JPWO2006082708A1 - Positive electrode for secondary battery, method for producing the same, and secondary battery - Google Patents

Abstract

In order to provide a positive electrode for a secondary battery having a low electrical resistance and a high mechanical strength, and a secondary battery that can be charged and discharged using a large current and has a large capacity and excellent storage characteristics. A positive electrode for a secondary battery having an active material layer containing at least a carbon fiber having an interlayer distance d002 in the range of 0.335 nm to 0.340 nm is used. The carbon fiber having such an interlayer distance has a tensile elastic modulus in the range of 200 GPa or more and 800 GPa or less, and in particular, the volume resistivity of the carbon fiber is preferably in the range of 200 μΩ · cm or more and 2000 μΩ · cm or less, The carbon fiber is preferably a graphitized carbon fiber having a vapor-grown carbon fiber or mesophase pitch as a precursor.

Description

  The present invention relates to a positive electrode for a secondary battery, a method for producing the same, and a secondary battery. More specifically, in the positive electrode for a secondary battery containing a radical compound, the electrical resistance of the positive electrode is reduced and the mechanical strength is improved. The present invention relates to a positive electrode for a secondary battery, a manufacturing method thereof, and a secondary battery.

  With the rapid market expansion of notebook personal computers, mobile phones, electric vehicles, etc., high capacity, high energy density, and high stability are required for power storage devices used for these. In order to satisfy these requirements, secondary batteries using various materials have been proposed as power storage devices.

  For example, in Patent Document 1 below, as a secondary battery having high energy density, high capacity, and excellent stability, a nitroxyl radical compound, an oxy radical compound, an aryloxy radical compound, and an aminotriazine are formed on an active material layer of a positive electrode. A lithium secondary battery using a radical compound such as a polymer compound having a structure has been proposed.

  Further, in Patent Document 2 below, as a secondary battery having a high energy density and usable at a large current, a nitroxyl compound having a nitroxyl cation partial structure in an oxidized state and a nitroxyl radical partial structure in a reduced state is used as a positive electrode. There has been proposed a lithium secondary battery that is contained in the active material layer and uses an electron transfer reaction between an oxidized state and a reduced state as an electrode reaction of the positive electrode.

  In Patent Document 3 below, as a secondary battery having a high energy density, a large capacity and a stability, at least a positive electrode, a negative electrode, and an electrolyte are used as constituent elements, and a radical is generated in at least one of an electrochemical oxidation reaction and a reduction reaction. There has been proposed a lithium secondary battery that includes particles containing an organic compound that generates a compound as an active material, and in which the active material layer for the positive electrode is formed of a composite that includes at least two regions having a composition.

Patent Document 4 listed below discloses an active material layer containing a disulfide group as a secondary battery that improves the conductivity and mechanical strength of an electrode, and the S—S bond of the disulfide group is electrochemically reduced. There has been proposed a lithium secondary battery using a conductive matrix that is cleaved by, and regenerated by electrochemical oxidation, as an active material layer of a positive electrode. In this lithium secondary battery, carbon nanotubes are dispersed in a conductive matrix.
Japanese Patent Laid-Open No. 2002-151084 JP-A-2002-304996 Japanese Patent Laid-Open No. 2002-298850 JP 11-329414 A

  However, in the lithium secondary batteries described in Patent Documents 1 to 3, since the radical compound contained in the active material layer has low conductivity, there is a problem that the electrode resistance of the active material layer is increased. In addition, since such an active material layer has a relatively low mechanical strength, the active material layer may be cracked, and as a result, the electrode resistance of the active material layer may be increased. A lithium secondary battery having an active material layer having a high electrical resistance is likely to have a problem that the capacity of the battery is insufficient particularly during charging / discharging with a large current, and therefore, a solution is required.

  Furthermore, since the lithium secondary batteries described in Patent Documents 1 to 3 have low mechanical strength, the active material layer may drop from the current collector during storage without charging or discharging the lithium secondary battery. The charge / discharge capacity (referred to as storage characteristics) of the active material layer during storage may be reduced.

  On the other hand, in the lithium secondary battery described in Patent Document 4, since the regeneration efficiency of the cleaved SS bond is small during the electrochemical reaction during charge and discharge, the radical compound described in Patent Documents 1 to 3 is used. Compared to the lithium secondary battery used for the active material layer, the stability during charging and discharging is poor. For this reason, the lithium secondary battery described in Patent Document 4 has a problem that it is difficult to use as a large-capacity secondary battery capable of charging and discharging using a large current, and a solution to this problem is required. It was.

  The present invention has been made to solve the above problems, and a first object thereof is to provide a positive electrode for a secondary battery having a low electrode resistance and a high mechanical strength, and a method for manufacturing the same. . A second object of the present invention is to provide a secondary battery having a large capacity and excellent storage characteristics that enables charging / discharging using a large current.

Secondary battery positive electrode of the present invention for solving the above problems includes a radical compound, the average value of the interlayer distance d ₀₀₂ of the graphite structure is a carbon fiber in the range of 0.340nm than 0.335nm least It has an active material layer.

According to the present invention, since the radical compound and the carbon fiber are included, it is considered that the interface resistance between the two is remarkably lowered, and the conductivity of the active material layer containing them can be increased. As a result, a positive electrode for a secondary battery having a low electric resistance can be configured. Further, in the range the average value is less 0.340nm than 0.335nm interlayer distance d ₀₀₂ of the graphite structure of the carbon fiber contained in the active material layer, since carbon fiber mechanical strength within the range is large, The mechanical strength of the active material layer containing such carbon fibers can be increased. As a result, a positive electrode for a secondary battery having an active material layer having high conductivity without cracking or falling off can be formed. Moreover, since the active material layer of the positive electrode for secondary batteries of the present invention contains a radical compound, a secondary battery using the positive electrode for secondary batteries can have a large capacity.

In the positive electrode for a secondary battery of the present invention, it is preferable that a tensile elastic modulus of the carbon fiber is in a range of 200 GPa to 800 GPa.

Carbon fiber in the range the average value is less 0.340nm than 0.335nm interlayer distance d ₀₀₂ of the above-described graphite structure is generally the tensile modulus has a large value in the range of less 800GPa least 200 GPa. According to the present invention, the mechanical strength of the active material layer containing such carbon fibers and the positive electrode for a secondary battery including the active material layer can be increased.

  In the positive electrode for a secondary battery of the present invention, the volume resistivity of the carbon fiber is preferably in the range of 200 μΩ · cm to 2000 μΩ · cm.

  According to this invention, since the volume resistivity of the carbon fibers contained in the active material layer is in the range of 200 μΩ · cm to 2000 μΩ · cm, the conductivity of the active material layer containing such carbon fibers is increased. As a result, the electrode resistance of the secondary battery positive electrode provided with such an active material layer can be reduced.

  In the positive electrode for a secondary battery of the present invention, the carbon fiber is preferably a vapor growth carbon fiber.

  According to this invention, since the carbon fiber is a vapor-grown carbon fiber excellent in dispersibility, the dispersibility of the carbon fiber in the radical compound at the time of producing the active material layer can be improved. As a result, an active material layer having uniform characteristics in each part and a secondary battery positive electrode including the active material layer can be easily obtained.

  Moreover, in the positive electrode for secondary batteries of this invention, it is preferable that the said carbon fiber graphitizes the carbon fiber which makes a mesophase pitch a precursor. The mesophase pitch is a polycyclic aromatic compound contained in coal tar or petroleum pitch having a uniform optical anisotropy by causing a polycondensation reaction by heating or the like. By firing carbon fibers having mesophase pitch as a precursor at a temperature of 2600 ° C. to 3000 ° C., carbon fibers having an extremely high degree of graphitization can be obtained. Since carbon fiber with such high graphitization degree is excellent in electrical conductivity and mechanical strength, when it is used for the positive electrode, it is easy to obtain a positive electrode for a secondary battery with low resistance and excellent mechanical strength. Can do.

  In the positive electrode for a secondary battery of the present invention, the content ratio of the carbon fiber in the active material layer is preferably in the range of 10% by weight to 50% by weight.

  According to this invention, since the carbon fiber content in the active material layer is 10% by weight or more, the mechanical strength of the active material layer can be increased, and as a result, the positive electrode for secondary battery of the present invention. The mechanical strength of can be increased. Moreover, since the content ratio of the carbon fiber in the active material layer is 50% by weight or less, the content ratio of the radical compound in the active material layer can be relatively increased, and as a result, the secondary battery of the present invention. The secondary battery using the positive electrode for the battery can have a large capacity.

  In the secondary battery positive electrode of the present invention, the radical compound preferably contains at least one of a nitroxyl radical compound, an oxy radical compound, and a nitrogen radical compound. In particular, in the nitroxyl radical compound, poly ( 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), poly (4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), or poly (4 -Vinyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) is preferable.

A method for producing a positive electrode for a secondary battery according to the present invention for solving the above problem is a method for producing a positive electrode for a secondary battery having an active material layer containing at least a radical compound and carbon fiber, in containing solvent, characterized by having a step of average value of the interlayer distance d ₀₀₂ of the graphite structure to disperse the carbon fibers in the range of 0.340nm than 0.335 nm.

  According to the present invention, a positive electrode for a secondary battery having a low electrical resistance and a high mechanical strength can be produced.

  In the manufacturing method of the positive electrode for secondary batteries of this invention, it is preferable to disperse | distribute so that the content rate of the said carbon fiber in an active material layer may be in the range of 10 to 50 weight%.

  According to this invention, since the content ratio of the carbon fiber in the active material layer is dispersed so as to be within the above range, an active material layer in which electric resistance and mechanical properties are uniform in each part can be formed, and as a result. In addition, a positive electrode for a secondary battery having a low electrical resistance and a high mechanical strength can be produced.

  The secondary battery of the present invention for solving the above problems is a secondary battery comprising at least a positive electrode, a negative electrode and an electrolyte solution, wherein the positive electrode is the above-described positive electrode for a secondary battery according to the present invention. Features.

  According to the present invention, since the secondary battery positive electrode including a radical compound and having an active material layer having a low electrode resistance and a large mechanical strength is provided, charging / discharging using a large current is possible, and a large capacity is stored. A secondary battery having excellent characteristics can be obtained.

  As described above, according to the positive electrode for secondary battery of the present invention, since the conductivity of the active material layer is increased and neither cracking nor dropping occurs, the positive electrode for secondary battery having low electrical resistance and high mechanical strength is obtained. Can be configured. Moreover, since the active material layer of the positive electrode for secondary batteries of the present invention contains a radical compound, a secondary battery using the positive electrode for secondary batteries can have a large capacity.

  In addition, according to the method for manufacturing a positive electrode for a secondary battery of the present invention, an active material layer having uniform electrical resistance and mechanical characteristics in each part can be formed, so that the secondary battery has a low electrical resistance and a high mechanical strength. A positive electrode can be manufactured.

  Further, according to the secondary battery of the present invention, since the secondary battery positive electrode having a large mechanical strength is provided, the storage characteristics due to the increase in the electrode resistance due to the crack of the active material layer and the falling off of the active material layer. Can be prevented. In addition, the secondary battery of the present invention includes a positive electrode for a secondary battery that includes a radical compound and has an active material layer having a low electrode resistance and a large mechanical strength, so that charge / discharge using a large current is possible, A secondary battery having a large capacity and excellent storage characteristics can be obtained.

It is a schematic cross section which shows an example of the secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Positive electrode collector 4 Negative electrode collector 5 Electrolyte 6 Positive electrode outer can 7 Negative electrode outer can 8 Insulation packing part 10 Lithium secondary battery 11 Positive electrode 12 Negative electrode 13 Separator

  Below, the positive electrode for secondary batteries of this invention, its manufacturing method, and a secondary battery are demonstrated.

(Positive electrode for secondary battery)
Secondary battery positive electrode of the present invention, comprises a radical compound, containing at least an active material layer and the carbon fiber in the range the average value is less 0.340nm than 0.335nm interlayer distance d ₀₀₂ of the graphite structure Yes. Such an active material layer is usually formed on a current collector and constitutes a part of a positive electrode for a secondary battery. The current collector is not particularly limited, and a common material and shape are preferably used. Examples of the current collector material include various materials such as aluminum, nickel, an aluminum alloy, a nickel alloy, and carbon. The shape of the current collector material includes, for example, a foil, a flat plate, and a mesh. Things can be mentioned.

(Radical compound)
A radical compound is a compound which comprises an active material layer as an active material. A radical compound is a compound having a free radical (that is, a radical) having an unpaired electron. The radical compound constituting the present invention has a high radical density and a spin concentration in an equilibrium state of 10 ²¹ spin / g or more. A state continues for 1 second or longer. Moreover, it is preferable that the charge state of the radical compound which comprises this invention is electrically neutral from the point of the ease of charging / discharging reaction.

  Since radicals have spin nuclear momentum, the radical density (unpaired electron density) is equal to the spin concentration. Here, the spin concentration is a value obtained by, for example, the following method from the absorption area intensity of an electron spin resonance spectrum (hereinafter referred to as ESR spectrum). First, a sample to be used for measuring the ESR spectrum is ground and ground with a mortar or the like. 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 crushed sample is filled into a quartz glass capillary having an inner diameter of 2 mm or less, preferably 1 to 0.5 mm, degassed to 1.33 to 0.67 kPa (10 to 5 mmHg) or less, and sealed. Measure the spectrum. The ESR spectrum can be 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. In the present invention, any measuring instrument and measurement condition are applicable as long as the spin concentration can be measured correctly.

  Examples of the radical compound include a polymer nitroxyl radical compound, a polymer oxy radical compound, and a polymer hydrazyl radical compound. In the present invention, at least one or more of these radical compounds can be used as the active material.

Among the above radical compounds, a polymer nitroxyl radical compound, that is, a polymer having nitroxyl is most preferably used. Nitroxyl is particularly preferable as an active material because of its extremely high stability due to the delocalization of radicals. Typical examples of the polymer nitroxyl radical compound include A-1 to A-8 of the following chemical structural formula. In these high-molecular nitroxyl radical compounds, the respective radicals are further stabilized by steric hindrance by nearby bulky substituents and resonance structures. In addition, poly (meth) acrylic acid, polyalkyl (meth) acrylates, polyvinyl ethers, and poly (meth) acrylamide polymers as the polymer main chain have high oxidation resistance and reduction resistance and are electrochemically stable. Is particularly preferable. In the formula, R _{1 to} R ₅ each independently represents an alkyl group, and as the alkyl group, a methyl group, an ethyl group, or the like is used. In particular, the methyl group has electrochemical stability and capacity. It is preferably used because of its size.

The polymer oxyradical compound is a polymer having an oxyradical, and typical examples thereof include A-9 to A-11 of the following chemical structural formulas. The high molecular hydrazyl radical compound is a polymer having a hydrazyl radical, and examples thereof include A-12 and A-13 having the following chemical structural formula. In the formula, R _{1 to} R ₆ each independently represents an alkyl group, and as the alkyl group, a methyl group, an ethyl group, or the like is used. In particular, the methyl group is electrochemically stable and has a large capacity. Therefore, it is preferably used.

(Carbon fiber)
Carbon fiber of the present invention is one in which the average value of the interlayer distance d ₀₀₂ of the graphite structure is in the range of 0.340nm than 0.335 nm. In the present invention, since such carbon fibers are contained in the active material layer, it is considered that the interface resistance with the above-described radical compound is remarkably lowered, and the conductivity of the active material layer containing these can be increased.

In the present invention, the average value of the interlayer distance d ₀₀₂ of the graphite structure of the carbon fibers can be obtained, for example, from X-ray diffraction. Specifically, it can be represented by an analysis result of an X-ray diffraction peak appearing as an average value of individual interlayer distances _d002 in the graphite structure of carbon fiber. Since the carbon fiber having an interlayer distance within the above range has a large mechanical strength (for example, tensile elastic modulus), the mechanical strength of the active material layer can be increased. As a result, the active material layer is free from cracking and falling off, and a positive electrode for a secondary battery having a highly conductive active material layer can be configured.

The average value is larger than 0.340nm interlayer distance d ₀₀₂ of the graphite structure of carbon fiber, for mechanical strength (such as tensile modulus) is insufficient, the mechanical strength of the active material layer contains carbon fibers There may be a shortage. On the other hand, the interlayer distance d ₀₀₂ of an ideal graphite structure is 0.335 nm, the carbon fiber having an interlayer distance of less than 0.335 nm are not present.

The tensile modulus of carbon fiber is preferably in the range of 200 GPa to 800 GPa. Carbon fiber average value of the interlayer distance d ₀₀₂ of the above-described graphite structure is in the range of 0.340nm than 0.335nm is usually the tensile modulus has a large value in the range of less 800GPa least 200 GPa. The active material layer containing such carbon fibers has high mechanical strength, and can increase the mechanical strength of the positive electrode for a secondary battery. If the tensile modulus of the carbon fiber is less than 200 GPa, the mechanical strength of the carbon fiber-containing active material layer may be insufficient because the mechanical strength is insufficient. On the other hand, the upper limit of the tensile elastic modulus of the carbon fiber was set to 800 GPa from the viewpoint of the production cost of the carbon fiber. In addition, the definition and measurement method of the tensile elasticity modulus of carbon fiber are based on JISR7601-1986 (carbon fiber test method).

  The active material layer containing the carbon fiber described above has a feature that the mechanical strength is increased, but in the present invention, the volume resistivity of the carbon fiber is in the range of 200 μΩ · cm to 2000 μΩ · cm. Is preferred. When carbon fibers having a volume resistivity in such a range are included in the active material layer, the conductivity of the active material layer is increased. As a result, the electrode resistance of the positive electrode for secondary batteries provided with the active material layer can be lowered. The lower limit of the volume resistivity of the carbon fiber was set to 200 μΩ · cm from the viewpoint of the production cost of the carbon fiber. On the other hand, when the volume resistivity of the carbon fiber exceeds 2000 μΩ · cm, the electrode resistance of the positive electrode may not be sufficiently lowered. In addition, also about the definition and measuring method of the volume resistivity of carbon fiber, it is based on JISR7601-1986 (carbon fiber test method) similarly to said tensile elasticity modulus.

  Although the kind of carbon fiber is classified according to the production method, the carbon fiber applicable to the present invention is not particularly limited, and various kinds of carbon fibers satisfying the above characteristics can be used. For example, using PAN carbon fiber obtained by carbonizing polyacrylonitrile (PAN) precursor, pitch obtained when refining petroleum or coal as a precursor, obtained by carbonizing and graphitizing this. Vapor-Grown Carbon Fibers (VGCF) obtained by growing fibers on a substrate in a reactor using a pitch-type carbon fiber, hydrocarbon-based steam, and arc discharge between graphite electrodes Carbon nanotubes (CNTs) obtained by the arc discharge method that has been used can be used. These may be used alone or in combination of two or more.

  When forming an active material layer using such a carbon fiber, a process of dispersing the carbon fiber in a radical compound in a solvent is performed. In particular, vapor grown carbon fiber (VGCF) is excellent in dispersibility at that time. Therefore, it is most preferably used.

  Also, mesophase pitch carbon fiber obtained by carbonizing and graphitizing mesophase pitch with optical anisotropy among the pitches obtained when refining petroleum and coal is used as the electrical conductivity. Particularly preferred because of its excellent mechanical strength. Further, it is preferable to use a precursor obtained by adding boron in the range of 10 to 50 ppm to the mesophase pitch, since graphitization is more likely to proceed.

  Although the size of the carbon fiber is not particularly limited, in the present invention, a fiber-like fiber having an average length of 10 μm to 200 μm and an average diameter of 0.4 μm to 4 μm is usually because of good dispersibility. Preferably used. Here, the average length and the average diameter are an average value of lengths and an average value of diameters when 1000 or more carbon fibers are observed with an electron microscope or the like.

(Active material layer)
The active material layer is formed on the current collector to constitute the positive electrode for a secondary battery of the present invention, and includes at least the radical compound and the carbon fiber.

  The active material layer preferably contains carbon fibers in a proportion in the range of 10 wt% to 50 wt%. By containing carbon fiber in this proportion in the active material layer, the mechanical strength of the active material layer can be increased and the electrical resistance can be decreased. When the content ratio of the carbon fiber in the active material layer is less than 10% by weight, the active material layer may be cracked or dropped, and the mechanical strength may be insufficient. On the other hand, when the content ratio of the carbon fiber in the active material layer exceeds 50% by weight, the ratio of the radical compound that functions as the active material is relatively decreased. Therefore, the positive electrode having the active material layer is used. The capacity of the secondary battery will be reduced.

  In addition, the active material layer which comprises the positive electrode for secondary batteries which concerns on this invention has the phenomenon that the electroconductivity becomes high remarkably when carbon fiber is contained. The cause is considered to be that the interface resistance between the radical compound and the carbon fiber is lowered because the energy barrier at the time of charge transfer between the radical compound and the carbon constituting the carbon fiber is substantially the same.

  Such a phenomenon is a remarkable effect obtained by the combination of the radical compound and the carbon fiber, and the present inventor is active when other conductors such as gold, silver, copper, etc. are used instead of the carbon fiber. It has been confirmed that the conductivity of the material layer does not increase.

  In the active material layer described in Patent Document 4 (active material layer in which carbon nanotubes are dispersed in a conductive matrix containing a disulfide group), silver, gold, copper, or the like having conductivity equivalent to that of carbon nanotubes is used. Even in the case where an active material layer is formed by dispersing them instead of carbon nanotubes, the active material layer is different from the active material layer used in the present invention in that the conductivity of the active material layer is similarly increased.

(Method for producing positive electrode for secondary battery)
Next, the manufacturing method of the positive electrode for secondary batteries is demonstrated. The method for producing a positive electrode for a secondary battery according to the present invention is a method for producing a positive electrode for a secondary battery having an active material layer containing at least a radical compound and carbon fiber. Specifically, in a solvent containing a radical compound, the average value of the interlayer distance d ₀₀₂ of the graphite structure is characterized by having a step of dispersing the carbon fibers in the range of 0.340nm than 0.335 nm.

  First, a solution in which the radical compound is dissolved in a solvent is prepared, the carbon fiber and a binder (also referred to as a binder) are mixed with the solution, and an ultrasonic wave is radiated to the mixed solution. A slurry is obtained by dispersing the carbon fibers therein. Next, after applying the slurry to a predetermined thickness on the current collector, the positive electrode for a secondary battery having an active material layer can be manufactured by evaporating the solvent.

  As the solvent, n-methylpyrrolidone (NMP), tetrahydrofuran (THF), toluene and the like can be used. These may be used alone or in combination of two or more.

  As the binder, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, or the like can be used. These may be used alone or in combination of two or more. The ratio of the binder contained in the active material layer is preferably in the range of 1% by weight to 10% by weight. When the ratio of the binder in the active material layer is less than 1% by weight, the adhesion between the formed active material layer and the current collector is poor, and peeling may occur. On the other hand, when the proportion of the binder in the active material layer exceeds 10% by weight, the proportion of the radical compound or carbon fiber in the active material layer is relatively lowered, and therefore the secondary using the positive electrode according to the present invention. The capacity of the battery may be reduced, and the mechanical strength of the active material layer may be insufficient.

  As another method for producing a positive electrode for a secondary battery, the radical compound is dissolved in a solvent, the solution is impregnated into a sheet made of the carbon fiber, and then the solvent is evaporated to thereby form an active material layer. The positive electrode for secondary batteries which has can be manufactured. In this case, since the function as the current collector is borne by the sheet in which the carbon fibers are entangled, the binder as described above is not included.

(Secondary battery)
Next, the secondary battery of the present invention will be described. The secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolytic solution, and the positive electrode for a secondary battery is used as the positive electrode. In this secondary battery, since the above-described positive electrode for a secondary battery according to the present invention is used, an increase in electrode resistance due to cracking of the active material layer and a deterioration in storage characteristics due to dropping of the active material layer. Can be suppressed. In addition, the active material layer of the positive electrode includes a radical compound that functions as an active material and has low electrode resistance, so that the charge / discharge capacity at a large current can be increased. Therefore, the secondary battery can be charged / discharged using a large current, has a large capacity and excellent storage characteristics.

  In this invention, it does not specifically limit about the lamination | stacking form of a positive electrode and a negative electrode, Arbitrary lamination | stacking forms are employable. For example, it can be set as the form which combined what laminated | stacked the multilayer laminated body and the both surfaces of the electrical power collector, and also wound these.

  The shape of the secondary battery of the present invention is not particularly limited, and a conventionally known battery can be used. For example, a coin type, a cylindrical type, a square type, a sheet type, and the like can be used.

  FIG. 1 is a schematic cross-sectional view of a coin-type secondary battery showing an example of the secondary battery of the present invention. A coin-type secondary battery 10 shown in FIG. 1 has a positive electrode 11 composed of an active material layer 1 and a current collector 3, and a negative electrode 12 composed of an active material layer 2 and a current collector 4, and the positive electrode 11 and the negative electrode A porous separator 13 for preventing electrical connection between the two is sandwiched between the two. The positive electrode 11, the negative electrode 12, and the separator 13 are immersed in the electrolytic solution 5, and are configured in a state where they are sealed in the positive electrode outer can 6 and the negative electrode outer can 7 by the insulating packing portion 8.

As in the positive electrode, the negative electrode is obtained by forming an active material layer for a negative electrode on a current collector, and the active material layer includes an active material for the negative electrode. The active material for the negative electrode is not particularly limited, and conventionally known materials can be used as long as the redox potential is lower than that of the positive electrode. 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 Any of carbon materials such as carbon fiber, fullerene, and carbon nanotube can be used. Further, metallic lithium, lithium alloy, lithium nitride, Li _3−x M _x N (where x is 0 <x <1, and M is at least one element selected from Co, Ni, and Cu) Li-based material can also be used. These materials may be used alone or in combination of two or more.

  As the current collector, one made of any material of copper, silver, copper alloy, silver alloy, and carbon can be used. Examples of the shape of the current collector include a foil shape, a flat plate shape, and a mesh shape. Examples of a method for forming an active material layer containing a negative electrode active material on a current collector include a method of applying a mixture of a negative electrode active material and a binder onto the current collector. Can do.

  The binder is not particularly limited, and conventionally known binders can be used. For example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer can be used. A polymer can be mentioned. These materials may be used alone or in combination of two or more. In particular, when metallic lithium or a lithium alloy is used as the active material of the negative electrode, the entire negative electrode can be formed of the same material by using the same current collector.

As the electrolytic solution, an electrolytic solution in which an electrolyte salt is dissolved is used. The materials used for these are not particularly limited, and conventionally known materials can be employed. The electrolytic solution desirably has an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at 20 ° C.

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. , Etc. can be selected and used. Other electrolyte salts include quaternary ammonium salts such as tetraammonium tetrafluoroborate and tetraethylammonium tetrafluoroborate, quaternary phosphonium salts such as tetraethylphosphonium tetrafluoroborate, and tetrafluoroboric acid. A salt selected from imidazolium salts such as ethylmethylimidazolium, and the like can be used. These materials may be used alone or in combination of two or more.

  The electrolyte solution solvent can dissolve the above electrolyte salt, and is arbitrarily selected according to the electrolyte salt to be used. Examples of the electrolyte 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), and ethyl methyl carbonate. (EMC), what mixed two or more types of chain carbonates, such as a dipropyl carbonate (DPC), can be used.

  The separator is not particularly limited, and conventionally known separators can be used. As a material for the separator, for example, a polyolefin such as polypropylene or polyethylene, a fluororesin, or the like can be used. As the shape of the separator, for example, a porous thin film is preferably used.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Example 1)
First, a positive electrode was produced. As a radical compound, poly (4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1) which is a cyclic nitroxyl structure-containing polymer represented by the chemical formula A-1 (all R _{1 to} R ₅ are methyl groups) -Oxyl) (PTME) was synthesized.

Synthesis example of cyclic nitroxyl structure-containing polymer: In a 100 ml eggplant flask equipped with a reflux tube, 20 g (0.089 mol) of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl monomer was added, Dissolved in 80 ml of dry tetrahydrofuran. Thereto was added 0.29 g (0.00187 mol) of azobisisobutyronitrile (AIBN) (monomer / AIBN = 50/1), and the mixture was stirred at 75 to 80 ° C. in an argon atmosphere. After reacting for 6 hours, it was allowed to cool to room temperature. The polymer was precipitated in hexane, separated by filtration, and dried under reduced pressure to obtain 18 g (yield 90%) of poly (2,2,6,6-tetramethylpiperidine methacrylate). Next, 10 g of the obtained poly (2,2,6,6-tetramethylpiperidine methacrylate) was dissolved in 100 ml of dry-treated dichloromethane. 100 ml of a dichloromethane solution of 15.2 g (0.088 mol) of m-chloroperbenzoic acid was added dropwise over 1 hour while stirring at room temperature. Further, after stirring for 6 hours, the precipitated m-chlorobenzoic acid was removed by filtration, and the filtrate was washed with an aqueous sodium carbonate solution and water, and then dichloromethane was distilled off. The remaining solid was pulverized, and the resulting powder was washed with diethyl carbonate (DEC), dried under reduced pressure, and poly (4-methacryloyloxy-), which is a cyclic nitroxyl structure-containing polymer represented by the chemical formula A-1. There were obtained 7.2 g of 2,2,6,6-tetramethylpiperidine-1-oxyl) (PTME) (yield 68.2%, brown powder). The structure of the obtained polymer was confirmed by IR. Moreover, as a result of measuring by GPC, the value of weight average molecular weight Mw = 89000 and dispersion degree Mw / Mn = 3.30 was obtained. The spin concentration determined by ESR spectrum was 2.48 × 10 ²¹ spin / g.

2800 carbon fibers grown on a substrate on which a radical compound composed of the above-mentioned cyclic nitroxyl structure-containing polymer, polyvinylidene fluoride as a binder (manufactured by Kureha Chemical), and benzene gas are thermally decomposed and sprayed with iron fine particles are sprayed. Vapor growth carbon fiber obtained by firing at 0 ° C. (average value of interlaminar distance d ₀₀₂ of graphite structure is 0.336 nm, tensile modulus is 700 GPa) so that the weight ratio is 4: 1: 5 Weighed and mixed them in the solvent n-methylpyrrolidone to make a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. The active material layer after drying did not crack or fall off from the current collector. The volume resistivity of the vapor grown carbon fiber was 300 μΩ · cm, the average length was 10 μm, and the average diameter was 0.5 μm.

  Next, a negative electrode was produced. For the negative electrode, artificial graphite (manufactured by Osaka Gas: MCMB25-28) and rubber-based binder (manufactured by Nippon Zeon: BM-400B) were dispersed in water at a weight ratio of 95: 5 to prepare a slurry. Using a blade, it was applied onto a copper foil having a thickness of 10 μm, dried at 80 ° C., and then compressed with a roller. The negative electrode active material layer thus obtained had a thickness of 20 μm. The active material layer after drying did not crack or fall off from the current collector.

As the electrolyte, one containing 0.9 mol / l LiPF ₆ as an electrolyte salt is used, and the electrolyte salt is dissolved in an electrolyte solvent composed of an ethylene carbonate / diethyl carbonate mixed solution (volume mixing ratio 3: 7). Made.

  The positive electrode and the negative electrode produced as described above are cut into a circular shape having a size of 12 mmφ, stacked with a 25 μm-thick porous polypropylene used as a separator, and stored in a stainless steel outer can. After the injection, it was sealed to produce a coin-type secondary battery having the form shown in FIG.

(Example 2)
The same radical compound as in Example 1, the same polyvinylidene fluoride as in Example 1, the same vapor grown carbon fiber as in Example 1, and acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) were used at 4: 1: A weight ratio of 3: 2 was weighed, and they were mixed in a solvent n-methylpyrrolidone to prepare a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. The active material layer after drying did not crack or fall off from the current collector. A coin-type secondary battery of Example 2 was fabricated in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Example 3)
A gas obtained by baking at 3000 ° C. the same radical compound as in Example 1, polyvinylidene fluoride as in Example 1, and carbon fiber grown on a substrate on which benzene gas was thermally decomposed and sprayed with iron fine particles. phase growth carbon fibers (average value of the interlayer distance d ₀₀₂ of the graphite structure is 0.335 nm, the tensile modulus was 800 GPa) and, the same acetylene black as in example 2, 4: 1: 1: weighing the weight ratio of 4 Then, they were mixed in n-methylpyrrolidone as a solvent to prepare a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. The active material layer after drying did not crack or fall off from the current collector. The volume resistivity of the above vapor-grown carbon fiber was 200 μΩ · cm, the average length was 10 μm, and the average diameter was 0.5 μm. A coin-type secondary battery of Example 3 was fabricated in the same manner as in Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

Example 4
As a radical compound, poly (4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1) which is a cyclic nitroxyl structure-containing polymer represented by chemical formula A-2 (R _{1 to} R ₄ are all methyl groups) -Oxyl) (PTAA) was synthesized.

Example of synthesis of cyclic nitroxyl structure-containing polymer: In a 100 ml eggplant flask equipped with a reflux tube, 10 g of 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl monomer was added and used as a catalyst in dry tetrahydrofuran Polymerization was performed at −20 ° C. for 48 hours using s-butyllithium to obtain 5.8 g of poly (4-acryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (yield 58). % Orange powder). The structure of the obtained polymer was confirmed by IR. Further, as a result of measurement by GPC, a value of weight average molecular weight Mw = 4300 was obtained. The spin concentration determined by ESR spectrum was 2.66 × 10 ²¹ spin / g.

The resulting radical compound comprising the cyclic nitroxyl structure-containing polymer, the same polyvinylidene fluoride as in Example 1, and benzene gas were pyrolyzed and carbon fibers grown on a substrate sprayed with iron fine particles were fired at 2500 ° C. It is allowed (the average value of the interlayer distance d ₀₀₂ of the graphite structure 0.337 nm, tensile modulus 500 GPa) obtained vapor-grown carbon fibers, and 4: 1: weigh the weight ratio of 5 them with solvent A slurry was prepared by mixing in some n-methylpyrrolidone. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. The active material layer after drying did not crack or fall off from the current collector. The volume resistivity of the vapor grown carbon fiber was 800 μΩ · cm, the average length was 20 μm, and the average diameter was 0.5 μm. A coin-type secondary battery of Example 4 was produced in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Example 5)
As a radical compound, poly (4-vinyloxy-2,2,6,6-tetramethylpiperidine-1-) which is a cyclic nitroxyl structure-containing polymer represented by chemical formula A-3 (R _{1 to} R ₄ are all methyl groups) Oxyl (PTVE) was synthesized.

Synthesis example of cyclic nitroxyl structure-containing polymer: Under argon atmosphere, 10.0 g of 2,2,6,6-tetramethylpiperidine-4-vinyl-1-oxyl (monomer) and 100 mL of dichloromethane were added to a 200 mL 3-neck round bottom flask. , Cooled to -78 ° C. Further, 280 mg (2 mmol) of boron trifluoride-diethyl ether complex was added to make it uniform, and then reacted for 20 hours. After completion of the reaction, the obtained solid was washed several times with methanol and vacuum dried to obtain poly (4-vinyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) ( PTVE) was obtained (yield 70%). The structure of the obtained polymer was confirmed by IR spectrum. Moreover, as a result of measuring the molecular weight of a DMF soluble part from GPC, the value of weight average molecular weight Mw = 89000 and dispersion degree Mw / Mn = 2.7 was obtained. The spin density determined by ESR spectrum was 3.05 × 10 ²¹ spin / g.

The radical compound comprising the cyclic nitroxyl structure-containing polymer thus obtained, the same polyvinylidene fluoride as in Example 1, benzene gas was pyrolyzed, and the carbon fiber grown on the substrate sprayed with iron fine particles was baked at 2300 ° C. Vapor-grown carbon fiber (average value of interlaminar distance d ₀₀₂ of graphite structure is 0.340 nm, tensile elastic modulus is 200 GPa) vapor-grown carbon fiber is measured at a weight ratio of 4: 1: 5 Then, they were mixed in n-methylpyrrolidone as a solvent to prepare a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. The active material layer after drying did not crack or fall off from the current collector. The volume resistivity of the vapor grown carbon fiber was 2000 μΩ · cm, the average length was 20 μm, and the average diameter was 0.5 μm. A coin-type secondary battery of Example 5 was produced in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Example 6)
And PTVE synthesized in the same manner as in Example 5, the same polyvinylidene fluoride as in Example 1, the mesophase pitch obtained by graphitizing carbon fibers and precursor (Petka Co., the average value of the interlayer distance d ₀₀₂ of the graphite structure 0.337 nm, tensile elastic modulus is 550 GPa, volume resistivity is 400 μΩ · cm, average length is 70 μm, average diameter is 0.6 μm), and they are weighed to a weight ratio of 4: 1: 5, and they are solvents n -Mixed in methylpyrrolidone to make slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The active material layer of the positive electrode obtained in this way was 135 μm thick. The active material layer after drying did not crack or fall off from the current collector. A coin-type secondary battery of Example 6 was produced in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Comparative Example 1)
The same radical compound as in Example 1, the same polyvinylidene fluoride as in Example 1, and the same acetylene black as in Example 2 were weighed in a weight ratio of 4: 1: 5, and these were used as a solvent, n-methylpyrrolidone To prepare a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. In the active material layer after drying, cracks and falling off from the current collector were observed. A coin-type secondary battery of Comparative Example 1 was produced in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Comparative Example 2)
The same radical compound as in Example 1, the same polyvinylidene fluoride as in Example 1, and gold powder (average particle size: 3 μm) were weighed in a weight ratio of 4: 1: 5, and these were used as a solvent for n-methylpyrrolidone. To prepare a slurry. This slurry was irradiated with 40 kHz ultrasonic waves for 30 minutes, and then applied onto a 20 μm thick aluminum foil as a positive electrode current collector using a doctor blade and dried at 125 ° C. to obtain n-methylpyrrolidone. The evaporated one was used as the positive electrode. The positive electrode active material layer thus obtained had a thickness of 150 μm. In the active material layer after drying, cracks and falling off from the current collector were observed. A coin-type secondary battery of Comparative Example 2 was produced in the same manner as Example 1 except for the negative electrode other than the positive electrode, the electrolytic solution, the separator, and the like.

(Battery characteristics evaluation)
The coin-type secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were charged and discharged with a constant current in a voltage range of 2V to 4V. Charging / discharging was performed in a thermostat set to 20 ° C. The charging current was 1C current, the discharging current was 1C current and 50C current, and the discharge capacity in each case was measured. The 1C current is a current value at which discharge is completed in one hour, and the 50C current is a current that is 50 times the 1C current. As a quantity indicating the capacity characteristics at the time of large current discharge of the secondary battery, the ratio of the discharge capacity at 50 C current to the discharge capacity at 1 C current was examined.

  Moreover, after charging the produced coin-type secondary battery to 4 V with 1 C current, it was stored for 1 week in a thermostat set at 20 ° C., then discharged to 2 V with 1 C current, and the remaining capacity was measured. As an amount indicating the storage characteristics of the secondary battery, the ratio of the remaining capacity after one week to the discharge capacity before storage was examined.

  For the secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 2, the appearance state of each positive electrode and the results of examining the above characteristics are shown in Table 1.

The positive electrodes of Examples 1 to 6 did not crack or drop, whereas the positive electrodes of Comparative Examples 1 and 2 were cracked or dropped. Example The positive electrode cracking and falling off was not a 1-6 carbon fibers within a range the average value is less 0.340nm than 0.335nm interlayer distance d ₀₀₂ of the graphite structure is contained in the active material layer This is because the mechanical strength of the active material layer of the positive electrode is improved.

  Regarding the ratio of the 50 C discharge capacity to the 1 C discharge capacity, the secondary batteries of Examples 1 to 6 were all larger than the secondary battery of Comparative Example 1. This is because in the secondary batteries of Examples 1 to 6, the active material layer of the positive electrode is not cracked and the active material layer has high conductivity and the electrode resistance of the positive electrode is low. It shows an improvement over the example.

  Regarding the ratio of the discharge capacity after one week storage to the discharge capacity before storage, the secondary batteries of Examples 1 to 6 were all larger than the secondary battery of Comparative Example 1. This indicates that in the secondary batteries of Examples 1 to 6, since the active material layer did not fall off, the storage characteristics of the capacity were improved as compared with the comparative example.

In addition, the secondary battery of Comparative Example 2 has no capacity at 1C discharge, and the ratio of 50C to the 1C discharge capacity and the ratio of the discharge capacity after storage for one week to the discharge capacity before storage cannot be obtained. It was. This is thought to be because the charge / discharge reaction did not proceed because the charge transfer resistance at the interface between the radical compound and the gold particles was significantly greater than that of carbon fiber. Therefore, even if the same conductor is used, a positive electrode with low electrode resistance cannot be obtained when an active material layer containing gold is used instead of carbon fiber.

Claims (11)

A radical compound, a positive electrode for a secondary battery, wherein the average value of the interlayer distance d ₀₀₂ of the graphite structure has an active material layer containing at least a carbon fiber in the range of 0.340nm than 0.335 nm.   2. The positive electrode for a secondary battery according to claim 1, wherein a tensile elastic modulus of the carbon fiber is in a range of 200 GPa to 800 GPa.   3. The positive electrode for a secondary battery according to claim 1, wherein the volume resistivity of the carbon fiber is in a range of 200 μΩ · cm to 2000 μΩ · cm.   The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein the carbon fiber is a vapor-grown carbon fiber.   The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein the carbon fiber is graphitized carbon fiber having a mesophase pitch as a precursor.   6. The positive electrode for a secondary battery according to claim 1, wherein a content ratio of the carbon fiber in the active material layer is in a range of 10 wt% or more and 50 wt% or less.   The said radical compound contains at least 1 type of a polymeric nitroxyl radical compound, a polymeric oxy radical compound, and a polymeric hydrazyl radical compound, The 2 of any one of Claims 1-6 characterized by the above-mentioned. Positive electrode for secondary battery.   The polymer nitroxyl radical compound is poly (4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), poly (4-acryloyloxy-2,2,6,6-tetramethyl). The positive electrode for a secondary battery according to claim 7, which is piperidine-1-oxyl) or poly (4-vinyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl). A carbon fiber radical compound is a positive electrode manufacturing method for a secondary battery having at least comprising an active material layer, in a solvent containing the radical compound, the average value of the interlayer distance d ₀₀₂ of the graphite structure is more 0.335nm The manufacturing method of the positive electrode for secondary batteries characterized by having the process of disperse | distributing the said carbon fiber within the range of 0.340 nm or less.   The method for producing a positive electrode for a secondary battery according to claim 9, wherein the content ratio of the carbon fiber in the active material layer is dispersed so as to fall within a range of 10 wt% or more and 50 wt% or less. A secondary battery comprising at least a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode is a positive electrode for a secondary battery according to any one of claims 1 to 8.

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