KR102332441B1 - Anode for non-aqueous electrolyte seconary battery and non-aqueous electrolyte seconary battery - Google Patents

Abstract

According to the present invention, a first anode active material layer disposed on the anode current collector and including styrene butadiene rubber as a first main binder, and an acrylate binder as a second main binder disposed on the first anode active material layer There is provided a negative electrode for a non-aqueous electrolyte secondary battery comprising a second negative electrode active material layer, wherein the areal density ratio of the first negative electrode active material layer to the second negative electrode active material layer is 0.25 to 1.

Description

NON-AQUEOUS ELECTROLYTE SECONARY BATTERY AND NON-AQUEOUS ELECTROLYTE SECONARY BATTERY}

The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

In recent years, with the miniaturization of information processing devices such as mobile phones and notebook PCs, high capacity and long life characteristics of nonaqueous electrolyte secondary batteries that can be used as power sources for these information processing devices are required. And, as a technology for increasing the capacity of the nonaqueous electrolyte secondary battery, thickening the electrode has been proposed.

However, there is a problem in that, simply by making the electrode thick, ion conductivity in the thickness direction of the electrode is lowered, and the lifespan characteristics of the nonaqueous electrolyte secondary battery are lowered.

Accordingly, as a technique for improving the deterioration of the lifespan characteristics accompanying the thickening of the electrode, a technique in which the cathode has a multilayer structure has been proposed. For example, it has been proposed to limit the particle size and ratio of each active material while containing an active material having a large particle size in the lower layer on the current collector side and containing an active material having a small particle size in the upper layer. At this time, as the binder, any one of PVDF, PTFE, and PVP may be used. Alternatively, it is proposed to contain an active material with a small particle size in the lower layer on the current collector side, contain an active material with a large particle size in the upper layer, and limit the particle size ratio or the size of the porosity of each layer. Alternatively, it has been proposed that the anode active material layer has a multilayer structure, and that the binder constituting each layer may be different.

However, the above-described technology could not sufficiently improve the lifespan characteristics of the nonaqueous electrolyte secondary battery.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress the deterioration of the lifespan characteristics accompanying the thickening of the electrode while increasing the capacity of the non-aqueous electrolyte secondary battery. To provide a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

However, there is a problem in that, simply by making the electrode thick, ion conductivity in the thickness direction of the electrode is lowered, and the lifespan characteristics of the nonaqueous electrolyte secondary battery are lowered.

Accordingly, as a technique for improving the deterioration of the lifespan characteristics accompanying the thickening of the electrode, a technique in which the cathode has a multilayer structure has been proposed. For example, it has been proposed to limit the particle size and ratio of each active material while containing an active material having a large particle size in the lower layer on the current collector side and containing an active material having a small particle size in the upper layer. At this time, as the binder, any one of PVDF, PTFE, and PVP may be used. Alternatively, it is proposed to contain an active material with a small particle size in the lower layer on the current collector side, contain an active material with a large particle size in the upper layer, and limit the particle size ratio or the size of the porosity of each layer. Alternatively, it has been proposed that the anode active material layer has a multilayer structure, and that the binder constituting each layer may be different.

However, the above-described technology could not sufficiently improve the lifespan characteristics of the nonaqueous electrolyte secondary battery.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress the deterioration of the lifespan characteristics accompanying the thickening of the electrode while increasing the capacity of the non-aqueous electrolyte secondary battery. To provide a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.

As described above, according to the present invention, it is possible to increase the capacity of the non-aqueous electrolyte secondary battery while suppressing deterioration of the lifespan characteristics of the non-aqueous electrolyte secondary battery.

1 is a plan sectional view showing a schematic configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawings, the same code|symbol is attached|subjected to the component which has substantially the same functional structure, and the duplicate description is abbreviate|omitted.

<1. Composition of Lithium Ion Secondary Battery>

First, the configuration of the nonaqueous electrolyte secondary battery 10 according to the present embodiment will be described with reference to FIG. 1 .

The non-aqueous electrolyte secondary battery 10 includes a positive electrode 20 , a negative electrode 30 , a separator 40 , and a non-aqueous electrolyte. The charging reached voltage (oxidation-reduction potential) of the non-aqueous electrolyte secondary battery 10 is, for example, 4.0 V (vs. Li/Li ⁺ ) or more and 5.0 V or less, particularly 4.2 V or more and 5.0 V or less. The shape of the nonaqueous electrolyte secondary battery 10 is not particularly limited. That is, the non-aqueous electrolyte secondary battery 10 may be any type, such as a cylindrical shape, a prismatic shape, a laminate type, or a button type.

(1-1. Anode (20))

The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 . The positive electrode current collector 21 may be any conductor as long as it is a conductor, and is made of, for example, aluminum, stainless steel, or nickel-coated steel.

The positive electrode active material layer 22 contains at least a positive electrode active material, and may further contain a conductive agent and a positive electrode binder. The positive active material is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions, and examples thereof include lithium-containing transition metal oxides, nickel sulfide, copper sulfide, sulfur, iron oxide, and vanadium oxide. Examples of the lithium-containing transition metal oxide include lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt acid, lithium nickel cobalt aluminate (hereinafter sometimes referred to as “NCA”), lithium nickel cobalt manganese acid (hereinafter, "NCM"), lithium manganate, lithium iron phosphate, etc. are mentioned. These positive electrode active materials may be used independently and 2 or more types may be used together.

Among the examples enumerated above, the cathode active material is preferably a lithium-containing transition metal oxide, particularly preferably a lithium salt of a transition metal oxide having a layered rock salt structure.

The conductive agent is, for example, carbon black such as Ketjenblack and acetylene black, carbon nanotubes, natural graphite, artificial graphite, and the like, but is not particularly limited as long as it is intended to increase the conductivity of the anode.

The positive electrode binder is, for example, polyvinylidene fluoride, acid-modified polyvinylidene fluoride, polyvinylidene fluoride copolymer, acid-modified polyvinylidene fluoride copolymer, and acrylonitrile-butadiene rubber. , hydrogenated acrylonitrile butadiene rubber, etc., but is not particularly limited as long as it can bind the positive electrode active material and the conductive agent on the positive electrode current collector 21 . The binder for the positive electrode may be a mixture of a plurality of types of the binders listed above.

The positive electrode active material layer 22 is produced, for example, by the following manufacturing method. That is, first, a positive electrode mixture is prepared by dry-mixing the positive electrode active material, the conductive agent, and the positive electrode binder. Next, a positive electrode mixture slurry is prepared by dispersing the positive electrode mixture in a suitable organic solvent, and the positive electrode mixture slurry is applied on the positive electrode current collector 21, dried and rolled to produce a positive electrode active material layer.

(1-2. Cathode (30))

The negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 . The anode active material layer 32 is divided into a first anode active material layer 32a and a second anode active material layer 32b. The negative electrode current collector 31 may be any conductor as long as it is a conductor, and is made of, for example, copper (Cu), nickel (Ni), stainless steel, and nickel-plated steel.

The first anode active material layer 32a is a layer disposed on the anode current collector 31 and includes at least an anode active material and a first main binder. The negative electrode active material is, for example, a graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), a mixture of fine particles of silicon or tin or their oxides and a graphite active material , fine particles of silicon or tin, alloys based on silicon or tin, and _{titanium oxide compounds such as Li 4} Ti ₅ O ₁₂ , lithium nitride, and the like. The oxide of silicon _{is represented by SiO x} (0≤x≤2). Examples of the negative electrode active material other than these include metallic lithium.

The first main binder includes styrene butadiene rubber (SBR). It is preferable that the first main binder is composed of only SBR. SBR has better adhesion to the negative electrode current collector 31 than an acrylate binder, which will be described later. In the present embodiment, the first negative electrode active material layer 32a in contact with the negative electrode current collector 31 contains SBR having high adhesion to the negative electrode current collector 31 . Accordingly, even when the non-aqueous electrolyte secondary battery 10 is repeatedly charged and discharged, the anode active material layer 32 can be firmly attached to the anode current collector 31 . As a result, deterioration of life characteristics can be suppressed.

The first negative electrode active material layer 32a may contain a binder other than the main binder, that is, a secondary binder, within a range that does not impair the effects of the present embodiment. Examples of such a sub-binder include carboxymethyl cellulose (CMC).

The first negative active material layer 32a may further contain a conductive agent. The conductive agent is, for example, carbon black such as Ketjenblack and acetylene black, carbon nanotubes, natural graphite, artificial graphite, and the like, but is not particularly limited as long as it is intended to increase the conductivity of the negative electrode.

The second anode active material layer 32b is a layer disposed on the first anode active material layer 31a and includes at least an anode active material and a second main binder. The negative electrode active material may be the same as or different from the negative electrode active material in the first negative electrode active material layer 32a.

The second main binder includes an acrylate binder. The second main binder is preferably composed of only an acrylate binder. The acrylate binder has better ion conductivity than SBR. Therefore, even if the second anode active material layer 32b is thickened in order to increase the capacity of the nonaqueous electrolyte secondary battery 10, a decrease in ion conductivity can be suppressed, and furthermore, the lifespan characteristics of the nonaqueous electrolyte secondary battery 10 are reduced. degradation can be suppressed. However, since it tends to have lower adhesiveness with the negative electrode active material than SBR, it is preferable to set the swelling ratio to a value within the following range.

Here, the acrylate binder is a binder usable as a binder of a negative active material of a non-aqueous electrolyte secondary battery among so-called acrylic resins. It is preferable that the swelling ratio of the acrylate binder with respect to electrolyte solution is 130-220%. When the swelling ratio of the acrylate binder falls within this range, the ionic conductivity becomes higher. When the swelling ratio of the acrylate binder is less than 130%, there is a possibility that the ion conductivity is insufficient. When the swelling ratio of the acrylate binder exceeds 220%, since the acrylate binder is substantially dissolved in the electrolyte, there is a possibility that the function as a binder may be insufficient. That is, there is a possibility that the adhesion between the acrylate binder and the negative electrode active material is insufficient.

Specifically, the acrylate binder is a copolymer of at least one selected from acrylic acid, itaconic acid, and acrylic acid ester, and at least one selected from styrene, acrylonitrile, acrylamide, butadiene, vinylidene fluoride, and hexafluoroethylene. and the like. Here, examples of the acrylic acid ester include, but are not limited to, butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and 4-hydroxybutyl acrylate. Any acrylic acid ester may be sufficient as long as the effect is obtained.

The second negative electrode active material layer 32b may contain a binder other than the main binder, that is, a secondary binder, within a range that does not impair the effects of the present embodiment. Examples of such a sub-binder include carboxymethyl cellulose (CMC).

The second negative active material layer 32b may further contain a conductive agent. The conductive agent is, for example, carbon black such as Ketjenblack and acetylene black, carbon nanotubes, natural graphite, artificial graphite, and the like, but is not particularly limited as long as it is intended to increase the conductivity of the negative electrode.

Although the areal density (area density before rolling) of the negative electrode active material layer 32 is not particularly limited, it ^{is preferably 10 mg/cm 2} or more. Also, the bulk density of the negative electrode active material layer 32 after rolling is not particularly limited, but is preferably 1.5 g/cc or more. Here, the areal density of the anode active material layer 32 is the mass of the anode active material layer 32 per unit area of the anode current collector 31 (that is, the first anode active material layer 32a and the second anode active material layer 32b). is the sum of the mass of ).

In addition, the bulk density of the anode active material layer 32 is the mass of the anode active material layer 32 per unit volume of the anode active material layer 32, and the mass of the anode active material layer 32 is the total mass of the anode active material layer 32. It is obtained by dividing by the volume.

Here, the areal density ratio (area density ratio before rolling) of the first negative electrode active material layer 32a to the second negative electrode active material layer 32b is preferably 0.25 to 1. It is more preferable that the areal density ratio is 0.45-0.55, and it is most preferable that it is 0.5. In this case, the adhesion of the negative electrode active material layer 32 to the negative electrode current collector 31 and the lifespan characteristics of the nonaqueous electrolyte secondary battery 10 are further improved. Here, the areal density of the first negative active material layer 32a is the mass of the first negative active material layer 32a per unit area of the negative electrode current collector 31, and the areal density of the second negative electrode active material layer 32b is the negative electrode current collector It is the mass of the second negative electrode active material layer 32b per unit area of (32).

Moreover, it is preferable that the bulk density ratio after rolling of the 1st anode active material layer 32a with respect to the 2nd anode active material layer 32b is 1 or more. Although the upper limit in particular of the bulk density ratio after rolling is not restrict|limited, It is preferable that it is 1.1 or less. In this case, the adhesion of the negative electrode active material layer 32 to the negative electrode current collector 31 and the lifespan characteristics of the nonaqueous electrolyte secondary battery 10 are further improved. Here, the bulk density of the first anode active material layer 32a is the mass of the first anode active material layer 32a per unit volume of the first anode active material layer 32a, and the bulk density of the second anode active material layer 32b. is the mass of the second anode active material layer 32b per unit volume of the second anode active material layer 32b.

On the other hand, the areal density of the first negative electrode active material layer 32a and the second negative electrode active material layer 32b can be adjusted by the amount of application of the negative electrode mixture slurry (slurry in which the components of each negative electrode active material layer are dispersed). The bulk density can be adjusted by the pressure at the time of rolling.

(1-5. Separator)

The separator 40 in particular is not restrict|limited, As long as it is used as a separator of a lithium ion secondary battery, what kind may be sufficient. As a separator, it is preferable to use individually or together a porous film, a nonwoven fabric, etc. which show the outstanding high rate discharge performance. As a resin constituting the separator, for example, a polyolefin-based resin represented by polyethylene, polypropylene, etc., polyethylene terephthalate, polybutylene terephthalate, etc. Representative polyester resins, PVDF, vinylidene fluoride (VDF)-hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether (par fluorovinyl ether) copolymer, vinylidene fluoride- Tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer , vinylidene fluoride-ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene- and a hexafluoropropylene copolymer, a vinylidene fluoride-ethylene (ethylene)-tetrafluoroethylene copolymer, and the like.

(1-6. Non-aqueous electrolyte)

As the non-aqueous electrolyte, the same non-aqueous electrolyte that has been conventionally used for a non-aqueous electrolyte secondary battery may be used without particular limitation. The non-aqueous electrolyte has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include cyclic carbonate esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate. (ester); cyclic esters such as ?-butyrolactone and ?-valerolactone; Chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; methyl formate, methyl acetate, butyric acid methyl Chain esters such as; Tetrahydrofuran or a derivative thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4 -Ethers such as dibutoxyethane and methyl diglyme; nitriles such as acetonitrile and benzonitrile; Dioxolane or its derivatives ; Ethylene sulfide (ethylene sulfide), sulfolane (sulfolane), sultone (sultone) or a derivative thereof alone or a mixture of two or more thereof, but is not limited thereto.

Further, as the electrolyte salt, for _{example, LiClO 4, LiBF 4, LiAsF} 6, LiPF 6, LiPF 6 - x (C n F 2n + 1) x [ stage, 1 <x <6, n = 1 or 2; , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B10Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, such as lithium (Li), sodium (Na) or potassium (K) Inorganic ionic salts containing, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ), LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF, (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ Nbr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C ₂ H ₅ ) ₄ N-phthalate, stearyl sulfonic acid lithium, octyl sulfonic acid, lithium dodecylbenzenesulfonate ( and organic ionic salts such as dodecyl benzene sulphonic acid), and it is possible to use these ionic compounds individually or in mixture of two or more types. Meanwhile, the concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte used in the conventional non-aqueous electrolyte secondary battery, and there is no particular limitation. In this embodiment, a non-aqueous electrolyte containing a suitable lithium compound (electrolyte salt) at a concentration of about 0.8 to 1.5 mol/L can be used.

Meanwhile, various additives may be added to the non-aqueous electrolyte. Such additives include anode action additives, anode action additives, ester additives, carbonate ester additives, sulfuric acid ester additives, phosphoric acid ester additives, boric acid ester additives, acid anhydride additives, and electrolytes. of additives. Any one of these may be added to the non-aqueous electrolyte, or a plurality of types of additives may be added to the non-aqueous electrolyte.

<2. Manufacturing method of lithium ion secondary battery>

Next, a method for manufacturing the nonaqueous electrolyte secondary battery 10 will be described. The anode 20 is manufactured as follows. First, a positive electrode mixture slurry is prepared by dispersing a mixture of a positive electrode active material, a conductive agent, and a positive electrode binder in the above ratio in a solvent (eg, N-methyl-2-pyrrolidone). Then, the positive electrode mixture slurry is applied on the positive electrode current collector 21 and dried to form the positive electrode active material layer 22 . In addition, the method of application|coating is not specifically limited. As a method of application|coating, the knife coater (knife coater) method, the gravure coater (gravure coater) method, etc. are considered, for example. Each of the following application|coating processes is also performed by the same method. Next, the positive electrode active material layer 22 is rolled by a press machine. Accordingly, the anode 20 is manufactured.

The negative electrode 30 is also manufactured in the same manner as the positive electrode 20 . First, by dispersing a mixture of the materials constituting the first negative electrode active material layer 32a in a solvent (for example, water), a first negative electrode mixture slurry is prepared. The first anode active material layer 32a is formed by coating and drying the entirety 31. Accordingly, the first anode active material layer 32a is formed on the anode current collector 31.

Next, by dispersing a mixture of the materials constituting the second negative electrode active material layer 32b in a solvent (for example, water), a second negative electrode mixture slurry is prepared. By coating on the negative electrode active material layer 32a and drying, the second negative electrode active material layer 32b is formed.Then, the first negative electrode active material layer 32a and the second negative electrode active material layer 32b are rolled by a press machine. Accordingly, the negative electrode 30 is manufactured.

Next, by placing the separator 40 between the positive electrode 20 and the negative electrode 30 , an electrode structure is manufactured. Then, the electrode structure is processed into a desired shape (eg, wound type, cylindrical shape, square shape, laminate type, button type, etc.) and inserted into a container of the above shape. Next, by injecting a non-aqueous electrolyte into the container, each pores in the separator 40 are impregnated with the electrolyte. Accordingly, a lithium ion secondary battery is manufactured.

As described above, according to the present embodiment, the negative electrode active material layer 32 has a two-layer structure, and SBR is included in the first negative electrode active material layer 32a on the negative electrode current collector 31 side. In addition, an acrylate binder is included in the second anode active material layer 32b formed on the first anode active material layer 32a. Accordingly, the adhesion of the negative electrode active material layer 32 to the negative electrode current collector 31 can be improved. In addition, even if the second negative electrode active material layer 32b is thickened, a decrease in ion conductivity is suppressed. Accordingly, it is possible to increase the capacity of the non-aqueous electrolyte secondary battery 10 while suppressing deterioration of the lifespan characteristics of the non-aqueous electrolyte secondary battery 10 .

[Example]

<1. Example 1>

Next, examples of the present embodiment will be described. In Example 1, a nonaqueous electrolyte secondary battery was produced by the following steps.

(1-1. Preparation of anode)

A first negative electrode mixture slurry was prepared by dissolving and dispersing graphite, styrene-butadiene rubber (SBR), and sodium salt of carboxymethylcellulose in a water solvent at a mass ratio of solid content of 98:1:1. Next, a second negative electrode mixture slurry was prepared by dissolving graphite, an acrylate binder, and sodium salt of carboxymethyl cellulose in a water solvent at a mass ratio of solid content of 98:1:1. Here, as the acrylate binder, Movinyl 752 (styrene/acrylate copolymer) from The Nippon Synthetic Chemical Industry Co., Ltd. was used.

Next, on both sides of the copper foil current collector (negative current collector 31) having a thickness of 6 μm, the first negative electrode mixture slurry so that the areal density per one side of the current collector (the surface density of the first negative electrode active material layer 32a) is 3 mg/cm ² After coating, it was dried. Accordingly, the first anode active material layer 32a was formed on the anode current collector 31 . Then, the second negative electrode mixture slurry was applied to both surfaces so that the areal density per one side of the current collector was 12 mg/cm ² (the areal density of the second negative electrode active material layer 32b), and dried. Accordingly, the second anode active material layer 32b was formed on the first anode active material layer 32a. Next, the negative electrode 30 was produced by rolling the negative electrode active material layer 32 to have a bulk density of 1.6 g/cc after rolling. By the above process, the negative electrode 30 was produced. Thereafter, a nickel lead wire was welded to the end of the negative electrode 30 .

(1-2. Production of positive electrode)

A positive electrode mixture slurry was prepared by dissolving and dispersing lithium cobaltate, carbon black, binder 1, and binder 2 in N-methylpyrrolidone at a mass ratio of solid content of 97.7:1.2:1.0:0.1. Here, the binder 1 was polyvinylidene fluoride, and the binder 2 was hydrogenated acrylonitrile butadiene rubber. Next, this positive electrode mixture slurry was applied to both surfaces of an aluminum foil current collector (positive electrode current collector 21) having a thickness of 12 μm to form a positive electrode active material layer 22 on the positive electrode current collector 21 . Next, the positive electrode 20 was produced by rolling the positive electrode current collector 21 and the positive electrode active material layer 22 so that the porosity of the positive electrode active material layer 22 was 17%. Then, an aluminum lead wire was welded to the end of the anode 20 .

(1-3. Fabrication of winding element)

The positive electrode 20, the separator 40 (ND314 manufactured by ASAHI KASEI E-MATERIALS), the negative electrode 30, and the separator 40 are laminated in this order, and this laminate is longitudinally stacked using a core having a diameter of 3 cm. wrapped around After fixing the ends with tape, the core was removed, and the cylindrical electrode wound element was sandwiched between two metal plates with a thickness of 3 cm and held for 3 seconds to obtain a flat wound element.

(1-4. Preparation of battery)

A battery was produced by sealing the electrode wound element on a laminate film composed of three layers of polypropylene/aluminum/nylon together with an electrolyte so that two lead wires came out. _{As the electrolyte solution, 10% by volume of FEC (fluoroethylene carbonate) and 1.3M LiPF 6} were dissolved in a solvent in which ethylene carbonate/dimethyl carbonate was mixed in a 3 to 7 (volume ratio) ratio was used. This battery was sandwiched between two metal plates with a thickness of 3 cm heated to 90 DEG C, and held for 5 minutes. Through the above steps, the nonaqueous electrolyte secondary battery 10 was produced.

(1-5. Measurement of swelling rate)

The swelling ratio of the acrylate binder was measured by the following process. First, a binder film was prepared by applying and drying an acrylate binder on the substrate. Next, the binder film was peeled off from the base material, and the binder film was immersed in the electrolyte solution used for production of the nonaqueous electrolyte secondary battery for 24 hours. The temperature of the electrolyte solution was maintained at 60°C. Next, the mass change rate of the binder film before and after immersion was made into the swelling rate of the acrylate binder. The mass change rate is a value obtained by dividing the change in mass by the mass of the binder film before immersion.

(1-6. Bulk density ratio after rolling)

After coating the first negative electrode mixture slurry on the negative electrode current collector, drying, the first negative electrode active material layer 32b is removed, 5 g of this sample is inserted into a cylindrical container with a diameter of 10 mm, and a pressure of 10 t/cm ² is applied in a hydraulic press. was applied, and the bulk density of the first anode active material layer 32a was measured. Similarly, the bulk density of the second anode active material layer 32b was measured, and the value obtained by dividing the bulk density of the first anode active material layer 32a by the bulk density of the second anode active material layer 32b was taken as the bulk density ratio after rolling. .

(1-7. Peel strength)

A 180 degree peel test was performed to peel the negative electrode active material layer 32 from the produced negative electrode 30 . As the test apparatus, a universal testing machine (AGS-X manufactured by Shimadzu Corporation) was used. And the force (N/m) applied to the negative electrode active material layer 32 when the negative electrode active material layer 32 was peeled from the negative electrode current collector 31 was made into the peeling strength of the negative electrode active material layer 32 .

(1-8. Cycle test)

The cycle test of the nonaqueous electrolyte secondary battery 10 was performed as follows. First, in the first cycle, CC-CV charging (constant current constant voltage charging) was performed at 0.1 C until the voltage reached 4.4 V, and CC discharge (constant current discharge) was performed at 0.1 C until the voltage reached 2.75 V. Then, in the second cycle, CC-CV charging was performed at 0.2 C until the voltage reached 4.4 V, and CC discharge was performed at 0.2 C until the voltage reached 2.75 V. Further, after the third cycle, a cycle of performing CC-CV charging at 1.0 C until the voltage reached 4.4 V and CC discharging at 1.0 C until the voltage reached 3.00 V was repeated. The numerical value obtained by dividing the discharge capacity at the 200th cycle by the discharge capacity at the 3rd cycle was defined as the capacity retention ratio. The higher the capacity retention ratio, the better the lifespan characteristics.

<2. Example 2>

In the above (1-1. Preparation of negative electrode), the areal density of the first negative electrode active material layer 32a is 5 mg/cm ² and the areal density of the second negative electrode active material layer 32b is 10 mg/cm ² . The same process as Example 1 was performed.

<3. Example 3>

In the above (1-1. Preparation of negative electrode), the areal density of the first negative electrode active material layer 32a is 7.5 mg/cm ² and the areal density of the second negative electrode active material layer 32b is 7.5 mg/cm ² Except that, the same processing as in Example 1 was performed.

<4. Example 4>

In the above (1-1. Preparation of negative electrode), the negative electrode active material constituting the second negative electrode active material layer 32b is harder than the graphite in the first negative electrode active material layer 32a and is implemented except that it is changed to poorly oriented graphite The same process as Example 2 was performed. In Example 4, the bulk density ratio after rolling became 1.02.

<5. Example 5>

In Example 2, except that the acrylate binder was Movinyl 749E (styrene/acrylate) manufactured by The Nippon Synthetic Chemical Industry Co., Ltd. in the above (1-1. Preparation of the negative electrode). The same treatment was performed.

<6. Comparative Example 1>

In the above (1-1. Preparation of negative electrode), the second negative electrode active material layer 32b was not formed and the areal density of the first negative electrode active material layer 32a was set to 15 mg/cm ² as in Example 1 The same treatment was performed.

<7. Comparative Example 2>

In the above (1-1. Preparation of negative electrode), the same processing as in Example 2 was performed except that the binder constituting the second negative electrode active material layer 32b was SBR.

<8. Comparative Example 3>

In the above (1-1. Preparation of negative electrode), the second negative electrode active material layer 32b was not formed, and the binder constituting the first negative electrode active material layer 32a was used as the acrylate binder of Example 1 , The same treatment as in Example 1 was performed except that the areal density of the first negative electrode active material layer 32a was 15 mg/cm ^{2 .}

<9. Comparative Example 4>

In the above (1-1. Preparation of negative electrode), the areal density of the first negative electrode active material layer 32a is 12 mg/cm ² , and the areal density of the second negative electrode active material layer 32b is 3 mg/cm ² . The same process as Example 1 was performed.

<10. Rating>

The evaluation results are summarized in Table 1 and shown. In Table 1, "1st layer" shows the 1st negative electrode active material layer 32a, and "2nd layer" shows the 2nd negative electrode active material layer 32b.

Binder type areal
(mg/cm ² ) area density ratio Swelling rate (%) Bulk density ratio after rolling
(1st floor/2nd floor) Peel strength (N/m) Capacity retention rate (%) 1st floor 2nd floor 1st floor 2nd floor Example 1 SBR acrylate 3 12 0.25 150 One 3.6 87.3 Example 2 SBR acrylate 5 10 0.5 150 One 3.8 88.2 Example 3 SBR acrylate 7.5 7.5 One 150 One 3.7 86.5 Example 4 SBR acrylate 5 10 0.5 150 1.02 3.0 90.1 Example 5 SBR acrylate 5 10 0.5 200 One 3.5 86.5 Comparative Example 1 SBR - 15 0 - - - 2.5 80.4 Comparative Example 2 SBR SBR 5 10 0.5 - One 4.0 84.2 Comparative Example 3 acrylate - 15 0 - - - 2.2 81.0 Comparative Example 4 SBR acrylate 12 3 4 150 One 2.8 82.5

According to Table 1, in Examples 1-5, both the peeling strength and the capacity|capacitance retention ratio became favorable results. In particular, in Example 2, the areal density ratio became a preferable range, and especially favorable results were obtained. In Example 4, the bulk density of the second anode active material layer 32b after rolling is small, and as a result, the bulk density ratio after rolling is higher than in Examples 1 to 3. That is, in Example 4, an anode active material that is difficult to compress is used for the second anode active material layer 32b. As a result, the porosity of the second anode active material layer 32b is increased compared to that of the first anode active material layer 32a, and the ion conductivity of the second anode active material layer 32b, which is easily subject to rate regulation, is improved, and the lifespan characteristics are improved. do.

On the other hand, in Comparative Example 1, since the negative electrode active material layer 32 was made of a single layer of SBR, the peel strength and capacity retention ratio were decreased. Here, it is thought that binder migration occurs in the negative electrode active material layer 32 that peeling strength is falling in the single layer of SBR, and peeling strength fell. Here, binder migration means that the binder is unevenly distributed on the surface of the coating layer when the anode active material layer 32 is manufactured (specifically, when the slurry is dried). As a result, it is considered that the peel strength fell and the capacity retention ratio also fell. In Comparative Example 2, the anode active material layer 32 has a multilayer structure, but SBR is used as a binder in all layers. For this reason, although the peeling strength was favorable, the capacity|capacitance retention rate fell. On the other hand, in Comparative Example 2, since the negative electrode active material layer 32 has a multilayer structure, binder migration can be suppressed, and it is thought that peeling strength was favorable. In Comparative Example 3, the anode active material layer 32 was formed of a single layer of an acrylate binder. For this reason, peeling strength and capacity|capacitance retention fell. In Comparative Example 4, the negative electrode active material layer 32 has a multilayer structure, and at the same time, the binder constituting each layer is the same as in Example 1. However, since the areal density ratio deviated from the range of the present embodiment, the peel strength and capacity retention ratio were lowered.

As mentioned above, although this invention was demonstrated in detail about preferable embodiment, referring an accompanying drawing, this invention is not limited to this example. It is clear that various changes or modifications can be made within the scope of the technical idea described in the claims by those having ordinary knowledge in the field of technology to which the present invention belongs. It is understood to be within the technical scope of the present invention.

10 Non-aqueous electrolyte secondary battery
20 anode
21 positive electrode current collector
22 cathode active material layer
30 cathode
31 Anode current collector
32 Anode active material layer
32a first anode active material layer
32b second anode active material layer

Claims (7)

negative electrode current collector; a first anode active material layer disposed on the anode current collector and comprising styrene butadiene rubber as a first main binder;
a second anode active material layer disposed on the first anode active material layer and including an acrylate binder as a second main binder;
A negative electrode for a non-aqueous electrolyte secondary battery in which an areal density ratio of the first negative active material layer to the second negative active material layer is 0.25 to 1. According to claim 1,
The first main binder is composed of only styrene butadiene rubber,
The second main binder is an anode for a non-aqueous electrolyte secondary battery comprising only an acrylate binder. 3. The method according to claim 1 or 2,
The bulk density ratio of the first anode active material layer to the second anode active material layer is 1 or more, and the bulk density ratio is a value obtained by dividing the bulk density of the first anode active material layer by the bulk density of the second anode active material layer, and the The bulk density of the first anode active material layer and the bulk density of the second anode active material layer are values obtained by applying pressure to the anode active material layer with a hydraulic press. 3. The method according to claim 1 or 2,
A negative electrode for a non-aqueous electrolyte secondary battery having a swelling ratio of 130 to 220% with respect to the electrolyte of the acrylate binder. 3. The method according to claim 1 or 2,
The first anode active material layer and the second anode active material layer include a conductive agent for a non-aqueous electrolyte secondary battery negative electrode. 3. The method according to claim 1 or 2,
The first anode active material layer and the second anode active material layer a negative electrode for a non-aqueous electrolyte secondary battery comprising carboxymethyl cellulose as a sub-binder. A non-aqueous electrolyte secondary battery comprising the negative electrode for a non-aqueous electrolyte secondary battery according to claim 1.

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