Zinc secondary battery

Abstract

Provided is a zinc secondary battery in which a short circuit caused by a defect at a lower end sealing portion of a bag-like hydroxide ion conductive separator hardly occurs. This zinc secondary battery comprises: a positive electrode plate including a positive electrode active material layer; a negative electrode plate that includes a negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds; a hydroxide ion conductive separator that has a bag-like shape for accommodating the negative electrode plate and that separates the positive electrode plate and the negative electrode plate such that hydroxide ions can pass therethrough; an electrolytic solution; and a battery case that vertically accommodates the positive electrode plate, the negative electrode plate, and the hydroxide ion conductive separator. The negative electrode active material layer extends to a position lower than the lower end of the positive electrode active material layer. The height of a portion from the lower end of the negative electrode active material layer to the bottom surface of the battery case is 2.0-8.0 mm. The difference in height between the lower end of the positive electrode active material layer and the lower end of the negative electrode active material layer is 3.0-4.0 mm.

Description

Technical Field

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

Background Art

[0002] In zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc is deposited in a dendrite shape from the negative electrode during charging, penetrates through the voids of a separator such as a nonwoven fabric, and reaches the positive electrode. As a result, it is known that a short circuit is caused. Such a short circuit caused by zinc dendrites leads to a shortening of the repeated charge-discharge life.

[0003] In order to address the above problems, a battery equipped with a layered double hydroxide (LDH) separator that prevents the penetration of zinc dendrites while selectively permeating hydroxide ions has been proposed. For example, Patent Document 1 (WO2013 / 118561) discloses providing an LDH separator between the positive electrode and the negative electrode in a nickel-zinc secondary battery. Further, Patent Document 2 (WO2016 / 076047) discloses a separator structure including an LDH separator fitted or joined to a resin outer frame, and discloses that the LDH separator has a high density such that it is gas-impermeable and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Furthermore, Patent Document 3 (WO2016 / 067884) discloses various methods for obtaining a composite material by forming an LDH dense film on the surface of a porous substrate. This method includes a step of uniformly adhering a starting material that can give a starting point for crystal growth of LDH to the porous substrate and subjecting the porous substrate to hydrothermal treatment in an aqueous raw material solution to form an LDH dense film on the surface of the porous substrate. An LDH separator that achieves further densification by roll-pressing a composite material of LDH / porous substrate produced through hydrothermal treatment has also been proposed. For example, Patent Document 4 (WO2019 / 124270) discloses an LDH separator including a polymer porous substrate and LDH filled in the porous substrate, having a linear transmittance of 1% or more at a wavelength of 1000 nm.

[0004] In addition, LDH-like compounds are known as hydroxides and / or oxides having a layered crystal structure similar to but not called LDH, and exhibit hydroxide ion conduction characteristics similar enough to be collectively referred to as hydroxide ion conducting layered compounds together with LDH. For example, Patent Document 5 (WO2020 / 255856) discloses a hydroxide ion conducting separator including 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 having a layered crystal structure containing Mg and at least one element selected from the group consisting of Ti, Y, and Al and including at least Ti. This hydroxide ion conducting separator is said to be superior in alkali resistance to conventional LDH separators and to be able to more effectively suppress short circuits caused by zinc dendrites.

[0005] By the way, Patent Documents 6 (WO2019 / 069760) and 7 (WO2019 / 077953) propose a zinc secondary battery configured to cover or enclose the entire negative electrode active material layer with a liquid retention member and an LDH separator and to cover or enclose the positive electrode active material layer with the liquid retention member. A non-woven fabric is used as the liquid retention member. According to such a configuration, it is said that a zinc secondary battery (especially its laminated battery) capable of preventing the growth of zinc dendrites can be produced very simply and with high productivity without the need for a complicated sealing joint between the LDH separator and the battery container.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0007] In Patent Documents 6 and 7, in order to prevent the growth of zinc dendrites, a configuration is adopted in which the negative electrode active material layer is covered or wrapped with a hydroxide ion conductive separator. However, as shown in FIG. 6, when the charge-discharge cycle is repeated for the zinc secondary battery 100 having such a configuration, a defect D of the hydroxide ion conductive separator 16 may occur at the lower end sealing portion of the hydroxide ion conductive separator 16 surrounding the negative electrode active material layer 14a. When such a defect D occurs, with the repetition of the charge-discharge cycle, metallic zinc derived from the negative electrode active material layer 14a precipitates and accumulates on the bottom of the battery case 20 from the defect D, and in the worst case, the accumulated metallic zinc may reach the lower end of the positive electrode plate 12 to cause a short circuit S.

[0008] The present inventors have now found that in a zinc secondary battery in which a negative electrode plate is housed in a bag-shaped hydroxide ion conductive separator, by extending the negative electrode active material layer to a position below the lower end of the positive electrode active material layer and controlling the height of the lower end of the negative electrode active material layer and the height difference between the lower end of the positive electrode active material layer and the lower end of the negative electrode active material layer, a short circuit caused by a defect at the lower end sealing portion of the bag-shaped hydroxide ion conductive separator is less likely to occur.

[0009] Accordingly, an object of the present invention is to provide a zinc secondary battery in which a short circuit caused by a defect at the lower end sealing portion of a bag-shaped hydroxide ion conductive separator is less likely to occur.

[0010] According to the present invention, the following aspects are provided. [Aspect 1] 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 alloy, and zinc compound, It has a bag-like form in which the negative electrode plate is accommodated, and a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so that hydroxide ions can be conducted, an electrolytic solution, a battery case in which the positive electrode plate, the negative electrode plate, and the hydroxide ion conductive separator are vertically accommodated, and is provided with the negative electrode active material layer extends to a position below the lower end of the positive electrode active material layer, a zinc secondary battery in which the height of the lower end of the negative electrode active material layer from the bottom surface of the battery case is 2.0 to 8.0 mm, and the height difference between the lower end of the positive electrode active material layer and the lower end of the negative electrode active material layer is 3.0 to 4.0 mm. [Aspect 2] The bag-like hydroxide ion conductive separator includes a lower end sealing portion sealed by thermal welding or ultrasonic welding of the hydroxide ion conductive separators to each other, the zinc secondary battery according to Aspect 1. [Aspect 3] A liquid retention member is interposed between the positive electrode plate and the negative electrode plate in addition to the hydroxide ion conductive separator, the zinc secondary battery according to Aspect 1 or 2. [Aspect 4] The positive electrode plate and / or the negative electrode plate is covered or wrapped by the liquid retention member, the zinc secondary battery according to Aspect 3. [Aspect 5] The liquid retention member is a non-woven fabric, the zinc secondary battery according to Aspect 3 or 4. [Aspect 6] The non-woven fabric has a thickness of 10 to 200 μm, the zinc secondary battery according to Aspect 5. [Aspect 7] The hydroxide ion conductive separator is an LDH separator containing a layered double hydroxide (LDH) and / or an LDH-like compound, the zinc secondary battery according to any one of Aspects 1 to 6. [Aspect 8] The LDH separator further includes a porous substrate, and the LDH and / or the LDH-like compound is compounded with the porous substrate in a form filled in the pores of the porous substrate, the zinc secondary battery according to Aspect 7. [Aspect 9] The zinc secondary battery according to Embodiment 8, wherein the porous substrate is made of a polymer material. [Embodiment 10] The zinc secondary battery according to any one of Embodiments 7 to 9, wherein the LDH separator has a thickness of 5 to 100 μm. [Embodiment 11] The zinc secondary battery according to any one of Embodiments 1 to 10, wherein the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, whereby the zinc secondary battery forms a nickel-zinc secondary battery. [Embodiment 12] The zinc secondary battery according to any one of Embodiments 1 to 10, wherein the positive electrode active material layer is an air electrode layer, whereby the zinc secondary battery forms an air-zinc secondary battery. [Embodiment 13] The zinc secondary battery according to any one of Embodiments 1 to 12, comprising a plurality of unit cells 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 form a multilayer cell as a whole.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0012] 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 solution of an alkali metal hydroxide). 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 various other alkaline zinc secondary batteries. For example, it is preferable that the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, whereby the zinc secondary battery forms a nickel-zinc secondary battery. Alternatively, the positive electrode active material layer may be an air electrode layer, whereby the zinc secondary battery forms an air-zinc secondary battery.

[0013] Figs. 1 to 5 show a zinc secondary battery 10 according to an aspect of the present invention. The zinc secondary battery 10 includes a battery element 11 in a battery case 20. The battery element 11 includes a unit cell 10a including a positive electrode plate 12, a negative electrode plate 14, a hydroxide ion conductive separator 16, and an electrolyte 18. The positive electrode plate 12 includes a positive electrode active material layer 12a. The negative electrode plate 14 includes a negative electrode active material layer 14a. The negative electrode active material layer 14a contains at least one selected from the group consisting of zinc, zinc oxide, zinc alloy, and zinc compound. The hydroxide ion conductive separator 16 has a bag-like form in which the negative electrode plate 14 is accommodated, and separates the positive electrode plate 12 and the negative electrode plate 14 so that hydroxide ions can be conducted. In the battery case 20, the positive electrode plate 12, the negative electrode plate 14, and the hydroxide ion conductive separator 16 are vertically accommodated. The negative electrode active material layer 14a extends to a position below the lower end of the positive electrode active material layer 12a. The height B from the bottom surface of the battery case 20 to the lower end of the negative electrode active material layer 14a is 2.0 to 8.0 mm, and the height difference A between the lower end of the positive electrode active material layer 12a and the lower end of the negative electrode active material layer 14a is 3.0 to 4.0 mm. In this way, by extending the negative electrode active material layer 14a to a position below the lower end of the positive electrode active material layer 12a and controlling the height B of the lower end of the negative electrode active material layer 14a and the height difference A between the lower end of the positive electrode active material layer 12a and the lower end of the negative electrode active material layer 14a, a short circuit caused by a defect at the lower end sealing portion of the bag-like hydroxide ion conductive separator 16 is less likely to occur.

[0014] That is, as described above with reference to FIG. 6, when the charge-discharge cycle is repeated for the conventional zinc secondary battery 100 configured to cover or enclose the negative electrode active material layer 14a with the hydroxide ion conductive separator 16, a defect D of the hydroxide ion conductive separator 16 may occur at the lower end sealing portion of the hydroxide ion conductive separator 16 surrounding the negative electrode active material layer 14a. The formation of such a defect D is considered to be caused by the expansion and contraction of the negative electrode active material layer 14a accompanying the charge-discharge cycle. In particular, the lower end sealing portion of the hydroxide ion conductive separator 16 is typically formed by thermal welding or ultrasonic welding of the hydroxide ion conductive separators 16, and a defect D may occur in such a welded portion. When such a defect D occurs, with the repetition of the charge-discharge cycle, metallic zinc derived from the negative electrode active material layer 14a precipitates and accumulates on the bottom of the battery case 20 from the defect D, and in the worst case, the accumulated metallic zinc may reach the lower end of the positive electrode plate 12 and cause a short circuit S. That is, since the negative electrode active material layer 14a changes shape with the repetition of the charge-discharge cycle, the precipitate of metallic zinc detached from the negative electrode active material layer 14a due to the shape change moves and accumulates on the bottom surface of the battery case 20 through the defect D according to gravity. Thus, as the deposition amount of metallic zinc increases, the height of the deposit increases, and ultimately it may reach the lower end of the positive electrode plate 12 and cause a short circuit S. In this regard, in the configuration of the zinc secondary battery 10 according to the present invention, as shown in FIG. 5, even when metallic zinc derived from the negative electrode active material layer 14a precipitates and accumulates on the bottom of the battery case 20 from the defect D, it can be accumulated in the lower surplus space significantly lower than the lower end of the positive electrode active material layer 12a. As a result, even if the deposition amount of metallic zinc increases and the height of the deposit increases, it becomes difficult for the deposited metallic zinc to reach the lower end of the positive electrode plate 12, and as a result, the short circuit S is less likely to occur. And such an advantageous effect is realized when the height B from the bottom surface of the battery case 20 to the lower end of the negative electrode active material layer 14a is 2.0 to 8.0 mm, and the height difference A between the lower end of the positive electrode active material layer 12a and the lower end of the negative electrode active material layer 14a is 3.0 to 4.0 mm.

[0015] The height B from the bottom surface of the battery case 20 to the lower end of the negative electrode active material layer 14a is 2.0 to 8.0 mm, preferably 2.0 to 6.0 mm, more preferably 2.0 to 5.0 mm, still more preferably 2.0 to 4.0 mm, and particularly preferably 2.0 to 3.0 mm. The height difference A between the lower end of the positive electrode active material layer 12a and the lower end of the negative electrode active material layer 14a is 3.0 to 4.0 mm, preferably 3.0 to 3.8 mm, more preferably 3.0 to 3.6 mm, still more preferably 3.0 to 3.4 mm, and particularly preferably 3.0 to 3.2 mm.

[0016] 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 appropriately selected from known positive electrode materials according to the type of the zinc secondary battery, and is not particularly limited. For example, in the case of a nickel-zinc secondary battery, a positive electrode containing nickel hydroxide and / or nickel oxyhydroxide may be used. Alternatively, in the case of an air-zinc secondary battery, an air electrode may be used as the positive electrode. The positive electrode plate 12 further includes a positive electrode current collector (not shown), and the positive electrode current collector preferably has a positive electrode current collecting tab 12b extending from an end portion (for example, the upper end) of the positive electrode plate 12. Preferred examples of the positive electrode current collector include nickel-made porous substrates such as foamed nickel plates. In this case, for example, a positive electrode plate composed of a positive electrode / positive electrode current collector can be preferably manufactured by uniformly applying a paste containing an electrode active material such as nickel hydroxide on the nickel-made porous substrate and drying it. At that time, it is also preferable to perform a pressing process on the dried positive electrode plate (that is, the positive electrode / positive electrode current collector) to prevent the electrode active material from falling off and improve the electrode density. Note that the positive electrode plate 12 shown in FIGS. 4 and 5 includes a positive electrode current collector (for example, foamed nickel) but is not shown. This is because in the case of a nickel-zinc secondary battery, the positive electrode current collector is integrally formed with the positive electrode active material, so the positive electrode current collector cannot be separately depicted. The zinc secondary battery 10 preferably further includes a positive electrode current collecting plate connected to the tip of the positive electrode current collecting tab 12b, and more preferably, a plurality of positive electrode current collecting tabs 12b are connected to one positive electrode current collecting plate. By doing so, current collection can be performed with a simple configuration and high space efficiency, and connection to the positive electrode terminal 26 is also facilitated. Further, the positive electrode current collecting plate itself may be used as the positive electrode terminal 26.

[0017] The positive electrode plate 12 may contain at least one additive selected from the group consisting of a silver compound, a manganese compound, and a titanium compound, and thereby can promote a positive electrode reaction that absorbs hydrogen gas generated by a self-discharge reaction. Further, the positive electrode plate 12 may further contain cobalt. Cobalt is preferably contained in the positive electrode plate 12 in the form of cobalt oxyhydroxide. In the positive electrode plate 12, cobalt functions as a conductive aid and contributes to an improvement in charge and discharge capacity.

[0018] 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 contains at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound. Zinc may be contained in any form of zinc metal, a zinc compound, and a zinc alloy as long as it has suitable electrochemical activity for the negative electrode. Preferred examples of the negative electrode material include zinc oxide, zinc metal, calcium zincate, etc., and a mixture of zinc metal and zinc oxide is more preferred. The negative electrode active material may be configured in a gel form or mixed with the electrolytic solution 18 to form a negative electrode composite material. For example, a negative electrode that is easily gelled can be obtained by adding an electrolytic solution and a thickening agent to the negative electrode active material. Examples of the thickening agent include polyvinyl alcohol, polyacrylate, CMC, alginic acid, etc., and polyacrylic acid is preferred because of its excellent chemical resistance to strong alkalis.

[0019] 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% by mass of indium, 0.005 to 0.02% by mass of bismuth, and 0.0035 to 0.015% by mass of aluminum is preferable because it has an 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 down the self-dissolution rate in an alkaline electrolytic solution.

[0020] The shape of the negative electrode material is not particularly limited, but it is preferably in powder form, whereby the surface area is increased and high-current discharge can be accommodated. In the case of a zinc alloy, the average particle diameter of the preferred negative electrode material is in the range of 3 to 100 μm in the minor axis, and being within this range is suitable for accommodating high-current discharge because the surface area is large, and it is easy to mix uniformly with the electrolytic solution and the gelling agent, and the handleability during battery assembly is also good.

[0021] The negative electrode plate 14 may include a negative electrode current collector 14b provided inside and / or on the surface of the negative electrode active material layer 14a (excluding the portion extending as the negative electrode current collecting tab 14c). That is, the negative electrode active material layer 14a may be disposed on both sides of the negative electrode current collector 14b, or the negative electrode active material layer 14a may be disposed only on one side of the negative electrode current collector 14b. The negative electrode plate 14 further includes a negative electrode current collector 14b, and the negative electrode current collector 14b preferably has a negative electrode current collecting tab 14c extending from an end portion (for example, the upper end) of the negative electrode plate 14. The negative electrode current collecting tab 14c is preferably provided at a position that does not overlap with the positive electrode current collecting tab 12b. The zinc secondary battery 10 preferably further includes a negative electrode current collecting plate connected to the tip of the negative electrode current collecting tab 14c, and more preferably, a plurality of negative electrode current collecting tabs 14c are connected to one negative electrode current collecting plate. By doing so, current collection can be performed with a simple configuration and high space efficiency, and it is also easy to connect to the negative electrode terminal 28. Further, the negative electrode current collecting plate itself may be used as the negative electrode terminal 28.

[0022] It is preferable to use a metal plate having a plurality (or a large number) of openings as the negative electrode current collector 14b 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, and metal mesh, and combinations thereof. More preferably, copper expanded metal, copper punched metal, and combinations thereof are included. Particularly preferably, copper expanded metal is included. In this case, for example, a mixture containing zinc oxide powder and / or zinc powder, and optionally a binder (for example, polytetrafluoroethylene particles) can be applied onto the copper expanded metal to preferably produce a negative electrode plate composed of a negative electrode / negative electrode current collector. At that time, it is also preferable to perform a pressing treatment on the dried negative electrode plate (that is, the negative electrode / negative electrode current collector) to prevent the electrode active material from falling off and to improve the electrode density. Note that expanded metal is a mesh-shaped metal plate obtained by expanding a metal plate while making cuts in a staggered pattern using an expand manufacturing machine and forming the cuts into a diamond shape or a tortoise shell shape. Punched metal is also called perforated metal and is obtained by making holes in a metal plate by punching. Metal mesh is a metal product having a wire mesh structure and is different from expanded metal and punched metal.

[0023] The hydroxide ion-conducting separator 16 has a bag-like form in which the negative electrode plate 14 is accommodated, and is provided to isolate the positive electrode plate 12 and the negative electrode plate 14 so that hydroxide ions can be conducted. A typical bag-like hydroxide ion-conducting separator 16 has a rectangular outer shape (shape in plan view), and three sides of the outer periphery are closed by sealing and / or bending to form a bag-like shape, and the remaining one side of the outer periphery is open to allow the extension of the negative electrode current collector tab 14c. The hydroxide ion-conducting separator 16 having a bag-like form in which the negative electrode plate 14 is accommodated can be a known one as disclosed in Patent Documents 6 and 7. As a result, as shown in FIGS. 4 and 5, the negative electrode plate 14 is configured to be covered or wrapped by the hydroxide ion-conducting separator 16. By adopting such a configuration, a nickel-zinc secondary battery (especially its laminated battery) capable of preventing zinc dendrite growth can be manufactured very simply and with high productivity, eliminating the need for a complicated sealing joint between the hydroxide ion-conducting separator 16 and the battery container. Also, the positive electrode plate 12 may also be configured to be covered or wrapped by the hydroxide ion-conducting separator 16. The bag-like hydroxide ion-conducting separator 16 preferably includes a lower end sealing portion sealed by thermal welding or ultrasonic welding between the hydroxide ion-conducting separators 16. Thermal welding between the hydroxide ion-conducting separators 16 is preferably performed by sandwiching a non-woven fabric as a liquid retaining member 17 between the hydroxide ion-conducting separators 16, because the non-woven fabric can function as an adhesive to perform effective welding. On the other hand, in the case of ultrasonic welding, the hydroxide ion-conducting separators 16 can be directly welded to each other.

[0024] The hydroxide ion-conducting separator 16 is not particularly limited as long as it can isolate the positive electrode plate 12 and the negative electrode plate 14 so that hydroxide ions can be conducted. Typically, it includes a hydroxide ion-conducting solid electrolyte and is a separator that selectively passes hydroxide ions by utilizing only the hydroxide ion conductivity. Preferred hydroxide ion-conducting solid electrolytes are layered double hydroxides (LDHs) and / or LDH-like compounds. Therefore, the hydroxide ion-conducting separator 16 is preferably an LDH separator. As used herein, an "LDH separator" is defined as a separator containing LDH and / or LDH-like compounds that selectively passes hydroxide ions by utilizing only the hydroxide ion conductivity of LDH and / or LDH-like compounds. As used herein, an "LDH-like compound" is a hydroxide and / or oxide having a layered crystal structure similar to LDH, which may not be called LDH but is equivalent to LDH. However, in a broad sense, "LDH" can also be interpreted to include not only LDH but also LDH-like compounds. The LDH separator is preferably combined with a porous substrate. Therefore, the LDH separator preferably further includes a porous substrate, and LDH and / or LDH-like compounds are combined with the porous substrate in a form in which the pores of the porous substrate are filled. That is, a preferred LDH separator has LDH and / or LDH-like compounds blocking the pores of the porous substrate 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 LDH is incorporated throughout the thickness direction of the polymer material-made porous substrate. For example, known LDH separators as 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, still more preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.

[0025] It is preferable that not only the hydroxide ion conductive separator 16 but also the liquid retention member 17 is interposed between the positive electrode plate 12 and the negative electrode plate 14. And it is preferable that the positive electrode plate 12 and / or the negative electrode plate 14 is covered or wrapped by 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 be adopted. In any case, by interposing the liquid retention member 17, the electrolyte solution 18 can be uniformly present between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16, and the transfer of hydroxide ions between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16 can be efficiently performed. The liquid retention member 17 is not particularly limited as long as it can hold the electrolyte solution 18, but is preferably a sheet-like member. Preferred examples of the liquid retention member 17 include non-woven fabrics, water-absorbing resins, liquid-retaining resins, porous sheets, and various spacers. Particularly preferably, it is a non-woven fabric in terms of being able to produce a negative electrode structure with low cost and good performance. The liquid retention member 17 or the non-woven fabric preferably has a thickness of 10 to 200 μm, more preferably 20 to 200 μm, still more preferably 20 to 150 μm, particularly preferably 20 to 100 μm, and most preferably 20 to 60 μm. When the thickness is within the above range, a sufficient amount of the electrolyte solution 18 can be retained in the liquid retention member 17 while suppressing the overall size of the positive electrode structure and / or the negative electrode structure to be compact without waste.

[0026] When the positive electrode plate 12 and / or the negative electrode plate 14 is covered or wrapped by the liquid retention member 17 and / or the separator 16, it is preferable that their outer edges are closed (excluding the sides where the positive electrode current collector tab 12b and the negative electrode current collector tab 14c extend). In this case, it is preferable that the closed sides of the outer edges of the liquid retention member 17 and / or the separator 16 are realized by bending the liquid retention member 17 and / or the separator 16, or by sealing the liquid retention members 17 and / or the separators 16 together. Preferred examples of the sealing method include adhesives, heat welding, ultrasonic welding, adhesive tapes, sealing tapes, and combinations thereof. In particular, since the LDH separator containing a porous substrate made of a polymer material has flexibility and thus has the advantage of being easily bent, it is preferable to form the LDH separator in a long shape and bend it to form a state where one side of the outer edge is closed. Heat welding and ultrasonic welding may be performed using a commercially available heat sealer or the like. However, in the case of sealing the LDH separators together, it is preferable to perform heat welding and ultrasonic welding by sandwiching the outer peripheral portion of the liquid retention member 17 between the LDH separators constituting the outer peripheral portion, in terms of being able to perform more effective sealing. On the other hand, commercially available products may be used for adhesives, adhesive tapes, and sealing tapes. However, in order to prevent deterioration in the alkaline electrolyte, those containing a resin having alkali resistance are preferable. From such a viewpoint, examples of preferable adhesives include epoxy resin-based adhesives, natural resin-based adhesives, modified olefin resin-based adhesives, and modified silicone resin-based adhesives. Among them, epoxy resin-based adhesives are more preferable in that they are particularly excellent in alkali resistance. An example of a product of an epoxy resin-based adhesive is epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

[0027] It is preferable that the outer edge of one side that forms the upper end of the separator 16 is open. This upper-open type configuration enables addressing issues during overcharging in nickel-zinc batteries and the like. That is, when overcharged in a nickel-zinc battery or the like, oxygen (O2) can be generated at the positive electrode plate 12. However, because the LDH separator has a high level of tightness such that it substantially only allows hydroxide ions to pass through, it does not allow O2 to pass through. In this regard, according to the upper-open type configuration, within the battery case 20, O2 can be released above the positive electrode plate 12 and sent through the upper open portion to the negative electrode plate 14 side, thereby oxidizing Zn of the negative electrode active material with O2 and returning it to ZnO. By going through such an oxygen reaction cycle, the overcharge tolerance can be improved by using the upper-open type battery element 11 in a sealed zinc secondary battery. Even when the outer edge of one side that forms the upper end of the separator 16 or the liquid retention member 17 is closed, by providing ventilation holes in a part of the closed outer edge, the same effect as the above-described open type configuration can be expected. For example, ventilation holes may be opened after sealing the outer edge of one side that forms the upper end of the LDH separator, or a part of the outer edge may be left unsealed so that ventilation holes are formed during sealing.

[0028] The electrolytic solution 18 preferably contains an aqueous solution of an alkali metal hydroxide. In FIGS. 4 and 5, the electrolytic solution 18 is only locally illustrated because it spreads over the entire positive electrode plate 12 and negative electrode plate 14. Examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide, lithium hydroxide, ammonium hydroxide, etc., and potassium hydroxide is more preferable. In order to suppress the self-dissolution of zinc and / or zinc oxide, zinc compounds such as zinc oxide and zinc hydroxide may be added to the electrolytic solution. As described above, the electrolytic solution may be mixed with the positive electrode active material and / or the negative electrode active material and exist in the form of a positive electrode composite material and / or a negative electrode composite material. Also, in order to prevent leakage of the electrolytic solution, the electrolytic solution may be gelled. As the gelling agent, it is desirable to use a polymer that absorbs the solvent of the electrolytic solution and swells, and polymers such as polyethylene oxide, polyvinyl alcohol, polyacrylamide, and starch are used.

[0029] The battery element 11 preferably has a form of a positive-negative electrode laminate in which a plurality of positive electrode plates 12, a plurality of negative electrode plates 14, and a plurality of separators 16 are provided and the unit of positive electrode plate 12 / separator 16 / negative electrode plate 14 is repeated. That is, the zinc secondary battery 10 preferably includes a plurality of unit cells 10a, and thereby a plurality of unit cells 10a form a multilayer cell as a whole. This is a configuration of a so-called assembled battery or laminated battery, which is advantageous in that a high voltage and a large current can be obtained.

[0030] The battery case 20 is preferably made of resin. The resin constituting the battery case 20 is preferably a resin having resistance to alkali metal hydroxides such as potassium hydroxide, more preferably a polyolefin resin, an ABS resin, or a modified polyphenylene ether, and still more preferably an ABS resin or a modified polyphenylene ether. The battery case 20 has an upper lid 20a. The battery case 20 (for example, the upper lid 20a) may have a pressure relief valve for discharging gas. Also, a case group in which two or more battery cases 20 are arranged may be housed in an outer frame to form a battery module.

[0031] LDH-like compound According to a preferred embodiment of the present invention, the LDH separator can contain an LDH-like compound. The definition of the LDH-like compound is as described above. Preferred LDH-like compounds are (a) a hydroxide and / or oxide having a layered crystal structure containing Mg and at least one element containing at least Ti selected from the group consisting of Ti, Y, and Al, or (b) (i) a hydroxide and / or oxide having a layered crystal structure containing Ti, Y, and optionally Al and / or Mg, and (ii) an additive element M which is at least one selected from the group consisting of In, Bi, Ca, Sr, and Ba, or (c) a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, and in (c), the LDH-like compound exists in the form of a mixture with In(OH)3.

[0032] According to a preferred embodiment (a) of the present invention, the LDH-like compound can be a hydroxide and / or oxide having a layered crystal structure containing Mg and at least one element containing 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. The above elements may be replaced with other elements or ions to such an extent that the basic properties of the LDH-like compound are not impaired, but the LDH-like compound preferably does not contain Ni. For example, the LDH-like compound may further contain Zn and / or K. By doing so, the ionic conductivity of the LDH separator can be further improved.

[0033] The LDH-like compound can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface of the LDH separator, peaks derived from the LDH-like compound are typically detected in the range of 5° ≤ 2θ ≤ 10°, more typically in the range of 7° ≤ 2θ ≤ 10°. As described above, LDH is a substance having an alternating laminate structure in which exchangeable anions and H2O are present as an intermediate layer between stacked hydroxide basic layers. In this regard, when LDH is measured by the X-ray diffraction method, a peak (i.e., the (003) peak of LDH) due to the crystal structure of LDH is originally detected at a position of 2θ = 11 to 12°. On the other hand, when the LDH-like compound is measured by the X-ray diffraction method, peaks are typically detected in the above range shifted to the low-angle side from the above peak position of LDH. Also, the interlayer distance of the layered crystal structure can be determined by Bragg's equation using 2θ corresponding to the peak derived from the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystal structure constituting the LDH-like compound thus determined is typically 0.883 to 1.8 nm, more typically 0.883 to 1.3 nm.

[0034] The LDH separator according to the above aspect (a) preferably has an atomic ratio of Mg / (Mg + Ti + Y + Al) in the LDH-like compound, determined by energy-dispersive X-ray spectroscopy (EDS), of 0.03 to 0.25, more preferably 0.05 to 0.2. Further, 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. Furthermore, 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. And 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. When within the above ranges, the alkaline resistance is further improved, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. Incidentally, the conventionally known LDH for the LDH separator has the general formula: M 2+ 1-x M 3+ x (OH)2A n- x / n ·mH2O (wherein M 2+ is a divalent cation, M 3+ is a trivalent cation, 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 above atomic ratios in the LDH-like compound generally deviate from the above general formula of LDH. Therefore, it can be said that the LDH-like compound in this aspect generally has a different composition ratio (atomic ratio) from conventional LDH. The EDS analysis is preferably performed by using an EDS analyzer (for example, X-act, manufactured by Oxford Instruments) to 1) capture an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) perform point analysis at intervals of about 5 μm in the point analysis mode, perform three-point analysis, 3) repeat the above 1) and 2) one more time, and 4) calculate the average value of a total of six points.

[0035] According to another preferred embodiment (b) of the present invention, the LDH-like compound can be a hydroxide and / or oxide having a layered crystal structure containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additive element M. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Ti, Y, additive element M, optionally Al, and optionally Mg. The additive element M is In, Bi, Ca, Sr, Ba, or a combination thereof. 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 the LDH-like compound preferably does not contain Ni.

[0036] For the LDH separator according to the above embodiment (b), the atomic ratio of Ti / (Mg + Al + Ti + Y + M) in the LDH-like compound, determined by energy-dispersive X-ray spectroscopy (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. And 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 ranges, the alkali resistance is further improved, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. By the way, the conventionally known LDH for the LDH separator has the general formula: M 2+ 1-x M 3+ x (OH)2A n- x / n ·mH2O (wherein M 2+ is a divalent cation, M 3+ is a trivalent cation, and A n-It can be represented by a basic composition of an n-valent anion (where n is an integer of 1 or more, x is from 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratios in the LDH-like compound generally deviate from those in the above general formula of LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a different composition ratio (atomic ratio) from that of conventional LDH. Note that EDS analysis is performed using an EDS analyzer (for example, X-act, manufactured by Oxford Instruments), by: 1) capturing an image at an acceleration voltage of 20 kV and a magnification of 5,000 times; 2) performing point analysis at intervals of about 5 μm in point analysis mode and conducting three-point analysis; 3) repeating the above 1) and 2) one more time; and 4) calculating the average value of a total of six points.

[0037] According to yet another preferred embodiment (c) of the present invention, the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, and the LDH-like compound may exist in the form of a mixture with 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 In that can be contained in the LDH-like compound may be not only intentionally added to the LDH-like compound but also unavoidably mixed into the LDH-like compound due to the formation of In(OH)3 or the like. 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 the LDH-like compound preferably does not contain Ni. By the way, a conventionally known LDH for an LDH separator has the general formula: M 2+ 1-x M 3+ x (OH)2A n- x / n ·mH2O (wherein M 2+ is a divalent cation, M 3+ is a trivalent cation, and A n-It can be represented by the following basic composition: (wherein A 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 above 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.

[0038] The mixture according to the above aspect (c) contains not only the LDH-like compound but also In(OH)3 (typically composed of the LDH-like compound and In(OH)3). The inclusion of In(OH)3 can effectively improve the alkali resistance and dendrite resistance in the LDH separator. The content ratio of In(OH)3 in the mixture is preferably an amount that can improve the alkali resistance and dendrite resistance without substantially impairing the hydroxide ion conductivity of the LDH separator, and is not particularly limited. In(OH)3 may have a cubic crystal structure, or the crystals of In(OH)3 may be surrounded by the LDH-like compound. In(OH)3 can be identified by X-ray diffraction.

Examples

[0039] The present invention will be further specifically described by the following examples.

[0040] Examples 1 to 6 (1) Fabrication of nickel-zinc secondary battery The following positive electrode plate, negative electrode plate, LDH separator, non-woven fabric, sealed container, and electrolyte were prepared. · Positive electrode plate: A foamed nickel plate filled with a positive electrode paste containing nickel hydroxide and a binder and dried, number of sheets: 13 · Negative electrode plate: A paste containing ZnO powder, metallic Zn powder, polytetrafluoroethylene (PTFE), and propylene glycol was pressure-bonded to a current collector (copper expanded metal), number of sheets: 14 · LDH separator: Ni-Al-Ti-LDH (layered double hydroxide) was precipitated by hydrothermal synthesis in the pores and on the surface of a polyethylene microporous membrane and roll-pressed, thickness: 0.009 mm · Non-woven fabric: made of polyethylene · Hermetic container: a housing made of modified polyphenylene ether resin (equipped with a pressure relief valve that can release the gas generated inside the case) · Electrolyte: 5.4 mol / L KOH aqueous solution in which 0.4 mol / L ZnO is dissolved

[0041] According to the configuration shown in FIGS. 1 to 4, the negative electrode plate was wrapped with an LDH separator and sealed by heat welding with a non-woven fabric interposed between the three sides other than the upper end, resulting in an upper-open negative electrode structure. On the other hand, the positive electrode plate was wrapped with a non-woven fabric and heat-sealed at the three sides other than the upper end to form an upper-open positive electrode structure. A total of 27 prepared positive electrode structures and negative electrode structures were placed in a hermetic container so that they were alternately positioned. At this time, the height difference A between the lower end of the positive electrode active material layer and the lower end of the negative electrode active material layer, and the height B of the lower end of the negative electrode active material layer from the bottom surface of the battery case were set to the values shown in Table 1. While connecting the positive electrode current collector tab extending upward from the positive electrode current collector to the positive electrode terminal, the negative electrode current collector tab extending upward from the negative electrode current collector was connected to the negative electrode terminal, and the lid was closed. The electrolyte was added through the liquid injection port, and after the electrolyte was sufficiently infiltrated into the positive electrode plate and the negative electrode plate by vacuum pumping or the like, the liquid injection port was sealed. Thus, a multi-layer cell type nickel-zinc secondary battery was obtained.

[0042] (2) Cycle test Using a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT3100), formation was performed on a simple hermetic cell at 0.1C charge and 0.2C discharge. Then, a 0.5C charge-discharge cycle was performed up to 200 times as long as the capacity retention rate with respect to the initial discharge capacity did not fall below 70%, and the presence or absence of short circuit was confirmed. The results were as shown in Table 1.

[0043]

Table 1

Claims

1. 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; a hydroxide ion conductive separator having a bag-like shape in which the negative electrode plate is housed and which separates the positive electrode plate and the negative electrode plate in a manner that allows hydroxide ions to be conducted therebetween; An electrolyte; a battery case in which the positive electrode plate, the negative electrode plate, and a hydroxide ion conductive separator are housed in a vertical orientation; Equipped with the negative electrode active material layer extends to a position below a lower end of the positive electrode active material layer, A zinc secondary battery, wherein the height of the lower end of the negative electrode active material layer from the bottom surface of the battery case is 2.0 to 8.0 mm, and the height difference between the lower end of the positive electrode active material layer and the lower end of the negative electrode active material layer is 3.0 to 4.0 mm.

2. 2. The zinc secondary battery according to claim 1, wherein the pouch-shaped hydroxide ion conductive separator includes a bottom sealing portion formed by sealing the hydroxide ion conductive separators together by thermal welding or ultrasonic welding.

3. 3. The zinc secondary battery according to claim 1, wherein not only the hydroxide ion conductive separator but also a liquid retaining member is interposed between the positive electrode plate and the negative electrode plate.

4. The zinc secondary battery according to claim 3 , wherein the positive electrode plate and / or the negative electrode plate is covered or enveloped in the liquid retaining member.

5. 4. The zinc secondary battery according to claim 3, wherein the liquid retaining member is a nonwoven fabric.

6. The zinc secondary battery according to claim 5, wherein the nonwoven fabric has a thickness of 10 to 200 μm.

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

8. The zinc secondary battery described in claim 7, wherein the LDH separator further comprises a porous substrate, and the LDH and / or LDH-like compound is composited with the porous substrate in a form where the LDH and / or LDH-like compound is filled in the pores of the porous substrate.

9. The zinc secondary battery according to claim 8 , wherein the porous substrate is made of a polymer material.

10. 8. The zinc secondary battery according to claim 7, wherein the LDH separator has a thickness of 5 to 100 μm.

11. 3. The zinc secondary battery according to claim 1, wherein the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, thereby forming the zinc secondary battery into a nickel-zinc secondary battery.

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

13. 3. The zinc secondary battery according to claim 1, comprising a plurality of unit cells each having a pair of said positive electrode plate and said negative electrode plate 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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