JP2002015721A - Nonaqueous electrolyte secondary battery and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which can be manufacture without generating wrinkles on a collector used as an electrode. SOLUTION: A laminated body pinching a separator between a pair of electrodes 4 having a region B with an electrode active material layer 22 formed on the surface of a collector 21 and a region A with the collector 21 exposed in a strip is made. The nonaqueous electrolyte secondary battery is provided with an electrode group wound around the laminated body and a collecting lead connected with the region B. By making film thickness of the collector in the region A thicker than that in the region B and heightening strength of the collector of the region A, generation of wrinkles on the collector 21 in the region A is curtailed in a process of rolling of an electrode.

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 having an improved electrode current collector and a method of manufacturing the same.

[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, power tools, cordless cleaners, and the like has been studied. In such applications, higher output characteristics are required as compared with conventional non-aqueous electrolyte secondary batteries.

In order to increase the output of a battery, it is necessary to reduce the internal resistance of the battery as much as possible. For that purpose, it is important to reduce the resistance of the electrode and the battery member and to increase the current collection efficiency. As one of the measures, the development of a cylindrical lithium ion secondary battery or a prismatic lithium ion secondary battery having a plurality of current collecting leads on the electrode has been advanced, and is disclosed in, for example, JP-A-9-92335. Have been. With such a structure, current collection efficiency is improved and the internal resistance of the battery can be reduced, so that a battery having excellent output characteristics can be formed.

[0005] By the way, industrially aside from the laboratory, the electrode for the secondary battery is obtained by adding an active material to a solution in which a binder is dispersed in water or an organic solvent, and stirring and mixing. It is produced by applying a coating liquid to a current collector, drying and rolling to form a thin plate. Here, the current collecting lead (current collecting tab) for connecting the electrode and the terminal is provided with an exposed portion of the current collector at the electrode side end, and connected to the exposed portion by a spot welding machine or an ultrasonic welding machine. I do.

As a method of forming the exposed portion, there is a method of performing intermittent coating using a coating apparatus having an intermittent coating function. However, this method has a problem that a special device is required and the production process is complicated, so that the production speed is reduced.

Therefore, as another method of forming the uncoated portion, a part of the current collector is protruded and the protruding portion is exposed, or the end portion of the current collector is exposed in a strip shape. A method for producing a connection region of a current collecting lead is given. This method is excellent in productivity in the step of applying the active material.

However, when the present inventors tried to use such an electrode in a cylindrical lithium ion secondary battery, the electrode was rolled to a desired thickness by a roll press or the like, or packed into a cylinder. If the current collector is exposed when the electrode is wound, the connection of the current collector lead may be wrinkled or broken in some cases, making it impossible to connect the current collector lead. It has been found that the conductivity of the conductor may be reduced. In order to prevent this, it is necessary to reduce the rolling load, so that it is difficult to increase the filling density of the electrode, and it is not possible to wind the electrode with a strong force, so that the capacity of the battery is increased. There was a problem that it became difficult.

[0009]

As described above, if an exposed portion of the current collector is provided as a connection region of the current collecting lead, a large load cannot be applied to the electrode when the electrode is manufactured. It was difficult to achieve capacity.

The present invention has been made in view of such a problem, and prevents deformation of a connection region (exposed portion of a current collector) of a current collecting lead due to a load during rolling or the like, and thus has a high capacity. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

[0011]

A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode sheet having a first current collector and a positive electrode active material layer formed on the surface of the first current collector. A negative electrode sheet having a second current collector and a negative electrode active material layer formed on the surface of the second current collector; and a nonaqueous electrolyte sandwiched between the positive electrode active material layer and the negative electrode active material layer. An electrode group obtained by winding a laminate including a separator, and a current collecting lead connected to each of the first and second current collectors, wherein at least one of the positive electrode sheet and the negative electrode sheet includes:
At the end of the electrode group in the winding axis direction, the first or second
In the non-aqueous electrolyte secondary battery having a strip-shaped connection region for connecting the current collector lead, exposing the current collector, a film thickness of the connection region of the first or second current collector Is characterized in that the thickness is larger than the thickness of the region where the positive electrode active material layer or the negative electrode active material layer is formed.

When an electrode having an electrode active material formed on a part of the surface of a current collector having a uniform thickness is rolled or wound, pressure is applied only to a region where the electrode active material is formed, and only this region is rolled. Therefore, stress acts on the exposed portion of the current collector. Since a portion of the electrode where the active material is formed is reinforced by the active material, wrinkles are generated in the exposed portion of the low-strength current collector.

According to the present invention, the mechanical strength of the connection region is increased by increasing the thickness of the current collector in the connection region, that is, the region where the current collector is exposed, as compared with the region where the active material is formed. And when the electrode (ie, the positive electrode sheet or the negative electrode sheet) is rolled, or when the electrode is wound, wrinkles are less likely to occur in the current collector connection region.

Preferably, the first and second electrodes have substantially the same thickness in the connection region and in the region where the positive electrode active material or the negative electrode active material is formed.

That is, by making the thickness of the electrode uniform in the connection region and the active material forming portion, the connection region of the current collector and the region where the active material is formed during rolling during electrode fabrication or electrode winding. Because pressure is applied to each,
The difference in the reduction ratio of the current collector between the region where the active material is formed and the connection region is reduced. As a result, generation of wrinkles in the connection region can be reduced.

Preferably, the width of the connection region in the winding axis direction is 15% or less of the width of the current collector in the winding axis direction.

That is, by reducing the width of the connection region, the strength of the connection region can be further increased.

In the method of manufacturing a nonaqueous electrolyte secondary battery according to the present invention, a positive electrode active material layer is formed on a first current collector surface having a positive electrode active material layer forming region and a band-like current collecting lead forming region. Rolling to form a positive electrode sheet, forming a negative electrode active material layer on the second current collector surface having a negative electrode active material layer forming region and a belt-shaped current collecting lead forming region, and then rolling to form a negative electrode sheet Connecting a current collecting lead to each of the current collecting lead forming region of the first current collector and the current collecting lead forming region of the second current collector; Forming a group of electrodes by winding a laminate sandwiching the separator in the non-aqueous electrolyte secondary battery, the thickness of the current collecting lead formation region is larger than the positive electrode active material layer formation region The first collection The collector, or the second current collector, in which the thickness of the current collecting lead forming region is larger than that of the negative electrode active material layer forming region, is rolled, and the current collecting lead forming region is wound in the winding axis direction of the electrode group It is characterized by being arranged at the end.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a cylindrical non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a plan view of the left half surface of the cylindrical nonaqueous electrolyte secondary battery and a vertical sectional view of the right half surface thereof. FIG. 2 is a partial cross-sectional view of the positive electrode sheet used in FIG.

However, the nonaqueous electrolyte secondary battery according to the present invention is not limited to the following embodiments as long as it is within the scope of the present invention.

For example, a cylindrical container 1 having a bottom made of stainless steel has an insulator 12 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
A belt-like material in which a positive electrode sheet 4, a separator 5, a negative electrode sheet 6, and another separator 5 are laminated in this order is spirally wound so that the negative electrode sheet 6 is located outside. The separator 5 is formed of, for example, a nonwoven fabric, a microporous polypropylene film, a microporous polyethylene film, or a microporous polyethylene-polypropylene laminated film. In addition, since the electrolyte is contained in the container 1, the electrolyte penetrates into the separator 5.

A PTC element 7 having an opening in the center, a safety valve 8 disposed on the PTC element 7, and a hat-shaped positive terminal 9 disposed on the safety valve 8 are provided in an upper opening of the container 1. It is caulked and fixed via an insulating gasket 10. One end of the current collecting lead 11 for the positive electrode is connected to the positive electrode sheet 4, and the other end is connected to the positive electrode terminal 9. The negative electrode sheet 6 is connected to the container 1 serving as a negative electrode terminal via a negative electrode current collecting lead 13.

The non-aqueous electrolyte secondary battery according to the present invention has a structure in which an exterior material is made of a laminate film, and a laminate of the positive electrode, the negative electrode, and the separator is flatly wound inside the exterior material. And a structure in which a non-aqueous electrolyte is accommodated.

Next, the positive electrode sheet 4, the negative electrode sheet 6, and the electrolyte will be specifically described.

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.

The current collector 21 has an L-shaped cross section.
The thick part of the current collector is exposed in a strip shape. The exposed region is a connection region for connecting a current collecting lead, and this connection region will be described below as a region A, and the remaining region having a small film thickness will be referred to as a region B where a positive electrode active material layer is formed. .

The positive electrode sheet as shown in FIG. 2 is laminated with a separator and a negative electrode sheet, which will be described later, and then rolled to obtain a columnar electrode group. Is wound so as to form the upper surface or the lower surface of the electrode group. That is, the direction shown by the arrow in FIG. 2 is the winding axis.

When pressure is applied in the thickness direction of the electrode sheet, only the region B is pressurized and expanded, so that a stress is generated in the region A in the direction indicated by the arrow in FIG. However, since the strength of the region A is increased by increasing the film thickness in the region A, it is possible to suppress the occurrence of wrinkles due to the stress in the region A.

If the difference between the thickness of the current collector in the region A and the thickness of the current collector in the region B is small, the above-mentioned effect cannot be sufficiently obtained.
Since the wrinkles may occur, the thickness of the current collector in the region A is 1.2 times to 1.times.
It is preferable to set about eight times.

When the width of the region A in the winding axis direction is reduced, wrinkles are less likely to occur in the region A. Therefore, the ratio of the width of the region A in the winding axis direction to the width of the electrode in the winding axis direction is 1%.
It is desirable to set it to 5% or less. However, if the width of the region A in the direction of the winding axis is too small, it is difficult to connect the current collecting lead to the region A.

The material used for the current collector can be used without particular limitation as long as it is a conductive material. In particular, the current collector for the positive electrode is hardly oxidized during the battery reaction, such as aluminum, stainless steel, titanium, etc. It is preferred to use Further, the thickness of the current collector in the region B can be used as long as it is substantially the same as that of a normally used current collector.
For the materials mentioned above, the thickness is usually about 10 to 50 μm. If the film thickness is less than 10 μm, mechanical strength and conductivity may be insufficient. If it exceeds 50 μm, the ratio of the current collector in the electrode group increases, and the ratio of the active material decreases, so that it becomes difficult to increase the battery capacity. The thickness of the current collector is particularly preferably 1 to 30 μm.

FIG. 3 shows an embodiment of the positive electrode sheet 4.

In the positive electrode sheet 4 shown in FIG. 3, the thickness of the region A at the end in the winding axis direction is larger than that of the sheet-like current collector 21-1 having a uniform thickness. The positive electrode sheet shown in FIG. 2 is different from the positive electrode sheet shown in FIG. 2 in that a current collector 21 in which a belt-shaped current collecting material 21-2 is joined for reinforcement is used. In this way, the processing of the current collector 21 can be simplified. The band-shaped current collecting material may be joined after forming the positive electrode active material layer 22 on the sheet-shaped current collecting material.

The positive electrode sheet 4 shown in FIG. 3 differs from the positive electrode sheet shown in FIG. 2 in that the positive electrode active material layers 22 are formed on both sides of the current collector. By doing so, the ratio of the positive electrode active material layer in the electrode group can be increased, and the capacity of the battery can be increased. Further, the current collector 21 in the region A
2 is different from the positive electrode sheet shown in FIG. 2 in that it has a T-shape in which both sides protrude.

Further, in FIG. 3, the positive electrode active material layer 2
2 differs from the positive electrode sheet shown in FIG. 2 in that the positive electrode sheet 4 has a uniform thickness when the current collector 21 is formed.

By making the thickness of the positive electrode sheet uniform, pressure is applied to both the region A and the region B of the current collector at the time of rolling or winding the positive electrode sheet.
Since the stress generated between the regions A and B can be reduced, the generation of wrinkles on the current collector can be further suppressed.

The above-mentioned uniform thickness does not need to be strictly uniform, but is uniform to such an extent that pressure is applied to each of the region A and the region B at the time of rolling in forming the electrode or when winding the electrode. Any thickness may be used.

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. A preferable range of the thickness is 50 μm to 65 μm. In the positive electrode 4, the packing density of the active material layer after rolling is 2.7 g / cm ^3.
The above is preferred. More preferably, it is 3.0 g / cm ³ or more. When the packing density is 3.0 g / cm ³ or more, 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 preferably 3.5 g / cm ² 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.
(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).

Such a lithium nickel composite metal oxide is preferable because of its high thermal stability and excellent safety.

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

B) Negative Electrode Sheet 6 The configuration of the negative electrode sheet 6 can be basically the same as that of the positive electrode sheet 4 except for the following points.

The material of the current collector used for the negative electrode sheet 6 is
Similar to the material of the current collector used for the positive electrode sheet 4, any material may be used as long as it has conductivity, but the current collector used for the negative electrode is preferably made of a material that is difficult to dissolve during a battery reaction. For example, it is preferable to use copper, nickel, or the like. In consideration of electrochemical stability, flexibility at the time of winding, and the like, copper is most preferable. At this time, the thickness of the region B is preferably 8 μm or more and 15 μm or more and 20 μm or less.

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 to form a negative electrode sheet 6. The negative electrode active material is made of, for example, a material containing a carbonaceous substance or a chalcogen compound that occludes and releases lithium ions, and a light metal. Above all, occludes lithium ions
A negative electrode containing a carbonaceous substance or a chalcogen compound to be released is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material that occludes and releases lithium ions include coke, carbon fiber, pyrolysis gas phase carbonaceous material, graphite, resin fired material, mesophase pitch-based carbon fiber, and mesophase spherical carbon fired material. 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. Examples of the binder constituting the negative electrode active material layer include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
dF), ethylene-propylene-diene copolymer (EP
DM), styrene-butadiene rubber (SBR) or the like is preferably used.

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. A preferable range of the thickness is 50 μm to 65 μm.

In the negative electrode sheet 6, the packing density of the active material layer after rolling is preferably 1.35 g / cm ³ or more. More preferably, it is 1.4 g / cm ³ or more. When the packing density is 1.4 g / cm ³ or more, 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 preferably 1.45 g / cm ² or less.

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. 4 schematically shows an enlarged view of the upper end and the lower end of the electrode group 3 shown in FIG.

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, The structure is repeated.

At this time, as shown in the figure, the connection area A for connecting the current collecting lead of the positive electrode sheet 4 and the connection area A for connecting the current collecting lead of the negative electrode sheet 6 project to the opposite side in the winding axis direction. It is preferable to stack the electrode groups 3 as described above.

The two electrode (positive electrode and negative electrode) sheets are connected to the current collecting leads 11 or 13, respectively. In order to reduce the electric resistance, a conductor having a diameter larger than the thickness of the separator 5 is usually used. Therefore, when the connection area A of the positive electrode sheet 4 and the connection area A of the negative electrode sheet 6 are formed on the same side in the winding axis direction, for example, the current collecting lead 11 for the positive electrode contacts the connection area A of the negative electrode sheet. And there is a risk of short circuit.

For example, if a region where the current collector is exposed is protruded from the lower end side of the positive electrode sheet 4 for a purpose other than the connection with the current collecting lead 11, the negative electrode sheet 4 comes into contact with the current collecting lead 13, There is a risk of short circuit.

In consideration of the above, it is preferable that the region where the current collector is exposed is formed only on one side in the winding axis direction. That is, as shown in FIGS. 2 and 3, an L-shape or T-shape is used rather than using an electrode sheet in which an active material layer is formed in a groove of a current collector having an I-type or U-type groove. Preferably, a current collector of the type is used.

[0065]

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 at a temperature of 110 ° C to 140 ° C. On this occasion,
The active material layer was not applied to the end of the current collector, and an exposed portion where the positive electrode active material layer was not formed on the current collector was formed in a band shape at the end of the positive electrode. The ratio of the width of the exposed portion to the width of the positive electrode was 0.1.

The positive electrode was rolled by applying a load of 1500 kgf / cm ² while controlling the temperature at 80 ° C. by a heated roller press, so that the packing density of the positive electrode active material layer was 3.
A positive electrode of 0 g / cm ³ was produced. During rolling, no wrinkling or breakage of the positive electrode was observed.
In this electrode, the thickness of one side of the positive electrode active material layer was 50 μm.

Next, a long strip-shaped aluminum 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 is cut out to the same length as the electrode length, and both ends and the central portion are formed so that a current collecting lead made of aluminum (thickness 0.1 mm × width 5 mm × length 50 mm) protrudes in a direction orthogonal to the longitudinal direction. Welded. Finally, by continuously welding this to the exposed area of the positive electrode current collector,
A positive electrode provided with three current collecting leads was produced.

<Preparation of Negative Electrode>
A mesophase pitch-based carbon fiber heat-treated at a temperature of ° C was prepared. The carbon fiber has an average fiber diameter of 8 μm, an average fiber length of 20 μm, and an average face spacing (d ₀₀₂ ) of 0.336.
It was 0 nm. A slurry was prepared by mixing 93% by weight of the carbonaceous material powder, 7% by weight of polyvinylidene fluoride (PVDF) as a binder, and an NMP solution. The obtained slurry was applied to a negative electrode current collector made of a copper foil having a thickness of 12 µm, and dried at a temperature of 110 ° C to 140 ° C. At this time, the negative electrode active material layer was not applied to the end of the current collector, and an exposed portion where the negative electrode active material layer was not formed on the current collector was formed in a band shape at the electrode end. The ratio of the width of the exposed portion to the electrode width was set to 0.1 as in the case of the positive electrode.

This negative electrode was rolled by roller pressing at normal temperature (20 ° C.) to produce a negative electrode having a packing density of the negative electrode active material layer of 1.4 g / cm ³ . No wrinkling or breakage of the electrode was observed during rolling. In this negative electrode, the thickness of one side of the negative electrode active material layer was 50 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 Group> A polyethylene separator having a thickness of 15 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 group. 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 (LiPF ₆ ) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2) at 1 mol / L. The solution was dissolved 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 the bottom, and the current collecting lead for the positive electrode is provided in the cylindrical shape having the bottom. Each was welded to a safety valve arranged at the opening of the container.

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 the positive electrode terminal was arranged on the safety valve, it was fixed by caulking.

As described above, a cylindrical non-aqueous electrolyte secondary battery (high output specification 18650 size) was assembled.

Example 2 A T-shaped current collector was prepared as a positive electrode current collector. This current collector has a thickness of 70 μm in a thick portion and 20 μm in a thin portion. The positive electrode slurry obtained in the same manner as in Example 1 is applied to a thin portion of the current collector, dried, cut, and the positive electrode has a ratio of the width of the exposed portion of the current collector to the electrode width of 0.1. An active material layer was formed.

The positive electrode was heated at a total pressure of 1500 kgf / cm while the temperature was controlled at 80 ° C. by a heated roller press.
Rolling was performed under a load of ² to produce a positive electrode having a packing density of the positive electrode active material layer of 3.0 g / cm ³ . During rolling, no wrinkling or breakage of the positive electrode was observed. In this positive electrode, the thickness of one side of the positive electrode active material layer was 50 μm.

Next, a current collecting lead made of aluminum (thickness 0.1 mm × width 5 mm × length 50 mm) was placed on the uncoated portion.
Was welded to both ends and the center so as to extend in a direction perpendicular to the longitudinal direction, to produce a positive electrode having three current collecting leads.

Thereafter, a cylindrical non-aqueous electrolyte secondary battery (high output specification, 18650 size) was assembled in the same manner as in Example 1.

The battery capacity of the thus obtained non-aqueous electrolyte secondary battery was implemented. The charging current value is 450 mA (0.
3C), the operation was performed up to 4.2 V at a constant current, and then the operation was performed at a constant voltage for 8 hours in total. Discharge was performed at a constant current of 300 mA to 2.7 V. The rest time after charging and discharging is 30
Minutes. The obtained discharge capacity was measured as the discharge capacity of the battery.

Further, the large current discharge characteristics of each battery were measured. As a method of defining the large current discharge characteristics, a method of defining the ratio by respective discharge capacities obtained when discharging at two current values is employed. That is, 1500 mAh, which is the design capacity of the battery, is discharged in one hour.
When the current of mA (1.5 A) is 1 C, the discharge capacity (0.2 C) when discharging at 0.2 C and the discharging capacity (10 C) when discharging at 5 C are measured. Discharge capacity (10 C) / discharge capacity (0.2
The value of C) is defined as a large current discharge capacity ratio, and will be used hereinafter in the text.

As a result, the non-aqueous electrolyte secondary battery produced in Example 1 had a battery capacity of 1511 mAh and a high current discharge ratio of 95%.

Comparative Example 1 A positive electrode slurry was obtained in the same manner as in Example 1. This was applied to a positive electrode current collector having a uniform thickness made of an aluminum foil having a thickness of 20 μm, and dried at a temperature of 110 ° C to 140 ° C. At this time, the active material layer was not applied to the end of the current collector, and the uncoated portion where the positive electrode layer was not formed on the current collector was continuously formed at the electrode end. The ratio of the width of the uncoated portion to the electrode width is 0.1.
And 2.

The electrode was heated at a total pressure of 1500 kgf / cm while controlling the temperature at 80 ° C. by a heated roller press.
It was rolled with a load of ² . However, wrinkles occurred on the electrode surface immediately after the start of rolling, and the electrode was broken shortly.
Next, the temperature was increased to 100 ° C. and the rolling was attempted, but the same result was obtained. Therefore, the rolling load is set to 1000 kgf / cm.
As a result of rolling down to ² , rolling and wrinkling and breakage of the positive electrode were no longer observed, but the packing density of the obtained positive electrode layer was 2.3 g / cm ³ .

The positive electrode was combined with the negative electrode obtained in Example 1 to assemble a cylindrical non-aqueous electrolyte secondary battery (high output specification 18650 size) in the same manner as in Example 1.

The battery capacity and the large current discharge ratio of the non-aqueous electrolyte secondary battery obtained in Comparative Example 1 were measured in the same manner as in Example 1, and found to be 1073 mAh and 88%, respectively.

Comparative Example 2 A positive electrode slurry was obtained in the same manner as in Example 1. This was applied to a positive electrode current collector having a uniform thickness made of an aluminum foil having a thickness of 20 μm, and dried at a temperature of 110 ° C to 140 ° C. At this time, the active material layer was not applied to the end of the current collector, and the uncoated portion where the positive electrode layer was not formed on the current collector was continuously formed at the electrode end. The ratio of the width of the uncoated portion to the electrode width is 0.1.
It was set to 15.

The electrode was heated at a total pressure of 1500 kgf / cm while controlling the temperature at 80 ° C. by a heated roller press.
It was rolled with a load of ² . However, immediately after the start of rolling, wrinkles occurred on the electrode surface, and eventually the electrode broke. Therefore, similarly to Comparative Example 1, the rolling load was set to 1000 kgf /
As a result of rolling to lower to ² cm ² , generation of wrinkles and breakage of the positive electrode were not recognized, but the packing density of the obtained positive electrode layer was 2.4 g / cm ³ .

The positive electrode and the negative electrode obtained in Example 1 were combined, and a cylindrical non-aqueous electrolyte secondary battery (high output specification 18650 size) was assembled in the same manner as in Example 1.

The battery capacity and the large current discharge ratio of the nonaqueous electrolyte secondary battery obtained in Comparative Example 2 were measured in the same manner as in Example 1. As a result, they were 1194 mAh and 89%, respectively.

[0092]

As described in detail above, according to the present invention,
Even if the rolling load is increased, wrinkling and breakage of the electrode can be prevented. Thus, according to the present invention,
A non-aqueous electrolyte secondary battery that can be manufactured by a simple method and has 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 nonaqueous electrolyte secondary battery showing an example of the present invention.

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

FIG. 3 is a perspective view showing a modified example of the positive electrode sheet according to the present invention.

FIG. 4 is a partially enlarged view of an upper end and a lower end of an electrode group 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 ... Current collecting lead for positive electrodes 13 ... Current collecting lead for negative electrodes 21 ... Current collecting Body 22 ... Positive electrode active material layer

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideaki Morishima 1st Toshiba R & D Center, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Yuji Sato Toshiba Komukai-shi, Kawasaki-shi, Kanagawa Shuji Yamada, Toshiba R & D Center, Ltd. (72) Inventor Shuji Yamada, Komukai Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Hideyuki Kanai, Kawayuki-shi, Kanagawa 1F, Komukai Toshiba-cho, Toshiba R & D Center, F-term (reference) BJ02 BJ14 CJ03 CJ05 CJ07 DJ05 DJ07 EJ01 HJ04 5H050 AA08 AA19 BA17 CA08 CA09 CB05 CB07 CB08 CB09 CB11 CB12 DA04 FA12 GA03 GA0 7 HA04

Claims (4)

[Claims] 1. A positive electrode sheet having a first current collector and a positive electrode active material layer formed on the surface of the first current collector, and a second current collector and a surface of the second current collector A negative electrode sheet having a negative electrode active material layer formed on, and an electrode group formed by winding a laminate having a separator containing a non-aqueous electrolyte sandwiched between the positive electrode active material layer and the negative electrode active material layer, A current collecting lead connected to each of the first and second current collectors, wherein at least one of the positive electrode sheet and the negative electrode sheet
A non-aqueous electrolyte secondary battery having a strip-shaped connection region connecting the current collector lead, exposing the first or second current collector at an end of the electrode group in a winding axis direction, The thickness of the connection region of the first or second current collector is larger than the thickness of the region where the positive electrode active material layer or the negative electrode active material layer is formed, wherein the non-aqueous electrolyte secondary battery. 2. The film thickness of the first and second electrodes is:
The non-aqueous electrolyte secondary battery according to claim 1, wherein the connection region and the region where the positive electrode active material layer or the negative electrode active material layer is formed are substantially equal. 3. The non-aqueous electrolyte according to claim 1, wherein the width of the connection region in the winding axis direction is 15% or less of the width of the current collector in the winding axis direction. Rechargeable battery. 4. A step of forming a positive electrode sheet on a surface of a first current collector having a positive electrode active material layer forming region and a belt-shaped current collecting lead forming region, followed by rolling to form a positive electrode sheet; Forming a negative electrode active material layer on the surface of the second current collector having a layer forming region and a band-shaped current collecting lead forming region, and then rolling to form a negative electrode sheet; and a current collecting lead of the first current collector Connecting a current collecting lead to each of the forming region and the current collecting lead forming region of the second current collector; forming a group of electrodes by winding a laminate in which a separator is sandwiched between the positive electrode sheet and the negative electrode sheet The first current collector, or the negative electrode active material layer, in which the thickness of the current collecting lead formation region is larger than that of the positive electrode active material layer formation region. Than the formation area Thickness of the serial current collector lead formation region rolling a large second current collector, the current collector lead formation regions,
A method for manufacturing a non-aqueous electrolyte secondary battery, comprising: disposing the electrode group at an end in the winding axis direction of the electrode group.