JP6677860B2 - Method for producing negative electrode structure for zinc secondary battery - Google Patents

Description

  The present invention relates to a method for manufacturing a negative electrode structure for a zinc secondary battery.

  In a zinc secondary battery such as a nickel zinc secondary battery and an air zinc secondary battery, metallic zinc precipitates from the negative electrode in the form of dendrites during charging, reaches the positive electrode through the voids of the separator such as a nonwoven fabric, and as a result, It is known to cause a short circuit. Such a short circuit caused by the zinc dendrite repeatedly shortens the charge / discharge life.

  To address the above problems, batteries have been proposed that include a layered double hydroxide (LDH) separator that blocks penetration of zinc dendrites while selectively allowing hydroxide ions to permeate. For example, Patent Document 1 (WO 2013/118561) discloses that an LDH separator is provided between a positive electrode and a negative electrode in a nickel zinc secondary battery. Patent Document 2 (International Publication No. 2016/076047) discloses a separator structure including an LDH separator fitted or joined to a resin outer frame. It is disclosed that the material has a high density enough to have water impermeability. This document also discloses that the LDH separator can be combined with a porous substrate. Furthermore, Patent Document 3 (WO 2016/068884) discloses various methods for forming a dense LDH film on the surface of a porous substrate to obtain a composite material (LDH separator). In this method, a starting substance capable of giving a starting point of LDH crystal growth is uniformly attached to a porous substrate, and the porous substrate is subjected to hydrothermal treatment in a raw material aqueous solution to form a dense LDH film on the surface of the porous substrate. Is formed.

WO 2013/118561 International Publication No. 2016/076047 International Publication No. WO 2016/068884

  When a zinc secondary battery such as a nickel zinc battery is configured using the LDH separator as described above, a short circuit or the like due to zinc dendrite can be prevented. In order to maximize this effect, it is desired that the positive electrode and the negative electrode be reliably separated by the LDH separator. In particular, it is very advantageous if a stacked battery can be easily assembled by combining a plurality of positive electrodes and a plurality of negative electrodes in order to obtain a high voltage and a large current while securing such a configuration. However, the separation of the positive electrode and the negative electrode by the LDH separator in the conventional zinc secondary battery is performed by skillfully and carefully sealing the LDH separator and the battery container using a resin frame or an adhesive so as to ensure liquid tightness. The battery configuration and the manufacturing process were likely to be complicated. Such complication of the battery configuration and the manufacturing process can be particularly remarkable when a laminated battery is configured. This is because it is necessary to perform sealing joining for ensuring liquid tightness for each of the plurality of cells constituting the stacked battery.

  The present inventors have recently proposed a negative electrode structure suitable for a zinc secondary battery (in particular, a laminated battery thereof) capable of preventing zinc dendrite extension by covering or enclosing the entire negative electrode active material layer with a liquid retaining member and an LDH separator. I learned that the body can be manufactured efficiently. In addition, by using the negative electrode structure manufactured in such a manner, complicated sealing joining between the LDH separator and the battery container is not required, and the zinc secondary battery capable of preventing zinc dendrite extension (particularly, the laminated battery ) Was found to be extremely easy to produce with high productivity.

  Accordingly, an object of the present invention is to efficiently manufacture a negative electrode structure that enables extremely easy and high productivity of a zinc secondary battery (in particular, a laminated battery thereof) capable of preventing zinc dendrite extension. It is in.

According to one embodiment of the present invention, a method for producing a negative electrode structure for a zinc secondary battery,
(A) The whole of the quadrilateral 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 is covered with a quadrilateral liquid retaining member having a larger size. Or wrapping and obtaining a first laminate,
(B) the whole of the first laminate is a single layered double hydroxide (LDH) separator bent at one side or at least two unfolded quadrilateral LDH separators, A step of sandwiching the overlapping portion protruding from the outer edge of the negative electrode active material layer so as to form over the entire area of the outer edge, to obtain a second laminate,
(C) In the case of using one bent LDH separator, an overlapped portion belonging to at least one outer edge adjacent to the bent side of the second laminate is sealed, or is not bent. When two LDH separators are used, the overlapping portion belonging to at least two outer edges adjacent to each other of the second laminate is sealed, and as a result, a negative electrode structure in which at least two outer edges adjacent to each other are closed Obtaining a body;
A method is provided, comprising:

It is a perspective view showing an example of the negative electrode structure manufactured by the manufacturing method of the present invention. FIG. 1B is a schematic cross-sectional view illustrating a layer configuration of the negative electrode structure illustrated in FIG. 1A. 3 is a process flowchart illustrating an example of a method for manufacturing a negative electrode structure according to the present invention. 4 is a process flowchart illustrating another example of the method for manufacturing a negative electrode structure according to the present invention. It is a schematic diagram for explaining the area covered with the LDH separator in an example of the negative electrode structure manufactured by the manufacturing method of the present invention. FIG. 2 is a schematic sectional view showing the electrochemical measurement system used in Example 1. FIG. 3 is an exploded perspective view of the closed container for measurement used in the denseness determination test of Example 1. FIG. 2 is a schematic cross-sectional view of a measurement system used in a denseness determination test of Example 1. FIG. 2 is a conceptual diagram showing an example of a He transmittance measurement system used in Example 1. FIG. 7B is a schematic cross-sectional view of a sample holder used in the measurement system shown in FIG. 7A and its peripheral configuration. 4 is an SEM image showing a cross-sectional microstructure of the LDH separator manufactured in Example 1.

The manufacturing method of a negative electrode structure TECHNICAL FIELD This invention relates to the manufacturing method of the negative electrode structure for zinc secondary batteries. 1A and 1B show an example of the negative electrode structure. The negative electrode structure 10 shown in FIGS. 1A and 1B includes a negative electrode active material layer 12, a liquid retaining member 14 that covers or wraps the entire negative electrode active material layer 12, and an entire negative electrode active material layer 12 and liquid retaining member 14. And an LDH separator 16 to cover or envelop. The negative electrode active material layer 12 includes at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound. In this specification, the “LDH separator” is defined as a separator containing LDH, which selectively allows hydroxide ions to pass exclusively using the hydroxide ion conductivity of LDH. In this way, by covering or enclosing the entire negative electrode active material layer 12 with the liquid retaining member 14 and the LDH separator 16, complicated sealing joining between the LDH separator and the battery container is unnecessary, and zinc dendrite extension can be prevented. It is possible to provide a negative electrode structure that enables extremely simple and highly productive zinc secondary batteries (especially stacked batteries).

  That is, as described above, the separation of the positive electrode and the negative electrode by the LDH separator in the conventional zinc secondary battery is subtle and careful using a resin frame, an adhesive, or the like so as to ensure liquid tightness between the LDH separator and the battery container. In this case, the battery structure and the manufacturing process are likely to be complicated. Such complication of the battery configuration and the manufacturing process can be particularly remarkable when a laminated battery is configured. In this regard, in the negative electrode structure 10 manufactured by the method of the present invention, since the entire negative electrode active material layer 12 is covered or wrapped by the liquid retaining member 14 and the LDH separator 16, the negative electrode structure 10 itself uses zinc. It has a function that can prevent short circuits and the like due to dendrite. Moreover, since the negative electrode structure 10 includes the liquid retaining member 14 between the negative electrode active material layer 12 and the LDH separator 16, if an electrolyte is injected into the negative electrode structure 10, the negative electrode chamber of the zinc secondary battery will It can be simply configured in a form that can prevent dendrite extension. Therefore, when the negative electrode structure 10 manufactured by the method of the present invention is used for manufacturing a zinc secondary battery, it is possible to realize the separation between the positive electrode and the negative electrode by the LDH separator simply by laminating the positive electrode plate and the negative electrode structure. it can. In particular, when a stacked battery including a plurality of unit cells is manufactured, it can be said that it is extremely advantageous in that a desired configuration can be realized only by alternately stacking the positive electrode plates and the negative electrode structures. This is because the necessity of a clever and elaborate sealing connection conventionally performed to separate the positive electrode and the negative electrode with the LDH separator is eliminated.

  The method for manufacturing a negative electrode structure according to the present invention includes, as shown in FIGS. 2 and 3, (a) a step of covering or wrapping the entire negative electrode active material layer 12 with a liquid retaining member 14 to obtain a first laminate 11. (B) a step of sandwiching the entire first laminate 11 with an LDH separator 16 to obtain a second laminate 18, and (c) sealing a predetermined outer edge S of the second laminate 18 to form a negative electrode structure. Obtaining step. The manufacturing method shown in FIG. 2 uses one bent LDH separator 16, while the manufacturing method shown in FIG. 3 uses at least two unfolded LDH separators 16. In any case, as shown in these figures, a zinc secondary battery (particularly a zinc secondary battery capable of preventing zinc dendrite extension can be prevented by covering or enclosing the entire negative electrode active material layer 12 with a liquid retaining member 14 and an LDH separator 16). The negative electrode structure 10 suitable for the laminated battery) can be efficiently manufactured. Hereinafter, each step will be specifically described.

(A) Production of First Laminated Body by Lamination of Liquid Retaining Member In the step (a), as shown in FIGS. 2 and 3, the entire negative electrode active material layer 12 is covered or wrapped with the liquid retaining member 14, and One laminated body 11 is obtained (see (a) in the figure). The negative electrode active material layer 12 has a quadrilateral shape (typically a square shape), but the liquid retaining member 14 has a quadrilateral shape (typically a quadrilateral shape) larger than the negative electrode active material layer 12. Therefore, the entire negative electrode active material layer 12 can be covered or wrapped by the liquid retaining member 14. As described above, since the liquid retaining member 14 surrounds the entire negative electrode active material layer 12, the electrolyte is always desirably held around the negative electrode active material layer 12 when the electrolyte is injected into the negative electrode structure 10. It is possible to do. That is, the electrolytic solution can be uniformly present between the negative electrode active material layer 12 and the LDH separator 16, and the transfer of hydroxide ions between the negative electrode active material layer 12 and the LDH separator 16 can be performed efficiently. be able to.

  The negative electrode active material layer 12 includes at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound. That is, zinc may be contained in any form of zinc metal, a zinc compound, and a zinc alloy as long as it has electrochemical activity suitable for a negative electrode. Preferable examples of the negative electrode material include zinc oxide, zinc metal, calcium zincate and the like, and a mixture of zinc metal and zinc oxide is more preferable. The negative electrode active material layer 12 may be formed in a gel state, or may be mixed with an electrolytic solution to form a negative electrode mixture. For example, a gelled negative electrode can be easily obtained by adding an electrolytic solution and a thickener to the negative electrode active material. Examples of the thickener include polyvinyl alcohol, polyacrylate, CMC, alginic acid, and the like. Polyacrylic acid is preferable because of its excellent chemical resistance to strong alkalis.

  As the zinc alloy, a zinc alloy containing no mercury and lead, which is known as a non-melonized zinc alloy, can be used. For example, a zinc alloy containing 0.01 to 0.1% by mass of indium, 0.005 to 0.02% by mass of bismuth, and 0.0035 to 0.015% by mass of aluminum has an effect of suppressing hydrogen gas generation. It is preferred. In particular, indium and bismuth are advantageous in improving discharge performance. When a zinc alloy is used for a negative electrode, by reducing the rate of self-dissolution in an alkaline electrolyte, hydrogen gas generation can be suppressed and safety can be improved.

  Although the shape of the negative electrode material is not particularly limited, it is preferably in the form of a powder, whereby the surface area increases and it becomes possible to cope with a large current discharge. The average particle size of the preferred negative electrode material is, in the case of a zinc alloy, a short diameter in the range of 3 to 100 μm. It is easy to mix uniformly with the agent and has good handleability during battery assembly.

  It is preferable that the negative electrode active material layer 12 has a current collector 13. That is, the negative electrode active material layer 12 is preferably provided with the current collector 13 in contact with the negative electrode active material layer 12. In particular, the current collector 13 preferably has a current collector extension 13 a extending from one side of the negative electrode active material layer 12. In this case, it is desired that the step (a) is performed so that the liquid retaining member 14 does not cover or enclose the distal end portion of the current collector extension 13a. This is because the end portion of the current collector extension 13a is an exposed portion that is not covered with the liquid retaining member 14 and the LDH separator 16, and the current collector 13 (particularly, the current collector extension 13a) passes through the exposed portion. Is desirably connected to the negative electrode terminal.

  Preferable examples of the negative electrode current collector 13 include copper foil, copper expanded metal, and copper punched metal, and more preferably copper expanded metal. In this case, for example, a mixture comprising zinc oxide powder and / or zinc powder and, if desired, a binder (for example, polytetrafluoroethylene particles) is coated on a copper expanded metal, and a negative electrode comprising a negative electrode / anode current collector Plates can be preferably made. At this time, it is also preferable to press the dried negative electrode plate (that is, the negative electrode / negative electrode current collector) to prevent the electrode active material from falling off and to improve the electrode density.

  The liquid retaining member 14 is not particularly limited as long as it can retain the electrolytic solution, but is preferably a sheet-shaped member. Preferred examples of the liquid retaining member include a nonwoven fabric, a water-absorbing resin, a liquid retaining resin, a porous sheet, and various spacers. Particularly preferred is a nonwoven fabric in that a low-cost, high-performance negative electrode structure 10 can be produced. is there. The liquid retaining member 14 preferably has a thickness of 0.01 to 0.20 mm, more preferably 0.02 to 0.20 mm, still more preferably 0.02 to 0.15 mm, and particularly preferably. It is 0.02 to 0.10 mm, most preferably 0.02 to 0.06 mm. When the thickness is within the above range, a sufficient amount of the electrolyte can be held in the liquid retaining member 14 while keeping the entire size of the negative electrode structure 10 compact without waste. The liquid retaining member 14 may have a quadrilateral shape (typically a rectangular shape) larger than the negative electrode active material layer 12, and may have the same size as the LDH separator 16 (or the bent LDH separator 16). .

  When the liquid retaining member 14 is a sheet-like member, the number thereof is typically one per side (two opposing or bent ones on both sides), but may be two or more. For example, a configuration may be employed in which several layers of the liquid retaining members 14 cover or wrap the entire negative electrode active material layer 12.

(B) Production of Second Laminate by Laminating LDH Separator In the step (b), as shown in FIGS. 2 and 3, the entire first laminate 11 is sandwiched by the LDH separator 16 and the second laminate 18 is formed. Get. At this time, the sandwiching of the first laminate 11 between the LDH separators 16 may be performed by using one LDH separator 16 bent at one side, as shown in FIG. 2B. As shown in FIG. 3B, the process may be performed using at least two LDH separators 16 that are not bent. The LDH separator 16 also has a quadrilateral shape (typically a square shape), like the negative electrode active material layer 12 and the liquid retaining member 14. In any method, the first laminate 11 is sandwiched between the LDH separators 16 so as to form an overlapping portion of the LDH separator 16 protruding from the outer edge of the negative electrode active material layer 12 over the entire outer edge. By doing so, a surplus portion for sealing the LDH separators 16 (the liquid retaining member 14 may be interposed therebetween) in the subsequent sealing step (c) is secured.

  According to a preferred embodiment of the present invention, as shown in FIGS. 2B and 2C, the whole of the first laminate 11 is negatively activated by one LDH separator 16 bent at one side F. The second laminated body 18 is obtained by sandwiching the overlapping portion protruding from the outer edge of the material layer 12 so as to form over the entire outer edge. In this case, the step (b) includes (i) a step of bending one LDH separator 16 and (ii) sandwiching the whole of the negative electrode active material layer 12 and the liquid retaining member 14 between the bent one LDH separator 16. And a step. By doing so, the number of sides to be sealed in the subsequent step (c) can be reduced, so that manufacturing efficiency can be improved. In this regard, the LDH separator 16 including a porous base material made of a polymer material is particularly advantageous because it is easy to bend because of its high flexibility. The LDH separator 16 has a quadrangular shape (typically, a quadrangular shape), but the LDH separator 16 is configured to be long so as to have a size suitable for covering the first laminate 11 when folded in half. Is preferred. Note that the bending is preferably performed so that the bending cross section of the LDH separator 16 is rounded in order to reduce the possibility of the LDH included in the LDH separator 16 being broken.

  According to another preferred embodiment of the present invention, as shown in FIGS. 3B and 3C, the entire first laminated body 11 is formed by at least two unfolded quadrilateral LDH separators 16. Alternatively, the second stacked body 18 may be obtained by sandwiching the overlapping portion protruding from the outer edge of the negative electrode active material layer 12 so as to form over the entire outer edge. In this case, the step (b) may include sandwiching the whole of the negative electrode active material layer 12 and the liquid retaining member 14 between two unfolded LDH separators 16. In this case, the production can be easily performed in that a simple planar LDH separator 16 may be used. The LDH separator 16 has a quadrilateral shape (typically, a quadrilateral shape), but is not bent, and thus may be configured to have a size suitable for covering the first laminate 11 as it is.

  In any of the embodiments, the step (b) may be performed such that the outer peripheral portion of the liquid retaining member 14 is interposed between the LDH separators 16 constituting the overlapping portion. By doing so, the predetermined outer edge of the second laminated body 18 in the subsequent step (c) can be effectively sealed by heat welding or ultrasonic welding. That is, the LDH separators 16 are indirectly heat-welded or ultrasonic-welded by interposing the heat-welding liquid retaining member 14 between the LDH separators 16 rather than directly heat-welding or ultrasonic-welding the LDH separators 16 to each other. This makes it possible to utilize the heat welding property of the liquid retaining member 14 itself, resulting in more effective sealing. That is, the end of the liquid retaining member 14 to be sealed can be used as if it were a hot melt adhesive. A preferable example of the liquid retaining member 11 in this case is a nonwoven fabric, particularly a nonwoven fabric made of a thermoplastic resin (for example, polyethylene or polypropylene). In this embodiment, the size of the liquid retaining member 14 can be the same size as the LDH separator 16 (or the bent LDH separator 16), and the outer edge of the LDH separator 16 and the outer edge of the liquid retaining member 14 match. It can be.

  When the tip portion of the current collector extension 13a is not covered or wrapped with the liquid retaining member 14, the step (b) is performed so that the tip portion of the current collector extension 13a is not sandwiched by the LDH separator 16. As a result, the end portion of the current collector extension 13a forms an exposed portion that is not covered with the liquid retaining member 14 and the LDH separator 16. Thereby, the current collector 13 (particularly, the current collector extension 13a) can be desirably connected to the negative electrode terminal (not shown) via the exposed portion. In this case, as shown in FIG. 4, a predetermined margin M (for example, an interval of 1 to 5 mm) is set so that the LDH separator 16 sufficiently covers the end of the negative electrode active material layer 12 on the side of the current collector extension 13a. It is preferred to cover or envelop with. By doing so, it is possible to more effectively prevent the zinc dendrite from extending from the end of the negative electrode active material layer 12 on the current collector extension 13a side or the vicinity thereof.

  The LDH separator 16 preferably comprises (typically consists of) LDH and a porous substrate, and the LDH separator 16 is designed to exhibit hydroxide ion conductivity and gas impermeability (hence, Preferably, the LDH blocks the pores of the porous substrate (to function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferable that LDH is incorporated over the entire region in the thickness direction of the polymer material porous substrate. Various preferable aspects of the LDH separator 16 will be described later in detail.

  The number of LDH separators 16 is typically one per side (two opposing or folded ones on both sides), but may be two or more. For example, a configuration may be employed in which several layers of LDH separators 16 cover or wrap the entire first stacked body 11.

(C) Sealing a predetermined outer edge of the second laminate In the step (c), as shown in FIGS. 2 and 3, an overlapping portion belonging to an outer edge of a predetermined side of the second laminate 18 is sealed. Thus, the negative electrode structure 10 in which at least two outer edges adjacent to each other are closed is obtained. Here, “at least two sides adjacent to each other” means that one end of one side is in contact with one end of another side. Further, "the outer edge is closed" may be a shape in which the outer edge is bent or a shape in which the outer edge is sealed. In any case, when the outer edge of at least two sides (which is also the outer edge of the LDH separator 16) of the second stacked body 18 adjacent to each other is closed, the negative electrode active material is mounted on the zinc secondary battery. The layer 12 can be reliably isolated from the positive electrode, and the extension of zinc dendrites from the outer edge can be effectively prevented. For example, when one folded LDH separator 16 is used, as shown in FIG. 2C, at least one outer edge S (or S) adjacent to the folded side F of the second laminate 18 is used. And overlapping portions belonging to S ′) are sealed. Note that the outer edge S ′ in the figure means a side that may or may not be closed. On the other hand, when two unfolded LDH separators 16 are used, as shown in FIG. 3C, the outer edges of at least two sides S (or S and S ′) of the second stacked body 18 adjacent to each other. The overlapping portion belonging to is sealed. However, in the case where the current collector extending portion 13a is provided, the side S (or S and S ') on which the sealing is performed is formed by the current collector extending portion so that the current collector extending portion 13a can be extended. It is desired that the side does not overlap with the protrusion 13a. In either case, as a result, the negative electrode structure 10 in which at least two outer edges adjacent to each other are closed is obtained.

  As shown in FIG. 2, the step (b) includes (i) a step of bending one LDH separator 16 and (ii) a step of bending the negative electrode active material layer 12 and the liquid retaining member 14 by one bent LDH separator 16. In an embodiment including a step of sandwiching the whole, the step (c) includes sealing an overlapping portion belonging to an outer edge of at least one side S (or S and S ′) adjacent to the folded side F of the second laminate 18. Preferably, it includes stopping. If necessary, the step (c) may be performed so as to seal an overlapping portion belonging to two outer edges S and S ′ adjacent to the folded side F of the second laminate 18, In this case, it is possible to obtain a negative electrode structure in which three outer edges are closed (thus, the extension of zinc dendrite can be more effectively prevented).

  On the other hand, as shown in FIG. 3, in an embodiment in which the step (b) includes sandwiching the whole of the negative electrode active material layer 12 and the liquid retaining member 14 between two unfolded LDH separators 16, ) Preferably includes a step of sealing an overlapping portion belonging to an outer edge of at least two sides S, S (or S, S and S ′) adjacent to each other of the second laminate 18. If necessary, the step (c) may be a step of sealing an overlapping portion belonging to the outer edges of the three sides S, S, S ′ of the second laminated body 18, in which case the outer edges of the three sides are sealed. It is possible to obtain a closed anode structure (which can more effectively prevent the extension of zinc dendrite).

  In any case, sealing may be performed by any method, and there is no particular limitation. Preferred examples of the sealing method include an adhesive, heat welding, ultrasonic welding, an adhesive tape, a sealing tape, and a combination thereof. The heat welding and the ultrasonic welding may be performed using a commercially available heat sealer or the like. In this case, as described above, the outer peripheral portion of the liquid retaining member 14 is sandwiched between the LDH separators 16 constituting the overlapping portion. It is preferable to perform heat welding and ultrasonic welding in order to achieve more effective sealing. On the other hand, as the adhesive, the adhesive tape, and the sealing tape, commercially available products may be used, but those containing a resin having alkali resistance are preferable in order to prevent deterioration in an alkaline electrolyte. From this viewpoint, examples of preferred adhesives include epoxy resin-based adhesives, natural resin-based adhesives, modified olefin resin-based adhesives, and modified silicone resin-based adhesives, among which epoxy resin-based adhesives are resistant. It is more preferable because it is particularly excellent in alkalinity. An example of a product of the epoxy resin-based adhesive is an epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

  The negative electrode structure 10 obtained in this manner has at least two outer edges adjacent to each other closed, but conversely, even if one or two sides of the outer edge of the negative electrode structure 10 are open. Means good. For example, even if one side of the upper end of the outer edge of the negative electrode structure 10 is left open, if a liquid is injected so that the electrolytic solution does not reach the one side of the upper end during the manufacture of the zinc secondary battery, the upper side of the upper end is Since there is no electrolytic solution, problems of liquid leakage and zinc dendrite extension can be avoided. In this regard, the negative electrode structure 10 can function as a main component of the sealed zinc secondary battery by being housed together with the positive electrode in a sealed container with the electrolyte also contained therein. For this reason, it is only necessary to ensure the hermeticity in a sealed container that is to be finally accommodated, so that the negative electrode structure 10 itself can have a simple structure with an open top. In addition, by opening one side of the outer edge of the negative electrode structure 10, the current collector extension 13a can be extended therefrom. One open side of the outer edge for extending the current collector extension portion 13a may be one side of the upper end providing the upper open portion, or may be one side of the other outer edge.

LDH Separator The LDH separator 16 is a separator containing a layered double hydroxide (LDH) and, when incorporated in a zinc secondary battery, separates the positive electrode plate and the negative electrode plate so as to conduct hydroxide ions. . That is, the LDH separator 16 functions as a hydroxide ion conductive separator. Preferred LDH separators 16 are gas impermeable and / or water impermeable. In other words, it is preferable that the LDH separator 16 be dense enough to have gas impermeability and / or water impermeability. In this specification, "having gas impermeability" means that helium gas is brought into contact with one surface side of an object to be measured in water at a differential pressure of 0.5 atm as described in Patent Documents 2 and 3. This means that no bubbles due to helium gas are generated from the other side. Further, in the present specification, “having water impermeability” means, as described in Patent Literatures 2 and 3, that water that has contacted one surface side of a measurement target does not transmit to the other surface side. . That is, the fact that the LDH separator 16 has gas impermeability and / or water impermeability means that the LDH separator 16 has a high degree of denseness that is impervious to gas or water, It is not a permeable porous film or other porous material. By doing so, the LDH separator 16 selectively passes only hydroxide ions due to its hydroxide ion conductivity, and can exhibit a function as a battery separator. For this reason, the configuration is extremely effective in physically preventing penetration of the separator by zinc dendrite generated during charging and preventing short circuit between the positive and negative electrodes. Since the LDH separator 16 has hydroxide ion conductivity, it is possible to efficiently transfer necessary hydroxide ions between the positive electrode plate and the negative electrode plate to realize a charge / discharge reaction in the positive electrode plate and the negative electrode plate. Can be.

The LDH separator 16 preferably has a He permeability per unit area of 10 cm / min · atm or less, more preferably 5.0 cm / min · atm or less, and still more preferably 1.0 cm / min · atm or less. . A separator having a He permeability of 10 cm / min · atm or less can extremely effectively suppress permeation of Zn (typically, permeation of zinc ions or zincate ions) in the electrolytic solution. As described above, it is considered that the separator of this embodiment is capable of effectively suppressing the growth of zinc dendrites when used in a zinc secondary battery, because the permeation of Zn is significantly suppressed. The He permeability is obtained through a step of supplying He gas to one surface of the separator to allow the He gas to pass through the separator, and a step of calculating the He permeability to evaluate the denseness of the hydroxide ion conductive separator. Measured. The He permeability is calculated by the formula of F / (P × S) using the permeation amount F of the He gas per unit time, the differential pressure P applied to the separator when the He gas permeates, and the membrane area S through which the He gas passes. calculate. By performing gas permeability evaluation using He gas as described above, it is possible to evaluate the presence / absence of denseness at a very high level. As a result, substances other than hydroxide ions (particularly, zinc dendrite growth) It is possible to effectively evaluate a high degree of denseness such as not transmitting (causing Zn) as much as possible (transmitting only a trace amount). This is because the He gas has the smallest structural unit among various kinds of atoms or molecules that can constitute the gas, and has very low reactivity. That is, He forms He gas with He atoms alone without forming molecules. In this regard, since the hydrogen gas is composed of H ₂ molecules, the gas constituent unit is smaller for He atoms alone. In the first place, H ₂ gas is dangerous because it is a combustible gas. Then, by employing the index of the He gas permeability defined by the above-described formula, it is possible to easily perform an objective evaluation of denseness regardless of various sample sizes and differences in measurement conditions. Thus, it can be simply, safely and effectively evaluated whether or not the separator has a sufficiently high density suitable for a separator for a zinc secondary battery. The measurement of the He transmittance can be preferably performed according to the procedure shown in Evaluation 7 of Example 1 described later.

As is generally known, an LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers. The hydroxide basic layer is mainly composed of a metal element (typically, a metal ion) and an OH group. Intermediate layer of LDH is composed of anionic and _{H 2} O. The anion is a monovalent or higher valent anion, preferably a monovalent or divalent ion. Preferably, anions in the LDH is OH ^- containing and / or _CO ^{3 2-} and. LDH also has excellent ionic conductivity due to its inherent properties.

Typically, LDH ^is, 2 O (wherein _{^{M 2+ 1-x M 3+ x}} (OH) 2 A n- x / n · mH, M 2+ is a divalent ^{cation, M 3+} is a trivalent is a ^{cation, a n-is} the n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, m is the base composition formula is 0 or more) It is known as being represented. In the above basic composition formula, M ²⁺ may be any divalent cation, but preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ can be any trivalent cation, but preferred examples include Al ³⁺ or Cr ³⁺ , more preferably Al ³⁺ . A ^n- may be any anion, preferred examples OH ^- and _CO ^{3 2-} and the like. Accordingly, in the above basic ^{formula, M 2+} comprises ^{Mg 2+, M 3+} comprises ^{Al 3+, A n-is} OH ^- and / or _CO preferably contains ^{3 2-.} n is an integer of 1 or more, preferably 1 or 2. x is from 0.1 to 0.4, preferably from 0.2 to 0.35. m is any number meaning the number of moles of water and is a real number greater than or equal to 0, typically greater than 0 or greater than or equal to 1. However, the above basic composition formula is merely a formula of “basic composition” typically exemplified for LDH, and the constituent ions can be appropriately replaced. For example, it may be replaced with some or all of the M ³⁺ tetravalent or higher valency cations in the basic formula, in which case, the anion A coefficient of ^n-x / n in the general formula May be changed as appropriate.

For example, the hydroxide base layer of the LDH may be composed of Ni, Ti, OH groups and possibly unavoidable impurities. The LDH intermediate layer is composed of anions and H ₂ O, as described above. Although the alternating layered structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the generally known layered structure of the LDH, the LDH of the present embodiment mainly includes the hydroxide basic layer of the LDH mainly composed of Ni, By being composed of Ti and OH groups, excellent alkali resistance can be exhibited. Although the reason is not clear, it is considered that an element (for example, Al) which is considered to be easily eluted into the alkaline solution is not intentionally or positively added to the LDH of this embodiment. Nevertheless, the LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in the LDH can take the form of nickel ions. The nickel ions in the LDH are typically considered to be Ni ²⁺ , but are not particularly limited since there may be other valences such as Ni ³⁺ . Ti in LDH can take the form of titanium ions. The titanium ion in the LDH is typically considered to be Ti ⁴⁺ , but is not particularly limited because there may be other valences such as Ti ³⁺ . The unavoidable impurities are optional elements that can be unavoidably mixed in the production method, and can be mixed into the LDH from, for example, a raw material or a base material. As described above, since the valences of Ni and Ti are not always known, it is impractical or impossible to strictly specify LDH by a general formula. If it is assumed that the hydroxide basic layer is mainly composed of Ni ²⁺ , Ti ⁴⁺ and OH groups, the corresponding LDH is represented by the general formula: Ni 2 ⁺ _{1 -x} Ti ⁴⁺ _x (OH) ₂ ^{An _{- 2x / n · mH 2 O}} ( ^{wherein, a n-n-valent} anion, n is an integer of 1 or more, preferably 1 or 2, 0 <x <1, preferably 0.01 ≦ x ≦ 0.5, m is a real number of 0 or more, typically more than 0 or 1 or more). However, the above general formula should be interpreted as “basic composition”, and other elements or ions (other valences of the same element) are not so large that elements such as Ni ²⁺ and Ti ⁴⁺ do not impair the basic properties of LDH. (Including a number of elements or ions or elements or ions which can be unavoidably mixed in the production process).

Alternatively, the hydroxide base layer of the LDH may contain Ni, Al, Ti and OH groups. Intermediate layer, as described above, composed of an anion and H _{2 O.} Although the alternating layered structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the generally known layered structure of the LDH, the LDH of the present embodiment is formed by converting the hydroxide basic layer of the LDH to Ni, Al , And a predetermined element or ion containing Ti and OH groups can exhibit excellent alkali resistance. The reason for this is not necessarily clear, but it is believed that the LDH of this embodiment is because Al, which was conventionally thought to be easily eluted into an alkaline solution, is less likely to elute into an alkaline solution due to some interaction with Ni and Ti. Can be Nevertheless, the LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in the LDH can take the form of nickel ions. The nickel ions in the LDH are typically considered to be Ni ²⁺ , but are not particularly limited since there may be other valences such as Ni ³⁺ . Al in the LDH can take the form of aluminum ions. The aluminum ion in the LDH is typically considered to be Al ³⁺ , but is not particularly limited because there may be other valences. Ti in LDH can take the form of titanium ions. The titanium ion in the LDH is typically considered to be Ti ⁴⁺ , but is not particularly limited because there may be other valences such as Ti ³⁺ . The hydroxide basic layer may contain other elements or ions as long as it contains Ni, Al, Ti and OH groups. However, the basic hydroxide layer preferably contains Ni, Al, Ti and OH groups as main constituent elements. That is, it is preferable that the hydroxide basic layer be mainly composed of Ni, Al, Ti and OH groups. Thus, the hydroxide base layer is typically composed of Ni, Al, Ti, OH groups and possibly unavoidable impurities. The unavoidable impurities are optional elements that can be unavoidably mixed in the production method, and can be mixed into the LDH from, for example, a raw material or a base material. As described above, since the valences of Ni, Al, and Ti are not always known, it is impractical or impossible to exactly specify LDH by a general formula. If mainly ^Ni 2+ hydroxide base ^layer, Al 3+, when assumed to consist of ^{Ti 4+} and OH groups, corresponding LDH has the general ^{_{formula: Ni 2+ 1-x-y}} Al 3+ x Ti ^{_{4+ y (OH) 2 a n-}} (x + 2y) / n · mH 2 O ( ^{wherein, a n-n-valent} anion, n is an integer of 1 or more, preferably 1 or 2, 0 <x <1, preferably 0.01 ≦ x ≦ 0.5, 0 <y <1, preferably 0.01 ≦ y ≦ 0.5, 0 <x + y <1, m is 0 or more, typically 0 Greater than or equal to one or more real numbers). However, the above general formula should be interpreted as the “basic composition”, and other elements or ions (of the same element) to the extent that elements such as Ni ²⁺ , Al ³⁺ , and Ti ⁴⁺ do not impair the basic characteristics of LDH. (Including elements or ions of other valences or elements or ions which can be inevitably mixed in the production process).

  The porous substrate has water permeability and gas permeability, and therefore, when incorporated in a zinc secondary battery, needless to say, the electrolyte can reach the LDH. This allows the LDH separator 16 to stably hold hydroxide ions. Further, since the strength can be given by the porous base material, the LDH separator 16 can be made thinner to reduce the resistance.

  As mentioned above, the LDH separator 16 preferably comprises (typically consists of) LDH and a porous substrate, such that the LDH separator 16 exhibits hydroxide ion conductivity and gas impermeability. Preferably, the LDH blocks the pores of the porous substrate (so that it functions as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferable that LDH is incorporated over the entire region in the thickness direction of the polymer material porous substrate. The thickness of the LDH separator 16 is preferably 5 to 200 μm, more preferably 5 to 100 μm, and still more preferably 5 to 30 μm.

  The porous substrate is preferably composed of a polymer material. Polymer porous substrates have the following features: 1) they have flexibility (thus, they are hard to crack even when they are thin); 2) they tend to increase porosity; and 3) they tend to increase conductivity (thickness while increasing porosity). 4) It is advantageous in that it is easy to manufacture and handle. In addition, taking advantage of the advantage derived from the flexibility of 1), 5) the LDH separator 16 including the porous substrate made of a polymer material can be easily bent or sealed and joined, as described above. In addition, there is also an advantage that a state in which at least one side of the outer edge of the negative electrode structure 10 is closed can be easily formed (in the case of bending, there is also an advantage that the step of sealing the outer edge 1 side can be reduced). Preferred examples of the polymer material include polystyrene, polyether sulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrofluorinated fluororesin (tetrafluorinated resin: PTFE, etc.), cellulose, nylon, polyethylene and any combination thereof. Is mentioned. All of the various preferable materials described above have alkali resistance as a resistance to the electrolyte of the battery. Particularly preferred polymer materials are polyolefins such as polypropylene and polyethylene, and most preferably polypropylene, because they are excellent in hot water resistance, acid resistance and alkali resistance, and are low in cost. When the porous substrate is composed of a polymer material, the LDH layer is incorporated over the entire area in the thickness direction of the porous substrate (for example, most or almost all pores inside the porous substrate are filled with LDH. Is particularly preferred. The preferred thickness of the polymer porous substrate in this case is 5 to 200 μm, more preferably 5 to 100 μm, and still more preferably 5 to 30 μm. As such a polymer porous substrate, a microporous membrane commercially available as a lithium battery separator can be preferably used, or a commercially available cellophane can also be used.

  The porous substrate preferably has an average pore size of at most 100 μm or less, more preferably at most 50 μm or less, for example, typically from 0.001 to 1.5 μm, more typically from 0.001 to 1.5 μm. １．２1.25 μm, more typically 0.001 to 1.0 μm, particularly typically 0.001 to 0.75 μm, most typically 0.001 to 0.5 μm. By setting the content within these ranges, a LDH separator dense enough to exhibit gas impermeability can be formed while securing desired water permeability and strength as a support for the porous substrate. In the present invention, the average pore diameter can be measured by measuring the longest distance of pores based on an electron microscope image of the surface of the porous substrate. The magnification of the electron microscope image used for this measurement is 20000 times or more, and all the obtained pore diameters are arranged in size order, and the upper 15 points and the lower 15 points are arranged in order from the average value to a total of 30 points per visual field. The average value of the two visual fields can be calculated to obtain the average pore diameter. For the length measurement, a length measurement function of SEM software, image analysis software (for example, Photoshop, manufactured by Adobe), or the like can be used.

  The porous substrate preferably has a porosity of 10 to 60%, more preferably 15 to 55%, and still more preferably 20 to 50%. By setting the content within these ranges, a LDH separator dense enough to exhibit gas impermeability can be formed while securing desired water permeability and strength as a support for the porous substrate. The porosity of the porous substrate can be preferably measured by the Archimedes method. However, when the porous substrate is composed of a polymer material and the LDH is incorporated throughout the thickness of the porous substrate, the porosity of the porous substrate is preferably 30 to 60%, more preferably. Is 40 to 60%.

The method of manufacturing the LDH separator 16 is not particularly limited, and is manufactured by appropriately changing various conditions of a known method of manufacturing an LDH-containing functional layer and a composite material (that is, an LDH separator) (for example, see Patent Documents 1 to 3). can do. For example, (1) a porous substrate is prepared, and (2) a titanium oxide layer or an alumina / titania layer is formed by applying a titanium oxide sol or a mixed sol of alumina and titania to the porous substrate and performing a heat treatment. (3) The porous substrate is immersed in a raw material aqueous solution containing nickel ions (Ni ²⁺ ) and urea, and (4) the porous substrate is hydrothermally treated in the raw material aqueous solution to form an LDH-containing functional layer on the porous substrate. By forming it on and / or in a porous substrate, an LDH-containing functional layer and a composite material (that is, an LDH separator) can be produced. In particular, by forming a titanium oxide layer or an alumina / titania layer on the porous substrate in the above step (2), not only is the raw material of LDH provided, but also the starting point of LDH crystal growth is used to form the porous substrate. A highly dense LDH-containing functional layer can be uniformly formed on the surface without unevenness. In addition, the presence of urea in the above step (3) causes the pH value to rise due to the generation of ammonia in the solution utilizing the hydrolysis of urea, and the coexisting metal ions form hydroxides. Can obtain LDH. Further, since carbon dioxide is generated in the hydrolysis, LDH in which the anion is a carbonate ion type can be obtained.

  In particular, when producing a composite material (that is, an LDH separator) in which the porous substrate is composed of a polymer material and the functional layer is incorporated over the entire area in the thickness direction of the porous substrate, the alumina in the above (2) is used. It is preferable to apply the mixed sol of titania and titania to the substrate in such a manner that the mixed sol penetrates all or most of the inside of the substrate. By doing so, most or almost all pores inside the porous substrate can be finally filled with LDH. Examples of preferred coating methods include dip coating and filtration coating, and dip coating is particularly preferred. By adjusting the number of times of dip coating or the like, the amount of the mixed sol to be applied can be adjusted. The substrate on which the mixed sol has been applied by dip coating or the like may be dried and then subjected to the steps (3) and (4).

Zinc secondary battery The negative electrode structure manufactured by the method of the present invention is preferably applied to a zinc secondary battery. Therefore, according to a preferred embodiment of the present invention, there is provided a zinc secondary battery including a positive electrode, a negative electrode structure, and an electrolytic solution, wherein the positive electrode and the negative electrode active material layer are separated from each other via an LDH separator. . The zinc secondary battery of the present invention is not particularly limited as long as it is a secondary battery using zinc as a negative electrode and using an electrolytic solution (typically, an aqueous alkali metal hydroxide solution). Therefore, it can be a nickel zinc secondary battery, a silver zinc oxide secondary battery, a manganese zinc secondary battery, a zinc air secondary battery, and other various alkaline zinc secondary batteries. Particularly, a nickel zinc secondary battery and a zinc air secondary battery are preferable. For example, it is preferable that the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, whereby the zinc secondary battery forms a nickel zinc secondary battery. Alternatively, the positive electrode may be an air electrode, whereby the zinc secondary battery may form a zinc air secondary battery.

  The LDH separator that can be used in the present invention will be described more specifically by the following examples.

Example 1
Using a polymer porous substrate, an LDH separator containing an LDH containing Ni, Al and Ti was prepared by the following procedure and evaluated.

(1) Preparation of Polymeric Porous Substrate A commercially available polypropylene porous substrate having a porosity of 50%, an average pore diameter of 0.1 μm, and a thickness of 20 μm was prepared to have a size of 2.0 cm × 2.0 cm. Cut out.

(2) Alumina-titania sol coating on polymer porous substrate Amorphous alumina solution (Al-ML15, manufactured by Taki Chemical Co., Ltd.) and titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) were converted to Ti / Al ( (Mole ratio) = 2 to prepare a mixed sol. The mixed sol was applied to the substrate prepared in the above (1) by dip coating. The dip coating was performed by immersing the substrate in 100 ml of the mixed sol, vertically lifting the substrate, and drying the substrate in a dryer at 90 ° C. for 5 minutes.

(3) Preparation of raw material aqueous solution As raw materials, nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ .6H ₂ O, manufactured by Kanto Chemical Co., Ltd., and urea ((NH ₂ ) ₂ CO, manufactured by Sigma-Aldrich) are prepared. Nickel nitrate hexahydrate was weighed and placed in a beaker so as to have a concentration of 0.015 mol / L, and ion-exchanged water was added thereto to make a total volume of 75 ml. Urea weighed at a ratio of urea / NO ₃ ⁻ (molar ratio) = 16 was added thereto, and further stirred to obtain a raw material aqueous solution.

(4) Film formation by hydrothermal treatment Both a raw material aqueous solution and a dip-coated substrate were sealed in a Teflon (registered trademark) sealed container (autoclave container, internal capacity 100 ml, stainless steel jacket on the outside). At this time, the substrate was floated and fixed from the bottom of a Teflon (registered trademark) closed container, and was horizontally set so that the solution was in contact with both surfaces of the substrate. Thereafter, by performing a hydrothermal treatment at a hydrothermal temperature of 120 ° C. for 24 hours, LDH was formed on the surface and inside of the substrate. After a lapse of a predetermined time, the substrate was taken out of the closed container, washed with ion-exchanged water, and dried at 70 ° C. for 10 hours to obtain LDH in a form incorporated in the porous substrate. Thus, an LDH separator was obtained.

(5) Evaluation Various evaluations shown below were performed on the obtained LDH separator.

Evaluation 1 : Identification of LDH Separator The crystal phase of the LDH separator was measured with an X-ray diffractometer (Rigaku RINT TTR III) under the following conditions: voltage: 50 kV, current value: 300 mA, measurement range: 10 to 70 °. To obtain an XRD profile. Regarding the obtained XRD profile, the JCPDS card NO. Identification was performed using a diffraction peak of LDH (hydrotalcite compound) described in 35-0964.

Evaluation 2 : Observation of microstructure The surface microstructure of the LDH separator was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL) at an acceleration voltage of 10 to 20 kV. In addition, after a cross-section polished surface of the LDH separator was obtained by using an ion milling apparatus (IM4000, manufactured by Hitachi High-Technologies Corporation), the microstructure of the cross-section polished surface was observed by SEM under the same conditions as the observation of the surface microstructure.

Evaluation 3 : Elemental analysis evaluation (EDS)
The cross-section polisher (CP) was polished so that the cross-section polished surface of the LDH separator could be observed. One field of view of a cross-sectional image of the LDH separator was obtained at a magnification of 10,000 times by FE-SEM (ULTRA55, manufactured by Carl Zeiss). The elemental analysis of the LDH film on the substrate surface and the LDH portion (point analysis) inside the substrate in the cross-sectional image was performed by an EDS analyzer (NORAN System SIX, manufactured by Thermo Fisher Scientific) under the conditions of an acceleration voltage of 15 kV. went.

Evaluation 4 : Evaluation of Alkali Resistance Zinc oxide was dissolved in a 6 mol / L aqueous potassium hydroxide solution to obtain a 5 mol / L aqueous potassium hydroxide solution containing zinc oxide at a concentration of 0.4 mol / L. 15 ml of the aqueous potassium hydroxide solution thus obtained was placed in a Teflon (registered trademark) sealed container. An LDH separator having a size of 1 cm × 0.6 cm was placed at the bottom of the closed container, and the lid was closed. Then, after keeping at 70 ° C. for 3 weeks (ie, 504 hours) or 7 weeks (ie, 1176 hours), the LDH separator was removed from the sealed container. The removed LDH separator was dried at room temperature overnight. The obtained sample was subjected to microstructure observation by SEM and crystal structure observation by XRD.

Evaluation 5 : Measurement of Ionic Conductivity The conductivity of the LDH separator in the electrolytic solution was measured as follows using the electrochemical measurement system shown in FIG. The LDH separator sample S was sandwiched between both sides by a silicone packing 40 having a thickness of 1 mm and assembled into a flange type cell 42 made of PTFE having an inner diameter of 6 mm. As the electrode 46, a nickel wire mesh of # 100 mesh was assembled into the cell 42 in a cylindrical shape having a diameter of 6 mm so that the distance between the electrodes was 2.2 mm. The cell 42 was filled with a 6 M KOH aqueous solution as the electrolytic solution 44. Using an electrochemical measurement system (potentiometer / galvano stud-frequency response analyzer, Model 1287A and Model 1255B manufactured by Solartron), measurement was performed under the conditions of a frequency range of 1 MHz to 0.1 Hz, an applied voltage of 10 mV, and a real axis intercept. Is the resistance of the LDH separator sample S. The same measurement as above was performed only on the porous substrate without the LDH film, and the resistance of only the porous substrate was also determined. The difference between the resistance of the LDH separator sample S and the resistance of the substrate alone was defined as the resistance of the LDH film. The conductivity was determined using the resistance of the LDH film and the thickness and area of the LDH.

Evaluation 6 : Density Judgment Test A densification judgment test was performed as follows to confirm that the LDH separator had such a high degree of gas impermeability. First, as shown in FIGS. 6A and 6B, an acrylic container 130 without a lid and an alumina jig 132 having a shape and a size capable of functioning as a lid of the acrylic container 130 were prepared. The acrylic container 130 has a gas supply port 130a for supplying a gas therein. An opening 132a having a diameter of 5 mm is formed in the alumina jig 132, and a sample mounting recess 132b is formed along the outer periphery of the opening 132a. An epoxy adhesive 134 was applied to the depression 132b of the alumina jig 132, and the LDH separator sample 136 was placed in the depression 132b, and was adhered to the alumina jig 132 in a gas-tight and liquid-tight manner. Then, the alumina jig 132 to which the LDH separator sample 136 is bonded is air-tightly and liquid-tightly adhered to the upper end of the acrylic container 130 using a silicone adhesive 138 so as to completely cover the open portion of the acrylic container 130, A closed container for measurement 140 was obtained. The closed container for measurement 140 was placed in a water tank 142, and the gas supply port 130 a of the acrylic container 130 was connected to a pressure gauge 144 and a flow meter 146 so that helium gas could be supplied into the acrylic container 130. Water 143 was placed in the water tank 142, and the closed container for measurement 140 was completely submerged. At this time, the airtightness and liquid tightness of the inside of the measurement closed container 140 are sufficiently ensured, and one side of the LDH separator sample 136 is exposed to the internal space of the measurement closed container 140, while the LDH separator sample 136 is exposed. Is in contact with the water in the water tank 142. In this state, helium gas was introduced into the acrylic container 130 through the gas supply port 130a into the sealed container 140 for measurement. By controlling the pressure gauge 144 and the flow meter 146, the differential pressure between the inside and outside of the LDH separator sample 136 becomes 0.5 atm (that is, the pressure applied to the side in contact with the helium gas becomes 0.5 atm higher than the water pressure applied to the opposite side). Then, it was observed whether or not bubbles of helium gas were generated in the water from the LDH separator sample 136. As a result, in the case where generation of bubbles due to the helium gas was not observed, it was determined that the LDH separator sample 136 had high density enough to exhibit gas impermeability.

Evaluation 7 : He Permeation Measurement A He permeation test was performed as follows to evaluate the denseness of the LDH separator from the viewpoint of He permeability. First, the He transmittance measurement system 310 shown in FIGS. 7A and 7B was constructed. In the He permeability measuring system 310, He gas from a gas cylinder filled with He gas is supplied to a sample holder 316 via a pressure gauge 312 and a flow meter 314 (digital flow meter), and the LDH held in the sample holder 316 The separator 318 is configured to be transmitted from one surface to the other surface and discharged.

  The sample holder 316 has a structure provided with a gas supply port 316a, a closed space 316b, and a gas discharge port 316c, and was assembled as follows. First, an adhesive 322 was applied along the outer periphery of the LDH separator 318 and attached to a jig 324 (made of ABS resin) having an opening at the center. Gaskets made of butyl rubber are disposed as sealing members 326a and 326b at the upper and lower ends of the jig 324, and supporting members 328a and 328b (made of PTFE) provided with openings formed of flanges from outside the sealing members 326a and 326b. ). Thus, the sealed space 316b was partitioned by the LDH separator 318, the jig 324, the sealing member 326a, and the support member 328a. The support members 328a and 328b were tightly fastened to each other by the fastening means 330 using screws so that the He gas did not leak from a portion other than the gas outlet 316c. The gas supply pipe 334 was connected via a joint 332 to the gas supply port 316a of the sample holder 316 thus assembled.

Next, He gas was supplied to the He permeability measuring system 310 via the gas supply pipe 334, and was passed through the LDH separator 318 held in the sample holder 316. At this time, the gas supply pressure and the flow rate were monitored by the pressure gauge 312 and the flow meter 314. After transmitting He gas for 1 to 30 minutes, the He permeability was calculated. The calculation of the He permeability is performed by calculating the permeation amount F of the He gas per unit time F (cm ³ / min), the differential pressure P (atm) applied to the LDH separator when the He gas passes, and the film area S (cm) through which the He gas passes. ² ) was calculated by the formula of F / (P × S). The He gas permeation amount F (cm ³ / min) was read directly from the flow meter 314. The gauge pressure read from the pressure gauge 312 was used as the differential pressure P. The He gas was supplied such that the differential pressure P was in the range of 0.05 to 0.90 atm.

(6) Evaluation results The evaluation results were as follows.
-Evaluation 1: From the obtained XRD profile, it was identified that the crystal phase contained in the LDH separator was LDH (hydrotalcite compound).
-Evaluation 2: The SEM image of the cross-sectional microstructure of the LDH separator was as shown in FIG. As can be seen from FIG. 8, it was observed that LDH was incorporated over the entire area in the thickness direction of the porous substrate, that is, that the pores of the porous substrate were uniformly filled with LDH.
-Evaluation 3: As a result of EDS elemental analysis, C, Al, Ti and Ni, which are LDH constituent elements, were detected from the LDH separator. That is, Al, Ti and Ni are constituent elements of the hydroxide basic layer, while C corresponds to CO ₃ ^2- which is an anion constituting the LDH intermediate layer.
-Evaluation 4: No change was observed in the microstructure of the LDH separator even after immersion in an aqueous potassium hydroxide solution at 70 ° C. for 3 to 7 weeks.
-Evaluation 5: The conductivity of the LDH separator was 2.0 mS / cm.
-Evaluation 6: It was confirmed that the LDH separator had high density enough to exhibit gas impermeability.
-Evaluation 7: The He permeability of the LDH separator was 0.0 cm / min · atm.

Claims (14)

A method for producing a negative electrode structure for a zinc secondary battery,
(A) The whole of the quadrilateral 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 is covered with a quadrilateral liquid retaining member having a larger size. Or wrapping and obtaining a first laminate,
(B) the whole of the first laminate is a single layered double hydroxide (LDH) separator bent at one side or at least two unfolded quadrilateral LDH separators, A step of sandwiching the overlapping portion protruding from the outer edge of the negative electrode active material layer so as to form over the entire area of the outer edge, to obtain a second laminate,
(C) In the case of using one bent LDH separator, an overlapped portion belonging to at least one outer edge adjacent to the bent side of the second laminate is sealed, or is not bent. When two LDH separators are used, the overlapping portion belonging to at least two outer edges adjacent to each other of the second laminate is sealed, and as a result, a negative electrode structure in which at least two outer edges adjacent to each other are closed Obtaining a body;
Including, methods.   The method according to claim 1, wherein the liquid retaining member is a nonwoven fabric.   Step (b) includes a step of bending one LDH separator, and a step of sandwiching the entire negative electrode active material layer and the liquid retaining member between the bent one LDH separator, and 3. The method according to claim 1 or 2, wherein c) comprises sealing an overlapping portion belonging to at least one outer edge adjacent to the folded side of the second laminate.   The method according to claim 3, wherein the bending in the step (b) is performed such that a bent cross section of the LDH separator is rounded.   The method according to claim 3 or 4, wherein step (c) is performed so as to seal an overlapped portion belonging to two outer edges adjacent to the folded side of the second laminate.   The step (b) includes sandwiching the entirety of the negative electrode active material layer and the liquid retaining member between the two unfolded LDH separators, and the step (c) includes the step of: 3. The method according to claim 1 or 2, comprising the step of sealing overlapping portions belonging to at least two adjacent outer edges.   The method according to claim 6, wherein step (c) seals an overlapping portion belonging to three outer edges of the second laminate.   The method according to any one of claims 1 to 7, wherein the sealing is performed by at least one selected from the group consisting of an adhesive, heat welding, ultrasonic welding, an adhesive tape, and a sealing tape.   Step (b) is performed so as to sandwich an outer peripheral portion of the liquid retaining member between the LDH separators constituting the overlapping portion, and the sealing in step (c) is performed by heat welding or ultrasonic welding. The method according to claim 1, wherein the method is performed by:   The LDH separator includes an LDH and a porous substrate, and the LDH blocks pores of the porous substrate such that the LDH separator exhibits hydroxide ion conductivity and gas impermeability. The method according to any one of claims 1 to 9.   The method according to claim 10, wherein the porous substrate is made of a polymer material.   The method according to claim 11, wherein the LDH is incorporated throughout the thickness of the porous substrate. The negative electrode active material layer is accompanied by a current collector, the current collector has a current collector extending portion extending from one side of the negative electrode active material layer,
Step (a) is performed so that the distal end portion of the current collector extension is not covered or wrapped with the liquid retaining member, and step (b) is performed at the distal end of the current collector extension. Is carried out so as not to be sandwiched by the LDH separator, and as a result, a tip portion of the current collector extension portion forms an exposed portion that is not covered by the liquid retaining member and the LDH separator. The method according to claim 1. The method according to claim 13, wherein the side on which the sealing is performed is a side that does not overlap with the current collector extension.