Zinc secondary battery

Abstract

Provided is a manganese zinc secondary battery that makes it possible to extend cycle service life. A zinc secondary battery according to the present invention comprises: a positive electrode that includes a positive electrode active material layer containing manganese dioxide; a positive electrode electrolyte in which the positive electrode is immersed; a negative electrode that includes a negative electrode active material layer containing at least one substance selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds; a negative electrode electrolyte in which the negative electrode is immersed; and a layered double hydroxide (LDH) separator including a hydroxide-ion-conductive layered compound that is a LDH and / or a LDH-like compound, the LDH separator isolating the positive electrode and the positive electrode electrolyte from the negative electrode and the negative electrode electrolyte in a manner that allows conduction of hydroxide ions. The zinc secondary battery includes a zinc ion scavenger at a position where it is possible to capture zinc ions that have been eluted from the negative electrode and reached the positive electrode electrolyte.

Description

Zinc secondary battery

[0001] The present disclosure relates to zinc secondary batteries, and in particular to manganese-zinc secondary batteries.

[0002] Alkaline manganese batteries (also called alkaline dry batteries) are widely used as primary batteries. In particular, alkaline manganese batteries that use zinc for the negative electrode and an alkaline aqueous solution for the electrolyte are widely used due to their versatility and low cost.

[0003] However, there are problems with using such manganese-zinc batteries as rechargeable secondary batteries. The discharge reaction of a manganese-zinc secondary battery is as follows, and the charge reaction is the reverse of the following: Positive electrode: MnO ２ +H ２ O+e － →MnOOH+OH － ・Negative electrode: 1 / 2 Zn+OH － →1 / 2ZnO+1 / 2H ２ O+e －

[0004] In such manganese-zinc secondary batteries, zinc ions (including zinc complexes such as zincate ions) dissolved in the electrolyte inhibit the reversible charge-discharge reaction at the positive electrode. That is, MnOOH, a discharge product at the positive electrode, reacts with zinc ions dissolved from the negative electrode to form ZnMn ２ O ４ This ZnMn ２ O ４ Since MnO has high resistance, it is ２ Therefore, repeated charge and discharge cycles cause the accumulation of high-resistance products, resulting in a decrease in capacity. This is thought to result in a shortened lifespan of manganese-zinc secondary batteries.

[0005] Therefore, zinc ions and MnO ２For example, Patent Document 1 (WO 2018 / 198607) discloses a manganese-zinc secondary battery that allows reversible charging and discharging without the use of a KOH electrolyte by including a conductive additive and a hydroxide ion-conductive inorganic solid electrolyte in the positive and negative electrodes and isolating the positive and negative electrodes with a separator containing a hydroxide ion-conductive inorganic solid electrolyte, such as a layered double hydroxide (LDH) separator.

[0006] In recent years, batteries equipped with LDH separators have also been proposed in the fields of nickel-zinc secondary batteries and air-zinc secondary batteries. For example, Patent Document 2 (WO 2013 / 118561) discloses providing an LDH separator between the positive and negative electrodes in a nickel-zinc secondary battery. Furthermore, Patent Document 3 (WO 2016 / 076047) discloses a separator structure equipped with an LDH separator fitted or joined to a resin outer frame, and discloses that the LDH separator has such high density that it is gas-impermeable and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Furthermore, Patent Document 4 (WO 2016 / 067884) discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to obtain a composite material. This method includes a step of uniformly attaching a starting substance capable of providing a starting point for LDH crystal growth to a porous substrate, and then subjecting the porous substrate to hydrothermal treatment in a raw material aqueous solution to form a dense LDH membrane on the surface of the porous substrate. LDH separators have also been proposed that achieve further densification by roll-pressing a composite material of LDH / porous substrate prepared through hydrothermal treatment. For example, Patent Document 5 (WO 2019 / 124270) discloses an LDH separator that includes a polymeric porous substrate and LDH loaded into the porous substrate, and has a linear transmittance of 1% or more at a wavelength of 1000 nm.

[0007] Furthermore, although they cannot be called LDHs, LDH-like compounds are known as hydroxides and / or oxides with a layered crystal structure similar to LDHs, and they exhibit hydroxide ion conductive properties similar enough to be collectively referred to as hydroxide ion conductive layered compounds together with LDHs. For example, Patent Document 6 (WO 2020 / 255856) discloses a hydroxide ion conductive separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate, wherein the LDH-like compound is a hydroxide and / or oxide with a layered crystal structure containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al. In addition, Patent Document 7 (WO 2021 / 229916) discloses an LDH separator using an LDH-like compound containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additional element M which is at least one selected from the group consisting of In, Bi, Ca, Sr, and Ba. Furthermore, Patent Document 8 (WO 2021 / 229917) discloses an LDH separator using an LDH-like compound and In(OH) ３ With regard to an LDH separator containing a mixture of the above, one has been disclosed in which the LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In. The separators disclosed in Patent Documents 6 to 8 are said to have superior alkali resistance compared to conventional LDH separators and to be able to more effectively suppress short circuits caused by zinc dendrites.

[0008] International Publication No. 2018 / 198607, International Publication No. 2013 / 118561, International Publication No. 2016 / 076047, International Publication No. 2016 / 067884, International Publication No. 2019 / 124270, International Publication No. 2020 / 255856, International Publication No. 2021 / 229916, International Publication No. 2021 / 229917

[0009] The manganese-zinc secondary battery disclosed in Patent Document 1 is based on the premise that it does not contain an alkaline electrolyte such as a KOH electrolyte, and as mentioned above, it is not easy to make a manganese-zinc battery that uses an electrolyte rechargeable and extend its cycle life.

[0010] The present inventors have now discovered that the cycle life of a manganese-zinc secondary battery can be extended by isolating the positive electrode electrolyte and the negative electrode electrolyte with an LDH separator and incorporating a zinc ion scavenger at a position where it can capture zinc ions that have eluted from the negative electrode and reached the positive electrode electrolyte.

[0011] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a manganese-zinc secondary battery that can extend the cycle life.

[0012] According to the present disclosure, the following aspects are provided: [Aspect 1] A zinc secondary battery comprising: a positive electrode including a positive electrode active material layer containing manganese dioxide; a positive electrode electrolyte in which the positive electrode is immersed; a negative electrode including a negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound; a negative electrode electrolyte in which the negative electrode is immersed; and an LDH separator including a hydroxide ion-conducting layered compound that is a layered double hydroxide (LDH) and / or an LDH-like compound, which separates the positive electrode and the positive electrode electrolyte from the negative electrode and the negative electrode electrolyte in a manner that allows hydroxide ions to be conducted between them, the zinc ion sequestering agent being present at a position where it can capture zinc ions that have eluted from the negative electrode and reached the positive electrode electrolyte. [Aspect 2] The zinc secondary battery according to Aspect 1, wherein the position where it can capture zinc ions is in the positive electrode electrolyte and / or a portion in contact with the positive electrode electrolyte. [Aspect 3] The zinc secondary battery according to Aspect 1 or 2, wherein the positive electrode active material layer contains the zinc ion scavenger. [Aspect 4] The zinc secondary battery according to any one of Aspects 1 to 3, wherein the positive electrode active material layer is covered or wrapped in a nonwoven fabric, and the nonwoven fabric contains the zinc ion scavenger. [Aspect 5] The zinc secondary battery according to any one of Aspects 1 to 4, wherein the positive electrode electrolyte contains the zinc ion scavenger. [Aspect 6] The zinc secondary battery according to any one of Aspects 1 to 5, wherein the zinc ion scavenger is a calcium compound and / or a bismuth compound. [Aspect 7] The zinc secondary battery according to any one of Aspects 1 to 6, wherein the zinc ion scavenger is calcium hydroxide. Aspect 8 The zinc secondary battery according to any one of Aspects 1 to 7, wherein the positive electrode active material layer, the negative electrode active material layer, and the LDH separator are each quadrilateral in shape, the positive electrode further includes a positive electrode current collector that has a positive electrode current collector tab extending from one side of the positive electrode active material layer, and the negative electrode further includes a negative electrode current collector that has a negative electrode current collector tab extending from one side of the negative electrode active material layer, the LDH separator covers or encases the entire positive electrode active material layer or the entire negative electrode active material layer, and outer edges of three sides of the LDH separator excluding one side overlapping with the positive electrode current collector tab or the negative electrode current collector tab are closed.[Aspect 9] The zinc secondary battery according to any one of Aspects 1 to 8, wherein the LDH separator further comprises a porous substrate, and the pores of the porous substrate are filled with the hydroxide ion-conducting layered compound.

[0013] 4A is a diagram conceptually showing the basic structure of the zinc secondary battery of the present invention and the zinc ion capture effect. FIG. 4B is a perspective view showing a configuration in which a quadrilateral negative electrode is covered with an LDH separator. FIG. 4C is a cross-sectional view schematically showing an electrode laminate of a zinc secondary battery. FIG. 4D is a conceptual diagram showing an example of a He permeability measurement system. FIG. 4E is a schematic cross-sectional view of a sample holder used in the measurement system shown in FIG. 4A and its surrounding configuration. FIG. 4F is a graph plotting the capacity retention rate versus the number of cycles for the zinc secondary batteries produced in Examples 1 to 4.

[0014] Zinc Secondary Battery FIG. 1 conceptually illustrates an example of a zinc secondary battery according to the present invention. The zinc secondary battery 10 shown in FIG. 1 includes a positive electrode 12, a negative electrode 14, an LDH separator 16, a positive electrode electrolyte 18, and a negative electrode electrolyte 20. The positive electrode 12 includes a positive electrode active material layer 12a. The positive electrode active material layer 12a includes manganese dioxide. The negative electrode 14 includes a negative electrode active material layer 14a. The negative electrode active material layer 14a includes at least one material selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound. Optionally, the positive electrode 12 further includes a positive electrode current collector 12b, and the negative electrode 14 further includes a negative electrode current collector 14b. The LDH separator 16 separates the positive electrode 12 and the positive electrode electrolyte 18 from the negative electrode 14 and the negative electrode electrolyte 20 in a manner that allows hydroxide ions to be conducted therebetween. The LDH separator 16 contains a hydroxide ion-conducting layered compound that is a layered double hydroxide (LDH) and / or an LDH-like compound. A preferred embodiment of the LDH separator 16 will be described later. The positive electrode 12 is immersed in the positive electrode electrolyte 18. The negative electrode 14 is immersed in the negative electrode electrolyte 20. The zinc secondary battery 10 contains a zinc ion scavenger at a position where it can capture zinc ions that have eluted from the negative electrode 14 and reached the positive electrode electrolyte 18. In this way, the positive electrode electrolyte 18 and the negative electrode electrolyte 20 are separated by the LDH separator 16, and the zinc ion scavenger is contained at a position where it can capture zinc ions that have eluted from the negative electrode 14 and reached the positive electrode electrolyte 18, thereby extending the cycle life of the zinc secondary battery.

[0015] The discharge reaction of a manganese-zinc secondary battery is as follows, and the charge reaction is the reverse of the following: Positive electrode: MnO ２ +H ２ O+e － →MnOOH+OH － ・Negative electrode: 1 / 2 Zn+OH － →1 / 2ZnO+1 / 2H ２ O+e －

[0016] As mentioned above, in manganese-zinc secondary batteries, zinc ions (including zinc complexes such as zincate ions) dissolved in the electrolyte inhibit the reversible charge-discharge reaction at the positive electrode. That is, MnOOH, a discharge product at the positive electrode, reacts with zinc ions dissolved from the negative electrode to form ZnMn ２ O ４ This ZnMn ２ O ４ Since MnO has high resistance, it is ２ Therefore, repeated charge and discharge cycles cause the accumulation of high-resistance products, resulting in a decrease in capacity. This is thought to result in a shortened lifespan of manganese-zinc secondary batteries.

[0017] In contrast, in the present invention, the LDH separator 16 separates the positive electrode electrolyte 18 from the negative electrode electrolyte 20. Therefore, as conceptually shown in FIG. 1 , the dense LDH separator 16 inhibits zinc ions dissolved in the negative electrode electrolyte 20 from migrating from the negative electrode 14 to the positive electrode electrolyte 18. However, in terms of battery design, it is practically difficult to completely separate the positive electrode electrolyte 18 from the negative electrode electrolyte 20 using the LDH separator 16. For example, if it is assumed that the negative electrode 14 is covered or wrapped with the LDH separator 16, it is difficult to completely cover or wrap the negative electrode 14 with the LDH separator 16 in order to expose the negative electrode current collecting tab 14c, as shown in FIG. 2 . Furthermore, when the LDH separator 16 is welded to the negative electrode 14, a portion of the LDH separator 16 may be damaged. Due to these factors and others, a small amount of zinc ions eluted from the negative electrode 14 permeates the LDH separator 16 and reaches the positive electrode electrolyte 18. In this regard, the zinc secondary battery 10 of the present invention includes a zinc ion trapping agent at a position where it can trap zinc ions that have reached the positive electrode electrolyte 18. Therefore, the zinc ion trapping agent traps zinc ions near the positive electrode 12 (e.g., forms a complex with the zinc ions), thereby preventing the reaction between the zinc ions and MnOOH, a discharge product at the positive electrode 12. Here, if a microporous membrane separator or the like that is permeable to zinc ions is used as the separator, zinc ions are constantly supplied from the negative electrode 14 to the positive electrode electrolyte 18, resulting in rapid depletion of the zinc ion trapping agent. In this regard, by separating the positive electrode electrolyte 18 and the negative electrode electrolyte 20 as much as possible using the LDH separator 16, zinc ions that have eluted from the negative electrode 14 and leaked into the positive electrode electrolyte 18 can be efficiently captured by the zinc ion trapping agent. As a result, it is believed that the generation of high resistance products due to repeated charge and discharge can be effectively suppressed, and the cycle life can be extended.

[0018] The position where the zinc ion trapping agent is contained in the zinc secondary battery 10 is not particularly limited as long as it is a position where zinc ions eluted from the negative electrode 14 and reached the positive electrode electrolyte 18 can be trapped. Examples of the position where the zinc ion trapping agent is provided (i.e., the position where zinc ions can be trapped) include in the positive electrode electrolyte 18 and / or a portion in contact with the positive electrode electrolyte 18. That is, the positive electrode electrolyte 18 may contain a zinc ion trapping agent, thereby trapping zinc ions in the positive electrode electrolyte 18. Alternatively, by providing the zinc ion trapping agent in a portion in contact with the positive electrode electrolyte 18, zinc ions may be trapped before the zinc ions reach the positive electrode 12 and the above-described reaction occurs. Examples of the portion in contact with the positive electrode electrolyte 18 include the positive electrode active material layer 12a, the surface of the LDH separator 16 on the positive electrode 12 side, and the surface of the exterior body in contact with the positive electrode electrolyte.

[0019] According to a preferred embodiment of the present invention, the positive electrode active material layer 12a contains a zinc ion trapping agent. This allows zinc ions to react with the zinc ion trapping agent when they reach the positive electrode 12, effectively suppressing the generation of high-resistance products and extending the cycle life. Furthermore, the zinc ion trapping agent contained in the positive electrode active material layer 12a may dissolve into the positive electrode electrolyte 18 and trap zinc ions near the positive electrode 12. The positive electrode active material layer 12a containing the zinc ion trapping agent can be preferably formed, for example, by mixing manganese dioxide, the zinc ion trapping agent, optionally a conductive additive, and a binder together with a solvent, applying the resulting mixture to the surface of the positive electrode current collector 12b, and drying the mixture.

[0020] According to another preferred embodiment of the present invention, as shown in FIG. 3 , the positive electrode active material layer 12 a is covered or wrapped with a nonwoven fabric 17, and the nonwoven fabric 17 contains a zinc ion scavenger. This allows zinc ions to be captured by the zinc ion scavenger before they reach the positive electrode 12, effectively suppressing the generation of high-resistance products and extending the cycle life. Furthermore, the zinc ion scavenger contained in the nonwoven fabric 17 may leach into the positive electrode electrolyte 18 and capture zinc ions near the positive electrode 12. In this specification, the term “nonwoven fabric” refers to a sheet-like material made by entangled fibers without weaving them, and includes not only those called nonwoven fabrics but also those called paper, regardless of the name. The method for forming the nonwoven fabric 17 containing the zinc ion scavenger is not particularly limited. For example, nonwoven fabric 17 containing a zinc ion scavenger can be preferably formed by applying a slurry containing a zinc ion scavenger to the surface of a commercially available nonwoven fabric, or by immersing the nonwoven fabric in the slurry to impregnate the nonwoven fabric with the slurry.

[0021] The zinc ion capturing agent is not particularly limited as long as it can react with zinc ions to suppress the reaction between the zinc ions and the positive electrode 12. Preferred examples of the zinc ion capturing agent include calcium compounds, bismuth compounds, and combinations thereof, and more preferably calcium hydroxide (Ca(OH) ２ ) and / or bismuth oxide (Bi ２ O ３ ), and calcium hydroxide is particularly preferred.

[0022] For example, calcium hydroxide reacts with zinc ions in an electrolyte solution as follows: 2Zn(OH) ４ ２－ + Ca(OH) ２ +2H ２ O → Ca(OH) ２ ・2Zn(OH) ２ ・2H ２ O + 4OH －This forms an insoluble complex. That is, it is believed that calcium hydroxide acts as a buffer for zinc ions (zinc complex), thereby effectively suppressing the reaction between the zinc ions and the positive electrode 12. Furthermore, when zinc ions (zincate ions) are present in the electrolyte, the amount of bismuth oxide that dissolves in the electrolyte increases, and the bismuth oxide forms a complex with the zincate ions (Bi-Zn complex). Therefore, it is believed that, similar to calcium hydroxide, it can effectively suppress the reaction between the zinc ions and the positive electrode 12.

[0023] The positive electrode 12 includes a positive electrode active material layer 12a. The positive electrode active material constituting the positive electrode active material layer 12a includes manganese dioxide. The manganese dioxide may be electrolytic manganese dioxide, which is commonly used in common alkaline manganese dry batteries. The manganese dioxide particles preferably have an average particle size of 15 to 50 μm, more preferably 15 to 25 μm. Typically, the positive electrode 12 further includes a positive electrode current collector 12b, which preferably has a positive electrode current collector tab (not shown) extending from one side (e.g., the upper side) of the quadrilateral (typically rectangular) positive electrode active material layer 12a. A preferred example of the positive electrode current collector 12b is a porous substrate such as an expanded metal made of stainless steel (e.g., SUS304). In this case, a positive electrode plate consisting of a positive electrode and a positive electrode current collector can be preferably fabricated by, for example, laminating an electrode sheet containing an electrode active material such as manganese dioxide onto the porous substrate. At this time, it is also preferable to subject the positive electrode plate (i.e., positive electrode / positive electrode current collector) to a press treatment to prevent the electrode active material from falling off and to improve the electrode density.

[0024] The positive electrode active material layer 12a preferably further contains a conductive additive to provide the desired conductivity. The conductive additive that can be contained in the positive electrode active material layer 12a is preferably a carbon-based material. Examples of carbon-based materials include various conductive carbons such as graphite, carbon black (e.g., ketjen black), carbon nanotubes, and graphene. The conductive additive or carbon-based material is preferably in particulate form. For example, in the case of the positive electrode active material layer 12a, it is preferable to mix manganese dioxide particles with conductive carbon particles. The conductive additive particles or conductive carbon particles preferably have an average particle size of 0.005 to 1 μm, more preferably 0.005 to 0.5 μm.

[0025] The negative electrode 14 includes a negative electrode active material layer 14a. The negative electrode active material constituting the negative electrode active material layer 14a includes at least one selected from the group consisting of zinc, zinc oxide, zinc alloys, and zinc compounds. Zinc may be contained in any form, such as zinc metal, zinc compounds, or zinc alloys, as long as it has electrochemical activity suitable for a negative electrode. Preferred examples of negative electrode materials include zinc oxide, zinc metal, and calcium zincate, with a mixture of zinc metal and zinc oxide being more preferred. The negative electrode active material may be in a gel form or may be mixed with an electrolyte to form a negative electrode mixture. For example, a gelled negative electrode can be easily obtained by adding an electrolyte and a thickener to the negative electrode active material. Examples of thickeners include polyvinyl alcohol, polyacrylate, CMC, and alginic acid, with polyacrylic acid being preferred due to its excellent chemical resistance to strong alkalis. The negative electrode active material layer 14a may also include a conductive additive. Examples of such conductive additives include the various conductive carbons mentioned above.

[0026] As the zinc alloy, a mercury- and lead-free zinc alloy known as a mercury-free zinc alloy can be used. For example, a zinc alloy containing 0.01 to 0.1 mass% indium, 0.005 to 0.02 mass% bismuth, and 0.0035 to 0.015 mass% aluminum is preferred because it has the effect of suppressing hydrogen gas generation. In particular, indium and bismuth are advantageous in terms of improving discharge performance. The use of a zinc alloy for the negative electrode can suppress hydrogen gas generation and improve safety by slowing the rate of self-dissolution in alkaline electrolyte.

[0027] The shape of the negative electrode material is not particularly limited, but is preferably in powder form, which increases the surface area and enables it to withstand large current discharge. In the case of a zinc alloy, the average particle size of the negative electrode material is preferably in the range of 3 to 100 μm in minor axis. Within this range, the large surface area makes it suitable for withstanding large current discharge, and it is also easy to mix uniformly with the electrolyte and gelling agent, making it easy to handle during battery assembly.

[0028] The negative electrode 14 typically further includes a negative electrode current collector 14b, which preferably has a negative electrode current collector tab 14c extending from one side (e.g., the upper side) of the quadrilateral (typically rectangular) negative electrode active material layer 14a. The negative electrode current collector tab 14c is preferably provided in a position that does not overlap with the positive electrode current collector tab. As shown in FIG. 2 , the negative electrode 14 may have an uncoated region along the upper edge of the negative electrode 14 where the negative electrode active material layer 14a is not present, and may have a portion W in this uncoated region where the negative electrode current collector tab 14c is welded to the negative electrode current collector 14b. The same applies to the positive electrode 12.

[0029] Preferred examples of the negative electrode current collector 14b include tin-plated copper foil, tin-plated copper expand metal, and tin-plated copper punched metal, with tin-plated copper expand metal being more preferred. In this case, for example, a mixture containing zinc oxide powder and / or zinc powder, and optionally a binder (e.g., polytetrafluoroethylene particles), can be applied to tin-plated copper expand metal to preferably produce a negative electrode plate consisting of a negative electrode / negative electrode current collector. In this case, it is also preferable to press the dried negative electrode plate (i.e., a negative electrode / negative electrode current collector) to prevent the electrode active material from falling off and improve the electrode density.

[0030] The positive electrode active material layer 12a, the negative electrode active material layer 14a, and the LDH separator 16 are preferably each quadrilateral (typically rectangular). The LDH separator 16 covers or encases the entire positive electrode active material layer 12a or the entire negative electrode active material layer 14a, and preferably has three closed outer edges, excluding one edge overlapping with the positive electrode current collector tab or the negative electrode current collector tab 14c. This configuration can more effectively prevent the permeation of zinc ions eluted from the negative electrode 14. This configuration can be achieved, for example, by arranging the LDH separator 16 so that it protrudes from the remaining three edges of the negative electrode 14, excluding the edge from which the negative electrode current collector tab 14c extends, and then sealing the protruding excess portion of the LDH separator 16 by heat fusion or the like.

[0031] The positive electrode electrolyte 18 and the negative electrode electrolyte 20 each preferably contain an aqueous solution of an alkali metal hydroxide. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being more preferred. A zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte to suppress the self-dissolution of zinc and / or zinc oxide. The positive electrode electrolyte 18 and the negative electrode electrolyte 20 may be gelled to prevent leakage. As the gelling agent, a polymer that swells upon absorbing the solvent of the electrolyte is preferably used, and examples of such a polymer include polyethylene oxide, polyvinyl alcohol, polyacrylamide, and starch.

[0032] As shown in Fig. 3, the zinc secondary battery 10 preferably has a positive electrode 12, a negative electrode 14, and a LDH separator 16, and is preferably in the form of a positive-negative electrode laminate in which the positive electrode 12 / LDH separator 16 / negative electrode 14 unit is repeatedly stacked. That is, the zinc secondary battery 10 preferably has a plurality of unit cells 10a, and the plurality of unit cells 10a as a whole form a multi-layer cell. This is a so-called assembled battery or stacked battery configuration, and is advantageous in that it can provide high voltage and large current. Typically, the zinc secondary battery 10 has a positive electrode 12, a negative electrode 14, an LDH separator 16, a positive electrode electrolyte 18, and a negative electrode electrolyte 20 enclosed in an exterior housing.

[0033] LDH Separator The LDH separator 16 is provided to separate the positive electrode 12 and positive electrode electrolyte 18 from the negative electrode 14 and negative electrode electrolyte 20 in a manner that allows hydroxide ions to be conducted between them. In this specification, an "LDH separator" is defined as a separator containing LDH and / or an LDH-like compound, which selectively passes hydroxide ions by utilizing the hydroxide ion conductivity of the LDH and / or LDH-like compound. In this specification, an "LDH-like compound" is a hydroxide and / or oxide with a layered crystal structure that has hydroxide ion conductivity, even if it may not be called an LDH, and can be considered an equivalent of LDH. However, in a broad sense, "LDH" can also be interpreted to include not only LDH but also LDH-like compounds. The denseness of the LDH separator 16 allows it to effectively prevent the permeation of zinc ions from the anode electrolyte 20 to the cathode electrolyte 18, and therefore a synergistic effect can be expected with the effect of the zinc ion scavenger in suppressing the reaction between the zinc ions and the cathode 12. For example, known LDH separators such as those disclosed in Patent Documents 1 to 8 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, even more preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.

[0034] The density of the LDH separator 16 can be evaluated by its He permeability. That is, the LDH separator 16 preferably has a He permeability per unit area of ​​10 cm / min·atm or less, more preferably 5.0 cm / min·atm or less, and even more preferably 1.0 cm / min·atm or less. An LDH separator 16 having a He permeability within this range can be said to have extremely high density. Therefore, a separator having a He permeability of 10 cm / min·atm or less can highly effectively prevent the passage of substances other than hydroxide ions. For example, in the case of a zinc secondary battery, the permeation of Zn (typically, the permeation of zinc ions or zincate ions) in the electrolyte can be extremely effectively suppressed. The He permeability is measured by supplying He gas to one side of the separator to allow the He gas to permeate the separator, and then calculating the He permeability to evaluate the density of the LDH separator. The He permeability is calculated by the formula F / (P×S) using the amount of He gas permeated per unit time, F, the differential pressure P applied to the separator during He gas permeation, and S, the membrane area through which He gas permeates. By evaluating 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, it is possible to effectively evaluate a high level of denseness, such as minimizing the permeation of substances other than hydroxide ions (especially Zn, which causes zinc dendrite growth and side reactions with the positive electrode active material) (permeating only a very small amount). This is because He gas has the smallest structural unit among the wide variety of atoms or molecules that can constitute gas, and is also extremely low in reactivity. In other words, He constitutes He gas as a single He atom without forming molecules. In this regard, hydrogen gas is H ２ Because it is composed of molecules, a single He atom is smaller as a gas constituent unit. ２ He gas is flammable and therefore dangerous. By using the He gas permeability index defined by the above formula, it is possible to easily and objectively evaluate the density of a separator, regardless of the size of the sample or the measurement conditions. In this way, it is possible to easily, safely, and effectively evaluate whether a separator has a sufficiently high density suitable for use in a zinc secondary battery.

[0035] Measurement of He permeability can be preferably carried out according to the following procedure. First, a He permeability measurement system 310 shown in Figures 4A and 4B is constructed. The He permeability measurement system 310 is configured so that He gas from a gas cylinder filled with He gas is supplied to a sample holder 316 via a pressure gauge 312 and a flow meter 314 (digital flow meter), and the He gas permeates from one side to the other side of an LDH separator 318 held by the sample holder 316 and is then discharged.

[0036] The sample holder 316 has a structure including a gas supply port 316a, a sealed space 316b, and a gas exhaust port 316c, and is assembled as follows. First, adhesive 322 is applied along the outer periphery of the LDH separator 318, and the LDH separator 318 is attached to a jig 324 (made of ABS resin) with a central opening. Butyl rubber packings are placed at the upper and lower ends of the jig 324 as sealing members 326a, 326b. Furthermore, the sealing members 326a, 326b are sandwiched from the outside by support members 328a, 328b (made of PTFE) with flanged openings. Thus, the LDH separator 318, jig 324, sealing member 326a, and support member 328a define a sealed space 316b. The support members 328a and 328b are tightly fastened together with screw fastening means 330 so that He gas does not leak from any part other than the gas exhaust port 316c. A gas supply pipe 334 is connected via a joint 332 to the gas supply port 316a of the sample holder 316 thus assembled.

[0037] Next, He gas is supplied to the He permeability measurement system 310 via a gas supply pipe 334 and is allowed to permeate through an LDH separator 318 held in a sample holder 316. At this time, the gas supply pressure and flow rate are monitored by a pressure gauge 312 and a flow meter 314. After permeating the He gas for 1 to 30 minutes, the He permeability is calculated. The He permeability is calculated based on the amount of He gas permeated per unit time F (cm ３ / min), the differential pressure P (atm) applied to the LDH separator during He gas permeation, and the membrane area S (cm ２ ) and calculate the amount of He gas permeation F (cm３ / min) can be read directly from the flow meter 314. The differential pressure P is the gauge pressure read from the pressure gauge 312. The He gas is supplied so that the differential pressure P is in the range of 0.05 to 0.90 atm.

[0038] The LDH separator 16 is preferably gas-impermeable and / or water-impermeable. In other words, the LDH separator 16 is preferably densified to the extent that it is gas-impermeable and / or water-impermeable. As used herein, "gas-impermeable" means that, as described in Patent Documents 3 and 4, even when helium gas is brought into contact with one side of an object to be measured in water at a differential pressure of 0.5 atm, no bubbles due to helium gas are generated from the other side. As used herein, "water-impermeable" means that water that has come into contact with one side of an object to be measured does not permeate to the other side, as described in Patent Documents 3 and 4. That is, the gas-impermeable and / or water-impermeable LDH separator 16 means that the LDH separator 16 is highly dense enough to prevent gas or water from passing through, and is not a porous film or other porous material that is water- or gas-permeable. In this way, the LDH separator 16 selectively passes only hydroxide ions due to its hydroxide ion conductivity, and can function as a battery separator. Therefore, it is extremely effective in physically preventing zinc dendrites generated during charging from penetrating the separator, thereby preventing short circuits between the positive and negative electrodes. Because the LDH separator 16 has hydroxide ion conductivity, it enables the efficient movement of hydroxide ions required between the positive electrode 12 and the negative electrode 14, thereby realizing charge / discharge reactions at the positive electrode 12 and the negative electrode 14.

[0039] The LDH separator 16 preferably further includes a porous substrate. In this case, it is preferable that the pores of the porous substrate are filled with a hydroxide ion-conducting layered compound and / or that a surface layer containing the hydroxide ion-conducting layered compound is provided on at least one surface of the porous substrate. The surface layer can effectively prevent zinc ion permeation and dendrite extension, so that the LDH separator 16 having such a surface layer has particularly excellent resistance to dendrite short-circuiting. The surface layer may be provided on only one surface of the porous substrate, or on both surfaces of the porous substrate. It is particularly preferable that the hydroxide ion-conducting layered compound is incorporated throughout the entire thickness of the porous substrate. However, the pores of the porous substrate do not need to be completely blocked, and a small amount of residual porosity may be present.

[0040] The porous substrate is preferably made of a polymer material. Polymeric porous substrates have the following advantages: 1) flexibility (hence, they are less likely to crack even when thinned); 2) ease of achieving high porosity; 3) ease of achieving high conductivity (because the thickness can be reduced while increasing porosity); and 4) ease of manufacturing and handling. Furthermore, by taking advantage of the flexibility (1), 5) an LDH separator including a porous substrate made of a polymer material can be easily folded or sealed. Preferred examples of polymer materials include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, fluororesin (e.g., tetrafluororesin: PTFE), cellulose, nylon, polyethylene, and any combination thereof. More preferred examples of thermoplastic resins suitable for hot pressing include polystyrene, polyethersulfone, polypropylene, epoxy resin, polyphenylene sulfide, fluororesin (e.g., tetrafluororesin: PTFE), nylon, polyethylene, and any combination thereof. All of the above-mentioned preferred materials are alkali-resistant to the battery electrolyte. Particularly preferred polymeric materials are polyolefins such as polypropylene and polyethylene, with polypropylene or polyethylene being the most preferred, due to their excellent hot water resistance, acid resistance, and alkali resistance, and low cost. It is particularly preferred that the hydroxide ion-conducting layered compound be incorporated throughout the entire thickness of the porous substrate (e.g., most or almost all of the pores within the polymeric porous substrate are filled with the hydroxide ion-conducting layered compound). Commercially available microporous polymeric membranes are preferably used as such polymeric porous substrates.

[0041] As described above, the hydroxide ion-conducting layered compound contained in the LDH separator 16 is an LDH and / or an LDH-like compound. Preferred embodiments of the LDH and LDH-like compound will be described below.

[0042] LDH is composed of multiple hydroxide base layers and intermediate layers interposed between these multiple hydroxide base layers. The hydroxide base layers are mainly composed of metal elements (typically metal ions) and OH groups. The intermediate layers of LDH are composed of anions and H ２ The anion is a monovalent or higher anion, preferably a monovalent or divalent ion. Preferably, the anion in LDH is OH. － and / or CO ３ ２－ In addition, LDH has excellent ion conductivity due to its inherent properties. Generally, LDH contains 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, and A ｎ－ is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more. ２＋ can be any divalent cation, but preferred examples include Mg ２＋ , Ca ２＋ and Zn ２＋ More preferably, Mg ２＋ It is. ３＋ can be any trivalent cation, but preferred examples include Al ３＋ or Cr ３＋ More preferably, Al ３＋ It is. A ｎ－ can be any anion, but preferred examples include OH － and CO ３ ２－ Therefore, in the above basic composition formula, M ２＋ is Mg ２＋ Including M ３＋ Al ３＋ Including A ｎ－ OH － and / or CO ３ ２－n is an integer of 1 or more, preferably 1 or 2. x is 0.1 to 0.4, preferably 0.2 to 0.35. m is an arbitrary number representing the number of moles of water, and is a real number of 0 or more, typically greater than 0 or 1 or more. However, the above basic composition formula is merely a formula of a "basic composition" typically exemplified for LDH, and the constituent ions can be replaced as appropriate. For example, in the above basic composition formula, M ３＋ A part or all of the cations may be tetravalent or more valent (e.g., Ti ４＋ In that case, the anion A in the above general formula may be replaced by ｎ－ The coefficient x / n may be changed as appropriate.

[0043] For example, the hydroxide basic layer of the LDH preferably contains Mg, Al, and OH groups, and further contains Ti (i.e., Mg, Al, Ti, and OH groups), which is particularly preferred in terms of excellent alkali resistance. In this case, the hydroxide basic layer may contain other elements or ions as long as it contains Mg, Al, and OH groups (and optionally Ti). For example, the LDH or hydroxide basic layer may contain Y and / or Zn. Furthermore, when the LDH or hydroxide basic layer contains Y and / or Zn, the LDH or hydroxide basic layer does not necessarily contain Al or Ti. However, the hydroxide basic layer preferably contains Mg, Al, Ti, and OH groups as its main components. That is, the hydroxide basic layer is preferably composed mainly of Mg, Al, Ti, and OH groups. Therefore, the hydroxide basic layer is typically composed of Mg, Al, Ti, OH groups, and, optionally, unavoidable impurities. The atomic ratio of Ti / Al in the LDH, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.5 to 12, more preferably 1.0 to 12. Within this range, the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively achieved without impairing ionic conductivity. For the same reason, the atomic ratio of Ti / (Mg + Ti + Al) in the LDH, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.1 to 0.7, more preferably 0.2 to 0.7. Furthermore, the atomic ratio of Al / (Mg + Ti + Al) in the LDH is preferably 0.05 to 0.4, more preferably 0.05 to 0.25. Furthermore, the atomic ratio of Mg / (Mg + Ti + Al) in the LDH is preferably 0.2 to 0.7, more preferably 0.2 to 0.6. The EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by: 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000; 2) performing three-point analysis in point analysis mode with an interval of about 5 μm; 3) repeating the above 1) and 2) once more; and 4) calculating the average value of the six points in total.

[0044] Alternatively, the hydroxide base layer of the LDH may contain Ni, Al, Ti, and OH groups. In this case, the hydroxide base layer may contain other elements or ions as long as it contains Ni, Al, Ti, and OH groups. However, it is preferable that the hydroxide base layer contains Ni, Al, Ti, and OH groups as its main components. That is, it is preferable that the hydroxide base layer is mainly composed of Ni, Al, Ti, and OH groups. Therefore, the hydroxide base layer is typically composed of Ni, Al, Ti, OH groups, and possibly unavoidable impurities. The atomic ratio of Ti / (Ni + Ti + Al) in the LDH, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.10 to 0.90, more preferably 0.20 to 0.80, even more preferably 0.25 to 0.70, and particularly preferably 0.30 to 0.61. Within the above ranges, both alkali resistance and ionic conductivity can be improved. Therefore, the hydroxide ion-conducting layered compound may contain a large amount of Ti so as to by-produce not only LDH but also titania. That is, the hydroxide ion-conducting layered compound may further contain titania. The inclusion of titania is expected to increase hydrophilicity and improve wettability with the electrolyte (i.e., improve conductivity).

[0045] The LDH-like compound preferably contains (i) Mg and (ii) one or more elements selected from the group consisting of Ti, Y, and Al, including at least Ti. Thus, by using an LDH-like compound, which is a hydroxide and / or oxide having a layered crystal structure containing at least Mg and Ti, as a hydroxide ion conductive material instead of a conventional LDH, excellent alkali resistance can be achieved and short circuits caused by zinc dendrites can be more effectively suppressed. Therefore, a preferred LDH-like compound is a hydroxide and / or oxide having a layered crystal structure containing (i) Mg and (ii) one or more elements selected from the group consisting of Ti, Y, and Al, including at least Ti. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Mg, Ti, optionally Y, and optionally Al, and particularly preferably a composite hydroxide and / or composite oxide of Mg, Ti, Y, and Al. The above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, but it is preferred that the LDH-like compound does not contain Ni.

[0046] The LDH-like compound can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface of the LDH separator 16, a peak derived from the LDH-like compound is typically detected in the range of 5°≦2θ≦10°, more typically in the range of 7°≦2θ≦10°. As described above, LDH has exchangeable anions and H as intermediate layers between stacked hydroxide base layers. ２ O is present. In this regard, when LDH is measured by X-ray diffraction, a peak due to the crystalline structure of LDH (i.e., the (003) peak of LDH) is inherently detected at 2θ = 11 to 12°. In contrast, when an LDH-like compound is measured by X-ray diffraction, a peak is typically detected in the above-mentioned range, which is shifted to a lower angle than the peak position of LDH. Furthermore, the interlayer distance of the layered crystalline structure can be determined by the Bragg equation using 2θ corresponding to the peak due to the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystalline structure constituting the LDH-like compound determined in this manner is typically 0.883 to 1.8 nm, more typically 0.883 to 1.3 nm.

[0047] The atomic ratio of Mg / (Mg + Ti + Y + Al) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.03 to 0.25, more preferably 0.05 to 0.2. The atomic ratio of Ti / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0.40 to 0.97, more preferably 0.47 to 0.94. The atomic ratio of Y / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.45, more preferably 0 to 0.37. The atomic ratio of Al / (Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.03. Within the above ranges, the alkali resistance is even better, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively achieved. Incidentally, conventionally known LDHs for LDH separators are represented by the general formula: 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, M ３＋ is a trivalent cation, and A ｎ－ is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratio in LDH-like compounds generally deviates from the general formula of LDH. For this reason, it can be said that LDH-like compounds generally have a composition ratio (atomic ratio) different from that of conventional LDH. It is preferable to perform EDS analysis using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis at intervals of about 5 μm in point analysis mode, 3) repeating the above 1) and 2) once more, and 4) calculating the average value of a total of six points.

[0048] According to another preferred embodiment of the present invention, the LDH-like compound may be a hydroxide and / or oxide having a layered crystal structure containing (i) Ti, Y, and optionally Al and / or Mg, and (ii) an additional element M. Thus, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Ti, Y, the additional element M, optionally Al, and optionally Mg. The additional element M is In, Bi, Ca, Sr, Ba, or a combination thereof. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferred that the LDH-like compound does not contain Ni.

[0049] In the LDH separator according to the above embodiment, the atomic ratio of Ti / (Mg+Al+Ti+Y+M) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.50 to 0.85, more preferably 0.56 to 0.81. The atomic ratio of Y / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.20, more preferably 0.07 to 0.15. The atomic ratio of M / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.35, more preferably 0.03 to 0.32. The atomic ratio of Mg / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.10, more preferably 0 to 0.02. The atomic ratio of Al / (Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.04. Within the above range, the alkali resistance is more excellent, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. Incidentally, LDHs conventionally known for LDH separators have the general formula: 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, M ３＋ is a trivalent cation, and A ｎ－is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratio in the LDH-like compound generally deviates from the general formula of LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDH. Note that EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis in point analysis mode with an interval of about 5 μm, 3) repeating the above 1) and 2) once more, and 4) calculating the average value of a total of six points.

[0050] According to yet another preferred embodiment of the present invention, the LDH-like compound is a hydroxide and / or oxide of a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, and the LDH-like compound is In(OH) ３ The LDH-like compound of this embodiment is a hydroxide and / or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In. Therefore, a typical LDH-like compound is a composite hydroxide and / or composite oxide of Mg, Ti, Y, optionally Al, and optionally In. Note that the In that can be contained in the LDH-like compound is not only that which is intentionally added to the LDH-like compound, but also In(OH) ３ The above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, but it is preferable that the LDH-like compound does not contain Ni. Incidentally, LDHs conventionally known for LDH separators are represented by the general formula: 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, M ３＋ is a trivalent cation, and A ｎ－is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more. In contrast, the atomic ratios in LDH-like compounds generally deviate from the above general formula of LDH. Therefore, it can be said that the LDH-like compounds in this embodiment generally have composition ratios (atomic ratios) different from those of conventional LDHs.

[0051] The mixture according to the above embodiment contains not only LDH-like compounds but also In(OH) ３ (typically LDH-like compounds and In(OH) ３ It is composed of In(OH) ３ The inclusion of In(OH) in the mixture can effectively improve the alkali resistance and dendrite resistance of the LDH separator. ３ The content of In(OH) is preferably an amount that can improve the alkali resistance and dendrite resistance of the LDH separator without substantially impairing the hydroxide ion conductivity, and is not particularly limited. ３ may have a cubic crystal structure, and In(OH) ３ The crystal may be surrounded by an LDH-like compound. ３ can be identified by X-ray diffraction.

[0052] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0053] Example 1 (Comparison) (1) Preparation of Positive Electrode The following raw materials were prepared. <Positive electrode active material> Manganese dioxide powder (HH-TF, manufactured by Tosoh Corporation) <Conductive additive> Ketjen black (EC300J, manufactured by Lion Specialty Chemicals Co., Ltd.) <Resin binder> Polyvinylidene fluoride (182702, manufactured by Sigma-Aldrich, weight average molecular weight measured by gel permeation chromatography (GPC): 534,000 or less)

[0054] Manganese dioxide powder was mixed with Ketjen black (KB) and polyvinylidene fluoride (PVDF) in a ratio of 75% by weight, 10% by weight, and 15% by weight, and then N-methylpyrrolidone (NMP) was added. The resulting mixture was applied to nickel foil and dried to form a positive electrode.

[0055] (2) Preparation of negative electrode The following raw materials were prepared. <Negative electrode active material> ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS standard type 1 grade, average particle size D50: 0.2 μm) Metallic Zn powder (manufactured by Mitsui Mining & Smelting Co., Ltd., doped with Bi and In, Bi: 1000 weight ppm, In: 1000 weight ppm, average particle size D50: 50 μm) <Resin binder> Polytetrafluoroethylene (PTFE) aqueous dispersion (manufactured by Daikin Industries, Ltd., solid content 60%)

[0056] Metallic Zn powder was added to ZnO powder in a blend ratio of 50.0 vol% ZnO, 46.9 vol% Zn, and 3.1 vol% PTFE solids. PTFE was then added and kneaded with propylene glycol. The resulting kneaded mixture was rolled using a roll press to obtain a negative electrode active material sheet. The negative electrode active material sheet was pressure-bonded to a tin-plated copper expand metal and dried to form a negative electrode.

[0057] (3) Preparation of Electrolyte Solution Ion-exchanged water was added to a 48% aqueous potassium hydroxide solution (special grade, manufactured by Kanto Chemical Co., Inc.) to adjust the KOH concentration to 5.4 mol%, and then zinc oxide was added thereto so that the concentration became 0.42 mol / L, and the mixture was dissolved by heating and stirring to obtain an electrolyte solution.

[0058] (4) Battery Assembly The prepared positive electrode was wrapped in a commercially available polypropylene nonwoven fabric (thickness: 100 μm), and a positive electrode current collector tab was welded. The prepared negative electrode was wrapped in a commercially available microporous membrane separator (manufactured by Shanghai Energy, material: polyethylene, thickness: 20 μm), and a negative electrode current collector tab was welded. At this time, the separator was slightly protruding from the remaining three sides except for the side from which the negative electrode current collector tab extended. The excess portion of the separator protruding from the three sides of the negative electrode was then heat-sealed. The prepared positive and negative electrodes were placed opposite each other with the separator interposed between them, sandwiched between laminate films, and the three sides of the laminate films were sealed. An electrolyte solution was added to the resulting open-top cell container, and the electrolyte solution was thoroughly permeated into the positive and negative electrodes by evacuation or the like. The remaining side of the laminate film was then sealed, and pressure was applied from the outside of the film with an acrylic plate. In this way, a manganese-zinc secondary battery was obtained as a prototype battery for cycle evaluation.

[0059] (5) Evaluation of Cycle Performance Using a charge / discharge device (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.), 0.2 C charge / discharge cycles were performed under conditions of a measurement temperature of 25°C, a charge cutoff voltage of 1.8 V, and a discharge cutoff voltage of 1.0 V. Charge / discharge cycles were repeated under the same conditions, and the number of charge / discharge cycles until the discharge capacity of the prototype battery decreased to 50% of the discharge capacity at the first cycle was recorded. The results are shown in Table 1 and FIG. 5.

[0060] A battery was fabricated and evaluated in the same manner as in Example 1, except that the positive electrode was fabricated in a blend ratio of 70 wt % manganese dioxide, 5 wt % calcium hydroxide, 10 wt % Ketjen Black (KB), and 15 wt % polyvinylidene fluoride (PVDF), and calcium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 038-16295) was further added as a zinc ion scavenger. The results are shown in Table 1 and FIG. 5.

[0061] Example 3 (Comparative) A battery was produced and evaluated in the same manner as in Example 1, except that the following LDH separator was used as the separator instead of the microporous membrane. The results are shown in Table 1 and FIG.

[0062] (Fabrication of LDH Separator) A commercially available polyethylene microporous membrane with a porosity of 50%, an average pore diameter of 0.1 μm, and a thickness of 20 μm was prepared as a polymeric porous substrate. This substrate was coated with a titania-yttria-alumina sol. The substrate was then immersed in a raw material aqueous solution containing magnesium nitrate hexahydrate and urea, and subjected to hydrothermal treatment to precipitate an Mg-Al-Ti-Y-LDH-like compound in the pores and on the surface of the substrate. Densification was then performed using a roll press to obtain an LDH separator.

[0063] Example 4 A battery was produced and evaluated in the same manner as in Example 2, except that an LDH separator similar to that in Example 3 was used as the separator instead of the microporous membrane. The results are shown in Table 1 and FIG.

[0064]

[0065] The results shown in Table 1 show that in Example 4, in which an LDH separator was used and a zinc ion scavenger was contained, the number of cycles required to reach a capacity retention rate of 50%, i.e., the cycle life, was significantly improved compared to Examples 1 to 3, in which an LDH separator was not used and / or a zinc ion scavenger was not contained.

Claims

1. A zinc secondary battery comprising: a positive electrode including a positive electrode active material layer containing manganese dioxide; a positive electrode electrolyte in which the positive electrode is immersed; a negative electrode including a negative electrode active material layer containing at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound; a negative electrode electrolyte in which the negative electrode is immersed; and an LDH separator including a hydroxide ion conductive layered compound which is a layered double hydroxide (LDH) and / or an LDH-like compound, which separates the positive electrode and the positive electrode electrolyte from the negative electrode and the negative electrode electrolyte in a manner that allows hydroxide ion conductivity, wherein the LDH separator contains a zinc ion scavenger at a position where it can capture zinc ions that have eluted from the negative electrode and reached the positive electrode electrolyte.

2. A zinc secondary battery according to claim 1, wherein the location capable of capturing zinc ions is in the positive electrode electrolyte and / or in a portion in contact with the positive electrode electrolyte.

3. The zinc secondary battery according to claim 1, wherein the positive electrode active material layer contains the zinc ion scavenger.

4. The zinc secondary battery according to claim 1, wherein the positive electrode active material layer is covered or wrapped in a nonwoven fabric, and the nonwoven fabric contains the zinc ion scavenger.

5. The zinc secondary battery according to claim 1, wherein the positive electrode electrolyte contains the zinc ion scavenger.

6. A zinc secondary battery according to any one of claims 1 to 5, wherein the zinc ion scavenger is a calcium compound and / or a bismuth compound.

7. A zinc secondary battery according to any one of claims 1 to 5, wherein the zinc ion scavenger is calcium hydroxide.

8. The zinc secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material layer, the negative electrode active material layer, and the LDH separator are each quadrilateral in shape, the positive electrode further includes a positive electrode current collector, which has a positive electrode current collector tab extending from one side of the positive electrode active material layer, and the negative electrode further includes a negative electrode current collector, which has a negative electrode current collector tab extending from one side of the negative electrode active material layer, the LDH separator covers or encases the entire positive electrode active material layer or the entire negative electrode active material layer, and the outer edges of three sides of the LDH separator, excluding one side overlapping with the positive electrode current collector tab or the negative electrode current collector tab, are closed.

9. The zinc secondary battery according to any one of claims 1 to 5, wherein the LDH separator further comprises a porous substrate, the pores of which are filled with the hydroxide ion-conducting layered compound.

Images