Zinc secondary battery

Abstract

Provided is a zinc secondary battery in which it is possible to suppress the discharge of an electrolyte from a pressure release valve. This zinc secondary battery comprises an electrode laminate, a box-shaped case in which the electrode laminate is accommodated in a vertical orientation, and an electrolyte in which the electrode laminate is immersed. The electrode laminate includes: a positive electrode plate; a positive electrode tab lead extending upward from an end part of the positive electrode plate; a negative electrode plate; a negative electrode tab lead extending upward from an end part of the negative electrode plate at a position not overlapping the positive electrode tab lead; and a hydroxide-ion-conductive separator. The box-shaped case has a bottom part, a pair of long side wall parts, a pair of short side wall parts, and a lid part. The lid part is provided with a liquid injection port via which the electrolyte can be injected into the box-shaped case. The liquid injection port is joined with a pressure release valve capable of releasing gas when the internal pressure of the box-shaped case rises. When the zinc secondary battery is seen in plan view from a direction perpendicular to the long side wall parts, the liquid injection port is positioned in a portion other than the central section of the lid part and is positioned above the positive electrode tab lead or the negative electrode tab lead.

Description

Zinc secondary battery

[0001] The present disclosure relates to zinc secondary batteries.

[0002] In zinc secondary batteries, such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrates the pores of the separator (e.g., nonwoven fabric) and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the battery's life after repeated charging and discharging.

[0003] To address the above-mentioned problems, batteries have been proposed that include a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing zinc dendrites from penetrating. For example, Patent Document 1 (WO 2013 / 118561) discloses a nickel-zinc secondary battery in which an LDH separator is provided between the positive and negative electrodes. Patent Document 2 (WO 2016 / 076047) also discloses a separator structure that includes an LDH separator fitted or bonded to a resin outer frame, and that the LDH separator has such high density that it is gas- and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Patent Document 3 (WO 2016 / 067884) also discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to obtain a composite material. This method includes a step of uniformly attaching a starting substance capable of providing a starting point for LDH crystal growth to a porous substrate, and then subjecting the porous substrate to hydrothermal treatment in a raw material aqueous solution to form a dense LDH membrane on the surface of the porous substrate. LDH separators have also been proposed in which the LDH / porous substrate composite material produced through hydrothermal treatment is roll-pressed to achieve further densification. For example, Patent Document 4 (WO 2019 / 124270) discloses an LDH separator comprising a polymeric porous substrate and LDH loaded into the porous substrate, and having a linear transmittance of 1% or more at a wavelength of 1000 nm.

[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 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, 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. This hydroxide ion conductive separator is 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] Incidentally, Patent Document 6 (WO2019 / 069760) and Patent Document 7 (WO2019 / 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. Furthermore, Patent Document 8 (WO2021 / 193436) discloses a zinc secondary battery that includes a stack of alternating positive and negative electrode plates, a positive electrode current collector tab connected to a positive electrode current collector in the positive electrode plate, and a negative electrode current collector tab connected to a negative electrode current collector in the negative electrode plate, oriented vertically, with the positive electrode current collector tab and the negative electrode current collector tab protruding upward from the stack.

[0006] WO2013 / 118561WO2016 / 076047WO2016 / 067884WO2019 / 124270WO2020 / 255856WO2019 / 069760WO2019 / 077953WO2021 / 193436

[0007] In zinc secondary batteries, a filler port for injecting electrolyte into the battery case may be provided in the case (e.g., the lid). In such cases, the filler port may be provided with a pressure relief valve that can release gas inside the case when the internal pressure of the case increases. Here, FIG. 8 shows an example of a zinc secondary battery 110 of the type in which a current collecting tab extends upward from an electrode stack (hereinafter referred to as an upper tab type), as disclosed in Patent Document 8. The zinc secondary battery 110 includes an electrode stack 111 including a positive electrode plate and a negative electrode plate, and an electrolyte 118, housed in a box-shaped case 120. In this regard, in conventional zinc secondary batteries 110, the filler port 122 and pressure relief valve 124 are typically located in the center of the lid 120d.

[0008] However, in the conventional zinc secondary battery 110, as shown in Figures 9A and 9B, an increase in the internal pressure of the box-shaped case 120 applies upward stress to the lid portion 120d, which may cause significant deformation of the lid portion 120d. The deformation of the lid portion 120d may then damage the joint between the liquid inlet 122 and the pressure release valve 124, causing a leak portion L. As a result, as shown in Figure 10, there is a concern that mist-like electrolyte 118, together with the gas inside the box-shaped case 120, may spray out of the case via the leak portion L.

[0009] The inventors have now discovered that in a top tab type zinc secondary battery, by providing a liquid inlet above the tab lead and in a location other than the center of the lid, and by joining a pressure release valve to this liquid inlet, it is possible to suppress the electrolyte from spraying out from the pressure release valve.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a zinc secondary battery capable of suppressing the ejection of electrolyte from the pressure release valve.

[0011] According to the present disclosure, the following aspects are provided: [Aspect 1] A zinc secondary battery comprising: an electrode stack; a box-shaped case in which the electrode stack is housed in a vertical orientation; and an electrolyte in which the electrode stack is immersed, wherein the electrode stack comprises: a positive electrode plate including a positive electrode active material layer and a positive electrode current collector, a positive electrode tab lead extending upward from an end of the positive electrode plate, a negative electrode plate including a negative electrode active material layer including at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound, and a negative electrode current collector, a negative electrode tab lead extending upward from the end of the negative electrode plate at a position not overlapping with the positive electrode tab lead, and a hydroxide ion conductive separator separating the positive electrode plate and the negative electrode plate so as to be conductive with hydroxide ions, wherein the box-shaped case has a bottom, a pair of long side walls parallel to the electrode stack, a pair of short side walls perpendicular to the electrode stack, and a lid, a zinc secondary battery according to claim 1, wherein, when the zinc secondary battery is viewed in plan view from a direction perpendicular to the longitudinal side wall portions, the left and right ends of the liquid inlet are located between an imaginary extension line formed by extending upward from the left end of the positive electrode tab lead and an imaginary extension line formed by extending upward from the right end of the positive electrode tab lead, or between an imaginary extension line formed by extending upward from the left end of the negative electrode tab lead and an imaginary extension line formed by extending upward from the right end of the negative electrode tab lead. [Aspect 3] The zinc secondary battery according to Aspect 1 or 2, wherein the positive electrode tab lead or the negative electrode tab lead is arranged so as to cover at least a part of the upper end of the electrode laminate, and the upper end covered by the positive electrode tab lead or the negative electrode tab lead is located below the liquid pouring hole. [Aspect 4] The zinc secondary battery according to any one of Aspects 1 to 3, wherein the box-shaped case is made of resin.[Aspect 5] The zinc secondary battery according to any one of Aspects 1 to 4, wherein the positive electrode plate and / or the negative electrode plate are covered or wrapped with the hydroxide ion-conductive separator. [Aspect 6] The zinc secondary battery according to any one of Aspects 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. [Aspect 7] The zinc secondary battery according to Aspect 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 filled in the pores of the porous substrate. [Aspect 8] The zinc secondary battery according to any one of Aspects 1 to 7, wherein the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, thereby forming a nickel-zinc secondary battery. [Aspect 9] The zinc secondary battery according to any one of Aspects 1 to 7, wherein the positive electrode active material layer is an air cathode layer, thereby forming an air-zinc secondary battery. [Aspect 10] The zinc secondary battery according to any one of Aspects 1 to 9, comprising a plurality of unit cells each having a pair of the positive electrode plate and the negative electrode plate together with the hydroxide ion conductive separator, whereby the plurality of unit cells as a whole form a multi-layer cell.

[0012] 1 is a schematic diagram showing an example of a zinc secondary battery according to the present invention. FIG. 2 is a diagram showing an example of a case where stress is applied to the lid portion due to an increase in internal pressure of the box-shaped case in the zinc secondary battery shown in FIG. 1. FIG. 2A is an enlarged view of a liquid inlet and a pressure release valve in the zinc secondary battery shown in FIG. 2A. FIG. 2B is a diagram showing a schematic cross section of the zinc secondary battery shown in FIG. 1 taken along line AA'. FIG. 1 is a perspective view showing a schematic electrode stack of the zinc secondary battery shown in FIG. 1. FIG. 2C is a cross section showing a schematic electrode stack of the zinc secondary battery shown in FIG. 1. FIG. 2D is a perspective view showing an example of a positive electrode plate or a negative electrode plate in the zinc secondary battery shown in FIG. 1. FIG. 6 is a perspective view showing a configuration of the positive electrode plate or the negative electrode plate shown in FIG. 6 covered with a hydroxide ion conductive separator or a liquid-retaining member. FIG. 9A is a schematic diagram showing an example of a conventional zinc secondary battery. FIG. 9D is a diagram showing an example of a case where stress is applied to the lid portion due to an increase in internal pressure of the box-shaped case in the zinc secondary battery shown in FIG. 9A. 9 is a diagram showing that electrolyte is sprayed from a leak part that occurs at the welding interface between the injection port and the pressure release valve in the zinc secondary battery shown in FIG. 8. It is a photograph of the pressure release valve in the zinc secondary battery of Example 2 (comparison) after the evaluation test.

[0013] Zinc Secondary Battery 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.

[0014] 1 to 7 show a zinc secondary battery 10 according to one embodiment of the present invention and its components. The zinc secondary battery 10 includes an electrode laminate 11 and an electrolyte 18 housed in a box-shaped case 20. The electrode laminate 11 is immersed in the electrolyte 18 and is housed vertically in the box-shaped case 20. The electrode laminate 11 includes a positive electrode plate 12, a positive electrode tab lead 13, a negative electrode plate 14, a negative electrode tab lead 15, and a hydroxide ion conductive separator 16. The positive electrode plate 12 includes a positive electrode active material layer 12a and a positive electrode current collector 12b, and the positive electrode tab lead 13 extends upward from an end of the positive electrode plate 12. The negative electrode plate 14 includes a negative electrode active material layer 14a and a negative electrode current collector 14b, and the negative electrode tab lead 15 extends upward from an end of the negative electrode plate 14 at a position that does not overlap with the positive electrode tab lead 13. The negative electrode active material layer 14a contains 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 ion conductivity. That is, in the electrode stack 11, the positive electrode plate 12, the positive electrode tab lead 13, the negative electrode plate 14, the negative electrode tab lead 15, and the hydroxide ion conductive separator 16 are each arranged vertically, and the positive electrode tab lead 13 and the negative electrode tab lead 15 extend upward. As shown in FIGS. 1 and 3 , the box-shaped case 20 has a bottom 20a, a pair of long side walls 20b parallel to the electrode stack 11, a pair of short side walls 20c perpendicular to the electrode stack 11, and a lid 20d. The lid 20d is provided with a liquid inlet 22 through which the electrolyte 18 can be poured into the box-shaped case 20. A pressure release valve 24 capable of releasing gas when the internal pressure of the box-shaped case 20 increases is joined to the liquid inlet 22. When the zinc secondary battery 10 is viewed in a plan view perpendicular to the longitudinal side wall 20b (hereinafter sometimes simply referred to as "when the zinc secondary battery 10 is viewed in a plan view"), as shown in Fig. 1, the liquid inlet 22 is located in a portion other than the center of the lid 20d and above the positive electrode tab lead 13 or the negative electrode tab lead 15 (hereinafter sometimes referred to as "tab lead 13 or 15"). In this way, in the top tab type zinc secondary battery 10, by providing the liquid inlet 22 above the tab lead 13 or 15 and in a portion other than the center of the lid 20d and joining the pressure release valve 24 to the liquid inlet 22, it is possible to suppress the electrolyte 18 from spraying out from the pressure release valve 24.

[0015] As described above with reference to Figures 8-10, in conventional top-tab zinc secondary batteries 110, the inlet 122 and pressure release valve 124 were typically located in the center of the lid 120d. In this regard, when the internal pressure of the box-shaped case 120 increases due to gas generation during battery operation, upward stress is applied to the lid 120d. The center of the lid 120d is most susceptible to this stress, and therefore, the center of the lid 120d is more likely to deform than other parts. As a result, as shown in Figure 9B, damage occurs at the joint between the inlet 122 and the pressure release valve 124, making it more likely that a leak point L will occur. Furthermore, because there is no shield between the electrolyte 118 and the pressure release valve 124, there is a concern that the mist-like electrolyte 118, along with the gas inside the box-shaped case 120, may spray out of the box-shaped case 120 via the leak point L.

[0016] In contrast, in the zinc secondary battery 10 of the present invention, the liquid inlet 22 is provided in a portion other than the center of the lid portion 20d. In other words, compared to the conventional zinc secondary battery 110, the liquid inlet 22 is provided closer to the short side wall portion 20c. Therefore, as shown in FIG. 2A , even if the internal pressure of the box-shaped case 20 increases, the short side wall portion 20c suppresses deflection of the portion of the lid portion 20d where the liquid inlet 22 is provided. This reduces deformation of the portion of the lid portion 20d where the liquid inlet 22 is provided, making it less likely that damage will occur at the joint between the liquid inlet 22 and the pressure release valve 24, as shown in FIG. 2B , thereby suppressing the occurrence of leaks at the joint. Furthermore, in the zinc secondary battery 10, the liquid inlet 22 is located above the tab lead 13 or 15. Therefore, the tab lead 13 or 15 serves as a shield between the electrolyte 18 and the pressure release valve 24. As a result, even if a leak occurs at the joint between the injection port 22 and the pressure release valve 24, the tab lead 13 or 15 can prevent the electrolyte 18 from spraying out. Thus, according to the zinc secondary battery 10 of the present invention, it is possible to suppress the electrolyte 18 from spraying out from the pressure release valve 24.

[0017] The liquid filling port 22 is a through-hole provided in a portion other than the center of the lid portion 20d, and allows the electrolyte 18 to be poured into the box-shaped case 20. In this specification, the "center" of the lid portion 20d means the central portion (third) of five equal parts obtained by dividing the lid portion 20d into the width direction (horizontal direction in FIG. 1 ). More specifically, when the zinc secondary battery 10 is viewed in plan as shown in FIG. 1 , the width of the lid portion 20d is defined by defining the contact position between the inner wall of the lid portion 20d and the inner wall of one of the short side wall portions 20c (e.g., the short side wall portion 20c closer to the negative electrode tab lead 15) as 0% (starting point) and the contact position between the inner wall of the lid portion 20d and the inner wall of the other short side wall portion 20c (e.g., the short side wall portion 20c closer to the positive electrode tab lead 13) as 100% (ending point). In this case, the center of the lid portion 20d refers to a position that is greater than 40% and less than 60% of the width of the lid portion 20d. In other words, the liquid inlet 22 is positioned at a position between 0% and 40% or between 60% and 100% of the width of the lid portion 20d, more preferably between 0% and 30% or between 70% and 100%, and even more preferably between 0% and 20% or between 80% and 100%. This further reduces deformation of the portion of the lid portion 20d where the liquid inlet 22 is located when the internal pressure of the box-shaped case 20 increases. As a result, damage to the joint between the liquid inlet 22 and the pressure release valve 24 is even less likely to occur, and leaks at the joint can be more effectively suppressed.

[0018] When the zinc secondary battery 10 is viewed from above, the left and right ends of the liquid filling port 22 are preferably located between an imaginary extension line E formed by extending upward from the left end of the negative electrode tab lead 15 and an imaginary extension line E' formed by extending upward from the right end of the negative electrode tab lead 15, as shown in FIG. 1 . Alternatively, the left and right ends of the liquid filling port 22 are also preferably located between an imaginary extension line formed by extending upward from the left end of the positive electrode tab lead 13 and an imaginary extension line formed by extending upward from the right end of the positive electrode tab lead 13. This allows the tab lead 13 or 15 to function even more effectively as a shield between the electrolyte 18 and the pressure release valve 24, thereby more effectively preventing the electrolyte 18 from spraying out. The opening width (or opening diameter) of the liquid filling port 22 when the zinc secondary battery 10 is viewed from above is not particularly limited, but is preferably 5 to 15 mm, more preferably 8 to 12 mm. Furthermore, the width of the positive electrode tab lead 13 and / or the negative electrode tab lead 15 when the zinc secondary battery 10 is viewed from above is preferably equal to or greater than the width of the liquid inlet 22, more preferably 5 to 15 mm, and even more preferably 8 to 12 mm. The shape of the liquid inlet 22 when viewed from above the box-shaped case 20 is not particularly limited, and may be any shape as long as the electrolyte 18 can be poured into the box-shaped case 20. The number of liquid inlets 22 provided in the lid portion 20d is not particularly limited, and may be one or more. When multiple liquid inlets 22 are provided in the lid portion 20d, each of them is typically provided in a portion other than the center of the lid portion 20d.

[0019] The pressure release valve 24 is joined to the liquid filling port 22 and is capable of releasing gas when the internal pressure of the box-shaped case 20 increases. That is, when the pressure inside the box-shaped case 20 reaches a predetermined level due to gas generation during battery operation, the pressure release valve 24 opens, releasing the gas to the outside of the box-shaped case 20. The type of pressure release valve 24 is not particularly limited as long as it has the above function. The operating pressure of the pressure release valve 24 is not particularly limited, but is preferably 0.01 to 0.2 MPa. The method of joining the liquid filling port 22 and the pressure release valve 24 is not particularly limited and known methods can be used, but welding by thermal welding, ultrasonic welding, or the like is preferred. In any case, it is preferable that the pressure release valve 24 be joined to the liquid filling port 22 in an airtight and liquid-tight manner to prevent the electrolyte 18 from spraying out. The number of pressure release valves 24 provided in the lid portion 20d is not particularly limited, as long as it corresponds to the number of liquid filling ports 22.

[0020] 1, the zinc secondary battery 10 preferably further includes a positive electrode terminal 26 and a negative electrode terminal 28, which extend from the lid portion 20d. In this case, it is preferable that at least a part of the portion of the positive electrode terminal 26 or the negative electrode terminal 28 that is disposed inside the box-shaped case 20 (internal terminal) is located below the liquid filling port 22. In this way, not only the tab lead 13 or 15 but also the internal terminal functions as a shield between the electrolyte 18 and the pressure release valve 24, so that the electrolyte 18 can be more effectively prevented from spraying out from the pressure release valve 24.

[0021] 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. In this case, the positive electrode active material layer 12a 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 active material layer 12a may also contain cobalt. Cobalt is preferably contained in the positive electrode plate 12 in the form of cobalt oxyhydroxide. In the positive electrode active material layer 12a, cobalt functions as a conductive additive, thereby contributing to improved charge / discharge capacity. Alternatively, in the case of an air-zinc secondary battery, an air electrode may be used as the positive electrode.

[0022] The positive electrode plate 12 further includes a positive electrode current collector 12b. A preferred example of the positive electrode current collector 12b 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 produced, for example, by uniformly applying a paste containing an electrode active material such as nickel hydroxide to the nickel porous substrate and drying it. In this case, 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 the electrode density. When the positive electrode current collector 12b is a nickel porous substrate such as a foamed nickel plate, the uncoated area of ​​the positive electrode current collector 12b may be pressed into a tab shape.

[0023] 6, the positive electrode plate 12 may have an uncoated region U along the upper edge of the positive electrode plate 12 where the positive electrode active material layer 12a is not present. In such a case, it is preferable that the positive electrode tab lead 13 is welded to the positive electrode current collector 12b in the uncoated region U, and that insulating tape 34 is applied to the uncoated region U so that the welded portion W is covered with the insulating tape 34. This makes it difficult for the tip of the positive electrode tab lead 13 to penetrate the hydroxide ion conductive separator 16 or the liquid retention member 17, and even if the tip does penetrate them and come into contact with the positive electrode plate 12, the insulating tape 34 functions as an insulator, making it difficult for a short circuit to occur.

[0024] The positive electrode tab lead 13 is provided so as to extend from an end of the positive electrode plate 12. The positive electrode tab lead 13 may be a commercially available metal foil, and is not particularly limited. As shown in FIG. 5 , it is preferable to form a positive electrode tab joint 30 by joining multiple positive electrode tab leads 13 to one positive electrode terminal 26 or a member electrically connected thereto. This allows for space-efficient current collection with a simple configuration and also facilitates connection to the positive electrode terminal 26. The joining of the positive electrode tab lead 13 to members such as the positive electrode current collector 12b and the positive electrode terminal 26 may be performed using a known joining method such as ultrasonic welding (ultrasonic welding), laser welding, TIG welding, or resistance welding.

[0025] The positive electrode tab lead 13 or the negative electrode tab lead 15 is preferably disposed so as to cover at least a portion of the upper end portion of the electrode stack 11. In this case, the upper end portion of the electrode stack 11 covered by the positive electrode tab lead 13 or the negative electrode tab lead 15 is preferably located below the liquid filling port 22. In this manner, the tab lead 13 or 15 can more effectively shield the electrolyte 18 from the pressure release valve 24, and can more effectively prevent the electrolyte 18 from spouting out.

[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 to form a negative electrode composite. For example, a gelled negative electrode can be easily obtained by adding an electrolyte 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.

[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 active material layer 14a may be disposed on both sides of the negative electrode current collector 14b, or may be disposed on only one side of the negative electrode current collector 14b. The negative electrode current collector 14b is preferably a metal plate having multiple (or many) openings from the viewpoint of fixing the negative electrode active material to the current collector. Preferred examples of such a negative electrode current collector 14b include expanded metal, punched metal, metal mesh, and combinations thereof. More preferred examples include 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 and a 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 a copper expanded metal. In this case, it is also preferable to press the dried negative electrode plate (i.e., negative electrode / negative electrode current collector) to prevent the electrode active material from falling off and improve the electrode density. Expanded metal is a mesh-like metal plate obtained by expanding a metal plate while making staggered cuts using an expander, and then shaping the cuts into a diamond or tortoiseshell shape. Perforated metal is also called perforated metal, and is a metal plate with holes punched out by a punching process. Metal mesh is a metal product with a wire mesh structure and is different from expanded metal and perforated metal.

[0030] 6, the negative electrode plate 14 may have an uncoated region U along the upper edge of the negative electrode plate 14 where the negative electrode active material layer 14a is not present. In such a case, it is preferable that the negative electrode tab lead 15 is welded to the negative electrode current collector 14b in the uncoated region U, and that insulating tape 34 is applied to the uncoated region U so that the welded portion W is covered with the insulating tape 34. This makes it difficult for the tip of the negative electrode tab lead 15 to penetrate the hydroxide ion conductive separator 16 or the liquid retention member 17, and even if the tip does penetrate them and come into contact with the negative electrode plate 14, the insulating tape 34 functions as an insulator, making it difficult for a short circuit to occur.

[0031] The negative electrode tab lead 15 is provided so as to extend from the end of the negative electrode plate 14 at a position where it does not overlap with the positive electrode tab lead 13 (see FIG. 4 ). The negative electrode tab lead 15 may be a commercially available metal foil, and is not particularly limited. As shown in FIG. 5 , it is preferable to form a negative electrode tab joint 32 by joining multiple negative electrode tab leads 15 to one negative electrode terminal 28 or a member electrically connected thereto. This allows for space-efficient current collection with a simple configuration and also facilitates connection to the negative electrode terminal 28. The joining of the negative electrode tab lead 15 to members such as the negative electrode current collector 14b and the negative electrode terminal 28 may be performed using a known joining method such as ultrasonic welding (ultrasonic welding), laser welding, TIG welding, or resistance welding.

[0032] The hydroxide ion conductive separator 16 is provided to separate the positive electrode plate 12 and the negative electrode plate 14 so as to allow hydroxide ion conductivity. For example, as shown in Figures 5 and 7, the positive electrode plate 12 and / or the negative electrode plate 14 (preferably 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 can prevent 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.

[0033] 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" refers to a hydroxide and / or oxide with a layered crystal structure similar to LDH, even if it may not be called 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 particularly preferably 5 to 40 μm.

[0034] It is preferable that not only the hydroxide ion conductive separator 16 but also a liquid retention member 17 be interposed between the positive electrode plate 12 and the negative electrode plate 14. As shown in FIGS. 5 and 7 , it is preferable that the positive electrode plate 12 and / or the negative electrode plate 14 be covered or wrapped with the liquid retention member 17. However, a simple configuration in which the liquid retention 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 retention member 17 allows the electrolyte 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 a material capable of retaining the electrolyte, but is preferably a sheet-like material. Preferred examples of the liquid-retaining member 17 include nonwoven fabric, water-absorbent resin, liquid-retaining resin, porous sheet, and various spacers, but 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 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 tab lead 13 and the negative electrode tab lead 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 electrolyte 18 preferably contains an aqueous solution of an alkali metal hydroxide. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being more preferred. A zinc compound, such as zinc oxide or zinc hydroxide, may be added to the electrolyte to suppress the self-dissolution of zinc and / or zinc oxide. As described above, the electrolyte may be mixed with a positive electrode active material and / or a negative electrode active material to form a positive electrode composite and / or a negative electrode composite. The electrolyte may also be gelled to more effectively prevent leakage of the electrolyte. A polymer that absorbs and swells in the electrolyte solvent 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.

[0038] The electrode laminate 11 is a laminate including a plurality of electrode layers. As shown in Figures 5 and 6, the electrode laminate 11 preferably has 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 having a pair of positive electrode plates 12 and negative electrode plates 14 together with a hydroxide ion conductive separator 16, whereby the plurality of unit cells 10a as a whole 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 obtain a high voltage and a large current.

[0039] 1 and 3, the box-shaped case 20 has a bottom 20a, a pair of long side walls 20b parallel to the electrode stack 11, a pair of short side walls 20c perpendicular to the electrode stack 11, and a lid 20d. The typical basic shape of the box-shaped case 20 is a rectangular parallelepiped, but it does not have to be a perfect rectangular parallelepiped, and as long as the overall general shape is box-shaped, it may have a shape with partially curved surfaces or unevenness.

[0040] The box-shaped case 20 is preferably made of resin. The resin constituting the box-shaped case 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 an ABS resin or modified polyphenylene ether. A battery module may be configured by housing a group of cases in which two or more box-shaped cases 20 are arranged within an outer frame.

[0041] LDH-Like Compound According to a preferred embodiment of the present invention, the LDH separator may contain an LDH-like compound. The definition of the LDH-like compound is as described above. Preferred LDH-like compounds are: (a) hydroxides and / or oxides having 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; or (b) hydroxides and / or oxides having a layered crystal structure containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) at least one additional element M selected from the group consisting of In, Bi, Ca, Sr, and Ba; or (c) hydroxides and / or oxides having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, wherein the LDH-like compound in (c) is In(OH). ３ It exists in the form of a mixture with

[0042] According to a preferred aspect (a) of the present invention, the LDH-like compound may be a hydroxide and / or oxide having 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. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Mg, Ti, optionally Y, and optionally Al. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferable that the LDH-like compound does not contain Ni. For example, the LDH-like compound may further contain Zn and / or K. This can further improve the ionic conductivity of the LDH separator.

[0043] LDH-like compounds can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface of an LDH separator, peaks attributable to LDH-like compounds are typically detected in the range of 5°≦2θ≦10°, more typically in the range of 7°≦2θ≦10°. As described above, LDHs are formed by stacking hydroxide base layers, with exchangeable anions and H as intermediate layers. ２O is present. In this regard, when LDH is measured by X-ray diffraction, a peak due to the crystalline structure of LDH (i.e., the (003) peak of LDH) is inherently detected at 2θ = 11 to 12°. In contrast, when an LDH-like compound is measured by X-ray diffraction, a peak is typically detected in the above-mentioned range, which is shifted to a lower angle than the peak position of LDH. Furthermore, the interlayer distance of the layered crystalline structure can be determined by the Bragg equation using 2θ corresponding to the peak due to the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystalline structure constituting the LDH-like compound determined in this manner is typically 0.883 to 1.8 nm, more typically 0.883 to 1.3 nm.

[0044] In the LDH separator according to the above aspect (a), the atomic ratio of Mg / (Mg + Ti + Y + Al) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.03 to 0.25, more preferably 0.05 to 0.2. The atomic ratio of Ti / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0.40 to 0.97, more preferably 0.47 to 0.94. The atomic ratio of Y / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.45, more preferably 0 to 0.37. The atomic ratio of Al / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.03. Within the above range, the alkali resistance is more excellent, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and A ｎ－is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratio in the LDH-like compound generally deviates from the general formula of LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDH. Note that EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis in point analysis mode with an interval of about 5 μm, 3) repeating the above 1) and 2) once more, and 4) calculating the average value of a total of six points.

[0045] According to another preferred aspect (b) of the present invention, the LDH-like compound may be a hydroxide and / or oxide having a layered crystal structure containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additional element M. Thus, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Ti, Y, the additional element M, optionally Al, and optionally Mg. The additional element M is In, Bi, Ca, Sr, Ba, or a combination thereof. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferred that the LDH-like compound does not contain Ni.

[0046] In the LDH separator according to the above aspect (b), the atomic ratio of Ti / (Mg+Al+Ti+Y+M) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.50 to 0.85, more preferably 0.56 to 0.81. The atomic ratio of Y / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.20, more preferably 0.07 to 0.15. The atomic ratio of M / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.35, more preferably 0.03 to 0.32. The atomic ratio of Mg / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.10, more preferably 0 to 0.02. The atomic ratio of Al / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.04. Within the above range, the alkali resistance is more excellent, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. Incidentally, LDHs conventionally known for LDH separators have the general formula: M ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and A ｎ－is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratio in the LDH-like compound generally deviates from the general formula of LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDH. Note that EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis in point analysis mode with an interval of about 5 μm, 3) repeating the above 1) and 2) once more, and 4) calculating the average value of a total of six points.

[0047] According to yet another preferred embodiment (c) of the present invention, the LDH-like compound is a hydroxide and / or oxide of a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, and the LDH-like compound is In(OH) ３ The LDH-like compound of this embodiment is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Mg, Ti, Y, optionally Al, and optionally In. Note that the In that can be contained in the LDH-like compound is not only that which is intentionally added to the LDH-like compound, but also In(OH) ３ The above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, but it is preferable that the LDH-like compound does not contain Ni. Incidentally, LDHs conventionally known for LDH separators are represented by the general formula: M ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and A ｎ－is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more. In contrast, the atomic ratios in LDH-like compounds generally deviate from the above general formula of LDH. Therefore, it can be said that the LDH-like compounds in this embodiment generally have composition ratios (atomic ratios) different from those of conventional LDHs.

[0048] The mixture according to the above embodiment (c) contains not only LDH-like compounds but also In(OH) ３ (typically LDH-like compounds and In(OH) ３ It is composed of In(OH) ３ The inclusion of In(OH) in the mixture can effectively improve the alkali resistance and dendrite resistance of the LDH separator. ３ The content of In(OH) is preferably an amount that can improve the alkali resistance and dendrite resistance of the LDH separator without substantially impairing the hydroxide ion conductivity, and is not particularly limited. ３ may have a cubic crystal structure, and In(OH) ３ The crystal may be surrounded by an LDH-like compound. ３ can be identified by X-ray diffraction.

[0049] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0050] Example 1 (1) Preparation of Zinc Secondary Battery A box-shaped case 20 and a plurality of unit cell elements having the following specifications were prepared, and the plurality of unit cell elements were housed vertically in the box-shaped case 20 in the form of a stacked battery, thereby assembling the zinc secondary battery 10 shown in FIG. 1 .

[0051] (Specifications of the box-shaped case) Material: modified polyphenylene ether resin Internal dimensions: width 200 mm, depth 30 mm, height 170 mm Center positions of the positive electrode tab lead 13 and the negative electrode tab lead 15: positions 55 mm away from the inner wall of the short side wall portion 20 c Width of the positive electrode tab lead 13 and the negative electrode tab lead 15: 40 mm Center position of the liquid injection port 22: position 60 mm away from the inner wall of the short side wall portion 20 c (above the negative electrode tab lead 15) Width of the liquid injection port 22: 10 mm Joining method of the liquid injection port 22 and the pressure release valve 24: ultrasonic welding Operating pressure of the pressure release valve 24: 0.20 MPa

[0052] (Specifications of the single cell element) Positive electrode structure: A positive electrode paste containing nickel hydroxide and a binder is filled into the pores of foamed nickel, dried, and covered with nonwoven fabric Negative electrode structure: A negative electrode active material layer containing metallic zinc and zinc oxide powder together with a binder is pressed onto a copper expanded metal, and the resulting structure is covered with nonwoven fabric LDH separator: A separator in which the pores of a porous substrate made of a polymer material (polyethylene) are blocked with LDH and pressed to exhibit hydroxide ion conductivity and gas impermeability Electrolyte: A 5.4 mol% potassium hydroxide aqueous solution

[0053] (2) Evaluation The fabricated zinc secondary battery 10 was subjected to an electrolyte spray evaluation test as follows. Specifically, the zinc secondary battery was stored in a high-temperature environment of 75°C for one month to promote gas generation inside the cell. After the storage period, the zinc secondary battery 10 of Example 1 was visually observed for leaks (damage) at the welded portions of the inlet 22 and the pressure release valve 24, and for the spraying of electrolyte from the pressure release valve 24. The results are shown in Table 1.

[0054] Example 2 (Comparison) Except for changing the positions of the liquid inlet 122 and the pressure release valve 124 to the center of the lid portion 120d, the zinc secondary battery 110 shown in Fig. 8 was assembled in the same manner as in Example 1. Specifically, the center position of the liquid inlet 122 was changed to a position 100 mm away from the inner wall of the short side wall portion (a position where the positive electrode tab lead 113 and the negative electrode tab lead 115 were not present directly below the liquid inlet 122).

[0055] The zinc secondary battery 110 of Example 2 was subjected to an electrolyte spray evaluation test in the same manner as in Example 1. The results are shown in Table 1. For reference, a photograph of the pressure release valve 124 and the electrolyte 118 (in a salt state) sprayed out from the pressure release valve 124 in the nickel-zinc secondary battery of Example 2 after the evaluation test is shown in Figure 11.

[0056]

[0057] 10, 110: zinc secondary battery, 10a: unit cell, 11, 111: electrode laminate, 12: positive electrode plate, 12a: positive electrode active material layer, 12b: positive electrode current collector, 13, 113: positive electrode tab lead, 14: negative electrode plate, 14a: negative electrode active material layer, 14b: negative electrode current collector, 15, 115: negative electrode tab lead, 16: hydroxide ion conductive separator, 17: liquid retaining member, 18, 118: electrolytic Liquid, 20, 120: box-shaped case, 20a: bottom, 20b: long side wall, 20c: short side wall, 20d, 120d: lid, 22, 122: liquid inlet, 24, 124: pressure relief valve, 26: positive electrode terminal, 28: negative electrode terminal, 30: positive electrode tab joint, 32: negative electrode tab joint, 34: insulating tape, E, E': imaginary extension line, L: leak portion, U: uncoated area, W: welded joint

Claims

1. A zinc secondary battery comprising: an electrode stack; a box-shaped case in which the electrode stack is housed in a vertical orientation; and an electrolyte in which the electrode stack is immersed, wherein the electrode stack comprises: a positive electrode plate including a positive electrode active material layer and a positive electrode current collector; a positive electrode tab lead extending upward from an end of the positive electrode plate; 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 negative electrode tab lead extending upward from the end of the negative electrode plate at a position not overlapping with the positive electrode tab lead; and a hydroxide ion conductive separator separating the positive electrode plate and the negative electrode plate so as to be conductive with hydroxide ions, wherein the box-shaped case has a bottom, a pair of long side walls parallel to the electrode stack, a pair of short side walls perpendicular to the electrode stack, and a lid, a zinc secondary battery in which the lid portion is provided with a liquid filling port through which the electrolyte can be poured into the box-shaped case, and a pressure release valve is joined to the liquid filling port so that gas can be released when the internal pressure of the box-shaped case increases, and when the zinc secondary battery is viewed in a plan view from a direction perpendicular to the longitudinal side wall portion, the liquid filling port is located in a part other than the center of the lid portion and is located above the positive electrode tab lead or the negative electrode tab lead.

2. The zinc secondary battery according to claim 1, wherein, when the zinc secondary battery is viewed in a plan view from a direction perpendicular to the longitudinal side wall portions, the left and right ends of the liquid filling port are located between an imaginary extension line formed by extending upward from the left end of the positive electrode tab lead and an imaginary extension line formed by extending upward from the right end of the positive electrode tab lead, or between an imaginary extension line formed by extending upward from the left end of the negative electrode tab lead and an imaginary extension line formed by extending upward from the right end of the negative electrode tab lead.

3. A zinc secondary battery according to claim 1 or 2, wherein the positive electrode tab lead or the negative electrode tab lead is arranged so as to cover at least a portion of the upper end of the electrode laminate, and the upper end covered by the positive electrode tab lead or the negative electrode tab lead is located below the liquid filling port.

4. The zinc secondary battery according to claim 1 or 2, wherein the box-shaped case is made of resin.

5. A zinc secondary battery according to claim 1 or 2, wherein the positive electrode plate and / or the negative electrode plate is covered or enveloped in the hydroxide ion conductive separator.

6. The zinc secondary battery according to claim 1 or 2, wherein the hydroxide ion-conducting separator is an LDH separator containing a layered double hydroxide (LDH) and / or an LDH-like compound.

7. A zinc secondary battery as described in 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 it is filled in the pores of the porous substrate.

8. A zinc secondary battery according to claim 1 or 2, 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.

9. A zinc secondary battery according to claim 1 or 2, wherein the positive electrode active material layer is an air electrode layer, thereby making the zinc secondary battery an air-zinc secondary battery.

10. A zinc secondary battery according to claim 1 or 2, comprising a plurality of unit cells each having a pair of said positive and negative electrode plates together with said hydroxide ion conductive separator, whereby the plurality of unit cells as a whole form a multi-layer cell.

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