Zinc negative electrode secondary battery

Abstract

To provide a zinc compound or zinc-manganese oxide secondary battery using an aqueous electrolyte.SOLUTION: In order to realize a zinc compound or zinc-manganese oxide secondary battery, a mixed aqueous solution containing zinc chloride as the main component of the electrolyte and manganese chloride as the secondary component of the electrolyte is used.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a secondary battery that combines a manganese oxide positive electrode and a zinc compound or zinc negative electrode. [Background technology]

[0002] As electronic devices become smaller, thinner, and lighter, secondary batteries capable of high-energy charging and high-efficiency discharging are being developed for use as power sources and backup batteries. Secondary batteries are also being developed for electric vehicles and distributed energy storage. Currently, the most widely used secondary battery is lithium-ion secondary batteries, but because they use organic electrolytes, they pose a risk of smoke, fire, and explosion if the battery shorts. In contrast, secondary batteries using aqueous electrolytes are expected to be used in a wide range of fields due to their safety and low environmental impact. To eliminate the risk of fire, secondary batteries using aqueous electrolytes instead of organic electrolytes are essential, especially for electric vehicles. Among secondary batteries using aqueous electrolytes, zinc-negative secondary batteries are highly important. In particular, zinc-manganese dioxide batteries, which use manganese dioxide for the cathode, have attracted attention due to their low cost. The following literature reports on batteries using manganese dioxide and zinc for the cathode and anode, respectively. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 3,019,141 [Non-patent literature]

[0004] [Non-Patent Document 1] Denki Kagaku 52, No.8(1984)509 Summary of the Invention [Problem to be solved by the invention]

[0005] Currently, dry batteries, which combine manganese dioxide and zinc, are widely used. This battery system uses zinc chloride as the electrolyte, and the discharge reaction is as follows: Positive electrode) MnO2+ H + + e - → MnOOH Negative electrode)4Zn + ZnCl2+ 8H2O → ZnCl2·4Zn(OH)2+ 8H + + 8e - Total reaction: 4Zn + 8MnO2 + ZnCl2 + 8H2O → ZnCl2·4Zn(OH)2 + 8MnOOH This battery is widely used around the world, but its only drawback is that it is a primary battery and therefore disposable. It goes without saying that if this battery could function as a secondary battery, its convenience would be greatly improved. If the charge / discharge reaction of this battery system is a one-electron reaction, the theoretical capacity would be 308 Ah / kg, but if MnO is used instead of MnO2, the theoretical charge capacity would be 377 Ah / kg, and the energy density would increase by more than 20%. [Means for solving the problem]

[0006] The zinc compound-manganese oxide battery of the present disclosure includes a cathode active material mainly composed of a mixture of at least one of manganese monoxide, manganese tetroxide, manganese trioxide, and manganese dioxide, an anode active material composed of an oxygen-containing zinc compound or metallic zinc, and an aqueous electrolyte containing zinc chloride as a major component and manganese chloride as a minor component. The oxygen-containing zinc compound is, for example, zinc oxide, zinc hydroxide, or a basic zinc compound, or a mixture thereof.

[0007] The aqueous electrolyte is an aqueous solution of zinc chloride and manganese chloride, with the respective concentrations adjusted to 2.1M or more and less than 4M and less than 2M, respectively. [Effects of the Invention]

[0008] The zinc or zinc compound-manganese oxide battery of the present disclosure operates as a rechargeable secondary battery that exhibits good cycle characteristics.

[0009] When MnO is used as the positive electrode active material, it is preferable to use an oxygen-containing zinc compound as the negative electrode active material. The reason for this is as follows: When MnO is used as the positive electrode active material, it is converted to Mn2O3 by an oxidation reaction during charging, so an active material that can supply oxygen is required on the negative electrode side. When metallic zinc is used for the negative electrode, it cannot serve as an oxygen source, so water in the electrolyte is used as the oxygen source. However, in this case, the pH of the electrolyte fluctuates, resulting in unstable battery characteristics.

[0010] When metallic zinc is used as the negative electrode active material, it is preferable to use manganese tetroxide, manganese trioxide, manganese dioxide, or a mixture of two or more of these as the positive electrode active material. For example, when MnO2 is used as the positive electrode active material, Mn2O3 or Mn3O4 is produced by a discharge reaction, and oxygen is released. Therefore, in this case, metallic zinc may be used in addition to an oxygen-containing zinc compound for the negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0011] The zinc compound-manganese oxide battery of the present disclosure comprises a positive electrode active material primarily composed of manganese monoxide, manganese tetroxide, manganese trioxide, manganese dioxide, or a mixture of two or more of these, a negative electrode active material composed of zinc oxide, zinc hydroxide, a mixture of at least one basic zinc compound, or metallic zinc, and an aqueous electrolyte. In this specification and claims, the term "primarily composed of" means that the total of the target substances accounts for 90% by mass or more of the total amount of the positive electrode active material or negative electrode active material.

[0012] Next, the aqueous electrolyte solution according to this embodiment will be described.

[0013] In the aqueous electrolyte according to this embodiment, the electrolyte contains zinc chloride as a major component and manganese chloride as a minor component. In this specification and claims, "major component" refers to the electrolyte component with the highest molar concentration in the electrolyte, and "minor component" refers to an electrolyte component that is not the major component. The respective concentrations of zinc chloride and manganese chloride in the aqueous electrolyte are preferably 2.1M to 4M and less than 2M, more preferably 2.1M to 3.5M and 0.5M to 1.5M, and even more preferably 2.1M to 2.7M and 0.5M to 1M. Manganese chloride precipitates when temperatures drop in winter at concentrations above 2M, so use at concentrations above 2M is not recommended.

[0014] The aqueous electrolyte solution according to this embodiment can exhibit suitable cycle characteristics for a secondary battery when the zinc chloride and manganese chloride concentrations are within the above ranges. If the concentrations are higher than this range, the viscosity of the electrolyte solution increases, and the internal resistance of the battery increases. If the concentrations are lower, zinc chloride precipitates, making the solution unusable as an electrolyte.

[0015] Next, the positive electrode active material according to this embodiment is mainly composed of manganese oxide, which will be described below.

[0016] The manganese oxide of this embodiment has a composition of MnOx (1≦x≦2), and specific examples include manganese dioxide (MnO2) (x=2), manganese trioxide (Mn2O3) (x=3 / 2), manganese tetroxide (Mn3O4) (x=4 / 3), and manganese monoxide (MnO) (x=1). The smaller the value of x, the lower the oxidation state of manganese, resulting in a higher charge capacity. In the case of MnO2 and Mn2O3, the oxidation state of manganese is so high that charging is not possible; instead, discharging must be initiated. Furthermore, by using a classifier to remove large particles by reducing the manganese oxide to 63 μm or less, electrodes with a uniform thickness can be produced, enabling the fabrication of batteries with stable electrochemical characteristics.

[0017] In the secondary battery according to this embodiment, the negative electrode active material is primarily an oxygen-containing zinc compound, metallic zinc, or a combination thereof. Examples of oxygen-containing zinc compounds include zinc oxide (ZnO), zinc hydroxide (Zn(OH)2), basic zinc compounds, or combinations thereof. Examples of basic zinc compounds include zinc chloride-zinc hydroxide hydrate (ZnCl2·4Zn(OH)2·H2O). By using a classifier to reduce the particle size of these zinc compounds to 63 μm or less and removing large particles, an electrode with a uniform film thickness can be fabricated, resulting in a battery with stable electrochemical characteristics.

[0018] Next, a method for preparing an electrode will be described. In this embodiment, applying a paste of active material to a current collector foil enables good charge and discharge. Specifically, graphite sheet, nickel foil, or the like is used as the positive electrode current collector foil, and acetylene black, carbon black, fine graphite particles, milled carbon fiber, or the like is used as a conductive additive. Furthermore, styrene butadiene resin (SBR), Teflon (registered trademark) powder, polyvinylidene fluoride, or the like is used as a binder. An electrode with good cycle characteristics can be prepared by mixing an appropriate amount of these materials with the active material, forming a paste, applying it to the current collector foil, and then drying it. The negative electrode is the same as the positive electrode, except that zinc foil is used as the current collector. [Example]

[0019] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

[0020] Example 1 The positive and negative electrode active materials were manganese monoxide (MnO) and zinc oxide (ZnO), manufactured by Kojundo Chemical Laboratory Co., Ltd. Each material was sieved to a particle size of 63 μm or less, then mixed with a conductive additive (acetylene black) and dispersed in a CMC solution of SBR binder to prepare a paste.

[0021] MnO paste was applied to the graphite sheet at 10 mg / cm 2The ZnO paste was applied to the zinc foil in a coating amount of 20 mg / cm. 2 The binder ratio was 8 parts by weight relative to 100 parts by weight of MnO and ZnO.

[0022] A bipolar sealed cell was assembled using the positive electrode prepared as described above, a negative electrode, and a mixed solution of 2.5M zinc chloride and 1M manganese chloride as the electrolyte, and a charge-discharge test was performed. Assuming the theoretical charge capacity of MnO to be 377 Ah / kg, the 10-hour discharge current value was calculated, and a charge-discharge cycle test was performed at a constant current over a voltage range of 0.1 to 1.9 V.

[0023] Example 2 A cell was produced in the same manner as in Example 1, except that the positive electrode active material was changed to manganese dioxide β-MnO2. After first performing a preliminary discharge once, a charge-discharge cycle test was carried out.

[0024] Example 3 In Example 1, zinc foil was used as the negative electrode current collector, and ZnO paste on the zinc foil was used as the negative electrode active material. In Example 3, ZnO paste was not applied to the zinc foil, and zinc foil was used as the negative electrode current collector and the negative electrode active material. The other configurations of the secondary battery were the same as those of the secondary battery of Example 1. A charge-discharge test was performed on the secondary battery of Example 3 in the same manner as in Example 1.

[0025] (Comparative Example 1) A charge-discharge test was carried out in the same manner as in Example 1, except that the electrolyte solution was changed to 2.5 M zinc chloride only.

[0026] The discharge capacities (Ah / kg) of Examples 1, 2, and 3 and Comparative Example 1 are shown in Table 1. The capacity increases of Examples 1, 2, and 3 are significant, and it is clear that the mixed electrolyte of zinc chloride and manganese chloride is superior.

[0027] Furthermore, when Example 1, which uses zinc oxide as the negative electrode active material, is compared with Example 3, which uses zinc, it is found that Example 1 has a larger discharge capacity at any cycle number. This is thought to be because when manganese monoxide is used as the positive electrode active material, zinc oxide is more suitable than zinc as the negative electrode active material. [Table 1]

[0028] Example 4 In Example 2, a charge-discharge test was performed in the same manner as in Example 2, except that the negative electrode was replaced with zinc foil (metallic zinc) which served as both the active material and current collector, the zinc chloride concentration was set to 2.5 M, the manganese chloride concentration was set to 0.5 M, and charge-discharge was performed at a 20-hour rate.

[0029] Example 5 A charge-discharge test was carried out in the same manner as in Example 4, except that the zinc chloride concentration was 2.5M and the manganese chloride concentration was 1.0M.

[0030] Example 6 A charge-discharge test was carried out in the same manner as in Example 4, except that the zinc chloride concentration was 2.5M and the manganese chloride concentration was 1.5M.

[0031] (Comparative Example 2) A charge-discharge test was carried out in the same manner as in Example 4, except that the zinc chloride concentration was 2.5M and the manganese chloride concentration was 0M.

[0032] The discharge capacities of Examples 4, 5, and 6 and Comparative Example 2 are shown in Table 2. The increase in capacity of the examples is remarkable, and it can be seen that the secondary batteries of Examples 4, 5, and 6, which used a mixed electrolyte of zinc chloride and manganese chloride, had larger discharge capacities than Comparative Example 2, which used an electrolyte of only zinc chloride. [Table 2]

[0033] A zinc compound-manganese oxide secondary battery using the mixed electrolyte of 2.1 M or more and less than 4 M zinc chloride and less than 2 M manganese chloride as an electrolytic solution according to the present disclosure exhibits good cycle characteristics. [Industrial Applicability]

[0034] The zinc compound or zinc-manganese oxide secondary battery of the present disclosure can be used as a power source or backup for electronic devices, as a power source for electric vehicles, and for distributed power storage.

Claims

1. A chargeable and dischargeable secondary battery including a positive electrode, a negative electrode, and an aqueous electrolyte, the positive electrode comprises a positive electrode active material mainly composed of manganese monoxide, manganese tetroxide, manganese trioxide, manganese dioxide, or a mixture of two or more thereof; the negative electrode comprises a negative electrode active material mainly composed of an oxygen-containing zinc compound, metallic zinc, or a combination thereof; The aqueous electrolyte of the secondary battery contains zinc chloride as a main component and manganese chloride as a secondary component.

2. The secondary battery according to claim 1, The secondary battery, wherein the aqueous electrolyte contains zinc chloride at a concentration of 2.1 M or more and less than 4 M as a main component, and manganese chloride at a concentration of less than 2 M as a secondary component.

3. The secondary battery according to claim 1, The secondary battery, wherein the positive electrode current collector is a graphite sheet.

4. The secondary battery according to claim 1, The negative electrode current collector is a zinc foil.

5. The secondary battery according to claim 4, The negative electrode active material and the current collector of the negative electrode are a common zinc foil.

6. The secondary battery according to claim 1, The negative electrode active material of the secondary battery is mainly composed of an oxygen-containing zinc compound.

7. 7. The secondary battery according to claim 6, The oxygen-containing zinc compound is zinc oxide.

8. 8. The secondary battery according to claim 6, The positive electrode active material of the secondary battery is mainly composed of manganese monoxide, manganese dioxide, or a mixture thereof.

9. The secondary battery according to claim 1, the negative electrode active material is mainly composed of metallic zinc, The secondary battery, wherein the positive electrode active material is mainly manganese tetroxide, manganese trioxide, manganese dioxide, or a mixture of two or more thereof.

10. The secondary battery according to claim 1, The oxygen-containing zinc compound is any one of zinc oxide, zinc hydroxide, and a basic zinc compound, or a combination thereof.

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