JP2017033773A - Method for manufacturing negative electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means capable of sufficiently reducing an amount of generated gas during initial charging 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 step 1: a step of removing moisture in CMC (salt), and a step 2: coating an aqueous slurry on a collector and drying the slurry to form a negative electrode, the aqueous slurry containing a negative electrode active material, CMC (salt) obtained during the step 1, and an aqueous binder.SELECTED DRAWING: None

Description

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

  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 includes 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 (a binder that dissolves / disperses in water). ). An organic solvent-based binder requires a large amount of costs for organic solvent materials, recovery costs, disposal, and the like, which may be industrially disadvantageous. 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. is there. However, when CMC (salt) is used, there is a problem that a large amount of gas is generated during initial charging. Furthermore, there is a problem that the charge / discharge cycle durability is impaired by this large amount of generated gas. For example, Patent Document 1 proposes to use a mixture of a high molecular weight CMC having a weight average molecular weight of 3 million or more and a low molecular weight CMC having a weight average molecular weight of less than 1 million in the production of a negative electrode. According to this, the adhesion between the active material layer and the current collector is good (effect of high molecular weight CMC), and the coating of the negative electrode active material by CMC is minimized (effect of low molecular weight CMC). The battery resistance can be kept low.

JP 2013-89422 A

  However, when the present inventors manufactured a negative electrode using the method described in Patent Document 1, the nonaqueous electrolyte secondary battery has the above characteristics (adhesion, low battery resistance), but a large amount during initial charging. It turned out that the problem of gas generation could not be solved.

  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 was found that the amount of gas generated during the initial charge can be significantly reduced by removing the water of CMC (salt) added to the aqueous slurry, and the present invention has been completed.

  That is, the method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to the present invention includes a step of removing moisture from CMC (salt), a negative electrode active material on the current collector, and CMC (salt) with a moisture content of 2% or less. And a water-based slurry containing a water-based binder are applied and dried to form a negative electrode.

  According to the present invention, the CMC (salt) is mixed with other materials to remove the moisture of the CMC (salt) before producing the aqueous slurry, thereby sufficiently reducing the amount of gas generated during the initial charge, It becomes possible to improve charge / discharge cycle durability.

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. FIG. 2A is a plan view of a non-aqueous electrolyte secondary battery which is a preferred embodiment of the present invention. FIG. 2B is a perspective view from A in FIG.

<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: removing moisture from CMC (salt) (moisture removal step of CMC (salt));
Step 2: A negative electrode is formed by applying and drying an aqueous slurry containing a negative electrode active material, CMC (salt) obtained in Step 1 and an aqueous binder on the current collector (application / drying step).

  According to this embodiment, the CMC (salt) is mixed with other materials to remove the moisture of the CMC (salt) before preparing the water-based slurry, thereby sufficiently reducing the amount of gas generated during the initial charge. The discharge cycle durability can be improved.

  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.

  CMC (salt) swells when it comes into contact with water, and then disperses in water as water enters the particles. However, since CMC (salt) has viscosity when swollen, the particles may stick together. When CMC (salt) particles adhere to each other, water cannot enter the particles, and undissolved lumps are generated. Therefore, when CMC (salt) is dissolved in water (when preparing an aqueous slurry), it is usually sufficiently stirred, but CMC (salt) itself has a hygroscopic property and usually contains a certain amount of moisture. In addition, it was found that it is necessary to pay attention to collective adhesion because it tends to have viscosity when it comes into contact with water. That is, it was found that the generation of undissolved lumps cannot be sufficiently suppressed even with sufficient stirring.

  When undissolved lumps are generated, the CMC (salt) distribution covering the surface of the active material (particles) becomes non-uniform when producing the negative electrode. Occurs.

  Further, in the electrode active material layer, the portion where the CMC (salt) lumps are present has a locally high resistance, so that the current concentrates at other portions. For this reason, it is considered that the battery is locally overcharged, the electrode is further deteriorated, and the charge / discharge capacity is lowered (= charge / discharge cycle durability is lowered).

  On the other hand, in the present invention, the water content of CMC (salt) is removed before making the water-based slurry (the water content is made 2% or less), so that the initial collective adhesion is suppressed when it comes into contact with water. It becomes easy to disperse (salt). As a result, it becomes easy for water to penetrate into the particles, and CMC (salt) undissolved lumps can be suppressed.

  By reducing the amount of undissolved CMC (salt), the surface of the active material (particles) is uniformly coated with CMC (salt), and the amount of gas generated during the initial charge is reduced. Further, since the distribution of CMC (salt) on the surface of the active material (particle) becomes uniform, the resistance on the surface of the active material (particle) becomes uniform, and the SEI on the surface of the active material (particle) is also formed uniformly. As a result, it is considered that capacity deterioration during the charge / discharge cycle is suppressed (= charge / discharge cycle durability is improved). In addition, the said action 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 (CMC (salt) water removal step)
In this process 1, the water | moisture content of CMC (salt) which is a viscous agent is removed. That is, in this step 1, before the water-based slurry is prepared in the next step 2, the moisture of CMC (salt) as a thickener is removed (preferably, the moisture content of CMC (salt) is 2% or less. To do).

(Carboxymethylcellulose or a salt thereof; CMC (salt))
The CMC (salt) used in this step 1 is not particularly limited, and a commercially available one may be used, or one produced by an existing method for producing CMC (salt) is used. May be. The moisture content of CMC (salt) such as such a commercial product is about 10% (see Examples). This is because the CMC (salt) used as a thickener is dissolved in water and used, and its moisture content has not been regarded as a problem. That is, since the introduction of moisture into the battery affects the battery performance, the moisture in the negative electrode active material layer including CMC (salt) is sufficiently removed in the process of drying after applying the aqueous slurry. It was considered that the introduction of moisture into the battery was sufficiently prevented during the drying process. Therefore, the purpose of drying CMC (salt) that dissolves in water is to increase the cost of the CMC (salt), not only to eliminate gas generation during initial charging, but also to improve performance. It was thought not to be involved. However, the present inventors know that it is meaningless in the process of searching for means (trial and error) in the dark to solve the problem of gas generation at the time of initial charging. This is an attempt to remove water from the salt. Surprisingly, it was found that the amount of gas generated during the initial charge can be sufficiently reduced, and that it can also contribute to the improvement of the charge / discharge cycle durability (due to trial and error that can be pointed out). is there. (In other words, the above mechanism of action is inferred from the results found from such trial and error).

Here, the carboxymethyl cellulose (CMC) used in this step 1 is a carboxymethyl group (—CH ₂ —COOH) bonded to a part of the hydroxyl group of cellulose. The salt of carboxymethyl cellulose (CMC salt) is a carboxymethyl group terminal proton (H ⁺ ) replaced by a cation (eg, Na ⁺ , Li ⁺ , K ⁺ , NH ₄ ⁺ ).

As described above, many types (compounds) of CMC (salt) are already commercially available, and can be appropriately selected from these and used in this step 1. 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 the present embodiment, since micelles are formed in a portion such as Na which is a cationic species such as —CH ₂ COONa, it is desirable to use a cationic species such as Na at the end of the molecular chain of CMC or CMC salt. .

  Although the weight average molecular weight of CMC (salt) used at this process 1 is not restrict | limited in particular, It is preferable that it is 5000-1200000, It is more preferable that it is 6000-1100000, It is further more preferable that it is 7000-1000000. If the weight average molecular weight of CMC (salt) is 5000 or more, the viscosity of the aqueous slurry can be maintained moderately by the CMC (salt) that has undergone Step 1. 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) that has undergone Step 1 is dissolved in water. In addition, in this specification, the weight average molecular weight of CMC (salt) is a pullulan conversion measured by size exclusion chromatography (SEC) using a solvent containing a metal-amine complex and / or a metal-alkali complex as a mobile phase. The value of shall be adopted. Here, size exclusion chromatography (SEC) is called gel filtration chromatography (GFC) when water-soluble polymers are handled, and gel permeation chromatography when measuring in an organic solvent system. (GPC).

CMC (salt) may be one obtained by etherifying a part of hydroxyl groups of each cellulose unit of CMC (salt) (chemical structure of CMC (salt)). There are three OR groups (R; H, or —CH ₂ —COOH or a salt thereof) in the cellulose unit. For example, in all cellulose units of CMC (salt), when one of OR groups (for example, hydroxyl groups) is etherified, the degree of etherification is 1.0. That is, the degree of etherification is an index indicating how much an OR group (for example, a hydroxyl group) contained in each cellulose unit of CMC (salt) is etherified. Among these, it is preferable to use those having a degree of etherification of less than 1.0 because good fluidity can be obtained when applying the aqueous slurry on the negative electrode side to the current collector.

  In this step 1, the above-mentioned CMC (salt) may be used singly or in combination of two or more, but preferably it is used alone. This is because the chemical structure (degree of etherification, functional group, etc.) of CMC (salt) used in this step 1 does not change even after passing through this step 1 by using CMC (salt) alone. Therefore, when the negative electrode (battery) is formed, the chemical structure of CMC (salt) becomes uniform within the electrode surface, and the uniformity of reactivity is improved. Due to the uniform reactivity, the SEI (surface film) formed on the active material surface by the decomposition of the electrolyte during charging becomes uniform. As a result, the capacity deterioration during the charge / discharge cycle is suppressed (= charge / discharge cycle durability is improved).

  In this step 1, as a means for removing the water of the CMC (salt) (preferably making the water content 2% or less), any means can be used as long as the water can be removed without decomposing the CMC (salt). There is no particular limitation. Preferably, a heating (heat treatment) means is used. Specifically, it is preferable to heat (heat-treat) at 60 to 160 ° C., preferably 100 to 130 ° C. If the heating (heat treatment) temperature is 60 ° C. or higher, water can be sufficiently removed up to the moisture content described above. Further, if the heating (heat treatment heat treatment) temperature is 160 ° C. or lower, CMC (salt) is not decomposed, and it is excellent in that the function as a thickener can be sufficiently expressed.

  Further, the heating (heat treatment) time varies depending on the heating (heat treatment) temperature, the amount of CMC (salt), the heating device, etc., but it is sufficient that sufficient water removal of CMC (salt) can be performed, and is not limited at all. Although it is not, it is usually about 30 minutes to 24 hours.

  The atmospheric pressure (pressure) at the time of heating (heat treatment) is not particularly limited as long as the moisture of CMC (salt) can be sufficiently removed by heating, but the atmospheric pressure at the time of heating (heat treatment) is usually 10 Pa. ˜about atmospheric pressure (101325 Pa). Therefore, it may be performed under atmospheric pressure (101325 Pa) or under reduced pressure (vacuum). Preferably, it is good to carry out under reduced pressure (for example, about 10 Pa) using a vacuum oven or the like. The degree of decompression at this time is not particularly limited, and may be appropriately selected within the range of the ability of the decompression device so that the purpose of Step 1 can be effectively achieved.

  Further, the gas (gas) at the time of heating (heat treatment) is not particularly limited as long as sufficient moisture removal of CMC (salt) can be performed. For example, inert gas such as nitrogen gas, argon gas, helium gas, etc. It can be carried out in gas or air (air). Although it is desirable to carry out in air (atmosphere) from the viewpoint of production cost, it is not limited to this.

  The heating (heat treatment) apparatus is not particularly limited as long as it can perform sufficient water removal of CMC (salt). Therefore, an existing heating (heat treatment) apparatus can be used. For example, a heating (heat treatment) apparatus using hot air drying or infrared drying can be used, or a heating (heat treatment) apparatus using vacuum heating drying ( Vacuum oven etc.) can be used. Moreover, you may use the heating (heat processing) apparatus which used hot air drying and infrared drying together. It should be noted that only the reduced pressure (vacuum) means may be used instead of the heating (heat treatment) means.

  In this step 1, it is sufficient that the moisture of the CMC (salt) can be removed by using the heating (heat treatment) means or the like, but the moisture content of the CMC (salt) is preferably 2% or less, more preferably 0. .5% or less, more preferably 0.2% or less. By removing the moisture of CMC (salt) (preferably reducing the moisture content to the above range), the amount of gas generated during the initial charge can be sufficiently reduced, and the charge / discharge cycle durability can be further improved. is there. In addition, about the minimum of a moisture content, it does not restrict | limit in particular, What is necessary is just 0% or more.

(Measurement of water content of CMC (salt) (calculation of water content))
The moisture content of CMC (salt) can be measured using an existing moisture meter, for example, a heat drying moisture meter (A & D, MX-50). A predetermined amount (for example, about 5 g) of a sample (CMC (salt)) is measured at a heating temperature of 160 ° C., and the weight loss when the weight change per minute is within 0.05% is measured as moisture. I do. Then, the weight of CMC (salt) in which the amount of weight change per minute of the end condition is within 0.05% is defined as “dry weight of CMC (salt) alone”. Thereby, the moisture content (%) of CMC (salt) is {(weight of CMC (salt) before heating (heat treatment) (g)) − (dry weight (g) of only CMC (salt))} ÷ ( Weight of CMC (salt) before heating (heat treatment) (g)) × 100. In addition, the moisture content (%) of CMC (salt) that has undergone the heating (heat treatment) in the above step 1 is {(weight (g) of CMC (salt) that has undergone the heating (heat treatment) in the above step 1) − (CMC ( Dry weight (g) of only salt)} / (weight of CMC (salt) subjected to heating (heat treatment) in the above step 1 (g)) × 100. Regarding the measurement of the heated (heat treated) sample, the measurement is performed immediately after the completion of the heating (heat treated) (in a dry atmosphere (specifically, in a dry atmosphere having a dew point of −20 ° C. or less), and after the completion, It shall be measured within 30 minutes).

(2) Step 2 (coating and drying step)
In Step 2, a negative electrode is formed by applying and drying an aqueous slurry containing a negative electrode active material, the CMC (salt) obtained in Step 1 and an aqueous binder on the current collector. In this step 2, by using the CMC (salt) after removing the water obtained in step 1, since the initial collective adhesion is suppressed when touched with water, it becomes easy for CMC to disperse, As a result, it becomes easy for water to penetrate into the particles, and CMC (salt) undissolved lumps can be suppressed. By reducing the amount of undissolved CMC (salt), the surface of the active material (particles) is uniformly coated with CMC (salt), and the amount of gas generated during the initial charge is reduced. Further, since the distribution of CMC (salt) on the surface of the active material (particle) becomes uniform, the resistance on the surface of the active material (particle) becomes uniform, and the SEI on the surface of the active material (particle) is also formed uniformly. As a result, capacity deterioration during the charge / discharge cycle is suppressed (= charge / discharge cycle durability is improved).

[Water based slurry]
First, the aqueous slurry used in this step 2 will be described. The aqueous slurry essentially contains the negative electrode active material, the CMC (salt) obtained in Step 1, and the 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, a lithium alloy negative electrode 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. Here, the average particle diameter of the negative electrode active material can be measured by a laser diffraction method, and D50 is used as an index. In addition, particle size analysis (measurement) can be performed by SEM (scanning electron microscope) observation, TEM (transmission electron microscope) observation, or the like. In some cases, the negative electrode active material (particles) or a cross section thereof may include powders having irregular shapes with different aspect ratios (aspect ratios) instead of spherical or circular shapes (cross sectional shapes). Therefore, the average particle diameter mentioned above is the absolute maximum length of the cut surface shape of each negative electrode active material (particle) in the observation image because the shape (or its cross-sectional shape) of the negative electrode active material (particle) is not uniform. It shall be expressed by the average value of. The absolute maximum length means the maximum length among the distances between any two points on the contour line of the negative electrode active material (particles) (or its cross-sectional shape). When using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) as the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields A value calculated as a value is adopted. The definition of the above (average) particle diameter and the measurement method of the average particle diameter are similarly obtained by applying to other particles (for example, a positive electrode active material, an aqueous binder, etc.) other than the negative electrode active material (particles). be able to.

BET specific surface area of the negative electrode active material is preferably 0.5 to 10 m ² / g, more preferably 1.0~6.0m ² / g, more preferably 1.5~4.2m ² / g. If the specific surface area of the negative electrode active material is a value equal to or greater than the lower limit, the risk of deterioration of low temperature characteristics accompanying an increase in internal resistance is reduced. On the other hand, if the value is not more than the upper limit value, it is possible to prevent the side reaction from proceeding with an increase in the contact area with the electrolytic solution.

  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 97% 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.

(CMC (salt) obtained in step 1)
The aqueous slurry of this embodiment essentially contains CMC (salt) obtained in step 1 as a thickener. Here, the CMC (salt) obtained in step 1 (moisture removal step) is as described in step 1 (moisture removal step).

  A water-based binder described later has excellent binding properties, but has a low viscosity unlike an organic solvent-based binder. Therefore, in this embodiment, in order to impart an appropriate viscosity to the aqueous slurry, further reduce the amount of gas generated during the initial charge, and improve the charge / discharge cycle durability, the water after removal of the water obtained in step 1 is improved. CMC (salt) is used as a thickener.

  In step 2, when CMC (salt) after the water removal obtained in step 1 is (1) dissolved in water immediately as a thickener to produce an aqueous slurry, the CMC in step 1 ( After removing the water from the salt, a water-based slurry is produced within a certain period. Specifically, after removing the water of CMC (salt) in step 1, the work until dissolved in water (until the preparation of the aqueous slurry) is performed under a dry atmosphere (specifically, the dew point is −20 ° C. or lower). In a dry atmosphere), it should be performed within 24 hours.

  In addition, after removing the water of CMC (salt) in step 1, (2) after storage, when dissolving in water to prepare an aqueous slurry, the water content of CMC (salt) in step 1 is constant after removing the water. Store in a storage container or storage (dark room) that has been replaced with a dry atmosphere within the period (preferably light-shielding). Specifically, the dew point is stored in a dry atmosphere with a dew point of −20 ° C. or lower in the storage container or storage. Here again, the work from the removal of CMC (salt) water in Step 1 to storage is performed within 24 hours in a dry atmosphere (specifically, in a dry atmosphere with a dew point of −20 ° C. or lower). To do. During storage, the moisture content of CMC (salt) is periodically measured and used as a thickener before it exceeds 2%. When the stored CMC (salt) is taken out and used as a thickener, an aqueous slurry is prepared within a certain period after taking out. Specifically, after taking out from the storage container or storage, the work until dissolved in water (until the preparation of the aqueous slurry) is performed in a dry atmosphere (specifically, in a dry atmosphere having a dew point of −20 ° C. or less). , Within 24 hours.

  The amount of CMC (salt) added to the aqueous slurry after removing the water is not particularly limited, but is preferably 0.1 to 10% by mass with respect to the total solid content of the aqueous slurry. It is more preferable that it is 2 mass%. If the content of CMC (salt) after the removal of water 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. Furthermore, the effect of reducing gas generation during initial charging can be sufficiently exhibited. On the other hand, if the content of CMC (salt) after moisture removal is 10% by mass or less, the amount of gas generated during initial charging can be greatly reduced.

(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) obtained in step 1 is not particularly limited. -Butadiene rubber: CMC (salt) obtained in Step 1 is preferably 1: 0.2 to 2, and more preferably 1: 0.5 to 1. When the content ratio of CMC (salt) obtained in step 1 with respect to styrene-butadiene rubber is 0.2 or more, the thickening effect of CMC (salt) obtained in step 1 and further the gas during initial charging The generation reduction effect can be sufficiently exhibited. On the other hand, if the content ratio of CMC (salt) obtained in step 1 to styrene-butadiene rubber is 2 or less, the CMC (salt) obtained in step 1 effectively generates gas during initial charging. 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)
As other additives to the aqueous slurry, a conductive additive, an electrolyte salt (lithium salt), an ion conductive polymer, and the like can be used as appropriate.

  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) obtained in step 1, an aqueous binder, an aqueous solvent as a viscosity adjusting solvent, and other additives, if necessary, in a slurry preparation container. In addition, an aqueous slurry is prepared by stirring and mixing.

[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 of applying the aqueous slurry described above on the current collector in Step 2 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 drying temperature is not particularly limited as long as the purpose of solidifying the slurry (removing water and the like) can be achieved, but is usually 40 to 160 ° C, preferably 60 to 155 ° C, more preferably 80 to 150 ° C. Range. When the drying temperature is 40 ° C. or higher, the drying time is not required for a long period of time, and the drying can be sufficiently performed without reducing the production efficiency, so that moisture can be prevented from being brought into the battery. In addition, the CMC (salt) oxidation reaction does not progress so much (the chemical structure does not change much), and the CMC (salt) with a moisture content of 2% or less greatly reduces the amount of gas generated during initial charging. Can do. On the other hand, when the drying temperature is 160 ° C. or lower, even when a current collector made of a metal material is used, oxidation of the current collector (metal foil) can be prevented and drying can be performed in a short time. Is excellent. In addition, the CMC (salt) oxidation reaction does not progress so much (the chemical structure does not change much), and the CMC (salt) with a moisture content of 2% or less greatly reduces the amount of gas generated during initial charging. Can do.

  The drying time varies depending on the apparatus to be used and the amount of aqueous slurry applied, but is not limited in any way as long as it can achieve the purpose of solidifying the slurry (removing water, etc.), but usually 1 minute to 20 hours Degree. The drying atmosphere is not particularly limited, and is preferably performed in an air atmosphere from the viewpoint of production cost, but is not limited thereto. 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. The drying apparatus can use a drying means using hot air drying and infrared (IR) drying, which can perform normal continuous drying, and can also use a drying means using vacuum drying. Moreover, you may use the drying means which used hot air drying and IR drying together.

  Through the above steps, a laminate (negative electrode) in which a dried aqueous slurry (negative electrode active material layer) 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. By passing through this process 2, 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 aspect 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.

  The content of the positive electrode active material contained in the positive electrode active material layer is not particularly limited as long as the desired charge / discharge capacity can be obtained. Preferably, the range of 50 to 99 mass% is preferable, the range of 70 to 97 mass% is more preferable, and the range of 80 to 96 mass% is more preferable with respect to the total amount of the positive electrode active material layer. When the content of the positive 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 positive 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.

  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 point of view, it is preferable that the above-mentioned 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, and particularly preferably 1.3 to 1.6. 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. 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 an 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 (1) Step 1 (CMC (salt) water removal step)
As a thickener, a CMC salt having —CH ₂ COONa in which the proton at the carboxymethyl group terminal was replaced by a cation of Na ⁺ (etherification degree 0.82, weight average molecular weight 350,000, manufactured by Nippon Paper Chemical Co., Ltd.) was prepared. . This was subjected to heat treatment (removal of CMC salt moisture) for 3 hours under a pressure of 130 Pa and a pressure of 10 Pa using a vacuum oven. In addition, the moisture content before and after the water removal (heat treatment) step of the CMC salt was measured according to the measurement method shown below. The obtained results are shown in Table 1.

(2) Step 2 (coating and drying step)
Spherical agglomerated artificial graphite (D50 = 15 μm, BET specific surface area 3.5 m ² / g, manufactured by Hitachi Chemical Co., Ltd.) 97 parts by mass as negative electrode active material, SBR (gel amount 90%, Tg 10 ° C., average particle diameter 150 nm) as aqueous binder , Manufactured by Nippon Zeon Co., Ltd.) and a solid content consisting of 1 part by mass of the CMC salt obtained in the above Step 1 were 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). At this time, after removing the moisture of CMC (salt) in Step 1, the work until dissolved in water (until the preparation of the aqueous slurry) is performed in a dry atmosphere (specifically, a dry atmosphere having a dew point of −20 ° C. or less). Bottom) Performed within 4 hours. 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 by a die coating method, and dried in air at 120 ° C. for 3 minutes. And pressed. 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.

2. Production of positive electrode NMC composite oxide (composition: Li ₁ Ni _0.5 Mn _0.3 Co _0.2 O ₂ , D50 = 10 μm) 92 parts by mass as a positive electrode active material, Super C65 (manufactured by Timcal); A solid content comprising 2 parts by mass of carbon black) and 2 parts by mass of KS6L (manufactured by Timcal; scale-like 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.) as a current collector by a die coating method, dried in air at 120 ° C. for 3 minutes, pressed, and positive electrode active A positive electrode having a material layer coated on both sides of 25 mg / cm ² and 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 rectangular shape (rectangular shape) of 210 × 184 mm, and the negative electrode was rectangular shape of 215 × 188 mm (corresponding to the length of the short side of the negative electrode active material layer). (Rectangular shape; electrode aspect ratio; 1.14) (21 positive electrodes, 22 negative electrodes). 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 1.4.

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 charge, a constant current charge (CC) was performed up to 4.2 V at a current value of 0.05 CA, and then a constant voltage (CV) was charged for a total of 25 hours.

(Example 2)
In the “preparation of negative electrode” in Example 1, the CMC salt as a thickener was subjected to a heat treatment (removal of water from the CMC salt) over 3 hours at a pressure of 10 Pa using a vacuum oven at a temperature of 100 ° C. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for the above.

(Comparative Example 1)
The nonaqueous electrolyte secondary was produced in the same manner as in Example 1 except that the heat treatment (removal of water from the CMC salt) was not performed on the CMC salt as the thickener during “preparation of the negative electrode” in Example 1. A battery was produced.

[Measurement of water content of CMC (salt) (calculation of water content of CMC (salt))]
The water content of CMC (salt) was measured using a heat drying moisture meter (A & D, MX-50). About 5 g of the sample was measured at a heating temperature of 160 ° C., and the weight loss when the weight change amount per minute was within 0.05% was measured as moisture as the end condition. Then, the weight of CMC (salt) when the amount of change in weight per minute of the end condition is within 0.05% is defined as “dry weight of CMC (salt) alone”. Thereby, the moisture content (%) of CMC (salt) is {(weight of CMC (salt) before heating (heat treatment) (g)) − (dry weight (g) of only CMC (salt))} ÷ ( Weight of CMC (salt) before heating (heat treatment) (g)) × 100. Further, the moisture content (%) of CMC (salt) after the heating (heat treatment) in the above step 1 is {(weight (g) of CMC (salt) after the heating (heat treatment) in the above step 1)-(CMC ( Dry weight (g) of only salt)} / (CMC (salt) weight (g) after heating (heat treatment) in step 1) × 100. The obtained results are shown in Table 1. About the measurement of the sample heated (heat treatment), it measured immediately after completion of heating (heat treatment).

[Gas generation amount at first charge]
About the nonaqueous electrolyte secondary battery produced in Examples 1-2 and Comparative Example 1, the battery volume change amount before the first charge and after the end of the charge for 25 hours is measured by the Archimedes method, and gas is generated at the first charge. The amount. The results are shown in Table 1. In Table 1, relative values when the amount of nonaqueous electrolyte secondary battery gas generated in Comparative Example 1 is set to 100 are shown.

[Measurement of capacity maintenance ratio]
About the nonaqueous electrolyte secondary battery produced in Examples 1-2 and Comparative Example 1, after the battery temperature was set to 25 ° C. in a constant temperature bath maintained at 25 ° C., charging was performed at a constant current up to 4.15 V at a current rate of 1C. The battery was charged (CC) and then charged at a constant voltage (CV) for 2.5 hours. Then, after providing a 10-minute rest period, discharging was performed at a current rate of 1 C to 3.0 V, followed by a 10-minute rest period. A charge / discharge test was conducted with these as one cycle. The ratio of the capacity (discharge capacity) discharged after 500 cycles with respect to the initial discharge capacity was defined as the capacity maintenance rate. The results are shown in Table 1. In Table 1, relative capacity retention ratios of the nonaqueous electrolyte secondary batteries produced in the respective examples when the capacity maintenance ratio value of the nonaqueous electrolyte secondary battery produced in Comparative Example 1 was 100.0. Values are listed.

  From the results of Table 1, in Examples 1 and 2 having the negative electrode obtained by the production method of the present invention (moisture removal of CMC salt), the gas at the initial charge was higher than that of Comparative Example 1 in which the moisture of CMC salt was not removed. It was confirmed that the generation amount can be significantly reduced and the charge / discharge cycle durability (capacity maintenance ratio) can be improved.

  Moreover, when it sees about Examples 1-2, the direction of Example 1 which removed more water | moisture content by the water | moisture-content removal process (process 1) of the CMC salt is the gas generation reduction effect at the time of the said initial charge, and a charge / discharge cycle It was found that the durability (capacity maintenance ratio) improving effect can be obtained more remarkably.

  Furthermore, a difference of 0.6 to 0.9% occurs in the capacity retention rate after 500 cycles between the example and the comparative example. On the other hand, the life required for EV batteries is at least 1000 to 2000 cycles. Therefore, when the charge / discharge cycle test is seen as an acceleration life test of an EV battery, for example, after 2000 cycles, the capacity retention rate is a large difference of 2.4 to 3.6% or more between the examples and the comparative example. It can be said that will occur.

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 outer package.

Claims (7)

Step 1: removing moisture from carboxymethylcellulose or a salt thereof (hereinafter also simply referred to as “CMC (salt)”);
Step 2: Applying an aqueous slurry containing a negative electrode active material, CMC (salt) obtained in Step 1 and an aqueous binder on the current collector, and drying to form a negative electrode;
The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries characterized by including.   In the said process 1, the moisture content of CMC (salt) shall be 2% or less, The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries of Claim 1 characterized by the above-mentioned.   In the said process 1, the CMC (salt) to be used is one type, The manufacturing method of the negative electrode for nonaqueous electrolyte secondary batteries of Claim 1 or 2 characterized by the above-mentioned. 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 1-3.   The nonaqueous electrolyte secondary battery according to claim 4, 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 4 or 5, 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 4 to 6, wherein an aspect ratio of the electrode defined as an aspect ratio of the rectangular negative electrode active material layer is 1 to 3.