Secondary battery

Abstract

The present invention provides a secondary battery comprising: a positive electrode that contains triquinoxalinylene; a negative electrode that contains zinc; and an electrolyte that is disposed between the positive electrode and the negative electrode and that contains magnesium chloride.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] Conventionally, batteries installed in small devices, sensors, mobile devices, 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).

[0003] Patent No. 4475326 JP 2014-82030 A

[0004] 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.

[0005] Currently, lithium-ion batteries are widely used as secondary batteries, but the deposits of not only cobalt and nickel, but also lithium, which are used as electrode materials, are unevenly distributed, making them subject to geopolitical influences. Therefore, secondary batteries using magnesium and other metals have been proposed, but these also often contain rare metals such as molybdenum as electrode materials.

[0006] The present disclosure has been made in view of the above circumstances, and aims to provide a secondary battery that does not use rare metals.

[0007] The secondary battery of the present disclosure includes a positive electrode containing triquinoxalinylene, a negative electrode containing zinc, and an electrolyte containing magnesium chloride disposed between the positive electrode and the negative electrode.

[0008] According to the present disclosure, a secondary battery that does not use rare metals can be provided.

[0009] Fig. 1 is a basic schematic diagram of the secondary battery of 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.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] 1 is a diagram showing the configuration of a secondary battery according to an embodiment of the present disclosure. This secondary battery includes a positive electrode 101 containing triquinoxalinylene, a negative electrode 103 containing zinc, and an electrolyte 102 containing magnesium chloride disposed between the positive electrode 101 and the negative electrode 103. Triquinoxalinylene is an organic compound containing nitrogen and having an -N= group as an active site.

[0012] The chemical formula of triquinoxalinylene (hereinafter referred to as "TQ") is shown below.

[0013]

[0014] The discharge reaction proceeds when TQ contained in the positive electrode 101 binds to magnesium ions that are responsible for charge transfer. During charging, the reaction proceeds in the reverse direction.

[0015] In the negative electrode 103, a zinc dissolution reaction occurs during discharge, and a zinc deposition reaction occurs during charge.

[0016] The secondary battery of this embodiment uses TQ as the positive electrode active material, zinc as the negative electrode active material, and an aqueous electrolyte containing magnesium chloride as a salt, thereby making it possible to fabricate a secondary battery with excellent charge-discharge characteristics without using rare metals.

[0017] Each of the above components of the secondary battery of this embodiment will be described below.

[0018] (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.

[0019] (1-1) Positive Electrode Active Material The positive electrode active material of this embodiment contains at least TQ. TQ does not contain rare metals, so it has a low environmental impact and is inexpensive. TQ can be obtained, for example, as a commercially available product or by synthesis using a known method.

[0020] (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.

[0021] To ensure sufficient conductive paths in the positive electrode, carbon particles with small diameters are suitable. Specifically, carbon particles with a diameter of 1 μm or less are desirable. Such carbons can be obtained, for example, as commercial products or by known synthesis methods.

[0022] The positive electrode may contain a binder. Specific examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, ethylene propylene diene rubber, and natural rubber.

[0023] A positive electrode can be prepared by mixing a powder of TQ as a positive electrode active material, the conductive additive, and the binder, and bonding the mixture to a conductive material. Alternatively, the positive electrode can be prepared by bonding the mixture to a current collector, which will be described later.

[0024] (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.

[0025] The following methods can be considered for supporting the positive electrode active material on the first or second current collector: For example, physical methods such as vapor deposition, sputtering, or planetary ball milling, methods in which the first or second current collector is immersed in a liquid in which the positive electrode active material is dissolved and then dried, chemical methods such as a sol-gel method, or known methods.

[0026] For the purpose of easily forming a high-quality positive electrode, a preferred method is to impregnate a first or second current collector with a liquid in which a positive electrode active material is dissolved, and then dry the liquid to support the positive electrode active material. Here, by applying cold pressing or hot pressing to the dried electrode (positive electrode), the strength of the electrode can be increased, and a positive electrode with superior stability can be produced.

[0027] The solvent for dissolving the positive electrode active material is specifically an aqueous solvent such as water, or an organic solvent 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, or chloroform, and two or more of these may be mixed.

[0028] 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 above-mentioned conductive additive and binder, when the specific surface area is increased, the binding strength between the conductive additives decreases, the structure deteriorates, making it difficult to discharge stably, and the discharge capacity decreases. Since the binder is an insulating substance, the inclusion of a large amount of binder reduces the conductivity, leading to a decrease in battery performance (discharge voltage, discharge capacity). Furthermore, when Ketjenblack powder is used as the conductive additive, it is difficult to increase the specific surface area from the viewpoint of binding strength.

[0029] 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 TQ, which is the positive electrode active material.

[0030] (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.

[0031] The negative electrode active material may contain zinc (Zn) as a main component, or may be an alloy containing other components (e.g., magnesium, iron, aluminum, etc.) The negative electrode 103 may contain, in addition to the negative electrode active material, a conductive additive and a binder as components.

[0032] (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 containing the electrolyte. This aqueous electrolyte contains magnesium chloride as the salt (electrolyte) and water as the solvent. The use of an aqueous electrolyte improves safety compared to the use of a flammable organic electrolyte, and can prevent accidents such as fires. In this embodiment, an aqueous electrolyte is used as the electrolyte, but this electrolyte may also be converted into a gel by mixing a polymer material. That is, the electrolyte may be in any form, such as a liquid, cream, gel, or film, by changing the amount of polymer added.

[0033] (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.

[0034] (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.

[0035] For example, a secondary battery may be prepared by assembling a positive electrode containing the above-described positive electrode active material, a negative electrode containing zinc (Zn), and an aqueous electrolyte solution disposed so as to be in contact with the positive electrode and the negative electrode according to conventional techniques.

[0036] As an embodiment of the method for manufacturing a secondary battery, for example, a coin-type secondary battery can be manufactured.

[0037] 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 a positive electrode case 201 in which the positive electrode 101 is placed, and an electrolyte solution 102 is poured into the placed separator. Next, a negative electrode 103 is placed on the electrolyte solution 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 the negative electrode case 202 are crimped using a coin cell crimping machine, thereby making it possible to fabricate a coin-type secondary battery including a propylene gasket 203.

[0038] Examples of the secondary battery according to this embodiment will be described in detail below. In each example, TQ was used for the positive electrode, zinc (Zn) was used for the negative electrode, and magnesium chloride (MgCl) was used for the electrolyte. ２ A secondary battery was fabricated using an aqueous solution containing the compound (II) and the compound (II). The present disclosure is not limited to the examples shown below, and can be appropriately modified and implemented within the scope of the present disclosure.

[0039] Example 1 In Example 1, the coin-type secondary battery (FIG. 2) described above was fabricated by the following procedure. Furthermore, TQ was used as the positive electrode active material, and was prepared by pressing TQ onto a copper-containing current collector (copper mesh, CU-118016, Nilaco Corporation). Zinc (Zn) powder was used as the negative electrode active material. The aqueous electrolyte contained 1.0 mol / L of magnesium chloride (MgCl ２ ) was used.

[0040] (Preparation of Positive Electrode) Commercially available TQ powder, 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 roll-molded 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 a circular copper mesh to obtain a positive electrode.

[0041] (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 dissolved 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.

[0042] (Preparation of Electrolyte Solution) Magnesium chloride (Sigma-Aldrich Co. LLC) was mixed with distilled water and stirred to give a concentration of 1.0 mol / L to prepare an electrolyte solution.

[0043] (Preparation of Secondary Battery) A coin-type secondary battery shown in FIG. 2 was prepared 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 on each positive electrode case 201 containing the positive electrode 101 prepared by the above method, and an aqueous electrolyte solution 102 containing magnesium chloride was poured into the placed separator. The negative electrode 103 was placed on the aqueous electrolyte solution 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.

[0044] (Battery Performance) The battery performance of the secondary battery prepared by the above procedure was measured 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) at a current density of 0.1 mA / cm per effective area of ​​the positive electrode. ２ The discharge voltage was measured until the battery voltage decreased from the open circuit voltage to 0 V (discharge end voltage). The charge was performed at a current density of 0.1 mA / cm per effective area of ​​the positive electrode. ２ The charge cut-off voltage was set to 1.2 V. The charge / discharge test of the battery was carried out under normal living conditions. The charge / discharge capacity was expressed as a value (mAh / g) per unit weight of the positive electrode active material (TQ).

[0045] FIG. 3 shows the discharge curve for the first discharge of Example 1. Table 1 shows the initial discharge capacity and the discharge capacity at 100 cycles of Example 1. As shown in FIG. 3 and Table 1, the initial open circuit voltage was 0.93 V, and the initial discharge capacity was 425 mAh / g. Furthermore, when the battery voltage at the intermediate value of the discharge capacity was taken as the average discharge voltage, it was 0.15 V. Furthermore, the discharge performance at 100 cycles was confirmed to have an average discharge voltage of 0.13 V, a slight voltage drop, and a decrease in discharge capacity of about 10%. Thus, it was confirmed that the secondary battery of Example 1 operates as a secondary battery capable of charge / discharge cycling.

[0046]

[0047] Comparative Examples 1, 2, and 3 In the comparative examples, secondary batteries were fabricated that differed from Example 1 only in the metal contained in the negative electrode (negative electrode active material). That is, in the comparative examples, coin-type secondary batteries were fabricated using the same procedure as in Example 1.

[0048] In Comparative Example 1, commercially available magnesium (Sigma-Aldrich Co. LLC) was used as the negative electrode active material, in Comparative Example 2, commercially available iron (Sigma-Aldrich Co. LLC) was used as the negative electrode active material, and in Comparative Example 3, commercially available aluminum (Sigma-Aldrich Co. LLC) was used as the negative electrode active material. Other battery configurations, fabrication procedures, experimental methods, etc. in the comparative examples were the same as in Example 1.

[0049] Table 1 shows the initial discharge capacity and the discharge capacity after charge-discharge cycles of the secondary batteries of the comparative examples. In all comparative examples, a rapid decrease in discharge capacity was observed in the relatively early charge-discharge cycles, indicating that the secondary batteries of the comparative examples were difficult to charge-discharge cycle. The discharge capacity after 10 cycles of Comparative Example 1 was 25 mAh / g, the discharge capacity after 10 cycles of Comparative Example 2 was 16 mAh / g, and the discharge capacity after 2 cycles of Comparative Example 3 was 15 mAh / g.

[0050] From the results of the comparative examples, it was confirmed that the secondary battery of Example 1, which employs a combination of TQ as the positive electrode active material, zinc as the negative electrode active material, and magnesium chloride as the electrolyte, can operate as a secondary battery capable of being charged and discharged.

[0051] As described above, 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 driving source for various electronic devices such as small devices, sensors, and mobile devices.

[0052] The present disclosure is not limited to the above-described embodiments, and various modifications and combinations are possible within the technical concept of the present disclosure.

[0053] 100: Secondary battery 101: Positive electrode 102: Aqueous electrolyte 103: Negative electrode 201: Positive electrode case 202: Negative electrode case 203: Propylene gasket

Claims

1. A secondary battery comprising: a positive electrode containing triquinoxalinylene; a negative electrode containing zinc; and an electrolyte containing magnesium chloride disposed between the positive electrode and the negative electrode.

2. The secondary battery according to claim 1, comprising an aqueous electrolytic solution containing the electrolyte.

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