KR101416805B1

KR101416805B1 - Folding cell and super capacitor folding type having the same

Info

Publication number: KR101416805B1
Application number: KR1020120033102A
Authority: KR
Inventors: 허진우
Original assignee: 비나텍주식회사
Priority date: 2012-03-30
Filing date: 2012-03-30
Publication date: 2014-07-09
Also published as: KR20130116466A

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a folding cell and a folding type super capacitor having the folding cell. The folding cell and the folding type supercap capacitor having the folding cell and the super- . The folding type supercapacitor according to the present invention includes a folding cell in which a sheet cell is wound and folded on a core plate, an electrolyte solution provided in the folding cell, a case in which the folding cell is sealed, and a cathode and an anode of the sheet cell, External terminals. At this time, the sheet cell is formed by sequentially stacking the first separator, the anode, the second separator, and the cathode, and is wound around the core plate a plurality of times.

Description

Folding Cell and Super Capacitor Having Folding Cell and Super Capacitor Having the Same "

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super capacitor, and more particularly, to a folding cell and a folding type super capacitor having the folding cell.

In addition to various portable electronic devices, there is a demand for electric power storage devices for electric vehicles and electric energy storage devices for systems for controlling or supplying instantaneous overload. Ni-MH A secondary battery such as a Ni-Cd battery, a lead-acid battery, and a lithium secondary battery, and a super capacitor, an aluminum electrolytic capacitor, and a ceramic capacitor having a high output density and close to unlimited charge / discharge life.

In particular, the super capacitor includes an electric double layer capacitor (EDLC), a pseudo capacitor, and a hybrid capacitor such as a lithium ion capacitor (LIC).

Here, the electric double layer capacitor is a capacitor using an electrostatic charge phenomenon occurring in an electric double layer formed at the interface of different phases, and has a faster charging / discharging speed, a higher charge / discharge efficiency than the battery in which the energy storage mechanism depends on the oxidation and reduction process, Is widely used for backup power supply, and the potential as an auxiliary power source for electric vehicles in the future is also unlimited.

A pseudocapacitor is a capacitor that converts a chemical reaction into electrical energy using an electrode and an oxidation-reduction reaction of the electrochemical oxide reactant. The pseudocapacitor has a storage capacity about 5 times larger than that of the electric double layer capacitor because the electric double layer capacitor can store the electric charge near the surface of the electrode material as compared with the electric double layer capacitor formed on the surface of the electrochemical double layer type electrode. As the metal oxide electrode material, RuOx, IrOx, MnOx and the like are used.

And the lithium ion capacitor is a new concept secondary battery system which combines the high output and long life characteristics of the existing electric double layer capacitors and the high energy density of the lithium ion battery. Electric double layer capacitors using the physical adsorption reaction of electric charges in the electric double layer have been limited in their application to various applications due to their low energy density despite excellent power characteristics and lifetime characteristics. As a means for solving the problem of such an electric double layer capacitor, a lithium ion capacitor using a carbon-based material capable of inserting and separating lithium ions as a negative electrode active material has been proposed. The lithium ion capacitor has a structure in which lithium ions, And the cell voltage can realize a high voltage of 3.8 V or more, which is much higher than that of the conventional electric double layer capacitor by 2.5 V, and can exhibit a high energy density.

The basic structure of such a supercapacitor is composed of an electrode, an electrolyte, a current collector, and a separator having a relatively large surface area such as a porous electrode. A voltage of several volts is applied to both ends of the unit cell electrode, And the electrochemical mechanism generated by adsorption on the surface of the electrode moves along the electric field. These cells are sealed to the upper and lower cases made of metal, and the upper and lower terminals are attached to the outer surfaces of the upper and lower cases.

Such a supercapacitor is manufactured and sold as a pouch type in which unit cells are laminated in a plate form and a winding type in which a sheet type cell is wound. In the case of the winding type super capacitor, a cell can be formed by winding in the form of a roll, and a cell (hereinafter, referred to as a folding cell) can be formed by winding in a folding form. Such a folding cell can be formed in a hexahedral shape.

However, in the folding cell, since the sheet-like cells are wound without using the core, the winding tension of the positive electrode and the negative electrode is different. As a result, the folded cell fabricated has a drawback that the winding shape is loosened, thereby causing a reduction in capacity, an increase in equivalent series resistance (ESR), and deterioration.

Further, since the folding cell is wound without using the core, there is a problem that the winding operation is also not easy.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a folding cell that is easy to take up and a folding type super capacitor having the same.

It is another object of the present invention to provide a folding cell that maintains a folding type and a stable winding form, and a folding type super capacitor having the same.

It is still another object of the present invention to provide a folding cell and a folding type super capacitor having the folding cell, which can suppress loosening of the winding form after winding.

In order to achieve the above object, the present invention provides a folding cell in which a sheet-shaped cell is wound on a core plate, and a folding type super capacitor having the folding cell.

The present invention provides a folding cell for a folding supercapacitor including a core plate and a sheet cell which is wound on the core plate and folded. At this time, the sheet cell is formed by sequentially stacking a first separator, an anode, a second separator, and a cathode, and is wound on the core plate a plurality of times.

A folding cell for a folding type supercapacitor according to the present invention comprises a first bonding member for fixing one end of the sheet cell to the core plate and fixing the other end to the other end of the sheet cell wound on the core plate, And a second adhesive member attached to the sheet cell portion under the other end of the cell to fix the wound state of the sheet cell.

In the folding cell for a folding supercapacitor according to the present invention, the first and second adhesive members may be adhesive tapes.

A folding cell for a folding supercapacitor according to the present invention includes a plurality of positive electrode lead wires having a first end portion joined to the positive electrode and a first other end portion connected to the first end portion protruding out of the sheet cell, And a plurality of negative electrode leads connected to the negative electrode and protruding from the sheet cell at a second other end portion connected to the second end portion. At this time, when the sheet cell is wound on the core plate, the plurality of positive electrode leads and the plurality of negative electrode leads are arranged in a line, and the plurality of positive electrode leads and the plurality of negative electrode leads are spaced apart from each other.

In the folding cell for a folding supercapacitor according to the present invention, a material that does not react with the electrolyte electrochemically may be used as the material of the core plate. At this time, the material of the core plate may include at least one of Teflon, stainless steel, ceramics, a polymer material, and a porous material.

In the folding cell for a folding type supercapacitor according to the present invention, at least one hole may be formed in the core plate.

In the folding cell for a folding supercapacitor according to the present invention, the core plate may protrude from both the winding region where the sheet cell is wound and the winding region, And may include a gripping region that is gripped by a rotating member that rotates the core plate.

In the folding cell for a folding supercapacitor according to the present invention, the core plate may have a rectangular parallelepiped shape, and both edge portions may be rounded and convex in a direction in which the sheet cell is wound.

In the folding cell for a folding supercapacitor according to the present invention, the surface of the core plate on which the sheet cell is wound may be roughly formed to have a concave portion and a convex portion.

In the folding cell for a folding supercapacitor according to the present invention, the sheet cell wound on the core plate is arranged so that the cathode of the sheet cell contacts the surface of the core plate, The first separation membrane can be located.

The present invention also provides a folding type super capacitor including the aforementioned folding cell, electrolyte, case, and external terminal. Wherein the folding cell comprises a core plate and a sheet cell which is wound and folded on the core plate, wherein the sheet cell is formed by stacking a first separator, a cathode, a second separator, and a cathode in this order, Is wound. The electrolytic solution is provided in the folding cell. The case seals the folding cell. The external terminals are connected to the cathodes and the anodes of the seat cells and are exposed to the outside of the case.

Since the folding cell according to the present invention has a structure in which the sheet cell is wound on the core plate, the winding process can be easily performed, and a folding type and stable winding form can be maintained. Since the folding cell according to the present invention can firmly wind the sheet cell on the core plate, loosening of the winding form of the sheet cell after winding can be suppressed.

Therefore, the folding type supercapacitor having the folding cell according to the present invention can maintain the distance between the gaps close to each other, thereby increasing the capacity and lowering the ESR, thereby providing a highly reliable supercapacitor.

The folding type supercapacitor according to the present invention is advantageous in that the manufacturing yield of folding type supercapacitors can be improved because folding cells can be easily manufactured and the manufacturing time can be shortened.

1 is a perspective view showing a folding cell of a folding type super capacitor according to an embodiment of the present invention.
FIGS. 2 and 3 are views showing respective steps according to the manufacturing method of the folding cell of FIG.
4 is a view illustrating a folding type super capacitor having folding cells according to an embodiment of the present invention.
5 is a perspective view showing a core plate for a folding type supercapacitor according to another embodiment of the present invention.

In the following description, only parts necessary for understanding the embodiments of the present invention will be described, and the description of other parts will be omitted so as not to obscure the gist of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and the inventor is not limited to the meaning of the terms in order to describe his invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention, so that various equivalents And variations are possible.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view showing a folding cell of a folding type super capacitor according to an embodiment of the present invention. FIGS. 2 and 3 are views showing respective steps according to the manufacturing method of the folding cell of FIG.

1 to 3, a folding cell 40 of a folding type supercapacitor according to an embodiment of the present invention includes a core plate 10 and a sheet cell 20 wound around the core plate 10 do. The sheet cell 20 is formed by sequentially stacking a first separator 21, an anode 23, a second separator 25 and a cathode 27 and is wound on the core plate 10 a plurality of times and fixed.

Since the folding cell 40 according to the present embodiment has a structure in which the sheet cell 20 is wound around the core plate 10, the winding process can be easily performed, and the folding cell 40 can be folded, . Since the folding cell 40 according to the present embodiment can firmly wind the sheet cell 20 on the core plate 10, it is possible to suppress loosening of the winding form of the sheet cell 20 after winding.

The folding cell 40 according to the present embodiment will be described in detail as follows.

The core plate 10 can be manufactured in a plate form using a material that does not electrochemically react with an electrolyte to be provided in the sheet cell 20. [ As the material of the core plate 10, Teflon, stainless steel, ceramics, a polymer material, a porous material, and the like can be used, but the present invention is not limited thereto. The porous material may be a porous ceramic material, a porous polymer material, or the like.

The core plate 10 has a winding region 12 in which the sheet cell 20 is wound and a core plate 10 that protrudes on both sides of the winding region 12 and winds the sheet cell 20 on the core plate 10. [ And a gripping region to which the rotary member for rotating the rotary member 10 is gripped. For example, the core plate 10 has a rectangular parallelepiped shape, and both edge portions of the core plate 10 in the direction in which the sheet cell 20 is wound so that the sheet cell 20 can be stably wound and wound It can be formed to be round and convex.

Although not shown, the surface of the core plate can be roughened so that the sheet cell 20 wound around the core plate 10 can be stably fixed. The surface on which the sheet cell 20 of the core plate 10 is wound can be roughly formed to have a concave portion and a convex portion. The convex portion of the surface of the core plate 10 may be formed to be inclined in the direction in which the sheet cell 20 is wound. The reason for this is that when the sheet cell 20 is wound around the core plate 10, the sheet cell 20 is wound around the core plate 10 in a state where a certain tension is applied, It is possible to stably wind the sheet cell 20 to the core plate 10 while giving tension to the sheet cell 20. [ Further, after the sheet cell 20 is wound on the core plate 10, the restoring force for restoring the original shape of the sheet cell 20 is applied. The restoring force acts in the opposite direction to the tension direction, The convex portion of the surface of the core plate 10 is formed in the opposite direction to the direction in which the restoring force acts so that the convex portion of the surface of the core plate 10 and the sheet cell 20 are engaged with each other, It can be stably fixed.

The sheet cell 20 has a structure in which a sheet-shaped first separation membrane 21, an anode 23, a second separation membrane 25, and a cathode 27 are laminated in order. The first separator 21 prevents a short circuit. The anode 23 is formed on the inside of the first separator 21 and includes a material capable of inserting and desorbing cations according to charging and discharging. The second separator 25 is interposed between the anode 23 and the cathode 27 to prevent a short circuit between the anode 23 and the cathode 27. The cathode 27 is formed on the inside of the second separator 25. At this time, the sheet cell 20 wound around the core plate 10 is positioned such that the cathode 27 of the sheet cell 20 faces the surface of the core plate 10 and the sheet cell 20 The first separation membrane 21 of the first embodiment is located.

At this time, the first and second separation membranes 21 and 25 may be made of any one of a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyester nonwoven fabric, a polyacrylonitrile porous separator, a poly (vinylidene fluoride) hexafluoropropane copolymer porous separator, , Kraft paper or rayon fiber, and the like, as long as it is a separator commonly used in the field of batteries and capacitors.

As the anode 23, a lithium foil can be used, and it is not particularly limited as long as it is an anode commonly used in the super capacitor field.

As the cathode 27, an electrode including activated carbon may be used, and it is not particularly limited as long as it is a cathode commonly used in the field of supercapacitors.

The sheet cell 20 also includes a plurality of positive electrode lead wires 24 and a plurality of negative electrode lead wires 26. [ Each of the plurality of positive electrode lead wires 24 has a first end connected to the anode 23 and a first other end connected to the first end protruding out of the seat cell 20. The plurality of negative electrode lead wires 26 have a second end joined to the cathode 27 and a second end connected to the second end protrudes out of the seat cell 20. The plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 may be formed in a line along one side of the sheet cell 20 and may have the same number. The plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 are arranged in a line and the plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 are wound on the core plate 10, 26 are spaced apart from each other. In this embodiment, a plurality of positive electrode lead wires 24 and a plurality of negative electrode lead wires 26 are protruded in the same direction. The plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 are formed in the following manner so that the plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 of the wound sheet cell 20 can be arranged in a row, Can be arranged together. For example, when the negative electrode lead wire 26 is disposed at one end of the sheet cell 20, the first negative electrode lead wire, the first positive electrode lead wire, the second positive electrode lead wire, the second negative electrode lead wire, the third negative electrode lead wire, The n-1 th positive lead wire, the n th positive lead wire, and the n th negative lead wire.

At least both end portions of the sheet cell 20 are joined to the first and second adhesive members 31 and 33 so that the sheet cell 20 can be stably wound on the core plate 10, ). &Lt; / RTI > The first adhesive member 31 attaches one end of the sheet cell 20 to the core plate 10 and fixes it. The second adhesive member 33 is attached to the other end of the sheet cell 20 wound on the core plate 10 and the sheet cell 20 portion below the other end of the wound sheet cell 20, Thereby fixing the wound state of the armature 20. At this time, as the first and second adhesive members 31 and 33, an adhesive tape may be used.

Since the folding cell 40 according to the present embodiment can stably maintain the wound state while stably winding the sheet cell 20 in the folded state using the core plate 10, The capacitance can be increased, and the ESR can be lowered to provide a highly reliable supercapacitor.

The method of manufacturing the folding cell 40 according to the present embodiment, that is, the winding method will be described as follows.

First, as shown in Fig. 2, a core plate 10 and a sheet cell 20 are prepared. At this time, the sheet cell 20 may be provided with the first and second adhesive members 31 and 33 attached thereto on the first separator 21 at both ends. Alternatively, the first and second adhesive members 31.33 may be provided separately from the sheet cell 20.

Next, as shown in Fig. 3, one end of the sheet cell 20 is attached to one surface of the core plate 10 via the first adhesive member 31. Then, as shown in Fig. At this time, the sheet cell 20 is attached to the winding area 12 of the core plate 10, and the cathode 27 is attached to one side of the core plate 10.

Next, as shown in Fig. 3, the core plate 10 is rotated counterclockwise to wind the sheet cell 20 on the core plate 10. Then, as shown in Fig. At this time, the sheet cell (20) is wound around the core plate (10) while a certain tension is applied to the sheet cell (20). The rotating member rotates the core plate 10 in the counterclockwise direction while grasping the grip regions 14 on both sides of the core plate 10. [

1, after the sheet cell 20 is wound on the core plate 10, the other end of the sheet cell 20 is wound around the sheet cell 20 through the second adhesive member 33 The folding cell 40 according to the present embodiment can be manufactured by attaching and fixing on the first separating film 21 of the sheet cell 20 adjacent to the end portion.

According to the manufacturing method of the folding cell 40 according to the present embodiment, since the folding cell 40 can be easily manufactured and the manufacturing time can be shortened by using the core plate 10, Type super-capacitor can be improved.

In the present embodiment, the other end of the sheet cell 20 is wound around the sheet 20 adjacent to the other end of the sheet cell 20 via the second adhesive member 33 after the sheet cell 20 is wound around the core plate 10, An example of attaching and fixing on the first separating film 21 of the cell 20 is described, but the present invention is not limited thereto. The entire outer surface of the sheet cell 20 can be wound with an adhesive tape to hold the wound state of the sheet cell 20 after the sheet cell 20 is wound around the core plate 10, for example.

An example of the folding type supercapacitor 100 having the folding cell 40 according to the present embodiment will now be described with reference to FIG. 4 is a view showing a folding type supercapacitor 100 having a folding cell 40 according to an embodiment of the present invention.

Referring to FIG. 4, the folding type supercapacitor 100 according to the embodiment of the present invention includes the folding cell 40, the electrolyte solution provided in the folding cell 40, and the folding cell 40, And external terminals 61 and 63, which are connected to the case 50 and the cathode of the seat cell 40 and are exposed to the outside of the case 50, respectively.

The electrolytic solution is provided so as to be impregnated in the folding cell 40, and an electrolytic solution in which the lithium salt is dissolved can be used. The lithium salt is not particularly limited as conventional lithium salts used in the supercapacitor, for example, _{LiPF 6, LiBF 4, LiClO 4} , Li (CF 3 SO 2) 2, LiCF 3 SO 3, LiSbF 6 or LiAsF ₆ can be used. The solvent constituting the electrolytic solution is not particularly limited, but a cyclic carbonate solvent, a chain carbonate solvent, an ester solvent, an ether solvent, a nitrile solvent, an amide solvent and the like can be used. As the cyclic carbonate-based solvent, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like can be used. As the chain carbonate solvent, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like can be used. As the ester solvent, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone and the like can be used. As the ether solvent, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 1,2-dioxane, 2-methyltetrahydrofuran and the like can be used. As the nitrile solvent, Nitrile and the like can be used. As the amide-based solvent, dimethylformamide or the like can be used.

As the case 50, a metal material such as aluminum (Al), a plastic material, a composite material in which a metal material and a plastic material are combined can be used as a material that protects the folding cell 40 and prevents electrolyte leakage have. Such a case may be a metal case in the form of a quadrangular prism having an internal space in which a pouch or folding cell can be accommodated.

As a material for the pouch, a composite material may be used from the viewpoints of downsizing and weight saving, and a laminate type composite film in which a polymer film such as aluminum and nylon, polypropylene or the like is laminated can be used.

In the case of a metal case, an aluminum case can be used. The metal case is formed with an inlet through which the folding cell can be inserted. The opening is covered with a sealing rubber, and then the upper part of the metal case is deformed to seal the inner space accommodating the folding cell.

The external terminals 61 and 63 include a positive electrode terminal 61 to which a plurality of positive electrode lead wires 24 are bonded and a negative electrode terminal 63 to which a plurality of negative electrode lead wires 26 are bonded. At this time, the plurality of positive electrode lead wires 24 and the plurality of negative electrode lead wires 26 may be electrically connected to the positive electrode terminal 61 and the negative electrode terminal 63, respectively, by riveting, welding, or mechanical contact.

In this embodiment, the core plate 10 of the folding cell 40 is formed in the shape of a rectangular plate, but the present invention is not limited thereto. For example, as shown in FIG. 5, at least one hole 16 may be formed in the core plate 110.

5 is a perspective view showing a core plate 110 for a folding type supercapacitor according to another embodiment of the present invention.

Referring to FIG. 5, a core plate 110 according to another embodiment of the present invention has a hole 16 formed at a central portion thereof. The hole 16 has a heat dissipating function for dissipating heat generated in the folding cell during the operation of the supercapacitor. At this time, an example in which the hole 16 is formed in the winding region 12 is disclosed.

In another embodiment of the present invention, an example in which one hole 16 is formed in the central portion of the core plate 110 is described, but a plurality of holes may be formed in the core plate.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention, and are not intended to limit the scope of the invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

10: core plate
12: Winding area
14:
16: hole
20: Seat cell
21: first separator
23: anode
24: Positive lead wire
25: Second separation membrane
26: Negative electrode lead wire
27: cathode
31: first adhesive member
33: second adhesive member
40: folding cell
50: Case
61: positive terminal
63: negative terminal
100: Folding type super capacitor

Claims

Core plate;
And a sheet cell formed by sequentially stacking a first separator, a cathode, a second separator, and a cathode, and wound on the core plate a plurality of times,
A first adhesive member attaching and fixing one end of the sheet cell to the core plate;
And a second adhesive member attached to the other end of the sheet cell wound on the core plate and the sheet cell portion below the other end of the wound sheet cell to fix the wound state of the sheet cell,
The surface of the core plate on which the sheet cell is wound is roughly formed to have a concave portion and a convex portion,
Wherein the convex portion is formed to be inclined in a direction in which the sheet cell is wound.

delete

The method according to claim 1,
Wherein the first and second adhesive members are adhesive tapes.

The method according to claim 1,
A plurality of positive electrode lead wires having a first end portion joined to the positive electrode and a first other end portion connected to the first end portion protruding from the sheet cell;
And a plurality of negative electrode lead wires having a second end portion joined to the negative electrode and a second end portion connected to the second end portion protruding from the sheet cell,
Wherein when the sheet cell is wound on the core plate, the plurality of positive electrode leads and the plurality of negative electrode leads are arranged in a line, and the plurality of positive electrode leads and the plurality of negative electrode leads are spaced apart from each other. Folding cells for capacitors.

The method according to claim 1,
Wherein the material of the core plate is a material that does not electrochemically react with the electrolyte. &Lt; RTI ID = 0.0 > 11. < / RTI >

The method according to claim 1,
Wherein the core plate includes at least one of Teflon, Stainless Steel, Ceramic, Polymer, and Porous.

The method according to claim 1,
Wherein at least one hole is formed in the core plate. &Lt; RTI ID = 0.0 > 11. < / RTI >

The apparatus of claim 1,
A winding region in which the sheet cell is wound;
A gripping region protruded on both sides of the winding region and gripped by a rotating member for rotating the core plate to wind the sheet cell on the core plate;
And a second electrode connected to the second electrode.

The apparatus of claim 1,
Wherein the sheet cell has a rectangular parallelepiped shape, and both edge portions of the folding cell are rounded and convex in a direction in which the sheet cell is wound.

delete

The stator of claim 1, wherein the sheet cell wound on the core plate
Wherein a cathode of the sheet cell is in contact with a surface of the core plate and a first separating film of the sheet cell is located outside the wound sheet cell.

A core plate,
A folding cell having a sheet cell which is formed by sequentially stacking a first separator, an anode, a second separator, and a cathode, and which is wound on the core plate a plurality of times;
An electrolytic solution provided in the folding cell;
A case for sealing the folding cell;
And external terminals connected to the cathodes and the anodes of the seat cells and exposed to the outside of the case,
A first adhesive member attaching and fixing one end of the sheet cell to the core plate;
And a second adhesive member attached to the other end of the sheet cell wound on the core plate and the sheet cell portion below the other end of the wound sheet cell to fix the wound state of the sheet cell,
The surface of the core plate on which the sheet cell is wound is roughly formed to have a concave portion and a convex portion,
Wherein the convex portion is formed to be inclined in a direction in which the sheet cell is wound. &Lt; RTI ID = 0.0 > 11. < / RTI >