Zinc secondary battery

Abstract

Provided is a multilayer cell zinc secondary battery in which short circuiting does not readily occur even with a joined structure in which collector tabs are bundled. This zinc secondary battery comprises a plurality of unit cells, each including a positive electrode plate, a positive electrode collector tab extending from the positive electrode plate, a negative electrode plate, a negative electrode collector tab extending from the negative electrode plate, a separator, and an electrolytic solution, where the plurality of unit cells are stacked to form a multilayer cell. When viewed in cross-section, each of the positive electrode collector tabs and the negative electrode collector tabs has a non-rounded bent shape in at least two places and thus each of the positive electrode collector tabs and the negative electrode collector tabs has at least two straight parts and a sloped part therebetween. In the positive electrode collector tabs, the straight parts that are further away from the positive electrode plates are stacked and joined to one another and in the negative electrode collector tabs, the straight parts that are further away from the negative electrode plates are stacked and joined to one another.

Description

[Technical field]

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

[0002] A multi-layer cell type secondary battery is known in which a plurality of positive and negative electrode plates from which a current collecting tab extends are alternately stacked. In these secondary batteries, a configuration in which a plurality of current collecting tabs are bundled and connected to a current collecting terminal is known. For example, Patent Document 1 (WO 2019 / 163220) discloses a secondary battery in which a current collecting tab has a curved portion that curves between an active material arrangement portion and a current collecting terminal, and a tip portion on the opposite side to the active material arrangement portion, and the tip portion is joined to the current collecting terminal. In addition, Patent Document 2 (WO 2020 / 071049) discloses a secondary battery in which a current collecting tab is accommodated in a battery case in a bent state, and the current collecting tab has a joint portion with the current collecting terminal and a bent portion that is spaced from the joint portion and is provided at a position on the electrode body side and serves as a starting point for bending the current collecting tab.

[0003] Incidentally, in zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries, it is known that metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrates the voids of the separator such as nonwoven fabric, and reaches the positive electrode, resulting in a short circuit. Such a short circuit caused by zinc dendrites shortens the repeated charge-discharge life. To address this problem, a battery equipped with a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing the penetration of zinc dendrites has been proposed (see, for example, Patent Document 3 (WO 2016 / 076047) and Patent Document 4 (WO 2019 / 124270)). In addition, although it cannot be called LDH, LDH-like compounds are known as hydroxides and / or oxides with a layered crystal structure similar to LDH, and exhibit hydroxide ion conductive properties similar to LDH that can be collectively referred to as hydroxide ion conductive layered compounds. For example, Patent Document 5 (WO 2020 / 255856) discloses a hydroxide ion conductive separator including a porous substrate and a layered double hydroxide (LDH)-like compound that blocks the pores of the porous substrate. Patent Document 6 (WO 2019 / 069760) and Patent Document 7 (WO 2019 / 077953) propose a zinc secondary battery in which the entire negative electrode active material layer is covered or wrapped with a liquid-retaining member and an LDH separator, and the positive electrode active material layer is covered or wrapped with a liquid-retaining member. A nonwoven fabric is used as the liquid-retaining member. According to this configuration, it is said that a zinc secondary battery (especially a stacked battery thereof) capable of preventing zinc dendrite extension can be produced extremely easily and with high productivity, eliminating the need for a complicated sealing joint between the LDH separator and the battery container. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 163220 [Patent Document 2] International Publication No. 2020 / 071049 [Patent Document 3] International Publication No. 2016 / 076047 [Patent Document 4] International Publication No. 2019 / 124270 [Patent Document 5] International Publication No. 2020 / 255856 [Patent Document 6] International Publication No. 2019 / 069760 [Patent Document 7] International Publication No. 2019 / 077953 Summary of the Invention

[0005] In the conventional current collecting tabs as disclosed in Patent Documents 1 and 2, when multiple current collecting tabs are bundled and joined to a terminal, the current collecting tabs are pulled. At that time, an excessive load is applied to the end of the electrode plate, which causes defects in the electrode plate (particularly the active material layer) and the separator, increasing the risk of short circuit. In addition, in the case of zinc secondary batteries, a shape change occurs in which the shape of the negative electrode changes as charging and discharging are repeated. There is a concern that the current collecting tab will be further pulled along with the deformation of the end of the negative electrode plate due to this shape change, further increasing the risk of short circuit. Therefore, a current collecting tab structure that is less likely to short circuit is required in a multi-layer cell type zinc secondary battery including a structure in which current collecting tabs are bundled and joined to a terminal.

[0006] The present inventors have now discovered that by employing a current collecting tab that is bent in at least two places and is not rounded, it is possible to provide a multi-layer cell type zinc secondary battery that is less susceptible to short circuits.

[0007] SUMMARY OF THE PRESENT DISCLOSURE ... An object of the present invention is to provide a multi-layer cell type zinc secondary battery which is less susceptible to short circuits even when it has a joint structure in which current collecting tabs are bundled together.

[0008] According to one aspect of the present invention, a positive electrode plate including a positive electrode active material layer and a positive electrode current collector; a positive electrode current collecting tab extending in a predetermined direction from an end of the positive electrode plate; a negative electrode plate including a negative electrode active material layer including at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound, and a negative electrode current collector; a negative electrode current collecting tab extending in the predetermined direction from an end of the negative electrode plate at a position not overlapping with the positive electrode current collecting tab; a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so as to be capable of conducting hydroxide ions; An electrolyte; A zinc secondary battery comprising a plurality of unit cells each including: each of the positive electrode current collector tab and the negative electrode current collector tab has a non-rounded shape folded at at least two places when viewed in cross section, whereby each of the positive electrode current collector tab and the negative electrode current collector tab has at least two straight portions parallel to the positive electrode plate and the negative electrode plate, and an inclined portion between the at least two straight portions; the straight portions of the positive electrode current collecting tabs that are away from the positive electrode plate are stacked and joined together to form a positive electrode tab joint, and the straight portions of the negative electrode current collecting tabs that are away from the negative electrode plate are stacked and joined together to form a negative electrode tab joint. However, in a case where the positive electrode current collector tab and / or the negative electrode current collector tab are present and are located in the same plane as the positive electrode tab joint and / or the negative electrode tab joint, the positive electrode current collector tab and / or the negative electrode current collector tab in the same plane may exceptionally consist of only one straight portion parallel to the positive electrode plate and / or the negative electrode plate without being bent, in a zinc secondary battery. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a zinc secondary battery according to the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a cross section of the zinc secondary battery shown in FIG. 1 taken along line AA'. [Diagram 3] 3 is an enlarged view of the joining structure of the current collecting tab shown in FIG. 2. [Figure 4] FIG. 2 is a perspective view showing a schematic diagram of a battery element of the zinc secondary battery shown in FIG. [Diagram 5]FIG. 2 is a cross-sectional view that illustrates a battery element of the zinc secondary battery shown in FIG. [Figure 6] 4A to 4C are diagrams showing a manufacturing procedure for the joining structure of the current collecting tab according to the present invention. [Figure 7] 4 is a cross-sectional view showing the inclination angle of the inclined portion of the current collecting tab according to the present invention. FIG. [Figure 8] 4 is a cross-sectional view conceptually showing the vicinity of a bent portion of a current collecting tab according to the present invention. FIG. [Figure 9] FIG. 1 is a cross-sectional view showing a schematic example of a joint structure of a conventional current collecting tab. [Figure 10] FIG. 11 is a cross-sectional view showing a schematic diagram of another example of a conventional joining structure of a current collecting tab. [Figure 11] 1A to 1C are diagrams illustrating a manufacturing procedure for a conventional current collecting tab joining structure. [Figure 12] FIG. 11 is a cross-sectional view showing a schematic view of the vicinity of a bent portion of a conventional current collecting tab. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Zinc secondary battery The zinc secondary battery of the present invention is not particularly limited as long as it is a secondary battery using zinc as the negative electrode and an alkaline electrolyte (typically an aqueous alkali metal hydroxide solution). Therefore, it can be a nickel-zinc secondary battery, a silver oxide zinc secondary battery, a manganese oxide zinc secondary battery, an air zinc secondary battery, or any other type of alkaline zinc secondary battery. For example, it is preferable that the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery. Alternatively, the positive electrode active material layer may be an air electrode layer, thereby making the zinc secondary battery an air zinc secondary battery.

[0011] 1 to 5 show an embodiment of a zinc secondary battery and its internal structure according to the present invention. The zinc secondary battery 10 shown in these figures includes a battery element 11 in a battery case 20, and includes a plurality of unit cells 10a each including a positive electrode plate 12, a positive electrode current collector tab 12b, a negative electrode plate 14, a negative electrode current collector tab 14c, a hydroxide ion conductive separator 16, and an electrolyte 18. Thus, a plurality of unit cells 10a are stacked to form a multi-layer cell. The positive electrode plate 12 includes a positive electrode active material layer 12a and a positive electrode current collector (not shown), and the positive electrode current collector tab 12b extends from the positive electrode plate 12 in a predetermined direction. The negative electrode plate 14 includes a negative electrode active material layer 14a and a negative electrode current collector 14b. The negative electrode active material layer 14a includes at least one selected from the group consisting of zinc, zinc oxide, zinc alloy, and zinc compound. The negative electrode current collector tab 14c extends in a predetermined direction from the negative electrode plate 14 at a position not overlapping with the positive electrode current collector tab 12b. The hydroxide ion conductive separator 16 separates the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ion conductivity. When viewed in cross section, each of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c has a non-rounded shape that is bent at at least two points F, so that each of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c has at least two straight portions S parallel to the positive electrode plate 12 and the negative electrode plate 14 and an inclined portion I between the at least two straight portions S. The straight portions S of the positive electrode current collector tabs 12b that are farther from the positive electrode plate 12 are stacked and joined together to form a positive electrode tab joint (not shown), and the straight portions S of the negative electrode current collector tabs 14c that are farther from the negative electrode plate 14 are stacked and joined together to form a negative electrode tab joint 30. However, when the positive electrode current collector tabs 12b and / or the negative electrode current collector tabs 14c that are located in the same plane as the positive electrode tab joint and / or the negative electrode tab joint 30 exist, the positive electrode current collector tabs 12b and / or the negative electrode current collector tabs 14c in the same plane may exceptionally be composed of only one straight portion that is parallel to the positive electrode plate 12 and / or the negative electrode plate 14 without being bent. In this way, by adopting a current collector tab that is bent at at least two places and has a rounded shape, it is possible to provide a multi-layer cell type zinc secondary battery that is less likely to cause a short circuit while having a joint structure in which the current collector tabs are bundled together.

[0012] That is, in the conventional current collecting tabs for multi-layer cells, the positive electrode current collecting tab 12b and the negative electrode current collecting tab 14c do not have a fold F as shown in Fig. 9, or the positive electrode current collecting tab 12b and the negative electrode current collecting tab 14c have only one fold F as shown in Fig. 10. Both of these include rounded shapes (curved shapes). In these cases, as described above, the current collecting tabs are pulled when multiple current collecting tabs are bundled and joined to a terminal. For example, in a conventional manufacturing method including stacking positive and negative electrode plates 12 and 14 alternately to form a multi-layer cell, bundling and pressing the positive electrode current collector tabs 12b together or the negative electrode current collector tabs 14c together, and joining them to a positive electrode terminal 26 or a negative electrode terminal (not shown), as shown in FIG. 11, an excessive load is applied to the ends of the positive electrode active material layer 12a or the negative electrode active material layer 14a, particularly during pressing, as shown in FIG. 12, and defects D are likely to occur in the positive electrode active material layer 12a, the negative electrode active material layer 14a, and / or the separator 16, increasing the risk of short circuit. Moreover, in the case of a zinc secondary battery, a shape change occurs in which the shape of the negative electrode changes as charging and discharging are repeated. This is a phenomenon in which the negative electrode active material layer 14a shrinks unevenly toward the center as charging and discharging are repeated, that is, the peripheral part of the negative electrode active material layer 14a (ZnO layer) is unevenly eroded and lost. There is a concern that the deformation of the end of the negative plate due to this shape change will cause the current collecting tab to be pulled further, further increasing the risk of a short circuit.

[0013] In contrast, in the present invention, as shown in FIG. 6, each of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c has a non-rounded shape bent at at least two points F when viewed in cross section, unlike conventional current collector tabs. As a result, each of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c has at least two straight portions S parallel to the positive electrode plate 12 and the negative electrode plate 14, and an inclined portion I between the at least two straight portions S. For this reason, when the positive electrode plate 12 and the negative electrode plate 14 are alternately stacked, the straight portions S of the positive electrode current collector tabs 12b that are away from the positive electrode plate 12 can be stacked (i.e., bundled) so as to be in contact with each other, while the straight portions S of the negative electrode current collector tabs 14c that are away from the negative electrode plate 14 can be stacked (i.e., bundled) so as to be in contact with each other. This is because the presence of the inclined portion I offsets the positional deviation (gap) in the lamination method between the straight portion S closer to the positive electrode plate 12 or the negative electrode plate 14 and the straight portion S farther from the positive electrode plate 12 or the negative electrode plate 14. Since the gap is different for each positive electrode plate 12 or each negative electrode plate 14, the inclination angle of the inclined portion I can be individually set to offset the individual gaps. As a result, it becomes possible to bundle the positive electrode current collector tabs 12b together and the negative electrode current collector tabs 14c together and join them to members such as terminals without pulling the positive electrode current collector tabs 12b and the negative electrode current collector tabs 14c. That is, in contrast to FIG. 12 of the conventional manufacturing method, as shown in FIG. 8, excessive load is not applied to the ends of the positive electrode active material layer 12a and the negative electrode active material layer 14a, and defects D are less likely to occur in the positive electrode active material layer 12a, the negative electrode active material layer 14a, and / or the separator 16, thereby reducing the risk of short circuit.

[0014] However, as shown in Figs. 6 and 7, there may be a positive electrode current collector tab 12b located in the same plane as the positive electrode tab joint (not shown). Similarly, there may be a negative electrode current collector tab 14c located in the same plane as the negative electrode tab joint 30. In such a case, the positive electrode current collector tab 12b and / or the negative electrode current collector tab 14c in the same plane may exceptionally be composed of only one straight portion S parallel to the positive electrode plate 12 and / or the negative electrode plate 14 without being bent. In such a case, since the positional deviation (gap) of the stacking method as described above does not occur in the first place, there is no point in providing the inclined portion I to offset the gap. Note that the above-mentioned "same plane" does not need to be a completely same plane, and may be an approximately same plane including a tolerance to the extent that the inclined portion I can be eliminated.

[0015] The inclination angle of the inclined portion I with respect to the straight portion S can be within a range of 0° to 90°, typically 0° to 85°, more typically 0° to 80°, and further typically 0° to 70°. Within such a range, even when a large number of positive electrode plates 12 and negative electrode plates 14 are stacked, the positive electrode current collector tab 12b or the negative electrode current collector tab 14c can be joined to a member such as a terminal without being pulled. When a current collector tab with an inclination angle of 90° exists, the length of the straight portion S can be changed individually so that the inclined portion I does not hit the adjacent current collector tab, thereby bundling multiple current collector tabs and joining them to a member such as a terminal without difficulty. The inclination angle of the inclined portion I with respect to the straight portion S is defined as an acute angle or an angle of 90° (i.e., not an obtuse angle) formed by the inclined portion I and a reference plane parallel to the straight portion S arranged in parallel to the plate surface of the positive electrode plate 12 or the negative electrode plate 14 as shown in FIG. 7. Therefore, in the case of a typical embodiment in which one inclined portion I exists between two straight portions S as shown in FIG. 7, the two inclination angles θ 1 and θ 2 are geometrically equal. However, θ 1 and θ 2 do not need to be completely equal, but may be approximately equal while allowing for a tolerance that allows the straight S portion on the terminal side to be bundled without problems.

[0016] 7, the inclination angle of each of the inclined portions I of the positive electrode collector tab 12b and the negative electrode collector tab 14c with respect to the straight portion S is set individually so as to offset the positional deviation in the stacking direction between the positive electrode tab joint (not shown) or the negative electrode tab joint 30 and the positive electrode plate 12 or the negative electrode plate 14, so that the inclined portions of adjacent positive electrode collector tabs 12b and negative electrode collector tabs 14c form different inclination angles. In this way, even when a large number of positive electrode plates 12 and negative electrode plates 14 are stacked, the positive electrode collector tabs 12b or negative electrode collector tabs 14c can be bound together and joined to a member such as a terminal without being pulled. In this case, it is preferable that the inclination angle of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c gradually decreases from the outside of the multi-layer cell (for example, the positive electrode plate 12 marked with #1 and the positive electrode plate 12 marked with #n in FIG. 7) toward the same plane as the positive electrode tab joint (not shown) and / or the negative electrode tab joint 30. Therefore, it is typical that the inclination angle of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c gradually decreases from the outside of the multi-layer cell toward the center, but is not limited thereto. For example, when the positive electrode tab joint (not shown) and / or the negative electrode tab joint 30 are offset from the center of the multi-layer cell, the inclination angle of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c may be gradually decreased toward the same plane as the joint offset from the center. Therefore, a configuration in which the inclination angle gradually decreases from one outside of the multi-layer cell toward the other outside of the multi-layer cell may be adopted.

[0017] 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 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 collector tab 12b extending in a predetermined direction (for example, upward) from an end (for example, an upper end) of the positive electrode plate 12. A preferred example of the positive electrode current collector is a nickel porous substrate such as a foamed nickel plate. In this case, for example, a paste containing an electrode active material such as nickel hydroxide is uniformly applied onto a nickel porous substrate and dried to preferably produce a positive electrode plate consisting of a positive electrode / positive electrode current collector. At that time, it is also preferable to perform a press process on the dried positive electrode plate (i.e., positive electrode / positive electrode current collector) to prevent the electrode active material from falling off and improve the electrode density. The positive electrode plate 12 shown in FIG. 5 includes a positive electrode current collector (e.g., nickel foam), but is not shown. This is because in the case of a nickel-zinc secondary battery, the positive electrode current collector is completely integrated with the positive electrode active material, and therefore the positive electrode current collector cannot be depicted separately. The positive electrode current collector tab 12b may be made of the same material as the positive electrode current collector, or may be made of a different material. When the positive electrode current collector is a nickel porous substrate such as a nickel foam plate, it can be processed into a tab shape by pressing it. In any case, the positive electrode current collector tab 12b may be extended by adding another current collecting member such as a tab lead to such a tab. In any case, it is preferable that a plurality of positive electrode current collector tabs 12b are joined to one positive electrode terminal 26 or a member electrically connected thereto to form a positive electrode tab joint (not shown). This allows current collection to be performed with a simple configuration and with good space efficiency, and also makes it easier to connect to the positive electrode terminal 26. The positive electrode current collecting tab 12b can be joined to a member such as a terminal by using a known joining method such as ultrasonic welding (ultrasonic joining), laser welding, TIG welding, or resistance welding.

[0018] The positive electrode plate 12 may contain at least one additive selected from the group consisting of silver compounds, manganese compounds, and titanium compounds, which can promote a positive electrode reaction that absorbs hydrogen gas generated by a self-discharge reaction. 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 additive, thereby contributing to an improvement in charge / discharge capacity.

[0019] 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 included in any form of zinc metal, zinc compound, or zinc alloy, so long as it has electrochemical activity suitable for the negative electrode. Preferred examples of the negative electrode material include zinc oxide, zinc metal, calcium zincate, and the like, with a mixture of zinc metal and zinc oxide being more preferred. The negative electrode active material may be configured in a gel form, or may be mixed with the electrolyte 18 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 the thickener include polyvinyl alcohol, polyacrylate, CMC, alginic acid, and the like, with polyacrylic acid being preferred because of its excellent chemical resistance to strong alkalis.

[0020] As the zinc alloy, a zinc alloy containing no mercury or lead, known as a mercury-free zinc alloy, can be used. For example, a zinc alloy containing 0.01 to 0.1 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is 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 improve safety by suppressing hydrogen gas generation by slowing down the self-dissolution rate in an alkaline electrolyte.

[0021] The shape of the negative electrode material is not particularly limited, but it is preferably in powder form, which increases the surface area and allows for high-current discharge. The average particle size of the negative electrode material is preferably in the range of 3 to 100 μm in minor axis in the case of a zinc alloy, and within this range, the large surface area makes it suitable for high-current discharge, and it is easy to mix uniformly with the electrolyte and gelling agent, and is easy to handle when assembling a battery.

[0022] The negative electrode plate 14 further includes a negative electrode collector 14b. The negative electrode collector 14b is provided inside and / or on the surface of the negative electrode active material layer 14a, except for a portion extending as a negative electrode current collector tab 14c. That is, the negative electrode active material layer 14a may be provided on both sides of the negative electrode collector 14b, or the negative electrode active material layer 14a may be provided only on one side of the negative electrode collector 14b. The negative electrode current collector tab 14c extends from an end (e.g., the upper end) of the negative electrode plate 14 in a predetermined direction (e.g., upward) at a position that does not overlap with the positive electrode current collector tab 12b. The negative electrode current collector tab 14c is preferably provided at a position that does not overlap with the positive electrode current collector tab 12b. The negative electrode current collector tab 14c may be made of the same material as the negative electrode current collector 14b, or may be made of a different material. In either case, the negative electrode current collecting tab 14c may be extended by adding another current collecting member such as a tab lead to such a tab. In either case, it is preferable to form the negative electrode tab joint 30 by joining a plurality of negative electrode current collecting tabs 14c to one negative electrode terminal 28 or a member electrically connected thereto. This allows current collection to be performed with a simple configuration and with good space efficiency, and also makes it easier to connect to the negative electrode terminal 28. The joining of the negative electrode current collecting tab 14c to a member such as a terminal may be performed using a known joining method such as ultrasonic welding (ultrasonic joining), laser welding, TIG welding, or resistance welding.

[0023] The negative electrode current collector 14b is preferably a metal plate having a plurality (or a large number) of 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 preferably copper expanded metal, copper punched metal, and combinations thereof, and particularly preferably copper expanded metal. In this case, for example, a mixture containing zinc oxide powder and / or zinc powder, and optionally a binder (e.g., polytetrafluoroethylene particles) can be applied onto the copper expanded metal to preferably prepare a negative electrode plate consisting of a negative electrode / a negative electrode current collector. In this case, it is also preferable to perform a press treatment on the negative electrode plate (i.e., a negative electrode / a negative electrode current collector) after drying to prevent the electrode active material from falling off and improve the electrode density. The expanded metal is a mesh-shaped metal plate obtained by pressing and expanding a metal plate while making staggered cuts using an expander, and shaping the cuts into a diamond or tortoiseshell shape. Punching metal, also known as perforated metal, is a metal plate with holes punched into it. Metal mesh is a metal product with a wire mesh structure, and is different from expanded metal and punching metal.

[0024] The hydroxide ion conductive separator 16 is provided so as to separate the positive electrode plate 12 and the negative electrode plate 14 in a manner allowing hydroxide ion conductivity. For example, as shown in FIG. 5, the negative electrode plate 14 may be configured to be covered or wrapped with the hydroxide ion conductive separator 16. This makes it possible to fabricate a nickel-zinc secondary battery (particularly a laminated battery thereof) capable of preventing zinc dendrite extension extremely easily and with high productivity, without the need for a complicated sealing joint between the hydroxide ion conductive separator 16 and the battery case. However, a simple configuration in which the hydroxide ion conductive separator 16 is disposed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used.

[0025] The hydroxide ion conductive separator 16 is not particularly limited as long as it is a separator capable of isolating the positive electrode plate 12 and the negative electrode plate 14 in a hydroxide ion conductive manner, but is typically a separator that includes a hydroxide ion conductive solid electrolyte and selectively passes hydroxide ions solely by utilizing hydroxide ion conductivity. A preferred hydroxide ion conductive solid electrolyte is a layered double hydroxide (LDH) and / or an LDH-like compound. Therefore, the hydroxide ion conductive separator 16 is preferably an LDH separator. In this specification, an "LDH separator" is defined as a separator that includes an LDH and / or an LDH-like compound and selectively passes hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and / or the LDH-like compound. In this specification, an "LDH-like compound" is a hydroxide and / or oxide with a layered crystal structure similar to LDH, which may not be called LDH, and can be said to be equivalent to LDH. However, in a broad sense, "LDH" can be interpreted as including not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and / or LDH-like compounds. That is, in a preferred LDH separator, the pores of the porous substrate are blocked with LDH and / or LDH-like compounds so as to exhibit hydroxide ion conductivity and gas impermeability (and therefore function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferred that the LDH is incorporated over the entire thickness of the porous substrate made of a polymer material. For example, known LDH separators such as those disclosed in Patent Documents 1 to 7 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, even more preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.

[0026] 1-3 and 5, the positive electrode plate 12, the positive electrode current collector tab 12b, the negative electrode plate 14, the negative electrode current collector tab 14c, and the hydroxide ion conductive separator 16 are preferably arranged vertically, thereby forming a multi-layer cell with multiple layers in the horizontal direction. Also, the positive electrode current collector tab 12b and the negative electrode current collector tab 14c preferably extend upward.

[0027] The zinc secondary battery 10 may further include a liquid retaining member 17 in contact with the positive electrode plate 12 and / or the negative electrode plate 14. For example, it is preferable that not only the hydroxide ion conductive separator 16 but also the liquid retaining member 17 is interposed between the positive electrode plate 12 and the negative electrode plate 14. As shown in FIG. 5, it is preferable that the positive electrode plate 12 and / or the negative electrode plate 14 is covered or wrapped with the liquid retaining member 17. However, a simple configuration in which the liquid retaining member 17 is disposed on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used. In any case, by interposing the liquid retaining member 17, the electrolyte 18 can be evenly present between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16, and hydroxide ions can be efficiently exchanged between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16. The liquid-retaining member 17 is not particularly limited as long as it is a member capable of retaining the electrolyte solution 18, but is preferably a sheet-like member. Preferred examples of the liquid-retaining member 17 include nonwoven fabric, water-absorbent resin, liquid-retaining resin, porous sheet, and various spacers, but nonwoven fabric is particularly preferred because it allows the production of a negative electrode structure with good performance 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. If the thickness is within the above range, a sufficient amount of electrolyte solution 18 can be retained in the liquid-retaining member 17 while keeping the overall size of the positive electrode structure and / or negative electrode structure compact and without waste.

[0028] When the positive electrode plate 12 and / or the negative electrode plate 14 are covered or wrapped with the liquid retaining member 17 and / or the separator 16, it is preferable that the outer edge of the positive electrode plate 12 and / or the separator 16 is closed (except for the edge from which 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 edge of the outer edge of the liquid retaining member 17 and / or the separator 16 is realized by folding the liquid retaining member 17 and / or the separator 16, or by sealing the liquid retaining members 17 together and / or the separators 16 together. Examples of the sealing method include adhesives, heat welding, ultrasonic welding, adhesive tape, sealing tape, and combinations thereof. In particular, since the LDH separator including the porous base material made of a polymer material has an advantage that it is flexible and therefore easy to bend, it is preferable to form the LDH separator into a long shape and fold it to form a state in which one side of the outer edge is closed. Thermal welding and ultrasonic welding may be performed using a commercially available heat sealer or the like, but in the case of sealing between LDH separators, it is preferable to perform thermal welding and ultrasonic welding by sandwiching the outer peripheral portion of the liquid retaining member 17 between the LDH separators constituting the outer peripheral portion, in order to perform more effective sealing. On the other hand, the adhesive, adhesive tape, and sealing tape may be commercially available products, but it is preferable to use those containing a resin having alkali resistance in order to prevent deterioration in an alkaline electrolyte. From this viewpoint, examples of preferable adhesives include epoxy resin adhesives, natural resin adhesives, modified olefin resin adhesives, and modified silicone resin adhesives, and among them, epoxy resin adhesives are more preferable because they are particularly excellent in alkali resistance. An example of a product of an epoxy resin adhesive is the epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

[0029] It is preferable that the outer edge of one side, which is the upper end of the separator 16, is open. This open-top structure makes it possible to deal with the problem of overcharging in nickel-zinc batteries and the like. That is, when a nickel-zinc battery or the like is overcharged, oxygen (O 2 ) may occur, but the LDH separator is highly dense and allows only hydroxide ions to pass through, so O 2In this respect, the open-top structure allows O 2 can be released above the positive electrode plate 12 and sent to the negative electrode plate 14 side through the upper open portion, thereby 2 The negative electrode active material Zn can be oxidized to ZnO by oxygen reaction. By going through such an oxygen reaction cycle, the open-top battery element 11 can be used in a sealed zinc secondary battery to improve overcharge resistance. Even if the outer edge of one side that is the upper end of the separator 16 or the liquid-retaining member 17 is closed, the same effect as that of the open-type configuration can be expected by providing a vent hole in a part of the closed outer edge. For example, the vent hole may be opened after sealing the outer edge of one side that is the upper end of the LDH separator, or a part of the outer edge may be left unsealed so that a vent hole is formed during sealing.

[0030] The electrolyte 18 preferably contains an aqueous solution of an alkali metal hydroxide. In FIG. 5, the electrolyte 18 is only partially illustrated because it is distributed over the entire positive electrode plate 12 and the negative electrode plate 14. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being more preferable. In order 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 described above, the electrolyte may be mixed with the positive electrode active material and / or the negative electrode active material to be present in the form of a positive electrode mixture and / or a negative electrode mixture. In addition, the electrolyte may be gelled to prevent leakage of the electrolyte. As the gelling agent, it is preferable to use a polymer that absorbs the solvent of the electrolyte and swells, and polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, or starch are used.

[0031] As shown in Figs. 3 to 7, the battery element 11 is in the form of a positive and negative electrode laminate, which includes a plurality of positive electrode plates 12, a plurality of negative electrode plates 14, and a plurality of separators 16, and is laminated so that the unit of positive electrode plate 12 / separator 16 / negative electrode plate 14 is repeated. That is, the zinc secondary battery 10 has a plurality of unit cells 10a, and the plurality of unit cells 10a as a whole form a multi-layer cell. This is the configuration of a so-called assembled battery or laminated battery, and is advantageous in that a high voltage and a large current can be obtained.

[0032] The battery case 20 is preferably made of resin. The resin constituting the battery 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 ABS resin or modified polyphenylene ether. The battery case 20 has a top lid 20a. The battery case 20 (e.g., the top lid 20a) may have a pressure relief valve for releasing gas. In addition, a group of cases in which two or more battery cases 20 are arranged may be housed in an outer frame to form a battery module. EXAMPLES

[0033] The present invention will now be further illustrated by the following examples.

[0034] Example 1 The following positive electrode plate, positive electrode current collector tab, negative electrode plate, negative electrode current collector tab, LDH separator, nonwoven fabric, battery case, and electrolyte are prepared. Positive electrode plate: The pores of the nickel foam are filled with a positive electrode paste containing nickel hydroxide and a binder, and then dried (there is an uncoated area near one edge of the nickel foam where the positive electrode paste is not applied). Positive electrode current collecting tab: The uncoated area of ​​the foamed nickel that makes up the positive electrode plate is compressed with a roll press to form a tab, and a tab lead (made of pure nickel, thickness: 100 μm) is ultrasonically welded to this tab to extend it. Negative electrode plate: A negative electrode paste containing ZnO powder, metallic Zn powder, polytetrafluoroethylene (PTFE) and propylene glycol is pressed onto a current collector (copper expanded metal) (there is an uncoated area near one edge of the copper expanded metal where the negative electrode paste is not applied). Negative electrode current collecting tab: A tab lead (made of copper, thickness: 100 μm) is connected to the uncoated part of the copper expanded metal by ultrasonic welding. LDH separator: Ni-Al-Ti-LDH (layered double hydroxide) is deposited on the inside and surface of a polyethylene microporous membrane by hydrothermal synthesis and then roll-pressed. Thickness: 20 μm Non-woven fabric: Polypropylene, thickness 100μm Battery case: Modified polyphenylene ether resin housing (equipped with a pressure relief valve to release gas generated inside the case) Electrolyte: 5.4mol / L KOH solution with 0.4mol / L ZnO dissolved in it

[0035] The positive electrode plate is wrapped in nonwoven fabric so as to cover both sides, so that the nonwoven fabric slightly protrudes from the remaining three sides except for the side from which the positive electrode current collector tab extends. The excess portion of the nonwoven fabric protruding from the three sides of the positive electrode plate is heat-sealed with a heat seal bar to obtain a positive electrode structure. The negative electrode plate is wrapped in nonwoven fabric and LDH separator in order from both sides, so that the nonwoven fabric and LDH separator slightly protrude from the remaining three sides except for the side from which the negative electrode current collector tab extends. The excess portion of the nonwoven fabric and LDH separator protruding from the three sides of the negative electrode plate is heat-sealed with a heat seal bar to obtain a negative electrode structure. In this way, a total of 19 electrode structures consisting of 9 positive electrode structures and 10 negative electrode structures are prepared.

[0036] A total of 19 electrode structures are given serial numbers of 1 to 19. At this time, the serial numbers are given so that the negative electrode plates 14 and the positive electrode plates 12 are alternately repeated as shown in FIG. 7. Then, the positive electrode current collector tabs 12b or the negative electrode current collector tabs 14c of each electrode structure with serial numbers 1 to 19 are bent at an inclination angle θ shown in Table 1 using a sheet metal bending machine. 1 and θ 2 (where θ 1=θ 2 ) are formed parallel to the sides of the positive electrode plate 12 and the negative electrode plate 14 from which the positive electrode current collector tab 12b or the negative electrode current collector tab 14c extends. In this way, each of the positive electrode current collector tab 12b and the negative electrode current collector tab 14c is plastically deformed (formed) so as to have two straight portions S that are parallel to the positive electrode plate 12 and the negative electrode plate 14 when viewed in cross section, and an inclined portion I between the two straight portions S.

[0037] [Table 1]

[0038] The electrode structures having the current collector tabs plastically deformed by forming are stacked in the order of serial numbers as shown in Figs. 6 and 7. At this time, as in the configuration shown in Fig. 4, the nine positive current collector tabs 12b and the ten negative current collector tabs 14c are designed to extend from different positions from each other from the electrode current collector when viewed in a plan view, so that the nine positive current collector tabs 12b are stacked on top of each other, while the ten negative current collector tabs 14c are stacked on top of each other at a different position. In this way, the overlapping portions of the straight portions S of the nine positive current collector tabs 12b that are farther from the positive electrode plate 12 are joined together to the positive electrode terminal 26 by laser welding to form a positive electrode tab joint (not shown). Similarly, the overlapping portions of the straight portions S of the ten negative current collector tabs 14c that are farther from the negative electrode plate 14 are joined together to the negative electrode terminal 28 by laser welding to form a negative electrode tab joint 30. In this way, the various inclination angles θ shown in Table 1 are formed. 1 and θ 2 A stack of electrode structures including a positive electrode current collector tab 12b and a negative electrode current collector tab 14c having an inclined portion I is obtained as a battery element 11. As shown in Figures 1 and 2, this battery element 11 is placed in a battery case 20, an electrolyte 18 is poured in to impregnate the battery element 11, and a lid 20a is closed and sealed.

[0039] Example 2 A total of 23 electrode structures consisting of 11 positive electrode structures and 12 negative electrode structures were prepared. The negative electrode plates 14 and the positive electrode plates 12 were assigned serial numbers so that they were alternately arranged, and the inclination angle θ 1 and θ 2 (where θ 1 =θ 2 A multi-layer cell type nickel-zinc secondary battery is fabricated in the same manner as in Example 1, except that two folds F are formed in the first fold F.

[0040] [Table 2]

[0041] Example 3 A total of 27 electrode structures consisting of 13 positive electrode structures and 14 negative electrode structures were prepared, and the negative electrode plates 14 and the positive electrode plates 12 were assigned serial numbers so as to be alternately repeated, and the inclination angles θ 1 and θ 2 (where θ 1 =θ 2 Three multi-layer cell type nickel-zinc secondary batteries were fabricated in the same manner as in Example 1, except that two folds F were formed in the first fold F.

[0042] [Table 3]

[0043] Example 4 (comparison) Three multi-layer cell type nickel-zinc secondary batteries were fabricated in the same manner as in Example 3, except that the formation of folds F, ie, plastic deformation (forming) was not carried out.

[0044] result The batteries prepared in Examples 3 and 4 (three batteries for each example) were evaluated for the presence or absence of short circuits as follows. The results are shown in Table 4.

[0045] (Evaluation of the presence or absence of a short circuit) A charge-discharge cycle test was carried out on the three batteries produced, and the cells that showed short-circuit behavior were disassembled and the presence or absence of dendrite penetration in the electrode plate was examined by visual observation. As a result, the battery of Example 4 (Comparative Example) produced through forming had many traces of dendrite short circuit in the electrode active material area near the tab. On the other hand, the battery of Example 3 produced through forming had no traces of dendrite short circuit near the electrode active material near the tab. Table 4 shows the conditions and results of each example.

[0046] [Table 4]

[0047] As can be seen from Table 4, the multilayer cell of Example 3 produced through plastic deformation (forming) according to the present invention was less likely to cause a short circuit than the multilayer cell of Example 4 (Comparative Example) produced by a conventional method. This is believed to be because a short circuit is less likely to occur not only during production but also during use (especially when the negative electrode shape changes) due to the load on the end of the electrode plate from which the short-circuiting current collecting tab extends. As for Examples 1 and 2, since the current collecting tabs produced through forming and bent at two places and not rounded are used, the current collecting tabs can be bundled together and joined to the terminal without being pulled, so that excessive load is not applied to the end of the active material layer, and therefore it can be said that short circuits are less likely to occur as in Example 3.

Claims

1. a positive electrode plate including a positive electrode active material layer and a positive electrode current collector; a positive electrode current collecting tab extending in a predetermined direction from an end of the positive electrode plate; a negative electrode plate including a negative electrode active material layer including at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound, and a negative electrode current collector; a negative electrode current collecting tab extending in the predetermined direction from an end of the negative electrode plate at a position not overlapping with the positive electrode current collecting tab; a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so as to be capable of conducting hydroxide ions; An electrolyte; A zinc secondary battery comprising a plurality of unit cells each including: each of the positive electrode current collector tab and the negative electrode current collector tab has a non-rounded shape folded at at least two places when viewed in cross section, whereby each of the positive electrode current collector tab and the negative electrode current collector tab has at least two straight portions parallel to the positive electrode plate and the negative electrode plate, and an inclined portion between the at least two straight portions; the straight portions of the positive electrode current collecting tabs that are away from the positive electrode plate are stacked and joined together to form a positive electrode tab joint, and the straight portions of the negative electrode current collecting tabs that are away from the negative electrode plate are stacked and joined together to form a negative electrode tab joint. However, when the positive electrode current collector tab and / or the negative electrode current collector tab are located in the same plane as the positive electrode tab joint portion and / or the negative electrode tab joint portion, the positive electrode current collector tab and / or the negative electrode current collector tab in the same plane may exceptionally be composed of only one straight portion parallel to the positive electrode plate and / or the negative electrode plate without being bent, A zinc secondary battery in which the inclined portions of the positive electrode current collector tab and the negative electrode current collector tab are individually set at an inclination angle within a range of 0° to 70° with respect to the straight portion so as to offset the misalignment in the stacking direction between the positive electrode tab joint or the negative electrode tab joint and the positive electrode plate or the negative electrode plate, thereby causing the inclined portions of adjacent positive electrode current collector tabs and negative electrode current collector tabs to form different inclination angles.

2. 2. The zinc secondary battery of claim 1, wherein each of the positive electrode plate, the positive electrode current collector tab, the negative electrode plate, the negative electrode current collector tab, and the hydroxide ion conductive separator are vertically oriented, thereby forming a horizontally multi-layered cell.

3. 3. The zinc secondary battery of claim 2, wherein the positive electrode current collector tab and the negative electrode current collector tab extend upwardly.

4. The zinc secondary battery according to any one of claims 1 to 3, wherein the inclination angle of the positive electrode current collector tab and the negative electrode current collector tab gradually decreases from the outside of the multi-layer cell toward the same plane as the positive electrode tab joint and / or the negative electrode tab joint.

5. 5. The zinc secondary battery according to claim 1, wherein the inclination angle of the positive electrode current collector tab and the negative electrode current collector tab gradually decreases from the outside to the center of the multi-layer cell.

6. The zinc secondary battery according to any one of claims 1 to 5, further comprising a liquid retaining member in contact with the positive electrode plate and / or the negative electrode plate.

7. 7. The zinc secondary battery according to claim 1, wherein the hydroxide ion conducting separator is a layered double hydroxide (LDH) separator comprising an 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 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 polymeric material.

10. The zinc secondary battery according to any one of claims 1 to 9, 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.

11. The zinc secondary battery according to any one of claims 1 to 9, wherein the positive electrode active material layer is an air electrode layer, thereby forming the zinc secondary battery into an air zinc secondary battery.

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