KR100900413B1 - Stack and Folding-Typed Electrode Assembly Having Improved Heat Safety and Electrochemical Cell Containing the Same - Google Patents

Abstract

The present invention is an electrode assembly having a structure in which a plurality of unit cells are sequentially wound on a porous separator having a longer length than the width thereof, and a state in which an excess portion of the outer peripheral surface of the separator included in the unit cells is coupled to the separator film In the present invention provides a stack / foldable electrode assembly which is manufactured by winding unit cells sequentially, and the electrode assembly may prevent internal short circuit due to shrinkage of the separator in a high temperature environment, There is an effect that can improve the fairness during the folding process of the unit cells.

Description

Stack and Folding-type Electrode Assembly Having Improved Heat Safety and Electrochemical Cell Containing the Same}

1 is a schematic diagram of an electrode assembly according to one embodiment of the present invention;

2A-2E are schematic diagrams of one exemplary full cell and bicell that can be preferably used as a unit cell in the electrode assembly of FIG. 1;

FIG. 3 is a schematic view of the electrode assembly of FIG. 1 assembled in one exemplary method; FIG.

4 is a schematic view of an electrode assembly according to another embodiment of the present invention.

The present invention relates to a stack / foldable electrode assembly having improved thermal stability, and more particularly, to an electrode assembly having a structure in which a plurality of unit cells are sequentially wound in a state where a plurality of unit cells are positioned on a porous separation film having a long length to width, And a stack / foldable electrode assembly, and a stack / foldable electrode assembly, which is manufactured by winding unit cells sequentially in a state in which a surplus of the outer peripheral surface of the separation film included in the unit cells is bonded to the separation film. It relates to an electrochemical cell consisting of.

The demand for secondary batteries is also rapidly increasing due to the development of technology and increasing demand for mobile devices. Among them, lithium secondary batteries with high energy density, high operating voltage, and excellent storage and life characteristics are energy of various electronic devices as well as various electronic products. It is widely used as a circle.

In general, the secondary battery is composed of a unit cell composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode in a stacked or wound state, embedded in a battery case of a metal can or laminate sheet, and then injected or impregnated with an electrolyte solution. have.

One of the major research tasks in such secondary batteries is to improve safety. For example, secondary batteries may be subjected to high temperatures inside the cell, which may be caused by abnormal operating conditions of the battery, such as internal short circuits, overcharge conditions exceeding the allowed currents and voltages, exposure to high temperatures, deformation due to drops or external shocks, and High pressure can cause the battery to explode.

As a safety problem, internal short circuits due to shrinkage or breakage of a separator generated when the battery is exposed to high temperature are very serious, and many studies have been made on the cause and alternatives.

Generally, a porous polymer film such as polyethylene or polypropylene is used as the separator, and the separator has an advantage of being inexpensive and excellent in chemical resistance, which is preferable for operation of a battery, but is easy to shrink in a high temperature environment.

On the other hand, the electrode assembly of the anode / separator / cathode structure constituting the secondary battery is largely divided into jelly-roll type (winding type) and stack type (lamination type) according to its structure. The jelly-roll type electrode assembly is coated with an electrode active material or the like on a metal foil used as a current collector, dried and pressed, cut into bands of a desired width and length, and the membrane is separated using a separator to form a spiral. It is manufactured by winding. Such a jelly-roll type electrode assembly may be preferably used in a cylindrical battery, but in application to a square or pouch type battery, the stress is locally concentrated and the electrode active material is peeled off or the battery shrinks due to shrinkage and expansion phenomenon repeated during charge and discharge. There is a problem that causes deformation. On the other hand, the stacked electrode assembly has a structure in which a plurality of anode and cathode unit cells are sequentially stacked, and has an advantage of easily obtaining a rectangular shape, but when the manufacturing process is complicated and an impact is applied, the electrode is pushed and a short circuit occurs. There is a disadvantage that is caused.

In order to solve this problem, the electrode assembly of the advanced structure of the jelly-roll type and the stacked form, a full cell or anode (cathode) / separator / cathode of a certain unit size of the anode / separator / cathode structure A stack / foldable electrode assembly was developed in which a bicell of (anode) / separator / anode (cathode) structure was folded using a continuous separation film of a long length, which was applied to the applicant's Korean patent application publication. No. 2001-82058, 2001-82059, 2001-82060, and the like.

However, in the stack / foldable electrode assembly, the separation film that folds the unit cells maintains the folding form even when contracted at high temperature, and does not cause direct short circuit between the electrodes, but is interposed between the anode and the cathode inside the unit cells. The separator has a problem that both ends of the separator are easily contracted between the interfaces of the electrodes in a high temperature environment, causing an internal short circuit.

Also, a stack / foldable electrode assembly is generally manufactured by winding the separator film in a state where only unit cells of a full cell or a bicell are placed on a long sheet type separator film. Therefore, in the winding process, the unit cells on the separation film may not be fixed in position, and thus, a lot of effort is required to obtain a precise position.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

After extensive research and various experiments, the inventors of the present application separate a surplus of the outer circumferential surface of the separator included in the unit cells in a stack / foldable electrode assembly in which a plurality of unit cells are folded by a separation film. When unit cells are folded in the state of being bonded to the film, it has been found that the internal short circuit due to shrinkage of the separator may be prevented in a high temperature environment, and processability may be improved during the folding process of the unit cells by the separator film. The invention has been completed.

Accordingly, the stack / foldable electrode assembly according to the present invention is an electrode assembly having a structure in which a plurality of unit cells are sequentially wound in a state where a plurality of unit cells are positioned on a porous separation film having a long length to width, and are included in the unit cells. The outer peripheral surface of the separator is configured to be wound by sequentially winding unit cells in a state of bonding to the separation film.

That is, the electrode assembly according to the present invention, by combining the outer peripheral surface surplus portion of the separator to the separation film, thereby suppressing the shrinkage of the separator upon application of high heat can ultimately ensure excellent safety, easy to unit cells when folding the separation film It can be fixed in place so that it has the advantage of improving the efficiency of the manufacturing process.

In the present invention, the unit cell may be formed of a bicell having the same electrode structure on both sides and / or a full cell having an electrode structure having different sides.

Specifically, a full cell as a unit cell is a cell composed of a unit structure of an anode, a separator, and a cathode, and is a cell in which an anode and a cathode are located on both sides of the cell, respectively. Such a full cell may include an anode / separator / cathode cell and an anode / separator / cathode / separator / anode / separator / cathode cell having the most basic structure. Among them, a schematic diagram of a full cell having a positive electrode / membrane / cathode structure is shown in FIG. 2A. In order to construct an electrochemical cell including a secondary battery using the full cell, the positive electrode and the negative electrode may be disposed in a state where a separator film is interposed. Multiple full cells must be stacked to face each other.

In addition, the bicell as a unit cell is a cell in which the same electrode is located on both sides of the cell, such as the unit structure of the anode / separator / cathode / separator / anode and the unit structure of the cathode / separator / anode / separator / cathode. Among them, a schematic diagram of a bicell having an anode / separation membrane / cathode / separation membrane / anode structure is shown in FIG. 2B, and a schematic diagram of a bicell having a cathode / separation membrane / anode / separation membrane / cathode structure is shown in FIG. 2C. In order to construct an electrochemical cell including a secondary battery using such a bicell, a bicell and a cathode, a separator, an anode, a separator, and a cathode structure of the anode / separator / cathode / separator / anode structure with the separator film interposed therebetween. A plurality of bicells should be stacked so that the bicells face each other.

In some cases, a larger number of stacks of bicells are also possible, such as a schematic of a bicell of anode / separator / cathode / separator / anode / separator / cathode / separator / anode structures as shown in FIG. 2D. And, a schematic diagram of the bicell of the cathode / separator / anode / separator / cathode / separator / anode / separator / cathode structure is shown in Figure 2e.

The outer peripheral surface surplus of the separator means a portion protruding to a predetermined length from each end of the electrodes in order to stably maintain the insulating state between the positive electrode and the negative electrode in the unit cell. The excess is not particularly limited as long as it can be bonded to the separation film while compensating for the length of heat shrinkage, preferably 1 to 10 mm in length from the outer circumferential surface of the anode or cathode of the unit cell, preferably 3 to 7 mm in length. Protrudes.

In one preferred example, the excess portion of the separator may be combined with the separator by thermal fusion. In this case, the heat fusion is preferably performed on the other side except for the side from which the electrode tabs protrude from the anode and the cathode in the unit cell. In addition, since the separation membrane and the separation film is melted or broken by heat and pressure applied during thermal fusion, it is preferable to apply heat and pressure to prevent this. As a result, the heat and pressure is a predetermined heat and pressure that can be combined with the separator and the separation film, can be appropriately adjusted in consideration of the material, shape, etc. of the separator and the separation film.

In another preferred example, the excess portion of the separator may be combined with the separator film by an adhesive. In this case, the adhesive may be applied to the excess portion of the separator and / or the separation film at a position corresponding to the excess portion. In addition, in the case of using the adhesive, since it is cumbersome to apply the adhesive between each of the separators and the separator and the separation film in the unit cell including a plurality of separators, it is preferable in the unit cell including one separator Can be applied. Specifically, the adhesive may be used in an electrode assembly in which full cells including one separator are folded by a separator film.

In addition, the application portion of the adhesive does not necessarily need to be the entire excess of the separator or the corresponding separation film portion, and may be applied to the inner side spaced by a predetermined length from the outer circumferential surface in consideration of the phenomenon in which the adhesive leaks along the outer circumferential surface of the separator. It may be.

In the above example, the adhesive does not cause an electrochemical reaction inside the electrode assembly, and if the adhesive includes an adhesive, it may be various without particular limitation, such as an inorganic adhesive ceramic-based adhesive, organic adhesive is epoxy Adhesives such as electrochemically stable and heat-resistant adhesives such as acrylic, polyimide and urethane adhesives.

The present invention also provides an electrochemical cell comprising the electrode assembly as described above, wherein the electrochemical cell provides electricity through an electrochemical reaction, for example, an electrochemical secondary battery or an electrochemical It may be a capacitor.

In particular, the present invention may be preferably applied to a lithium secondary battery manufactured by injecting a lithium electrolyte in a state in which the electrode assembly is mounted inside a battery case including a metal layer and a resin layer.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

1 is a schematic diagram of an electrode assembly according to an embodiment of the present invention.

Referring to FIG. 1, the electrode assembly 100 includes the bicells 200 and the anode 210 having a structure of a cathode 220, a separator 250, an anode 210, a separator 250, and an anode 210. / Bipolar membrane (250) / negative electrode (220) / bipolar membrane (250) / bipolar (210) structure of the bi-cell 201, and the sheet-like separation film 300, the bi-cell (200, 201) Separating membranes 260, 261, 262, 263 protruding from the heat-sealed with the separation film 300, it characterized in that the bi-cell (200, 201) is fixed to the separation film (300).

The bi-cells 200 and 201 may have a structure of a cathode 220, a separator 250, an anode 210, a separator 250, and a cathode 210 so that they may be sequentially connected in manufacturing the electrode assembly 100. The bi-cell 200 and the bi-cell 201 having the structure of the anode 210, the separator 250, the cathode 220, the separator 250, and the anode 210 are alternately arranged on the separator film 300. The positive electrode tab 230 protruding from the positive electrode 210 and the negative electrode tab 240 protruding from the negative electrode are arranged to face the same direction at the same position.

These bi-cells 200, 201 are opposed to the surplus 260 of the side of the separator surpluses 260, 261, 262, 263 protruding therefrom from which the electrode tabs 230, 240 protrude. Both sides of the surplus parts 261 and 262 except the surplus part 263 may be fixed by heat-sealing the separation film 300. In this case, the thermal fusion may be performed in the remaining membrane excess portions 261, 262, and 263 except for the excess portion 260 on the side from which the electrode tabs 230 and 240 protrude.

The electrode assembly 100 is manufactured by folding the bi-cells 200 and 201 arranged in the above structure into the separation film 300, and this folding structure can be more easily confirmed in FIG. 4.

Referring to FIG. 4, the electrode assembly 100 includes a first bi-cell having a structure in which a separator film 300 has a structure of a cathode 220, a separator 250, an anode 210, a separator 250, and an anode 210 in the center. Wrap the outer surface of the (200) once, and the first and second of the bi-cell structure of the anode 210 / separator 250 / cathode 220 / separator 250 / anode 210 respectively The bi-cells 201 may be manufactured by folding the bi-cells 200 and 201 in a structure of wrapping the outer surface of the bi-cell 201 once. In this case, the folding operation of the electrode assembly 100 may be easily performed because the bi-cells 200 and 201 are stably fixed to the separation film 300 at the heat fusion site A. FIG.

Although not shown in the drawings, the electrode assembly may be manufactured by folding the bicells in a structure in which the separation film is wrapped in a Z shape from the lowermost bicell to the uppermost bicell.

4 is a schematic view of an electrode assembly according to another embodiment of the present invention.

Referring to FIG. 4, the electrode assembly 101 includes a full cell 202 having a structure of an anode 210 / separator 250 / a cathode 220 and a separator film 300 having a sheet shape. The adhesive 400 is applied between the separator excess portions 260, 261, 262, and 263 protruding from the 202 and the separation film 300 to fix the full cells 202 to the separation film 300. It can be prepared by folding the separation film 300 in the.

A method of assembling the electrode assembly 101 using the adhesive 400 may include separation separators 260, 261, 262, and 263 and separation membranes 260, 261, 262, and 263 and the separation film 300. Since the trouble to apply the adhesive 400 to each of the generated occurs, it can be preferably used in the full cell 202 including one separator (250).

In addition, the folding of the electrode assembly 101 using the adhesive 400 may also have a structure as described above.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductor) and 2.5% by weight of PVdF (binder) were added to NMP (N-methyl-2-pyrrolidone) as a cathode active material to prepare a cathode mixture slurry. 95% by weight of artificial graphite, 1.5% by weight of Super-P (conductor) and 3.5% by weight of PVdF (binder) were added to NMP as a solvent to prepare a negative electrode mixture slurry, and then onto aluminum foil and copper foil, respectively. Coating, drying and pressing produced positive and negative electrodes.

After using Celgard ^TM as a separator and assembling the anode bipolar and the cathode bicells as shown in FIGS. 2B and 2C, respectively, the bicells were arranged on the separator as shown in FIG. 1, and then the excess portion of the separator was heat-sealed. It was. Then, as shown in FIG. 3, the electrode assembly was manufactured by sequentially folding the positive electrode and the negative electrode with a separator film, and the electrode assembly was embedded in a pouch-type battery case, followed by injecting electrolyte to complete the battery. It was.

Comparative Example 1

A battery was completed in the same manner as in Example 1, except that thermal fusion was not performed in the separator excess.

Experimental Example 1

High temperature exposure experiments were performed on 20 batteries prepared in Example 1 and Comparative Example 1, and the results are shown in Table 1 below. In this experiment, each of the 20 cells was repeatedly performed, and the high temperature exposure experiment was performed under the condition of maintaining at 160 ° C. for 10 minutes.

TABLE 1

As shown in Table 1, the cells of Example 1 according to the present invention did not cause a short circuit in all 20 cells in the high temperature exposure experiment. That is, the excess portion of the separator protruding from the unit cells is coupled to the separator film, and thus the separator is not shrunk even at a high temperature, and thus a short circuit is not caused. On the other hand, in the battery of Comparative Example 1, short circuit and ignition were confirmed in many cells. In addition, the battery of Comparative Example 1 required precise workability when folding the cell while the unit cells were placed on the separation film in the manufacturing process of the electrode assembly.

As described above, the stack / foldable electrode assembly according to the present invention can prevent internal short circuit caused by shrinkage of the separator in a high temperature environment, and can improve processability in the folding process of the unit cells by the separator film. It works.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (10)

An electrode assembly having a structure in which a plurality of unit cells are sequentially wound on a porous separator having a longer length than the width thereof, and the unit cells are sequentially disposed in a state in which a separator surplus included in the unit cells is combined with the separator film. Stacked / foldable electrode assembly, characterized in that is produced by winding. The stack / foldable electrode assembly of claim 1, wherein the unit cell is a full cell having different structures on both sides of the unit cell. The stack / foldable electrode assembly of claim 1, wherein the unit cell is a bicell having a structure in which electrodes on both sides are identical to each other. The stack / foldable electrode assembly of claim 1, wherein the separator excess portion protrudes from the outer circumferential surface of the unit cell anode or cathode in a length of 1 to 10 mm. The stack / foldable electrode assembly of claim 1, wherein the separator surplus is bonded to the separator by thermal fusion. The stack / foldable electrode assembly according to claim 1, wherein an adhesive is applied to (i) the separator excess portion, or (ii) the separator film, or (iii) the separator excess portion and the separator film. . 7. The stack / foldable electrode assembly of claim 6, wherein the adhesive is a heat resistant acrylic, polyimide, urethane, or heat resistant ceramic adhesive. An electrochemical cell comprising the electrode assembly according to any one of claims 1 to 7. 9. The electrochemical cell of claim 8, wherein said cell is a secondary battery or a capacitor. A lithium secondary battery prepared by injecting a lithium electrolyte solution in a state where the electrode assembly according to any one of claims 1 to 7 is mounted inside a battery case including a metal layer and a resin layer.

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