WO2025163918A1 - Secondary battery - Google Patents

Abstract

This secondary battery comprises: a positive electrode containing a quinone organic compound; a negative electrode containing zinc; and an electrolyte that is disposed between the positive electrode and the negative electrode, and that contains magnesium chloride. (In the formula, R₁ to R₈ denote a hydrogen atom or a hydroxy group or a methoxy group.)

Description

secondary battery

This disclosure relates to secondary batteries.

Conventionally, batteries installed in small devices, sensors, mobile equipment, etc. include primary batteries that only discharge, and secondary batteries that can be recharged. Primary batteries include alkaline batteries, manganese dry batteries, and lithium primary batteries, while secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, and lithium-ion batteries (Patent Documents 1 and 2).

Patent No. 4475326 Japanese Patent Application Laid-Open No. 2014-82030

The batteries mentioned above often use rare metals such as cobalt and nickel as electrode active materials, raising concerns about the sustainability of these resources.

Lithium-ion batteries are currently widely used as secondary batteries, but because deposits of not only cobalt and nickel, which are used as electrode materials, but also lithium, are unevenly distributed, they are subject to geopolitical influences. Therefore, secondary batteries using magnesium and other materials have been proposed, but these also often contain rare metals such as molybdenum as electrode materials.

This disclosure was made in light of the above circumstances, and aims to provide a secondary battery that does not use rare metals.

The secondary battery disclosed herein comprises a positive electrode containing a quinone organic compound of the following chemical formula, a negative electrode containing zinc, and an electrolyte containing magnesium chloride disposed between the positive electrode and the negative electrode.

(wherein R ₁ to R ₈ represent a hydrogen atom, a hydroxy group, or a methoxy group).

This disclosure makes it possible to provide a secondary battery that does not use rare metals.

FIG. 1 is a basic schematic diagram of a secondary battery according to this embodiment. FIG. 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery. FIG. 3 is a graph showing the discharge curve of the secondary battery of Example 1.

The following describes embodiments of the present disclosure with reference to the drawings.

[Configuration of secondary battery]
1 is a diagram showing the configuration of a secondary battery according to an embodiment of the present disclosure. The secondary battery includes a positive electrode 101 containing a quinone-based organic compound, a negative electrode 103 containing zinc, and an electrolyte 102 containing magnesium chloride disposed between the positive electrode 101 and the negative electrode 103.

The chemical formula of the quinone organic compound of this embodiment is shown below: In the formula, R ₁ to R ₈ represent a hydrogen atom, a hydroxy group, or a methoxy group.

Quinone organic compounds include, for example, 2,5-dimethoxy-1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2,5-dihydroxy-1,4-benzoquinone, and 1,4-benzoquinone.

A discharge reaction occurs when the quinone organic compound contained in the positive electrode 101 combines with the magnesium ions responsible for charge transfer. During charging, the reaction proceeds in the opposite direction.

At the negative electrode 103, a zinc dissolution reaction occurs during discharge, and a zinc precipitation reaction occurs during charge.

The secondary battery of this embodiment uses a quinone-based organic compound as the positive electrode active material, zinc as the negative electrode active material, and an aqueous electrolyte containing magnesium chloride as the salt. As a result, this embodiment can produce a secondary battery with excellent charge/discharge characteristics without using rare metals.

The following describes each of the above components of the secondary battery of this embodiment.

(1) Positive Electrode The positive electrode of this embodiment contains at least a positive electrode active material and may contain a conductive additive or a current collector as needed, as described below. The positive electrode may also contain a binder. The current collector may be a current collector containing at least one selected from the group consisting of aluminum, copper, and iron, or a nonwoven fabric current collector containing carbon.

(1-1) Positive Electrode Active Material The positive electrode active material of this embodiment contains at least a quinone-based organic compound. Because quinone-based organic compounds do not contain rare metals, they have a low environmental impact and are inexpensive. The quinone-based organic compound can be obtained, for example, as a commercially available product or by synthesis using a known method.

(1-2) Preparation of Positive Electrode Using Conductive Aid In this embodiment, the positive electrode may contain a conductive aid. Examples of the conductive aid include carbon. Specific examples include carbon blacks such as ketjen black and acetylene black, activated carbons, graphites, and carbon fibers.

In order to ensure sufficient conductive paths in the positive electrode, carbon with small particles is suitable. Specifically, a particle diameter of 1 μm or less is desirable. Such carbon can be obtained, for example, as a commercially available product or by known synthesis.

The positive electrode may contain a binder. Specific examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, ethylene propylene diene rubber, and natural rubber.

A positive electrode can be prepared by mixing the quinone-based organic compound powder as the positive electrode active material with the conductive additive and the binder, and then bonding this mixture to a conductive material. Alternatively, a positive electrode can be prepared by bonding this mixture to a current collector, as described below.

(1-3) Preparation of Positive Electrode Using Current Collector The positive electrode is formed on a current collector containing at least one selected from the group consisting of aluminum, copper, and iron (hereinafter referred to as the "first current collector"), or a nonwoven current collector containing carbon (hereinafter referred to as the "second current collector"), and the positive electrode may not contain a binder. Specifically, the positive electrode active material may be directly supported on such a current collector. Direct support means that the positive electrode active material is bonded to the current collector in a three-dimensional structure, thereby increasing conductivity. The first current collector and the second current collector are, for example, commercially available.

To easily form a high-quality positive electrode, a preferred method is to impregnate the first or second current collector with a liquid in which the positive electrode active material has been dissolved, and then dry it to support the positive electrode active material. Here, by cold pressing or hot pressing the dried electrode (positive electrode), the strength of the electrode can be increased, resulting in a positive electrode with superior stability.

Specific examples of solvents for dissolving the positive electrode active material include aqueous solvents such as water, and organic solvents such as tetrahydrofuran (THF), tetrahydrofuran (THP), dioxane, diethyl ether, N-methyl-2-pyrrolidone (NMP), hexamethylphosphoramide (HMPA), tetramethylurea (TMU), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), m-cresol, and chloroform, and two or more of these may be mixed.

In the secondary battery of this embodiment, the reaction proceeds on the surface of the positive electrode, so it is considered preferable to generate a large number of reaction sites inside the positive electrode. In the case of a positive electrode formed using the aforementioned conductive additives and binders, increasing the specific surface area reduces the binding strength between the conductive additives, degrading the structure and making stable discharge difficult, resulting in a decrease in discharge capacity. Because binders are insulating substances, containing a large amount of binder reduces conductivity, leading to a decrease in battery performance (discharge voltage, discharge capacity). Furthermore, when using ketjen black powder as the conductive additive, it is difficult to increase the specific surface area from the perspective of binding strength.

As described above, by forming the positive electrode on the first or second current collector, it is possible to fully utilize the electrochemical activity of the quinone-based organic compound, which is the positive electrode active material.

(2) Negative Electrode The secondary battery of this embodiment contains at least zinc (Zn) as the negative electrode active material. As the negative electrode active material, any material that operates at a potential lower than the positive electrode potential, such as magnesium, iron, or aluminum, can be used. However, from the viewpoints of stability in aqueous solution and reversibility of charge and discharge, it is preferable to use zinc as the negative electrode active material. That is, in this embodiment, zinc, which is a stable metal in an aqueous electrolyte, is used as the negative electrode active material.

The negative electrode active material may contain zinc (Zn) as its main component, or may be an alloy containing other components (e.g., magnesium, iron, aluminum, etc.). In addition to the negative electrode active material, the negative electrode 103 may also contain a conductive additive and a binder as components.

(3) Aqueous electrolyte (electrolyte)
The secondary battery of this embodiment includes an electrolyte containing magnesium chloride. The secondary battery may also include an aqueous electrolyte solution containing the electrolyte. This aqueous electrolyte solution contains magnesium chloride as a salt (electrolyte) and water as a solvent. The use of an aqueous electrolyte solution improves safety compared to the use of a flammable organic electrolyte solution, and can prevent accidents such as fires. In this embodiment, an aqueous electrolyte solution is used as the electrolyte, but this electrolyte solution may also be converted into a gel by mixing a polymer material. In other words, the electrolyte solution may be in any form, such as a liquid, cream, gel, or film, by changing the amount of polymer added.

(4) Other Elements In addition to the above-described components, the secondary battery of this embodiment may include structural members such as a separator and a battery case, as well as other elements required for a secondary battery. These may be conventionally known components.

(5) Method for Manufacturing Secondary Battery As described above, the secondary battery of this embodiment includes at least a positive electrode, a negative electrode, and an aqueous electrolyte solution (electrolyte), and the aqueous electrolyte solution is disposed between the positive electrode and the negative electrode so as to be in contact with the positive electrode and the negative electrode, as illustrated in Fig. 1. A secondary battery having such a configuration can be prepared in the same manner as a conventional secondary battery.

For example, a secondary battery can be made by assembling a positive electrode containing the above-mentioned positive electrode active material, a negative electrode containing zinc (Zn), and an aqueous electrolyte solution placed in contact with the positive and negative electrodes according to conventional technology.

As one embodiment of the method for manufacturing a secondary battery, for example, a coin-type secondary battery can be manufactured.

Figure 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery. Specifically, first, a separator (not shown) is placed on the positive electrode case 201 in which the positive electrode 101 is placed, and electrolyte 102 is poured into the placed separator. Next, the negative electrode 103 is placed on top of the electrolyte 102, and the negative electrode case 202 is placed over the positive electrode case 201. Next, the peripheral portions of the positive electrode case 201 and negative electrode case 202 are crimped using a coin cell crimping machine, making it possible to produce a coin-type secondary battery including a propylene gasket 203.

[Example]
Examples of secondary batteries according to this embodiment are described in detail below. In each example, secondary batteries were fabricated using 2,5-dimethoxy-1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2,5-dihydroxy-1,4-benzoquinone, or 1,4-benzoquinone as a quinone organic compound for the positive electrode, zinc (Zn) for the negative electrode, and an aqueous solution containing magnesium chloride (MgCl ₂ ) for the electrolyte. Note that the present disclosure is not limited to the examples shown below, and can be modified as appropriate within the scope of the present disclosure.

Example 1
In Example 1, the coin-type secondary battery (Figure 2) described above was fabricated using the following procedure. 2,5-dimethoxy-1,4-benzoquinone was used as the positive electrode active material, which was prepared by pressing 2,5-dimethoxy-1,4-benzoquinone onto a copper-containing current collector (copper mesh, CU-118016, Nilaco Corporation). Zinc (Zn) powder was used as the negative electrode active material. An aqueous solution containing 1.0 mol/L of magnesium chloride (MgCl ₂ ) was used as the aqueous electrolyte.

(Preparation of Positive Electrode)
As the positive electrode active material, commercially available 2,5-dimethoxy-1,4-benzoquinone powder (Tokyo Chemical Industry Co., Ltd.), Ketjenblack powder (EC600JD, Lion Specialty Chemicals Co., Ltd.), and polytetrafluoroethylene (PTFE) powder were thoroughly pulverized and mixed in a weight ratio of 40:40:20 using a grinder, and then roll-formed to prepare a sheet electrode (thickness: 0.5 mm). This sheet electrode and a copper mesh current collector were each cut into a circle with a diameter of 16 mm, and the circular sheet electrode was pressed and pressure-bonded onto the circular copper mesh to obtain a positive electrode.

(Preparation of negative electrode)
Zinc (Zn) powder (Sigma-Aldrich Co. LLC) and acetylene black (Denka Co., Ltd.) were mixed in a weight ratio of 8:2 and dispersed in N,N-dimethylformamide (DMF) to prepare a mixture. After stirring this mixture for 5 hours with a magnetic stirrer, it was applied to a copper foil (Nilaco Corporation) current collector, annealed at 300°C in an inert atmosphere, and cut into a circle with a diameter of 16 mm to obtain a negative electrode.

(Preparation of Electrolyte)
An electrolyte solution was prepared by mixing and stirring magnesium chloride (Sigma-Aldrich Co. LLC) with distilled water to a concentration of 1.0 mol/L.

(Fabrication of secondary battery)
A coin-type secondary battery shown in Fig. 2 was fabricated using a coin battery case (Hosen Co., Ltd.). A cellulose-based separator (Nippon Kodoshi Kogyo Co., Ltd.) cut to a diameter of 18 mm was placed in each positive electrode case 201 containing the positive electrode 101 prepared by the above method, and an aqueous solution containing magnesium chloride was poured into the placed separator as the aqueous electrolyte 102. The negative electrode 103 was placed on top of the aqueous electrolyte 102, and the negative electrode case 202 was placed over the positive electrode case 201. The peripheral portions of the positive electrode case 201 and the negative electrode case 202 were crimped using a coin cell crimping machine, thereby obtaining a coin-type secondary battery including a propylene gasket 203.

(Battery performance)
The secondary battery prepared by the above procedure was measured for battery performance in a thermostatic chamber maintained at 30°C. The battery cycle test was performed using a charge/discharge measurement system (VMP-3, manufactured by Bio Logic) by passing a current density of 0.1 mA/ ^cm2 per effective area of the positive electrode, and measuring the discharge voltage until the battery voltage decreased from the open circuit voltage to 0 V (discharge cut-off voltage). The charging was performed by passing a current density of 0.1 mA/ ^cm2 per effective area of the positive electrode, and the charge cut-off voltage was 1.3 V. The battery charge/discharge test was performed under normal living conditions. The charge/discharge capacity was expressed as a value per unit weight of the positive electrode active material (mAh/g).

Figure 3 shows the discharge curve for Example 1 during the initial discharge. Table 1 shows the initial discharge capacity and discharge capacity after 100 cycles for Example 1. As shown in Figure 3 and Table 1, when 2,5-dimethoxy-1,4-benzoquinone was used in Example 1, the open circuit voltage during the initial discharge was 1.2 V, the average discharge voltage was 0.92 V, and the discharge capacity was 193 mAh/g. Here, the average discharge voltage is defined as the battery voltage at half the total discharge capacity. Furthermore, a slight voltage drop and a decrease in discharge capacity of approximately 10% were observed after 100 cycles. The discharge voltage after 100 cycles was 0.85 V. Thus, it was confirmed that the secondary battery of Example 1 is capable of charge/discharge cycling and operates as a high-performance secondary battery. This is thought to be due to the molecular structure of 2,5-dimethoxy-1,4-benzoquinone maintaining its interaction with magnesium ions.

<Examples 2, 3, and 4>
In Examples 2, 3, and 4, secondary batteries were fabricated in which only the quinone organic compound in the positive electrode was different from that in Example 1. That is, as the quinone organic compound, 2,6-dimethoxy-1,4-benzoquinone powder (Tokyo Chemical Industry Co., Ltd.) was used in Example 2, 2,5-dihydroxy-1,4-benzoquinone powder (Tokyo Chemical Industry Co., Ltd.) was used in Example 3, and 1,4-benzoquinone powder (Tokyo Chemical Industry Co., Ltd.) was used in Example 4.

In Examples 2, 3, and 4, coin-type secondary batteries were fabricated using the same procedures as in Example 1. Other battery configurations and experimental methods in Examples 2, 3, and 4 were the same as in Example 1.

Table 1 shows the initial discharge capacity and discharge capacity at 100 cycles for the secondary batteries of Examples 2, 3, and 4. As shown in Table 1, a decrease in discharge capacity of approximately 40% was confirmed, but in all Examples, the secondary batteries were still able to function. The initial discharge voltages for Examples 2, 3, and 4 were 0.95V, 0.86V, and 0.66V, respectively, and at 100 cycles they were 0.73V, 0.55V, and 0.32V, respectively.

The results of this example confirm that the secondary battery of Example 1, which uses a combination of 2,5-dimethoxy-1,4-benzoquinone as the positive electrode active material, zinc as the negative electrode active material, and magnesium chloride as the electrolyte, is preferable as a secondary battery that can be charged and discharged.

<Comparative Examples 1, 2, and 3>
In the comparative example, a secondary battery was fabricated that differed from Example 1 only in the metal contained in the negative electrode (negative electrode active material). That is, in the comparative example, a coin-type secondary battery was fabricated using the same procedure as in Example 1.

In Comparative Example 1, commercially available magnesium (Sigma-Aldrich Co. LLC) was used as the negative electrode active material, in Comparative Example 2 iron (Sigma-Aldrich Co. LLC) was used, and in Comparative Example 3 aluminum (Sigma-Aldrich Co. LLC) was used. Other battery configurations, fabrication procedures, and experimental methods in the comparative examples were the same as in Example 1.

Table 1 shows the initial discharge capacity of the secondary batteries of the comparative examples and the discharge capacity after charge-discharge cycling. In all comparative examples, a rapid decrease in discharge capacity was observed in the relatively early charge-discharge cycles, indicating that charge-discharge cycling is difficult for the batteries of these comparative examples. The discharge capacity after 10 cycles of Comparative Example 1 was 15 mAh/g, the discharge capacity after 10 cycles of Comparative Example 2 was 10 mAh/g, and the discharge capacity after 2 cycles of Comparative Example 3 was 0 mAh/g.

As a result, the secondary battery of this embodiment is a secondary battery with excellent charge/discharge characteristics without using rare metals, and can be effectively used as a new power source for various electronic devices such as small devices, sensors, and mobile equipment.

Note that this disclosure is not limited to the above-described embodiments, and various modifications and combinations are possible within the technical concept of this disclosure.

100: Secondary battery 101: Positive electrode 102: Aqueous electrolyte 103: Negative electrode 201: Positive electrode case 202: Negative electrode case 203: Propylene gasket

Claims (3)

a positive electrode containing a quinone organic compound of the following chemical formula;
a negative electrode containing zinc;
and an electrolyte containing magnesium chloride disposed between the positive electrode and the negative electrode.
(wherein R ₁ to R ₈ represent a hydrogen atom, a hydroxy group, or a methoxy group). 2. The secondary battery according to claim 1, wherein the quinone organic compound includes 2,5-dimethoxy-1,4-benzoquinone. The secondary battery according to claim 1 , comprising an aqueous electrolytic solution containing the electrolyte.