WO2024247231A1 - Secondary battery - Google Patents

Abstract

A secondary battery according to the present invention is provided with: a positive electrode that contains triquinoxalinylene; a negative electrode that contains magnesium; and an electrolyte that is disposed between the positive electrode and the negative electrode and that contains magnesium chloride and dipropyl sulfone.

Description

Secondary battery

This disclosure relates to secondary batteries.

Conventionally, batteries installed in small devices, sensors, mobile devices, etc. include primary batteries that only discharge, and secondary batteries that can be charged. 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 JP 2014-82030 A

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.

Currently, lithium-ion batteries are 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. As a result, secondary batteries using magnesium and other elements have been proposed, but these also often contain rare metals such as molybdenum as electrode materials.

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

The secondary battery disclosed herein comprises a positive electrode containing triquinoxalinylene, a negative electrode containing magnesium, and an electrolyte containing magnesium chloride and dipropyl sulfone disposed between the positive electrode and the negative electrode.

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 the present embodiment. FIG. 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery.

The following describes an embodiment of this disclosure with reference to the figures.

[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 triquinoxalinylene, a negative electrode 103 containing magnesium, and an electrolyte 102 containing magnesium chloride and dipropyl sulfone and disposed between the positive electrode 101 and the negative electrode 103.

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

 
 

 
 

The chemical formula for dipropyl sulfone is shown below.

 
 

The discharge reaction proceeds when the TQ contained in the positive electrode 101 binds with the magnesium ions that are responsible for charge transfer. During charging, the reaction proceeds in the opposite direction.

The secondary battery of this embodiment uses TQ as the positive electrode active material, magnesium as the negative electrode active material, and a non-aqueous electrolyte containing magnesium chloride as the salt and dipropyl sulfone as the solvent. 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 assistant or a current collector as necessary. 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 current collector containing carbon.

(1-1) Positive Electrode Active Material The positive electrode active material of this embodiment contains at least TQ. TQ is rare metal-free, so it has a low environmental impact, and is also inexpensive.

TQ can be obtained, for example, as a commercially available product or by synthesis using known methods.

(1-2) Preparation of Positive Electrode Using Conductive Auxiliary Agent In this embodiment, the positive electrode may contain a conductive auxiliary agent. For example, carbon or the like can be used as the conductive auxiliary agent. Specific examples of the conductive auxiliary agent 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 size of 1 μm or less is preferable. Such carbon can be obtained, for example, as a commercial product or by known synthesis.

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.

The positive electrode can be prepared by mixing the positive electrode active material DMBQ powder with the conductive additive and the binder, and bonding this mixture to a conductive material. The positive electrode can also be prepared by bonding this mixture to a current collector, which will be described later.

(1-3) Preparation of a positive electrode using a 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 a "first current collector"), or a nonwoven current collector containing carbon (hereinafter referred to as a "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 finely bonded to the current collector in a three-dimensional structure. This can increase the conductivity. The first current collector and the second current collector can be obtained, for example, as a commercially available product.

The following methods can be used to support the positive electrode active material on the first or second current collector. For example, physical methods such as vapor deposition, sputtering, and planetary ball milling, a method 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, a chemical method such as the sol-gel method, or a known method can be used.

To easily form a positive electrode of good quality, a preferred method is to impregnate the first or second current collector with a liquid in which the 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.

Specific examples of the solvent for dissolving the positive electrode active material include aqueous solvents such as water, or organic solvents such as tetrahydrofuran (THF), tetrahydrofuran (THP), dioxane, diethyl ether, N-methyl-2-pyrrolidone (NMP), hexamethylphosphoramide (HMPA), tetramethylurea (TMU), dimethylacetamide (DMAc), dimethylformaldehyde (DMF), dimethylsulfoxide (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 better to generate a large number of reaction sites inside the positive electrode. In the case of a positive electrode formed using the conductive assistant and binder described above, when the specific surface area is increased, the bonding strength between the conductive assistants decreases, and the structure deteriorates, making it difficult to discharge stably and reducing the discharge capacity. Since the binder is an insulating material, the conductivity decreases when a large amount of binder is included, leading to a decrease in battery performance (discharge voltage, discharge capacity). Furthermore, when Ketjenblack powder is used as the conductive assistant, it is difficult to increase the specific surface area in terms of bonding strength.

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

(2) Negative Electrode The secondary battery of this embodiment contains at least magnesium (Mg) as a negative electrode active material. This negative electrode active material may contain magnesium (Mg) as a main component, and may also be an alloy containing at least one component selected from the group consisting of lithium (Li), sodium (Na), zinc (Zn), aluminum (Al), manganese (Mn), iron (Fe), tin (Sn), and carbon (C). The negative electrode 103 may contain a conductive assistant and a binder as components other than the negative electrode active material.

(3) Non-aqueous electrolyte (electrolyte)
The secondary battery of this embodiment contains a non-aqueous electrolyte solution. The non-aqueous electrolyte solution contains magnesium chloride as a salt and dipropyl sulfone as a solvent.

In this embodiment, a non-aqueous electrolyte is used as the electrolyte, but this electrolyte may be changed to a gel by mixing it with a polymer material. In other words, the electrolyte 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-mentioned components, the secondary battery of the present embodiment may include structural members such as a separator and a battery case, and other elements required for a secondary battery. These may be conventionally known.

(5) Method for Producing Secondary Battery As described above, the secondary battery of this embodiment includes at least a positive electrode, a negative electrode, and a nonaqueous electrolyte solution, and the nonaqueous 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 magnesium (Mg), and a non-aqueous electrolyte solution arranged in contact with the positive electrode and the negative electrode 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.

FIG. 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery. Specifically, 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 the electrolyte 102, and the negative electrode case 202 is placed over the positive electrode case 201. Next, the periphery of the positive electrode case 201 and the negative electrode case 202 are crimped with a coin cell crimping machine, making it possible to produce a coin-type secondary battery including a propylene gasket 203.

[Example]
Examples of the secondary battery according to this embodiment will be described in detail below. In each example, a secondary battery was produced using TQ for the positive electrode, magnesium (Mg) for the negative electrode, and a dipropylsulfone solution containing magnesium chloride (MgCl ₂ ) for the non-aqueous electrolyte. 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 (FIG. 2) described above was fabricated by the following procedure. 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). TQ was synthesized by a known method. Magnesium (Mg) powder was used as the negative electrode active material. A dipropyl sulfone solution containing 0.8 mol/L of magnesium chloride (MgCl ₂ ) was used as the non-aqueous electrolyte.

(Preparation of Positive Electrode)
A commercially available TQ powder, Ketjen Black 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-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 a circular copper mesh to obtain a positive electrode.

(Preparation of negative electrode)
Magnesium (Mg) powder (Nilaco Corporation) and carbon black were mixed in a weight ratio of 8:2 and dissolved in N,N-dimethylformamide (DMF) to prepare a mixture. After stirring the 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 anhydrous magnesium chloride (Sigma-Aldrich Co. LLC) to a predetermined amount of liquid dipropyl sulfone (Tokyo Chemical Industry Co., Ltd.) heated to 40° C. so as to have a concentration of 0.8 mol/L.

(Preparation of secondary battery)
A coin-type secondary battery shown in FIG. 2 was produced 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 in which the positive electrode 101 prepared by the above method was placed, and a dipropyl sulfone solution containing magnesium chloride was poured into the placed separator as a non-aqueous electrolyte 102. The negative electrode 103 was placed on the non-aqueous electrolyte 102, the negative electrode case 202 was placed on the positive electrode case 201, and the periphery of the positive electrode case 201 and the negative electrode case 202 was crimped with a coin cell crimping machine to obtain 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 cycle test of the battery was performed using a charge/discharge measurement system (VMP-3, manufactured by Bio Logic) by passing a current density of 0.1 mA/cm ² per effective area of the positive electrode, and measuring the discharge voltage from the open circuit voltage until the battery voltage decreased to 0.10 V (discharge end voltage). In addition, charging was performed by passing a current density of 0.1 mA/cm ² per effective area of the positive electrode, and the charge end voltage was 3.0 V. The charge/discharge test of the battery was performed 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).

The discharge capacity and discharge voltage of the secondary battery of Example 1 are shown in Table 1. As shown in Table 1, the discharge voltage at the time of the first discharge was 1.21 V, and the discharge capacity was 396 mAh/g. Here, the discharge voltage is defined as the discharge voltage at 1/2 the total discharge capacity. In addition, the discharge performance after 20 cycles showed a slight voltage drop and a decrease in discharge capacity of about 10%. In this way, it was confirmed that the battery of Example 1 operates as a secondary battery capable of charge and discharge cycles.

<Comparative Example 1>
In Comparative Example 1, a secondary battery was produced in which only the electrolyte solution was different from that in Example 1. That is, in Comparative Example 1, a coin-type secondary battery was produced in the same manner as in Example 1. In addition, in Comparative Example 1, the secondary battery was evaluated in the same manner as in Example 1.

The electrolyte of the secondary battery of Comparative Example 1 was a propylene carbonate solution containing Mg( _ClO4 ) ₂ (Kishida Chemical Co., Ltd.). The electrolyte was synthesized by adding a predetermined amount of commercially available Mg( _ClO4 ) ₂ to commercially available liquid propylene carbonate and stirring until it was completely dissolved. The other battery configurations and experimental methods of Comparative Example 1 were the same as those of Example 1.

The discharge capacity and discharge voltage of the secondary battery of Comparative Example 1 are shown in Table 1. As shown in Table 1, the discharge voltage at the first discharge was 1.19 V and the discharge capacity was 399 mAh/g, and no significant difference in performance was observed from Example 1. However, after 20 cycles, the discharge performance showed a voltage drop of about 1 V and a decrease in discharge capacity of about 90%, indicating that the battery in Comparative Example 1 is a secondary battery that is difficult to cycle for charging and discharging.

Compared with Comparative Example 1, it was confirmed that the secondary battery of Example 1, which uses a combination of TQ as the positive electrode active material, magnesium as the negative electrode active material, and a dipropyl sulfone solution containing magnesium chloride as the electrolyte and a non-aqueous electrolyte, can function as a secondary battery capable of charging and discharging.

As described above, the secondary battery of this embodiment is a secondary battery with excellent charge and 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.

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: Non-aqueous electrolyte (electrolyte)
103: negative electrode 201: positive electrode case 202: negative electrode case 203: propylene gasket

Claims (1)

a positive electrode including triquinoxalinylene;
a negative electrode containing magnesium;
and an electrolyte containing magnesium chloride and dipropyl sulfone disposed between the positive electrode and the negative electrode.

Images