Zinc negative electrode secondary battery

Abstract

To provide a zinc-manganese oxide secondary battery using an aqueous electrolyte.SOLUTION: A secondary battery contains manganese oxide as a positive electrode active material, zinc as a negative electrode active material, and an aqueous zinc chloride solution as an electrolyte. The concentration of zinc chloride in the electrolyte is from 2.1 mol / L to 4 mol / L.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 negative electrode. [Background technology]

[0002] As electronic devices become smaller, thinner, and lighter, secondary batteries that can be charged at high energy density and discharged with high efficiency have been developed as power sources for electronic devices and backup batteries. Secondary batteries are also being developed as power sources for electric vehicles and distributed power storage batteries. Lithium-ion secondary batteries, which are currently the most widely used secondary batteries, use organic electrolytes, so there is a risk of smoke, fire, and explosion when the battery is short-circuited. 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. In particular, in electric vehicle applications, secondary batteries using aqueous electrolytes instead of organic electrolytes are indispensable to eliminate the risk of fire. As secondary batteries using aqueous electrolytes, zinc negative electrode secondary batteries are highly important. In particular, zinc-manganese dioxide batteries using manganese dioxide for the positive electrode have attracted attention because of their low cost. Non-patent document 1 is known as a report on a battery using manganese dioxide and zinc for the positive and negative electrodes, respectively. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Battery Handbook Published by Maruzen Co., Ltd. Published on August 20, 1990 Summary of the Invention [Problem to be solved by the invention]

[0004] At present, dry batteries that combine manganese dioxide and zinc are widely used. In this battery system, zinc chloride is used 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

[0005] This battery is widely used around the world, but its only drawback is that it is a primary battery and is therefore disposable. Needless to say, if this battery could be used as a secondary battery, its convenience would be greatly improved. [Means for solving the problem]

[0006] The secondary battery of the present disclosure is a secondary battery that uses manganese oxide as a positive electrode active material, zinc as a negative electrode active material, and an aqueous zinc chloride solution as an electrolyte, and the zinc chloride concentration in the electrolyte is 2.1 mol / L to 4 mol / L.

[0007] This disclosure enables the zinc-manganese dioxide battery to be used as a secondary battery by adjusting the aqueous electrolyte concentration within a specific range. Furthermore, it enables the battery to function as a secondary battery even when a manganese oxide other than γ-MnO2 used in conventional primary batteries is used for the positive electrode. Effect of the Invention

[0008] The zinc-manganese oxide battery of the present disclosure is first discharged as a primary battery, and after discharge is complete, it operates as a rechargeable secondary battery. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the cycle number dependence of the discharge capacity of each of the samples of Examples 1 to 5 and 8. As shown in FIG. [Diagram 2] FIG. 2 is a graph showing the cycle number dependence of the charge / discharge efficiency of each of the samples of Examples 1 to 5 and 8. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The secondary battery of this embodiment is a zinc-manganese oxide battery. The secondary battery includes a zinc negative electrode, a separator, a manganese oxide positive electrode, and an aqueous electrolyte. The secondary battery has a laminated structure of the zinc negative electrode, the separator, and the manganese oxide positive electrode.

[0011] In this embodiment, an aqueous electrolyte solution containing zinc chloride as an electrolyte is used, which will be described in detail below.

[0012] In the aqueous electrolyte solution according to this embodiment, the electrolyte is zinc chloride, and the concentration thereof is preferably 2.1 mol / L to 4 mol / L, more preferably 2.1 mol / L to 3.5 mol / L, and even more preferably 2.1 mol / L to 2.7 mol / L.

[0013] The pH of the electrolytic solution of this embodiment is preferably 3.7 to 4.8. The pH of the electrolytic solution is more preferably 3.9 to 4.8, and even more preferably 4.4 to 4.8. The aqueous electrolytic solution according to this embodiment can exhibit suitable cycle characteristics when its pH is within the above range. If the pH is less than 3.7, the cycle characteristics are significantly deteriorated. If the pH exceeds 4.8, zinc chloride, which is an electrolyte, precipitates from the solution, and the concentration of the electrolytic solution decreases.

[0014] When the aqueous electrolyte solution according to this embodiment has a zinc chloride concentration within the above range or a pH within the above range, it can exhibit suitable cycle characteristics as a secondary battery.

[0015] Next, the manganese oxide according to this embodiment will be described.

[0016] The manganese oxide according to this embodiment is MnO xIt is expressed by a composition of (1≦x≦2), and specific examples include MnO2, Mn2O3, Mn3O4, and MnO. The larger the value of x, the higher the oxidation number of manganese, and therefore the larger the initial discharge capacity. In particular, manganese dioxide containing a β-type crystal structure is preferable. Commercially available manganese dioxide includes, for example, γ-type electrolytic manganese dioxide. Specifically, there is one made by Tosoh Corporation. In addition, in the case of MnO, the oxidation state of manganese is the lowest, so it is not possible to start with discharging. Although it is necessary to start with charging, the initial charging reaction is extremely difficult to proceed, and a good charging and discharging reaction will proceed if the charging and discharging are forcibly performed several times. Furthermore, if the manganese oxide is classified to 63 μm or less to remove large particles, an electrode with a uniform film thickness can be produced, and a battery with stable electrochemical properties can be produced.

[0017] Next, a method for producing the electrodes will be described.

[0018] Commercially available dry batteries are disposable primary batteries and cannot be charged. In the present invention, an active material is made into a paste and applied to a collector foil, as in the case of an electrode for a Li-ion battery. This allows for good charging and discharging. That is, graphite sheets, nickel foils, etc. are used as the collector foil. Acetylene black, carbon black, fine graphite particles, milled carbon fiber, etc. are used as the conductive assistant. Styrene butadiene resin (SBR), Teflon (registered trademark) powder, polyvinylidene fluoride, etc. are used as the binder. An electrode with good cycle characteristics can be produced by mixing an appropriate amount of such materials with an active material, making a paste, applying it to the collector foil, and then drying it. As the separator, filter paper, glass filter, or polyolefin-based microporous membrane, etc. can be used. EXAMPLES

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

[0020] Example 1 β-MnO2 was used as the positive electrode active material. Specifically, it was obtained by heat-treating γ-MnOOH at 350℃ in an air atmosphere. The obtained β-MnO2 was sieved to a size of 63μm or less, and then mixed with a conductive additive (acetylene black) and dispersed in a CMC solution of SBR binder to prepare a paste.

[0021] This paste is applied to the graphite sheet at 10 mg / cm 2 The ratio of the binder was 8 parts by weight per 100 parts by weight of β-MnO2.

[0022] A bipolar sealed cell was assembled using the electrode (positive electrode) prepared as above, a metal zinc foil (negative electrode) as the counter electrode, and a 2.1 mol / L (pH=4.80) zinc chloride solution as the electrolyte, and a charge-discharge test was performed. Filter paper was used as the separator. The theoretical discharge capacity was assumed to be 308 Ah / kg, and the 20-hour rate discharge current value was calculated. Discharge was performed at a constant current to 0.9 V, and then a charge-discharge cycle test was performed in the voltage range of 0.1 to 1.9 V.

[0023] Example 2 A charge / discharge test was carried out in the same manner as in Example 1, except that the electrolyte concentration was 2.3 mol / L (pH=4.67).

[0024] Example 3 A charge / discharge test was carried out in the same manner as in Example 1, except that the electrolyte concentration was 2.5 mol / L (pH=4.53).

[0025] Example 4 A charge / discharge test was carried out in the same manner as in Example 1, except that the electrolyte concentration was 2.7 mol / L (pH=4.42).

[0026] Example 5 A charge / discharge test was carried out in the same manner as in Example 1, except that the electrolyte concentration was 4 mol / L (pH=3.71).

[0027] Example 6 In Example 3, the active material was changed from MnO2 to Mn2O3 (sold by Kojundo Chemical Laboratory Co., Ltd.), and the charge / discharge test was performed in the same manner as in Example 1, except that the theoretical discharge capacity was set to 340 Ah / kg and the charge / discharge current was set.

[0028] Example 7 In Example 3, the active material was changed from MnO2 to MnO (sold by Kojundo Chemical Laboratory Co., Ltd.), the charge / discharge current was set to a theoretical discharge capacity of 378 Ah / kg, and charging was started in the same manner as in Example 1, except that a charge / discharge test was performed.

[0029] Example 8 In Example 3, a charge / discharge test was carried out in the same manner as in Example 1, except that electrolytic manganese dioxide (γ-MnO2) manufactured by Tosoh Corporation was used as the positive electrode active material and the electrolyte concentration was set to 4 mol / L.

[0030] Tables 1 and 2 show the discharge capacity and charge / discharge efficiency in each cycle of Examples 1 to 5 and 8. For the same samples, FIG. 1 shows the cycle number dependency of the discharge capacity, and FIG. 2 shows the cycle number dependency of the charge / discharge efficiency. It can be seen that the cycle characteristics of β-MnO2 in Examples 1 to 5 are superior to those of γ-MnO2 in Example 8. Also, the charge / discharge efficiency in Example 8 varies widely, but in Examples 1 to 5, it can be seen that the efficiency improves with increasing cycles. [Table 1] [Table 2]

[0031] The discharge capacity and charge / discharge efficiency in each cycle of Examples 6 and 7 are shown in Tables 3 and 4. It was confirmed that manganese oxides other than MnO2 were also capable of charging and discharging. [Table 3] [Table 4] In summary, in the zinc-manganese oxide secondary battery of this embodiment, by using a ZnCl2 aqueous solution with a concentration of 2.1 mol / L to 4 mol / L as the electrolyte, a secondary battery exhibiting good cycle characteristics can be realized. [Industrial Applicability]

[0032] The zinc-manganese oxide secondary battery of the present disclosure uses an aqueous ZnCl2 solution with a concentration of 2.1 mol / L to 4 mol / L as an electrolyte, and therefore exhibits good cycle characteristics. The 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 secondary battery using manganese oxide as a positive electrode active material, zinc as a negative electrode active material, and a zinc chloride aqueous solution as an electrolyte, A secondary battery, wherein the concentration of zinc chloride in the electrolyte is 2.1 mol / L to 4 mol / L.

2. The manganese oxide is MnO ｘ 2. The secondary battery according to claim 1, wherein the compound is represented by (1≦x≦2).

3. The manganese oxide is β-MnO ２ , Mn ２ O ３ , Mn ３ O ４ 2. The secondary battery according to claim 1, wherein the material is one selected from the group consisting of MnO, MnO, and a mixture thereof.

4. The manganese oxide is β-MnO ２ The secondary battery according to claim 1 .

5. 2. The secondary battery according to claim 1, wherein a positive electrode current collector used together with the positive electrode active material is a nickel foil or a graphite sheet.

6. 2. The secondary battery according to claim 1, wherein the pH of the electrolyte is 3.7 to 4.

8.

7. 2. The secondary battery according to claim 1, having a laminated structure comprising a positive electrode made of manganese oxide coated on a graphite sheet or nickel foil, a separator, and a negative electrode made of zinc foil.

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