JP2002093406A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having an improved charging/discharging cycle characteristic at high temperatures by improving a negative electrode. SOLUTION: This secondary battery has a positive electrode capable of storing and releasing lithium, a negative electrode capable of storing and releasing lithium, a separator, and a nonaqueous electrolyte. The positive electrode and the negative electrode have respective structures in which respective collectors are coated with a positive electrode material and a negative electrode material, the negative electrode material contains carbonaceous material containing fibrous carbon materials a and b and non-fibrous carbon material c, the fibrous carbon material b is mesophase low temperature cold burning carbon, and the negative electrode has 15 to 30 mAh/g as a discharge capacity between 1 to 3V in negative electrode voltage.

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. Thereafter, a so-called lithium ion secondary battery using various carbon 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, 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 carbon material for a negative electrode is known. It has various features depending on 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 An object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved high-temperature charge / discharge cycle characteristics by improving a negative electrode.

[0007]

A non-aqueous electrolyte secondary battery according to the present invention for achieving the above object has 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. 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 comprises fibrous carbon materials (a) and (b) and non-fiber And a carbonaceous material containing a base carbon material (c), the fibrous carbon material (b) is mesophase low-temperature calcined carbon, and the negative electrode has a negative electrode potential of 1 V
It has a discharge capacity of 15 to 30 mAh / g between -3 V.

[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 carbon material (a),
(B) and a non-fibrous carbon material (c), and a binder. This fibrous carbon material (b) is mesophase low-temperature calcined carbon.

The fibrous carbon material (a) functions as a main carbon material of the negative electrode material. Examples of the fibrous carbon material (a) include mesophase pitch-based carbon fiber, PAN-based carbon fiber, a fibrous carbon material made of phenol resin and polyimide, and a fibrous vapor-grown carbon body. it can. Particularly, mesophase pitch-based carbon fibers are preferable.

The fibrous carbon material (a) has an average fiber diameter of 8
１８18 μm, average fiber length 10-50 μm, true density 2.2
It is preferably at least 4 g / cc. Such a fibrous carbon material (a) contributes to an improvement in charge / discharge cycle characteristics. In particular, when the average fiber length is less than 10 μm, the ratio of showing the fiber morphology becomes small and the powder becomes powdery, which may lower the charge / discharge efficiency. On the other hand, the average fiber length is 50μ.
If it exceeds m, the physical properties of the negative electrode including the negative electrode material containing the fibrous carbon material (a), for example, the adhesion between the current collector and the negative electrode material may be reduced.

The fibrous carbon material (a) has (101) diffraction peaks P ₁₀₁ and (1) in the X-ray diffraction method using Cu-Kα.
00) More preferably, the intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the diffraction peak P ₁₀₀ is from 1.2 to 1.9. The fibrous carbon material (a) has a surface distance (d ₀₀₂ ) of 0.3354 or more.
0.3370 nm (more preferably from 0.3354 to 0.3.
3359 nm), the size of the crystallite in the a-axis direction (La)
Is more preferably 60 nm or more, and the crystallite size (Lc) in the c-axis direction is 40 nm or more.

The fibrous carbon material (a) permits the addition of boron to increase the interplanar spacing (d ₀₀₂ ) of graphite crystals, that is, to increase the degree of graphitization.

The fibrous mesophase low-temperature fired carbon (b) is fired at a comparatively low temperature, and contributes to an increase in negative electrode capacity and an improvement in charge / discharge cycle characteristics. This fibrous carbon (b) has an average fiber diameter of 8 to 20 μm and an average fiber length of 8 to 2
It is preferably 0 μm and a true density of 1.50 to 1.75 g / cc.

Examples of the non-fibrous carbon material (c) include scaly or spherical graphite, and they can be used alone or in the form of a mixture of two or more. This graphite preferably has an average particle size of 3 to 30 μm. When the average particle size of the graphite 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 may increase. . On the other hand, when the average particle size of the graphite 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 the reduction linear pressure required for press molding may increase.

The mixing ratio of the fibrous carbon materials (a) and (b) and the non-fibrous carbon material (c) is 20 to 85 for the former.
% By weight, and the latter preferably from 15 to 80% by weight. If the former compounding ratio exceeds 85% by weight, the amount of the fibrous carbon material increases and the preparation of the negative electrode slurry at a high solid content becomes possible, which is advantageous in terms of production, but the adhesion of the negative electrode material to the current collector is improved. It becomes difficult to increase the density of the material of the negative electrode due to the deterioration of the property. On the other hand, when the latter exceeds 80% by weight, the amount of non-fibrous carbon material such as flaky graphite increases, which is advantageous in increasing the electrode density. The charge / discharge cycle characteristics may be reduced.

The fibrous carbon material (b) accounts for 1 to 10% by weight, more preferably 2 to 9% by weight, based on the carbonaceous material.
It is desirable to be blended. If the amount of the fibrous carbon material (b) is less than 1% 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 carbon material (b) exceeds 10% by weight, the charge / discharge cycle life may be shortened.

The negative electrode has a negative electrode material containing a carbonaceous material containing the above-mentioned fibrous carbon materials (a) and (b) and a non-fibrous carbon material (c), and has a negative electrode potential of 1 V to 3 V. Has a discharge capacity of 15 to 30 mAh / g. If the capacity of the negative electrode under the above conditions deviates from the above range, the charge / discharge cycle characteristics at high temperatures deteriorate. More preferably, the capacity of the negative electrode under the above conditions is 20 to 25 mAh / g.

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 compounding amount of the binder is less than 1.0% by weight, although it is preferable from the viewpoint of electrode performance such as improvement in capacity, the adhesiveness of the negative electrode material to the current collector is reduced and the negative electrode material is processed at the time of processing the negative electrode (particularly, cutting). Chip) at the time of chipping or peeling, and, for example, when winding a belt-like material having a separator between the positive and negative electrodes to produce an electrode group, minute defects are mixed into the electrode group and short-circuiting of the positive and negative electrodes may occur. May be invited. On the other hand, the compounding amount of the binder is 6.0% by weight.
If it exceeds 300, 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 cathode material is allowed to further contain graphite such as acetylene black and powdered expanded graphite, ground carbon fiber, ground graphite carbon fiber, and the like as a conductive auxiliary material.

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

4) Non-Aqueous Electrolyte This non-aqueous electrolyte is prepared by mixing a non-aqueous solvent containing at least one selected from ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and γ-butyrolactone with lithium perchlorate ( 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 in combination 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. In particular,
The non-aqueous solvent desirably contains 10-80% by weight (more preferably 45-70% by weight) of γ-butyrolactone.

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 a stunning pore also serves as a positive electrode terminal, and an insulating gasket 1 is provided at an upper end opening of the outer can 1.
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) Rectangular Nonaqueous Electrolyte Secondary Battery An outer can 21 made of a 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 is formed by a positive electrode active material layer 42 which is a positive electrode material containing, for example, 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 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 a structure in which 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 includes fibrous carbon materials (a) and (b) and a non-fibrous carbon material (c). The fibrous carbon material (b) is a mesophase low-temperature fired carbon, and the negative electrode has a discharge capacity of 15 to 3 as a discharge capacity between negative electrode potentials 1 V to 3 V.
0 mAh / g.

As such a carbonaceous material, a negative electrode material containing a fibrous mesophase low-temperature fired carbon (b) together with a fibrous carbon material (a) and a non-fibrous carbon material (c) is applied to a current collector. In addition, by providing an improved negative electrode having a discharge capacity of 15 to 30 mAh / g between the negative electrode potentials of 1 V to 3 V (that is, having a predetermined capacity even in the overdischarge region), high temperature (for example, 35 to 60 ° C.) ), A non-aqueous electrolytic secondary battery having improved charge / discharge cycle characteristics can be obtained. In other words, since the negative electrode has a predetermined capacity in the overdischarge area, even if the secondary battery is left in a high-temperature environment for a long time after discharging, the capacity of the secondary battery is not lost, and the initial charge and discharge characteristics are exhibited by subsequent charging. it can.

In particular, as the fibrous carbon material (a), the average fiber diameter is 8 to 18 μm, the average fiber length is 10 to 50 μm, the true density is 2.24 g / cc or more (more preferably, in addition to these properties, Cu-Kα and more preferably in the X-ray diffraction method (101) and the diffraction peak P ₁₀₁ (100) intensity ratio of the diffraction peak _{P 100 (P 101 / P 100} ) is 1.2 to 1.9. the fibrous carbon The material (a) is the surface distance (d ₀₀₂ )
Is 0.3354 to 0.3370 nm, the crystallite size in the a-axis direction (La) is 60 nm or more, and the crystallite size in the c-axis direction (Lc) is 40 nm or more). A non-aqueous electrolytic secondary battery having improved charge / discharge cycle life at high temperatures can be obtained.

Further, it is fired at a comparatively low temperature as the fibrous carbon material (b). This fibrous carbon has an average fiber diameter of 8-20.
μm, average fiber length 8-20 μm, true density 1.50-1.
By using a battery of 75 g / cc, it is possible to obtain a non-aqueous electrolytic secondary battery having an improved charge / discharge cycle life at a higher temperature.

Further, the use of flake-like or spheroidal graphite (preferably graphite having an average particle diameter of 3 to 30 μm) as the non-fibrous carbon material further improves the charge / discharge cycle life at higher temperatures. The obtained non-aqueous electrolytic secondary battery can be obtained.

Further, the capacity of the negative electrode can be increased by using a non-aqueous solvent containing 10-80% by weight (more preferably 45-70% by weight) of γ-butyrolactone as a non-aqueous solvent for the non-aqueous electrolyte. Thus, it is possible to obtain a non-aqueous electrolyte secondary battery that can compensate for a decrease in the performance of the positive electrode due to the above, improve the high-temperature charge / discharge cycle characteristics, and have balanced performance.

[0047]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail.

"Preparation of fibrous carbon material (a)" A mesophase pitch was spun and made infusible, and 680 under an argon atmosphere.
Carbonized at 300 ° C and pulverized to an appropriate degree.
By graphitizing at 0 ° C., a fibrous carbon material was obtained.

The obtained fibrous carbon material had a crystallite (Lc) size of 60 nm in the c-axis direction, an average fiber diameter of 8.5 μm,
Average fiber length 18.5 μm, true density 2.26 g / cc, spacing (d ₀₀₂ ) 0.3359 nm, X by Cu-Kα
(101) diffraction peaks _P101 and (100)
The intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the diffraction peak P ₁₀₀ is 1.45.
Met.

[Preparation of Fibrous Mesophase Low-Temperature Carbon Material (b)] Several types of fibrous materials having an average fiber diameter of 17 μm and a true density of 1.50 to 1.80 g / cc were fired by changing the graphitization temperature. A mesophase low-temperature calcined carbon material was prepared.

[Preparation of Graphite] Natural graphite was disassembled into spherical lumps to obtain predetermined graphite. This graphite has an average particle size of 8.5μ.
m, specific surface area 6.7 m ² / g, spacing (d ₀₀₂ ) 0.33
It was 58 nm.

Example 1 <Preparation of Negative Electrode> First, 177 parts by weight of a viscous aqueous solution of carboxymethylcellulose having a concentration of 0.68% by weight was added to 50 parts by weight of the fibrous carbon material (a) and the true density was 1.55 g. / C
After adding 2 parts by weight of the fibrous mesophase low temperature calcined carbon material (b) and 48 parts by weight of the spherical graphite (c), the mixture was shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm to a thickness of 103 g / m ² by a knife edge coater and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

With respect to the obtained negative electrode, a negative electrode potential of 1 V to 3
The discharge capacity between V was measured by the following method.

Cut to a size of 2 × 2 cm from the prepared negative electrode.
Subtract the weight of the current collector from the total weight
The amount of the substance (the amount of the negative electrode material) is calculated. Pair with the sample
Intermediate glass filter between lithium metal
Use metallic lithium for the poles
In a container. Γ-butyrolact is added to this glass container.
Ton and ethylene carbonate mixed solvent (mixed volume
Ratio 2: 1) to LiBF _Four1.5mol / L dissolved
Evacuated to remove bubbles after injecting electrolyte with
Assemble the glass cell. The work up to this point is
Perform in a glove box in Lugon atmosphere.

The assembled glass cell is connected to a charger / discharger, and 2
Place in a thermostat in an atmosphere of 5 ° C. In the charger / discharger,
The voltage and current when a current flows between the sample and the counter electrode and the voltage between the counter electrode and the sample are monitored. The charging condition is such that 320 mAh per gram of the active material is 1 C, and the 1 C current is determined according to the weight of the sample active material.

In the first to third cycles, 0.3 C × 10 mV
The charge and discharge were performed under the conditions of × 8h charge and 0.3C × 3.0V cutoff, and the fourth cycle was 0.3C × 10
The charging and discharging are performed under the conditions of charging of mV × 8h and discharging of cutoff of 0.1 C × 1.0V. Here, charging means that a current flows in a direction in which Li ions are intercalated in the negative electrode sample.

Next, in the fourth cycle, the value obtained by subtracting the discharge amount up to 3V from the discharge amount up to 1V is 1V to 3V.
It is calculated as the discharge capacity between V (mAh / g).

From these tests and calculations, the discharge capacity of the negative electrode at a potential of 1 V to 3 V was 15 mAh / g.

<Preparation of Positive Electrode> First, LiCoO as an active material was added to 41.7 parts by weight of an N-methylpyrrolidone solution of polyvinylidene fluoride (PVdF) having a concentration of 12% by weight.
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 the mixture, and the solid was dispersed using a bead mill to prepare a positive electrode coating slurry.

Next, the positive electrode coating slurry was applied to a thickness of 15
255 g / m on both sides of μm Al foil (current collector)
² and dried, then pressed and slit to a thickness of 167 μm and a width of 42.00 m
m of the positive electrode was produced.

<Assembly of Secondary Battery> Next, a lead tab is joined to each of the positive and negative electrode current collectors, spirally wound through two polyethylene porous membranes using an automatic winding machine, and further pressed. Thus, a flat electrode body was manufactured. 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 body determined as a non-defective product was inserted into an aluminum outer can having a bottomed rectangular cylindrical shape having a thickness of 4.8 mm, a width of 30 mm, and a height of 47 mm, and then a non-aqueous electrolyte was injected. The above-mentioned prismatic lithium ion secondary battery shown in FIG. 2 was assembled by hermetically bonding an aluminum lid to the opening of the outer can. The non-aqueous electrolyte has a composition in which 1.5 mol / L of LiBF ₄ is dissolved in a mixed solvent of γ-butyrolactone and ethylene carbonate (mixing volume ratio 2: 1).

(Example 2) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) and 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight and a true density of 1.
After adding 2 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 70 g / cc and 48 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both surfaces of a copper foil (current collector) having a thickness of 15 μm by a knife edge coater so as to have a thickness of 103 g / m ² and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 16 mAh / by the same test and calculation as in Example 1.
g.

(Example 3) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight was added to 50 parts by weight of the fibrous carbon material (a) and the true density was 1.
After adding 4 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 60 g / cc and 46 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both surfaces of a 15 μm-thick copper foil (current collector) with a knife edge coater so as to have a thickness of 103 g / m ² , respectively, and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 20 mAh /
g.

(Example 4) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) was added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, and the true density was 1.
After adding 4 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 55 g / cc and 46 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm to a thickness of 103 g / m ² by a knife edge coater and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 15 mAh /
g.

(Example 5) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight was mixed with 50 parts by weight of the fibrous carbon material (a) and the true density was 1.
After adding 9 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 70 g / cc and 41 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both surfaces of a 15 μm-thick copper foil (current collector) with a knife edge coater so as to have a thickness of 103 g / m ² , respectively, and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 30 mAh / by the same test and calculation as in Example 1.
g.

(Example 6) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) were added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, and the true density was 1.
After adding 4 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 55 g / cc and 46 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both surfaces of a 15 μm-thick copper foil (current collector) with a knife edge coater so as to obtain 103 g / m ² , and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 30 mAh / by the same test and calculation as in Example 1.
g.

(Comparative Example 1) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) and 50 parts by weight of the spheroidal graphite (c) were added to 177 parts by weight of a viscous aqueous solution having a concentration of 0.68% by weight of carboxymethyl cellulose. After addition, the mixture was sheared and dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

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 so as to have a thickness of 103 g / m ² and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 7 mAh / g by the same test and calculation as in Example 1.
Met.

(Comparative Example 2) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) were added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, and the true density was 1.
After adding 1 part by weight of the fibrous mesophase low-temperature fired carbon material (b) of 63 g / cc and 49 parts by weight of the spheroidal graphite (c), the mixture was shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a 15 μm-thick copper foil (current collector) by a knife edge coater so as to be 103 g / m ² , and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 10 mAh /
g.

(Comparative Example 3) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) were added to 177 parts by weight of a viscous aqueous solution of 0.68% by weight of carboxymethylcellulose, and the true density was 1.
After adding 7 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 55 g / cc and 43 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm by a knife edge coater so as to have a thickness of 103 g / m ² and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 40 mAh / by the same test and calculation as in Example 1.
g.

(Comparative Example 4) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) were added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, and the true density was 1.
After adding 12 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) of 70 g / cc and 38 parts by weight of the spheroidal graphite (c), they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a 15 μm-thick copper foil (current collector) with a knife edge coater so as to obtain 103 g / m ² , and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity between the potential of 1 V and 3 V of the obtained negative electrode was determined to be 40 mAh /
g.

(Comparative Example 5) A prismatic 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. After the production of the electrode body having the positive and negative electrodes and the separator, Example 1 was used.
The same good / bad judgment was made as in the above, and only the electrode bodies judged as good were used.

<Preparation of Negative Electrode> First, 50 parts by weight of the fibrous carbon material (a) were added to 177 parts by weight of a viscous aqueous solution of carboxymethyl cellulose having a concentration of 0.68% by weight, and the true density was 1.
After adding 13 parts by weight of the fibrous mesophase low-temperature calcined carbon material (b) and 37 parts by weight of the spheroidal graphite (c) at 52 g / cc, they were shear-dispersed. Subsequently, 3.4 parts by weight of SBR latex was added to the mixture, and the mixture was uniformly mixed and stirred to prepare a negative electrode coating slurry.

Next, the coating slurry was applied to both sides of a copper foil (current collector) having a thickness of 15 μm by a knife edge coater so as to have a thickness of 103 g / m ² and dried.
At this time, the density of the negative electrode material on the copper foil was 1.23 g / cc.
Met. After that, it is subjected to pressing and slitting to have a thickness of 149 μm (density of the negative electrode material; 1.5 g / cc) and a width of 4 μm.
A 3.25 mm strip-shaped negative electrode was produced.

The discharge capacity at a potential of 1 V to 3 V of the obtained negative electrode was determined to be 70 mAh / by the same test and calculation as in Example 1.
g.

The obtained Examples 1 to 6 and Comparative Examples 1 to 5
700 mA at 25 ° C., 4.2
After initial charging at V and 6 h, and aging for 12 hours, the average capacity when discharging at 25 ° C. at 700 mA and a cutoff of 3.0 V was measured.

After the completion of the initial charging, each secondary battery was moved to an atmosphere of 60 ° C., aged for 12 hours, and then charged at the same temperature at 700 mA, 4.2 V, 6 h, 700 m
A, a discharge with a cutoff of 3.0 V as one cycle,
The discharge capacity retention ratio (cycle characteristics) with respect to the initial discharge capacity when the test was repeated 00 times was measured.

The results are shown in Table 1 below. Table 1 also shows the discharge capacities of the negative electrodes incorporated in the secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 5 between the potentials of 1 V and 3 V.

[0107]

[Table 1]

As is clear from Table 1, after the 3V cut discharge, the secondary batteries of Examples 1 to 6 provided with the negative electrodes having a capacity of 15 to 30 mAh / g as a deep discharge from 3 V to 1 V during discharge are as follows. , The capacity of the negative electrode is 15 to 30 m
It can be seen that the charge / discharge cycling characteristics at high temperatures are superior to the secondary batteries of Comparative Examples 1 to 5, which are out of the range of Ah / g.

In the above-described embodiment, the rectangular lithium ion secondary battery shown in FIG. 2 has been described. However, the present invention is not limited to the cylindrical lithium ion secondary battery shown in FIG. Even when applied to an ion secondary battery, it has the same excellent high-temperature charge / discharge cycle characteristics.

[0110]

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

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical non-aqueous electrolyte secondary battery (cylindrical lithium ion secondary battery) as one embodiment of the non-aqueous 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;

[Explanation of symbols]

 1, 21: exterior 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.

Continued on the front page (72) Inventor Takayuki Nakajima 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Inside A / T Battery Inc. (72) Inventor Koichi Matsumoto 3-4-1 Minamishinagawa, Shinagawa-ku, Tokyo Stock (72) Inventor Shinichi Uebayashi 7-1-1 Nisshin-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term (reference) 5H029 AJ05 AK03 AL06 AL07 AM03 AM05 AM07 BJ02 BJ04 BJ14 DJ04 HJ01 HJ04 HJ08 HJ19 5H050 AA07 BA17 CA08 CA09 CA29 CB07 CB08 DA03 EA23 EA24 HA01 HA04 HA08 HA19

Claims (8)

[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 a carbonaceous material including fibrous carbon materials (a) and (b) and a non-fibrous carbon material (c), and the fibrous carbon material (b) Is mesophase low-temperature calcined carbon, and the negative electrode has a discharge capacity of 1 V to 3 V as a discharge capacity of 1 V to 3 V.
A non-aqueous electrolyte secondary battery having 5 to 30 mAh / g. 2. The fibrous carbon material (a) has an average fiber diameter of 8 to 18 μm, an average fiber length of 10 to 50 μm, and a true density of 2.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least 24 g / cc. 3. The fibrous carbon material (b) has an average fiber diameter of 8 to 20 μm, an average fiber length of 8 to 20 μm, and a true density of 1.5.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is a mesophase low-temperature fired carbon of 0 to 1.75 g / cc. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-fibrous carbon material (c) is scaly or spherical graphite. 5. The non-aqueous electrolyte secondary battery according to claim 3, wherein the fibrous carbon material (b) is blended in an amount of 1 to 10% by weight based on the carbonaceous material. 6. The non-aqueous electrolyte secondary battery according to claim 3, wherein the fibrous carbon material (b) is blended in an amount of 2 to 9% by weight based on the carbonaceous material. 7. The non-aqueous electrolytic solution comprises γ as a non-aqueous solvent.
-Butyrolactone is contained.
The non-aqueous electrolyte secondary battery according to the above. 8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the γ-butyrolactone accounts for 45 to 70% by weight of the non-aqueous solvent.