Patent Application
20230207965
The present invention relates to an LDH-like compound separator and a secondary zinc battery.
In secondary zinc batteries, such as secondary nickel-zinc batteries and secondary air-zinc batteries, it is known that metallic zinc dendrites precipitate on negative electrodes during a charge mode, penetrate through voids in separators composed of, for example, non-woven fabrics, and reach positive electrodes, resulting in short circuit. The short circuit caused by such zinc dendrites occurs during repeated charge/discharge operations, leading to a reduction in service lives of the secondary zinc batteries.
In order to solve such a problem, secondary zinc batteries have been proposed that include layered double hydroxide (LDH) separators that selectively permeate hydroxide ions while blocking the penetration of zinc dendrites. For example, Patent Literature 1 (WO2013/118561) discloses a secondary nickel-zinc battery including an LDH separator disposed between a positive electrode and a negative electrode. Patent Literature 2 (WO2016/076047) discloses a separator structure including an LDH separator that is fit in or joined to a resin frame and is dense enough to restrict permeation of gas and/or water. Patent Literature 2 also discloses that the LDH separator may be a composite with a porous substrate. In addition, Patent Literature 3 (WO2016/067884) discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to give a composite material (an LDH separator). These methods include the steps of: uniformly bonding an initiating material capable of giving origins of crystal growth of LDH to the porous substrate; and then subjecting the porous substrate to hydrothermal treatment in an aqueous raw material solution to form a dense LDH membrane on the surface of the porous substrate.
In the meantime, Patent Literature 4 (WO2019/131688) discloses an LDH separator for secondary zinc batteries, comprising a porous substrate made of a polymer material; and a layered double hydroxide (LDH) plugging pores in the porous substrate, where the LDH separator has in its inside a dendrite buffer layer. This dendrite buffer layer is at least one selected from the group consisting of: (i) a pore-rich internal porous layer in the porous substrate, which is free from the LDH or deficient in the LDH; (ii) a releasable interfacial layer, which is provided by two adjacent layers constituting part of the LDH separator being in releasable contact with each other; and (iii) an internal gap layer being free from the LDH and the porous substrate, which is provided by two adjacent layers constituting part of the LDH separator being formed apart from each other.
Secondary zinc batteries, for example, nickel-zinc batteries, constructed with the LDH separator as described above usually do not cause short circuit by zinc dendrites; however, penetration of zinc dendrites and thus short circuit between positive and negative electrodes may eventually occur in an abnormal situation, i.e., intrusion of zinc dendrites into the LDH separator due to, for example, some defects. Accordingly, a further improvement is desired for a preventive effect of the short circuit caused by the dendrites.
The inventors have now found that by using an LDH-like compound described hereinafter as a hydroxide ion-conductive substance instead of conventional LDHs, it is possible to provide a hydroxide ion-conductive separator (LDH-like compound separator) having excellent alkali resistance and capable of suppressing short circuits due to zinc dendrites further effectively. The inventors have also found that an LDH-like compound separator that can more effectively restrain the short circuit caused by zinc dendrites can be provided through providing a dendrite buffer layer with a predetermined configuration inside the LDH-like compound separator.
Accordingly, an object of the present invention is to provide a hydroxide ion-conductive separator having excellent alkali resistance and capable of suppressing short circuits due to zinc dendrites further effectively, which is superior to the LDH separator.
According to an aspect of the present invention, there is provided an LDH-like compound separator for secondary zinc batteries, comprising a porous substrate made of a polymer material; and a layered double hydroxide (LDH)-like compound plugging pores in the porous substrate, wherein the LDH-like compound separator has in its inside a dendrite buffer layer, wherein the dendrite buffer layer is at least one selected from the group consisting of:
According to another aspect of the present invention, there is provided a secondary zinc battery comprising the LDH-like compound separator described above.
The LDH-like compound separator of the present invention, which is used in secondary zinc batteries, comprises a porous substrate and a layered double hydroxide (LDH)-like compound. The “LDH-like compound separator” is defined herein as a separator including an LDH-like compound and configured to selectively pass hydroxide ions exclusively by means of the hydroxide ion conductivity of the LDH-like compound. The “LDH-like compound” is defined herein as a hydroxide and/or an oxide having a layered crystal structure that cannot be called LDH but is analogous to LDH, for which no peak attributable to LDH is detected in X-ray diffraction method. The porous substrate is composed of a polymeric material, and the pores in the porous substrate are filled with the LDH-like compound. The LDH-like compound separator has in its inside a dendrite buffer layer. The dendrite buffer layer may include: (i) a pore-rich internal porous layer 10b in the porous substrate, the internal porous layer 10b being free from the LDH-like compound or deficient in the LDH-like compound, as shown in
As described above, a secondary zinc battery, such as a nickel-zinc battery, constructed with a conventional LDH separator usually can prevent short circuit caused by zinc dendrites; however, penetration of zinc dendrites and thus short circuit between positive and negative electrodes may eventually occur in an abnormal situation, i.e., intrusion of zinc dendrites into the LDH separator due to, for example, some defects. It is presumed that the penetration of zinc dendrites through the conventional separator occurs based on the following mechanism: (a) the zinc dendrites intrude into voids or defects contained in the separator; (b) the dendrites grow and develop while expanding the separator, and then (c) the dendrites eventually penetrate through the separator. In contrast, the LDH-like compound separator of the present invention is intentionally provided with a dendrite buffer layer, inside the separator, that has a configuration in a manner such as above (i) to (iii) to allow the zinc dendrites to grow, and the deposition and growth of zinc dendrites D can be confined only in the dendrite buffer layer, for example, shown in
Furthermore, the LDH-like compound separator of the present invention has excellent flexibility and strength, as well as a desired ionic conductivity based on the hydroxide ionic conductivity of the LDH-like compound. The flexibility and strength are caused by those of the polymeric porous substrate itself of the LDH-like compound separator. In other words, the LDH-like compound separator is densified in such a manner that the pores of the porous polymer substrate are filled with the LDH-like compound, thereby high rigidity and low ductility caused by the LDH-like compound, which is ceramic material, can be balanced with or reduced by high flexibility and high strength of the porous polymeric substrate.
In a preferred embodiment of the present invention, the dendrite buffer layer is (i) a pore-rich internal porous layer 10b in the porous substrate, the internal porous layer being free from the LDH-like compound or deficient in the LDH-like compound as the LDH-like compound separator 10 shown in
According to another preferred embodiment of the present invention, the dendrite buffer layer is (ii) a releasable interfacial layer 10b′ at which two adjacent layers composing part of the LDH-like compound separator are in releasable contact with each other, like the LDH-like compound separator 10′ shown in
According to another preferred embodiment of the present invention, the dendrite buffer layer is (iii) an inner space layer 10b″ (without the LDH-like compound and the porous substrate), like the LDH-like compound separator 10″ shown in
The LDH-like compound separator includes a layered double hydroxide (LDH)-like compound, and can isolate a positive electrode plate from a negative electrode plate and ensures hydroxide ionic conductivity therebetween in a secondary zinc battery. The LDH-like compound separator functions as a hydroxide ionic conductive separator. Preferred LDH-like compound separator has gas-impermeability and/or water-impermeability. In other words, the LDH-like compound separator is preferably densified to an extent that exhibits gas-impermeability and/or water-impermeability. The phrase “having gas-impermeability” throughout the specification indicates that no bubbling of helium gas is observed at one side of a sample when helium gas is brought into contact with the other side in water at a differential pressure of 0.5 atm across the thickness as described in Patent Literatures 2 and 3. In addition, the phrase “having water-impermeability” throughout the specification indicates that water in contact with one side of the sample does not permeate to the other side as described in Patent Literatures 2 and 3. As a result, the LDH-like compound separator having gas-impermeability and/or water-impermeability indicates having high density to an extent that no gas or no water permeates, and not being a porous membrane or any other porous material that has gas-permeability or water-permeability. Accordingly, the LDH-like compound separator can selectively permeate only hydroxide ions due to its hydroxide ionic conductivity, and can serve as a battery separator. The LDH-like compound separator thereby has a physical configuration that prevents penetration of zinc dendrites generated during a charge mode through the separator, resulting in prevention of short circuit between positive and negative electrodes. Since the LDH-like compound separator has hydroxide ionic conductivity, the ionic conductivity allows a necessary amount of hydroxide ions to efficiently move between the positive electrode plate and the negative electrode plate, and thereby charge/discharge reaction can be achieved on the positive electrode plate and the negative electrode plate.
The LDH-like compound separator preferably has a helium permeability per unit area of 3.0 cm/min atm or less, more preferably 2.0 cm/min atm or less, further more preferably 1.0 cm/min atm or less. A separator having a helium permeability of 3.0 cm/min atm or less can remarkably restrain the permeation of Zn (typically, the permeation of zinc ions or zincate ions) in the electrolytic solution. Thus, it is conceivable in principle that the separator of the present embodiment can effectively restrain the growth of zinc dendrites when used in secondary zinc batteries because Zn permeation is significantly suppressed. The helium permeability is measured through the steps of: supplying helium gas to one side of the separator to allow the helium gas to permeate into the separator; and calculating the helium permeability to evaluate the density of the hydroxide ion conductive separator. The helium permeability is calculated from the expression of F/(P×S) where F is the volume of permeated helium gas per unit time, P is the differential pressure applied to the separator when helium gas permeates through, and S is the area of the membrane through which helium gas permeates. Evaluation of the permeability of helium gas in this manner can extremely precisely determine the density. As a result, a high degree of density that does not permeate as much as possible (or permeate only a trace amount) substances other than hydroxide ions (in particular, zinc that causes deposition of dendritic zinc) can be effectively evaluated. Helium gas is suitable for this evaluation because the helium gas has the smallest constitutional unit among various atoms or molecules which can constitute the gas and its reactivity is extremely low. That is, helium does not form a molecule, and helium gas is present in the atomic form. In this respect, since hydrogen gas is present in the molecular form (H2), atomic helium is smaller than molecular H2 in a gaseous state. Basically, H2 gas is combustible and dangerous. By using the helium gas permeability defined by the above expression as an index, the density can be precisely and readily evaluated regardless of differences in sample size and measurement condition. Thus, whether the separator has sufficiently high density suitable for separators of secondary zinc batteries can be evaluated readily, safely and effectively. The helium permeability can be preferably measured in accordance with the procedure shown in Evaluation 5 in Examples described later.
In the LDH-like compound separator of the present invention, the pores (except for the dendrite buffer layer) in the porous substrate are filled with the LDH-like compound, preferably completely filled with the LDH-like compound. Preferably, the LDH-like compound is:
According to a preferred embodiment (a) of the present invention, the LDH-like compound is a hydroxide and/or an oxide with a layered crystal structure containing: Mg; and one or more elements, which include at least Ti, selected from the group consisting of Ti, Y, and Al. Accordingly, the LDH-like compound is typically a composite hydroxide and/or a composite oxide of Mg, Ti, optionally Y, and optionally Al. The aforementioned 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 is preferably free from Ni. For example, the LDH-like compound may further contain Zn and/or K. This can further improve the ion conductivity of the LDH-like compound separator.
The LDH-like compound can be identified by X-ray diffraction. Specifically, the LDH-like compound separator has a peak that is derived from the LDH-like compound and detected in the range of typically 5° ≤ 2θ ≤ 10°, more typically 7° ≤ 2θ ≤ 10°, when X-ray diffraction is performed on its surface. As described above, an LDH is a substance having an alternating laminated structure in which exchangeable anions and H2O are present as an interlayer between stacked basic hydroxide layers. In this regard, when the LDH is measured by X-ray diffraction, a peak due to the crystal structure of the LDH (that is, the (003) peak of LDH) is originally detected at a position of 2θ = 11° to 12°. In contrast, when the LDH-like compound is measured by X-ray diffraction, a peak is typically detected in such a range shifted toward the low angle side from the peak position of the LDH. Further, the interlayer distance in the layered crystal structure can be determined by Bragg’s equation using 2θ corresponding to peaks derived from the LDH-like compound in X-ray diffraction. The interlayer distance in 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.
The LDH-like compound separator according to the above embodiment (a) preferably has an atomic ratio Mg/(Mg + Ti + Y + Al) in the LDH-like compound, as determined by energy dispersive X-ray spectroscopy (EDS), of 0.03 to 0.25, more preferably 0.05 to 0.2. Further, an atomic ratio 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, an atomic ratio Y/(Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.45, more preferably 0 to 0.37. Further, an atomic ratio Al/(Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.03. Within such a range, the alkali resistance is further excellent, and the effect of suppressing short circuits due to zinc dendrites (that is, dendrite resistance) can be achieved more effectively. Meanwhile, LDHs conventionally known for LDH separators can be expressed by a basic composition represented by the formula: M2+1-xM3+x (OH)2An-x/n·mH2O (in the formula, M2+ is a divalent cation, M3+ is a trivalent cation, An- 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 contrast, the aforementioned atomic ratios in the LDH-like compound generally deviate from those in the aforementioned formula of LDH. Therefore, it can be said that the LDH-like compound in the present embodiment generally has composition ratios (atomic ratios) different from those of such a conventional LDH. The EDS analysis is preferably performed by 1) capturing an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) performing analysis at three points at intervals of about 5 µm in the point analysis mode, 3) repeating procedures 1) and 2) above once again, and 4) calculating an average of the six points in total, using an EDS analyzer (for example, X-act, manufactured by Oxford Instruments).
According to another embodiment (b), the LDH-like compound may be a hydroxide and/or an oxide with a layered crystal structure containing (i) Ti, Y, and optionally Al and/or Mg, and (ii) an additive element M. Therefore, the LDH-like compound is typically a complex hydroxide and/or a complex oxide with Ti, Y, the additive element M, and optionally Al and optionally Mg. The additive element M is In, Bi, Ca, Sr, Ba, or combinations thereof. The elements described above may be replaced by other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, and the LDH-like compound is preferably free of Ni.
The LDH-like compound separator according to the above embodiment (b) preferably has an atomic ratio of Ti/(Mg + Al + Ti + Y + M) of 0.50 to 0.85 in the LDH-like compound, as determined by energy dispersive X-ray spectroscopy (EDS) and more preferably has the atomic ratio of 0.56 to 0.81. An atomic ratio of Y/(Mg + Al + Ti + Y + M) in the LDH-like compound is preferably 0.03 to 0.20 and more preferably 0.07 to 0.15. An atomic ratio of M/(Mg + Al + Ti + Y + M) in the LDH-like compound is preferably 0.03 to 0.35 and more preferably 0.03 and 0.32. An atomic ratio of Mg/(Mg + Al + Ti + Y + M) in the LDH-like compound is preferably 0 to 0.10 and more preferably 0 to 0.02. In addition, an atomic ratio of Al/(Mg + Al + Ti + Y + M) in the LDH-like compound is preferably 0 to 0.05 and more preferably 0 to 0.04. The ratios within the above ranges enable to achieve more excellent alkali resistance and a short-circuit inhibition effect caused by zinc dendrite (i.e., dendrite resistance) in more efficient manner. By the way, an LDH that is conventionally known with respect to an LDH separator, can be represented by the basic composition of the formula: M2+1-xM3+x(OH)2An-x/n·mH2O wherein M2+ is a divalent cation, M3+ is a trivalent cation, An- is an n-valent anion, n is an integer of 1 or greater, x is 0.1 to 0.4, and m is an integer of to 0 or greater. In contrast, the above atomic ratio in the LDH-like compound generally deviates from that of the above formula of LDH. Therefore, the LDH-like compound in the present embodiment can be generally said to have a composition ratio (atomic ratio) different from that of conventional LDH. The EDS analysis is preferably carried out with an EDS analyzer (for example, X-act manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5.000 times, 2) carrying out a three-point analysis at about 5 µm intervals in a point analysis mode, 3) repeating the above 1) and 2) once more, and 4) calculating an average value of a total of 6 points.
According to yet another embodiment (c), the LDH-like compound may be a hydroxide and/or an oxide with a layered crystal structure, comprising Mg, Ti, Y, and optionally Al and/or In, in which the LDH-like compound dis present in a form of a mixture with In(OH)3. The LDH-like compound of the present embodiment is a hydroxide and/or an oxide with a layered crystal structure containing Mg, Ti, Y, and optionally Al and/or In. Therefore, the typical LDH-like compound is a complex hydroxide and/or a complex oxide with Mg, Ti, Y, optionally Al, and optionally In. Here, In that can be contained in the LDH-like compound may be not only one intentionally added, but also one unavoidably incorporated in the LDH-like compound derived from formation of In(OH)3 or the like. The elements described above may be replaced by other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, and the LDH-like compound is preferably free of Ni. By the way, an LDH that is conventionally known with respect to an LDH separator, can be represented by the basic composition of the formula: M2+1-xM3+x(OH)2An-x/n·mH2O wherein M2+ is a divalent cation, M3+ is a trivalent cation, An- is an n-valent anion, n is an integer of 1 or greater, x is 0.1 to 0.4, and m is 0 or greater. In contrast, the atomic ratio in the LDH-like compound generally deviates from that of the above formula of LDH. Therefore, the LDH-like compound in the present embodiment can be generally said to have a composition ratio (atomic ratio) different from that of conventional LDH.
The mixture according to the above embodiment (c) contains not only the LDH-like compound but also In(OH)3 (typically composed of the LDH-like compound and In(OH)3). In(OH)3 contained effectively improves alkali resistance and dendrite resistance in the LDH-like compound separator. The content ratio of In(OH)3 in the mixture is preferably an amount that can improve the alkali resistance and dendrite resistance without impairing hydroxide-ion conductivity of the LDH-like compound separator and is not limited to any particular amount. In(OH)3 may have a cubic crystal structure and may be in a configuration where the crystals thereof are surrounded by the LDH-like compounds. The In(OH)3 can be identified by X-ray diffraction; and X-ray diffraction measurement is preferably conducted according to the procedure described in the Example below.
As described above, the LDH-like compound separator comprises the LDH-like compound and the porous substrate (typically consists of the porous substrate and the LDH-like compound), and the LDH-like compound plugs the pores in the porous substrate such that the LDH-like compound separator exhibits hydroxide ionic conductivity and gas-impermeability (thus, so as to serve as an LDH-like compound separator exhibiting hydroxide ionic conductivity). In particular, the LDH-like compound is preferably embedded over the entire thickness of the porous substrate other than the dendrite buffer layer (For example, the LDH-like compound preferably plugs most or all pores inside the porous substrate other than the dendrite buffer layer). The LDH-like compound separator has an overall thickness (a thickness including the dendrite buffer layer) of preferably 5 µm to 5 mm, more preferably 5 µm to 1 mm, further more preferably 5 µm to 0.5 mm, particularly more preferably 5 µm to 0.3 mm.
The porous substrate is composed of a polymeric material. The polymeric porous substrate has the following advantages; (1) high flexibility (hard to crack even if thinned), (2) high porosity, (3) high conductivity (small thickness with high porosity), and (4) good manufacturability and handling ability. The polymeric porous substrate has a further advantage; (5) readily folding and sealing the LDH-like compound separator including the porous substrate composed of the polymeric material based on the advantage (1): high flexibility. Preferred examples of the polymeric material include polystyrene, poly(ether sulfone), polypropylene, epoxy resin, poly(phenylene sulfide), fluorocarbon resin (tetra-fluorinated resin such as PTFE), cellulose, nylon, polyethylene and any combination thereof. More preferred examples include polystyrene, poly(ether sulfone), polypropylene, epoxy resin, poly(phenylene sulfide), fluorocarbon resin (tetra-fluorinated resin such as PTFE), nylon, polyethylene and any combination thereof from the viewpoint of a thermoplastic resin suitable for hot pressing. All the various preferred materials described above have alkali resistance to be resistant to the electrolytic solution of batteries. More preferred polymeric materials are polyolefins, such as polypropylene and polyethylene, most preferred are polypropylene and polyethylene from the viewpoint of excellent hot-water resistance, acid resistance and alkali resistance, and low material cost. A polymeric microporous membrane commercially available can be preferably used as such a polymeric porous substrate.
The dendrite buffer layer may be produced by the process described above, and a portion of the LDH-like compound separator other than the dendrite buffer layer or the LDH-like compound separator body 10a can be produced by any process, preferably with appropriate modification of various conditions in known methods (e.g., see Patent Literatures 1 to 4) for producing the LDH-containing functional layer and the composite material (that is, the LDH separator). For example, an LDH-like compound-containing function layer and a composite material (that is, an LDH-like compound separator) can be produced by (1) preparing a porous substrate, (2) applying a solution containing titania sol (or further containing yttrium sol and/or alumina sol) to the porous substrate, followed by drying, to form a titania-containing layer, (3) immersing the porous substrate in a raw material aqueous solution containing magnesium ions (Mg2+) and urea (or further containing yttrium ions (Y3+)), and (4) hydrothermally treating the porous substrate in the raw material aqueous solution, to form an LDH-like compound-containing function layer on the porous substrate and/or in the porous substrate. It is considered that the presence of urea in step (3) above generates ammonia in the solution through hydrolysis of urea, to increase the pH value, and coexisting metal ions form a hydroxide and/or an oxide, so that the LDH-like compound can be obtained.
In particular, in the case of producing a composite material (that is, an LDH-like compound separator) in which the porous substrate is composed of a polymer material, and the LDH-like compound is incorporated over the entire thickness direction of the porous substrate, the mixed sol solution is preferably applied to the substrate in step (2) above by a technique that allows the mixed sol solution to penetrate all or most of the inside of the substrate. This allows most or almost all the pores inside the porous substrate to be finally filled with the LDH-like compound. Preferable examples of the application technique include dip coating and filtration coating, particularly preferably dip coating. Adjusting the number of applications such as dip coating enables adjustment of the amount of the mixed sol solution to be applied. The substrate coated with the mixed sol solution by dip coating or the like may be dried and then subjected to steps (3) and (4) above.
When the porous substrate is composed of a polymer material, an LDH-like compound separator obtained by the aforementioned method or the like is preferably pressed. This enables an LDH-like compound separator with further excellent denseness to be obtained. The pressing technique is not specifically limited and may be, for example, roll pressing, uniaxial compression press, CIP (cold isotropic pressing) or the like but is preferably roll pressing. This pressing is preferably performed under heating, since the porous polymer substrate is softened, so that the pores of the porous substrate can be sufficiently filled with the LDH-like compound. For sufficient softening, the heating temperature is preferably 60 to 200° C., for example, in the case of polypropylene or polyethylene. The pressing such as roll pressing within such a temperature range can considerably reduce residual pores in the LDH-like compound separator. As a result, the LDH-like compound separator can be extremely densified, and short circuits due to zinc dendrites can be thus suppressed further effectively. Appropriately adjusting the roll gap and the roll temperature in roll pressing enables the morphology of residual pores to be controlled, thereby enabling an LDH-like compound separator with desired denseness to be obtained.
The LDH-like compound separator of the present invention is preferably applied to secondary zinc batteries. According to a preferred embodiment of the present invention, a secondary zinc battery comprising the LDH-like compound separator are provided. A typical secondary zinc battery includes a positive electrode, a negative electrode, and an electrolytic solution, and isolates the positive electrode from the negative electrode with the LDH-like compound separator therebetween. The secondary zinc battery of the present invention may be of any type that includes a zinc negative electrode and an electrolytic solution (typically, an aqueous alkali metal hydroxide solution). Accordingly, examples of the secondary zinc battery include secondary nickel-zinc batteries, secondary silver oxide-zinc batteries, secondary manganese oxide-zinc batteries, secondary zinc-air batteries, and various other secondary alkaline zinc batteries. For example, the secondary zinc battery may preferably be a secondary nickel-zinc battery, the positive electrode of which contains nickel hydroxide and/or nickel oxyhydroxide. Alternatively, the secondary zinc battery may be a secondary zinc-air battery, the positive electrode of which is an air electrode.
The LDH-like compound separator of the present invention can be used not only in secondary zinc batteries such as nickel-zinc batteries but also in, for example, nickel-hydrogen batteries. In this case, the LDH-like compound separator serves to block a nitride shuttle (movement of nitrate groups between electrodes), which is a factor of the self-discharging in the battery. The LDH-like compound separator of the present invention can also be applied in, for example, lithium batteries (batteries having a negative electrode composed of lithium metal), lithium ion batteries (batteries having a negative electrode composed of, for example, carbon), or lithium-air batteries.
The invention will be further described in more detail by the following Examples.
Examples A1 to A8 shown below are reference examples or comparative examples for LDH separators, but the experimental procedures and results in these examples are generally applicable to LDH-like compound separators as well. The following procedures were used to evaluate the LDH separator produced in these Examples.
The crystalline phase of the LDH layer was measured with an X-ray diffractometer (RINT TTR III manufactured by Rigaku Corporation) at a voltage of 50 kV, a current of 300 mA, and a measuring range of 10° to 70° to give an XRD profile. The resultant XRD profile was identified with the diffraction peaks of LDH (hydrotalcite compound) described in JCPDS card NO.35-0964.
The density was determined to confirm that the LDH separator had density having no gas permeability. As shown in
A cross-sectional polished surface of the LDH separator was prepared with an ion milling system (IM4000, manufactured by Hitachi High-Technologies Corporation). The microstructure on the cross-sectional polished surface was observed at an acceleration voltage of 10 kV, and each view was photographed at magnifications of 500 folds, 1000 folds, 2500 folds, 5000 folds and 10000 folds with a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL Ltd.).
A device 210 was assembled as shown in
A helium permeation test was conducted to evaluate the density of the LDH separator from the viewpoint of helium permeability. The helium permeability measurement system 310 shown in
The sample holder 316 had a structure including a gas supply port 316a, a sealed space 316b and a gas discharge port 316c, and was assembled as follows: An adhesive 322 was applied along the outer periphery of the LDH separator 318 and bonded to a jig 324 (made of ABS resin) having a central opening. Gaskets or sealing members 326a, 326b made of butyl rubber were disposed at the upper end and the lower end, respectively, of the jig 324, and then the outer sides of the members 326a, 326b were held with supporting members 328a, 328b (made of PTFE) each including a flange having an opening. Thus, the sealed space 316b was partitioned by the LDH separator 318, the jig 324, the sealing member 326a, and the supporting member 328a. The supporting members 328a and 328b were tightly fastened to each other with fastening means 330 with screws not to cause leakage of helium gas from portions 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 assembled as above through a joint 332.
Helium gas was then supplied to the helium permeability measurement system 310 via the gas supply pipe 334, and the gas was permeated through the LDH separator 318 held in the sample holder 316. A gas supply pressure and a flow rate were then monitored with a pressure gauge 312 and a flow meter 314. After permeation of helium gas for one to thirty minutes, the helium permeability was calculated. The helium permeability was calculated from the expression of F/(P×S) where F (cm3/min) was the volume of permeated helium gas per unit time, P (atm) was the differential pressure applied to the LDH separator when helium gas permeated through, and S (cm2) was the area of the membrane through which helium gas permeates. The permeation rate F (cm3/min) of helium gas was read directly from the flow meter 314. The gauge pressure read from the pressure gauge 312 was used for the differential pressure P. Helium gas was supplied such that the differential pressure P was within the range of 0.05 to 0.90 atm.
A commercially available polypropylene porous substrate having a porosity of 60%, a mean pore size of 0.05 µm, and a thickness of 20 µm was cut out into a size of 2.0 cm × 2.0 cm.
An amorphous alumina solution (Al-ML15, manufactured by Taki Chemical Co., Ltd.) and a titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) were mixed at Ti/Al molar ratio of 2 to yield a mixed sol. The substrate prepared in Process (1) was immersed in ethanol for one minute, and then immediately transferred into the mixed sol before being dried. The mixed sol was applied onto the substrate by dip coating. In dip coating, the substrate was immersed in 100 mL of the mixed sol, pulled up vertically and dried in a dryer at 90° C. for five minutes.
Nickel nitrate hexahydrate (Ni(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.), and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were provided as raw materials. Nickel nitrate hexahydrate was weighed to be 0.015 mol/L and placed in a beaker. Ion-exchanged water was added into a total volume of 75 mL. After stirring the solution, the urea weighed at a urea/NO3- molar ratio of 16 was added, and further stirred to give an aqueous raw material solution.
The aqueous raw material solution and the dip-coated substrate were encapsulated into a Teflon® autoclave (the internal volume: 100 mL, covered with stainless steel jacket). The substrate was horizontally fixed away from the bottom of the Teflon® autoclave such that the solution was in contact with the two surfaces of the substrate. An LDH was then formed on the surface and the interior of the substrate by a hydrothermal treatment at a temperature of 120° C. for 24 hour. After a predetermined period, the substrate was removed from the autoclave, washed with ion-exchanged water, and dried at 70° C. for ten hours to form the LDH in the pores of porous substrate and give the LDH separator.
The resultant LDH separator was evaluated in accordance with Evaluations 1 to 5. As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3, as shown in
An LDH separator layer including no internal porous layer was produced as in Example A1 except that the mixed sol was applied onto the substrate by dip coating without immersion in ethanol in Process (2). Two sheets of the LDH separator layer produced as above were stacked. The stack was disposed between a pair of PET films (Lumirror® manufactured by Toray Industries, Inc., a thickness of 40 µm), and roll-pressed at a rotation rate of 3 mm/s, at a roller temperature of 100° C., and with a gap between rollers of 150 µm to give an LDH separator including a releasable interfacial layer. The resultant LDH separator was evaluated as in Example A1. As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3, as shown in
An LDH separator layer including no internal porous layer was produced as in Example A1 except that the mixed sol was applied onto the substrate by dip coating without immersion in ethanol in Process (2). Two sheets of the LDH separator layer produced as above were disposed to face each other with a gap of about 5 µm to give an LDH separator including an internal gap layer. The resultant LDH separator was evaluated as in Example A1. As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3, as shown in
An LDH separator layer including no internal porous layer was produced as in Example A1 except that the mixed sol was applied onto the substrate by dip coating without immersion in ethanol in Process (2). The resultant LDH separator was evaluated as in Example A1. As a result of Evaluation 1, this LDH separator is identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3 indicated that this LDH separator was composed only of a single LDH layer, and no dendrite buffer layer was found. The results of Evaluations 4 and 5 are shown in Table 1.
An LDH separator was produced and evaluated as in Example A1 except for the following conditions a) to c).
a) A commercially available polyethylene porous substrate having a porosity of 40%, a mean pore size of 0.05 µm and a thickness of 20 µm was used for the polymeric porous substrate in Process (1).
b) Magnesium nitrate hexahydrate (Mg(NO3)2′6H2O, manufactured by Kanto Chemical Co., Ltd.) was used instead of the nickel nitrate hexahydrate in Process (3), weighed to be 0.03 mol/L, and placed in a beaker. Ion-exchanged water was added into a total volume of 75 mL. After stirring the resultant solution, the urea weighed at a urea/NO3- molar ratio of 8 was added, and further stirred to give an aqueous raw material solution.
c) The hydrothermal temperature in Process (4) was 90° C.
As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3 indicated that this LDH separator had an internal porous layer being free from or deficient in the LDH between a pair of LDH separator bodies, similar to Example A1. The results of Evaluations 4 and 5 are shown in Table 1.
An LDH separator layer including no internal porous layer was produced as in Example A1 except for the following conditions a) to d).
a) A commercially available polyethylene porous substrate having a porosity of 40%, a mean pore size of 0.05 µm and a thickness of 20 µm was used for the polymeric porous substrate in Process (1).
b) The mixed sol was applied onto the substrate by dip coating without immersion in ethanol in Process (2).
c) Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Ltd.) was used instead of the nickel nitrate hexahydrate in Process (3), weighed to be 0.03 mol/L, and placed in a beaker. Ion-exchanged water was added into a total volume of 75 mL. After stirring the resultant solution, the urea weighed at a urea/NO3- molar ratio of 8 was added, and further stirred to give an aqueous raw material solution.
d) The hydrothermal temperature in Process (4) was 90° C.
Two sheets of the LDH separator layer produced as above was stacked. The stack was disposed between a pair of PET films (Lumirror® manufactured by Toray Industries, Inc., a thickness of 40 µm), and roll-pressed at a rotation rate of 3 mm/s, at a roller temperature of 100° C., and with a gap between rollers of 150 µm to give an LDH separator including a releasable interfacial layer. The resultant LDH separator was evaluated as in Example A1. As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3 indicated this LDH separator had the releasable interfacial layer, between a pair of LDH separator bodies, thereby two LDH separator bodies were in releasable contact with each other, similar to Example A2. The results of Evaluations 4 and 5 are shown in Table 1.
An LDH separator layer including no internal porous layer was produced as in Example A1 except for the following conditions a) to d).
a) A commercially available polyethylene porous substrate having a porosity of 40%, a mean pore size of 0.05 µm and a thickness of 20 µm was used for the polymeric porous substrate in Process (1).
b) The mixed sol was applied onto the substrate by dip coating without the immersion in ethanol in Process (2).
c) Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Ltd.) was used instead of the nickel nitrate hexahydrate in Process (3), weighed to be 0.03 mol/L, and placed in a beaker. Ion-exchanged water was added into a total volume of 75 mL. After stirring the resultant solution, the urea weighed at a urea/NO3- molar ratio of 8 was added, and further stirred to give an aqueous raw material solution.
d) The hydrothermal temperature in Process (4) was 90° C.
Two sheets of the LDH separator layer produced as above were disposed to face each other with a gap of about 5 µm to give an LDH separator including an internal gap layer as a whole. The resultant LDH separator was evaluated as in Example A1. As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3 indicated that this LDH separator had, between a pair of LDH separator bodies, the internal gap layer being free from the LDH and the porous substrate, similarly to Example A3. The results of Evaluations 4 and 5 are shown in Table 1.
An LDH separator layer including no internal porous layer was produced as in Example A1 except for the following conditions a) to c).
a) A commercially available polyethylene porous substrate having a porosity of 40%, a mean pore size of 0.05 µm and a thickness of 20 µm was used for the polymeric porous substrate in Process (1).
b) The mixed sol was applied onto the substrate by dip coating without immersion in ethanol in Process (2).
c) Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Ltd.) was used instead of the nickel nitrate hexahydrate in Process (3), weighed to be 0.03 mol/L, and placed in a beaker. Ion-exchanged water was added into a total volume of 75 mL. After stirring the resultant solution, the urea weighed at a urea/NO3- molar ratio of 8 was added, and further stirred to give an aqueous raw material solution.
d) The hydrothermal temperature in Process (4) was 90° C.
As a result of Evaluation 1, this LDH separator was identified as LDH (hydrotalcite compound). As a result of Evaluation 2, bubbling of helium gas was not observed in this LDH separator. Evaluation 3 indicated that this LDH separator was composed only of a single LDH layer, and no dendrite buffer layer was found. The results of Evaluations 4 and 5 are shown in Table 1.
[Table 1]
Examples B1 to B7 shown below are reference examples for LDH-like compound separators, while Examples B8 shown below is a comparative example for an LDH separator. The LDH-like compound separators and LDH separator will be collectively referred to as hydroxide ion-conductive separators. The method for evaluating the hydroxide ion-conductive separators produced in the following examples was as follows.
The surface microstructure of the hydroxide ion-conductive separator was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL Ltd.) at an acceleration voltage of 10 to 20 kV.
The layered structure of the hydroxide ion-conductive separator was observed using a scanning transmission electron microscope (STEM) (product name: JEM-ARM200F, manufactured by JEOL Ltd.) at an acceleration voltage of 200 kV.
A surface of the hydroxide ion-conductive separator was subjected to compositional analysis using an EDS analyzer (device name: X-act, manufactured by Oxford Instruments), to calculate the composition ratio (atomic ratio) Mg:Ti:Y:Al. This analysis was performed by 1) capturing an image at an acceleration voltage of 20 kV and a magnification of 5,000 times, 2) performing analysis at three points at intervals of about 5 µm in the point analysis mode, 3) repeating procedures 1) and 2) above once again, and 4) calculating an average of the six points in total.
Using an X-ray diffractometer (RINT TTR III, manufactured by Rigaku Corporation), the crystalline phase of the hydroxide ion-conductive separator was measured under the measurement conditions of voltage: 50 kV, current value: 300 mA, and measurement range: 5 to 40°, to obtain an XRD profile. Further, the interlayer distance in the layered crystal structure was determined by Bragg’s equation using 2θ corresponding to peaks derived from the LDH-like compound.
In order to evaluate the denseness of the hydroxide ion-conductive separator in view of the He permeation, a He permeation test was performed in the same procedure as in Evaluation 5 of Examples A1 to A15.
The conductivity of the hydroxide ion-conductive separator in the electrolytic solution was measured using the electrochemical measurement system shown in
A 5.4 M KOH aqueous solution containing zinc oxide at a concentration of 0.4 M was prepared. 0.5 mL of the KOH aqueous solution prepared and a hydroxide ion-conductive separator sample with a size of 2 cm square were put into a closed container made of Teflon®. Thereafter, it was maintained at 90° C. for one week (that is, 168 hours), and then the hydroxide ion-conductive separator sample was taken out of the closed container. The hydroxide ion-conductive separator sample taken out was dried overnight at room temperature. For the sample obtained, the He permeability was calculated in the same manner as in Evaluation 5, to determine whether or not the He permeability changed before and after the immersion in alkali.
In order to evaluate the effect of suppressing short circuits due to zinc dendrites (dendrite resistance) of the hydroxide ion-conductive separator, a cycle test was performed, as follows. First, each of the positive electrode (containing nickel hydroxide and/or nickel oxyhydroxide) and the negative electrode (containing zinc and/or zinc oxide) was wrapped with a non-woven fabric, and the current extraction terminal was welded thereto. The positive electrode and the negative electrode thus prepared were opposed to each other via the hydroxide ion-conductive separator and sandwiched between laminate films provided with current outlets, and three sides of the laminate films were heat-sealed. An electrolytic solution (a solution in which 0.4 M zinc oxide was dissolved in a 5.4 M KOH aqueous solution) was added to the cell container with the top open thus obtained, and the positive electrode and the negative electrode was sufficiently impregnated with the electrolytic solution by vacuuming or the like. Thereafter, the remaining one side of the laminate films was heat-sealed, to form a simple sealed cell. Using a charge/discharge device (TOSCAT3100, manufactured by TOYO SYSTEM CO., LTD.), the simple sealed cell was charged at 0.1 C and discharged at 0.2 C for chemical conversion. Thereafter, a 1-C charge/discharge cycle was conducted. While repeating the charge/discharge cycle under the same conditions, the voltage between the positive electrode and the negative electrode was monitored with a voltmeter, and the presence or absence of sudden voltage drops (specifically, voltage drops of 5 mV or more from the voltage that was just previously plotted) following short circuits due to zinc dendrites between the positive electrode and the negative electrode was examined and evaluated according to the following criteria.
A commercially available polyethylene microporous membrane with a porosity of 50%, a mean pore size of 0.1 µm, and a thickness of 20 µm was prepared as a porous polymer substrate and cut out into a size of 2.0 cm × 2.0 cm.
The substrate prepared by procedure (1) above was coated with a titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the sol solution and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by KANTO CHEMICAL CO., INC.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were prepared. The magnesium nitrate hexahydrate was weighed to 0.015 mol/L and put into a beaker, and deionized water was added thereto so that the total amount was 75 ml. After stirring the solution obtained, urea weighed at a ratio urea/NO3- (molar ratio) of 48 was added into the solution, followed by further stirring, to obtain a raw material aqueous solution.
The raw material aqueous solution and the dip-coated substrate were enclosed together in a closed container made of Teflon® (autoclave container, content: 100 ml, with an outer stainless steel jacket). At this time, the substrate was lifted from the bottom of the closed container made of Teflon® and fixed and installed vertically so that the solution was in contact with both sides of the substrate. Thereafter, an LDH-like compound was formed on the surface and inside the substrate by applying hydrothermal treatment at a hydrothermal temperature of 120° C. for 24 hours. After a lapse of a predetermined time, the substrate was taken out of the closed container, washed with deionized water, and dried at 70° C. for 10 hours, to form an LDH-like compound in the pores of the porous substrate. Thus, an LDH-like compound separator was obtained.
The LDH-like compound separator was sandwiched by a pair of PET films (Lumirror®, manufactured by Toray Industries, Inc., with a thickness of 40 µm) and roll-pressed at a roll rotation speed of 3 mm/s and a roller heating temperature of 70° C. with a roll gap of 70 µm, to obtain an LDH-like compound separator that was further densified.
The LDH-like compound separator obtained was subjected to Evaluations 1 to 8. The results were as follows.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B1 except that the raw material aqueous solution was produced as follows in procedure (3) above, and the temperature for the hydrothermal treatment was changed to 90° C. in procedure (4) above.
As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by KANTO CHEMICAL CO., INC.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were prepared. The magnesium nitrate hexahydrate was weighed to 0.03 mol/L and put into a beaker, and deionized water was added thereto so that the total amount was 75 ml. After stirring the solution obtained, urea weighed at a ratio urea/NO3- (molar ratio) of 8 was added into the solution, followed by further stirring, to obtain a raw material aqueous solution.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B1 except that the porous polymer substrate was coated with titania and yttria sols as follows, instead of procedure (2) above.
A titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) and a yttrium sol were mixed at a molar ratio Ti/Y of 4. The substrate prepared in procedure (1) above was coated with the mixed solution obtained by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the mixed solution and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B1 except that the porous polymer substrate was coated with titania, yttria, and alumina sols as follows, instead of procedure (2) above.
A titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.), a yttrium sol, and an amorphous alumina solution (Al-ML15, manufactured by Taki Chemical Co., Ltd.) were mixed at a molar ratio Ti/(Y + Al) of 2 and a molar ratio Y/Al of 8. The substrate prepared in procedure (1) above was coated with the mixed solution by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the mixed solution and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B1 except that the porous polymer substrate was coated with titania and yttria sols as follows, instead of procedure (2) above, and the raw material aqueous solution was produced as follows in procedure (3) above.
A titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) and a yttrium sol were mixed at a molar ratio Ti/Y of 18. The substrate prepared in procedure (1) above was coated with the mixed solution obtained by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the mixed solution and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by KANTO CHEMICAL CO., INC.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were prepared. The magnesium nitrate hexahydrate was weighed to 0.0075 mol/L and put into a beaker, and deionized water was added thereto so that the total amount was 75 ml. Then, the solution obtained was stirred. Urea weighed at a ratio urea/NO3- (molar ratio) = 96 was added into the solution, followed by further stirring, to obtain a raw material aqueous solution.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B1 except that the porous polymer substrate was coated with titania and alumina sols as follows, instead of procedure (2) above, and the raw material aqueous solution was produced as follows in procedure (3) above.
A titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) and an amorphous alumina solution (Al-ML15, manufactured by Taki Chemical Co., Ltd.) were mixed at a molar ratio Ti/Al of 18. The substrate prepared in procedure (1) above was coated with the mixed solution by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the mixed solution and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by KANTO CHEMICAL CO., INC.), yttrium nitrate n hydrate (Y(NO3)3·nH2O, manufactured by FUJIFILM Wako Pure Chemical Corporation), and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were prepared. The magnesium nitrate hexahydrate was weighed to 0.0015 mol/L and put into a beaker. Further, the yttrium nitrate n hydrate was weighed to 0.0075 mol/L and put into the beaker, and deionized water was added thereto so that the total amount was 75 ml. Then, the solution obtained was stirred. Urea weighed at a ratio urea/NO3- (molar ratio) of 9.8 was added into the solution, followed by further stirring, to obtain a raw material aqueous solution.
An LDH-like compound separator was produced and evaluated in the same manner as in Example B6 except that the raw material aqueous solution was produced as follows in procedure (3) above.
As raw materials, magnesium nitrate hexahydrate (Mg(NO3)2′6H2O, manufactured by KANTO CHEMICAL CO., INC.), yttrium nitrate n hydrate (Y(NO3)3·nH2O, manufactured by FUJIFILM Wako Pure Chemical Corporation), and urea ((NH2)2CO, manufactured by Sigma-Aldrich Corporation) were prepared. The magnesium nitrate hexahydrate was weighed to 0.0075 mol/L and put into a beaker. Further, the yttrium nitrate n hydrate was weighed to 0.0075 mol/L and put into the beaker, and deionized water was added thereto so that the total amount was 75 ml. Then, the solution obtained was stirred. Urea weighed at a ratio urea/NO3- (molar ratio) of 25.6 was added into the solution, followed by further stirring, to obtain a raw material aqueous solution.
An LDH separator was produced and evaluated in the same manner as in Example B1 except that alumina sol coating was performed as follows, instead of procedure (2) above.
The substrate prepared in procedure (1) above was coated with an amorphous alumina sol (AI-ML15, manufactured by Taki Chemical Co., Ltd.) by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the amorphous alumina sol and pulling it out perpendicularly, followed by drying at room temperature for 3 hours.
[Table 2]
Examples C1 to C9 shown below are reference examples for LDH-like compound separators. The method for evaluating the LDH-like compound separators produced in the following examples was the same as in Examples B1 to B8, except that the composition ratio (atomic ratio) of Mg: Al: Ti: Y: additive element M was calculated in Evaluation 3.
A commercially available polyethylene microporous membrane having a porosity of 50%, an average pore diameter of 0.1 µm, and a thickness of 20 µm was prepared as a polymer porous substrate and cut out to a size of 2.0 cm × 2.0 cm.
A titanium dioxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.), an yttrium sol, and an amorphous alumina solution (Al-ML15, manufactured by Taki Chemical Co. Ltd.) were mixed so that Ti/(Y + Al) (molar ratio) = 2, and Y/Al (molar ratio) = 8. The substrate prepared in (1) above was coated with the mixed solution by dip coating. The dip coating was carried out by dipping the substrate into 100 ml of the mixed solution, pulling up the coating substrate vertically, and allowing it to dry for 3 hours at room temperature.
Magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.) and urea ((NH2)2CO, manufactured by Sigma-Aldrich Co. LLC) were prepared as raw materials. Magnesium nitrate hexahydrate was weighed so that it would be 0.015 mol/L and placed in a beaker, and ion-exchanged water was added therein to make a total amount of 75 ml. After stirring the obtained solution, the urea weighed at a ratio that urea/NO3- (molar ratio) = 48 was added to the solution, and the mixture was further stirred to obtain a raw material aqueous solution (I).
Both the raw material aqueous solution (I) and the dip-coated substrate were sealed in a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel). At this time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container, and installed vertically so that the solution was in contact with both sides of the substrate. Thereafter, an LDH-like compound was formed on the surface and the inside of the substrate by subjecting it to hydrothermal treatment at a hydrothermal temperature of 120° C. for 22 hours. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to form an LDH-like compound inside the pores of the porous substrate.
Indium sulfate n-hydrate (In2(SO4)3▪nH2O, manufactured by FUJIFILM Wako Pure Chemical Corporation) was prepared as the raw material. The Indium sulfate n-hydrate was weighed so that it would be 0.0075 mol/L and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution (II).
In a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel), the raw material aqueous solution (II) and the LDH-like compound separator obtained in (4) above were enclosed together. At that time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container and arranged vertically so that the solution was in contact with both sides of the substrate. Thereafter Indium was added on the substrate by subjecting it to immersion treatment at 30° C. for 1 hour. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to obtain an LDH-like compound separator with Indium added thereon.
The LDH-like compound separator was sandwiched between a pair of PET films (Lumiler® manufactured by Toray Industries, Inc., thickness of 40 µm), and roll-pressed 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-like compound separator.
Various evaluations were conducted on the LDH-like compound separators obtained. The results were as follows.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the time of immersion treatment was changed to 24 hours in indium addition by the immersion treatment of (6) above.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the titania-yttria sol coating was carried out as follows instead of (2) above.
A titanium dioxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) and an yttrium sol were mixed so that Ti/Y (molar ratio) = 2. The substrate prepared in (1) above was coated with the obtained mixed solution by dip coating. The dip coating was carried out by dipping the substrate into 100 ml of the mixed solution, pulling up the coating substrate vertically, and allowing it to dry for 3 hours at room temperature.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the preparation of the raw material aqueous solution (II) in (5) above was carried out as follows, and bismuth was added by immersion treatment as follows instead of (6) above.
Bismuth nitrate pentahydrate (Bi(NO3)3▪5H2O) was prepared as the raw material. The bismuth nitrate pentahydrate was weighed so that it would be 0.00075 mol/L and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution (II).
In a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel), the raw material aqueous solution (II) and the LDH-like compound separator obtained in (4) above were enclosed together. At that time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container and arranged vertically so that the solution was in contact with both sides of the substrate. Thereafter bismuth was added on the substrate by subjecting it to immersion treatment at 30° C. for 1 hour. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to obtain an LDH-like compound separator with bismuth added thereon.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C4 except that the time of immersion treatment was changed to 12 hours in bismuth addition by the immersion treatment described above.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C4 except that the time of immersion treatment was changed to 24 hours in bismuth addition by the immersion treatment described above.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the preparation of the raw material aqueous solution (II) in (5) above was carried out as follows, and calcium was added by immersion treatment as follows instead of (6) above.
Calcium nitrate tetrahydrate (Ca(NO3)2▪4H2O) was prepared as the raw material. The calcium nitrate tetrahydrate was weighed so that it would be 0.015 mol/L and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution (II).
In a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel), the raw material aqueous solution (II) and the LDH-like compound separator obtained in (4) above were enclosed together. At that time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container and arranged vertically so that the solution was in contact with both sides of the substrate. Thereafter calcium was added on the substrate by subjecting it to immersion treatment at 30° C. for 6 hours. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to obtain an LDH-like compound separator with calcium added thereon.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the preparation of the raw material aqueous solution (II) in (5) above was carried out as follows, and strontium was added by immersion treatment as follows instead of (6) above.
Strontium nitrate (Sr(NO3)2) was prepared as the raw material. The strontium nitrate was weighed so that it would be 0.015 mol/L and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution (II).
In a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel), the raw material aqueous solution (II) and the LDH-like compound separator obtained in (4) above were enclosed together. At that time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container and arranged vertically so that the solution was in contact with both sides of the substrate. Thereafter strontium was added on the substrate by subjecting it to immersion treatment at 30° C. for 6 hours. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to obtain an LDH-like compound separator with strontium added thereon.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example C1 except that the preparation of the raw material aqueous solution (II) in (5) above was carried out as follows, and barium was added by immersion treatment as follows instead of (6) above.
Barium nitrate (Ba(NO3)2) was prepared as the raw material. The barium nitrate was weighed so that it would be 0.015 mol/L and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution (II).
In a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel), the raw material aqueous solution (II) and the LDH-like compound separator obtained in (4) above were enclosed together. At that time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container and arranged vertically so that the solution was in contact with both sides of the substrate. Thereafter barium was added on the substrate by subjecting it to immersion treatment at 30° C. for 6 hours. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to obtain an LDH-like compound separator with barium added thereon.
[Table 3]
Examples D1 and D2 shown below are reference examples for LDH-like compound separators. The method for evaluating the LDH-like compound separators produced in the following examples was the same as in Examples B1 to B8, except that the composition ratio (atomic ratio) of Mg: Al: Ti: Y: In was calculated in Evaluation 3.
A commercially available polyethylene microporous membrane having a porosity of 50%, an average pore diameter of 0.1 µm, and a thickness of 20 µm was prepared as a polymer porous substrate and cut out to a size of 2.0 cm × 2.0 cm.
A titanium dioxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.), an yttrium sol, and an amorphous alumina solution (AI-ML15, manufactured by Taki Chemical Co. Ltd.) were mixed so that Ti/(Y + Al) (molar ratio) = 2, and Y/AI (molar ratio) = 8. The substrate prepared in (1) above was coated with the mixed solution by dip coating. The dip coating was carried out by dipping the substrate into 100 ml of the mixed solution, pulling up the coating substrate vertically, and allowing it to dry for 3 hours at room tem perature.
As the raw materials, magnesium nitrate hexahydrate (Mg(NO3)2 •6H2O, manufactured by Kanto Chemical Co., Inc.), indium sulfate n-hydrate (In(SO4)3 •nH2O, manufactured by FUJIFILM Wako Pure Chemicals Corporation), and urea ((NH2)2CO, manufactured by Sigma-Aldrich Co. LLC) were prepared. Magnesium nitrate hexahydrate, indium sulfate n-hydrate, and the urea were weighed so as to adjust the concentrations thereof to 0.0075 mol/L, 0.0075 mol/L, and 1.44 mol/L, respectively and placed in a beaker, to which ion-exchanged water was added to make a total volume 75 ml. The resulting solution was stirred to obtain a raw material aqueous solution.
Both the raw material aqueous solution and the dip-coated substrate were sealed in a Teflon® airtight container (autoclave container having a content of 100 ml and an outer side jacket made of stainless steel). At this time, a substrate was fixed while being floated from the bottom of the Teflon® airtight container, and installed vertically so that the solution was in contact with both sides of the substrate. Thereafter, an LDH-like compound was formed on the surface and the inside of the substrate by subjecting it to hydrothermal treatment at a hydrothermal temperature of 120° C. for 22 hours. With an elapse of the predetermined time, the substrate was taken out from the airtight container, washed with ion-exchanged water, and dried at 70° C. for 10 hours to allow for forming of a functional layer including an LDH-like compound and In(OH)3 inside pores of the porous substrates. Thus, an LDH-like compound separator was obtained.
The LDH-like compound separator was sandwiched between a pair of PET films (Lumiler® manufactured by Toray Industries, Inc., thickness of 40 µm), and roll-pressed 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-like compound separator.
Evaluations 1 to 8 were conducted for the LDH-like compound separators obtained. The results were as follows.
An LDH-like compound separator was fabricated and evaluated in the same manner as in Example D1 except that the titania-yttria sol coating was carried out as follows instead of (2) above.
A titanium dioxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) and an yttrium sol were mixed so that Ti/Y (molar ratio) = 2. The substrate prepared in (1) above was coated with the obtained mixed solution by dip coating. The dip coating was carried out by dipping the substrate into 100 ml of the mixed solution, pulling up the coating substrate vertically, and allowing it to dry for 3 hours at room temperature.
[Table 4]
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-199924 | Dec 2020 | JP | national |
This application is a Continuation Application of PCT/JP2021/030376 filed Aug. 19, 2021, which claims priority to Japanese Patent Application No. 2020-199924 filed Dec. 1, 2020, the entire contents all of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/030376 | Aug 2021 | WO |
| Child | 18167176 | US |
