Secondary battery

Abstract

A secondary battery comprising: a positive electrode containing a quinone-based organic compound of the following formula; a negative electrode containing lithium or a lithium compound; and an electrolyte which is disposed between the positive electrode and the negative electrode and contains lithium ions and dimethyl sulfoxide. The secondary battery does not use fluorine and a fluorine compound.　(In the formula, R1 to R8 each represent a hydrogen atom, a hydroxy group, or a methoxy group.)

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 oxide.

[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 fluorine compounds.

[0009] A lithium secondary battery according to one embodiment of the present disclosure includes a positive electrode containing a quinone-based organic compound represented by the following chemical formula, 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] (wherein R1 to R8 represent a hydrogen atom, a hydroxy group, or a methoxy group)

[0011] According to the present disclosure, a secondary battery that does not use fluorine or a fluorine compound can be provided.

[0012] Fig. 1 is a basic schematic diagram of a 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 table showing the battery performance of secondary batteries of examples. Fig. 4 is a table showing the battery performance of secondary batteries of comparative examples.

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0014] 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 a quinone-based organic compound, a negative electrode 103 containing lithium or a lithium compound, and an electrolytic 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.

[0015] The chemical formula of the quinone-based organic compound of this embodiment is shown below: In the formula, R1 to R8 represent a hydrogen atom, a hydroxy group, or a methoxy group.

[0016]

[0017] The 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.

[0018] The quinone organic compound contained in the positive electrode 101 binds with lithium ions, which are responsible for charge transfer, to initiate a discharge reaction. During charging, the reaction proceeds in the opposite direction. At the negative electrode 103, a lithium dissolution reaction occurs during discharge, and a lithium deposition reaction occurs during charging.

[0019] The secondary battery of this embodiment uses a quinone-based organic compound as the positive electrode active material, lithium as the negative electrode active material, and an electrolyte containing a 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.

[0020] Each of the above components of the secondary battery of this embodiment will be described below.

[0021] (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 necessary, 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.

[0022] (1-1) Positive Electrode Active Material The positive electrode active material of this embodiment includes at least the quinone-based organic compound. Quinones are highly electrochemically reactive with fluorine-free electrolytes, and provide good dispersibility and electrode strength with fluorine-free binders, allowing the fabrication of batteries with excellent charge-discharge characteristics. Furthermore, quinone-based organic compounds are organic compounds that are less likely to adversely affect the human body and the environment than metal oxides such as manganese compounds and vanadium compounds, and therefore have a low environmental impact and are inexpensive. Quinones are available, for example, as commercially available products or can be synthesized using known methods. Among quinone-based organic compounds, 2,5-dimethoxy-1,4-benzoquinone is preferred because it has low solubility in electrolytes and a good cycle life.

[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] A 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 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.

[0031] As described above, by forming a positive electrode on the current collector, it is possible to fully utilize the electrochemical activity of the quinone organic compound that is the 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 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 the quinone organic compound for the positive electrode, lithium (Li) for the negative electrode, and lithium chloride (LiCl) as the salt and dimethyl sulfoxide (DMSO) as the solvent 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.

[0038] Example 1 In Example 1, the coin-type secondary battery (FIG. 2) described above was fabricated using the following procedure. 2,5-dimethoxy-1,4-benzoquinone was used as the positive electrode active material, and the battery was prepared by pressing 2,5-dimethoxy-1,4-benzoquinone 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 2,5-dimethoxy-1,4-benzoquinone powder (Tokyo Chemical Industry Co., Ltd.), Ketjen Black 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: 50 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) metal foil (thickness: 200 μm, Honjo Metals Co., Ltd.) was cut into a circle with a diameter of 16 mm, which 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 each 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 charging 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] FIG. 3 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. 3, Example 1 had an initial discharge voltage of 2.7 V, an initial discharge capacity of 313 mAh / g, and a discharge capacity after 100 cycles of 296 mAh / g. The discharge voltage after 100 cycles was 2.5 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.

[0045] This is thought to be due to the smooth electrochemical reaction at the interface between the positive electrode containing a quinone-based organic compound using styrene-butadiene rubber and carboxymethyl cellulose as binders and the dimethyl sulfoxide electrolyte containing lithium chloride. In particular, with 2,5-dimethoxy-1,4-benzoquinone in Example 1, the capacity loss rate after 100 cycles was less than 10%, demonstrating good cycle characteristics. This is thought to be due to the low solubility of 2,5-dimethoxy-1,4-benzoquinone used as the positive electrode active material in the dimethyl sulfoxide electrolyte, which reduced the amount of deactivation of the positive electrode active material.

[0046] 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.

[0047] In Examples 2, 3, and 4, coin-type secondary batteries were fabricated in the same manner as in Example 1. Other battery configurations and experimental methods in Examples 2, 3, and 4 were the same as in Example 1.

[0048] Figure 3 shows the discharge voltage, initial discharge capacity, and discharge capacity after 100 cycles for the secondary batteries of Examples 2, 3, and 4. Example 2 (2,6-dimethoxy-1,4-benzoquinone) had an initial discharge voltage of 2.7 V, an initial discharge capacity of 308 mAh / g, and a discharge capacity after 100 cycles of 202 mAh / g. Example 3 (2,5-dihydroxy-1,4-benzoquinone) had an initial discharge voltage of 2.8 V, an initial discharge capacity of 298 mAh / g, and a discharge capacity after 100 cycles of 165 mAh / g. Example 4 (1,4-benzoquinone) had an initial discharge voltage of 2.4 V, an initial discharge capacity of 261 mAh / g, and a discharge capacity after 100 cycles of 52 mAh / g. The discharge voltage after 100 cycles was 2.2 V for Example 2, 2.1 V for Example 3, and 1.5 V for Example 4. In all the examples, it was confirmed that the battery operated as a secondary battery capable of charge / discharge cycling.

[0049] The results of Examples 1 to 4 confirmed that the secondary batteries of Examples 1 to 4, which employ a combination of a quinone-based organic compound as the positive electrode active material, lithium as the negative electrode active material, and a dimethyl sulfoxide solution containing lithium chloride as the electrolyte, can operate as secondary batteries with good charge-discharge performance without containing fluorine or fluorine compounds. Furthermore, it was confirmed that the secondary battery of Example 1, which uses 2,5-dimethoxy-1,4-benzoquinone, is preferable.

[0050] 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.

[0051] In Comparative Example 1, lithium hexafluorophosphate, a fluorine compound, was used as the lithium salt contained in the electrolyte solution, and a secondary battery was fabricated in the same manner as in Example 1. That is, the electrolyte solution in Comparative Example 1 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.

[0052] 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 2.7 V, an initial discharge capacity of 256 mAh / g, and a discharge capacity after 100 cycles of 124 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.

[0053] The reason why Example 1 had a higher initial discharge capacity is thought to be because lithium chloride, used as the lithium salt, has better electrochemical reactivity with the quinone organic compound than lithium hexafluorophosphate, resulting in a higher utilization rate of the quinone organic compound 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 the quinone organic compound during charge and discharge, thereby maintaining its utilization rate as a positive electrode active material.

[0054] 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.

[0055] A secondary battery of Comparative Example 2 was fabricated using polyvinylidene fluoride, a fluorine compound, as a binder for the positive electrode in the secondary battery of Comparative Example 2 in the same manner as in Example 1. Other battery configurations and experimental methods in Comparative Example 2 were the same as in Example 1.

[0056] 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 2.6 V, an initial discharge capacity of 288 mAh / g, and a discharge capacity after 100 cycles of 242 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.

[0057] This is thought to be because the use of styrene butadiene rubber and carboxymethyl cellulose as binders improved the dispersibility of the quinone organic compound and Ketjen black and the electrode strength.

[0058] From the results of Comparative Examples 1 and 2, it was confirmed that the secondary battery of Example 1, which did not contain a fluorine compound, could operate as a secondary battery with better charge / discharge performance than Comparative Examples 1 and 2, which used an electrolyte solution or electrodes containing a fluorine compound.

[0059] 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.

[0060] 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.

[0061] 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 which does not use fluorine or a fluorine compound, comprising: a positive electrode containing a quinone-based organic compound of the following chemical formula; a negative electrode containing lithium or a lithium compound; and an electrolyte solution which contains lithium ions and dimethyl sulfoxide and is disposed between the positive electrode and the negative electrode. (wherein R1 to R8 represent a hydrogen atom, a hydroxy group, or a methoxy group) 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.

4. The secondary battery according to claim 1, wherein the quinone-based organic compound includes 2,5-dimethoxy-1,4-benzoquinone.

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