JP7017445B2 - Negative electrode structure for zinc secondary battery - Google Patents

Description

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

In zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates in the form of dendrite from the negative electrode during charging and reaches the positive electrode through the voids of the separator such as non-woven fabric. It is known to cause short circuits. Such a short circuit caused by zinc dendrite shortens the repeated charge / discharge life.

To address the above problems, a battery provided with a layered double hydroxide (LDH) separator that selectively permeates hydroxide ions and blocks the penetration of zinc dendrites has been proposed. For example, Patent Document 1 (International Publication No. 2013/118561) discloses that an LDH separator is provided between a positive electrode and a 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 bonded to a resin outer frame, and the LDH separator is gas impermeable and has a gas impermeable property. / Or it is disclosed that it has a high degree of density enough to have water impermeableness. The document also discloses that LDH separators can be composited with porous substrates. Further, Patent Document 3 (International Publication No. 2016/067884) discloses various methods for forming an LDH dense film on the surface of a porous substrate to obtain a composite material (LDH separator). In this method, a starting substance that can give a starting point for LDH crystal growth is uniformly adhered to the porous substrate, and the porous substrate is subjected to hydrothermal treatment in an aqueous solution of the raw material to form an LDH dense film on the surface of the porous substrate. It includes a step of forming the above.

International Publication No. 2013/118561 International Publication No. 2016/076047 International Publication No. 2016/067884

When a zinc secondary battery such as a nickel-zinc battery is configured by using the LDH separator as described above, a short circuit or the like due to zinc dendrite can be prevented. Then, in order to maximize this effect, it is desired to surely isolate the positive electrode and the negative electrode with an LDH separator. In particular, it is extremely convenient if a laminated battery can be easily assembled by combining a plurality of positive electrodes and a plurality of negative electrodes in order to obtain a high voltage and a large current while ensuring such a configuration. However, in the conventional zinc secondary battery, the positive electrode and the negative electrode are separated by the LDH separator, and the LDH separator and the battery container are cleverly and carefully sealed and joined by using a resin frame or an adhesive so as to ensure liquidtightness. This was done by doing so, and the battery configuration and manufacturing process tended to be complicated. Such complexity of the battery configuration and the manufacturing process can be particularly remarkable when constructing a laminated battery. This is because it is necessary to perform sealing bonding for ensuring liquidtightness for each of the plurality of cells constituting the laminated battery.

Therefore, as shown in FIG. 10, both sides of the negative electrode active material layer 112 are completely covered with a pair of LDH separators 114, and the ends of the pair of LDH separators 114 are sealed to form an LDH separator. It is conceivable to manufacture a zinc secondary battery (particularly its laminated battery) capable of preventing the spread of zinc dendrite by eliminating the need for complicated sealing and joining with the battery container, with extremely simple and high productivity. Since the negative electrode structure 110 having such a configuration is entirely covered with the LDH separator 114, the negative electrode structure 110 itself can be provided with a function of preventing a short circuit due to zinc dendrite. There are advantages. On the other hand, as shown in FIG. 10, a surplus space E is formed between the LDH separator 114 and the negative electrode active material layer 112 in the vicinity of the sealing end 114b of the LDH separator 114. This is due to the distance D between the sealing end 114b and the end face of the negative electrode active material layer 112 on the surplus space E side. If the surplus space E is large, not only the battery housing becomes large and the volume energy density decreases, but also a large amount of zinc dendrite precipitation is allowed in the surplus space E.

The present inventors have now covered the entire negative electrode active material layer with a pair of LDH separators whose ends are sealed, thereby eliminating the need for complicated sealing and bonding between the LDH separator and the battery container, and zinc. It has been found that it is possible to provide a negative electrode structure capable of producing a zinc secondary battery (particularly its laminated battery) capable of preventing dendrite extension very easily and with high productivity. In addition, by giving the outer edge of the negative electrode active material layer near the sealing end a tapered cross-sectional shape and adapting the LDH separator to that shape, the excess space in the negative electrode structure can be significantly reduced, i. ) It was found that it is possible to reduce the size of the battery housing and thereby improve the volumetric energy density, ii) suppress the precipitation of zinc dendrite in the surplus space, and / or ii) reduce the amount of separator material used.

Therefore, one object of the present invention is to make a zinc secondary battery (particularly its laminated battery) capable of preventing zinc dendrite extension by eliminating the complicated sealing joint between the LDH separator and the battery container, which is extremely simple and expensive. It is an object of the present invention to provide a negative electrode structure which can be manufactured with productivity. Another object of the present invention is to significantly reduce the surplus space in the negative electrode structure, i) downsize the battery housing and thereby improve the volumetric energy density, and ii) suppress the precipitation of zinc dendrite in the surplus space. , And / or iii) The purpose is to reduce the amount of separator material used.

According to one aspect of the present invention, it is a negative electrode structure for a zinc secondary battery.
A negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds, and
A pair of layered double hydroxide (LDH) separators that completely cover both sides of the negative electrode active material layer and have a surplus portion extending beyond the end of the negative electrode active material layer.
Equipped with
At least one side of the outer edge of the pair of LDH separators is sealed to form a sealing end.
At least one side of the outer edge of the negative electrode active material layer close to the sealing end has a tapered cross-sectional shape whose thickness decreases toward the outer edge of the negative electrode active material layer.
The excess portion of the pair of LDH separators and the vicinity thereof are configured to fit the tapered cross-sectional shape, and the separation distance of the pair of LDH separators decreases toward the sealing end. , Negative electrode structure is provided.

According to another aspect of the present invention, a zinc secondary battery comprising a positive electrode, the negative electrode structure, and an electrolytic solution, wherein the positive electrode and the negative electrode active material layer are separated from each other via the LDH separator. Is provided.

It is a schematic cross-sectional view which shows an example of the sealing end of the negative electrode structure of this invention. It is a schematic cross-sectional view which shows another example of the sealing end of the negative electrode structure of this invention. It is a schematic cross-sectional view which shows still another example of the sealing end of the negative electrode structure of this invention. It is a perspective view which shows an example of the negative electrode structure of this invention. It is a schematic cross-sectional view which shows the layer structure of the negative electrode structure shown in FIG. 4A. It is a schematic diagram for demonstrating the region covered with LDH separator in an example of the negative electrode structure of this invention. It is a schematic cross-sectional view which shows the electrochemical measurement system used in Example 1. FIG. It is an exploded perspective view of the closed container for measurement used in the precision determination test of Example 1. FIG. It is a schematic cross-sectional view of the measurement system used in the precision determination test of Example 1. FIG. It is a conceptual diagram which shows an example of the He permeability measurement system used in Example 1. FIG. FIG. 8A is a schematic cross-sectional view of a sample holder used in the measurement system shown in FIG. 8A and its peripheral configuration. 6 is an SEM image showing a cross-sectional microstructure of the LDH separator produced in Example 1. It is a schematic cross-sectional view which shows an example of the sealing end of the negative electrode structure which has not been improved by this invention.

Negative electrode structure The negative electrode structure of the present invention is used for a zinc secondary battery. FIG. 1 shows an example of the negative electrode structure of the present invention. The negative electrode structure 10 shown in FIG. 1 includes a negative electrode active material layer 12 and a pair of layered double hydroxide (LDH) separators 14. In the present specification, the "LDH separator" is defined as a separator containing LDH, which selectively passes hydroxide ions by utilizing the hydroxide ion conductivity of LDH. The negative electrode active material layer 12 contains at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds. The pair of LDH separators 14 has a surplus portion 14a that covers both sides of the negative electrode active material layer 12 as a whole and extends beyond the end portion of the negative electrode active material layer 12. At least one side of the outer edge of the pair of LDH separators 14 is sealed to form a sealing end 14b, and at least one side of the outer edge of the negative electrode active material layer 12 adjacent to the sealing end 14b is the negative electrode active material layer 12. It has a tapered cross-sectional shape whose thickness decreases toward the outer edge of the. Then, the separation distance of the pair of LDH separators 14 decreases toward the sealing end 14b so that the surplus portion 14a of the pair of LDH separators 14 and its vicinity conform to (or follow) the tapered cross-sectional shape. It is configured as follows. By covering the entire negative electrode active material layer 12 with a pair of LDH separators 14 whose ends are sealed in this way, the zinc dendrite extension eliminates the need for complicated sealing and bonding between the LDH separator and the battery container. It is possible to provide a negative electrode structure capable of producing a zinc secondary battery (particularly, a laminated battery thereof) capable of preventing the above-mentioned problems very easily and with high productivity. Further, by giving the outer edge of the negative electrode active material layer 12 near the sealing end a tapered cross-sectional shape and adapting the LDH separator 14 to that shape, the excess space in the negative electrode structure 10 is significantly reduced. , I) It is possible to realize miniaturization of the battery housing and thereby improvement of the volumetric energy density, ii) suppression of zinc dendrite precipitation in the surplus space, and / or iii) reduction of the amount of the separator material used.

That is, as described above, the separation of the positive electrode and the negative electrode by the LDH separator in the conventional zinc secondary battery is skillfully and carefully performed by using a resin frame, an adhesive or the like so as to secure the liquidtightness between the LDH separator and the battery container. This is done by sealing and joining to the battery, which tends to complicate the battery configuration and manufacturing process. Such complexity of the battery configuration and the manufacturing process can be particularly remarkable when constructing a laminated battery. In this respect, in the negative electrode structure 10 of the present invention, since both sides of the negative electrode active material layer 12 are entirely covered with a pair of LDH separators 14, the negative electrode structure 10 itself prevents short circuits due to zinc dendrites. It has a function that can be done. Moreover, if the electrolytic solution is injected into the negative electrode structure 10, the negative electrode chamber of the zinc secondary battery can be easily configured in a form capable of preventing the extension of zinc dendrite. Therefore, when the negative electrode structure 10 of the present invention is adopted for manufacturing a zinc secondary battery, the positive electrode and the negative electrode can be separated by the LDH separator only by laminating the positive electrode plate and the negative electrode structure. In particular, when manufacturing a laminated battery including a plurality of cells, it can be said that it is extremely advantageous in that a desired configuration can be realized only by alternately laminating the positive electrode plate and the negative electrode structure. This is because the clever and elaborate sealing joint that has been conventionally performed to separate the positive electrode and the negative electrode with the LDH separator becomes unnecessary.

However, even with the above configuration, as described above with reference to FIG. 10, the negative electrode structure 110 simply covers both sides of the negative electrode active material layer 112 with a pair of LDH separators 114 as a whole. In the case of the above case, a surplus space E is formed between the LDH separator 114 and the negative electrode active material layer 112 in the vicinity of the sealing end 114b of the LDH separator 114. If the surplus space E is large, not only the battery housing becomes large and the volume energy density decreases, but also a large amount of zinc dendrite precipitation is allowed in the surplus space E. On the other hand, in the negative electrode structure 10 of the present invention, as shown in FIG. 1, at least one side of the outer edge of the negative electrode active material layer 12 near the sealing end 14b faces the outer edge of the negative electrode active material layer 12. It has a tapered cross-sectional shape with a reduced thickness. Then, the surplus portion 14a of the pair of LDH separators 14 and its vicinity are configured to fit the tapered cross-sectional shape, and the separation distance of the pair of LDH separators 14 is configured to decrease toward the sealing end 14b. ing. By doing so, the distance D between the sealing end 14b and the end surface of the negative electrode active material layer 12 on the surplus space E side is shortened, and the surplus space E can be significantly reduced. Then, the battery housing can be miniaturized by the amount that the surplus space E in the negative electrode structure 10 is reduced, and the volume energy density can be improved as the battery housing is miniaturized. Further, as the surplus space E becomes smaller, the room for the amount of zinc dendrite to precipitate and grow in the surplus space E is minimized, and as a result, the precipitation of zinc dendrite in the negative electrode structure 10 can be suppressed. Further, the smaller the surplus space E, the smaller the amount of the LDH separator 14 required to partition the surplus space E, so that the amount of the separator material used can be reduced.

According to a preferred embodiment of the present invention, the tapered cross-sectional shape and each cross-sectional shape of the pair of LDH separators 14 corresponding to the tapered cross-sectional shape are formed by compression of the end portion of the laminated portion of the LDH separator 14 and the negative electrode active material layer 12. It is preferable that the surplus space E formed by the surplus portion of the LDH separator 14 and the end portion of the negative electrode active material layer 12 is minimized. By doing so, it is possible to preferably realize the minimization of the surplus space E by an extremely simple method of compressioning the end portion. Further, by minimizing the surplus space E in this way, the above-mentioned advantages of i), ii) and iii) can be realized even more effectively. The compression of the end portion may be performed by a known method such as sandwiching the end portion between a pair of plates and pressing the end portion, and is not particularly limited.

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

As the zinc alloy, a mercury- and lead-free zinc alloy known as a non-mercury zinc alloy can be used. For example, a zinc alloy containing 0.01 to 0.06% by mass of indium, 0.005 to 0.02% by mass of bismuth, and 0.0035 to 0.015% by mass of aluminum has an effect of suppressing hydrogen gas generation. Therefore, it is preferable. In particular, indium and bismuth are advantageous in improving discharge performance. When the zinc alloy is used for the negative electrode, the self-dissolution rate in the alkaline electrolytic solution is slowed down, so that the generation of hydrogen gas can be suppressed and the safety can be improved.

The shape of the negative electrode material is not particularly limited, but it is preferably in the form of powder, which increases the surface area and makes it possible to cope with a large current discharge. In the case of a zinc alloy, the average particle size of the preferred negative electrode material is in the range of 90 to 210 μm, and if it is within this range, the surface area is large, so that it is suitable for dealing with a large current discharge, and also with an electrolytic solution and a gelling agent. It is easy to mix evenly and is easy to handle when assembling the battery.

As shown in FIGS. 4A and 4B, it is preferable that the negative electrode structure 10 further includes a current collector 13 in contact with the negative electrode active material layer 12. In particular, the current collector 13 preferably has a current collector extending portion 13a extending from one side of the negative electrode active material layer 12, and the tip portion of the current collector extending portion 13a is not covered with the LDH separator 14. It is preferable to form an exposed portion (however, the sealed side is a side that does not contact the current collector extending portion 13a). As a result, the current collector 13 (particularly, the current collector extending portion 13a) can be preferably connected to the negative electrode terminal (not shown) via the exposed portion. In this case, as shown in FIG. 5, the LDH separator 14 covers or wraps the negative electrode active material layer 12 with a predetermined margin M so as to sufficiently hide the end portion of the current collector extending portion 13a on the current collector extending portion 13a side. preferable. By doing so, it is possible to more effectively prevent the spread of zinc dendrite from the end portion of the negative electrode active material layer 12 on the current collector extending portion 13a side or its vicinity.

Preferred examples of the negative electrode current collector 13 include a copper foil, a copper expanded metal, and a copper punching metal, and a copper expanded metal is more preferable. In this case, for example, a mixture containing zinc oxide powder and / or zinc powder and, if desired, a binder (for example, polytetrafluoroethylene particles) is applied onto the copper expanded metal, and the negative electrode is composed of a negative electrode / negative electrode current collector. The plate can be preferably manufactured. At that time, it is also preferable to press the negative electrode plate (that is, the negative electrode / negative electrode current collector) after drying to prevent the electrode active material from falling off and to improve the electrode density.

As shown in FIGS. 4A and 4B, the negative electrode structure 10 further includes a liquid retaining member 16 that is interposed between the negative electrode active material layer 12 and the LDH separator 14 and that covers or encloses the entire negative electrode active material layer 12. It is preferable to prepare. By doing so, the electrolytic solution can be evenly present between the negative electrode active material layer 12 and the LDH separator 14, and hydroxide ions can be exchanged between the negative electrode active material layer 12 and the LDH separator 14. It can be done efficiently.

The liquid-retaining member 16 is not particularly limited as long as it can hold the electrolytic solution, but is preferably a sheet-shaped member. Preferred examples of the liquid-retaining member include a non-woven fabric, a water-absorbent resin, a liquid-retaining resin, a porous sheet, and various spacers, but a non-woven fabric is particularly preferable in that a negative electrode structure 10 having good performance can be produced at low cost. be. The liquid-retaining member 16 preferably has a thickness of 0.01 to 0.20 mm, more preferably 0.02 to 0.20 mm, still more preferably 0.02 to 0.15 mm, and particularly preferably 0.02 to 0.15 mm. It is 0.02 to 0.10 mm, most preferably 0.02 to 0.06 mm. When the thickness is within the above range, a sufficient amount of electrolytic solution can be held in the liquid retaining member 16 while keeping the overall size of the negative electrode structure 10 compact without waste.

Although the liquid-retaining member 16 is drawn as a size smaller than the LDH separator 14 in FIGS. 4A and 4B, the liquid-retaining member 16 may have the same size as the LDH separator 14, and the outer edge of the liquid-retaining member 16 is an LDH separator. 14 outer edges can be reached. That is, the outer peripheral portion of the liquid retaining member 16 may be sandwiched between the LDH separators 14 constituting the outer peripheral portion. By doing so, the outer edge sealing of the LDH separator 14, which will be described later, can be effectively performed by heat welding or ultrasonic welding. That is, rather than directly heat-welding or ultrasonic welding the LDH separators 14, the LDH separators 14 are indirectly heat-welded or ultrasonically welded by interposing a heat-welding liquid-retaining member 16 between them. As a result of being able to utilize the heat welding property of the liquid retaining member 16 itself, more effective sealing can be performed. For example, the end portion of the liquid retaining member 16 to be sealed can be used as if it were a hot melt adhesive. Preferred examples of the liquid-retaining member 16 in this case include a non-woven fabric, particularly a non-woven fabric made of a thermoplastic resin (for example, polyethylene or polypropylene).

The LDH separator 14 preferably contains LDH and a porous substrate made of a polymer material. Then, it is preferable that LDH closes the pores of the porous substrate so that the LDH separator 14 exhibits hydroxide ion conductivity and gas impermeableness. LDH is preferably incorporated over the entire thickness direction of the porous substrate. The thickness of the LDH separator 14 is preferably 5 to 200 μm, more preferably 5 to 100 μm, and even more preferably 5 to 30 μm.

That is, the LDH separator 14 is a separator containing a layered double hydroxide (LDH), and when incorporated in a zinc secondary battery, separates a positive electrode plate and a negative electrode plate so that hydroxide ions can be conducted. .. That is, the LDH separator 14 functions as a hydroxide ion conduction separator. The preferred LDH separator 14 has gas impermeable and / or water impermeable. In other words, the LDH separator 14 is preferably densified to have gas impermeableness and / or water impermeableness. As described in Patent Documents 2 and 3, "having gas impermeable" in the present specification means that helium gas is brought into contact with one side of an object to be measured in water with a differential pressure of 0.5 atm. However, it means that no bubbles are generated due to helium gas from the other side. Further, in the present specification, "having water impermeable" means that water in contact with one side of the object to be measured does not permeate to the other side as described in Patent Documents 2 and 3. .. That is, the fact that the LDH separator 14 has gas impermeableness and / or water impermeableness means that the LDH separator 14 has a high degree of porosity to the extent that gas or water does not pass through, and is water permeable or gas. It means that it is not a permeable porous film or other porous material. By doing so, the LDH separator 14 selectively passes only hydroxide ions due to its hydroxide ion conductivity, and can exhibit a function as a battery separator. Therefore, the configuration is extremely effective in physically preventing the penetration of the separator by the zinc dendrite generated during charging to prevent a short circuit between the positive and negative electrodes. Since the LDH separator 14 has hydroxide ion conductivity, it is possible to efficiently move the required hydroxide ion between the positive electrode plate and the negative electrode plate, and to realize the charge / discharge reaction in the positive electrode plate and the negative electrode plate. Can be done.

The LDH separator 14 preferably has a He permeability per unit area of 10 cm / min · atm or less, more preferably 5.0 cm / min · atm or less, and further preferably 1.0 cm / min · atm or less. .. A separator having a He permeability of 10 cm / min · atm or less can extremely effectively suppress the permeation of Zn (typically the permeation of zinc ion or zinc acid ion) in the electrolytic solution. As described above, it is considered in principle that the separator of this embodiment can effectively suppress the growth of zinc dendrite when used in a zinc secondary battery by significantly suppressing Zn permeation. The He permeability is determined through a step of supplying He gas to one surface of the separator and allowing the He gas to permeate through the separator, and a step of calculating the He permeability and evaluating the denseness of the hydroxide ion conduction separator. Be measured. The He permeability is determined by the formula of F / (P × S) using the permeation amount F of the He gas per unit time, the differential pressure P applied to the separator when the He gas permeates, and the membrane area S through which the He gas permeates. calculate. By evaluating the gas permeability using He gas in this way, it is possible to evaluate the presence or absence of denseness at an extremely high level, and as a result, substances other than hydroxide ions (particularly zinc dendrite growth) can be evaluated. It is possible to effectively evaluate a high degree of fineness such that the causing Zn) is not permeated as much as possible (only a very small amount is permeated). This is because He gas has the smallest structural unit among the various atoms or molecules that can compose the gas, and its reactivity is extremely low. That is, He constitutes He gas by a single He atom without forming a molecule. In this respect, since hydrogen gas is composed of H ₂ molecules, the He atom alone is smaller as a gas constituent unit. In the first place, H ₂ gas is dangerous because it is a flammable gas. Then, by adopting the index of He gas permeability defined by the above formula, it is possible to easily perform an objective evaluation of the fineness regardless of the difference in various sample sizes and measurement conditions. In this way, it is possible to easily, safely and effectively evaluate whether or not the separator has sufficiently high density suitable for a separator for a zinc secondary battery. The measurement of He permeability can be preferably performed according to the procedure shown in Evaluation 7 of Example 1 described later.

As is generally known, LDH is composed of a plurality of hydroxide basic layers and an intermediate layer interposed between the plurality of hydroxide basic layers. The basic hydroxide layer is mainly composed of metal elements (typically metal ions) and OH groups. The middle layer of LDH is composed of anions and _H2O . The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anions in ^LDH contain OH ^- and / or CO _3-2- . LDH also has excellent ionic conductivity due to its unique properties.

In general, LDH is M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ^n- _{x / n} · mH ₂ O (in the formula, M ²⁺ is a divalent cation and M ³⁺ is a trivalent cation. It is a 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). It is known as a representative. In the above basic composition formula, M ²⁺ can be any divalent cation, but preferred examples include Mg ²⁺ , Ca ²⁺ and Zn ²⁺ , and more preferably Mg ²⁺ . M ³⁺ can be any trivalent cation, with preferred examples being Al ³⁺ or Cr ³⁺ , more preferably Al ³⁺ . An _- can be any anion, but preferred examples include ^{OH- and} CO ^32- . Therefore, in the above basic composition formula, it is preferable that M ²⁺ contains ^{Mg 2+} , M ³⁺ contains Al ³⁺ , and An − contains OH ⁻ and / or CO ₃ ^2- . n is an integer of 1 or more, but is preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is any number that means the number of moles of water and is a real number greater than or equal to 0, typically greater than or equal to 0 or greater than or equal to 1. However, the above-mentioned basic composition formula is merely a formula of the "basic composition" generally exemplified with respect to LDH, and the constituent ions can be appropriately replaced. For example, in the above basic composition formula, a part or all of M ³⁺ may be replaced with a cation having a valence of 4 or more, and in that case, the coefficient x / ⁿ of the anion An − in the above general formula may be replaced. May be changed as appropriate.

For example, the hydroxide basic layer of LDH may be composed of Ni, Ti, OH groups and optionally unavoidable impurities. The intermediate layer of LDH is composed of anions and _H2O as described above. The alternating laminated structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the generally known LDH alternating laminated structure, but the LDH of this embodiment mainly contains the hydroxide basic layer of LDH as Ni. By being composed of Ti and OH groups, excellent alkali resistance can be exhibited. The reason is not necessarily clear, but it is considered that LDH of this embodiment does not intentionally or positively add an element (for example, Al) that is considered to be easily eluted in an alkaline solution. Nevertheless, LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH can take the form of nickel ions. Nickel ions in LDH are typically considered to be Ni ²⁺ , but are not particularly limited as other valences such as Ni ³⁺ are possible. Ti in LDH can take the form of titanium ions. Titanium ions in LDH are typically considered to be Ti ⁴⁺ , but are not particularly limited as other valences such as Ti ³⁺ are possible. The unavoidable impurity is an arbitrary element that can be unavoidably mixed in the production method, and can be mixed in LDH, for example, derived from a raw material or a base material. As mentioned above, since the valences of Ni and Ti are not always fixed, it is impractical or impossible to specify LDH strictly by a general formula. Assuming that the basic hydroxide layer is mainly composed of Ni ²⁺ , Ti ⁴⁺ and OH groups, the corresponding LDH can be expressed as the general formula: Ni ²⁺ _1-x Ti ⁴⁺ _x (OH) ₂ ^An . ⁻ _{2x / n} · mH ₂ O (in the formula, An − is an n-valent anion, ⁿ is an integer of 1 or more, preferably 1 or 2, 0 <x <1, preferably 0.01 ≦ x. ≤0.5, m is a real number greater than or equal to 0, typically greater than or equal to 0 or greater than or equal to 1). However, the above general formula should be understood as "basic composition" to the extent that elements such as Ni ²⁺ and Ti ⁴⁺ do not impair the basic characteristics of LDH, and other elements or ions (other values of the same element). It should be understood as replaceable with a number of elements or ions or elements or ions that are unavoidably mixed in the process.

Alternatively, the hydroxide basic layer of LDH may contain Ni, Al, Ti and OH groups. The intermediate layer is composed of anions and _H2O as described above. The alternating laminated structure of the hydroxide basic layer and the intermediate layer itself is basically the same as the generally known LDH alternating laminated structure, but in the LDH of this embodiment, the hydroxide basic layer of LDH is made of Ni, Al. By being composed of a predetermined element or ion containing Ti and OH groups, excellent alkali resistance can be exhibited. The reason is not necessarily clear, but LDH in this embodiment is thought to be because Al, which was conventionally thought to be easily eluted in an alkaline solution, becomes difficult to elute in an alkaline solution due to some interaction with Ni and Ti. Be done. Nevertheless, LDH of this embodiment can also exhibit high ionic conductivity suitable for use as a separator for an alkaline secondary battery. Ni in LDH can take the form of nickel ions. Nickel ions in LDH are typically considered to be Ni ²⁺ , but are not particularly limited as other valences such as Ni ³⁺ are possible. Al in LDH can take the form of aluminum ions. Aluminum ions in LDH are typically considered to be Al ³⁺ , but are not particularly limited as other valences are possible. Ti in LDH can take the form of titanium ions. Titanium ions in LDH are typically considered to be Ti ⁴⁺ , but are not particularly limited as other valences such as Ti ³⁺ are possible. The hydroxide basic layer may contain other elements or ions as long as it contains Ni, Al, Ti and OH groups. However, the hydroxide basic layer preferably contains Ni, Al, Ti and OH groups as main components. That is, it is preferable that the hydroxide basic layer is mainly composed of Ni, Al, Ti and OH groups. Therefore, the hydroxide basic layer is typically composed of Ni, Al, Ti, OH groups and, in some cases, unavoidable impurities. The unavoidable impurity is an arbitrary element that can be unavoidably mixed in the production method, and can be mixed in LDH, for example, derived from a raw material or a base material. As mentioned above, since the valences of Ni, Al and Ti are not always fixed, it is impractical or impossible to specify LDH strictly by a general formula. Assuming that the basic hydroxide layer is mainly composed of Ni ²⁺ , Al ³⁺ , Ti ⁴⁺ and OH groups, the corresponding LDH can be expressed as the general formula: Ni ²⁺ _1-xy Al ³⁺ _x Ti. ^{4 +} _y (OH) ₂ A ^n- _{(x + 2y) / n} · mH ₂ O (In the formula, An- is an n-valent anion, ⁿ is an integer of 1 or more, preferably 1 or 2, and 0 <x. <1, preferably 0.01 ≦ x ≦ 0.5, 0 <y <1, preferably 0.01 ≦ y ≦ 0.5, 0 <x + y <1, m is 0 or more, typically 0. It can be represented by a basic composition (which is a real number greater than or equal to 1). However, the above general formula should be understood as "basic composition" to the extent that elements such as Ni ²⁺ , Al ³⁺ , and Ti ⁴⁺ do not impair the basic characteristics of LDH, and other elements or ions (of the same element). It should be understood as replaceable with elements or ions of other valences or elements or ions that can be unavoidably mixed in the process.

It goes without saying that the porous substrate has water permeability and gas permeability, and therefore, when incorporated into a zinc secondary battery, the electrolytic solution can reach LDH, but the porous substrate is This makes it possible for the LDH separator 14 to stably retain hydroxide ions. Further, since the strength can be imparted by the porous substrate, the LDH separator 14 can be thinned to reduce the resistance.

The porous substrate is preferably composed of a polymer material. The polymer porous substrate has 1) flexibility (hence, it is hard to break even if it is thin), 2) easy to increase the porosity, and 3) easy to increase the conductivity (thickness while increasing the porosity). It has the advantages of being easy to manufacture and handle) (because it can be made thinner). Further, taking advantage of the flexibility of 1) above, LDH separator 14 containing a porous substrate made of a polymer material can be easily sealed and bonded, thereby LDH as described later. There is also an advantage that at least one side of the outer edge of the separator 14 can be easily sealed. Preferred examples of the polymer material are polystyrene, polyether sulfone, polypropylene, epoxy resin, polyphenylene sulfide, hydrophilized fluororesin (tetrafluororesin: PTFE, etc.), cellulose, nylon, polyethylene and any combination thereof. Can be mentioned. All of the various preferable materials described above have alkali resistance as resistance to the electrolytic solution of the battery. Particularly preferable polymer materials are polyolefins such as polypropylene and polyethylene, and most preferably polypropylene, because they are excellent in heat resistance, acid resistance and alkali resistance, and are low in cost. When the porous substrate is composed of a polymer material, the LDH layer is incorporated over the entire thickness direction of the porous substrate (for example, most or almost all the pores inside the porous substrate are filled with LDH). ) Is particularly preferable. In this case, the thickness of the polymer porous substrate is preferably 5 to 200 μm, more preferably 5 to 100 μm, and even more preferably 5 to 30 μm. As such a polymer porous substrate, a microporous membrane as commercially available as a separator for a lithium battery can be preferably used, or commercially available cellophane can also be used.

The porous substrate preferably has an average pore diameter of 100 μm or less, more preferably 50 μm or less, typically 0.001 to 1.5 μm, and more typically 0.001. It is 1.25 μm, more typically 0.001 to 1.0 μm, particularly typically 0.001 to 0.75 μm, and most typically 0.001 to 0.5 μm. Within these ranges, it is possible to form an LDH separator that is dense enough to exhibit gas impermeableness while ensuring the desired water permeability and strength as a support for the porous substrate. In the present invention, the average pore diameter can be measured by measuring the longest distance of the pores based on the electron microscope image of the surface of the porous substrate. The magnification of the electron microscope image used for this measurement is 20000 times or more, and all the obtained pore diameters are arranged in order of size, and the top 15 points and the bottom 15 points are arranged in order from the average value, for a total of 30 points per field of view. The average pore diameter can be obtained by calculating the average value for two fields of view. For the length measurement, the length measurement function of SEM software, image analysis software (for example, Photoshop, manufactured by Adobe) and the like can be used.

The porous substrate preferably has a porosity of 10 to 60%, more preferably 15 to 55%, still more preferably 20 to 50%. Within these ranges, it is possible to form an LDH separator that is dense enough to exhibit gas impermeableness while ensuring the desired water permeability and strength as a support for the porous substrate. The porosity of the porous substrate can be preferably measured by the Archimedes method. However, when the porous substrate is composed of a polymer material and LDH is incorporated over the entire thickness direction of the porous substrate, the porosity of the porous substrate is preferably 30 to 60%, which is more preferable. Is 40-60%.

The method for producing the LDH separator 14 is not particularly limited, and the LDH separator 14 is produced by appropriately changing the conditions of the already known LDH-containing functional layer and the method for producing a composite material (that is, LDH separator) (see, for example, Patent Documents 1 to 3). can do. For example, (1) a porous substrate is prepared, and (2) a titanium oxide sol or an alumina / titania layer is formed by applying a titanium oxide sol or a mixed sol of alumina and titania to the porous substrate and heat-treating the mixture. (3) The porous base material is immersed in a raw material aqueous solution containing nickel ions (Ni ²⁺ ) and urea, and (4) the porous base material is hydrothermally heat-treated in the raw material aqueous solution to make the LDH-containing functional layer a porous base material. LDH-containing functional layers and composite materials (ie, LDH separators) can be produced by forming them in the top and / or the porous substrate. In particular, by forming the titanium oxide layer or the alumina / titania layer on the porous substrate in the above step (2), not only the raw material for LDH is provided, but also the porous substrate is made to function as a starting point for LDH crystal growth. The LDH-containing functional layer highly densified on the surface can be uniformly and uniformly formed. Further, in the presence of urea in the above step (3), the pH value rises due to the generation of ammonia in the solution by utilizing the hydrolysis of urea, and the coexisting metal ions form a hydroxide. Can obtain LDH. In addition, since hydrolysis is accompanied by the generation of carbon dioxide, LDH in which anions are carbonate ion can be obtained.

In particular, when a composite material (that is, an LDH separator) in which the porous base material is composed of a polymer material and the functional layer is incorporated over the entire thickness direction of the porous base material is produced, the alumina in the above (2) And, it is preferable to apply the mixed sol of titania to the substrate by a method in which the mixed sol permeates the whole or most of the inside of the substrate. By doing so, most or almost all the pores inside the porous substrate can be finally filled with LDH. Examples of the preferred coating method include a dip coat, a filtration coat and the like, and a dip coat is particularly preferable. By adjusting the number of times of application of the dip coat or the like, the amount of the mixed sol adhered can be adjusted. The base material coated with the mixed sol by a dip coat or the like may be dried and then the above steps (3) and (4) may be carried out.

Typically, the negative electrode active material layer 12 and the LDH separator 14 each have a quadrilateral shape (typically a quadrangular shape). In this case, it is preferable that at least two sides of the outer edge of the LDH separator 14 are sealed to form a sealing end 14b. By doing so, the negative electrode active material layer 12 can be reliably isolated from the positive electrode when mounted on the zinc secondary battery, and the extension of zinc dendrite can be prevented more effectively. However, when the negative electrode structure 10 has the current collector extending portion 13a, the current collector extending portion 13a can be extended, so that at least two sealed sides thereof are the current collector extending portions. It is desirable that the side does not touch the portion 13a.

By the way, one side or two sides of the outer edge of the LDH separator 14 may be open. For example, even if one upper end side of the outer edge of the LDH separator 14 is left open, if the liquid is injected so that the electrolytic solution does not reach the upper end one side at the time of manufacturing the zinc secondary battery, electrolysis is performed on the upper end one side. Since there is no liquid, problems of liquid leakage and zinc dendrite extension can be avoided. In this regard, the negative electrode structure 10 can function as a main component of the sealed zinc secondary battery by being housed together with the positive electrode in a closed container with an electrolytic solution contained therein. Therefore, since it is sufficient to secure the airtightness in the airtight container that will be finally accommodated, the negative electrode structure 10 itself can be a simple structure with an open top. Further, by opening one side of the outer edge of the LDH separator 14, the current collector extending portion 13a can be extended from there. The open outer edge 1 side for extending the current collector extending portion 13a may be the upper end 1 side that provides the upper open portion, or may be the other outer edge 1 side.

In any case, it is preferable that at least one side, preferably at least two sides, of the outer edge of the LDH separator 14 is sealed. Therefore, the three sides of the outer edge of the LDH separator 14 may be sealed. Preferred examples of the sealing method include adhesives, heat welding, ultrasonic welding, adhesive tapes, sealing tapes, and combinations thereof. For reference, FIG. 2 schematically shows the sealing end 14b ′ sealed with the sealing tape, while FIG. 3 schematically shows the sealing end 14b ″ sealed with the adhesive 15. Further, since the LDH separator 14 containing a porous substrate made of a polymer material has an advantage that it is easy to bend because it has flexibility, the LDH separator 14 is formed into a long shape and bent to form an outer edge. You may form a state equivalent to the one side of which is sealed. Heat welding and ultrasonic welding may be performed using a commercially available heat sealer or the like, but when the liquid retaining member 16 is used, the outer peripheral portion of the liquid retaining member 16 is sandwiched between the LDH separators 14 constituting the outer peripheral portion. It is preferable to perform heat welding and ultrasonic welding in this way because more effective sealing can be performed. On the other hand, as the adhesive, the adhesive tape and the sealing tape, commercially available products may be used, but those containing an alkali-resistant resin are preferable in order to prevent deterioration in the alkaline electrolytic solution. From this point of view, examples of preferable adhesives include epoxy resin adhesives, natural resin adhesives, modified olefin resin adhesives, and modified silicone resin adhesives, and among them, epoxy resin adhesives are resistant. It is more preferable because it is particularly excellent in alkalinity. Examples of product examples of the epoxy resin adhesive include the epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

In any of the above-described embodiments, the LDH separator 14 and the end portion of the negative electrode active material layer 12 have a structure in which they are in direct or indirect contact with each other, whereby the LDH separator 14 and the end portion of the negative electrode active material layer 12 are in close contact with each other. It is also possible that there is no surplus space E that allows the electrolyte to accumulate between the portions. That is, if a large amount of excess electrolytic solution is present between the LDH separator 14 and the end of the negative electrode active material layer 12, metal Zn is concentrated at the end of the negative electrode active material layer 12 (ZnO layer) during the charging reaction. During the discharge reaction, the metal Zn becomes Zn (OH) ₄₂ ^2- and diffuses to precipitate as ZnO at the center of the negative electrode, which may cause a change in the shape of the negative electrode plate. Therefore, by eliminating the surplus space E that allows the accumulation of the electrolytic solution, it is possible to effectively prevent the shape change of the negative electrode plate (particularly the negative electrode active material layer 12) due to repeated charging and discharging. A liquid retaining member 16 may be present between the LDH separator 14 and the end of the negative electrode active material layer 12 so as not to provide a surplus space E that allows the electrolytic solution to accumulate. Further, as shown in FIG. 3, even if a resin such as an adhesive 15 is filled between the LDH separator 14 and the end portion of the negative electrode active material layer 12, the surplus space E that allows the electrolytic solution to be accumulated is eliminated. good.

Zinc secondary battery The negative electrode structure of the present invention is preferably applied to a zinc secondary battery. Therefore, according to a preferred embodiment of the present invention, there is provided a zinc secondary battery comprising a positive electrode, a negative electrode structure, and an electrolytic solution, wherein the positive electrode and the negative electrode active material layer are separated from each other via an LDH separator. .. The zinc secondary battery of the present invention is not particularly limited as long as it is a secondary battery using zinc as a negative electrode and an electrolytic solution (typically an alkali metal hydroxide aqueous solution). Therefore, it can be a nickel-zinc secondary battery, a silver-zinc oxide secondary battery, a manganese zinc oxide secondary battery, an air-zinc secondary battery, and 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 may be an air zinc secondary battery.

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

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

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

(2) Alumina-titania sol coating on polymer porous substrate Atypical alumina solution (Al-ML15, manufactured by Taki Chemical Co., Ltd.) and titanium oxide sol solution (M6, manufactured by Taki Chemical Co., Ltd.) are mixed with Ti / Al (M6, manufactured by Taki Chemical Co., Ltd.). A mixed sol was prepared by mixing so that the molar ratio) = 2. The mixed sol was applied to the substrate prepared in (1) above by dip coating. Dip coating was performed by immersing the substrate in 100 ml of the mixed sol, pulling it up vertically, and drying it in a dryer at 90 ° C. for 5 minutes.

(3) Preparation of raw material aqueous solution Nickel nitrate hexahydrate (Ni (NO ₃ ) 2.6H ₂ O, manufactured by Kanto Chemical Co., Inc., and urea ((NH ₂ ) ₂ CO, manufactured by Sigma _- Aldrich)) are prepared as raw materials. Nickel nitrate hexahydrate was weighed to 0.015 mol / L and placed in a beaker, and ion-exchanged water was added thereto to make the total volume 75 ml. After stirring the obtained solution, the solution was added. Urea weighed at a ratio of urea / NO _3- ⁽ molar ratio) = 16 was added thereto, and the mixture was further stirred to obtain an aqueous raw material solution.

(4) Film formation by hydrothermal treatment A Teflon (registered trademark) closed container (autoclave container, content 100 ml, jacket made of stainless steel on the outside) was filled with the raw material aqueous solution and the dip-coated base material. At this time, the base material was floated and fixed from the bottom of a closed container made of Teflon (registered trademark), and placed horizontally so that the solution was in contact with both sides of the base material. Then, LDH 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 24 hours. After a lapse of a predetermined time, the substrate was taken out of the closed container, washed with ion-exchanged water, and dried at 70 ° C. for 10 hours to obtain LDH incorporated in the porous substrate. In this way, an LDH separator was obtained.

(5) Evaluation The obtained LDH separators were evaluated in various ways as shown below.

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

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

Evaluation 3 : Elemental analysis evaluation (EDS)
The LDH separator was polished with a cross-section polisher (CP) so that the cross-section polished surface could be observed. By FE-SEM (ULTRA55, manufactured by Carl Zeiss), a cross-sectional image of an LDH separator was acquired in one field of view at a magnification of 10000 times. Elemental analysis of the LDH film on the surface of the substrate and the LDH portion (point analysis) inside the substrate in this cross-sectional image was performed using an EDS analyzer (NORAN System SIX, manufactured by Thermo Fisher Scientific) under the condition of an acceleration voltage of 15 kV. went.

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

Evaluation 5 : Measurement of ionic conductivity The conductivity of the LDH separator in the electrolytic solution was measured as follows using the electrochemical measurement system shown in FIG. The LDH separator sample S was sandwiched between the silicone packings 40 having a thickness of 1 mm from both sides and incorporated into a PTFE flange type cell 42 having an inner diameter of 6 mm. As the electrodes 46, a nickel wire mesh of # 100 mesh was incorporated into the cell 42 in a cylindrical shape having a diameter of 6 mm so that the distance between the electrodes was 2.2 mm. As the electrolytic solution 44, a 6M KOH aqueous solution was filled in the cell 42. Using an electrochemical measurement system (potential / galvanostad-frequency response analyzer, Solartron 1287A and 1255B types), the measurement was performed under the conditions of a frequency range of 1 MHz to 0.1 Hz and an applied voltage of 10 mV, and a section of the real number axis. Was taken as the resistance of the LDH separator sample S. The same measurement as above was performed only on the porous substrate without the LDH film, and the resistance of only the porous substrate was determined. The difference between the resistance of the LDH separator sample S and the resistance of the base material alone was taken as the resistance of the LDH film. The conductivity was determined using the resistance of the LDH film and the film thickness and area of the LDH.

Evaluation 6 : Denseness determination test In order to confirm that the LDH separator has a denseness enough to exhibit gas impermeableness, a density determination test was conducted as follows. First, as shown in FIGS. 7A and 7B, an acrylic container 130 without a lid and an alumina jig 132 having a shape and size capable of functioning as a lid of the acrylic container 130 were prepared. The acrylic container 130 is formed with a gas supply port 130a for supplying gas. Further, the alumina jig 132 is formed with an opening 132a having a diameter of 5 mm, and a recess 132b for mounting a sample is formed along the outer periphery of the opening 132a. The epoxy adhesive 134 was applied to the recess 132b of the alumina jig 132, and the LDH separator sample 136 was placed in the recess 132b and adhered to the alumina jig 132 in an airtight and liquid-tight manner. Then, the alumina jig 132 to which the LDH separator sample 136 is bonded is airtightly and liquid-tightly adhered to the upper end of the acrylic container 130 using a silicone adhesive 138 so as to completely close the open portion of the acrylic container 130. A closed container 140 for measurement was obtained. The closed container 140 for measurement was placed in the water tank 142, and the gas supply port 130a of the acrylic container 130 was connected to the pressure gauge 144 and the flow meter 146 so that the helium gas could be supplied into the acrylic container 130. Water 143 was placed in the water tank 142, and the airtight container 140 for measurement was completely submerged. At this time, the inside of the airtight container 140 for measurement is sufficiently airtight and liquidtight, and one side of the LDH separator sample 136 is exposed to the internal space of the airtight container 140 for measurement, while the LDH separator sample 136. The other side of the water tank 142 is in contact with the water in the water tank 142. In this state, helium gas was introduced into the acrylic container 130 through the gas supply port 130a into the airtight container 140 for measurement. The pressure gauge 144 and the flow meter 146 are controlled so that the differential pressure inside and outside the LDH separator sample 136 is 0.5 atm (that is, the pressure applied to the side in contact with the helium gas is 0.5 atm higher than the water pressure applied to the opposite side). Then, it was observed whether or not helium gas bubbles were generated in the water from the LDH separator sample 136. As a result, when the generation of bubbles due to helium gas was not observed, it was determined that the LDH separator sample 136 had high density enough to exhibit gas impermeableness.

Evaluation 7 : He Permeation Measurement A He permeation test was conducted as follows in order to evaluate the denseness of the LDH separator from the viewpoint of He permeability. First, the He permeability measuring system 310 shown in FIGS. 8A and 8B was constructed. In the He permeability measuring system 310, He gas from a gas cylinder filled with He gas is supplied to the sample holder 316 via a pressure gauge 312 and a flow meter 314 (digital flow meter), and the LDH held in the sample holder 316. The separator 318 was configured to be permeated from one surface to the other surface and discharged.

The sample holder 316 has a structure including a gas supply port 316a, a closed space 316b, and a gas discharge port 316c, and was assembled as follows. First, the adhesive 322 was applied along the outer circumference of the LDH separator 318 and attached to a jig 324 (made of ABS resin) having an opening in the center. Packing made of butyl rubber is arranged as sealing members 326a and 326b at the upper and lower ends of the jig 324, and support members 328a and 328b (manufactured by PTFE) having an opening made of a flange from the outside of the sealing members 326a and 326b. ). 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 fastened to each other by the fastening means 330 using screws so that the He gas did not leak from the portion other than the gas discharge port 316c. A gas supply pipe 334 was connected to the gas supply port 316a of the sample holder 316 thus assembled via a joint 332.

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

(6) Evaluation results The evaluation results were as follows.
-Evaluation 1: From the obtained XRD profile, it was identified that the crystal phase contained in the LDH separator is LDH (hydrotalcite compound).
-Evaluation 2: The SEM image of the cross-sectional microstructure of the LDH separator was as shown in FIG. As can be seen from FIG. 9, it was observed that LDH was incorporated over the entire area of the porous substrate in the thickness direction, that is, the pores of the porous substrate were evenly filled with LDH.
-Evaluation 3: As a result of EDS elemental analysis, LDH constituent elements C, Al, Ti and Ni were detected from the LDH separator. That is, Al, Ti and Ni are constituent elements of the basic hydroxide layer, while C corresponds to ^{CO 32-2} _, which is an anion constituting the intermediate layer of LDH.
-Evaluation 4: No change was observed in the microstructure of the LDH separator even after being immersed in a potassium hydroxide aqueous solution at 70 ° C. for 3 to 7 weeks.
-Evaluation 5: The conductivity of the LDH separator was 2.0 mS / cm.
-Evaluation 6: It was confirmed that the LDH separator has high density so as to exhibit gas impermeableness.
-Evaluation 7: The He permeability of the LDH separator was 0.0 cm / min · atm.

10,110 Negative electrode structure 12,112 Negative electrode active material layer 13 Current collector 13a Current collector extension part 14,114 LDH separator 14a Surplus part 14b, 114b Sealing end 15 Adhesive 16 Liquid retaining member

Claims (10)

Negative electrode structure for zinc secondary batteries
A negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds, and
A pair of layered double hydroxide (LDH) separators that completely cover both sides of the negative electrode active material layer and have a surplus portion extending beyond the end of the negative electrode active material layer.
Equipped with
At least one side of the outer edge of the pair of LDH separators is sealed to form a sealing end.
At least one side of the outer edge of the negative electrode active material layer close to the sealing end has a tapered cross-sectional shape whose thickness decreases toward the outer edge of the negative electrode active material layer.
The excess portion of the pair of LDH separators and the vicinity thereof are configured to fit the tapered cross-sectional shape, and the separation distance of the pair of LDH separators decreases toward the sealing end. ,
The LDH separator contains LDH and a porous substrate made of a polymer material, and the LDH has pores in the porous substrate so that the LDH separator exhibits hydroxide ion conductivity and gas impermeableness. Negative structure that is blocking the . The tapered cross-sectional shape and each cross-sectional shape of the pair of LDH separators matching the tapered cross-sectional shape are brought about by compression of the end portion of the laminated portion between the LDH separator and the negative electrode active material layer. The negative electrode structure according to claim 1, wherein the surplus space formed by the surplus portion of the LDH separator and the end portion of the negative electrode active material layer is minimized. The negative electrode structure according to claim 1 or 2, further comprising a liquid retaining member that is interposed between the negative electrode active material layer and the LDH separator and that covers or encloses the entire negative electrode active material layer. The negative electrode structure according to claim 3, wherein the liquid-retaining member is a non-woven fabric. The negative electrode structure according to any one of claims 1 to 4, wherein the LDH is incorporated over the entire area of the porous substrate in the thickness direction. The negative electrode according to any one of claims 1 to 5 , wherein the negative electrode active material layer and the LDH separator each have a four-sided shape, and at least two sides of the outer edge of the LDH separator are sealed to form a sealing end. Structure. The negative electrode structure further includes a current collector in contact with the negative electrode active material layer, and the current collector has a collector extending portion extending from one side of the outer edge of the negative electrode active material layer. Claims 1 to 6 wherein the tip portion of the current collector extension portion forms an exposed portion that is not covered by the LDH separator, but the sealed side is a side that does not contact the current collector extension portion. The negative electrode structure according to any one of the above items. With the positive electrode
The negative electrode structure according to any one of claims 1 to 7 .
With the electrolyte
A zinc secondary battery comprising the LDH separator, wherein the positive electrode and the negative electrode active material layer are separated from each other. The zinc secondary battery according to claim 8 , wherein the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, whereby the zinc secondary battery forms a nickel-zinc secondary battery. The zinc secondary battery according to claim 8 , wherein the positive electrode is an air electrode, whereby the zinc secondary battery forms an air zinc secondary battery.

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