JP2002110254A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a non-aqueous electrolyte secondary battery that can be manufactured without causing wrinkles in a current collector used for an electrode. A positive electrode sheet coated with Li _x MO ₂ as a positive electrode active material and a negative electrode sheet coated with a carbon material capable of occluding and releasing lithium ions as a negative electrode active material are wound via a separator 5. In the non-aqueous electrolyte secondary battery using the electrode body, the one-side thickness L of the positive electrode active material layer 22 is set to a predetermined range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery which is capable of discharging at a large current and has been improved to a battery having high output power. .

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and portable personal computers have been reduced in size and demand has increased, higher performance has been required for secondary batteries which are power sources of these electronic devices. As such a secondary battery, a non-aqueous electrolyte battery using a material capable of occluding and releasing lithium, such as a carbon material, as a negative electrode material has been developed and is widely used as a power source for portable electronic devices. This non-aqueous electrolyte secondary battery is different from a conventional battery in that it is lightweight and has a high electromotive force of 4V class, and its excellent performance has attracted attention.

[0003] Therefore, application of the non-aqueous electrolyte secondary battery as a power source for electric vehicles, electric tools, cordless cleaners, and the like has been studied. In such applications, however, conventional non-aqueous electrolyte secondary batteries are used. In comparison, it is required to have discharge characteristics at a large current and higher output characteristics.

In order to increase the output of a battery, it is essential to reduce the output resistance (internal resistance) of the battery. To this end, it is extremely important to reduce the resistance of the electrode assembly and battery components. is there. As one of the measures, development of a cylindrical lithium ion secondary battery or a prismatic lithium ion secondary battery having a plurality of current collecting leads on an electrode is being promoted. For example, Japanese Patent Application Laid-Open No. H11-317218 and It is disclosed in Japanese Unexamined Patent Publication No. Hei 11-339758. With such a configuration, current collection efficiency is improved and the output resistance of the battery can be reduced, so that a battery with excellent output characteristics can be formed.

[0005] However, the above-described effect of only lowering the resistance of the battery components has not been improved at all from the viewpoint of improving the utilization efficiency of the active material which is a reactant of the battery.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and enables discharge at a large current without impairing the current capacity of a battery.
It is another object of the present invention to provide a non-aqueous electrolyte secondary battery having excellent output characteristics such as pulse discharge characteristics.

[0007]

Means for Solving the Problems Lithium-ion secondary batteries, which are representative of non-aqueous electrolyte secondary batteries, are used for high output specifications such as electric vehicles and electric tools due to their high energy density. Has been actively developed in recent years. In view of such applications, it is possible to discharge at a large current of 100 A and 200 A (10 CA), but it is possible to obtain a large instantaneous large discharge pulse discharge even though the capacity is up to 20 Ah class. Is required. However, the conventional lithium-ion secondary battery has a problem that it can only take out a current of up to about 3 CA because it is used for low-power devices such as mobile phones and personal computers.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION
The following is a description. It is considered that the diffusion capacity of the lithium ion in the positive electrode determines the discharge capacity of the lithium ion secondary battery. The diffusion of lithium ions in the positive electrode is determined by the diffusion equation

(Equation 1) Described by Here, D is the effective chemical diffusion coefficient (cm ² / sec) of the electrode. In the high-power battery according to the first aspect, the current density on the electrode sheet is small.

(Equation 2) Given by Therefore, by solving the diffusion equation,
The lithium ion concentration on the positive electrode surface is

(Equation 3) Becomes Here, L is the thickness (cm) of one side of the electrode active material, F is the Faraday constant (9.649 × 10 ⁴ (c / mol)), and the discharge capacity is given by the lithium ion concentration on the positive electrode surface. The discharge capacity when performing double-sided coating is

(Equation 4) Becomes Here, Vm is an effective molar volume (cm ³ / mo).
l), I is the discharge current (A) of 0.2 C, and h is the height (cm) of the electrode. Therefore,

(Equation 5) When the discharge current of 10 C is satisfied, the condition for obtaining a discharge capacity of 90% or more is as follows.

(Equation 6) Becomes In addition, this equation

(Equation 7) Can be rewritten. Here, the V _M gives the effective molar volume, but since the internal electrodes are crowded viewed electrolyte immersion, the value varies depending on the state of the grains of the electrode active material. Generally, the amount of the electrolyte is ingrained as V _M is larger electrode is large, the greater the value of effective chemical diffusion coefficient D of the electrode. When these two values are experimentally examined for a positive electrode of a normal lithium ion secondary battery, the values are proportional to each other, and VM / _D = 8.5 × 10 ⁷ cm ·
it was found that given in _{sec / mol (20 ≦ V M} ≦ 25cm 3 / mol). Therefore, the above conditional expression is a conditional expression according to claim 1.

(Equation 8) Is rewritten as

A) Positive electrode sheet 4 As shown in FIG. 2, a positive electrode material paste obtained by dispersing, for example, a positive electrode active material, a conductive agent and a binder in an appropriate solvent is applied to the current collector 21. After coating and drying on one or both surfaces of the positive electrode and forming a positive electrode active material layer 22 on the surface of the current collector 21, the positive electrode active material layer is rolled with a roll press or the like to increase the density.

[0010] The thickness of one side of the positive electrode active material layer is 30 to
It is preferably 80 μm. When the thickness is in this range, the large current discharge characteristics are improved. The preferred range of the thickness is 35 μm to 65 μm.

In the positive electrode 4, the active material layer preferably has a packing density of 2.5 g / cm ³ or more after rolling. More preferably, it is 2.8 g / cm ³ or more. 3.0 packing density
When the g / cm ³ or more is set, the capacity of the battery can be increased. However, if the packing density is too high, the high-current discharge characteristics may be reduced. Therefore, the upper limit of the packing density is 3.5 g / g.
It is preferable cm ³ or less.

As the positive electrode active material, LiCoO is used.₂,
Alternatively, the composition formula LiCo_1-xM_xO₂, LiNi
_1-xM_xO₂(Where M is one or more elements,
x represents 0 <x ≦ 0.5) lithium composite gold represented by
Group oxides can be used. Specifically, LiCo
_1-xNi_xO₂, LiNi_1-xCo_xO₂, LiN
i _1-xyCo_xB_yO₂, LiNi_1-xyCo
_xAl_yO₂, LiNi_{1 -Xy}Co_xMn_yO₂,
LiNi_1-xyCo_xFe_yO₂Etc.
(The above x and y are 0 <x ≦ 0.5, 0 ≦ y <0.
5, and 0 <x + y ≦ 0.5).

The positive electrode active material may be lithium.
Nickel composite metal oxide and spinel lithium manganese
Mixtures with oxides can be used. The lithium
As the composite oxide, LiNiO₂, LiNi_0.7C
o_0.3O ₂, LiCo_0.8Ni_0.2O₂, Li
_1.075Ni_0.755Co_0.17O_1.9F_{0.1 ,}Li_1.10Ni
_0.74Co_0.16O_1.85F_{0.15 ,}Li_1.075Ni_0.705Co
_0.17Al_{0 . 05}O_1.9F_{0.1 ,}Li_1.10Ni_0.72Co
_0.16Nb_0.02O_1.85F_{0.15 ,}LiNi_1-xyC
o_xM_yO₂(However, M is selected from Al, B and Nb.
At least one element, x and y are 0 <x ≦
0.5, 0 <y <0.5 and 0 <x + y ≦ 0.5
Li) Nickel composite oxide represented by
_{To list Can be.}Among them, the composition formula LiNi
_1-xyCo_xM_yO₂(Where M is Al,
B, at least one element selected from Nb, x,
y is 0 <x ≦ 0.5, 0 <y <0.5, and 0 <x + y
≤0.5) lithium nickel composite oxidation
It is preferable to use a substance. Specifically, LiNi
_1-xyCo_xAl _yO₂, LiNi_1-xyCo
_xB_yO₂, LiNi_1-xyCo_xNb_yO_2,L
iNi_1-abcCo_aAl_bNb_cO_TwoEtc.
Can be (X and y are 0 <x ≦ 0.5, 0 <
y <0.5 and 0 <x + y ≦ 0.5, a, b, c
Are 0 <a ≦ 0.5, 0 <b <0.5, 0 <c <0.
5 and 0 <a + b + c ≦ 0.5)
Lithium nickel composite metal oxides have high thermal stability and are inexpensive.
It is preferable because it has excellent integrity.

The above spinel type lithium manganese oxide
Then, specifically, Li_{1 + a}Mn_2-aO₄, Li
_{1 + a}Mn_2-abCo_bO₄, Li_{1 + a}Mn_2-abA
l_bO₄, Li_{1 + a}Mn_2-abFe_bO₄, Li
_{1 + a}Mn_2-abMg_bO₄, Li _{1 + a}Mn_2-abT
i_bO₄, Li_{1 + a}Mn_2-abNb_bO₄, Li
_{1 + a}Mn_2-abGe_bO₄Etc. can be mentioned
(The a represents 0 <a and 2> a + b).

As the conductive agent, for example, acetylene black, carbon black, artificial graphite, natural graphite and the like can be used.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and hydrogen or fluorine of PVdF.
A modified PVdF in which at least one is substituted with another substituent,
A copolymer of vinylidene fluoride-6-propylene fluoride, a terpolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride, and the like can be used.

As an organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like are used.

B) Negative Electrode Sheet 6 The negative electrode sheet 6 can adopt basically the same configuration as the above-described positive electrode sheet 4 except for the following points.

The material of the current collector used for the negative electrode sheet 6 is as follows.
It is preferable to use a material that does not easily dissolve during the battery reaction, and for example, it is preferable to use copper, nickel, or the like. Particularly, copper is most preferable in consideration of electrochemical stability and flexibility at the time of winding. At this time, the thickness of the current collector is preferably 6 μm or more and 20 μm or less.

Further, the positive electrode active material in the positive electrode active material layer in the positive electrode sheet 4 is replaced with a negative electrode active material, and
And

The negative electrode active material is made of, for example, a material containing a carbonaceous substance or a chalcogen compound which inserts and extracts lithium ions, and a light metal. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material that occludes / releases lithium ions include coke, carbon fiber, pyrolysis gas phase carbonaceous material, graphite, fired resin, fired mesophase pitch-based carbon fiber and fired mesophase spherical carbon. be able to. Among them, it is preferable to use mesophase pitch-based carbon fiber or mesophase spherical carbon which has been graphitized at 2500 ° C. or higher because the electrode capacity is increased.

The chalcogen compounds that occlude and release lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbS).
e ₂ ) and the like. When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode increases although the voltage of the secondary battery drops, and the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like.

As the binder constituting the negative electrode active material layer, for example, polytetrafluoroethylene (PTF
E), polyvinylidene fluoride (PVdF), ethylene-
Propylene-diene copolymer (EPDM), styrene
It is preferable to use butadiene rubber (SBR) or the like.

The thickness of one side of the negative electrode active material layer is 30 to
It is preferably 80 μm. When the thickness is in this range, the large current discharge characteristics are improved. The preferred range of the thickness is 40 μm to 70 μm.

In the negative electrode sheet 6, the pressure of the active material layer
The packing density after rolling is 1.30 g / cm ³The above is preferred.
More preferably, 1.35 g / cm³That is all. Packing density
Degree of 1.4g / cm³This will increase the capacity of the battery
be able to. However, if the packing density is too high,
Since the electrical characteristics may decrease, the upper limit of the packing density is
1.5g / cm³The following is preferred.

C) Electrolytic Solution The electrolytic solution has a composition in which an electrolyte is dissolved in a non-aqueous solvent.

As the non-aqueous solvent, for example, propylene carbonate (PC), ethylene carbonate (EC)
And cyclic carbonates such as dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC), and linear chains such as 1,2-dimethoxyethane (DME) and diethoxyethane (DEE). Ether, tetrahydrofuran (THF) or 2-methyltetrahydrofuran (2-
Cyclic ethers and crown ethers such as MeTHF),
At least one selected from fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO) can be used.

Among them, those comprising at least one selected from EC, PC and γ-BL, EC, PC and γ-B
L, DMC, MEC, DE
It is desirable to use a mixed solvent comprising at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN. Further, when using a negative electrode containing a carbonaceous material that occludes and releases lithium ions, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC and γ-BL, EC and PC And MEC, E
C and PC and DEC, EC and PC and DEE, EC and AN,
EC and MEC, PC and DMC, PC and DEC, or E
It is desirable to use a mixed solvent consisting of C and DEC.

As the electrolyte, for example, lithium perchlorate
(LiClO₄), Lithium hexafluorophosphate (Li
PF₆), Lithium borofluoride (LiBF₄), Six foot
Lithium arsenide (LiAsF)₆), Trifluorometas
Lithium sulfonate (LiCF ₃SO₃), Aluminum tetrachloride
Lithium (LiAlCl₄), Bistrifluoro
Lithium methylsulfonylimide [LiN (CF₃SO
₂)₂] And the like. Inside
Also LiPF₆, LiBF₄, LiN (CF₃SO₂)₂
Is preferred because conductivity and safety are improved.
No.

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L.

FIG. 1 schematically shows a partial cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery.

The electrode group 3 was wound as described above, and as a result, as shown in the figure, the positive electrode sheet 4, the separator 5, the negative electrode sheet 6, the separator 5, the positive electrode sheet 4, the separator 5, the negative electrode sheet 6, the separator 5, and the like. The structure is repeated.

At this time, it is preferable that the electrode group 3 is laminated so that the current collecting lead of the positive electrode sheet 4 and the current collecting lead of the negative electrode sheet 6 protrude on the opposite side in the winding axis direction as shown in the figure. (Examples) Examples of the present invention will be specifically described below.

Example 1 <Preparation of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; where x is 0 ≦ x ≦ 1) 90.5% by weight of powder
With acetylene black 2.5% by weight, graphite 3% by weight, polyvinylidene fluoride (PVdF) 4% by weight,
A slurry was prepared by adding and mixing an N-methyl-2-pyrrolidone (NMP) solution. The slurry was applied to a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, and dried with hot air at a temperature of 110 ° C to 140 ° C.
The dried positive electrode is heated roller press (φ300mm)
About 1000kgf while controlling the temperature to 100 ° C
/ Cm and continuously rolled under a linear pressure load to produce a positive electrode having a filling density of the positive electrode active material layer of 3.23 g / cm ³ .
In this electrode, the thickness of one side of the positive electrode active material layer was 61 μm.
m, electrode length is 59.0 cm, electrode height is 5.4c
m.

Next, the current collector has the same width as the exposed portion.
Prepare a long strip of aluminum foil with a thickness of 50 μm
Was. This is cut out to the same length as the electrode length, and
Current collector lead (0.1 mm thick x 5 mm wide x length
50mm) in the direction perpendicular to its longitudinal direction.
In this way, both ends and the center were welded. Finally, this is
By continuously welding to the exposed area of the current collector,
A positive electrode provided with three current collecting leads was produced. <Preparation of negative electrode> Heat treatment at 3000 ° C. as negative electrode active material
Prepared mesophase pitch-based carbon fiber (MCF)
Was. The carbon fiber has an average fiber diameter of 8 μm,
The length is 20 μm, and the average spacing (d₀₀₂) Is 0.336
It was 0 nm. 93% by weight of the carbonaceous material powder, binding
7% by weight of polyvinylidene fluoride (PVDF)
And a slurry by mixing the NMP solution
Was. The obtained slurry is made of a copper foil having a thickness of 12 μm.
Apply to the negative electrode current collector and apply hot air at a temperature of 110 to 140 ° C.
Dried. Roll the dried negative electrode at room temperature (20 ° C)
Continuous rolling by pressing (φ300mm)
The packing density of the negative electrode active material layer is 1.36 g / cm. ³Negative electrode
Was prepared. In this negative electrode, one side of the negative electrode active material layer
The thickness was 60 μm.

Next, a long strip-shaped copper foil having a thickness of 50 μm and having the same width as the width of the exposed portion of the current collector was prepared. This was cut out to the same length as the electrode length, and was welded so as to extend a current collecting lead made of copper (thickness 0.1 mm × width 5 mm × length 50 mm) in a direction perpendicular to the longitudinal direction. As the welding position, when the negative electrode is divided into four in the longitudinal direction,
The position was set at a length of 1/4 and 3/4 from the end. Lastly, this was continuously welded to the uncoated portion of the electrode to produce a negative electrode having two current collecting leads. <Preparation of Electrode Body> A polyethylene separator having a thickness of 25 μm and a porosity of 50% was prepared. A positive electrode, a separator, a negative electrode, and a separator were sequentially laminated, and the laminate was spirally wound to produce an electrode body. The directions of the positive electrode and the negative electrode, and the direction of the winding axis were set so that the current collecting leads for the positive electrode and the negative electrode were separated at both ends in the winding axis direction. <Preparation of non-aqueous electrolyte> Lithium hexafluorophosphate (LiP) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2).
F ₆ ) was dissolved at 1 mol / L to prepare a non-aqueous electrolyte. <Battery assembly> The electrode group is housed in a cylindrical container having a bottom, the current collecting lead for the negative electrode is provided at the bottom of the cylindrical container having a bottom, and the current collecting lead for the positive electrode is provided at the opening of the cylindrical container having a bottom. Welded to each safety valve located in the section.

Subsequently, the electrolytic solution was injected under reduced pressure into the bottomed cylindrical container, and the electrode group was sufficiently impregnated with the nonaqueous electrolytic solution. Then, after arranging the positive electrode terminal on the safety valve, it was caulked and sealed to form a sealed structure.

As described above, the design capacity of the cylindrical non-aqueous electrolyte secondary battery (high output specification 18650 size) is 15
A 33 mAh battery was assembled.

The measured battery capacity and large current discharge ratio (10 C ratio) of the nonaqueous electrolyte secondary battery obtained in Example 1 were measured to be 1520 mAh and 91%, respectively. Example 2 <Preparation of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; where x is 0 ≦ x ≦ 1) 90.5% by weight of powder
With acetylene black 2.5% by weight, graphite 3% by weight, polyvinylidene fluoride (PVdF) 4% by weight,
A slurry was prepared by adding and mixing an N-methyl-2-pyrrolidone (NMP) solution. The slurry was applied to a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, and dried with hot air at a temperature of 110 ° C to 140 ° C.
The dried positive electrode is heated roller press (φ300mm)
About 1000kgf while controlling the temperature to 100 ° C
/ Cm and continuously rolled under a linear pressure load to produce a positive electrode having a filling density of the positive electrode active material layer of 3.23 g / cm ³ .
In this electrode, the thickness of one side of the positive electrode active material layer was 46 μm.
m, electrode length is 72.7 cm, electrode height is 5.4c
m.

Next, the same width as the width of the exposed portion of the current collector is used.
Prepare a long strip of aluminum foil with a thickness of 50 μm
Was. This is cut out to the same length as the electrode length, and
Current collector lead (0.1 mm thick x 5 mm wide x length
50mm) in the direction perpendicular to its longitudinal direction.
In this way, both ends and the center were welded. Finally, this is
By continuously welding to the exposed area of the current collector,
A positive electrode provided with three current collecting leads was produced. <Preparation of negative electrode> Heat treatment at 3000 ° C. as negative electrode active material
Prepared mesophase pitch-based carbon fiber (MCF)
Was. The carbon fiber has an average fiber diameter of 8 μm,
The length is 20 μm, and the average spacing (d₀₀₂) Is 0.336
It was 0 nm. 93% by weight of the carbonaceous material powder, binding
7% by weight of polyvinylidene fluoride (PVDF)
And a slurry by mixing the NMP solution
Was. The obtained slurry is made of a copper foil having a thickness of 12 μm.
Apply to the negative electrode current collector and apply hot air at a temperature of 110 to 140 ° C.
Dried. Roll the dried negative electrode at room temperature (20 ° C)
Continuous rolling by pressing (φ300mm)
The packing density of the negative electrode active material layer is 1.36 g / cm. ³Negative electrode
Was prepared. In this negative electrode, one side of the negative electrode active material layer
The thickness was 45 μm.

Next, a long strip-shaped copper foil having a thickness of 30 μm and having the same width as the width of the exposed portion of the current collector was prepared. This was cut out to the same length as the electrode length, and was welded so as to extend a current collecting lead made of copper (thickness 0.1 mm × width 5 mm × length 50 mm) in a direction perpendicular to the longitudinal direction. As the welding position, when the negative electrode is divided into four in the longitudinal direction,
The position was set at a length of 1/4 and 3/4 from the end. Lastly, this was continuously welded to the uncoated portion of the electrode to produce a negative electrode having two current collecting leads. <Preparation of Electrode Body> A polyethylene separator having a thickness of 25 μm and a porosity of 50% was prepared. A positive electrode, a separator, a negative electrode, and a separator were sequentially laminated, and the laminate was spirally wound to produce an electrode body. The directions of the positive electrode and the negative electrode, and the direction of the winding axis were set so that the current collecting leads for the positive electrode and the negative electrode were separated at both ends in the winding axis direction. <Preparation of Nonaqueous Electrolyte> Lithium hexafluorophosphate (LiP) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2).
F ₆ ) was dissolved at 1 mol / L to prepare a non-aqueous electrolyte. <Assembly of Battery> The electrode group is housed in a cylindrical container having a bottom, the current collecting lead for the negative electrode is provided at the bottom of the cylindrical container having a bottom, and the current collecting lead for the positive electrode is provided at an opening of the cylindrical container having a bottom. Welded to each safety valve located in the section.

Subsequently, the electrolytic solution was poured into the bottomed cylindrical container under reduced pressure, and the non-aqueous electrolytic solution w
Fully impregnated. Then, after arranging the positive electrode terminal on the safety valve, it was caulked and sealed to form a sealed structure.

As described above, the design capacity of the cylindrical non-aqueous electrolyte secondary battery (high output specification 18650 size) is 14
A 20 mAh battery was assembled.

In the same manner as in Example 1, the measured battery capacity and large current discharge ratio (10C ratio) of the nonaqueous electrolyte secondary battery obtained in Example 2 were measured, and each was 1405 mA.
h, 95%. Comparative Example 1 A dry positive electrode was obtained in the same manner as in Example 1. The temperature of the dried positive electrode was adjusted to 1 by a heated roller press (φ300 mm).
Continuous rolling was performed while applying a linear pressure load of about 1000 kgf / cm while controlling the temperature to 00 ° C., thereby producing a positive electrode having a packing density of 3.23 g / cm ³ of the positive electrode active material layer. In this electrode, the thickness of one side of the positive electrode active material layer was 83 μm, the length of the electrode was 47.1 cm, and the height of the electrode was 5.4 cm. <Production of Negative Electrode> A dry negative electrode was obtained in the same manner as in Example 1.
After drying, the negative electrode is pressed with a roller press (φ
300 mm) to produce a negative electrode having a packing density of the negative electrode active material layer of 1.36 g / cm ³ . In this negative electrode, the thickness of one side of the negative electrode active material layer is:
It was 79 μm.

Next, a long strip-shaped copper foil having a thickness of 50 μm and having the same width as the width of the exposed portion of the current collector was prepared. This was cut out to the same length as the electrode length, and was welded so as to extend a current collecting lead made of copper (thickness 0.1 mm × width 5 mm × length 50 mm) in a direction perpendicular to the longitudinal direction. As the welding position, when the negative electrode is divided into four in the longitudinal direction,
The position was set at a length of 1/4 and 3/4 from the end. Lastly, this was continuously welded to the uncoated portion of the electrode to produce a negative electrode having two current collecting leads. <Preparation of Electrode Body> A polyethylene separator having a thickness of 25 μm and a porosity of 50% was prepared. A positive electrode, a separator, a negative electrode, and a separator were sequentially laminated, and the laminate was spirally wound to produce an electrode body. The directions of the positive electrode and the negative electrode, and the direction of the winding axis were set so that the current collecting leads for the positive electrode and the negative electrode were separated at both ends in the winding axis direction. <Preparation of non-aqueous electrolyte> Lithium hexafluorophosphate (LiP) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2).
F ₆ ) was dissolved at 1 mol / L to prepare a non-aqueous electrolyte. <Battery assembly> The electrode group is housed in a cylindrical container having a bottom, the current collecting lead for the negative electrode is provided at the bottom of the cylindrical container having a bottom, and the current collecting lead for the positive electrode is provided at the opening of the cylindrical container having a bottom. Welded to each safety valve located in the section.

Subsequently, the electrolytic solution was injected into the bottomed cylindrical container, and the electrode group was sufficiently impregnated with the non-aqueous electrolytic solution. After arranging the positive electrode terminal on the safety valve, it was crimped and sealed to form a sealed structure.

As described above, the cylindrical non-aqueous electrolyte secondary battery (18650 size) has a design capacity of 1635 mAh.
Battery was assembled.

In the same manner as in Example 1, the measured battery capacity and the large current discharge ratio (10C ratio) of the non-aqueous electrolyte secondary battery obtained in Comparative Example 1 were measured, and each was 1620 mA.
h, 5%.

The following Table summarizes Examples 1 and 2 and Comparative Examples.

[Table 1] FIGS. 3 and 4 show the measurement results of the rate characteristics of each battery.
As shown in the graph, the discharge current rate characteristics of the batteries of Examples 1 and 2 of the present invention have excellent performance.
The discharge curve in FIG. 4 shows the voltage behavior at the time of 10C discharge. In Examples 1 and 2, the voltage at the time of discharge was high and the capacity was sufficiently taken out. On the other hand, in the battery of the comparative example, 3C in FIG.
The capacity that can be taken out by the discharge current is about 50% or less. It is apparent from the voltage behavior in FIG. 4 that the battery is not suitable for large-current discharge with a large voltage effect.

[0052]

As described in detail above, according to the present invention,
It can be seen that there is much battery capacity that can be taken out even with a large current discharge such as 10C.

Therefore, according to the present invention, a non-aqueous electrolyte secondary battery having high capacity and excellent output characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery.

FIG. 2 is a sectional view showing a positive electrode sheet according to the present invention.

FIG. 3 is a comparison diagram of rate characteristics of the battery according to the present invention.

FIG. 4 is a discharge curve comparison diagram of the battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container 3 ... Electrode group 4 ... Positive electrode sheet 5 ... Separator 6 ... Negative electrode sheet 11 ... Positive current collecting lead 12 ... Negative current collecting lead 21 ... Current collecting Body 22 ... Positive electrode active material layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiyuki Isazaki 1 Toshiba R & D Center, Komukai-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Shuji Yamada Toshiba Komukai-shi, Kawasaki-shi, Kanagawa No. 1 town Toshiba R & D Center F-term (reference) GA22 HA02 HA04 HA12 HA19

Claims (4)

[Claims] Claims: 1. A Li _x MO ₂ (where,
M is one or more transition metals, preferably Co, Mn, N
Nonaqueous electrolyte secondary battery using an electrode body obtained by winding a positive electrode sheet coated with i) and a negative electrode sheet coated with a carbon material capable of occluding and releasing lithium ions as a negative electrode active material via a separator In the above, the thickness L (cm) of one side of the positive electrode active material layer is 0 ≦ IL / lhF ≦ 7.22 × 10 ⁻¹¹ (where I is discharge current (A), and L is one side thickness (cm) of the electrode active material). , D is the chemical diffusion coefficient (cm ² / sec), Vm
Is the molar volume (cm ³ / mol), l is the length of the electrode (c
m) and h are electrode heights (cm), and F satisfies the Faraday constant (9.649 × 10 ⁴ (c / mol)). 2. The method according to claim 1, wherein Li _x MO ₂ (however,
M is one or more transition metals, preferably Co, Mn, N
Non-aqueous electrolyte using an electrode body formed by laminating a positive electrode sheet coated with i) and a negative electrode sheet coated with a carbon material capable of occluding and releasing lithium ions as a negative electrode active material via a separator In the secondary battery, one side thickness L (cm) of the positive electrode active material layer is 0 ≦ IL / lhF ≦ 7.22 × 10 ⁻¹¹ (where I is discharge current (A), and L is one side thickness of the electrode active material). (Cm), D is the chemical diffusion coefficient (cm ² / sec), Vm
Is the molar volume (cm ³ / mol), l is the length of the electrode (c
m) and h are electrode heights (cm), and F satisfies the Faraday constant (9.649 × 10 ⁴ (c / mol)). 3. The thickness L of one side of the positive electrode active material is 0.003 (c
m) or more and 0.01 (cm) or less, and the battery capacity is 0.5 or more.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least 5 Ah and at most 20 Ah. 4. The thickness L of one side of the positive electrode active material is 0.003 (c
m) or more and 0.01 (cm) or less, and the battery capacity is 0.5 or more.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least 5 Ah and at most 20 Ah.