Zinc secondary battery

Abstract

Provided is a zinc secondary battery which has favorable battery resistance while being able to effectively suppress leakage of an electrolyte solution caused by creep. This zinc secondary battery comprises: a positive electrode plate that includes a positive electrode active substance layer and a positive electrode current collector; a negative electrode plate that includes a negative electrode active substance layer containing at least one type selected from the group consisting of zinc, zinc oxide, a zinc alloy and a zinc compound, and a negative electrode current collector; a hydroxide ion-conducting separator that separates the positive electrode plate and the negative electrode plate in a hydroxide ion-conducting way; and an electrolyte solution. The electrolyte solution is an aqueous solution that contains at least an alkali metal hydroxide including sodium hydroxide. The total alkali metal hydroxide concentration in the electrolyte solution is 5.0-6.0 mol / L. The sodium hydroxide concentration in the electrolyte solution is 0.5-6.0 mol / L.

Description

Zinc secondary battery

[0001] The present invention relates to a zinc secondary battery.

[0002] A phenomenon known as creep (hereinafter referred to as creep) is known 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 addressing this creep problem have been proposed. For example, Patent Document 1 (JP-A-7-254396) discloses that, in a button-type alkaline battery using 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 the surface is polished to control the amount of tin oxide on the surface to a predetermined level. Patent Document 2 (JP Patent No. 6561915) also 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 the non-conductive layer.

[0003] 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, penetrates the pores of separators such as nonwoven fabrics, and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the repetitive 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, Patent Document 5 (WO 2019 / 069760) and Patent Document 6 (WO 2019 / 077953) propose a zinc secondary battery configured such that 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 is said to eliminate the need for a complicated sealing joint between the LDH separator and the battery container, and to enable extremely simple and highly productive production of a zinc secondary battery (particularly a stacked battery thereof) capable of preventing zinc dendrite extension.

[0004] Furthermore, although they cannot be called LDHs, LDH-like compounds are known as hydroxides and / or oxides with a layered crystal structure similar to LDHs, and they exhibit hydroxide ion conductive properties similar enough to be collectively referred to as hydroxide ion conductive layered compounds together with LDHs. For example, Patent Document 7 (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, wherein the LDH-like compound is a hydroxide and / or oxide with a layered crystal structure containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al. In addition, Patent Document 8 (WO 2021 / 229916) discloses an LDH separator using an LDH-like compound containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additional element M which is at least one selected from the group consisting of In, Bi, Ca, Sr, and Ba. Furthermore, Patent Document 9 (WO 2021 / 229917) discloses an LDH separator using an LDH-like compound and In(OH) ３ With regard to an LDH separator containing a mixture of the above, one has been disclosed in which the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In. The separators disclosed in Patent Documents 7 to 9 are said to have superior alkali resistance compared to conventional LDH separators and to be able to more effectively suppress short circuits caused by zinc dendrites.

[0005] Japanese Patent Publication No. 7-254396, Japanese Patent No. 6561915, International Publication No. 2016 / 076047, International Publication No. 2019 / 124270, International Publication No. 2019 / 069760, International Publication No. 2019 / 077953, International Publication No. 2020 / 255856, International Publication No. 2021 / 229916, International Publication No. 2021 / 229917

[0006] As disclosed in Patent Documents 1 and 2, various attempts have been proposed to address the creep phenomenon in alkaline batteries, but there is a need for a method that can more effectively suppress electrolyte leakage.

[0007] The present inventors have now discovered that in a zinc secondary battery, by setting the total concentration of alkali metal hydroxides in the electrolyte to 5.0 to 6.0 mol / L and the concentration of sodium hydroxide to 0.5 to 6.0 mol / L, leakage of the electrolyte due to creep can be effectively suppressed while maintaining good battery resistance.

[0008] Therefore, an object of the present invention is to provide a zinc secondary battery that has good battery resistance and can effectively suppress leakage of electrolyte due to creep.

[0009] The present invention provides the following aspects. [Aspect 1] A zinc secondary battery comprising: a positive electrode plate including a positive electrode active material layer and a positive electrode current collector; a negative electrode plate including a negative electrode active material layer containing at least one material selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound, and a negative electrode current collector; a hydroxide ion conductive separator separating the positive electrode plate and the negative electrode plate so as to allow hydroxide ion conductivity; and an electrolyte solution, wherein the electrolyte solution is an aqueous solution containing alkali metal hydroxides including at least sodium hydroxide, the total concentration of the alkali metal hydroxides in the electrolyte solution being 5.0 to 6.0 mol / L, and the concentration of the sodium hydroxide in the electrolyte solution being 0.5 to 6.0 mol / L. [Aspect 2] The zinc secondary battery according to Aspect 1, wherein the concentration of the sodium hydroxide in the electrolyte solution is 2.5 to 6.0 mol / L. [Aspect 3] The zinc secondary battery according to Aspect 1 or 2, wherein the ratio of the concentration of the sodium hydroxide to the total concentration of the alkali metal hydroxides is 0.4 to 1.0. [Aspect 4] The zinc secondary battery according to any one of Aspects 1 to 3, wherein the alkali metal hydroxide consists solely of the sodium hydroxide. [Aspect 5] The zinc secondary battery according to any one of Aspects 1 to 3, wherein the alkali metal hydroxide further contains potassium hydroxide. [Aspect 6] The zinc secondary battery according to Aspect 5, wherein the concentration of the potassium hydroxide in the electrolyte is 3.0 mol / L or less. [Aspect 7] The zinc secondary battery according to Aspects 1 to 3, 5, or 6, wherein the alkali metal hydroxide further contains lithium hydroxide. [Aspect 8] The zinc secondary battery according to Aspect 7, wherein the concentration of the lithium hydroxide in the electrolyte is 1.5 mol / L or less. [Aspect 9] The zinc secondary battery according to any one of Aspects 1 to 8, wherein the hydroxide ion-conducting separator is an LDH separator containing a layered double hydroxide (LDH) and / or an LDH-like compound. [Aspect 10] The zinc secondary battery according to Aspect 9, 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. [Aspect 11] The zinc secondary battery according to Aspect 10, wherein the porous substrate is made of a polymer material.[Aspect 12] The zinc secondary battery according to any one of Aspects 1 to 11, wherein 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. [Aspect 13] The zinc secondary battery according to any one of Aspects 1 to 11, wherein the positive electrode active material layer is an air cathode layer, thereby forming the zinc secondary battery into a zinc-air secondary battery.

[0010] FIG. 1 is a schematic cross-sectional view showing an example of a zinc secondary battery according to the present invention. FIG. 2 is a diagram showing a cross section of the zinc secondary battery shown in FIG. 1 taken along line AA'. FIG. 3 is a perspective view showing an electrode laminate of the zinc secondary battery shown in FIG. 1. FIG. 4 is a cross-sectional view showing an electrode laminate of the zinc secondary battery shown in FIG. 1. FIG. 5 is a cross-sectional view showing an example of a mechanism by which creep is prevented in the zinc secondary battery of the present invention. FIG. 6 is a conceptual diagram for explaining the mechanism of creep when an aqueous potassium hydroxide solution is used as the electrolyte. FIG. 7 is a cross-sectional view showing an example of a mechanism by which the electrolyte in FIG. 6 passes through a minute gap between a metal member and a sealing member.

[0011] Zinc Secondary Battery The zinc secondary battery of the present invention is not particularly limited as long as it is a secondary battery that uses zinc as the negative electrode and an alkali metal hydroxide aqueous solution having the composition described below as the electrolyte. 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.

[0012] 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 includes a positive electrode plate 12, a negative electrode plate 14, a hydroxide ion-conductive separator 16, and an electrolyte 18. Note that in Figure 4, the electrolyte 18 is only partially illustrated because it is distributed throughout the positive electrode plate 12 and the negative electrode plate 14. The positive electrode plate 12 includes a positive electrode active material layer 12a and a positive electrode current collector (not shown). 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, a zinc alloy, and a zinc compound. 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 electrolyte 18 is an aqueous solution containing an alkali metal hydroxide. The alkali metal hydroxide includes at least sodium hydroxide. The total concentration of alkali metal hydroxides in the electrolyte 18 is 5.0 to 6.0 mol / L. The concentration of sodium hydroxide in the electrolyte 18 is 0.5 to 6.0 mol / L. In this way, by using the electrolyte 18 in which the total concentration of alkali metal hydroxides and the concentration of sodium hydroxide are each within a predetermined range in a zinc secondary battery, leakage of the electrolyte due to creep can be effectively suppressed while maintaining good battery resistance.

[0013] As mentioned above, creeping is a phenomenon in which the electrolyte creeps up the surface of the electrode terminal and leaks out of the battery container. Figure 6 conceptually shows the mechanism of creeping when a part of a metal member 30 (which is assumed to be an electrode terminal or a current collecting member) is immersed in electrolyte 118 (which is assumed to be an aqueous potassium hydroxide solution). As shown in Figure 6, creeping can be caused by: 1) H2O2 from the surrounding environment; ２ O molecule and electrons e present in the metal member 30 － is bonded to OH － 2) generating this OH － K in electrolyte 118 ＋The creep phenomenon develops as the electrolyte 118 is attracted to the metal member 30. In this way, the component of the electrolyte 118 (KOH) is produced in the area of ​​the metal member 30 where the electrolyte 118 is not present, and as a result, this phenomenon is observed as the electrolyte 118 creeping up the metal member 30. Note that leakage of the electrolyte due to the creep phenomenon typically occurs only on the negative electrode side.

[0014] In order to prevent leakage of the electrolyte, a terminal inside the container and a terminal outside the container are connected via a sealing member such as an O-ring or a gasket. However, as shown in Fig. 7, since there are minute irregularities on the surface of a metal member 30 such as an electrode terminal, a minute gap is generated between the metal member 30 and the sealing member 32, and the electrolyte 118 passes through this minute gap. In contrast, in the present invention, by using an electrolyte 18 containing sodium hydroxide at a predetermined concentration as described above, leakage of the electrolyte due to the creep phenomenon is effectively suppressed. That is, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide have a high content of potassium hydroxide. ＋ and Na ＋ In this respect, as opposed to the ionic radius, Na ＋ The hydrated ionic radius of (approximately 1.8 Å) is K ＋ The hydrated ionic radius (approximately 1.3 Å) of sodium hydroxide is larger than that of the electrolyte 18 (approximately 1.3 Å). Therefore, as shown in FIG. 5 , it is believed that the electrolyte 18 containing sodium hydroxide is less likely to pass through the minute gap between the metal member 30 and the sealing member 32 than the potassium hydroxide aqueous solution that has been commonly used as an electrolyte. Furthermore, the electrolyte 18 containing a predetermined concentration of sodium hydroxide has a higher viscosity than the potassium hydroxide aqueous solution. As a result, the speed at which the electrolyte 18 creeps up the metal member 30 is slowed, which is also believed to be one of the factors that can suppress electrolyte leakage due to creep.

[0015] The electrolyte 18 is an aqueous solution containing alkali metal hydroxides. The total concentration C of alkali metal hydroxides in the electrolyte 18 Ａis 5.0 to 6.0 mol / L, preferably 5.0 to 5.8 mol / L, more preferably 5.0 to 5.6 mol / L, and particularly preferably 5.2 to 5.6 mol / L. Within such ranges, the resistance of the electrolyte can be desirably reduced, and the performance of the zinc secondary battery can be improved. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.

[0016] The alkali metal hydroxide contained in the electrolytic solution 18 includes sodium hydroxide. The concentration C of sodium hydroxide in the electrolytic solution 18 Ｂ is 0.5 to 6.0 mol / L, preferably 2.5 to 6.0 mol / L, more preferably 3.0 to 6.0 mol / L, even more preferably 4.0 to 6.0 mol / L, even more preferably 5.0 to 6.0 mol / L, particularly preferably 5.0 to 5.8 mol / L, and most preferably 5.2 to 5.6 mol / L. Within such ranges, leakage of the electrolyte due to creep can be effectively prevented. Note that the concentration C of this sodium hydroxide Ｂ is the total concentration C of the alkali metal hydroxides Ａ Below (i.e. C Ｂ ≦C Ａ ) needless to say.

[0017] The electrolyte 18 has a total concentration of alkali metal hydroxides C Ａ Concentration of sodium hydroxide C Ｂ The ratio (= C Ｂ / C Ａ ) is preferably 0.4 to 1.0, more preferably 0.6 to 1.0, even more preferably 0.8 to 1.0, and particularly preferably 0.9 to 1.0. By increasing the proportion of sodium hydroxide in the alkali metal hydroxides in this way, leakage of the electrolyte due to the creep phenomenon can be more effectively suppressed.

[0018] The alkali metal hydroxide contained in the electrolytic solution 18 may be composed only of sodium hydroxide. That is, the electrolytic solution 18 has a total alkali metal hydroxide concentration C Ａ and the concentration of sodium hydroxide C Ｂ and are the same (CＡ =C Ｂ ) may be used. This makes it possible to extremely effectively prevent leakage of the electrolyte. However, it is permissible for alkali metals other than Na to be mixed into the electrolyte 18 as inevitable impurities due to raw materials, manufacturing processes, etc. That is, even if the alkali metal hydroxide is composed only of sodium hydroxide, the electrolyte 18 may contain alkali metal hydroxides other than sodium hydroxide as inevitable impurities (for example, at a concentration of less than 0.1 mol / L).

[0019] Alternatively, an alkali metal hydroxide other than sodium hydroxide may be intentionally added to the electrolytic solution 18. For example, the electrolytic solution 18 may further contain potassium hydroxide and / or lithium hydroxide, which are described above as alkali metal hydroxides.

[0020] When the alkali metal hydroxide in the electrolyte 18 further contains potassium hydroxide, the battery resistance can be further reduced. On the other hand, from the viewpoint of effectively suppressing leakage of the electrolyte, it is desirable to limit the amount of potassium hydroxide added. From these viewpoints, when the alkali metal hydroxide further contains potassium hydroxide, the concentration C of potassium hydroxide in the electrolyte 18 is Ｃ is preferably 4.0 mol / L or less, more preferably 3.0 mol / L or less, even more preferably 2.0 mol / L or less, particularly preferably 1.5 mol / L or less, and most preferably 1.0 mol / L or less. Ａ The concentration of potassium hydroxide C Ｃ The ratio (= C Ｃ / C Ａ ) is preferably 0.8 or less, more preferably 0.6 or less, even more preferably 0.4 or less, and particularly preferably 0.3 or less.

[0021] When the alkali metal hydroxide in the electrolyte solution 18 further contains lithium hydroxide, leakage of the electrolyte solution can be further suppressed. ＋ Is, K ＋ and Na ＋The hydrated ionic radius is larger (about 2.4 Å) than that of the lithium hydroxide solution. Furthermore, the viscosity of a lithium hydroxide solution is higher than that of a sodium hydroxide solution of the same concentration. Therefore, adding lithium hydroxide to the electrolyte 18 can more effectively prevent creep. On the other hand, from the viewpoint of effectively reducing the battery resistance, it is desirable to limit the amount of lithium hydroxide added. From these viewpoints, when the alkali metal hydroxide further contains lithium hydroxide, the concentration C of lithium hydroxide in the electrolyte 18 is Ｄ is preferably 1.5 mol / L or less, more preferably 1.0 mol / L or less, even more preferably 0.1 to 0.8 mol / L or less, and particularly preferably 0.2 to 0.5 mol / L or less. Ａ Concentration of lithium hydroxide C Ｄ The ratio (= C Ｄ / C Ａ ) is preferably 0.3 or less, more preferably 0 to 0.2, even more preferably 0 to 0.15, and particularly preferably 0 to 0.1. When lithium hydroxide is added to the electrolyte solution 18, it is desirable to also add potassium hydroxide to the electrolyte solution 18, from the viewpoint of achieving a good balance between reducing the battery resistance and suppressing leakage of the electrolyte. In other words, when the alkali metal hydroxide contains sodium hydroxide and lithium hydroxide, it is desirable to further contain potassium hydroxide.

[0022] To suppress the self-dissolution of zinc and / or zinc oxide, a zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte. To more effectively prevent leakage of the electrolyte, the electrolyte 18 may be gelled. As the gelling agent, it is desirable to use a polymer that absorbs the solvent of the electrolyte and swells, and examples of such gelling agents include polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, as well as starch.

[0023] The zinc secondary battery 10 preferably includes an electrode laminate 11 and an electrolyte 18 in a battery container 20. As shown in Figures 3 and 4, the electrode laminate 11 is in the form of a positive / negative electrode laminate including a plurality of positive electrode plates 12, a plurality of negative electrode plates 14, and a plurality of hydroxide ion conductive separators 16, stacked so that the unit of positive electrode plate 12 / hydroxide ion conductive separator 16 / negative electrode plate 14 is repeated. That is, the zinc secondary battery 10 preferably includes a plurality of unit cells 10a each 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, with the plurality of unit cells 10a forming a multilayer cell as a whole. 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.

[0024] 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 appropriately 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 preferably further includes a metallic positive electrode current collector 13 extending (e.g., upward) from or connected to the positive electrode current collector. A preferred example of the 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 onto 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. 4 includes a positive electrode current collector (e.g., nickel foam), but this is not shown. This is because, in the case of a nickel-zinc secondary battery, the positive electrode current collector is integrally integrated 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 formed into a tab shape by pressing. In either case, the positive electrode current collector 13 may be extended by attaching another current collector, such as a tab lead, to such a tab. In either case, it is preferable that multiple positive electrode current collectors 13 are joined to a single positive electrode terminal 26 or to another positive electrode current collector 13 electrically connected thereto. A positive terminal 26 is connected to the positive current collecting member 13 and typically protrudes from the battery container 20 .

[0025] The positive electrode plate 12 may contain at least one additive selected from the group consisting of a silver compound, a manganese compound, and a titanium compound, which can promote the positive electrode reaction of absorbing hydrogen gas generated by the self-discharge reaction. The positive electrode plate 12 may also contain cobalt. The 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, thereby contributing to improving the charge / discharge capacity.

[0026] 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 selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds. Zinc may be contained in any form, such as zinc metal, zinc compounds, or zinc alloys, 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 an electrolyte solution 18 to form a negative electrode composite. For example, a gelled negative electrode can be easily obtained by adding an electrolyte solution and a thickener to the negative electrode active material. Examples of thickeners include polyvinyl alcohol, polyacrylate, CMC, and alginic acid. Polyacrylic acid is preferred due to its excellent chemical resistance to strong alkalis.

[0027] As the zinc alloy, a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy can be used. 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 has the effect of suppressing hydrogen gas generation. In particular, indium and bismuth are advantageous in terms of improving discharge performance. The use of a zinc alloy for the negative electrode can suppress hydrogen gas generation and improve safety by slowing the rate of self-dissolution in alkaline electrolyte.

[0028] The shape of the negative electrode material is not particularly limited, but is preferably in powder form, which increases the surface area and enables it to withstand large current discharge. In the case of a zinc alloy, the average particle size of the negative electrode material is preferably in the range of 3 to 100 μm in minor axis. Within this range, the large surface area makes it suitable for withstanding large current discharge, and it is also easy to mix uniformly with the electrolyte and gelling agent, making it easy to handle during battery assembly.

[0029] The negative electrode plate 14 further includes a negative electrode current collector 14b. The negative electrode current collector 14b is provided 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 provided on both sides of the negative electrode current collector 14b, or the negative electrode active material layer 14a may be provided on only one side of the negative electrode current collector 14b. A metallic negative electrode current collector 15 is preferably provided, extending from or connected to the negative electrode current collector 14b (e.g., upward). The negative electrode current collector 15 is preferably provided 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 connecting another current collector, such as a tab lead, to the tab. In either case, it is preferable that a plurality of negative electrode current collecting members 15 are joined to one negative electrode terminal 28 or to a further negative electrode current collecting member 15 electrically connected thereto. The negative electrode terminal 28 is typically connected to the negative electrode current collecting member 15 and protrudes from the battery container 20.

[0030] From the viewpoint of active material adhesion, it is preferable to use a metal plate having multiple (or many) openings as 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, for example, 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. The expanded metal is a mesh-like metal plate produced by expanding a metal plate while making staggered cuts using an expansion machine, and then shaping the cuts into a diamond or tortoiseshell shape. 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 punched metal.

[0031] The hydroxide ion conductive separator 16 is provided to separate the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ion conductivity. 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 produce a zinc secondary battery (particularly a stacked battery thereof) that is capable of preventing zinc dendrite extension extremely easily and with high productivity. However, a simple configuration in which the hydroxide ion conductive separator 16 is disposed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used.

[0032] The hydroxide ion-conductive separator 16 is not particularly limited as long as it is a separator capable of separating the positive electrode plate 12 and the negative electrode plate 14 in a hydroxide ion conductive manner. Typically, however, it is a separator that includes a hydroxide ion-conductive solid electrolyte and selectively transmits hydroxide ions solely by utilizing 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 that includes an LDH and / or an LDH-like compound and selectively transmits hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and / or LDH-like compound. As used herein, an "LDH-like compound" is a hydroxide and / or oxide with a layered crystal structure that has hydroxide ion conductivity, even if it may not be called an LDH, and can be considered an equivalent of an 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 and / or LDH-like compounds are 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 3 to 9 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 particularly preferably 5 to 40 μm.

[0033] 1, 2, and 4, the positive electrode plate 12, the positive electrode current collecting member 13, the negative electrode plate 14, the negative electrode current collecting member 15, and the hydroxide ion conductive separator 16 are preferably arranged vertically, and the positive electrode terminal 26 and the negative electrode terminal 28 are preferably provided on the top cover 20a of the battery container 20. Therefore, in the case of a multi-layer cell, it is preferable that the cells are multi-layered in the horizontal direction. It is also preferable that the positive electrode current collecting member 13 and the negative electrode current collecting member 15 extend upward.

[0034] 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-retaining member 17 is not particularly limited as long as it is a material capable of retaining the electrolyte solution 18, but is preferably a sheet-like member. Preferred examples of the liquid-retaining 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-retaining 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-retaining member 17 while keeping the overall size of the positive electrode structure and / or negative electrode structure compact and efficient.

[0035] When the positive electrode plate 12 and / or the negative electrode plate 14 are covered or wrapped with the liquid retention member 17 and / or the hydroxide ion conductive separator 16, their outer edges are preferably 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 hydroxide ion conductive separator 16 are preferably realized by folding the liquid retention member 17 and / or the hydroxide ion conductive separator 16, or by sealing the liquid retention members 17 together and / or the hydroxide ion conductive 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 including 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, etc., 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 examples of adhesives include epoxy resin-based adhesives, natural resin-based adhesives, modified olefin resin-based adhesives, and modified silicone resin-based adhesives. Of these, epoxy resin-based adhesives are particularly preferred due to their excellent alkali resistance. An example of a product of an epoxy resin-based adhesive is the epoxy adhesive Hysol® (manufactured by Henkel).

[0036] It is preferable that the outer edge of one side of the hydroxide ion conductive separator 16, which is the upper end, is open. This open-top configuration makes it possible to deal with the problem of overcharging in nickel-zinc batteries and the like. That is, when a nickel-zinc battery or the like is overcharged, oxygen (O ２ ) may occur, but the LDH separator has such a high density that it allows only hydroxide ions to pass through, so O２ In this respect, the open-top structure allows O ２ can escape above the positive electrode plate 12 and be sent to the negative electrode plate 14 side through the upper open portion, thereby ２ The Zn in the negative electrode active material can be oxidized and returned to ZnO by this oxygen reaction cycle. By using the open-top electrode laminate 11 in a sealed zinc secondary battery, overcharge resistance can be improved. Even when the outer edge of one side serving as the upper end of the hydroxide ion conductive separator 16 or the liquid-retaining member 17 is closed, the same effect as the open-top configuration can be expected by providing a vent hole in part of the closed outer edge. For example, the vent hole may be opened after sealing the outer edge of one side serving as the upper end of the LDH separator, or a part of the outer edge may be left unsealed during sealing so that a vent hole is formed.

[0037] 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., the 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 in an outer frame to form a battery module.

[0038] The present invention is further illustrated by the following examples.

[0039] Examples 1 to 9 (1) Fabrication of Nickel-Zinc Secondary Batteries The following positive electrode plate, positive electrode current collector, negative electrode plate, negative electrode current collector, LDH separator, nonwoven fabric, battery container, and electrolyte were prepared. Various electrolytes were prepared, varying the type and concentration of alkali metal hydroxide. Positive electrode plate: A positive electrode paste containing nickel hydroxide and a binder was filled into the pores of foamed nickel and then dried (an uncoated area near one edge of the foamed nickel where the positive electrode paste was not applied existed). Positive electrode current collector: The uncoated area of ​​the foamed nickel constituting the positive electrode plate was compressed with a roll press to form a tab, and a tab lead (made of pure nickel, thickness: 100 μm) was ultrasonically welded to the tab to extend it. Negative electrode plate: A negative electrode paste containing ZnO powder, metallic Zn powder, polytetrafluoroethylene (PTFE), and propylene glycol is pressed onto a current collector (copper expanded metal) (there is an uncoated area near one end of the copper expanded metal where the negative electrode paste is not applied). Negative electrode current collecting member: A tab lead (made of copper, thickness: 100 μm) is connected to the uncoated area of ​​the copper expanded metal by ultrasonic welding. LDH separator: Ni-Al-Ti-LDH (layered double hydroxide) is deposited by hydrothermal synthesis on the inside and surface of a polyethylene microporous membrane and then roll-pressed, thickness: 20 μm Nonwoven fabric: Polypropylene, thickness: 100 μm Battery container: Modified polyphenylene ether resin box-shaped case (equipped with a pressure relief valve that allows gas generated inside the case to be released), internal dimensions: length 190 mm, width 24 mm, height 165 mm, external dimensions: length 200 mm, width 30 mm, height 170 mm (not including the height of the positive and negative electrode terminals) Electrolyte: 0.4 mol / L ZnO dissolved in an alkali metal hydroxide aqueous solution of the composition shown in Table 1

[0040] The positive electrode plate was wrapped in nonwoven fabric so that it covered both sides, with the nonwoven fabric slightly protruding from the remaining three sides except for one side from which the positive electrode current collector extended. The excess portions of the nonwoven fabric protruding from the three sides of the positive electrode plate were heat-sealed with a heat seal bar to obtain a positive electrode structure. The negative electrode plate was also wrapped in nonwoven fabric and an LDH separator in this order from both sides, with the nonwoven fabric and the LDH separator slightly protruding from the remaining three sides except for the one side from which the negative electrode current collector extended. The excess portions of the nonwoven fabric and the LDH separator protruding from the three sides of the negative electrode plate were heat-sealed with a heat seal bar to obtain a negative electrode structure. In this way, multiple positive electrode structures and multiple negative electrode structures were prepared.

[0041] An electrode stack was fabricated by alternately stacking 12 positive electrode structures and 13 negative electrode structures. Similar to the configuration shown in FIG. 3 , the positive electrode current collectors 13 and the negative electrode current collectors 15 were designed to extend from different positions from each other when viewed in plan. Therefore, the positive electrode current collectors 13 were stacked on top of each other, while the negative electrode current collectors 15 were stacked on top of each other at different positions. As shown in FIGS. 1 and 2 , the overlapping portions of the positive electrode current collectors 13 were joined together to a positive electrode terminal 26 by laser welding. Similarly, the overlapping portions of the negative electrode current collectors 15 were joined together to a negative electrode terminal 28 by laser welding. In this way, a stack of electrode structures including the positive electrode current collectors 13 and the negative electrode current collectors 15 was obtained as the electrode stack 11. The electrode stack 11 was placed in a box-shaped battery container 20, and the electrolyte 18 was poured in to impregnate the electrode stack 11, and the top lid 20a was closed and sealed to produce a nickel-zinc secondary battery.

[0042] (2) Evaluation of Battery Resistance Using a charge / discharge device (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.), the fabricated nickel-zinc secondary battery was subjected to formation by charging at 0.1 C and discharging at 0.2 C. Thereafter, a 0.5 C charge / discharge cycle was performed once, and the coulombic efficiency value was calculated by dividing the discharge capacity by the charge capacity and multiplying the result by 100 (= (discharge capacity / charge capacity) × 100). The obtained coulombic efficiency value was ranked and evaluated according to the following criteria. The results are shown in Table 1. Note that, for samples with a battery resistance rating of C, it is presumed that the discharge reaction was not completed due to high resistance of the electrolyte, resulting in a deterioration in coulombic efficiency. <Battery Resistance Evaluation Criteria> - Rating A: Coulombic efficiency value of 99% or more - Rating B: Coulombic efficiency value of more than 95% but less than 99% - Rating C: Coulombic efficiency value of 95% or less (failure)

[0043] (3) Evaluation of Leakage Resistance The manufactured nickel-zinc secondary batteries were stored in a high-temperature, high-humidity (65°C / 80%) environment. The number of days from the start of storage until carbonate derived from the electrolyte precipitated on the top of the negative electrode terminal 28 was first visually observed was measured. The number of days until salt precipitation was rated and evaluated according to the following criteria. The results are shown in Table 1. <Leakage Resistance Evaluation Criteria> - Rating A: 50 days or more until salt precipitation - Rating B: 11 to 49 days until salt precipitation - Rating C: 10 days or less until salt precipitation (failure)

[0044]

Claims

1. a positive electrode plate including a positive electrode active material layer and a 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 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 zinc secondary battery comprising: the electrolyte is an aqueous solution containing an alkali metal hydroxide consisting solely of sodium hydroxide, A zinc secondary battery, wherein the concentration of the sodium hydroxide in the electrolyte is 5.0 to 6.0 mol / L.

2. 2. The zinc secondary battery according to claim 1, wherein the concentration of the sodium hydroxide in the electrolyte is 5.0 to 5.8 mol / L.

3. 3. The zinc secondary battery according to claim 1, wherein the hydroxide ion-conducting separator is an LDH separator containing a layered double hydroxide (LDH) and / or an LDH-like compound.

4. The zinc secondary battery according to claim 3, 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 in which the LDH and / or LDH-like compound is filled in the pores of the porous substrate.

5. The zinc secondary battery according to claim 4 , wherein the porous substrate is made of a polymer material.

6. 3. The zinc secondary battery according to claim 1, wherein 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.

7. 3. The zinc secondary battery according to claim 1, wherein the positive electrode active material layer is an air cathode layer, thereby forming the zinc secondary battery into a zinc-air secondary battery.