JPH11273661A - Sheet electrode for battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve volume energy density, discharge capacity and power density, and to stabilize quality by connecting current collecting tabs in the width direction of the current collecting metalic sheet surface, and forming an electrode active material layer by coating on the current collecting metallic sheet surface from above the current collecting tabs. SOLUTION: Paper strip-like current collecting tabs 2 are connected at prescribed intervals in the lengthwise direction of the current collecting metallic sheet 1 surface to a sheet electrode 3 by ultrasonic welding in the welding part 2a. An electrode active material layer 4 is formed by coating over the whole surface of a current collecting metallic sheet 1 from above these current collecting tabs 2. The joining area of the current collecting tabs 2 and the current collecting metallic sheet 1 is secured large by cutting down a noncoating edge area of the current collecting metallic sheet 1 surface, and the length of a battery can is reduced to realize high performance/compactness. Since a noncoating area of an electrode active material is practically eliminated, deformation of the current collecting electrode sheet 1 is avoided when wound in a roll shape to eliminate damage and winding dislocation of an electrode by uniformizing tensile force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet electrode for a battery, and more particularly to a sheet electrode for a battery suitable for a lithium secondary battery and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a lithium secondary battery is generally constructed as shown in FIG.
As shown in FIG. 1, a positive electrode sheet 52 and a negative electrode sheet 5 are placed in a battery case 50 filled with a non-aqueous electrolyte.
4 are arranged spirally via a separator 56, and a safety valve (explosion-proof valve) 58 which is deformed when the internal pressure of the battery rises is provided at the opening on the upper surface of the battery case 50. A polyswitch plate (PTC element) 60 for blocking the flow of the current and a sealing cap (lid) 62 are mounted via an insulating gasket 64.

Various forms of battery sheet electrodes for lithium secondary batteries are known. For example, an electrode active material is coated on both sides of a current collector sheet in advance, and then the current collector sheet is coated with an electrode active material. In order to connect a lead member such as a current collecting tab or a lead plate to the electrode sheet, a material obtained by partially removing the electrode active material on the electrode sheet surface is often used.

For example, Japanese Unexamined Patent Publication No. 1-255555 discloses a method in which an electrode active material laminated on both sides of a current collector sheet is pressed against an ultrasonic horn against the surface of the current collector sheet by ultrasonic vibration. It is obtained by pulverization and removal, and a lead plate is welded to the exposed portion.

In Japanese Patent Application Laid-Open No. 8-167410, a mask sheet is applied to partially remove an electrode active material applied to a current collector sheet, and a fluid such as water is applied to the opening of the current collector sheet under high pressure. An electrode is disclosed in which the electrode active material is crushed and removed at that portion, and a lead member such as a current collecting tab or a lead plate is connected thereto.

On the other hand, a sheet electrode for a large battery such as an electric vehicle has a length of 5 m or more, and the number of lead members such as current collecting tabs may be as large as 50 or more. Therefore, in the sheet electrode for a large battery, the electrode active material is not removed to connect the lead member for current collection after coating, but a width of 5 to 10 mm is applied to one end of the sheet electrode to weld the lead member. The one that leaves a portion where the current collector sheet is exposed (uncoated portion) is adopted.

As a manufacturing process of a battery sheet electrode having such a configuration, first, as shown in FIG. 5A, a current collector sheet 10 made of a strip-shaped (strip-shaped) metal material having a predetermined width is used. A paste in which the electrode active material is dissolved in a solvent is continuously applied to the surface (actually, both surfaces) while being sequentially fed. At this time, uncoated portions 3a and 3b to be cut off later are provided at both end edges in the width direction of the current collector sheet 10, but the uncoated portions 3a on the side to which the current collecting tab 2 is welded are large. And the width.

After the application of the electrode active material, one uncoated portion 3b is cut off, and the other uncoated portion 3a is cut while leaving a connection portion of a current collecting tab. The dotted line in FIG.
A cutting line is shown. After cutting, the current collector sheet 10 coated with the electrode active material is pressed under pressure to form the coated portion 3c with a predetermined thickness or density. 2), the current collecting tab 2 is connected to the edge of the current collector sheet 10 on the uncoated portion 3a side.

[0009]

However, the above-mentioned conventionally known sheet electrodes for batteries have various problems. First, in a device manufactured by grinding and removing an electrode active material using an ultrasonic horn disclosed in Japanese Patent Application Laid-Open No. 1-251555, when an ultrasonic vibration is applied to the electrode sheet surface in the manufacturing process, the electrode In addition to removing the active material, there is a problem that the electrode sheet is damaged and the electrode sheet is cracked.

[0010] On the other hand, in a device disclosed in JP-A-8-167410 manufactured by injecting a fluid at a high pressure and pulverizing and removing the electrode active material, damage to the electrode sheet in the manufacturing stage is reduced. However, since the electrode active material at the point where the lead member is welded is not completely removed,
There is a problem that poor welding occurs. Particularly, in an electrode manufactured to improve the cycle characteristics, the electrode active material has a high adhesion force, so that the effect appears very large.

In order to manufacture this sheet electrode,
It is necessary to prevent the fluid from being scattered in places other than the target location, and a device for that purpose becomes very complicated. In addition, in the vicinity of the target portion, even if the fluid does not directly hit, the adhesive force of the electrode active material is reduced, so that there is a problem that the electrode characteristics are reduced. Furthermore, since it is necessary to dry the fluid after finishing the ejection of the fluid,
Sheets cannot be supplied continuously, and it must be said that productivity is poor.

Next, a conventional sheet electrode in which an uncoated portion for welding a lead member to a current collector sheet surface is left is disclosed in Japanese Patent Application Laid-Open Nos. 1-251555 and 8-167.
Although there is no problem with the publication No. 410, that is, there is no problem such as damage to the electrode sheet, poor welding, or the inability to manufacture continuously, it cannot be said to be complete due to the following reasons.

In the sheet electrode having the conventional uncoated portion, a large portion of the uncoated portion does not contribute to the electrode reaction and is not used for welding the lead member. Therefore, there is a problem that battery performance is impaired. Further, in this sheet electrode, current collection is performed only at one end of the electrode, so that current collection efficiency is poor and load characteristics and power characteristics of the battery are low.

Further, in this electrode, the thickness of the coated portion and the thickness of the uncoated portion are different, so that only the thick coated portion is compressed when pressed and pressed, and the electrode sheet is greatly curved. When a battery is manufactured using a bent electrode sheet, uniform tension cannot be applied to the electrode sheet in the winding process when the electrode sheet is spirally arranged as shown in FIG. In addition, there has been a problem that winding deviation and damage to the electrode sheet are caused.

The problem to be solved by the present invention is to improve the volume energy density, discharge capacity and power density of a battery, and to obtain a uniform tension when wound into a roll, thereby improving quality. An object of the present invention is to provide a stable battery sheet electrode and a method for manufacturing the same.

[0016]

In order to solve this problem, a battery sheet electrode according to the present invention has a current collecting tab connected in a width direction of a current collecting metal sheet surface, and the current collecting tab. The gist is that an electrode active material layer is formed by coating on the surface of the metal sheet for current collection from above the tab.

Further, in the method for manufacturing a sheet electrode for a battery according to the present invention, a tab connecting step of connecting a current collecting tab to a current collecting metal sheet surface in advance, and the current collecting tab is joined by the tab connecting step. An electrode active material layer coating step of coating and forming an electrode active material on the surface of the formed current collecting metal sheet, and a current collecting metal sheet having an electrode active material layer formed by the electrode active material layer coating step. The method further comprises an uncoated area cutting step of cutting off an uncoated edge area of the surface.

In this case, the current-collecting metal sheet includes:
A conductive metal foil such as aluminum, nickel, and stainless steel is applied.

The current collecting tab is usually provided with one tab in the longitudinal direction of the metal foil.
Or a plurality of two or more batteries are attached at a predetermined interval.
The number may be as large as zero or more.

As the electrode active material, in the case of a lithium secondary battery, for the positive electrode, one prepared by mixing lithium cobaltate, lithium manganate, or the like with a conductive material such as carbon black or graphite and a binder resin such as polyvinylidene fluoride. It is used as a suitable material, and for the negative electrode, one obtained by blending a binder resin with mesocarbon microbeads or the like as a negative electrode active material is used.

The joining portion of the current collecting tab may be connected to one end of the current collecting metal sheet in the width direction, but is preferably joined over the entire width of the current collecting metal sheet in the width direction. In this case, the current collection efficiency is improved by increasing the bonding area between the current collecting tab and the current collecting metal sheet, and the load characteristics and the power density are improved. As the joining method, for example, ultrasonic welding or the like is mentioned as a suitable joining method.

The method for applying the electrode active material layer includes brushing, roll coating and the like. In that case,
The productivity can be increased by performing continuous coating while conveying the current collector metal sheet in a certain direction.

When cutting the uncoated edge region of the current collecting metal sheet, only the uncoated portion of the current collecting metal sheet is cut off while leaving the current collecting tab. At this time, if the current collecting tab is in the way, the current collecting tab may be bent. As a cutting method, a slitter or the like is used.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 1 shows a plan view of a sheet electrode according to one embodiment of the present invention, and FIG. 2 shows a cross-sectional view thereof. The sheet electrode 3 is connected to the current collecting metal sheet 1 by ultrasonic welding at a predetermined interval in the longitudinal direction of the surface of the current collecting metal sheet 1 at the welding portion 2a. The electrode active material layer 4 is formed by coating over the entire surface of the current collecting metal sheet 1.

The current collecting metal sheet 1 is made of aluminum foil,
Nickel foil, stainless steel foil or the like is used. In this embodiment, an aluminum foil having a thickness of 15 μm is used, and its width is set to 50 mm.

The current collecting tab 2 having a thickness of 30 μm and a width of 10 mm is connected over substantially the entire width of the current collecting metal sheet 1. Further, in this example, lithium manganate, carbon black, and polyvinylidene fluoride were used as the electrode active material in a weight ratio of 90: 5: 5.
Is used.

Next, FIGS. 3A to 3C show steps of manufacturing the sheet electrode of this embodiment, which will be described in order. First, in the step of FIG. 3A, a roll-shaped current collecting metal sheet 1 is formed.
And the current collecting tabs are joined at predetermined intervals in the longitudinal direction of the current collecting metal sheet 1 by ultrasonic welding. In this embodiment, the current collecting metal sheet 1 has a thickness of 15 mm.
μm × a 60 mm width aluminum foil is used, and the current collecting tab is 100 m in the longitudinal direction of the current collecting metal sheet 1.
They are joined at an interval of m.

In this case, the thickness of the current collecting tab 2 is 3
0 μm, width 10 mm, length of weld 2 a is 45 m
m. Ultrasonic welding is a process in which an ultrasonic horn is pressed against a welded joint and the horn is laterally vibrated to generate frictional heat and perform welding.
Ultrasonic welding is used in this embodiment because it can be used for joining difficult-to-weld metals and is suitable for welding fine structures and fine wires.

Next, an electrode active material layer coating step of coating and forming an electrode active material on the surface of the current collecting metal sheet 1 to which the current collecting tabs 2 are joined in the tab connecting step will be described with reference to FIG. Will be explained. First, a paste in which an electrode active material is dissolved in an organic solvent or the like is prepared. As a composition of this paste, an electrode sheet used as a positive electrode uses lithium manganate as a positive electrode active material, carbon black as a conductive material, polyvinylidene fluoride as a binder resin, and n-methyl-2-pyrrolidone as a solvent. I have.

Then, a paste prepared by dissolving an electrode active material prepared in advance is applied to the above-mentioned current collecting metal sheet 1 so as to leave uncoated portions 3a having a width of 3 mm at both end edges. Coating is performed to a thickness of 70 μm to form a coated portion 3c. In this coating step, the thickness of the current collecting tab 2 welded in the welding step is smaller than the coating thickness, so that the paste in which the electrode active material is dissolved in the solvent is passed through the predetermined clearance onto the current collecting metal sheet 1. A method of continuous coating was used. At the stage where this coating step is completed, there is no step between the current collecting tab 2 and the current collecting metal sheet 1 which has been present, and the current collecting metal sheet 1 to which the current collecting tab 2 is welded.
Has a uniform thickness.

Next, an uncoated area cutting step of cutting off an uncoated edge area of the current collecting metal sheet 1 on which the electrode active material layer has been formed by the electrode active material layer coating step is shown in FIG. ). First, the current collecting tab 2 is bent at the boundary between the welded portion and the non-welded portion to prevent the current collecting tab 2 from being cut off. In FIG. 3C, the dotted line indicates a cutting line by the slitter. In the present embodiment, the specific position of the cutting line is such that both end edges of the current collecting metal sheet 1 are cut off by 5 mm. did. The cutting line in this embodiment is selected so that the uncoated portion 3a is completely eliminated. The cutting method is to cut off the uncoated portions 3a at both ends of the current collecting metal sheet using a slitter along a predetermined cutting line.

Through the above-described steps, a sheet electrode 3 having a width of 50 mm in which the electrode active material is coated on the entire surface of the current collecting metal sheet 1 as shown in FIG. 1 is obtained. Finally, the sheet electrode 3 is passed through a pair of pressure rolls in a pressurized state so that the sheet electrode 3 has a predetermined thickness or density, and the electrode active material is pressed onto the current collecting metal sheet 1 by pressing. ,
The sheet electrode of the present embodiment is obtained.

Next, an evaluation test was performed on the above-mentioned example products. Specifically, the welding junction area of the current collecting tab, the length of the battery can, the volume energy density, the discharge capacity, and the power density were measured and summarized in Table 1. The battery can used in this experiment has the form shown in FIG. 4 described above. As the non-aqueous electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) in an equal volume of lithium phosphide ( LiPF ₆ ) was used in which an electrolyte was dissolved at a rate of 1 mol / l.

[0034]

[Table 1]

The negative electrode sheet of the battery can is composed of mesocarbon microbeads as a negative electrode active material and polyvinylidene fluoride as a binder resin in a weight ratio of 90:10.
And a material dissolved in n-methyl-2-pyrrolidone was used, and a copper foil was used as a metal sheet for current collection.

As the comparative product, the one manufactured according to FIG. 5 described as the prior art was used. By the way, this comparative product is 10mm at both ends of 70mm wide current collector metal sheet.
The electrode active material is applied over a width of 50 mm except for the end of each part.
b is cut off (with a width of 10 mm), and the edge to which the current collecting tab is joined is obtained by cutting off the uncoated portion 3a by a width of 5 mm and leaving a width of 5 mm for tab connection. A 30 μm thick, 10 mm wide current collecting tab was welded to the uncoated portion having a width of 5 mm by ultrasonic waves over a length of 5 mm in the width direction of the metal sheet. FIG. 6 shows a cross-sectional view of this comparative product.

The examples are evaluated against comparative examples. First, with respect to the welded joint portion, in Examples and Comparative Examples, there is no residue that is a problem in welding which has been a problem in the sheet electrode to which the tab is welded by removing the electrode active material once applied, tab bonding area 450 mm ² with respect to the tab bonding area 50 mm ² of the comparative example, the weld interface area is in 9 times. As a result, the welding becomes stronger and can withstand long-term use, and the discharge capacity under high load (9C) is 2
It can be seen that 0% and the power density increased by 30%, respectively, and that a welded portion which plays a part in improving the load characteristics and the power characteristics of the battery was formed.

Next, the lengths of the battery cans will be compared. In this embodiment, the sheet electrode has no uncoated portion, so the width of the sheet electrode is 50 mm, and the comparative product has an uncoated portion, so that the width of the sheet electrode is 55 mm. Therefore, the length of 85 mm of the battery can of the present example could be shortened by 10 mm from the length of 95 mm of the battery can of the comparative example. Further, the electrode sheet of the present example has the same electrode active material coating area as that of the comparative example, and the sheet width is shortened. As a result, the volume energy density of the battery is lower than that of the comparative example. That was up 11%.

Further, as shown in FIG. 6, the thickness of the coated portion and the uncoated portion of the comparative product are not uniform after press-pressing, so that only the coated portion is compressed and curved. Resulting in. On the other hand, in the example, as can be seen from FIG. 2, since the thickness was uniform, it was confirmed that the entire surface could be uniformly compressed and the deformation was small.

That is, when a comparative product having a large deformation is used in winding or the like in a later step of battery production, it is inevitable that the tension applied to the sheet electrode becomes nonuniform, and the local stress is reduced. Concentration causes breakage of the sheet electrode and winding deviation,
Although the production yield of the battery is reduced, in the case of the embodiment having a small deformation, the tension can be uniformly applied by winding or the like, so that the electrode is damaged or the winding is displaced due to local concentration of tension. Is eliminated, and the efficiency of the battery manufacturing process is improved.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, as the current collecting metal sheet, a conductive metal foil such as nickel, stainless steel and the like may be used in addition to aluminum.

Also, various types of electrode active materials are applied, and furthermore, the number of current collecting tabs, the bonding interval, the bonding length in the width direction of the current collecting electrode sheet, and the like can be arbitrarily selected. Although the battery sheet electrode of the present invention has been described with the main object of the positive electrode sheet of the lithium secondary battery being used, the use of the current collector tab sheet is not limited as long as the current collector tab sheet is joined thereto. Not something.

In the manufacturing method, the joining method between the current collecting tab and the current collecting electrode sheet is not limited to ultrasonic welding, and various joining methods are conceivable. As a method of applying the electrode active material layer, brush coating, roll coating, and the like can be mentioned. In such a case, production is performed by continuously applying a current collector metal sheet while conveying the metal sheet in a certain direction. It is also conceivable to raise the character.

[0044]

In the battery sheet electrode according to the present invention, a current collecting tab is connected in the width direction of the current collecting metal sheet surface, and the current collecting metal sheet surface is connected to the current collecting metal sheet surface from above the current collecting tab. Since the electrode active material layer is manufactured by cutting off the uncoated edge area of the surface of the current-collecting metal sheet on which the electrode active material layer is formed, the bonding area between the current-collecting tab and the current-collecting metal sheet is reduced. As a result, the discharge capacity under a high load is high, and the power density is high. In addition, since it is possible to remove the uncoated portion of the electrode active material from the metal sheet surface for current collection as much as possible,
The volume energy density of the battery can be improved, the length of the battery can can be reduced, and a high-performance and compact battery can be provided.

Furthermore, since there is almost no uncoated area of the electrode active material, deformation of the electrode sheet when wound in a roll is avoided, and the uniformity of the tension eliminates damage to the electrode and winding deviation. Therefore, the battery sheet electrode according to the present invention has extremely excellent load characteristics and power characteristics, and can be said to be industrially useful.

According to the method of manufacturing a sheet electrode for a battery according to the present invention, a current collecting tab is connected to the current collecting metal sheet surface in advance, and the current collecting tab is joined to the current collecting metal sheet. After forming the electrode active material on the surface, the uncoated edge region of the current collecting metal sheet surface is cut off to manufacture the battery sheet electrode with good performance as described above. In addition, the sheet electrode can be efficiently produced.

[Brief description of the drawings]

FIG. 1 is a plan view of a battery sheet electrode according to the present invention.

FIG. 2 is a cross-sectional view of a battery sheet electrode according to the present invention.

FIG. 3 (a) is a view showing a tab welding step in the method for producing a battery sheet electrode according to the present invention, and FIG. 3 (b) is an electrode active material in the method for producing a battery sheet electrode according to the present invention. (C) is a view showing a cutting step of an uncoated portion in the method for producing a battery sheet electrode according to the present invention.

FIG. 4 is a diagram showing a schematic configuration of a conventional lithium secondary battery.

FIG. 5A is a diagram showing a coating process of an electrode active material and a cutting process of an uncoated portion in a method of manufacturing a sheet electrode for a battery generally known in the related art, and FIG. FIG. 4 is a view showing a tab welding step in the manufacturing method shown in FIG.

6 is a cross-sectional view of a battery sheet electrode manufactured by the manufacturing method shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal sheet for current collection 2 Tab for current collection 2a Welded part 3 Sheet electrode 3a Uncoated part 3c Coated part 4 Electrode active material layer

Claims (2)

[Claims] 1. A current collecting tab is connected in the width direction of a surface of a current collecting metal sheet, and an electrode active material layer is formed by coating on the current collecting metal sheet from above the current collecting tab. A sheet electrode for a battery. 2. A tab connecting step of connecting a current collecting tab to a current collecting metal sheet surface in advance, and applying an electrode active material to the current collecting metal sheet surface to which the current collecting tab is joined by the tab connecting step. An electrode active material layer coating process to be formed, and an uncoated region for cutting off an uncoated edge region of the current collecting metal sheet surface on which the electrode active material layer is formed by the electrode active material layer coating process. A method for producing a sheet electrode for a battery, comprising a cutting step.