KR100898070B1 - Lithium secondary battery - Google Patents

Abstract

The present invention includes an electrode assembly having two electrode tabs, an outer material surrounding the electrode assembly so that the electrode tab protrudes, and an insulating member on the electrode tab to prevent a short circuit between the electrode tab and the outer material. Provided is a lithium secondary battery comprising polypropylene, at least one rubber selected from natural rubber and synthetic rubber. According to the present invention, it is possible to effectively prevent a short circuit between the electrode tab and the exterior material, especially aluminum, while maintaining the airtightness while maintaining the predetermined thickness of the insulating tape itself as it is during electrode tab sealing.

Description

Lithium secondary battery {Lithium secondary battery}

1 is an exploded perspective view of a typical lithium secondary battery.

<Brief description of the major symbols in the drawings>

11 ... anode plate 12 ... cathode plate

13 ... Separator 14 ... Anode Tab

15 ... cathode tab 16 ... second junction

17 ... First junction 18 ... Exterior

19 ... Insulation member 20 ... Wing

The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery using a pouch as a battery packaging material.

In general, as the light weight and high functionality of a portable wireless device such as a video camera, a portable telephone, a portable PC, and the like have progressed, many studies have been conducted on a secondary battery used as a driving power source. Such secondary batteries include, for example, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, and lithium secondary batteries. Among them, lithium secondary battery has the advantage of long life and large capacity.

Lithium secondary batteries can be classified into batteries employing a liquid electrolyte and batteries employing a polymer electrolyte according to the type of electrolyte. Generally, a battery employing a liquid electrolyte is called a lithium ion battery, and a polymer electrolyte is used. The battery is called a lithium polymer battery.

A typical lithium secondary battery includes a positive electrode plate and a negative electrode plate, and a separator interposed therebetween to insulate the positive electrode plate and the negative electrode plate, and includes a positive electrode tab electrically connected to each of the positive electrode plates, and a negative electrode electrically connected to each negative electrode plate. An electrode assembly having a tab.

The electrode assembly is sealed by a pouch, which is an exterior material, and the positive electrode tab and the negative electrode tab are exposed to the outside of the pouch to serve as battery terminals.

A polypropylene tape is interposed between the positive and negative tabs and the upper and lower surfaces of the pouch to insulate them.

However, in the case of using the polypropylene tape as described above, when sealing the upper and lower portions of the pouch, the polypropylene tape is melted all at once, making it difficult to secure a constant thickness, causing short circuits due to contact between the electrode tab and the upper surface of the pouch (particularly, aluminum foil). There is this.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a lithium secondary battery that can effectively prevent a short circuit between an electrode tab and an exterior member while maintaining a good sealing state between a case and an electrode tab by solving the above problems.

In order to achieve the above technical problem, in the present invention, an electrode assembly having two electrode tabs,

An exterior member surrounding the electrode assembly to protrude the electrode tab;

An insulating member formed on the electrode tab to prevent a short circuit between the electrode tab and the exterior member;

Provided is a lithium secondary battery, wherein the insulating member comprises polypropylene, at least one rubber selected from natural rubber and synthetic rubber.

The rubber content is 1 to 5% by weight based on the total weight of polypropylene and rubber.

The particle size of the rubber contained in the insulating member is 10 to 100 mu m.

The distance between particles of rubber contained in the insulating member is 20 to 200 mu m.

The synthetic rubber contained in the insulating member is at least one selected from the group consisting of butadiene rubber, butadiene-styrene rubber and EPDM.

The crystallinity of the polypropylene contained in the insulating member is 30 to 70%, and the melting point is 130 to 170 ° C.

The present invention is a lithium secondary battery using a pouch as an outer packaging material, when sealing the upper surface and the lower surface of the packaging material, the insulation made of a blend of polypropylene and rubber as an insulating member to prevent a short circuit between the electrode tab and the packaging material. Use tape. Herein, the content of rubber in the blend is preferably 1 to 5% based on the total weight of polypropylene and rubber. If the content of the rubber exceeds 5%, the pouch sealing due to thermocompression may occur poorly and less than 1%, which is not preferable because the rubber addition effect is insignificant.

Natural rubber, synthetic rubber or a mixture thereof is used as the rubber, butadiene rubber, butadiene-styrene rubber, EPDM and the like are used as the synthetic rubber, and among them, butadiene rubber is particularly preferable. Here, EPDM is an ethylene propylene terpolymer, and refers to a synthetic rubber made of ethylene propylene non-conjugated diene.

The particle diameter and the particle-particle distance of the rubber contained in the insulating member are closely related to fluidity, sealing property, work handling and the like of the insulating member under heat treatment conditions for sealing the upper and lower surfaces of the pouch.

Preferably the particle size of the rubber is preferably 10 to 100㎛. If the diameter of the rubber particles exceeds 100 μm, the rubber distribution in the polypropylene matrix may be nonuniform, and if less than 10 μm, entanglement between the rubber particles may occur, resulting in non-uniform size distribution.

It is preferable that the distance between the said rubber particle and particle | grains is 20-200 micrometers. If the distance between the rubber particles and the particles is less than 20 μm, interference between the rubber particles occurs, and if it exceeds 200 μm, the effect of the rubber is weak, which is not preferable.

It is preferable that the polypropylene has a crystallinity of 30 to 70% and a melting point of 130 to 170 ° C. If the crystallinity of the polypropylene is out of the above range, there is a problem that the melting point is different and it is difficult to obtain a uniform dispersibility when blending with the rubber.

Although the shape of the insulating member is not particularly limited, it is appropriate that the width is 0.5 to 1.0 Cm, and the thickness is 0.3-0.8 Cm.

1 is a cross-sectional view showing an example of a lithium secondary battery according to the present invention.

Referring to FIG. 1, a positive electrode plate 11 and a negative electrode plate 12 and a separator 13 interposed therebetween to insulate the positive electrode plate 11 and the negative electrode plate 12 are interposed therebetween. And an electrode assembly 10 having a positive electrode tab 14 electrically connected to the negative electrode tab 14 and a negative electrode tab 15 electrically connected to the respective negative electrode plates 12.

The electrode assembly 10 is wrapped and enclosed by a flexible material 18 made of a flexible material, and the positive electrode tab 14 and the negative electrode tab 15 are exposed to the outside of the external material 10 to serve as battery terminals. Will be

The exterior material 18 is not particularly limited in material, but any exterior material 18 may be used as long as it has a predetermined tensile force and is flexible enough to be insulated from the electrode assembly 10. As a specific example of the packaging material, the electrode assembly has a structure in which a polypropylene layer, a poly (ethylene acrylic acid: EAA) layer, an aluminum layer, a poly (ethylene acrylic acid: EAA) layer, and a nylon layer are laminated. The PP layer has the function of strengthening the strength of the exterior material and preventing the short circuit caused by the lead wires, the EAA layer has the adhesive function, the aluminum layer has the function of preventing moisture penetration and electrolyte leakage, and the nylon layer has the external function. It has a function of smoothing the inner layer forming process while preventing cracks in the layer.

An insulating member 19 having a predetermined length between the positive electrode tab 14 and the positive electrode tab 15, and the first and second bonding portions 17 and 16 of the packaging material surrounding the electrode assembly 10. ) Is interposed. Here, the first junction 17 and the second junction 16 are fused and sealed to each other. At this time, the fusion process for sealing the first joint 17 and the second joint 16 is carried out by pressing for 5 to 15 seconds at 130-150 ℃.

As shown in FIG. 1, the insulating member 19 is coated on the positive electrode tab 14 and the negative electrode tab 15 with a predetermined width and has a wing portion 20 extending a predetermined length to both sides of the electrode tab. And a tape consisting of a blend of polypropylene and rubber in a mixing ratio of 99: 1 to 95: 5.

Since the tape as described above is interposed between the first bonding portion, the second bonding portion, and the electrode tab in the exterior material, the electrode tab is sealed to seal the electrode tab, so that the insulating tape itself is not melted at once but slowly melts for a predetermined time, thereby maintaining a constant thickness of the tape itself. It is excellent in sealing property and insulation. As a result, a short circuit between the electrode tab and the packaging material can be effectively prevented.

Hereinafter, the present invention will be exemplified by the following examples, but the present invention is not limited only to these examples.

<Example 1>

The insulation tape was made using a blend of 95 parts by weight of polypropylene and 5 parts by weight of butadiene rubber.

The insulating tape was attached to a predetermined position of the cathode tab and the anode tab as shown in FIG. 1, and the upper and lower surfaces of the pouch were sealed in the middle to manufacture a lithium secondary battery. At this time, the sealing was carried out by heat-sealing at 145 ° C. for 5 seconds.

Comparative Example 1

A lithium secondary battery was manufactured according to the same method as Example 1 except for using a polypropylene insulating tape instead of an insulating tape made of a blend of polypropylene and butadiene rubber.

In the lithium secondary battery prepared according to Example 1 and Comparative Example 1, the presence or absence of a short circuit was investigated. Here, short-circuit evaluation can be discriminated by OCV measurement and was performed under normal temperature and normal pressure.

As a result of the evaluation, it was confirmed that the number of short circuits was significantly reduced in the lithium secondary battery prepared according to Example 1 compared with the case of Comparative Example 1 using a polypropylene tape.

As described above, according to the present invention, it is possible to effectively prevent a short circuit between the electrode tab and the exterior material, especially aluminum, while maintaining the airtightness while maintaining a predetermined thickness of the insulating tape itself as it is during electrode tab sealing.

Although described with reference to one embodiment shown in the drawings of the present invention, this is merely exemplary, those skilled in the art should understand that various modifications and equivalent other embodiments are possible from this. something to do. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (6)

An electrode assembly having two electrode tabs, An exterior member surrounding the electrode assembly to protrude the electrode tab; An insulating member formed on the electrode tab to prevent a short circuit between the electrode tab and the exterior member; The insulation member, With polypropylene, Butadiene rubber, butadiene-styrene rubber and synthetic rubber, at least one selected from the group consisting of ethylene propylene non-conjugated diene (EPDM), The content of the synthetic rubber is 1 to 5% by weight based on the total weight of polypropylene and synthetic rubber, The particle size of the rubber contained in the insulating member is 10 to 100㎛, A lithium battery, wherein the distance between particles of rubber contained in the insulating member is 20 to 200 µm. delete delete delete delete The lithium battery according to claim 1, wherein the polypropylene has a crystallinity of 30 to 70% and a melting point of 130 to 170 ° C.

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