KR20220037770A - Sealing film for lead tap of secondary battery - Google Patents

Abstract

The present invention relates to a sealing film for a lead tab of a secondary battery, which prevents a metal layer of an outer pouch (1) and a conductor of the lead tab (3) from being short-circuited with each other as a surface melts and slides out during a bonding process of the sealing film (2), and at the same time prevents the sealing film (2) from melting and sliding out.

Description

Sealing film for lead tab of secondary battery {SEALING FILM FOR LEAD TAP OF SECONDARY BATTERY}

The present invention relates to a sealing film for a lead tab of a secondary battery, and more particularly, it can be manufactured without adversely affecting molding equipment or products, and does not cause a short circuit between the metal layer of the exterior pouch and the conductor of the lead tab, It relates to a sealing film for a lead tab of a secondary battery capable of maintaining the adhesion between the lead tab and the exterior pouch.

In general, electronic products such as mobile phones, laptops, drones, and cameras have a built-in battery as a driving power source.

Secondary batteries that can be charged and discharged are widely used in consideration of economical aspects. As secondary batteries, there are nickel-cadmium batteries, nickel-hydrogen batteries, lithium batteries, lithium ion batteries, and lithium polymer batteries. As higher voltages and energy densities are required, the use of lithium-ion batteries is increasing.

Conventional lithium-ion batteries have a cylindrical structure, but pouch-type lithium-ion batteries have recently been developed in order to reduce the space occupied by the battery and reduce weight in electronic devices, and recently, it is also used in large-capacity batteries used in medium and large-sized devices such as electric vehicles. A pouch-type lithium-ion battery is being used.

A lithium ion battery is composed of a cathode material, an anode material, a separator, and an electrolyte, and the pouch sealing them is key to preventing leakage of electrolyte or release of gas, as well as preventing moisture penetration from the outside. This is because, when the lithium compound is exposed to moisture, gas may be generated, which may rupture the battery or lead to a fire.

The exterior pouch uses a laminate pouch film coated with a resin, such as a metal layer such as aluminum foil, which can effectively block oxygen, gas, and moisture.

In general, the fusion part (the inner surface in contact with the electrolyte) of the external pouch of the secondary battery is composed of polypropylene, and the outer layer of the metal layer is composed of nylon or PET resin layer.

1 is a perspective view of a main part showing the structure of a general secondary battery.

A typical secondary battery has lead tabs 3 drawn out from a positive electrode and a negative electrode as shown in FIG. 1, and these lead tabs 3 and the exterior pouch 1 are sealed with a sealing film 2 sealed through

The lead tab 3 is made of aluminum, nickel, copper, or an alloy thereof with excellent conductivity, and a sealing film 2 is used for a complete sealing at the bonding site between the lead tab 3 and the exterior pouch 1 . .

The sealing film (2) seals the lead tab (3) and the outer pouch (1) to each other, prevents a short circuit between the metal layer of the outer pouch (1) and the conductors of the lead tab (3), and the lead tab (3) ) conductor and the metal layer of the exterior pouch (1) should maintain the bonding between each other.

Thermal fusion of the exterior pouch (1) and lead tab (3) with the sealing film (2) in between is usually performed by applying heat at 220 ° C. for about 3 to 5 seconds. At this time, the sealing film 2 or the exterior pouch ( As the surface of 1) melts and slides aside, a phenomenon in which the fusion is not uniform occurs. This causes the metal layer of the exterior pouch 1 and the conductor of the lead tab 3 to short-circuit with each other to reduce battery performance or damage the junction. Moisture permeates through the battery, deteriorating battery performance, and causing problems in stability.

Republic of Korea Patent Publication No. 2018-0067633 Republic of Korea Patent Publication No. 1414417 Republic of Korea Patent Publication No. 1240588 Republic of Korea Patent Publication No. 1240496

It is an object of the present invention to provide a sealing film for a lead tab of a secondary battery that prevents the surface of the sealing film from being melted and pushed out during the bonding process of the sealing film so that the metal layer of the exterior pouch and the conductor of the lead tab are not short-circuited, and at the same time, the sealing film is not melted and pushed out. is in providing.

An object of the present invention is to be able to manufacture without adversely affecting molding equipment or products, and to maintain the adhesion between the lead tab and the exterior pouch without causing a short circuit between the conductor of the lead tab and the metal layer of the exterior pouch. To provide a sealing film for a lead tab of a battery.

An object of the present invention is polyethylene powder. Polypropylene powder, polypropylene copolymer powder, polyethylene copolymer powder, etc. are crosslinked with radiation (electron beam, gamma ray, X-ray) to prevent melting by heat, and by mixing this with heat when manufacturing the sealing film, these crosslinked powders are placed on the exterior pouch It is to provide a sealing film for a lead tab of a secondary battery that prevents a short circuit between the lead tab and the lead tab and at the same time prevents leakage of electrolyte by fusion of the lead tab and the external pouch.

It is an object of the present invention to provide a sealing film for a lead tab of a secondary battery in which crosslinked polyolefin powder is chemically crosslinked and melted and pushed out during thermal fusion so that the metal layer of the exterior pouch and the conductor of the lead tab are not short-circuited.

An object of the present invention is to provide a sealing film for a lead tab of a secondary battery having excellent adhesion to the lead tab.

The present invention for achieving the above object,

A sealing film for a lead tab of a secondary battery comprising a first insulating layer, a second insulating layer and a third insulating layer to seal each other between the lead tab and the exterior pouch,

The first insulating layer is an insulating layer in contact with the exterior pouch, and is a polypropylene-based or polyethylene-based resin,

The second insulating layer is embedded between the first insulating layer and the third insulating layer to maintain heat resistance, and to prevent a short circuit between the external pouch and the lead tab, polyolefin powder crosslinked with radiation is added;

The third insulating layer has a basic feature in terms of its technical configuration that modified polyolefin is applied in consideration of adhesion to the lead tab.

The present invention has the effect of preventing the metal layer of the exterior pouch and the conductor of the lead tab from being short-circuited with each other as the surface is melted and pushed out during the bonding process of the sealing film, and at the same time, the sealing film is not melted and pushed out.

The present invention can be manufactured without adversely affecting molding equipment or products, and does not cause a short circuit between the conductor of the lead tab and the metal layer of the exterior pouch, and has the effect of maintaining the adhesion between the lead tab and the exterior pouch. .

The present invention is a polyethylene powder. Polypropylene powder, polypropylene copolymer powder, polyethylene copolymer powder, etc. are crosslinked with radiation (electron beam, gamma ray, X-ray) to prevent melting by heat, and by mixing this with heat when manufacturing the sealing film, these crosslinked powders are placed on the exterior pouch It prevents the short circuit between the lead tab and the lead tab, and at the same time, the lead tab and the external pouch are fused, thereby eliminating leakage of electrolyte.

According to the present invention, the crosslinked polyolefin powder is chemically crosslinked and melted and pushed out during thermal fusion to prevent short circuit between the metal layer of the exterior pouch and the conductor of the lead tab.

The present invention has an effect of excellent adhesion to the lead tab.

1 is a perspective view showing the main part of the structure of a general secondary battery.
2 is a cross-sectional view of a main part for explaining a sealing film for a lead tab of a secondary battery according to an embodiment of the present invention;
3 is a cross-sectional view showing a sealing film for a lead tab of a secondary battery according to another embodiment of the present invention.

A preferred embodiment of the sealing film for a lead tab of a secondary battery according to the present invention will be described with reference to the drawings, and as such an embodiment, there may be a plurality of them, and the objects, features and advantages of the present invention can be achieved through these embodiments. you will be able to better understand

2 is a cross-sectional view of a main part for explaining a sealing film for a lead tab of a secondary battery according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of a main part showing a sealing film for a lead tab of a secondary battery according to another embodiment of the present invention.

The sealing film (2) seals the lead tab (3) and the outer pouch (1) to each other, prevents a short circuit between the metal layer of the outer pouch (1) and the conductors of the lead tab (3), and the lead tab (3) ) and the exterior pouch (1) to maintain the bonding between each other.

Thermal fusion of the lead tab 3 is usually performed by applying heat at 220° C., but the sealing film 2 or the exterior pouch 1 melts and slides out to the side so that the adhesion is not uniform, or the metal layer of the exterior pouch 1 The conductor of the lead tab 3 and the lead tab 3 are short-circuited to deteriorate the battery performance, and moisture penetrates through this portion to deteriorate the battery performance as well as cause a problem in stability.

Therefore, in the present invention, the surface of the sealing film 2 is melted and pushed out during the bonding process to prevent the metal layer of the exterior pouch 1 and the conductor of the lead tab 3 from being short-circuited, and at the same time, the sealing film 2 is melted. It is intended to provide a new sealing film (2) not to be pushed out.

Specifically, the sealing film for the lead tab of the secondary battery of the present invention for sealing the lead tab 3 and the external pouch 1 of the secondary battery to each other is composed of three layers as shown in FIG. 2, and a first insulating layer ( 2-1) is an insulating layer in contact with the exterior pouch 1, polypropylene or polyethylene-based resin is applied, and the second insulating layer 2-2 is a first insulating layer 2-1 and a third insulating layer ( 2-3) to maintain heat resistance as an insulating layer embedded in between, and to prevent a short circuit between the outer pouch (1) and the lead tab (3), polyolefin powder crosslinked with radiation (electron beam, gamma ray) is added. , the third insulating layer 2-3 is a layer in contact with the lead tab 3 so that modified polyolefin having excellent adhesion can be used.

On the other hand, although the present invention is basically composed of three layers, as shown in FIG. 3 , in consideration of economic feasibility, cross-linked polyolefin powder is added to one layer in contact with the lead tab 3 to form a sealing film for the lead tab of a secondary battery. It can also be configured.

According to the embodiment of the present invention, it can be manufactured without adversely affecting molding equipment or products, and without causing a short circuit between the conductors of the metal layer of the exterior pouch 1 and the lead tab 3, the lead tab ( 3) and a sealing film for the lead tab of a secondary battery capable of maintaining the adhesiveness of the exterior pouch (1), polyethylene powder. Polypropylene powder, polypropylene copolymer powder, polyethylene copolymer powder, etc. are crosslinked with radiation (electron beam, gamma ray, X-ray) to prevent melting by heat, and these crosslinked powders are published by mixing this with the sealing film (2). This prevents short circuit between the external pouch 1 and the lead tab 3, and at the same time, the lead tab 3 and the external pouch 1 are fused to prevent leakage of the electrolyte.

In a secondary battery, a lead tap (Lead Tap; 3) refers to a portion in which an electrode terminal (tab) drawn out from an electrode group of a secondary battery is exposed to the outside of the external pouch (1).

In the battery assembly process, if the adhesion between the external pouch (1) and the lead tab (3) is not complete, the possibility of electrolyte leakage from the joint area increases, which is a cause of defects in this part.

The first insulating layer 2-1 of the lead tab 3 of the present invention is an insulating layer bonded to the inner layer (mainly using a polypropylene film) of the exterior pouch 1, and homopolypropylene is used, but suitable film characteristics are used. For this purpose, random polypropylene, block polypropylene, low density polyethylene, EPR or EPM can be mixed. In addition, modified polyethylene or modified polyethylene may be mixed in order to adjust the melt viscosity.

The second insulating layer 2-2 is an insulating layer embedded between the first insulating layer 2-1 and the third insulating layer 2-3 to maintain heat resistance, and the metal layer of the exterior pouch 1 and In order to prevent a short circuit between the conductors of the lead tab 3, polyolefin powder crosslinked with radiation (electron beam, gamma ray) is added in the present invention.

Here, since the crosslinked polyolefin powder is chemically crosslinked, it is melted and pushed out during thermal fusion so that the metal layer of the exterior pouch 1 and the conductor of the lead tab 3 are not short-circuited with each other.

As the polyolefin powder, polyethylene powder, polypropylene powder, modified polyethylene powder, or modified polypropylene may be used, and the particle size of the powder is more preferably 10 to 100 μm. When the particle size is 10 μm or less, the particle size is too small to expect the particle to act as a spacer, and when the particle size is 100 μm or more, the film thickness is 100 μm or more, making it difficult to apply as a sealant film.

In order to crosslink the polymer powder, electron beams, gamma rays, and X-rays can be used as radiation, and a dose in the range of 50 to 300 kGy is more preferable. When the irradiation amount is 50 kGy or less, the gelation rate is too low, so that the powder is dissolved during processing and there is no effect of adding the crosslinked powder.

The polyolefin powder preferably has a gelation rate of 30 to 80%. As for the electron beam irradiation method, a polymer powder is put in a plastic bag and irradiated, or the powder is placed on a conveyor and irradiated. After radiation treatment, heat treatment may be performed at 100 to 130° C. in order to remove free radicals in the polymer particles.

The amount of crosslinked polyethylene powder added is important. When the crosslinked polyethylene powder is not added or the amount added is small (2% by weight), the film thickness becomes extremely thin when the crosslinked polyethylene powder is pressed by a press in the molten state because the crosslinked powder does not or does not act as a spacer. Since polypropylene is one of the polymers with the lowest melt strength, it is easily deformed by external pressure above the melting point, and the film thickness is significantly reduced as the molten polymer is pushed aside. On the other hand, in the case of a polypropylene film with crosslinked polyethylene powder added, the crosslinked polyethylene does not melt even at the film forming temperature, so powdered polyethylene acts as a spacer to maintain the thickness of the particle size. The content of polyethylene powder is good up to 30% by weight, but it is preferable not to exceed 30% by weight because film forming is difficult and film strength is weakened at 40% by weight or more.

The third insulating layer 2-3 is a layer bonded to the lead tab 3 and uses modified polyolefin having excellent adhesion.

General polypropylene or polyethylene is non-polar, so it has poor adhesion to metal.

Therefore, a modified polyolefin having excellent adhesion is used, and the modified polyolefin used is maleic anhydride graft polypropylene, acrylic acid graft polypropylene, methacrylic acid graft polypropylene, butylacrylic acid graft polypropylene, 1,6- Nucleic acid diol acrylic acid polypropylene, glycytyl methacrylate graft polypropylene, butyl methacrylate graft polypropylene, acrylamide graft polypropylene, ethyl acrylate graft polypropylene, n-isopropyl acrylamide polypropylene, Maleic anhydride graft polypropylene, acrylic acid graft polyethylene, methacrylic acid graft polyethylene, butyl acrylic acid methacrylic acid graft polyethylene, 1,6-hexanediol acrylic acid polyethylene, glycytyl methacrylic acid graft polyethylene, butyl methacrylate It includes acrylate graft polyethylene, acrylamide graft polyethylene, ethyl acrylate graft polyethylene or n-isopropyl acrylamide graft polyethylene, and the like, and may include one or two or more of these, and general It may include one or more of polypropylene, polypropylene copolymer, random polypropylene, polyethylene, and polyethylene copolymer.

[Example 1]

Polyethylene powder (80㎛, EPOLDER EHP040, TWO H Chem) was hot-pressed to make a 500㎛ film, and this was heated to 20, 50, 100, 150, 200, 300, and 400kGy using an electron accelerator (IB Tech, 2.5MeV), respectively. was investigated, and the gelation rate was measured [Table 1].

For the gelation rate, cut a 120-mesh stainless steel net into a width of 80 mm and 40 mm, fold the ends of three sides to 6-7 mm and seal them with staples, put a 0.3 g polyethylene sample into this net, and then staple the upper end (inlet). was finally sealed, and the sample was placed in a Round-Bottom Flask containing xylene and extracted.

Immediately after extraction, it was dried in an oven at 150°C.

Gelation rate (%) = M1/M0 x 100

M0: sample weight before extraction

M1: Remaining sample weight after extraction

[Table 1]

The gelation rate showed a tendency to increase according to the amount of electron beam irradiation. At 20 kGy or less, the gelation rate is very low, so the effect of adding polyethylene powder cannot be expected, and the effect of adding polyethylene powder irradiated at 50 kGy or more can be expected.

[Example 2]

Polyethylene powder (80㎛, EPOLDER EHP040, TWO H Chem) was crosslinked with electron beam (gelation rate 70%), and then this was added to polypropylene (Lotte Chemical, FC-340R) with 0, 2, 5, 10, 20, 30, Each of 40 and 50 wt% was added and blended.

The blending temperature was 200° C. and was carried out for 5 minutes. After blending, a film having a thickness of 1000 μm was prepared by hot press. The film was cut to prepare a specimen having a length of 5 cm and a width of 1 cm.

An aluminum sheet (100 μm) was cut to prepare a specimen of the same size as above. The above polypropylene specimen was superimposed on top and bottom of the aluminum specimen, and was maintained at 180° C., 20 kg/cm 2 , for 3 minutes in a hot press, and then taken out. The thickness change before and after compression of the polypropylene specimen between the aluminum specimens was measured [Table 2].

[Table 2]

When the crosslinked polyethylene powder is not added or the amount added is extremely small, the film thickness becomes extremely thin because the crosslinked powder does not or does not act as a spacer. Since polypropylene is one of the polymers with the lowest melt strength, it is easily deformed by external pressure above the melting point, and the film thickness is significantly reduced as the molten polymer is pushed aside. On the other hand, in the case of a polypropylene film with crosslinked polyethylene powder added, the crosslinked polyethylene did not melt even at the film forming temperature, so powdered polyethylene served as a spacer to maintain the thickness of the particle size.

If the content of the polyethylene powder is 30% by weight or more, it is difficult to form a film and there is a disadvantage in that the film is easily torn.

[Example 3]

Using polypropylene (Lotte Chemical, FC-340R), a first insulating layer 2-1 having a thickness of 80 μm was made by hot pressing.

20wt% of polyethylene powder (80㎛, EPOLDER EHP040, TWO H Chem) crosslinked with an electron beam (gelation rate 40%) was added to polypropylene (Lotte Chemical, FC-340R) to form a second insulating layer with a thickness of 80㎛ (2-2) was made.

A third insulating layer (2-3) film having a thickness of 80 μm was prepared using maleic anhydride graft polypropylene (Lotte Chemical, BP-402). The three types of films were cut to a length of 10 cm and a width of 1 cm. Also, a specimen was cut to the same size from an aluminum (thickness 80 μm) sheet. Aluminum, graft polypropylene, polypropylene with crosslinked powder, and polypropylene samples were stacked in order, and pressed in a hot press at 180° C., 10 kg/cm ² , for 1 minute to complete a sealing film for lead tab (2). The adhesive strength between the resin and aluminum was measured using a tensile tester to measure the instantaneous strength when pulling it off in the 180 degree direction, and the adhesive strength of 18 N/cm was excellent.

[Example 4]

After 20 wt% of the crosslinked powder was mixed with maleic anhydride-grafted polypropylene, a film having a thickness of 200 μm, a width of 20 cm, and a length of 20 cm was prepared from this. A specimen having a length of 10 cm and a width of 1 cm was cut out from this. It overlapped with an aluminum sheet specimen cut to the same size as this polymer specimen, and held at 180° C., 10 kg/cm ² , for 1 minute in a hot press, and then taken out, and mutual adhesion was evaluated. For comparison, the adhesive force between the maleic anhydride-grafted polypropylene film and the aluminum sheet to which crosslinked powder was not added was also evaluated. As a result of a peel test using a tensile tester, good adhesion of about 18 N/cm was shown regardless of whether crosslinked powdered polyethylene was added.

The present invention can be used in the secondary battery industry.

1: External pouch
2: sealing film
2-1: first insulating layer
2-2: second insulating layer
2-3: third insulating layer
3: lead tap

Claims (10)

A secondary battery comprising a first insulating layer (2-1), a second insulating layer (2-2), and a third insulating layer (2-3) sealing each other between the lead tab (3) and the exterior pouch (1) In the sealing film for the lead tab of
The first insulating layer 2-1 is an insulating layer in contact with the exterior pouch 1, and is a polypropylene-based or polyethylene-based resin,
The second insulating layer (2-2) is embedded between the first insulating layer (2-1) and the third insulating layer (2-3) to maintain heat resistance, and the external pouch (1) and the lead tab (3) ) to prevent short circuit between each other, polyolefin powder crosslinked by radiation is added,
The third insulating layer (2-3) is a sealing film for a lead tab of a secondary battery, characterized in that a modified polyolefin in consideration of the adhesion to the lead tab (3) is applied. According to claim 1,
The first insulating layer (2-1) is a secondary characterized in that it contains one or two or more of homopolypropylene, random polypropylene, block polypropylene, polypropylene copolymer, EPR, EPDM, and modified polypropylene. Sealing film for lead tabs of batteries. According to claim 1,
The second insulating layer 2-2 is an intermediate layer that is interposed between the first insulating layer 2-1 and the third insulating layer 2-3 and requires heat resistance, and is polypropylene having a low melt index (MI). Or LCB (Linear Chain Branch) structure polypropylene, polypropylene copolymer, EPR and EPDM sealing film for a lead tab of a secondary battery, characterized in that it contains one or two or more types. According to claim 1,
The modified polyolefin is maleic anhydride grafted polypropylene, acrylic acid grafted polypropylene, methacrylic acid grafted polypropylene, butylacrylic acid grafted polypropylene, 1,6-nucleic acid diol acrylic acid polypropylene, glycytyl methacrylate graft polypropylene, butyl methacrylate graft polypropylene, acrylamide graft polypropylene, ethyl acrylate graft polypropylene, n-isopropyl acrylamide polypropylene, maleic anhydride graft polypropylene, acrylic acid graft polyethylene, Methacrylic acid graft polyethylene, butyl acrylic acid methacrylic acid graft polyethylene, 1,6-nucleic acid diol acrylic acid polyethylene, glycyethyl methacrylic acid graft polyethylene, butyl methacrylate graft polyethylene, acrylamide graft polyethylene, ethyl A sealing film for a lead tab of a secondary battery, comprising acrylate graft polyethylene or n-isopropyl acrylamide graft polyethylene, and comprising one or two or more of them. 5. The method of claim 4,
A polyolefin having the polar group listed in claim 4 is used alone, and it comprises one or more resins of homopolypropylene, random polypropylene, block polypropylene, polypropylene copolymer, EPR and EPDM. Sealing film for lead tabs of secondary batteries. According to claim 1,
The radiation-crosslinked polyolefin powder includes polyethylene powder, polypropylene powder, modified polyethylene powder or modified polypropylene. A sealing film for a lead tab of a secondary battery. 7. The method of claim 6,
The polyolefin powder is a sealing film for a lead tab of a secondary battery, characterized in that it has a size of 10 to 100㎛. 7. The method of claim 6,
The radiation is an electron beam, gamma ray or X-ray, the sealing film for a lead tab of a secondary battery, characterized in that the irradiation dose is 50 ~ 300 kGy. 9. The method of claim 8,
The sealing film for a lead tab of a secondary battery, characterized in that the polyolefin powder is added in an amount of 5 to 20 wt%. 9. The method of claim 8,
The electron beam irradiation is a sealing film for a lead tab of a secondary battery, characterized in that the polymer powder is put in a plastic bag and irradiated or the powder is placed on a conveyor and irradiated.

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