Secondary batteries

Abstract

A secondary battery comprising: a positive electrode containing an organic sulfur compound represented by the depicted formula (in the formula, R1 represents a propyl group or an allyl group, and n represents an integer of 2-3); a negative electrode containing magnesium, sodium, or calcium; and an electrolyte disposed between the positive electrode and the negative electrode.

Description

[Technical Field]

[0001] This disclosure relates to secondary batteries. [Background technology]

[0002] Traditionally, lead-acid batteries, lithium-ion batteries, lithium-ion polymer batteries, nickel-metal hydride batteries, and nickel-cadmium batteries have been widely used as secondary batteries in small devices, sensors, mobile devices, and the like.

[0003] In recent years, with the development of the Internet of Things (IoT), the development of scattered sensors that can be installed in various natural environments such as soil and forests is also progressing. Aiming to apply these sensors, Patent Document 1 describes the study of air batteries that use resource-abundant materials and have low cost and environmental impact.

[0004] On the other hand, research and development of batteries using organic materials as the positive electrode active material is also progressing. Non-patent document 1 describes the study of a battery using poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (PTMA), which is synthesized from 2,2,6,6-tetramethylpiperidine methacrylate as the starting material, as the positive electrode active material. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6711915 [Non-patent literature]

[0006] [Non-Patent Document 1] K. Nakahara, et al., “Rechargeable batteries with organic radical cathodes”, 359, (2002), 351-354 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventional batteries use environmentally harmful materials such as lead compounds, cadmium compounds, manganese compounds, nickel compounds, and fluorine compounds, and require special disposal. Therefore, these conventional batteries are unsuitable for use in scattered sensors, where disposal and collection as general waste is extremely difficult. Consequently, there is a need for batteries composed solely of low-environmental-impact materials that can be disposed of as general waste or do not require collection.

[0008] The air battery described in Patent Document 1 utilizes oxygen from the air as the positive electrode active material, thus requiring an air intake port. However, this air battery suffers from the drawback of electrolyte evaporation from the air intake port, making it unsuitable for long-term use. Therefore, there is a need for a new, environmentally friendly battery that does not require oxygen as the positive electrode active material.

[0009] The battery described in Non-Patent Document 1 does not require an air intake because it uses an organic material for the positive electrode active material, and it can be designed to prevent the evaporation of the electrolyte, making it a battery that can be used for a long period of time. However, 2,2,6,6-tetramethylpiperidine methacrylate, which is the starting material for the synthesis of PTMA used as the positive electrode active material, does not exist in the environment, thus having a high environmental impact.

[0010] Secondary batteries can be recharged and discharged and reused repeatedly. Therefore, compared to primary batteries of the same capacity and voltage, they can reduce the amount of waste and have a low environmental impact.

[0011] This disclosure is made in view of the above circumstances and aims to provide a secondary battery that has a low environmental impact and can be used for a long period of time. [Means for solving the problem]

[0012] A secondary battery in one aspect of this disclosure is

[0013] [Chemical formula]

[0014] (In the formula, R1 represents a propyl group or an allyl group, and n represents an integer of 2 to 3) and a negative electrode containing magnesium, sodium or calcium, and an electrolyte disposed between the positive electrode and the negative electrode. [Advantages of the Invention]

[0015] According to the present disclosure, a secondary battery with low environmental impact and capable of long-term storage can be provided. [Brief Description of the Drawings]

[0016] [Figure 1] FIG. 1 is a basic schematic diagram of the secondary battery of the present embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery. [Modes for Carrying Out the Invention]

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0018] [Configuration of Secondary Battery] FIG. 1 is a configuration diagram showing the configuration of a secondary battery in an embodiment of the present disclosure. The illustrated secondary battery includes a positive electrode 101 containing an organic sulfur compound, a negative electrode 103 containing magnesium, sodium or calcium, and an electrolyte 102 disposed between the positive electrode 101 and the negative electrode 103. As the electrolyte 102, it is preferable to use a non-aqueous electrolyte 102.

[0019] The organic sulfur compound of the present embodiment is a compound represented by the following general formula.

[0020] [Chemical formula]

[0021] In the formula, R1 represents a propyl group or an allyl group, and n represents an integer between 2 and 3. Examples of organosulfur compounds with the above general formula include dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, and diallyl disulfide.

[0022] Dipropyl trisulfide is an organic sulfur compound in which two propyl groups are trisulfide-bonded via three sulfur atoms. Dipropyl disulfide is an organic sulfur compound in which two propyl groups are disulfide-bonded via two sulfur atoms. Diallyl trisulfide is an organic sulfur compound in which two allyl groups are trisulfide-bonded via three sulfur atoms. Diallyl disulfide is an organic sulfur compound in which two allyl groups are disulfide-bonded via two sulfur atoms. The general formulas of these compounds are shown below.

[0023] [ka]

[0024] In the embodiments described below, a case in which dipropyl trisulfide is used as the organic sulfur compound in the positive electrode 101, magnesium as the negative electrode 103, and a non-aqueous electrolyte 102 as the electrolyte 102 is described as an example, but the embodiment is not limited to this.

[0025] The charge-discharge reaction at the negative electrode 103 is shown in equation (1), and the charge-discharge reaction at the positive electrode 101 is shown in equation (2).

[0026] [ka]

[0027] The two trisulfide bonds of the dipropyl trisulfide contained in the positive electrode 101 are cleaved by electrochemical reduction and regenerated by electrochemical oxidation. During discharge, electrochemical oxidation occurs at the negative electrode 103, that is, magnesium is converted into magnesium ions (Mg +) and electrons (e - ) releases.

[0028] On the other hand, electrochemical reduction occurs at the positive electrode 101, meaning that the two trisulfide bonds of dipropyl trisulfide are cleaved and react with the aforementioned magnesium ions and electrons to produce a magnesium salt. During charging, the reaction proceeds in the reverse direction. Specifically, electrochemical oxidation occurs at the positive electrode 101, and the magnesium salt returns to dipropyl trisulfide, while electrochemical reduction occurs at the negative electrode 103, and the magnesium ions return to magnesium.

[0029] The secondary battery of this embodiment is expected to be an environmentally friendly battery because it uses an organic sulfur compound such as dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, or diallyl disulfide as the positive electrode active material, magnesium, sodium, or calcium as the negative electrode active material, and a non-aqueous electrolyte that is not a fluorine compound as the electrolyte.

[0030] Furthermore, the secondary battery of this embodiment uses the above-mentioned organic sulfur compound as the positive electrode active material, resulting in a sealed battery that does not require an air intake port necessary for air batteries. Therefore, the electrolyte does not volatilize from the air intake port, allowing for long-term storage.

[0031] The positive electrode 101 may include a positive electrode active material and a conductive additive as components, and the negative electrode 103 may include a negative electrode active material and a conductive additive as components.

[0032] The following describes each of the above-mentioned components of a secondary battery.

[0033] (1) Positive electrode The positive electrode contains at least a positive electrode active material and may optionally contain a conductive additive or current collector as described below. Furthermore, it is preferable that the positive electrode is formed without a binder on a porous body containing at least one selected from the group consisting of aluminum, copper, and iron, or on a nonwoven fabric current collector containing carbon.

[0034] Furthermore, the positive electrode is preferably formed without a binder in a cocontinuum having a three-dimensional network structure, in which multiple nanostructures are integrated. The cocontinuum has a three-dimensional network structure because the integrated multiple nanostructures have branches.

[0035] Here, specific examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, ethylene propylene diene rubber, and natural rubber.

[0036] As described above, by fabricating a positive electrode containing dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, or diallyl disulfide as the positive electrode active material, a positive electrode with high activity for charging and discharging reactions can be obtained. Furthermore, by fabricating a positive electrode for a secondary battery with the above configuration, it is possible to fully extract the electrochemical activity of the positive electrode active material, dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, or diallyl disulfide.

[0037] Furthermore, by forming the positive electrode on the porous current collector, the carbon-containing nonwoven fabric current collector, or the cocontinuum, it is possible to fully extract the potential of the positive electrode active material.

[0038] (1-1) Positive electrode active material The positive electrode active material of this embodiment includes at least one organic sulfur compound, such as dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, or diallyl disulfide. These organic sulfur compounds are found in garlic, onions, and other vegetables, thus having a low environmental impact and being inexpensive.

[0039] The above-mentioned organosulfur compounds can be obtained, for example, as commercially available products or through known synthesis methods.

[0040] (1-2) Preparation of a positive electrode using a conductive additive In this embodiment, the positive electrode may contain a conductive additive. Examples of conductive additives include carbon. Specifically, examples include carbon blacks such as Ketjenblack and acetylene black, activated carbons, graphites, and carbon fibers.

[0041] To ensure sufficient reaction sites within the cathode, carbon particles with small size are suitable. Specifically, particles with a diameter of 1 μm or less are desirable. These carbon particles can be obtained, for example, as commercially available products or through known synthesis methods.

[0042] A positive electrode can be prepared by dropping the liquid organic sulfur compound, which is the positive electrode active material, into a mixture of the above conductive additive and the above binder, and then joining it with a conductive material.

[0043] (1-3) Preparation of a positive electrode using a current collector The positive electrode is formed as a porous current collector containing at least one selected from the group consisting of aluminum, copper, and iron, or as a nonwoven fabric current collector containing carbon, and the positive electrode does not need to contain a binder.

[0044] Specifically, the positive electrode active material may be directly supported on the porous current collector or the nonwoven fabric current collector. Direct support means that the positive electrode active material is finely bonded to the three-dimensional structure of the current collector. This can improve conductivity. If direct support is not used, for example, when the current collector's disc is placed on top of the positive electrode active material's disc, the current collector and the positive electrode active material are in surface contact, resulting in lower conductivity compared to the direct support case. The above-mentioned porous current collector and nonwoven fabric current collector can be obtained, for example, as commercially available products.

[0045] Furthermore, a positive electrode is formed in a cocontinuum of a three-dimensional network structure in which multiple nanostructures are integrated by non-covalent bonds, and the positive electrode does not necessarily contain a binder. Specifically, a positive electrode active material may be supported on the cocontinuum.

[0046] Here, the cocontinuum is defined as a stretchable, integrated structure in which the connections between nanostructures are deformable. Preferably, the cocontinuum has an average pore size of 0.1 μm to 50 μm.

[0047] Nanostructures include, for example, nanosheets or nanofibers, and are characterized by their conductivity. An example of a nanosheet is graphene. Graphene nanofibers include, for example, iron oxide, manganese oxide, silicon, and cellulose carbide, and are fibrous materials with a diameter of 1 nm to 1 μm and a length of 100 times or more their diameter. Here, cellulose carbide can be produced by creating a gel in which nanofibers of cellulose are dispersed, and then carbonizing this gel by heating it in an inert gas atmosphere.

[0048] The above-mentioned cocontinuum can be manufactured by drying a frozen material obtained by freezing a sol or gel in which nanostructures such as nanosheets or nanofibers are dispersed, in a vacuum.

[0049] The dispersion medium for the sol is specifically an aqueous system such as water, or an organic system such as carboxylic acid, methanol, ethanol, propanol, n-butanol, isobutanol, n-butylamine, dodecane, unsaturated fatty acid, ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, or glycerin, and two or more of these may be mixed.

[0050] The dispersion medium for the gel is specifically an aqueous system such as water (H2O), or an organic system such as carboxylic acid, methanol (CH3OH), ethanol (C2H5OH), propanol (C3H7OH), n-butanol, isobutanol, n-butylamine, dodecane, unsaturated fatty acids, ethylene glycol, heptane, hexadecane, isoamyl alcohol, octanol, isopropanol, acetone, or glycerin, and two or more of these may be mixed.

[0051] The vacuum level in the drying process varies depending on the dispersion medium used, but there are no particular restrictions as long as the vacuum level is such that the dispersion medium sublimes. For example, when water is used as the dispersion medium, the vacuum level must be such that the pressure is 0.06 MPa or less, but since heat is removed as latent heat of sublimation, drying takes time. For this reason, the vacuum level is 1.0 × 10⁻⁶ ―6 From 1.0 × 10 ―2 Pa is preferred. Furthermore, heat may be applied during drying using a heater or the like.

[0052] This cocontinuum allows for a larger specific surface area compared to commercially available conductive porous materials and nonwoven fabric current collectors. The specific surface area of ​​this copolymer is 200 m². 2 It is preferable that the amount is 1 / g or more. Note that the cocontinuum is also called a copolymer.

[0053] The following methods can be considered for supporting positive electrode active material on the porous current collector, nonwoven fabric current collector, and coconvex body described above. For example, physical methods such as vapor deposition, sputtering, and planetary ball milling; chemical methods such as dropping or impregnating the nonwoven fabric current collector and coconvex body with liquid or dissolved positive electrode active material; the sol-gel method; or known methods.

[0054] For the formation of a positive electrode that is simple and of good quality, a method of dropping liquid or dissolved positive electrode active material onto a nonwoven fabric current collector and copolymer is preferred. Here, by applying cold pressing or hot pressing to the electrode, the strength of the electrode can be increased, and a more stable positive electrode can be produced.

[0055] In this embodiment of the secondary battery, since the reaction shown in formula (2) proceeds on the surface of the positive electrode 101, it is considered preferable to generate a large number of reaction sites inside the positive electrode 101. In the case of a positive electrode molded using the aforementioned conductive additive and binder, when the specific surface area is increased, the bonding strength between the conductive additives decreases, the structure deteriorates, making stable discharge difficult and reducing the discharge capacity. Furthermore, polytetrafluoroethylene (PTFE) and the like used as binders are fluorine-based compounds, resulting in a high environmental impact.

[0056] In contrast, positive electrodes formed using the aforementioned porous current collector, nonwoven fabric current collector, or copolymer can secure a large number of reaction sites and solve the aforementioned problems, thereby enabling higher discharge capacity. In particular, the above-mentioned cocontinuum has a high bulk density and can support more positive electrode active material, thus improving battery efficiency. Furthermore, since the positive electrode does not contain binders such as polytetrafluoroethylene (PTFE), which have a high environmental impact, a reduction in environmental burden can be expected.

[0057] As described above, by fabricating a positive electrode containing the above-mentioned organic sulfur compound as the positive electrode active material, a positive electrode with high activity for charging and discharging reactions can be obtained. Furthermore, by fabricating a positive electrode for a secondary battery with the above-described configuration, it is possible to fully extract the electrochemical activity of the above-mentioned organic sulfur compound, which is the positive electrode active material.

[0058] (2) Negative electrode The secondary battery of this embodiment contains at least magnesium (Mg), sodium (Na), or calcium (Ca) as the negative electrode active material. This negative electrode active material only needs to contain magnesium (Mg), sodium (Na), or calcium (Ca) as its main component, and may also be an alloy containing at least one component selected from the group consisting of lithium (Li), zinc (Zn), aluminum (Al), iron (Fe), tin (Sn), and carbon (C).

[0059] (3) Non-aqueous electrolyte (electrolyte) The secondary battery of this embodiment contains a non-aqueous electrolyte. This non-aqueous electrolyte contains magnesium ions (Mg 2+ ), sodium ions (Na + ) or calcium ions (Ca 2+ It is a solution containing an electrolyte that allows for the movement of )

[0060] The non-aqueous electrolyte uses an organic solvent as the main solvent and may contain, for example, water in addition to the organic solvent. Examples of the non-aqueous electrolyte include carbonate solvents such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate (MBC), diethyl carbonate (DEC), ethyl propyl carbonate (EPC), ethyl isopropyl carbonate (EIPC), ethyl butyl carbonate (EBC), dipropyl carbonate (DPC), diisopropyl carbonate (DIPC), dibutyl carbonate (DBC), ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate (1,2-BC), etc., ether solvents such as 1,2-dimethoxyethane (DME), tetraethylene glycol dimethyl ether (TEGDME), etc., lactone solvents such as γ-butyrolactone (GBL), or an electrolyte in which a magnesium salt or a sodium salt or a calcium salt is dissolved in at least one organic solvent selected from the group consisting of sulfoxide solvents such as dimethyl sulfoxide (DMSO) can be used.

[0061] The magnesium salt, sodium salt, and calcium salt are represented by Mg-X2, Na-X, and Ca-X2, respectively, where X is, for example, Cl, Br, I, BF4, PF6, CF3SO3, ClO4, CF3CO2, AsF6, SbF6, AlCl4, N(CF3SO2)2, N(CF3CF2SO2)2, PF3(C2F5)3, N(FSO2)2, N(FSO2)(CF3SO2), N(CF3CF2SO2)2, N(C2F4S2O4), N(C3F6S2O4), N(CN)2, N(CF3SO2)(CF3CO), R 1 FBF3 (where R 1 F = n-C m F 2m+1 , m is a natural number from 1 to 4) and R 2 BF3 (where R 2 = n-C p H 2p+1 , p is a natural number from 1 to 5) can be mentioned. From the perspective of environmental load, Cl, Br, I, ClO4, AlCl, N(CN)2, which are not fluorine compounds, are preferred. Furthermore, metal salts mixed with two or more of these can be used.

[0062] In this embodiment, a non-aqueous electrolyte is used, but a solid electrolyte such as a gel or solid may also be used. That is, the electrolyte may be in any form, such as liquid, cream, gel, or solid.

[0063] (4) Other elements In addition to the above-mentioned components, the secondary battery of this embodiment may include structural members such as separators and battery cases, as well as other elements required for a secondary battery. While conventionally known materials can be used for these, it is preferable that they do not contain harmful substances, precious metals, etc., from the viewpoint of environmental impact and waste disposal. Furthermore, it is even more preferable that these other elements be of biological origin and biodegradable materials.

[0064] (5) Method of manufacturing secondary batteries As described above, the secondary battery of this embodiment includes at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, and as illustrated in Figure 1, the non-aqueous electrolyte is arranged between the positive electrode and the negative electrode so as to be in contact with both electrodes. A secondary battery with such a configuration can be prepared in the same way as a conventional secondary battery.

[0065] For example, a secondary battery can be assembled according to prior art by comprising a positive electrode containing the above-mentioned organic sulfur compound as the positive electrode active material, a negative electrode containing magnesium (Mg), sodium (Na), or calcium (Ca), and a non-aqueous electrolyte arranged in contact with the positive and negative electrodes. The positive electrode may also contain a conductive additive and a binder.

[0066] As one embodiment of the method for manufacturing a secondary battery, for example, a coin-type secondary battery can be manufactured.

[0067] Figure 2 is a schematic cross-sectional view showing the structure of a coin-type secondary battery. Specifically, first, a separator (not shown) is placed on the positive electrode case 201 on which the positive electrode 101 is installed, and electrolyte 102 is injected into the placed separator. Next, the negative electrode 103 is placed on top of the electrolyte 102, and the negative electrode case 202 is placed over the positive electrode case 201. Then, by crimping the peripheral edges of the positive electrode case 201 and the negative electrode case 202 with a coin cell crimping machine, it is possible to manufacture a coin-type secondary battery including a propylene gasket 203.

[0068] The coin-type secondary battery shown in the illustration utilizes dipropyl trisulfide, dipropyl disulfide, diallyl trisulfide, or diallyl disulfide as the positive electrode active material. Therefore, unlike air batteries that use oxygen from the air as the positive electrode active material, the positive electrode case 201 of this embodiment does not need to have an air intake. In other words, a sealed battery can be manufactured in this embodiment. Consequently, the secondary battery of this embodiment can be stored for a long period of time without the electrolyte volatilizing from the air intake.

[0069] [Examples] Examples of secondary batteries according to this embodiment are described in detail below. In each example, magnesium (Mg), sodium (Na), and calcium (Ca) were used as the negative electrode, and a secondary battery was fabricated using a propylene carbonate solution containing Mg(ClO4)2, NaClO4, and Ca(ClO4)2, respectively, as the non-aqueous electrolyte. This disclosure is not limited to the examples shown below, and can be implemented with appropriate modifications without changing the gist of the invention.

[0070] <Example 1> In Example 1, the coin-type secondary battery (Figure 2) described above was fabricated using the following procedure. The positive electrode of Example 1 was prepared using dipropyl trisulfide as the positive electrode active material, with a conductive additive (Ketjenbrak) and a binder (PTFE). Magnesium (Mg) foil, sodium (Na) foil, and calcium (Ca) foil were used as the negative electrode active materials, respectively. For the non-aqueous electrolyte, a propylene carbonate solution containing 1 mol / L Mg(ClO4)2, NaClO4, and Ca(ClO4)2 was used, respectively.

[0071] (Preparation of the positive electrode) Ketjenblack powder (EC600JD, Lion Specialty Chemicals) and polytetrafluoroethylene (PTFE) powder were thoroughly ground and mixed in a weight ratio of 80:20 using a grinder, and roll-formed to create a sheet electrode (thickness: 0.5 mm). Dipropyl trisulfide (Tokyo Chemical Industries, Ltd., 60 μL) was dropped onto this sheet electrode, cut into a circle with a diameter of 16 mm, and pressed onto an aluminum mesh to obtain a positive electrode.

[0072] (Preparation of the negative electrode) Magnesium (Mg) foil (150 μm thick), sodium (Na) foil (150 μm thick), and calcium (Ca) foil (150 μm thick) were cut into circles with a diameter of 16 mm, and these were then joined to copper foil (Niraco Co., Ltd.) using an ultrasonic welding machine.

[0073] (Preparation of secondary batteries) Using a coin cell battery case (Hosensha), a coin-type rechargeable battery as shown in Figure 2 was fabricated.

[0074] A cellulose separator (Nippon Kodo Paper Industry 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 installed. A propylene carbonate solution (Kishida Chemical Co., Ltd., 200 μL) containing 1 mol / L of Mg(ClO4)2, NaClO4, and Ca(ClO4)2 was injected into the placed separator as a non-aqueous electrolyte 102. The negative electrode 103 was placed on top of the non-aqueous electrolyte 102, the negative electrode case 202 was placed over the positive electrode case 201, and the peripheral edges of the positive electrode case 201 and the negative electrode case 202 were crimped with a coin cell crimping machine to obtain a coin-type secondary battery containing a propylene gasket 203.

[0075] (Charge / Discharge Test Method) The battery performance of the secondary battery prepared using the above procedure was measured. The battery cycle test was performed using a charge / discharge measurement system (manufactured by Bio Logic), with a current density of 0.1 mA / cm² per effective area of ​​the positive electrode. 2 The system was energized, and the discharge voltage was measured until the battery voltage dropped from the open-circuit voltage to 0.50 V (discharge termination voltage).

[0076] Furthermore, the charging current density per unit area of ​​the positive electrode is 0.1 mA / cm². 2 The battery was energized, and the charging termination voltage was set to 3.0 V. The battery charge and discharge tests were conducted under normal living conditions. The charge and discharge capacity was expressed as the value per unit weight of the positive electrode active material (mAh / g). Here, the discharge voltage was defined as the discharge voltage at half the total discharge capacity.

[0077] (Battery performance) Table 1 shows the discharge voltage, discharge capacity, and discharge capacity after 20 cycles of the secondary battery of Example 1. As shown in Table 1, the discharge voltages of Example 1, using magnesium (Mg), sodium (Na), and calcium (Ca) as the negative electrode, were 1.0 V, 1.4 V, and 1.5 V, respectively, and the discharge capacities were 410 mAh / g, 420 mAh / g, and 380 mAh / g, respectively. Furthermore, the discharge capacities after 20 cycles were 340 mAh / g, 350 mAh / g, and 270 mAh / g, respectively. Thus, it was found that the secondary battery of Example 1 has excellent battery performance.

[0078] [Table 1]

[0079] <Example 2> In Example 2, the coin-type secondary battery described above was fabricated using the following procedure. The preparation of the negative electrode, the preparation of the secondary battery, and the charge / discharge test method in Example 2 were carried out in the same manner as in Example 1. For the positive electrode in Example 2, dipropyl trisulfide was used as the positive electrode active material, and dipropyl trisulfide was formed on a carbon-containing nonwoven current collector (carbon felt).

[0080] (Preparation of the positive electrode) Dipropyl trisulfide (Tokyo Chemical Industries, Ltd., 60 μL) was dropped onto carbon felt (Toyobo Co., Ltd.). Next, this dipropyl trisulfide-containing carbon felt was cut into a circle with a diameter of 16 mm to obtain the positive electrode.

[0081] (Battery performance) Table 1 shows the discharge voltage, discharge capacity, and discharge capacity after 20 cycles of the secondary battery in Example 2. As shown in Table 1, the discharge capacity of the battery in Example 2 using magnesium (Mg) as the negative electrode was 450 mAh / g, which was higher than that of Example 1. Furthermore, the discharge capacity after 20 cycles was 360 mAh / g, which was also higher than that of Example 1. Batteries using sodium (Na) and calcium (Ca) as the negative electrode also showed higher discharge capacities than those of Example 1.

[0082] Furthermore, as shown in Table 1, the discharge voltage in Example 2 is greater than that in Example 1. In other words, in Example 2, a reduction in overvoltage was observed compared to Example 1, and an improvement in the energy efficiency of the discharge was achieved.

[0083] These improvements in characteristics are thought to be due to the use of a positive electrode formed by bonding the positive electrode active material to carbon felt, which reduced the internal resistance of the battery and allowed the battery reaction to proceed more efficiently.

[0084] Furthermore, Example 2 does not contain polytetrafluoroethylene (PTFE), which has a high environmental impact, in the positive electrode, thus having a lower environmental impact than Example 1.

[0085] <Example 3> In Example 3, the coin-type secondary battery described above was fabricated using the following procedure. The preparation of the negative electrode, the preparation of the secondary battery, and the charge / discharge test method in Example 3 were carried out in the same manner as in Example 1 and Example 2. For the positive electrode in Example 3, dipropyl trisulfide was used as the positive electrode active material, and dipropyl trisulfide was formed in a cocontinuum.

[0086] (Preparation of the positive electrode) Dipropyl trisulfide (Tokyo Chemical Industries, Ltd., 60 μL) was added dropwise to the cocontinuum. This dipropyl trisulfide-containing cocontinuum was then cut into a circle with a diameter of 16 mm to obtain the positive electrode.

[0087] The above cocontinuum was produced by first placing a bacterial cellulose gel produced by the acetic acid bacterium Acetobacter xylinum into a test tube and immersing the test tube in liquid nitrogen for 30 minutes to completely freeze the bacterial cellulose gel. Next, the frozen bacterial cellulose gel was transferred to a round-bottom flask and dried in a freeze-dryer (Tokyo Rikakikai Co., Ltd.) under a vacuum of less than 10 Pa. After that, the cocontinuum was produced by carbonizing it by firing at 1200°C for 2 hours under a nitrogen atmosphere.

[0088] (Battery performance) Table 1 shows the discharge voltage, discharge capacity, and discharge capacity after 20 cycles of the secondary battery in Example 3. As shown in Table 1, the discharge capacity of the battery in Example 3 using magnesium (Mg) as the negative electrode was 490 mAh / g, which was larger than that of Examples 1 and 2. Furthermore, the discharge capacity after 20 cycles was 380 mAh / g, which was also larger than that of Examples 1 and 2. The batteries using sodium (Na) and calcium (Ca) as the negative electrode also showed larger discharge capacities than those of Examples 1 and 2.

[0089] Furthermore, as shown in Table 1, the discharge voltage in Example 3 is greater than that of Examples 1 and 2. In other words, Example 3 showed a reduction in overvoltage compared to Examples 1 and 2, and an improvement in the energy efficiency of the discharge was achieved.

[0090] These improvements in properties are thought to be due to the improved dispersibility of the positive electrode active material, which was achieved by using a positive electrode formed by bonding the positive electrode active material to a cocontinuum.

[0091] Furthermore, Example 3 does not contain polytetrafluoroethylene (PTFE), which has a high environmental impact, in the cathode, thus having a lower environmental impact than Example 1.

[0092] <Examples 1A~3A, 1B~3B, 1C~3C> This embodiment is a secondary battery in which dipropyl disulfide, diallyl trisulfide, or diallyl disulfide is used as the positive electrode active material in each of the above-described Examples 1 to 3, instead of dipropyl trisulfide. The secondary battery of this embodiment is the same as that of Examples 1 to 3, except for the positive electrode active material. The charge and discharge test method of this embodiment was also carried out in the same manner as in Examples 1 to 3.

[0093] Examples 1A to 3A are examples of secondary batteries in which dipropyl disulfide (Tokyo Chemical Industries, Ltd.) is used as the positive electrode active material in each of Examples 1 to 3. Examples 1B to 3B are examples of secondary batteries in which diallyl trisulfide (Tokyo Chemical Industries, Ltd.) is used as the positive electrode active material in each of Examples 1 to 3. Examples 1C to 3C are examples of secondary batteries in which diallyl disulfide (Fujifilm Wako Corporation) is used as the positive electrode active material in each of Examples 1 to 3.

[0094] In Examples 1A, 1B, and 1C, the positive electrode contains a conductive additive (Ketjenblack) and a binder (PTFE). In Examples 2A, 2B, and 2C, the positive electrode active material was formed on a carbon-containing nonwoven current collector (carbon felt). In Examples 3A, 3B, and 3C, the positive electrode active material was formed on a coconvex body.

[0095] Table 2 shows the discharge voltage, discharge capacity, and discharge capacity after 20 cycles for the secondary batteries of Examples 1A-3A, 1B-3B, and 1C-3C. As shown in Table 2, the secondary batteries of this embodiment obtained the same results as the secondary batteries of Examples 1-3, which used dipropyl trisulfide as the positive electrode active material.

[0096] [Table 2]

[0097] Since the organic sulfur compound represented by the above general formula is in liquid form, it does not require a solvent to dissolve the active material, and a large-capacity cathode can be manufactured in a short time.

[0098] Furthermore, unlike air batteries, the secondary battery of this embodiment is a sealed battery that does not require an air intake. Therefore, the secondary battery of this embodiment can be stored for a long period of time without the electrolyte evaporating from the air intake.

[0099] Therefore, the secondary battery of this embodiment can be effectively utilized as a new power source for various electronic devices such as small devices, sensors, and mobile devices.

[0100] This disclosure is not limited to the embodiments described above, and various modifications and combinations are possible within the technical concept of this disclosure. [Explanation of symbols]

[0101] 101: Positive electrode 102: Non-aqueous electrolyte (electrolyte) 103: Negative electrode 201: Positive electrode case 202: Negative electrode case 203: Propylene gasket

Claims

【Request Item 1】 【Chemistry 1】 (In the formula, R １ A positive electrode containing an organic sulfur compound represented as (where represents a propyl group or an allyl group, and n is an integer between 2 and 3) as a positive electrode active material, A negative electrode containing magnesium, sodium, or calcium as a negative electrode active material, an electrolyte disposed between the positive electrode and the negative electrode, Secondary battery.

2. The positive electrode is formed in a porous current collector containing at least one selected from the group consisting of aluminum, copper, and iron, or in a nonwoven fabric current collector containing carbon. The positive electrode does not contain a binder. The secondary battery according to claim 1.

3. The positive electrode is formed by integrating multiple nanostructures to create a cocontinuum having a three-dimensional network structure. The positive electrode does not contain a binder. The secondary battery according to claim 1.

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