KR20160060375A - Film for lead tab of secondary battery and secondary battery comprising the same - Google Patents

Abstract

Disclosed in the present specification are a film for a secondary battery lead tab to seal a gap between the secondary battery lead tab and an exterior material and a secondary battery including the film. The film for the lead tab comprises: a main layer which includes inorganic filler and nonpolar polymer resin; and a skin layer which is formed on one side or both sides of the main layer and includes polar polymer resin. The present invention shows increased adhesion between the lead tab and the exterior material, excellent physical stability, excellent high-temperature dimensional stability, etc.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a film for a lead tab of a secondary battery,

Disclosed herein is a film for a lead tab of a secondary battery which seals between a lead tab of a secondary battery and a casing, and a secondary battery including the same.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Lithium secondary batteries, which have high energy density and voltage and long cycle life and low self-discharge rate, are commercialized Widely used.

Such a lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery depending on the configuration of an electrode and an electrolytic solution. The amount of the lithium ion polymer battery Is growing. Lithium ion polymer battery (LiPB) is a structure in which an electrolyte solution is impregnated in an electrode assembly in which an electrode (an anode and a cathode) and a separator are thermally fused, and is often used as a form in which a stacked electrode assembly is sealed in a pouch case of an aluminum laminate sheet have. Therefore, a lithium ion polymer battery is often referred to as a pouch type battery.

The pouch type secondary battery is advantageous in weight and miniaturization as compared with a cylindrical or prismatic secondary battery, and has attracted attention as a power source for battery automobiles and hybrid electric automobiles. At this time, most of the pouch type secondary batteries have a lead tab drawn out from the electrode group, and the lead tab and the casing (pouch) are sealed through a sealing film.

The sealing film is thermally adhered to the lead tab and the casing through heat and pressure. At this time, the sealing film according to the related art has a problem in that the thermal adhesive force with the lead tab and the casing is weak. The lead tab is made of metal for conductivity. The sealing film according to the related art has a problem in that the sealing property is poor due to the low thermal adhesion strength with the lead tab of the metal material.

In addition, the sealing film according to the prior art has a problem of low physical stability and dimensional stability. Specifically, the sealing film according to the prior art has a poor physical stability such as tensile strength and bending strength, so that the side bonding portion with the lead tab, that is, the side bonding portion indicated by the red dotted line in FIG. 1, (Broken). In addition, there is a problem that it is easily deformed due to heat or humidity, and in particular, there is a problem that the heat resistance is low and stability at high temperature is inferior.

Korean Patent No. 10-0821856 Korean Patent Laid-Open No. 10-2012-0124613

In one aspect, the technique disclosed in this specification is a polymer film having a structure for preventing the degradation of the sealing performance around the tab, and is a polymer film having a sealing property between a tap and a polymer film, It is an object of the present invention to provide a lead tear film for a battery.

In another aspect, the present invention aims to provide a secondary battery in which a lead tab and a casing of a secondary battery are sealed using the film for a lead tab.

In one aspect, the technique disclosed herein includes a main layer comprising an inorganic filler and a nonpolar polymer resin; And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.

According to an exemplary embodiment, the inorganic filler may be a nanowire.

According to an exemplary embodiment, the nanowire may have a diameter of 0.1 to 100 nm and a length of 1 to 100 [mu] m.

According to an exemplary embodiment, the inorganic filler may be at least one selected from the group consisting of silica, magnesium oxide, zinc oxide, aluminum hydroxide, titanium dioxide, and titanium hydroxide.

According to an exemplary embodiment, the inorganic filler may be contained in an amount of 0.5 to 20% by weight based on the total weight of the main layer composition.

According to an exemplary embodiment, the nonpolar polymer resin is selected from the group consisting of stretched polypropylene (OPP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate Polyimide (PI), and the like.

According to an exemplary embodiment, the polar polymer resin may be one in which at least one polar group selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, maleimide, maleic anhydride, itaconic acid, have.

According to an exemplary embodiment, the melting point of the nonpolar polymer resin may be 155 to 260 ° C, and the melting point of the polar polymer resin may be 120 to 150 ° C.

According to an exemplary embodiment, the main layer or skin layer may further comprise an elastomeric or elastomeric grafted polymeric resin.

According to another aspect of the present invention, there is provided a secondary battery in which a lead tab and a shell of a secondary battery are sealed with a film, the film comprising: a main layer including an inorganic filler and a non-polar polymer resin; And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.

In one aspect, the technique disclosed in this specification relates to a method of forming a polymer film in a multi-layer structure in which heat resistance between polymer layers is different and an inorganic filler, that is, metal oxide nanowires, is mixed with a main layer, There is an effect of providing a film for a lead tab of a battery.

In another aspect, the technique disclosed in this specification has an effect of providing a secondary battery in which a lead tab and a casing of the secondary battery are sealed by using the film for a lead tab.

FIG. 1 shows a film for a lead tab of a secondary battery, showing a state in which a sealing film is thermally adhered to the lead tab.
2A is a schematic view of a lead tab film of a secondary battery according to an exemplary embodiment of the present invention, which shows a lead tab film in which a nanowire inorganic filler is added to a main layer.
2B is a schematic view of a lead tapped film of a secondary battery according to an exemplary embodiment of the present invention, which shows a lead tapped film in which a spherical inorganic filler is added to a main layer.
3 is a photograph showing the nanowire-type titanium dioxide used in Example 1 of the present invention.

Hereinafter, the present invention will be described in detail.

In one aspect, the technique disclosed herein includes a main layer comprising an inorganic filler and a nonpolar polymer resin; And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.

The method for producing the lead tab tap film is not particularly limited. According to an exemplary embodiment, the main layer and the skin layer may be laminated together with the formation of each layer through co-extrusion, or each layer may be separately extruded and then laminated through an adhesive or thermal lamination. At this time, the adhesive may be selected from resin adhesives such as acrylic, urethane, epoxy, etc., and it is preferable that the adhesive is applied to a thickness of, for example, 2 to 3 탆. Further, when laminated through thermal lamination, it is preferable to be laminated at a temperature of, for example, 100 to 150 ° C.

The main layer acts as a base of the film and preferably has high stiffness and a melting point of 155 to 260 ° C, which improves physical stability and heat resistance. The main layer contains a nonpolar polymer resin and has a high melting point, thereby making it possible to maintain the dimensional stability at high temperature and to maintain sealing performance with the wrapping material by making a difference in heat resistance between the polymer film layers.

Specifically, the main layer may be a non-polar polypropylene resin having a melting point of 155 to 260 캜. On the other hand, since the non-polar polypropylene resin alone does not have dimensional stability suitable for the lead taps film, it is possible to introduce another resin in the form of non-polar polypropylene as an additive in order to impart appropriate dimensional stability to the lead taps film, , The introduction of PEN may increase the melting point and improve the heat resistance and dimensional stability, but peeling may occur with the polar polymer resin layer, i.e., the skin layer. Thus, the techniques disclosed herein add an inorganic filler to the main layer for delamination and good dimensional stability.

According to an exemplary embodiment, the inorganic filler can be a nanowire, specifically a metal oxide nanowire. In comparison with the case of using spherical, plate or random inorganic filler, the inorganic filler of the nanowire type maintains a constant linear model, and the dimensional deformation is remarkably reduced at high temperature. As shown in FIG. 2, when the nanowire inorganic filler is added, the shrinkage can be reduced through the arrangement of the nanowires when shrinking in the MD direction.

According to an exemplary embodiment, the nanowire may have a diameter of 0.1 to 100 nm and a length of 1 to 100 [mu] m. More specifically, the nanowires may have a diameter of 1 to 20 nm and a length of 1 to 50 탆. By using the nanowires having the diameter and the length in the above range, it is possible to prevent coagulation and nonuniform mixing with each other, It is possible to mix smoothly.

According to an exemplary embodiment, the inorganic filler may be at least one selected from the group consisting of silica, magnesium oxide, zinc oxide, aluminum hydroxide, titanium dioxide, and titanium hydroxide.

According to an exemplary embodiment, the inorganic filler may be contained in an amount of 0.5 to 20% by weight, preferably 1 to 10% by weight, based on the total weight of the main layer composition. The addition of an inorganic filler in an amount of 20% by weight improves the tensile elongation of the film and lowers the uniformity between the mixed resins. The inorganic filler is added in an amount of 0.5% by weight or more.

According to an exemplary embodiment, the nonpolar polymer resin is selected from the group consisting of stretched polypropylene (OPP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate Polyimide (PI), and the like.

The skin layer may be formed on one side of the main layer with the main layer as a center, or a first skin layer may be formed on one side of the main layer and a second skin layer may be formed on the opposite side. At this time, the skin layer may have a single-layer or multi-layer structure. Further, the skin layer is brought into contact with the lead tab and the casing, and is thermally bonded to the lead tab and the casing.

The skin layer is composed of a polar polymer resin having a melting point lower than that of the nonpolar polymer resin constituting the main layer. By introducing the polar group, the adhesion strength to the electrode terminal (metal plate) is improved and the skin layer has a low melting point, The adhesive force is improved. In the case of nonpolar polymer resin, there is a danger that the sealing performance with the electrode terminal is poor, and when the melting point is too high, there is a problem in adhesion with the casing.

The polar polymer resin is a nonpolar polymer resin in which at least one polar group is introduced into the main chain and / or side chain based on a nonpolar polymer resin, and the polar monomer may be polymerized to have a polar group, or may have a polar group in the polymerization process or after polymerization. According to an exemplary embodiment, the polypropylene resin may be a modified polypropylene resin into which a polar group is introduced by treatment with a peroxide and a carboxylic acid. The polypropylene resin may be selected from a propylene polymer (homopolypropylene), a propylene copolymer (PP co-polymer), and a PP ter-polymer. The propylene copolymer (PP co-polymer) is exemplified by propylene-ethylene block copolymer. The propylene terpolymer (PP ter-polymer) is exemplified by propylene-ethylene-butylene block copolymer and the like .

According to an exemplary embodiment, the polar polymer resin may be one in which at least one polar group selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, maleimide, maleic anhydride, itaconic acid, have.

According to an exemplary embodiment, the melting point of the nonpolar polymer resin may be 155 to 260 ° C, and the melting point of the polar polymer resin may be 120 to 150 ° C.

According to an exemplary embodiment, the main layer or the skin layer further includes a polymer resin in which an elastomer or an elastomer is grafted, so that it is very effective in improving physical stability such as bending strength and dimensional stability. In one embodiment, the main or skin layer may comprise polyethylene, elastomer, elastomer grafted polypropylene, or elastomer grafted polyethylene as the reinforcing resin or may constitute a layer. The elastomer is not particularly limited as long as it is an elastic polymer, and examples thereof include a butadiene rubber, a urethane rubber, and an acrylic rubber.

The lead tear film may further include at least one additive selected from a filler, a slip agent, an anti-blocking agent, and an antistatic agent, and the additive may be included in the main layer and / or the skin layer.

The filler may be selected from inorganic materials, for example, talc, silica, magnesium oxide, titanium oxide, and the like. The slip agent may impart slip property (or releasability) upon extrusion, and it may use at least one selected from, for example, silicone, siloxane, silane, wax, and oleic acid amide. At this time, any slip agent may be used as long as it can impart lubricity to the surface of each layer and reduce the coefficient of friction in addition to those listed above.

The anti-blocking agent is capable of preventing adhesion between films during winding after extrusion, and it may use at least one selected from inorganic particles such as silica, diatomaceous earth, kaolin and talc, and the like. Such an anti-blocking agent is preferably contained in the skin layer constituting the outermost surface, and is not particularly limited, but may be included in an amount of 0.005 to 10 parts by weight, specifically 0.01 to 5 parts by weight, based on 100 parts by weight of the polar polypropylene resin have.

The antistatic agent is not particularly limited as long as it has antistatic (antistatic) performance. The antistatic agent may be at least one selected from the group consisting of, for example, a conductive polymer, a carbon material, and a surfactant. Examples of the conductive polymer include polyethylene dioxythiophene, polythiophene, polyaniline, and polypyrrole.

The main layer or the skin layer may further include at least one selected from an ultraviolet stabilizer, an antioxidant, a surface smoothing agent, and a color pigment in addition to the additives, and the components thereof are not particularly limited.

According to another aspect of the present invention, there is provided a secondary battery in which a lead tab and a shell of a secondary battery are sealed with a film, the film comprising: a main layer including an inorganic filler and a non-polar polymer resin; And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

Example 1.

A 3-layer pilot machine was used to fabricate a lead tear film with a total thickness of 100 μm in a three-layer structure. The main layer (B layer) and the skin layer (A) each consisted of 40 μm and 30 μm, respectively.

The B layer was made of nonpolar PP and Homo PP with high melting point was used. In addition, an inorganic filler (titanium dioxide nanowire) was added in an amount of 7%. Polar PP was used as the A layer and PP with maleic anhydride graft was used.

The film was prepared by coextrusion with a 3-layer machine and extrusion temperature was 220 ~ 260 ℃.

Example 2.

A lead tab film was prepared in the same manner as in Example 1 except that an inorganic filler (spherical titanium dioxide) was added to the main layer in an amount of 7% to prepare a lead tab film.

Comparative Example 1

A lead tapped film was prepared in the same manner as in Example 1, except that a non-polarized PP was used for the main layer to prepare a lead tapped film.

Test example.

The film thus prepared was bonded onto the AL plate (between 120 and 150 degrees), and thereafter subjected to true bonding (between 180 and 230 degrees), and the pressure was applied at 5 to 10 kgf. The results of the comparative evaluation after manufacturing the lead taps are shown in Table 4, and the shrinkage ratios were calculated as follows.

Shrinkage (%) = difference in length (mm) / length after joining (mm) × 100

As shown in Table 4, in the case of the lead tab tapes according to Examples 1 and 2 in which the inorganic filler was added, the shrinkage ratio was reduced as compared with Comparative Example 1 in which the inorganic filler was not added, and it was confirmed that the stability at high temperature was improved. In particular, when nanowire type inorganic filler was added, the shrinkage was greatly reduced to 0.51%, indicating very good high temperature stability.

Having described specific portions of the present invention in detail, it will be apparent to those skilled in the art that this specific description is only a preferred embodiment and that the scope of the present invention is not limited thereby. It will be obvious. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (10)

A main layer comprising an inorganic filler and a nonpolar polymer resin; And
And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.
The method according to claim 1,
Wherein the inorganic filler is a nanowire.
3. The method of claim 2,
Wherein the nanowire has a diameter of 0.1 to 100 nm and a length of 1 to 100 탆.
The method according to claim 1,
Wherein the inorganic filler is at least one selected from the group consisting of silica, magnesium oxide, zinc oxide, aluminum hydroxide, titanium dioxide, and titanium hydroxide.
The method according to claim 1,
Wherein the inorganic filler is contained in an amount of 0.5 to 20% by weight based on the total weight of the main layer composition.
The method according to claim 1,
The nonpolar polymer resin is preferably composed of stretched polypropylene (OPP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN) and polyimide Wherein the lead tab film has a thickness of at least 1 mm.
The method according to claim 1,
Wherein the polar polymer resin has at least one polar group selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, maleimide, maleic anhydride, itaconic acid, itaconic anhydride and derivatives thereof. film.
The method according to claim 1,
Wherein the melting point of the non-polar polymer resin is 155 to 260 캜, and the melting point of the polar polymer resin is 120 to 150 캜.
The method according to claim 1,
Wherein the main layer or the skin layer further comprises a polymer resin in which an elastomer or an elastomer is grafted.
A secondary battery in which a lead tab of a secondary battery and a casing are sealed with a film,
Wherein the film comprises a main layer comprising an inorganic filler and a nonpolar polymer resin; And a skin layer formed on one or both surfaces of the main layer and including a polar polymer resin, wherein the non-polar polymer resin has a melting point higher than that of the polar polymer resin.

Images