KR101132169B1 - Laminate Sheet for Battery Case and Lithium Secondary Battery Employed with the Same - Google Patents

Abstract

The present invention is a laminate sheet used in the manufacture of a battery case, an outer coating layer based on excellent tensile strength and weather resistance polymer resin, a functional barrier layer based on a polymer resin that can block moisture and gas, and heat sealability Provided is a laminate sheet comprising an inner sealant layer based on a polymer resin.

Description

Laminate Sheet for Battery Case and Lithium Secondary Battery Containing It {Laminate Sheet for Battery Case and Lithium Secondary Battery Employed with the Same}

The present invention relates to a laminate sheet for a battery case and a lithium secondary battery comprising the same, and more particularly, to a laminate sheet used in the manufacture of a battery case, an outer coating layer based on a polymer resin having excellent tensile strength and weather resistance, A laminate sheet composed of a functional barrier layer based on a polymer resin capable of blocking water and gas, and an inner sealant layer based on a heat sealable polymer resin, and using the laminate sheet as a battery case It relates to a lithium secondary battery.

With the development of technology and increasing demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, lithium secondary batteries with high energy density, high operating voltage, and excellent storage and life characteristics are used for various mobile devices as well as various electronic products. It is widely used as an energy source.

Lithium secondary batteries are largely classified into cylindrical batteries, square batteries, pouch-type batteries, and the like according to their appearance, and may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, and the like depending on the type of electrolyte.

Due to the recent trend toward the miniaturization of mobile devices, there is an increasing demand for thinner rectangular batteries and pouch-type batteries. In particular, for pouch-type batteries that are easy to deform, low in manufacturing cost and light in weight. Interest is high. A pouch type battery is a battery in which an electrode assembly having a cathode / separation membrane / cathode structure is built in a battery case in which a laminate sheet including a resin layer and a metal layer is formed in a pouch type.

1 schematically illustrates a cross-sectional structure of a laminate sheet generally used in a pouch-type battery.

Referring to FIG. 1, the laminate sheet 10 includes an outermost outer covering layer 11, a metal barrier layer 12 that prevents penetration of a material, an adhesive layer 13, and an inner sealant layer 14 for sealing. It consists of.

Since the outer coating layer 11 serves to protect the battery from the outside, excellent tensile strength and weather resistance to the thickness are required, and ONy (stretched nylon film) is frequently used. The metal barrier layer 12 serves to prevent air, moisture, and the like from flowing into the battery, and mainly aluminum (Al) is used. The inner sealant layer 14 is thermally fused to each other by an applied heat and pressure in a state in which the electrode assembly is embedded, and serves to provide a sealability, and mainly consists of CPP (non-stretched polypropylene film). The adhesive layer 13 serves to compensate for the low adhesion of the CPP inner sealant layer 14 to the metal barrier layer 12.

The battery case sheet of such a multilayer laminate structure has a metal barrier layer of the laminate sheet exposed to the outside or a metal barrier layer of the laminate sheet exposed to the outside during the process of manufacturing the battery or using the battery. Occasionally an electrical connection with a plate or the like occurs. For example, during the manufacturing process of the battery, in the deep drawing process for forming the electrode assembly accommodating portion in the battery case or the heat fusion sealing process for the formation of the battery case outer peripheral surface sealing portion, locally excessive strain or excessive heat fusion is applied. By doing so, the outer barrier layer and / or inner sealant layer can be broken while the metal barrier layer is exposed and the exposed metal barrier layer can be energized with the cell.

As such, when the metal barrier layer is exposed or the exposed metal barrier layer is placed in electrical connection with other parts of the battery, the laminate sheet may be referred to as 'breakdown of insulation resistance'. It is very unfavorable in terms of lifespan characteristics and safety.

For example, when charge and discharge of a secondary battery is performed while aluminum in the barrier layer is exposed and energized with the battery, as shown in FIG. 2, aluminum is oxidized to form a lithium aluminum alloy, and the aluminum alloy is used as an electrolyte. Elution results in the formation of micropores in the aluminum barrier layer. Therefore, moisture is introduced into the battery case through the outer coating layer having no moisture barrier property, resulting in swelling of the battery. As a result, the battery life is rapidly shortened and the safety of the battery is also greatly threatened.

Therefore, various techniques have been tried to solve the problems caused by the destruction of the insulation resistance.

For example, Japanese Patent Application Laid-Open No. 2007-265989 is a laminate film having a structure in which two or more layers of resin films are laminated, and in the battery element packaging material used to package battery elements, the laminated structure does not include metal foil, Disclosed is a battery element packaging material, characterized in that at least one resin film layer comprises a moisture absorbing material. However, since the battery element packaging material is formed in a two-layer structure, it is difficult to maintain a predetermined stiffness from external forces such as needle penetration, and only one moisture absorbing material for preventing moisture absorption is contained in one resin layer of the two-layer resin layer. There is a problem that it is difficult to prevent the blocking of the internal gas generated in an abnormal situation during the chemical reaction of the positive electrode and the negative electrode of the battery element.

Further, Japanese Patent Application Laid-Open No. 2005-056729 is an aluminum laminate material for battery packaging used for packaging batteries, wherein an unstretched polypropylene layer having a thickness of 10 to 60 µm and an acid-modified polypropylene having a thickness of 1 to 5 µm are formed from an inner surface thereof. A layer, a first chemical coating layer having a coating weight of 5 to 30 mg / m ² , an inner lamination part in which an aluminum barrier layer having a thickness of 10 to 100 μm is sequentially laminated, and a synthetic resin provided outside the aluminum barrier layer. Disclosed is an aluminum laminate material for battery packaging including an outermost layer including an outermost layer and laminated in a plurality of layers. However, the above technique requires complicated lamination of an unstretched polypropylene layer, an acid-modified polypropylene layer, and a first chemical coating layer in order from the inner surface in order to compensate for the problem of aluminum laminate material. There is a problem in that the manufacturing cost is high.

Therefore, there is a high need for a technology that can solve the problems of the laminate sheet for a battery case, to ensure the life and safety of the battery and to improve the manufacturing processability.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

After extensive research and various experiments, the inventors of the present application have developed a laminate sheet including an outer coating layer, a functional barrier layer based on a polymer resin capable of blocking moisture and gas, and an inner sealant layer. When it was used as a battery case, it was confirmed that processing was easy and the lifespan characteristics and safety of the secondary battery could be secured to a desired level.

Accordingly, it is an object of the present invention to provide a laminate sheet for a battery case having a specific structure and a secondary battery including the same, which can improve manufacturing processability, lifespan characteristics, safety, and the like of a secondary battery.

Laminate sheet according to the present invention for achieving this object is a laminate sheet used in the manufacture of a battery case, a polymer resin that can block the outer coating layer, water and gas based on excellent tensile strength and weather resistance polymer resin And an inner sealant layer based on a heat sealable polymer resin.

That is, in the laminate sheet according to the present invention, since a functional blocking layer based on a polymer resin capable of blocking moisture and gas is interposed between the outer coating layer and the inner sealant layer, moisture outside the battery case, without using a metal layer, It is possible to prevent inflow of foreign matters into the battery and to effectively prevent outflow of the gas generated inside the battery to the outside.

In addition, since the laminate sheet according to the present invention is formed of a polymer resin which is non-conductive and easy to be molded as a whole, it prevents the reduction of the life of the battery due to corrosion and microporosity of the aluminum barrier layer as described above, and the safety and manufacturing processability. Can improve.

Furthermore, each layer of the laminate sheet is formed of polymers that are easy to thermally bond with each other, so that high bonding strength can be achieved without using a separate adhesive layer.

In one preferred example, the functional barrier layer may be of a two-layer structure or a multi-layer structure.

That is, since the functional blocking layer should perform a complex function of blocking water and gas, the functional blocking layer may be formed in a two-layer structure or a multi-layer structure in which a layer for blocking water and a layer for blocking gas are respectively configured separately.

The gas barrier polymer resin in the functional barrier layer is not particularly limited as long as it is a polymer resin capable of exhibiting a gas barrier function without affecting the physical and chemical properties of the laminate sheet, for example, polyester elastomer ( TPEE) and / or polyvinyl alcohol (PVA).

In the above structure, polyester elastomer and polyvinyl alcohol are polymer resins having excellent gas and organic solvent barrier properties, and have good processability, and have physical properties that can impart a predetermined strength to the laminated film when manufactured in a thin film form. have.

Therefore, by adding polyester elastomer and polyvinyl alcohol to the functional barrier layer, it is possible to easily produce a laminate sheet having both a predetermined strength and a gas barrier effect.

The polyvinyl alcohol basically has a high degree of polymerization (DP) and a degree of saponification (DS). If the degree of polymerization is too high, the workability is poor, the elastic force is reduced, on the contrary, if the degree of polymerization is too low, there may be a problem that the mechanical strength, adhesion, solvent resistance, and the like fall. In addition, polyvinyl alcohol having a high degree of saponification is improved by adhesion of the polymer resins to surrounding polymer resins by a hydroxy (OH) functional group, and thus, a higher degree of saponification within a predetermined range is preferable. In consideration of this point, the polyvinyl alcohol has a saponification degree of 99.5 mol% or less, and more preferably, a polymerization degree of 300 to 3000.

On the other hand, the water barrier polymer resin in the functional barrier layer is not particularly limited as long as it is a polymer resin capable of exhibiting a moisture barrier function without affecting the physical and chemical properties of the laminate sheet, for example, light weight and processability It is good, it can be made of a structure containing a polyolefin resin excellent in moisture barrier properties.

In the above structure, the polyolefin resin is, for example, polyethylene (HDPE, LDPE, LLDPE, MDPE, VLDPE), polypropylene, polybutene, ethylene-propylene rubber (EP rubber), ethylene-propylene diene rubber (EPD rubber) , Poly-4-methyl-1-pentene (TPX), a copolymer of propylene, butene, hexene and / or octene and ethylene, and one or more polymers or copolymers selected from the group consisting of olefinic thermoplastic elastomers. have.

In some cases, the functional barrier layer may be formed between the outer coating layer and the inner sealant layer in a two-layer structure of the gas barrier layer and the moisture barrier layer. For example, a polyester elastomer (TPEE) providing gas barrier property may be provided. ) It may be made of a two-layer structure of the film layer and the polyolefin-based resin layer to provide moisture barrier properties.

As another example, the functional barrier layer may be formed of a two-layered structure of a polyvinyl alcohol resin layer providing gas barrier properties and a polyolefin resin layer providing moisture barrier properties.

Such a two-layer structure is a polyolefin having excellent properties of water barrier property, light weight and excellent processability while maximizing the advantages of the polyolefin, and having low barrier property to gas and organic solvents, and having relatively weak mechanical strength. It is preferable because it can effectively compensate for the disadvantages.

On the other hand, the functional barrier layer can be easily prepared by known methods for producing a film of a laminate structure, for example, it can be prepared by coextrusion (Coextrusion). Co-extrusion is a method of manufacturing a multi-layered composite film by connecting two or more extruders to a die and extruding a variety of polymer resins, and the manufacturing process of the composite film is relatively simple, flexibility and thermal properties It is a way to produce products with good shaping. Therefore, the coextrusion method is preferable because a laminate sheet including a functional barrier layer composed of a two-layer structure or a multilayer structure can be produced with high productivity and excellent quality.

Since the outer coating layer must have excellent resistance from the external environment, a predetermined tensile strength and weather resistance are required. In this aspect, the polymeric resin of the outer coating layer may comprise polyethylene terephthalate (PET) or stretched nylon.

As the polymer resin of the inner sealant layer, a polyolefin-based resin having heat sealability (heat adhesiveness), low hygroscopicity to suppress invasion of the electrolyte solution, and not expanded or eroded by the electrolyte solution is preferably used. And more preferably, an unstretched polypropylene film (CPP).

In one preferred embodiment, the laminate sheet according to the present invention, the thickness of the outer coating layer is 5 to 30 ㎛, the thickness of the functional barrier layer is 30 to 150 ㎛, the thickness of the inner sealant layer is 15 to 150 ㎛ Can be. If the thicknesses are too thin, it is difficult to expect the blocking function and the strength improvement of the material, on the contrary, too thick is not preferable because of the poor workability and causing an increase in the thickness of the sheet.

The laminate sheet can be produced in a variety of ways. For example, the films constituting the respective resin layers may be sequentially laminated and then bonded to each other, and dry lamination or extrusion lamination methods may be used as such an adhesion method. have.

The dry lamination method is a method in which the two materials are bonded to each other by a temperature and pressure higher than room temperature using a heating roll after drying by interposing an adhesive between one material and the other material. In addition, the extrusion lamination method is a method of interposing the two materials by a constant pressure at room temperature using a pressing roll after the adhesive is interposed between the one material and the other material.

The present invention also provides a secondary battery case manufactured using the laminate sheet as described above.

The battery case according to the present invention may have various forms, and preferably, may include a form in which the electrode assembly is formed in a pouch form. That is, one side of the laminate sheet may be manufactured in a pouch form by forming an accommodating part in which the electrode assembly may be seated by deep drawing and bending the other side in the form of a cover.

The present invention also provides a lithium secondary battery including the battery case as described above.

Representative examples of the secondary battery include a lithium secondary battery, and among them, a lithium ion polymer secondary battery in which an electrode assembly is embedded in a pouch type case made of the laminate sheet and a lithium salt-containing electrolyte is impregnated therein. Is preferred.

Since the specific structure and manufacturing method of the lithium ion polymer secondary battery is known in the art, the description thereof is omitted herein.

In addition, the lithium secondary battery according to the present invention may be preferably used as a unit cell of a medium and large battery pack, in particular, because of the excellent life and safety of the battery case.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings, but the scope of the present invention is not limited thereto.

Figure 3 is a schematic cross-sectional view of a laminate sheet according to an embodiment of the present invention, Figure 4 is a perspective view of a pouch type battery case formed of the laminate sheet of Figure 3 schematically.

Referring to these drawings, the laminate sheet 100 is a functional barrier layer between the outer coating layer 110 as the outermost layer and the heat sealable inner sealant layer 130, and the polyester elastomer film layer 120 and the poly It has a structure in which the propylene layer 140 is laminated. That is, the outer coating layer 110, the polyester elastomer film layer 120, the polypropylene layer 140 and the inner sealant layer 130 are laminated in order from the outside.

Since the outer coating layer 110 forms an outer surface of the pouch case 200, tensile strength and weather resistance that can stably protect the electrode assembly (not shown) against the external environment are required, and polyethylene is required to satisfy these requirements. It consists of terephthalate (PET) or stretched nylon (Ony).

Since the functional barrier layer 150 is composed of a polyester elastomer film layer 120 for blocking a gas including air and a polypropylene layer 140 for blocking moisture, the functional barrier layer 150 has excellent moldability compared to a conventional aluminum barrier layer. In addition, even when electrically contacted with an electrode terminal (not shown) or the like of the battery cell, current is not generated as a non-conductor.

The inner sealant layer 130 forms an inner portion of the accommodating part 210 and the cover 220 in which the electrode assembly (not shown) may be mounted in the pouch case 200, thereby easily securing resistance to lithium-containing electrolyte. Do. In addition, the inner sealant layer 130 may be coupled to each other by thermal fusion in a state in contact with the inside of the cover 220 in the outer peripheral portion 230 of the housing 210, the material of the inner sealant layer 130 It consists of CPP (non-stretched polypropylene film) which combines electrolyte solution and heat sealability.

In addition, since the laminate sheet 100 is made of a polymer resin that is easy to mutually heat-sealed as a whole, there is no need for a separate adhesive layer as shown in FIG. 1 between the inner sealant layer 130 and the polypropylene layer 140.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, and the scope of the present invention is not limited thereto.

Example 1

Polyvinyl alcohol having a degree of saponification of 88 mol% and a polymerization degree of 1,700 was mixed with 20 parts by weight of a plasticizer, 2 parts by weight of a processing aid and 0.05 parts by weight of an antioxidant with a Super Mixer based on 100 parts by weight of polyvinyl alcohol, After drying for 12 hours in a dryer at 80 ℃ extruded in a twin screw extruder (Φ 40, Dae Ae Co., Ltd.). At this time, the temperature gradient of the extruder was 170 ℃-190 ℃-200 ℃-210 ℃-220 ℃-200 ℃, was extruded at 40 rpm to make a pellet.

Low density polyethylene (LDPE; melt index (MI) = 1, density (ρ) = 0.918) based on 100 parts by weight of low density polyethylene, 1 part by weight of maleic anhydride, a low molecular weight compatibilizer, and dicumyl peroxide, an initiator, 0.1 parts by weight of dicumyl peroxide) was coated on LDPE, mixed in a supermixer, dried for 12 hours in a dryer at 80 ° C, and extruded on a twin screw extruder (Φ40, Dae-A Zinc Co., Ltd.). At this time, the temperature gradient of the extruder was 170 ℃-190 ℃-200 ℃-210 ℃-220 ℃-200 ℃, was extruded at 40 rpm to make a pellet.

Polyvinyl alcohol pellets and low density polyethylene pellets were introduced into a two-layer extruder and extruded into a two-layer film while maintaining the temperature at 230 ° C., thereby preparing a functional barrier layer film having a two-layer structure. At this time, the gap of the T-die was fixed at 1 mm, the screw at 10 rpm, and the take-off speed at 0.8 m / min.

The bilayer functional barrier layer film is interposed between an unstretched polypropylene (cPP) film and a polyethylene terephthalate (PET) film, and then extruded in a state where both sides are coated in a three-layer extruder. And a laminate sheet comprising a functional barrier layer film.

The thickness of the laminate sheet was 110 m, the polypropylene (cPP) film layer and the polyethylene terephthalate (PET) film layer were 45 m and 12 m, respectively, and the thickness of the functional barrier layer film was 50 m.

Comparative Example 1

A laminate sheet was manufactured in the same manner as in Example 1, except that a barrier aluminum metal foil having a thickness of 50 μm was used instead of the functional barrier layer film having a two-layer structure.

Experimental Example 1

The laminate sheets of Example 1 and Comparative Example 1 were respectively subjected to gas permeability test and moisture permeation test, and the results are shown in Table 1 below. In the gas permeability experiment, each laminate sheet is formed as a center boundary in the glass box of the rectangular parallelepiped, and one of the spaces (A) is a vacuum and the other space of the inside of the rectangular glass box divided into two spaces. (B) was performed by charging carbon dioxide and leaving it at room temperature for one day, then measuring the concentration of carbon dioxide in the space (A).

In addition, the moisture permeation experiment is to fill the space (A) with humidity of 20% air, and the space (B) with 80% humidity of the air and leave it at room temperature for one day, and then measure the humidity of the space (A). Was performed.

TABLE 1

As shown in Table 1, the laminate sheet of Example 1 according to the present invention, as in the laminate sheet of Comparative Example 1 using aluminum metal foil as a barrier layer, hardly generated gas permeation and moisture penetration.

Experimental Example 2

Using the laminate sheets of Example 1 and Comparative Example 1, respectively, a pouch-type battery case was manufactured in the shape as shown in FIG. 4.

In addition, a slurry prepared by adding 94% by weight of LiCoO ₂ , 3.5% by weight of Super-P (conductor), and 2.5% by weight of PVdF (binder) to a solvent, N-methyl-2-pyrrolidone (NMP), was coated on aluminum foil. Coating, drying and pressing the positive electrode formed by coating, drying and pressing on a copper foil, and a slurry prepared by adding 94% by weight of artificial graphite, 1% by weight of Super-P, and 5% by weight of PVdF to a solvent, NMP. The electrode assembly having a structure of a polypropylene separator formed by Celgard between the negative electrodes formed in the pouch-type battery case, and injected with a 1M LiPF ₆ carbonate solution electrolyte, and then the outer peripheral surface of the battery case was subjected to thermal fusion. Sealing to prepare a battery cell.

Insulation resistance was checked for 30 battery cells manufactured in the same manner as described above, and after performing 50 charge / discharge cycles, swelling was measured and shown in Table 2 below.

The insulation resistance measurement is a method of checking whether electricity is supplied between a layer (Example 1: functional blocking layer, Comparative Example 1: aluminum layer) positioned between an outer coating layer and an inner sealant layer in a battery case and a negative electrode terminal of a battery cell. Was performed.

Whether or not the swelling was determined by measuring the thickness of the battery cell, the occurrence of swelling when the thickness change of the battery cell after 50 charge and discharge based on the battery cell thickness of the initial state is more than 30%.

TABLE 2

As shown in Table 2, in the battery cell using the laminate sheet of Example 1 according to the present invention, the breakdown of the insulation resistance and the occurrence of swelling were not confirmed. On the other hand, in some of the battery cells using the laminate sheet of Comparative Example 1, breakdown of insulation resistance and occurrence of swelling were confirmed.

As described above, in the laminate sheet according to the present invention, since a functional blocking layer based on a polymer resin capable of blocking moisture and gas is formed between the outer coating layer and the inner sealant layer, the laminate sheet may be generated inside and outside the battery case. This can effectively prevent the inflow or leakage of foreign substances such as gas, moisture.

In addition, since the laminate sheet of the present invention is made entirely of a non-conductive and easily molded polymer resin, it prevents battery life reduction due to corrosion and micropore generation of the barrier layer generated in the laminate sheet including the conventional metal barrier layer. And safety and manufacturing processability can be improved.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

1 is a schematic cross-sectional view of a laminate sheet for a conventional battery case;

2 is a schematic diagram of a process in which fine pores are formed in the aluminum barrier layer when the secondary battery is charged and discharged in a state in which aluminum of the barrier layer is exposed and energized with the battery;

3 is a schematic cross-sectional view of a laminate sheet according to one embodiment of the present invention;

4 is a perspective view of a pouch-shaped battery case formed of the laminate sheet of FIG.

Claims (19)

A laminate sheet used in the manufacture of a battery case, comprising: an outer coating layer made of a polymer resin providing tensile strength and weather resistance, a functional blocking layer made of a polymer resin capable of blocking moisture and gas, and an inner sealant made of a heat-sealing polymer resin Consisting of layers, The thickness of the outer coating layer is 5 to 30 ㎛, the thickness of the functional barrier layer is 30 to 150 ㎛, the thickness of the inner sealant layer is a laminate sheet, characterized in that 15 to 150 ㎛. The laminate sheet according to claim 1, wherein the functional barrier layer has a two-layer structure or a multilayer structure. The method of claim 1, wherein the functional barrier layer is a gas barrier polymer resin (i) polyester elastomer (TPEE), or (ii) polyvinyl alcohol (PVA), or (iii) polyester elastomer And polyvinyl alcohol. 4. The laminate sheet of claim 3, wherein the polyvinyl alcohol has a degree of saponification of 99.5 mol% or less and a degree of polymerization of 300 to 3000. The laminate sheet according to claim 1, wherein the functional barrier layer comprises a polyolefin resin as a moisture barrier polymer resin. The method of claim 5, wherein the polyolefin resin is polyethylene (HDPE, LDPE, LLDPE, MDPE, VLDPE), polypropylene, polybutene, ethylene-propylene rubber (EP rubber), ethylene-propylene diene rubber (EPD rubber), poly One or two or more selected from the group consisting of -4-methyl-1-pentene (TPX), propylene-ethylene copolymer, butene-ethylene copolymer, hexene-ethylene copolymer, octene-ethylene copolymer, and olefinic thermoplastic elastomer Laminate sheet, characterized in that the polymer or copolymer. The laminate sheet according to claim 1, wherein the functional barrier layer comprises a two-layer structure of a polyester elastomer (TPEE) film layer and a polyolefin resin layer. The laminate sheet according to claim 1, wherein the functional barrier layer comprises a two-layer structure of a polyvinyl alcohol resin layer and a polyolefin resin layer. 3. The laminate sheet of claim 2, wherein said functional barrier layer is made by coextrusion. The laminate sheet according to claim 1, wherein the polymer resin of the outer coating layer comprises polyethylene terephthalate (PET) or stretched nylon. The laminate sheet according to claim 1, wherein the polymer resin of the inner sealant layer comprises unstretched polypropylene. delete A secondary battery case manufactured using the laminate sheet according to claim 1. The secondary battery case according to claim 13, wherein the secondary battery case is formed in a pouch form by forming an accommodating part on which one side of the laminate sheet may be seated by deep drawing and bending the other side in the form of a cover. A lithium secondary battery comprising the battery case according to claim 14. The lithium secondary battery according to claim 15, wherein the secondary battery is a lithium ion polymer battery in which an electrode assembly is embedded in a pouch type case made of the laminate sheet, and the lithium salt-containing electrolyte is impregnated in a gel form. The lithium secondary battery of claim 16, wherein the secondary battery is used as a unit cell of a medium-large battery pack. A laminate sheet used in the manufacture of a battery case, comprising: an outer coating layer made of a polymer resin providing tensile strength and weather resistance, a functional blocking layer made of a polymer resin capable of blocking moisture and gas, and an inner sealant made of a heat-sealing polymer resin Consisting of layers, The functional barrier layer is a laminate sheet, characterized in that consisting of a two-layer structure of a polyester elastomer (TPEE) film layer and a polyolefin-based resin layer. A laminate sheet used in the manufacture of a battery case, comprising: an outer coating layer made of a polymer resin providing tensile strength and weather resistance, a functional blocking layer made of a polymer resin capable of blocking moisture and gas, and an inner sealant made of a heat-sealing polymer resin Consisting of layers, The functional barrier layer is a laminate sheet comprising a two-layered structure of a polyvinyl alcohol resin layer and a polyolefin resin layer.

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