Alkaline secondary battery

Abstract

To provide an alkaline secondary battery capable of applying a pressure uniformly in a case where the alkaline secondary battery is made into a module battery.SOLUTION: An alkaline secondary battery comprises: a multilayer battery configured by laminating a plurality of single battery elements each having a configuration of the alkaline secondary battery; and a resin box-shaped case in which the multilayer battery is stored in a longitudinal direction. The box-shaped case includes a bottom, a pair of length-side walls, a pair of width-side walls, and a lid abutted with the length-side walls and the width-side walls. The length-side wall includes: a thick part which constitutes a main portion of the length-side wall and includes a flat outer surface where no rib is included; and a thin part which extends upward from an upper end of the thick part and thinner than the thick part. Thus, the thick part and the thin part form a step such that an outer surface of the thin part is positioned closer to an inner periphery of the box-shaped case than the outer surface of the thick part. A lower end of the lid and an upper end of the thin part are joined by deposition, and a resin protrusion which protrudes from a joint portion by the deposition has a protrusion height equal to or lower than the step.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to alkaline secondary batteries. [Background technology]

[0002] Stacked batteries made by combining multiple unit cells are widely used to obtain high voltages and large currents. A stacked battery has a configuration in which a stack of multiple unit cells connected in series or parallel is housed in a single battery container. For example, Patent Document 1 (WO2017 / 086278) discloses a zinc secondary battery in which multiple electrode cartridges equipped with electrodes and separators (particularly the LDH separator described below) are housed in a sealed container.

[0003] Furthermore, in order to achieve even greater capacity and power output, it is common practice to arrange a plurality of battery units each incorporating a stacked battery to form a battery module. For example, Patent Document 2 (WO2018 / 173110) discloses a battery module in which a plurality of rectangular parallelepiped battery units are housed within a frame structure, and it is described as being preferable that the battery unit house a plurality of alkaline secondary battery cells (e.g., nickel-zinc secondary batteries and zinc-air secondary batteries) in the form of a battery pack or battery module.

[0004] Furthermore, in battery units that include stacked batteries such as nickel-zinc batteries in a case, and in battery modules that include such units, pressure is applied from the outside of the case to maximize battery performance. For example, Patent Document 3 (JP 2020-095955 A) describes how, in alkaline secondary batteries, providing multiple ribs on the flat outer surface of the long side wall of a box-shaped case ensures excellent heat dissipation when the battery module is made into a battery module while maintaining a shape that is suitable for applying pressure.

[0005] 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 have been proposed that include a layered double hydroxide (LDH) separator, which selectively allows hydroxide ions to pass through while preventing the penetration of zinc dendrites. For example, Patent Document 4 (WO 2013 / 118561) discloses a nickel-zinc secondary battery in which an LDH separator is provided between the positive and negative electrodes. Patent Document 5 (WO 2016 / 076047) also discloses a separator structure including an LDH separator fitted or bonded to a resin outer frame, and discloses that the LDH separator has such high density that it is gas- and / or water-impermeable. This document also discloses that an LDH separator can be composited with a porous substrate. Furthermore, Patent Document 6 (WO2016 / 067884) discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to obtain a composite material (LDH separator). This method includes a step of uniformly attaching an initiator substance capable of providing initiation points for LDH crystal growth to the 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. Furthermore, Patent Document 7 (WO2019 / 069762) discloses a method for efficiently producing a negative electrode structure suitable for zinc secondary batteries (especially stacked batteries) that can prevent zinc dendrite extension by covering or enveloping the entire negative electrode active material layer with a liquid-retaining member and an LDH separator.

[0006] Additionally, although not specifically classifiable as 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-conducting layered compounds. For example, Patent Document 8 (WO 2020 / 255856) discloses a hydroxide ion-conducting separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate, where the LDH-like compound is a layered crystal structure hydroxide and / or oxide containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al. This hydroxide ion-conducting 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. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] WO2017 / 086278 [Patent Document 2] WO2018 / 173110 [Patent Document 3] Japanese Patent Publication No. 2020-095955 [Patent Document 4] WO2013 / 118561 [Patent Document 5] WO2016 / 076047 [Patent Document 6] WO2016 / 067884 [Patent Document 7] WO2019 / 069762 [Patent Document 8] WO2020 / 255856 Summary of the Invention

[0008] While alkaline secondary batteries having multiple ribs on the long side walls of a box-shaped case, as disclosed in Patent Document 3, have excellent heat dissipation properties, a case without ribs is preferable from the perspective of uniformly distributing pressure on the battery unit. An example of a box-shaped case 120 without ribs is shown in FIGS. 9 and 10. The box-shaped case 120 has a bottom 120a, a pair of long side walls 120b with flat outer surfaces, a pair of short side walls 120c, and a lid 120d. Furthermore, the lower end of the lid 120d and the upper end of the long side wall 120b are joined by welding, resulting in the presence of a resin protrusion P that protrudes from the joint.

[0009] However, when multiple alkaline secondary batteries 110 using box-shaped cases 120 without ribs are arranged and pressurized, as shown in Figure 11, the resin protrusions P of adjacent alkaline secondary batteries 110 may interfere with each other, resulting in uneven pressure being applied to the alkaline secondary batteries 110.

[0010] The present inventors have now discovered that by providing a thick portion with a flat outer surface and a thin portion that is thinner than the thick portion so as to form a predetermined step on the longitudinal side wall portion of a box-shaped case, it is possible to provide an alkaline secondary battery that can be subjected to uniform pressure when made into a module battery.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an alkaline secondary battery that can be subjected to uniform pressure when assembled into a battery module.

[0012] According to the present disclosure, the following aspects are provided. [Aspect 1] a stacked battery in which a plurality of unit cell elements each having the configuration of an alkaline secondary battery are stacked; a resin box-shaped case in which the stacked battery is housed in a vertical orientation; An alkaline secondary battery comprising: the box-shaped case has a bottom, a pair of long side walls parallel to the battery stack, a pair of short side walls perpendicular to the battery stack, and a lid abutting the long side walls and the short side walls; the longitudinal side wall portion has a thick portion constituting a major portion of the longitudinal side wall portion and having a flat outer surface with no ribs, and a thin portion extending upward from an upper end of the thick portion and thinner than the thick portion, whereby the thick portion and the thin portion form a step such that the outer surface of the thin portion is located closer to the inner periphery of the box-shaped case than the outer surface of the thick portion; An alkaline secondary battery in which the lower end of the lid portion and the upper end of the thin portion are joined by welding, and a resin protrusion that protrudes from the joint by welding has a protrusion height that is the same as or smaller than the step. [Aspect 2] 2. The alkaline secondary battery of claim 1, wherein the protrusion height is 0.6 mm or less. [Aspect 3] 3. The alkaline secondary battery according to aspect 1 or 2, wherein the step between the thick portion and the thin portion on the longitudinal side wall has a height difference of 0.6 to 1.0 mm. [Aspect 4] 4. The alkaline secondary battery according to any one of aspects 1 to 3, wherein, in a plan view of the longitudinal side wall portion, the area ratio of the thick portion to the total area of ​​the thick portion and the thin portion is 90% or more. [Aspect 5] 5. The alkaline secondary battery according to any one of Aspects 1 to 4, wherein, when the box-shaped case is viewed from above, the outer periphery of the lid portion coincides with the outer periphery of the top end of the box-shaped case or is located inside the outer periphery of the top end of the box-shaped case. [Aspect 6] 6. The alkaline secondary battery according to any one of aspects 1 to 5, wherein the alkaline secondary battery is a zinc secondary battery. [Aspect 7] The cell element is a positive electrode plate including a positive electrode active material layer; 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; an LDH separator containing a layered double hydroxide (LDH) and / or an LDH-like compound; An electrolyte; The alkaline secondary battery of any one of Aspects 1 to 6, wherein the positive electrode active material layer and the negative electrode active material layer are isolated from each other via the LDH separator. [Aspect 8] An alkaline secondary battery module including a plurality of alkaline secondary batteries according to any one of aspects 1 to 7, the alkaline secondary battery module, wherein the plurality of alkaline secondary batteries are arranged so that the longitudinal side wall portions face each other and the thick portions abut each other. [Aspect 9] 9. The alkaline secondary battery module of claim 8, wherein a pressing means is provided on the outside of the battery module to pressurize the longitudinal side wall portion in a thickness direction, whereby the box-shaped case is pressed by the pressing means and bends, thereby pressing the single cell element. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic cross-sectional view showing an example of an alkaline secondary battery of the present invention. [Figure 2] FIG. 2 is a diagram schematically showing a cross section of the alkaline secondary battery shown in FIG. 1 taken along line AA'. [Figure 3] FIG. 2 is a perspective view showing an example of a box-shaped case in the alkaline secondary battery shown in FIG. [Figure 4] 4 is a side view of the lid welded to the long side wall of the box-shaped case shown in FIG. 3 and its surrounding area, as viewed from the short side wall side. FIG. [Figure 5] FIG. 2 is a perspective view schematically showing a stacked battery that constitutes the alkaline secondary battery shown in FIG. [Figure 6] FIG. 2 is a cross-sectional view schematically showing a stacked battery that constitutes the alkaline secondary battery shown in FIG. [Figure 7] FIG. 2 is a perspective view showing an example of a positive electrode plate or a negative electrode plate in the alkaline secondary battery shown in FIG. [Figure 8] FIG. 8 is a perspective view showing the positive electrode plate or the negative electrode plate shown in FIG. 7 covered with a hydroxide ion conductive separator or a liquid-retaining member. [Figure 9]FIG. 1 is a perspective view showing an example of a conventional box-shaped case without steps. [Figure 10] 11 is a side view of the lid welded to the long side wall of the box-shaped case shown in FIG. 10 and its surrounding area, as viewed from the short side wall side. FIG. [Figure 11] 11 is a flow chart showing an example of constructing a module battery using the box-shaped case shown in FIG. 10. DETAILED DESCRIPTION OF THE INVENTION

[0014] alkaline secondary battery 1 and 2 show an example of an alkaline secondary battery of the present invention. The alkaline secondary battery 10 shown in FIGS. 1 and 2 includes a stacked battery 11 and a resin box-shaped case 20 in which the stacked battery 11 is housed in a vertical orientation. As shown in FIG. 6, the stacked battery 11 is formed by stacking a plurality of unit cell elements 10a having the configuration of an alkaline secondary battery, and is advantageous in that it can obtain a high voltage and a large current. The box-shaped case 20 has a bottom 20a, a pair of long side walls 20b parallel to the stacked battery 11, a pair of short side walls 20c perpendicular to the stacked battery 11, and a lid 20d abutting the long side walls 20b and the short side walls 20c. As shown in FIG. 3, the long side walls 20b have a thick portion T A and thin-walled section T B Thick section T A The thin-walled portion T forms the main portion of the longitudinal side wall portion 20b and has a flat outer surface without ribs. B is the thick part T A A thick portion T extending upward from the upper end of A As shown in Figure 4, the thick part T A and thin-walled section T B is the thin-walled part T B The outer surface of the thick part T A The box-shaped case 20 has a step S formed therebetween, which is located closer to the inner periphery of the box-shaped case 20 than the outer surface of the cover 20d. BThe upper ends of the resin protrusions P are welded together, and the resin protrusions P protrude from the welded joints. The resin protrusions P have a protruding height equal to or lower than the step S. In this way, the thick-walled portions T having flat outer surfaces are formed on the long side wall portions 20b of the box-shaped case so as to form the predetermined step S. A and thick part T A Thinner part T B By providing the above, it is possible to provide an alkaline secondary battery 10 that can apply pressure uniformly when assembled into a module battery.

[0015] As mentioned above, it is desirable to apply pressure from outside a battery unit containing stacked batteries such as nickel-zinc batteries inside the case to maximize battery performance. To achieve this, it is desirable for the side surfaces of the case to be as flat as possible so that pressure can be applied to each battery unit when multiple battery units are arranged and modularized. Therefore, from the perspective of applying pressure evenly to the battery units, a box-type case without ribs is preferable to a box-type case with multiple ribs. An example of such a case without ribs is the box-type case 120 shown in FIGS. 9 and 10 . As shown in FIG. 10 , the bottom end of the lid portion 120d and the top end of the longitudinal side wall portion 120b are welded together, resulting in the presence of a resin protrusion P that protrudes from the joint. Specifically, when the lid portion 120d and the longitudinal side wall portion 120b are welded together, molten resin is forced outward, creating a protrusion that protrudes from the flat surface of the longitudinal side wall portion 120b. Because the resin protrusions P are located on the outermost side of the box-shaped case 120, when alkaline secondary batteries 110 using the box-shaped case 120 are lined up and pressurized, the resin protrusions P of adjacent alkaline secondary batteries 110 will interfere with each other, as shown in Fig. 11. In other words, unintended gaps or the like will occur between the batteries, which can cause uneven pressure to be applied to the alkaline secondary batteries 110.

[0016] In contrast, in the alkaline secondary battery 10 of the present invention, as shown in FIG. 4, the long side wall portion 20b is formed with the thick portion T so as to form the step S. Aand thin-walled section T B Therefore, when a plurality of alkaline secondary batteries 10 are arranged with their long side wall portions 20b facing each other, the resin protrusion portion P is within the range of the height difference of the step S. A The flat outer surfaces of the box-shaped case 20 can be tightly attached to each other. In this way, the influence of the resin protrusions P that accompany the welding of the box-shaped case 20 is eliminated, and pressure can be applied uniformly to the alkaline secondary battery 10.

[0017] Therefore, according to a preferred embodiment of the present invention, there is provided an alkaline secondary battery module (not shown) including a plurality of alkaline secondary batteries 10. In this embodiment, the plurality of alkaline secondary batteries are arranged such that the long side wall portions 20b face each other and the thick portion T A Preferably, a pressing means (not shown) is provided on the outside of the alkaline secondary battery module to pressurize the longitudinal side wall portions 20b in the thickness direction, and the box-shaped case 20 is pressed by the pressing means and bends, thereby pressing the single cell elements 10a.

[0018] The box-shaped case 20 is 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. Furthermore, 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.

[0019] As shown in FIGS. 1 to 4, the box-shaped case 20 has a bottom 20a, a pair of long side walls 20b parallel to the battery stack 11, a pair of short side walls 20c perpendicular to the battery stack 11, and a lid 20d. In the box-shaped case 20, the case body (bottom and side walls) and the lid are joined by welding (e.g., thermal welding). The battery stack 11 is formed by stacking a plurality of cell elements 10a, as shown in FIG. 6, i.e., an assembly of a plurality of cell elements 10a. The box-shaped case 20 typically has a basic rectangular parallelepiped shape, but it does not need to be a perfect rectangular parallelepiped. As long as the overall shape is box-shaped, it may have partially curved surfaces or unevenness. The box-shaped case 20 (e.g., the lid 20d) may also have a liquid inlet for injecting electrolyte into the case, a pressure relief valve for releasing gas, and the like.

[0020] As shown in FIG. 3, the pair of longitudinal side wall portions 20b are thick portions T A and thin-walled section T B Thick section T A The thick portions T form the main portions of the longitudinal sidewall portions 20b and have flat outer surfaces without ribs. Therefore, when a plurality of alkaline secondary batteries 10 are assembled into a module battery, the thick portions T of the adjacent alkaline secondary batteries 10 are A When the long side wall portion 20b is viewed from above, the thick portion T A and thin-walled section T B The thick part T A The area ratio of the thick portion T is preferably 90% or more, and more preferably 90 to 95%. By doing so, when a battery module is formed, the contact area between adjacent batteries increases, allowing the alkaline secondary batteries 10 to be more stably arranged and pressurized. A and thin-walled section T B The method for forming the case body 20 is not particularly limited, and the case body 20 can be preferably manufactured, for example, by injection molding using a mold with a step in the side wall portion. From the viewpoint of ease of manufacturing and avoiding resin protrusion onto the long side wall portions 20b, the pair of short side wall portions 20c may also have thick and thin portions that fit the long side wall portions 20b.

[0021] Thin portion T of the longitudinal side wall portion 20b B is the thick part T A A thick portion T extending upward from the upper end of A The thin-walled portion T is a portion having a thickness thinner than B The upper end of the thin-walled portion T is welded to the lower end of the lid portion 20d, thereby joining the case body and the lid portion 20d. B By providing the thin-walled section T B The outer surface of the thick part T A As described above, the step S prevents the resin protrusion P from being in contact with the thick-walled portion T. A The thin-walled portion T can be prevented from protruding outside the outer surface of the box-shaped case 20 (toward the outer periphery of the box-shaped case 20). B Also, thick part T A Similarly, it may have a flat outer surface without ribs.

[0022] Thick portion T in the longitudinal side wall portion 20b A and thin-walled section T B The difference in height S between the resin protrusions P and the box-shaped case 20 is equal to or greater than the protrusion height of the resin protrusions P, and is preferably 0.6 to 1.0 mm, more preferably 0.6 to 0.9 mm, and even more preferably 0.6 to 0.8 mm. This eliminates the influence of the resin protrusions P that accompanies welding of the box-shaped case 20, and allows pressure to be applied uniformly to the alkaline secondary battery 10.

[0023] The resin protrusion P is formed between the lower end of the lid portion 20d and the thin portion T B Therefore, the resin protrusion P is typically made of the same type of resin as the resin that constitutes the box-shaped case 20. The protrusion height of the resin protrusion P (i.e., the thickness of the thin-walled portion T BThe height of the resin protrusions P (the height of the resin protrusions P that protrudes furthest from the outer surface of the battery) is preferably 0.6 mm or less, more preferably 0.5 mm or less, and even more preferably 0.4 mm or less. Such a low protrusion height makes it even less likely for interference between the resin protrusions P to occur when the battery module is assembled. The lower the protrusion height of the resin protrusions P, the more preferable it is, and the lower limit is not particularly limited, but is, for example, 0.2 mm or more. Note that the resin portion that protrudes from the joint during welding typically has a protrusion height that exceeds the aforementioned upper limit (for example, 1.0 mm or more). In this regard, the protrusion height of the resin protrusions P can be controlled within a predetermined range by, for example, pressing a hot plate against the resin that protrudes from the joint to smooth it out.

[0024] When the box-shaped case 20 is viewed from above, it is preferable that the outer periphery of the lid portion 20d coincides with the outer periphery of the upper end of the box-shaped case 20 (particularly the long side wall portion 20b). Alternatively, it is preferable that the outer periphery of the lid portion 20d is located inside the outer periphery of the upper end of the box-shaped case 20 (particularly the long side wall portion 20b). By doing so, when a module battery is formed, the lid portions 20d of adjacent alkaline secondary batteries 10 do not interfere with each other, and pressure can be applied more uniformly to the cell elements 10a. However, the outer periphery of the lid portion 20d may also be located outside the outer periphery of the upper end of the box-shaped case 20. In this case, from the viewpoint of suppressing interference between the lid portions 20d when a module battery is formed, it is preferable that the outer periphery of the lid portion 20d is located outside the thick-walled portion T of the long side wall portion 20b. A It is preferable that the contact hole 24 is located closer to the inner periphery of the box-shaped case 20 than the outer surface of the contact hole 24.

[0025] The alkaline secondary battery 10 is not particularly limited as long as it is a secondary battery that uses an alkaline electrolyte (typically, an aqueous alkali metal hydroxide solution), but is preferably a zinc secondary battery that uses zinc as the negative electrode. Therefore, it may be a nickel-zinc secondary battery, a silver-zinc oxide secondary battery, a manganese-zinc oxide secondary battery, or any other type of alkaline zinc secondary battery. For example, it is preferable that the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery.

[0026] The alkaline secondary battery 10, when it is a zinc secondary battery, will be described below with reference to FIGS. 5 to 8. The alkaline secondary battery 10 (i.e., zinc secondary battery) shown in FIGS. 5 to 8 includes a cell element 10a, which includes a positive electrode plate 12, a negative electrode plate 14, a layered double hydroxide (LDH) separator 16, and an electrolyte (not shown). The positive electrode plate 12 includes a positive electrode active material layer 12a and, optionally, a positive electrode current collector 12b. The negative electrode plate 14 includes a negative electrode active material layer 14a and, optionally, a negative electrode current collector 14b, and 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 positive electrode active material layer 12a and the negative electrode active material layer 14a are separated from each other by the LDH separator 16. For example, the LDH separator 16 preferably covers or encases the entire negative electrode active material layer 14a. In this specification, an "LDH separator" is defined as a separator containing LDH and / or an LDH-like compound, which selectively passes hydroxide ions by utilizing the hydroxide ion conductivity of the LDH and / or the LDH-like compound. In this specification, an "LDH-like compound" refers to a hydroxide and / or oxide having a layered crystal structure similar to LDH, which may not be called an LDH, and can be considered an equivalent of LDH. However, in a broad sense, "LDH" can be interpreted as including not only LDH but also LDH-like compounds. Typically, the positive electrode active material layer 12a, the negative electrode active material layer 14a, and the LDH separator 16 each have a quadrilateral shape (typically, a square shape).

[0027] Preferably, the alkaline secondary battery 10 further includes a positive electrode tab lead 13 extending upward from the end of the positive electrode plate 12, and a negative electrode tab lead 15 extending upward from the end of the negative electrode plate 14 at a position not overlapping with the positive electrode tab lead 13. As shown in Fig. 1, the alkaline secondary battery 10 further includes a positive electrode terminal 22 and a negative electrode terminal 24, and it is preferable that the positive electrode terminal 22 and the negative electrode terminal 24 extend from the lid portion 20d.

[0028] 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 of absorbing 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.

[0029] The positive electrode plate 12 preferably 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 by, for example, uniformly applying a paste containing an electrode active material such as nickel hydroxide onto the nickel porous substrate and drying it. In this case, it is also preferred 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.

[0030] 7, 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 18 is attached to the uncoated region U so that the welded portion W is covered with the insulating tape 18. This makes it difficult for the tip of the positive electrode tab lead 13 to penetrate the LDH separator 16 or the liquid retention member 17, and even if the tip penetrates them and comes into contact with the positive electrode plate 12, the insulating tape 18 functions as an insulator, making it difficult for a short circuit to occur.

[0031] The positive electrode tab lead 13 is preferably provided so as to extend from the 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. 6 , it is preferable that a plurality of positive electrode tab leads 13 are joined to one positive electrode terminal 22 or a member electrically connected thereto to form a positive electrode tab joint 26. This allows for space-efficient current collection with a simple configuration and facilitates connection to the positive electrode terminal 22. The positive electrode tab lead 13 may be joined to members such as the positive electrode current collector 12b and the positive electrode terminal 22 using a known joining method such as ultrasonic welding (ultrasonic welding), laser welding, TIG welding, or resistance welding.

[0032] 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 mixture. 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.

[0033] The zinc alloy can be a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy. For example, a zinc alloy containing 0.01 to 0.1 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is preferred because it suppresses hydrogen gas generation. In particular, indium and bismuth are advantageous in improving discharge performance. The use of a zinc alloy for the negative electrode can improve safety by slowing the rate of self-dissolution in alkaline electrolyte, thereby suppressing hydrogen gas generation.

[0034] The shape of the negative electrode material is not particularly limited, but it 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.

[0035] The negative electrode plate 14 preferably 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 are copper expanded metal, copper punched metal, and combinations thereof. Copper expanded metal is 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. At this time, 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 made by expanding a metal plate while making staggered cuts using an expander, and then shaping the cuts into a diamond or tortoiseshell shape. Punching metal is also called perforated metal, and is made by punching holes into a metal plate. Metal mesh is a metal product with a wire mesh structure and is different from expanded metal and punched metal.

[0036] 7, 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 18 is attached to the uncoated region U so that the welded portion W is covered with the insulating tape 18. This makes it difficult for the tip of the negative electrode tab lead 15 to penetrate the LDH 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 18 functions as an insulator, making it difficult for a short circuit to occur.

[0037] The negative electrode tab lead 15 is preferably 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. 5 ). The negative electrode tab lead 15 is not particularly limited and may be a commercially available metal foil. As shown in FIG. 6 , it is preferable that a plurality of negative electrode tab leads 15 are joined to one negative electrode terminal 24 or a member electrically connected thereto to form a negative electrode tab joint 28. This allows for space-efficient current collection with a simple configuration and facilitates connection to the negative electrode terminal 24. The joining of the negative electrode tab lead 15 to members such as the negative electrode current collector 14b and the negative electrode terminal 24 may be performed using a known joining method such as ultrasonic welding (ultrasonic welding), laser welding, TIG welding, or resistance welding.

[0038] The LDH separator 16 is provided to separate the positive electrode active material layer 12a and the negative electrode active material layer 14a in a manner that allows hydroxide ion conductivity. For example, as shown in FIGS. 6 and 8, 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 LDH separator 16. This eliminates the need for a complicated sealing joint between the LDH 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 LDH separator 16 is disposed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used.

[0039] As described above, the LDH separator 16 contains LDH and / or an LDH-like compound. The LDH separator 16 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 LDH and / or LDH-like compound fills the pores of the porous substrate. That is, in a preferred LDH separator 16, the pores of the porous substrate are filled with the LDH and / or LDH-like compound 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 polymeric material, and it is particularly preferred that the LDH and / or LDH-like compound be incorporated throughout the entire thickness of the porous substrate made of a polymeric material. 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.

[0040] It is preferable that not only the LDH separator 16 but also a liquid-retaining member 17 be interposed between the positive electrode plate 12 and the negative electrode plate 14. As shown in FIGS. 6 and 8 , it is preferable that the positive electrode plate 12 and / or the negative electrode plate 14 be covered or wrapped with the liquid-retaining member 17. Alternatively, 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 be used. In any case, the interposition of the liquid-retaining member 17 allows the electrolyte to be evenly distributed between the positive electrode plate 12 / negative electrode plate 14 and the LDH separator 16, thereby enabling efficient exchange of hydroxide ions between the positive electrode plate 12 / negative electrode plate 14 and the LDH separator 16. The liquid-retaining 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.

[0041] 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 LDH separator 16, it is preferable that their outer edges are closed (except for the edges from which the positive electrode tab lead 13 and the negative electrode tab lead 15 extend). In this case, it is preferable that the closed edge of the outer edge of the liquid retention member 17 and / or the LDH separator 16 is realized by folding the liquid retention member 17 and / or the LDH separator 16, or by sealing the liquid retention members 17 together and / or the LDH separators 16 together. Preferred examples of sealing methods include adhesives, heat welding, ultrasonic welding, adhesive tape, sealing tape, and combinations thereof. In particular, an LDH separator including a porous substrate made of a polymer material has 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 allows for 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 commercially available epoxy resin-based adhesive is the epoxy adhesive Hysol® (manufactured by Henkel).

[0042] The outer edge of one side of the LDH separator 16, which is the upper end, is preferably open. This open-top configuration can address the problem of overcharging in nickel-zinc batteries and the like. Specifically, when a nickel-zinc battery or the like is overcharged, oxygen (O2) can be generated at the positive electrode plate 12. However, the LDH separator has a high density that allows only hydroxide ions to pass through, preventing O2 from passing through. In this regard, the open-top configuration allows O2 to escape above the positive electrode plate 12 and be transported to the negative electrode plate 14 through the open-top portion within the box-shaped case 20. This allows O2 to oxidize the Zn in the negative electrode active material back to ZnO. By undergoing this oxygen reaction cycle, the open-top stacked battery 11 can be used in a sealed zinc secondary battery to improve overcharge resistance. Even if the outer edge of one side of the LDH separator 16 or the liquid-retaining member 17, which is the upper end, is closed, providing a vent hole in part of the closed outer edge can be expected to achieve the same effect as the open-top configuration. For example, the vent hole may be opened after sealing the outer edge of one side that will be the upper end of the LDH separator, or during sealing, part of the outer edge may be left unsealed so that the vent hole is formed.

[0043] The electrolyte preferably contains an aqueous solution of alkali metal hydroxide. The electrolyte is not shown because it is distributed throughout the positive electrode plate 12 (particularly the positive electrode active material layer 12a) and the negative electrode plate 14 (particularly the negative electrode active material layer 14a). Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being preferred. To suppress the self-dissolution of zinc and / or zinc oxide, a zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte. As mentioned above, the electrolyte may be mixed with the positive electrode active material and / or the negative electrode active material to form a positive electrode composite and / or a negative electrode composite. The electrolyte may also be gelled to prevent leakage of the electrolyte. A polymer that absorbs the solvent in the electrolyte and swells is preferably used as the gelling agent. Examples of suitable gelling agents include polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, as well as starch. [Explanation of symbols]

[0044] 10,110 alkaline secondary battery 10a cell element 11 Stacked battery 12 Positive electrode plate 12a Cathode active material layer 12b Positive electrode current collector 13 Positive electrode tab lead 14 Negative plate 14a Negative electrode active material layer 14b Negative electrode current collector 15 Negative electrode tab lead 16 LDH separator 17 Liquid-retaining material 18 Electrical tape 20,120 Box case 20a,120a bottom 20b, 120b Longitudinal side wall 20c,120c Short side wall 20d,120c Lid 22 Positive terminal 24 Negative terminal 26 Positive electrode tab joint 28 Negative electrode tab joint P Resin protrusion S step T A Thick part T B Thin-walled section U Uncoated area W Welded joint

Claims

1. a stacked battery in which a plurality of unit cell elements each having the configuration of an alkaline secondary battery are stacked; a resin box-shaped case in which the stacked battery is housed in a vertical orientation; An alkaline secondary battery comprising: the box-shaped case has a bottom, a pair of long side walls parallel to the battery stack, a pair of short side walls perpendicular to the battery stack, and a lid abutting the long side walls and the short side walls; the longitudinal side wall portion has a thick portion constituting a major portion of the longitudinal side wall portion and having a flat outer surface with no ribs, and a thin portion extending upward from an upper end of the thick portion and thinner than the thick portion, whereby the thick portion and the thin portion form a step such that the outer surface of the thin portion is located closer to the inner periphery of the box-shaped case than the outer surface of the thick portion; An alkaline secondary battery in which the lower end of the lid portion and the upper end of the thin portion are joined by welding, and a resin protrusion that protrudes from the joint by welding has a protrusion height that is the same as or smaller than the step.

2. 2. The alkaline secondary battery according to claim 1, wherein the protrusion height is 0.6 mm or less.

3. 3. The alkaline secondary battery according to claim 1, wherein the step between the thick portion and the thin portion on the longitudinal side wall has a height difference of 0.6 to 1.0 mm.

4. 3. The alkaline secondary battery according to claim 1, wherein, in a plan view of the longitudinal side wall portion, an area ratio of the thick portion to a total area of ​​the thick portion and the thin portion is 90% or more.

5. 3. The alkaline secondary battery according to claim 1, wherein, when the box-shaped case is viewed from above, the outer periphery of the lid portion coincides with the outer periphery of the upper end of the box-shaped case or is located inside the outer periphery of the upper end of the box-shaped case.

6. 3. The alkaline secondary battery according to claim 1, wherein the alkaline secondary battery is a zinc secondary battery.

7. The cell element is a positive electrode plate including a positive electrode active material layer; 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; an LDH separator comprising a layered double hydroxide (LDH) and / or an LDH-like compound; An electrolyte; 3. The alkaline secondary battery according to claim 1, wherein the positive electrode active material layer and the negative electrode active material layer are separated from each other by the LDH separator.

8. An alkaline secondary battery module comprising a plurality of alkaline secondary batteries according to claim 1 or 2, the alkaline secondary battery module, wherein the plurality of alkaline secondary batteries are arranged so that the longitudinal side wall portions face each other and the thick portions abut each other.

9. 9. The alkaline secondary battery module according to claim 8, wherein a pressing means is provided on the outside of the battery module to pressurize the longitudinal side wall portions in a thickness direction, whereby the box-shaped case is pressed by the pressing means and bends, thereby pressing the single battery elements.

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