KR20040110156A - Pouch type secondary battery with safty vent - Google Patents

Abstract

PURPOSE: A pouch type secondary battery having a safety valve is provided to improve battery safety, and thus to prevent explosion and ignition of the battery under extreme conditions including overcharge, overdischarge and internal short circuit. CONSTITUTION: The pouch type secondary battery comprises: an electrode assembly(20) including a first electrode plate, a second electrode plate and a separator interposed between both plates and provided with a first and a second electrode tabs(21,22) each extending from the first and the second electrode plates; a pouch casing(10) having an inner space(13) for housing the electrode assembly(20) and sealed so that at least the first electrode tab(21) can be exposed to the exterior, wherein the casing is electrically insulated at least at the inner surface thereof; and a first tab tape(23) attached to at least one surface of the portion of the first electrode tab(21) overlapped with the sealing portion of the pouch casing, wherein the first tab tape(23) is formed of a resin material having a melting point lower than that of the sealing portion(14) of the pouch casing.

Description

Pouch type secondary battery with safety valve {Pouch type secondary battery with safty vent}

The present invention relates to a secondary battery, and more particularly, to a pouch-type secondary battery having a safety valve to prevent explosion and ignition of the battery.

In general, secondary batteries are rechargeable and can be miniaturized and large-capacity. Typically, nickel-hydrogen (Ni-MH) batteries and lithium (Li) secondary batteries are used.

The secondary battery may be classified into a cylindrical battery using a cylindrical aluminum can, a square battery using a square aluminum can, and a pouch-type battery housed in a thin pouch case according to the appearance of a case housing the electrode plate assembly.

Among these, the pouch type secondary battery has a structure in which an electrode assembly is sealed inside a pouch case insulated from inside and outside of a metal thin plate such as an aluminum thin plate, and the pouch case is different from the can of a can type secondary battery. Otherwise, it is made of sheet metal and is very flexible.

On the other hand, when the secondary battery is overcharged and the voltage inside thereof increases, gas may be generated to expand and explode. In particular, a lithium ion battery releases gases such as carbon dioxide and carbon monoxide as the liquid electrolyte decomposes due to overcharging, thereby increasing the internal pressure of the battery. In addition, when an overcurrent flows due to over-discharge or short circuit, the temperature inside the battery rises and the liquid electrolyte turns into a gas. Accordingly, the pressure and temperature inside the battery rise. In particular, there is a risk of ignition. come.

In addition, the secondary battery as described above can be safely used by keeping the temperature conditions at the time of charging and the temperature at the time of use. In the case of severe use environment, that is, the temperature at the time of charging / discharging is excessively high, If the operating temperature is too high, such external temperature conditions may increase the temperature of the battery, causing an explosion or fire.

Therefore, due to the safety issues of such secondary batteries, in addition to safety tests such as overcharge and forced discharge, the high temperature storage test, thermal shock test and thermal exposure ( Various thermal safety tests, including thermal exposure tests, are conducted. This thermal safety test is to leave the battery in different temperature conditions for several tens of minutes to several tens of hours, at which time there should be no explosion or ignition of the battery, and in extreme cases, the battery should be unsealed to prevent explosion and ignition.

Attempts to solve the safety problem of the secondary battery has been progressed so far, in particular, many technologies have been developed to install the safety valve in the battery case to remove the gas inside. Accordingly, a can-type secondary battery using a rectangular or cylindrical can as a battery case is provided with safety valves having various structures on the cap plate or the can itself so that the battery does not rupture when the temperature or pressure inside the battery is increased. However, in the case of the pouch type secondary battery, since the battery case itself is made of a flexible material, there is a problem that it is difficult to install a safety valve structure such as the can type battery in the case.

Korean Patent Publication No. 98-44210 discloses a safety valve structure of a pouch type secondary battery. The disclosed technology makes a separate gas discharge port or check valve made of a material having a low tear resistance at the upper front of the battery, that is, the upper cover of the pouch case as described above, and in case of expansion due to overcharge and discharge. May be ruptured or internal gas may be discharged through the check valve. However, the separate equipment installed at the top of the battery in this way requires a further process in producing the battery, there is a problem that the productivity is lowered.

In addition, the technique disclosed in U.S. Patent No. 4,678,725 is such that when the internal pressure rises above a certain pressure between the fusion portions of the electrode tabs at the top of the battery, the heat fusion portion bursts so that the gas inside may be discharged. However, even in such a technology, the installation of a separate safety valve (safty valve) has to be different from the original pack structure itself, and accordingly there is a problem that must be manufactured by manufacturing a separate case other than the conventional casing. In addition, even in the case of manufacturing a conventional case, the safety valve structure forms an unsealed portion, and attaches a clip thereon, which requires a large number of processes because it must be separately bonded in consideration of the breaking strength of the clip. Rather, the reliability of the rupture is reduced.

The present invention is to solve the above problems, a pouch that can prevent the explosion and heat generation by releasing the sealing of the pouch case when the internal temperature of the battery rises due to overheating conditions such as overcharge, overdischarge or internal short circuit with a simple structure The object is to provide a type secondary battery.

1 is an exploded perspective view of a pouch-type secondary battery according to an embodiment of the present invention.

2 is a cross-sectional view showing the material of the pouch case of FIG.

3 is a plan view of the pouch type secondary battery of FIG. 1.

4 and 5 is an operating state diagram of the pouch-type secondary battery according to an embodiment of the present invention according to FIG.

<Brief description of symbols for the main parts of the drawings>

10: pouch case 11: case body

12: pouch cover 13: space

14: seal 20: electrode assembly

21: first electrode tab 22: second electrode tab

23: first tab tape 24: second tab tape

The present invention for achieving the above object is provided with a first electrode plate and a second electrode plate via a separator, the first and the second electrode plate and the electrode assembly extending from the first and second electrode tab, respectively; A pouch case having a space part therein, wherein the electrode assembly is accommodated in the space part, the pouch case is sealed to expose at least the first electrode tab to the outside, and at least an inner surface thereof is electrically insulated; Provided is a pouch type secondary battery, comprising a first tab tape attached to at least one surface of a portion overlapping the sealing portion of the pouch case and formed of a resin material having a lower melting point than the sealing portion of the pouch case.

According to another feature of the invention, the melting point of the first tab tape may be in the range of 120 to 200 ℃.

According to another feature of the invention, the first tab tape can start to deform at approximately 150 ° C.

According to another feature of the invention, the first tab tape may be made of polyethylene or modified polypropylene.

According to another feature of the present invention, the first electrode plate may be provided with copper or a copper alloy, and the first electrode tab may be provided with nickel or a nickel alloy.

According to another feature of the present invention, the first electrode tab may be attached to the first electrode uncoated portion to which the first electrode mixture containing the first electrode active material of the first electrode plate is not applied.

According to another feature of the invention, the first electrode plate may be a negative electrode.

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

1 is an exploded perspective view showing a pouch type secondary battery according to an embodiment of the present invention, Figure 2 is a cross-sectional view showing the material of the pouch case, Figure 3 shows a state in which the pouch type secondary battery is coupled. Top view.

Referring to the drawings, a pouch type secondary battery according to an exemplary embodiment of the present invention includes an electrode assembly 20 in which a first electrode plate and a second electrode plate are provided through a separator, and a pouch case in which the electrode assembly is housed ( 10) is provided. In the figure, the electrode assembly 20 is provided with an electrode jelly roll in which the first electrode plate and the second electrode plate are wound through the separator, but are not limited thereto, and the first electrode plate and the second electrode plate are interposed between the separators. It may be provided as a stacked electrode assembly stacked. This applies equally in all embodiments of the present invention to be described below.

On the other hand, in the electrode assembly 20, when the first electrode plate is a negative electrode plate, the second electrode plate may be a positive electrode plate, of course, may be configured with different polarities.

The negative electrode plate may include a negative electrode current collector made of a strip-shaped metal thin plate, and a copper thin plate may be used as the negative electrode current collector.

At least one surface of the negative electrode current collector is coated with a negative electrode mixture, and the negative electrode mixture may be formed of a mixture containing a binder, a plasticizer, a conductive material, and the like in a negative electrode active material of a carbon material.

The positive electrode plate includes a positive electrode current collector made of a strip-shaped metal thin plate, and an aluminum thin plate may be used as the positive electrode current collector.

At least one surface of the positive electrode current collector is coated with a positive electrode mixture including a positive electrode active material, and the positive electrode mixture may include a mixture containing a binder, a plasticizer, a conductive material, and the like in a positive electrode active material of a lithium oxide.

A separator is provided between one side of the negative electrode plate and one side of the positive electrode plate, and the laminate is wound to form an electrode assembly. The separator mutually insulates between the positive electrode plate and the negative electrode plate, and allows active material ions to be exchanged between the electrode plates. The separator is preferably made of sufficient length so as to completely insulate between the electrode plates even if the electrode assembly is contracted and expanded. The electrode assembly can be applied to the present invention in addition to the electrode assembly of any structure.

The first electrode tab 21 and the second electrode tab 22 are drawn out of the electrode assembly 20 formed as described above. The first electrode tab 21 and the second electrode tab 22 are bonded to the first electrode plate and the second electrode plate, respectively. According to a preferred embodiment of the present invention, the first electrode tab ( 21 may be a negative electrode tab, and the second electrode tab 22 may be a positive electrode tab. In this case, the first electrode tab 21 may be made of nickel or a nickel alloy, and the second electrode tab 22 may be made of aluminum or an aluminum alloy. As described above, the first electrode tab 21 and the second electrode tab 22 may be configured to have different polarities.

In the first and second electrode tabs 21 and 22, a first tab tape 23 and a second tab tape 24 as shown in FIG. 1 include a predetermined portion of at least one surface of each electrode tab. Is attached to. The first tab tape 23 and the second tab tape 24 are generally used to prevent a short circuit between the pouch case and each electrode tab, which will be described later, and may be made of an insulating resin material having an adhesive surface. According to this invention, the said tab tape is provided so that it may function as a safety valve as mentioned later. A more detailed description will be described later.

The electrode assembly 20 as described above is accommodated in the pouch case 10 having a space 13 therein, the pouch case 10 as shown in Figure 1, the space 13 ) And a pouch cover 12 that covers the case body 11 and seals the space 13. One end of the pouch cover 12 extends from the case body 11, and a flange for joining the pouch cover 12 to the periphery of the space 13 is formed at the case body 11. The pouch cover 12 is joined to the flange to form a seal 14. As one end of the pouch cover 12 is connected to the case main body 11, the sealing parts for sealing the space 13 may be three, as shown in FIG. 3. However, the shape of the pouch case is not necessarily limited to the above, and although not illustrated in the drawings, the pouch case may be applied to a method of accommodating the electrode assembly in a pouch case having an open side and sealing the one side. Of course, one seal is formed at this time. Hereinafter, a description will be given focusing on the case of the pouch case described above, that is, a pouch case having a case body and a pouch cover.

On the other hand, the pouch case 10 of the pouch-type secondary battery as described above may be made of a thin plate mixed with a metal material and a resin material, as can be seen in Figure 2, of the metal plate (11a) (12a), such as aluminum Modified polypropylene, which is a polymer resin on the inner side, for example, CPP (Casted Poly-Propylene) forms a heat-adhesive layer 11b, 12b, and an outer side resin material 11c such as nylon or polyethylene terephthalate (PET) on the outer side. 12c may be formed of a composite material which is compressed through the thermal bonding layers 11b and 11c. 2 illustrates a case of the case body 11 and the pouch cover 12 facing each other, wherein the pouch case 10 is formed such that the heat-adhesive layers of the case body 11 and the pouch cover 12 come into contact with each other. It can be sealed by thermocompression bonding in a state.

The pouch case 10 having the structure and the material as described above is assembled, as can be seen in FIG. That is, the sealing part 14 is formed along the edge of the pouch case 10, and the 1st electrode tab 21 and the 2nd electrode tab 22 are pulled out outside this sealing part 14. As shown in FIG. . In addition, the first tab tape 23 and the second tab tape 24 bonded to the first electrode tab 21 and the second electrode tab 22, respectively, are positioned to span the seal 14. At this time, the first tab tape 23 and the second tab tape 24 may be provided such that both ends in the longitudinal direction of the battery are exposed to the outside of the sealing portion 14, as shown in FIG. Although not shown, it may be provided so as not to deviate from the seal 14, that is, the length thereof is smaller than the width of the seal 14.

In the pouch type secondary battery provided as above, according to the present invention, the first tab tape 23 is formed of an insulating resin material having a lower melting point than the sealing portion 14. This is for the case where the internal pressure of the battery is increased due to an internal short circuit or the like, so that the portion of the sealing portion 14 interposed with the first tab tape 23 may be ruptured first, as described above. It can be formed in a tab tape. This is because, in the case of the negative electrode, a carbon-based active material is used, and the current collector is also made of a copper thin plate, and when the internal short circuit of the battery occurs, the temperature rise is significantly higher than that of the positive electrode. In the case of the normal high temperature short-circuit test, the temperature of the negative electrode tab is about 50 ° C to 100 ° C higher than the temperature of the positive electrode tab.

Therefore, in the present invention, the first tab tape 23 of the first electrode tab 21, which can be used as the negative electrode tab, is formed of a resin material having a melting point lower than that of the sealing portion 14, thereby increasing the battery internal temperature. The portion in which the first tab tape 23 is interposed prior to the sealing portion can be ruptured. At this time, it is preferable that the first tab tape 23 is formed of a bonded portion of the sealing portion 14, that is, a material having a lower melting point than that of the thermal adhesive layers 11b and 12b. This is because the portion in which the sealing portion 14 is bonded is the heat-adhesive layers 11b and 12b on the surfaces of the case body 11 and the pouch cover 12 that face each other.

According to a preferred embodiment of the present invention, the first tab tape 23 may be determined according to the material of the pouch case 10, in particular, the material of the heat adhesive layer, but the melting point is preferably in the range of 120 to 200 ° C. It is preferable that the deformation be started at about 150 ° C. To this end, as the first tab tape 23, a polyethylene type having a lower melting point than that of the modified polypropylene (CPP), which is generally used as the thermal adhesive layers 11b and 12b, may be used, and the melting point is higher than that of the thermal adhesive layer. Low modified polypropylenes can be used.

In addition, the first electrode tab 21 is an uncoated portion of the first electrode plate, that is, an electrode including an active material so that heat transfer to the first tab tape 23 through the first electrode tab 21 can be smoothly performed. It is preferable to bond to the surface of the electrode collector in which the mixture is not applied.

Next, the operation of the pouch type secondary battery according to the present invention configured as described above will be described.

In the pouch type secondary battery as shown in FIG. 2 and FIG. 3, when the battery is overcharged or used at a high temperature, gas is generated inside the battery, thereby expanding the battery as shown in FIG. 4. This swelling is further increased when swelling occurs. If it is left as it is, ignition or explosion occurs inside the battery. Therefore, the gas inside the battery must be discharged before such a ignition and explosion occurs.

As described above, when the pressure and the temperature increase due to gas generation inside the battery, when the internal temperature of the battery rises above a predetermined temperature and reaches the melting point of the first tap tape 23, the first temperature is increased. The tab tape 23 is melted, so that the bonding strength of the sealing part with the first tab tape 23 is lower than that of the other parts. As the bonding strength of the position where the first tab tape 23 is located is lowered, this part becomes vulnerable to the pressure inside the battery, and as a result, as shown in FIG. 5, the sealing with the first tap tape 23 is provided. The part of the part is ruptured. The gas inside the battery is discharged through the portion of the broken seal so that the battery may not be ignited or exploded.

According to the present invention as described above, the following effects can be obtained.

First, by increasing the thermal safety of the battery, it is possible to prevent the battery from exploding and igniting when the battery is used in a high temperature environment, or when the battery thermal runaway (thermal runaway).

Second, safety may be ensured even when excessive gas pressure occurs inside the battery due to swelling due to overcharging and other internal short circuits.

Third, the battery can be secured with a simple structure.

Fourth, the existing battery manufacturing process can be used as it is, the productivity can be increased.

Although the present invention has been described with reference to one embodiment shown in the accompanying drawings, this is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. Could be. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

Claims (7)

An electrode assembly having a first electrode plate and a second electrode plate interposed between the separators, and having first and second electrode tabs extending from the first and second electrode plates, respectively; A pouch case having a space part therein, the electrode assembly being accommodated in the space part, the pouch case sealed to expose at least the first electrode tab to the outside, and having at least an inner surface thereof electrically insulated; And And a first tab tape attached to at least one surface of a portion overlapping the sealing portion of the pouch case of the first electrode tab and formed of a resin material having a lower melting point than the sealing portion of the pouch case. Pouch type secondary battery. The method of claim 1, The melting point of the first tab tape is a pouch type secondary battery, characterized in that 120 to 200 ℃. The method of claim 1, The first tab tape is a pouch type secondary battery, characterized in that the deformation begins at about 150 ℃. The method according to any one of claims 1 to 3, The first tab tape is a pouch type secondary battery, characterized in that made of polyethylene or modified polypropylene. The method according to any one of claims 1 to 3, The first electrode plate is provided with copper or a copper alloy, and the first electrode tab is a pouch type secondary battery, characterized in that provided with nickel or nickel alloy. The method according to any one of claims 1 to 3, The first electrode tab is a pouch type secondary battery, characterized in that attached to the first electrode uncoated portion, the first electrode mixture containing the first electrode active material of the first electrode plate is not applied. The method according to any one of claims 1 to 3, The first electrode plate is a pouch type secondary battery, characterized in that the negative electrode.