JP5483523B2 - Electrode active material and secondary battery - Google Patents

Description

  The present invention relates to an electrode active material and a secondary battery, and more particularly to an electrode active material using an organic compound, and a secondary battery such as a lithium secondary battery that repeatedly charges and discharges using an electrode reaction of the electrode active material. .

  With the expansion of the market for portable electronic devices such as mobile phones, notebook computers, and PDAs (Personal Data Assistants), secondary batteries with high energy density and long life are expected as cordless power sources for these electronic devices. .

  In response to such demands, secondary batteries have been developed that use an alkali metal ion such as lithium ion as a charge carrier and use an electrochemical reaction associated with the charge exchange. In particular, lithium ion secondary batteries having a high energy density are now widely used.

  This type of lithium ion secondary battery uses a lithium-containing transition metal oxide as a positive electrode active material and a carbon material as a negative electrode active material, and utilizes lithium ion insertion and desorption reactions with these active materials. Charging / discharging is performed.

  However, the lithium ion secondary battery has a problem that the rate of charge and discharge is limited because the movement of lithium ions in the positive electrode is rate-limiting. That is, in the above-described lithium ion secondary battery, the migration rate of lithium ions in the transition metal oxide of the positive electrode is slower than that of the electrolyte and the negative electrode, and therefore the battery reaction rate at the positive electrode becomes the rate-determining rate. As a result, there is a problem that there is a limit to increasing the output and shortening the charging time.

  By the way, the electrode active material is a substance that directly contributes to a battery electrode reaction such as a charge reaction and a discharge reaction, and has a central role of a secondary battery. That is, the battery electrode reaction is a reaction that occurs with the transfer of electrons by applying a voltage to an electrode active material that is electrically connected to an electrode disposed in the electrolyte, and proceeds during charging and discharging of the battery. To do. Therefore, as described above, the electrode active material has a central role of the secondary battery in terms of system.

  From this point of view, research and development of electrode active materials have been actively conducted. For example, various electrode active materials using organic compounds have been proposed.

  For example, Patent Document 1 proposes a battery using a conductive polymer as a positive electrode or negative electrode active material.

  This patent document 1 uses the doping reaction of the electrolyte ion with respect to a conductive polymer, and the dedoping reaction for charging / discharging. Here, the doping reaction refers to a reaction that stabilizes charged solitons, polarons, and the like generated by the electrochemical oxidation reaction or reduction reaction of the conductive polymer with a counter ion, and the dedoping reaction is the reverse of the doping reaction. A reaction, that is, a reaction that electrochemically oxidizes or reduces charged solitons or polarons stabilized by a counter ion. And in this patent document 1, since the organic compound which uses small elements, such as carbon, hydrogen, and nitrogen, as an active material is used as an active material, it is thought that the weight reduction of a battery is possible.

  Patent Documents 2 and 3 propose secondary batteries in which organic radical compounds are used as reaction starting materials (substances that cause a chemical reaction by battery electrode reactions) or products (substances resulting from chemical reactions). .

  That is, Patent Document 2 discloses a secondary battery active material using a nitroxyl radical compound, an oxy radical compound, and a nitrogen radical compound having a radical on a nitrogen atom. Patent Document 3 discloses a cyclic active material. A secondary battery using a compound composed of a nitroxyl radical as an electrode active material is disclosed.

  The secondary batteries of Patent Documents 2 and 3 are charged / discharged using a redox reaction of radicals and have a high reaction rate, so that they have a high output and can be charged in a relatively short time. it is conceivable that.

  Patent Documents 4 to 8 use 7,7,8,8-tetracyanoquinodimethane (hereinafter referred to as “TCNQ”) represented by the following general formula (1 ′) as a positive electrode active material. In addition, a battery using an alkali metal such as lithium as a negative electrode active material is proposed, and Patent Document 9 proposes a lithium ion secondary battery using a lithium salt of TCNQ as a positive electrode active material.

  A compound having a cyanoquinodimethane structure is known to be a typical electron acceptor molecule, and Patent Documents 4 to 9 utilize such characteristics of TCNQ and are applied to an active material of a secondary battery. It has been tried to do.

U.S. Pat. No. 4,442,187 JP 2004-207249 A JP 2002-304996 A JP 55-133767 A JP 55-133768 A Japanese Patent Laid-Open No. 55-133372 Japanese Patent Laid-Open No. 55-161372 JP-A-57-210567 Japanese Patent Laid-Open No. 11-3708

  However, in the conductive polymer of Patent Document 1, charged solitons and polarons generated by the redox reaction are delocalized over a wide range of π-electron conjugated systems, and they interact to cause charge repulsion. There is a limit to the concentration of charged solitons and polarons that are generated. That is, since there is a limit to the concentration of charged soliton or polaron, the battery capacity is limited as a result. Therefore, even if the battery can be reduced in weight, it is difficult to obtain a battery having a large capacity.

  Moreover, in order to stabilize a radical, the organic radical compound like patent document 2 and 3 needs to make a bulky substituent couple | bonded with carbon connected to this radical. For this reason, the ratio of the radical to the mass of the whole molecule | numerator became small, and there existed a problem that capacity density fell.

  Furthermore, TCNQ or its lithium salt used in Patent Documents 4 to 9 has poor cycle characteristics, and is currently considered unsuitable for secondary batteries that repeat charge and discharge, and is difficult to put into practical use. It is in.

  Thus, although secondary batteries using various active materials have been proposed in the past, an electrode active material having a sufficient energy density, high output, and long life cycle characteristics has not been obtained yet. is the current situation.

  The present invention has been made in view of such circumstances, and an electrode active material capable of obtaining good cycle characteristics with a large energy density, high output, and little reduction in capacity even after repeated charge and discharge, and the electrode An object is to provide a secondary battery using an active material.

The present inventors have intensively studied to obtain an organic compound having a conjugated quinone system as a skeleton and capable of accumulating electricity. As a result, a specific organic compound containing a cyanoquinodiimine structure as a structural unit is used as an electrode active material. As a result, it has been found that a secondary battery having a large capacity density of the battery and capable of stably obtaining a secondary battery with little reduction in capacity even after repeated charging and discharging at a high output can be obtained.

で表されるシアノキノジイミン構造を構成単位として含有した有機化合物を主体としていることを特徴としている。 The present invention has been made based on such knowledge, the electrode active material according to the present invention is an electrode active material used as an active material of a secondary battery that repeats charge and discharge by a battery electrode reaction, General formula

It is characterized by comprising mainly an organic compound containing a cyanoquinodiimine structure represented by

In the formula, m is an integer of 1 or more, and R ₁ ~ R ₆ Is a hydrogen atom, halogen atom, hydroxyl group, nitro group, cyano group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted cycloalkenyl group, substituted or unsubstituted An aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aryloxy group, Any one of a substituted or unsubstituted alkoxycarbonyl group, a substituted or unsubstituted aryloxycarbonyl group, a substituted or unsubstituted acyl group, and a substituted or unsubstituted acyloxy group; R ₁ ~ R ₆ The case where a ring structure is formed by a combination of these is also included.

  The electrode active material of the present invention is characterized in that the organic compound has a molecular weight of 200 or more.

The electrode active material of the present invention is characterized in that the organic compound has two or more redox potentials in the range of 1.2 to 4.2 V vs. Li / Li ⁺ .

  The secondary battery according to the present invention is a secondary battery that performs charge and discharge by a battery electrode reaction, and the electrode active material described above is a reaction starting material, product, and intermediate in at least the discharge reaction of the battery electrode reaction. It is characterized by being included in any of the products.

  The secondary battery according to the present invention is characterized in that the discharge reaction has at least two discharge voltages.

  Moreover, the secondary battery of the present invention has a positive electrode, a negative electrode, and an electrolyte, and the positive electrode is mainly composed of the electrode active material.

According to the electrode active material of the present invention , the molecular weight is smaller than that of an organic compound having a cyanoquinodimethane structure, such as TCNQ, because the above-mentioned specific organic compound containing a cyanoquinodiimine structure as a constituent unit is mainly used. it is Ru can be. That is, the cyanoquinodiimine structure has a (= N-CN) group as a characteristic group, and the cyanoquinodimethane structure has a (= C- (CN) ₂ ) group as a characteristic group . If only the characteristic group is different and the other molecular structures are the same, the specific organic compound can have a lower molecular weight than an organic compound having a cyanoquinodimethane structure. Therefore, the capacity density of the battery can be increased, and as a result, the energy density can be increased. The specific organic compound having a cyanoquinodiimine structure as a structural unit has a large reaction rate constant for redox reaction, and can be charged and discharged with a large current. Therefore, a stable secondary battery having a long life can be obtained even when charging and discharging are repeated.

Moreover, since the specific organic compound has two or more redox potentials in the range of 1.2 to 4.2 V vs. Li / Li ⁺ , two or more electrons are involved per unit of the cyanoquinodiimine structure. Therefore, it is possible to obtain a capacity density more than twice that of a secondary battery using a one-electron reaction, and to obtain a high output secondary battery having a larger energy density. Is possible.

In addition, the above-mentioned specific organic compound having a cyanoquinodiimine structure as a structural unit is stable even when the redox reaction is repeated and has low solubility in the electrolyte. A secondary battery with good cycle characteristics can be obtained.

  Next, an embodiment of the present invention will be described in detail.

The electrode active material of the present invention is mainly composed of a specific organic compound containing a cyanoquinodiimine structure as a structural unit. As a result, the capacity density of the battery can be increased. Therefore, a secondary battery having a high energy density and a long life cycle characteristic with a small decrease in battery capacity even when charging and discharging are repeated at a high output is obtained. be able to.

The specific organic compound is specifically represented by the following general formula (1).

In the general formula (1), m is an integer of 1 or more, R ₁ to R ₆ is a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a cyano group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted Or an unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted aralkyl group, substituted or unsubstituted Amino group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, substituted or unsubstituted alkoxycarbonyl group, substituted or unsubstituted aryloxycarbonyl group, substituted or unsubstituted acyl group, and substituted or it indicates one of unsubstituted acyloxy group, form a ring structure by a combination of R ₁ to R ₆ Also it includes the case that.

  Here, each of the above-listed substituents is not particularly limited as long as it belongs to each category. For example, when an alkyl group, an alkenyl group, and an aromatic hydrocarbon group are exemplified, the followings are listed. Can be mentioned.

  Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, and a linear alkyl group such as n-octyl, an isopropyl group. , Isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, tert-pentyl group, neo-pentyl group, isohexyl group, methylhexyl group, methylheptyl group, dimethylhexyl group, 2-ethylhexyl group, etc. Examples thereof include an alkyl group substituted with an aryl group such as a chain alkyl group, a benzyl group, and a phenethyl group.

  Examples of the alkenyl group include a vinyl group, an allyl group, an isopropenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, and an octenyl group.

  Aromatic hydrocarbon groups include phenyl groups, naphthyl groups, unsubstituted aryl groups such as (o-, m-, p-), cresyl groups, (o-, m-, p-) tolyl groups, (2, 3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-) xylyl group, mesityl group, trimethylphenyl group, ethylphenyl group, propylphenyl group, butylphenyl group, Examples thereof include substituted aryl groups such as a nitrophenyl group and a methoxyphenyl group.

And as an organic compound contained in the category of General formula (1), there exists a substance represented by Chemical formula (1A)-( 1C ).

The chemical formula ( 1A ) is the general formula ( 1 ), R _{1 to} R ₆ are H, m is 1, the chemical formula ( 1B ) is R _{1 to} R ₆ is H, m is 2, and the chemical formula ( 1C ) Is an isomer of the chemical formula ( 1B ).

The electrode active material forms a complex salt with the electrode reaction. The following chemical reaction formula (2) is an example showing a charge / discharge reaction when an organic compound having a cyanoquinodiimine structure is used as an electrode active material and Li is used as a cation of an electrolyte salt.

  Since the electrode active material mainly comprises an organic compound containing a cyanoquinodiimine structure as a structural unit, for example, a cyanoquinodimethane structure (chemical formula (1 ′) such as TCNQ described in Patent Documents 4 to 9). ), The molecular weight of the battery can be relatively increased.

  That is, the theoretical capacity density Q (mAh / g) is expressed by the mathematical formula (1), where W is the molecular weight and Z is the number of electrons involved in the reaction.

  Therefore, the theoretical capacity density Q increases as the molecular weight W decreases and the number of electrons Z increases.

For example, when the cyanoquinodiimine structure of the present invention is compared with the cyanoquinodimethane structure, the cyanoquinodiimine structure has a (= N—CN) group as a characteristic group, and the cyanoquinodimethane structure has a characteristic group. (= C- (CN) ₂ ) group. The molecular weight of both characteristic groups is 40 for the (= N-CN) group and 64 for the (= C- (CN) ₂ ) group. Therefore, if only the above-mentioned characteristic groups are different and the other molecular structures are the same, the number of electrons Z involved in the battery electrode reaction is considered to be the same. Therefore, as is clear from Equation (1), the cyanoquinodiimine structure It is possible to increase the theoretical capacity density Q of an organic compound having a structural unit of. And since the capacity density of a battery becomes large in this way, it becomes possible to obtain an electrode active material with a large energy density.

The capacity density of the actual battery is reduced in comparison with the theoretical capacity density Q due to impurities being mixed in the process of synthesizing the organic compound that is the main component of the electrode active material. Therefore, it is possible to approach the theoretical capacity density Q as much as possible. As described above, if only the characteristic group is different and the other molecular structures are the same , the electrode active material has a cyanoquinodiimine structure, so that the battery has a relatively lower capacity than the cyanoquinodimethane structure. It is possible to increase the capacity density.

  Further, the molecular weight of the organic compound constituting the electrode active material is not particularly limited. However, when the molecular weight is small, at least 200 or more is preferable because it may be easily dissolved in the electrolyte. However, since the appearance of the desired effect of the present invention depends on the cyanoquinodiimine structure, when the portion other than the cyanoquinodiimine structure becomes large, the capacity that can be stored per unit mass, that is, the capacity density is small. Become.

Furthermore, in the present invention, the organic compound constituting the electrode active material, has two or more oxidation-reduction potential in the range of 1.2~4.2Vvs.Li / Li ^+.

  And by having at least two or more redox potentials in this way, two or more reactions with different energies will occur. Therefore, since the number of electrons Z involved in the battery electrode reaction is twice or more than that in the case of one electron, as is clear from the formula (1), the capacity density is also twice or more than that in the case of one electron. As a result, it is possible to obtain a secondary battery having a large energy density, a large capacity and a high output.

  In addition, since the electrode active material of the present invention described above is stable even after repeated oxidation-reduction reactions and has low solubility in the electrolyte, there is little decrease in capacity even after repeated charge and discharge, long life, and good cycle characteristics. A battery can be obtained.

Incidentally, the range that causes two or more redox potential was 1.2~4.2Vvs.Li / Li ^+, the oxidation-reduction potential is less than 1.2Vvs.Li/Li ^+, energy density is low This is because practical use is difficult, and in the region where the oxidation-reduction potential exceeds 4.2 V vs. Li ^/ Li ⁺ , the electrolyte is severely deteriorated and lacks stability as a secondary battery.

  As described above, the electrode active material of the present invention has two or more redox potentials within a range where it can be stably driven as a secondary battery.

  Next, a secondary battery using the 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 a secondary battery according to the present invention. In this embodiment, the electrode active material of the present invention is used as a positive electrode active material. ing.

  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-like thin plate shape. And the positive electrode 4 which formed the electrode active material in the sheet form is distribute | arranged to the center of the bottom part of the positive electrode case 2 which comprises a positive electrode electrical power collector. A separator 5 made of a porous film such as polypropylene 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, one obtained by superimposing a lithium metal foil on Cu or one obtained by applying a lithium storage material such as graphite or hard carbon to the metal foil can be used. A negative electrode current collector 7 made of Cu or the like is laminated on the negative electrode 6, and a metal spring 8 is placed on the negative electrode current collector 7. The electrolyte 9 is filled in the internal space, and the negative electrode case 3 is fixed to the positive electrode case 2 against the urging force of the metal spring 8 and sealed with a gasket 10.

  Next, an example of a method for manufacturing the secondary battery will be described in detail.

  First, an electrode active material is formed into an electrode shape. For example, an electrode active material is mixed with a conductive auxiliary agent and a binder, an organic solvent is added to form a slurry, and the slurry is applied on the positive electrode current collector by an arbitrary coating method and dried. Form.

  Here, the conductive auxiliary agent is not particularly limited, for example, carbonaceous fine particles such as graphite, carbon black, and acetylene black, vapor grown carbon fibers, carbon nanotubes, carbon fibers such as carbon nanohorns, polyaniline, Conductive polymers such as polypyrrole, polythiophene, polyacetylene, and polyacene can be used. Further, two or more kinds of conductive assistants can be mixed and used. In addition, as for the content rate in the positive electrode 4 of a conductive support agent, 10 to 80 weight% is preferable.

  Further, the binder is not particularly limited, and various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, carboxymethylcellulose, and the like can be used.

  Further, the organic solvent is not particularly limited, and examples thereof include basic solvents such as dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone, acetonitrile, tetrahydrofuran, Nonaqueous solvents such as nitrobenzene and acetone, and protic solvents such as methanol and ethanol can be used.

  Moreover, the kind of organic solvent, the compounding ratio of the organic compound and the organic solvent, the kind of additive and the addition amount thereof can be arbitrarily set in consideration of the required characteristics and productivity of the secondary battery.

  Next, the positive electrode 4 is impregnated in the electrolyte 9 so that the positive electrode 4 is impregnated with the electrolyte 9, and then the positive electrode 4 is placed on the positive electrode current collector at the bottom center of the positive electrode case 2. Next, the separator 5 impregnated with the electrolyte 9 is laminated on the positive electrode 4, the negative electrode 6 and the negative electrode current collector 7 are sequentially laminated, and then the electrolyte 9 is injected into the internal space. Then, a metal spring 8 is placed on the negative electrode current collector 9 and a gasket 10 is arranged on the periphery, and the negative electrode case 3 is fixed to the positive electrode case 2 by a caulking machine or the like, and the outer casing is sealed. A type secondary battery is produced.

The electrolyte 9 is interposed between the positive electrode (electrode active material) 4 and the negative electrode 6 which is the counter electrode, and transports charge carriers between the two electrodes. Those having an electric conductivity of ⁻⁵ to 10 ⁻¹ S / cm can be used. For example, an electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used.

Here, as the electrolyte salt, for example, LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ , Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, Li (C ₂ F ₅ SO ₂ ) ₃ C, or the like can be used.

  As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc. are used. be able to.

  The electrolyte 9 may be a solid electrolyte. Examples of the polymer compound used for the solid electrolyte include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and fluoride. Vinylidene fluoride polymers such as vinylidene-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and acrylonitrile-methyl methacrylate copolymer Polymer, acrylonitrile-methyl acrylate copolymer, acrylonitrile-ethyl methacrylate copolymer, acrylonitrile-ethyl acrylate copolymer, acrylonitrile-methacrylic acid copolymer, acrylonitrile-acrylic Acrylic nitrile polymers such as formic acid copolymers, acrylonitrile-vinyl acetate copolymers, polyethylene oxide, ethylene oxide-propylene oxide copolymers, and polymers of these acrylates and methacrylates Can do. Further, these polymer compounds containing an electrolytic solution in a gel form may be used as the electrolyte 9 or only a polymer compound containing an electrolyte salt may be used as the electrolyte 9 as it is.

  And, since the electrode active material of the secondary battery is reversibly oxidized or reduced by charging and discharging, it takes a different structure and state depending on the charged state, discharged state, or intermediate state. The electrode active material is included in at least one of reaction starting materials, products, and intermediate products in the discharge reaction, and the discharge reaction has at least two discharge voltages.

  As described above, according to the present embodiment, since the secondary battery is configured using the electrode active material, a secondary battery having a large energy density, a high output, and a large capacity can be obtained. In addition, even if charging / discharging is repeated, the capacity is hardly reduced, the life is long, and the cycle characteristics are good.

In addition, this invention is not limited to the said embodiment, A various modification can be considered in the range which does not deviate from a summary. For example, the organic compound which is the main component of the electrode active material may contain a cyanoquinodiimine structure belonging to the category of the general formula (1) as a structural unit. The chemical formulas (1A) to ( 1C ) listed above are It is an example, and is not limited to these. That is, in the present invention, it is important that the organic compound that is the main component of the electrode active material satisfies the general formula (1). By using such an organic compound as the electrode active material, cycle characteristics are improved. Various secondary batteries can be obtained that have a large energy density and can suppress a decrease in capacity as much as possible even when charging and discharging are repeated at a high output.

  In the above embodiment, the coin-type secondary battery has been described. However, the battery shape is not particularly limited, and can be applied to a cylindrical type, a square type, a sheet type, and the like. Also, the exterior method is not particularly limited, and a metal case, mold resin, aluminum laminate film, or the like may be used.

  Moreover, in the said embodiment, although the electrode active material was used for the positive electrode active material, using for a negative electrode active material is also useful.

Reference example

  As described above, the electrode active material according to the present invention is mainly composed of a specific organic compound containing a cyanoquinodiamine structure as a structural unit. As an organic compound containing a cyanoquinodiamine structure as a structural unit, the following general compounds can be used. What is represented by Formula (10) is also included.

  Where R ₇ ~ R _Ten Represents R represented by the general formula (1) of the present invention. ₁ ~ R ₆ And R ₇ ~ R _Ten The case where a ring structure is formed by a combination of these is also included.

In the following, battery characteristics were evaluated using an organic compound included in the category of the general formula (10), and compared with an organic compound having a TCNQ structure.

[Reference Example 1]
(Synthesis of organic compounds)
A dicyanoquinodiimine (hereinafter referred to as “DCNQI”) dimer (II) was prepared according to the following synthesis scheme ( A ).

That is, first, 100 mL of methylene chloride (CH ₂ Cl ₂ ) was put into a three-neck flask having a volume of 200 mL, and then 52 mL of bis (trimethylsilyl) carbodiimide ((CH ₃ ) ₃ SiNCNSi (CH ₃ ) ₃ ) was put into the three-neck flask. After dissolution, 44 g of titanium tetrachloride (TiCl ₄ ) was further added and stirred at 0 ° C. Thereafter, a methylene chloride solution containing 5 g of 2,2′-bis (1,4-benzoquinone) (I) was dropped into a three-necked flask and reacted at a temperature of 0 ° C. for 24 hours. When the obtained black product was measured by an infrared absorption spectrum, absorption derived from a cyano group (—CN) was confirmed, and absorption derived from a carbon-nitrogen double bond (C═N) having a quinoid structure was observed. From the confirmation, the product was considered to be a DCNQI dimer.

[Production of secondary battery]
300 mg of the above DCNQI dimer, 600 mg of graphite powder as a conductive auxiliary agent, and 100 mg of polytetrafluoroethylene resin as a binder were weighed and kneaded while uniformly mixing the weighed material. This mixture was pressure-molded to produce a sheet-like member having a thickness of about 150 μm. Next, this sheet-like member was dried in a vacuum at 80 ° C. for 1 hour, and then punched into a circle having a diameter of 12 mm to produce a positive electrode (positive electrode active material) mainly composed of a DCNQI dimer.

Next, the positive electrode was impregnated with the electrolytic solution, and the electrolytic solution was infiltrated into the voids in the positive electrode. As the electrolytic solution, an ethylene carbonate / diethyl carbonate mixed solution, which is an organic solvent containing LiPF ₆ (electrolyte salt) having a molar concentration of 1.0 mol / L, was used. In addition, the mixing ratio of ethylene carbonate / diethyl carbonate as an organic solvent was ethylene carbonate: diethyl carbonate = 3: 7 in volume%.

  Next, this positive electrode was placed on a positive electrode current collector, and a separator having a thickness of 20 μm made of a polypropylene porous film impregnated with the electrolytic solution was laminated on the positive electrode. The negative electrode to which was attached was laminated on the separator. And after laminating | stacking the negative electrode collector made from Cu on a negative electrode, inject | pouring electrolyte solution into interior space, and mounting a metal spring on a negative electrode collector after that, and having arrange | positioned the gasket to the periphery The negative electrode case was joined to the positive electrode case and sealed with a caulking machine, whereby a sealed coin-type battery having a DCNQI dimer as a positive electrode active material and metallic lithium as a negative electrode active material was produced.

[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.1 mA. As a result, the charge / discharge voltage was shown at two locations of 3.2 V and 2.55 V, and it was confirmed that the secondary battery had a discharge capacity of 0.4 mAh. The discharge capacity (actual capacity density) per electrode active material was determined to be 200 mAh / g.

  Subsequently, when charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V, the initial capacity of 80% or more could be secured even after 100 cycles. That is, it was possible to obtain a secondary battery having good cycle characteristics with little decrease in capacity even after repeated charge and discharge.

Further, a similarly manufactured secondary battery was charged at a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged at a constant current of 5.0 mA. As a result, although the discharge capacity decreased as compared with the case of discharging at a constant current of 0.1 mA, it was possible to ensure 80% or more of the discharge capacity when discharged at 0.1 mA. That is, it was found that a secondary battery having a high output density capable of taking out a large capacity even with a large current can be obtained.

[Calculation of theoretical capacity density]
For the DCNQI dimer and the TCNQ dimer, the theoretical capacity density Q was calculated according to the formula (1), and the two were compared.

  Here, Z is the number of electrons involved in the battery electrode reaction, and W is the molecular weight of the electrode active material.

  Since the molecular weight W of the DCNQI dimer is 310.3 and the molecular weight W of the TCNQ dimer is 406.3, assuming that the number of electrons Z involved in the battery electrode reaction is 4, the formula (1) shows that The capacity density Q is 345 mAh / g for the DCNQI dimer and 264 mAh / g for the TCNQ dimer.

  Therefore, it was found that the DCNQI dimer can improve the capacity density by about 31% compared to the TCNQ dimer.

  The actual capacity density is 200 mAh / g, which is about 58% of the theoretical capacity density. This is probably because impurities were mixed in the synthesis process of the DCNQI dimer. Therefore, it is considered possible to bring the actual capacity density closer to the theoretical capacity density Q by avoiding the mixing of such impurities by appropriate means.

[Reference Example 2]
In Reference Example 2 , the DCNQI dimer prepared in [ Reference Example 1] was used, a secondary battery was manufactured by an industrial method, and operation was confirmed.

First, 10 g of N-methylpyrrolidone as an organic solvent was weighed in a small homogenizer container, 400 mg of polyvinylidene fluoride as a binder was added, and stirred for 30 minutes to completely dissolve. To this, 0.5 g of DCNQI dimer was added and stirred until uniform. Next, 0.5 g of graphite powder as a conductive auxiliary agent was added and stirred to obtain a black slurry. This slurry was applied onto a high-purity aluminum foil and dried at 120 ° C., thereby producing a positive electrode having a thickness of 95 μm mainly composed of DCNQI dimer. This was punched out into a circle with a diameter of 12 mm, and then a secondary battery was produced in the same manner as in [ Reference Example 1].

As in [ Reference Example 1], the secondary battery manufactured as described above was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then with a constant current of 0.1 mA to 2.0 V. Discharge was performed. As a result, charging / discharging voltage was shown at two locations of 3.2V and 2.6V, and it was confirmed that the secondary battery had a discharge capacity of 0.42 mAh. Moreover, it was 210 mAh / g when the discharge capacity (actual capacity density) per electrode active material was calculated | required.

  Next, charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V. As a result, the initial capacity of 80% or more could be secured even after 100 cycles. That is, it was possible to obtain a secondary battery having good cycle characteristics with little decrease in capacity even after repeated charge and discharge.

Similarly, a prototype coin-type battery was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged with a constant current of 5.0 mA. As a result, although the discharge capacity decreased as compared with the case of discharging at a constant current of 0.1 mA, it was possible to ensure 80% or more of the discharge capacity when discharged at 0.1 mA. That is, it was confirmed that a high power density secondary battery capable of extracting a large capacity even with a large current can be obtained in Reference Example 2.

  That is, it was confirmed that there was almost no difference in characteristics depending on the manufacturing method.

[Reference Example 3]
(Synthesis of organic compounds)
In accordance with the synthesis scheme ( B ), a polymer of dicyanoquinodiimine (hereinafter referred to as “DCNQI polymer”) was produced.

In a nitrogen stream, 5 g of 1,4-bis (aminomethyl) -2,5-dimethoxybenzene (I) was dissolved in an excess amount of dimethyl malonate ((COOCH ₃ ) ₂ CH ₂ ), and a temperature of 150 ° C. Stir for hours. The reaction mixture was added with 100 mL of water, extracted with methylene chloride, dried over anhydrous sodium sulfate, and concentrated to dryness. The resulting solid (II) was dissolved in 300 mL of tetrahydrofuran (THF) in a nitrogen stream. ₄ g of lithium aluminum hydride (LiAlH ₄ ) was added and stirred at room temperature for 4 hours. Next, the reaction mixture was poured into ice water, stirred, extracted with ethyl acetate, dried over anhydrous sodium sulfate, and concentrated to dryness. The resulting colorless oil (III) was dissolved in 300 mL of methylene chloride. Into the solution, 56 g of diammonium cerium nitrate (II) (Ce (NH ₄ ) ₂ (NO ₃ ) ₆ ) was added, and the resulting yellow solid was collected by filtration and washed to obtain a benzoquinone polymer (IV). . The benzoquinone polymer (IV) was sufficiently dried in a desiccator.

On the other hand, 100 mL of methylene chloride (CH ₂ Cl ₂ ) is put into a three-necked flask having a volume of 200 mL, and then 52 mL of bis (trimethylsilyl) carbodiimide ((CH ₃ ) ₃ SiNCNSi (CH ₃ ) ₃ ) is put into this three-necked flask and dissolved. Further, 44 g of titanium tetrachloride (TiCl ₄ ) was added and stirred at 0 ° C.

  Thereafter, a methylene chloride solution containing the polymer (IV) of benzoquinone was dropped into the three-necked flask and reacted at a temperature of 0 ° C. for 24 hours. When the obtained black product was measured by an infrared absorption spectrum, absorption derived from a cyano group (—CN) was confirmed, and absorption derived from a carbon-nitrogen double bond (C═N) having a quinoid structure was observed. From the confirmation, the product is considered to be DCNQI polymer (V).

[Production of secondary battery]
A secondary battery was fabricated in the same manner as in [ Reference Example 1] except that a DCNQI polymer was used as the electrode active material.

[Confirmation of secondary battery operation]
As in [ Reference Example 1], this secondary battery was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged with a constant current of 0.1 mA to 2.0 V. As a result, this secondary battery showed a charge / discharge voltage at two locations of 3.1 V and 2.5 V, and was confirmed to be a secondary battery having a discharge capacity of 0.19 mAh. Further, when the discharge capacity (actual capacity density) per electrode active material was determined, it was 180 mAh / g.

  Subsequently, charge and discharge were repeated 100 cycles in the range of 4.0 to 2.0 V. As a result, the initial capacity of 80% or more could be secured even after 100 cycles. That is, it was possible to obtain a secondary battery having good cycle characteristics with little decrease in capacity even after repeated charge and discharge.

In addition, a secondary battery produced in the same manner was charged at a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged at a constant current of 5.0 mA. As a result, as in [ Reference Example 1], the discharge capacity was reduced compared with the case of discharging at a constant current of 0.1 mA, but 80% or more was secured relative to the discharge capacity when discharging at 0.1 mA. We were able to. That is, it was found that a secondary battery having a high output density capable of taking out a large capacity even with a large current can be obtained.

[Calculation of theoretical capacity density]
For the DCNQI polymer and the TCNQ polymer, the theoretical capacity density Q was calculated based on the above formula (1), and the two were compared. The TCNQ polymer has the same polymer structure except that the DCNQI structure is changed to the TCNQ structure.

  Since the molecular weight W of the DCNQI polymer is 310.3 and the molecular weight W of the TCNQ polymer is 304.3, assuming that the number of electrons Z involved in the battery electrode reaction is 2, the theoretical capacity density Q is DCNQI polymer is 209 mAh / g and TCNQ polymer is 176 mAh / g.

  Accordingly, it was found that the DCNQI polymer can improve the capacity density by about 19% compared to the TCNQ polymer.

The actual capacity density is 180 mAh / g and about 86% of the theoretical capacity density is considered to be because impurities were mixed in the synthesis process of the DCNQI polymer as in [ Reference Example 1]. It is considered that the actual capacity density can be brought close to the theoretical capacity density by avoiding such contamination by means.

[Reference Example 4]
As an organic compound having a dicyanoquinodiimine structure as a structural unit, 2,5-dimethyl-N, N′-dicyanoquinodiimine (hereinafter referred to as “DCNQI-OMe2”) represented by the chemical formula (C) was prepared. . In addition, this DCNQI-OMe2 used the commercially available thing (made by Tokyo Chemical Industry Co., Ltd.).

[Production of secondary battery]
A secondary battery was fabricated in the same manner as in [ Reference Example 1] except that DCNQI-OMe2 was used as the positive electrode active material.

[Confirmation of secondary battery operation]
As in [ Reference Example 1], this secondary battery was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged with a constant current of 0.1 mA to 2.0 V. As a result, this secondary battery showed a charge / discharge voltage at two locations of 3.3V and 2.8V, and was confirmed to be a secondary battery having a discharge capacity of 0.45 mAh. Moreover, it was 180 mAh / g when the discharge capacity per electrode active material (real capacity density) was calculated | required.

  Next, charging and discharging were repeated 100 cycles in the range of 3.6 to 2.0 V. As a result, it was found that the secondary battery had a long cycle life with little reduction in capacity even after 100 cycles and little reduction in capacity even after repeated charge and discharge.

Similarly, a prototype secondary battery was charged with a constant current of 0.1 mA until the voltage reached 3.6 V, and then discharged with a constant current of 5.0 mA. As a result, as in [ Reference Example 1], although the discharge capacity was reduced compared to the case of discharging at a constant current of 0.1 mA, 80% or more was secured relative to the discharge capacity when discharging at 0.1 mA. We were able to. That is, it was found that a secondary battery having a high output density capable of taking out a large capacity even with a large current can be obtained.

[Calculation of theoretical capacity density]
For DCNQI-OMe2 and 2,5-dimethyl-N, N′-dicyanoquinodimethane (hereinafter referred to as “TCNQ-OMe2”), the theoretical capacity density Q is calculated based on the above formula (1), Compared.

  Since the molecular weight W of DCNQI-OMe2 is 216.2 and the molecular weight W of TCNQ-OMe2 is 264.2, if the number of electrons Z involved in the battery electrode reaction is 2, the theoretical capacity density can be calculated from Equation (1). For Q, DCNQI-OMe2 is 248 mAh / g, and TCNQ-OMe2 is 203 mAh / g.

  Therefore, it was found that DCNQI-OMe2 can improve the capacity density by about 22% compared with TCNQ-OMe2.

The actual capacity density is 180 mAh / g, and therefore about 38% of the theoretical capacity density is considered to be because impurities were mixed in the synthesis process of DCNQI-OMe2 as in [ Reference Example 1]. It is considered that the actual capacity density can be brought close to the theoretical capacity density by avoiding the mixing of such impurities by appropriate means.

Thus, as is clear from the comparison between the DCNQI structure and the TCNQ structure of each reference example, the organic compound having the TCNQ structure has a larger molecular weight than the corresponding organic compound having the DCNQI structure, and thus the theoretical capacity density Q is also small. Become. Accordingly, it is confirmed that the battery capacity is greatly reduced by repeated charging and discharging, and is not suitable for an electrode active material for a secondary battery.

[Reference Example 5]
A secondary battery was fabricated in the same manner as in [ Reference Example 1] except that TCNQ was used as the positive electrode active material. As TCNQ, a commercially available product (manufactured by Tokyo Chemical Industry Co., Ltd.) was used.

  Next, this secondary battery was charged with a constant current of 0.1 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.1 mA. As a result, the first discharge had voltage flat portions at 3.1 V and 2.5 V, and the discharge capacity showed 0.2 mAh. However, after the second discharge, both the charge capacity and the discharge capacity were reduced to 0.1 mAh or less. Diminished.

It is sectional drawing which shows one Embodiment of the coin-type battery as a secondary battery which concerns on this invention.

Claims (6)

An electrode active material used as an active material of a secondary battery that repeats charging and discharging by a battery electrode reaction,
General formula

[Wherein, m is an integer of 1 or more, and R _{1 to} R ₆ are a hydrogen atom, a halogen atom, a hydroxyl group, a nitro group, a cyano group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted group. Alkenyl group, substituted or unsubstituted cycloalkenyl group, substituted or unsubstituted aromatic hydrocarbon group, substituted or unsubstituted aromatic heterocyclic group, substituted or unsubstituted aralkyl group, substituted or unsubstituted amino group Substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, substituted or unsubstituted alkoxycarbonyl group, substituted or unsubstituted aryloxycarbonyl group, substituted or unsubstituted acyl group, and substituted or unsubstituted Including a case where a ring structure is formed by a combination of R _{1 to} R _6. Mu ]
An electrode active material comprising mainly an organic compound containing a cyanoquinodiimine structure represented by The electrode active material according to claim 1 , wherein the organic compound has a molecular weight of 200 or more. The electrode active material according to claim 1 , wherein the organic compound has two or more oxidation-reduction potentials in a range of 1.2 to 4.2 V vs. Li / Li ⁺ . A secondary battery that charges and discharges by a battery electrode reaction,
The electrode active material according to any one of claims 1 to 3 is included in any one of a reaction starting material, a product, and an intermediate product in at least a discharge reaction of the battery electrode reaction. Secondary battery. The secondary battery according to claim 4 , wherein the discharge reaction has at least two discharge voltages. The secondary battery according to claim 4 , comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is mainly composed of the electrode active material.

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