JP2000208129A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a high-density electrode active material layer reduced in deformation such as a corrugation or wrinkles generated in an electrode plate to facilitate flattening of the electrode plate and in electrode plate resistance. SOLUTION: A lithium secondary battery comprises an internal electrode body composed by winding positive and negative electrodes of a collector substrate coated with an electrode active material around a core circumference through a separator and a nonaqueous electrolyte. On a collector substrate 12 in an electrode active material non-coated area 7 formed on the end part in the width direction (Y-axis direction) of a positive electrode plate 2, a slit 21 parallel to the width direction of the charge collector substrate 12 is formed. Similarly, a negative electrode is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-density electrode active material layer which reduces distortion such as waving and wrinkles generated in an electrode plate, promotes flattening of the electrode plate, and reduces resistance of the electrode plate. And a lithium secondary battery having:

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, since lithium secondary batteries have a high energy density, not only the portable electronic devices but also electric vehicles (eg, electric vehicles, which are being actively spread as low-emission vehicles due to recent environmental problems). It is also attracting attention as a motor drive power supply for EVs or hybrid electric vehicles (HEVs).

[0003] Here, in order to obtain predetermined acceleration performance, uphill performance, continuous running performance, and the like, the EV battery has a large capacity,
High power is first required. For this reason,
It is necessary to increase the electrode area in the electrode body for performing the battery reaction. Therefore, in the EV battery, as shown in FIG. 1, a wound body constituted by winding the positive electrode plate 2 and the negative electrode plate 3 around the outer periphery of the core 9 with the separator 4 interposed therebetween is used as the internal electrode body. At the ends in the width direction of the positive electrode plate 2 and the negative electrode plate 3, that is, near the end surfaces in the length direction of the internal electrode body 1, the positive electrode tabs 5 ( Hereinafter, a "tab 5") and a negative electrode tab 6 (hereinafter, referred to as a "tab 6") are provided.

Here, the manufacturing process of the positive electrode plate 2 will be described in more detail. Generally, the positive electrode plate 2 is formed of a band-shaped metal foil such as an aluminum foil as a current collecting substrate (hereinafter, simply referred to as “substrate”). Using, the positive electrode active material slurried on both surfaces of this substrate is applied, and after drying, further using a roll press or the like,
It is manufactured by applying a continuous pressure in the length direction of the positive electrode plate 2. The press treatment by a roll press or the like is performed mainly for the purpose of increasing the density of the positive electrode active material layer, increasing the contact area of the positive electrode active material particles, and reducing the internal resistance. Since the tab 5 needs to be directly attached to the substrate, the application of the positive electrode active material is not performed on at least one end in the width direction of the substrate.

Therefore, the surface of the produced positive electrode plate 2
As shown in FIG. 2, at least one electrode active material uncoated region 7 (hereinafter, referred to as “uncoated region”) formed at the end of the positive electrode plate 2 in the Y-axis direction, which is the width direction. An electrode active material coating region 8 (hereinafter, referred to as a “coating region”, and the coating region is an electrode active material layer). Forming the uncoated region 7 and providing a plurality of tabs 5 in the uncoated region 7 can reduce the current collection resistance and increase the battery It is indispensable for reducing the internal resistance. The negative electrode plate 3 is manufactured in the same manner as the positive electrode plate 2 by coating a negative electrode active material on both surfaces of a metal foil such as a copper foil as a substrate.

[0006]

As described above, an electrode plate (a positive electrode plate and a negative electrode plate) is applied after coating an electrode active material (a positive electrode active material and a negative electrode active material) on a substrate, as described above. ) When pressure is applied by a roll press,
Due to the thickness difference, pressure is applied only to the coating area,
No pressure is applied to one uncoated area. For example, while the thickness of the substrate is about 10 to 20 μm, the thickness of the electrode active material layer is about 100 μm, so that the thickness difference between the coated area and the uncoated area is obvious.

For this reason, pressure is transmitted to the substrate portion directly below the coating region via the electrode active material layer, but the pressure is not applied to the substrate portion in the non-coating region. Causes a tensile stress in the longitudinal direction of the substrate. As a result, distortion was concentrated particularly at the boundary between the uncoated region and the coated region, and usually, wavy and wrinkles were generated.

In the case of using an electrode plate having such waving or the like, the workability of attaching the tab at the time of winding is reduced, and a fold having a large gap is formed on the end face of the internal electrode body. As a result, a gap is formed between the electrode active materials, which causes a problem that the internal resistance of the battery increases. On the other hand, when the pressure of the roll press is reduced so as not to cause waving or the like, the packing density of the electrode active material decreases, the contact area between the electrode active material particles decreases, and the internal resistance increases.

[0009] Such a problem does not occur in a small battery when a wound internal electrode body is used. The reason for this is that, in a small battery, as shown in FIG.
Only one end portion in the length direction (X-axis direction) of one electrode is sufficient, so that the application of the electrode active material 93 can be performed over the entire width of the electrode plate 91 (Y-axis direction). That is, the distortion in the width direction hardly occurs even when the pressing is performed, and the distortion generated when the pressing is performed is smaller than that in the case of a large-area electrode plate.

[0010]

Means for Solving the Problems The present invention has been made in view of such problems of the prior art, and has as its object to increase the internal resistance of a large-area electrode plate. Another object of the present invention is to provide a lithium secondary battery having good battery characteristics by producing an electrode plate excellent in winding workability while preventing occurrence of waving or the like.

That is, according to the present invention, an internal electrode body and a non-aqueous electrolyte obtained by winding a positive electrode plate and a negative electrode plate each formed by coating an electrode active material on a current collecting substrate around the outer periphery of a core through a separator. In the lithium secondary battery using, the current collector substrate in the electrode active material uncoated region formed at the width direction end of the positive electrode plate and the negative electrode plate, in the width direction of the current collector substrate A lithium secondary battery is provided, wherein a parallel slit is formed. Here, it is preferable that the slit is formed so as to reach a boundary between the electrode active material coated region and the electrode active material uncoated region.

Further, according to the present invention, an internal electrode body and a non-aqueous electrolyte obtained by winding a positive electrode plate and a negative electrode plate each formed by coating an electrode active material on a current collecting substrate around a core around a separator. In the lithium secondary battery using, the positive electrode plate and the electrode active material uncoated region in the negative electrode plate, after forming an electrode active material layer on the entire surface of the current collecting substrate,
There is provided a lithium secondary battery formed by removing a part of the electrode active material layer. Here, the removal of the electrode active material layer is suitably performed by trimming with a laser, peeling using an organic solvent, or peeling off a masking material previously applied or pasted to a current collecting substrate.

[0013] In the positive electrode plate and the negative electrode plate used in the lithium secondary battery of the present invention, a metal foil is preferably used as a current collecting substrate, and a plurality of collectors are formed in the electrode active material uncoated region. A power tab is attached. Further, the positive electrode plate and the negative electrode plate are produced by applying a roll press treatment after coating the electrode active material. The lithium secondary battery of the present invention
The present invention is suitably applied to a battery having a large battery capacity of Ah or more, and has excellent productivity and battery characteristics, and thus is suitably used as a motor driving power source of an electric vehicle or a hybrid electric vehicle.

[0014]

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. The configuration of the wound internal electrode body used in the lithium secondary battery of the present invention is the same as that shown in FIG. 1 described above. That is, the internal electrode body 1
Is formed by winding the positive electrode plate 2 and the negative electrode plate 3 around the outer periphery of the core 9 via the separator 4.

FIG. 3 is an explanatory view showing one embodiment of a method for producing the positive electrode plate 2 suitably used for the lithium secondary battery of the present invention. The current collecting substrate 12 (hereinafter, referred to as the positive electrode plate 2)
It is described as “substrate 12”. As (12), a metal foil having good corrosion resistance to a positive electrode electrochemical reaction, such as an aluminum foil or a titanium foil, is used. As shown in FIG. 3A, the substrate 12 before the application of the positive electrode active material is in a state of a single band.

In addition, as the substrate 12, a punched metal or a mesh (net) in which a plurality of holes are formed by punching can be used. Also in the case of using these, similarly to the case of using a metal foil described later,
The effect of stress relaxation in the press treatment intended by the present invention can be obtained.

A positive electrode active material is applied to the substrate 12.
Here, as the positive electrode active material, lithium transition metal composite oxides such as lithium manganate, lithium cobaltate, and lithium nickelate are preferably used, and preferably, carbon fine powder such as acetylene black is added to the conductive auxiliary material. Is added. A slurry or paste prepared by adding a solvent, a binder, or the like to such a positive electrode active material powder is applied to a width direction (Y-axis direction) of the substrate 12 by using a roll coater method or the like.
While forming the uncoated region 7 at least at one end of
A coating region 8 is formed by applying and fixing both surfaces of the substrate 12. FIG. 3B shows a form in which the uncoated region 7 is formed at both ends in the width direction of the substrate 12 with a constant width.

Subsequently, as shown in FIG.
In the present invention, a slit 2 parallel to the width direction is formed in the uncoated region 7 thus formed at the end in the width direction of the substrate 12.
Then, a pressing process is performed. In the pressing process of the electrode plate which is long in one direction as in the positive electrode plate 2 by the pressing process, the positive electrode plate 2 is continuously pressed by a roll press so that the positive electrode plate 2 passes between the rolls in the length direction (X-axis direction). As shown in FIG. 3D, the thickness of the positive electrode active material layer in the coating region 8 of the positive electrode plate 2 is reduced while maintaining a constant thickness, as shown in FIG. Is achieved. Here, the number of times of roll pressing is not limited to one, and it is also preferable to gradually reduce the thickness of the coating region over several times.

In the pressing process, the coating area 8
Since no pressure is applied to the uncoated area 7 which is thinner than
Tensile stress is generated in the length direction in the substrate portion immediately below the coating region 8, and strain is particularly concentrated on the boundary between the uncoated region 7 and the coating region 8. Since the slit 21 is formed, the tensile stress is relaxed by the slit 21, and as a result, it is possible to avoid the generation of waving and wrinkles at the width direction end of the positive electrode plate 2.

In order to make the stress relaxation effective, it is preferable that the slit 21 is formed so as to reach the boundary between the coated region 8 and the uncoated region 7. Such a slit 21 can be formed on the substrate 12 in advance before coating the slurry of the positive electrode active material or the like,
Considering that there is a possibility that the slurry flows out through the slit 21 and that there is a possibility that the positive electrode active material formed on the slit 21 may be broken at the time of winding or the like and adversely affect other normal parts. The formation of the slits 21 is preferably performed after the coating of the positive electrode active material and before the press treatment.

It goes without saying that the negative electrode plate 3 can be manufactured in the same manner as the positive electrode plate 2. As the current collector of the negative electrode plate 3, a metal foil having good corrosion resistance to a negative electrode electrochemical reaction such as a copper foil or a nickel foil is used. As a negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon is used. Alternatively, highly graphitized carbonaceous powders such as artificial graphite and natural graphite are used.

As shown in FIG. 1, the positive electrode plate 2 and the negative electrode plate 3 which are excellent in flatness are combined with the core 9 so that the positive electrode plate 2 and the negative electrode plate 3 do not come into contact with each other via the separator 4 as shown in FIG. By winding it around the outer periphery, the internal electrode body 1 with less distortion in shape can be obtained. Here, as the separator 4, a lithium ion permeable polyethylene film having micropores (PE film) and a porous lithium ion permeable polypropylene film (P
A three-layer structure sandwiched between P films) is preferably used. This is because when the temperature of the internal electrode body rises,
The PE film softens at about 130 ° C. and the micropores are crushed, which also serves as a safety mechanism for suppressing the movement of lithium ions, that is, the battery reaction. By sandwiching this PE film between PP films having a higher softening temperature, even when the PE film is softened, PP
The contact between the positive electrode plate 2 and the negative electrode plate 3 while maintaining the shape of the film
Short-circuits can be prevented, and battery reaction can be reliably suppressed and safety can be ensured.

At the time of this winding operation, tabs 5 and 6 are attached to uncoated areas 7 formed on the positive electrode plate 2 and the negative electrode plate 3, respectively. As the tabs 5 and 6, the positive electrode plate 2
A foil-like material made of the same material as the metal foil as the substrate of the negative electrode plate 3 is preferably used. In this case, tabs 5 and 6
And the uncoated area 7 can be welded to each other between the surfaces, so that even if the slit 21 is formed in the uncoated area 7, there is no hindrance in attaching the tabs 5 and 6.

The attachment of the tabs 5 and 6 to the uncoated area 7 can be performed using ultrasonic welding, spot welding, or the like. At this time, as shown in FIG. 1, the tabs 5 and 6 are arranged such that one tab is disposed on one end surface of the internal electrode body 1.
It is preferable to attach each of them to prevent contact between the tabs 5 and 6, which is preferable.

The produced internal electrode body 1 is inserted and placed in a battery case while ensuring conduction between terminals for extracting current to the outside and the tabs 5 and 6, and impregnated with a non-aqueous electrolyte. After that, a battery is manufactured by sealing the battery case.

Here, it goes without saying that the shape of the battery case and the structure at the battery end are not particularly limited.
FIG. 5 is a cross-sectional view showing one embodiment of a battery using the obtained internal electrode body 1. The tabs 5 and 6 of the internal electrode body 1
The rivets used as the positive electrode internal terminal 74A (made of aluminum) and the negative electrode internal terminal 74B (made of copper) are collectively connected by caulking. The positive electrode internal terminal 74A is a positive electrode lid 71A made of aluminum.
And a female screw-shaped positive external terminal 73A also made of aluminum is bonded to the positive electrode lid 71A. The positive electrode cover 71 is provided below the positive external terminal 73A.
An electrolyte injection port 77 is provided so as to penetrate A.

The structure on the negative electrode side is the same as that on the positive electrode side,
A copper member is preferably used for all of the negative electrode internal terminal 74B, the negative electrode cover 71B, and the externally threaded negative electrode external terminal 73B.
However, the electrolyte inlet 77 is not provided in the negative electrode lid 71B. It is preferable that the external terminals 73A and 73B of the respective poles be set in a complementary shape so as to facilitate the mutual coupling, because the series connection between the batteries 50 can be easily performed. In the battery 50, the battery 50 may be rotated to screw the negative external terminal 73B into the positive internal terminal 73A.

Projection 81 formed on battery case 72
Is formed by inserting the internal electrode body 1 to which the positive and negative internal terminals 74A and 74B are attached into the cylindrical battery case 72, and then drawing the battery case 72 near both ends of the internal electrode body 1. You. Then, the battery case 72
Are formed by caulking both ends of the battery case 72 by using a sealing material 82 made of an insulating material so as to prevent conduction between the battery case 72 and the lids 71A and 71B of the positive and negative electrodes. In addition, an insulating polymer film 79 is disposed between the internal electrode body 1 and the inner peripheral surface of the battery case 72, and in the present invention, it is preferable to use a porous film having air permeability.

To fill the battery with the non-aqueous electrolyte in the battery 50, the battery 50 is placed under a reduced pressure atmosphere with the electrolyte inlet 77 facing upward, and penetrates through the electrolyte inlet 77 and the hollow portion of the core 9. So that the electrolyte injection nozzle is inserted into the bottom of the battery, a predetermined amount of the electrolyte is injected, and the internal electrode body 1 is sufficiently impregnated.
Unnecessary electrolytic solution can be easily discharged using a method of discharging the electrolytic solution with an electrolytic solution injection nozzle and sealing the electrolytic solution injection port 77 with a screw or the like.

Examples of the non-aqueous electrolyte include carbonate-based solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC), and organic solvents such as propylene carbonate (PC), γ-butyrolactone, tetrahydrofuran, and acetonitrile. In a single solvent or a mixed solvent of solvents, L as an electrolyte
A non-aqueous electrolyte in which one or two or more lithium complex fluorine compounds such as iPF ₆ and LiBF ₄ or lithium halides such as LiClO ₄ are dissolved is preferably used.

When an abnormally large current flows through the lithium secondary battery due to an internal short circuit, an external short circuit, or the like, the battery temperature rises rapidly, the electrolyte evaporates, and the battery internal pressure rises sharply. Various pressure relief valves are provided to prevent accidental battery rupture. Although such a pressure relief valve is not shown in FIG. 5, the present inventors have previously disclosed in Japanese Patent Application No. 10-165213 various pressure relief valves (pressure release valves) using a V-shaped groove or metal foil. Mechanism). Such a pressure relief valve is suitably applied to the lithium secondary battery of the present invention.

Next, another method for manufacturing an electrode plate used in the lithium secondary battery of the present invention will be described with reference to FIG. As described above, the coated area 8 and the uncoated area 7
Is caused by the difference in thickness between the coated region 8 and the uncoated region 7, and thus, it is possible to suppress the occurrence of tensile stress by eliminating the thickness difference during the press processing. It is considered possible. Therefore, in the present invention, the uncoated region 7 in the positive electrode plate 2 and the negative electrode plate 3 is formed after forming the electrode active material layer (coated region 8) on the surface of the substrate 12, and then forming the electrode active material layer (coated region). The method of forming by removing a part of 8) is used.

That is, the positive electrode plate 2 will be described. When the positive electrode active material is coated on the entire surface of the substrate 12 shown in FIG. 4A, the entire surface of the substrate 12 is coated as shown in FIG. The positive electrode plate 2 including the processing region 8 and having no uncoated region 7 is manufactured. Even if the positive electrode plate 2 is pressed by a roll press in this state, the positive electrode plate 2 itself does not have a slight thickness variation of about the thickness variation due to the application of the positive electrode active material. A uniform pressing process can be performed over the entire surface. In this manner, the occurrence of tensile stress on the substrate 12 is suppressed, so that the occurrence of waving and wrinkles at the end in the width direction of the positive electrode plate 2 is avoided.
As shown in (c), the positive electrode plate 2 in which the thickness of the coating region 8 is reduced is obtained.

After the pressing, the electrode active material at the end in the width direction in the coating region 8 is removed, whereby the uncoated region 7 can be formed, and the positive electrode plate 2 having excellent flatness can be obtained. Can be. At this time, as shown in FIG. 4D, the uncoated region 7 may be formed with a constant width at the width direction end of the positive electrode plate 2, while, as shown in FIG. Alternatively, the uncoated region 7 may be formed only in the portion where the tab 5 is attached and in the vicinity thereof. The negative electrode plate 3 is similarly manufactured.

The removal of the electrode active material layer from the coating region 8 in such a method for manufacturing an electrode plate is performed by the fourth harmonic Y.
Trimming using an AG laser, excimer laser, or the like is preferable because it can be performed in a dry manner with good shape accuracy and in a short time. Further, since the electrode active material layer is formed by drying a slurry or the like prepared by adding a solvent, the binder between the electrode active material particles is partially released by the binder using an organic solvent, and the electrode active material layer is formed. It is also possible to elute from the material layer.

Further, on the substrate before the slurry of the electrode active material is applied, a masking material is applied or affixed to a portion to be finally uncoated region 7 so as not to cause waving or the like by press processing. In addition, after applying and pressing the electrode active material, the masking material can be easily peeled off from the substrate, and at the same time, the electrode active material layer on the masking material can be peeled off. Examples of the masking material include a masking tape and a curable resin.

Although the embodiment of the lithium secondary battery of the present invention using the electrode plate having low resistance and excellent flatness has been described above, from the above-mentioned point, the uncoated area of the electrode active material in the electrode plate. Is provided with a plurality of tabs. That is, the present invention is suitably applied to a large-capacity battery that needs to be collected at a plurality of locations. Battery capacity is 2A
h or more.

Further, the lithium secondary battery of the present invention has good charge / discharge characteristics due to low internal resistance.
Since the productivity in manufacturing the internal electrode body is good, it can be suitably used as a power supply for driving a motor of an electric vehicle or a hybrid electric vehicle which requires high reliability and low cost.

[0039]

As described above, according to the lithium secondary battery of the present invention, an internal electrode body having small shape distortion can be manufactured using an electrode plate having low resistance and excellent flatness. Battery reaction is uniformly induced in the body,
Thereby, a remarkable effect of obtaining a battery having excellent charge / discharge characteristics is recognized. In addition, productivity is improved as compared with the case where a conventional electrode plate having poor flatness is used, and the effect of reducing cost is also achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a general structure of an internal electrode body used for a lithium secondary battery.

FIG. 2 is a plan view of a positive electrode plate (electrode plate) used in a lithium secondary battery.

FIG. 3 is an explanatory view showing an example of a method for manufacturing a positive electrode plate (electrode plate) suitably used for the lithium secondary battery of the present invention.

FIG. 4 is an explanatory view showing another example of a method for manufacturing a positive electrode plate (electrode plate) suitably used for the lithium secondary battery of the present invention.

FIG. 5 is a cross-sectional view showing one embodiment of a battery structure suitably adopted for the lithium secondary battery of the present invention.

FIG. 6 is a plan view showing one embodiment of a structure of an electrode plate used in a conventional small lithium secondary battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Positive electrode tab, 6 ... Negative electrode tab, 7 ... Electrode active material uncoated area (uncoated area), 8 ... Electrode active material coating area (coating area), 9: winding core, 12: current collecting substrate (substrate), 2
DESCRIPTION OF SYMBOLS 1 ... Slit, 50 ... Battery, 71A ... Positive electrode cover, 71B ...
Negative electrode cover, 72: battery case, 73A: positive electrode external terminal, 7
3B: negative external terminal, 74A: positive internal terminal, 74B:
Negative electrode internal terminal, 77: electrolyte injection port, 79: insulating film, 81: protrusion, 82: sealing material, 91: electrode plate, 9
2. Tab, 93: Electrode active material.

Continued on the front page F term (reference) 5H022 AA09 AA18 BB01 BB02 BB17 BB21 CC12 CC19 CC22 5H029 AJ02 AJ14 AK03 AL06 AL07 AL08 AM03 AM04 AM05 AM07 BJ02 BJ14 CJ03 CJ04 DJ05 DJ07

Claims (9)

[Claims] 1. An internal electrode body obtained by winding a positive electrode plate and a negative electrode plate each having a current collector substrate coated with an electrode active material around a winding core via a separator, and a lithium secondary battery using a nonaqueous electrolyte. In the secondary battery, a slit parallel to the width direction of the current collecting substrate is formed in the current collecting substrate in the electrode active material uncoated region formed at the width direction end of the positive electrode plate and the negative electrode plate. A lithium secondary battery characterized by the following. 2. The lithium secondary battery according to claim 1, wherein the slit reaches a boundary between the electrode active material coated region and the electrode active material uncoated region. 3. An internal electrode body obtained by winding a positive electrode plate and a negative electrode plate each having a current collector substrate coated with an electrode active material around the outer periphery of a core through a separator, and a lithium secondary battery using a nonaqueous electrolyte. In the secondary battery, after the electrode active material uncoated region in the positive electrode plate and the negative electrode plate forms an electrode active material layer on the entire surface of the current collecting substrate, a part of the electrode active material layer is removed. And a lithium secondary battery formed by the above-described method. 4. The method according to claim 1, wherein the removal of the electrode active material layer is performed by trimming with a laser, elution using an organic solvent, or peeling of a masking material previously applied or affixed to the current collecting substrate. Claim 3
The lithium secondary battery as described in the above. 5. The lithium secondary battery according to claim 1, wherein the current collecting substrate is a metal foil. 6. The lithium secondary battery according to claim 1, wherein a plurality of current collecting tabs are attached to the electrode active material uncoated region. 7. The lithium secondary battery according to claim 1, wherein said positive electrode plate and said negative electrode plate are roll-pressed after application of an electrode active material. Next battery. 8. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is used as a power supply for driving a motor of an electric vehicle or a hybrid electric vehicle. 9. The lithium secondary battery according to claim 1, having a battery capacity of 2 Ah or more.