Zinc secondary battery

Abstract

To provide a zinc secondary battery capable of effectively suppressing the growth of zinc dendrites.SOLUTION: A zinc secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including 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, and an electrolyte, and further includes an oxidizing agent capable of oxidizing zinc into locations accessible for zinc dendrites that can grow from the negative electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a zinc secondary battery. [Background technology]

[0002] In zinc secondary batteries, such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrates the pores of the separator (e.g., nonwoven fabric) and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the battery's life after repeated charging and discharging.

[0003] To address the above-mentioned problems, batteries have been proposed that include a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing zinc dendrites from penetrating. For example, Patent Document 1 (WO 2013 / 118561) discloses a nickel-zinc secondary battery in which an LDH separator is provided between the positive and negative electrodes. Patent Document 2 (WO 2016 / 076047) also discloses a separator structure that includes an LDH separator fitted or bonded to a resin outer frame, and that the LDH separator has such high density that it is gas- and / or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Patent Document 3 (WO 2016 / 067884) also discloses various methods for forming a dense LDH film on the surface of a porous substrate to obtain a composite material. This method includes the steps of uniformly attaching a starting substance capable of providing starting points 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 an LDH / porous substrate composite material produced through hydrothermal treatment. For example, Patent Document 4 (WO 2019 / 124270) discloses an LDH separator that includes a polymeric porous substrate and an LDH filled in the porous substrate, and has an in-line transmittance of 1% or more at a wavelength of 1000 nm.

[0004] Additionally, although not classified as 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-conducting layered compounds together with LDHs. For example, Patent Document 5 (WO 2020 / 255856) discloses a hydroxide ion-conducting separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that plugs the pores of the porous substrate, in which 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. This hydroxide ion-conducting separator is 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 118561 [Patent Document 2] International Publication No. 2016 / 076047 [Patent Document 3] International Publication No. 2016 / 067884 [Patent Document 4] International Publication No. 2019 / 124270 [Patent Document 5] International Publication No. 2020 / 255856 Summary of the Invention

[0006] The LDH separator described above can only physically prevent 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, this would be advantageous in that it would be possible to address the problem of zinc dendrites not only in zinc secondary batteries using hydroxide ion conductive dense separators such as LDH separators, but also in zinc secondary batteries using microporous membrane separators.

[0007] The present inventors have now discovered that the growth of zinc dendrites can be effectively suppressed by disposing an oxidizing agent capable of oxidizing zinc at a position within a zinc secondary battery that is reachable by zinc dendrites.

[0008] Therefore, an object of the present invention is to provide a zinc secondary battery that can effectively suppress the growth of zinc dendrites.

[0009] According to one aspect of the present invention, a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material including 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: There is provided a zinc secondary battery further comprising an oxidizing agent capable of oxidizing zinc at a location accessible to zinc dendrites that can grow from the negative electrode. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram conceptually showing the basic structure of a zinc secondary battery of the present invention and the zinc dendrite growth suppression effect. [Figure 2A] FIG. 1 is a conceptual diagram showing an example of a He permeability measurement system used in Examples 1 to 10. [Figure 2B]2B is a schematic cross-sectional view of a sample holder and its peripheral configuration used in the measurement system shown in FIG. 2A. [Figure 3] 1 is a photograph of the microporous membrane separator used in Example 1. [Figure 4] 1 shows a cross-sectional SEM image of the bismuth oxide coated separator produced in Example 1 and an enlarged image thereof. [Figure 5] 1 is a photograph of the Cu electrode used in Example 1 before and after zinc dendrite deposition. [Figure 6] 1 is a photograph of a Cu electrode on which zinc dendrites have grown in Example 1, taken before and after contact with a bismuth oxide-coated separator. [Figure 7] 3 is a photograph of the bismuth oxide coated separator in Example 1 before and after contact with zinc dendrites. [Figure 8] 10 is a photograph of the working electrode used in Example 2 before and after being wrapped with nonwoven fabric. [Figure 9] 1 is a photograph of the cell used in Example 2. [Figure 10A] 1 is a photograph of the surface of the nonwoven fabric taken 90 minutes after the start of voltage application in Example 2. [Figure 10B] 10B is an enlarged photograph of the surface of the nonwoven fabric shown in FIG. 10A. [Figure 10C] 10B is an enlarged photograph of the surface of the nonwoven fabric shown in FIG. 10A. [Figure 11A] 1 is a photograph of zinc dendrites that penetrated the surface of the nonwoven fabric within 30 minutes of starting voltage application in Example 3 (Comparative Example). [Figure 11B] FIG. 11B is a magnified photograph of the zinc dendrite shown in FIG. 11A. [Figure 11C] FIG. 11B is a magnified photograph of the zinc dendrite shown in FIG. 11A. DETAILED DESCRIPTION OF THE INVENTION

[0011] Zinc secondary battery The zinc secondary battery of the present invention is not particularly limited as long as it uses zinc as the negative electrode and an alkaline electrolyte (typically an aqueous alkali metal hydroxide solution). Therefore, it can be a nickel-zinc secondary battery, a silver oxide-zinc secondary battery, a manganese oxide-zinc secondary battery, an air-zinc secondary battery, or any other type of alkaline zinc secondary battery. For example, it is preferable that the positive electrode active material layer contains nickel hydroxide and / or nickel oxyhydroxide, thereby forming the zinc secondary battery into a nickel-zinc secondary battery. Alternatively, the positive electrode active material layer may be an air cathode layer, thereby forming the zinc secondary battery into an air-zinc secondary battery.

[0012] 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, a separator 16, and an electrolyte 18. The negative electrode 14 contains zinc and / or zinc oxide. The positive electrode 12 includes a positive electrode active material. The negative electrode 14 includes a negative electrode active material, which includes at least one selected from the group consisting of zinc, zinc oxide, a zinc alloy, and a zinc compound. The separator 16 is interposed between the positive electrode 12 and the negative electrode 14. The zinc secondary battery 10 further includes an oxidizer 20 capable of oxidizing zinc, located at a position accessible to zinc dendrites D that may grow from the negative electrode 14. By disposing the oxidizer 20 capable of oxidizing zinc at a position accessible to zinc dendrites D within the zinc secondary battery 10, the growth of zinc dendrites D can be effectively suppressed. That is, when zinc dendrite D growing from negative electrode 14 comes into contact with oxidizing agent 20 in electrolyte 18, zinc dendrite D is oxidized or dissolved, thereby stopping the growth of zinc dendrite D. That is, zinc dendrite D is deactivated by oxidation or disappears by dissolution. As a result, it is possible to prevent short circuits and improve cycle durability in zinc secondary battery 10.

[0013] The oxidizing agent 20 is not particularly limited as long as it can oxidize zinc, but it is desirable that it does not react with the electrolyte 18. Preferred examples of the oxidizing agent 20 include bismuth oxide (Bi2O3), lead oxide (PbO, Pb3O4, or PbO2), tin oxide (SnO2), manganese dioxide (MnO2), etc., and bismuth oxide is particularly preferred. For example, when zinc dendrites come into contact with bismuth oxide in the electrolyte 18, the following reaction occurs: 3Zn + Bi2O3 → 3ZnO + 2Bi, and / or 3Zn+3H2O+6OH - +Bi2O3→3Zn(OH)4 2- +2Bi As a result, the zinc dendrites are oxidized (Bi2O3 is reduced), and as a result, the growth of zinc dendrites D is blocked by the oxidizing agent 20. Therefore, in order to more reliably block the growth of zinc dendrites D from the negative electrode 14, it is preferable that the oxidizing agent 20 is provided in a layered form to form an oxidizing agent porous layer 21 as shown in FIG. 1, or that the separator 16 contains the oxidizing agent 20, thereby forming an oxidizing agent-containing layer. The oxidizing agent porous layer 21 is made porous so that it can pass through the electrolyte 18.

[0014] The location where the oxidizer 20 is provided is not particularly limited as long as it is a location reachable by zinc dendrites D that can grow from the negative electrode 14. The oxidizer 20 may be provided at a location that does not come into direct contact with the negative electrode 14, or may be provided at a location that comes into direct contact with the negative electrode 14 (since most of the negative electrode active material is ZnO in the initial state and only a small amount of Zn is exposed on the surface, oxidation (deterioration) of the negative electrode 14 by the oxidizer 20 is thought to not occur). In any case, it is desirable to determine the location of the oxidizer 20 so that the zinc dendrites D growing from the negative electrode 14 can be blocked at a location before they reach the positive electrode 12. From this perspective, preferred examples of the location where the oxidizer 20 is provided (i.e., a location reachable by zinc dendrites D that can grow from the negative electrode 14) include the surface of the separator 16, the inside of the separator 16, between the positive electrode 12 and the separator 16, between the negative electrode 14 and the separator 16, and combinations thereof.

[0015] 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 be a so-called separator used to separate the positive electrode 12 and the negative electrode 14. Furthermore, a member (e.g., a nonwoven fabric) that wraps or covers the positive electrode 12 and / or the negative electrode 14 is also considered to fall under the term "separator 16" in this specification, since it is interposed between the positive electrode 12 and the negative electrode 14. Therefore, the separator 16 may include a hydroxide ion conductive dense separator such as a layered double hydroxide (LDH) separator, or a microporous membrane separator. LDH separators will be described later. The separator 16 may also include a nonwoven fabric. In this specification, the term "nonwoven fabric" refers to a sheet-like material in which fibers are intertwined without being woven, and includes not only those called nonwoven fabrics but also those called paper, regardless of the name. Furthermore, the separator 16 may include 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 nonwoven fabric. Particularly preferably, the separator 16 includes an LDH separator and a nonwoven fabric, and the oxidizer 20 is provided on the surface and / or inside of either the LDH separator or the nonwoven fabric. For example, the positive electrode 12 and the negative electrode 14 may be separated by an LDH separator, and either or both of the separated positive electrode 12 and the negative electrode 14 may be wrapped or covered with a nonwoven fabric.

[0016] Examples of preferred embodiments of the separator 16 loaded with the oxidizing agent 20 include the following: (i) An embodiment in which an oxidant porous layer 21 is provided on the surface of a hydroxide ion conductive dense separator such as an LDH separator; (ii) In the above embodiment (i), an oxidizing agent 20 is also provided inside the oxide ion conductive dense separator; and (iii) an embodiment with an oxidizer 20 inside an oxide-ion conducting dense separator, such as an LDH separator; and (iv) An embodiment in which the oxidizing agent 20 is contained on the surface and / or inside the pores of the nonwoven fabric and / or microporous membrane separator.

[0017] The method for supporting the oxidant 20 on the separator 16 is not particularly limited, but is preferably carried out by applying a slurry containing particles of the oxidant 20 to the separator 16. For example, by applying a slurry of oxidant particles to the surface of the separator 16, an oxidant porous layer 21 can be formed on the surface of the separator 16. Alternatively, by immersing the separator 16 in a slurry of oxidant particles to impregnate the separator 16 with the slurry, an oxidant-containing layer can be formed inside the separator 16. The slurry of oxidant particles may contain a binder for adhering the oxidant particles to the separator 16.

[0018] The positive electrode 12 contains a positive electrode active material. The positive electrode active material may be selected appropriately from known positive electrode materials depending on 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 an air-zinc secondary battery, an air electrode may be used as the positive electrode.

[0019] The negative electrode 14 includes a negative electrode active material. The negative electrode active material 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 solution 18 to form a negative electrode composite. For example, a gelled negative electrode can be easily obtained by adding an electrolyte solution 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.

[0020] The electrolyte 18 preferably contains 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. To suppress the self-dissolution of zinc and / or zinc oxide, a zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte. As described above, the electrolyte may be mixed with a positive electrode active material and / or a negative electrode active material to form a positive electrode composite and / or a negative electrode composite. The electrolyte may also be gelled to prevent leakage of the electrolyte. A polymer that absorbs the solvent of the electrolyte and swells is preferably used as the gelling agent. Examples of suitable gelling agents include polymers such as polyethylene oxide, polyvinyl alcohol, and polyacrylamide, as well as starch.

[0021] LDH separator Separator 16 preferably includes a hydroxide ion-conducting dense separator that contains a hydroxide ion-conducting solid electrolyte and selectively transmits hydroxide ions solely by utilizing its hydroxide ion conductivity. Such dense separators can physically block zinc dendrites due to their denseness, which is expected to have a synergistic effect with the chemical zinc dendrite suppression effect of oxidizer 20. A preferred hydroxide ion-conducting solid electrolyte is a layered double hydroxide (LDH) and / or an LDH-like compound. Therefore, the hydroxide ion-conducting dense separator is preferably an LDH separator. As used herein, an "LDH separator" is defined as a separator containing LDH and / or an LDH-like compound that selectively transmits hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and / or LDH-like compound. As used herein, an "LDH-like compound" refers to a hydroxide and / or oxide with a layered crystal structure similar to LDH, even if it may not be called an LDH, and can be considered an equivalent of LDH. However, in a broad sense, "LDH" can be interpreted as encompassing not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and / or LDH-like compounds. That is, in a preferred LDH separator, the pores of the porous substrate are filled with LDH and / or LDH-like compounds so as to exhibit hydroxide ion conductivity and gas impermeability (and therefore function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferred that the LDH is incorporated throughout the entire thickness of the porous substrate made of a polymer material. For example, known LDH separators such as those disclosed in Patent Documents 1 to 5 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.

[0022] 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, and even more preferably 1.0 cm / min·atm or less. LDH separators with He permeabilities within this range are considered to have extremely high density. Therefore, separators with 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 zinc secondary batteries, they can effectively suppress the permeation of Zn (typically zinc ions or zincate ions) in the electrolyte. 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 using the formula F / (P×S), where F is the amount of He gas permeated per unit time, P is the differential pressure applied to the separator during He gas permeation, and S is the membrane area through which He gas permeates. Evaluating gas permeability using He gas in this way allows for an extremely high level of densification, which effectively evaluates the high level of densification, such as minimizing (or allowing only trace amounts of) permeation of substances other than hydroxide ions (especially Zn, which induces zinc dendrite growth). This is because He gas has the smallest structural unit of the various atoms and molecules that can constitute gases and is also extremely low in reactivity. He is composed of single He atoms without forming molecules. In contrast, hydrogen gas is composed of H2 molecules, so single He atoms are smaller as gas structural units. H2 gas is inherently flammable and therefore dangerous. Furthermore, by employing the He gas permeability index defined by the above formula, objective evaluation of densification can be easily performed regardless of differences in sample size and measurement conditions. In this way, it is possible to simply, safely, and effectively evaluate whether a separator has a sufficiently high densification suitable for use in zinc secondary batteries.

[0023] Measurement of He permeability can be preferably carried out according to the following procedure. First, a He permeability measurement system 310 shown in Figures 2A and 2B 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 is transmitted from one side to the other side of an LDH separator 318 held by the sample holder 316 and then discharged.

[0024] 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, 328b are tightly fastened together using fastening means 330 using screws to prevent He gas leakage from areas other than the gas exhaust 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.

[0025] Next, He gas was supplied to the He permeability measurement system 310 via the gas supply pipe 334 and allowed to permeate through the LDH separator 318 held in the sample holder 316. At this time, the gas supply pressure and flow rate were monitored by the pressure gauge 312 and flow meter 314. After the He gas permeation was allowed to continue for 1 to 30 minutes, the He permeability was calculated. The He permeability was 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 when He gas permeates, and the membrane area S (cm 2 ) was used to calculate the He gas permeation rate F (cm 3 / min) was read directly from the flow meter 314. The differential pressure P was measured using a gauge pressure read from the pressure gauge 312. The He gas was supplied so that the differential pressure P was in the range of 0.05 to 0.90 atm. [Example]

[0026] The present invention will be further illustrated by the following examples.

[0027] Example 1 In order to verify the effect of an oxidizing agent (bismuth oxide) in inhibiting the growth of zinc dendrites, a contact test between the oxidizing agent and zinc dendrites was carried out as follows.

[0028] (1) Preparation of bismuth oxide coated separator A bismuth oxide (Bi2O3) slurry (average particle size of bismuth oxide particles: approximately 0.5 μm) was applied to the surface of a commercially available microporous membrane separator (made of polypropylene, thickness: 25 μm) shown in Figure 3 and then dried. In this way, a separator whose surface was covered with a bismuth oxide porous layer was produced, as shown in Figure 4.

[0029] (2) Zinc dendrite formation As shown in Figure 5, zinc dendrites were grown by electrodepositing zinc on the surface of a Cu electrode. Zinc was deposited by applying a voltage of -1.7 V (vs. SHE (standard hydrogen electrode)) to the surface of the Cu electrode for 90 minutes in an electrolyte (5.4 mol / L KOH aqueous solution in which 0.4 mol / L ZnO was dissolved).

[0030] (3) Contact between zinc dendrites and bismuth oxide-coated separator When the separator coated with the bismuth oxide porous layer was brought into contact with the zinc dendrites grown in this way in an electrolyte for about 5 minutes, the zinc dendrites were oxidized and dissolved, exposing the copper surface of the Cu electrode that had been covered with the zinc dendrites, as shown in Figure 6. When the change in the appearance of the separator before and after contact with the zinc dendrites was confirmed, it was found that the bismuth oxide in the area that had come into contact with the zinc dendrites had changed color, as shown in Figure 7. This is because bismuth oxide reacts with the following reaction: 3Zn + Bi2O3 → 3ZnO + 2Bi, and / or 3Zn+3H2O+6OH - +Bi2O3→3Zn(OH)4 2- +2Bi This is thought to be because bismuth (Bi) was reduced by the oxidizer to form metallic bismuth (Bi). This shows that bismuth oxide functions as an oxidizing agent to oxidize zinc dendrites, thereby significantly suppressing the growth of zinc dendrites.

[0031] Example 2 To further verify the effect of the oxidizing agent (bismuth oxide) in inhibiting the growth of zinc dendrites, a test of zinc dendrite penetration into nonwoven fabric was carried out as follows.

[0032] (1) Preparation of working electrode As shown in Figure 8, a 3 mm diameter Cu electrode embedded in a PEEK (polyether ether ketone) tube was prepared. The tip, including the Cu electrode, was wrapped in two layers of nonwoven fabric and secured with an O-ring. A commercially available polypropylene nonwoven fabric (100 μm thick) without bismuth oxide coating was used on the Cu electrode side, while a nonwoven fabric coated with bismuth oxide was used on the opposite side. The bismuth oxide-coated nonwoven fabric was obtained by impregnating a commercially available polypropylene nonwoven fabric (100 μm thick) with bismuth oxide (BiO) slurry (average particle size of bismuth oxide particles: approximately 0.5 μm) and drying it. The nonwoven fabric contained a porous layer of bismuth oxide particles. Furthermore, no gaps were present between the Cu electrode and the nonwoven fabric, or between the nonwoven fabrics themselves. In this way, a working electrode wrapped in nonwoven fabric was obtained.

[0033] (2) Cell preparation A working electrode (Cu electrode) wrapped in nonwoven fabric, a reference electrode, a counter electrode, and an electrolyte 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: 5.4 mol / L KOH aqueous solution with 0.4 mol / L ZnO dissolved

[0034] (3) Precipitation and growth of zinc dendrites In the fabricated cell, a voltage of −1.7 V (vs. SHE (standard hydrogen electrode)) was applied to the working electrode to precipitate and grow zinc dendrites on the working electrode (Cu electrode) wrapped with a nonwoven fabric. Whether or not the zinc dendrites penetrated the nonwoven fabric within a predetermined time was evaluated. Specifically, by measuring whether or not the zinc dendrites penetrated two outer layers of nonwoven fabric (one of which was coated with bismuth oxide) within a predetermined time, the effect of bismuth oxide in inhibiting the growth of zinc dendrites could be evaluated by comparison with Example 3 described below. As a result, as shown in Figures 10A to 10C, even 90 minutes after the start of voltage application, the zinc dendrites did not penetrate the two layers of nonwoven fabric. Furthermore, Figures 10B and 10C, which are enlarged images of Figure 10A, confirmed the presence of granular material on the surface of the nonwoven fabric instead of dendrites. Analysis of this granular material revealed that it was granular zinc. This indicates that granular zinc precipitated on the surface of metallic bismuth produced by the reduction of bismuth oxide. These results indicate that bismuth oxide not only oxidizes zinc dendrites, but also affects the growth morphology of zinc after it is reduced to metallic bismuth, suppressing further growth of zinc dendrites. In other words, if the bismuth oxide is in the form of such a granular substance, it cannot grow in a dendritic form toward the positive electrode like zinc dendrites, and therefore zinc dendrite problems such as short circuits do not occur.

[0035] Example 3 (comparison) A working electrode and cell were fabricated and evaluated in the same manner as in Example 2, except that bismuth oxide was not applied to the nonwoven fabric (i.e., neither of the two layers of nonwoven fabric contained bismuth oxide). As a result, as shown in Figures 11A to 11C, zinc dendrites penetrated the two layers of nonwoven fabric within 30 minutes of the start of voltage application. Comparing this result (without bismuth oxide) with the result of Example 2 (with bismuth oxide), the effect of bismuth oxide in inhibiting the growth of zinc dendrites is clear. [Explanation of symbols]

[0036] 10 Zinc secondary battery 12 Positive electrode 14 Negative electrode 16 Separator 18 Electrolyte 20 Oxidizing Agents 21 Oxidant porous layer D zinc dendrite

Claims

1. a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material including 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: an oxidizing agent capable of oxidizing zinc is provided at a location accessible to zinc dendrites that may grow from the negative electrode; A zinc secondary battery, wherein the oxidizing agent comprises at least one selected from the group consisting of bismuth oxide, lead oxide, and manganese dioxide.

2. 2. The zinc secondary battery according to claim 1, wherein the oxidant is provided in a layered form to form an oxidant porous layer, or the separator contains the oxidant, thereby forming an oxidant-containing layer.

3. 3. The zinc secondary battery according to claim 1, wherein the accessible position of zinc dendrites that can grow from the negative electrode is at least one 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.

4. The zinc secondary battery according to any one of claims 1 to 3, wherein the oxidizing agent comprises bismuth oxide.

5. The zinc secondary battery according to any one of claims 1 to 4, wherein the separator comprises a layered double hydroxide (LDH) separator.

6. The zinc secondary battery according to any one of claims 1 to 5, wherein the separator comprises a microporous membrane separator.

7. The zinc secondary battery according to any one of claims 1 to 6, wherein the separator comprises a nonwoven fabric.

8. The zinc secondary battery according to any one of claims 1 to 7, wherein the separator comprises a layered double hydroxide (LDH) separator and a nonwoven fabric, and the oxidant is provided on the surface and / or inside of either the LDH separator or the nonwoven fabric.

9. 9. The zinc secondary battery according to claim 5, wherein the layered double hydroxide (LDH) separator has a He permeability per unit area of ​​10 cm / min·atm or less.

10. The zinc secondary battery according to any one of claims 1 to 9, wherein the positive electrode contains nickel hydroxide and / or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery.

11. The zinc secondary battery according to any one of claims 1 to 9, wherein the positive electrode is an air electrode, thereby forming the zinc secondary battery into an air-zinc secondary battery.

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