JP2019091586A - Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide a positive electrode for a nonaqueous electrolyte secondary battery, which enables the enhancement of output characteristics of a nonaqueous electrolyte secondary battery.SOLUTION: A positive electrode is used for a nonaqueous electrolyte secondary battery. The positive electrode for a nonaqueous electrolyte secondary battery comprises: a carbon material having a graphene laminate structure; and a positive electrode active substance. The porosity of the positive electrode measured according to a method of mercury penetration is 10% or more and 45% or less. Supposing that, in a pore distribution of the positive electrode measured according to the method of mercury penetration, the maximum peak value in a range of 1 μm or more and 6 μm or less in pore size is X, and the maximum peak value in a range of 8 μm or more and 20 μm or less in pore size is Y, the ratio X/Y is in a range of 3.0 or more and 10.0 or less.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery containing a positive electrode active material and a carbon material, and a non-aqueous electrolyte secondary battery using the positive electrode for the non-aqueous electrolyte secondary battery.

  BACKGROUND ART In recent years, research and development of non-aqueous electrolyte secondary batteries have been actively carried out for portable devices, hybrid vehicles, electric vehicles, household storage applications and the like.

  For example, Patent Document 1 below discloses a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode mixture layer constituting the positive electrode has a peak A in the range of 0.2 μm to 2 μm in pore diameter and a peak B in the range of 0.05 μm to 0.5 μm in pore diameter in the pore distribution curve. Have. In addition, the positive electrode mixture layer contains a positive electrode active material and a conductive additive. Moreover, in patent document 1, carbon black, a carbon fiber, etc. are used as a conductive support agent.

Patent No. 5963022 gazette

  However, in the non-aqueous electrolyte secondary battery of Patent Document 1, there are cases in which battery characteristics such as output characteristics of the non-aqueous electrolyte secondary battery can not be sufficiently enhanced.

  The inventors of the present invention have not been able to move and diffuse lithium ions smoothly because of the small pore diameter of the positive electrode of the non-aqueous electrolyte secondary battery of Patent Document 1 for this cause, and as a result, the output characteristics And the like have been found to occur.

  An object of the present invention is to provide a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the positive electrode for a non-aqueous electrolyte secondary battery, which can enhance the output characteristics of the non-aqueous electrolyte secondary battery. is there.

  The positive electrode for a non-aqueous electrolyte secondary battery according to the present invention is a positive electrode for use in a non-aqueous electrolyte secondary battery, and the positive electrode includes a carbon material having a graphene laminated structure and a positive electrode active material. The porosity of the positive electrode measured according to the method is 10% or more and 45% or less, and in the pore distribution of the positive electrode measured according to the mercury intrusion method, the pore diameter is 1 μm or more and 6 μm or less The ratio X / Y is in the range of 3.0 or more and 10.0 or less, where X is the maximum peak value in the range of, and Y is the maximum peak value in the range of pore diameters of 8 μm to 20 μm.

In a specific aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, two pieces of the positive electrode are cut out so as to have a volume of 18.5 mm ³ , and two cut out positive electrodes are subjected to a tuning fork physical property test In the state of being attached to the two sensitive plates of the machine, and immersed in 30 mL of dimethyl carbonate having a specific gravity of 1.071, and when the sensitive plate is vibrated with a natural frequency of 30 Hz, it is immersed in the dimethyl carbonate and vibrated. Assuming that the stress immediately after the start is A1 mN, and the stress after immersing in dimethyl carbonate for 8 hours after starting vibration is A2 mN, the ratio A2 / A1 is 1.15 or more and 1.50 or less It is in the range.

In another particular aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the BET specific surface area of the carbon material is 10 m ² / g or more and 200 m ² / g or less, and is measured according to the HK method The pore volume of the diameter of 0.3 nm or more and 1.0 nm in the pore distribution of the carbon material is 0.2 mL / g or more, and the DBP oil absorption of the carbon material is 150 mL / 100 g or more.

  In still another particular aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material is exfoliated graphite.

  In yet another specific aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, 2θ is 24 when an X-ray diffraction spectrum of the mixture of the carbon material and Si at a weight ratio of 1: 1 is measured. The ratio c / d of the height c of the highest peak in the range of not less than 28 ° to the height d of the highest peak in the range of 28 ° to less than 30 ° is 0.2 or more , 1.0 or less.

  In still another particular aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material is a conductive aid.

  In still another specific aspect of the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material and the positive electrode active material are complexed to form a complex.

  A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode for a non-aqueous electrolyte secondary battery constructed according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode for nonaqueous electrolyte secondary batteries which can improve the output characteristic of a nonaqueous electrolyte secondary battery can be provided.

  Hereinafter, the present invention will be described in detail.

[Positive Electrode for Nonaqueous Electrolyte Secondary Battery]
The positive electrode for a non-aqueous electrolyte secondary battery of the present invention contains at least a carbon material having a graphene laminated structure and a positive electrode active material. Details will be described below.

(Carbon material with graphene stack structure)
As a carbon material which has a graphene laminated structure used for the positive electrode for non-aqueous electrolyte secondary batteries of this invention, graphite or exfoliated graphite etc. are mentioned, for example.

  Graphite is a laminate of a plurality of graphene sheets. The number of stacked graphene sheets is usually about 100,000 to 1,000,000. As the graphite, for example, natural graphite, artificial graphite or expanded graphite can be used. Expanded graphite has a high ratio in which the interlayer distance between graphene layers is larger than that of ordinary graphite. Therefore, it is preferable to use expanded graphite as the graphite.

  The exfoliated graphite is obtained by exfoliating the original graphite, and refers to a graphene sheet laminate thinner than the original graphite. The number of stacked graphene sheets in exfoliated graphite may be smaller than that of the original graphite. The exfoliated graphite may be oxidized exfoliated graphite.

  In exfoliated graphite, the number of stacked graphene sheets is not particularly limited, but is preferably 2 or more, more preferably 5 or more, preferably 1000 or less, and more preferably 500 or less. When the number of stacked graphene sheets is the above lower limit or more, the conductivity of exfoliated graphite can be further enhanced. When the number of stacked graphene sheets is equal to or less than the upper limit, the specific surface area of exfoliated graphite can be further increased.

  The exfoliated graphite is preferably a partially exfoliated exfoliated graphite having a structure in which graphite is exfoliated partially. Since the partially exfoliated exfoliated graphite has a bulky structure, the porosity and the ratio X / Y of the positive electrode described later can be adjusted more easily to the above range. Therefore, the pore diameter can be further increased, and migration and diffusion of ions such as lithium ions can be performed more smoothly. Therefore, battery characteristics such as output characteristics of the non-aqueous electrolyte secondary battery can be further enhanced.

  As an example of the “partially exfoliated graphite” structure, in the graphene stack, the graphene layers are open from the edge to a certain extent inward, that is, part of the graphite is exfoliated at the edge In the central part, it means that the graphite layer is laminated in the same manner as the original graphite or the primary exfoliated graphite. Therefore, the part where a part of graphite exfoliates at the edge is connected to the central part. Furthermore, the partially exfoliated exfoliated graphite may include exfoliated and exfoliated graphite at the edge.

  In the partially exfoliated exfoliated graphite, the graphite layer is laminated in the same manner as the original graphite or primary exfoliated graphite in the central portion, so the degree of graphitization is higher than that of conventional graphene oxide and carbon black, and the conductivity is conductive It is excellent in sex. In addition, since the graphite has a partially exfoliated structure, the specific surface area is large, so that the area of the portion in contact with the active material can be increased. Therefore, since the positive electrode for a non-aqueous electrolyte secondary battery containing the partially exfoliated graphite exfoliated graphite can reduce the resistance of the non-aqueous electrolyte secondary battery, it also suppresses heat generation during charging and discharging at a large current. be able to.

  The partially exfoliated exfoliated graphite can be obtained, for example, by heat-treating a composition in which a resin is fixed to graphite or primary exfoliated graphite by grafting or adsorption. Note that the heat treatment may be performed until thermal decomposition while leaving a part of the resin, or heat treatment may be performed until the resin is completely thermally decomposed.

  The method of producing the partially exfoliated graphite can be referred to, for example, WO 2014/034156.

  The carbon material having a graphene laminated structure used in the present invention can be produced, for example, by subjecting graphite as a raw material or primary exfoliated graphite to a grinding step.

  The primary exfoliated graphite broadly includes exfoliated graphite obtained by exfoliating graphite by various methods. The primary exfoliated graphite may be partially exfoliated exfoliated graphite. Since primary exfoliated graphite is obtained by exfoliating graphite, its specific surface area may be larger than that of graphite.

  Examples of the pulverizing method include wet pulverization in which ultrasonic waves are irradiated after dispersing the graphite in a suitable solvent, or dry pulverization in which jet pulverization, pulverization in a ball mill, etc. may be mentioned, for example. From the viewpoint of being highly effective in reducing the powder resistance of the carbon material having a laminated structure, dry pulverization including jet milling, pulverization using a ball mill, and the like is preferable.

  The average particle diameter of the dry-ground graphite or primary exfoliated graphite of the present invention is preferably 1.0 μm or more, more preferably 2.0 μm or more, preferably 30 μm or less, more preferably 20 μm or less. When the average particle size of the dry-ground graphite or the primary exfoliated graphite is within the above range, not only the reduction of the powder resistance, but also the range of the pore volume of the obtained carbon material and the DBP oil absorption are further optimized. It can be adjusted to further enhance the retention of the electrolytic solution. In addition, an average particle diameter says the value calculated by volume reference distribution by laser diffraction method using laser diffraction / scattering type particle size distribution measuring apparatus.

  The dry-pulverized graphite or primary exfoliated graphite may be used as it is or may be the above-mentioned partially exfoliated exfoliated graphite. The dry-ground graphite or primary exfoliated graphite may be changed to partially exfoliated graphite.

  The resin is not particularly limited, but is preferably a polymer of a radically polymerizable monomer. In this case, it may be a homopolymer of one type of radically polymerizable monomer, or may be a copolymer of a plurality of types of radically polymerizable monomer. The radically polymerizable monomer is not particularly limited as long as it is a monomer having a radically polymerizable functional group.

  As a radical polymerizable monomer, for example, styrene, methyl α-ethyl acrylate, methyl α-benzyl acrylate, methyl α- [2,2-bis (carbomethoxy) ethyl] acrylate, dibutyl itaconate, dimethyl itaconate , Itaconic acid dicyclohexyl, α-methylene-δ-valerolactone, α-methylstyrene, α-substituted acrylic acid ester composed of α-acetoxystyrene, glycidyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate, hydroxyethyl methacrylate, hydroxy Vinyl monomers having a glycidyl group or hydroxyl group such as ethyl acrylate, hydroxypropyl acrylate, 4-hydroxybutyl methacrylate, etc .; allylamine, diethylaminoethyl (meth) acrylate, dimethylamine Vinyl monomers having an amino group such as minoethyl (meth) acrylate, methacrylic acid, maleic anhydride, maleic acid, maleic acid, itaconic acid, acrylic acid, crotonic acid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, Monomers having a carboxyl group such as 2-methacryloyloxyethyl phthalic acid; Unichemical Co., Ltd., Phosmer (registered trademark) M, Phosmer (registered trademark) CL, Phosmer (registered trademark) PE, Phosmer (registered trademark) MH, Phosmer (Registered trademark) monomers having a phosphoric acid group such as PP; monomers having an alkoxysilyl group such as vinyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane; (meth) acrylate monomers having an alkyl group, benzyl group and the like etc It is below.

  Examples of the resin to be used include polyethylene glycol, polypropylene glycol, polyglycidyl methacrylate, polyvinyl acetate, polybutyral (butyral resin), poly (meth) acrylate, polystyrene and the like.

  Preferably, polyethylene glycol, polypropylene glycol and polyvinyl acetate can be used as a resin used for the partially exfoliated graphite. When polyethylene glycol, polypropylene glycol and polyvinyl acetate are used, the specific surface area of partially exfoliated exfoliated graphite can be further increased. The resin type can be appropriately selected in view of the affinity to the solvent used.

  The content of the residual resin is preferably 0 parts by weight or more and 40 parts by weight or less, and is 1 part by weight or more and 35 parts by weight or less, based on 100 parts by weight of partially exfoliated graphite except the resin component. Is more preferably 3 parts by weight or more and 30 parts by weight or less. Moreover, when the amount of residual resin is larger than the said upper limit, a manufacturing cost may increase.

  The amount of residual resin remaining in the partially exfoliated graphite can be calculated, for example, by measuring the weight change associated with the heating temperature by thermogravimetric analysis (hereinafter, TG).

  In addition, in the case of producing a complex with a positive electrode active material described later, the resin may be removed after producing a complex with the positive electrode active material. As a method of removing the resin, a method of heat treatment at a temperature above the decomposition temperature of the resin and below the decomposition temperature of the positive electrode active material is preferable. This heat treatment may be performed in the air, under an inert gas atmosphere, under a low oxygen atmosphere, or under vacuum.

In the above-mentioned production method, the partially exfoliated exfoliated graphite obtained is excellent in conductivity as compared with conventional graphene oxide and graphene obtained by reducing the graphene oxide because the oxidation process has not been performed. It is considered that conventional graphene oxide and redox graphene can not sufficiently ensure the sp ² structure. The positive electrode for a non-aqueous electrolyte secondary battery using the partially exfoliated graphite exfoliated graphite is more excellent in conductivity than conventional graphene oxide and redox graphene, and thus the resistance of the non-aqueous electrolyte secondary battery is more enhanced. The size can be further reduced, and heat generation during charging and discharging with a large current can be suppressed. Further, since the partially exfoliated graphite obtained has few active sites on the surface, the electrolytic solution is more difficult to be decomposed compared to graphene oxide. Therefore, when the partially exfoliated graphite obtained is used, the generation of gas can be further suppressed.

The BET specific surface area of the carbon material used in the present invention is preferably 10 m ² / g or more and 200 m ² / g or less. When the BET specific surface area is in the above-mentioned range, the coatability at the time of forming the electrode by coating the slurry containing the carbon material on the current collector can be enhanced. Therefore, the yield of the electrode can be enhanced, and battery characteristics such as rate characteristics can also be enhanced.

In the present invention, the BET specific surface area of the carbon material is preferably 10 m ² / g or more, more preferably 15 m ² / g or more, preferably 200 m ² / g or less, more preferably 160 m ² / g or less. When the BET specific surface area of the carbon material is equal to or more than the lower limit, the liquid replacement property of the electrolytic solution can be further enhanced, and battery characteristics such as the capacity of the non-aqueous electrolyte secondary battery can be further enhanced. Moreover, when the BET specific surface area of a carbon material is below the said upper limit, the coating property at the time of coating the slurry containing the said carbon material on a collector, and forming an electrode can be raised further. In addition, the conductivity can be further enhanced. Furthermore, deterioration of the electrolytic solution can be further suppressed.

  In the present invention, the pore volume of the diameter of 0.3 nm or more and 1.0 nm or less in the pore distribution of the carbon material is preferably 0.20 mL / g or more, more preferably 0.25 mL / g or more. When the pore volume of the carbon material is equal to or more than the lower limit, the liquid retention of the electrolytic solution can be further enhanced. The upper limit of the pore volume of the carbon material is not particularly limited. However, from the viewpoint of further suppressing deterioration of the electrolyte, the pore volume of the carbon material is preferably 3.5 mL / g or less, more preferably 3.2 mL / g or less, still more preferably 3.0 mL / g or less It is.

  In the present invention, the DBP oil absorption of the carbon material is preferably 150 mL / 100 g or more, more preferably 200 mL / 100 g or more. When the DBP oil absorption amount of the carbon material is equal to or more than the lower limit, the liquid retention of the electrolytic solution can be further enhanced. The upper limit of the DBP oil absorption of the carbon material is not particularly limited. However, from the viewpoint of further suppressing deterioration of the electrolytic solution, the DBP oil absorption of the carbon material is preferably 450 mL / 100 g or less, more preferably 400 mL / 100 g or less, and still more preferably 300 mL / 100 g or less.

  The BET specific surface area of the carbon material can be measured from the adsorption isotherm of nitrogen according to the BET method. As a measuring apparatus, Shimadzu Corporation make and a product number "ASAP-2000" can be used, for example.

  The pore distribution of the carbon material can be measured from the argon adsorption isotherm according to the HK method (Horvath-Kawazoe method). As a measuring apparatus, Microtrac BEL company make, product number "BELSORP-MAX" can be used, for example. The pore volume is a volume occupied by pores with a diameter of 0.3 nm or more and 1.0 nm or less.

  Moreover, DBP oil absorption amount of a carbon material can be measured based on JISK6217-4. The DBP oil absorption can be measured, for example, using an absorption amount measuring device (manufactured by Asahi Soken Co., product number "S500").

  In the present invention, when the X-ray diffraction spectrum of the mixture of the carbon material and Si at a weight ratio of 1: 1 is measured, it is preferable to fall within the following range. That is, the ratio c / d of the height c of the highest peak in the range of 24 ° or more and less than 28 ° to the height d of the highest peak in the range of 28 ° or more and less than 30 ° Is preferably 0.2 or more and 1.0 or less. In addition, as said Si, the silicon powder of (phi) = 100 nm or less can be used, for example.

  The X-ray diffraction spectrum can be measured by wide-angle X-ray diffraction. As the X-ray, a CuKα ray (wavelength 1.541 Å) can be used. For example, SmartLab (manufactured by Rigaku Corporation) can be used as the X-ray diffraction apparatus.

  In the X-ray diffraction spectrum, a peak derived from a graphene laminated structure represented by a graphite structure appears near 2θ = 26.4 °. On the other hand, a peak derived from Si such as silicon powder appears near 2θ = 28.5 °. Therefore, the ratio c / d is the peak ratio between the peak near 2θ = 26.4 ° and the peak near 2θ = 28.5 ° (peak around 2θ = 26.4 ° / 2θ = 28.5 ° The peak of the

  If the c / d is less than 0.2, the carbon material itself is immature in formation of a graphite structure and has defects in addition to low electron conductivity, so the resistance value of the positive electrode or negative electrode is increased. The battery characteristics may be degraded.

  When the c / d is larger than 1.0, the carbon material itself becomes rigid, and it may be difficult to disperse in the positive electrode and the negative electrode of the storage device, and it may be difficult to form a good electron conduction path.

  The ratio c / d is more preferably 0.22 or more, still more preferably 0.25 or more, more preferably 0.9 or less from the viewpoint of facilitating formation of an electron conduction path in the electrode of the storage device. More preferably, it is 0.8 or less.

In the present invention, the powder resistance of the carbon material is preferably less than 1 × 10 ⁻³ Ωcm, more preferably 8 × 10 ⁻⁴ Ωcm or less. In the case of the powder resistance, since the resistance of the power storage device itself can be reduced, battery characteristics such as output characteristics can be further enhanced. Moreover, the lower limit of the powder resistance is not particularly limited, but can be, for example, 4 × 10 ⁻⁵ Ωcm or more. The powder resistance can be obtained, for example, by applying a pressure of 4 kN to the powder by the four-terminal method and measuring the resistance value at 20 kN. The powder resistance can be measured, for example, using a low-resistance powder measuring device (Loresta GX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

  Further, in the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, it is preferable that the carbon material be used as a conductive additive of the positive electrode. In this case, since the conductivity can be further enhanced by the carbon material, the content of the conductive aid in the positive electrode can be reduced. Therefore, the content of the positive electrode active material can be further increased, and the capacity of the non-aqueous electrolyte secondary battery can be further increased.

  Further, in the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, when the carbon material having the graphene laminated structure is a first carbon material (simply referred to as a carbon material unless otherwise noted). And the second carbon material different from the first carbon material may be further included.

  The second carbon material is not particularly limited, and graphene, artificial graphite, particulate graphite compound, fibrous graphite compound, carbon black or activated carbon is exemplified.

  The graphene may be graphene oxide or may be a reduced graphene oxide.

  The particulate graphite compound is not particularly limited, and natural graphite, artificial graphite, expanded graphite and the like are exemplified.

  The fibrous graphite compound is not particularly limited, and carbon nanohorns, carbon nanotubes, or carbon fibers are exemplified.

  The carbon black is not particularly limited, and examples thereof include furnace black, ketjen black, and acetylene black.

  The content of the carbon material in 100% by weight of the positive electrode for a non-aqueous electrolyte secondary battery is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and still more preferably 0.4% by weight or more. Preferably, it is 10% by weight or less, more preferably 5% by weight or less, still more preferably 3% by weight or less. When the content of the carbon material is in the above range, the content of the active material can be further increased, and the capacity of the non-aqueous electrolyte secondary battery can be further increased.

(Positive electrode active material)
The positive electrode active material used for the positive electrode for a non-aqueous electrolyte secondary battery of the present invention may be nobler than the battery reaction potential of the negative electrode active material. In that case, the battery reaction may involve ions of group 1 or 2 and examples of such ions include H ions, Li ions, Na ions, K ions, Mg ions, Ca ions, or Al ion is mentioned. Hereinafter, details of a system in which Li ions participate in a cell reaction will be exemplified.

  In this case, examples of the positive electrode active material include lithium metal oxides, lithium sulfides, and sulfur.

  As a lithium metal oxide, what has a spinel structure, a layered rock salt structure, or an olivine structure, or these mixtures are mentioned.

  A lithium manganate etc. are illustrated as a lithium metal oxide which has a spinel structure.

  Examples of lithium metal oxides having a layered rock salt structure include lithium cobaltate, lithium nickelate, and ternary systems.

  Examples of lithium metal oxides having an olivine structure include lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate and the like.

  The positive electrode active material may contain a so-called doping element.

  The positive electrode active material may be used alone or in combination of two or more.

(binder)
The positive electrode may be formed only of a positive electrode active material and the carbon material, but a binder may be contained from the viewpoint of more easily forming the positive electrode.

  The binder is not particularly limited, and, for example, at least one resin selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof. It can be used.

  The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of more easily preparing the positive electrode for secondary battery.

  The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate or tetrahydrofuran. You may add a dispersing agent and a thickener to these.

  The amount of the binder contained in the positive electrode for the secondary battery is preferably 0.3 parts by weight or more and 30 parts by weight or less, more preferably 0.5 parts by weight or more, with respect to 100 parts by weight of the positive electrode active material. It is 15 parts by weight or less. When the amount of the binder is within the above range, the adhesion between the positive electrode active material and the carbon material can be maintained, and the adhesion with the current collector can be further enhanced.

(Positive electrode for non-aqueous electrolyte secondary battery)
The porosity of the positive electrode for a non-aqueous electrolyte secondary battery of the present invention is 10% or more and 45% or less. In the pore distribution of the positive electrode, when the maximum peak value in the range of pore diameters of 1 μm to 6 μm is X and the maximum peak value in the range of pore diameters of 8 μm to 20 μm is Y, the ratio X / Y is in the range of 3.0 or more and 10.0 or less. In addition, the said largest peak value means the thing of the height of the highest peak in the range of a specific pore diameter.

  Moreover, the porosity and pore distribution of the said positive electrode can be measured based on the mercury intrusion method. As a measuring device, for example, a mercury porosimeter (for example, manufactured by micromeritics, trade name: Autopore IV9520) can be used.

  In the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, since the porosity and the ratio X / Y are in the above-mentioned range, the size of the pores which can smoothly move and diffuse ions such as lithium ions is selected. Have. Therefore, battery characteristics such as output characteristics of the non-aqueous electrolyte secondary battery can be enhanced.

  In the present invention, the porosity is preferably 10% or more, more preferably 15% or more, preferably 45% or less, more preferably 30% or less. When the porosity is equal to or higher than the lower limit, movement and diffusion of ions such as lithium ions can be performed more smoothly. In addition, when the porosity is equal to or less than the upper limit, the cathode active material and the conductive additive can be further contained, so that battery characteristics such as output characteristics of the non-aqueous electrolyte secondary battery can be further enhanced. it can.

  In the present invention, the ratio X / Y is preferably 3.0 or more, more preferably 5.0 or more, preferably 10.0 or less, more preferably 8.0 or less. When the ratio X / Y is equal to or more than the lower limit, it is possible to further include a portion having a large pore diameter, so that movement and diffusion of ions such as lithium ions can be performed more smoothly. In addition, when the ratio X / Y is less than or equal to the upper limit, the cathode active material and the conductive additive can be further contained, so that the battery characteristics such as output characteristics of the non-aqueous electrolyte secondary battery are further enhanced. be able to.

  In the present invention, in the electrolyte solution retention test, the stress immediately after being immersed in the electrolytic solution and starting the vibration was A1 mN, and the stress when it was immersed in the electrolytic solution and the vibration was started for 8 hours was made A2 mN It is preferred that the ratio A2 / A1 be in the range of 1.15 or more and 1.50 or less. When ratio A2 / A1 is more than the said minimum, the liquid retention property of electrolyte solution can be improved further. Therefore, the electrolytic solution can be sufficiently diffused to the electrode active material on the current collector side, and battery characteristics such as the capacity of the non-aqueous electrolyte secondary battery can be further enhanced. In particular, the capacity after repeated charge and discharge in the non-aqueous electrolyte secondary battery can be further enhanced, that is, the cycle characteristics can be further enhanced. Moreover, when ratio A2 / A1 is below the said upper limit, deterioration of electrolyte solution can be suppressed further and battery characteristics, such as a cycle characteristic, can be improved further.

  In addition, the said electrolyte solution retention property test can be implemented as follows.

First, two positive electrodes to be measured are cut out so as to have a volume of 18.5 mm ³ . Next, the positive electrodes cut out are attached one by one to the two sensitive plates of the tuning fork type physical property tester, and immersed in 30 mL of dimethyl carbonate (specific gravity: 1.071). Finally, the characteristic frequency of the sensitive plate is vibrated at 30 Hz to calculate the detected stress. The vibration of the sensitive plate is performed in a state of being completely immersed in dimethyl carbonate which is an electrolytic solution.

  As a tuning fork type physical property tester, for example, TFP-10 manufactured by A & D Co., Ltd. can be used. The tuning fork type physical property tester comprises a sensitive plate, an electromagnetic drive unit for driving the sensitive plate, a displacement sensor for detecting the swing width, and a drive current drive circuit for maintaining the swing width. The natural frequency of the two sensitive plates is fixed at 30 Hz, and the stress acting on the solution can be detected by determining the current necessary to maintain the swing width. In the case of the positive electrode, when the electrolytic solution penetrates and immerses the positive electrode, the mass of the vibrating portion increases, so the driving current increases and the stress to be detected increases. From this, it is possible to relatively evaluate the amount of electrolytic solution that has permeated into the positive electrode.

(Method of manufacturing positive electrode)
Examples of the method for producing the positive electrode for secondary batteries include a method of producing a mixture of a positive electrode active material, a carbon material, and a binder on a current collector.

  From the viewpoint of producing the above-mentioned positive electrode for secondary battery more easily, it is preferable to produce as follows. First, a slurry is prepared by adding a binder solution or a dispersion to a positive electrode active material and a carbon material and mixing them. Next, the prepared slurry is applied onto a current collector and finally the solvent is removed to prepare a positive electrode for a secondary battery.

  An existing method can be used as a method of producing the slurry. For example, the method of mixing using a mixer etc. is mentioned. Although it does not specifically limit as a mixer used for mixing, A planetary mixer, a disper, a thin film whirl mixer, a jet mixer, a self-public rotation mixer, etc. are mentioned.

  The solid content concentration of the slurry is preferably 30% by weight or more and 95% by weight or less from the viewpoint of easier application. From the viewpoint of further enhancing the storage stability, the solid content concentration of the slurry is more preferably 35% by weight or more and 90% by weight or less. In addition, from the viewpoint of further suppressing the manufacturing cost, the solid content concentration of the slurry is more preferably 40% by weight or more and 85% by weight or less.

  The solid concentration can be controlled by a dilution solvent. As the dilution solvent, it is preferable to use the same type of solvent as the binder solution or the dispersion. In addition, other solvents may be used as long as the solvents are compatible.

  The current collector used for the positive electrode for the secondary battery is preferably aluminum or an alloy containing aluminum. Aluminum is not particularly limited because it is stable in a positive electrode reaction atmosphere, but is preferably high purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99 and the like.

  The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. When the thickness of the current collector is less than 10 μm, handling may be difficult from the viewpoint of production. On the other hand, if the thickness of the current collector is greater than 100 μm, it may be disadvantageous from an economic viewpoint.

  The current collector may be one obtained by coating a surface of a metal other than aluminum (copper, SUS, nickel, titanium, and their alloys) with aluminum.

  The method of applying the slurry to the current collector is not particularly limited. For example, a method of removing the solvent after applying the slurry by a doctor blade, a die coater, a comma coater or the like, or removing the solvent after applying the spray A method or a method of removing the solvent after application by screen printing may, for example, be mentioned.

  The method of removing the solvent is preferably drying using a blast oven or a vacuum oven because it is simpler. Examples of the atmosphere for removing the solvent include an air atmosphere, an inert gas atmosphere, and a vacuum state. The temperature for removing the solvent is not particularly limited, but is preferably 60 ° C. or more and 250 ° C. or less. If the temperature for removing the solvent is less than 60 ° C., it may take time to remove the solvent. On the other hand, if the temperature for removing the solvent is higher than 250 ° C., the binder may be degraded.

  The positive electrode for a non-aqueous electrolyte secondary battery may be compressed to a desired thickness and density. The compression is not particularly limited, but can be performed using, for example, a roll press, a hydraulic press, or the like. The porosity of the above-mentioned positive electrode can also be controlled by the compression.

  The thickness of the positive electrode for a non-aqueous electrolyte secondary battery after compression is not particularly limited, but is preferably 10 μm or more and 1000 μm or less. If the thickness is less than 10 μm, it may be difficult to obtain a desired capacity. On the other hand, when the thickness is thicker than 1000 μm, it may be difficult to obtain a desired output density.

The positive electrode for a non-aqueous electrolyte secondary battery preferably has an electrical capacity of 0.5 mAh or more and 10.0 mAh or less per 1 cm ² of the positive electrode. If the electrical capacity is less than 0.5 mAh, the size of the battery of the desired capacity may be increased. On the other hand, when the electric capacity is larger than 10.0 mAh, it may be difficult to obtain a desired output density. The calculation of the electric capacity per 1 cm ^{2 of the} positive electrode may be calculated by preparing a positive electrode for a non-aqueous electrolyte secondary battery, preparing a half battery using lithium metal as a counter electrode, and measuring the charge / discharge characteristics.

The electrical capacity per 1 cm ^{2 of the} positive electrode of the positive electrode for a non-aqueous electrolyte secondary battery is not particularly limited, but can be controlled by the weight of the positive electrode formed per unit area of the current collector. For example, it can control by the coating thickness at the time of the above-mentioned slurry coating.

  Further, the positive electrode may be produced using a composite of a positive electrode active material and the carbon material. The positive electrode active material-carbon material composite is produced, for example, by the following procedure.

  First, a dispersion of the carbon material in which the carbon material is dispersed in a solvent (hereinafter, dispersion 1 of the carbon material) is prepared. Next, separately from the dispersion 1, a dispersion of the positive electrode active material (hereinafter, dispersion 2 of the positive electrode active material) in which the positive electrode active material is dispersed in a solvent is prepared.

  Next, the dispersion 1 of the carbon material and the dispersion 2 of the positive electrode active material are mixed. Finally, by removing the solvent of the dispersion liquid containing the carbon material and the positive electrode active material, a composite of the positive electrode active material and the carbon material used for an electrode for a storage battery device (active material-carbon material composite) Is made.

  Moreover, the order of mixing may be changed other than the above-mentioned preparation method, either of the said dispersion liquids 1 and 2 may be not a dispersion liquid but a dry type, and the method of mixing all in a dry state May be. Moreover, the method of mixing the mixture of a carbon material, a positive electrode active material, and a solvent with a mixer, ie, preparation of the slurry of the below-mentioned positive electrode, and preparation of a composite may be performed.

  The solvent for dispersing the positive electrode active material and the carbon material may be any of aqueous, non-aqueous, mixed solvent of aqueous and non-aqueous, or mixed solvent of different non-aqueous solvents. The solvent for dispersing the carbon material and the solvent for dispersing the positive electrode active material may be the same or different. When they are different, they are preferably compatible with each other.

  The non-aqueous solvent is not particularly limited, but for example, an alcohol-based solvent typified by methanol, ethanol and propanol, non-aqueous solvent such as tetrahydrofuran or N-methyl-2-pyrrolidone can be used because of ease of dispersion. . Further, in order to further improve the dispersibility, the solvent may contain a dispersing agent such as a surfactant.

  The dispersion method is not particularly limited, and dispersion by ultrasonic waves, dispersion by a mixer, dispersion by a jet mill, or dispersion by a stirrer may be mentioned.

  The solid content concentration of the dispersion liquid of the carbon material is not particularly limited, but when the weight of the carbon material is 1, it is preferable that the weight of the solvent is 0.5 or more and 1000 or less. From the viewpoint of further enhancing the handleability, when the weight of the carbon material is 1, it is more preferable that the weight of the solvent is 1 or more and 750 or less. Further, from the viewpoint of further enhancing the dispersibility, when the weight of the carbon material is 1, it is more preferable that the weight of the solvent is 2 or more and 500 or less.

  If the weight of the solvent is less than the above lower limit, the carbon material may not be able to be dispersed to the desired dispersed state. On the other hand, if the weight of the solvent is larger than the upper limit, the production cost may increase.

  The solid content concentration of the dispersion liquid of the positive electrode active material is not particularly limited, but when the weight of the positive electrode active material is 1, the weight of the solvent is preferably 0.5 or more and 100 or less. From the viewpoint of further enhancing the handleability, the weight of the solvent is more preferably 1 or more and 75 or less. Further, from the viewpoint of further enhancing the dispersibility, the weight of the solvent is more preferably 5 or more and 50 or less. When the weight of the solvent is less than the lower limit, the positive electrode active material may not be dispersed to a desired dispersed state. On the other hand, if the weight of the solvent is larger than the upper limit, the production cost may increase.

  The method of mixing the dispersion of the positive electrode active material and the dispersion of the carbon material is not particularly limited, but the method of mixing the dispersions of each other at one time, or the dispersion of one dispersion in the other dispersion several times The method of dividing and adding is mentioned.

  As a method of adding one dispersion liquid to the other dispersion liquid in multiple times, for example, a method of dropping using a dropper such as a droper, a method using a pump, or a method using a dispenser can be mentioned.

  The method of removing the solvent from the mixture of the carbon material, the positive electrode active material and the solvent is not particularly limited, but a method of removing the solvent by filtration and drying in an oven or the like can be mentioned. It is preferable that the said filtration is suction filtration from a viewpoint of improving productivity further. Moreover, as a drying method, when making it dry by vacuum after making it dry with a ventilation oven, it is preferable from the ability to remove the solvent which remains in the pore.

  When the weight ratio of the positive electrode active material to the carbon material in the active material-carbon material composite is 100, the weight of the carbon material is 0.2 or more and 10.0 or less. Is preferred. From the viewpoint of further improving the rate characteristics, the weight of the carbon material is more preferably 0.3 or more and 8.0 or less. Further, from the viewpoint of further improving the cycle characteristics, the weight of the carbon material is more preferably 0.5 or more and 7.0 or less.

[Electric storage device]
An electricity storage device of the present invention comprises the electrode for an electricity storage device of the present invention. Therefore, since the electrode resistance is low and the liquid retention of the electrolytic solution is excellent, improvement in battery performance can be expected.

  As described above, the electricity storage device of the present invention is not particularly limited, but is preferably a non-aqueous electrolyte primary battery, an aqueous electrolyte primary battery, a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, a capacitor, an electric double layer capacitor, or A lithium ion capacitor etc. are illustrated.

  The secondary battery as an example of the electricity storage device of the present invention may be a secondary battery that uses a compound in which the insertion and elimination reaction of an alkali metal ion or an alkaline earth metal ion proceeds. Examples of the alkali metal ion include lithium ion, sodium ion and potassium ion. As an alkaline earth metal ion, calcium ion or magnesium ion is illustrated. In particular, the present invention has a large effect on the positive electrode of the non-aqueous electrolyte secondary battery, and among them, the one using lithium ion is suitable. Hereinafter, a non-aqueous electrolyte secondary battery using lithium ion (hereinafter, lithium ion secondary battery) will be described as an example.

  The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery may have the same electrode formed on both sides of the current collector. The positive electrode is formed on one side of the current collector, and the negative electrode is formed on the other side. That is, it may be a bipolar electrode.

  The non-aqueous electrolyte secondary battery may be one in which a separator is disposed between the positive electrode side and the negative electrode side may be wound or may be stacked. The positive electrode, the negative electrode and the separator contain a non-aqueous electrolyte responsible for lithium ion conduction.

  The non-aqueous electrolyte secondary battery may be coated with a laminate film after winding or laminating a plurality of the laminates, and a square, oval, cylindrical, coin, button or sheet metal. It may be covered with a can. The exterior may have a mechanism for releasing the generated gas. The number of laminations of the laminated body is not particularly limited, and the lamination can be performed until a desired voltage value and battery capacity are exhibited.

  The non-aqueous electrolyte secondary battery can be a battery assembly suitably connected in series and in parallel according to a desired size, capacity and voltage. In the assembled battery, it is preferable that a control circuit be attached to the assembled battery in order to check the state of charge of each battery and to improve the safety.

  EXAMPLES Hereinafter, the present invention will be more specifically described by way of examples. However, the present invention is not limited at all by these examples, and can be appropriately modified without departing from the scope of the present invention.

Example 1
First, expanded graphite (manufactured by Toyo Carbon Co., Ltd., trade name “PF powder 8F, BET specific surface area = 22 m ² / g) was dry-pulverized by jet milling, to prepare a graphite powder having an average particle diameter of 10 μm. In addition, average particle diameter was computed by volume reference | standard distribution by the laser diffraction method using the laser diffraction / scattering type particle size distribution measuring apparatus (The HORIBA company make, brand name "LA-950").

  Next, a mixture of 16 g of dry-ground expanded graphite, 0.48 g of carboxymethylcellulose and 530 g of water is irradiated with ultrasonic waves for 5 hours with an ultrasonic treatment device, 80 g of polyethylene glycol is added, and 30 minutes is obtained by homomixer The raw material composition was produced by mixing.

  As carboxymethylcellulose, one manufactured by Aldrich (average molecular weight = 250,000) was used. As polyethylene glycol, Sanyo Chemical Industries, Ltd. make, brand name "PG600" was used. The ultrasonic processor is SMT. CO. Model No. “UH-600SR” manufactured by LTD. Moreover, the homomixer made from TOKUSHU KIKA company, and the model number "TK. HOMO MIXER MARKII" was used.

  Next, water was removed by heat-processing the produced raw material composition at 150 degreeC. Thereafter, the composition from which water was removed was heat treated at a temperature of 380 ° C. for 1 hour to produce a carbon material in which a part of polyethylene glycol remains.

  Finally, the produced carbon material was subjected to heat treatment at 420 ° C. for one hour in order to obtain a carbon material having a graphite structure and partially exfoliated graphite. The obtained carbon material contained 8% by weight of resin based on the total weight. The amount of resin was calculated as the amount of resin by using TG (manufactured by Hitachi High-Tech Science, product number "STA7300") and the weight loss in the range of 200 ° C to 600 ° C.

(Example 2)
A carbon material was obtained in the same manner as in Example 1 except that the final heating conditions were changed to heat treatment at 420 ° C. for 0.5 hours in order. The carbon material obtained in Example 2 contained 15% by weight of resin based on the total weight.

(Comparative example 1)
A carbon material of Comparative Example 1 was obtained using wet-pulverized exfoliated graphite (trade name "UP-5-α", BET specific surface area = 9 m ² / g, manufactured by Nippon Graphite Industry Co., Ltd.) using an ultrasonic homogenizer. .

(Comparative example 2)
Jet milling of expanded graphite (trade name "PF powder 8F", BET specific surface area = 22 m ² / g) (trade name, manufactured by Toyo Tanso Co., Ltd.) was changed to wet grinding with an ultrasonic homogenizer, and heating conditions were 460 ° C. A carbon material was obtained in the same manner as in Example 2 except that only 0.5 hours were used. The carbon material obtained in Comparative Example 1 contained 35% by weight of resin based on the total weight.

(Evaluation of carbon materials)
The following evaluation was performed using the carbon material obtained in Examples 1-2 and Comparative Examples 1-2. The results are shown in Table 1 below.

BET specific surface area;
The BET specific surface area was measured using a specific surface area measuring device (manufactured by Shimadzu Corporation, product number “ASAP-2000”, nitrogen gas).

Evaluation of pore volume;
The pore distribution of the carbon material was measured from an argon adsorption isotherm according to the HK method using Microtrac BEL, product number "BELSORP-MAX". From the measured pore distribution, a pore volume of 0.3 nm or more and 1.0 nm or less in diameter was determined.

Assessment of DBP oil absorption;
The DBP oil absorption amount was measured using an absorption amount measuring device (manufactured by Asahi Soken Co., product number “S500”) in accordance with JIS K 6217-4.

X-ray diffraction evaluation;
In addition, the obtained carbon material and silicon powder (Nano Powder, purity 98 98%, particle size ≦ 100 nm, manufactured by Aldrich) are mixed in a sample bottle at a weight ratio of 1: 1 to obtain a measurement sample. The mixed powder as was produced. The prepared mixed powder was put in a non-reflective Si sample stand and placed in an X-ray diffractometer (Smart Lab, manufactured by Rigaku Corporation). Thereafter, an X-ray diffraction spectrum was measured by a wide-angle X-ray diffraction method under the conditions of X-ray source: CuKα (wavelength 1.541 Å), measurement range: 3 ° to 80 °, and scan speed: 5 ° / min. From the obtained measurement results, the height d of the highest peak in the range of 2θ = 28 ° or more and less than 30 ° is normalized as 1, and then the highest peak in the range of 2θ = 24 ° or more and less than 28 ° C. The height c of was calculated. Finally, the ratio of c to d, that is, c / d was calculated.

Powder resistance;
100 mg or more of the carbon material was weighed, and measurement was performed by a four-end needle method using a low resistance powder measuring device (Loresta GX, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). A pressure of 4 kN was applied to the powder, and the resistance value at 20 kN was used.

Evaluation of coatability, electrolyte retention, and battery characteristics;
The coatability, the electrolyte solution retention property, and the battery characteristics were evaluated by preparing a non-aqueous electrolyte secondary battery as follows.

(Positive electrode)
First, 5 g of ethanol is added to 0.10 g of each carbon material of Examples 1 and 2 and Comparative Examples 1 and 2 and treated with an ultrasonic cleaner (manufactured by AS ONE) for 5 hours to prepare a dispersion of the carbon material. did.

Next, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as a positive electrode active material is described in a non-patent document (Journal of PowerSources, Vol. 146, pp. 636-639 (2005)) It was made by the method.

  That is, first, lithium hydroxide and a ternary hydroxide having a molar ratio of cobalt, nickel and manganese of 1: 1: 1 were mixed to obtain a mixture. Next, the mixture was heated at 1000 ° C. in an air atmosphere to prepare a positive electrode active material.

Next, 3 g of the obtained positive electrode active material (LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ ) is added to 9 g of ethanol, and the resulting mixture is stirred at 600 rpm for 10 minutes with a magnetic stirrer to obtain a positive electrode active material A dispersion was prepared.

  Furthermore, the dispersion liquid of the positive electrode active material was dropped to the dispersion liquid of the carbon material by a dropper. In addition, at the time of dripping, the dispersion liquid of the carbon material was continued to be treated by an ultrasonic cleaner (manufactured by AS ONE). Thereafter, the mixture of dispersions was stirred with a magnetic stirrer for 3 hours.

  Finally, the liquid mixture of the dispersion liquid was subjected to suction filtration and vacuum drying at 110 ° C. for 1 hour to produce a composite of the positive electrode active material and the carbon material (active material-carbon material composite). The amount needed to make the positive electrode was made by repeating the above steps.

  Next, a binder (PVdF, solid content concentration 12% by weight, NMP solution) was mixed with 96 parts by weight of the complex so that the solid content was 4 parts by weight, to prepare a slurry. Next, the slurry was applied to an aluminum foil (20 μm) and heated in a blast oven at 120 ° C. for 1 hour to remove the solvent, and then vacuum dried at 120 ° C. for 12 hours. Next, the slurry was similarly coated and dried on the back surface of the aluminum foil. In this case, the coatability was evaluated by the following evaluation criteria.

[Evaluation criteria]
○ ... not cracked, peeled off × ... cracked and / or peeled off

  Finally, it pressed by the roll press machine, and produced the positive electrode (double-sided coating). The electrode density was calculated from the weight and thickness of the electrode per unit area.

The capacity of the positive electrode was calculated from the weight of the electrode per unit area and the theoretical capacity (150 mAh / g) of the positive electrode active material. As a result, the capacity of the positive electrode (per one side) was 5 mAh / cm ² .

(Evaluation of positive electrode)
The following evaluation was performed using the positive electrode obtained in Examples 1-2 and Comparative Examples 1-2. The results are shown in Table 1 below.

Evaluation of porosity;
The porosity of the positive electrode was measured according to a mercury intrusion method using a mercury porosimeter (manufactured by micromeritics, trade name: Autopore IV 9520).

Evaluation of the ratio X / Y;
The pore distribution of the positive electrode was measured according to the mercury intrusion method using a mercury porosimeter (manufactured by micromeritics, trade name: Autopore IV 9520). In the obtained pore distribution, the maximum peak value in the range of pore diameters of 1 μm to 6 μm was X, and the maximum peak value in the range of pore diameters of 8 μm to 20 μm was Y, and the ratio X / Y was determined.

Evaluation of electrolyte retention
About the produced positive electrode, evaluation of electrolyte solution retention property was performed as follows.

Specifically, the liquid holding amount of the electrolyte was measured using a tuning fork type physical property tester (manufactured by A & D Co., Ltd., part number “TFP-10”). As a measurement procedure, two pieces of the produced positive electrode are cut in a circle so that the volume becomes 18.5 mm ^3, and a double-sided adhesive tape of a polyimide film substrate is attached to the aluminum foil side, and two pieces of tuning fork type physical property tester The positive electrodes were attached one by one to the sensitive plate of. The natural frequency of the two sensitive plates was 30 Hz, and dimethyl carbonate (DMC) with a specific gravity of 1.071 was used as the electrolyte. The vibration of the sensitive plate is started, the stress when immersed in the electrolyte is A1, the stress after 8 hours after immersion is A2, and the ratio A2 / A1 is defined as the relative electrolyte holding capacity. Evaluation was performed on the following evaluation criteria.

[Evaluation criteria]
○ ... ratio A2 / A1 is 1.15 or more and 1.50 or less × ... ratio A2 / A1 is less than 1.15 or greater than 1.50

Evaluation of output characteristics;
The output characteristics were evaluated by producing a negative electrode and a non-aqueous electrolyte secondary battery as follows.

(Negative electrode)
The negative electrode was produced as follows.

  First, a binder (PVdF, solid content concentration 12% by weight, NMP solution) was mixed with 100 parts by weight of a negative electrode active material (artificial graphite) so that the solid content was 5 parts by weight, to prepare a slurry. Next, the slurry was coated on a copper foil (20 μm) and heated in a blowing oven at 120 ° C. for 1 hour to remove the solvent, and then vacuum dried at 120 ° C. for 12 hours. Next, the slurry was coated and dried on the back of the copper foil in the same manner.

  Finally, it pressed by the roll press machine, and produced the negative electrode. The electrode density was calculated from the weight and thickness of the electrode per unit area.

The capacity of the negative electrode was calculated from the weight of the electrode per unit area and the theoretical capacity (350 mAh / g) of the negative electrode active material. As a result, the capacity (per one side) of the negative electrode was 6.0 mAh / cm ² .

(Manufacture of non-aqueous electrolyte secondary battery)
First, the prepared positive electrode (electrode part: 40 mm × 50 mm), negative electrode (electrode part: 45 mm × 55 mm) and separator (microporous polyolefin film, 25 μm, 50 mm × 60 mm), negative electrode / separator / positive electrode / separator / It laminated | stacked so that the capacity | capacitance of a positive electrode might be set to 200 mAh (one positive electrode, two negative electrodes) in the order of a negative electrode. Next, the aluminum tab and the nickel-plated copper tab are vibration-welded to the positive and negative electrodes at both ends, and then put in a bag-like aluminum laminate sheet, heat-welded in three directions, and the non-aqueous electrolyte secondary before electrolyte sealing. A battery was made. Furthermore, after vacuum drying the non-aqueous electrolyte secondary battery before sealing the electrolyte solution for 3 hours at 60 ° C., 20 g of non-aqueous electrolyte (ethylene carbonate / dimethyl carbonate = 1/2 volume%, LiPF ₆ 1 mol / L) is introduced A non-aqueous electrolyte secondary battery was produced by sealing under reduced pressure. In addition, the process to here was implemented by the atmosphere (dry box) whose dew point is -40 degrees C or less. Finally, after charging the non-aqueous electrolyte secondary battery to 4.25 V, it is allowed to stand at 25 ° C. for 100 hours, and the gas generated in the atmosphere (dry box) with a dew point of −40 ° C. or less and excess electrolysis After removing the liquid, the non-aqueous electrolyte secondary battery was manufactured by sealing again under reduced pressure.

(Output characteristics)
The produced non-aqueous electrolyte secondary battery was charged and discharged from 2.5 V to 4.25 V, and the output characteristic was calculated from the value of 2 C discharge capacity, with the value of the discharge capacity at 0.2 C being 100%.

  The results are shown in Table 1 below.

  When the carbon material of Examples 1-2 was used, it has confirmed that coatability and output characteristics were improved (appearability evaluation is (circle)). In addition, the carbon material of the comparative example 2 has a bad coatability (coatability evaluation is x), and it was not able to evaluate an electrode and a battery.

Claims (8)

A positive electrode used for a non-aqueous electrolyte secondary battery,
The positive electrode includes a carbon material having a graphene laminated structure, and a positive electrode active material,
The porosity of the positive electrode measured according to the mercury intrusion method is 10% or more and 45% or less,
In the pore distribution of the positive electrode measured according to the mercury intrusion method, assuming that the maximum peak value in the range of the pore diameter of 1 μm to 6 μm is X, the maximum peak value in the range of the pore diameter of 8 μm to 20 μm is Y The positive electrode for a non-aqueous electrolyte secondary battery, wherein the ratio X / Y is in the range of 3.0 or more and 10.0 or less. Two pieces of the positive electrode were cut out to have a volume of 18.5 mm ³ , and the cut out two positive electrodes were attached to two sensitive plates of a tuning fork type physical property tester, respectively, with a specific gravity of 1.071 When immersed in 30 mL of dimethyl carbonate and vibrating the sensitive plate at a natural frequency of 30 Hz,
The ratio A2 / A1 is 1. when the stress immediately after starting the vibration by immersing in the dimethyl carbonate is A1 mN, and the stress when 8 hours has elapsed after the vibration is started by immersing the dimethyl carbonate in the dimethyl carbonate is A2 mN. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, which is in the range of 15 or more and 1.50 or less. The BET specific surface area of the carbon material is 10 m ² / g or more and 200 m ² / g or less,
In the pore distribution of the carbon material measured according to the HK method, the pore volume of 0.3 nm or more and 1.0 nm in pore diameter is 0.2 mL / g or more,
The positive electrode for nonaqueous electrolyte secondary batteries according to claim 1 or 2, wherein the DBP oil absorption amount of the carbon material is 150 mL / 100 g or more.   The positive electrode for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 3, wherein the carbon material is exfoliated graphite.   When the X-ray diffraction spectrum of the mixture of the carbon material and Si at a weight ratio of 1: 1 is measured, the height c of the highest peak in the range of 24 ° to less than 28 ° and 2θ are The ratio c / d to the height d of the highest peak in the range of 28 ° or more and less than 30 ° is 0.2 or more and 1.0 or less. Positive electrode for non-aqueous electrolyte secondary batteries.   The positive electrode for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 5, wherein the carbon material is a conductive additive.   The positive electrode for non-aqueous electrolyte secondary batteries according to any one of claims 1 to 6, wherein the carbon material and the positive electrode active material are complexed to form a complex.   The nonaqueous electrolyte secondary battery provided with the positive electrode for nonaqueous electrolyte secondary batteries of any one of Claims 1-7.