KR100882489B1 - Stack and Folding-typed Electrode Assembly Capable of Preventing Internal Short to be Caused by Thermal Shrinkage and Electrochemical Cell Containing the Same - Google Patents

Abstract

The present invention relates to an electrode assembly in which a plurality of unit cells are folded by a long sheet-type separation film, wherein the unit cells include two or more separators, and one end of adjacent separators is closely connected to the side of the electrode. Providing an electrode assembly, characterized in that the electrode assembly can not only improve the safety of the battery by suppressing the thermal contraction phenomenon of the separator interposed between the anode and the cathode of the unit cell in a high temperature environment, It is possible to reduce the manufacturing cost by reducing the use amount of the separator, there is an effect that can increase the battery capacity compared to the same standard.

Description

Stack and Folding-type Electrode Assembly Capable of Preventing Internal Short to be Caused by Thermal Shrinkage and Electrochemical Cell Containing the Same}

1A-1E are schematic diagrams of one exemplary full cell and bicell that can be used as a unit cell in an electrode assembly of the present invention;

2 is a schematic diagram of an electrode assembly composed of full cells as shown in FIG. 1A as a unit cell according to one embodiment of the present invention;

3A and 3B are schematic views of an electrode assembly including bicells as shown in FIGS. 1B and 1C as unit cells according to another embodiment of the present invention.

The present invention relates to a stack / foldable electrode assembly capable of preventing internal short circuit due to thermal contraction, and more particularly, an electrode assembly in which a plurality of unit cells are folded by a long sheet-type separation film. Is an electrode assembly comprising two or more separators and one end of adjacent separators is in close contact with the side of the electrode, and an electrochemical cell comprising such an electrode assembly.

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.

In general, 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 secondary battery is classified into a substantially cylindrical battery, a square battery and a pouch-type battery according to the external and internal structural features, among which can be stacked with a high degree of integration, the square battery and pouch-type battery having a small width to length It is especially attracting attention.

The electrode assembly of the anode / separation membrane / cathode structure constituting the secondary battery is largely divided into a jelly-roll type (wound type) and a 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 / folding electrode assembly was developed in which a bicell of (anode) / separation membrane / anode (cathode) structure was folded using a continuous separation film of a long length, and this 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.

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.

An object of the present invention is to provide an electrode assembly that can improve the safety of the battery by suppressing the thermal contraction of the separator interposed between the positive electrode and the negative electrode of the unit cell in a high temperature environment.

Another object of the present invention is to provide an electrode assembly that can reduce the amount of use of the separator in the manufacturing process to reduce the manufacturing cost, maximize the battery capacity by reducing the size of the separator excess.

Still another object of the present invention is to provide an electrochemical cell consisting of the electrode assembly described above.

An electrode assembly according to the present invention for achieving this purpose is an electrode assembly in which a plurality of unit cells are folded by a long sheet-type separation film, the unit cell includes two or more separators and one end of adjacent separators Is in close contact with the side of the electrode in an interconnected state.

Therefore, in the electrode assembly according to the present invention by interconnecting the separator interposed between the positive electrode and the negative electrode at one end in the unit cell folded by the separation film, it is possible to prevent the internal short circuit due to thermal contraction of the separator at high temperature In addition, the manufacturing cost can be reduced by reducing the usage amount of the excess portion at the end portion of the separator which protrudes from the side thereof, and the battery capacity can be increased compared to the same standard by being closely attached to the side of the electrode.

In the present invention, the unit cell may be formed of a bicell having the same electrode structure at both sides and / or a full cell having different electrode structures at both 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. In order to construct an electrochemical cell including a secondary battery using such a full cell, a plurality of full cells should be stacked such that the positive electrode and the negative electrode face each other with the separation film interposed therebetween.

In addition, a bicell as a unit cell is a cell in which the same electrodes are located on both sides of the cell, such as a unit structure of an anode / separator / cathode / separator / anode and a unit structure of a cathode / separator / anode / separator / cathode. In order to construct an electrochemical cell including a secondary battery using such a bicell, a bicell (anode bicell) and a cathode / separator / anode / of a cathode / separator / cathode / separator / anode structure with a separator film interposed therebetween. A plurality of bicells should be stacked such that the bicell of the separator / cathode structure (cathode bicell) faces each other.

In some cases, a larger number of stacks of bicells are also possible, e.g. anode / separator / cathode / cathode / anode / separator / cathode / separator / anode and cathode / separator / anode / separator / cathode / separator It is also possible to bicell the anode / separator / cathode structure.

In one preferred example, the separators are separated from each other, and may be bent according to the electrode structure. For example, in the case of a bicell having a first anode / first separator / cathode / second separator / second anode structure, the first separator and the second separator are exemplarily illustrated at the right side of the unit cell. As one entity connected to each other, the connection portions of the separators may be bent to be located on the right side of the cathode. In the above structure, the separator includes a first separator positioned between the bottom surface of the first anode and the top surface of the cathode, a bent portion surrounding the right side of the cathode, and a second separator continuous to the first separator is formed on the bottom surface of the cathode and the second anode. It can be bent in a c-shape to be located between the top surfaces. Here, the bent connection portion of the separator is in close contact with the right side of the cathode.

As an example of a preferred structure, the electrode assembly includes at least one positive electrode and a negative electrode as a unit cell, the separation membrane of each bicell may have a structure in which the separation membrane of one object is bent. That is, in the above structure, the separator may be bent according to the structure of the electrode as one object in each bicell constituting the unit cell. Here, the "anode bicell" refers to a cell in which the positive electrode is located on both sides of the cell, for example, a unit structure of the anode / separator / cathode / separator / anode, the "cathode bicell" is a negative electrode It refers to a cell in which cathodes are positioned on both sides of a cell, such as a unit structure of a separator, an anode, a separator, and an anode.

As another example of the preferred structure, the electrode assembly includes at least two full cells as each unit cell, and the separation membranes of each unit cell composed of the full cells may have a structure in which one separation membrane is bent. . That is, in the above structure, the separator may be bent according to the structure of the electrode as one individual in two full cells constituting the unit cell. Specifically, when the unit cell has a structure in which two full cells (first full cell and second full cell) of anode / separation membrane / cathode are stacked, a separator interposed between the anode and the cathode of the first full cell and the second full cell, respectively. And the separator interposed between the first full cell and the second full cell are connected to each other at the right side of the cathode 1b positioned at the bottom of the first full cell and at the left side of the anode 2a positioned at the top of the second full cell. It can be one entity. Here, the separator may have a structure that is bent at a connection portion located on the right side of the cathode 1b and the left side of the anode 2a to be in close contact with the side surfaces of the electrodes 1b and 2a.

The present invention also provides an electrochemical cell consisting of the electrode assembly as described above.

The electrochemical cell provides electricity through an electrochemical reaction, and may be, for example, an electrochemical secondary battery or an electrochemical capacitor, and may be preferably applied in a lithium secondary battery.

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.

1A-1E are schematic diagrams of one exemplary full cell and bicell that can be used as a unit cell in an electrode assembly of the present invention.

First, referring to FIG. 1A, the full cell 400 is a unit cell of an electrode assembly according to the present invention, and includes a first unit full cell 400a including anodes 100a and 100b and cathodes 200a and 200b, respectively. ) And the second unit full cell 400b. Thus, the structure of the anode / separator / cathode / separator / anode / separator / cathode as a whole.

The separator 300 is first bent in a form covering the right side surface of the cathode 200a in a state interposed between the anode 100a and the cathode 200a of the first unit full cell 400a, and the first unit full cell 400a. In the state interposed between the cathode (200a) and the anode (100b) of the second unit full cell (400b) of the second bend in a form covering the left side of the anode (100b), the anode of the second unit full cell 400b again It is interposed between 100b and the cathode 200b. In addition, the separator 300 has a structure in which an end portion 310 of the separator 300 protrudes by a predetermined length from a left side surface of the first unit full cell 400a and a right side surface of the second unit full cell 400b.

The bent portion is bent in close contact with the side of the corresponding electrode. This close contact state also applies to the following examples.

Since inside of the unit full cells 400a and 400b and the separator 300 positioned therebetween are interconnected, thermal contraction is minimized due to the connection (that is, the bent portion) even in a high temperature environment.

1B and 1C, the positive electrode bicell 500 has a structure of a positive electrode 100, a separator 300, a negative electrode 200, a separator 300, and a positive electrode 100, and has a negative electrode bicell 600. ) Has a structure of a cathode 200 / separator 300 / anode 100 / separator 300 / cathode 200.

In the positive electrode bicell 500 of FIG. 1B, the separator 300 is bent in a structure surrounding the right side surface of the negative electrode 200 while being interposed between the positive electrode 100 and the negative electrode 200, and the negative electrode bicell of FIG. 1C. In 600, the separator 300 is bent in a structure surrounding the right side surface of the anode 100 in a state interposed between the anode 100 and the cathode 200. Also in these drawings, the separator 300 has a structure in which its end portion protrudes by a predetermined length from the left side of the unit cell.

The positive electrode bicell 500 and the negative electrode bicell 600 may have a structure in which a larger number of the positive electrode 100 and the negative electrode 200 are sequentially stacked as shown in FIGS. 1D and 1E. In this case, the separator 300 is bent several times to cover one side of the electrodes 100 and 200 according to the structures of the anode 100 and the cathode 200.

The separation membrane connection form as described above, as well as the suppression of heat shrinkage as described above, as shown in Figure 1b to 1d, since the end side of the separator does not exist on the right side where the bent portion of the separator 300 is compact electrode assembly To provide. Therefore, in the battery case of the same standard to increase the size of the electrode assembly to increase the capacity of the battery, or to be used for other purposes. Here, the excess portion at the end of the separator means a residual portion generated when the size of the separator is larger than that of the electrode so as to compensate for the decrease in size due to heat shrinkage. In FIGS. 1B to 1D, the excess portion protrudes from the left side of the electrode. Corresponds to the end of the membrane.

2 is a schematic diagram of an electrode assembly composed of full cells as shown in FIG. 1A as a unit cell according to one embodiment of the present invention.

Referring to FIG. 2, the electrode assembly 800 has a structure in which a plurality of full cells 401, 402, 403... Are folded by a long separation film 700. The electrode assembly 800 has a separation film 700 once surrounding the outer surface of the first full cell 401, the second full cell 402 and the third full cell on the upper and lower portions of the first full cell 401, respectively. It can be manufactured by folding the full cells (401, 402, 403 ...) in a structure that wraps the outer surface of them once in the state 403 is positioned.

3A and 3B are schematic views of an electrode assembly including bicells as shown in FIGS. 1B and 1C as unit cells according to another embodiment of the present invention.

Referring to these drawings, the electrode assemblies 900 and 901 are formed by a plurality of anode bicells 501, 504, 505... And a plurality of cathode bicells 502, 504. It consists of a structure that is folded sequentially.

In the electrode assemblies 900 and 901, as shown in FIG. 3A, the separator film 700 once wraps the outer surface of the positive anode bicell 501, and the cathode is disposed on the upper and lower portions of the positive electrode bicell 501, respectively. Folding the bicells 501, 602, 603 ... in a structure that wraps the outer surface of the cells in the state where the bicells 602 and 603 are positioned, or as shown in FIG. 3B, the separation film 700 is the lowest. The bi-cells 510... 603, 501, 602... 520 of the bi-cell 510 of the bi-cell 510 in the Z shape from the center bi-cells 501, 602, 603 to the top bi-cell 520. It can be manufactured by folding.

For the same reason as described above, the electrode assemblies 900 and 901 of FIGS. 3A and 3B have the separators interposed inside the bicells bent in a state of being in close contact with the right side of the corresponding electrode. No addition may be present to increase battery capacity or allow for other uses.

In addition, when folding the full cells 401, 402, 403... Or bicells 501, 602, 603... With the method of FIGS. Since the thickness of the separation film 700 covering both sides of the thickened, in order to allow for such a thickness increase, the width of the bi-cell (401, 501) may be configured to be narrow.

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 bicell as shown in FIGS. 1B and 1C, respectively, the positive bipolar and the negative bipolar were sequentially folded with a separation film made of the same material as the separator. An electrode assembly was prepared, and the electrode assembly was embedded in a pouch-type battery case, and then electrolyte was injected to complete the battery.

Comparative Example 1

A battery was completed in the same manner as in Example 1, except that the separators were separated between the electrodes.

Experimental Example 1

High temperature exposure experiments were carried out 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 20 cells was repeatedly performed, and the high temperature exposure experiment was performed under conditions of maintaining at 160 ° C for 10 minutes.

TABLE 1

Number of cells shorted at high temperatures Example 1 0 Comparative Example 1 6

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, even when the separators interconnected in each unit cell are shrunk at a high temperature, the electrodes may be folded to prevent contact between the anode and the cathode. On the other hand, the batteries of Comparative Example 1 were found to cause short circuits in a plurality of batteries.

As described above, the electrode assembly according to the present invention can not only improve the safety of the battery by suppressing the thermal contraction phenomenon of the separator interposed between the anode and the cathode of the unit cell in a high temperature environment, the amount of the separator used By reducing the manufacturing cost can be reduced, there is an effect that can increase the battery capacity compared to the same standard.

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 (8)

An electrode assembly in which a plurality of unit cells are folded by a long sheet-type separation film, wherein the unit cell includes two or more separators, and adjacent separators of the unit cells are disposed on the side of the electrode with one end connected to each other. An electrode assembly, which is bent according to an electrode structure as a separator of one object so as to be in close contact. The method of claim 1, wherein the unit cell is characterized in that (i) a bicell of the same electrode structure on both sides, or (ii) a full cell of the electrode structure on both sides, or (iii) the bicell and the full cell Electrode assembly. delete The electrode assembly of claim 1, wherein the electrode assembly has a structure including at least one positive electrode and a negative electrode as a unit cell. The electrode assembly of claim 1, wherein the electrode assembly has a structure including at least two full cells as a unit cell. An electrochemical cell comprising the electrode assembly according to claim 1. 7. The electrochemical cell of claim 6, wherein said cell is a secondary battery or a capacitor. 8. The electrochemical cell of claim 7, wherein said cell is a lithium secondary battery.

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