LDH Separator, Method for Producing the Same, and Zinc Secondary Battery

Abstract

Provided is an LDH separator that enables further enhancement of the cycle characteristic of a battery. The LDH separator comprises: a porous substrate; and a surface layer that is provided to at least one surface of the porous substrate and that includes a layered double hydroxide (LDH) and / or a hydroxide-ion conductive layered compound, which is a layered double hydroxide (LDH)-like compound. The LDH separator has an ion conductivity of 1.0 mS / cm or more, and the adhesion between the surface layer and the porous substrate is 5.0 mN or more. The adhesion is a critical load value that is measured by performing micro-scratch testing on a surface including the surface layer of the LDH separator, according to protocol JIS R3255-1997, under the conditions of a scratching speed of 10 μm / s, a diamond-indenter needle tip radius of curvature of 25 μm, a load application speed of 30 mN / min, an excitation amplitude of 50 μm, and an excitation frequency of 45 Hz.

Description

Technical Field

[0001] The present invention relates to an LDH separator, a method for manufacturing the same, 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 non-woven 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 and discharge life.

[0003] In order to address the above problems, a battery equipped with a layered double hydroxide (LDH) separator that selectively transmits hydroxide ions 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 electrode and the negative electrode 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 degree of denseness such that it is gas-impermeable and / or water-impermeable. This document also discloses that the LDH separator can be combined 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 attaching a starting material capable of providing 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 prepared 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, LDH-like compounds are known as hydroxides and / or oxides having a layered crystal structure similar to but not called LDH, and exhibit hydroxide ion conduction characteristics similar enough to be collectively referred to as hydroxide ion conducting layered compounds together with LDH. For example, Patent Document 5 (International Publication No. 2020 / 255856) discloses a hydroxide ion conducting separator including a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate, wherein the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing Mg and at least one element selected from the group consisting of Ti, Y, and Al and containing at least Ti. This hydroxide ion conducting separator is said to be superior in alkali resistance to conventional LDH separators and to be able to more effectively suppress short circuits caused by zinc dendrites.

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] When a zinc secondary battery such as a nickel-zinc battery is configured using an LDH separator as disclosed in Patent Documents 1 to 5, short circuits due to zinc dendrites can be prevented to some extent. However, further improvement in cycle characteristics (especially dendrite short circuit prevention characteristics when charge and discharge cycles are repeated) is desired.

[0007] The present inventors have now found that in an LDH separator comprising a porous substrate and a surface layer provided on the surface thereof, by having an ionic conductivity of 1.0 mS / cm or more and a adhesion force between the surface layer and the porous substrate of 5.0 mN or more, the cycle characteristics of a battery provided with this can be further improved.

[0008] Accordingly, an object of the present invention is to provide an LDH separator capable of further improving the cycle characteristics of a battery.

[0009] According to the present invention, the following aspects are provided. [Aspect 1] 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, An LDH separator comprising: The LDH separator has an ionic conductivity of 1.0 mS / cm or more, and the adhesion force between the surface layer and the porous substrate is 5.0 mN or more, The adhesion force is a critical load value measured by performing a micro scratch test on the surface including the surface layer of the LDH separator under the conditions of a scratch speed of 10 μm / s, a tip curvature radius of a diamond indenter needle of 25 μm, a load application acceleration of 30 mN / min, an excitation amplitude of 50 μm, and an excitation frequency of 45 Hz in accordance with JIS R3255-1997. [Aspect 2] The LDH separator according to Aspect 1, wherein the pores of the porous substrate are filled with the hydroxide ion-conductive layered compound. [Aspect 3] The LDH separator according to Aspect 1 or 2, wherein the hydroxide ion-conductive 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. [Aspect 4] The hydroxide ion-conductive layered compound is LDH, and the LDH is composed of a plurality of hydroxide basic layers containing Mg, Al, and OH groups, and an intermediate layer composed of an anion and H2O intervening between the plurality of hydroxide basic layers. The LDH separator according to Aspect 1 or 2. [Aspect 5] The LDH separator according to Aspect 4, wherein the plurality of hydroxide basic layers further contain Ti. [Aspect 6] The LDH separator according to any one of Aspects 1 to 5, wherein the thickness of the surface layer is 0.01 to 10 μm. [Aspect 7] The LDH separator according to any one of Aspects 1 to 6, wherein the thickness of the LDH separator is 3 to 80 μm. [Aspect 8] The LDH separator according to any one of Aspects 1 to 7, wherein the porous substrate is made of a polymer material. [Aspect 9] The LDH separator according to any one of Aspects 1 to 8, wherein the He permeability per unit area of the LDH separator is 10 cm / min·atm or less. [Aspect 10] The LDH separator according to any one of Aspects 1 to 9, wherein the LDH separator is pressed in the thickness direction of the LDH separator. [Aspect 11] The LDH separator according to any one of Aspects 1 to 10, wherein the surface layer does not contain a binder resin. [Aspect 12] A step of coating at least one surface of the porous substrate with a binder resin; A step of subjecting the porous substrate coated with the binder resin to hydrothermal treatment in an aqueous raw material solution containing constituent elements of a hydroxide ion-conductive layered compound that is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound, to form a surface layer containing the hydroxide ion-conductive layered compound on the surface of the porous substrate containing the binder resin; A method for manufacturing an LDH separator, comprising: [Aspect 13] The method for manufacturing the LDH separator according to aspect 12, wherein the coating of the porous substrate with the binder resin includes applying a solution in which the binder resin is dissolved to the surface of the porous substrate. [Aspect 14] A zinc secondary battery comprising the LDH separator according to any one of aspects 1 to 11. [Aspect 15] A solid alkaline fuel cell comprising the LDH separator according to any one of aspects 1 to 11.

Brief Description of Drawings

[0010]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4A

Figure 4B

Modes for Carrying Out the Invention

[0011] 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. And the LDH separator 10 has an ionic conductivity of 1.0 mS / cm or more and an adhesion between the surface layer 14 and the porous substrate 12 of 5.0 mN or more. As used herein, an "LDH separator" is defined as a separator containing LDH and / or an LDH-like compound that selectively passes hydroxide ions by utilizing the hydroxide ion conductivity of LDH and / or an LDH-like compound exclusively. As used herein, 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 equivalent to LDH. However, as a broad definition, it is also possible to interpret "LDH" as including not only LDH but also LDH-like compounds. Thus, in the LDH separator including the porous substrate 12 and the surface layer 14 provided on its surface, by having an ionic conductivity of 1.0 mS / cm or more and an adhesion between the surface layer 14 and the porous substrate 12 of 5.0 mN or more, the cycle characteristics of a battery equipped with this can be further improved.

[0012] As described above, when a zinc secondary battery such as a nickel-zinc battery is configured using a conventional LDH separator, short circuits due to zinc dendrites can be prevented to some extent, but further improvement in cycle characteristics (especially the dendrite short circuit prevention characteristics when charge-discharge cycles are repeated) is desired. In this regard, according to the configuration of the present invention, further improvement in cycle characteristics can be preferably achieved. The mechanism is not necessarily clear, but it is considered to be due to the effective reduction of surface defects that can occur in the LDH separator (which is considered to affect the cycle characteristics). Such surface defects can occur, for example, when a roll press is performed to further densify the LDH separator and the surface layer is peeled off by the carrier film. And at the location where the surface defect occurs (the surface layer peeling part), since the porous base material is exposed, the effect of preventing short circuits due to zinc dendrites may be inferior. In this regard, the LDH separator 10 of the present invention has excellent adhesion such that the adhesion between the surface layer 14 and the porous base material 12 is 5.0 mN or more. As a result, it can be said that peeling of the surface layer 14 due to roll pressing or the like during the manufacture of the LDH separator 10 can be prevented, the occurrence of surface defects is effectively suppressed, and moreover, the occurrence of surface defects is continuously suppressed even thereafter (for example, after being incorporated into the battery). Also, when the ion conductivity of the separator is low, it has an adverse effect on the cycle characteristics. The LDH separator 10 also has a high ion conductivity of 1.0 mS / cm or more. Thus, according to the LDH separator of the present invention, it is considered that the cycle characteristics of the battery can be further improved compared with the conventional LDH separator.

[0013] The LDH separator 10 has an adhesion force between the surface layer 14 and the porous base material 12 of 5.0 mN or more, preferably 7.5 mN or more, more preferably 10.0 mN or more, and even more preferably 12.5 mN or more. Since the higher the adhesion force between the surface layer 14 and the porous base material 12, the better, the upper limit value is not particularly limited, but is typically 70 mN or less, and more typically 50 mN or less. This adhesion force is the critical load value (i.e., the applied load value when the surface layer is first peeled off) measured by performing a micro scratch test on the surface including the surface layer 14 of the LDH separator 10. The micro scratch test is a test method that can highly sensitively evaluate the adhesion of a thin film from the load when a stylus needle (probe) is pressed against a test piece at a constant load application acceleration and scratch speed while horizontally vibrating it slightly, as defined in JIS R3255-1997. The micro scratch test in this specification shall be performed under the conditions of a scratch speed of 10 μm / s, a tip curvature radius of 25 μm for a diamond stylus needle, a load application acceleration of 30 mN / min, an excitation amplitude of 50 μm, and an excitation frequency of 45 Hz in accordance with JIS R3255-1997. In addition, the measurement of the adhesion force by the micro scratch test can be preferably performed according to the procedure shown in Evaluation 7 of the examples described later.

[0014] The LDH separator 10 has an ionic conductivity of 1.0 mS / cm or more, preferably 1.5 mS / cm or more, more preferably 2.0 mS / cm or more, and even more preferably 2.5 mS / cm or more. The upper limit of the ionic conductivity is not particularly limited, but is, for example, 10.0 mS / cm or less.

[0015] The thickness of the surface layer 14 is preferably 0.01 to 10 μm, more preferably 0.01 to 8 μm, even 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 characteristics of the battery can be further improved.

[0016] The surface layer 14 preferably does not contain a binder resin. By doing so, it is possible to suppress the occurrence of unevenness in the in-plane resistance of the surface layer 14 due to the binder resin and reduce the risk of current concentration. However, it is acceptable for the surface layer 14 to contain a binder resin as an inevitable impurity. That is, the surface layer 14 is preferably composed of a hydroxide ion-conductive layered compound and, optionally, inevitable impurities. For example, the LDH separator 10 may contain a binder resin as a surface adhesion layer at the interface between the porous substrate 12 and the surface layer 14. In such a case, the binder resin may be unavoidably mixed into the surface layer 14 as an inevitable impurity derived from the surface adhesion layer. The amount of inevitable impurities that may be contained in the surface layer 14 is typically 0.1 wt% or less.

[0017] 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 effectively block the passage of substances other than hydroxide ions. For example, in the case of a zinc secondary battery, the permeation of Zn (typically the permeation of zinc ions or zincate ions) in the electrolyte can be extremely effectively suppressed. The He permeability is measured through a process of supplying He gas to one side 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 single He atom as a 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 regarding 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 a sufficiently high tightness suitable for a zinc secondary battery separator.The measurement of He transmittance can be preferably carried out according to the procedure shown in Evaluation 4 of the examples described later.

[0018] 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 aspect, 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 necessarily 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 (that is, 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 still more preferably 3 to 40 μm.

[0019] 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 OH groups. 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 0.1 to 0.4, preferably 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 only the 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.

[0020] 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 optionally Ti), 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 analysis (EDS) is preferably 0.5 to 12, more preferably 1.0 to 12. When 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 analysis (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) to 1) capture an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) perform three-point analysis at intervals of about 5 μm in the point analysis mode, 3) repeat the above 1) and 2) one more time, and 4) calculate the average value of a total of six points.

[0021] Alternatively, the hydroxide basic layer of 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 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 ion 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. The inclusion of titania can be expected to increase the hydrophilicity and improve the wettability with the electrolyte (i.e., improve the conductivity).

[0022] Although the LDH-like compound may not be called LDH, it 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, as a hydroxide ion conductive material, an LDH-like compound which is a hydroxide and / or oxide having a layered crystal structure containing at least Mg and Ti, instead of conventional LDH, a hydroxide ion conductive separator excellent in alkali resistance and capable of more effectively suppressing a short circuit caused by zinc dendrite can be provided. Therefore, a preferable 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 such an extent that the basic characteristics of the LDH-like compound are not impaired, but the LDH-like compound preferably does not contain Ni.

[0023] The LDH-like compound can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface on 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 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 = 11~12°. On the other hand, when the LDH-like compound is measured by X-ray diffraction method, peaks are typically detected in the above-mentioned range shifted to the low-angle side from the above peak position of LDH. Also, using 2θ corresponding to the peak derived from the LDH-like compound in X-ray diffraction, the interlayer distance of the layered crystal structure can be determined by Bragg's equation. The interlayer distance of the layered crystal structure constituting the LDH-like compound thus determined is typically 0.883~1.8 nm, more typically 0.883~1.3 nm.

[0024] The atomic ratio of Mg / (Mg + Ti + Y + Al) in the LDH-like compound determined by energy dispersive X-ray spectroscopy (EDS) is preferably 0.03~0.25, more preferably 0.05~0.2. Also, the atomic ratio of Ti / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0.40~0.97, more preferably 0.47~0.94. Further, the atomic ratio of Y / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0~0.45, more preferably 0~0.37. And the atomic ratio of Al / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0~0.05, more preferably 0~0.03. When within the above range, the alkali resistance is further improved, and the suppression effect of short circuit caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. By the way, the conventionally known LDH for the LDH separator has the general formula: M 2+ 1-x M 3+x (OH)2A n- x / n ·mH2O (wherein M 2+ is a divalent cation, M 3+ is a trivalent cation, and A n- 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 ratios in the LDH-like compound generally deviate from those of the 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 the 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.

[0025] 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, it is preferable that the LDH separator 10 (especially the surface layer 14) is densified to have gas impermeability and / or water impermeability. In this 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 this 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 the charge and discharge reactions in the positive electrode plate and the negative electrode plate.

[0026] The porous substrate 12 is preferably composed of a polymer material. The polymer porous substrate has the following advantages: 1) It has flexibility (therefore, it is not easily cracked even when made thin), 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), and 4) It is easy to manufacture and handle. Also, taking advantage of the flexibility in 1) above, there is an advantage that 5) 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 included. Each of the various preferred materials described above has alkali resistance as the resistance to the electrolyte of the battery. Particularly preferred polymer materials are polyolefins such as polypropylene and polyethylene because they are excellent in heat water resistance, acid resistance, and alkali resistance and are also low in cost. Most preferably, they are polypropylene or polyethylene. It is particularly preferred that the hydroxide ion conductive layered 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 layered compound). As such a polymer porous substrate, a commercially available polymer microporous membrane can be preferably used.

[0027] Manufacturing method of LDH separator The LDH separator of the present invention can be preferably manufactured by (1) coating the surface of the porous substrate with a binder resin and (2) subjecting the porous substrate to hydrothermal treatment in an aqueous raw material solution to form a surface layer containing a hydroxide ion conductive layered compound on the surface of the porous substrate including the binder resin.

[0028] (1) Coating of the porous substrate with a binder resin At least one surface of the porous substrate 12 is coated with a binder resin. The porous substrate 12 is as described above, and it is preferable to use a polymer porous substrate. Preferred examples of the binder resin include polyolefins (such as polypropylene and polyethylene), polystyrene, polyethersulfone, epoxy resin, polyphenylene sulfide, fluororesin, cellulose, nylon, acrylonitrile styrene, polysulfone, acrylonitrile-butadiene-styrene (ABS) resin, polyvinyl chloride, acetal resin, polyvinyl alcohol (PVA) resin, polyvinylidene chloride, polyvinylidene fluoride, phenol resin, allyl resin, furan resin, and any combination thereof. More preferably, from the viewpoint of improving the adhesion between the surface layer 14 and the porous substrate 12 (especially the polymer porous substrate), polyolefins can be mentioned. The above-listed polymers or resins may be non-modified or modified. For example, the polyolefin may be a modified polyolefin.

[0029] The coating of the porous substrate 12 with the binder resin preferably includes applying a solution in which the binder resin is dissolved to the surface of the porous substrate 12. The concentration of the binder resin contained in the solution is preferably 0.5 to 10 wt%, more preferably 1 to 5 wt%. Examples of preferred coating methods include dip coating, filtration coating, etc., and dip coating is particularly preferred. By adjusting the concentration of the binder resin contained in the solution and / or the number of coating times such as dip coating, the amount of the binder resin adhered can be adjusted. The amount of the binder resin adhered per 1 cm of the substrate 3 is preferably 14 to 290 mg, more preferably 30 to 150 mg. After the binder resin is applied to the substrate and dried, the hydrothermal treatment described below may be carried out.

[0030] (2) Formation of the surface layer by hydrothermal treatment In an aqueous raw material solution containing constituent elements of a hydroxide ion-conducting layered compound that is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound, a porous substrate 12 coated with a binder resin is subjected to hydrothermal treatment. By doing so, a surface layer 14 containing a hydroxide ion-conducting layered compound can be formed on the surface of the porous substrate 12 containing the binder resin, and an LDH separator 10 can be obtained. According to such a manufacturing method, a binder resin will exist at the interface between the porous substrate 12 and the surface layer 14. That is, the binder resin coated on the substrate surface functions as a surface layer adhesion layer, improving the adhesion between the porous substrate 12 and the surface layer 14. As a result, surface layer peeling (surface defects) can be prevented, and the cycle characteristics of the battery can be further improved.

[0031] The formation of the surface layer 14 involving hydrothermal treatment can be carried out by appropriately changing the various conditions of 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, (a) for the porous substrate 12 coated with a binder resin, i) a solution containing alumina sol (or further titania sol) (when forming LDH), or ii) a solution containing titania sol (or further yttria sol and / or alumina sol) (when forming an LDH-like compound) is applied and dried, (b) the porous substrate 12 is immersed in an aqueous raw material solution containing magnesium ions (Mg 2+ ) and urea (or further yttrium ions (Y 3+ ), and (c) the porous substrate 12 is hydrothermally treated in the aqueous raw material solution to form a hydroxide ion-conducting layered compound on and / or in the porous substrate, whereby the LDH separator 10 can be preferably manufactured.

[0032] At this time, in the above step (b), the presence of urea causes ammonia to be generated in the solution by utilizing the hydrolysis of urea, thereby increasing the pH value. It is considered that the coexisting metal ions form hydroxides and / or oxides to obtain a hydroxide ion-conducting layered compound (i.e., LDH and / or LDH-like compound). And since the hydrolysis is accompanied by the generation of carbon dioxide, when forming LDH, an anion can obtain a carbonate-type LDH.

[0033] In particular, when producing the LDH separator 10 in which the hydroxide ion-conducting layered compound is incorporated over the entire thickness direction of the porous substrate 12, it is preferable to apply the sol solution to the substrate in the above (a) by a method that allows the sol solution to penetrate into the whole or most of the inside of the substrate. By doing so, most or almost all of the pores inside the porous substrate 12 can finally be filled with the hydroxide ion-conducting layered compound. Examples of preferable coating methods include dip coating, filtration coating, etc., and dip coating is particularly preferable. By adjusting the number of coating times such as dip coating, the adhesion amount of the sol solution can be adjusted. After the substrate coated with the sol solution by dip coating or the like is dried, the steps (b) and (c) described above may be carried out.

[0034] 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. Therefore, it is preferable that the LDH separator 10 of the present invention is pressed in the thickness direction. 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. It is preferable to perform this pressing 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-conducting layered compound. As the temperature for sufficient softening, for example, in the case of polypropylene or polyethylene, it is preferable to heat 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, thereby obtaining an LDH separator with a desired tightness.

[0035] 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 including an LDH separator is provided. A typical zinc secondary battery includes a positive electrode, a negative electrode, and an electrolytic 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 electrolytic 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.

[0036] 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 permeation of fuel to the air electrode side (for example, methanol crossover) can be provided. This is because permeation of fuels such as methanol through the LDH separator can be effectively suppressed while exerting the hydroxide ion conductivity of the LDH separator. Therefore, according to another preferred aspect 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 aspect includes an air electrode to which oxygen is supplied, a fuel electrode to which liquid fuel and / or gaseous fuel is supplied, and an LDH separator interposed between the fuel electrode and the air electrode.

[0037] 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 (inter-electrode movement of nitrate groups), 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 a lithium metal as the negative electrode), lithium-ion batteries (batteries with a carbon or the like as the negative electrode), or lithium-air batteries.

Examples

[0038] 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.

[0039] 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.).

[0040] Evaluation 2 : Elemental analysis evaluation (EDS) For the LDH separator surface, compositional analysis was performed using an EDS analyzer (equipment 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 mode was used with an interval of approximately 5 μm, and three-point analysis was performed; 3) Steps 1) and 2) were repeated one more time.

[0041] 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.

[0042] Evaluation 4 : He permeation measurement To evaluate the tightness of the LDH separator from the perspective of He permeability, a He permeation test was conducted as follows. First, a He permeation measurement system 310 shown in FIGS. 2A and 2B was constructed. The He permeation measurement system 310 was configured such that He gas from a gas cylinder filled with He gas was supplied to a sample holder 316 through a pressure gauge 312 and a flow meter 314 (digital flow meter), and was permeated from one side to the other side of the LDH separator 318 held in the sample holder 316 and then discharged.

[0043] 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 at the center. Butyl rubber packings were disposed as sealing members 326a and 326b at the upper and lower ends of the jig 324, and further clamped from the outside of the sealing members 326a and 326b by support members 328a and 328b (made of PTFE) each having an opening formed by a flange. 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 to each other 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 assembled sample holder 316 via a joint 332.

[0044] Next, He gas was supplied to the He permeability 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 carried out for 1 to 30 minutes, the He permeability was calculated. The calculation of the He permeability was performed using the formula F / (P×S), where F (cm 3 / min) is the permeation amount of He gas per unit time, P (atm) is the differential pressure applied to the LDH separator during He gas permeation, and S (cm 2 ) is the membrane area through which the He gas permeates. The permeation amount F (cm 3 / min) of the He gas was directly read from the flow meter 314. Also, the differential pressure P used the gauge pressure read from the pressure gauge 312. Note that the He gas was supplied so that the differential pressure P was within the range of 0.05 to 0.90 atm.

[0045] 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. 3. 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 with an inner diameter of 6 mm. As the electrode 446, a #100 mesh nickel-gold mesh was incorporated into the cell 442 in a cylindrical shape with a diameter of 6 mm 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 carried out 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 carried out with a configuration without the LDH separator sample S, and the blank resistance was also obtained. 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.

[0046] 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 a laminated film provided with a current extraction port, 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 rapid 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 rapid voltage drop was observed during charging even after a predetermined number of cycles. · Short circuit: A rapid voltage drop was observed during charging before a predetermined number of cycles.

[0047] Evaluation 7 : Adhesion measurement (micro scratch test) To evaluate the adhesion between the base material and the surface layer of the LDH separator, a micro scratch test was conducted as follows in accordance with JIS R3255-1997. First, the LDH separator sample was placed on the sample stage of an ultra-thin film scratch tester (manufactured by Reska Corporation, CSR5100) with the surface layer facing upward, and a diamond indenter needle (tip curvature radius 25 μm, model number: S.N.D-0056) was brought into contact with the surface layer of the LDH separator sample. Then, as shown in Figure 4A, while the indenter needle was micro-vibrated horizontally (the vertical direction in the figure) with an excitation amplitude of 50 μm and an excitation frequency of 45 Hz, it was scratched in the width direction (the horizontal direction in the figure) of the LDH separator sample S at a scratch speed of 10 μm / s. At this time, as shown in Figure 4B, the load of the indenter needle I applied to the surface of the LDH separator sample S was gradually increased at a load printing acceleration of 30 mN / min. And the point where the surface layer of the LDH separator sample S was peeled off by the indenter needle I was detected by an acceleration sensor (vertical direction) and an electromagnetic coil (horizontal direction), and the applied load (mN) at this time was taken as the adhesion between the base material and the surface layer. The above operation was repeated 3 times, and the average value of the adhesion of the total 3 calculated points was taken as the adhesion of the LDH separator. Note that the above measurement was carried out under the temperature and humidity in the standard state (temperature 23 °C, relative humidity 50%).

[0048] Examples A1 - A6 The production and evaluation of the LDH separator containing Mg-Al-LDH were carried out as follows.

[0049] (1) Preparation of the polymer porous base material 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 base material and cut into a size of 5.0 cm × 5.0 cm.

[0050] (2) Primer treatment of the polymer porous base material A binder solution containing a modified polyolefin resin (Auroren (registered trademark) AE-202, manufactured by Nippon Paper Industries Co., Ltd.) at the concentration shown in Table 1 was applied by dip coating to the substrate prepared in (1) above. Dip coating was performed by immersing the substrate in 100 mL of the binder solution and then vertically lifting it up. The dip-coated substrate was then dried at room temperature for 1 hour. In this way, a substrate coated with the binder resin was obtained. Here, the adhesion weight of the binder resin applied to the porous substrate (1 cm of porous substrate) was calculated. 3 The adhesion weight is calculated by subtracting the weight of the porous substrate before primer treatment, W0 (mg), from the weight of the porous substrate after primer treatment, W1 (mg), to obtain the volume V (cm 3 ) was divided by (=(W1-W0) / V).

[0051] (3) Alumina sol coating on polymeric porous substrate An amorphous alumina solution (Al-L7, manufactured by Taki Chemical Co., Ltd.) was applied by dip coating to the substrate that had been subjected to the primer treatment in (2) above. The dip coating was performed by immersing the substrate in 100 mL of the sol solution and then lifting it up vertically. The dip-coated substrate was then dried at room temperature for 1 hour.

[0052] (4) Preparation of raw material aqueous solution Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Ltd.) and urea ((NH2)2CO3, manufactured by Sigma-Aldrich) were prepared as raw materials. Magnesium nitrate hexahydrate was 0.015 mol / L, and urea / NO3 - The raw materials were weighed out so that the molar ratio was 32 and placed in a beaker, and ion-exchanged water was added to make the total volume 80 mL. After that, the mixture was stirred to obtain a raw material aqueous solution.

[0053] (5) Film formation by hydrothermal treatment An aqueous raw material solution and a substrate dip-coated with the sol solution in (3) above were both sealed in a Teflon (registered trademark) airtight 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) airtight container and installed vertically so that the solution contacted both sides of the substrate. Then, hydrothermal treatment was carried out 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 of the airtight 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.

[0054] (6) 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 carried out at a roll rotation speed of 3 mm / s, a roller heating temperature of 70 °C, and a roll gap of 70 μm to obtain a further densified LDH separator.

[0055] (7) Various evaluations Evaluations 1 to 7 were carried out 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 was identified as LDH (hydrotalcite-like compound). This identification was carried out 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 0.00 cm / min·atm was confirmed. Note that Table 1 also shows the He permeability of the porous substrate after primer treatment. - Evaluation 5: As shown in Table 1, in Examples A1 to A4, an ionic conductivity higher than that of Examples A5 and A6 (comparative examples) (1.0 mS / cm or higher) was confirmed. - Evaluation 6: As shown in Table 1, in Examples A3 and A4, excellent cycle durability performance (dendrite resistance), i.e., no short circuit due to zinc dendrites even after 200 cycles, was confirmed. On the other hand, in Examples A1, A2, A5, and A6 (comparative examples), since a short circuit due to zinc dendrites occurred before 200 cycles, it was found that they were inferior in cycle durability performance. - Evaluation 7: In Examples A3 to A6, an adhesive strength higher than that of Examples A1 and A2 (comparative examples) (5.0 mN or higher) was confirmed.

[0056]

Table 1

[0057] Examples B1 - B6 The preparation and evaluation of the LDH separator containing Mg-(Al,Ti)-LDH were carried out as follows.

[0058] (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.

[0059] (2) Primer treatment of the polymer porous substrate A binder solution containing a modified polyolefin resin (Auroline (registered trademark) AE-202, manufactured by Nippon Paper Industries Co., Ltd.) at the concentration shown in Table 2 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 binder solution and then pulling it up vertically. Thereafter, the dip-coated substrate was dried at room temperature for 1 hour. Thus, a substrate coated with the binder resin was obtained. Here, the adhesion weight of the binder resin coated on the porous substrate (per 1 cm of the porous substrate) 3The adhesion weight (mg) is shown in Table 2. This adhesion weight is calculated by subtracting the weight W0 (mg) of the porous substrate before primer treatment from the weight W1 (mg) of the porous substrate after primer treatment and dividing by the volume V (cm 3 3) of the porous substrate (=(W1 - W0) / V).

[0060] (3) 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 that had been subjected to the primer treatment in (2) 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 carried out 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.

[0061] (4) 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 - (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.

[0062] (5) Film formation by hydrothermal treatment An aqueous raw material solution and a substrate dip-coated with the sol solution in (3) above were sealed together in a Teflon (registered trademark) airtight 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) airtight 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 16 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 airtight 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.

[0063] (6) 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 a roll rotation speed of 3 mm / s, a roller heating temperature of 70 °C, and a roll gap of 70 μm to obtain a further densified LDH separator.

[0064] (6) Various evaluations Evaluations 1 to 7 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 was identified as LDH (hydrotalcite-like compound). This identification was performed using the diffraction peak of LDH (hydrotalcite-like compound) described in JCPDS Card No. 35-0964. - Evaluation 4: As shown in Table 2, an extremely high tightness of He permeability of 0.00 cm / min·atm was confirmed. In addition, Table 2 also shows the He permeability of the porous substrate after primer treatment. - Evaluation 5: As shown in Table 2, in Examples B1 to B4, an ionic conductivity higher than that in Examples B5 and B6 (comparative examples) (1.0 mS / cm or more) was confirmed. - Evaluation 6: As shown in Table 2, in Examples B3 and B4, excellent cycle durability performance (dendrite resistance) was confirmed, that is, there was no short circuit caused by zinc dendrites even after 200 cycles. On the other hand, in Examples B1, B2, B5, and B6 (comparative examples), since a short circuit caused by zinc dendrites occurred before 200 cycles, it was found that they were inferior in cycle durability performance. - Evaluation 7: In Examples B3 to B6, an adhesive strength higher than that in Examples B1 and B2 (comparative examples) (5.0 mN or more) was confirmed.

[0065]

Table 2

[0066] Examples C1 - C9 The production and evaluation of the LDH separator containing the Mg-(Al,Ti,Y)-LDH-like compound were carried out as follows.

[0067] (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.

[0068] (2) Primer treatment of the polymer porous substrate A binder solution containing a modified polyolefin resin (Aurelen (registered trademark) AE-202, manufactured by Nippon Paper Industries Co., Ltd.) at the concentration shown in Table 3 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 binder solution and then pulling it up vertically. Thereafter, the dip-coated substrate was dried at room temperature for 1 hour. Thus, a substrate coated with the binder resin was obtained. Here, the adhesion weight of the binder resin coated on the porous substrate (per 1 cm of the porous substrate) 3The adhesion weight (mg) is shown in Table 3. This adhesion weight was calculated by subtracting the weight W0 (mg) of the porous substrate before the primer treatment from the weight W1 (mg) of the porous substrate after the primer treatment and dividing by the volume V (cm 3 3) of the porous substrate (=(W1 - W0) / V).

[0069] (3) Alumina-Titania-Yttria Sol Coating on the Polymer Porous Substrate An amorphous alumina solution (Al-L7, manufactured by Takaki Chemical Co., Ltd.), a titania solution (AM-15, manufactured by Takaki Chemical Co., Ltd.), and a yttria sol were applied by dip coating onto the substrate that had been subjected to the primer treatment in (2) above. 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] (4) Preparation of the Aqueous Raw Material 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. The raw materials were weighed so that magnesium nitrate hexahydrate was 0.0075 mol / L and urea / NO3 - (molar ratio) = 96, placed in a beaker, and ion-exchanged water was added thereto to make the total volume 80 mL. Thereafter, the mixture was stirred to obtain an aqueous raw material solution.

[0071] (5) Film Formation by Hydrothermal Treatment A raw material aqueous solution and a substrate dip-coated with the sol solution in the above (3) were enclosed 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 by floating it 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 carried out at a hydrothermal temperature of 120 °C for 16 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 of the sealed container, washed with ion-exchanged water, and dried overnight at room temperature to form an LDH-like compound on the surface and inside the pores of the porous substrate. Thus, an LDH separator was obtained.

[0072] (6) 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 a roll rotation speed of 3 mm / s, a roller heating temperature of 70 °C, and a roll gap of 70 μm to obtain a further densified LDH separator.

[0073] (7) Various evaluations Evaluations 1 to 7 were carried out on the obtained LDH separator. The results were as follows. - Evaluation 1: A large number of plate-like shapes characteristic of 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 - 12°. Therefore, it is considered that the above peak is a shifted version of the (003) peak of LDH to the low-angle side. Thus, although the above peak cannot be called LDH, it suggests that it is a peak derived from a compound similar to it (i.e., an LDH-like compound). - Evaluation 4: As shown in Table 3, an extremely high tightness with a He permeability of 0.00 cm / min·atm was confirmed. Table 3 also shows the He permeability of the porous substrate after primer treatment. - Evaluation 5: As shown in Table 3, in Examples C1 to C6, an ionic conductivity higher than that in Examples C7 to C9 (comparative examples) (1.0 mS / cm or more) was confirmed. - Evaluation 6: As shown in Table 3, in Examples C3 to C6, excellent dendrite resistance was confirmed, i.e., no short circuit due to zinc dendrites occurred even after 400 cycles. On the other hand, in Examples C1, C2 and C7 to C9 (comparative examples), a short circuit due to zinc dendrites occurred before 400 cycles, indicating inferior dendrite resistance. - Evaluation 7: In Examples C3 to C9, an adhesive strength higher than that in Examples C1 and C2 (comparative examples) (5.0 mN or more) was confirmed.

[0074]

Table 3

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: The LDH separator has an ionic conductivity of 1.0 mS / cm or more, and the adhesion between the surface layer and the porous substrate is 5.0 mN or more, The adhesion is a critical load value measured by performing a micro scratch test on the surface including the surface layer of the LDH separator under the conditions of a scratch speed of 10 μm / s, a tip curvature radius of 25 μm of a diamond indenter needle, a load application speed of 30 mN / min, an excitation amplitude of 50 μm, and an excitation frequency of 45 Hz in accordance with JIS R3255-1997. The LDH separator.

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 claim 1 or 2, wherein the thickness of the surface layer is 0.01 to 10 μm.

7. The LDH separator according to claim 1 or 2, wherein the thickness of the LDH separator is 3 to 80 μm.

8. The LDH separator according to claim 1 or 2, wherein the porous substrate is made of a polymer material.

9. The LDH separator according to claim 1 or 2, wherein the He permeability per unit area of the LDH separator is 10 cm / min·atm or less.

10. The LDH separator according to claim 1 or 2, wherein the LDH separator is pressed in the thickness direction of the LDH separator.

11. The LDH separator according to claim 1 or 2, wherein the surface layer does not contain a binder resin.

12. A step of coating at least one surface of the porous substrate with a binder resin, wherein the amount of the binder resin adhered per 1 cm3 of the porous substrate is 14 to 290 mg. In an aqueous raw material solution containing constituent elements of a hydroxide ion-conductive layered compound that is a layered double hydroxide (LDH) and / or a layered double hydroxide (LDH)-like compound, a hydrothermal treatment is performed on the porous substrate coated with the binder resin to form a surface layer containing the hydroxide ion-conductive layered compound on the surface of the porous substrate containing the binder resin of the porous substrate. A method for manufacturing an LDH separator, comprising: **Claim 13** The method for manufacturing an LDH separator according to claim 12, wherein the coating of the porous substrate with the binder resin includes applying a solution in which the binder resin is dissolved to the surface of the porous substrate. **Claim 14** A zinc secondary battery comprising the LDH separator according to claim 1 or 2. **Claim 15** A solid alkaline fuel cell comprising the LDH separator according to claim 1 or 2.

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