JPH11317218A - Sheet electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an active material uncoated part which is provided in a width direction of a belt-like current collector of a sheet electrode to obtain an electrode body whose dead space is small in order to improve an energy volume density of a spiral battery. SOLUTION: A sheet electrode 10 comprises, a belt-like current collector 11, an electrode active material layer 12 which is intermittently formed in the longitudinal direction on the current collector 11, and a strip lead 14 which is formed to project in a width direction to go over one side end of the current collector 11 from a part 13 where the electrode active material layer 12 of the current collector 11 is not formed. An electrode body of a spiral battery is constructed by using the sheet electrode 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet electrode used for a spiral type battery in which an electrode is wound via a separator.

[0002]

2. Description of the Related Art Spiral-type batteries in which a belt-like positive electrode and a negative electrode are wound via a separator are common and widely used in lithium ion secondary batteries and the like. As electronic devices such as personal computers and mobile phones are becoming smaller and electric vehicles are being developed due to environmental issues, there is a growing demand for these spiral-type batteries to have large capacity and small size. The development of large batteries is desired.

Usually, the electrodes of a spiral type battery are a positive electrode,
The negative electrode is also manufactured by applying a paste of an active material that causes an electrode reaction to a surface of a belt-shaped current collector made of a metal foil, followed by drying. That is, the portion where the active material is applied is formed as an electrode active material layer. These electrodes are interposed with a separator between them and wound to form an electrode body,
Since this electrode body is sealed in a cylindrical case together with the electrolyte to form the battery, the volume of the electrode element that functions for actual discharge relative to the volume of the battery itself has a large effect on the energy volume density of the battery. Will do.

Conventionally, an electrode of a spiral type battery has an uncoated portion on which an active material is not continuously applied at one end in a width direction of a current collector, and a plurality of strip-shaped portions are formed on the uncoated portion. The leads (tabs) were joined by means of ultrasonic joining, resistance welding, or the like to collect current from the electrodes to the external terminals. FIG. 5 shows a conventional electrode to which leads are joined. And a positive electrode,
In the negative electrode, the electrode configured as described above was wound through a separator as shown in FIG. 6 to form an electrode body.

The winding of the electrodes is performed so that the leads of the positive electrode and the negative electrode extend in the directions opposite to each other in the winding axis direction. In this case, the positions where the electrode active material layers overlap each other in the radial direction are used. The electrode was shifted in the width direction so as to come to the right side. Therefore, as shown in FIG. 7, the formed cylindrical electrode body has portions where the active material is not applied to the wound end faces on both sides thereof, so-called dead spaces. This dead space has been a major obstacle when trying to improve the energy volume density of the battery.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the energy density of a battery by forming an electrode body having a small dead space. For this reason, in the present invention, the active material uncoated portion provided on the conventional electrode, that is, the active material uncoated portion continuously formed at one end in the width direction of the belt-shaped current collector is reduced. For the purpose, in place of the conventional active material uncoated portion, a plurality of uncoated portions are provided in the width where the active material is applied, and an electrode having a current collecting lead formed in this portion is used. By doing so, it is intended to form an electrode body having a small dead space.

[0007] Ideally, an electrode having no active material uncoated portion at the end in the width direction of the current collector, but conventionally, an uncoated portion is provided over the entire width of the belt-shaped current collector. Since there was no appropriate technique for applying the active material without using the active material, the current collector was slit after application of the active material in order to remove the active material uncoated portion existing at the end in the width direction. Therefore, as a method for manufacturing the sheet electrode of the present invention, a simple method different from the conventional method is employed, and by this method, the active material is applied over the entire width of the current collector, and the electrode body having no dead space at the winding end portion. It is also intended to facilitate the production of.

[0008]

As described above, the inventor of the present invention has made it possible to reduce the dead space of the electrode body by reducing the active material uncoated portion provided in the width direction of the belt-shaped current collector. Having arrived at the present invention, the following invention has been reached. The present invention provides a band-shaped current collector, an electrode active material layer formed intermittently in the longitudinal direction on the surface of the current collector, and a portion of the current collector where the electrode active material layer is not formed. By forming an electrode body of a spiral type battery using a sheet electrode having a strip-shaped lead formed to extend in the width direction beyond one side end of the current collector, the energy volume density of the battery is increased. The object of the present invention is to solve the above-mentioned problem of improving the above.

In other words, the sheet electrode of the present invention is formed by extending a section of a predetermined length in which the active material is coated on the entire surface of the belt-shaped current collector in the width direction over the entire length of the current collector at a predetermined interval. A plurality of power supply leads are formed in an active material non-coated portion perpendicular to the longitudinal direction of the current collector between the active material coated portions. The electrode body in which such an electrode is wound has a very small dead space due to the active material uncoated portion on the wound end surface.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a sheet electrode and a method of manufacturing the same according to the present invention will be described below in detail with reference to the drawings. The electrode for a lithium ion secondary battery will be described below for convenience, but the sheet electrode and the method of manufacturing the same according to the present invention are not limited to those for a lithium ion secondary battery.

FIG. 1 shows an embodiment of the sheet electrode according to the present invention. The sheet electrode 10 of the present embodiment has a strip-shaped current collector 11.
And an electrode active material layer 12 intermittently formed in the longitudinal direction on the surface of the current collector 11, and the electrode active material layer 12 of the current collector 11
And a strip-shaped lead 14 formed so as to extend in the width direction beyond one side end of the current collector 11 from a portion where no is formed (hereinafter referred to as an active material uncoated portion 13). I have. First, regarding the current collector 11, usually, a belt-shaped aluminum foil having a thickness of 10 to 20 μm is used for the positive electrode, and a band-shaped copper foil having a thickness of 10 to 20 μm is used for the negative electrode. The width and length of the current collector 11 vary depending on the discharge capacity of the battery. However, a large battery having a large discharge capacity may have a width of 150 mm or more and a length of 5 m or more.

Next, the electrode active material layer 12 will be described.
The electrode active material layer 12 is formed by mixing a binder or the like with an electrode active material to form a paste-like mixture (hereinafter referred to as an active material paste) for both the positive electrode and the negative electrode on the surface of the current collector 11. , Dried and then roll pressed to increase the density. The active material is LiCoO _{2 for} the positive electrode,
Lithium-containing metal oxide powder such as LiMn ₂ O ₄
For the negative electrode, a powder of a carbon material such as graphite or a fired organic compound is used. The positive electrode active material paste is prepared by mixing the above positive electrode active material powder with a conductive agent such as graphite and acetylene black, a binder such as polyvinylidene fluoride, and a dispersant such as N-methylpyrrolidone. The negative electrode active material paste is prepared by mixing the above negative electrode active material with a composite binder such as carboxymethylcellulose and styrene-butadiene rubber as a binder.

In this embodiment, the electrode active material layers 12 are formed intermittently in the length direction of the current collector 11, and the number of the electrode active material layers 12 and the area of each of the electrode active material layers 12 are different depending on the battery. Can be arbitrarily selected according to the design of the battery itself, which is made in consideration of the discharge capacity, electrode width, number of leads, and the like. Further, it is desirable to arrange the current collecting leads 14 at equal intervals in the length direction of the current collector 11 in order to uniformly collect the current from the entire sheet electrode 10. The area is desirably uniform, and the width of the active material uncoated portion 13 existing between the electrode active material layers 12 is slightly larger than the width of the lead 14 formed in the uncoated portion. I just need.

The electrode active material layer 12 with respect to the width of the current collector 11
Regarding the width of the current collector, continuous active material uncoated portions may be provided at both ends in the width direction of the current collector in consideration of the easiness of application of the active material paste to the surface of the current collector 11. In this embodiment, the electrode active material layer 12 is formed over the entire width of the current collector 11 in order to minimize the dead space of the electrode body. The electrode active material layer 12 may be formed on only one surface of the current collector 11, but is preferably formed on both surfaces of the current collector 11 in consideration of the energy volume density of the battery. In the case of forming on both surfaces, if the lead 14 is formed after forming the electrode active material layers on both surfaces, the electrode active material layer on the back surface is replaced with the electrode active material layer 12 on the front surface.
It must be formed at the same position as On the other hand, when the electrode active material layer 12 on the front surface is formed and the lead 14 is formed, and then the electrode active material layer on the rear surface is formed, or when the electrode active material layer on both surfaces is formed after the lead is formed. Is
The electrode active material layer on the back surface may not be intermittent and may be continuous in the length direction of the current collector 11.

The lead 14 formed on the current collector 11 in the sheet electrode 10 of this embodiment uses a metal foil of the same material as the current collector 11 for both the positive electrode and the negative electrode. Lead 1
4 must not exceed the thickness of the electrode active material layer 12, and is usually about the same as the current collector 11, ie, 10
About 30 μm. Also, the width of the lead 14 should not be too wide in consideration of the winding of the sheet electrode 10, and is usually about several to ten mm. On the other hand, the length of the lead 14 can be arbitrarily set depending on the method of the current collection processing.

The method for forming the leads 14 on the current collector 11 is as follows.
Ultrasonic bonding, resistance welding, caulking, and the like can be used, but ultrasonic bonding is desirable in consideration of thermal effects, spatter, workability, and the like. The lead 14 is joined at a right angle to the length direction of the current collector 11, and a part thereof protrudes from one end of the current collector 11 in the width direction and extends. Then, the protruding ends are connected to the external terminals so as to be collected, and current collection is performed. The number of leads 14 varies depending on the discharge capacity of the battery. However, in the case of a sheet electrode used for a battery having a large discharge capacity, the number of leads increases to several tens. In the sheet electrode 10 of the present embodiment, unlike the conventional electrode, a plurality of junctions 15 can be provided for one lead, and the electric resistance at the time of current collection can be reduced. This has the effect of reducing the number of leads 14 and improving the strength reliability of the joint.

FIG. 2 shows another embodiment in which the method of forming the current collecting leads 14 is different. In the present embodiment, a cut 16 having a constant width is formed in the active material uncoated portion 13 of the current collector 11 so that an end of the cut portion protrudes from one end in the width direction of the current collector. The lead 14 is folded back. Unlike the previous embodiment, since the joining means is not used, the reliability of the formed portion can be further improved, and the material cost of the electrode can be reduced since no separate member is required as a lead material. In addition, there is an effect that the weight of the electrode can be reduced. The cut 16 can be made by any means such as pressing, laser cutting, and the like, and since the aim is to improve the energy volume density of the battery, the width of the cut 16 is set to be substantially equal to the width of the active material uncoated portion 13. It is desirable to make the area of the electrode active material layer 12 as large as possible. Although two parallel lines can be cut from one end surface to the center of the current collector, the winding of the sheet electrode 11 requires a certain amount of tension. Should not be cut at both ends, and it is desirable to make a U-shaped cut 16 at the center of the current collector as shown in FIG.

Next, in the method for producing a sheet electrode according to the present invention, the active material paste is intermittently applied in the longitudinal direction of the current collector without leaving an uncoated portion at an end in the width direction of the current collector. A coating method for coating will be described. In this coating method, the active material is continuously applied to the current collector surface by a reverse roll method in which the active material paste is transferred and applied to the current collector by an application roll while the current collector is supported and transported by a backup roll. A method of applying the active material paste to the surface of the application roll, wherein the width of the paste supplied to the surface of the application roll matches the width of the current collector. Adjusting the paste width by removing a portion of the paste wider than the current collector width by a paste removing means provided on the application roll; and providing the backup roll and the application roll at predetermined time intervals. And intermittently transferring and applying the active material paste whose width has been adjusted to the current collector by the application roll while changing the gap amount between the active material paste and the active material paste.

In other words, the present active material paste is applied to a knife edge provided on an application roll by supplying the active material paste having a constant thickness to the application roll and having a width slightly larger than the width of the current collector. By scraping off a portion larger than the width of the current collector from both sides in the width direction by means such as a blade in the shape of a current collector, the width of the current collector is matched to the width of the current collector, and the current is supported and conveyed to the backup roll. An uncoated portion of the active material that is perpendicular to the length direction of the current collector is formed by applying the coating so that it is transferred, and making the backup roll perform an intermittent operation that moves close to or away from the coating roll. It is to let. By this means, both ends of the active material paste on the application roll in the width direction are shaped, and the active material is applied evenly to the end of the current collector and intermittently without leaving an uncoated portion in the width direction. It is easy to do.

The reverse roll type coater used in the present coating method is a coater including three mutually parallel rolls of a coating roll (application roll), a measuring roll (metering roll), and a backup roll. The agent serves to supply the agent to the application roll while keeping the surface smooth at a constant thickness, and the backup roll serves to support and transport the application substrate. The application roll and the backup roll are close to each other, and are rotated so that the adjacent portions move in different directions. When the base material is supported by the backup roll and passes through the gap between the two, the coating material supplied on the application roll is transferred and applied to the surface of the base material.
This type of coater was adopted because the viscosity range of the applicable coating agent is large and the thickness of the applied coating is easily adjusted.

FIG. 3 shows an actual coating state. Hereinafter, the coating process of the active material paste will be described with reference to FIG. In this coating method, a metal comma roll 21 having a comma-shaped cross section is used as a measuring roll.
A method using a knife blade, a doctor roll, or the like may be used, but the thickness of the applied active material paste is easily adjusted,
This comma roll method was adopted because the surface can be smoothed.

The comma roll 21 was provided above the metal application roll 22, and a weir 24 was provided on the back of the comma roll 21 above the application roll 22 to form a paste reservoir 25. Into this paste reservoir 25, the active material paste which has been made into the positive electrode mixture and the negative electrode mixture flows. Although the comma roll 21 does not rotate, in order to change the size of the gap between the coating roll 22 and the blade of the comma roll 22,
It can be moved in a direction perpendicular to the application roll 22. As the application roll 22 rotates, the active material paste is supplied from the gap to the surface of the application roll 22. The thickness of the supplied active material paste is adjusted by the size of the gap.

Next, the width adjustment of the active material paste, which is the most important point of the present coating method, will be described. Application roll 2
The width of the active material paste supplied on 2 is determined to some extent by the width of paste reservoir 25. However, this width varies depending on the size of the gap between the comma roll 21 and the application roll 22, the viscosity of the active material paste, and the like. Further, the widthwise end portion of the supplied active material paste may be thicker or thinner than the central portion, or may meander in a wavy shape, depending on the relationship of viscosity and the like. Since the purpose is to apply the paste uniformly over the entire surface of the current collector 11, it is necessary to adjust the end of the active material paste.

Therefore, in the present coating method, a pair of knife blades 26 are disposed on the coating roll 22 so as to be in contact with the roll, and the widthwise ends of the active material paste are adjusted.
That is, the portion of the paste supplied on the surface of the application roll 22 in a width slightly larger than the width of the current collector 11, which protrudes from the widthwise end of the current collector 11, is scraped off by the knife blade 26. Has been removed. By inserting this step into the coating step, the application width of the active material paste can be made to match the width of the current collector 11.

The active material paste whose width has been adjusted on the surface of the application roll 22 is then transferred to a step of being transferred and applied to the current collector 11. The current collector 11 is tensioned in the length direction, and the surface thereof is supported by a backup roll 23 made of silicone rubber while being tensioned. Further, the backup roll 23 makes a rotational movement at a constant speed, and the current collector 11 is transported at a constant speed.

The application roll 22 is a backup roll 23
And the rotation direction is the same for both rolls, and in the vicinity of both rolls, they rotate in opposite directions. When the current collector 11 is transported and passes through the gap between the backup roll 23 and the application roll 22, the active material paste on the surface of the application roll 22 is applied so as to be transferred to the surface of the current collector 11.

However, in the sheet electrode 10 of the present invention, since the electrode active material layer 12 needs to be formed intermittently in the longitudinal direction of the current collector 11, in the present coating step,
The active material paste must be applied intermittently. Therefore, in this coating step, the active material paste is transferred and applied to the current collector 11 while changing the distance between the backup roll 23 and the application roll 22. That is, the electrode active material layer 1
In the part where the active material 2 is formed, the backup roll 23 is brought close to the application roll 22, and in the part where the active material is not coated, the backup roll 23 is caused to intermittently move away from the application roll 22. I have. By adjusting the close time and the long time, the electrode active material layer 1 formed on the current collector 11 is adjusted.
2 and the width of the active material uncoated portion 13 can be arbitrarily determined.

By this step, the application of the active material paste to the current collector 11 is completed, and the process proceeds to the next step, a drying step. When the active material paste is transferred and applied, the paste remaining on the application roll 22 is removed by a scraping blade 27 provided below the application roll 22. When the active material paste is applied to the back surface of the current collector 11, the same process may be repeated once.

The active material coating process is completed in this manner. However, the width adjusting means using the knife blade 26 also causes the active material paste to change its width due to a change in the viscosity of the active material paste. In some cases, it may be applied so as to protrude. If such protrusion occurs, the protruding active material paste adheres to the backup roll 23 and further adheres to the back surface of the current collector 11, so that a uniform electrode cannot be obtained. Assuming this case, the present coating method employs another means.

This means is arranged such that a sheet 28 having a width larger than the width of the current collector 11 is sandwiched between the backup roll 23 and the current collector 11, and the current collector 11 is placed together with the sheet 28. To be transported. The sheet 28 prevents the paste from adhering to the back surface of the current collector 11 even when the active material paste overflows. In the present coating method, a polypropylene sheet is used, but a thin strip having appropriate strength may be used, and the present invention is not limited to this.

Instead of the means using the sheet 28, the following means can be used. The backup roll has two stages of diameters, the central portion having a large diameter has the same length as the width of the current collector 11, and both ends thereof have small diameter portions. The large-diameter portion serves as the backup unit 31 to support and convey the current collector 11. This example is shown in FIG. According to this means, the active material paste which has protruded from the current collector 11 only drools on the small-diameter portion 32 of the two-stage backup roll 30, and prevents the paste from wrapping around and attaching to the back surface of the current collector 11. can do. When the sheet 28 is used, the sheet 28 is disposable, which leads to an increase in the manufacturing cost of the electrode.
Is an effective means from the viewpoint of manufacturing cost.

As mentioned above, the method for manufacturing the sheet electrode of the present invention has been described with reference to the examples, but the manufacturing method is not limited to the examples. For example, in the method of applying the active material paste, the active material paste is applied to the current collector 11 on which the leads 14 are not formed.
Using the current collector 11 in which the lead 14 has been formed in advance,
It is also possible to make the backup roll 23 intermittently move so that the active material paste is not applied to the portion where the leads 14 are formed. In addition, an active material paste is applied to a wide metal foil, dried, slit so as to be divided in the width direction, and a plurality of electrodes can be manufactured at the same time. As described above, the method for applying the active material paste can form an electrode active material layer intermittently in the longitudinal direction without an uncoated portion in the width direction of the current collector by a simple method. The range is wide.

[0033]

According to the present invention, an electrode used for a spiral type battery in which an electrode is wound with a separator interposed therebetween is formed on a band-shaped current collector and intermittently in the longitudinal direction on the surface of the current collector. An electrode active material layer, and a strip-shaped lead formed so as to extend in a width direction beyond one side end of the current collector from a portion of the current collector where the electrode active material layer is not formed. The electrode body in which the electrode is wound can have a very small dead space existing on the winding end surface and not serving as a power generating element. Therefore, the battery using the sheet electrode of the present invention has an effect of improving the energy volume density. This has led not only to the miniaturization of electronic devices, but also to the development of secondary batteries that serve as power sources for electric vehicles.

[Brief description of the drawings]

FIG. 1 is a plan view showing a sheet electrode according to one embodiment of the present invention.

FIG. 2 is a plan view showing a sheet electrode according to another embodiment of the present invention.

FIG. 3 is a perspective view showing an embodiment of a method for applying an electrode active material to a sheet electrode according to the present invention.

FIG. 4 is a perspective view showing a two-stage diameter backup roll used in an embodiment of another active material coating method.

FIG. 5 is a plan view showing a conventional sheet electrode.

FIG. 6 is a perspective view showing a state where a sheet electrode is wound;

FIG. 7 is a conceptual diagram showing a dead space of an electrode body.

[Description of Signs] 10: Sheet electrode (10a: positive electrode 10b: negative electrode) 11: Current collector 12: Electrode active material layer 13: Active material uncoated portion 14: Lead 15: Junction point 16: Cut 20: Reverse roll Coating machine 21: Comma roll 22: Application roll 23: Backup roll 24: Weir 25: Paste reservoir 26: Knife blade 27: Scraping blade 28: Sheet 30: Two-stage diameter backup roll 31: Backup part 32: Small diameter part 40 : Electrode body 41: Separator 42: Electrode element part 43: Dead space

Claims (1)

[Claims] 1. A belt-shaped current collector, an electrode active material layer formed intermittently in a longitudinal direction on a surface of the current collector, and a portion of the current collector where the electrode active material layer is not formed And a strip-shaped lead formed so as to extend in the width direction beyond one side end of the current collector.