JP2010073401A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new secondary battery which is superior in self discharge characteristics and of which discharge capacity is not deteriorated even in usage after preservation. <P>SOLUTION: The secondary battery has at least a positive electrode, a negative electrode, and an electrolyte as a constituent element. A reactant or a product in electrode reaction of the positive electrode active material is a neutral radical compound expressed by the following general formula (1), and a reactant or a product in the electrode reaction of the negative electrode active material contains a neutral radical compound. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a secondary battery.

  With the rapid market expansion of notebook computers, mobile phones, etc., there is an increasing demand for small high-capacity secondary batteries with high energy density used for these. In order to meet this demand, a secondary battery using an alkali metal ion such as lithium ion as a charge carrier and utilizing an electrochemical reaction accompanying charge transfer has been developed. Among these, lithium ion secondary batteries are used in various electronic devices as high-capacity secondary batteries having excellent stability and large energy density.

However, such a lithium ion secondary battery uses a lithium-containing transition metal oxide such as lithium cobaltate as an active material as an active material, which has a large environmental load and has limited resources. On the other hand, a secondary battery in which an electrode active material is made of an organic radical compound has been proposed (see, for example, Patent Document 1). Certainly, this is a high energy density and organic material, so the environmental impact is small and there is almost no risk of depletion of resources. On the other hand, storage after charging discharges in a relatively short period of time. However, there was room for further improvement in these respects.
JP 2008-174725 A

  An object of the present invention is to provide a novel secondary battery that has excellent self-discharge characteristics and does not have a reduced discharge capacity even after use after storage.

  The above object of the present invention can be achieved by the following configuration.

  1. In a secondary battery having at least a positive electrode, a negative electrode, and an electrolyte as constituents, the reactant or product in the electrode reaction of the positive electrode active material is a neutral radical compound represented by the following general formula (1); A secondary battery, wherein a reaction product or product in an electrode reaction of an active material of a negative electrode is a neutral radical compound.

[Wherein, X represents —N—Y or —CR ₁ (R ₂ ), and at least one of X is —N—Y, and Y represents a hydrogen atom, an alkyl group, an aryl group, or —O ·. And at least one of all Y is -O., R _{a to} R _d and R ₁ and R ₂ represent a hydrogen atom or a substituent, and at least one of R _{a to} R _d represents a polymer chain. To express. ]
2. The polymer chain of the compound represented by the general formula (1) is a polymer having as a repeating unit at least one selected from structures represented by the following (B-1) to (B-6). 2. The secondary battery as described in 1 above.

[Wherein, R represents a hydrogen atom or a methyl group. * Indicates a bonding position between the polymer chain and the ring structure mother nucleus. ]
3. The polymer chain of the compound represented by the general formula (1) has at least one selected from the structures represented by (B-1), (B-2), and (B-5) as a repeating unit. 2. The secondary battery as described in 1 above, which is a polymer.

  4). In the general formula (1), at least two of X are -N-Y, Y represents a hydrogen atom, an alkyl group, an aryl group, or -O., And at least one of all Ys is -O. The secondary battery as described in any one of 1 to 3 above.

  5. A secondary battery, wherein the negative electrode active material is a neutral radical compound represented by the following general formula (2) or general formula (3).

[Wherein R ₃ and R ₄ represent an electron-withdrawing group, and R ₅ represents a hydrogen atom or a methyl group. ]

[Wherein R ₆ represents an electron-withdrawing group, and m represents an integer of 0 to 5. R ₇ and R ₈ represent hydrogen or an electron-withdrawing group, and R ₉ represents a hydrogen atom or a methyl group. ]

  According to the present invention, it was possible to provide a novel secondary battery that has excellent self-discharge characteristics and does not have a reduced discharge capacity even when used after storage.

  The present invention will be described in more detail. In the secondary battery according to the present invention, the following configuration can be adopted.

[Positive electrode active material]
The active material used for the positive electrode in the present invention is a neutral radical compound whose reactant or product in the electrode reaction is represented by the general formula (1).

In the general formula (1), the substituent represented by R _{a to} R _d and R ₁ and R ₂ is not particularly limited, and examples thereof include an alkyl group (methyl, ethyl, i-propyl, hydroxyethyl, stearyl, Dodecyl, eicosyl, docosyl, oleyl, etc.), cycloalkyl groups (cyclopropyl, cyclohexyl, etc.), aryl groups (phenyl, p-tetradecanyloxyphenyl, o-octadecanylaminophenyl, naphthyl, hydroxyphenyl, etc.), hydroxyl Group, carboxyl group, nitro group, trifluoromethyl group, amide group (acetamide, benzamide, etc.), carbamoyl group (methylcarbamoyl, butylcarbamoyl, phenylcarbamoyl etc.), ester group (ethyloxycarbonyl, i-propyloxycarbonyl, phenyl) Oxyca Bonyl etc.), carbonyloxy group (methylcarbonyloxy, propylcarbonyloxy, phenylcarbonyloxy etc.), cyano group, halogen atom (chlorine, bromine, iodine, fluorine), alkoxy group (methoxy, ethoxy, butoxy etc.), aryloxy Groups (phenoxy, naphthyloxy, etc.), sulfonyl groups (methanesulfonyl, p-toluenesulfonyl, etc.), alkylthio groups (methylthio, ethylthio, butylthio, etc.), arylthio (phenylthio, etc.), sulfonamide groups (methanesulfonamide, dodecylsulfonamide) , P-toluenesulfonamide, etc.), sulfamoyl group (methylsulfamoyl, phenylsulfamoyl etc.), amino group, alkylamino group (ethylamino, dimethylamino, hydroxyamino etc.), aryla Amino group (phenylamino, naphthylamino and the like).

  The polymer chain is not particularly limited as long as it is a polymer obtained by polymerizing a monomer having a polymerizable group with a known method. Examples thereof include polymers having the following structure as a repeating unit.

[Wherein, R ¹ represents a hydrogen atom or a methyl group, and R ′ represents an alkylene group or an arylene group. * Indicates a bonding position between the polymer chain and the ring structure mother nucleus. ]
Preferably, the polymer which used the structure represented by said (B-1)-(B-6) as a repeating unit is mentioned, More preferably, said (B-1), (B-2), (B And a polymer having the structure represented by −5) as a repeating unit.

  In the general formula (1), it is preferable that the ratio of —NH and —NO · in X is represented by the following formula and the following relationship is satisfied.

Z can be determined from the conversion rate to radicals, and the conversion rate to radicals can be calculated by determining the spin concentration from the ESR spectrum. The spin concentration means the number of unpaired electrons (radicals) per unit mass, and is a value obtained by the following method from the absorption area intensity of an electron spin resonance spectrum (hereinafter referred to as ESR spectrum), for example. First, a sample to be measured for ESR spectrum is ground with a mortar or the like and pulverized. By this treatment, the skin effect (a phenomenon in which the microwave does not pass through to the inside) can be pulverized into particles having a size that can be ignored. A certain amount of the pulverized sample is filled in a quartz glass capillary having an inner diameter of 2 mm or less, preferably 1 to 0.5 mm, degassed to 10 ⁻⁵ mmHg (1 mmHg is 133.322 Pa) or less, and sealed. The ESR spectrum is measured. The ESR spectrum is measured using, for example, a JEOL-JES-FR30 type ESR spectrometer. The spin concentration can be obtained by integrating the obtained ESR signal twice and comparing it with a calibration curve. However, in the present invention, any measuring machine and measurement conditions are applicable as long as the spin concentration can be measured correctly. For example, when the conversion rate to radicals is 80%, Z = 4 from the following.

  Hereinafter, although the compound represented by General formula (1) is described, it is not limited to these.

  In the above (B-1) to (B-6) and chemical formula 5, * indicates the bonding position between the polymer chain and the ring structure mother nucleus, so for example in the case of a combination of (A-1) and (B-1) Is the following structure.

  The weight average molecular weight of the compound represented by the general formula (1) is not particularly limited, but is preferably converted from a calibration curve prepared using standard polystyrene (for example, STK standard polystyrene (manufactured by Tosoh Corporation)), Is Mw 3000 or more and 1000000 or less, more preferably 10,000 or more and 500000 or less, and most preferably 30000 or more and 200000 or less.

[Negative electrode active material]
The active material used for the negative electrode in the present invention is a radical compound in which the reaction product or product in the electrode reaction is neutral. The radical compound is called an n-type radical compound, and is a compound capable of reversible reaction that becomes an anion upon charge and returns to a radical upon discharge. The neutral compound represented by the general formula (2) or the general formula (3) Although the radical compound of the formula (3) is used, more preferable results can be obtained.

  In general formula (2) or general formula (3), an electron withdrawing group refers to a group having a Hammett's sigma value greater than zero. Hammett's sigma value is described in documents such as Naoki Inamoto's “Hammett's Rule” (1983, Maruzen). Examples of the electron withdrawing group include a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), a halogenated alkyl group (for example, a trifluoromethyl group, a perfluorobutyl group, and a trichloromethyl group), Cyano group, nitro group, carboxyl group, acyloxy group, carbamoyloxy group, alkylsulfonylamino group, arylsulfonylamino group, sulfamoyl group, sulfo group, alkylsulfinyl group, arylsulfinyl group, alkylsulfonyl group, arylsulfonyl group, acyl group Aryloxycarbonyl group, alkoxycarbonyl group, carbamoyl group, arylazo group, heterocyclic azo group, imide group, phosphino group, phosphinyl group, phosphinyloxy group and the like. Among these, the electron-withdrawing group is preferably a halogen atom or a trifluoromethyl group, and more preferably a trifluoromethyl group.

  Specific examples of the compound represented by formula (2) or formula (3) are shown below.

  The weight average molecular weight of the compound represented by the general formula (2) or the general formula (3) is not particularly limited, but a calibration prepared using standard polystyrene (for example, STK standard polystyrene (manufactured by Tosoh Corporation)). Converted from the curve, it is preferably Mw 3000 or more and 1000000 or less, more preferably 10,000 or more and 500000 or less, and most preferably 30000 or more and 200000 or less.

[Conductive auxiliary material and ion conductive auxiliary material]
In this invention, when forming an electrode, you may mix a conductive support material and an ion conductive support material in order to reduce an impedance. Conductive auxiliary materials include graphite, carbon black, acetylene black, carbonaceous fine particles such as vapor-grown carbon fibers, metal fine particles such as copper, silver, gold, and platinum, and conductive properties such as polyaniline, polypyrrole, polythiophene, polyacetylene, and polyacene. Examples include polymers. Examples of the ion conduction auxiliary material include gel electrolytes and solid electrolytes.

[Binder]
In the present invention, a binder may be mixed with the electrode material in order to strengthen the connection between the constituent materials of the electrode. Examples of such a binder include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, polyethylene. And resin binders such as polyimide.

[Current collector and separator]
As the current collector in the present invention, a metal foil such as nickel, aluminum, copper, gold, silver, aluminum alloy, stainless steel, a metal flat plate, a mesh electrode, a carbon electrode, or the like can be used. Further, such a current collector may have a catalytic effect, or the active material and the current collector may be chemically bonded.

  In addition, for the purpose of preventing electrical contact between the negative electrode current collector and the positive electrode current collector, an insulating packing made of a plastic resin or the like may be disposed between them.

  Moreover, as a separator which can be used in the lithium secondary battery of the present invention, a polyolefin film such as polypropylene or polyethylene, or a porous film such as a fluororesin can be used.

[Electrolyte and electrolyte]
In the present invention, the electrolyte performs charge carrier transport between both the negative electrode and the positive electrode, and generally has an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at room temperature. Examples of the electrolytic solution in the present invention include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1, 2 -Chain ethers such as diethoxyethane and 1-ethoxy-1-methoxyethane, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethyl Formamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- One or two or more of aprotic organic solvents such as oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, etc. are mixed and used. A solution in which a lithium salt is dissolved in a solvent can be used.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ). ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides and the like.

  Further, a polymer electrolyte may be used instead of the electrolytic solution. Polymeric substances used in these solid electrolytes include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-ethylene copolymer, vinylidene fluoride-monofluoroethylene copolymer, and vinylidene fluoride. -Vinylidene fluoride polymers such as 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 Acid copolymer, an acrylonitrile - acrylonitrile polymers such as vinyl acetate copolymer, further polyethylene oxide, ethylene oxide - propylene oxide copolymers, and polymers of these acrylates body or methacrylate body thereof. These polymer substances can be used in the form of a gel containing an electrolytic solution, or only the polymer substance may be used as it is.

[Method for producing positive electrode and negative electrode]
In this invention, it does not specifically limit about the manufacturing method of a positive electrode and a negative electrode, A conventionally well-known method is employable. For example, a method in which a solvent is added to the constituent materials of the positive electrode and the negative electrode to form a slurry, and the mixture is applied to the electrode current collector, a method in which a binder resin is added to the constituent materials of the positive electrode and the negative electrode and solidified by applying pressure, The method of baking and hardening by heating.

[Lamination of electrodes]
In the present invention, the laminated form of the positive electrode and the negative electrode is not particularly limited, and any laminated form can be adopted, and a multilayer laminated body, a form obtained by combining those laminated on both sides of the current collector, These can be wound.

[Battery shape]
The shape and appearance of the battery of the present invention are not particularly limited, and conventionally known ones can be adopted. That is, as such a battery shape, for example, an electrode laminate or a wound body is sealed with a metal case, a resin case, or a laminate film composed of a metal foil such as an aluminum foil and a synthetic resin film, or the like. Can be mentioned. Examples of the external appearance of the battery include a cylindrical shape, a square shape, a coin shape, and a sheet shape.

  The present invention will be described more specifically below, but the present invention is not limited to these examples.

(1) Production of Battery 75% by mass of the radical compound represented by the compound (1) and 20% by mass of graphite powder as an auxiliary conductive material were mixed, and 5% by mass of polyvinylidene fluoride copolymer and N- Methyl pyrrolidone was added and mixed to prepare a slurry.

  This slurry was applied to the surface of an aluminum foil (thickness: 20 μm) provided with a lead wire, developed with a wire bar so as to have a uniform thickness, dried, and pressed to produce a positive electrode.

  Next, 85% by mass of the radical compound represented by the compound (2-1) and 10% by mass of graphite powder as an auxiliary conductive material are mixed, and 5% by mass of polyvinylidene fluoride and N-methylpyrrolidone are added thereto. Furthermore, it added and mixed and the slurry was prepared.

  The obtained slurry is applied to the surface of a copper foil (thickness: 20 μm) provided with a lead wire, developed to have a uniform thickness with a wire bar, dried, and pressed to obtain a negative electrode. It was.

  After laminating the positive electrode, a separator made of a polyethylene porous film with a thickness of 25 μm, and a negative electrode in this order, the thickness is composed of an aluminum foil having a thickness of 40 μm and a polypropylene layer formed on both surfaces of the aluminum foil. Was stored in a pack made of a laminate laminate film of 0.1 mm, and vacuum-dried at 80 ° C. for 24 hours.

A liquid non-aqueous electrolyte was prepared by dissolving 1 mol / L of LiPF ₆ as an electrolyte in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7.

  After injecting the liquid non-aqueous electrolyte into the laminate film pack containing the electrode group, the pack was completely sealed by heat sealing to produce a battery 101.

  Instead of the radical compound represented by the positive electrode compound (1), the radical compound described in Table 2, and the neutral radical compound represented by the general formula (2) or general formula (3) described in Table 2 on the negative electrode Batteries 102 to 120 and Comparative 1 were produced in the same manner as described above except that was used. In comparison 1, graphite was used as the negative electrode active material.

(2) Battery charging / discharging evaluation conditions After charging at a constant voltage of 2.8 V in a 25 ° C. environment, a constant rate discharge of 0.1 mA was performed, and a discharge capacity of 0.1 mA was measured.

(3) Evaluation of preservability Ten batteries 101 to 120 and Comparative Example 1 prepared above were prepared, 10 initial charge / discharge cycles were performed, and the average value of the 10th cycle was “discharge capacity before storage”. It was. Subsequently, after charging under the same conditions as described above, each battery was stored in a thermostatic chamber having an explosion-proof structure set to 60 ° C. Seven days later, the battery was taken out and discharged under the same conditions as described above, and the average of the measured values was defined as “discharge capacity after storage”. For each battery, “self-discharge rate (%)” was calculated according to the following calculation formula.

  Next, charging and discharging were performed under the same conditions. Thus, the obtained discharge capacity was set as “recovery discharge capacity”, and the ratio of each battery to the “discharge capacity before storage” was obtained and set as “recovery capacity ratio (%)”.

  As is apparent from Table 3, the secondary battery of the present invention has excellent self-discharge characteristics, and the discharge capacity does not decrease even after use after storage.

Claims (5)

In a secondary battery having at least a positive electrode, a negative electrode, and an electrolyte as constituents, the reactant or product in the electrode reaction of the positive electrode active material is a neutral radical compound represented by the following general formula (1); A secondary battery, wherein a reaction product or product in an electrode reaction of an active material of a negative electrode is a neutral radical compound.

[Wherein, X represents —N—Y or —CR ₁ (R ₂ ), and at least one of X is —N—Y, and Y represents a hydrogen atom, an alkyl group, an aryl group, or —O ·. And at least one of all Y is -O., R _{a to} R _d and R ₁ and R ₂ represent a hydrogen atom or a substituent, and at least one of R _{a to} R _d represents a polymer chain. To express. ] The polymer chain of the compound represented by the general formula (1) is a polymer having at least one selected from structures represented by the following (B-1) to (B-6) as a repeating unit. The secondary battery according to claim 1, characterized in that:

[Wherein, R represents a hydrogen atom or a methyl group. * Indicates a bonding position between the polymer chain and the ring structure mother nucleus. ] The polymer chain of the compound represented by the general formula (1) has at least one selected from the structures represented by (B-1), (B-2), and (B-5) as a repeating unit. The secondary battery according to claim 1, wherein the secondary battery is a polymer. In the general formula (1), at least two of X are -N-Y, Y represents a hydrogen atom, an alkyl group, an aryl group, or -O., And at least one of all Ys is -O. The secondary battery according to claim 1, wherein the secondary battery is provided. A secondary battery, wherein the negative electrode active material is a neutral radical compound represented by the following general formula (2) or general formula (3).

[Wherein R ₃ and R ₄ represent an electron-withdrawing group, and R ₅ represents a hydrogen atom or a methyl group. ]

[Wherein R ₆ represents an electron-withdrawing group, and m represents an integer of 0 to 5. R ₇ and R ₈ represent hydrogen or an electron-withdrawing group, and R ₉ represents a hydrogen atom or a methyl group. ]