LDH Separator and Zinc Secondary Battery

Abstract

To provide an LDH separator capable of further improving the yield of a battery while having excellent cycle durability performance.SOLUTION: An LDH separator includes a porous substrate, and a surface layer provided on at least one surface of a porous substrate and containing a hydroxide ion-conducting layered compound that is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound. This LDH separator includes a surface layer residual portion where the surface layer exists, and a surface layer peeling portion where the surface layer does not exist when the surface on the surface layer side is observed with a scanning electron microscope (SEM), and the surface layer residual ratio, which is the ratio of the area of the surface layer residual portion to the total area of the surface layer residual portion and the surface layer peeled portion, is 80 to 99%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an LDH separator and a zinc secondary battery.

Background Art

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

[0003] To address the above problems, a battery equipped with a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to permeate while preventing the penetration of zinc dendrites has been proposed. For example, Patent Document 1 (International Publication No. 2013 / 118561) discloses providing an LDH separator between the positive and negative electrodes in a nickel-zinc secondary battery. Further, Patent Document 2 (International Publication No. 2016 / 076047) discloses a separator structure including an LDH separator fitted or joined to a resin outer frame, and discloses that the LDH separator has a high density such that it is gas-impermeable and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Furthermore, Patent Document 3 (International Publication No. 2016 / 067884) discloses various methods for obtaining a composite material by forming an LDH dense film on the surface of a porous substrate. This method includes a step of uniformly adhering a starting material capable of giving a starting point for crystal growth of LDH to the porous substrate and subjecting the porous substrate to hydrothermal treatment in an aqueous raw material solution to form an LDH dense film on the surface of the porous substrate. An LDH separator that achieves further densification by roll-pressing a composite material of LDH / porous substrate produced through hydrothermal treatment has also been proposed. For example, Patent Document 4 (International Publication No. 2019 / 124270) discloses an LDH separator including a polymer porous substrate and LDH filled in the porous substrate, having a linear transmittance of 1% or more at a wavelength of 1000 nm.

[0004] In addition, although not called LDH, LDH-like compounds are known as hydroxides and / or oxides having a layered crystal structure similar thereto, and exhibit hydroxide ion conduction characteristics similar enough to be collectively referred to as hydroxide ion conductive layered compounds together with LDH. For example, Patent Document 5 (International Publication No. 2020 / 255856) discloses a hydroxide ion conductive separator including a porous substrate and a layered double hydroxide (LDH)-like compound that plugs pores of the porous substrate, wherein the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure including Mg and at least one element selected from the group consisting of Ti, Y, and Al and including at least Ti. This hydroxide ion conductive separator is said to be superior in alkali resistance to a conventional LDH separator and to be able to more effectively suppress a short circuit caused by zinc dendrites.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

[0006] By using a hydroxide ion conductive separator (hereinafter collectively referred to as an LDH separator) including LDH and LDH-like compounds as described above in a zinc secondary battery, it is possible to prevent a short circuit caused by zinc dendrites and improve cycle durability performance. On the other hand, when assembling a zinc secondary battery using such an LDH separator, the battery yield may decrease.

[0007] The inventors of the present invention have now found that in an LDH separator including a porous substrate and a surface layer provided on the surface thereof, by peeling a part of the surface layer so as to achieve a predetermined remaining ratio, it is possible to further improve the battery yield while having excellent cycle durability performance.

[0008] Therefore, an object of the present invention is to provide an LDH separator that has excellent cycle durability performance and can further improve the battery yield.

[0009] According to one aspect of the present invention, a porous substrate, a surface layer provided on at least one surface of the porous substrate and containing a hydroxide ion-conductive layered compound which is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound, and an LDH separator comprising: when the surface on the surface layer side of the LDH separator is observed with a scanning electron microscope (SEM), the LDH separator has a surface remaining portion where the surface layer exists and a surface peeling portion where the surface layer does not exist, an LDH separator is provided in which the surface remaining ratio, which is the ratio of the area of the surface remaining portion to the total area of the surface remaining portion and the surface peeling portion, is 80 to 99%.

[0010] According to another aspect of the present invention, a zinc secondary battery including the LDH separator is provided.

[0011] According to another aspect of the present invention, a solid alkaline fuel cell including the LDH separator is provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Figure 8

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] LDH separator As conceptually shown in FIG. 1, the LDH separator 10 of the present invention includes a porous substrate 12 and a surface layer 14 provided on at least one surface of the porous substrate 12. The surface layer 14 contains a hydroxide ion conductive layered compound. The hydroxide ion conductive layered compound is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound. When the surface on the surface layer 14 side of the LDH separator 10 is observed with a scanning electron microscope (SEM), it has a surface layer remaining portion R where the surface layer 14 exists and a surface layer peeling portion P where the surface layer 14 does not exist. And the LDH separator 10 has a surface layer remaining ratio, which is the ratio of the area of the surface layer remaining portion R to the total area of the surface layer remaining portion R and the surface layer peeling portion P, of 80 to 99%. In this specification, an "LDH separator" is a separator containing LDH and / or an LDH-like compound, and is defined as selectively passing hydroxide ions by utilizing only the hydroxide ion conductivity of LDH and / or an LDH-like compound. In this specification, an "LDH-like compound" is a hydroxide and / or oxide having a layered crystal structure similar to LDH, although it may not be called LDH, and can be said to be an equivalent of LDH. However, as a broad definition, it is also possible to interpret that "LDH" includes not only LDH but also LDH-like compounds. Thus, in the LDH separator 10 including the porous substrate 12 and the surface layer 14 provided on its surface, by peeling a part of the surface layer 14 so as to have a predetermined remaining ratio, it is possible to further improve the battery yield while having excellent cycle durability performance.

[0014] Although the mechanism by which the yield of the battery is improved by using the LDH separator having the above-mentioned predetermined surface layer survival rate is not necessarily clear, it is considered as follows. That is, at the time of assembling the battery, for example, production of the negative electrode structure by bonding and welding the LDH separator and the negative electrode plate, and lamination of the negative electrode structure and the positive electrode plate are performed. For this reason, various loads are applied to the LDH separator in the subsequent process (battery assembly process). In this regard, FIG. 3 shows a schematic cross-sectional view of the conventional LDH separator 100 in which the surface layer 104 is provided without peeling on the surface of the porous base material 102 before and after battery assembly. As shown in FIG. 3, the LDH separator 100 having no peeling portion in the surface layer 104 is vulnerable to the load applied at the time of battery assembly, and the surface layer 104 is likely to be deformed and collapsed by pressure. Therefore, in order to avoid deformation and collapse of the surface layer 104, it is necessary to suppress the load at the time of battery assembly, for example. On the other hand, as shown in FIG. 2, in the LDH separator 10 in which the surface layer 14 is partially peeled off, the surface layer 14 is not easily broken even when pressure is applied at the time of battery assembly. That is, since the LDH separator 10 has the surface layer peeling portion P, it is possible to relieve the stress applied to the surface layer 14 at the surface layer peeling portion P. Thus, since the destruction of the LDH separator is less likely to occur, the yield of the battery is improved even when an assembly process is performed in which a load is applied such that deformation or collapse of the surface layer occurs conventionally.

[0015] On the other hand, the LDH separator 10 can prevent the intrusion of zinc dendrites by the surface layer 14. In this regard, by controlling the surface layer survival rate of the LDH separator within a predetermined range of 80 to 99%, it is possible to more effectively prevent the intrusion of zinc dendrites as compared with the LDH separator having an excessive peeling amount of the surface layer 14, and as a result, the cycle durability performance can be improved. Therefore, according to the LDH separator of the present invention, it is possible to improve the yield of the battery while having excellent cycle durability performance.

[0016] From the perspective of achieving a good balance between improving the cycle durability performance and the battery yield by stress relaxation, the surface layer residual rate of the LDH separator is 80 to 99%, preferably 85 to 99%, more preferably 90 to 99%, still more preferably 95 to 99%, and particularly preferably 97 to 99%. The surface layer residual rate can be calculated by observing the surface of the surface layer 14 side of the LDH separator 10 with a scanning electron microscope (SEM) and obtaining the areas of the surface layer residual part R and the surface layer peeling part P, respectively. Regarding the preferred calculation method of the surface layer residual rate using a scanning electron microscope, it shall be as shown in Evaluation 7 of the examples described later.

[0017] The thickness of the surface layer 14 is preferably 0.01 to 10 μm, more preferably 0.01 to 8 μm, still more preferably 0.05 to 8 μm, and particularly preferably 0.05 to 5 μm. Within these ranges, the penetration of the separator by zinc dendrites can be more reliably blocked by the surface layer 14, and as a result, the cycle durability performance can be further improved.

[0018] The LDH separator 10 preferably has an ion conductivity of 1.0 mS / cm or more, more preferably 1.5 mS / cm or more, still more preferably 2.0 mS / cm or more, particularly preferably 2.2 mS / cm or more, and most preferably 2.5 mS / cm or more. Since it is desirable that the ion conductivity be as high as possible, the upper limit is not limited, but for example, it is 10 mS / cm or less.

[0019] The tightness of the LDH separator 10 can be evaluated by the He permeability. That is, the LDH separator 10 preferably has a He permeability of 10 cm / min·atm or less per unit area, more preferably 5.0 cm / min·atm or less, and still more preferably 1.0 cm / min·atm or less. The LDH separator 10 having a He permeability within such a range can be said to have extremely high tightness. Therefore, a separator with a He permeability of 10 cm / min·atm or less can block the passage of substances other than hydroxide ions at a high level. For example, in the case of a zinc secondary battery, the permeation of Zn in the electrolyte (typically the permeation of zinc ions or zincate ions) can be extremely effectively suppressed. The He permeability is measured through a process of supplying He gas to one surface of the separator to allow the He gas to permeate through the separator and a process of calculating the He permeability to evaluate the tightness of the hydroxide ion conductive separator. The He permeability is calculated by the formula F / (P×S) using the permeation amount F of He gas per unit time, the differential pressure P applied to the separator during He gas permeation, and the membrane area S through which the He gas permeates. By evaluating the gas permeability using He gas in this way, the presence or absence of tightness at an extremely high level can be evaluated. As a result, a high level of tightness such as not allowing substances other than hydroxide ions (especially Zn that causes zinc dendrite growth) to permeate as much as possible (only a very small amount permeates) can be effectively evaluated. This is because He gas has the smallest structural unit among various atoms or molecules that can form a gas and has extremely low reactivity. That is, He constitutes He gas as single He atoms without forming molecules. In this regard, since hydrogen gas is composed of H2 molecules, the He atom as a single gas constituent unit is smaller. Moreover, H2 gas is dangerous because it is a flammable gas. By adopting the index of He gas permeability defined by the above formula, an objective evaluation of tightness can be easily performed regardless of differences in various sample sizes and measurement conditions. In this way, it is possible to simply, safely and effectively evaluate whether the separator has sufficiently high tightness suitable for a zinc secondary battery separator.The measurement of the He permeability can be preferably carried out according to the procedure shown in Evaluation 4 of the examples described later.

[0020] The LDH separator 10 preferably has a hydroxide ion-conductive layered compound filled in the pores of the porous substrate 12. According to such an embodiment, the hydroxide ion-conductive layered compound is connected between the upper surface and the lower surface of the porous substrate 12, thereby ensuring the hydroxide ion conductivity of the LDH separator 10. The hydroxide ion-conductive layered compound is particularly preferably incorporated throughout the thickness direction of the porous substrate 12. However, the pores of the porous substrate 12 do not have to be completely blocked, and a small amount of residual pores may be present. Alternatively, the LDH separator 10 may not have a hydroxide ion-conductive layered compound filled in the pores of the porous substrate 12. The thickness of the LDH separator 10 (i.e., the total thickness of the porous substrate 12 and the surface layer 14) is preferably 3 to 80 μm, more preferably 3 to 60 μm, and even more preferably 3 to 40 μm.

[0021] LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between these plurality of hydroxide basic layers. The hydroxide basic layer is mainly composed of a metal element (typically a metal ion) and an OH group. The intermediate layer of LDH is composed of an anion and H2O. The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anion in LDH is OH - and / or CO3 2- is included. Also, LDH has excellent ion conductivity due to its inherent properties. Generally, LDH is known to be represented by the basic composition formula of M 2+ 1-x M 3+ x (OH)2A n- x / n ·mH2O (wherein M 2+ is a divalent cation, M 3+ is a trivalent cation, A n- is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In the above basic composition formula, M 2+can be any divalent cation, and preferred examples include Mg 2+ , Ca 2+ and Zn 2+ , and more preferably Mg 2+ . M 3+ can be any trivalent cation, and preferred examples include Al 3+ or Cr 3+ , and more preferably Al 3+ . A n- can be any anion, and preferred examples include OH - and CO3 2- . Therefore, in the above basic composition formula, M 2+ contains Mg 2+ , M 3+ contains Al 3+ , and A n- preferably contains OH - and / or CO3 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 representing the number of moles of water, a real number of 0 or more, typically greater than 0 or 1 or more. However, the above basic composition formula is merely a formula of the "basic composition" typically exemplified for LDH, and the constituent ions can be replaced as appropriate. For example, in the above basic composition formula, part or all of M 3+ can be replaced with a cation of tetravalent or higher valence (for example, Ti 4+ ), and in that case, the coefficient x / n of the anion A n- in the above general formula may be changed as appropriate.

[0022] For example, the hydroxide basic layer of LDH preferably contains Mg, Al, and OH groups, and more preferably contains Ti (i.e., contains Mg, Al, Ti, and OH groups) in terms of exhibiting excellent alkali resistance. In this case, as long as the hydroxide basic layer contains Mg, Al, and OH groups (and Ti if desired), it may contain other elements or ions. For example, Y and / or Zn may be contained in the LDH or the hydroxide basic layer. Also, when Y and / or Zn are contained in the LDH or the hydroxide basic layer, the LDH or the hydroxide basic layer may not contain Al or Ti. However, it is preferable that the hydroxide basic layer contains Mg, Al, Ti, and OH groups as main components. That is, it is preferable that the hydroxide basic layer mainly consists of Mg, Al, Ti, and OH groups. Therefore, the hydroxide basic layer is typically composed of Mg, Al, Ti, OH groups, and optionally inevitable impurities. The atomic ratio of Ti / Al in LDH determined by energy dispersive X-ray spectroscopy (EDS) is preferably 0.5 to 12, more preferably 1.0 to 12. Within the above range, the suppression effect of short circuit caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized without impairing ion conductivity. For the same reason, the atomic ratio of Ti / (Mg + Ti + Al) in LDH determined by energy dispersive X-ray spectroscopy (EDS) is preferably 0.1 to 0.7, more preferably 0.2 to 0.7. Also, the atomic ratio of Al / (Mg + Ti + Al) in LDH is preferably 0.05 to 0.4, more preferably 0.05 to 0.25. Further, the atomic ratio of Mg / (Mg + Ti + Al) in LDH is preferably 0.2 to 0.7, more preferably 0.2 to 0.6. Note that the EDS analysis is preferably performed by using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments), 1) capturing an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) performing point analysis at intervals of about 5 μm in point analysis mode, 3) repeating the above 1) and 2) one more time, and 4) calculating the average value of a total of 6 points.

[0023] Alternatively, the hydroxide basic layer of the LDH may contain Ni, Al, Ti, and OH groups. In this case, as long as the hydroxide basic layer contains Ni, Al, Ti, and OH groups, it may contain other elements or ions. However, it is preferable that the hydroxide basic layer contains Ni, Al, Ti, and OH groups as main components. That is, it is preferable that the hydroxide basic layer mainly consists of Ni, Al, Ti, and OH groups. Therefore, the hydroxide basic layer is typically composed of Ni, Al, Ti, OH groups, and optionally inevitable impurities. The atomic ratio of Ti / (Ni + Ti + Al) in the LDH determined by energy dispersive X-ray analysis (EDS) is preferably from 0.10 to 0.90, more preferably from 0.20 to 0.80, still more preferably from 0.25 to 0.70, and particularly preferably from 0.30 to 0.61. Within the above range, both the alkali resistance and the ionic conductivity can be improved. Therefore, the hydroxide ion conductive layered compound may contain not only LDH but also a large amount of Ti that by-produces titania. That is, the hydroxide ion conductive layered compound may further contain titania. It is expected that the hydrophilicity is increased and the wettability with the electrolyte is improved (i.e., the conductivity is improved) by the inclusion of titania.

[0024] The LDH-like compound may not be called LDH, but is a hydroxide and / or oxide having a layered crystal structure similar thereto, and preferably contains (i) Mg and (ii) at least one element containing at least Ti selected from the group consisting of Ti, Y, and Al. Thus, by using, instead of the conventional LDH, an LDH-like compound which is a hydroxide and / or oxide having a layered crystal structure containing at least Mg and Ti as a hydroxide ion conductive material, a hydroxide ion conductive separator excellent in alkali resistance and capable of more effectively suppressing a short circuit caused by zinc dendrites can be provided. Therefore, a preferred LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing (i) Mg and (ii) at least one element containing at least Ti selected from the group consisting of Ti, Y, and Al. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Mg, Ti, optionally Y, and optionally Al, and particularly preferably a composite hydroxide and / or composite oxide of Mg, Ti, Y, and Al. The above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, but the LDH-like compound preferably does not contain Ni.

[0025] The LDH-like compound can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface of the surface layer 14 side of the LDH separator 10, typically peaks derived from the LDH-like compound are detected in the range of 5° ≤ 2θ ≤ 10°, more typically in the range of 7° ≤ 2θ ≤ 10°. As described above, LDH is a substance having an alternating layered structure in which exchangeable anions and H2O exist as intermediate layers between stacked hydroxide basic layers. In this regard, when LDH is measured by the X-ray diffraction method, a peak (i.e., the (003) peak of LDH) due to the crystal structure of LDH is originally detected at the position of 2θ = 11 to 12°. On the other hand, when the LDH-like compound is measured by the X-ray diffraction method, peaks are typically detected in the above range shifted to the low-angle side from the above peak position of LDH. Also, the interlayer distance of the layered crystal structure can be determined by Bragg's equation using 2θ corresponding to the peak derived from the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystal structure constituting the LDH-like compound thus determined is typically 0.883 to 1.8 nm, more typically 0.883 to 1.3 nm.

[0026] The atomic ratio of Mg / (Mg + Ti + Y + Al) in the LDH-like compound determined by energy dispersive X-ray analysis (EDS) is preferably 0.03 to 0.25, more preferably 0.05 to 0.2. Also, the atomic ratio of Ti / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0.40 to 0.97, more preferably 0.47 to 0.94. Further, the atomic ratio of Y / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.45, more preferably 0 to 0.37. And the atomic ratio of Al / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.03. When within the above range, the alkali resistance is further improved, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. By the way, the conventionally known LDH for the LDH separator has the general formula: M 2+ 1-x M 3+x (OH)2A n- x / n ·mH2O (where M 2+ is a divalent cation, M 3+ is a trivalent cation, and A n- is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). It can be represented by this basic composition. In contrast, the above atomic ratio in the LDH-like compound generally deviates from that of LDH in the above general formula. Therefore, it can be said that the LDH-like compound generally has a composition ratio (atomic ratio) different from that of conventional LDH. Note that the EDS analysis is preferably performed by using an EDS analyzer (for example, X-act, manufactured by Oxford Instruments), 1) capturing an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) performing three-point analysis at intervals of about 5 μm in the point analysis mode, 3) repeating the above 1) and 2) one more time, and 4) calculating the average value of a total of six points.

[0027] When incorporated into a zinc secondary battery, the LDH separator 10 separates the positive electrode plate and the negative electrode plate so that hydroxide ions can be conducted. The preferred LDH separator 10 has gas impermeability and / or water impermeability. In other words, the LDH separator 10 (especially the surface layer 14) is preferably densified to have gas impermeability and / or water impermeability. In the present specification, "having gas impermeability" means that, as described in Patent Documents 2 and 3, even when helium gas is brought into contact with one side of the object to be measured in water at a differential pressure of 0.5 atm, no bubbles caused by helium gas are observed on the other side. Also, in the present specification, "having water impermeability" means that, as described in Patent Documents 2 and 3, water in contact with one side of the object to be measured does not permeate to the other side. That is, the fact that the LDH separator 10 has gas impermeability and / or water impermeability means that the LDH separator 10 has a high degree of density such that it does not allow gas or water to pass through, and it means that it is not a porous film or other porous material having water permeability or gas permeability. By doing so, the LDH separator 10 selectively allows only hydroxide ions to pass through due to its hydroxide ion conductivity, and can exhibit the function as a battery separator. Therefore, it is a very effective configuration for physically preventing the separator from being penetrated by zinc dendrites generated during charging and preventing a short circuit between the positive and negative electrodes. Since the LDH separator 10 has hydroxide ion conductivity, it enables efficient movement of necessary hydroxide ions between the positive electrode plate and the negative electrode plate, and realizes charge and discharge reactions in the positive electrode plate and the negative electrode plate.

[0028] The porous substrate 12 is preferably made of a polymer material. The polymer porous substrate has the following advantages: 1) It has flexibility (so it is not easily cracked even when thinned), 2) It is easy to increase the porosity, 3) It is easy to increase the conductivity (because the thickness can be reduced while increasing the porosity), 4) It is easy to manufacture and handle. Also, taking advantage of the flexibility in 1) above, there is an advantage that a hydroxide ion conductive separator including a porous substrate made of a polymer material can be easily bent or hermetically joined. Preferred examples of the polymer material include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, fluororesin (tetrafluorinated resin: PTFE, etc.), cellulose, nylon, polyethylene, and any combination thereof. More preferably, from the viewpoint of a thermoplastic resin suitable for hot pressing, polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, fluororesin (tetrafluorinated resin: PTFE, etc.), nylon, polyethylene, and any combination thereof, etc. are mentioned. All of the various preferred materials described above have alkalinity resistance as resistance to the electrolyte of the battery. A particularly preferred polymer material is a polyolefin such as polypropylene or polyethylene because it is excellent in heat and water resistance, acid resistance, and alkalinity resistance, and is also low in cost. Most preferably, it is polypropylene or polyethylene. It is particularly preferred that the hydroxide ion conductive layer compound is incorporated throughout the thickness direction of the porous substrate 12 (for example, most or almost all of the pores inside the polymer porous substrate are filled with the hydroxide ion conductive layer compound). As such a polymer porous substrate, a commercially available polymer microporous membrane can be preferably used.

[0029] The manufacturing method of the LDH separator 10 is not particularly limited, and it can be produced by appropriately changing the various conditions of the known manufacturing methods of LDH separators (or LDH-containing functional layers and composite materials) (for example, refer to Patent Documents 1 to 5). For example, (1) prepare a porous substrate, (2) apply a solution containing i) alumina sol (or further titania sol) (when forming LDH), or ii) titania sol (or further yttria sol and / or alumina sol) (when forming an LDH-like compound) to the porous substrate and dry it, (3) immerse the porous substrate in an aqueous raw material solution containing magnesium ions (Mg 2+ ) and urea (or further yttrium ions (Y 3+ ))), and (4) hydrothermally treat the porous substrate in the aqueous raw material solution to form a hydroxide ion-conductive layered compound on and / or in the porous substrate, whereby an LDH separator can be manufactured. At this time, the presence of urea in the above step (3) causes ammonia to be generated in the solution by utilizing the hydrolysis of urea, thereby increasing the pH value, and the coexisting metal ions form hydroxides and / or oxides, so that a hydroxide ion-conductive layered compound (that is, LDH and / or LDH-like compound) can be obtained. And since the generation of carbon dioxide accompanies the hydrolysis, when forming LDH, an anion can obtain an LDH of the carbonate ion type.

[0030] In particular, when manufacturing the LDH separator 10 in which the hydroxide ion-conductive layered compound is incorporated throughout the thickness direction of the porous substrate 12, it is preferable to perform the application of the sol solution to the substrate in the above (2) by a method that allows the sol solution to penetrate into the whole or most of the inside of the substrate. By doing so, finally, most or almost all of the pores inside the porous substrate 12 can be filled with the hydroxide ion-conductive layered compound. Examples of preferable coating methods include dip coating, filtration coating, etc., and dip coating is particularly preferable. The amount of the sol solution adhered can be adjusted by adjusting the number of coating times such as dip coating. After the substrate coated with the sol solution by dip coating or the like is dried, the above steps (3) and (4) may be carried out.

[0031] The LDH separator obtained by the above method or the like may be subjected to a pressing process. By doing so, an LDH separator with even better tightness can be obtained. The pressing method may be, for example, roll pressing, uniaxial pressure pressing, CIP (cold isostatic pressing), etc., and is not particularly limited, but roll pressing is preferably used. This pressing is preferably performed while heating to soften the polymer porous substrate, so that the pores of the polymer porous substrate can be sufficiently blocked by the hydroxide ion conductive layered compound. As the temperature for sufficient softening, for example, in the case of polypropylene or polyethylene, it is preferably heated at 60 to 200 °C. By performing pressing such as roll pressing in such a temperature range, the residual pores of the LDH separator can be significantly reduced. As a result, the LDH separator can be made extremely dense, and therefore, the short circuit caused by zinc dendrites can be more effectively suppressed. When performing roll pressing, the form of the residual pores can be controlled by appropriately adjusting the roll gap and the roll temperature, whereby an LDH separator with a desired tightness can be obtained. Therefore, the LDH separator of the present invention is preferably pressed in the thickness direction.

[0032] From the viewpoint of controlling the surface residual rate, it is preferable to perform a process of peeling a part of the surface on the LDH separator obtained by the above method or the like. An example of such a process is the roll press process described above. That is, by sandwiching the LDH separator between a pair of PET films or the like and performing roll pressing, a part of the surface adheres to the PET film and is peeled off from the porous substrate. At this time, the surface residual rate can be controlled by adjusting the roll temperature and the load (roll linear pressure). That is, the higher the roll temperature, the easier it is for the surface layer to be peeled off, and the greater the roll linear pressure, the higher the density of the LDH separator. In this regard, from the viewpoint of easily controlling the surface residual rate within a predetermined range, it is preferable to perform roll pressing on the LDH separator under the conditions of a roll temperature of 60 to 140°C and a roll linear pressure exceeding 100 kg / cm and less than 300 kg / cm. More preferably, it is performed under the conditions of a roll temperature of 60 to 90°C and a roll linear pressure of 120 to 200 kg / cm. Even more preferably, it is performed under the conditions of a roll temperature of 60 to 70°C and a roll linear pressure of 120 to 130 kg / cm. Alternatively, the surface residual rate may be controlled by performing a scratch treatment (scraping) on the LDH separator. That is, a part of the surface layer can be peeled off by moving the LDH separator in the horizontal direction with a rubber roll or the like pressed vertically against the surface layer. From the viewpoint of more appropriately controlling the surface peeling amount of the LDH separator, both the roll press treatment and the scratch treatment may be combined and performed on the LDH separator.

[0033] Zinc secondary battery The LDH separator of the present invention is preferably applied to a zinc secondary battery. Therefore, according to a preferred embodiment of the present invention, a zinc secondary battery equipped with an LDH separator is provided. A typical zinc secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution, and the positive electrode and the negative electrode are isolated from each other via the LDH separator. The zinc secondary battery of the present invention is not particularly limited as long as it uses zinc as the negative electrode and an electrolyte solution (typically an aqueous solution of an alkali metal hydroxide). Therefore, it can be a nickel-zinc secondary battery, a silver oxide-zinc secondary battery, a manganese oxide-zinc secondary battery, a zinc-air secondary battery, or various other alkaline zinc secondary batteries. 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 forms a zinc-air secondary battery.

[0034] Solid alkaline fuel cell The LDH separator of the present invention can also be applied to a solid alkaline fuel cell. That is, by using a highly densified LDH separator, a solid alkaline fuel cell capable of effectively suppressing a decrease in electromotive force caused by the permeation of fuel to the air electrode side (for example, methanol crossover) can be provided. This is because while the hydroxide ion conductivity of the LDH separator is exhibited, the permeation of fuels such as methanol through the LDH separator can be effectively suppressed. Therefore, according to another preferred embodiment of the present invention, a solid alkaline fuel cell equipped with an LDH separator is provided. A typical solid alkaline fuel cell according to this embodiment includes an air electrode to which oxygen is supplied, a fuel electrode to which a liquid fuel and / or a gaseous fuel is supplied, and an LDH separator interposed between the fuel electrode and the air electrode.

[0035] Other batteries The LDH separator of the present invention can be used not only for nickel-zinc batteries and solid alkaline fuel cells, but also for, for example, nickel-metal hydride batteries. In this case, the LDH separator functions to block the nitride shuttle (the movement of nitrate groups between electrodes), which is a cause of self-discharge of the battery. Further, the LDH separator of the present invention can also be used for lithium batteries (batteries with lithium metal as the negative electrode), lithium-ion batteries (batteries with a carbon negative electrode, etc.), or lithium-air batteries, etc.

Examples

[0036] The present invention will be described more specifically by the following examples. The evaluation method of the LDH separator produced in the following examples was as follows.

[0037] Evaluation 1 : Observation of microstructure The surface microstructure of the LDH separator was observed at an acceleration voltage of 10 to 20 kV using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL Ltd.).

[0038] Evaluation 2 : Elemental analysis evaluation (EDS) Composition analysis was performed on the surface of the LDH separator using an EDS analyzer (device name: X-act, manufactured by Oxford Instruments) to confirm that a predetermined element was incorporated into the crystal. This analysis was carried out as follows: 1) An image was captured at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) Point analysis was performed at intervals of about 5 μm, and three-point analysis was carried out, and 3) Steps 1) and 2) were repeated once more.

[0039] Evaluation 3 : Identification of hydroxide ion-conducting layered compounds Using an X-ray diffractometer (manufactured by Rigaku, RINT TTR III), the crystal phase of the hydroxide ion-conducting layered compound was measured under the measurement conditions of voltage: 50 kV, current value: 300 mA, and measurement range: 5 to 70° to obtain an XRD profile.

[0040] Evaluation 4 : He permeation measurement To evaluate the tightness of the LDH separator from the perspective of He permeability, the He permeation test was conducted as follows. First, the He permeation measurement system 310 shown in FIGS. 4A and 4B was constructed. The He permeation measurement system 310 is configured such that He gas from a gas cylinder filled with He gas is supplied to a sample holder 316 through a pressure gauge 312 and a flow meter 314 (digital flow meter), and permeates from one side to the other side of the LDH separator 318 held in this sample holder 316 and is discharged.

[0041] The sample holder 316 has a structure including a gas supply port 316a, a sealed 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 in the center. Butyl rubber packings were disposed as sealing members 326a and 326b at the upper and lower ends of this jig 324, and further clamped from the outside of the sealing members 326a and 326b by support members 328a and 328b (made of PTFE) having openings formed of flanges. In this way, 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 firmly tightened together by fastening means 330 using screws so that no He gas leakage occurred from parts other than the gas discharge port 316c. A gas supply pipe 334 was connected to the gas supply port 316a of the sample holder 316 thus assembled via a joint 332.

[0042] Next, He gas was supplied to the He permeation measurement system 310 through the gas supply pipe 334 and permeated through the LDH separator 318 held in the sample holder 316. At this time, the gas supply pressure and flow rate were monitored by the pressure gauge 312 and the flow meter 314. After the He gas permeation was performed for 1 to 30 minutes, the He permeability was calculated. The calculation of the He permeability was performed using the permeation amount F (cm 3 / min) of He gas per unit time, the differential pressure P (atm) applied to the LDH separator during He gas permeation, and the membrane area S (cm 2 ) through which the He gas permeates, according to the formula F / (P×S). The permeation amount F (cm of He gas3 The flow rate (mL / min) was directly read from the flow meter 314. Also, the differential pressure P used the gauge pressure read from the pressure gauge 312. The He gas was supplied so that the differential pressure P was within the range of 0.05 to 0.90 atm.

[0043] Evaluation 5 : Measurement of ionic conductivity The conductivity of the LDH separator in the electrolyte was measured as follows using the electrochemical measurement system shown in Fig. 5. The LDH separator sample S was sandwiched from both sides with silicone packing 440 having a thickness of 1 mm and incorporated into a PTFE flange-type cell 442 having an inner diameter of 6 mm. As the electrode 446, a #100 mesh nickel-gold mesh was formed into a cylindrical shape with a diameter of 6 mm inside the cell 442 so that the distance between the electrodes was 2.2 mm. As the electrolyte 444, a 6M KOH aqueous solution was filled into the cell 442. Using an electrochemical measurement system (Potentiostat / Galvanostat - Frequency Response Analyzer, Solartron models 1287A and 1255B), measurements were performed under the conditions of a frequency range of 1 MHz to 0.1 Hz and an applied voltage of 10 mV, and the intercept on the real axis was taken as the resistance of the LDH separator sample S. The same measurement as above was performed with a configuration without the LDH separator sample S to obtain the blank resistance. The difference between the resistance of the LDH separator sample S and the blank resistance was taken as the resistance of the LDH separator. The conductivity was determined using the obtained resistance of the LDH separator, the thickness, and the area of the LDH separator.

[0044] Evaluation 6 : Evaluation of dendrite resistance (cycle test) To evaluate the suppression effect (dendrite resistance) of short circuits caused by zinc dendrites in the LDH separator, a cycle test was conducted as follows. First, each of the positive electrode (including nickel hydroxide and / or nickel oxyhydroxide) and the negative electrode (including zinc and / or zinc oxide) was wrapped with a non-woven fabric, and current extraction terminals were welded. The thus-prepared positive and negative electrodes were opposed to each other via the LDH separator, sandwiched between laminated films provided with current extraction ports, and three sides of the laminated film were heat-sealed. An electrolytic solution (prepared by dissolving 0.4 M zinc oxide in a 5.4 M KOH aqueous solution) was added to the thus-obtained cell container with an open top, and the electrolytic solution was sufficiently permeated into the positive and negative electrodes by evacuation or the like. Thereafter, the remaining one side of the laminated film was also heat-sealed to form a simple sealed cell. Using a charge-discharge device (manufactured by Toyo System Co., Ltd., TOSCAT3100), formation was carried out on the simple sealed cell at 0.1C charge and 0.2C discharge. Thereafter, 1C charge-discharge cycles were carried out. While repeatedly carrying out charge-discharge cycles under the same conditions, the voltage between the positive and negative electrodes was monitored with a voltmeter, and the presence or absence of a sudden voltage drop (specifically, a voltage drop of 5 mV or more with respect to the voltage plotted immediately before) associated with a short circuit caused by zinc dendrites between the positive and negative electrodes was examined and evaluated according to the following criteria. · No short circuit: No sudden voltage drop was observed during charging even after a predetermined number of cycles. · Short circuit present: A sudden voltage drop was observed during charging before a predetermined number of cycles was reached.

[0045] Evaluation 7 : Calculation of surface layer residual ratio The surface residual rate of the LDH separator was calculated as follows. First, for the surface on the surface side of the LDH separator, observation was carried out using a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation, SU-3500) under the conditions of a magnification of 50 times and an acceleration voltage of 10 kV, and a surface SEM image of 1280×898 px was obtained (see Fig. 6(i)). The obtained surface SEM image was resized to 300×210 px (see Fig. 6(ii)), and for the resized surface SEM image, the luminance value of each pixel was obtained. This luminance value is on a 256-gray scale from 0 (representing black) to 255 (representing white). Typically, the luminance value of a portion where the surface layer does not exist (the portion where the porous substrate is exposed) shows a lower value (i.e., closer to black) compared to the luminance value of the portion where the surface layer exists.

[0046] Next, in the surface SEM image, within a total range of 500 pixels in the portion where the surface layer exists, the average luminance value L R was obtained, and within a total range of 500 pixels in the portion where the surface layer does not exist, the average luminance value L P was obtained, and these average values (=(L R +L P ) / 2) were used as the determination threshold. Here, the average luminance value L R and the average luminance value L P shall each use an integer obtained by rounding off the decimal part for the calculation of the determination threshold, and the calculated determination threshold shall also be represented by an integer obtained by rounding off the decimal part. For example, when the average luminance value L R is "189.1···" and the average luminance value L P is "129.9···", the calculation of the determination threshold is "(189 + 130) / 2 = 159.5", and the determination threshold is "160".

[0047] Thereafter, pixels with a luminance value equal to or greater than the determination threshold value were determined as the surface remaining portion, and pixels with a luminance value less than the determination threshold value were determined as the surface peeling portion. Then, the surface remaining ratio (%) was calculated by dividing the number of pixels in the surface remaining portion by the total number of pixels (300 × 210 = 63000) in the surface SEM image and multiplying by 100. The above operations were repeated 6 times, and the average value of the total 6 calculated surface remaining ratios was taken as the surface remaining ratio of the LDH separator.

[0048] Evaluation 8 : Battery yield To evaluate the resistance to breakage (or ease of breakage) of the LDH separator in the battery assembly process, an evaluation cell was fabricated as follows, and the yield was calculated. First, a positive electrode plate, a negative electrode plate, a nonwoven fabric, a battery case, and an electrolytic solution shown below were prepared. · Positive electrode plate: A foam nickel plate filled with a positive electrode paste containing nickel hydroxide and a binder in its pores and dried · Negative electrode plate: A negative electrode paste containing ZnO powder, metallic Zn powder, polytetrafluoroethylene (PTFE), and propylene glycol was pressure-bonded to a current collector (copper expanded metal) · Nonwoven fabric: Made of polypropylene, with a thickness of 100 μm · Battery case: A housing made of a modified polyphenylene ether resin · Electrolytic solution: A 5.4 mol / L KOH aqueous solution in which 0.4 mol / L of ZnO was dissolved

[0049] The negative electrode plate was wrapped from both sides with a non-woven fabric and an LDH separator in that order, such that the non-woven fabric and the LDH separator slightly protruded from the remaining three sides excluding the side where the negative electrode current collector extended. The surplus portions of the non-woven fabric and the LDH separator protruding from the three sides of the negative electrode plate were heat-sealed and sealed with a heat-sealing bar to obtain a negative electrode structure. The negative electrode structure and the positive electrode plate were alternately laminated, and while in the laminated state, the positive electrode current collector was welded to the positive electrode current collecting terminal of the resin lid, and the negative electrode current collector was welded to the negative electrode current collecting terminal of the resin lid, respectively, placed in a resin case, and the resin case and the resin lid were heat-welded and integrated. Thereafter, an electrolytic solution was added from the liquid injection port, and the electrolytic solution was sufficiently permeated into the positive electrode plate and the negative electrode plate by means of vacuum pumping or the like. Thereafter, the liquid injection port was closed to form a sealed cell. Thus, 10 evaluation cells were fabricated.

[0050] For each evaluation cell, the negative electrode structure was taken out from the battery case, and whether or not the LDH separator was damaged was visually observed. Those in which the LDH separator was not damaged were judged as non-defective products. The yield (%) was calculated by dividing the number of non-defective products by the total number (10) and multiplying by 100, and grading and evaluation were performed according to the following criteria. · Evaluation A: Yield is 90% or more · Evaluation B: Yield is 80% or more and less than 90% · Evaluation C: Yield is 50% or more and less than 80% · Evaluation D: Yield is less than 50%

[0051] Examples A1 - A3 The production and evaluation of the LDH separator containing Mg-Al-LDH were carried out as follows.

[0052] (1) Preparation of a polymer porous substrate A commercially available polyethylene microporous membrane having a porosity of 50%, an average pore diameter of 0.1 μm, and a thickness of 10 μm was prepared as a polymer porous substrate and cut out to a size of 5.0 cm × 5.0 cm.

[0053] (2) Alumina sol coating on the polymer porous substrate An amorphous alumina solution (Al-L7, manufactured by Taki Chemical Co., Ltd.) was applied to the substrate prepared in (1) above by dip coating. The dip coating was performed by immersing the substrate in 100 mL of the sol solution and then pulling it up vertically. Thereafter, the dip-coated substrate was dried at room temperature for 1 hour.

[0054] (3) Preparation of the raw material aqueous solution As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich) were prepared. Magnesium nitrate hexahydrate was weighed into a beaker at 0.015 mol / L, and urea / NO3 - (mol ratio) = 32, and ion-exchanged water was added thereto to make the total volume 80 mL. Thereafter, the mixture was stirred to obtain a raw material aqueous solution.

[0055] (4) Film formation by hydrothermal treatment Both the raw material aqueous solution and the dip-coated substrate were sealed in a Teflon (registered trademark) sealed container (autoclave container, internal volume 100 mL, outer jacket made of stainless steel). At this time, the substrate was fixed by floating it from the bottom of the Teflon (registered trademark) sealed container, and was vertically installed so that the solution contacted both sides of the substrate. Thereafter, hydrothermal treatment was performed at a hydrothermal temperature of 90°C for 16 hours to form LDH on the surface and inside of the substrate. After a predetermined time had elapsed, the substrate was taken out from the sealed container, washed with ion-exchanged water, and dried overnight at room temperature to form LDH on the surface and inside the pores of the porous substrate. Thus, an LDH separator was obtained.

[0056] (5) Densification by roll pressing The above LDH separator was sandwiched between a pair of PET films (manufactured by Toray Industries, Inc., Lumirror (registered trademark), thickness 40 μm), and roll pressing was performed at the roll temperature and roll linear pressure shown in Table 1 to obtain a further densified LDH separator. At this time, by appropriately changing the roll temperature and roll linear pressure as shown in Table 1, a plurality of LDH separators with different surface layer residual ratios were produced.

[0057] (6) Various evaluations Evaluations 1 to 8 were conducted on the obtained LDH separator. The results were as follows. - Evaluation 1: A large number of plate-like crystals characteristic of LDH were confirmed. - Evaluation 2: As a result of EDS elemental analysis, Mg and Al, which are constituent elements of LDH, were detected. That is, it was confirmed that these elements were incorporated and crystallized as a hydroxide ion-conducting layered compound. - Evaluation 3: In the XRD profile, a peak was detected near 2θ = 11.5°, and it was identified as LDH (hydrotalcite-like compound). This identification was performed using the diffraction peaks of LDH (hydrotalcite-like compound) described in JCPDS Card No. 35-0964. - Evaluation 4: As shown in Table 1, an extremely high tightness with a He permeability of 0.0 cm / min·atm was confirmed. - Evaluation 5: As shown in Table 1, a high ionic conductivity was confirmed. - Evaluation 6: As shown in Table 1, in Examples A2 and A3, excellent cycle durability performance (dendrite resistance) was confirmed, that is, there was no short circuit caused by zinc dendrites even after 150 cycles. On the other hand, in Example A1 (comparative example), a short circuit caused by zinc dendrites occurred before 150 cycles, indicating that it was inferior in cycle durability performance. - Evaluation 7: As shown in Table 1, it was confirmed that LDH separators with different surface layer retention rates were produced in Examples A1 to A3. - Evaluation 8: As shown in Table 1, in Examples A1 and A2, a high yield during battery assembly, Evaluation A, was obtained, confirming that the LDH separator was less likely to break in the subsequent process. On the other hand, in Example A3 (comparative example), a low yield during battery assembly, Evaluation D, was obtained, indicating that the LDH separator was likely to break in the subsequent process.

[0058]

Table 1

[0059] Examples B1 - B3 The preparation and evaluation of the LDH separator containing Mg-(Al,Ti)-LDH were carried out as follows.

[0060] (1) Preparation of the polymer porous substrate A commercially available polyethylene microporous membrane with a porosity of 50%, an average pore diameter of 0.1 μm, and a thickness of 10 μm was prepared as the polymer porous substrate and cut into a size of 5.0 cm × 5.0 cm.

[0061] (2) Alumina-titania sol coating on the polymer porous substrate An amorphous alumina solution (Al-L7, manufactured by Takaki Chemical Co., Ltd.) and a titania sol solution (AM-15, manufactured by Takaki Chemical Co., Ltd.) were applied to the substrate prepared in (1) above by dip coating. The dip solution was prepared by mixing the amorphous alumina solution and the titania sol solution so that the Ti / Al (molar ratio) = 2. The dip coating was performed by immersing the substrate in 100 mL of the sol solution and then pulling it up vertically. Thereafter, the dip-coated substrate was dried at room temperature for 1 hour.

[0062] (3) Preparation of the raw material aqueous solution As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich) were prepared. Magnesium nitrate hexahydrate was weighed into a beaker so that the concentration was 0.015 mol / L and the urea / NO3 - (molar ratio) = 32, and ion-exchanged water was added thereto to make the total volume 80 mL. Thereafter, it was stirred to obtain a raw material aqueous solution.

[0063] (4) Film formation by hydrothermal treatment An aqueous raw material solution and a substrate coated with a dip coat were sealed together in a Teflon (registered trademark) sealed container (autoclave container, internal volume 100 mL, with a stainless steel jacket on the outside). At this time, the substrate was fixed floating from the bottom of the Teflon (registered trademark) sealed container and installed vertically so that the solution contacted both sides of the substrate. Then, hydrothermal treatment was performed at a hydrothermal temperature of 90 °C for 12 hours to form LDH on the surface and inside of the substrate. After a predetermined time had elapsed, the substrate was taken out of the sealed container, washed with ion-exchanged water, and dried overnight at room temperature to form LDH on the surface and in the pores of the porous substrate. In this way, an LDH separator was obtained.

[0064] (5) Densification by roll press The above LDH separator was sandwiched between a pair of PET films (manufactured by Toray Industries, Inc., Lumirror (registered trademark), thickness 40 μm), and roll pressing was performed at the roll temperature and roll line pressure shown in Table 2 to obtain a further densified LDH separator. At this time, by appropriately changing the roll temperature and roll line pressure as shown in Table 2, a plurality of LDH separators with different surface layer remaining ratios were produced.

[0065] (6) Various evaluations Evaluations 1 to 8 were performed on the obtained LDH separator. The results were as follows. - Evaluation 1: A large number of plate-like crystals characteristic of LDH were confirmed. - Evaluation 2: As a result of EDS elemental analysis, Mg, Al, and Ti, which are constituent elements of LDH, were detected. That is, it was confirmed that these elements were incorporated and crystallized as a hydroxide ion-conducting layered compound. - Evaluation 3: In the XRD profile, a peak was detected near 2θ = 11.5°, and it was identified as LDH (hydrotalcite-like compound). This identification was performed using the diffraction peaks of LDH (hydrotalcite-like compound) described in JCPDS Card No. 35-0964. - Evaluation 4: As shown in Table 2, an extremely high tightness with a He permeability of 0.0 cm / min·atm was confirmed. - Evaluation 5: As shown in Table 2, a high ion conductivity was confirmed. - Evaluation 6: As shown in Table 2, in Examples B2 and B3, excellent cycle durability performance (dendrite resistance), that is, no short circuit caused by zinc dendrites even after 150 cycles, was confirmed. On the other hand, in Example B1 (comparative example), since a short circuit caused by zinc dendrites occurred before 150 cycles, it was found to be inferior in cycle durability performance. - Evaluation 7: As shown in Table 2, in Examples B1 to B3, it was confirmed that LDH separators with different surface layer retention rates were produced. - Evaluation 8: As shown in Table 2, in Examples B1 and B2, a high yield during battery assembly, Evaluation A, was obtained, and it was confirmed that the LDH separator was not easily broken in the subsequent process. On the other hand, in Example B3 (comparative example), a low yield during battery assembly, Evaluation D, was obtained, and it was found that the LDH separator was easily broken in the subsequent process.

[0066]

Table 2

[0067] Examples C1 - C7 The production and evaluation of the LDH separator containing the Mg-(Al,Ti,Y)-LDH-like compound were carried out as follows.

[0068] (1) Preparation of the polymer porous substrate A commercially available polyethylene microporous membrane with a porosity of 50%, an average pore diameter of 0.1 μm, and a thickness of 10 μm was prepared as the polymer porous substrate and cut into a size of 5.0 cm × 5.0 cm.

[0069] (2) Alumina·titania·yttria sol coating on the polymer porous substrate An amorphous alumina solution (Al-L7, manufactured by Taki Chemical Co., Ltd.), a titania solution (AM-15, manufactured by Taki Chemical Co., Ltd.), and an yttria sol were applied to the substrate prepared in (1) above by dip coating. The dip solution was prepared by mixing the amorphous alumina solution, the titania solution, and the yttria sol so that Ti / (Y + Al) (molar ratio) = 2 and Y / Al (molar ratio) = 8. The dip coating was performed by immersing the substrate in 100 mL of the sol solution and then pulling it up vertically. Thereafter, the dip-coated substrate was dried at room temperature for 1 hour.

[0070] (3) Preparation of the raw material aqueous solution As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich) were prepared. Magnesium nitrate hexahydrate was weighed into a beaker so as to be 0.0075 mol / L and urea / NO3 - (molar ratio) = 96, and ion-exchanged water was added thereto to make the total volume 80 mL. Thereafter, the mixture was stirred to obtain a raw material aqueous solution.

[0071] (4) Film formation by hydrothermal treatment Both the raw material aqueous solution and the dip-coated substrate were sealed in a Teflon (registered trademark) sealed container (autoclave container, internal volume 100 mL, stainless steel jacket on the outside). At this time, the substrate was floated and fixed from the bottom of the Teflon (registered trademark) sealed container and installed vertically so that the solution was in contact with both sides of the substrate. Thereafter, hydrothermal treatment was performed at a hydrothermal temperature of 120 °C for 12 hours to form an LDH-like compound on the surface and inside of the substrate. After a predetermined time had elapsed, the substrate was taken out from the sealed container, washed with ion-exchanged water, and dried overnight at room temperature to form an LDH-like compound on the surface and in the pores of the porous substrate. Thus, an LDH separator was obtained.

[0072] (5) Densification by roll pressing The above LDH separator was sandwiched between a pair of PET films (manufactured by Toray Industries, Inc., Lumirror (registered trademark), thickness 40 μm), and roll pressing was performed at the roll temperature and roll line pressure shown in Table 3 to obtain a further densified LDH separator. At this time, by appropriately changing the roll temperature and roll line pressure as shown in Table 3, a plurality of LDH separators with different surface layer residual ratios were produced.

[0073] (6) Various evaluations Evaluations 1 to 8 were performed on the obtained LDH separator. The results were as follows. - Evaluation 1: A large number of plate-like shapes peculiar to LDH were confirmed. - Evaluation 2: As a result of EDS elemental analysis, Mg, Al, Ti, and Y, which are constituent elements of the LDH-like compound, were detected. That is, it was confirmed that these elements were incorporated and crystallized as a hydroxide ion-conducting layered compound. - Evaluation 3: In the XRD profile, peaks derived from the LDH-like compound were detected in the range of 5° ≤ 2θ ≤ 10°. Usually, the (003) peak position of LDH is observed at 2θ = 11 to 12°. Therefore, it is considered that the above peak is a shifted version of the (003) peak of LDH to the low-angle side. For this reason, although the above peak cannot be called LDH, it suggests that it is a peak derived from a compound similar thereto (that is, an LDH-like compound). - Evaluation 4: As shown in Table 3, an extremely high tightness with a He permeability of 0.0 cm / min·atm was confirmed. - Evaluation 5: As shown in Table 3, a high ionic conductivity was confirmed in any of Examples C1 to C7. - Evaluation 6: As shown in Table 3, in Examples C3 to C7, excellent dendrite resistance was confirmed, that is, there was no short circuit caused by zinc dendrites even after 300 cycles. On the other hand, in Examples C1 and C2 (comparative examples), since a short circuit caused by zinc dendrites occurred before 300 cycles, it was found that they were inferior in dendrite resistance. - Evaluation 7: As shown in Table 3, it was confirmed that LDH separators with different surface residual ratios were produced in Examples C1 to C7. For reference, the surface SEM image of the LDH separator produced in Example C4 (surface residual ratio 90%) is shown in Fig. 7, and the surface SEM image of the LDH separator produced in Example C2 (comparative example) (surface residual ratio 48%) is shown in Fig. 8. - Evaluation 8: As shown in Table 3, in Examples C2 to C6, the yield during battery assembly was high for Evaluation A, and it was confirmed that the LDH separator was less likely to break in the subsequent process. On the other hand, in Example C7 (comparative example), the yield during battery assembly was low for Evaluation D, and it was found that the LDH separator was likely to break in the subsequent process.

[0074]

Table 3

Explanation of symbols

[0075] 10 LDH separator 12 Porous substrate 14 Surface layer R Surface residual part P Surface peeling part

Claims

1. A porous substrate, A surface layer provided on at least one surface of the porous substrate and containing a hydroxide ion-conducting layered compound which is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound, An LDH separator comprising: When the surface on the surface layer side of the LDH separator is observed with a scanning electron microscope (SEM), the LDH separator has a surface remaining portion where the surface layer is present and a surface peeling portion where the surface layer is not present, The surface remaining ratio, which is the ratio of the area of the surface remaining portion to the total area of the surface remaining portion and the surface peeling portion, is 80 to 99%, An LDH separator, wherein the thickness of the surface layer is 0.01 to 10 μm.

2. The LDH separator according to claim 1, wherein the pores of the porous substrate are filled with the hydroxide ion-conducting layered compound.

3. The hydroxide ion-conducting layered compound is an LDH-like compound, and the LDH-like compound contains (i) Mg and (ii) at least one element selected from the group consisting of Ti, Y, and Al and containing at least Ti. The LDH separator according to claim 1 or 2.

4. The hydroxide ion-conductive layered compound is LDH, and the LDH includes a plurality of hydroxide basic layers containing Mg, Al, and OH groups, and anions and H ２ O intervening between the plurality of hydroxide basic layers, and the LDH separator according to claim 1 or 2.

5. The LDH separator according to claim 4, wherein the plurality of hydroxide basic layers further contain Ti.

6. The LDH separator according to any one of claims 1 to 5, wherein the thickness of the surface layer is 0.01 to 8 μm.

7. The LDH separator according to any one of claims 1 to 6, wherein the thickness of the LDH separator is 3 to 80 μm.

8. The LDH separator according to any one of claims 1 to 7, wherein the porous substrate is made of a polymer material.

9. The LDH separator according to any one of claims 1 to 8, wherein the ion conductivity of the LDH separator is 2.0 mS / cm or more.

10. The LDH separator according to any one of claims 1 to 9, wherein the He permeability per unit area of the LDH separator is 10 cm / min·atm or less.

11. The LDH separator according to any one of claims 1 to 10, wherein the LDH separator is pressed in the thickness direction of the LDH separator.

12. A zinc secondary battery comprising the LDH separator according to any one of claims 1 to 11.

13. A solid alkaline fuel cell comprising the LDH separator according to any one of claims 1 to 11.

Images