Electrode active material, electrode, and secondary battery

Abstract

[Problem] To provide: an electrode active material which has high energy density, high output, and good cycle characteristics with little decrease in the capacity even after repeated charge and discharge; an electrode which uses this electrode active material; and a secondary battery. [Solution] An electrode active material which contains a compound having a dithiadiazine group and is used as an active material for a secondary battery that repeats charge and discharge by means of a battery electrode reaction; and an electrode which contains this electrode active material and an electroconductive material. In addition, a secondary battery wherein this electrode active material is contained in any one of a reaction starting material, a product and an intermediate product of at least a discharge reaction of the battery electrode reaction.

Description

Technical Field

[0001] The present invention relates to an electrode active material, an electrode, and a secondary battery, and more particularly to an electrode active material that repeats charge and discharge using a battery electrode reaction, an electrode using the electrode active material, and a secondary battery.

Background Art

[0002] With the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and digital cameras, there has been a long-felt need for a secondary battery that has a high energy density, can provide high output, and has a long life as a cordless power source for these electronic devices.

[0003] To meet such requirements, secondary batteries have been developed that use alkali metal ions such as lithium ions as charge carriers and utilize the electrochemical reactions associated with the transfer of their charges. In particular, lithium ion secondary batteries have a high energy density and are becoming widely popular as in-vehicle batteries.

[0004] By the way, among the components of a secondary battery, the electrode active material is a substance that directly contributes to the battery electrode reaction such as the charge reaction and the discharge reaction, and has a central role in the secondary battery. That is, the battery electrode reaction is a reaction that occurs with the transfer of electrons by applying a voltage to the electrode active material that constitutes the electrode disposed in the electrolyte, and proceeds during charging and discharging of the battery. Therefore, as described above, the electrode active material systematically has a central role in the secondary battery.

[0005] In the above lithium ion secondary battery, a lithium-containing transition metal oxide is used as the positive electrode active material, and a carbon material is used as the negative electrode active material, and charging and discharging are performed using the insertion reaction and the desorption reaction of lithium ions with respect to these electrode active materials.

[0006] However, since the lithium-containing transition metal compound contains a transition metal as a constituent element, there is a problem that the molecular weight is large and the capacity density per mass of the electrode active material does not increase. In addition, there is also a problem that the amount of transition metal resources is limited.

[0007] Therefore, in order to solve such problems, research and development of secondary batteries using organic compounds with abundant resource amounts, such as organic radical compounds, organic sulfur compounds, and further quinone compounds, as electrode active materials have been actively conducted.

[0008] As a prior art document using an organic radical compound as an electrode active material, Patent Document 1 is known.

[0009] This Patent Document 1 discloses an active material for a secondary battery using a nitroxyl radical compound, an oxyl radical compound, and a nitrogen radical compound having a radical on a nitrogen atom.

[0010] Since the unpaired electrons involved in the reaction of an organic radical compound are localized on the radical atom, the concentration of the reaction site can be increased, and thus the realization of a high-capacity secondary battery can be expected. And in this Patent Document 1, an example using a highly stable nitroxyl radical as a radical is described. For example, when a secondary battery is fabricated with an electrode layer containing a nitronyl nitroxide compound as the positive electrode and a lithium-clad copper foil as the negative electrode, and repeatedly charged and discharged, it has been confirmed that charging and discharging are possible over 10 cycles or more.

[0011] In addition, as prior art documents using an organic sulfur compound as an electrode active material, Patent Documents 2 and 3 are known.

[0012] Patent Document 2 proposes a novel metal-sulfur type battery cell in which an organic sulfur compound as a positive electrode material has an S-S bond in the charged state, and the S-S bond cleaves during discharge of the positive electrode to form an organic sulfur metal salt having a metal ion.

[0013] In this Patent Document 2, as the organic sulfur compound, a disulfide-based organic compound represented by the general formula (10) (hereinafter referred to as "disulfide compound") is used. R-S-S-R …(10) [Here, R represents an aliphatic organic group or an aromatic organic group, each including cases where they are the same or different.]

[0014] The disulfide compound is capable of a two-electron reaction. In the reduced state (discharged state), the S-S bond cleaves, thereby forming an organic thiolate (R-S-). Then, this organic thiolate forms an S-S bond in the oxidized state (charged state) and is reduced to the disulfide compound represented by the general formula (10). That is, since the disulfide compound forms an S-S bond with a small binding energy, a reversible redox reaction occurs by utilizing the bond formation and cleavage due to the reaction, and thus charge and discharge can be performed.

[0015] Also, Patent Document 3 proposes a battery electrode containing rubic acid or a rubic acid polymer having a structural unit represented by the general formula (11) and capable of binding to lithium ions. -(NH-CS-CS-NH)- …(11)

[0016] Rubic acid or a rubic acid polymer containing a dithione structure represented by the general formula (11) binds to lithium ions during reduction and releases the bound lithium ions during oxidation. Charge and discharge can be performed by utilizing such a reversible redox reaction of rubic acid or a rubic acid polymer.

[0017] In this Patent Document 3, when rubic acid is used as the positive electrode active material, a two-electron reaction is possible, and a secondary battery having a capacity density of 400 Ah / kg at room temperature is obtained.

[0018] Also, as a prior art document using a quinone compound as the electrode active material, Patent Document 4 is known.

[0019] Patent Document 4 proposes an electrode active material containing a specific phenanthrenequinone compound having two quinone groups in the ortho-position relationship.

[0020] The specific phenanthrenequinone compound described in Patent Document 4 can undergo a two-electron reaction specific to quinone compounds with lithium ions and can cause a reversible redox reaction. Furthermore, by oligomerizing or polymerizing the above specific phenanthrenequinone compound, insolubilization in an organic solvent is achieved without a decrease in the number of reaction electrons due to electron repulsion. And in Patent Document 4, it is shown that the phenanthrenequinone dimer exhibits two redox voltages (around 2.9 V and around 2.5 V), and the initial discharge capacity reaches 200 Ah / kg.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0022] However, in Patent Document 1, although an organic radical compound such as a nitroxyl radical compound is used as an electrode active material, the charge-discharge reaction is limited to a one-electron reaction in which only one electron is involved. That is, in the case of an organic radical compound, if a multi-electron reaction in which two or more electrons are involved occurs, the radical lacks stability and decomposition etc. occur, the radical disappears, and the reversibility of the charge-discharge reaction is lost. For this reason, an organic radical compound such as that in Patent Document 1 has no choice but to be limited to a one-electron reaction, and it is difficult to realize a multi-electron reaction that can be expected to have a high capacity.

[0023] In addition, in Patent Document 2, a low-molecular-weight disulfide compound involving two electrons is used. However, since it repeatedly binds to and cleaves other molecules during the charge-discharge reaction, it lacks stability, and there is a risk that the capacity will decrease when the charge-discharge reaction is repeated.

[0024] In Patent Document 3, a leucoanthraquinone compound containing a dithione structure is used to cause a two-electron reaction. However, when a high-molecular compound such as a leucoanthraquinone polymer is used, the intermolecular interaction within the leucoanthraquinone polymer is large, resulting in hindrance to ion movement. As a result, it is difficult to obtain a sufficient reaction rate, and the proportion of the active material that can be effectively used is small, making it difficult to realize a secondary battery having a desired high capacity.

[0025] Patent Document 4 uses a phenanthrenequinone compound having two quinone groups in the ortho-position relationship as an electrode active material. Therefore, although it has excellent stability, it is difficult to synthesize because it is a condensed-ring compound, and the capacity density is not sufficient.

[0026] Thus, conventionally, even when using organic compounds such as organic radical compounds, disulfide compounds, and leucoanthraquinone as electrode active materials, it is difficult to achieve both a multi-electron reaction and stability against charge-discharge cycles. Therefore, at present, an electrode active material having a sufficiently large capacity density, excellent cycle characteristics with high output and long life has not been realized yet.

[0027] The present invention has been made in view of such circumstances, and an object thereof is to provide an electrode active material having a large capacity density, good cycle characteristics with little capacity decrease even when charge-discharge is repeated, an electrode using this electrode active material, and a secondary battery.

Means for Solving the Problems

[0028] To achieve the above object, the present invention includes the following embodiments.

[0029] [1] An electrode active material used as an active material of a secondary battery that repeats charge and discharge by a battery electrode reaction, characterized in that it contains a compound having a dithiadiazine group.

[0030] [2] The electrode active material according to [1], characterized in that the compound having a dithiadiazine group is a compound having a dithiadiazine group and a thioamide group.

[0031] [3] The electrode active material according to [1] or [2], characterized in that the compound having a dithiadiazine group is a compound represented by the following formula (2). [Chemical formula] [However, n is an integer of 20 or less]

[0032] [4] An electrode characterized by containing the electrode active material according to any one of [1] to [3] and a conductive material.

[0033] [5] The electrode according to [4], characterized in that it is impregnated with a liquid electrolyte containing hydrofluoroether.

[0034] [6] The electrode according to [5], characterized in that the hydrofluoroether is contained in the liquid electrolyte in an amount of 5 to 60% by mass.

[0035] [7] The electrode according to any one of [4] to [6], characterized in that the compound having a dithiadiazine group is contained in an amount of 50 to 95% by mass.

[0036] [8] A secondary battery, characterized in that the electrode active material according to any one of [1] to [3] is contained in any one of reaction starting materials, products, and intermediate products in at least the discharge reaction of the battery electrode reaction. [Advantages of the Invention]

[0037] According to the present invention, it is possible to realize an electrode active material having a large energy density, good cycle characteristics with little capacity degradation even when charge and discharge are repeated, an electrode using this electrode active material, and a secondary battery.

Brief Description of the Drawings

[0038]

Figure 1

Mode for Carrying Out the Invention

[0039] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described.

[0040] The electrode active material of the present embodiment contains a compound having a dithiadiazine group and is used as an active material of a secondary battery that repeats charge and discharge by a battery electrode reaction. By using a compound having a dithiadiazine group, the charge and discharge reaction is stabilized, and an electrode active material having a high capacity and good cycle characteristics can be obtained. As a result, a secondary battery having a large energy density with improved stability during charge and discharge can be obtained.

[0041] In addition, the content of the compound having a dithiadiazine group in the electrode active material is not particularly limited. However, if it is less than 10% by mass, there is a possibility that sufficient effects cannot be obtained from the viewpoint of realizing a high capacity. Further, the capacity density of the electrode increases as the content of the compound having a dithiadiazine group increases. However, a conductive material and a binder are required to form the electrode, and if the content of the conductive material becomes too small, the output of the secondary battery decreases. Therefore, the content of the compound having a dithiadiazine group is preferably approximately 95% or less.

[0042] Here, the dithiadiazine group can be represented by the following general formula (1).

Chemical formula

[0043] In addition, the compound having a dithiadiazine group can be represented by the following general formula (2). [Chemical formula] [However, n is an integer of 20 or less]

[0044] The electrode active material according to this embodiment is considered to generate a complex salt along with the battery electrode reaction. The following chemical reaction formula (A) shows an example of a charge-discharge reaction expected when the organic compound represented by the above general formula (2) is used as the electrode active material and lithium ions are used as the cations of the electrolyte salt. [Chemical formula]

[0045] As shown in the above chemical reaction formula (A), in the electrode active material according to this embodiment, 2 electrons are involved in the reaction during charge and discharge, and the dithione moiety (C-S-S-C) contained in the compound having a dithiadiazine group binds to Li during reduction and releases Li during oxidation. That is, since the compound having a dithiadiazine group can be redoxed with 2 or more electrons per dithiadiazine group, an electrode active material with good charge-discharge efficiency and high capacity density per mass can be obtained. In addition, the electrode active material according to this embodiment is stable even when the reaction is repeated and the decrease in the number of electrons is small. Therefore, it is stable even when charge and discharge are repeated (good cycle characteristics). As a result, the stability during charge and discharge is improved by the electrode active material according to this embodiment, and a secondary battery with high energy (high energy density) can be realized. + and releases Li + during oxidation. That is, since the compound having a dithiadiazine group can be redoxed with 2 or more electrons per dithiadiazine group, an electrode active material with good charge-discharge efficiency and high capacity density per mass can be obtained. In addition, the electrode active material according to this embodiment is stable even when the reaction is repeated and the decrease in the number of electrons is small. Therefore, it is stable even when charge and discharge are repeated (good cycle characteristics). As a result, the stability during charge and discharge is improved by the electrode active material according to this embodiment, and a secondary battery with high energy (high energy density) can be realized.

[0046] The degree of polymerization n of the dithiadiazine group constituting the above electrode active material is not particularly limited, but when it is 20 or more, the free volume becomes small due to the molecular rigidity and the rate of the redox reaction, which is the charge-discharge reaction, decreases. Therefore, n is preferably in the range of about 1 to 20. In addition, in this embodiment, compounds with a plurality of n can also be mixed and used.

[0047] In this embodiment, the method for synthesizing the compound having a dithiadiazine group is not particularly limited. For example, it can be synthesized by a cyclization reaction of diamino-N-alkyl ethanethioamide and alkyliminochloromethanesulfenyl chloride, or by oxidative polymerization of dithiooxamide, etc.

[0048] That the active material constituting the electrode of the secondary battery according to this embodiment contains a compound having a dithiadiazine group can be confirmed by Raman mapping measurement of the electrode surface. That is, in any of the charged state, discharged state, and intermediate state, the positive electrode constituting the secondary battery is taken out in a dry atmosphere, washed, dried, and then a region with less conductive material is observed and identified by the Raman mapping method. When it has a dithiadiazine group, there are peaks derived from S-S bonds at 530 to 545 cm -1 and peaks derived from N-N bonds at 1150 to 1250 cm -1 are observed. Also, the degree of polymerization n can be measured by comparing the peak intensity derived from the C=S bond that appears at 1000 to 1100 cm -1 with the peak intensities of the above S-S bond and N-N bond in the Raman mapping method of the electrode taken out in the charged state.

[0049] Next, the secondary battery using the above electrode active material will be described in detail. FIG. 1 is a cross-sectional view showing a coin-type secondary battery as an embodiment of the secondary battery according to the present invention. In the example of FIG. 1, the electrode active material according to the above embodiment is used as the positive electrode active material.

[0050] In FIG. 1, the battery can 1 has a positive electrode case 2 and a negative electrode case 3, and both the positive electrode case 2 and the negative electrode case 3 are formed in a disk-shaped thin plate shape. At the central region of the bottom of the positive electrode case 2 constituting the positive electrode current collector, a positive electrode 4 formed by shaping a mixture containing a positive electrode active material (electrode active material) and a conductive auxiliary agent (conductive material) into a sheet shape is disposed. Further, a separator 5 formed of a porous sheet or film such as a microporous membrane, a woven fabric, or a non-woven fabric is laminated on the positive electrode 4, and a negative electrode 6 is further laminated on the separator 5. As the negative electrode 6, for example, a stainless steel foil or a copper foil with a lithium metal foil laminated thereon, or a copper foil coated with a lithium storage material such as graphite or hard carbon can be used. A negative electrode current collector 7 made of metal is laminated on the negative electrode 6, and a metal spring 8 is placed on the negative electrode current collector 7. The internal space of the battery can 1 is filled with an electrolyte 9. Further, the negative electrode case 3 is fixed to the positive electrode case 2 via a gasket 10 against the biasing force of the metal spring 8, and the battery can 1 is sealed by the gasket 10.

[0051] Next, an example of the manufacturing method of the secondary battery will be described in detail. First, the electrode active material is formed into an electrode shape. For example, the electrode active material is mixed with a conductive auxiliary agent and a binder, a solvent is added to form a slurry, and the slurry is applied onto a positive electrode current collector (positive electrode case 2) by an arbitrary coating method and dried to form the positive electrode 4. Here, the conductive auxiliary agent is not particularly limited, and for example, carbonaceous fine particles such as graphite, carbon black, and acetylene black, carbon fibers such as vapor-grown carbon fibers and other carbon nanowires, carbon nanotubes, and carbon nanohorns, and conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene can be used. Also, two or more kinds of conductive auxiliary agents can be mixed and used. The content of the conductive auxiliary agent in the positive electrode 4 is preferably 10 to 80% by mass.

[0052] Also, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, and carboxymethyl cellulose can be used.

[0053] Furthermore, the solvent is not particularly limited either. For example, basic solvents such as dimethyl sulfoxide, dimethylformamide, 1-methyl-2-pyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, non-aqueous solvents such as acetonitrile, tetrahydrofuran, nitrobenzene, and acetone, and protic solvents such as methanol, ethanol, and water can be used.

[0054] Also, the type of solvent and the mixing ratio of the electrode active material and the solvent can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery. Note that the positive electrode 4 may be formed by pressure molding a powder obtained by mixing the electrode active material, the conductive auxiliary agent, and the binder without using the above solvent (without making a slurry).

[0055] Next, this positive electrode 4 is immersed in the liquid electrolyte used as the electrolyte 9 to allow the electrolyte 9 to penetrate into the positive electrode 4, and then the positive electrode 4 is placed at the center of the bottom of the positive electrode case 2 constituting the positive electrode current collector. When a solid electrolyte is used as the electrolyte 9, a step of mixing the solid electrolyte is carried out during the above manufacturing process of the positive electrode 4. In this case, the separator 5 described later is not used.

[0056] Next, a separator 5 impregnated with the liquid electrolyte used as the electrolyte 9 is laminated on the positive electrode 4, and then the negative electrode 6 and the negative electrode current collector 7 are sequentially laminated. Then, if necessary, the electrolyte 9 is injected into the internal space. Then, a metal spring 8 is placed on the negative electrode current collector 7, a gasket 10 is arranged on the periphery, and the negative electrode case 3 is fixed to the positive electrode case 2 with a caulking machine or the like for external sealing, thereby manufacturing a coin-type secondary battery.

[0057] The electrolyte 9 is interposed between the positive electrode 4 and the negative electrode 6 which is the counter electrode of the positive electrode 4, and conducts charge carrier transport between the two electrodes. As such an electrolyte 9, one having an ionic conductivity of 10 -5 ~10 -1 S / cm at room temperature can be used. Such electrolytes 9 include liquid electrolytes and solid electrolytes.

[0058] Examples of the liquid electrolyte include an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent, an ionic liquid in which an anion and a cation are combined, etc. These liquid electrolytes can be used alone or in combination of multiple kinds.

[0059] In the case of the electrolytic solution in which the electrolyte salt is dissolved in an organic solvent, as the electrolyte salt, for example, LiPF6, LiClO4, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiC(CF3SO2)3, LiC(C2F5SO2)3, etc. can be used.

[0060] Moreover, as the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, dimethylformamide, dimethylacetamide, 1-methyl-2-pyrrolidone, methyl triglyme, ethyl triglyme, butyl triglyme, methyl tetraglyme, ethyl tetraglyme, butyl tetraglyme as glymes, sulfolane as cyclic sulfones, ethyl isopropyl sulfone, 2-(ethylsulfonyl)propane, 2-(ethylsulfonyl)butane as chain sulfones, etc. can be used.

[0061] In addition, as the ionic liquid, the cation may be imidazolium such as 2-ethylimidazolium, 3-propylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1,3-dimethylimidazolium, etc., ammonium such as diethylmethylammonium, tetrabutylammonium, cyclohexyltrimethylammonium, methyltri-n-octylammonium, triethyl(2-methoxyethoxymethyl)ammonium, benzyldimethyltetradecylammonium, benzyltrimethylammonium, etc., or other alkylpyridinium, dialkylpyrrolidinium, tetraalkylphosphonium, trialkylsulfonium, etc. can be used, and the anion may be a halide anion such as Cl - 、Br - 、I - etc., boride anions such as BF4 - 、B(CN)4 - 、B(C2O4)2 - etc., amide anions or imide anions such as (CN)2N - 、[N(CF3)2] - 、[N(SO2CF3)2] - etc., sulfate anions or sulfonate anions such as RSO3 - (R represents an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The same applies hereinafter), RSO4 - 、R f SO3 - (R f represents a fluorine-containing halogenated hydrocarbon group. The same applies hereinafter), R f SO4 - etc., phosphate anions such as R f 2P(O)O - 、PF6 - 、R f 3PF3 - etc., antimonate anions such as SbF6, and other lactate, nitrate ions, trifluoroacetate, etc. can be used.

[0062] In addition, examples of the polymer compound used in the above solid electrolyte include vinylidene fluoride polymers such as polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, vinylidene fluoride - ethylene copolymer, vinylidene fluoride - monofluoroethylene copolymer, vinylidene fluoride - trifluoroethylene copolymer, vinylidene fluoride - tetrafluoroethylene copolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, etc.; acrylonitrile polymers such as acrylonitrile - methyl methacrylate copolymer, acrylonitrile - methyl acrylate copolymer, acrylonitrile - ethyl methacrylate copolymer, acrylonitrile - ethyl acrylate copolymer, acrylonitrile - methacrylic acid copolymer, acrylonitrile - acrylic acid copolymer, acrylonitrile - vinyl acetate copolymer, etc.; and furthermore, polyethylene oxide, ethylene oxide - propylene oxide copolymer, and polymers of their acrylate and methacrylate forms, etc. can be mentioned. Also, a gel - like substance obtained by incorporating an electrolyte solution into these polymer compounds can be used as electrolyte 9, or only the polymer compound containing an electrolyte salt can be directly used as electrolyte 9.

[0063] When using a liquid electrolyte as the above electrolyte 9, it is preferable to dissolve hydrofluoroether in the liquid electrolyte. Generally, a liquid electrolyte is difficult to penetrate into the positive electrode 4, separator 5, etc. However, by including hydrofluoroether in the liquid electrolyte, the liquid electrolyte can be made more likely to penetrate into the positive electrode 4, separator 5, etc. From the viewpoint of making the liquid electrolyte more likely to penetrate into the positive electrode 4, separator 5, etc., it is preferable that such hydrofluoroether is contained in the liquid electrolyte at 5 - 60% by mass.

[0064] Examples of the above hydrofluoroether include 1,1,2,2 - tetrafluoroethyl - 2,2,2 - trifluoroethyl ether and 1,1,1,2,2,3,3,4,4 - nonafluoro - 4 - methoxybutane, etc.

[0065] As described above, since the electrode according to the present embodiment contains the above-described electrode active material and a conductive auxiliary agent (conductive material), the charge-discharge efficiency is good, charging can be performed in a short time, and high output can be achieved.

[0066] In addition, since the electrode active material of the secondary battery is reversibly oxidized or reduced by charge and discharge, it has different structures and states in the charged state, discharged state, or an intermediate state thereof. In the present embodiment, the electrode active material is included in at least any one of the reaction starting materials (substances that cause a chemical reaction in the battery electrode reaction), products (substances generated as a result of the chemical reaction), and intermediate products in the discharge reaction. As a result, it is possible to realize a secondary battery with a large energy density, capable of rapid charging, capable of discharging at high power, having good cycle characteristics with little capacity degradation even when charge and discharge are repeated, and stable battery characteristics and long life.

[0067] Moreover, since the electrode active material is mainly composed of an organic compound, it does not contain heavy metals such as Pb and Mn, has a low environmental load, and does not contain oxygen, so abnormal reactions can be suppressed and a secondary battery considering safety can be obtained.

[0068] Note that the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist. For example, regarding the organic compound that is the main component of the electrode active material, if it is a compound having a dithiadiazine group, since the same battery electrode reaction as the above chemical reaction formula (A) proceeds, a compound containing a dithiadiazine group as part of the structure can also obtain a certain effect.

[0069] In addition, in the present embodiment, the coin-type secondary battery has been described, but it goes without saying that the battery shape is not particularly limited, and it can also be applied to cylindrical, rectangular, sheet-type, etc. Also, the packaging method is not particularly limited, and a metal case, a molded resin, an aluminum laminate film, etc. may be used.

[0070] In addition, in the present embodiment, the electrode active material is used as the positive electrode active material, but it is also useful to use it as the negative electrode active material.

Examples

[0071] Hereinafter, embodiments of the present invention will be specifically described. Note that the following embodiments are for facilitating the understanding of the present invention, and the present invention is not limited to these embodiments.

[0072] Example 1. [Preparation of secondary battery] A sulfolane solution containing 0.05 M of dithiooxamide was placed in a glass container, and lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2) was added to make it 0.25 M, followed by stirring. Two platinum electrodes were immersed in this solution, and a constant voltage of 4.2 V was applied while stirring, and the reaction was continued for 24 hours. After the reaction was completed, the black solution was filtered and dried to obtain a black powder. From the Raman spectroscopy (Raman mapping) and infrared spectroscopy of this compound, it was found that the product is 1,2,4,5-dithiadiazine-3,6-dithiocarboxamide represented by chemical formula (3). [Chemical formula]

[0073] 300 mg of the above 1,2,4,5-dithiadiazine-3,6-dithiocarboxamide as a positive electrode active material, 600 mg of graphite powder as a conductive auxiliary agent, and 100 mg of polytetrafluoroethylene as a binder were mixed and kneaded, and then pressure-molded to obtain a sheet-like member having a thickness of about 150 μm. Next, this sheet-like member was dried in a vacuum at 70 °C for 1 hour, and then punched into a circle with a diameter of 12 mm to produce a positive electrode containing a mixture for the active material. Next, the positive electrode was impregnated with an electrolytic solution to allow the electrolytic solution to penetrate into the voids in the positive electrode. Here, as the electrolytic solution, a mixed solution containing equimolar amounts of methyltetraglyme (organic solvent) and LiN(CF3SO2)2 (electrolyte salt) was used.

[0074] Next, this positive electrode was placed on a positive electrode current collector, and further, a separator made of a polypropylene porous film having a thickness of 20 μm and impregnated with the above electrolytic solution was laminated on the positive electrode. On top of that, a lithium extrusion plate with a thickness of 0.2 mm punched out to a diameter of 14 mm was installed, and further, a stainless steel current collector with a diameter of 16 mm was laminated. Then, a metal spring was placed on the current collector, and the negative electrode case was joined to the positive electrode case with a gasket arranged at the periphery, and the exterior was sealed with a caulking machine to produce a sealed coin-type secondary battery having 1,2,4,5-dithiadiazine-3,6-dithiocarboxamide as the positive electrode active material and metallic lithium as the negative electrode active material. In this case, since the positive electrode and the separator were immersed in the electrolytic solution and used while being wet, the filling of the electrolytic solution into the internal space of the coin-type secondary battery was omitted.

[0075] [Operation confirmation of secondary battery] The coin-type secondary battery fabricated as described above was charged with a constant current of 0.1 mA using a charge / discharge tester (TOSCAT3100 manufactured by Toyo System Co., Ltd.) until the voltage reached 4.2 V, and then discharged with a constant current of 0.1 mA until the voltage reached 1.5 V. As a result, it was confirmed that this battery is a secondary battery having a discharge capacity of 0.36 mAh with a voltage plateau at a charge / discharge voltage of 2.1 V.

[0076] The capacity density per mass of the positive electrode active material calculated from the above discharge capacity was 660 Ah / kg, and it was found that the compound used for the positive electrode active material is a high-capacity density electrode active material suitable for a high-energy density battery.

[0077] Thereafter, charge and discharge were repeated 100 cycles in the range of 1.5 to 4.2 V using the above charge / discharge tester. As a result, the discharge capacity after 100 cycles of repetition was 0.35 mAh (97% of the initial capacity), and it was found that the battery has excellent stability.

[0078] Example 2. [Fabrication of secondary battery] As the electrolyte, instead of the mixed solution of methyltetraglyme and LiN(CF3SO2)2, an ionic liquid composed of 1-ethyl-3-methylimidazolium and bis(trifluoromethanesulfonyl)imide (NH(SO2CF3)2) was used, and a coin-type half cell was fabricated in the same manner as in Example 1 except that an electrolyte solution containing 1 M LiN(CF3SO2)2 (electrolyte salt) was used.

[0079] [Verification of the operation of the secondary battery] Using the same charge-discharge tester as in Example 1, the above coin-type secondary battery was charged at a constant current of 0.1 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.1 mA to 1.5 V. As a result, it was confirmed that this battery is a secondary battery with a discharge capacity of 0.48 mAh having a voltage plateau at a charge-discharge voltage of 2.1 V.

[0080] The capacity density per unit mass of the positive electrode active material calculated from the above discharge capacity was 640 Ah / kg, and it was found that the compound used for the positive electrode active material is a high-capacity density electrode active material suitable for a high energy density battery.

[0081] Thereafter, charge and discharge were repeated 100 cycles in the range of 1.5 to 4.2 V using the above charge-discharge tester. As a result, the discharge capacity after 100 cycles of repetition was 0.38 mAh (79% of the initial capacity), indicating excellent stability.

[0082] Example 3. [Fabrication of the secondary battery] An ethanol solution containing 0.01 M dithiooxamide was placed in a glass container, and lithium hexafluorophosphate was added to make the concentration 0.25 M, followed by stirring. Two platinum electrodes were immersed in this solution, and a constant voltage of 4.2 V was applied while stirring, and the reaction was continued for 48 hours. After the reaction was completed, the black solution was filtered and dried to obtain a black powder. From Raman spectroscopic measurement (Raman mapping) and infrared spectroscopic measurement of this compound, it was found that the product mainly consists of [3,3'-bis-1,2,4,5-dithiadiazine]-6,6'-dithiocarboxamide represented by Chemical Formula (4). [Chemical formula]

[0083] A coin-type battery was fabricated in the same manner as in Example 1, except that [3,3'-bis-1,2,4,5-dithiadiazine]-6,6'-dithiocarboxamide was used instead of 1,2,4,5-dithiadiazine-3,6-dithiocarboxamide of Example 1 as the positive electrode active material.

[0084] [Verification of the operation of the secondary battery] Using the same charge-discharge tester as in Example 1, the above coin-type secondary battery was charged at a constant current of 0.1 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.1 mA to 1.5 V. As a result, it was confirmed that this battery is a secondary battery with a discharge capacity of 0.31 mAh having a voltage plateau at a charge-discharge voltage of 2.2 V.

[0085] The capacity density per unit mass of the active material calculated from the above discharge capacity was 480 Ah / kg, and it was found that the compound used as the above positive electrode active material is an electrode active material with a high capacity density suitable for a high energy density battery.

[0086] Thereafter, charge and discharge were repeated 100 cycles in the range of 1.5 to 4.2 V using the above charge-discharge tester. As a result, the discharge capacity after 100 cycles of repetition was 0.25 mAh (80% of the initial capacity), indicating excellent stability.

[0087] Example 4. 750 mg of 1,2,4,5-dithiadiazine-3,6-dithiocarboxamide of Example 1 as the positive electrode active material, 150 mg of graphite powder as the conductive auxiliary agent, 20 mg of vapor-grown carbon fiber, 40 mg of 20% polyethylene resin emulsion as the binder, and 40 mg of carboxymethyl cellulose were mixed and kneaded. The resulting slurry was applied onto an aluminum foil with a thickness of 15 μm and dried to obtain a coated electrode with a thickness of about 70 μm. This electrode was punched out into a circle with a diameter of 12 mm to fabricate a positive electrode containing a mixture for the active material.

[0088] Next, this positive electrode was placed on the positive electrode current collector of the coin-type battery, and a separator with a thickness of 20 μm made of a polypropylene porous film was further laminated on the positive electrode. The electrolyte was dropped, and pressure reduction impregnation was performed three times in which the pressure was changed in the range from normal pressure to a pressure reduction rate of 70%. Here, the electrolyte used was a mixed solvent (mass ratio 90:10) of sulfolane containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether as a hydrofluoroether.

[0089] Next, a lithium extrusion plate with a thickness of 0.2 mm punched out to a diameter of 14 mm was installed, and a stainless steel current collector with a diameter of 16 mm was laminated. Then, a metal spring was placed on the current collector, and the negative electrode case was joined to the positive electrode case with a gasket arranged at the periphery, and the exterior was sealed with a caulking machine to fabricate a sealed coin-type secondary battery having 1,2,4,5-dithiadiazine-3,6-dicarbonthioamide as the positive electrode active material and metallic lithium as the negative electrode active material.

[0090] [Operation confirmation of secondary battery] The coin-type secondary battery fabricated as described above was charged with a constant current of 0.1 mA using the same charge-discharge tester as in Example 1 until the voltage reached 4.2 V, and then discharged with a constant current of 0.1 mA until the voltage reached 1.5 V. As a result, it was confirmed that this battery was a secondary battery having a discharge capacity of 2.4 mAh with a voltage plateau at a charge-discharge voltage of 2.1 V.

[0091] The capacity density per mass of the positive electrode active material calculated from the above discharge capacity was 600 Ah / kg, and it was found that the compound used for the positive electrode active material was a high-capacity density electrode active material suitable for a high-energy density battery.

[0092] After that, charging and discharging were repeated 100 cycles in the range of 1.5 to 4.2 V using the above charge-discharge tester. As a result, the discharge capacity after 100 cycles of repetition was 1.95 mAh (81% of the initial capacity), and it was found that the stability was excellent.

[0093] Example 5. [Fabrication of Secondary Battery] As the electrolyte, instead of the mixed solvent (mass ratio 90:10) of sulfolane containing 1 M lithium bis(trifluoromethanesulfonyl)imide and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, a mixed solvent (mass ratio 90:10) of ethyl isopropyl sulfone containing 1 M lithium bis(trifluoromethanesulfonyl)imide and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether as a hydrofluoroether was used, and a coin-type half-cell was fabricated in the same manner as in Example 4.

[0094] [Confirmation of Operation of Secondary Battery] The above coin-type secondary battery was charged with a constant current of 0.1 mA using the same charge-discharge tester as in Example 1 until the voltage reached 4.2 V, and then discharged with a constant current of 0.1 mA to 1.5 V. As a result, it was confirmed that this battery is a secondary battery with a discharge capacity of 0.45 mAh having a voltage plateau at a charge-discharge voltage of 2.1 V.

[0095] The capacity density per unit mass of the positive electrode active material calculated from the above discharge capacity was 600 Ah / kg, and it was found that the compound used for the positive electrode active material is a high-capacity density electrode active material suitable for a high-energy density battery.

[0096] After that, charging and discharging were repeated 100 cycles in the range of 1.5 to 4.2 V using the above charge-discharge tester. As a result, the discharge capacity after 100 cycles of repetition was 0.36 mAh (80% of the initial capacity) of the initial capacity, and it was confirmed that the stability was excellent. [Description of Reference Signs]

[0097] 1 Battery can, 2 Positive electrode case, 3 Negative electrode case, 4 Positive electrode, 5 Separator, 6 Negative electrode, 7 Negative electrode current collector, 8 Metal spring, 9 Electrolyte, 10 Gasket.

Claims

1. An electrode active material used as an active material of a secondary battery that repeats charge and discharge by a battery electrode reaction, characterized in that it contains a compound having a dithiadiazine group.

2. The electrode active material according to claim 1, characterized in that the compound having a dithiadiazine group is a compound having a dithiadiazine group and a thioamide group.

3. The electrode active material according to claim 1 or 2, characterized in that the compound having a dithiadiazine group is a compound represented by the following formula (2). [Chemical Formula 2] [However, n is an integer of 20 or less]

4. An electrode characterized by containing the electrode active material according to any one of claims 1 to 3 and a conductive material.

5. The electrode according to claim 4, characterized in that it is impregnated with a liquid electrolyte containing a hydrofluoroether.

6. The electrode according to claim 5, characterized in that the hydrofluoroether is contained in the liquid electrolyte in an amount of 5 to 60% by mass.

7. The electrode according to any one of claims 4 to 6, characterized in that the compound having a dithiadiazine group is contained in an amount of 20 to 95% by mass.

8. A secondary battery, characterized in that the electrode active material according to any one of claims 1 to 3 is contained in any one of reaction starting materials, products, and intermediate products in at least the discharge reaction of the battery electrode reaction.

Images