JP2002033104A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having an improved charge-discharge cycle life while realizing high capacity by improving the negative electrode thereof. SOLUTION: This battery is provided with a positive electrode capable of storing and releasing lithium, the negative electrode capable of storing and releasing lithium, a separator and a nonaqueous electrolyte. The positive electrode and the negative electrode each have a structure composed by applying a positive electrode material and a negative electrode material on a collector, respectively. The negative electrode material contains fibrous carbonaceous materials (a) and (b), and scale-like or spherical lump-like graphite (c). The battery is characterized in that the size Lc of crystal in the c-axis direction of the fibrous carbonaceous material (a) is 40-60 nm, and the size Lc of crystal in the c-axis direction of the fibrous carbonaceous material (b) is 100 nm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, various types of electronic devices such as VTRs, mobile phones, and personal computers, and small-sized cordless portable electronic devices have been developed.
Along with the weight reduction, the demand for a high energy density of the power supply of such devices has been increased, and non-aqueous electrolyte secondary batteries represented by lithium secondary batteries using metallic lithium as a negative electrode active material have been proposed. However, in a lithium secondary battery using metallic lithium as the negative electrode active material, lithium dissolved in the electrolyte as lithium ions at the time of discharge reacts with the nonaqueous solvent in the electrolyte to become partially inactive. Therefore, when charge and discharge are repeated, lithium is electrodeposited on the convex portion on the surface of the negative electrode and precipitates in a dendrite shape (dendritic shape), and this dendrite-like lithium penetrates the separator and comes into contact with the positive electrode, thereby causing an internal short circuit. There was a problem.

In view of the above, Japanese Patent Application Laid-Open No. 63-121
No. 260 discloses a lightweight secondary battery using carbon for the negative electrode. After that, a so-called lithium ion secondary battery using various carbonaceous materials such as coke, graphite, a resin fired body, and pyrolysis gas phase carbon as a negative electrode active material has been proposed and put into practical use.

As the lithium ion secondary battery, there is known a lithium ion secondary battery using a chalcogen compound such as LiCoO ₂ , LiNiO ₂ or LiMn ₂ O ₄ for a positive electrode and using the carbonaceous material for a negative electrode. It has various features depending on the material of the material. For example, a lithium ion secondary battery containing carbon fibers having a lamellar structure in the cross-sectional direction of the fiber diameter as a negative electrode active material as disclosed in JP-A-5-89879 has excellent charge / discharge characteristics. Further, a lithium ion secondary battery containing graphite having a high degree of graphite as a negative electrode active material has high charging energy. Further, the lithium ion secondary battery has higher safety than a secondary battery using metallic lithium as a negative electrode, and is widely used as a power source for various portable terminals.

As described above, coke, graphite,
Resin fired bodies, pyrolytic gas-phase carbon, etc. are used as the active material of the negative electrode. However, in lithium ion secondary batteries equipped with these negative electrodes, the required characteristics of mobile terminals, such as thinning, lightening, and high capacity And all of the high cycle maintenance rates have not been satisfied.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having improved charge / discharge cycle life while achieving high capacity by improving the negative electrode.

[0007]

In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, a separator, and a battery. An aqueous electrolyte solution, wherein the positive electrode and the negative electrode have a structure in which a positive electrode material and a negative electrode material are applied to a current collector, respectively; and the negative electrode material includes fibrous carbonaceous materials (a) and (b). The fibrous carbonaceous material (a) has a crystallite size (Lc) of 40 to 60 nm in the c-axis direction, and the fibrous carbonaceous material ( b) is the size (L) of the crystallite in the c-axis direction.
c) is 100 nm or more.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a non-aqueous electrolyte secondary battery according to the present invention will be described in detail.

This non-aqueous electrolyte secondary battery includes a positive electrode capable of inserting and extracting lithium, a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte.

Next, the negative electrode, the positive electrode, the separator and the non-aqueous electrolyte will be described.

1) Negative Electrode The negative electrode has a structure in which a current collector is coated with a negative electrode material.

Examples of the current collector include a copper plate and a copper mesh material.

The negative electrode material is a fibrous carbonaceous material (a),
(B) and flaky or spherical graphite (c), and a binder.

As the fibrous carbonaceous materials (a) and (b), for example, mesophase pitch-based carbon fibers, PAN
Examples thereof include a fibrous carbonaceous material made of a base carbon fiber, a phenol resin, and a polyimide, and a fibrous vapor-grown carbon body. Particularly, mesophase pitch-based carbon fibers are preferable.

The fibrous carbonaceous material (a) is 40-60
having a crystallite size (Lc) in the c-axis direction of nm.
It functions as the main carbon material of the negative electrode material. This fibrous
The carbonaceous material (a) has an average fiber diameter of 8 to 18 μm,
10-50 μm long, true density 2.24 g / cc or more, Cu
(101) diffraction peak P in the X-ray diffraction method using -Kα
₁₀₁And (100) diffraction peak P₁₀₀Strength ratio (P₁₀₁/ P
₁₀₀) Is preferably from 1.2 to 1.8. In particular,
When the average fiber length is less than 10 μm, the properties as fiber
And the charge / discharge efficiency is low due to the fine powder state.
May fall. On the other hand, the average fiber length exceeds 50 μm
In this case, the adhesion of the negative electrode material to the current collector decreases,
The negative electrode properties such as chipping may be reduced. The fiber
The carbonaceous material (a) has an interplanar spacing (d₀₀₂) Is 0.3358
〜0.3370 nm, the size of the crystallite in the a-axis direction (L
More preferably, a) is at least 60 nm.

The fibrous carbonaceous material (b) has a thickness of 100 nm.
It has the above-mentioned crystallite size (Lc) in the c-axis direction. This
The fibrous carbonaceous material (b) has an average fiber diameter of 8 to 18 μm,
Average fiber length 10-50μm, true density 2.24g / cc or less
Above, the (101) diffraction peak in the X-ray diffraction method using Cu-Kα
Ark P₁₀₁And (100) diffraction peak P₁₀₀Strength ratio (P
₁₀₁/ P₁₀₀) Is preferably greater than 1.8.
New The fibrous carbonaceous material (a) has an interplanar spacing (d₀₀₂)
Is from 0.3355 to 0.3357 nm.
preferable.

[0017] The fibrous carbonaceous material (a), (b), the former having an average fiber diameter of the d _a, the latter having an average fiber diameter of the When _{d b, d b = 1.15d a} ~1.35d a It is more preferable to satisfy the following relationship.

The mixing ratio of the fibrous carbonaceous materials (a) and (b) is such that the fibrous carbonaceous material (b) is mixed with the total amount of the fibrous carbonaceous materials (a) and (b). Preferably, it occupies 10 to 90% by weight, more preferably 20 to 70% by weight. If the blending amount of the fibrous carbonaceous material (b) is less than 10% by weight, it is difficult not only to increase the capacity but also to increase the electrode density. On the other hand, if the amount of the fibrous carbonaceous material (b) exceeds 90% by weight, the charge / discharge cycle life may be shortened.

The scaly or spherical graphite (c) is
It preferably has an average particle size of 3 to 30 μm. When the average particle size of the graphite (c) is less than 3 μm, the specific surface area and the oil absorption increase, the solid content ratio when the negative electrode material is applied to the current collector decreases, and the irreversible capacity of the negative electrode increases. There is fear. On the other hand, if the average particle size of the graphite (c) exceeds 30 μm, there is a possibility that physical properties such as a decrease in the adhesion of the negative electrode material to the current collector and a reduction linear pressure required in press molding may increase.

The scaly or spherical graphite (c) is
It is preferable to contain the fibrous carbonaceous materials (a), (b) and the graphite (c) at a ratio of 5 to 50% by weight based on the total amount.

As the binder, a polymer material having solubility in an organic solvent represented by PVdF, a polymer material easily dispersed in water represented by CMC and SBR, and the like can be used. The polymer material is merely an example and is not particularly limited. However, in consideration of the environment in the future, a polymer material that is easily dispersed in water is preferable.

The binder is used in an amount of 1.0 to 1.0 with respect to the negative electrode material.
It is preferred to be blended at 6.0% by weight. When the amount of the binder is less than 1.0% by weight, although it is preferable from the viewpoint of electrode performance such as improvement of capacity, the adhesiveness of the negative electrode material to the current collector is reduced and the negative electrode is processed at the time of processing the negative electrode (especially at the time of cutting). ) Causes chipping or peeling, and, for example, when winding a belt-like material having a separator interposed between the positive and negative electrodes to produce an electrode group, minute defects are mixed into the electrode group to cause a short circuit between the positive and negative electrodes. There is fear. On the other hand, when the compounding amount of the binder exceeds 6.0% by weight, the amount of the binder occupying in the negative electrode may increase, leading to a decrease in capacity.

2) Positive electrode This positive electrode has a structure in which a positive electrode material is applied to a current collector.

Examples of the current collector include an aluminum plate and an aluminum mesh material.

The positive electrode material contains, for example, an active material and a binder. Examples of the active material include manganese dioxide, molybdenum disulfide, LiCoO ₂ , LiNiO ₂ , L
Chalcogen compounds such as iMn ₂ O ₄ can be mentioned. These chalcogen compounds can be used in a mixture of two or more. As the binder, for example, a thermoplastic elastomer resin such as a fluorine resin, a polyolefin resin, a styrene resin, and an acrylic resin, or a rubber resin such as a fluorine rubber can be used. Specifically, polytetrafluoroethylene,
Polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polyacrylonitrile, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, polysulfide rubber,
Examples include nitrocellulose, cyanoethylcellulose, carboxymethylcellulose, and the like. Among these binders, elastomers, cross-linked rubbers or modified compounds having polar groups introduced are preferably used in view of improving the adhesion between the current collector and the positive electrode material and improving the resistance increasing effect during overcharge. It is suitable.

The positive electrode material is allowed to further contain acetylene black, graphite such as powdered expanded graphite, crushed carbon fiber, crushed graphitized carbon fiber, and the like as a conductive auxiliary material.

3) Separator As the separator, for example, a porous polyethylene film or a porous polypropylene film having a thickness of 20 to 30 μm can be used.

4) Non-aqueous Electrolyte This non-aqueous electrolyte is prepared, for example, by adding lithium perchlorate to a non-aqueous solvent comprising at least one selected from ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and γ-butyrolactone. L
iClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ),
For example, those having a composition in which lithium borofluoride (LiBF ₄ ) or lithium arsenic hexafluoride (LiAsF ₆ ) is dissolved can be used.

The non-aqueous solvent is preferably used as a mixture of two or three types rather than used alone in view of viscosity. The concentration of the electrolyte dissolved in this non-aqueous solvent is 0.5%.
It is preferably in the range of 1.5 mol / L. The electrolyte can be used alone or in the form of a mixture.

The non-aqueous electrolyte secondary battery according to the present invention includes a cylindrical type shown in FIG. 1 and a rectangular type shown in FIG.
3 and 4 have a thin structure.

(1) Cylindrical Nonaqueous Electrolyte Secondary Battery As shown in FIG. 1, a metal outer can 1 having a bottomed cylindrical shape is
For example, the lower insulating plate 2 is disposed on the inner surface of the bottom portion also serving as a negative electrode terminal. The electrode body 3 as a power generating element is provided with the outer can 1
Is housed inside. The electrode body 3 is manufactured by spirally winding the negative electrode 4, the separator 5, and the positive electrode 6 such that the separator 5 is located at the outermost periphery. A negative electrode lead tab 7 is formed on the lower end surface of the negative electrode 4, and the other end of the lead tab 7 is connected to the bottom inner surface of the outer can 1. An upper insulating plate 8 having a positive electrode lead tab extraction hole near the center is disposed on the electrode body 3 in the outer can 1.

A sealing member 9 having stomatal pores also serves as a positive electrode terminal.
It is swaged and fixed through 0. This sealing member 9
Dish-shaped sealing plate 12 with vent hole 11 opened near the center
And a valve membrane latch 1 made of, for example, aluminum fixed to the sealing plate 12 so as to cover the gas vent hole 11.
3 and a ring-shaped P disposed on the periphery of the sealing plate 12.
TC (Positive Temperature Coefficient) 14 and hat-shaped positive electrode terminal 16 having a plurality of vent holes 15
It is composed of A positive electrode lead tab 17 is connected to the lower surface of the sealing plate 12 and
Is connected to the positive electrode 6 of the electrode 3 through a lead extraction hole of the upper insulating plate 8.

(2) Prismatic Nonaqueous Electrolyte Secondary Battery An outer can 21 made of metal having a bottomed rectangular cylindrical shape, for example, aluminum as shown in FIG. 2 also serves as, for example, a positive electrode terminal.
An insulating film 22 is disposed on the inner surface of the bottom. The electrode body 23 as a power generation element is housed in the outer can 21. When the outer can is made of stainless steel or iron, it also serves as the negative electrode terminal. The electrode body 23 is formed by spirally winding the negative electrode 24, the separator 25, and the positive electrode 26 such that the positive electrode 26 is located at the outermost periphery, and then press-molding the flat electrode into a flat shape. Spacer 27 made of, for example, synthetic resin and having a lead extraction hole near the center
Is disposed on the electrode body 23 in the outer can 21.

The metal lid 28 is hermetically joined to the upper end opening of the outer can 1 by, for example, laser welding.
In the vicinity of the center of the lid 28, an extraction hole 29 for a negative electrode terminal is opened. The negative electrode terminal 30 is connected to the hole 2 of the lid 28.
9 is hermetically sealed via an insulating material 31 made of glass or resin. A lead 32 is connected to the lower end surface of the negative electrode terminal 30, and the other end of the lead 32 is connected to the negative electrode 24 of the electrode body 23.

The upper insulating paper 33 covers the entire outer surface of the lid 28. The lower insulating paper 35 having the slit 34 is disposed on the bottom surface of the outer can 21. PTC element (Positive Temperatur)
e Coefficient) 36, one surface is interposed between the bottom surface of the outer can 21 and the lower insulating paper 35, and the other surface is extended outside the insulating paper 35 through the slit 34. I have. The outer tube 37 is made of the outer can 2.
The upper insulating paper 33 and the lower insulating paper 35 are fixed to the outer can 21 so as to extend from the side surface 1 to the periphery of the insulating papers 33 and 35 on the upper and lower surfaces. Due to such an arrangement of the outer tube 37, the other surface of the PTC element 36 extended to the outside is connected to the lower insulating paper 35.
It is bent toward the bottom of.

(3) Thin Non-Aqueous Electrolyte Secondary Battery As shown in FIGS. 3 and 4, the power generating element 41 includes a current collector, for example, a positive electrode active material layer 42 which is a positive electrode material containing an active material and a binder. The positive electrode 44 and the separator 4 supported on both surfaces of the negative electrode 43
5, a negative electrode active material layer 46, which is a negative electrode material containing an active material and a binder, spirally winds a negative electrode 48 supported on both surfaces of a current collector 47 and a separator 45, and further forms a flat and rectangular shape. Make External lead terminals 49 and 50 connected to the positive electrode 44 and the negative electrode 48 are connected to the power generating element 4 respectively.
1 extend outside from the same side.

As shown in FIG. 3, the power generating element 41 includes a cup 52 of a two-fold cup-shaped exterior film 51, for example.
The bent portion is enclosed so as to be located on the side surface opposite to the side surface on which the external lead terminals 49 and 50 of the power generation element 41 extend. This exterior film 51
Is a sealant film 53 located on the inner side as shown in FIG.
4 and a rigid organic resin film 55 laminated in this order. Three side portions corresponding to two long side surfaces and one short side surface of the power generation element 1 excluding the bent portion in the exterior film 51 are seals extending in the horizontal direction by heat sealing the sealant films 53 to each other. Parts 56a, 56b, 56c are formed, and the power generating element 41 is sealed by these seal parts 56a, 56b, 56c. External terminals 49 and 50 connected to the positive electrode 44 and the negative electrode 48 of the power generation element 41 extend to the outside through a seal portion 56b on the opposite side to the bent portion. Inside the power generating element 41 and the seal portion 56
A non-aqueous electrolytic solution is impregnated and contained in the exterior film 51 sealed by a, 56b, and 56c.

In the above-mentioned thin non-aqueous electrolyte secondary battery, the exterior film is not limited to the cup type, but may be a pillow type or a pouch type.

As described above, the non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, a separator, and a non-aqueous electrolyte. And the negative electrode has a structure in which a positive electrode material and a negative electrode material are applied to a current collector, respectively.
And the negative electrode material contains fibrous carbonaceous materials (a) and (b) and flaky or spherical mass graphite (c), and the fibrous carbonaceous material (a) has a c-axis direction of 40 to 60 nm. And the fibrous carbonaceous material (b) has a crystallite size (Lc) of 1
It has a crystallite size (Lc) in the c-axis direction of at least 00 nm.

As described above, the negative electrode material having the fibrous carbonaceous materials (a) and (b) having different crystallites, that is, having different degrees of graphitization, and the flaky or spherical lumpy graphite (c) is used as a current collector. By providing the coated and improved negative electrode, a nonaqueous electrolytic secondary battery having a high capacity and an improved charge / discharge cycle life can be obtained.

In particular, as the fibrous carbonaceous material (a),
Average fiber diameter 8 ~ 18μm, average fiber length 10 ~ 50μm,
With a true density of 2.24 g / cc or more, the intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the (101) diffraction peak P ₁₀₁ and the (100) diffraction peak P _{100 in} the X-ray diffraction method using Cu-Kα is 1.2 to 1 .
8 and the fibrous carbonaceous material (b) has an average fiber diameter of 8 to 18 μm and an average fiber length of 10 to 50 μm.
m, true density 2.24 g / cc or more, X by Cu-Kα
(101) diffraction peaks _P101 and (100)
By the intensity ratio of the diffraction peak _{P 100 (P 101 / P 100} ) is used as a value greater than 1.8, a higher capacity,
A nonaqueous electrolyte secondary battery with improved charge / discharge cycle life can be obtained.

Further, the fibrous carbonaceous material (a),
The average fiber diameter of (b) a fibrous carbonaceous material having an average fiber diameter of _(a) (d a) and the fibrous carbonaceous material (b) (d _b) and is d _b
= 1.15d _a ~1.35d _a the fibrous carbonaceous material so as to satisfy the relation of (a), (b) or select, the fibrous the blending ratio of the fibrous carbonaceous material (b) To obtain a non-aqueous electrolytic secondary battery having a higher capacity and an improved charge / discharge cycle life by adjusting the range of 10 to 90% by weight based on the total amount of the carbonaceous materials (a) and (b). Can be.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail using a cylindrical lithium ion secondary battery as an example.

[Preparation of fibrous carbonaceous material (a)] A mesophase pitch was spun and made infusible, and the mesophase pitch was spun at 65 ° C. under an argon atmosphere.
After carbonization at 0 ° C and pulverization to an appropriate degree, 30
By graphitizing at 00 ° C., a fibrous carbonaceous material was obtained.

The obtained fibrous carbonaceous material had a crystallite (Lc) size of 55 nm in the c-axis direction and an average fiber diameter of 8.2 μm.
m, average fiber length 17.2 μm, true density 2.24 g / c
c, spacing (d ₀₀₂ ) 0.3360 nm, (101) diffraction peak P ₁₀₁ and (1)
00) The intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the diffraction peak P ₁₀₀ was 1.42.

[Preparation of fibrous carbonaceous material (b)] The mesophase pitch was spun with a large diameter, made infusible, carbonized at 600 ° C in an argon atmosphere, pulverized appropriately, and then 3,000 in a nitrogen atmosphere. By graphitizing at ℃, a fibrous carbonaceous material was obtained.

The obtained fibrous carbonaceous material had a crystallite (Lc) size in the c-axis direction> 100 nm and an average fiber diameter of 9.8.
μm, average fiber length 16.5 μm, true density 2.25 g / c
c, spacing (d ₀₀₂ ) 0.3356 nm, (101) diffraction peak P ₁₀₁ and (1) in X-ray diffraction method by Cu-Kα
00) the intensity ratio of the diffraction peak _{P 100 (P 101 / P 100} ) had 2.1.

[Preparation of graphite] Natural graphite was disguised into a pseudospherical shape to obtain predetermined graphite. This graphite has an average particle size of 21μ.
m, specific surface area 3.1 m ² / g, spacing between planes (d ₀₀₂ ) 0.33
It was 56 nm.

Example 1 <Preparation of Negative Electrode> First, 65 parts by weight of the fibrous carbonaceous material (a) were added to 177 parts by weight of a viscous aqueous solution of carboxymethylcellulose having a concentration of 0.74% by weight. After adding 7 parts by weight of the material (b) and 28 parts by weight of the spheroidal graphite (c), the mixture was shear-dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight.

Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm using a knife edge coater.
05g / m ^2, was coated so as to 114 g / m ^2, and dried. At this time, the density of the negative electrode material on the copper foil was 1.23 g.
/ Cc. Then, it is pressed and slit to give a thickness of 158 μm (density of negative electrode material: 1.5 g / c
c) A negative electrode having a width of 56.5 mm was produced.

<Preparation of Positive Electrode> First, LiCoO as an active material was added to 41.7 parts by weight of a 12% by weight solution of polyvinylidene fluoride resin (PVdF) in N-methylpyrrolidone.
₂ 100 parts by weight of powder and 5 parts by weight of graphite powder (trade name: KS4, manufactured by Lonza) as a conductive filler were mixed and kneaded. Subsequently, 15 parts by weight of N-methylpyrrolidone was further added to this mixture, and the solid was dispersed using a dissolver and a bead mill to prepare a positive electrode coating slurry.

Next, the positive electrode coating slurry was applied to a thickness of 15
280 g / m on both sides of μm Al foil (current collector)
² and dried, then pressed and slit to give a thickness of 180 μm and a width of 54.5 mm
Was produced.

Next, lead tabs were joined to the positive and negative electrode current collectors, respectively, and spirally wound through two polyethylene porous membranes using an automatic winding machine to produce an electrode body. A voltage of 100 V was applied from a DC power supply to the obtained electrode body for 5 seconds, and a current flowing at 10 μV or more was judged to be defective and excluded.

Next, the electrode assembly determined as a non-defective product was inserted into a bottomed cylindrical outer can having a diameter of 18 mm and a height of 65 mm, a non-aqueous electrolyte was injected, and the opening of the outer can was sealed with a sealing body. As a result, a cylindrical non-lithium ion secondary battery having the structure shown in FIG. 1 was assembled. The non-aqueous electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / L in a mixed non-aqueous solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a weight ratio of 1: 2. Having.

(Example 2) A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

8 parts by weight of the fibrous carbonaceous material (a), 70 parts by weight of the fibrous carbonaceous material (b) and spheroidal graphite (177 parts by weight) of a 0.74% by weight viscous aqueous solution of carboxymethylcellulose were used. c) After adding 22 parts by weight,
Shear dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the coating slurry was coated so as to ^{105g / m 2, 114g / m} 2 on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current collector) and dried. At this time, the density of the negative electrode material on the copper foil is
1.24 g / cc. After that, it is pressed and slit to a thickness of 158 μm (density of negative electrode material: 1.5
g / cc) and a negative electrode having a width of 56.5 mm was produced.

Example 3 A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

40 parts by weight of the fibrous carbonaceous material (a), 40 parts by weight of the fibrous carbonaceous material (b) and spheroidal graphite (177 parts by weight) of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.74% by weight. c) After adding 20 parts by weight, the mixture was shear-dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the coating slurry was coated so as to ^{105g / m 2, 114g / m} 2 on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current collector) and dried. At this time, the density of the negative electrode material on the copper foil was 1.24 g / cc. Then, it is pressed and slit to a thickness of 158 μm (density of the negative electrode material;
1.5 g / cc) and a negative electrode having a width of 56.5 mm were produced.

(Example 4) A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

45 parts by weight of the fibrous carbonaceous material (a), 45 parts by weight of the fibrous carbonaceous material (b) and spheroidal graphite (177 parts by weight) of a viscous aqueous solution of carboxymethylcellulose having a concentration of 0.74% by weight. c) After adding 10 parts by weight, the mixture was sheared and dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the coating slurry was coated so as to ^{105g / m 2, 114g / m} 2 on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current collector) and dried. At this time, the density of the negative electrode material on the copper foil was 1.24 g / cc. Then, it is pressed and slit to a thickness of 158 μm (density of the negative electrode material;
1.5 g / cc) and a negative electrode having a width of 56.5 mm were produced.

Example 5 A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

In 193 parts by weight of a 1.1% by weight viscous aqueous solution of carboxymethyl cellulose, 25 parts by weight of the fibrous carbonaceous material (a), 25 parts by weight of the fibrous carbonaceous material (b) and the spherical graphite ( c) after adding 50 parts by weight,
Shear dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the coating slurry was coated so as to ^{105g / m 2, 114g / m} 2 on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current collector) and dried. At this time, the density of the negative electrode material on the copper foil is
1.21 g / cc. After that, it is pressed and slit to a thickness of 158 μm (density of negative electrode material: 1.5
g / cc) and a negative electrode having a width of 56.5 mm was produced.

Example 6 A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

20 parts by weight of the fibrous carbonaceous material (a), 40 parts by weight of the fibrous carbonaceous material (b) and spheroidal graphite (192 parts by weight) of a viscous aqueous solution of carboxymethylcellulose having a concentration of 0.90% by weight. c) After adding 40 parts by weight, the mixture was sheared and dispersed. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the coating slurry was coated so as to ^{105g / m 2, 114g / m} 2 on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current collector) and dried. At this time, the density of the negative electrode material on the copper foil was 1.21 g / cc. Then, it is pressed and slit to a thickness of 158 μm (density of the negative electrode material;
1.5 g / cc) and a negative electrode having a width of 56.5 mm were produced.

(Comparative Example 1) A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

80 parts by weight of the fibrous carbonaceous material (a) and 20 parts by weight of the spheroidal graphite (c) were added to 177 parts by weight of a viscous aqueous solution of carboxymethylcellulose having a concentration of 0.74% by weight, followed by shear dispersion. . Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the 105g coating slurry on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current ^{collector) / m 2, 114g / m} 2
And dried. At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a negative electrode having a thickness of 158 μm (density of negative electrode material; 1.5 g / cc) and a width of 56.5 mm.

(Comparative Example 2) A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

After adding 80 parts by weight of the fibrous carbonaceous material (b) and 20 parts by weight of the spheroidal graphite (c) to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.74% by weight, the mixture was shear-dispersed. . Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 58% by weight. Then, the 105g coating slurry on both surfaces of a copper foil with a thickness of 15μm by a knife edge coater (current ^{collector) / m 2, 114g / m} 2
And dried. At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc. Thereafter, pressing and slitting were performed to produce a negative electrode having a thickness of 158 μm (density of negative electrode material; 1.5 g / cc) and a width of 56.5 mm.

Comparative Example 3 A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

100 parts by weight of the fibrous carbonaceous material (a) was added to 166 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.73% by weight, followed by shearing dispersion.
Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 62% by weight. Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm with a knife edge coater at 105 g /
m ² , 114 g / m ² , and dried. At this time, the density of the negative electrode material on the copper foil was 1.24 g / cc. After that, press and slit processing is performed to make the thickness 1
58 μm (density of negative electrode material; 1.5 g / cc), width 5
A 6.5 mm negative electrode was produced.

(Comparative Example 4) A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

100 parts by weight of the fibrous carbonaceous material (b) was added to 166 parts by weight of a 0.73% by weight viscous aqueous solution of carboxymethylcellulose, followed by shearing dispersion.
Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 62% by weight. Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm with a knife edge coater at 105 g /
m ² , 114 g / m ² , and dried. At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc. After that, press and slit processing is performed to make the thickness 1
58 μm (density of negative electrode material; 1.5 g / cc), width 5
A 6.5 mm negative electrode was produced.

Comparative Example 5 A cylindrical lithium ion secondary battery having the same structure as in Example 1 was assembled except that a negative electrode produced by the method described below was used. In addition,
After the production of the electrode body having the positive and negative electrodes and the separator, the same good / bad judgment as in Example 1 was performed, and only the electrode body judged as good was used.

100 parts by weight of the spheroidal graphite (c) was added to 302 parts by weight of a viscous aqueous solution having a concentration of 1.11% by weight of carboxymethylcellulose, followed by shear dispersion. Subsequently, 3.6 parts by weight of SBR latex was added to this mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry. This coating slurry had a solid content of 35% by weight. Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm with a knife edge coater at 105 g /
m ² , 114 g / m ² , and dried. At this time, the density of the negative electrode material on the copper foil was 1.18 g / cc. After that, press and slit processing is performed to make the thickness 1
58 μm (density of negative electrode material; 1.5 g / cc), width 5
A 6.5 mm negative electrode was produced.

The obtained Examples 1 to 6 and Comparative Examples 1 to 5
About 6 hours at 950 mAh,
After aging for 3 days, the average capacity was measured when the battery was discharged at 20 ° C. at 0.5C. The results are shown in Table 1 below.
Shown in

[0076]

[Table 1]

The secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 were charged at 1 ° C. (1900 mA) at 20 ° C.
h), the discharge capacity retention ratio (cycle characteristics) with respect to the initial discharge capacity when charging and discharging were repeated 500 times under the conditions of charging and discharging 1 C (cutoff voltage 3.0 V) was measured.
FIG. 5 shows the results of the secondary batteries of Examples 1 to 6, and Comparative Examples 1 to 5.
6 shows the results of the secondary batteries.

As apparent from Table 1 above, Examples 1 to 6
Although the secondary batteries of Comparative Examples 1 to 5 and the secondary batteries of Comparative Examples 1 to 5 do not have a large difference in capacity, as is clear from FIGS. 5 and 6, the secondary batteries of Comparative Examples 1 to 5 While the capacity retention ratio is 65% at the maximum, the secondary batteries of Examples 1 to 6 including the negative electrode containing the specific carbon material have a capacity retention ratio of about 80 to 87.
%, Which indicates that it has excellent cycle characteristics.

In the above-described embodiment, the cylindrical lithium ion secondary battery shown in FIG. 1 has been described. However, the rectangular lithium ion secondary battery shown in FIG.
Even when applied to the thin lithium ion secondary battery shown in (1), a high capacity and an improvement in charge / discharge cycle life can be achieved as in the embodiment.

[0080]

As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having improved charge / discharge cycle life while achieving high capacity by improving the negative electrode. it can.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical nonaqueous electrolyte secondary battery (cylindrical lithium ion secondary battery), which is an embodiment of the nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a partially cutaway perspective view showing a prismatic nonaqueous electrolyte secondary battery (square lithium ion secondary battery) as another embodiment of the nonaqueous electrolyte secondary battery according to the present invention.

FIG. 3 is a perspective view showing a thin non-aqueous electrolyte secondary battery (thin lithium ion secondary battery) as still another embodiment of the non-aqueous electrolyte secondary battery according to the present invention.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a diagram showing cycle characteristics of the lithium ion secondary batteries of Examples 1 to 6 according to the present invention.

FIG. 6 is a diagram showing cycle characteristics of the lithium ion secondary batteries of Comparative Examples 1 to 5.

[Explanation of symbols]

 1, 21: outer can, 3,23 electrode body, 4, 24, 48 ... negative electrode, 5, 25, 45 ... separator, 6, 26, 44 ... positive electrode, 12 ... sealing plate, 28 ... lid, 41 ... power generation Elements, 43, 46: current collector, 51: exterior film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takayuki Nakajima 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside AT Battery Co., Ltd. (72) Koichi Matsumoto 3-4-1 Minamishinagawa, Shinagawa-ku, Tokyo No. 10 Inside A / T Battery Co., Ltd. (72) Shinichi Uebayashi 7-in-1 Nisshin-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term (reference) 5H029 AJ03 AJ05 AK03 AL07 AM03 AM04 AM05 AM07 BJ02 BJ14 HJ01 HJ04 HJ13 5H050 AA07 AA08 CA08 CB08 EA09 EA24 FA16 FA17 FA19 HA01 HA04 HA08 HA13

Claims (4)

[Claims] 1. A positive electrode capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, a separator, and a non-aqueous electrolyte. The positive electrode and the negative electrode each include a positive electrode material and a negative electrode material as a current collector. The negative electrode material contains fibrous carbonaceous materials (a) and (b) and flaky or spherical lumpy graphite (c), and the fibrous carbonaceous material (a) Indicates that the crystallite size (Lc) in the c-axis direction is 40 to
The non-aqueous electrolyte secondary battery according to claim 1, wherein the fibrous carbonaceous material (b) has a crystallite size (Lc) in the c-axis direction of 100 nm or more at 60 nm. 2. The fibrous carbonaceous material (a) has an average fiber diameter of 8 to 18 μm, an average fiber length of 10 to 50 μm, a true density of at least 2.24 g / cc, and an X-ray diffraction method using Cu-Kα. 101) and a diffraction peak P ₁₀₁ (100) intensity ratio of the diffraction peak _{P 100 (P 101 / P 100} ) is 1.2 to 1.8, and wherein the fibrous carbonaceous material (b) has an average fiber diameter 8 ~
18 μm, average fiber length 10-50 μm, true density 2.24
g / cc or more, (10
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the intensity ratio (P ₁₀₁ / P ₁₀₀ ) between the diffraction peak P ₁₀₁ and the (100) diffraction peak P ₁₀₀ is a value exceeding 1.8. . Wherein an average fiber diameter (d _b) of the average fiber diameter of the fibrous carbonaceous material _(a) (d a) and the fibrous carbonaceous material (b) and is d _b = 1.15d _a ~ 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein _a relationship of 1.35 da is satisfied. 4. The fibrous carbonaceous material (b) occupies a ratio of 10 to 90% by weight based on the total amount of the fibrous carbonaceous materials (a) and (b). Item 2. The non-aqueous electrolyte secondary battery according to Item 1.