Secondary battery

Abstract

Disclosed is a secondary battery which is provided with: a positive electrode 101 that contains triquinoxalinylene; a negative electrode 103 that contains lithium or a lithium compound; and an electrolyte solution 102 that is disposed between the positive electrode 101 and the negative electrode 103, and contains lithium ions and dimethyl sulfoxide. This secondary battery uses neither fluorine nor a fluorine compound.

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 Document 1).

[0003] Patent No. 4475326

[0004] “A high-energy dual-ion battery based on chloride-inserted polyviologen cathode and LiCl / DMSO electrolyte”, Energy Storage Materials 50 (2022) 658-667

[0005] The electrolytes and electrodes of the above-mentioned batteries often contain organic fluorine compounds, which have been identified as harmful to humans and the environment, and in recent years there have been concerns that their use may be restricted. Furthermore, metal oxides such as manganese compounds and vanadium compounds, which are highly electrochemically reactive with the electrolytes and electrodes, may also have adverse effects on humans and the environment when the batteries are disposed of or released into the environment.

[0006] The battery described in Non-Patent Document 1 uses lithium chloride as the electrolyte salt, dimethyl sulfoxide as the solvent, and an organic compound called poly(butyl viologen dichloride) for the positive electrode. This battery is thought to have less impact on the human body and the environment than conventional batteries because the electrolyte is fluorine-free and the positive electrode does not contain the metal oxides.

[0007] However, because the positive electrode made of poly(butyl viologen dichloride) uses a fluorine compound called polyvinylidene fluoride (PVDF) as a binder, the entire battery cell has not been fluorine-free. Therefore, there is a demand for batteries that combine fluorine-free positive electrodes, negative electrodes, and electrolytes.

[0008] The present disclosure has been made in view of the above circumstances, and has an object to provide a secondary battery that does not use fluorine or a fluorine compound.

[0009] A secondary battery according to one embodiment of the present disclosure includes a positive electrode containing triquinoxalinylene, a negative electrode containing lithium or a lithium compound, and an electrolyte solution containing lithium ions and dimethyl sulfoxide disposed between the positive electrode and the negative electrode, and does not use fluorine or a fluorine compound.

[0010] According to the present disclosure, a secondary battery that does not use fluorine or a fluorine compound can be provided.

[0011] 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 surface SEM image of a battery using triquinoxalinylene as a positive electrode. FIG. 4 is a table showing the battery performance of examples and comparative examples. FIG. 5 is a surface SEM image of a battery using 2,6-dimethoxy-1,4-benzoquinone as a positive electrode.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] 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 lithium or a lithium compound, and an electrolyte solution 102 (electrolyte) containing lithium ions and dimethyl sulfoxide, disposed between the positive electrode 101 and the negative electrode 103. Examples of lithium compounds include lithium titanate and graphite occluding Li.

[0014] The chemical formula of triquinoxalinylene (hereinafter referred to as "TQ") is shown below.

[0015]

[0016] The discharge reaction proceeds when TQ contained in the positive electrode 101 binds with lithium ions responsible for charge transfer. The reaction proceeds in the opposite direction during charging. In the negative electrode 103, a lithium dissolution reaction proceeds during discharging, and a lithium precipitation reaction proceeds during charging.

[0017] The secondary battery of this embodiment uses TQ as the positive electrode active material, lithium as the negative electrode active material, and an electrolyte containing lithium salt and dimethyl sulfoxide as a solvent, thereby making it possible to fabricate a secondary battery that can be charged and discharged without using fluorine or fluorine compounds.

[0018] Each of the above components of the secondary battery of this embodiment will be described below.

[0019] (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.

[0020] (1-1) Positive Electrode Active Material The positive electrode active material of this embodiment contains at least TQ. TQ has high electrochemical reactivity with a fluorine-free electrolyte solution, and the use of TQ allows the production of a battery with excellent charge-discharge characteristics.

[0021] Furthermore, when a slurry containing styrene-butadiene rubber, carboxymethyl cellulose, Ketjen black, and TQ, which will be described later, is dried, an electrode is obtained in which fibrous TQ, styrene-butadiene rubber, carboxymethyl cellulose, and Ketjen black are entangled, resulting in good electrode strength.

[0022] TQ is an organic compound and, unlike metal oxides such as manganese compounds and vanadium compounds, is less likely to have adverse effects on the human body and the environment, making it a low-environmental-impact compound. Furthermore, TQ is inexpensive. For example, TQ can be obtained as a commercial product or by synthesis using known methods.

[0023] (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. To ensure sufficient conductive paths in the positive electrode, carbon with small particles is preferred. Specifically, carbon with a particle diameter of 1 μm or less is desirable. These carbons can be obtained, for example, as commercially available products or by known synthesis.

[0024] The positive electrode may contain a binder. Specific examples of binders include styrene-butadiene rubber, ethylene-propylene-diene rubber, carboxymethyl cellulose, and natural rubber. It is particularly preferable to use stable styrene-butadiene rubber in a voltage range (up to 3.1 V) where lithium chloride, the lithium salt in the electrolyte, is not oxidized.

[0025] The positive electrode can be prepared by mixing a powder of the positive electrode active material, the conductive additive, and the binder, and bonding the mixture to a conductive material. Alternatively, the positive electrode may be prepared by bonding the mixture to a current collector, which will be described later.

[0026] (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, or a nonwoven current collector containing carbon, 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 current collector can be obtained, for example, as a commercially available product.

[0027] The positive electrode active material can be supported on the current collector by the following methods: For example, physical methods such as vapor deposition, sputtering, and planetary ball milling, methods in which the 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, and known methods.

[0028] For the purpose of easily forming a high-quality positive electrode, a preferred method is to impregnate the 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 cold pressing or hot pressing the dried electrode (positive electrode), the strength of the electrode can be increased, and a positive electrode with excellent stability can be produced.

[0029] 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.

[0030] 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 binder is an insulating material, 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.

[0031] As described above, by forming a positive electrode on the current collector, it is possible to fully utilize the electrochemical activity of TQ, which is a positive electrode active material.

[0032] (2) Negative Electrode The secondary battery of this embodiment contains at least lithium (Li) 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, lithium is preferably used from the viewpoint of reversibility of charge and discharge. The negative electrode active material may contain lithium (Li) as a constituent element, and may also contain a lithium compound containing other components. In addition to the negative electrode active material, the negative electrode 103 may contain a conductive additive and a binder as constituent elements.

[0033] (3) Electrolyte The secondary battery of this embodiment includes an electrolyte containing lithium ions and dimethyl sulfoxide. This electrolyte may contain lithium chloride as a salt (electrolyte) and dimethyl sulfoxide as a solvent. In this embodiment, a non-aqueous electrolyte is used as the electrolyte, but this electrolyte may 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.

[0034] (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.

[0035] (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 electrolyte solution. As illustrated in FIG. 1 , the electrolyte solution is disposed between the positive electrode and the negative electrode so as to contact the positive electrode and the negative electrode. 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 prepared by assembling a positive electrode containing the above-described positive electrode active material, a negative electrode containing lithium (Li), and an electrolyte solution disposed so as to contact 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.

[0036] 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.

[0037] [Examples] Examples of secondary batteries according to this embodiment will be described in detail below. In each example, a secondary battery was fabricated using TQ as the positive electrode, lithium (Li) as the negative electrode, lithium chloride (LiCl) as the salt for the electrolyte, and dimethyl sulfoxide (DMSO) as the solvent. 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.

[0038] 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 the battery was prepared by pressing the TQ onto an Al foil current collector. Lithium metal foil (thickness: 200 μm) was used as the negative electrode active material. A dimethyl sulfoxide solution containing 1.0 mol / L of lithium chloride (LiCl) was used as the electrolyte.

[0039] (Preparation of Positive Electrode) A slurry containing commercially available TQ (Tokyo Chemical Industry Co., Ltd.), Ketjenblack powder (EC600JD, Lion Specialty Chemicals Co., Ltd.), styrene butadiene rubber, and carboxymethyl cellulose in a weight ratio of 80:10:8:2 was prepared as the positive electrode active material. The slurry was applied to an Al foil current collector to prepare a sheet electrode (thickness: 500 μm). Each of these sheet electrodes was cut into a circle with a diameter of 16 mm and press-bonded to obtain a positive electrode.

[0040] (Preparation of Negative Electrode) A lithium (Li) foil (thickness: 200 μm, Honjo Metals Co., Ltd.) was cut into a circle with a diameter of 16 mm, and this was bonded to a copper foil (Nilaco Corporation) current collector using an ultrasonic welder.

[0041] (Preparation of Electrolyte Solution) An electrolyte solution was prepared by mixing and stirring anhydrous lithium chloride (Sigma-Aldrich Co. LLC) with dimethyl sulfoxide to a concentration of 1.0 mol / L.

[0042] (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 the positive electrode case 201 containing the positive electrode 101 prepared by the above method, and a dimethyl sulfoxide solution containing lithium chloride was poured into the placed separator as the electrolyte 102. The negative electrode 103 was placed on the nonaqueous 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.

[0043] (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 1.8 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 3.1 V. The charge / discharge test of the battery was carried out under normal living conditions. The charge / discharge capacity was expressed as a value per unit weight of the positive electrode active material (mAh / g).

[0044] Figure 3 shows an SEM image of the surface of the positive electrode prepared in Example 1. In Figure 3, the surface state of fibrous TQ intertwined with styrene-butadiene rubber, carboxymethyl cellulose, and Ketjen black could be observed.

[0045] FIG. 4 shows the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles of the secondary battery of Example 1. Here, the discharge voltage is defined as the battery voltage at a discharge capacity of half the total discharge capacity. As shown in the table of FIG. 4, Example 1 had an initial discharge voltage of 2.5 V, an initial discharge capacity of 398 mAh / g, and a discharge capacity after 100 cycles of 376 mAh / g. The discharge voltage after 100 cycles was 2.3 V. Thus, it was confirmed that the battery of Example 1 is capable of charge / discharge cycling and operates as a secondary battery with excellent charge / discharge characteristics.

[0046] This is thought to be because the structure of TQ intertwined with styrene-butadiene rubber, carboxymethyl cellulose, and ketjen black provides good electrode strength and minimizes electrode degradation during charge and discharge. Furthermore, the interface between the positive electrode containing TQ, which uses styrene-butadiene rubber and carboxymethyl cellulose as a binder, and the dimethyl sulfoxide electrolyte containing lithium chloride is thought to facilitate smooth electrochemical reactions. In particular, Example 1 exhibited excellent cycle characteristics, with a capacity loss rate of less than 10% after 100 cycles. This is thought to be due to the low solubility of TQ in the electrolyte, dimethyl sulfoxide, resulting in minimal deactivation as a positive electrode active material.

[0047] Comparative Example 1 In Comparative Example 1, a secondary battery was fabricated that differed from Example 1 only in the lithium salt contained in the electrolyte. In Comparative Example 1, a coin-type secondary battery was fabricated in the same manner as in Example 1.

[0048] The lithium salt contained in the electrolyte solution of Comparative Example 1 was lithium hexafluorophosphate, a fluorine compound, and the electrolyte solution was prepared in the same manner as in Example 1. That is, the electrolyte solution was prepared by mixing and stirring lithium hexafluorophosphate with dimethyl sulfoxide to a concentration of 1.0 mol / L. Other battery configurations and experimental methods in Comparative Example 1 were the same as in Example 1.

[0049] 4 shows the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles of the secondary battery of Comparative Example 1. Comparative Example 1 had a discharge voltage of 2.5 V, an initial discharge capacity of 288 mAh / g, and a discharge capacity after 100 cycles of 136 mAh / g. The results of Comparative Example 1 and Example 1 show that the initial discharge capacity and discharge capacity after 100 cycles were higher when a lithium chloride / dimethyl sulfoxide solution was used than when a highly reactive lithium hexafluorophosphate / dimethyl sulfoxide solution was used.

[0050] The reason why Example 1 had a higher initial discharge capacity is thought to be because lithium chloride, used as a lithium salt, has better electrochemical reactivity with TQ than lithium hexafluorophosphate, resulting in a higher utilization rate of TQ contained in the electrode. Furthermore, the reason why Example 1 had a higher discharge capacity after 100 cycles is thought to be because the use of a lithium chloride / dimethyl sulfoxide solution as the electrolyte reduced the degradation and decomposition of TQ during charge and discharge, maintaining its utilization rate as a positive electrode active material.

[0051] Comparative Example 2 In Comparative Example 2, a secondary battery was fabricated in which only the positive electrode binder was different from that in Example 1. In Comparative Example 2, a coin-type secondary battery was fabricated in the same manner as in Example 1.

[0052] The secondary battery of Comparative Example 2 was produced using polyvinylidene fluoride, a fluorine compound, as a binder for the positive electrode in the same manner as in Example 1. Other aspects of the battery configuration and experimental method in Comparative Example 2 were the same as in Example 1.

[0053] 4 shows the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles of the secondary battery of Comparative Example 2. Comparative Example 2 had a discharge voltage of 2.4 V, an initial discharge capacity of 342 mAh / g, and a discharge capacity after 100 cycles of 294 mAh / g. The results of Comparative Example 2 and Example 1 show that the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles were slightly higher when styrene butadiene rubber and carboxymethyl cellulose were used than when polyvinylidene fluoride, which is commonly used as a positive electrode for lithium batteries, was used.

[0054] This is thought to be because the use of styrene butadiene rubber and carboxymethyl cellulose as binders improved the dispersibility of TQ and Ketjen Black and the electrode strength.

[0055] Comparative Example 3 In Comparative Example 3, a secondary battery was fabricated using a different positive electrode active material from that in Example 1. In Comparative Example 3, a coin-type secondary battery was fabricated using the same procedure as in Example 1.

[0056] The secondary battery of Comparative Example 3 was fabricated using 2,6-dimethoxy-1,4-benzoquinone as the positive electrode active material, using the same method as in Example 1. Other aspects of the battery configuration and experimental method in Comparative Example 3 were the same as in Example 1.

[0057] Figure 5 shows an SEM image of the surface of the positive electrode prepared in Comparative Example 2. In Figure 5, styrene-butadiene rubber, carboxymethyl cellulose, and Ketjen black were adhered around the 2,6-dimethoxy-1,4-benzoquinone particles, and the surface condition in which cracks had occurred was observed.

[0058] FIG. 4 shows the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles of the secondary battery of Comparative Example 3. Comparative Example 3 had a discharge voltage of 2.6 V, an initial discharge capacity of 152 mAh / g, and a discharge capacity after 100 cycles of 26 mAh / g. The results of Comparative Example 3 and Example 1 indicate that the capacity loss rate after 100 cycles was lower when TQ was used than when 2,6-dimethoxy-1,4-benzoquinone was used. The higher capacity loss rate after 100 cycles in Example 1 is likely due to the electrode using TQ as the positive electrode active material being more stable in shape than the electrode using 2,6-dimethoxy-1,4-benzoquinone, and therefore less degradation due to charge / discharge cycles.

[0059] From the results of the comparative examples, it was confirmed that the secondary batteries of the examples, which employ a combination of TQ as the positive electrode active material and lithium as the negative electrode active material and an electrolyte solution containing lithium salt and dimethyl sulfoxide, can operate as secondary batteries capable of being charged and discharged without containing fluorine or fluorine compounds.

[0060] As described above, the secondary battery of the present embodiment is a chargeable and dischargeable secondary battery that does not contain fluorine or fluorine compounds, and can be effectively used as a new driving source for various electronic devices such as small devices, sensors, and mobile devices.

[0061] 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.

[0062] 100: Secondary battery 101: Positive electrode 102: 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 lithium or a lithium compound; and an electrolyte solution containing lithium ions and dimethyl sulfoxide, disposed between the positive electrode and the negative electrode; wherein the secondary battery does not use fluorine or a fluorine compound.

2. The secondary battery according to claim 1, wherein the electrolyte contains lithium chloride.

3. The secondary battery according to claim 1, wherein the positive electrode contains styrene butadiene rubber and carboxymethyl cellulose.

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