JP2005209498A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery superior in large current charge and discharge characteristics. <P>SOLUTION: In the nonaqueous electrolyte secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution; the positive electrode comprises a sheet composite including at least a stable organic radical polymer and carbon. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a secondary battery.

  With the rapid market expansion of notebook PCs, mobile phones, electric cars, etc., high output power storage devices are required. Among them, lithium ion secondary batteries using a lithium-containing transition metal oxide for the positive electrode and a carbon material for the negative electrode are used in various portable devices as high energy density batteries having excellent charge / discharge characteristics.

Patent Document 1 discloses a secondary battery in which at least one active material of a positive electrode and a negative electrode contains a radical compound. Patent Document 2 discloses an electricity storage device containing a nitroxyl compound in a positive electrode. This electricity storage device is said to be able to charge and discharge with a large current because of its fast electrode reaction. Patent Document 3 discloses a secondary battery having composite particles composed of at least two or more composition regions as active materials.
Japanese Patent Laid-Open No. 2002-151084 JP-A-2002-304996 Japanese Patent Laid-Open No. 2002-298850

  However, in the first place, the lithium ion secondary battery cannot be said to have a high reaction rate of the electrode reaction, and has a problem that the capacity is remarkably lowered when a large current is passed. Some of the batteries described in Patent Documents 1 to 3 are capable of charging and discharging at about 30 C because the electrode reaction is fast, but there is still room for improvement in terms of increasing the current to about 50 C. Here, C in any battery is defined as follows. When a battery having an arbitrary capacity is discharged or charged with an arbitrary constant current and the discharge or charging is completed in n hours, the constant current is defined as C / n.

  An object of this invention is to provide the secondary battery excellent in the large current charging / discharging characteristic.

  The present inventors provide a non-aqueous electrolyte secondary battery including at least a positive electrode, a negative electrode, and an electrolyte, by using a sheet-like composite including at least a stable organic radical polymer and carbon for the positive electrode. The present inventors have found that a further increase in current can be realized and have completed the present invention.

  That is, the present invention provides a non-aqueous electrolyte secondary battery having at least a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode has a sheet-like composite containing at least a stable organic radical polymer and carbon. It is a water electrolyte secondary battery.

  The stable organic radical polymer preferably has a weight average molecular weight in the range of 20000 to 150,000.

  The main chain of the stable organic radical polymer is preferably one selected from the group consisting of poly (meth) acrylic acid, poly (meth) acrylamide polymers, and polyalkyl (meth) acrylates.

  It is preferable that the sheet composite is a gel containing at least the stable organic radical polymer, the carbon, and an organic solvent. The organic solvent preferably contains one or more selected from the group consisting of chain carbonates, cyclic carbonates, and lactones.

  As in the present invention, in a non-aqueous electrolyte secondary battery having at least a positive electrode, a negative electrode, and an electrolytic solution, the positive electrode has a sheet-like composite containing at least a stable organic radical polymer and carbon. With the electrolyte secondary battery, it is possible to obtain a secondary battery excellent in large current charge / discharge characteristics of about 50C.

[1] Stable Organic Radical Polymer In the present invention, an organic polymer in which the state where the spin concentration in the equilibrium state is 10 ²¹ spin / g or more continues for 1 second or longer is referred to as a stable organic radical polymer. Examples of such a stable organic radical polymer include a polymer having a nitroxyl radical, a polymer having an oxy radical, a polymer having a nitrogen radical, and the like, which can be appropriately selected from these. A polymer having plural kinds of radicals can also be used. A mixture of a plurality of types of polymers can also be used. Typical polymer structures are shown in Chemical Formulas 1 to 13 below.

  Such a stable organic radical polymer can be electrochemically reversibly oxidized and reduced, and can be used as an active material of a secondary battery. In addition, since there is no change in the polymer skeleton during this redox process, the redox reaction rate is high, and the secondary battery of the present invention using a sheet-like composite containing these polymers and carbon as the positive electrode is charged with a large current. Discharge is possible.

  The stable organic radical polymer preferably has a weight average molecular weight in the range of 20,000 to 150,000. By setting the weight average molecular weight to 20000 or more, it is difficult to dissolve in an organic solvent for forming a gel described later, and gelation is easy. Moreover, by setting it as 150,000 or less, it is easy to swell and gelatinize easily. More preferably, it is in the range of 50,000 to 100,000.

The main chain of the stable organic radical polymer is not particularly limited, but more preferably
Poly (meth) acrylic acid;
Poly (meth) acrylonitrile;
Poly (meth) acrylamide polymers such as poly (meth) acrylamide, polymethyl (meth) acrylamide, polydimethyl (meth) acrylamide, polyisopropyl (meth) acrylamide;
Polyalkyl (meth) acrylate polymers such as polymethyl (meth) acrylate, polyethyl (meth) acrylate, and polybutyl (meth) acrylate;
Fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene;
Vinyl polymers such as polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride, polyvinyl methyl ether, polyvinyl carbazole, polyvinyl pyridine, and polyvinyl pyrrolidone;
Polyethers such as polyethylene oxide, polypropylene oxide, polybutene oxide, polyoxymethylene, polyacetaldehyde, polymethyl vinyl ether, polypropyl vinyl ether, polybutyl vinyl ether, polybenzyl vinyl ether;
Polyesters such as polyethylene terephthalate, polyethylene adipate, polyethylene isophthalate, polyethylene naphthalate, polyethylene paraphenylene diacetate, polyethylene isopropylidene dibenzoate;
Polyurethanes such as polytrimethylene ethylene urethane;
Polyamine polymers such as polyethyleneamine, polyhexamethyleneamine, polyethylenetrimethyleneamine;
Etc. The polymer having the main chain is excellent in the ability to hold an organic solvent for forming a gel described later, and is easily gelled.

  Among these, one selected from the group consisting of poly (meth) acrylic acid, poly (meth) acrylamide polymers, and polyalkyl (meth) acrylates is more preferable in terms of excellent electrochemical resistance. . Polyalkyl (meth) acrylates are particularly preferred. The main chain is a carbon chain having the largest number of carbon atoms in the polymer molecule.

[2] Sheet Composite, Positive Electrode The positive electrode in the nonaqueous electrolyte secondary battery of the present invention has a sheet composite including at least a stable organic radical polymer and carbon. As a method for obtaining a sheet-like composite, for example, a slurry in which the above stable organic radical polymer is dissolved in a solvent and carbon particles are dispersed in the solution is prepared, and after applying the slurry on a current collector, the solvent is added. The method of evaporating is mentioned. After radiating ultrasonic waves to the slurry, it may be applied to the current collector. By emitting ultrasonic waves, the carbon particles are more easily dispersed. Further, a sheet-like composite can be obtained in the same manner by impregnating a porous sheet containing carbon with a solution obtained by dissolving the above stable organic radical polymer in a solvent and then evaporating the solvent.

  Such a sheet-like composite has high electron conductivity because there is no contact resistance between the particles as compared to a sheet prepared by simply mixing stable organic radical polymer particles and carbon particles. Therefore, a battery using a sheet-like composite as a positive electrode is excellent in charge / discharge characteristics at a large current.

  The mixing ratio of the stable organic radical polymer and carbon for forming the sheet-like composite is not particularly limited, but the weight ratio of the stable organic radical polymer to carbon is in the range of 20/80 to 90/10. Is preferable, and 60/40 to 80/20 is more preferable. When the weight ratio of the stable organic radical polymer is 20% or more, the ratio of the battery active material contained in the sheet-like composite increases, and the battery capacity increases. When the weight ratio of the stable organic radical polymer is 90% or less, that is, when the weight ratio of carbon is 10% or more, a network structure composed of carbon responsible for electronic conduction is easily formed in the sheet-like composite, and charging with a large current is possible. Discharge characteristics are improved.

  The thickness of the sheet composite is not particularly limited, but is preferably in the range of 5 μm to 400 μm. By setting it as 5 micrometers or more, the ratio of other members, such as a collector which occupies for a battery, becomes small, and the energy density of a battery increases. Moreover, by setting it as 400 micrometers or less, resistance of an electrode becomes small and a large current charging / discharging characteristic improves.

  The carbon contained in the sheet composite is preferably uniformly distributed throughout the sheet composite. Therefore, the shape of carbon is preferably a particle or a porous sheet.

  In the case of particles, the particle size is preferably in the range of 0.05 μm to 200 μm, more preferably in the range of 0.1 μm to 50 μm, and most preferably in the range of 0.5 μm to 5 μm. Particles having a particle size of 0.05 μm or more are less likely to aggregate and can be easily dispersed uniformly throughout the composite. Further, particles having a particle size of 200 μm or less are unlikely to settle even when mixed in the above solution, and can be easily dispersed uniformly throughout the sheet-like composite.

Also those DBP oil absorption among carbon particles is in the range of 70cm ³ / 100g~250cm ³ / 100g is particularly preferred. By using such a carbon material, the sheet-like composite is easily swelled.

  The shape of the particle is not particularly limited, but carbon having a secondary particle structure in which primary particles are arranged in a bead shape or fibrous carbon tends to form a network structure responsible for electronic conduction in the sheet-like composite. preferable. The carbon having the secondary particle structure and the fibrous carbon are aggregates, but the particle size is not so large and can be uniformly dispersed throughout the sheet composite. Examples of such a carbon material include carbon black such as acetylene black and ketjen black, vapor grown carbon fiber (VGCF), mesophase pitch carbon fiber, and carbon nanotube.

  Carbon porous sheets include activated carbon mixed with phenolic resin and pyrolytic resin, molded into a sheet and baked, and activated carbon fiber cloth obtained by carbonizing a woven fabric of phenolic fibers. It is done. The porous sheet preferably has a porosity in the range of 10% by volume to 90% by volume, more preferably 30% by volume to 80% by volume, in order to facilitate impregnation with a solution in which a stable organic radical polymer is dissolved in a solvent. Most preferably, it is in the range of 40% to 70% by volume.

  In order to increase the physical strength of the sheet-like composite, a binder such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, etc. is added. Also good. These binders are particularly preferably dissolved together in a solvent that dissolves the stable organic radical polymer and integrated into the sheet-like composite. Thereby, a binder can be uniformly distributed over the whole sheet-like composite.

[3] Gel When the sheet-like composite is immersed in an organic solvent, the stable organic radical polymer swells with the organic solvent to obtain a gel. By gelling a stable organic radical polymer that is a battery active material, ion diffusion in the active material accompanying the charge / discharge reaction is accelerated, and charge / discharge characteristics at a large current when a battery is formed are improved. Therefore, it is preferable that the sheet-like composite used for the positive electrode of the nonaqueous electrolyte secondary battery of the present invention is a gel containing at least a stable organic radical polymer, carbon, and an organic solvent.

  When the sheet-like composite is immersed in an organic solvent, the sheet-like composite may be heated in order to facilitate swelling. The heating temperature is preferably not higher than the boiling point of the organic solvent. When heated at a temperature higher than the boiling point of the organic solvent, the organic solvent evaporates and the sheet-like composite is less likely to swell. Moreover, you may immerse a sheet-like composite in an organic solvent under the pressure below atmospheric pressure.

  The organic solvent preferably contains at least one selected from the group consisting of chain carbonates, cyclic carbonates, and lactones. Since these organic solvents are excellent in oxidation resistance and reduction resistance, when a gel containing these organic solvents is used for the positive electrode, the charge / discharge cycle characteristics of the secondary battery are improved. The above organic solvents may be used alone or in combination of several kinds.

  In addition, it is particularly preferable that the electrolyte salt is dissolved in an organic solvent in advance and swelled with the organic solvent to give ion conductivity in the sheet composite. Although there is no restriction | limiting in particular in the electrolyte salt to dissolve, The same thing as the electrolyte salt contained in electrolyte solution is the most preferable in order to improve the ionic conductivity of a battery.

[4] Electrolytic Solution The electrolytic solution used for the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and conventionally known ones can be employed. The electrolytic solution is responsible for transporting the charge carriers between the electrodes, and generally has an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at 20 ° C. An electrolytic solution in which an electrolyte salt is dissolved in an organic solvent can be used.

  Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC); dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate ( EMC), chain carbonates such as dipropyl carbonate (DPC); or the like, aprotic organic solvents such as one or a mixture of two or more are used, and an electrolyte salt dissolved in these organic solvents is dissolved.

Examples of the electrolyte 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 , lithium salt of lower aliphatic carboxylic acid carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl and the like. In addition, quaternary ammonium salts such as tetraammonium tetrafluoroborate and tetraethylammonium tetrafluoroborate, quaternary phosphonium salts such as tetraethylphosphonium tetrafluoroborate and ethylmethylimidazolium tetrafluoroborate Imidazolium salts such as can be used. These electrolyte salts can be used alone or in combination of two or more.

[5] Negative Electrode The negative electrode active material used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and conventionally known materials can be employed. For example, natural graphite, petroleum coke, coal coke, pitch coke, carbon black, activated carbon, resin-fired carbon, organic polymer fired body, pyrolytic vapor-grown carbon fiber, mesocarbon microbead, mesophase pitch-based carbon fiber, polyacrylonitrile Carbon fiber, carbon material such as low-temperature calcined carbon, fullerene, carbon nanotube, metallic lithium, lithium alloy, lithium nitride, Li _3-x M _x N (0 <x <1, M = Co, Ni or Cu) and these These can be used, and these can be used alone or in combination of two or more.

  Among these, natural graphite, petroleum coke, coal coke, pitch coke, carbon black, activated carbon, resin-fired carbon, organic polymer fired body, pyrolytic vapor-grown carbon fiber, mesocarbon microbead, mesophase pitch-based carbon fiber, poly Carbon materials such as acrylonitrile-based carbon fiber, low-temperature calcined carbon, fullerene, and carbon nanotube are preferable because they can be charged and discharged with a large current.

  In the present invention, it is preferable to use the active material layer formed on the current collector as the negative electrode. Moreover, in order to strengthen the connection between these constituent materials, a binder can also be used. As a binder, the thing similar to what was shown to the sheet-like composite used for a positive electrode can be used.

[6] Current collector The current collector used for the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and conventionally known ones can be employed. Examples of the material include metals such as nickel, aluminum, copper, gold, silver, aluminum alloy, and stainless steel, and carbon materials. As the shape, for example, a foil, a plate, or a mesh 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.

[7] Separator A separator can be disposed between the positive electrode and the negative electrode in the non-aqueous electrolyte secondary battery of the present invention as necessary. About a separator, it does not specifically limit and a conventionally well-known thing is employable. For example, a polyolefin such as polypropylene or polyethylene, a porous film such as a fluororesin, or the like can be used.

[8] Stacked Form of Electrode In the present invention, the stacked form of the positive electrode and the negative electrode is not particularly limited, and any stacked form can be adopted, which is stacked on both surfaces of the multilayer stacked body and the current collector. The form which combined these, Furthermore, it can be set as the form which wound these.

[9] Shape of Battery The shape and appearance of the battery of the present invention are not particularly limited, and conventionally known ones can be adopted. Examples of such battery shapes include those in which 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. . Examples of the external appearance of the battery include a cylindrical shape, a square shape, a coin shape, and a sheet shape.

  Hereinafter, the present invention will be specifically described by way of examples.

Example 1
[Positive electrode]
5.5 g of a homopolymer consisting of a repeating unit represented by the chemical formula 1 (particle size 20 μm, weight average molecular weight 89000 (measured by gel permeation chromatography)) and 0.5 g of polyvinylidene fluoride are dissolved in 60 g of n-methylpyrrolidone. is an average particle diameter of 5μm to the solution, the specific surface area of 300m ² / g, DBP oil absorption amount were mixed acetylene black 4.5g of 140cm ^3/100 g, to prepare a slurry. The slurry was irradiated with ultrasonic waves of 40 kHz for 30 minutes, and then applied to a thickness of 70 μm on a 20 μm thick aluminum current collector using a doctor blade, and dried at 125 ° C. to obtain n-methylpyrrolidone. Evaporated into a sheet composite. The sheet-like composite of ethylene carbonate / diethyl carbonate mixed solution containing LiPF ₆ electrolytic salt 1 mol / l (EC and DEC mixing ratio 3: 7 (volume ratio)) in the, 40 ℃, 66.6hPa conditions The gel was prepared by being immersed in and left to stand for 20 minutes and used as a positive electrode.

[Negative electrode]
A slurry obtained by dispersing artificial graphite, styrene butadiene rubber, and cellulose in water on a copper foil was applied, dried, and then compressed with a roller, and used as a negative electrode.

[Electrolyte]
An ethylene carbonate / diethyl carbonate mixed solution (mixing ratio of EC and DEC 3: 7 (volume ratio)) containing 0.9 mol / l LiPF ₆ electrolyte salt was used.

[Create battery]
The above positive electrode and negative electrode were overlapped via a separator, housed in a stainless steel outer can, and sealed to produce a coin-type secondary battery.

(Example 2)
[Positive electrode]
5.5 g of a homopolymer consisting of repeating units represented by the chemical formula 1 (particle size 20 μm, weight average molecular weight 89000 (measured by gel permeation chromatography)) and 0.5 g of polyvinylidene fluoride were dissolved in 100 g of tetrahydrofuran. The solution was impregnated into 4.5 g of an activated carbon sheet (thickness 70 μm) having a porosity of 60% by volume, and then tetrahydrofuran was evaporated to obtain a sheet-like composite. This composite was immersed in an ethylene carbonate / diethyl carbonate mixed solution (EC / DEC mixing ratio 3: 7 (volume ratio)) containing 1 mol / l LiPF ₆ electrolyte salt at 40 ° C. and 66.6 hPa. The gel was prepared by leaving it to stand for 20 minutes and used as a positive electrode.

  Other than that, a coin-type secondary battery was fabricated in the same manner as in Example 1.

(Example 3)
[Positive electrode]
5.5 g of a homopolymer consisting of a repeating unit represented by the chemical formula 1 (particle size 20 μm, weight average molecular weight 89000 (measured by gel permeation chromatography)) and 0.5 g of polyvinylidene fluoride are dissolved in 60 g of n-methylpyrrolidone. is an average particle diameter of 5μm to the solution, the specific surface area of 300m ² / g, DBP oil absorption amount were mixed acetylene black 4.5g of 140cm ^3/100 g, to prepare a slurry. The slurry was irradiated with ultrasonic waves of 40 kHz for 30 minutes, and then applied to a thickness of 70 μm on a 20 μm thick aluminum current collector using a doctor blade, and dried at 125 ° C. to obtain n-methylpyrrolidone. Evaporated into a sheet composite. This sheet composite was used as a positive electrode.

  Other than that, a coin-type secondary battery was fabricated in the same manner as in Example 1.

(Comparative Example 1)
[Positive electrode]
Disperse 5.0 g of a homopolymer (particle size 20 μm, weight average molecular weight 89000 (measured by gel permeation chromatography)) and 0.5 g of a styrene-butadiene copolymer in water, which is a repeating unit represented by Chemical Formula 1, the thickness of a specific surface area in the dispersion 300m ² / g, after DBP oil absorption was mixed with acetylene black 4.5g of 140cm ³ / 100g, 70μm in thickness 20μm aluminum current collector on the body with a doctor blade And heated at 80 ° C. to evaporate water to obtain a positive electrode.

  Other than that, a coin-type secondary battery was fabricated in the same manner as in Example 1.

(Comparative Example 2)
[Positive electrode]
5.5 g of a homopolymer consisting of a repeating unit represented by the chemical formula 1 (particle size 20 μm, weight average molecular weight 89000 (measured by gel permeation chromatography)) and 0.5 g of polyvinylidene fluoride are dissolved in 60 g of n-methylpyrrolidone. Then, 4.5 g of gold powder having an average particle diameter of 2 μm was mixed with the solution to prepare a slurry. This slurry was applied to a thickness of 70 μm on a 20 μm thick aluminum current collector using a doctor blade and dried at 125 ° C. to evaporate n-methylpyrrolidone to obtain a sheet composite. This sheet composite was placed in an ethylene carbonate / diethyl carbonate mixed solution containing 1 mol / l LiPF6 electrolyte salt (mixing ratio of EC and DEC 3: 7 (volume ratio)) at 40 ° C. and 66.6 hPa. The gel was prepared by being immersed and left for 20 minutes, and used as a positive electrode.

  Other than that, a coin-type secondary battery was fabricated in the same manner as in Example 1.

  The produced coin-type secondary battery was charged and discharged at a constant current in a voltage range of 2V to 4V.

  Table 1 shows the ratio of 50 C discharge capacity to 1 C discharge capacity. Here, the 1C discharge is a discharge at a constant current that completes the discharge in one hour. A 50C discharge is a discharge at a current 50 times that of a 1C discharge.

  As described above, the nonaqueous electrolyte secondary batteries of the present invention produced in Examples 1, 2, and 3 are secondary batteries having a large ratio of 50 C discharge capacity to 1 C discharge capacity and excellent large current charge / discharge characteristics. I understood.

Claims (5)

  A non-aqueous electrolyte secondary battery having at least a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode has a sheet-like composite containing at least a stable organic radical polymer and carbon. Next battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the stable organic radical polymer has a weight average molecular weight in the range of 20000 to 150,000.   The main chain of the stable organic radical polymer is one selected from the group consisting of poly (meth) acrylic acid, poly (meth) acrylamide polymers, and polyalkyl (meth) acrylates. Item 3. The nonaqueous electrolyte secondary battery according to Item 1 or 2.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the sheet-like composite is a gel including at least the stable organic radical polymer, the carbon, and an organic solvent.   The non-aqueous electrolyte secondary battery according to claim 4, wherein the organic solvent contains one or more selected from the group consisting of chain carbonates, cyclic carbonates, and lactones.