JP2016219285A - Negative electrode for nonaqueous electrolyte secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means capable of sufficiently reducing gas yield in initial charge, in a nonaqueous electrolyte secondary battery.SOLUTION: A method for manufacturing a negative electrode for a nonaqueous electrolyte secondary battery of the present invention includes: a drying step of coating, on a current collector, an aqueous slurry containing a negative electrode active material, carboxymethyl cellulose or a salt thereof, and an aqueous binder and then drying the coated aqueous slurry; and a heat treatment step of performing heat treatment after the drying step. The drying step is performed at a temperature of 130°C or above under an atmosphere with an oxygen concentration at 20°C of 8.0×10mol/L or more, and the heat treatment step is performed at a temperature of 90°C or above under an atmosphere with an oxygen concentration at 20°C of 5.3×10mol/L or less.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode for a nonaqueous electrolyte secondary battery and a method for producing the same.

  In recent years, the development of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) has been promoted against the background of the increasing environmental protection movement. A secondary battery that can be repeatedly charged and discharged is suitable as a power source for driving these motors, and a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery that can be expected to have a high capacity and a high output is attracting attention.

Nonaqueous electrolyte secondary batteries generally have a configuration in which a positive electrode and a negative electrode are connected via an electrolyte layer. The positive electrode has a positive electrode active material layer containing a positive electrode active material (for example, LiCoO ₂ , LiMnO ₂ , LiNiO _2, etc.) formed on the current collector surface. The negative electrode includes a negative electrode active material (for example, a carbonaceous material such as metallic lithium, coke and natural / artificial graphite, a metal such as Sn and Si, and an oxide material thereof) formed on the surface of the current collector. It has an active material layer. Furthermore, the electrolyte layer usually has a configuration in which a solid electrolyte, a gel electrolyte, or a liquid electrolyte (electrolytic solution) is held in the pores of the separator.

  The binder for binding the active material used in the active material layer is an organic solvent binder using an organic solvent as a solvent or dispersion medium and an aqueous binder using water as a solvent or dispersion medium (binder that dissolves / disperses in water). are categorized. Organic solvent binders can be industrially disadvantageous due to the high costs of organic solvent materials, recovery costs, disposal, and the like. On the other hand, water-based binders make it easy to procure water as a raw material, and because steam is generated during drying, capital investment in the production line can be greatly suppressed, and environmental burdens are reduced. There is an advantage that you can. Further, the water-based binder has an advantage that the binding effect is large even in a small amount as compared with the organic solvent-based binder, the active material ratio per volume can be increased, and the capacity of the negative electrode can be increased.

  Because of such advantages, various attempts have been made to form a negative electrode using an aqueous binder as a binder for forming an active material layer. However, when forming a negative electrode with an aqueous slurry using an aqueous binder, in addition to the aqueous binder, a thickener such as carboxymethyl cellulose or a salt thereof (hereinafter also simply referred to as “CMC (salt)”) is required. However, when CMC (salt) is used, there is a problem that a large amount of gas is generated during initial charging.

  In order to solve this problem, for example, in Patent Document 1, in the production of a negative electrode, an aqueous slurry containing a water-based binder such as styrene-butadiene rubber (SBR) and CMC is applied on a current collector such as a copper foil. A technique for heat treatment at 120 to 250 ° C. is disclosed. According to Patent Document 1, it is said that CMC as a thickener can be decomposed by the heat treatment to suppress gas generation during initial charging.

Japanese Patent Laid-Open No. 2001-210318

  However, when the present inventors manufactured a negative electrode using the method described in Patent Document 1, the amount of gas generated during initial charging in the nonaqueous electrolyte secondary battery can be reduced to some extent, but the reduction amount is at a desired level. It turned out not to reach.

  Therefore, an object of the present invention is to provide a means capable of sufficiently reducing the amount of gas generated during initial charging in a nonaqueous electrolyte secondary battery.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, it has been found that the amount of gas generated during initial charging can be significantly reduced by performing drying and heat treatment for removing water in the aqueous slurry in two stages under specific conditions. The present invention has been completed.

That is, in the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention, a drying step of drying a negative electrode active material, carboxymethyl cellulose or a salt thereof, and an aqueous slurry containing an aqueous binder on a current collector is performed. And a heat treatment step for heat treatment thereafter. Then, the drying process is performed in an atmosphere having a temperature of 130 ° C. or higher and an oxygen concentration of 8.0 × 10 ⁻³ mol / L or higher at 20 ° C., and the heat treatment process is performed at a temperature of 90 ° C. or higher and an oxygen concentration of 5 at 20 ° C. .3 × 10 ⁻⁶ mol / L or less in the atmosphere.

  According to the present invention, by performing drying and heat treatment in two stages under specific conditions, the oxidation reaction and dehydration condensation reaction of CMC (salt) can proceed well. As a result, since the number of hydroxyl groups (—OH) in CMC (salt) that causes gas generation is reduced, it is possible to sufficiently reduce the amount of gas generated during initial charging.

1 is a schematic cross-sectional view showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery that is not a flat (stacked) bipolar type, which is an embodiment of a non-aqueous electrolyte secondary battery. 1 is a plan view of a nonaqueous electrolyte secondary battery which is a preferred embodiment of the present invention. FIG. 3 is a perspective view from A in FIG. FIG. 3 is an explanatory view of the peel strength test method for the negative electrode active material layer performed in the examples, and FIG. 3 (a) is a side view schematically showing a form in which the sample (negative electrode) is fixed. FIG. 3B is a side view schematically showing a state where the negative electrode active material layer of the sample (negative electrode) is peeled off.

<Method for producing negative electrode for nonaqueous electrolyte secondary battery>
The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries which concerns on one form of this invention is characterized by including the following processes.

Step 1: An aqueous slurry containing a negative electrode active material, carboxymethylcellulose or a salt thereof, and an aqueous binder on a current collector, and an oxygen concentration of 8.0 × 10 ⁻ at a temperature of 130 ° C. or higher and 20 ° C. Drying in an atmosphere of ³ mol / L or more (drying step);
Step 2: After the drying step, heat treatment is performed in an atmosphere at a temperature of 90 ° C. or higher and an oxygen concentration of 5.3 × 10 ⁻⁶ mol / L or less at 20 ° C. (heat treatment step).

  According to this embodiment, the drying and heat treatment of the water-based slurry coating applied to the current collector are performed in two stages under specific conditions (particularly in atmospheres having different oxygen concentrations), so that the initial charging can be performed. It is possible to sufficiently reduce the amount of gas generated.

Although the reason why such an effect is achieved by the manufacturing method of the present embodiment is not clear, the present inventors presume as follows. That is, when CMC (salt) is used as a thickener, gas generation during initial charging is mainly caused by bound water adhering to CMC (salt) or the like, or hydroxyl group (—OH) in CMC (salt). It is thought to be caused. According to the manufacturing method of this embodiment, first, drying is performed in an atmosphere having an oxygen concentration of 8.0 × 10 ⁻³ mol / L or more at a temperature of 130 ° C. or higher and 20 ° C. This drying step is mainly intended to remove the solvent (water) in the aqueous slurry, but by performing the drying in an atmosphere having an oxygen concentration of a certain amount or more, as shown in the following reaction formula: A part of functional groups such as hydroxymethyl group (—CH ₂ OH) contained in CMC (salt) can be oxidized and converted to carboxyl group (—COOH) or the like. After that, heat treatment is performed in an atmosphere having a temperature of 90 ° C. or higher and an oxygen concentration of 5.3 × 10 ⁻⁶ mol / L or lower at 20 ° C. This heat treatment step is mainly intended to remove bound water adhering to CMC (salt) and the like, but during the heat treatment, a hydroxyl group (—OH) and a carboxyl group (— -COOH). As a result, since the hydroxyl group (—OH) contained in CMC (salt) is reduced, it is considered that the amount of gas generated during initial charging can be significantly reduced. In addition, the said mechanism is a speculation to the last, and this invention is not necessarily limitedly interpreted by this. Hereinafter, each process in this manufacturing method is demonstrated.

(1) Step 1 (Drying step)
In this step, a current collector coated with an aqueous slurry containing a negative electrode active material, carboxymethyl cellulose or a salt thereof, and an aqueous binder is used at a temperature of 130 ° C. or higher and an oxygen concentration of 8.0 × 10 at 20 ° C. ^-3 Dry under an atmosphere of mol / L or more.

[Water based slurry]
First, the aqueous slurry used in step 1 will be described. The aqueous slurry essentially includes a negative electrode active material, CMC (salt), and an aqueous binder. Further, the aqueous slurry may contain other additives such as an aqueous solvent and a conductive aid, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and a lithium salt for enhancing ionic conductivity, if necessary. .

(Negative electrode active material)
A conventionally well-known thing currently used as a negative electrode active material of a nonaqueous electrolyte secondary battery can be suitably employ | adopted for a negative electrode active material. For example, when the nonaqueous electrolyte secondary battery is a lithium ion secondary battery, the negative electrode active material is not particularly limited as long as it can reversibly store and release lithium.

For example, for example, carbon materials such as graphite (natural graphite, artificial graphite), soft carbon, hard carbon, lithium-transition metal composite oxide (for example, Li ₄ Ti ₅ O ₁₂ ), metal material, lithium alloy system A negative electrode material etc. are mentioned. In some cases, two or more negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. Of course, negative electrode active materials other than those described above may be used.

  In the lithium alloy-based negative electrode material, the element alloying with lithium is not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like. Among these, from the viewpoint of constructing a battery having excellent capacity and energy density, it preferably contains at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. Or it is especially preferable that Sn is included. These elements may be used alone or in combination of two or more.

  The average particle diameter of the negative electrode active material is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 30 μm from the viewpoint of increasing the output.

  The content of the negative electrode active material in the aqueous slurry is not particularly limited, but is preferably 50 to 99% by mass and more preferably 70 to 97% by mass with respect to the total solid content in the aqueous slurry. 80 to 96% by mass is more preferable. When the content of the negative electrode active material is 50% by mass or more, a desired charge / discharge capacity can be obtained. On the other hand, if the content of the negative electrode active material is 99% by mass or less, the charge / discharge capacity per unit volume can be increased while preventing a significant decrease in electrode peel strength.

(Carboxymethylcellulose or its salt)
The aqueous slurry of this embodiment essentially contains carboxymethyl cellulose or a salt thereof as a thickener. Carboxymethyl cellulose (CMC) is obtained by bonding a carboxymethyl group (—CH ₂ —COOH) to a part of hydroxyl groups of cellulose. The salt of carboxymethyl cellulose (CMC salt) is a carboxymethyl group proton (H ⁺ ) replaced with a cation (eg, Na ⁺ , Li ⁺ , K ⁺ , NH ₄ ⁺ ).

  Although an aqueous binder described later has excellent binding properties, unlike an organic solvent-based binder, it has a low viscosity, so that CMC (salt) needs to be used as a thickener in order to impart an appropriate viscosity to the aqueous slurry.

Many types (compounds) of CMC (salt) are already commercially available, and can be appropriately selected from these. Many of these commercially available products are CMC salts in which some or all of the protons of the carboxymethyl group are substituted with cations such as Na ⁺ , Li ⁺ , K ⁺ , NH ₄ ⁺ , and the type and amount of the cation are arbitrary. It can be adjusted. In this embodiment, since micelles are formed in a portion of Na, which is a cationic species such as —CH ₂ COONa, it can be said that it is desirable to use a cationic species such as Na at the end of the molecular chain of CMC or CMC salt.

  The weight average molecular weight of CMC (salt) is not particularly limited, but is preferably 5000 to 1200000, more preferably 6000 to 1100000, and still more preferably 7000 to 1000000. If the weight average molecular weight of CMC (salt) is 5000 or more, the viscosity of the aqueous slurry can be kept moderate. On the other hand, if the weight average molecular weight of CMC (salt) is 1200000 or less, it is possible to prevent gelation when CMC (salt) is dissolved in water. In the present specification, the weight average molecular weight of CMC (salt) was measured by gel permeation chromatography (GPC) using a solvent containing a metal-amine complex and / or a metal-alkali complex as a mobile phase. The value shall be adopted.

  The content of CMC (salt) in the aqueous slurry is not particularly limited, but is preferably 0.1 to 10% by mass, and 0.5 to 2% by mass with respect to the total solid content in the aqueous slurry. More preferably. When the content of CMC (salt) is 0.1% by mass or more, a sufficient viscosity can be imparted to the aqueous slurry, and a flat and smooth negative electrode active material layer can be formed. On the other hand, if the content of CMC (salt) is 10% by mass or less, the amount of gas generated during initial charging can be suppressed.

(Water-based binder)
The aqueous slurry of this embodiment essentially includes an aqueous binder as a binder. In addition to easy procurement of water as a viscosity-adjusting solvent, water-based binders can be greatly reduced in capital investment on the production line and reduced environmental burden because water vapor is generated during drying. There is an advantage that can be. Further, the binding force for binding the active material is high, and the mass ratio of the binder in the negative electrode active material layer can be reduced, and the mass ratio of the active material can be increased accordingly.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder containing water as a dispersion medium refers to a polymer that includes all expressed as a latex or an emulsion and is emulsified or suspended in water. Kind.

  Specific examples of aqueous binders include styrene polymers (styrene-butadiene rubber (SBR), styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, and methyl methacrylate-butadiene rubber. , (Meth) acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, Polyhexyl acrylate, polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylaur Yl methacrylate), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer Polymer, polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, saponification degree is preferably 80 mol% or more, more preferably 90 mol% or more) and a modified product thereof (ethylene / vinyl acetate = 2/98 to 30/70 mol ratio of vinyl acetate units of 1 to 80 mol% of vinyl acetate units). Products, 1 to 50 mol% partially acetalized products of polyvinyl alcohol, starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxy) Ethyl cellulose, and salts thereof), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) Acrylamide- (meth) acrylate copolymer, alkyl (meth) acrylate (carbon number 1 to 4) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich modified products, formalin condensation resins (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, and mannangalactan derivatives A functional polymer. These aqueous binders may be used alone or in combination of two or more.

  The water-based binder may include at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  In the case of using styrene-butadiene rubber as the aqueous binder, the ratio (mass ratio) of the content of styrene-butadiene rubber and CMC (salt) is not particularly limited, but styrene-butadiene rubber: CMC ( Salt) is preferably 1: 0.2-2, more preferably 1: 0.5-1. When the content ratio of CMC (salt) to styrene-butadiene rubber is 0.2 or more, the thickening effect of CMC (salt) can be sufficiently exhibited. On the other hand, when the content ratio of CMC (salt) to styrene-butadiene rubber is 2 or less, the generation of gas during initial charging due to CMC (salt) can be suppressed.

  The content of the binder in the aqueous slurry is not particularly limited as long as it is an amount capable of binding the negative electrode active material, but 0.5 to 15 mass with respect to the total solid content in the aqueous slurry. %, More preferably 1 to 10% by mass, and even more preferably 2 to 5% by mass. If the content of the aqueous binder is within the above range, an appropriate amount of the aqueous binder can be present at the interface with the current collector. Therefore, it is particularly excellent in that optimum adhesion, peel resistance, and vibration resistance can be exhibited without causing cohesive failure when the active material layer is shifted due to vibration input from the outside.

  Of the binder contained in the aqueous slurry, the content of the aqueous binder is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and particularly preferably 100% by mass. Examples of the binder other than the water-based binder include binders (organic solvent-based binders) used in the following positive electrode active material layer.

  Furthermore, a binder (organic solvent-based binder) such as hydrophilic PVdF increases the liquid absorption speed by increasing its content, but it is disadvantageous in terms of energy density. Also, an excessive amount of binder increases battery resistance. Therefore, the active material can be efficiently bound by setting the amount of the aqueous binder contained in the aqueous slurry within the above range. As a result, uniform film formation, high energy density, and good cycle characteristics can be further improved.

(Aqueous solvent)
The aqueous slurry of this embodiment contains an aqueous solvent such as water as a viscosity adjusting solvent as necessary. The water is not particularly limited, and for example, pure water, ultrapure water, distilled water, ion exchange water, or the like can be used. If necessary, an organic solvent that can be dissolved in water such as alcohol can be used as the viscosity adjusting solvent together with water. As the alcohol, for example, ethyl alcohol, methyl alcohol, isopropyl alcohol and the like can be used.

  The content of the aqueous solvent in the aqueous slurry is not particularly limited, and can be appropriately adjusted by those skilled in the art so that the aqueous slurry is in a desired viscosity range.

(Other additives)
A conductive support agent means the additive mix | blended in order to improve the electroconductivity of an active material layer. Examples of the conductive auxiliary include carbon materials such as carbon black such as ketjen black and acetylene black, and carbon fiber. When the active material layer contains a conductive additive, a conductive network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  In this embodiment, the viscosity of the aqueous slurry is not particularly limited, but is preferably 500 to 10000 mPa · s, more preferably 800 to 9000 mPa · s, and further preferably 1000 to 8000 mPa · s. If the viscosity of the water-based slurry is 500 mPa · s or more, the negative electrode having a uniform and flat surface can be applied to the current collector uniformly on the current collector using a coating machine. An active material layer can be formed. On the other hand, if the viscosity of the aqueous slurry is 100,000 mPa · s or less, drying after applying the aqueous slurry on the current collector can be performed in a short time.

[Method of preparing aqueous slurry]
The method for preparing the aqueous slurry is not particularly limited, and a conventionally known method can be appropriately used. For example, a negative electrode active material, CMC (salt), and an aqueous binder, and an aqueous solvent as a viscosity adjusting solvent and other additives, if necessary, are added to a slurry preparation container, and stirred and mixed. To prepare an aqueous slurry.

[Current collector]
The current collector is not particularly limited, and an existing current collector can be used. For example, in addition to the metal foil, a punching metal sheet or an expanded metal sheet can be used for a current collector used in a battery that is not a bipolar type.

  The current collector material is not particularly limited as long as it is a conductive material. For example, a conductive resin in which a conductive filler is added to a metal, a conductive polymer material, or a non-conductive polymer material is employed. sell. A metal is preferably used.

  Examples of the metal include aluminum, copper, platinum, nickel, tantalum, titanium, iron, stainless steel, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoint of conductivity and battery operating potential.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Examples of non-conductive polymer materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide ( PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals. It is preferable to include an alloy or metal oxide. Further, the conductive carbon is not particularly limited, but is at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. Preferably it contains seeds. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  In a non-aqueous electrolyte secondary battery that is not a bipolar type, when a punching metal sheet or an expanded metal sheet having a plurality of through-holes is used as a current collector, the shape of the through-hole is, for example, square, rhombus, turtle shell shape, hexagon , Round shape, square shape, star shape, cross shape, etc. A so-called punching metal sheet or the like is formed by pressing a large number of holes having such a predetermined shape, for example, in a staggered arrangement or a parallel arrangement. A so-called expanded metal sheet or the like is formed by stretching a sheet with staggered cuts to form a large number of substantially diamond-shaped through holes.

  When the current collector having the plurality of through holes described above is used for the current collector, the aperture ratio of the through holes of the current collector is not particularly limited. However, the lower limit of the aperture ratio of the current collector is preferably 10 area% or more, more preferably 30 area% or more, further preferably 50 area% or more, more preferably 70 area% or more, and further preferably 90 area. % Or more. Thus, in the electrode of this embodiment, a current collector having an aperture ratio of 90 area% or more can also be used. Moreover, as an upper limit, it is 99 area% or less, or 97 area% or less, for example. Thus, a battery with an electrode formed with a current collector having a significantly large aperture ratio can significantly reduce its weight, and thus increase its capacity, high density Can be made.

  When the current collector having the plurality of through holes is used as the current collector, the diameter (opening diameter) of the through holes of the current collector is not particularly limited as well. However, the lower limit of the opening diameter of the current collector is preferably 10 μm or more, more preferably 20 μm or more, still more preferably 50 μm or more, and particularly preferably 150 μm or more. As an upper limit, it is 300 micrometers or less, for example, Preferably, it is about 200 micrometers or less. In addition, the opening diameter here is the diameter of the circumscribed circle of the through hole = opening. The diameter of the circumscribed circle is obtained by observing the surface of the current collector with a laser microscope or a tool microscope, fitting the circumscribed circle to the opening, and averaging the results.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. Although there is no restriction | limiting in particular also about the thickness of an electrical power collector, Preferably it is 1-100 micrometers, More preferably, it is 3-80 micrometers, More preferably, it is 5-40 micrometers.

In this embodiment, in particular, when the current collector is made of a metal material, it is preferable to have an antioxidant film on the surface of the current collector. By using a current collector having an antioxidant film on the surface, the metal material on the surface of the current collector is prevented from being oxidized in the drying step in the atmosphere in which the oxygen concentration in step 1 is a certain level or more. Can be maintained. Moreover, in a lithium ion secondary battery, when using the collector which does not have an antioxidant film | membrane on the surface, the following bad influences are considered. That is, when the surface of the current collector reacts with Li or LiPF ₆ or the like is used as a lithium salt, hydrogen fluoride is generated by the reaction between the water in the electrolyte and LiPF _6, and the current is collected by the hydrogen fluoride. The body surface may dissolve. If the surface of the current collector reacts or dissolves, the surface state of the current collector cannot be maintained, the binding property with the active material layer is lowered, and the peel strength may be adversely affected. By using a current collector having a prevention film, such adverse effects can be suppressed.

  The method for forming the antioxidant film on the surface of the current collector is not particularly limited, and known knowledge can be referred to appropriately. For example, rust prevention treatment using an organic rust inhibitor such as benzotriazole (BTA), imidazole, thiadiazole compound, chromate treatment using chromate, and TiN or TaN on the collector surface. Examples thereof include a method of forming a barrier layer by a dry method, a method of forming a barrier layer made of a Ni-based alloy or the like by electroless plating, and the like. Further, an antioxidant film (passive film) may be formed on the surface of the current collector by natural oxidation. In addition to this, the antioxidant film may be formed using a metal deactivator, a protective film forming agent, or the like. In particular, in the examples described later, a current collector in which the surface of the copper foil is chromated is used, but the present invention is not limited to this form. Note that the current collector having an antioxidant film may be prepared by subjecting the current collector to the above-described antioxidant treatment, or a commercially available product may be obtained.

The thickness of the antioxidant film on the surface of the current collector is not particularly limited as long as the above effects are exhibited. However, in the case of chromate treatment, the amount of chromium deposited is 0.005 to 0.05 mg / dm ² , Preferably it is 0.01-0.03 mg / dm < ² >.

[Application of water-based slurry]
Next, a method for applying the aqueous slurry described above on the current collector will be described. In this embodiment, the method for applying the aqueous slurry onto the current collector is not particularly limited, and can be performed by appropriately referring to known knowledge such as die coating, spray coating, and dip coating.

As for the coating amount of the aqueous slurry is not particularly limited, the weight per unit area of one surface of the final negative electrode active material layer (coating amount) is 1 to 30 mg / cm ^2, preferably from 2 to 20 mg / cm ² It can be appropriately adjusted by those skilled in the art to be within the range. At this time, it is preferable that the coating is uniformly performed so that the basis weight per unit area (coating amount) is within ± 5% by mass of the target in the same negative electrode active material layer.

[Drying aqueous slurry]
Next, drying for solidifying the aqueous slurry applied on the current collector is performed. The drying is intended to solidify the slurry (removal of water and the like), and is usually performed in a short time in order to prevent oxidation of the current collector (metal foil).

  In this embodiment, the lower limit of the drying temperature is essentially 130 ° C. or higher, preferably 135 ° C. or higher, more preferably 140 ° C. or higher. When the drying temperature is less than 130 ° C., the oxidation reaction of CMC (salt) does not proceed so much, and the amount of gas generated during the initial charge cannot be sufficiently reduced. On the other hand, although the upper limit of drying temperature is not specifically limited, Preferably it is less than 160 degreeC, More preferably, it is 155 degreeC or less. When the drying temperature is less than 160 ° C., oxidation of the current collector (metal foil) can be suppressed even when a current collector made of a metal material is used.

In this embodiment, the dry atmosphere has a constant oxygen concentration. Specifically, the lower limit value of the oxygen concentration in the dry atmosphere (20 ° C.) is essentially 8.0 × 10 ⁻³ mol / L or more, preferably 8.9 × 10 ⁻³ mol / L or more. is there. When the oxygen concentration is less than 8.0 × 10 ⁻³ mol / L, the oxidation reaction of CMC (salt) does not proceed so much, and the amount of gas generated during initial charging cannot be sufficiently reduced. On the other hand, the upper limit value of the oxygen concentration is not particularly limited, but is preferably 1.3 × 10 ⁻² mol / L or less, more preferably 1.1 × 10 ⁻² mol / L or less. When the oxygen concentration is 1.3 × 10 ⁻² mol / L or less, the oxidation of the copper foil can be suppressed, and the binding force is weakened due to excessive oxidation of CMC (salt) and aqueous binder. It is preferable at the point that it can prevent that the peeling strength of an active material layer falls.

Further, when a lithium-transition metal composite oxide is included as the negative electrode active material, the drying and / or heat treatment described below is preferably performed in an atmosphere containing CO ₂ at a higher concentration than in the air (air). Since the CO ₂ concentration in the atmosphere is about 0.04%, in other words, it is preferable to perform the drying in an atmosphere having a CO ₂ concentration exceeding 0.04%. Thus, by increasing the CO ₂ concentration, the surface of the lithium-transition metal composite oxide that is the negative electrode active material can be converted to Li ₂ CO ₃ , and the initial charge / discharge efficiency can be increased, Generation of gas can be further suppressed. Since Li ₂ CO ₃ is also a component of the SEI (surface coating) of the negative electrode active material, it is excellent in that the life performance can be improved.

  The atmospheric pressure of the drying atmosphere may be under reduced pressure or atmospheric pressure (normal pressure) as long as sufficient drying is performed, but from the viewpoint of reducing equipment costs, etc. Preferably there is.

  In this embodiment, the drying time is preferably 30 to 300 seconds, more preferably 60 to 180 seconds, although it varies depending on the apparatus used and the amount of slurry applied. If the drying time is 30 seconds or more, the aqueous solvent in the coating film (aqueous slurry) can be sufficiently removed. On the other hand, if the drying time is 300 seconds or less, the current collector (for example, copper foil) made of a metal material can be prevented from being oxidized.

  Through the above steps, a laminate in which a dried aqueous slurry is laminated on the current collector can be obtained. In addition, after the said drying, the coating film after drying may be pressed (rolled) as needed, and the density of a negative electrode active material layer may be adjusted.

(2) Step 2 (heat treatment step)
In this step, the dried laminate obtained in step 1 is heat-treated. The heat treatment is performed in an atmosphere having a temperature of 90 ° C. or more and an oxygen concentration of 5.3 × 10 ⁻⁶ mol / L or less at 20 ° C.

[Heat treatment of laminate]
In this embodiment, it is essential that the lower limit of the heat treatment temperature is 90 ° C. or higher, preferably 100 ° C. or higher, more preferably 110 ° C. or higher, still more preferably 120 ° C. or higher, particularly preferably. It is 130 ° C. or higher, and most preferably 140 ° C. or higher. If the lower limit of the heat treatment temperature is less than 90 ° C., the dehydration condensation between the hydroxyl group (—OH) and the carboxyl group (—COOH) in the CMC (salt) does not proceed so much, so the amount of gas generated during the initial charge is reduced. It cannot be reduced sufficiently. On the other hand, the upper limit of the heat treatment temperature is not particularly limited, but is preferably less than 200 ° C, more preferably 195 ° C or less, and further preferably 190 ° C or less. When the heat treatment temperature is lower than 200 ° C., it is possible to suppress a decrease in peel strength between the current collector and the negative electrode active material layer due to decomposition of the aqueous binder or the like.

In this embodiment, the upper limit of the oxygen concentration in the heat treatment atmosphere (20 ° C.) is essentially 5.3 × 10 ⁻⁶ mol / L or less, preferably 3.5 × 10 ⁻⁶ mol / L or less. It is. When the oxygen concentration exceeds 5.3 × 10 ⁻⁶ mol / L, problems such as an increase in resistance due to oxidation of the current collector (metal foil) and a decrease in peel strength due to oxidation of the aqueous binder may occur. On the other hand, the lower limit value of the oxygen concentration is not particularly limited, but is preferably 4.4 × 10 ⁻⁸ mol / L or more from the viewpoint of reducing the equipment cost.

  In the heat treatment in this step, the type and ratio of gas components other than atmospheric pressure and oxygen are not particularly limited as long as the oxygen concentration during the heat treatment is within the above range. For example, the oxygen concentration can be easily within the above range by reducing the pressure of the atmosphere (air). Further, an inert gas such as nitrogen and oxygen may be mixed under normal pressure to make the oxygen concentration within the above range, which is advantageous in that heat transfer is performed favorably.

  In this embodiment, the heat treatment time can be appropriately set depending on the size of the negative electrode to be produced, the basis weight of the negative electrode active material layer, and the heat treatment apparatus to be used, but is generally 1 minute to 24 hours, preferably 5 minutes to 12 hours. Preferably, it is in the range of 10 minutes to 8 hours.

  In addition, as an apparatus used for the above drying and / or heat processing, the heat processing furnace etc. which can be adjusted to said heat processing temperature and oxygen concentration can be utilized suitably.

  By passing through the above process, the negative electrode for nonaqueous electrolyte secondary batteries which has a negative electrode active material layer on a collector is obtained.

<Nonaqueous electrolyte secondary battery>
According to another embodiment of the present invention, a nonaqueous electrolyte secondary battery having a negative electrode for a nonaqueous electrolyte secondary battery manufactured by the above-described manufacturing method is provided. That is, the non-aqueous electrolyte secondary battery of this embodiment has a power generation element enclosed in an exterior body. The power generation element includes a positive electrode in which a positive electrode active material layer is formed on the surface of a current collector, a negative electrode in which a negative electrode active material layer is formed on the surface of the current collector, and a nonaqueous electrolyte held in a separator. An electrolyte layer. And the said negative electrode is manufactured by the above-mentioned manufacturing method, It is characterized by the above-mentioned.

  The nonaqueous electrolyte secondary battery of the present embodiment can sufficiently reduce the amount of gas generated during initial charging by having the negative electrode manufactured by the above-described manufacturing method.

  Hereinafter, although a nonaqueous electrolyte lithium ion secondary battery will be described as a preferred embodiment of the nonaqueous electrolyte secondary battery, it is not limited to only the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic cross-sectional view schematically showing a basic configuration of a non-aqueous electrolyte lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type. As shown in FIG. 1, the stacked battery 10 of this embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery outer body 28 that is an outer body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, an electrolyte layer 17 holding a nonaqueous electrolyte in a separator, and a negative electrode are laminated. The electrolyte layer 17 contains a nonaqueous electrolyte (for example, a liquid electrolyte). The positive electrode has a structure in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11. The negative electrode has a structure in which the negative electrode active material layers 15 are disposed on both surfaces of the negative electrode current collector 12. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. . Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the positive electrode active material layer 13 is arrange | positioned only at one side in the outermost layer positive electrode collector located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. In addition, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 1, so that the outermost layer negative electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost layer negative electrode current collector is disposed on one or both surfaces. A negative electrode active material layer may be disposed.

  The positive electrode current collector 11 and the negative electrode current collector 12 are each provided with a positive electrode current collector plate (tab) 25 and a negative electrode current collector plate (tab) 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out to the exterior of the battery exterior body 28 so that it may be pinched | interposed into the edge part. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  Note that FIG. 1 shows a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector.

  Hereinafter, each member will be described in more detail.

[Negative electrode active material layer]
In this embodiment, the material constituting the negative electrode active material layer, the blending ratio, the size, and the like are as described in the above-described negative electrode manufacturing method, and thus detailed description thereof is omitted here.

The density of the negative electrode active material layer is preferably 1.2~1.8g / cm ^3, more preferably 1.4~1.6g / cm ^3. In general, when a water-based binder is used for the negative electrode active material layer, a thickener is required. Therefore, compared with a solvent-based binder such as PVdF that is often used in the past, the gas generated during the initial charge of the battery There is a phenomenon that the amount increases. Such a phenomenon can be solved by employing the method for producing a negative electrode of the present invention. In this connection, if the density of the negative electrode active material layer is 1.8 g / cm ³ or less, the slightly generated gas can sufficiently escape from the inside of the power generation element, and the long-term cycle characteristics can be further improved. . Moreover, if the density of the negative electrode active material layer is 1.2 g / cm ³ or more, the connectivity of the active material is ensured and the electron conductivity is sufficiently maintained. As a result, the battery performance can be further improved. Furthermore, by setting the density of the negative electrode active material layer in the above range, a battery having a uniform film formation, a high energy density, and good cycle characteristics is obtained. Note that the density of the negative electrode active material layer represents the mass of the active material layer per unit volume. Specifically, after removing the negative electrode active material layer from the battery, removing the solvent and the like present in the electrolyte solution, the electrode volume is obtained from the long side, the short side, and the height, and after measuring the weight of the active material layer, It can be determined by dividing weight by volume.

  Moreover, in this embodiment, it is preferable that the centerline average roughness (Ra) of the separator side surface of a negative electrode active material layer is 0.5-1.0 micrometer. If the center line average roughness (Ra) of the negative electrode active material layer is 0.5 μm or more, the long-term cycle characteristics can be further improved. This is considered to be because if the surface roughness is 0.5 μm or more, the gas generated in the power generation element is easily discharged out of the system. Moreover, if the centerline average roughness (Ra) of the negative electrode active material layer is 1.0 μm or less, the electron conductivity in the battery element is sufficiently secured, and the battery characteristics can be further improved.

  Here, the centerline average roughness Ra means that only the reference length is extracted from the roughness curve in the direction of the average line, the x axis is in the direction of the average line of the extracted portion, and the y axis is in the direction of the vertical magnification. When the roughness curve is expressed by y = f (x), the value obtained by the following formula 1 is expressed in micrometers (μm) (JIS-B0601-1994).

  The value of Ra is measured using a stylus type or non-contact type surface roughness meter that is widely used in general, for example, by a method defined in JIS-B0601-1994. There are no restrictions on the manufacturer or model of the device. In the examination in the present invention, Ra was obtained by a roughness analyzer (attached to the apparatus) according to a method defined in JIS-B0601, using Olympus Corporation model number: LEXT-OLS3000. Either the contact method (stylus type using a diamond needle or the like) or the non-contact method (non-contact detection using a laser beam or the like) can be measured, but in the study in the present invention, the measurement was performed by the contact method.

  Moreover, since it can measure comparatively easily, surface roughness Ra prescribed | regulated to this invention is measured in the step in which the active material layer was formed on the electrical power collector in the manufacture process. However, the measurement can be performed even after the battery is completed, and the results are almost the same as those in the manufacturing stage. Therefore, the surface roughness after the battery is completed may satisfy the above Ra range. The surface roughness of the negative electrode active material layer is that on the separator side of the negative electrode active material layer.

  The surface roughness of the negative electrode is, for example, by adjusting the press pressure at the time of forming the active material layer in consideration of the shape of the active material contained in the negative electrode active material layer, the particle diameter, the amount of the active material, etc. It can adjust so that it may become the said range. The shape of the active material varies depending on the type and manufacturing method, and the shape can be controlled by pulverization, for example, spherical (powder), plate, needle, column, square Etc. Therefore, in order to adjust the surface roughness in consideration of the shape used for the active material layer, active materials having various shapes may be combined.

  Further, the porosity of the negative electrode active material layer is 25 to 40%, preferably 30 to 35%, more preferably 32 to 33%. Increasing the porosity of the active material layer increases the liquid absorption speed, but it is disadvantageous in terms of energy density. Also, the porosity of the active material layer that is too high may affect the cycle life. Therefore, the porosity of the positive electrode active material layer is made appropriate (20 to 30%) so that the ratio of the liquid absorption rate of the positive electrode and the negative electrode active material layer is in an appropriate range, and the porosity of the negative electrode material layer is also made. It is desirable to make the value appropriate (25 to 40%). Thereby, the surface film formation in the first charging step is uniform, and the battery has good energy density and cycle characteristics. For the porosity of the active material layer, a value obtained as a volume ratio from the density of the raw material of the active material layer and the density of the active material layer of the final product is adopted. For example, when the density of the raw material is ρ and the bulk density of the active material layer is ρ ′, the porosity of the active material layer = 100 × (1−ρ ′ / ρ).

[Positive electrode active material layer]
The positive electrode active material layer contains an active material, and if necessary, other additives such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and a lithium salt to enhance ionic conductivity. An agent is further included.

The positive electrode active material layer includes a positive electrode active material. Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those in which a part of these transition metals is substituted with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, Li (Ni—Mn—Co) O ₂ and those in which some of these transition metals are substituted with other elements (hereinafter, also simply referred to as “NMC composite oxide”) are used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti and the like partially replace the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

  As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable that it is excellent in balance between capacity and durability.

  Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

  Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene Examples thereof include vinylidene fluoride-based fluororubber such as fluororubber (VDF-CTFE-based fluororubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15 mass with respect to the positive electrode active material layer. %, Preferably 1 to 10% by mass, more preferably 2 to 6% by mass. A binder (organic solvent-based binder) such as hydrophilic PVdF increases the liquid absorption rate by increasing its content, but it is disadvantageous in terms of energy density. Also, an excessive amount of binder increases battery resistance. Therefore, by making the amount of the binder contained in the positive electrode active material layer within the above range, the active material can be bound efficiently, and the effect of the present invention can be further enhanced.

  About other additives other than a binder, the thing similar to what was demonstrated by the manufacturing method of the said negative electrode can be used.

  Further, the porosity of the positive electrode active material layer is 20 to 30%, preferably 22 to 28%, more preferably 23 to 25%. Increasing the porosity of the active material layer increases the liquid absorption speed, but it is disadvantageous in terms of energy density. Also, the porosity of the active material layer that is too high may affect the cycle life. Therefore, the porosity of the positive electrode active material layer is made appropriate (20 to 30%) so that the ratio of the liquid absorption rate of the positive electrode and the negative electrode active material layer is in an appropriate range, and the porosity of the negative electrode material layer is also made. It is desirable to make the value appropriate (25 to 40%). Thereby, the surface film formation in the first charging step is uniform, and the battery has good energy density and cycle characteristics.

[Separator (electrolyte layer)]
The separator has a function of holding a non-aqueous electrolyte and ensuring lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition between the positive electrode and the negative electrode.

  Here, in order to further improve the release of the gas generated during the initial charge of the battery from the power generation element, it is preferable to consider the release of the gas that has passed through the negative electrode active material layer and reached the separator. From such a viewpoint, it is more preferable to set the air permeability or porosity of the separator within an appropriate range.

  Specifically, the air permeability (Gurley value) of the separator is preferably 200 (seconds / 100 cc) or less. When the separator has an air permeability of 200 (seconds / 100 cc) or less, the escape of gas generated is improved, the battery has a good capacity retention rate after cycling, and the short circuit prevention and machine functions as a separator The physical properties are also sufficient. The lower limit of the air permeability is not particularly limited, but is usually 50 (second / 100 cc) or more. The air permeability of the separator is a value according to the measurement method of JIS P8117 (2009).

  The porosity of the separator is 40 to 65%, preferably 45 to 60%, more preferably 50 to 58%. When the separator has a porosity of 40 to 65%, the release of generated gas is improved, the battery has better long-term cycle characteristics, and the short circuit prevention and mechanical properties that are functions as a separator are also provided. It will be enough. For the porosity, a value obtained as a volume ratio from the density of the resin as the raw material of the separator and the density of the separator of the final product is adopted. For example, when the density of the raw material resin is ρ and the bulk density of the separator is ρ ′, the porosity is represented by 100 × (1−ρ ′ / ρ).

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds an electrolyte.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include, for example, polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it is 4 to 60 μm in a single layer or multiple layers. Is desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

  As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated polymer gel electrolyte.

  The porosity of the nonwoven fabric separator is 50 to 90%, preferably 60 to 80%. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  Here, the separator may be a separator in which a heat-resistant insulating layer is laminated on at least one surface of a resin porous substrate (the above-mentioned microporous film or nonwoven fabric separator). The heat resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the electrical device manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength. Further, the ceramic layer is preferable because it can also function as a gas releasing means for improving the gas releasing property from the power generation element.

  In the present invention, the center line average roughness (Ra) of the negative electrode active material layer side surface of the separator having a heat-resistant insulating layer is 0.1 to 1.2 μm, preferably 0.2 to 1.1 μm, more preferably. It is preferable that it is 0.25-0.9 micrometers. If the center line average roughness (Ra) of the surface of the heat-resistant insulating layer of the separator is 0.1 μm or more, it is effective for preventing the electrode and the separator from being displaced during the production of the battery, and the long-term cycle characteristics can be further improved. This is considered to be because if the surface roughness is 0.1 μm or more, the gas generated in the power generation element is easily discharged out of the system. In addition, if the center line average roughness (Ra) of the surface of the heat-resistant insulating layer of the separator is 1.2 μm or less, local variations in separator thickness can be suppressed, so that the ion conductivity in the plane becomes uniform, and the battery The characteristics can be further improved. The center line average roughness Ra is as described in the above-described center line average roughness (Ra) of the negative electrode active material layer, and thus description thereof is omitted here.

  Further, as described above, the separator includes a non-aqueous electrolyte. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a gel polymer electrolyte is used.

The liquid electrolyte functions as a lithium ion carrier. The liquid electrolyte has a form in which a lithium salt is dissolved in an organic solvent. Examples of the organic solvent used include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). As the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, such as _{LiPF 6, LiBF 4, LiClO 4} , LiAsF 6, LiTaF 6, LiCF 3 SO 3 A compound that can be added to the active material layer of the electrode can be similarly employed. The liquid electrolyte may further contain additives other than the components described above. Specific examples of such compounds include, for example, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinyl ethylene carbonate, 1,2-divinyl ethylene carbonate. 1-methyl-1-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate, allylethylene carbonate, vinyl Oxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloxymethyl ethylene carbonate, methacrylate Oxy methylethylene carbonate, ethynyl ethylene carbonate, propargyl carbonate, ethynyloxy methylethylene carbonate, propargyloxy ethylene carbonate, methylene carbonate, etc. 1,1-dimethyl-2-methylene-ethylene carbonate. Among these, vinylene carbonate, methyl vinylene carbonate, and vinyl ethylene carbonate are preferable, and vinylene carbonate and vinyl ethylene carbonate are more preferable. These cyclic carbonates may be used alone or in combination of two or more.

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. The use of a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and the ion conductivity between the layers is easily cut off. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Current collector]
Since the material constituting the current collector and the shape, size, and the like thereof are as described in the above-described negative electrode manufacturing method, detailed description thereof is omitted here.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and leaking electricity. It is preferable to coat with a tube or the like.

[Battery exterior]
The battery outer body 28 is a member that encloses the power generation element therein, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the power generation element applied from the outside can be easily adjusted and the battery can be enlarged, the power generation element has a laminated structure, and the exterior body is more preferably a laminate film containing aluminum.

  The internal volume of the battery outer body 28 is configured to be larger than the volume of the power generation element 21 so that the power generation element 21 can be enclosed. Here, the internal volume of the exterior body refers to the volume in the exterior body before evacuation after sealing with the exterior body. The volume of the power generation element is the volume of the space occupied by the power generation element, and includes a hole in the power generation element. Since the inner volume of the exterior body is larger than the volume of the power generation element, there is a space in which gas can be stored when gas is generated. Thereby, the gas release property from the power generation element is improved, the generated gas is less likely to affect the battery behavior, and the battery characteristics are improved.

Moreover, in this embodiment, the value (L / V ₁ ) of the ratio of the volume L of the electrolyte injected into the exterior body to the volume V ₁ of the pores of the power generation element 21 is 1.2 to _1. .6 is preferable. If the amount (volume L) of the nonaqueous electrolyte (especially the electrolyte) is large, even if the electrolyte is unevenly distributed on the positive electrode side, a sufficient amount of the electrolyte solution is present on the negative electrode side. This is advantageous from the viewpoint of making the formation of a homogeneous progress. On the other hand, if the amount (volume L) of the electrolytic solution is large, the cost of increasing the electrolytic solution is generated, and too much electrolytic solution leads to an increase in the distance between the electrodes, resulting in an increase in battery resistance. Therefore, it is desirable that the amount of the electrolytic solution (specifically, the value L / V ₁ of the ratio of the electrolytic solution volume L to the void volume V ₁ of the power generation element 21) be appropriate. Thereby, it is excellent at the point which can make uniform film formation, cost, and cell resistance compatible. From this viewpoint, it is preferable the value of L / _{V 1} is configured to be in the range of 1.2 to 1.6, more preferably 1.25 to 1.55, particularly preferably 1.3 to The range is 1.5.

Further, in the present embodiment, the value (V ₂ / V) of the ratio of the volume V ₂ of the excess space (reference numeral 29 shown in FIG. 1) in the battery outer body 28 to the volume V ₁ of the pores of the power generation element 21. ₁ ) is preferably 0.5 to 1.0. Furthermore, the ratio (L / V ₂ ) of the volume L of the electrolyte injected into the exterior body to the volume V ₂ of the excess space inside the exterior body is configured to be 0.4 to 0.7. Is preferred. Thereby, it becomes possible to make the part which was not absorbed with the binder among the electrolyte solution inject | poured inside the exterior body exist reliably in the said excess space. In addition, the movement of lithium ions within the battery can be reliably ensured. As a result, the occurrence of a heterogeneous reaction due to an increase in the distance between the electrode plates due to the presence of an excessive amount of the electrolytic solution that may be a problem when using a large amount of the electrolytic solution similar to that when using a solvent-based binder such as PVdF. Is prevented. For this reason, the nonaqueous electrolyte secondary battery excellent in a long-term cycle characteristic (life characteristic) can be provided.

Here, the “volume of voids (V ₁ ) of the power generation element” can be calculated in the form of adding all the void volumes of the positive electrode, the negative electrode, and the separator. That is, it can be calculated as the total sum of the holes of the constituent members constituting the power generation element. In addition, the battery is usually manufactured by sealing the power generation element inside the exterior body, injecting an electrolytic solution, and evacuating and sealing the interior of the exterior body. When gas is generated inside the exterior body in this state, if there is a space in the exterior body where the generated gas can accumulate, the generated gas accumulates in the space and the exterior body expands. In this specification, such a space is defined as “surplus space”, and the volume of the surplus space when the outer body expands to the maximum without rupturing is defined as V ₂ . As described above, the value of V ₂ / V ₁ is preferably 0.5 to 1.0, more preferably 0.6 to 0.9, and particularly preferably 0.7 to 0.8. is there.

Further, as described above, in the present invention, the ratio value between the volume of the electrolyte to be injected and the volume of the surplus space described above is controlled to a value within a predetermined range. Specifically, the ratio (L / V ₂ ) of the volume (L) of the electrolyte injected into the exterior body to the volume V ₂ of the excess space inside the exterior body is 0.4 to 0.7. It is desirable to control. The value of L / V ₂ is more preferably 0.45 to 0.65, and particularly preferably 0.5 to 0.6.

  In the present embodiment, it is preferable that the above-described excess space existing inside the exterior body is disposed at least vertically above the power generation element. With such a configuration, the generated gas can be accumulated in the vertical upper part of the power generation element in which the surplus space exists. Thereby, compared with the case where surplus space exists in the side part and lower part of an electric power generation element, electrolyte solution can preferentially exist in the lower part in which an electric power generation element exists in an exterior body. As a result, it is possible to ensure that the power generation element is always immersed in a larger amount of the electrolytic solution, and it is possible to minimize a decrease in battery performance due to the liquid draining. Although there is no particular limitation on the specific configuration for arranging the surplus space vertically above the power generation element, for example, the material or shape of the exterior body itself is placed on the side part or the lower part of the power generation element. For example, it may be configured not to swell toward the outside, or a member that prevents the exterior body from bulging toward a side portion or a lower portion thereof may be disposed outside the exterior body.

  In automobile applications and the like, recently, a large-sized battery is required. And the effect of this invention is exhibited more effectively in the case of a large area battery in which both the positive electrode active material layer and the negative electrode active material layer have a large electrode area. Furthermore, the effect of preventing the non-uniform formation of the coating film (SEI) on the surface of the negative electrode active material is more effective in the case of a large area battery having a large amount of coating film (SEI) formed on the surface of the negative electrode active material. Is demonstrated. Furthermore, in the case where an aqueous binder is used for the negative electrode active material layer, the friction coefficient between the negative electrode active material layer and the separator is made lower than a certain value, so that the adhesion between the electrode and the separator is moderately adjusted when the electrode is displaced. In the case of a large-area battery, the effect of reducing the effect is exhibited more effectively. That is, in the case of a large area battery, the cohesive failure from the electrode surface due to the friction between the electrode and the separator is further suppressed, and the battery characteristics can be maintained even when vibration is input. Therefore, in this embodiment, it is preferable in the meaning that the effect of this invention is exhibited more that the battery structure which covered the electric power generation element with the exterior body is large sized. Specifically, the negative electrode active material layer is preferably rectangular, and the length of the short side of the rectangle is preferably 100 mm or more. Such a large battery can be used for vehicle applications. Here, the length of the short side of the negative electrode active material layer refers to the side having the shortest length among the electrodes. The upper limit of the length of the short side of the battery structure is not particularly limited, but is usually 250 mm or less.

Further, as a viewpoint of a large-sized battery, which is different from the viewpoint of the physical size of the electrode, it is possible to regulate the size of the battery from the relationship between the battery area and the battery capacity. For example, in the case of a flat laminated battery, the value of the ratio of the battery area to the rated capacity (the maximum value of the projected area of the battery including the battery outer casing) is 5 cm ² / Ah or more, and the rated capacity is In a battery having a capacity of 3 Ah or more, since the battery area per unit capacity is large, it is difficult to remove the gas generated between the electrodes. Due to such gas generation, if a gas retention portion exists between large electrodes, the heterogeneous reaction tends to proceed starting from that portion. Therefore, the problem of deterioration of battery performance (particularly, life characteristics after long-term cycle) in a large-sized battery using an aqueous binder such as SBR for forming the negative electrode active material layer is more easily manifested. Therefore, it is preferable that the nonaqueous electrolyte secondary battery according to the present embodiment is a battery that is enlarged as described above, because the merit due to the manifestation of the effects of the present invention is greater. Furthermore, the aspect ratio of the rectangular electrode is preferably 1 to 3, and more preferably 1 to 2. The electrode aspect ratio is defined as the aspect ratio of the rectangular negative electrode active material layer. By making the aspect ratio within such a range, in the present invention, which requires the use of an aqueous binder, it becomes possible to discharge gas uniformly in the surface direction, and further suppress the generation of a non-uniform film. There is an advantage that can be.

  The rated capacity of the battery is determined as follows.

≪Measurement of rated capacity≫
The rated capacity of the test battery is left to stand for about 10 hours after injecting the electrolytic solution, and the initial charge is performed. Then, it measures by the following procedures 1-5 in the temperature range of 25 degreeC and the voltage range of 3.0V to 4.15V.

  Procedure 1: After reaching 4.15 V by constant current charging at 0.2 C, pause for 5 minutes.

  Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.

  Procedure 3: After reaching 3.0 V by constant current discharge of 0.2 C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.

  Procedure 4: After reaching 4.1 V by constant current charging at 0.2 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.

  Procedure 5: After reaching 3.0 V by constant current discharge of 0.2 C, discharge by constant voltage discharge for 2 hours, and then stop for 10 seconds.

  Rated capacity: The discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 5 is defined as the rated capacity.

[Group pressure on power generation elements]
In the present embodiment, the group pressure applied to the power generation element is preferably 0.07 to 2.0 kgf / cm ² (6.86 to 196 kPa). By pressurizing the power generation element so that the group pressure becomes 0.07 to 2.0 kgf / cm ² , non-uniform spread of the distance between the electrode plates can be prevented, and lithium ions between the electrode plates can be prevented. It is possible to secure enough traffic. In addition, the discharge of gas generated by the battery reaction to the outside of the system is improved, and the surplus electrolyte in the battery does not remain between the electrodes, so that an increase in cell resistance can be suppressed. Further, the swelling of the battery is suppressed, and the cell resistance and the capacity retention rate after a long-term cycle are improved. More preferably, the group pressure applied to the power generation element is 0.1 to 2.0 kgf / cm ² (9.80 to 196 kPa). Here, the group pressure refers to an external force applied to the power generation element, and the group pressure applied to the power generation element can be easily measured using a film-type pressure distribution measuring system. A value measured using a film-type pressure distribution measuring system is adopted.

The control of the group pressure is not particularly limited, but can be controlled by applying an external force physically or directly to the power generation element and controlling the external force. As a method for applying such external force, it is preferable to use a pressure member that applies pressure to the exterior body. That is, a preferred embodiment of the present invention further includes a pressure member that applies pressure to the outer package so that the group pressure applied to the power generation element is 0.07 to 2.0 kgf / cm ^2. It is a secondary battery.

FIG. 2A is a plan view of a nonaqueous electrolyte secondary battery which is a preferred embodiment of the present invention, and FIG. 2B is a view as viewed from the arrow A in FIG. The exterior body 1 enclosing the power generation element has a rectangular flat shape, and an electrode tab 4 for taking out electric power is drawn out from the side portion. The power generation element is wrapped by a battery outer package, and the periphery thereof is heat-sealed. The power generation element is sealed with the electrode tab 4 pulled out. Here, the power generation element corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 1 described above. In FIG. 2, 2 is a SUS plate which is a pressure member, 3 is a fixing jig which is a fixing member, and 4 is an electrode tab (negative electrode tab or positive electrode tab). The pressurizing member is disposed for the purpose of controlling the group pressure applied to the power generation element to be 0.07 to 2.0 kgf / cm ² . Examples of the pressure member include rubber materials such as urethane rubber sheets, metal plates such as aluminum and SUS, resin materials including polyethylene and polypropylene, resin plates such as bakelite and Teflon (registered trademark), and the like. In addition, since the pressure member can continuously apply a constant pressure to the power generation element, it is preferable to further include a fixing member for fixing the pressure member. Further, the group pressure applied to the power generation element can be easily controlled by adjusting the fixing of the fixing jig to the pressing member.

  Note that the tab removal shown in FIG. 2 is not particularly limited. The positive electrode tab and the negative electrode tab may be pulled out from both sides, or the positive electrode tab and the negative electrode tab may be divided into a plurality of parts and taken out from each side. It is not a thing.

  In the present embodiment, Tc / Ta is in the range of 0.6 to 1.3, where Tc is the electrolyte soaking time into the positive electrode active material layer and Ta is the electrolyte soaking time into the negative electrode active material layer. It is desirable to be in In particular, when a water-based binder is used for the negative electrode active material layer, the wettability of the positive and negative electrode active material layers is adjusted by adjusting the ratio of the rate of liquid absorption (dipping) of the electrolyte into the positive and negative electrode active material layers. To maintain and improve battery characteristics (long-term cycle characteristics). From this viewpoint, the Tc / Ta may be in the range of 0.6 to 1.3, but is preferably in the range of 0.8 to 1.2.

  The measurement of the penetration time of the electrolytic solution into the positive electrode active material layer and the negative electrode active material layer can be performed by the following method. That is, when the electrolyte solution soak time Tc into the positive electrode active material layer is 1 μL of propylene carbonate (PC) dropped on the center of the positive electrode active material layer surface, it is completely absorbed in the active material layer ( Visual judgment) shall be used. For example, the same electrolyte solution composition as that used for the non-aqueous electrolyte secondary battery may be used. However, since a volatile component is contained, the electrolyte solution has disappeared due to evaporation, or the active material layer is soaked. It is difficult to distinguish whether it disappeared from the surface. Therefore, the PC soaking time that is less likely to volatilize is used as the soaking time Tc of the electrolytic solution into the positive electrode active material layer. Similarly, the penetration time Ta of the electrolytic solution into the negative electrode active material layer is the penetration time of PC.

[Battery]
The assembled battery is configured by connecting a plurality of batteries. Specifically, at least two or more are used, and are configured by serialization, parallelization, or both. Capacitance and voltage can be freely adjusted by paralleling in series.

  A plurality of batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the battery capacity of the mounted vehicle (electric vehicle) It may be determined according to the output.

[vehicle]
The battery or an assembled battery (electric device) formed by combining a plurality of these batteries has excellent output characteristics, maintains discharge capacity even after long-term use, and has good cycle characteristics. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the electric device can be suitably used as a vehicle power source, for example, a vehicle driving power source or an auxiliary power source.

  Specifically, a battery or an assembled battery formed by combining a plurality of these batteries can be mounted on a vehicle. In the present invention, since a battery having a long life with excellent long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage or an electric vehicle having a long charge mileage can be formed by mounting such a battery. . For example, in the case of a car, a hybrid car, a fuel cell car, an electric car (four-wheeled vehicles (passenger cars, trucks, buses, commercial vehicles, light cars, etc.) This is because it can be used for motorcycles (including motorcycles) and tricycles) to provide a long-life and highly reliable automobile. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  Hereinafter, although it demonstrates still in detail using an Example and a comparative example, this invention is not limited only to a following example.

<Preparation of nonaqueous electrolyte secondary battery>
[Example 1]
1. Production of negative electrode 97 parts by mass of spherical agglomerated artificial graphite (D50 = 15 μm, BET specific surface area 3.5 m ² / g, manufactured by Hitachi Chemical Co., Ltd.) as negative electrode active material, SBR (gel amount 90%, Tg 10 ° C., average) as aqueous binder particle size 150 nm, manufactured by Nippon Zeon Co., Ltd.) 2 parts by weight, and as a thickener, CMC salt (degree of etherification 0.82 with _-CH 2 COONa protons of carboxymethyl group is substituted by Na ⁺ cations, the weight A solid content consisting of 1 part by mass of an average molecular weight of 350,000, manufactured by Nippon Paper Chemicals Co., Ltd. was prepared. An appropriate amount of ion-exchanged water, which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a negative electrode slurry (aqueous slurry). Next, the negative electrode slurry was applied to both surfaces of a copper foil (foil thickness 10 μm, manufactured by Furukawa Electric Co., Ltd.) subjected to surface oxidation treatment as a current collector, and dried, pressed and heat-treated. Thus, a negative electrode having a negative electrode active material layer coated on both sides of 18.0 mg / cm ² and a density of 1.5 g / cm ³ was produced.

In addition, the said collector (copper foil) used what formed the surface oxidation prevention layer (protective film) of chromium adhesion amount 0.02 mg / dm < ² > on the copper foil surface by the chromate process.

  The negative electrode slurry was applied to the current collector by intermittently applying the negative electrode slurry to the current collector using a slot die type coating coater.

Moreover, the said drying was performed by applying a hot air, conveying in the drying furnace with a furnace length of 20 m. At this time, the preset temperature of the drying furnace was set to 130 ° C., and adjustment was performed so as to convey over 60 seconds in the atmosphere (oxygen concentration of 9.4 × 10 ⁻³ mol / L at 20 ° C.). And the laminated body after drying was wound up in roll shape.

The subsequent heat treatment was performed using a vacuum oven at a temperature of 90 ° C. and an atmospheric pressure of 10 Pa (oxygen concentration at 20 ° C. 8.8 × 10 ⁻⁸ mol / L) over 6 hours.

2. Production of positive electrode 92 parts by mass of NMC composite oxide (composition: Li ₁ Ni ₅ Mn ₃ Co ₂ O ₂ ) as a positive electrode active material, ₂ parts by mass of Super C65 (manufactured by Timcal; carbon black) and KS6L (Timcal) A solid content consisting of 2 parts by mass; flaky graphite) and 4 parts by mass of # 7200 (manufactured by Kureha; vinylidene fluoride resin (PVdF)) as a binder was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a positive electrode slurry. Next, the positive electrode slurry was applied to both sides of an aluminum foil (thickness 20 μm, manufactured by Sumitomo Light Metal Co., Ltd.), which is a current collector, dried and pressed, and the coated amount of both surfaces of the positive electrode active material layer was 25 mg / cm ² . A positive electrode having a density of 3.2 g / cm ³ was produced.

3. Preparation of Electrolyte Solution A mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 30: 70 (volume ratio)) was used as a solvent, and LiPF ₆ was dissolved at a concentration of 1.0 M in the solvent. . Further, 2% by mass of vinylene carbonate was added to the total of 100% by mass of the solvent and the lithium salt to prepare an electrolytic solution.

4). Production of Nonaqueous Electrolyte Secondary Battery The positive electrode produced above was cut into a 210 × 184 mm rectangular shape (rectangular shape), and the negative electrode was cut into a 215 × 188 mm rectangular shape (rectangular shape) (21 positive electrodes, negative electrode 22). Sheet). The positive electrode and the negative electrode were alternately stacked via a 219 × 191 mm rectangular (rectangular) separator (polypropylene microporous film, thickness 25 μm, porosity 55%) to produce a power generation element.

A tab was welded to each of the positive electrode and the negative electrode of the power generation element, and sealed together with the electrolyte in an exterior body made of an aluminum laminate film, thereby completing a nonaqueous electrolyte secondary battery. The rated capacity of the battery was 40 Ah, and the ratio of the battery area to the rated capacity was 12 cm ² / Ah. Moreover, the value (L / V ₁ ) of the ratio of the volume L of the electrolytic solution injected into the outer package to the volume V ₁ of the pores of the power generation element was 1.45.

5. Initial charging of non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery was held for 24 hours in a thermostatic bath maintained at 25 ° C., and then the initial charging was performed. In the initial charging, constant current charging (CC) was performed up to 4.2 V at a current value of 0.05 CA, and then charging was performed at a constant voltage (CV) for a total of 24 hours.

[Example 2]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the preset temperature of the drying furnace in the drying step was 130 ° C. and the temperature in the heat treatment step was 150 ° C. during the production of the negative electrode. A secondary battery was produced.

[Example 3]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying step was set to 130 ° C. and the temperature in the heat treatment step was set to 190 ° C. during the production of the negative electrode. A secondary battery was produced.

[Example 4]
In the production of the negative electrode, the non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the set temperature of the drying furnace in the drying step was 140 ° C. and the temperature in the heat treatment step was 150 ° C. A secondary battery was produced.

[Example 5]
In producing the negative electrode, the nonaqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the set temperature of the drying furnace in the drying step was 155 ° C. and the temperature in the heat treatment step was 90 ° C. A secondary battery was produced.

[Example 6]
In the production of the negative electrode, the nonaqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the set temperature of the drying furnace in the drying step was 155 ° C. and the temperature in the heat treatment step was 130 ° C. A secondary battery was produced.

[Example 7]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying step was set to 155 ° C. and the temperature in the heat treatment step was set to 150 ° C. A secondary battery was produced.

[Example 8]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying step was set to 155 ° C. and the temperature in the heat treatment step was set to 190 ° C. during the production of the negative electrode. A secondary battery was produced.

[Example 9]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying step was set to 155 ° C. and the temperature in the heat treatment step was set to 200 ° C. during the production of the negative electrode. A secondary battery was produced.

[Comparative Example 1]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying process was set to 120 ° C. and the temperature in the heat treatment process was set to 90 ° C. during the production of the negative electrode. A secondary battery was produced.

[Comparative Example 2]
In the production of the negative electrode, the nonaqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the set temperature of the drying furnace in the drying process was 120 ° C. and the temperature in the heat treatment process was 190 ° C. A secondary battery was produced.

[Comparative Example 3]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying process was set to 130 ° C. and the temperature in the heat treatment process was set to 80 ° C. during the production of the negative electrode. A secondary battery was produced.

[Comparative Example 4]
The non-aqueous electrolyte 2 was prepared in the same manner as in Example 1 except that the temperature of the drying furnace in the drying process was set to 155 ° C. and the temperature in the heat treatment process was set to 80 ° C. during the production of the negative electrode. A secondary battery was produced.

[Comparative Example 5]
A non-aqueous electrolyte secondary battery was fabricated in the same manner as in Example 1 except that the temperature of the drying furnace in the drying process was set to 160 ° C. and the heat treatment process was not performed during the production of the negative electrode. Produced.

<Evaluation of non-aqueous electrolyte secondary battery>
For the non-aqueous electrolyte secondary batteries of Examples 1 to 9 and Comparative Examples 1 to 5, the amount of gas generated in the first charge performed earlier, the degree of oxidation of the negative electrode current collector (copper foil), and the peel strength, respectively It was measured.

(1) Gas generation amount at the first charge The battery volume change amount before the first charge and after the completion of the charge for 24 hours was measured by the Archimedes method and used as the gas generation amount at the first charge. The results are shown in Table 1. In Table 1, relative values are shown when the gas generation amount of Example 1 is 1.0.

(2) Degree of oxidation of negative electrode current collector (copper foil) (2.1) Content of measurement Depth direction of sample (using negative electrode current collector (copper foil) taken out by disassembling battery after initial charge) ( (Thickness direction) analysis was performed by X-ray photoelectron spectroscopy (hereinafter referred to as XPS analysis). The equipment names and measurement conditions used are shown below.

(2.1.1) XPS analysis apparatus name: Composite electron spectrometer PCA ESCA-5800
X-ray source: Monochromated-Al-Kα ray (1486.6 eV) 300 W
Photoelectron extraction angle: 45 ° (measurement depth: about 4 nm)
Measurement area: φ0.8mm oval Sputtering rate: 2.8nm / min
Pretreatment conditions: Uncleaned electrode (negative electrode current collector (copper foil)) is cut to an appropriate size with scissors in a high purity Ar atmosphere (both oxygen and moisture are 1 ppm or less) and air is transferred using a transfer vessel. Introduced into the device without exposure. After the sample was dried in the preliminary exhaust chamber of the apparatus, it was transported to a measurement tank and measured.

  Etching from the surface of the sample under the above measurement conditions using the above apparatus, and when oxygen atoms are no longer detected, the depth is the thickness of the oxide film of the negative electrode current collector (copper foil) (copper oxide depth). )). In addition, since the influence of oxidation is small if the thickness of the oxide film (copper oxide depth) is 15 nm or less, in Table 1, for the oxide film thickness (copper oxide depth) of 15 nm or less, It was written as “15 nm or less”. When the thickness exceeds 15 nm, the measured thickness of the oxide film (copper oxide depth) is described as it is. In addition, the presence or absence of discoloration was visually confirmed for the pretreated sample (negative electrode current collector (copper foil)).

(3) Peel test The peel strength (binding force between the negative electrode active material layer and the current collector) was measured by a peel test. FIG. 3 is a diagram for explaining a peel strength test method. FIG. 3A is a side view schematically showing a form in which the negative electrode is fixed. The negative electrodes manufactured in Examples 1 to 9 and Comparative Examples 1 to 5 (negative electrode before battery assembly) were cut into strips with a width of 20 mm, and negative electrode samples 30 (negative electrode active material layers 34 were formed on both surfaces of the negative electrode current collector 33). The formed negative electrode sample 30) was prepared, and one end of the negative electrode sample 30 was fixed to the sample fixing plate 31 with a double-sided adhesive tape 32. FIG. 3B is a side view schematically showing a state where the negative electrode active material layer is peeled off. The other end of the negative electrode sample 30 (the end not fixed to the sample fixing plate 31 with the double-sided adhesive tape 32) is sandwiched between the clamps 35 and pulled up vertically in the direction of the arrow, and the negative electrode active material layer is removed from the negative electrode current collector 33. The load when 34 peeled was measured with a tensile testing machine. The results are shown in Table 1.

  The reason why the amount of gas generated in Comparative Example 5 in Table 1 is set to “cell not assembled” is as follows. That is, the negative electrode of Comparative Example 5 was dried at a high temperature of 160 ° C. under atmospheric pressure. As a result, oxidation of the copper foil current collector progressed, and many negative electrodes with foil breakage were generated. Furthermore, the CMC salt and water-based binder are excessively oxidized and the binding force is weakened, the peel strength of the negative electrode active material layer is lowered, and so-called powder falling (active material powder falling off and peeling) occurs in the negative electrode when the cell is assembled. Many negative electrodes were generated. Even if a cell (battery) is assembled using a negative electrode with defects such as foil breakage or powder fall, it will be rejected by a short check before charging, and a cell (battery) that becomes a qualified product cannot be assembled, so the first charge can be performed Since there was no cell, it was decided not to assemble cells.

  From the results of Table 1, in Examples 1 to 9 having the negative electrode obtained by the production method of the present invention, it was shown that the amount of gas generated at the initial charge was significantly reduced as compared with Comparative Examples 1 to 5. . This is because drying and heat treatment are performed in two stages under specific conditions with different oxygen concentrations, so that the oxidation reaction and dehydration condensation reaction of CMC (salt) proceed well, and CMC (cause of gas generation) This is considered to be because the number of hydroxyl groups (—OH) in the salt) decreases.

  Moreover, it was confirmed that the oxidation of the negative electrode current collector (copper foil) can be suppressed even in an atmosphere in which oxygen is present at a certain concentration or more by setting the drying temperature in the drying step to less than 160 ° C. Furthermore, it was confirmed that the binding force is weakened by excessive oxidation of CMC (salt) and the aqueous binder, and the peel strength of the negative electrode active material layer can be prevented from significantly decreasing.

  It was also confirmed that by setting the heat treatment temperature in the heat treatment step to less than 200 ° C., decomposition of the aqueous binder (SBR) and the like can be suppressed, and the peel strength between the negative electrode active material layer and the negative electrode current collector can be maintained stronger. .

  Moreover, when it sees about Examples 1-9, by making the temperature of a drying process into the range of 135 degreeC or more and less than 160 degreeC (more preferably 140 degreeC or more and 155 degrees C or less) more suitable than the range of 130 degreeC or more. It has been found that the effect of reducing the amount of gas generation and the effect of improving the peel strength, which are in a trade-off relationship, can be maintained in a balanced manner. Similarly, by setting the temperature of the heat treatment step to a more preferable range of 100 ° C. or higher and lower than 200 ° C. (more preferably 130 ° C. or higher and 190 ° C. or lower) rather than a range of 90 ° C. or higher, a gas that has a trade-off relationship. It was found that the effect of reducing the generation amount and the effect of improving the peel strength can be maintained in a well-balanced manner.

1 Exterior body enclosing power generation elements,
2 pressure members,
3 fixing members,
4 electrode tabs,
10 Lithium ion secondary battery,
11 positive electrode current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
25 positive current collector,
27 negative current collector,
28 Battery exterior body,
29 Excess space inside the battery exterior body,
30 negative electrode sample,
31 Sample fixing plate,
32 Double-sided adhesive tape,
33 Negative electrode current collector (copper foil),
34 negative electrode active material layer,
35 Clamp.

Claims (8)

A current collector coated with an aqueous slurry containing a negative electrode active material, carboxymethyl cellulose or a salt thereof, and an aqueous binder, and an oxygen concentration at a temperature of 130 ° C. or higher and an oxygen concentration of 8.0 × 10 ⁻³ mol / 20 ° C. A drying step of drying in an atmosphere of L or higher;
And a heat treatment step of performing a heat treatment in an atmosphere having an oxygen concentration of 5.3 × 10 ⁻⁶ mol / L or less at a temperature of 90 ° C. or higher and a temperature of 20 ° C. or lower after the drying step, for a negative electrode for a non-aqueous electrolyte secondary battery Production method.   The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the drying step is performed at a temperature of less than 160 ° C.   The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries of Claim 1 or 2 which heat-processes at the temperature of less than 200 degreeC in the said heat treatment process.   The method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein in the drying step, the drying time is 30 to 300 seconds. A non-aqueous electrolyte secondary battery in which a power generation element is enclosed in an exterior body,
The power generation element is
A positive electrode in which a positive electrode active material layer is formed on the surface of the current collector;
A negative electrode in which a negative electrode active material layer is formed on the surface of the current collector;
An electrolyte layer in which a non-aqueous electrolyte is held in a separator,
The non-aqueous electrolyte secondary battery in which the said negative electrode is manufactured by the manufacturing method of any one of Claims 1-4.   The nonaqueous electrolyte secondary battery according to claim 5, wherein the negative electrode active material layer has a rectangular shape, and a length of a short side of the rectangle is 100 mm or more. The non-aqueous solution according to claim 5 or 6, wherein the ratio of the battery area to the rated capacity (projected area of the battery including the battery outer casing) is 5 cm ² / Ah or more, and the rated capacity is 3 Ah or more. Electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to any one of claims 5 to 7, wherein an aspect ratio of the electrode defined as an aspect ratio of the rectangular negative electrode active material layer is 1 to 3.