KR101814481B1 - Sealing member for lead tab of secondary battery and method of manufacturing the member - Google Patents

Abstract

 A seal member for a lead tab of a secondary battery having a high resistance to electrolytes and having good adhesion between the lead tab and the casing, and a method of manufacturing the same. The seal member and the method are characterized in that an intermediate layer in which the component is homo-propylene is adhered to the lead tab, one side is bonded to the lead tab and the other side is bonded to the intermediate layer, and 85 to 95 mol% of polypropylene (PP) and 5 to 15 mol% (PP-g-MA), one side of which is adhered to the exterior material and the other side of which is bonded to the intermediate layer, and is composed of 1 to 10 mol% of polyethylene, 80 to 98 mol% of polypropylene, 1 to 10 mol of polybutylene % Of a copolymer (E-PP-B) copolymerized with a copolymer (E-PP-B), and co-extruded by a water-cooled inflation method.

Description

Technical Field The present invention relates to a seal member for a lead tab of a secondary battery, and a manufacturing method thereof.

More particularly, the present invention relates to a seal member for sealing between a lead tab of a battery and a casing, and a manufacturing method thereof.

The secondary battery is used as a driving power source for portable wireless devices, electric vehicles, and the like. In particular, lithium secondary batteries have a long lifetime and high energy density, and their demand is rapidly increasing. In recent years, a lithium polymer battery is made of a flexible material and its shape can be freely designed. In addition, the lithium polymer battery is excellent in safety and light in weight, so that it is suitable for portable electronic devices. BACKGROUND ART A pouch-type lithium ion polymer battery is used as a large-capacity battery used in medium-sized devices such as an electric vehicle. The large-capacity pouch-type battery includes lead tabs for electrical connection between the battery body and the outside when the electrode assembly is housed in a pouch as a casing.

On the other hand, when the large-capacity pouch-type battery is exposed to the external environment, a short circuit occurs due to condensation of the metal layer of the pouch and the lead tab or electrode contact. When a short circuit occurs, water penetration into the electrode assembly or loss of an electrolytic solution occurs, thereby deteriorating the performance of the battery. In order to prevent this, the seal member is placed on the joint portion between the lead tab and the casing, and the lead tab and the casing are sealed by heat fusion. The seal member generally has a two-layer or three-layer multi-layer structure. For example, the two-layer structure is disclosed in Japanese Patent No. 5402547, and the three-layer structure is disclosed in Japanese Patent Publication No. 5108228. [

However, the conventional multi-layered seal member is manufactured by the air-cooling type non-smoothing roll method. The air-cooled, non-smelting new-roll method has a simple facility and simple process conditions, which are easy to manufacture. However, since there is no orientation process, the mechanical properties are deteriorated and the cooling rate is low. In addition, the surface of the polypropylene film produced by the air-cooling type is composed of an? -Crystal mainly having a large crystal size, and thus the resistance to the electrolyte deteriorates.

A problem to be solved by the present invention is to provide a seal member for a lead tab of a secondary battery, which has a high resistance to electrolytes and has good adhesiveness to a lead tab and a casing, and a manufacturing method thereof.

In order to solve the problems of the present invention, the lead tapped seal member of a secondary battery of the present invention comprises: an intermediate layer having a component of homo propylene; one end bonded to the lead tab and the other end bonded to the intermediate layer; (PP-g-MA) copolymerized with 5 to 15 mol% of maleic acid (MA). (E-PP-1) copolymerized with 1 to 10 mol% of polyethylene, 80 to 98 mol% of polypropylene and 1 to 10 mol% of polybutylene, one side of which is adhered to the exterior material and the other side of which is adhered to the intermediate layer. B).

In the seal member of the present invention, the thickness ratio of the lead tab adhesive layer, the intermediate layer, and the facing material adhesive layer is preferably 1: 1: 1 to 3: 1: 1. The thickness of the seal member is preferably 75 to 150 mu m. The seal member is disposed between the lead tab adhesive layer and the facing material adhesive layer and comprises polypropylene (PP) as a main component, and is preferably an ethylene-acrylic acid copolymer (E-AA), an ethylene-propylene diene copolymer (EDPM) (E-EA), hydrogenated natural rubbers, ethylene-methyl methacrylate copolymers (E-EA), poly (4-methyl-1-pentene) MMA), and a polyethylene ionomer may be added to the main component.

In the preferred seal member of the present invention, the surface of the exterior material adhesive layer is preferably made of an olefin oligomer containing a polar functional group, an ionomer resin, polyvinyl chloride (PVC), polyvinyl acetate (PVAc) (PVA), a copolymer of polyvinyl acetate (PVAc) and polyvinyl alcohol (PVA), or a mixture thereof. The seal member adhered to the lead tab and the casing member maintains an adhesion force of 20 N / 17 mm or more after standing in a Li-P-F type electrolyte at 80 캜 for 24 hours.

In order to solve the problems of the present invention, a manufacturing method of a lead tapped seal member of a secondary battery is manufactured by co-extrusion through a compounding (kneading) process and a water-cooled inflation method. At this time, it is molded at a temperature condition of Tm + 20 ° C? T _extrusion ? Tm + 40 占 폚 and Tm-120 占 폚 T _casting ? Tm-100 占 폚, and has an extrusion amount of 150 kg / hr to 300 kg / hr. The seal member can be produced by an air-cooled type non-smoothing roll method, but water-cooled inflation is used to enhance the resistance to electrolytes. Water-cooled inflation increases the content of β-type crystals with a smaller crystal structure than α-type crystals with large crystal sizes on the film surface.

According to the seal member for lead taps of a secondary battery of the present invention and the method for producing the seal member, it is possible to provide a seal member for a lead tab and a method for producing the seal member, By forming a seal member having a layer structure in a water-cooling inflation manner, resistance to electrolytes is large, and adhesiveness to the lead tab and the casing is good.

1 is a perspective view illustrating a state in which a seal member for a lead tab according to the present invention is applied.
2 is a cross-sectional view illustrating one seal member for a lead tab according to the present invention.
3 is a cross-sectional view illustrating another lead tab thread member according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

An embodiment of the present invention is a method of manufacturing a three-layered seal member comprising a lead tab tapping adhesive layer composed of a PP-g-MA based copolymer resin, a homo PP intermediate layer and an E-PP- The present invention proposes a seal member having a high resistance to an electrolyte and having good adhesion between the lead tab and the casing. To this end, the structure of the seal member will be described in detail and the characteristics of each layer will be described in detail. Next, the process of manufacturing the seal member of the present invention by the water-cooled inflation method and its effect will be described in detail.

≪ Seal member of the present invention &

1 is a perspective view for explaining a state in which a seal member for a lead tab according to an embodiment of the present invention is applied.

Referring to FIG. 1, the pouch type secondary battery includes an electrode structure 10, an electrode terminal 20, a lead tab 30, and a casing 50. The electrode structure 10 is laminated in a plurality of units including a positive electrode, a separator and a negative electrode, and the electrode terminal 20 is bonded to the lead tab 30 by welding, riveting, or the like. The lead tab 30 is drawn out from the electrode structure 10 through the electrode terminal 20 and connected to the external terminal. The outer sheath 50 includes a protective layer, a metal foil and a sealing layer, though not specifically shown, and the metal foil is also called a barrier layer because it prevents moisture and air from entering and exiting. An adhesion-promoting layer may be added between the protective layer and the metal foil or between the metal foil and the sealing layer. In addition, the casing member 50 may have various layers that function as insulation, gas permeation prevention, peeling, water trapping, and the like.

The sealing layer is formed by heat sealing the lead tab 30 to prevent leakage of an electrolytic solution or gas and heat sealing is possible and a low melting point resin such as polypropylene (PP) . The lead tab 30 is generally formed in a plate or rod shape and is made of a metal material having electrical conductivity. The lead tab 30 may be made of any one of aluminum (Al), nickel (Ni), copper (Cu), and alloys thereof. The lead tab 30 may be surface-treated with a chromium compound, a phosphorus compound, or the like in order to improve adhesion with the seal member 40 and prevent corrosion.

2 is a cross-sectional view illustrating a seal member for a lead taps according to an embodiment of the present invention.

2, the seal member 40 has a three-layer structure of a lead tab adhesive layer 41, an intermediate layer 42, and a facer adhesive layer 43 adhered to the facer 50, which are thermally fused with the lead tab 30 . The lead tab 30 can round the side surface to improve the adhesion with the seal member 40. [ The lead tab adhesive layer 41 is made of a copolymer (PP-g-MA) copolymerized with 85 to 95 mol% of polypropylene (PP) and 5 to 15 mol% of maleic acid (MA) When the content of maleic acid (MA) is less than 5 mol%, the electrolyte resistance is deteriorated to deteriorate the adhesiveness after the electrolyte solution accumulation. If the content is more than 15 mol%, the melting strength and heat resistance may be deteriorated and thermal deformation may occur. The lead tab adhesive layer 41 improves the adhesive force with the lead tab made of metal.

The intermediate layer 42 is made of homopolypropylene. The homopolypropylene is composed of only a single bond of propylene, which has high crystallinity and excellent mechanical properties such as tensile strength and rigidity. The melt index (g / 10 min) is preferably 0.3 to 30, and the melting point is preferably 160 ° C or more. On the other hand, homopolypropylene can be used by mixing regenerated polypropylene. The regenerated polypropylene can be mixed in such an amount that the melting point of the intermediate layer 42 becomes 160 캜 or higher. That is, if too much regenerated polypropylene is mixed, the melting point may be lowered to 160 ° C or lower. If necessary, various additives such as an antioxidant, a flame retardant, an ultraviolet absorber, a light stabilizer, a heat stabilizer, a lubricant, and a colorant may be added to the intermediate layer. Further, within the scope of the present invention, other resins may be mixed. At this time, in the case of mixing the nonconforming resin, it is preferable to use a compatibilizing agent in combination.

The exterior material adhesive layer 43 is made of a copolymer (E-PP-B) copolymerized with 1 to 10 mol% of polyethylene, 80 to 98 mol% of polypropylene and 1 to 10 mol% of polybutylene. If the content of polyethylene and polybutylene is smaller than 1 mol%, the adhesive strength to the exterior material is lowered. If the content is larger than 10 mol%, the polyethylene and polybutylene are easily bonded at a low temperature and deformed at a high temperature.

(E-AA), an ethylene-propylene diene copolymer (EDPM), a novone (Novon) copolymer, and the like. The sealing member is disposed between the lead tab and the facing material adhesive layer, , Ethylene-ethyl acrylate copolymer (E-EA), hydrogenated natural rubber, ethylene-methyl methacrylate copolymer (E-MMA), poly And a polyethylene ionomer may be added to the main component.

 (PVAc), polyvinyl acetate (PVAc), polyvinyl alcohol (PVAc), polyvinyl alcohol (PVAc), polyvinyl pyrrolidone (PVAc), and the like, which contain polar functional groups such as an oligomer, an ionomer resin, polyvinyl chloride PVA), or a mixture thereof may be applied to the surface or added in a small amount. Most of the olefinic oligomers consist of a combination of carbon and hydrogen only atoms, and refer to linear or branched polymers.

The ionomer resin is preferably an ethylene-based ionomer resin. The ethylene-based ionomer resin is a resin that is pseudo-crosslinked with an ethylene copolymer such as an ethylene methacrylic acid copolymer or an ethylene acrylic acid copolymer with a metal ion such as a zinc ion, a potassium ion, a sodium ion, a magnesium ion or a lithium ion. The ethylene-based ionomer resin includes those obtained by mixing an ethylene copolymer having a carboxyl group in its molecule with a metal oxide, a metal hydroxide, or a metal salt. When the ethylene copolymer having a carboxyl group is mixed with a metal salt or the like, the carboxyl group is neutralized by the metal ion to become a carboxylic acid ion, and forms a salt with the metal ion. As a plurality of carboxylic acid ions associate with metal ions, the kind of ethylene copolymer is pseudo-crosslinked to form an ionomer resin.

The polyvinyl acetate is a vinyl polymer and is produced by free radical polymerization of a vinyl acetate monomer. When some of the acetates are replaced by hydroxyl groups in polyvinyl acetate, a copolymer of polyvinyl acetate and polyvinyl alcohol is formed. The polyvinyl alcohol enhances the adhesive strength between the lead tab adhesive layer 41 and the lead tab 30 of the present invention, and the polyvinyl acetate maintains the bonding strength of the lead tab conformal layer 41.

The adhesion between the lead tab and the seal member bonded to the casing must be maintained at 20 N / 17 mm or more even after standing at 80 ° C for 24 hours in a Li-P-F electrolyte.

The seal member of the present invention has a thickness ratio of the lead tab adhesive layer 41: the intermediate layer 42: the cover material adhesive layer 43 of 1: 1: 1 to 3: 1: 1, . That is, the thickness of the intermediate layer 42 and the facer adhesive layer 43 are designed to be equal to each other. However, the lead tab adhesive layer 41 has a thickness ratio of 1 to 3 times that of the intermediate layer 42 and the facer adhesive layer 43. If the thickness ratio of the lead tab adhesive layer 41 is less than 1, the electrolyte resistance deteriorates to deteriorate the adhesion. If the thickness of the lead tab adhesive layer 41 is larger than 3, the thickness of the intermediate layer and the outer cover material adhesive layer becomes thinner and the adhesive force to the outer cover material is lowered and the durability and heat resistance against external stress are deteriorated.

3 is a cross-sectional view illustrating a seal member for a lead tab according to another embodiment of the present invention. 2, except for the adhesion-assisting layer 60, so that redundant description will be omitted or simplified.

3, an adhesion assisting layer 60 may be further provided between the intermediate layer 42 and the facing material adhesive layer 43 to increase the adhesion between the two layers. The adhesion-assisting layer 60 is made mainly of polypropylene (PP) and high-density polyethylene (HDPE), and auxiliary components are mixed. The polypropylene (PP) may be at least one of isotatic, syndiotactic, atactic, and ethylene-propylene copolymers. The auxiliary component may be selected from the group consisting of ethylene-acrylic acid copolymer (E-AA), ethylene-propylene diene copolymer (EDPM), novone, poly (4-methyl- (E-EA), a hydrogenated natural rubber, an ethylene-methyl methacrylate copolymer (E-MMA), and a polyethylene ionomer. The adhesion-assisting layer 60 improves the adhesiveness and heat resistance of the intermediate layer 42 and the facer adhesive layer 43.

At this time, the auxiliary component is preferably 1% to 10% by weight based on the entirety of the adhesion-promoting layer 60. If it is larger than 10%, there is a problem of heat resistance deterioration. If it is smaller than 1%, there is a problem of deterioration of adhesion. In the main component, polypropylene (PP) and high density polyethylene (HDPE) are preferably 70% to 80% by weight, and 5% to 10% by weight based on the total main component. This suggests an optimum fraction in consideration of the characteristics of the adhesion-promoting layer 60 of the present invention.

≪ Method of producing a seal member of the present invention &

The seal member of the present invention is manufactured by co-extrusion through a compounding process and a water-cooled inflation method. The compounding process is performed in the same manner as the seal member 42 composed of the lead tab adhesive layer 41 / the intermediate layer 42 / the facer adhesive layer 43 or the lead tab adhesive layer 41 / the intermediate layer 42 / the adhesion assisting layer 60 / The resin and the functional additive to be used in each layer of the resin layer 40 are made of a uniform resin, for example, by a twin-screw compounding apparatus. Since the compounding method is a known method, a detailed description thereof will be omitted. However, the compounding apparatus of the present invention optimizes the length (L) / diameter (D) by 18 to 25 and the temperature per zone to 200 to 280 ° C. At this time, the extruding temperature of the resin compounded was 190 to 200 占 폚, and the unmelted resin was minimized.

The inflation method is to mold a mold with a ring-shaped lip at the end of the compounding and to continuously mold it using a tubular material. An air hole is provided at the center of the mold, and the compressed air is blown into the air hole to expand the tube several times. The expanded tube is pulled by the roller, cooled, and pulled out to the film. Here, the width of the film and the discharge amount of the resin are determined by adjusting the diameter of the mold and the pressure of the compressed air, and the thickness of the film can be changed at the pulling speed of the roller. Since the inflation method does not use the feed block, the necking phenomenon is prevented, the heat shrinkage rate of the film constituting the seal member 40 can be minimized, and a constant heat shrinkage rate can be obtained.

At this time, the molding conditions for manufacturing the seal member of the present invention by the inflation method are as follows.

Tm + 20 ° C? T _extrusion ? Tm + 40 ° C ... Equation (1)

Tm-120 ℃ ≤T _casting ≤Tm-100 ℃ ... Equation (2)

Tm is the melting temperature, T _extrusion is the melt extrusion temperature, and T _casting is the solid temperature. When molded under the above temperature conditions, it has an extrusion amount of 150 kg / hr to 300 kg / hr.

The seal member according to the embodiment of the present invention maintains the adhesion force of 20 N / 17 mm or more after standing at 80 ° C for 24 hours in the Li-P-F type electrolyte. Herein, 17 mm means the width of the lead tab, and if the adhesion is less than 20 N / 17 mm, the electrolyte leaks and causes electric appliances and electric car failure.

In the embodiment of the present invention, a water-cooled inflation system is applied. The air-cooled, non-rolled new roll manufacturing method has a low cooling rate and a low mechanical property, and the electrolyte resistance is poor because a large amount of? -Type crystal having a large crystal size exists on the film surface of the seal member 40. However, in the water-cooled inflation system, the content of the β-form crystal having a small crystal size is increased on the surface of the polypropylene film applied to the seal member 40. The? -Form crystal is produced in a quenching condition, and when the content of the? -Form crystal is increased, the electrolyte resistance of the polypropylene film is increased. Also, when the content of the? -Form crystal is increased, the heat resistance and the mechanical properties of the film are also improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but many variations and modifications may be made without departing from the spirit and scope of the invention. It is possible.

10; An electrode assembly 20; Electrode terminal
30; Lead tab 40; Seal member
41; A lead tab adhesive layer 42; Middle layer
43; An exterior material adhesive layer 50; Exterior material
60; Adhesion auxiliary layer

Claims (8)

An intermediate layer wherein the component is homopropylene;
(PP-g-MA) copolymerized with 85 to 95 mol% of polypropylene (PP) and 5 to 15 mol% of maleic acid (MA), one side of which is adhered to the lead tab and the other side of which is adhered to the intermediate layer A lead tab adhesive layer; And
(E-PP-B) copolymerized with 1 to 10 mol% of polyethylene, 80 to 98 mol% of polypropylene and 1 to 10 mol% of polybutylene, with one side adhered to the exterior material and the other side adhered to the intermediate layer And an outer covering material adhesive layer formed on the outer covering material,
(E-AA), an ethylene-propylene diene copolymer (EDPM), a novolak (N-vinylpyrrolidone) copolymer, and the like, which are positioned between the lead tab and the lead tab adhesive layer and contain polypropylene , Ethylene-ethyl acrylate copolymer (E-EA), hydrogenated natural rubber, ethylene-methyl methacrylate copolymer (E-MMA), poly Wherein at least one selected from the group consisting of polyethylene terephthalate and polyethylene ionomer is added to the main component. The lead tab tap thread member according to claim 1, wherein a thickness ratio of the lead tab adhesive layer, the intermediate layer, and the facing material adhesive layer is 1: 1: 1 to 3: 1: 1. The lead member for a lead tab of a secondary battery according to claim 1, wherein the thickness of the seal member is 75 to 150 占 퐉. delete The seal member according to claim 1, characterized in that the seal member adhered to the lead tab and the casing is maintained at an adhesive force of 20 N / 17 mm or more after standing for 24 hours at a temperature of 80 캜 in a Li-PF electrolyte solution A lead member for a lead tab of a secondary battery. An intermediate layer wherein the component is homopropylene;
(PP-g-MA) copolymerized with 85 to 95 mol% of polypropylene (PP) and 5 to 15 mol% of maleic acid (MA), one side of which is adhered to the lead tab and the other side of which is adhered to the intermediate layer A lead tab adhesive layer; And
(E-PP-B) copolymerized with 1 to 10 mol% of polyethylene, 80 to 98 mol% of polypropylene and 1 to 10 mol% of polybutylene, with one side adhered to the exterior material and the other side adhered to the intermediate layer A method for manufacturing a seal member for a lead tab of a secondary battery,
The seal member is manufactured by co-extrusion through a compounding (kneading) process, a water-cooled inflation method,
(E-AA), an ethylene-propylene-diene copolymer (EDPM), a novone (Novon) copolymer, and the like are laminated between the lead tab and the lead- , Ethylene-ethyl acrylate copolymer (E-EA), hydrogenated natural rubber, ethylene-methyl methacrylate copolymer (E-MMA), poly Wherein at least one selected from the group consisting of polyethylene terephthalate and polyethylene ionomer is added to the main component. The method of manufacturing a seal member for a lead tab of a secondary battery according to claim 6, wherein the forming of the seal member is performed under the temperature conditions as expressed by the following formulas.
Tm + 20 ° C? T _extrusion ? Tm + 40 ° C ... Equation (1)
Tm-120 ℃ ≤T _casting ≤Tm-100 ℃ ... Equation (2)
In this case, Tm is the melting temperature of the resin, T _extrusion is the melt extrusion temperature, and T _casting is the quenching solid temperature. The method according to claim 7, wherein the extruded amount is 150 kg / hr to 300 kg / hr while the film is molded under the temperature condition.

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