JP7720711B2 - Zinc secondary battery - Google Patents

Description

The present invention relates to a zinc secondary battery.

A phenomenon known as creep (hereafter referred to as "creep") is known to occur in alkaline batteries. Creep occurs when alkaline components in the electrolyte creep up the surface of the electrode terminal and leak out of the battery container. Several batteries that address this creep problem have been proposed. For example, Patent Document 1 (Japanese Patent Laid-Open Publication No. 7-254396) discloses that in a button-type alkaline battery that uses mercury-free zinc as the negative electrode active material, the inner surface of the negative electrode terminal plate is coated with tin or a tin alloy to a thickness of 10 to 100 μm and then polished to control the amount of tin oxide on the surface to a predetermined level. Furthermore, Patent Document 2 (Japanese Patent No. 6,561,915) discloses a nickel-metal hydride battery in which a non-conductive layer is formed on the surface of the electrode terminal, and a metal layer containing nickel and/or a nickel-iron alloy is laminated on this non-conductive layer.

In zinc secondary batteries, such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates from the negative electrode in the form of dendrites during charging, penetrating the pores of separators such as nonwoven fabrics and reaching the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the charge-discharge life. To address this issue, batteries equipped with layered double hydroxide (LDH) separators that selectively allow hydroxide ions to pass through while preventing the penetration of zinc dendrites have been proposed (see, for example, Patent Document 3 (WO 2016/076047) and Patent Document 4 (WO 2019/124270)). Furthermore, although not specifically referred to as LDHs, LDH-like compounds are known as hydroxides and/or oxides with a layered crystalline structure similar to LDHs. These compounds exhibit hydroxide ion conducting properties similar to LDHs and can be collectively referred to as hydroxide ion conducting layered compounds. For example, Patent Document 5 (WO 2020/255856) discloses a hydroxide ion-conductive separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate. Patent Document 6 (WO 2019/069760) and Patent Document 7 (WO 2019/077953) propose zinc secondary batteries in which the entire negative electrode active material layer is covered or wrapped with a liquid-retaining member and an LDH separator, and the positive electrode active material layer is covered or wrapped with a liquid-retaining member. A nonwoven fabric is used as the liquid-retaining member. This configuration eliminates the need for complicated sealing and joining between the LDH separator and the battery container, and is said to enable extremely simple and highly productive production of zinc secondary batteries (especially stacked batteries) that can prevent zinc dendrite extension.

Japanese Patent Application Publication No. 7-254396 Patent No. 6561915 International Publication No. 2016/076047 International Publication No. 2019/124270 International Publication No. 2020/255856 International Publication No. 2019/069760 International Publication No. 2019/077953

Conventional creep prevention measures, such as those disclosed in Patent Documents 1 and 2, involve providing a coating such as a metal layer on the surface of the terminal, but even when such a method is adopted, it is not effective enough in preventing creep. Therefore, there is a need for a method that can more effectively prevent creep.

The inventors have now discovered that creep in zinc secondary batteries can be effectively prevented by making a specific section of a current collecting member or electrode terminal nonconductive over its entire circumference through surface modification and/or vapor phase deposition.

Therefore, the object of the present invention is to provide a zinc secondary battery that can effectively prevent creep.

According to one aspect of the present invention,
(a) a positive electrode plate including a positive electrode active material layer and a positive electrode current collector;
a metallic positive electrode current collecting member extending from or connected to the positive electrode current collector;
a negative electrode plate including a negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds, and a negative electrode current collector;
a metallic negative electrode current collecting member extending from or connected to the negative electrode current collector;
a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so as to be conductive with hydroxide ions;
An electrolyte;
a unit cell comprising:
(b) a battery container that houses the unit cell;
(c1) a positive electrode terminal connected to the positive electrode current collecting member and protruding from the battery container;
(c2) a negative electrode terminal connected to the negative electrode current collecting member and protruding from the battery container;
A zinc secondary battery comprising:
The positive current collecting member and/or the positive terminal has a creep prevention region formed of a surface that is made non-conductive by surface modification and/or vapor phase film formation over the entire periphery of a portion of a section between the tip of the positive terminal and the positive electrode plate that is not immersed in the electrolyte, and
the negative electrode current collecting member and/or the negative electrode terminal has a creep prevention region formed of a surface passivated by surface modification and/or vapor phase film formation over the entire periphery of a part of a section between the tip of the negative electrode terminal and the negative electrode plate that is not immersed in the electrolyte,
A zinc secondary battery is provided in which the passivated surface is exposed without any further coating thereon.

1 is a schematic cross-sectional view showing an example of a zinc secondary battery according to the present invention. 2 is a diagram schematically showing a cross section of the zinc secondary battery shown in FIG. 1 taken along line A-A'. FIG. 2 is a perspective view schematically showing a battery element of the zinc secondary battery shown in FIG. 1. FIG. 2 is a cross-sectional view schematically showing a battery element of the zinc secondary battery shown in FIG. 1. FIG. 1 is a conceptual diagram for explaining the mechanism by which creep is prevented on the passivated surface (creep prevention region) of the current collecting member in the zinc secondary battery of the present invention. FIG. 2 is a cross-sectional view schematically showing the surface state of a creep prevention region of a current collecting member in a zinc secondary battery of the present invention. FIG. 2 is a diagram schematically illustrating the arrangement of current collecting members in a measurement system used in an evaluation test of creep suppression effect in the examples. FIG. 1 is a conceptual diagram for explaining the mechanism of creep phenomenon in the prior art. FIG. 1 is a cross-sectional view schematically showing an example of a current collecting member wrapped with insulating tape as a countermeasure against creep in the prior art, together with the estimated surface state thereof. FIG. 1 is a cross-sectional view schematically showing an example of a current collecting member coated with paint as a countermeasure against creep in the prior art, together with an estimated surface state thereof.

The zinc secondary battery of the present invention is not particularly limited as long as it uses zinc as the negative electrode and an alkaline electrolyte (typically an aqueous alkali metal hydroxide solution). Therefore, it can be a nickel-zinc secondary battery, a silver oxide-zinc secondary battery, a manganese oxide-zinc secondary battery, an air-zinc secondary battery, or any other type of alkaline zinc secondary battery. For example, it is preferable that the positive electrode active material layer contains nickel hydroxide and/or nickel oxyhydroxide, thereby forming the zinc secondary battery into a nickel-zinc secondary battery. Alternatively, the positive electrode active material layer may be an air cathode layer, thereby forming the zinc secondary battery into an air-zinc secondary battery.

Figures 1 to 4 show one embodiment of a zinc secondary battery and its internal structure according to the present invention. The zinc secondary battery 10 shown in these figures comprises (a) a unit cell 10a including a positive electrode plate 12, a positive electrode current collector 13, a negative electrode plate 14, a negative electrode current collector 15, a hydroxide ion conductive separator 16, and an electrolyte 18; (b) a battery container 20; (c1) a positive electrode terminal 26; and (c2) a negative electrode terminal 28. The positive electrode plate 12 includes a positive electrode active material layer 12a and a positive electrode current collector (not shown). The positive electrode current collector 13 is a metal member extending from or connected to the positive electrode current collector. The negative electrode plate 14 includes a negative electrode active material layer 14a and a negative electrode current collector 14b. The negative electrode active material layer 14a includes at least one material selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds. The negative electrode current collecting member 15 is a metal member extending from or connected to the negative electrode current collecting member 14b. The hydroxide ion conductive separator 16 separates the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ions to be conducted between them. The battery container 20 houses the unit cell 10a. The positive electrode terminal 26 is connected to the positive electrode current collecting member 13 and protrudes from the battery container 20. The negative electrode terminal 28 is connected to the negative electrode current collecting member 15 and protrudes from the battery container 20.

The positive current collecting member 13 and/or the positive terminal 26 has a creep prevention region C, which is made of a surface that has been made passivating by surface modification and/or vapor deposition, over the entire circumference of a portion of the section between the tip of the positive terminal 26 and the positive plate 12 that is not immersed in the electrolyte 18. This separates the region of the positive current collecting member 13 and/or the positive terminal 26 near the positive terminal 26 or its tip from the region of the positive current collecting member 13 and/or the positive terminal 26 near the positive plate 12 by the creep prevention region C. Similarly, the negative current collecting member 15 and/or the negative terminal 28 has a creep prevention region C, which is made of a surface that has been made passivating by surface modification and/or vapor deposition, over the entire circumference of a portion of the section between the tip of the negative terminal 28 and the negative plate 14 that is not immersed in the electrolyte 18. As a result, the region of the negative current collecting member 15 and/or the negative terminal 28 near the negative terminal 28 or its tip and the region of the negative current collecting member 15 and/or the negative terminal 28 near the negative plate 14 are separated by the creep prevention region C. These passivated surfaces are exposed without any additional coating thereon. In this way, by forming the creep prevention region C, which is composed of a surface passivated by surface modification and/or vapor deposition over the entire circumference of a predetermined section of the current collecting member between the electrode terminal and the electrode plate, creep in the zinc secondary battery 10 can be effectively prevented.

Creep refers to the phenomenon in which electrolyte creeps up the surface of an electrode terminal and leaks out of the battery container. Figure 8 conceptually illustrates the mechanism of creep when a metal member 30 (presumably an electrode terminal or current collector) is partially immersed in electrolyte 18 (presumably a potassium hydroxide aqueous solution). As shown in Figure 8, creep progresses as follows: 1) H ₂ O molecules from the surrounding environment combine with electrons e ⁻ present in the metal member 30 to generate OH ⁻ , 2) K ⁺ in the electrolyte 18 is attracted to this OH ⁻ , and 3) K ⁺ and OH ⁻ combine to generate salt (KOH). In this way, a component of the electrolyte 18 (KOH) is generated in areas of the metal member 30 where electrolyte 18 is not present. As a result, this phenomenon is observed as electrolyte 18 creeping up the metal member 30. As mentioned above, conventional techniques for addressing creep include applying a coating to the surface of the terminal. However, even with this approach, the effectiveness of preventing creep is insufficient. This is likely due to the fact that OH ⁻ can pass from the electrolyte toward the terminal through gaps between the coating layer and the metal member or defects in the coating layer. For example, as shown in Figure 9, when creep prevention is implemented by wrapping the metal member 30 with insulating tape 32, a small gap occurs between the insulating tape 32 and the metal member 30. Furthermore, when creep prevention is implemented by applying paint to the metal member 30 as shown in Figure 10, not only does a gap occur between the paint 34 and the metal member 30, but partial cracking and peeling of the paint 34 due to differences in thermal expansion coefficients also progress, resulting in defects. The existence of such gaps and defects is presumably the reason why conventional creep prevention measures are ineffective.

In contrast, in the present invention, the positive current collecting member 13 and/or the positive terminal 26 have a creep prevention region C in a portion of a predetermined section, which is formed by a passivated surface over its entire circumference. Similarly, the negative current collecting member 15 and/or the negative terminal 28 have a creep prevention region C in a portion of a predetermined section, which is formed by a passivated surface through surface modification and/or vapor-phase deposition over its entire circumference. This passivated surface is achieved through surface modification and/or vapor-phase deposition and is exposed without any additional coating thereon. This configuration effectively prevents creep in the zinc secondary battery 10. FIG. 5 conceptually illustrates a presumed mechanism of the phenomenon that occurs when a metal member 30 (e.g., an electrode terminal or a current collecting member) having a passivated surface 30a formed as the creep prevention region C according to the present invention is immersed in the electrolyte 18. In this configuration, as shown in FIG. 5, air-derived H ₂ O and electrons e ⁻ do not encounter each other, and OH ⁻ is not generated. As a result, in the creep-inhibited region C, the opportunity for K ⁺ and OH ⁻ to bond is lost, and salt (KOH) is not produced. In other words, salt precipitation and progression (i.e., creep-up of the electrolyte 18) only progresses to just below the creep-inhibited region C. Therefore, it is believed that creep is effectively prevented in the creep-inhibited region C. This is because the passivated surface 30a according to the present invention is formed by surface modification and/or vapor-phase deposition (rather than by conventional coating) and is exposed without any additional coating thereon. Therefore, as shown in FIG. 6 , it is believed that no molecular-level voids exist between the metal base material of the metal component 30 and the passivated surface in the creep-inhibited region C. In other words, surface modification and vapor-phase deposition can form an insulating layer that is completely adhered to the surface irregularities of the metal component 30. As a result, there are no gaps that allow electrolyte-derived OH ⁻ to pass toward the terminal, and therefore it is believed that OH ⁻ migration is prevented at the locations marked with "x" in FIG. 6 .

As described above, the creep prevention region C may be formed on the positive electrode current collecting member 13 or the negative electrode current collecting member 15, or on the positive electrode terminal 26 or the negative electrode terminal 28. Furthermore, the creep prevention region C may be located inside or outside the battery container 20, or both. However, from the perspective of maintaining and ensuring battery function, it is preferable for the creep prevention region C to be located inside the battery container 20. The creep prevention region C inside the battery container 20 is typically formed on the positive electrode current collecting member 13 or the negative electrode current collecting member 15. However, if the positive electrode terminal 26 or the negative electrode terminal 28 extends into the battery container 20, the creep prevention region C may be formed on the portion of the positive electrode terminal 26 or the negative electrode terminal 28 located inside the battery container 20. The creep prevention region C outside the battery container 20 is typically formed on the positive electrode terminal 26 or the negative electrode terminal 28 (preferably at their bases near the top lid 20a). However, if the positive electrode current collector 13 or the negative electrode current collector 15 extends outside the battery container 20, the creep prevention region C may also be formed on the portion of the positive electrode current collector 13 or the negative electrode current collector 15 located outside the battery container 20 (preferably at their bases near the top lid 20a). In either case, it is desirable for the creep prevention region C to have a width suitable for preventing creep. From this perspective, the preferred width of the creep prevention region C (the length in the direction parallel to the current flow) is 1 to 20 mm, more preferably 1 to 15 mm, and even more preferably 1 to 10 mm, 1 to 5 mm, or 1 to 2 mm.

The passivated surface is formed by surface modification and/or vapor deposition. Passivation by surface modification is preferably achieved by nitriding or oxidizing the metal constituting at least one of the positive current collecting member 13, the positive terminal 26, the negative current collecting member 15, and the negative terminal 28. Nitriding or oxidizing can be achieved by various known techniques, without particular limitation. From the perspective of uniformity, plasma nitriding or plasma oxidation is particularly preferred. In this case, nitriding or oxidation can be achieved by supplying a process gas between electrodes in a commercially available plasma processing device to generate plasma. While high-frequency power sources are typically used for this device, microwaves can also be used. Both low-pressure and high-pressure (atmospheric) pressures can be used within the device. Plasma jets and in-liquid plasma processing, which involves processing in a liquid, can also be used as plasma sources. Alternatively, a passivated surface can be formed by partially stripping away any corrosion-resistant plating that may be present on the surface of the current collecting member or terminal, and then promoting oxidation (e.g., natural oxidation) of the stripped portions. On the other hand, passivation by vapor phase deposition can be achieved by a variety of known techniques, and is not particularly limited; however, it is preferable to form an insulating film by sputtering, for example.

The positive electrode plate 12 includes a positive electrode active material layer 12a. The positive electrode active material constituting the positive electrode active material layer 12a may be selected from known positive electrode materials depending on the type of zinc secondary battery, and is not particularly limited. For example, in the case of a nickel-zinc secondary battery, a positive electrode containing nickel hydroxide and/or nickel oxyhydroxide may be used. Alternatively, in the case of an air-zinc secondary battery, an air electrode may be used as the positive electrode. The positive electrode plate 12 further includes a positive electrode current collector (not shown), and is further provided with a metallic positive electrode current collector 13 extending (e.g., upward) from or connected to the positive electrode current collector. A preferred example of a positive electrode current collector is a nickel porous substrate such as a foamed nickel plate. In this case, a positive electrode plate consisting of a positive electrode/positive electrode current collector can be preferably fabricated by, for example, uniformly applying a paste containing an electrode active material such as nickel hydroxide to a nickel porous substrate and drying it. At this time, it is also preferable to press the dried positive electrode plate (i.e., the positive electrode/positive electrode current collector) to prevent the electrode active material from falling off and improve electrode density. The positive electrode plate 12 shown in FIG. 5 includes a positive electrode current collector (e.g., nickel foam), but this is not shown. This is because, in the case of nickel-zinc secondary batteries, the positive electrode current collector is integral with the positive electrode active material, making it impossible to depict the positive electrode current collector separately. The positive electrode current collector 13 may be composed of the same material as the positive electrode current collector, or a different material. If the positive electrode current collector is a porous nickel substrate such as a nickel foam plate, it can be pressed into a tab shape. In either case, the positive electrode current collector 13 may be extended by attaching another current collector, such as a tab lead, to the tab. In either case, it is preferable that multiple positive electrode current collectors 13 be joined to a single positive electrode terminal 26 or to an additional positive electrode current collector 13 electrically connected thereto.

The positive electrode plate 12 may contain at least one additive selected from the group consisting of silver compounds, manganese compounds, and titanium compounds, which can promote the positive electrode reaction that absorbs hydrogen gas generated by the self-discharge reaction. The positive electrode plate 12 may also contain cobalt. Cobalt is preferably contained in the positive electrode plate 12 in the form of cobalt oxyhydroxide. In the positive electrode plate 12, cobalt functions as a conductive additive, contributing to improved charge/discharge capacity.

The negative electrode plate 14 includes a negative electrode active material layer 14a. The negative electrode active material constituting the negative electrode active material layer 14a includes at least one material selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds. Zinc may be included in any form—zinc metal, zinc compound, or zinc alloy—as long as it has electrochemical activity suitable for a negative electrode. Preferred examples of negative electrode materials include zinc oxide, zinc metal, and calcium zincate, with a mixture of zinc metal and zinc oxide being more preferred. The negative electrode active material may be in a gel form or may be mixed with the electrolyte solution 18 to form a negative electrode composite. For example, a gelled negative electrode can be easily obtained by adding the electrolyte solution and a thickener to the negative electrode active material. Examples of thickeners include polyvinyl alcohol, polyacrylate, CMC, and alginic acid, with polyacrylic acid being preferred due to its excellent chemical resistance to strong alkalis.

The zinc alloy can be a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy. For example, a zinc alloy containing 0.01 to 0.1 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is preferred because it suppresses hydrogen gas generation. In particular, indium and bismuth are advantageous in terms of improving discharge performance. Using a zinc alloy for the negative electrode can improve safety by slowing the rate of self-dissolution in alkaline electrolyte, thereby suppressing hydrogen gas generation.

The shape of the negative electrode material is not particularly limited, but it is preferably in powder form, which increases the surface area and allows for high-current discharge. The average particle size of the negative electrode material, preferably a zinc alloy, is in the range of 3 to 100 μm in minor axis. Within this range, the large surface area makes it suitable for high-current discharge, and it is easy to mix uniformly with the electrolyte and gelling agent, making it easy to handle during battery assembly.

The negative electrode plate 14 further includes a negative electrode current collector 14b. The negative electrode current collector 14b is disposed inside and/or on the surface of the negative electrode active material layer 14a, excluding the portion extending as the negative electrode current collector 15. That is, the negative electrode active material layer 14a may be disposed on both sides of the negative electrode current collector 14b, or the negative electrode active material layer 14a may be disposed on only one side of the negative electrode current collector 14b. A metallic negative electrode current collector 15 is further provided, extending (e.g., upward) from or connected to the negative electrode current collector 14b. The negative electrode current collector 15 is preferably disposed in a position that does not overlap with the positive electrode current collector 13. The negative electrode current collector 15 may be made of the same material as the negative electrode current collector 14b, or may be made of a different material. In either case, the negative electrode current collector 15 may be extended by attaching another current collector, such as a tab lead, to the tab. In any case, it is preferable that multiple negative electrode current collectors 15 are joined to one negative electrode terminal 28 or to a further negative electrode current collector 15 electrically connected thereto.

From the perspective of active material adhesion, it is preferable to use a metal plate with multiple (or many) openings for the negative electrode current collector 14b. Preferred examples of such a negative electrode current collector 14b include expanded metal, punched metal, metal mesh, and combinations thereof. More preferred are copper expanded metal, copper punched metal, and combinations thereof, with copper expanded metal being particularly preferred. In this case, a negative electrode plate consisting of a negative electrode/negative electrode current collector can be preferably produced by applying a mixture containing zinc oxide powder and/or zinc powder, and optionally a binder (e.g., polytetrafluoroethylene particles), to the copper expanded metal. In this case, it is also preferable to press the dried negative electrode plate (i.e., the negative electrode/negative electrode current collector) to prevent the electrode active material from falling off and improve electrode density. Expanded metal is a mesh-like metal plate made by expanding a metal plate while making staggered cuts using an expansion machine, and then shaping the cuts into a diamond or tortoiseshell pattern. Punched metal, also known as perforated metal, is a metal plate with holes punched into it. Metal mesh is a metal product with a wire mesh structure, and is different from expanded metal and perforated metal.

The hydroxide ion conductive separator 16 is provided to separate the positive electrode plate 12 and the negative electrode plate 14 while allowing hydroxide ions to be conducted between them. For example, as shown in FIG. 4, the negative electrode plate 14 may be configured to be covered or wrapped with the hydroxide ion conductive separator 16. This eliminates the need for a complicated sealing joint between the hydroxide ion conductive separator 16 and the battery container, making it possible to manufacture nickel-zinc secondary batteries (particularly stacked batteries) that can prevent zinc dendrite extension extremely easily and with high productivity. However, a simple configuration in which the hydroxide ion conductive separator 16 is placed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used.

The hydroxide ion-conductive separator 16 is not particularly limited as long as it is capable of separating the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ions to be conductively separated. However, it typically contains a hydroxide ion-conductive solid electrolyte and selectively transmits hydroxide ions solely through its hydroxide ion conductivity. A preferred hydroxide ion-conductive solid electrolyte is a layered double hydroxide (LDH) and/or an LDH-like compound. Therefore, the hydroxide ion-conductive separator 16 is preferably an LDH separator. As used herein, an "LDH separator" is defined as a separator containing LDH and/or an LDH-like compound that selectively transmits hydroxide ions solely through the hydroxide ion conductivity of the LDH and/or LDH-like compound. As used herein, an "LDH-like compound" refers to a hydroxide and/or oxide with a layered crystal structure similar to LDH, even if it may not be considered an LDH, and can be considered an equivalent of LDH. However, in a broad definition, "LDH" can be interpreted as encompassing not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and/or LDH-like compounds. That is, in a preferred LDH separator, the pores of the porous substrate are filled with LDH and/or LDH-like compounds so as to exhibit hydroxide ion conductivity and gas impermeability (and thus function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferred that the LDH is incorporated throughout the entire thickness of the porous substrate made of a polymer material. For example, known LDH separators such as those disclosed in Patent Documents 1 to 7 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, even more preferably 5 to 60 μm, and especially preferably 5 to 40 μm.

As shown in Figures 1, 2, and 4, the positive electrode plate 12, positive electrode current collector 13, negative electrode plate 14, negative electrode current collector 15, and hydroxide ion conductive separator 16 are preferably arranged vertically, with the positive electrode terminal 26 and negative electrode terminal 28 provided on the top lid 20a of the battery container 20. Therefore, in the case of a multi-layer cell, it is preferable that the cells are multi-layered horizontally. It is also preferable that the positive electrode current collector 13 and negative electrode current collector 15 extend upward.

The zinc secondary battery 10 may further include a liquid-retaining member 17 in contact with the positive electrode plate 12 and/or the negative electrode plate 14. For example, it is preferable that not only the hydroxide ion conductive separator 16 but also the liquid-retaining member 17 be interposed between the positive electrode plate 12 and the negative electrode plate 14. As shown in FIG. 4, it is preferable that the positive electrode plate 12 and/or the negative electrode plate 14 be covered or enclosed by the liquid-retaining member 17. However, a simple configuration in which the liquid-retaining member 17 is disposed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used. In either case, the interposition of the liquid-retaining member 17 allows the electrolyte 18 to be evenly distributed between the positive electrode plate 12 and/or the negative electrode plate 14 and the hydroxide ion conductive separator 16, thereby enabling efficient exchange of hydroxide ions between the positive electrode plate 12 and/or the negative electrode plate 14 and the hydroxide ion conductive separator 16. The liquid retention member 17 is not particularly limited as long as it is capable of retaining the electrolyte solution 18, but is preferably a sheet-like member. Preferred examples of the liquid retention member 17 include nonwoven fabric, water-absorbent resin, liquid-retaining resin, porous sheet, and various spacers. Nonwoven fabric is particularly preferred because it allows for the production of a high-performance negative electrode structure at low cost. The liquid retention member 17 or nonwoven fabric preferably has a thickness of 10 to 200 μm, more preferably 20 to 200 μm, even more preferably 20 to 150 μm, particularly preferably 20 to 100 μm, and most preferably 20 to 60 μm. A thickness within the above range allows a sufficient amount of electrolyte solution 18 to be retained within the liquid retention member 17 while keeping the overall size of the positive electrode structure and/or negative electrode structure compact and efficient.

When the positive electrode plate 12 and/or the negative electrode plate 14 are covered or enclosed by the liquid retention member 17 and/or the separator 16, it is preferable that their outer edges be closed (except for the edges from which the positive electrode current collector 13 and the negative electrode current collector 15 extend). In this case, the closed edges of the outer edges of the liquid retention member 17 and/or the separator 16 are preferably achieved by folding the liquid retention member 17 and/or the separator 16, or by sealing the liquid retention members 17 together and/or the separators 16 together. Preferred examples of sealing methods include adhesives, heat welding, ultrasonic welding, adhesive tape, sealing tape, and combinations thereof. In particular, LDH separators containing a porous substrate made of a polymer material have the advantage of being flexible and therefore easily bendable. Therefore, it is preferable to form the LDH separator into a long shape and then fold it to close one edge of the outer edge. Thermal welding and ultrasonic welding can be performed using a commercially available heat sealer, but when sealing LDH separators together, it is preferable to perform thermal welding and ultrasonic welding by sandwiching the outer periphery of the liquid-retaining member 17 between the LDH separators that make up the outer periphery, as this provides more effective sealing. Commercially available adhesives, adhesive tapes, and sealing tapes can be used, but those containing alkali-resistant resins are preferred to prevent deterioration in alkaline electrolyte. From this perspective, preferred adhesives include epoxy resin adhesives, natural resin adhesives, modified olefin resin adhesives, and modified silicone resin adhesives. Of these, epoxy resin adhesives are particularly preferred due to their excellent alkali resistance. An example of a commercially available epoxy resin adhesive is the epoxy adhesive Hysol® (manufactured by Henkel).

Preferably, the outer edge of one side of the separator 16, which is the upper end, is open. This open-top configuration can address problems that occur during overcharging in nickel-zinc batteries and the like. Specifically, when a nickel-zinc battery or the like is overcharged, oxygen (O ₂ ) can be generated at the positive electrode plate 12. However, the LDH separator is highly dense, allowing only hydroxide ions to pass through, and therefore does not allow O ₂ to pass through. In this regard, the open-top configuration allows O ₂ to escape above the positive electrode plate 12 and be transported to the negative electrode plate 14 through the open-top portion within the battery container 20, thereby oxidizing Zn in the negative electrode active material with O ₂ and returning it to ZnO. By undergoing this oxygen reaction cycle, the use of the open-top battery element 11 in a sealed zinc secondary battery can improve overcharge resistance. Even if the outer edge of one side of the separator 16 or the liquid-retaining member 17, which is the upper end, is closed, providing a vent hole in part of the closed outer edge can be expected to achieve the same effect as the open-top configuration. For example, the vent hole may be opened after sealing the outer edge of one side that will be the upper end of the LDH separator, or during sealing, part of the outer edge may be left unsealed so that the vent hole is formed.

The electrolyte 18 preferably contains an aqueous solution of an alkali metal hydroxide. While the electrolyte 18 is only shown locally in FIG. 4, this is because it is distributed throughout the positive and negative electrode plates 12 and 14. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being preferred. To suppress the self-dissolution of zinc and/or zinc oxide, zinc compounds such as zinc oxide and zinc hydroxide may be added to the electrolyte. As mentioned above, the electrolyte may be mixed with the positive electrode active material and/or the negative electrode active material to form a positive electrode composite and/or a negative electrode composite. The electrolyte may also be gelled to prevent leakage. A polymer that absorbs the solvent in the electrolyte and swells is preferably used as the gelling agent. Examples of suitable gelling agents include polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, as well as starch.

As shown in Figures 3 and 4, the battery element 11 comprises multiple positive electrode plates 12, multiple negative electrode plates 14, and multiple separators 16, and is in the form of a positive/negative electrode laminate in which the positive electrode plate 12/separator 16/negative electrode plate 14 unit is repeatedly stacked. In other words, the zinc secondary battery 10 has multiple unit cells 10a, which together form a multi-layer cell. This is the configuration of a so-called assembled battery or stacked battery, and is advantageous in that it can provide high voltage and large current.

The battery container 20 is preferably made of resin. The resin constituting the battery container 20 is preferably a resin resistant to alkali metal hydroxides such as potassium hydroxide, more preferably a polyolefin resin, ABS resin, or modified polyphenylene ether, and even more preferably ABS resin or modified polyphenylene ether. The battery container 20 has a top lid 20a. The battery container 20 (e.g., top lid 20a) may have a pressure relief valve for releasing gas. Furthermore, a group of containers in which two or more battery containers 20 are arranged may be housed within an outer frame to form a battery module.

The present invention will be further illustrated by the following examples.

Example 1 (Comparison)
A long metal plate (copper, size: 10 mm × 150 mm, thickness: 0.5 mm) was prepared as a current collector. One end of the metal plate in the longitudinal direction and its vicinity were immersed vertically in an electrolyte (5.4 mol/L KOH aqueous solution containing 0.4 mol/L ZnO). After leaving the plate for 24 hours while supplying electrons at an applied voltage of −1.2 V (vs. SHE (standard hydrogen electrode)), creeping of the electrolyte along the metal plate surface was observed. Because the metal plate in this example did not have a creep-inhibiting region, creeping of the electrolyte was significantly observed.

Example 2 (Comparison)
As shown in Figure 10, an epoxy resin (product name: Araldite, manufactured by CIBA, Switzerland) was applied as a fluororesin paint around the entire periphery of the central portion of the long metal plate and then dried. This resulted in a creep-blocking region coated with the fluororesin paint, isolating one end of the metal plate from the other end. One end of the metal plate along its length and its vicinity were immersed vertically in an electrolyte (5.4 mol/L KOH solution containing 0.4 mol/L ZnO) so as not to contact the creep-blocking region. After leaving the metal plate for 24 hours while supplying electrons at an applied voltage of -1.2 V (vs. SHE: standard hydrogen electrode), it was observed whether the creep-blocking region prevented the electrolyte from creeping up along the metal plate surface.

Example 3 (Comparison)
Test pieces were prepared and evaluated in the same manner as in Example 2, except that the creep-preventing region was formed using polytetrafluoroethylene (PTFE) resin (product name: New TFE Coat, manufactured by Fine Chemical Japan) as the fluororesin-based paint.

Example 4 (Comparison)
Test pieces were prepared and evaluated in the same manner as in Example 2, except that the creep-preventing region was formed using a polyolefin adhesive (product name: Arrowbase, manufactured by Unitika Ltd.) as the fluororesin-based paint.

Example 5 (Comparison)
As shown in Figure 9, test specimens were prepared and evaluated in the same manner as in Example 2, except that instead of applying a fluororesin-based paint, a butyl rubber tape (manufactured by Nitto Denko Corporation) was attached around the entire periphery of the central part of the metal plate to form a creep-preventing region.

Example 6
Test specimens were prepared and evaluated in the same manner as in Example 2, except that instead of applying a fluororesin-based paint, a creep-prevention region was formed by forming rust on the surface (i.e., making it non-conductive) around the entire periphery of the central part of the long metal plate through natural oxidation by exposure to the atmosphere.

Results The results of Examples 1 to 6 were ranked and evaluated according to the following criteria: Table 1 shows the treatment conditions and evaluation results for each example.
Evaluation A: Creep-up of the electrolyte was reliably prevented in the creep-prevention region, i.e., a significant creep-prevention effect was stably observed.
Rating B: Although creep-up of the electrolyte was suppressed to some extent in the creep-prevention region, there were other regions where this was not the case, and there was a large variation depending on the interface state. In other words, the creep-prevention effect was limited and not stably obtained.
C: The creep-up of the electrolyte was only slightly inhibited in the creep-inhibiting region, i.e., the creep-inhibiting effect was small.
Evaluation D: Creep-up of the electrolyte was significantly observed, i.e., no creep suppression or prevention effect was observed at all.

REFERENCE SIGNS LIST 10 Zinc secondary battery 10a Unit cell 11 Battery element 12 Positive electrode plate 12a Positive electrode active material layer 13 Positive electrode current collector 14 Negative electrode plate 14a Negative electrode active material layer 14b Negative electrode current collector 15 Negative electrode current collector 16 Hydroxide ion conductive separator 17 Liquid retaining member 18 Electrolyte 20 Battery container 20a Top cover 26 Positive electrode terminal 28 Negative electrode terminal 30 Metal member 30a Passivated surface 32 Insulating tape 34 Paint C Creep prevention area

Claims (11)

(a) a positive electrode plate including a positive electrode active material layer and a positive electrode current collector;
a metallic positive electrode current collecting member extending from or connected to the positive electrode current collector;
a negative electrode plate including a negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds, and a negative electrode current collector;
a metallic negative electrode current collecting member extending from or connected to the negative electrode current collector;
a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so as to be conductive with hydroxide ions;
An electrolyte;
a unit cell comprising:
(b) a battery container that houses the unit cell;
(c1) a positive electrode terminal connected to the positive electrode current collecting member and protruding from the battery container;
(c2) a negative electrode terminal connected to the negative electrode current collecting member and protruding from the battery container;
A method for manufacturing a zinc secondary battery, comprising:
A creep prevention region is formed over the entire periphery of a portion of a section of the positive current collecting member and/or the positive terminal between the tip of the positive terminal and the positive electrode plate that is not immersed in the electrolyte, the portion being made of a non-conductive surface by surface modification; and
A creep prevention region is formed over the entire periphery of a portion of the section of the negative electrode current collecting member and/or the negative electrode terminal between the tip of the negative electrode terminal and the negative electrode plate that is not immersed in the electrolyte, the portion being made of a non-conductive surface by surface modification.
Including ,
the passivated surface is exposed without any further coating thereon;
A method for manufacturing a zinc secondary battery, wherein the non-conductivity due to the surface modification is achieved by nitriding or oxidizing a metal constituting at least one of the positive electrode current collecting member, the positive electrode terminal, the negative electrode current collecting member, and the negative electrode terminal . 2. The method for manufacturing a zinc secondary battery according to claim 1, wherein the positive electrode plate, the positive electrode current collector, the negative electrode plate, the negative electrode current collector, and the hydroxide ion conductive separator are each arranged vertically, and the positive electrode terminal and the negative electrode terminal are provided on the upper lid of the battery container. The method for producing a zinc secondary battery according to claim 1 or 2 , wherein the nitriding or oxidation is plasma nitriding or plasma oxidation. The method for producing a zinc secondary battery according to any one of claims 1 to 3 , wherein the creep prevention region has a width of 1 to 20 mm. The method for producing a zinc secondary battery according to any one of claims 1 to 4 , wherein the creep prevention region is present inside the battery container. The method for producing a zinc secondary battery according to any one of claims 1 to 5 , wherein the hydroxide ion conductive separator is an LDH separator containing a layered double hydroxide (LDH) and/or an LDH-like compound. The method for producing a zinc secondary battery according to claim 6, wherein the LDH separator further comprises a porous substrate, and the LDH and/or LDH-like compound is composited with the porous substrate in a form where the LDH and/or LDH-like compound is filled in the pores of the porous substrate. The method for producing a zinc secondary battery according to claim 7 , wherein the porous substrate is made of a polymer material. The method for producing a zinc secondary battery according to any one of claims 1 to 8 , wherein the positive electrode active material layer contains nickel hydroxide and/or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery. The method for producing a zinc secondary battery according to any one of claims 1 to 8 , wherein the positive electrode active material layer is an air cathode layer, thereby making the zinc secondary battery an air-zinc secondary battery. The method for manufacturing a zinc secondary battery according to any one of claims 1 to 10 , wherein a plurality of the unit cells are contained in the battery container, and the plurality of unit cells as a whole form a multi-layer cell.