed on the other side of the metal foil. When the aqueous electrolyte battery of the present disclosure satisfies the sixth condition, the battery capacity per unit volume of the aqueous electrolyte battery is improved compared to when the sixth condition is not satisfied.

[0059] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited in any way by these examples, and other embodiments may also fall within the scope of the present disclosure as long as they are consistent with the spirit of the present disclosure.

[0060] [1] Reference Example [1.1] Reference Example 1 A solution of N-methylpyrrolidone in which polyvinyl alcohol (PVA) with a degree of saponification of 70 mol% is dissolved, and nickel hydroxide (Ni(OH) ２)( ) and acetylene blank (AB) were mixed and dispersed to prepare an electrode coating slurry. Ni(OH) ２ and AB and PVA, the mass ratio of the solid contents (Ni(OH) ２ :AB:PVA) was 60:20:20. After applying the slurry to a nickel foil and drying it, N-methylpyrrolidone was removed to obtain an electrode. The electrode included a nickel foil (current collector) and an electrode mixture layer. The electrode mixture layer contained Ni(OH) ２ (positive electrode active material), PVA (binder) and AB (conductive aid). A scanning electron microscope (SEM) image of the surface of the electrode mixture layer is shown in FIG. 2.

[0061] [1.2] Reference Example 2 In an N-methylpyrrolidone solution in which meta-type wholly aromatic polyamide (''CONEX (registered trademark)'' manufactured by Teijin Limited) (m-Aramid) was dissolved, nickel hydroxide (Ni(OH) ２ )( ) and acetylene blank (AB) were mixed and dispersed to prepare an electrode coating slurry. Ni(OH) ２ and AB and m-Aramid, the mass ratio of the solid contents (Ni(OH) ２ :AB:m-Aramid) was 60:20:20. After applying the slurry to a nickel foil and drying it, N-methylpyrrolidone was removed to obtain an electrode. The electrode included a nickel foil (current collector) and an electrode mixture layer. The electrode mixture layer contained Ni(OH) ２ (positive electrode active material), m-Aramid (binder) and AB (conductive aid). An SEM image of the surface of the electrode mixture layer is shown in FIG. 2.

[0062] [1.3] Reference Example 3 In an N-methylpyrrolidone solution in which meta-type wholly aromatic polyamide (''CONEX (registered trademark)'' manufactured by Teijin Limited) (m-Aramid) and polyvinyl alcohol (PVA) with a saponification degree of 70 mol% were dissolved, nickel hydroxide (Ni(OH) ２ )( ) and acetylene blank (AB) were mixed and dispersed to prepare an electrode coating slurry. Ni(OH) ２ and AB and m-Aramid and PVA, the mass ratio of the solid contents (Ni(OH) ２The ratio of AB:m-Aramid:PVA was 60:20:10:10. After coating the slurry onto nickel foil and drying it, N-methylpyrrolidone was removed to obtain an electrode. The electrode consisted of nickel foil (current collector) and an electrode mixture layer. The electrode mixture layer was Ni(OH) ２ The mixture contained (positive electrode active material), m-Aramid (binder), PVA (binder), and AB (conductive additive). Figure 2 shows an SEM image of the surface of the electrode mixture layer.

[0063] [2] Evaluation [2.1] Bonding strength test The electrodes of Reference Examples 1 to 3 were immersed in a 3 M potassium hydroxide (KOH) aqueous solution and ultrasonic waves were applied for 30 minutes using an ultrasonic cleaner. Electrodes in which the electrode mixture layer was destroyed during this ultrasonic treatment were deemed "failed," while those in which the shape of the electrode mixture layer was maintained were deemed "passed." The test results are shown in Table 1.

[0064] In Reference Example 1 and Reference Example 3, Figure 3 shows the appearance of the electrodes in the potassium hydroxide aqueous solution before and after ultrasonic cleaning. As shown in Figure 3, in Reference Example 1, the active material (Ni(OH)) of the electrode after ultrasonic cleaning is shown. ２ Most of the active material (Ni(OH)) dissolved in the potassium hydroxide aqueous solution, and the electrode mixture layer was destroyed during ultrasonic treatment. In Reference Example 3, the active material of the electrode after ultrasonic cleaning was ２ Although some of the material dissolved in the potassium hydroxide solution, the shape of the electrode mixture layer was maintained during ultrasonic treatment.

[0065]

[0066] From the results of the binding strength test, the PVA (binder) of Reference Example 1 was found to have Ni(OH) in an aqueous potassium hydroxide (KOH) solution. ２ It was found that the bonding force between the positive electrode active material and AB (conductive additive) and the nickel foil (current collector) was weak. In Reference Example 2, m-Aramid (binder) was found to be Ni(OH) in an aqueous potassium hydroxide (KOH) solution. ２ It was found that the binding force for bonding (positive electrode active material) and AB (conductive additive) to nickel foil (current collector) is strong. In Reference Example 3, m-Aramid (binder) and PVA (binder) were found to have Ni(OH) in an aqueous potassium hydroxide (KOH) solution.２ It was found that the bonding force between the positive electrode active material and AB (conductive additive) and the nickel foil (current collector) was strong. From these results, it was found that by using a binder containing all aromatic polyamide, the active material and conductive additive can be strongly bonded to the metal foil (nickel foil).

[0067] [2.2] Hydrophilicity Evaluation Test A 3M potassium hydroxide aqueous solution was dropped onto the electrode mixture layer of the electrodes of Reference Examples 1 to 3, and it was visually observed whether or not seepage occurred.

[0068] Figure 4 shows the appearance of a drop of potassium hydroxide aqueous solution on the electrode mixture layer of the electrode at the time of dropping and 10 minutes after dropping in Reference Examples 1 to 3. As shown in Figure 4, in Reference Example 1, the drop of potassium hydroxide aqueous solution had completely permeated the electrode mixture layer immediately after dropping. In Reference Example 2, the drop of potassium hydroxide aqueous solution had not completely permeated the electrode mixture layer immediately after dropping, but had completely permeated the electrode mixture layer 10 minutes after dropping. In Reference Example 3, the drop of potassium hydroxide aqueous solution had not completely permeated the electrode mixture layer even 10 minutes after dropping.

[0069] From the hydrophilicity evaluation test results, it was found that the affinity (hereinafter also simply referred to as "affinity") of the electrode mixture layer of Reference Example 1 to the potassium hydroxide aqueous solution was high. The affinity of Reference Example 2 was found to be low. The affinity of Reference Example 3 was found to be relatively high.

[0070] [2.3] Capacity Measurement Capacity measurements were performed using a two-electrode cell with a hydrogen storage alloy electrode as the counter electrode. The charge / discharge voltage was set to 0.8V to 2.0V, and the charge / discharge current was set to 580mA per g of nickel oxyhydroxide.

[0071] [2.3.1] Comparative Example 1 A two-electrode cell (aqueous electrolyte battery) was prepared using the electrode from Reference Example 1 as the working electrode, a hydrogen storage alloy electrode as the counter electrode, four layers of nonwoven fabric as the separator, and a 3M potassium hydroxide aqueous solution as the electrolyte.

[0072] [2.3.2] Example 1 A two-electrode cell (aqueous electrolyte battery) was prepared in the same manner as in Comparative Example 1, except that the electrodes of Reference Example 1 were changed to the electrodes of Reference Example 2.

[0073] [2.3.3] Example 2 A two-electrode cell (aqueous electrolyte battery) was fabricated in the same manner as in Comparative Example 1, except that the electrodes of Reference Example 1 were changed to the electrodes of Reference Example 3.

[0074] [2.3.4] Measurement 1 Using a two-electrode cell, the charge and discharge cycles were repeatedly performed by constant current charge and discharge, and the charge and discharge capacity of the working electrode (electrodes of Reference Examples 1 and 2) was measured. The measurement results are shown in Figure 5. Figure 5 is a graph showing the relationship between the number of cycles and the percentage (%) relative to the peak value of the charge and discharge capacity.

[0075] As shown in Figure 5, the charge / discharge capacity ratio of Example 1 increased rapidly up to around 10 cycles, peaking thereafter, and the capacity was almost maintained up to 150 cycles, showing good cycle characteristics. On the other hand, the charge / discharge capacity ratio of Comparative Example 1 had a relatively slow rise, peaking around 50 cycles, and then the capacity decreased more rapidly than in Example 1.

[0076] [2.3.5] Measurement 2 Using a two-electrode cell, the charge and discharge cycles were repeatedly performed by constant current charge and discharge, and the charge and discharge capacity of the working electrode (electrodes of Reference Examples 1 to 3) was measured. The measurement results are shown in Figure 6. Figure 6 is a graph showing the measured values ​​of charge and discharge capacity against the number of cycles in Examples 1 and 2 and Comparative Example 1.

[0077] As shown in Figure 6, the measured charge / discharge capacity of Comparative Example 1 tended to decrease significantly as the number of cycles increased after 70 cycles. On the other hand, the measured charge / discharge capacity of Examples 1 and 2 tended to decrease less than that of Comparative Example 1 even as the number of cycles increased after 70 cycles, and the measured charge / discharge capacity remained almost constant even after 70 cycles. From these results, it was found that the two-electrode cell of Comparative Example 1 is not an aqueous electrolyte battery in which the charge / discharge capacity does not decrease easily with repeated charging and discharging. It was found that the two-electrode cells of Examples 1 and 2 are aqueous electrolyte batteries in which the charge / discharge capacity does not decrease easily with repeated charging and discharging.

[0078] The disclosure of Japanese Patent Application No. 2024-159566, filed on 13 September 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated herein by reference.

Claims

1. An aqueous electrolyte battery comprising: an aqueous electrolyte; a positive electrode mixture layer containing a positive electrode active material and a positive electrode binder; a negative electrode mixture layer containing a negative electrode active material and a negative electrode binder; a current collector; and a separator disposed between the positive electrode mixture layer and the negative electrode mixture layer, wherein at least one of the positive electrode binder and the negative electrode binder contains a fully aromatic polyamide.

2. The aqueous electrolyte battery according to claim 1, wherein at least one of the positive electrode binder and the negative electrode binder comprises the all-aromatic polyamide and polyvinyl alcohol.

3. The aqueous electrolyte battery according to claim 2, wherein the mass ratio of the total aromatic polyamide to the polyvinyl alcohol (total aromatic polyamide: polyvinyl alcohol) is 1:99 to 99:

1.

4. The aqueous electrolyte battery according to claim 1, wherein the all-aromatic polyamide is a meta-type all-aromatic polyamide.

5. The aqueous electrolyte battery according to any one of claims 1 to 4, wherein the current collector is a metal foil.

6. The aqueous electrolyte battery according to claim 5, comprising a plurality of bipolar electrodes, wherein each bipolar electrode comprises a metal foil, a positive electrode mixture layer disposed on one side of the metal foil, and a negative electrode mixture layer disposed on the other side of the metal foil.

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