JP2023028015A - zinc secondary battery - Google Patents

Abstract

A zinc secondary battery capable of effectively suppressing the growth of zinc dendrites is provided.
A positive electrode containing a positive electrode active material; a negative electrode containing a negative electrode active material containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds; and interposed between the positive electrode and the negative electrode. and an electrolytic solution, further comprising an oxidizing agent capable of oxidizing zinc at a position accessible to zinc dendrites that can grow from the negative electrode. .
[Selection drawing] Fig. 1

Description

The present invention relates to zinc secondary batteries.

In zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc deposits in the form of dendrites from the negative electrode during charging, and penetrates the pores of a separator such as a non-woven fabric to reach the positive electrode. known to cause short circuits. Short circuits caused by such zinc dendrites lead to shortening of repeated charge/discharge life.

In order to address the above problems, a battery has been proposed that includes a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to permeate while blocking the penetration of zinc dendrites. For example, Patent Document 1 (International Publication No. 2013/118561) discloses providing an LDH separator 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 provided with an LDH separator fitted or joined to a resin outer frame, wherein the LDH separator is gas impermeable and and/or are disclosed to have such a high density that they are impermeable to water. This document also discloses that the LDH separator can be composited with a porous substrate. Furthermore, Patent Document 3 (International Publication No. 2016/067884) discloses various methods for forming an LDH dense film on the surface of a porous substrate to obtain a composite material. In this method, a starting material capable of providing starting points for LDH crystal growth is uniformly attached to a porous substrate, and the porous substrate is subjected to hydrothermal treatment in an aqueous raw material solution to form an LDH dense film on the surface of the porous substrate. It includes a step of forming There has also been proposed an LDH separator in which further densification is realized by roll-pressing a composite material of LDH/porous substrate produced through hydrothermal treatment. For example, Patent Document 4 (International Publication No. 2019/124270) includes a polymer porous substrate and LDH filled in the porous substrate, and has a linear transmittance of 1% or more at a wavelength of 1000 nm. An LDH separator is disclosed.

LDH-like compounds are known as hydroxides and/or oxides having a layered crystal structure similar to LDH, although they cannot be called LDH. exhibit ionic conduction properties. For example, Patent Document 5 (International Publication No. 2020/255856) describes hydroxide ions containing a porous substrate and a layered double hydroxide (LDH)-like compound that closes the pores of the porous substrate. A hydroxide and/or oxide of layered crystal structure, wherein the LDH-like compound comprises Mg and one or more elements including at least Ti selected from the group consisting of Ti, Y and Al. is disclosed. This hydroxide ion-conducting separator is said to be superior to conventional LDH separators in alkali resistance and to more effectively suppress short circuits caused by zinc dendrites.

WO2013/118561 WO2016/076047 WO2016/067884 WO2019/124270 WO2020/255856

The LDH separator as described above can only physically block zinc dendrites due to its denseness. Therefore, in order to more effectively suppress the growth of zinc dendrites, it is desirable to chemically suppress zinc dendrites. If zinc dendrites can be chemically suppressed, zinc can be added not only to zinc secondary batteries using a hydroxide ion conducting dense separator such as an LDH separator, but also to zinc secondary batteries using a microporous membrane separator. It can be said to be advantageous in that it becomes possible to deal with the problem of dendrites.

The present inventors have recently found that the growth of zinc dendrites can be effectively suppressed by disposing an oxidizing agent capable of oxidizing zinc at a position within which zinc dendrites can reach in a zinc secondary battery. Obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a zinc secondary battery capable of effectively suppressing the growth of zinc dendrites.

According to one aspect of the invention,
a positive electrode comprising a positive electrode active material;
a negative electrode comprising a negative electrode active material containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds;
a separator interposed between the positive electrode and the negative electrode;
an electrolyte;
A zinc secondary battery comprising
A zinc secondary battery is provided, further comprising an oxidizing agent capable of oxidizing zinc at a position accessible to zinc dendrites that can grow from the negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram conceptually showing the basic configuration of a zinc secondary battery of the present invention and the effect of inhibiting the growth of zinc dendrites. FIG. 2 is a conceptual diagram showing an example of a He permeation measurement system used in Examples 1-10; 2B is a schematic cross-sectional view of a sample holder and its peripheral configuration used in the measurement system shown in FIG. 2A; FIG. 1 is a photograph of a microporous membrane separator used in Example 1. FIG. 1 is a cross-sectional SEM image of the bismuth oxide-coated separator produced in Example 1 and its enlarged image. 1 is a photograph of a Cu electrode used in Example 1 before and after zinc dendrite deposition. 4 is a photograph of the zinc dendrite-grown Cu electrode in Example 1 before and after contact with a bismuth oxide coated separator. 1 is a photograph of the bismuth oxide coated separator in Example 1 before and after contact with zinc dendrites. 4 is a photograph of the working electrode used in Example 2 before and after being wrapped with a nonwoven fabric. 4 is a photograph of the cell used in Example 2. FIG. 2 is a photograph of the surface of a nonwoven fabric taken 90 minutes after the start of voltage application in Example 2. FIG. 10B is an enlarged photograph of the surface of the nonwoven fabric shown in FIG. 10A. FIG. 10B is an enlarged photograph of the surface of the nonwoven fabric shown in FIG. 10A. FIG. 10 is a photograph of zinc dendrites penetrating through the nonwoven fabric surface within 30 minutes from the start of voltage application in Example 3 (comparative example). 11B is a magnified photograph of the zinc dendrite shown in FIG. 11A. FIG. 11B is a magnified photograph of the zinc dendrite shown in FIG. 11A. FIG.

Zinc Secondary Battery 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 using an alkaline electrolyte (typically an aqueous alkali metal hydroxide 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, the positive electrode active material layer preferably contains nickel hydroxide and/or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery. Alternatively, the positive electrode active material layer may be the air electrode layer, whereby the zinc secondary battery may form a zinc air secondary battery.

FIG. 1 conceptually shows an example of a zinc secondary battery according to the present invention. A zinc secondary battery 10 shown in FIG. 1 includes a positive electrode 12, a negative electrode 14, a separator 16, and an electrolytic solution 18. Anode 14 includes zinc and/or zinc oxide. The positive electrode 12 contains a positive electrode active material. The negative electrode 14 contains a negative electrode active material, and this negative electrode active material contains at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds. A separator 16 is interposed between the positive electrode 12 and the negative electrode 14 . This zinc secondary battery 10 further includes an oxidizing agent 20 capable of oxidizing zinc at a position where the zinc dendrites D that can grow from the negative electrode 14 can reach. By arranging the oxidizing agent 20 capable of oxidizing zinc at a position accessible by the zinc dendrites D in the zinc secondary battery 10 in this manner, the growth of the zinc dendrites D can be effectively suppressed. That is, when the zinc dendrite D grown from the negative electrode 14 contacts the oxidizing agent 20 in the electrolytic solution 18, the zinc dendrite D is oxidized or dissolved, thereby stopping the growth of the zinc dendrite D. That is, the zinc dendrite D is deactivated by oxidation or disappears by dissolution. As a result, the zinc secondary battery 10 can be prevented from short-circuiting and improved in cycle durability performance.

The oxidizing agent 20 is not particularly limited as long as it can oxidize zinc, but preferably does not react with the electrolytic solution 18 . Preferred examples of the oxidizing agent 20 include bismuth oxide (Bi ₂ O ₃ ), lead oxide (PbO, Pb ₃ O ₄ or PbO ₂ ), tin oxide (SnO ₂ ), manganese dioxide (MnO ₂ ), etc. Bismuth oxide is particularly preferred. For example, when zinc dendrites contact bismuth oxide in electrolyte 18, the following reactions occur:
3Zn+Bi ₂ O ₃ →3ZnO+2Bi and/or 3Zn+3H ₂ O+6OH ⁻ +Bi ₂ O ₃ →3Zn(OH) ₄ ²⁻ +2Bi
The zinc dendrites are oxidized (Bi ₂ O ₃ is reduced), so that the growth of zinc dendrites D is blocked by the oxidizing agent 20 . Therefore, in order to more reliably prevent the growth of zinc dendrites D from the negative electrode 14, the oxidant 20 is provided in layers as shown in FIG. Preferably, the separator 16 contains an oxidant 20 so that the separator 16 forms an oxidant-containing layer. The reason why the oxidant porous layer 21 is porous is to allow the electrolytic solution 18 to pass through.

The position where the oxidizing agent 20 is provided is not particularly limited as long as it is a position where the zinc dendrites D that can grow from the negative electrode 14 can reach. (In the initial state, most of the negative electrode active material is ZnO, and only a small portion of Zn is exposed on the surface. Therefore, it is assumed that the negative electrode 14 is not oxidized (deteriorated) by the oxidizing agent 20. Conceivable). In any case, it is desired to determine the position of the oxidant 20 so that the zinc dendrites D growing from the negative electrode 14 can be blocked at a position before reaching the positive electrode 12 . From this point of view, preferred examples of the position where the oxidizing agent 20 is provided (that is, the position where the zinc dendrite D that can grow from the negative electrode 14 can reach) include the surface of the separator 16, the inside of the separator 16, and between the positive electrode 12 and the separator 16. , between the negative electrode 14 and the separator 16, and combinations thereof.

The separator 16 is not particularly limited as long as it is a member interposed between the positive electrode 12 and the negative electrode 14 . Therefore, the separator 16 can of course be a so-called separator used for separating the positive electrode 12 and the negative electrode 14, and a member (for example, non-woven fabric) that wraps or covers the positive electrode 12 and/or the negative electrode 14 can also be the positive electrode 12 and the negative electrode 14. Since it is interposed between the negative electrodes 14, it corresponds to the separator 16 in this specification. Accordingly, the separator 16 may include a hydroxide ion conducting dense separator such as a layered double hydroxide (LDH) separator, or may include a microporous membrane separator. The LDH separator will be described later. Moreover, the separator 16 may contain a nonwoven fabric. In this specification, the term "nonwoven fabric" refers to a sheet-like material in which fibers are entangled without being woven, and includes not only what is called nonwoven fabric but also what is called paper. , that is, no matter what you call it. Furthermore, the separator 16 may contain at least two or more selected from the group consisting of a hydroxide ion conductive dense separator such as an LDH separator, a microporous membrane separator, and a non-woven fabric. Particularly preferably, the separator 16 includes an LDH separator and a nonwoven fabric, and the oxidizing agent 20 is provided on and/or inside one of the LDH separator and the nonwoven fabric. For example, the positive electrode 12 and negative electrode 14 may be separated by an LDH separator, and each or one of the separated positive electrode 12 and negative electrode 14 may be wrapped or covered with a nonwoven fabric.

Examples of preferred embodiments of the separator 16 supporting the oxidizing agent 20 include the following:
(i) A mode in which an oxidant porous layer 21 is provided on the surface of a hydroxide ion conducting dense separator such as an LDH separator,
(ii) in the aspect (i) above, an aspect in which the oxide ion conducting dense separator is also provided with the oxidizing agent 20; and (iv) an embodiment comprising an oxidizing agent 20 on the surface and/or inside the pores of the nonwoven fabric and/or microporous membrane separator.

A method for supporting the oxidizing agent 20 on the separator 16 is not particularly limited, but it can be preferably carried out by applying a slurry containing particles of the oxidizing agent 20 to the separator 16 . For example, the oxidant porous layer 21 can be formed on the surface of the separator 16 by applying slurry of oxidant particles to the surface of the separator 16 . In addition, an oxidant-containing layer can be formed inside the separator 16 by immersing the separator 16 in a slurry of oxidant particles and impregnating the separator 16 with the slurry. The slurry of oxidant particles may contain a binder for fixing the oxidant particles to the separator 16 .

The positive electrode 12 contains a positive electrode active material. The positive electrode active material may be appropriately selected from known positive electrode materials according to the type of zinc secondary battery, and is not particularly limited. For example, in the case of a nickel-zinc secondary battery, a positive electrode containing nickel hydroxide and/or nickel oxyhydroxide may be used. Alternatively, in the case of a zinc-air secondary battery, the air electrode may be used as the positive electrode.

The negative electrode 14 contains a negative electrode active material. The negative electrode active material contains at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds. Zinc may be contained in any form of zinc metal, zinc compound, and zinc alloy as long as it has electrochemical activity suitable for the negative electrode. Preferred examples of the negative electrode material include zinc oxide, zinc metal, calcium zincate, etc., and a mixture of zinc metal and zinc oxide is more preferred. The negative electrode active material may be configured in a gel form, or may be mixed with the electrolytic solution 18 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, polyacrylate, CMC, alginic acid, etc. Polyacrylic acid is preferable because of its excellent chemical resistance to strong alkali.

The electrolytic solution 18 preferably contains an aqueous alkali metal hydroxide solution. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide and ammonium hydroxide, with potassium hydroxide being more preferred. Zinc compounds such as zinc oxide and zinc hydroxide may be added to the electrolytic solution in order to suppress self-dissolution of zinc and/or zinc oxide. As described above, the electrolyte may be mixed with the positive electrode active material and/or the negative electrode active material to exist in the form of a positive electrode mixture and/or a negative electrode mixture. Also, the electrolyte may be gelled to prevent leakage of the electrolyte. As the gelling agent, it is desirable to use a polymer that absorbs the solvent of the electrolytic solution and swells, and polymers such as polyethylene oxide, polyvinyl alcohol and polyacrylamide, and starch are used.

LDH Separator Separator 16 contains a hydroxide ion conducting solid electrolyte, and preferably contains a hydroxide ion conducting dense separator that selectively allows hydroxide ions to pass through exclusively by utilizing hydroxide ion conductivity. Since such a dense separator can physically block zinc dendrites due to its denseness, a synergistic effect with the chemical effect of suppressing zinc dendrites by the oxidizing agent 20 can be expected. Preferred hydroxide ion-conducting solid electrolytes are layered double hydroxides (LDH) and/or LDH-like compounds. Therefore, the hydroxide ion conducting dense separator is preferably an LDH separator. As used herein, the term "LDH separator" refers to a separator containing LDH and/or LDH-like compounds, which selectively removes hydroxide ions by exclusively utilizing the hydroxide ion conductivity of LDH and/or LDH-like compounds. defined as passing through In the present specification, "LDH-like compounds" are hydroxides and/or oxides of layered crystal structure similar to LDH, although they may not be called LDH, and can be said to be equivalents of LDH. However, as a broad definition, "LDH" can be interpreted as including not only LDH but also LDH-like compounds. The LDH separator is preferably composited with the porous substrate. Therefore, it is preferable that the LDH separator further includes a porous substrate, and the LDH and/or the LDH-like compound are combined with the porous substrate in a form in which the pores of the porous substrate are filled. That is, preferred LDH separators are those in which LDH and/or LDH-like compounds are porous so as to exhibit hydroxide ion conductivity and gas impermeability (and thus function as LDH separators exhibiting hydroxide ion conductivity). block the pores of the base material. The porous substrate is preferably made of a polymeric material, and it is particularly preferable that the LDH is incorporated throughout the entire thickness direction of the porous substrate made of polymeric material. For example, known LDH separators as disclosed in Patent Documents 1-5 can be used. The thickness of the LDH separator is preferably 5-100 μm, more preferably 5-80 μm, still more preferably 5-60 μm, particularly preferably 5-40 μm.

The LDH separator preferably has a He permeability per unit area of 10 cm/min·atm or less, more preferably 5.0 cm/min·atm or less, still more preferably 1.0 cm/min·atm or less. It can be said that an LDH separator having a He permeability within such a range has extremely high density. Therefore, a separator having a He permeability of 10 cm/min·atm or less can block passage of substances other than hydroxide ions at a high level. For example, in the case of a zinc secondary battery, permeation of Zn (typically permeation of zinc ions or zincate ions) in the electrolyte can be very effectively suppressed. The He permeability is measured through a step of supplying He gas to one surface of the separator to allow the He gas to permeate the separator, and a step of calculating the He permeability and evaluating the compactness of the LDH separator. The degree of He permeation is determined by the formula F/(P×S) using the permeation amount F of He gas per unit time, the differential pressure P applied to the separator when the He gas permeates, and the membrane area S through which the He gas permeates. calculate. 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. It is possible to effectively evaluate the high degree of denseness such that the Zn that causes Zn) is not allowed to penetrate as much as possible (only a very small amount of Zn is allowed to penetrate). This is because He gas has the smallest constitutional unit among a wide variety of atoms and molecules that can constitute gas, and is extremely low in reactivity. That is, He does not form molecules, and constitutes He gas by He atoms alone. In this regard, since hydrogen gas is composed of H ₂ molecules, a single He atom is smaller as a gas constituent unit. First of all, _H2 gas is dangerous because it is a combustible gas. By adopting the index of He gas permeability defined by the above formula, objective evaluation of compactness can be easily performed regardless of various sample sizes and differences in measurement conditions. Thus, it is possible to easily, safely and effectively evaluate whether or not the separator has a sufficiently high density suitable for a zinc secondary battery separator.

The He permeation rate can be preferably measured according to the following procedure. First, a He permeation measurement system 310 shown in FIGS. 2A and 2B is constructed. In the He permeation measurement system 310, 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). The separator 318 is constructed so that it is 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 is assembled as follows. First, an adhesive 322 is applied along the outer periphery of the LDH separator 318, and attached to a jig 324 (made of ABS resin) having an opening in the center. Butyl rubber packings are provided as sealing members 326a and 326b at the upper and lower ends of the jig 324, and support members 328a and 328b (made of PTFE) having openings formed of flanges are applied from the outside of the sealing members 326a and 326b. ). Thus, the LDH separator 318, the jig 324, the sealing member 326a and the support member 328a partition the closed space 316b. The support members 328a and 328b are tightly fastened together by fastening means 330 using screws so that He gas does not leak from portions other than the gas discharge port 316c. A gas supply pipe 334 is connected via a joint 332 to the gas supply port 316 a of the sample holder 316 thus assembled.

Next, He gas is supplied to the He permeation measurement system 310 through the gas supply pipe 334 and allowed to permeate the LDH separator 318 held in the sample holder 316 . At this time, the gas supply pressure and flow rate are monitored by the pressure gauge 312 and flow meter 314 . After the He gas permeation was performed for 1 to 30 minutes, the He permeability was calculated. The He permeation rate is calculated based on the permeation amount F (cm ³ /min) of He gas per unit time, the differential pressure P (atm) applied to the LDH separator during He gas permeation, and the membrane area S (cm ² ), it was calculated by the formula of F/(P×S). The permeation amount F (cm ³ /min) of He gas was directly read from the flow meter 314 . A gauge pressure read from the pressure gauge 312 is used as the differential pressure P. The He gas is supplied so that the differential pressure P is within the range of 0.05 to 0.90 atm.

The invention is further illustrated by the following examples.

Example 1
In order to verify the effect of an oxidizing agent (bismuth oxide) on inhibiting the growth of zinc dendrites, a contact test between an oxidizing agent and zinc dendrites was conducted as follows.

(1) Preparation of bismuth oxide-coated separator A bismuth oxide (Bi ₂ O ₃ ) slurry (average particle diameter of bismuth oxide particles: about 0.5 μm) was applied and dried. Thus, a separator whose surface was coated with a bismuth oxide porous layer was produced as shown in FIG.

(2) Zinc dendrite formation As shown in FIG. 5, zinc was electrodeposited on the surface of the Cu electrode to grow zinc dendrites. Electrodeposition of zinc is performed by applying −1.7 V (vs. SHE (standard hydrogen electrode)) on the surface of the Cu electrode in an electrolytic solution (5.4 mol/L KOH aqueous solution in which 0.4 mol/L ZnO is dissolved). This was done by applying voltage for 90 minutes.

(3) Contact between zinc dendrite and bismuth oxide-coated separator A separator coated with a bismuth oxide porous layer was brought into contact with the thus-grown zinc dendrite in an electrolytic solution for about 5 minutes. , zinc dendrites were oxidized and dissolved, exposing the copper surface of the Cu electrode covered with zinc dendrites. When the change in the appearance of the separator before and after contact with zinc dendrites was confirmed, as shown in FIG. 7, it was found that the bismuth oxide in the portion contacted with zinc dendrites changed color. This is because bismuth oxide reacts with:
3Zn+Bi ₂ O ₃ →3ZnO+2Bi and/or 3Zn+3H ₂ O+6OH ⁻ +Bi ₂ O ₃ →3Zn(OH) ₄ ²⁻ +2Bi
This is thought to be because the metal bismuth (Bi) was reduced by . From this, it can be seen that bis oxide functions as an oxidizing agent to oxidize zinc dendrites, thereby significantly suppressing the growth of zinc dendrites.

Example 2
In order to further verify the zinc dendrite growth inhibitory effect of the oxidizing agent (bismuth oxide), a zinc dendrite penetration test was performed as follows.

(1) Preparation of Working Electrode As shown in FIG. 8, a Cu electrode with a diameter of 3 mm embedded in a tube made of PEEK (polyetheretherketone) was prepared, and the tip portion including this Cu electrode was stacked in two layers. It was wrapped with a non-woven fabric and fixed with an O-ring. At this time, a commercially available polypropylene nonwoven fabric (thickness: 100 μm) not coated with bismuth oxide was used on the Cu electrode side, while a nonwoven fabric coated with bismuth oxide was used on the side opposite to the Cu electrode. The nonwoven fabric coated with bismuth oxide is obtained by impregnating a commercially available polypropylene nonwoven fabric (100 μm thick) with a bismuth oxide (Bi ₂ O ₃ ) slurry (average particle diameter of bismuth oxide particles: about 0.5 μm) and drying. It contains a porous layer of bismuth oxide particles inside the nonwoven fabric. Also, no gaps were present between the Cu electrode and the nonwoven fabric and between the nonwoven fabrics. Thus, a working electrode wrapped with nonwoven fabric was obtained.

(2) Fabrication of Cell A working electrode (Cu electrode) wrapped with a non-woven fabric, a reference electrode, a counter electrode and an electrolytic solution described below were placed in a cell container to assemble a cell as shown in FIG.
・Reference electrode: Hg/HgO electrode ・Counter electrode: Pt electrode (coiled, total length 23 cm)
・Electrolyte solution: 5.4 mol/L KOH aqueous solution in which 0.4 mol/L ZnO is dissolved

(3) Precipitation and growth of zinc dendrite A voltage of −1.7 V (vs. SHE (standard hydrogen electrode)) was applied to the working electrode in the fabricated cell to deposit zinc dendrites on the working electrode (Cu electrode) wound with nonwoven fabric. It was deposited and grown, and evaluated whether it penetrated the nonwoven fabric in a given time. Specifically, by measuring whether or not the zinc dendrite penetrates two nonwoven fabrics (one of which is coated with bismuth oxide) provided on the outside thereof for a predetermined period of time, the results are as follows. , it is possible to evaluate the zinc dendrite growth inhibitory effect of bismuth oxide. As a result, zinc dendrites did not penetrate the two nonwoven fabrics even after 90 minutes from the start of voltage application, as shown in FIGS. 10A to 10C. Also, from FIGS. 10B and 10C, which are enlarged images of FIG. 10A, the presence of particulate matter instead of dendrites was confirmed on the surface of the nonwoven fabric. Analysis of this particulate matter revealed that it was particulate zinc. From this, it was found that granular zinc was deposited on the surface of metallic bismuth produced by reduction of bismuth oxide. From these results, bismuth oxide not only oxidizes zinc dendrites, but also affects the growth morphology of zinc even after it is reduced to metallic bismuth, and also has the effect of suppressing further growth of zinc dendrites. I understand. That is, in the form of such particulate matter, unlike zinc dendrites, they cannot grow in a tree-like manner toward the positive electrode, so it can be said that zinc dendrite problems such as short circuits do not occur.

Example 3 (Comparison)
A working electrode and a cell were prepared and evaluated in the same manner as in Example 2, except that the nonwoven fabric was not coated with bismuth oxide (that is, none of the two-ply nonwoven fabrics contained bismuth oxide). rice field. As a result, zinc dendrites penetrated the two nonwoven fabrics within 30 minutes from the start of voltage application, as shown in FIGS. 11A to 11C. A comparison of this result (without bismuth oxide) and the results of Example 2 (with bismuth oxide) clearly demonstrates the effect of bismuth oxide on inhibiting the growth of zinc dendrites.

REFERENCE SIGNS LIST 10 Zinc secondary battery 12 Positive electrode 14 Negative electrode 16 Separator 18 Electrolytic solution 20 Oxidant 21 Oxidant porous layer D Zinc dendrite

Claims (11)

a positive electrode comprising a positive electrode active material;
a negative electrode comprising a negative electrode active material containing at least one selected from the group consisting of zinc, zinc oxide, zinc alloys and zinc compounds;
a separator interposed between the positive electrode and the negative electrode;
an electrolyte;
A zinc secondary battery comprising
A zinc secondary battery, further comprising an oxidizing agent capable of oxidizing zinc at a position accessible to zinc dendrites that can grow from the negative electrode. 2. The method according to claim 1, wherein the oxidant is provided in layers to form an oxidant porous layer, or the separator contains the oxidant, whereby the separator forms an oxidant-containing layer. Zinc secondary battery. At least one position where zinc dendrites that can grow from the negative electrode can reach is selected from the group consisting of the surface of the separator, the inside of the separator, between the positive electrode and the separator, and between the negative electrode and the separator. The zinc secondary battery according to claim 1 or 2, wherein The zinc secondary battery according to any one of claims 1 to 3, wherein the oxidizing agent contains bismuth oxide. The zinc secondary battery according to any one of claims 1 to 4, wherein the separator comprises a layered double hydroxide (LDH) separator. The zinc secondary battery according to any one of claims 1 to 5, wherein the separator comprises a microporous membrane separator. The zinc secondary battery according to any one of claims 1 to 6, wherein the separator comprises a non-woven fabric. Any one of claims 1 to 7, wherein the separator comprises a layered double hydroxide (LDH) separator and a nonwoven fabric, and the oxidizing agent is provided on and/or inside one of the LDH separator and the nonwoven fabric. 1. The zinc secondary battery according to item 1. The zinc secondary battery according to claim 5 or 8, wherein said layered double hydroxide (LDH) separator has a He permeability per unit area of 10 cm/min·atm or less. The zinc secondary battery according to any one of claims 1 to 9, wherein said positive electrode comprises nickel hydroxide and/or nickel oxyhydroxide, whereby said zinc secondary battery constitutes a nickel-zinc secondary battery. The zinc secondary battery according to any one of claims 1 to 9, wherein said positive electrode is an air electrode, whereby said zinc secondary battery constitutes a zinc air secondary battery.

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