JP2023027578A - Current collector for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery - Google Patents

Abstract

To provide a current collector for a non-aqueous electrolyte secondary battery that can reduce the battery resistance of the non-aqueous electrolyte secondary battery and improve safety.SOLUTION: A current collector used for a positive electrode or a negative electrode of a non-aqueous electrolyte secondary battery includes a resin, and a carbon material having a graphene laminated structure, and in the carbon material, in the X-ray diffraction measurement in a case in which the carbon material and Si are mixed at a weight ratio of 1:1, when the ratio a/b of the highest peak height a in the range of 2θ=24° or more and less than 28° to the highest peak height b in the range of 2θ=28° or more and less than 30° is 0.2 or more and 10.0 or less.SELECTED DRAWING: None

Description

The present invention relates to a current collector for nonaqueous electrolyte secondary batteries and a nonaqueous electrolyte secondary battery using the current collector for nonaqueous electrolyte secondary batteries.

BACKGROUND ART In recent years, research and development of non-aqueous electrolyte secondary batteries have been vigorously carried out for mobile devices, hybrid vehicles, electric vehicles, household power storage applications, and the like. Metal foils such as aluminum foil and copper foil are known as current collectors used for positive and negative electrodes of such non-aqueous electrolyte secondary batteries.

In recent years, resin current collectors have been studied as current collectors used for positive and negative electrodes of non-aqueous electrolyte secondary batteries. Since the resin current collector is lighter than the metal foil, the weight of the battery can be reduced. Therefore, the use of this resin current collector is expected to improve the output per unit weight of the battery, that is, the output density.

For example, Patent Literature 1 below discloses a positive electrode resin current collector formed by molding a resin composition. The resin composition is composed of a polyolefin resin and a conductive filler dispersed in the polyolefin resin. Further, Patent Document 1 describes that a carbon material such as carbon black is used as a conductive filler.

JP 2020-102387 A

However, as in Patent Document 1, a resin current collector using carbon black as a conductive filler has a higher resistance than a metal current collector using a metal foil, so the battery resistance can be sufficiently lowered. However, there is a problem that it is difficult to obtain desired battery characteristics. On the other hand, metal current collectors have the problem of insufficient battery safety.

An object of the present invention is to provide a current collector for a non-aqueous electrolyte secondary battery and a current collector for the non-aqueous electrolyte secondary battery that can reduce the battery resistance of the non-aqueous electrolyte secondary battery and improve the safety. An object of the present invention is to provide a non-aqueous electrolyte secondary battery using a conductor.

A current collector for a non-aqueous electrolyte secondary battery according to the present invention is a current collector used for a positive electrode or a negative electrode of a non-aqueous electrolyte secondary battery, comprising a resin and a carbon material having a graphene laminated structure, In the X-ray diffraction measurement when the carbon material and Si are mixed at a weight ratio of 1:1, the carbon material has the highest peak height a in the range of 2θ = 24 ° or more and less than 28 ° and 2θ ==28° or more and less than 30°, the ratio a/b to the height b of the highest peak is 0.2 or more and 10.0 or less.

In a specific aspect of the current collector for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material has a BET specific surface area of 20 m ² /g or more and 300 m ² /g or less.

In another specific aspect of the current collector for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material is partially exfoliated graphite having a structure in which graphite is partially exfoliated from edges.

In still another specific aspect of the current collector for a non-aqueous electrolyte secondary battery according to the present invention, the carbon material has an average particle size of 0.05 μm or more and 10.0 μm or less.

In still another specific aspect of the current collector for non-aqueous electrolyte secondary batteries according to the present invention, the resin is at least one selected from the group consisting of polyolefin resins, engineering plastics, and super engineering plastics.

A non-aqueous electrolyte secondary battery according to the present invention includes a current collector for a non-aqueous electrolyte secondary battery configured according to the present invention.

INDUSTRIAL APPLICABILITY According to the present invention, a current collector for a non-aqueous electrolyte secondary battery and a current collector for the non-aqueous electrolyte secondary battery that can reduce the battery resistance of the non-aqueous electrolyte secondary battery and improve safety. A non-aqueous electrolyte secondary battery using a conductor can be provided.

FIG. 1 is a schematic diagram for explaining the nail penetration test method. FIG. 2 is a schematic diagram showing an example of partially exfoliated graphite.

The details of the present invention are described below.

[Current collector for non-aqueous electrolyte secondary battery]
A current collector for a non-aqueous electrolyte secondary battery of the present invention is a current collector used for a positive electrode or a negative electrode of a non-aqueous electrolyte secondary battery. The current collector is a resin current collector containing a resin and a carbon material having a graphene laminated structure.

In the present invention, whether or not the carbon material has a graphene laminated structure is determined by measuring the X-ray diffraction spectrum of the carbon material using CuKα rays (wavelength: 1.541 Å), the peak near 2θ = 26° ( It can be confirmed by whether or not a peak derived from the graphene laminated structure) is observed. An X-ray diffraction spectrum can be measured by a wide-angle X-ray diffraction method. As an X-ray diffraction device, for example, SmartLab (manufactured by Rigaku Corporation) can be used.

In particular, in the present invention, in the X-ray diffraction measurement when the carbon material and Si are mixed at a weight ratio of 1:1, the height a of the highest peak in the range of 2θ = 24 ° or more and less than 28 °, The ratio a/b to the height b of the highest peak in the range of 2θ=28° or more and less than 30° is 0.2 or more and 10.0 or less. As Si, for example, silicon powder having a particle size of 100 nm or less can be used.

In the X-ray diffraction spectrum, a peak derived from the 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 a/b is the peak ratio between the peak near 2θ=26.4° and the peak near 2θ=28.5° (peak near 2θ=26.4°/near 2θ=28.5° peak).

ADVANTAGE OF THE INVENTION Since the collector for non-aqueous electrolyte secondary batteries of this invention is provided with the said structure, the battery resistance of a non-aqueous electrolyte secondary battery can be reduced, and also safety|security can be improved.

Conventionally, a resin current collector using carbon black has a higher resistance than a metal current collector using metal foil, so the battery resistance cannot be sufficiently lowered, and it is difficult to obtain the desired battery characteristics. There was a problem. On the other hand, metal current collectors have the problem of insufficient battery safety.

On the other hand, the present inventors focused on a carbon material used for a resin current collector, particularly having a graphene laminated structure, and furthermore, the ratio a/b obtained by X-ray diffraction measurement was the above-mentioned specific carbon material. It was found that by using a carbon material within the range, the battery resistance of the non-aqueous electrolyte secondary battery can be lowered, and the safety thereof can be improved.

In addition, when the ratio a/b is equal to or higher than the lower limit, the graphene laminated structure can be formed more reliably, so that the electron conductivity can be further enhanced. Therefore, battery resistance can be further reduced.

When the ratio a/b is equal to or less than the upper limit, the dispersibility of the carbon material in the resin can be enhanced, so that the electron conductivity can be further enhanced. Therefore, battery resistance can be further reduced.

Moreover, the safety can be explained by the nail penetration test shown in FIG.

FIG. 1 is a schematic diagram for explaining the nail penetration test method. In addition, Fig.1 (a) is a schematic diagram of the non-aqueous electrolyte secondary battery 1 before a nail penetration test. In the non-aqueous electrolyte secondary battery 1 , a positive electrode 3 and a negative electrode 4 are separated by a separator 2 . Current collectors 5 and 6 are provided on the positive electrode 3 and the negative electrode 4, respectively. FIG. 1(b) is a schematic diagram of the non-aqueous electrolyte secondary battery 1 immediately after the nail 7 has been pierced, and FIG. 1 is a schematic diagram of a secondary battery 1; FIG.

When metal current collectors are used as the current collectors 5 and 6, the electron conductivity in the plane direction X shown in FIG. Sometimes. This may cause the battery to generate abnormal heat, leading to an accidental discharge of the battery.

On the other hand, when the current collectors for a non-aqueous electrolyte secondary battery of the present invention are used as the current collectors 5 and 6, by adjusting the ratio a/b to the upper limit value or less, as shown in FIG. The electron conductivity in the plane direction X shown in c) can be appropriately controlled. Therefore, after the nail 7 is pierced, a large current is less likely to flow through the entire electrode, and abnormal heat generation of the battery can be suppressed. Thereby, the safety of the battery can be improved.

(Carbon material having graphene laminated structure)
The shape of the carbon material having a graphene laminated structure is not particularly limited, and examples thereof include a two-dimensionally spreading shape, a spherical shape, a fibrous shape, and an irregular shape. The shape of the carbon material is preferably a shape extending two-dimensionally. Examples of the two-dimensional shape include a scale-like shape and a plate-like shape (flat plate shape). In the case of having such a two-dimensionally spreading shape, an electron conducting path can be formed more easily than a particulate carbon material such as carbon black. Therefore, battery resistance can be further reduced.

Carbon materials having a graphene laminated structure include, for example, graphite and exfoliated graphite.

Graphite is a laminate of multiple graphene sheets. The number of laminated graphene sheets of graphite is usually about 100,000 to 1,000,000. As graphite, for example, natural graphite, artificial graphite, expanded graphite, or the like can be used.

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

In exfoliated graphite, the number of laminated graphene sheets is not particularly limited, but is preferably 2 layers or more, more preferably 5 layers or more, preferably 3000 layers or less, more preferably 1000 layers or less, and still more preferably 500 layers or less. be. When the number of laminated graphene sheets is equal to or more than the above lower limit, the conductivity of exfoliated graphite can be further enhanced. When the number of laminated graphene sheets is equal to or less than the above upper limit, the specific surface area of exfoliated graphite can be further increased.

Further, the exfoliated graphite is preferably partially exfoliated graphite having a structure in which graphite is partially exfoliated from edges. With partially exfoliated graphite, electron conduction paths can be formed more easily than with particulate carbon materials such as carbon black. In addition, when the partially exfoliated graphite is resin-retained partially exfoliated graphite, unlike carbon black, it is difficult to aggregate in the resin, and the electron conduction paths are formed more uniformly in the resin. can be done. In addition, partially exfoliated graphite itself has excellent electron conductivity compared to carbon black or the like. Therefore, when partially exfoliated graphite is used as the carbon material having a graphene laminated structure, the battery resistance can be further reduced.

As an example of a structure in which graphite is partially exfoliated, in a graphene laminate, the graphene layers are open from the edge to the inside to some extent, that is, part of the graphite is exfoliated at the edge. , and a structure in which graphite layers are laminated in the same manner as the original graphite or primary exfoliated graphite in the central portion. In this case, the part where the graphite is partly peeled off at the edge continues to the part on the central side. Furthermore, the partially exfoliated graphite may include exfoliated graphite at the edges.

In the partially exfoliated graphite, graphite layers are laminated in the same manner as the original graphite or primary exfoliated graphite in the central portion. Therefore, it has a higher degree of graphitization than conventional graphene oxide and carbon black, and has excellent conductivity. Moreover, since it has a structure in which graphite is partially exfoliated, it has a large specific surface area.

FIG. 2 is a schematic diagram showing an example of partially exfoliated graphite. As shown in FIG. 2, the partially exfoliated graphite 10 has a structure in which the edge portions 11 are exfoliated. On the other hand, the central portion 12 has the same graphite structure as the original graphite or primary exfoliated graphite. Also, in the edge portion 11, the resin 13 is arranged between the separated graphene layers. Incidentally, the resin 13 may be completely removed. However, from the viewpoint of forming more uniform electron conduction paths in the resin, as shown in FIG. 2, resin-retained partially exfoliated graphite is preferable.

The number of graphene layers in the partially exfoliated graphite is preferably 2 or more and 3000 or less, more preferably 5 or more and 1000 or less, and 10 or more and 500 or less. More preferred. When the number of graphene layers is within the above range, the battery resistance of the non-aqueous electrolyte secondary battery can be further reduced.

Although the method for calculating the number of graphene layers is not particularly limited, it can be calculated by visual observation using a transmission electron microscope (TEM) or the like.

Partially exfoliated graphite, for example, comprises graphite or primary exfoliated graphite and a resin, and prepares a composition in which the resin is fixed to graphite or primary exfoliated graphite by grafting or adsorption, and can be obtained by thermally decomposing the resin contained in When the resin is thermally decomposed, the resin may be thermally decomposed while a part of the resin remains, or the resin may be thermally decomposed completely.

Partially exfoliated graphite can be produced, for example, by a method similar to the method for producing an exfoliated graphite-resin composite material described in WO 2014/034156. Further, as the graphite, it is preferable to use expanded graphite because it is possible to exfoliate the graphite more easily. Alternatively, it is preferable to use artificial graphite from the viewpoint that the degree of graphitization is high and the conductivity is even higher. When the resin is thermally decomposed, the resin may be thermally decomposed while a part of the resin remains, or the resin may be thermally decomposed completely.

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

The graphite or primary exfoliated graphite to be used may be one subjected to layer thinning treatment. Examples of devices used for the thinning process include dry atomization devices, wet atomization devices, high-pressure emulsification devices, vacuum emulsification devices, vacuum bead mills, and stirring devices.

The heating temperature for the thermal decomposition of the resin is not particularly limited depending on the type of resin, but can be, for example, 250°C to 1000°C. The heating time can be, for example, 10 minutes to 5 hours. Moreover, the heating may be performed in the air or in an atmosphere of an inert gas such as nitrogen gas. However, from the viewpoint of further increasing the conductivity of the obtained partially exfoliated graphite, it is desirable to perform the heating in an atmosphere of an inert gas such as nitrogen gas.

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

Examples of radically polymerizable monomers include styrene, methyl α-ethylacrylate, methyl α-benzylacrylate, methyl α-[2,2-bis(carbomethoxy)ethyl]acrylate, dibutyl itaconate, and dimethyl itaconate. , dicyclohexyl itaconate, α-methylene-δ-valerolactone, α-methylstyrene, α-substituted acrylic acid ester consisting of α-acetoxystyrene, glycidyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate, hydroxyethyl methacrylate, hydroxy vinyl monomers having a glycidyl group or a hydroxyl group such as ethyl acrylate, hydroxypropyl acrylate and 4-hydroxybutyl methacrylate; vinyl monomers and methacryl having an amino group such as allylamine, diethylaminoethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate acid, maleic anhydride, maleic acid, itaconic acid, acrylic acid, crotonic acid, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, 2-methacryloyloxyethyl phthalic acid and other monomers having a carboxyl group; Phosmer (registered trademark) M, Phosmer (registered trademark) CL, Phosmer (registered trademark) PE, Phosmer (registered trademark) MH, Phosmer (registered trademark) PP manufactured by Unichemical Co., Ltd.; monomers having an alkoxysilyl group such as methoxysilane and 3-methacryloxypropyltrimethoxysilane; and (meth)acrylate monomers having an alkyl group or a benzyl group.

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

Among the above resins, polyethylene glycol, polypropylene glycol, polyvinyl acetate, polyvinyl alcohol, and polyvinyl butyral (butyral resin) can be preferably used. When polyethylene glycol, polypropylene glycol, polyvinyl acetate, polyvinyl alcohol, or polyvinyl butyral (butyral resin) is used, the specific surface area of the partially exfoliated graphite can be further increased. Incidentally, the resin species can be appropriately selected in view of the affinity with the solvent to be used.

The content of the resin fixed to the graphite or primary exfoliated graphite before pyrolysis is preferably 1 part by weight or more, more preferably 10 parts by weight, with respect to 100 parts by weight of graphite or primary exfoliated graphite excluding the resin content. Above, preferably 1000 parts by weight or less, more preferably 500 parts by weight or less. When the content of the resin before thermal decomposition is equal to or higher than the above lower limit, it is easier to control the content of the residual resin after thermal decomposition. Moreover, when the content of the resin before thermal decomposition is equal to or less than the above upper limit, it is more advantageous in terms of cost.

The content of the residual resin after thermal decomposition is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and preferably 800 parts by weight or less with respect to 100 parts by weight of the partially exfoliated graphite containing the resin content. , more preferably 400 parts by weight or less. When the content of the residual resin is equal to or higher than the above lower limit, electron conduction paths can be formed more uniformly in the resin. Further, when the content of the residual resin is equal to or less than the above upper limit, the electronic conductivity of the partially exfoliated graphite itself can be further enhanced.

The content of the resin before thermal decomposition and the content of the residual resin after thermal decomposition can be calculated by, for example, thermogravimetric analysis (hereinafter referred to as TG) measuring the weight change accompanying the heating temperature.

When producing partially exfoliated graphite, gas activation treatment may be further performed to form pores. The residual resin may be carbonized by the gas activation treatment. Examples of gas activation treatments include steam activation, carbon dioxide activation, and oxygen activation.

The temperature of the gas activation treatment can be, for example, 400.degree. C. to 950.degree. Also, the holding time at that temperature can be, for example, 15 minutes to 3 hours. Above all, the temperature of the gas activation treatment is preferably 400° C. to 600° C. in a low oxygen atmosphere, and preferably 800° C. to 1000° C. in a carbon dioxide atmosphere. The holding time at that temperature is preferably 30 minutes to 2 hours.

In addition, the obtained partially exfoliated graphite can be pulverized by mills such as mill mixers, blender mills, jet mills and ball mills, classified, or added to water, methanol, ethanol, N-methylpyrrolidone (NMP). It may be used after being placed in a representative organic solvent and then subjected to ultrasonic treatment. For example, when pulverizing with a mixer, the particle size can be adjusted by adjusting the pulverization time.

When the carbon material having a graphene laminated structure is partially exfoliated graphite, the ratio a/b measured by the X-ray diffraction method is, for example, the amount of resin before pyrolysis, or the amount of resin before pyrolysis. It can be adjusted by the type of resin used, the heating temperature and heating time during thermal decomposition, the oxygen concentration, and the like. Specifically, the ratio a/b is increased by reducing the amount of resin before thermal decomposition, shortening the heating time during thermal decomposition, lowering the heating temperature, and increasing the oxygen concentration. can do.

In the present invention, the BET specific surface area of the carbon material having a graphene laminated structure is not particularly limited, but is preferably 20 m ² /g or more, more preferably 30 m ² /g or more, preferably 300 m ² /g or less, and more preferably 200 m ² /g or less. When the BET specific surface area of the carbon material having the graphene laminated structure is within the above range, the battery resistance can be further reduced.

The BET specific surface area can be measured from a nitrogen adsorption isotherm according to the BET method. As a measuring device, for example, Shimadzu Corporation's product number "ASAP-2000" can be used.

In the present invention, the average particle size of the carbon material having a graphene laminated structure is preferably 0.05 μm or more, more preferably 0.1 μm or more, preferably 10.0 μm or less, and more preferably 7.0 μm or less. When the average particle size of the carbon material having the graphene laminated structure is within the above range, the battery resistance can be further reduced. The average particle size of the carbon material can be determined, for example, from the volume average particle size (D50) measured by a laser diffraction/scattering particle size distribution analyzer manufactured by Microtrack Bell.

The content of the carbon material having a graphene laminated structure is preferably 1.0% by weight or more, more preferably 5.0% by weight or more, and preferably 80% by weight, based on the total amount of the current collector for a non-aqueous electrolyte secondary battery. 60% by weight or less, more preferably 60% by weight or less. When the content of the carbon material having a graphene laminated structure is within the above range, the battery resistance can be further reduced.

(Other carbon materials)
The current collector for a non-aqueous electrolyte secondary battery of the present invention contains a second carbon material different from the first carbon material when the carbon material having the graphene laminated structure is used as the first carbon material. You can

Examples of the second carbon material include, but are not limited to, graphene, granular graphite compounds, fibrous graphite compounds, carbon black, or activated carbon. Among them, from the viewpoint of further lowering the battery resistance, the second carbon material is preferably carbon black.

The graphene may be graphene oxide or reduced graphene oxide.

The particulate graphite compound is not particularly limited, and examples thereof include natural graphite, artificial graphite, expanded graphite, and the like.

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

These second carbon materials may be used singly or in combination.

The BET specific surface area of the second carbon material is preferably 5 m ² /g or more, more preferably 10 m ² /g or more, preferably 2500 m ² /g or less, more preferably 2000 m ² /g or less. When the BET specific surface area of the second carbon material is within the above range, the battery resistance can be further reduced.

The average particle size of the second carbon material is preferably 30 nm or more, more preferably 50 nm or more, preferably 1000 nm or less, and more preferably 800 nm or less. When the average particle size of the second carbon material is within the above range, the battery resistance can be further reduced. The average particle size of the second carbon material is a value obtained by measuring the size of each particle using a SEM (scanning electron microscope) and calculating the average particle size.

The content of the second carbon material is preferably 1% by weight or more, more preferably 5% by weight or more, preferably 80% by weight or less, more preferably 60% by weight, based on the total amount of the current collector for non-aqueous electrolyte secondary batteries. % by weight or less. When the content of the second carbon material is within the above range, the battery resistance can be further reduced.

The first carbon material and the second carbon material can be distinguished from each other by, for example, scanning electron microscope (SEM) or transmission electron microscope (TEM).

(resin)
A current collector for a non-aqueous electrolyte secondary battery of the present invention contains a resin. In addition, resin here is resin used as the matrix of the collector for nonaqueous electrolyte secondary batteries. In the present invention, it is desirable that a carbon material having a graphene laminated structure is dispersed in this resin.

The resin is not particularly limited as long as it is a group 1 or group 2 resin that does not have ion conductivity, and examples thereof include polyolefin resins, engineering plastics, and super engineering plastics. These resins may be used individually by 1 type, and may use multiple types together.

Examples of polyolefin resins include polypropylene and polyethylene.

Engineering plastics include, for example, polyamide, polyacetal, polycarbonate, polyphenylene ether, polybutylene terephthalate, ultra-high molecular weight polyethylene, and polyvinylidene fluoride.

Examples of super engineering plastics include polysulfone, polyethersulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, polyetheretherketone, polyimide, and polytetrafluoroethylene.

Among these resins, polypropylene, polyethylene, polyphenylene ether, ultra-high molecular weight polyethylene, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, polyether ether ketone, and polyimide are preferable because they are easy to mold in sheet form. . Among these resins, polypropylene, polyethylene, and ultra-high molecular weight polyethylene are more preferable because they are superior in terms of cost.

The content of the resin is preferably 20% by weight or more, more preferably 40% by weight or more, preferably 99% by weight or less, and more preferably 95% by weight or less, relative to the total amount of the current collector for non-aqueous electrolyte secondary batteries. be. When the resin content is equal to or higher than the above lower limit, the weight of the battery can be further reduced. Moreover, when the content of the resin is equal to or less than the above upper limit value, the battery resistance can be further reduced.

(Current collector for non-aqueous electrolyte secondary battery)
A current collector for a non-aqueous electrolyte secondary battery can be produced, for example, by melt-kneading and molding a resin composition containing a resin and a carbon material having a graphene laminated structure. For example, it can be obtained by melt-kneading the resin composition using an extruder and molding it into a film. Alternatively, it can be obtained by molding a slurry of a resin composition containing a resin dissolved in a solvent and a carbon material having a graphene laminated structure into a film by a casting method. Examples of the solvent include dimethylsulfoxide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, alcohols such as methanol, and water.

The melt-kneading temperature may be higher than the temperature at which the resin melts and lower than the temperature at which the resin is decomposed. Moreover, the time for melting and kneading can be, for example, 1 minute or more and 5 hours or less.

The thickness of the current collector for non-aqueous electrolyte secondary batteries is not particularly limited, but can be, for example, 5 μm or more and 100 μm or less.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention may be one that uses a compound that allows the insertion and elimination reactions of alkali metal ions or alkaline earth metal ions to proceed. Alkali metal ions are exemplified by lithium ions, sodium ions, or potassium ions. Examples of alkaline earth metal ions include calcium ions and magnesium ions. In particular, a lithium ion secondary battery using lithium ions can be suitably used.

(current collector)
The non-aqueous electrolyte secondary battery of the present invention includes the current collector for a non-aqueous electrolyte secondary battery of the present invention described above. Therefore, in the non-aqueous electrolyte secondary battery of the present invention, the battery resistance can be lowered and the safety of the battery can be improved. The current collector for a non-aqueous electrolyte secondary battery of the present invention may be provided on at least one of the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery, but is preferably provided on both the positive electrode and the negative electrode.

(positive electrode)
The positive electrode used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and for example, an electrode containing a positive electrode active material and a conductive aid can be used.

When the non-aqueous electrolyte secondary battery of the present invention is a lithium ion secondary battery, examples of the positive electrode active material include lithium metal oxide, lithium sulfide, and sulfur.

Lithium metal oxides include those having a spinel structure, layered rock salt structure, olivine structure, or mixtures thereof.

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, and lithium manganese phosphate.

The conductive aid is not particularly limited, and graphene, granular graphite compound, fibrous graphite compound, carbon black, activated carbon, or the like can be used. Graphite, exfoliated graphite, or partially exfoliated graphite described above may also be used as the conductive aid.

(negative electrode)
The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but one containing a negative electrode active material such as natural graphite, artificial graphite, hard carbon, metal oxide, lithium titanate, or silicon is used. can be done.

(separator)
The separator used in the non-aqueous electrolyte secondary battery of the present invention may be placed between the positive electrode and the negative electrode, and has insulating properties and a structure capable of containing the later-described non-aqueous electrolyte. Examples of such separators include nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, and polyethylene terephthalate. In addition, woven fabrics, non-woven fabrics, microporous membranes, etc., which are composites of two or more of these, can also be mentioned.

The separator may contain various plasticizers, antioxidants, and flame retardants, or may be coated with metal oxide or the like.

Although the thickness of the separator is not particularly limited, it is preferably 5 μm or more and 100 μm or less. When the thickness of the separator is equal to or greater than the above lower limit value, contact between the positive electrode and the negative electrode can be made more difficult. When the thickness of the separator is equal to or less than the upper limit, the battery resistance can be further reduced. From the viewpoint of economic efficiency and handleability, the thickness of the separator is more preferably 10 μm or more and 50 μm or less.

(Non-aqueous electrolyte)
The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but for example, an electrolytic solution obtained by dissolving a solute in a non-aqueous solvent can be used. In addition, a gel electrolyte in which a polymer is impregnated with an electrolytic solution in which a solute is dissolved in a non-aqueous solvent, a polymer solid electrolyte such as polyethylene oxide or polypropylene oxide, or an inorganic solid electrolyte such as sulfide glass or oxynitride is used. good too.

The non-aqueous solvent preferably contains a cyclic aprotic solvent and/or a chain aprotic solvent, since the solute described later can be dissolved more easily.

Examples of cyclic aprotic solvents include cyclic carbonates, cyclic esters, cyclic sulfones, and cyclic ethers.

Examples of chain aprotic solvents include chain carbonates, chain carboxylic acid esters and chain ethers.

A solvent such as acetonitrile that is generally used as a solvent for non-aqueous electrolytes may also be used. More specifically, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, sulfolane, dioxolane, propion Methyl acid and the like can be used. These solvents may be used alone, or two or more solvents may be mixed and used. However, it is preferable to use a solvent in which two or more kinds of solvents are mixed, from the viewpoint of more easily dissolving the solute described later and further increasing the ion conductivity of lithium ions and the like.

The solute is not particularly limited, but LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBOB (Lithium Bis (Oxalato) Borate), or LiN(SO ₂ CF ₃ ) ₂ is preferably used. . In this case, it can be dissolved more easily with a non-aqueous solvent. The concentration of the solute contained in the electrolytic solution is preferably 0.5 mol/L or more and 2.0 mol/L or less. When the solute concentration is equal to or higher than the above lower limit, desired lithium ion conductivity can be obtained more reliably. On the other hand, when the concentration of the solute is equal to or less than the above upper limit, the solute can be made easier to dissolve.

In addition, the non-aqueous electrolyte may further contain additives such as flame retardants and stabilizers.

(Non-aqueous electrolyte secondary battery)
The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery of the present invention may be in the form of forming the same electrode on both sides of the current collector. It may also be in the form of a bipolar electrode.

The above-mentioned non-aqueous electrolyte secondary battery may be one in which a separator is arranged between the positive electrode side and the negative electrode side, and may be wound or laminated. The positive electrode, negative electrode, and separator contain a non-aqueous electrolyte that conducts ions such as lithium.

The non-aqueous electrolyte secondary battery may be wrapped with a laminate film after winding the laminate or laminated in multiple layers, or may be a rectangular, elliptical, cylindrical, coin-shaped, button-shaped, or sheet-shaped metal battery. It may be packaged in a can. The exterior may be provided with a mechanism for releasing generated gas. The number of stacked layers is not particularly limited, and the layers can be stacked until a desired voltage value and battery capacity are obtained.

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

Hereinafter, the effects of the present invention will be clarified by giving specific examples and comparative examples of the present invention. In addition, the present invention is not limited to the following examples.

(Production example 1 of carbon material)
First, a mixture of 16 g of expanded graphite, 0.48 g of carboxymethylcellulose, and 530 g of water was irradiated with ultrasonic waves for 5 hours with an ultrasonicator, and then 80 g of polyethylene glycol was added and mixed for 30 minutes with a homomixer. , to prepare a raw material composition.

The expanded graphite used was trade name “PF Powder 8F” (BET specific surface area=22 m ² /g) manufactured by Toyo Tanso Co., Ltd. Carboxymethylcellulose used was Aldrich's product (weight average molecular weight = 250,000). Polyethylene glycol used was Sanyo Chemical Industries Co., Ltd., trade name “PG600”. The ultrasonic processor is SMT. CO. , Ltd., model number "UH-600SR" was used. As the homomixer, model number "TK HOMOMIXER MARKII" manufactured by TOKUSHU KIKA was used.

Next, water was removed by heat-treating the prepared raw material composition at 150° C. (first heat-treating). After that, the composition from which water was removed was subjected to a heat treatment (second heat treatment) at a temperature of 380° C. for 1 hour to prepare a carbon material in which a part of polyethylene glycol remained.

Finally, the produced carbon material is heat-treated at 400° C. for 30 minutes and then at 350° C. for 2 hours (third heat treatment), thereby having a graphite structure and partially exfoliating graphite from the edges. , we obtained a carbon material.

The obtained carbon material and silicon powder (Nano Powder, purity ≧98%, particle size ≦100 nm, manufactured by Aldrich) were mixed in a sample bottle at a weight ratio of 1:1 to obtain a measurement sample. A mixed powder was produced. The prepared mixed powder was placed in a non-reflecting Si sample stage, and placed in an X-ray diffractometer (manufactured by Rigaku, product number "Smart Lab"). After that, the X-ray diffraction spectrum was measured by the wide-angle X-ray diffraction method under the conditions of X-ray source: CuKα (wavelength: 1.541 Å), measurement range: 3° to 80°, scan speed: 5°/min. From the obtained measurement results, the height b of the highest peak in the range of 2θ = 28 ° or more and less than 30 ° is normalized as 1, and the highest peak in the range of 2θ = 24 ° or more and less than 28 ° C. was calculated. Finally, the ratio between a and b, that is, the ratio a/b was calculated. As a result, the ratio a/b of the highest peak height a in the range of 2θ = 24° or more and less than 28°C and the highest peak height b in the range of 2θ = 28° or more and less than 30° is , 0.65.

In addition, the BET specific surface area of the obtained carbon material was measured using a specific surface area measuring device (manufactured by Shimadzu Corporation, product number “ASAP-2000”, nitrogen gas) and found to be 95 m ² /g.

(Production example 2 of carbon material)
A carbon material was obtained in the same manner as in Production Example 1, except that the conditions for the third heat treatment were 420° C. for 30 minutes. Moreover, the ratio a/b measured in the same manner as in Production Example 1 was 0.80, and the BET specific surface area was 38 m ² /g.

(Production example 3 of carbon material)
A carbon material was obtained in the same manner as in Production Example 1, except that the conditions for the third heat treatment were 400° C. for 10 minutes. Moreover, the ratio a/b measured in the same manner as in Production Example 1 was 0.32, and the BET specific surface area was 155 m ² /g.

(Production example 4 of carbon material)
Instead of the carbon material produced in Production Example 1, untreated expanded graphite (manufactured by Toyo Tanso Co., Ltd., trade name "PF Powder 8F", BET surface area = 22 m ² /g) was used as it was.

The untreated expanded graphite had a ratio a/b of 2.20 and a BET specific surface area of 22 m ² /g, which were measured in the same manner as in Production Example 1.

(Example 1)
Preparation of resin current collector;
The resin current collector of Production Example 1 was produced as follows. First, 80 parts by weight of homopolypropylene (weight average molecular weight = 413,000, melting point 163°C) and the carbon material of Production Example 1 (ratio a/b: 0.65, BET specific surface area: 95 m ² /g) 20 parts by weight were supplied to an extruder and melt-kneaded at a resin temperature of 200°C. Next, a homopolypropylene film containing the carbon material of Production Example 1 ( thickness of 50 μm).

preparation of the positive electrode;
First, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ as a positive electrode active material is described in Non-Patent Literature (Journal of PowerSources, Vol. 146, pp. 636-639 (2005)). method. That is, after mixing lithium hydroxide and a ternary hydroxide in which the molar ratio of cobalt, nickel and manganese is Co:Ni:Mn=2:5:3, the mixture was placed in an air atmosphere at 1000 ° C. A positive electrode active material was produced by heating.

Next, 93 g of the positive electrode active material (LiNi _0.5 Mn _0.3 Co _0.2 O ₂ ), 5 g of carbon black (Denka Black, manufactured by Denka), a binder (polyvinylidene fluoride (PVdF), solid content A slurry was prepared by mixing 25 g of an N-methyl-2-pyrrolidone (NMP) solution with a concentration of 8% by weight and 30 g of NMP. This slurry was applied to one side (surface) of the resin current collector obtained above, heated at 80° C. for 10 minutes in an air blowing oven, and then vacuum-dried at 150° C. for 12 hours. Next, the slurry was applied to the back surface of the resin current collector in the same manner and dried. Finally, the positive electrode used in Example 1 was produced by pressing the resin current collector with a roll press. The capacity of the positive electrode was calculated from the electrode weight per unit area and the theoretical capacity (160 mAh/g) of the positive electrode active material. As a result, the capacity of the positive electrode (per side) was 2 mAh/cm ² .

Preparation of the negative electrode;
First, 93 g of a negative electrode active material (artificial graphite), 5 g of carbon black (Denka Black, manufactured by Denka), 25 g of a binder (PVdF, solid content concentration weight %, NMP solution), and 30 g of NMP are mixed to prepare a slurry. bottom. Next, the slurry was applied to one side (surface) of the resin current collector obtained above, and heated at 80° C. for 10 minutes in a fan oven. Moreover, after removing the solvent, it was vacuum-dried at 100° C. for 12 hours. Next, the slurry was applied to the back surface of the resin current collector in the same manner and dried. Finally, it was pressed with a roll press machine to produce a negative electrode. The capacity of the negative electrode was calculated from the electrode weight per unit area and the theoretical capacity (350 mAh/g) of the negative electrode active material. As a result, the capacity of the negative electrode (per side) was 2.5 mAh/cm ² .

Manufacture of non-aqueous electrolyte secondary batteries;
First, the positive electrode (electrode part: 50 mm × 100 mm), the negative electrode (electrode part: 55 mm × 105 mm), and the separator (polyolefin-based microporous film, thickness: 25 µm, 60 mm × 100 mm) were prepared. They were laminated in the order of positive electrode/separator/negative electrode so that the capacity of the positive electrode was 1000 mAh (5 positive electrodes, 6 negative electrodes). Next, an aluminum tab and a nickel-plated copper tab were connected to the positive electrode and the negative electrode at both ends, respectively, and an aluminum needle and a copper needle were respectively connected using a stapler.

After that, it was placed in a bag-like aluminum laminate sheet and heat-sealed on three sides to produce a non-aqueous electrolyte secondary battery before enclosing the electrolyte. Furthermore, the non-aqueous electrolyte secondary battery before enclosing the electrolyte solution was vacuum-dried at 60 ° C. for 3 hours, and the non-aqueous electrolyte (LiPF ₆ 1 mol / L ethylene carbonate / dimethyl carbonate solution, volume ratio ethylene carbonate: dimethyl carbonate = 1:2) was added and sealed while reducing the pressure to produce a non-aqueous electrolyte secondary battery. The steps up to this point were performed in an atmosphere (dry box) with a dew point of −40° C. or lower. Finally, after charging the non-aqueous electrolyte secondary battery to 4.25 V, it was left at 25 ° C. for 100 hours, and the gas generated in an atmosphere (dry box) with a dew point of −40 ° C. or less and excessive electrolysis After removing the liquid, the non-aqueous electrolyte secondary battery of Example 1 was produced by sealing again while reducing the pressure.

(Example 2)
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the carbon material of Production Example 2 was used instead of the carbon material of Production Example 1.

(Example 3)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the carbon material of Production Example 3 was used instead of the carbon material of Production Example 1.

(Example 4)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that the carbon material of Production Example 4 was used instead of the carbon material of Production Example 1.

(Comparative example 1)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that instead of the carbon material of Production Example 1, acetylene black was used as it was. The ratio a/b of acetylene black was 0.09, and the BET specific surface area was 65 m ² /g.

(Comparative example 2)
Instead of the resin current collector used in Example 1, aluminum foil (thickness: 15 µm) was used as the current collector on the positive electrode side, and copper foil (thickness: 15 µm) was used as the current collector on the negative electrode side. produced a non-aqueous electrolyte secondary battery in the same manner as in Example 1.

(Comparative Example 3)
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1, except that instead of the carbon material of Production Example 1, commercially available highly oriented pyrolytic graphite (HOPG) was used as it was. The ratio a/b of HOPG was 11.90, and the BET specific surface area was 3 m ² /g.

[evaluation]
Battery resistance evaluation of non-aqueous electrolyte secondary battery;
Battery resistance evaluation was performed as follows. First, the battery was connected to a charge/discharge tester (TOSCAT3100, manufactured by Toyo System Co., Ltd.) and left for 12 hours without applying current. Next, 0.2C CCCV charge (charge end voltage: 4.25V, CV STOP: 3 hours, or current value reaches 0.02C, rest time after charge: 1 minute), and 0.2C CC discharge (discharge end Voltage: 2.5 V, rest time after discharge: 1 minute), charging and discharging were repeated 5 times. This confirms whether it functions as a battery. Subsequently, for the resistance measurement, the voltage values were recorded when the battery was discharged at 0.5C, 1.0C, and 2.0C for 10 seconds from the state of 50% discharge at 0.2C from the fully charged state. Using these values, create a graph of X-axis: rate current value, Y-axis: recorded voltage value, and from Ohm's law "V (voltage) = I (current) x R (resistance)", the slope By calculating the battery resistance was calculated. In addition, the battery resistance of less than 30 mΩ was evaluated as ◯, and the battery resistance of 30 mΩ or more was evaluated as x.

Safety evaluation of non-aqueous electrolyte secondary batteries;
The safety evaluation of the non-aqueous electrolyte secondary battery was evaluated by a nail penetration test as follows. First, the battery was connected to a charge/discharge tester (TOSCAT3100, manufactured by Toyo System Co., Ltd.) and left for 12 hours without applying current. After that, 0.2C CCCV charging (charging end voltage: 4.25 V, CV STOP: 3 hours, or current value reached 0.02C, rest time after charging: 1 minute) was performed. Next, the charged battery is placed in a special aluminum box in the draft, and a nail (nail diameter: 3 mmφ, tip angle: 60 degrees) is pierced through the center of the battery at a penetration speed of 100 mm/sec. The temperature rise of the battery was measured. In addition, the thermometer was measured at a point 1 cm away from the penetration point of the nail. In the safety evaluation, ◯ is given when the temperature is lower than 50°C, and x is given when the temperature is 50°C or higher.

The results are shown in Table 1 below.

It was confirmed that the batteries using the resin current collectors of Examples 1-4 had lower battery resistance and superior safety than the batteries using the current collectors of Comparative Examples 1-3.

DESCRIPTION OF SYMBOLS 1... Nonaqueous electrolyte secondary battery 2... Separator 3... Positive electrode 4... Negative electrode 5, 6... Current collector 7... Nail 10... Partial exfoliation type exfoliated graphite 11... Edge part 12... Central part 13... Resin

Claims (6)

A current collector used for the positive electrode or negative electrode of a non-aqueous electrolyte secondary battery,
a resin;
a carbon material having a graphene laminated structure;
including
In the X-ray diffraction measurement when the carbon material and Si are mixed at a weight ratio of 1:1, the carbon material has the highest peak height a in the range of 2θ = 24 ° or more and less than 28 ° and 2θ A current collector for a non-aqueous electrolyte secondary battery, wherein the ratio a/b to the height b of the highest peak in the range of =28° or more and less than 30° is 0.2 or more and 10.0 or less. The current collector for a non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon material has a BET specific surface area of 20 ^m2 /g or more and 300 ^m2 /g or less. 3. The current collector for a non-aqueous electrolyte secondary battery according to claim 1, wherein said carbon material is partially exfoliated graphite having a structure in which graphite is partially exfoliated from edges. The current collector for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the carbon material has an average particle size of 0.05 µm or more and 10.0 µm or less. The current collector for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein said resin is at least one selected from the group consisting of polyolefin resins, engineering plastics, and super engineering plastics. A nonaqueous electrolyte secondary battery comprising the current collector for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 5.

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