Nickel-zinc secondary battery

Abstract

The present invention provides a nickel zinc secondary battery which has a significantly improved calender life. This nickel zinc secondary battery is provided with an airtight container in which a positive electrode, a negative electrode, a separator that is interposed between the positive electrode and the negative electrode, and an electrolyte solution are arranged. This nickel zinc secondary battery is also provided with an oxygen absorption material within the airtight container at a position where oxygen generated at the positive electrode is able to be absorbed thereby.

Description

[Technical Field]

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

[0002] In zinc secondary batteries, such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates from the negative electrode in the form of dendrites during charging, penetrates the pores of separators such as nonwoven fabrics, and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the repetitive charge-discharge life. To address this issue, batteries equipped with layered double hydroxide (LDH) separators that selectively allow hydroxide ions to pass through while preventing the penetration of zinc dendrites have been proposed (see, for example, Patent Document 1 (WO 2016 / 076047) and Patent Document 2 (WO 2019 / 124270)). Furthermore, although not specifically referred to as LDHs, LDH-like compounds are known as hydroxides and / or oxides with a layered crystalline structure similar to LDHs. These compounds exhibit hydroxide ion conducting properties similar to LDHs and can be collectively referred to as hydroxide ion conducting layered compounds. For example, Patent Document 3 (WO 2020 / 255856) discloses a hydroxide ion conductive separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that blocks the pores of the porous substrate. Patent Document 4 (WO 2019 / 069760) and Patent Document 5 (WO 2019 / 077953) propose a zinc secondary battery configured such that the entire negative electrode active material layer is covered or wrapped with a liquid-retaining member and an LDH separator, and the positive electrode active material layer is covered or wrapped with a liquid-retaining member. A nonwoven fabric is used as the liquid-retaining member. This configuration eliminates the need for a complicated sealing joint between the LDH separator and the battery container, and is said to enable extremely simple and highly productive production of zinc secondary batteries (especially stacked batteries) capable of preventing zinc dendrite extension.

[0003] Incidentally, vinylon nonwoven fabrics and separators are commercially available. In particular, vinylon separators are used in alkaline batteries such as alkaline manganese batteries (alkaline dry batteries). Vinylon is a general term for polyvinyl alcohol (PVA)-based synthetic fibers and generally refers to synthetic fibers obtained using PVA as a raw material. However, the polyvinyl alcohol used in vinylon is known to deteriorate due to heat at temperatures above 200°C in air and to deteriorate in alkaline aqueous solutions. For example, Non-Patent Document 1 (see Imai Kiyokazu, "Degradation of Polyvinyl Alcohol," Polymer, 1962, Vol. 11, No. 6, pp. 426-430, published September 21, 2011) describes the thermal degradation of PVA in air at 200°C or higher, with a reaction formula for the degradation mechanism, stating that the main degradation reactions are carbonyl group (oxidation), double bond (dehydration) (conjugated enone structure or polyene structure), formation of crosslinked or branched bonds, and main chain cleavage. This document also describes that PVA cleaves in an alkaline aqueous solution in the presence of air but not in nitrogen, and that this is because PVA undergoes air oxidation to form carbonyl groups in the main chain, which then cleaves via a retro-aldol reaction. Non-Patent Document 2 (Hideji Matsuzawa, "Decomposition and Crosslinking of Polyvinyl Alcohol," Polymer, 1963, Vol. 12, No. 4, pp. 283-287, published September 21, 2011) describes that PVA decomposes when heated in air at temperatures above 200°C. The document describes a reaction mechanism, including a reaction formula, in which ketone groups are formed by oxidation in air, causing the PVA to decompose, forming aldehyde groups at the decomposition sites, and the PVA containing these aldehyde groups further decomposes. This document also describes, along with a reaction formula, that a retro-aldol reaction occurs when PVA is boiled in an alkaline aqueous solution, and that the resulting terminal group is likely an aldehyde group. It also describes that PVA with carbonyl groups introduced into the main chain other than the terminals also decomposes in the same manner via the retro-aldol reaction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 076047 [Patent Document 2] International Publication No. 2019 / 124270 [Patent Document 3] International Publication No. 2020 / 255856 [Patent Document 4] International Publication No. 2019 / 069760 [Patent Document 5] International Publication No. 2019 / 077953 [Patent Document 6] Japanese Patent Application Laid-Open No. 2000-037820 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-334467 [Patent Document 8] International Publication No. 2008 / 140004 [Patent Document 9] Japanese Patent Application Laid-Open No. 2002-35579 [Patent Document 10] Japanese Patent Application Publication No. 5-7773 [Patent Document 11] Japanese Patent Application Laid-Open No. 2003-79354 [Patent Document 12] Japanese Patent Application Laid-Open No. 2005-8699 [Patent Document 13] Japanese Patent Application Laid-Open No. 2008-221065 [Patent Document 14] Japanese Patent Application Laid-Open No. 2011-184482 [Patent Document 15] International Publication No. 2006 / 101020 [Patent Document 16] Japanese Patent Application Laid-Open No. 2012-207234 [Patent Document 17] International Publication No. 2013 / 187455 [Non-patent literature]

[0005] [Non-Patent Document 1] Kiyokazu Imai, "Degradation of Polyvinyl Alcohol," Polymer, 1962, Vol. 11, No. 6, pp. 426-430, Published 2011 / 09 / 21, Online ISSN 2185-9825, Print ISSN 0454-1138, https: / / doi.org / 10.1295 / kobunshi.11.426, https: / / www.jstage.jst.go.jp / article / kobunshi1952 / 11 / 6 / 11_6_426 / _article / -char / ja [Non-patent document 2] Shuji Matsuzawa, "Decomposition and Crosslinking of Polyvinyl Alcohol," Polymer, 1963, Vol. 12, No. 4, pp. 283-287, Published 2011 / 09 / 21, Online ISSN 2185-9825, Print ISSN 0454-1138, https: / / doi.org / 10.1295 / kobunshi.12.283, https: / / www.jstage.jst.go.jp / article / kobunshi1952 / 12 / 4 / 12_4_283 / _article / -char / ja Summary of the Invention

[0006] By taking measures against dendrites as described above, the cycle life of nickel-zinc secondary batteries can be extended. However, the life of nickel-zinc secondary batteries is determined not only by the cycle life but also by the calendar life. Therefore, there is a demand for improving the calendar life of nickel-zinc secondary batteries.

[0007] The present inventors have now discovered that the calendar life of a nickel-zinc secondary battery can be significantly improved by providing an oxygen absorber inside the battery.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a nickel-zinc secondary battery with significantly improved calendar life.

[0009] According to the present invention, the following aspects are provided. [Aspect 1] A nickel-zinc secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, all contained in a sealed container, a nickel-zinc secondary battery, wherein an oxygen absorber is disposed in the sealed container at a position where it can absorb oxygen generated at the positive electrode; [Aspect 2] 2. The nickel-zinc secondary battery of claim 1, wherein the location capable of absorbing oxygen generated by the positive electrode is at least one selected from the group consisting of a surface or periphery of the positive electrode, a surface or periphery of the negative electrode, a space between the positive electrode and the negative electrode, a surface or periphery of the separator, an inner wall of the sealed container, a surface of a positive electrode current collector tab extending from the positive electrode, a surface of a negative electrode current collector tab extending from the negative electrode, and an excess space within the sealed container. [Aspect 3] 3. The nickel-zinc secondary battery of claim 1, wherein the oxygen absorber is at least one selected from the group consisting of metal powder, titanium dioxide, cerium oxide, a transition metal salt, a ferrous salt, a dithionite, a zeolite, vinylon, benzenetriol, a polyhydric phenol compound, a polyhydric alcohol compound, an ascorbic acid compound, a cyclohexene compound, a polyene polymer having an unsaturated double bond, and an ethylene-vinyl alcohol copolymer. [Aspect 4] A nickel-zinc secondary battery according to any one of aspects 1 to 3, wherein the oxygen absorber is in the form of a nonwoven fabric, and the positive electrode and / or the negative electrode is covered with the nonwoven fabric. [Aspect 5] 5. The nickel-zinc secondary battery of claim 4, wherein the nonwoven fabric comprises vinylon. [Aspect 6] A nickel-zinc secondary battery according to any one of aspects 1 to 5, wherein the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, and the negative electrode contains zinc and / or zinc oxide. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing an example of a nickel-zinc secondary battery according to the present invention. [Figure 2]FIG. 2 is a diagram schematically illustrating an example of a cross section of the nickel-zinc secondary battery shown in FIG. 1 taken along line AA'. [Figure 3] FIG. 1 is a diagram for conceptually explaining the storage deterioration mechanism in a nickel-zinc secondary battery. [Figure 4] These are optical microscope images (upper row: bright-field observation image, lower row: dark-field observation image) of the cross section of the negative electrode of the nickel-zinc secondary battery prepared in Example 2 (comparison) at the initial point (day 0) and after storing the battery at 65°C for 30, 60, 90, and 120 days. [Figure 5] These are optical microscope images (upper row: bright-field observation image, lower row: dark-field observation image) of the cross section of the negative electrode of the nickel-zinc secondary battery produced in Example 2 (comparison) after storage at 65°C for 120 days. [Figure 6] 1 shows optical microscope images (upper row: bright-field observation image, lower row: dark-field observation image) of the cross section of the negative electrode of the nickel-zinc secondary battery produced in Example 3 after storage at 65° C. for 120 days. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 and 2 show one embodiment of a nickel-zinc secondary battery according to the present invention. The nickel-zinc secondary battery 10 shown in FIGS. 1 and 2 includes a battery element 11 housed in a sealed container 20. The battery element 11 includes a positive electrode 12, a negative electrode 14, a separator 16 interposed between the positive electrode 12 and the negative electrode 14, and an electrolyte 18. An oxygen absorber 17 is disposed in the sealed container 20 at a position where it can absorb oxygen generated at the positive electrode 12. By disposing the oxygen absorber 17 inside the nickel-zinc secondary battery 10 in this manner, the calendar life can be significantly improved. That is, as described above, the life of a nickel-zinc secondary battery is determined not only by its cycle life but also by its calendar life. Therefore, there is a demand for improving the calendar life of nickel-zinc secondary batteries. In this regard, the shortening of calendar life due to performance degradation after long-term storage is caused by a capacity discrepancy between the positive and negative electrodes due to a loss of negative electrode capacity over a long period of storage, but according to the present invention, this problem can be suppressed by disposing an oxygen absorber 17 inside the nickel-zinc secondary battery 10. In other words, oxygen generated in the positive electrode 12 can be absorbed by the oxygen absorber 17, suppressing the capacity consumption of the negative electrode 14, thereby solving the problem of the calendar life. The mechanism behind this is explained below.

[0012] Figure 3 conceptually illustrates the storage degradation mechanism in nickel-zinc secondary batteries. As shown in Figure 3, this storage degradation mechanism can be explained as including four stages: "1. Initial charging," "2. Storage," "3. Discharge," and "4. Charging." First, initially, as shown in "1. Initial charging" in the figure, the battery is typically configured to have a residual capacity in the negative electrode so that the positive electrode can be fully discharged, and even when charged to 100% SOC relative to the positive electrode capacity, there is still some capacity left in the negative electrode. Next, the charged battery is stored. During this storage, the following self-discharge reaction occurs, as shown in "2. Storage" in the figure: <Positive electrode self-discharge reaction> Oxidation reaction of H2O 2NiOOH + H2O → 2Ni(OH)2+ 1 / 2O2↑ (a1) H2 absorption reaction (slow) 2NiOOH + H2 → 2Ni(OH)2(a2) <Negative electrode self-discharge reaction> Reduction reaction of H2O Zn + H2O → ZnO + H2↑ (b1) O2 absorption reaction (fast) Zn + 1 / 2O2 → ZnO (b2) This self-discharge gradually progresses. During this self-discharge, the consumption of the negative electrode discharge capacity during storage is greater than the consumption of the positive electrode discharge capacity, resulting in a greater decrease in the remaining capacity of the negative electrode than of the positive electrode. This is because, as shown in Figure 3, the O absorption reaction (formula (b2)) in the negative electrode self-discharge reaction is faster than the H absorption reaction (formula (a2)) in the positive electrode self-discharge reaction. That is, the generation and absorption of oxygen (O) according to formulas (a1) and (b2) proceeds faster than the generation and absorption of hydrogen (H) according to formulas (b1) and (a2). When discharging is performed after the above storage, the capacity of the negative electrode may be less than that of the positive electrode, as shown in "3. Discharge" in the figure. In this case, the negative electrode capacity is depleted first, and the positive electrode cannot fully discharge. If charging is performed in this state, the battery will reach the installed capacity of the positive electrode, preventing full charge, resulting in a decrease in discharge capacity, as shown in "4. Charge" in the figure. Therefore, by repeating the steps of "2. Storage" to "4. Charging", the battery will no longer be able to discharge completely, and the charge capacity and discharge capacity will decrease, eventually reaching the end of its life.

[0013] Thus, the factor that most significantly impacts the shortening of calendar life is believed to be the consumption of negative electrode discharge capacity, which is greater than the consumption of positive electrode discharge capacity, due to the self-discharge reaction. One cause of the consumption of negative electrode discharge capacity is the water electrolysis reaction, in which oxygen is generated from the positive electrode and hydrogen is generated from the negative electrode. Conventional approaches have not addressed the reaction (formula (b2)) in which oxygen generated at the positive electrode is absorbed by the negative electrode. As a result, the generation and absorption of oxygen according to formulas (a1) and (b2) proceeds faster than the generation and absorption of hydrogen according to formulas (b1) and (a2), resulting in a shortening of calendar life. Therefore, in the present invention, as shown in FIG. 2, an oxygen absorber 17 is disposed inside a nickel-zinc secondary battery 10, allowing oxygen generated at the positive electrode 12 according to formula (a1) to be absorbed by the oxygen absorber 17. This effectively suppresses the progress of the oxygen absorption reaction according to formula (b2), which is believed to be the factor most significantly impacting the shortening of calendar life. As a result, the calendar life of the nickel-zinc secondary battery can be significantly improved.

[0014] The oxygen absorber 17 is disposed in a position in the sealed container 20 where it can absorb oxygen generated at the positive electrode 12. Therefore, although the oxygen absorber 17 is disposed so as to cover the surface or periphery of each of the positive electrode 12 and the negative electrode 14 in Figures 1 and 2, this is not limited thereto, and the oxygen absorber 17 may be disposed in any position as long as it can absorb oxygen within the sealed container 20. Preferred examples of positions where it can absorb oxygen generated at the positive electrode 12 include the surface or periphery of the positive electrode 12, the surface or periphery of the negative electrode 14, the space between the positive electrode 12 and the negative electrode 14, the surface or periphery of the separator 16, the inner wall of the sealed container 20, the surface of the positive electrode current collector tab 13 extending from the positive electrode 12, the surface of the negative electrode current collector tab 15a extending from the negative electrode 14, excess space within the sealed container 20 (e.g., upper excess space and / or lower excess space), and any combination thereof. The surplus space refers to the space within the sealed container 20 that is not occupied by battery components such as the positive electrode 12, the negative electrode 14, and the separator 16. As shown in FIG. 2, the surplus space is preferably the surface or periphery of the positive electrode 12, the surface or periphery of the negative electrode 14, and / or the surface or periphery of the separator 16, and most preferably the surface or periphery of the positive electrode 12 and / or the surface or periphery of the negative electrode 14. This allows oxygen generated at the positive electrode 12 to come into contact with the oxygen absorber 17 before reaching the negative electrode 14. That is, oxygen can be absorbed by the oxygen absorber 17 faster than it is consumed in the oxidation reaction of metallic zinc at the negative electrode 14, thereby effectively reducing the amount of oxygen reaching the negative electrode 14. In this case, the oxygen absorber 17 is preferably a nonwoven fabric. In any case, since it is desirable for the oxygen absorber 17 to absorb oxygen faster than the negative electrode 14 absorbs oxygen, the closer the oxygen absorber 17 is located to the positive electrode 12, the more effective it is (not limited to the case of a nonwoven fabric).

[0015] The oxygen absorber 17 is not particularly limited as long as it is a material capable of absorbing, adsorbing, or capturing oxygen, and can be any of a variety of known materials. Examples of the oxygen absorber 17 include metal powder, titanium dioxide, cerium oxide, transition metal salts, ferrous salts, dithionite, zeolite, vinylon, benzenetriol, polyhydric phenol compounds, polyhydric alcohol compounds, ascorbic acid compounds, cyclohexene compounds, polyene polymers having unsaturated double bonds, ethylene-vinyl alcohol copolymers, and combinations thereof. Specific examples of these oxygen absorbers 17 include those shown in the following table.

[0016] [Table 1]

[0017] The form of the oxygen absorber 17 is not particularly limited and may be selected appropriately depending on the form and type of oxygen absorber used, and may be in various forms such as fiber products such as nonwoven fabric, powder, paste, coating, film, plate, tablet, bulk, etc.

[0018] The oxygen absorber 17 is preferably in the form of a nonwoven fabric. In this specification, the term "nonwoven fabric" refers to a sheet-like material made of intertwined fibers, regardless of the name. It encompasses not only nonwoven fabrics but also paper, regardless of the name. As shown in FIG. 2 , the positive electrode 12 and / or negative electrode 14 are preferably covered with the oxygen absorber 17 in the form of a nonwoven fabric. This allows oxygen generated at the positive electrode 12 to come into contact with the oxygen absorber 17 before reaching the negative electrode 14. In other words, oxygen can be absorbed by the oxygen absorber 17 faster than it is consumed in the oxidation reaction of metallic zinc at the negative electrode 14, thereby effectively reducing the amount of oxygen reaching the negative electrode 14. In this case, the material of the nonwoven fabric serving as the oxygen absorber 17 is not particularly limited as long as it is a fibrous material capable of absorbing, adsorbing, or capturing oxygen. However, alcohol compounds or materials derived therefrom are preferred because they are expected to have an oxygen absorption effect due to the oxidation reaction, and vinylon is particularly preferred. Vinylon is a general term for polyvinyl alcohol (PVA)-based synthetic fibers. In other words, it is particularly preferable that the nonwoven fabric serving as the oxygen absorber 17 contains vinylon. Commercially available vinylon separators (nonwoven fabrics) can be used as the nonwoven fabric. Vinylon nonwoven fabrics undergo dehydration and splitting due to oxidation in the presence of oxygen and an alkaline electrolyte, allowing the nonwoven fabric serving as the oxygen absorber 17 to absorb oxygen faster than the oxidation of the metallic zinc in the negative electrode 14. This effectively suppresses the loss of metallic zinc in the negative electrode 14. As mentioned above, polyvinyl alcohol used in vinylon is known to deteriorate due to heat at temperatures above 200°C in air and in alkaline aqueous solutions (see Non-Patent Documents 1 and 2). However, in this embodiment, vinylon is used as the oxygen absorber 17 to actively utilize these properties, which have been considered to be disadvantages. As mentioned above, the problem with calendar life is that during charging, oxygen on the positive electrode 12 side reaches the metallic zinc on the negative electrode 14, causing the metallic zinc to oxidize, resulting in a decrease in the overall metallic zinc, and the capacities of the positive electrode 12 and negative electrode 14 being reversed.In this regard, by using a vinylon nonwoven fabric, the oxygen generated in the positive electrode 12 can be consumed in the oxidation reaction of the nonwoven fabric itself, reducing the capacity consumption of the negative electrode 14, thereby particularly effectively resolving the above-mentioned problem of calender durability. However, the material constituting such a nonwoven fabric is not limited to vinylon; as described above, any alcohol compound or material derived therefrom can be expected to have the oxygen absorption effect through an oxidation reaction, similar to vinylon. Furthermore, the oxygen absorber 17 in the form of a nonwoven fabric can be used in various arrangements, such as being interposed between the positive electrode 12 and the negative electrode 14 together with the separator 16, in addition to being arranged to cover the positive electrode 12 and / or the negative electrode 14 as shown in FIG. 2.

[0019] The positive electrode 12 includes a positive electrode active material. The positive electrode active material preferably includes nickel hydroxide and / or nickel oxyhydroxide. Typically, the positive electrode 12 further includes a positive electrode current collector (not shown), which preferably has a positive electrode current collector tab 13 extending from an end (e.g., the upper end) of the positive electrode 12. A preferred example of the positive electrode current collector is a nickel porous substrate such as a foamed nickel plate. In this case, a positive electrode plate consisting of a positive electrode / positive electrode current collector can be preferably produced by, for example, uniformly applying a paste containing an electrode active material such as nickel hydroxide onto a porous nickel substrate and drying it. In this case, it is also preferable to press the dried positive electrode plate (i.e., the positive electrode / positive electrode current collector) to prevent the electrode active material from falling off and improve the electrode density. Note that the positive electrode 12 shown in FIG. 2 includes a positive electrode current collector (e.g., foamed nickel), but this is not shown. This is because, in the case of a nickel-zinc secondary battery, the positive electrode current collector is integral with the positive electrode active material, making it impossible to depict the positive electrode current collector separately. The nickel-zinc secondary battery 10 preferably further includes a positive electrode current collector plate connected to the tip of the positive electrode current collector tab 13, and more preferably, multiple positive electrode current collector tabs 13 are connected to a single positive electrode current collector plate. This allows for space-efficient current collection with a simple configuration and also facilitates connection to the positive electrode terminal 26. Alternatively, the positive electrode current collector plate itself may be used as the positive electrode terminal 26.

[0020] The positive electrode 12 may contain at least one additive selected from the group consisting of a silver compound, a manganese compound, and a titanium compound, which can promote the positive electrode reaction of absorbing hydrogen gas generated by the self-discharge reaction. The positive electrode 12 may also contain cobalt. The cobalt is preferably contained in the positive electrode 12 in the form of cobalt oxyhydroxide. In the positive electrode 12, cobalt functions as a conductive additive, thereby contributing to improving the charge / discharge capacity.

[0021] The negative electrode 14 includes a negative electrode active material. The negative electrode active material preferably includes zinc and / or zinc oxide. Zinc may be contained in any form, such as zinc metal, a zinc compound, or a zinc alloy, as long as it has electrochemical activity suitable for a negative electrode. Preferred examples of negative electrode materials include zinc oxide, zinc metal, and calcium zincate, with a mixture of zinc metal and zinc oxide being more preferred. The negative electrode active material may be in the form of a gel, or may be mixed with an electrolyte solution 18 to form a negative electrode mixture. For example, a gelled negative electrode can be easily obtained by adding an electrolyte solution and a thickener to the negative electrode active material. Examples of thickeners include polyvinyl alcohol, polyacrylate, CMC, and alginic acid, with polyacrylic acid being preferred due to its excellent chemical resistance to strong alkalis.

[0022] The zinc alloy can be a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy. For example, a zinc alloy containing 0.01 to 0.1 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is preferred because it suppresses hydrogen gas generation. In particular, indium and bismuth are advantageous in improving discharge performance. The use of a zinc alloy for the negative electrode can improve safety by slowing the rate of self-dissolution in alkaline electrolyte, thereby suppressing hydrogen gas generation.

[0023] The shape of the negative electrode material is not particularly limited, but it is preferably in powder form, which increases the surface area and enables it to withstand large current discharge. In the case of a zinc alloy, the average particle size of the negative electrode material is preferably in the range of 3 to 100 μm in minor axis. Within this range, the large surface area makes it suitable for withstanding large current discharge, and it is also easy to mix uniformly with the electrolyte and gelling agent, making it easy to handle during battery assembly.

[0024] Preferably, the negative electrode 14 further includes a negative electrode current collector 15, which has a negative electrode current collector tab 15a extending from an end (e.g., the upper end) of the negative electrode 14. The negative electrode current collector tab 15a is preferably provided in a position where it does not overlap with the positive electrode current collector tab 13. The nickel-zinc secondary battery 10 preferably further includes a negative electrode current collector plate connected to the tip of the negative electrode current collector tab 15a, and more preferably, multiple negative electrode current collector tabs 15a are connected to one negative electrode current collector plate. This allows for space-efficient current collection with a simple configuration and also facilitates connection to the negative electrode terminal 28. Alternatively, the negative electrode current collector plate itself may be used as the negative electrode terminal 28.

[0025] Preferred examples of the negative electrode current collector 15 include copper foil, copper expanded metal, and copper punched metal, with copper expanded metal being more preferred. 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 to the copper expanded metal to preferably produce a negative electrode plate consisting of a negative electrode / negative electrode current collector. In this case, it is also preferred to press the dried negative electrode plate (i.e., a negative electrode / negative electrode current collector) to prevent the electrode active material from falling off and improve the electrode density.

[0026] The liquid retaining member may be provided so as to cover or encase the positive electrode 12 and / or the negative electrode 14. or The electrolyte 18 can be distributed evenly between the negative electrode 14 and the separator 16. positive electrode 12This allows for efficient exchange of hydroxide ions between the negative electrode 14 and the separator 16, and / or between the negative electrode 14 and the separator 16. The liquid-retaining member is not particularly limited as long as it is a material capable of retaining the electrolyte solution 18, but is preferably a sheet-like member. Preferred examples of the liquid-retaining member include nonwoven fabric, water-absorbent resin, liquid-retaining resin, porous sheet, and various spacers. However, nonwoven fabric is particularly preferred because it allows for the production of a high-performance negative electrode structure at low cost. Therefore, it is most preferable to use a nonwoven fabric (e.g., a vinylon nonwoven fabric) as the oxygen absorber 17 as the liquid-retaining member. As mentioned above, the term "nonwoven fabric" in this specification refers to a sheet-like material in which fibers are intertwined without being woven, and includes not only what is called a nonwoven fabric but also what is called paper, regardless of the name.

[0027] The liquid-retaining member or nonwoven fabric (which may be oxygen absorber 17) preferably has a thickness of 10 to 200 μm, more preferably 20 to 200 μm, even more preferably 20 to 150 μm, particularly preferably 20 to 100 μm, and most preferably 20 to 60 μm. A thickness within the above range allows a sufficient amount of electrolyte solution 18 to be retained within the liquid-retaining member while keeping the overall size of the negative electrode structure compact and efficient.

[0028] The separator 16 is disposed between the positive electrode 12 and the negative electrode 14. As the separator 16, a separator generally used in alkaline secondary batteries or zinc secondary batteries may be used, and a microporous membrane separator (e.g., made of a polyolefin such as polyethylene or polypropylene) may also be used. However, it is preferable to use a hydroxide ion conductive separator such as an LDH separator, since it can selectively allow hydroxide ions to pass through while preventing the penetration of zinc dendrites. When a hydroxide ion conductive separator is used, for example, as shown in FIG. 2, the positive electrode 12 and the negative electrode 14 are electrically connected to each other. negative electrodePreferably, one or both of the positive electrode 12 and negative electrode 14 are covered or wrapped with the hydroxide ion conductive separator 16. By adopting such a configuration, it becomes possible to eliminate the need for a complicated sealing joint between the hydroxide ion conductive separator 16 and the battery container, and to produce a nickel-zinc secondary battery (particularly a laminated battery thereof) that can prevent zinc dendrite extension extremely easily and with high productivity. However, a simple configuration in which the hydroxide ion conductive separator 16 is disposed on one side of the positive electrode 12 or the negative electrode 14 may also be used.

[0029] The hydroxide ion-conductive separator 16 is not particularly limited as long as it is a separator capable of separating the positive electrode 12 and the negative electrode 14 in a hydroxide ion-conductive manner. Typically, however, it is a separator containing a hydroxide ion-conductive solid electrolyte and selectively passing 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 containing LDH and / or an LDH-like compound and selectively passing hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and / or 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 but can be considered an equivalent of LDH. However, in a broader sense, "LDH" can also be interpreted as encompassing not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and / or an LDH-like compound. That is, in a preferred LDH separator, the pores of the porous substrate are filled with LDH and / or an LDH-like compound 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 polymeric material, and it is particularly preferred that the LDH is incorporated throughout the entire thickness of the porous substrate made of a polymeric material. For example, known LDH separators such as those disclosed in Patent Documents 1 to 5 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.

[0030] When the positive electrode 12 and / or the negative electrode 14 are covered or wrapped with a liquid-retaining member (which may be the oxygen absorber 17) and / or a separator 16, it is preferable that the outer edges thereof are closed (except for the edges from which the positive electrode current collector tab 13 and the negative electrode current collector tab 15a extend). In this case, the closed edges of the outer edges of the liquid-retaining member and / or the separator 16 are preferably realized by folding the liquid-retaining member and / or the separator 16, or by sealing the liquid-retaining members and / or the separators 16 together. Preferred examples of sealing methods include adhesives, heat welding, ultrasonic welding, adhesive tape, sealing tape, and combinations thereof. In particular, an LDH separator including a porous substrate made of a polymer material has the advantage of being flexible and therefore easily bendable. Therefore, it is preferable to form the LDH separator into a long shape and then fold it to close one edge of the outer edge. Thermal welding and ultrasonic welding can be performed using a commercially available heat sealer, etc., but when sealing LDH separators together, it is preferable to perform thermal welding and ultrasonic welding by sandwiching the outer periphery of the liquid-retaining member between the LDH separators that make up the outer periphery, as this allows for more effective sealing. On the other hand, commercially available adhesives, adhesive tapes, and sealing tapes can be used, but those containing alkali-resistant resins are preferred to prevent deterioration in alkaline electrolyte. From this perspective, examples of preferred adhesives include epoxy resin-based adhesives, natural resin-based adhesives, modified olefin resin-based adhesives, and modified silicone resin-based adhesives, with epoxy resin-based adhesives being particularly preferred due to their excellent alkali resistance. An example of a product epoxy resin-based adhesive is the epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

[0031] The electrolyte 18 preferably contains an aqueous solution of an alkali metal hydroxide. Although the electrolyte 18 is only partially illustrated in FIG. 2 , this is because it is distributed throughout the positive electrode 12 and the negative electrode 14. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being preferred. To suppress the self-dissolution of zinc and / or zinc oxide, a zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte. As mentioned above, the electrolyte may be mixed with the positive electrode active material and / or the negative electrode active material to form a positive electrode composite and / or a negative electrode composite. The electrolyte may also be gelled to prevent leakage of the electrolyte. A polymer that absorbs the solvent in the electrolyte and swells is preferably used as the gelling agent. Examples of suitable gelling agents include polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, as well as starch.

[0032] As shown in Fig. 2, the battery element 11 preferably has a positive / negative electrode laminate configuration, in which a plurality of positive electrodes 12, a plurality of negative electrodes 14, and a plurality of separators 16 are laminated so that the unit of positive electrode 12 / separator 16 / negative electrode 14 is repeated. That is, the nickel-zinc secondary battery 10 preferably has a plurality of unit cells 10a, which together form a multi-layer cell. This is the configuration of a so-called assembled battery or laminated battery, and is advantageous in that it can provide a high voltage and a large current.

[0033] The sealed container 20 is preferably made of resin. The resin constituting the sealed container 20 is preferably a resin resistant to alkali metal hydroxides such as potassium hydroxide, more preferably a polyolefin resin, ABS resin, or modified polyphenylene ether, and even more preferably an ABS resin or modified polyphenylene ether. The sealed container 20 has an upper lid 20a. The sealed container 20 (e.g., the upper lid 20a) may have a pressure relief valve for releasing gas. Furthermore, a battery module may be configured by housing a group of cases in which two or more sealed containers 20 are arranged within an outer frame. [Example]

[0034] The present invention is further illustrated by the following examples.

[0035] Example 1 (comparison) (1) Fabrication of nickel-zinc secondary batteries The following positive electrode plate, negative electrode plate, LDH separator, nonwoven fabric, battery case, and electrolyte were prepared. Positive electrode plate: A 0.7 mm thick plate made by filling the pores of foamed nickel with a positive electrode paste containing nickel hydroxide and a binder and then drying it (an uncoated area near one edge of the foamed nickel where the positive electrode paste is not applied is pressed and processed into a positive electrode current collecting tab). Negative electrode plate: A negative electrode paste containing 92.7% by volume of ZnO powder, 2.9% by volume of metallic Zn powder, 3.1% by volume of 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, which serves as a negative electrode current collecting tab). Microporous membrane separator: Commercially available polypropylene microporous membrane separator, thickness: 20 μm Nonwoven fabric: Commercially available polypropylene nonwoven fabric, thickness 100 μm Battery case: Modified polyphenylene ether resin housing Electrolyte: 5.4 mol / L KOH aqueous solution with 0.4 mol / L ZnO dissolved

[0036] The positive electrode plate was wrapped in nonwoven fabric so that it covered both sides, with the nonwoven fabric slightly protruding from the remaining three sides except for the side from which the positive electrode current collector tab extended. The excess portions of the nonwoven fabric protruding from the three sides of the positive electrode plate were heat-sealed with a heat seal bar to obtain a positive electrode assembly. The negative electrode plate was wrapped in nonwoven fabric and a microporous membrane separator, in that order, from both sides, with the nonwoven fabric and microporous membrane separator slightly protruding from the remaining three sides except for the side from which the negative electrode current collector tab extended. The excess portions of the nonwoven fabric and microporous membrane separator protruding from the three sides of the negative electrode plate were heat-sealed with a heat seal bar to obtain a negative electrode assembly. In this way, a total of 25 electrode assemblies were prepared, consisting of 12 positive electrode assemblies and 13 negative electrode assemblies. The positive electrode assemblies and negative electrode assemblies were alternately stacked and placed in a battery case. The positive electrode current collector was connected to the positive electrode current collector terminal, and the negative electrode current collector was connected to the negative electrode current collector terminal, and the resin case and resin lid were heat-welded to form an integrated unit. Then, an electrolyte was added through the inlet, and the electrolyte was thoroughly permeated into the positive and negative electrode plates by evacuation or the like. The inlet was then sealed to form a sealed cell.

[0037] (2) Evaluation of calendar durability Using a charge / discharge device (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.), the sealed cells were subjected to chemical formation with a 0.1 C charge and a 0.2 C discharge. Subsequently, a 0.5 C charge / discharge was performed, and the initial discharge capacity was measured at 25°C. After measuring the discharge capacity, the sealed cells were charged to an SOC of 50% and stored in this charged state for 30 days at 65°C. The discharge capacity was then measured in the same manner as above. The ratio of the discharge capacity after storage to the initial discharge capacity was calculated to obtain the discharge capacity retention rate (%). This series of operations was repeated until the discharge capacity retention rate reached 70% or less. The number of days until the discharge capacity retention rate reached 70% or less was evaluated as an index of calender durability. Higher calender durability indicates a longer calender life. The storage temperature was set at a high temperature of 65°C in order to accelerate the evaluation of calender durability and calender life.

[0038] Example 2 (comparison) A battery was produced and evaluated in the same manner as in Example 1, except that the following LDH separator was used as the separator instead of the microporous membrane. LDH separator: Ni-Al-Ti-LDH (layered double hydroxide) is deposited on the surface and pores of a polyethylene microporous membrane by hydrothermal synthesis and then roll-pressed. Thickness: 9 μm

[0039] Example 3 A battery was produced and evaluated in the same manner as in Example 2, except that a vinylon nonwoven fabric (product name: BFN No. 2, manufactured by Kuraray Co., Ltd., thickness 84 μm) was used as the nonwoven fabric oxygen absorber covering the positive and negative electrode plates instead of the polyolefin nonwoven fabric.

[0040] result Table 2 shows the results obtained in Examples 1 to 3. The calendar life in each example was calculated as a relative value to the calendar life obtained in Example 1 (the number of days until the discharge capacity retention rate reached 70% or less).

[0041] [Table 2]

[0042] The results shown in Table 2 show that in Example 3 (Example), which used the oxygen absorber vinylon, the calender durability performance, i.e., the calender life, was improved by 1.5 times compared to Examples 1 and 2 (Comparative Examples), which did not use the oxygen absorber vinylon.

[0043] FIG. 4 shows optical microscope images of the cross section of the negative electrode of the nickel-zinc secondary battery prepared in Example 2 (comparison) at the initial point (day 0) and after storing the battery at 65° C. for 30, 60, 90, and 120 days. image (The upper row shows a bright-field image, and the lower row shows a dark-field image.) Figures 5 and 6 show optical microscope images of the cross section of the negative electrode of the nickel-zinc secondary batteries fabricated in Examples 2 and 3, respectively, after storage at 65°C for 120 days. image(The upper row shows a bright-field observation image, and the lower row shows a dark-field observation image.) Figures 4 and 5 show that in Example 2 (Comparative Example), which did not use the oxygen absorber vinylon, the metallic zinc particles (particle size approximately 100 μm) that were observed as a white metallic luster at the initial time point (day 0) almost disappeared after 90 days, and the metallic zinc completely disappeared after 120 days. In contrast, in Example 3 (Example), which used the oxygen absorber vinylon, as shown in Figure 6, large particles of the initial metallic zinc remained even after 120 days in a 65°C environment, indicating that negative electrode capacity consumption was suppressed. These facts can be said to be consistent with the improved calendar life effect of the oxygen absorber shown in Table 2.

Claims

1. A nickel-zinc secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution, all contained in a sealed container, an oxygen absorber is disposed in the sealed container at a position where it can absorb oxygen generated at the positive electrode; A nickel-zinc secondary battery, wherein the oxygen absorber is in the form of a nonwoven fabric, and the positive electrode and / or the negative electrode is covered with the nonwoven fabric.

2. 2. The nickel-zinc secondary battery according to claim 1, wherein the position capable of absorbing oxygen generated at the positive electrode is at least one selected from the group consisting of the surface or periphery of the positive electrode, the surface or periphery of the negative electrode, a space between the positive electrode and the negative electrode, the surface or periphery of the separator, an inner wall of the sealed container, the surface of a positive electrode current collector tab extending from the positive electrode, the surface of a negative electrode current collector tab extending from the negative electrode, and excess space within the sealed container.

3. The nickel-zinc secondary battery according to claim 1 or 2, wherein the nonwoven fabric comprises vinylon.

4. 3. The nickel-zinc secondary battery according to claim 1, wherein the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, and the negative electrode contains zinc and / or zinc oxide.

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