KR101073180B1 - A multi-layer separator, manufacturing method thereof, and a secondary battery having the same - Google Patents

Abstract

The present invention relates to a separator that can be used in a secondary battery, a manufacturing method thereof, and a secondary battery having the same. The separator according to the present invention is a multilayer separator including a porous polymer film and a porous nonwoven fabric sheet laminated on at least one surface of the porous polymer film, and further comprising an adhesive layer made of a gel-forming polymer between the porous polymer film and the porous nonwoven fabric sheet. It is characterized by including. According to the present invention, the gel-forming polymer adhesive layer interposed between the porous polymer film and the porous nonwoven fabric may minimize the deterioration of battery performance due to the introduction of the adhesive layer while significantly reducing the risk of the multilayer separator separating between layers.

Description

Multi-layered separator, manufacturing method thereof and secondary battery having same {A MULTI-LAYER SEPARATOR, MANUFACTURING METHOD THEREOF, AND A SECONDARY BATTERY HAVING THE SAME}

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the presently preferred embodiments of the invention and, together with the description of the following preferred embodiments, serve to explain the principles of the invention.

1 is a cross-sectional view schematically showing a multilayer separator having a two-layer structure according to an embodiment of the present invention.

2 is a cross-sectional view schematically showing a multi-layer separator of a three-layer structure according to another embodiment of the present invention.

3 is a schematic cross-sectional view of a multi-layer separator of a three-layer structure according to another embodiment of the present invention.

The present invention relates to a separator that can be used in a secondary battery, a method for manufacturing the same, and a secondary battery having the same, and more particularly, to a multilayer type separator including a porous nonwoven fabric sheet laminated on at least one surface of a porous polymer film. It relates to a method and a secondary battery having the same.

In general, rechargeable batteries capable of charging and discharging are being actively researched by developing portable electronic devices such as cellular phones, notebook computers, and camcorders. Examples of such secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-hydrogen batteries, and lithium secondary batteries. Among them, lithium secondary batteries are considered the most promising and have high future prospects because they have superior operating voltage characteristics and energy density per unit weight compared to nickel-cadmium batteries or nickel-metal hydride batteries, which are widely used as power sources for electronic devices. .

The lithium secondary battery may be manufactured in various forms, and typical shapes include cylindrical and rectangular shapes mainly used in lithium ion batteries. Lithium polymer batteries, which are in the spotlight in recent years, are made of flexible materials and their shapes are relatively free. In addition, since the safety and light weight is excellent, it can be said that it is advantageous to slim and lighten portable electronic devices.

A lithium secondary battery is a separator formed by applying a positive electrode active material to both surfaces of a positive electrode current collector, a negative electrode formed by applying a negative electrode active material to both sides of a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode to electrically insulate them. It is prepared by injecting a non-aqueous electrolyte solution containing a lithium salt and an organic solvent into the electrode structure.

The separator should generally be stable and resistant to degradation of the components of the cell it is in contact with, exhibit high electroconductivity, and when the separator is manufactured and processed or used in a cell, It must have sufficient strength to keep the separator circular while preventing contact.

In particular, lithium secondary batteries can provide excellent shelf life and high energy density compared to other types of batteries, while lithium is very reactive, so if the battery is overheated and thermal runaway occurs or the separator penetrates, There is a high risk of causing an explosion. However, porous polyolefin-based films, which are separators commonly used in lithium secondary batteries, suffer from problems such as shrinkage by heat to cause internal short circuits.

In order to solve this problem, Japanese Patent Laid-Open Nos. 1998-12211, 2004-127555, 2005-44675, 2000-208122 and the like have a multilayer type in which a porous nonwoven fabric sheet is laminated on at least one surface of a porous polyolefin-based film. The separator is starting.

However, the above-described multilayer separators are prepared by stacking a porous polyolefin-based film and a porous nonwoven fabric sheet and then heating and pressing. The multilayer separators thus prepared have collapsed pores of the porous polymer film during hot pressing, thereby reducing the battery capacity. It causes the problem of deterioration. When the processing conditions of the heating and pressing process are alleviated in order not to reduce the capacity of the battery, the adhesive force between the porous polymer film and the porous nonwoven sheet is weakened, so that the multilayer separator is wound or separated from each other by external impact when used in the battery. The safety of the secondary battery is compromised.

The technical problem to be solved by the present invention is to solve the above problems, while significantly reducing the risk of separation between layers, while reducing the performance of the battery due to the adhesion of the multilayer-type separator, a manufacturing method and the same It is to provide a secondary battery.

In order to achieve the above technical problem, the multi-layer separator of the present invention is a multi-layer separator comprising a porous polymer film and a porous non-woven fabric sheet laminated on at least one surface of the porous polymer film, between the porous polymer film and the porous non-woven fabric sheet It is characterized by further comprising an adhesive layer made of a gel-forming polymer.

According to the present invention, the gel-forming polymer adhesive layer interposed between the porous polymer film and the porous nonwoven fabric significantly reduces the risk of the multilayer separator separating between layers. In addition, since the porous polymer film and the porous nonwoven fabric are not exposed to high temperature, the pores of the porous polymer film can be suppressed from being collapsed. The gelation is performed by the electrolyte injected during the battery assembly process to facilitate the movement of lithium ions. It is possible to minimize the degradation of the battery performance.

In the multilayer separator of the present invention, the gel-forming polymer may be vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene Oxide, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyacetate, etc. can be used individually or in mixture of 2 or more types, respectively.

In the multilayer separator of the present invention, the porous nonwoven fabric sheet includes polyethylene terephthalate, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, and polyparaphenylene benzobisoxazole having excellent heat resistance. The nonwoven fabric sheet which formed the fiber of materials, such as a polyarylate and glass, individually or in mixture of two or more fibers of these materials can be used.

The multilayer separator described above is interposed between the positive electrode and the negative electrode to be used in a secondary battery.

In addition, the present invention (S1) applying a polymer solution in which a gel-forming polymer dissolved in a solvent on one surface of a porous polymer film or a porous nonwoven sheet; (S2) laminating a porous nonwoven fabric sheet on the surface of the porous polymer film to which the polymer solution is applied, or laminating a porous polymer film on the surface of the porous nonwoven fabric sheet to which the polymer solution is applied; And (S3) provides a method for producing a multi-layer separator comprising the step of adhering the polymer film and the porous nonwoven sheet by pressing the resultant of the step (S2).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

1 is a schematic cross-sectional view of a multi-layer separator according to an embodiment of the present invention.

Referring to FIG. 1, the multilayer separator 10 of the present invention includes a porous polymer film 5 and a porous nonwoven fabric sheet 3 laminated on one surface thereof. An adhesive layer 7 made of a gel-forming polymer is interposed between the porous polymer film 5 and the porous nonwoven sheet 3 to enhance the adhesive force between the porous polymer film 5 and the porous nonwoven sheet 3. As shown in FIG. 2, the multilayer separator 10 of the present invention includes porous nonwoven fabric sheets 3a and 3b stacked on both sides of the porous polymer film 5, and has a porous polymer film 5 and a porous structure. Gel-forming polymer adhesive layers 7a and 7b may be interposed between the nonwoven sheets 3a and 3b, respectively. On the contrary, as shown in FIG. 3, the multilayer separator 10 of the present invention includes porous polymer films 5a and 5b laminated on both sides of the porous nonwoven fabric sheet 3, and the porous polymer films 5a and Gel-forming polymer adhesive layers 7a and 7b may be interposed between 5b) and porous nonwoven sheet 3, respectively.

According to the present invention, the gel-forming polymer adhesive layer interposed between the porous polymer film and the porous nonwoven fabric enhances the adhesive force between the film and the nonwoven fabric, and thus, a process of winding a separator or assembling a battery or using a secondary battery employing a multilayer separator. This significantly reduces the risk of the multilayer separator separating between layers, improving battery safety. In addition, since the porous polymer film and the porous nonwoven fabric are not exposed to high temperature, pore collapse of the porous polymer film is suppressed. In addition, since the adhesive layer is made of a gel-forming polymer, the adhesive layer is gelled by the electrolyte solution injected in the battery assembly process, thereby smoothing the movement of lithium ions, thereby minimizing degradation of battery performance due to the introduction of the adhesive layer.

In the multilayer separator according to the present invention, the polymer forming the gel-forming polymer adhesive layer is vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride Gel-forming polymers such as polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyacetate, and the like may be used alone or in combination thereof, but are not limited thereto.

In the multilayer separator according to the present invention, the porous polymer film may be a conventional porous polymer film conventionally used as a separator, for example, ethylene homopolymer, propylene homopolymer, ethylene / propylene copolymer, ethylene / butene copolymer, Porous polymer films made of polyolefin-based polymers such as ethylene / hexene copolymers and ethylene / methacrylate copolymers may be used alone or in combination of them. In particular, the porous polymer film disclosed in the above-described multilayered separators of Japanese Patent Application Laid-Open Nos. 1998-12211, 2004-127555, 2005-44675, and 2000-208122 can be suitably applied.

Further, in the multilayer separator according to the present invention, the porous nonwoven fabric sheet may be a conventional porous nonwoven fabric used as a separator of a secondary battery, for example, polyethylene terephthalate having a high melting point, polyacrylonitrile, polyimide, and polyamide. , Non-woven fabric sheet formed by mixing fibers of a material such as cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, glass, or two or more of these materials It may be, but is not limited to such. In particular, the porous nonwoven fabric sheet disclosed in the above-described multilayered separators of Japanese Patent Laid-Open Nos. 1998-12211, 2004-127555, 2005-44675, and 2000-208122 can be suitably applied.

The multi-layered separator of the present invention described above may be used as a lithium secondary battery by manufacturing a non-aqueous electrolyte containing a lithium salt and an organic solvent after the electrode structure is interposed between the positive electrode and the negative electrode.

The method for producing a multilayer separator according to the present invention is as follows.

First, a polymer solution in which a gel-forming polymer is dissolved in a solvent is applied to one surface of a porous polymer film or a porous nonwoven fabric sheet (step S1).

As described above, in the multilayer separator according to the present invention, the polymer forming the gel-forming polymer adhesive layer may be vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, Gel-forming polymers such as polyvinylidene fluoride, polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyacetate, and the like may be used alone or in combination thereof, but are not limited thereto. Do not. In addition, a solvent for dissolving the gel-forming polymer may be used a conventional solvent such as acetone, methylpyrrolidone (NMP), and any solvent that can dissolve the gel-forming polymer to prepare a polymer solution. It is possible. Some of the polymer solution applied can penetrate into the pores present in the porous polymer film or porous nonwoven sheet, and some are present in the surface layer to impart interlayer adhesion.

Subsequently, the porous nonwoven fabric sheet is laminated on the surface of the porous polymer film to which the polymer solution is applied, or the porous polymer film is laminated to the surface of the porous nonwoven fabric sheet to which the polymer solution is applied (step S2).

Then, the resultant of the step (S2) is pressed so that the gel-forming polymer adhesive layer sufficiently adheres between the porous polymer film and the porous nonwoven sheet. The solvent used to dissolve the gel-forming polymer is preferably removed by drying before or after the pressing step or during the pressing step.

The multilayer separator of the present invention manufactured as described above is manufactured in the form of a thin card after the process of a conventional secondary battery, for example, after winding a cylindrical structure in which a multilayer separator is interposed between a positive electrode and a negative electrode in a cylindrical shape, After injecting the non-aqueous electrolyte, the lithium secondary battery is completed by vacuum sealing the packaging material coated with polymer on aluminum. The gel-forming polymer adhesive layer in the completed lithium secondary battery absorbs the organic solvent of the injected nonaqueous electrolyte to form a gel.

As the organic solvent of the nonaqueous electrolyte, a carbonate-based organic solvent or the like, which is typically used in the nonaqueous electrolyte of a lithium secondary battery, may be used. Specific examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, gamma-butyro Lactone, ethylene sulfite, propylene sulfite, tetrahydrofuran, and the like may be used alone or in combination thereof, but is not limited thereto. Preferably, alkylene carbonate organic solvents such as ethylene carbonate and propylene carbonate, which are highly dielectric solvents having excellent electrochemical properties, are preferably used, and low viscosity solvents such as dimethyl carbonate, diethyl carbonate, It is more preferable to mix and use ethylmethyl carbonate.

In addition, any lithium salt used in the nonaqueous electrolyte may be used as long as it is used in a conventional lithium secondary battery. Examples of lithium salts include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), and hexafluoride. Lithium phosphate (LiPF ₆ ), lithium arsenic fluoride (LiAsF ₆ ), lithium trifluoride methanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethanesulfonylamide (LiN (CF ₃ SO ₂ ) ₂ ), and the like Or may be used as a mixture thereof, but is not limited thereto.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example  One

Vinylidene fluoride-hexafluoropropylene copolymer (P (VdF-co-HFP)) was mixed in a weight ratio of 10:90 to acetone and a polymer solution was prepared. Subsequently, the prepared polymer solution was applied to the porous polyethylene film having a thickness of 12 μm by using a dip coating method, and then the porous nonwoven fabric sheet having a thickness of 20 μm made of glass fiber was laminated. Then, the adhesive was bonded between the porous film and the nonwoven sheet while pressing with a press. The multilayer separator thus prepared was interposed between a positive electrode (LiCoO ₂ ) and a negative electrode (carbon) having a diameter of 3 cm and a width of 5 cm, and then vacuum sealed using a packaging material coated with a polymer on aluminum to complete a lithium secondary battery.

Example  2

A battery was manufactured in the same manner as in Example 1, except that a polymer solution of vinylidene fluoride-hexafluoropropylene copolymer (P (VdF-co-HFP) with acetone in a ratio of 5:95) was prepared.

Comparative example  One

Except for using only the porous polymer film used in Example 1 as a separator was prepared in the same manner as in Example 1.

Comparative example  2

It was prepared in the same manner as in Example 1 except that the porous polymer film and the porous nonwoven fabric sheet were directly heated and pressed without forming a contact layer using a polymer solution.

The interlayer adhesion of the multilayer separators of Examples and Comparative Examples prepared by the respective methods was measured, and capacity ratio and stability were tested for each of the 20 batteries prepared. The stability test of the battery was carried out by heating test at 160 ^o C for 1 hour in a fully charged state to confirm whether it was ignited and the results are shown in Table 1.

Referring to the results of Table 1, the cells of Examples 1 and 2 attached with a porous polymer film and a porous nonwoven sheet using an adhesive layer composed of a gel-forming polymer showed a capacity of 80% or more even at 3C discharge, and 160 ^° C. No battery ignited even at high temperature exposure.

On the other hand, a battery composed of a separator using only a porous polymer film has a good capacity ratio, but ignition occurred in many batteries. In addition, even when the porous polymer film and the porous nonwoven fabric sheet were hot pressed, there was no battery to ignite, but the capacity ratio of the battery was significantly reduced to 65%. This is because the pores of the porous polymer film collapsed during hot pressing.

As described above, the gel-forming polymer adhesive layer interposed between the porous polymer film and the porous nonwoven fabric according to the present invention enhances the adhesive force between the film and the nonwoven fabric, thereby employing a separator winding or battery assembly process or a multilayer separator. In the use of one secondary battery, the multilayer separator is significantly reduced in interlayer separation, thereby improving the defective rate of the battery. In addition, since the porous polymer film and the porous nonwoven fabric are not exposed to high temperatures, the pores of the porous polymer film may be prevented from being collapsed, and the adhesive layer may be gelled by the injected electrolyte to minimize degradation of battery performance.

Claims (11)

In the multi-layer separator comprising a porous polymer film and a porous nonwoven fabric sheet laminated on at least one surface of the porous polymer film, The porous polymer film is made of a polyolefin-based polymer, A multilayer separator, further comprising an adhesive layer of a gel-forming polymer gelled by an electrolyte between the porous polymer film and the porous nonwoven fabric sheet. The method of claim 1, The gel-forming polymer may be vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl Multilayered separator, characterized in that any one selected from the group consisting of methacrylate, polyacrylamide, polyacetate and mixtures thereof. delete The method of claim 1, The polyolefin-based polymer is at least one selected from the group consisting of ethylene homopolymer, propylene homopolymer, ethylene / propylene copolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer Multi-layer separator. The method of claim 1, The porous nonwoven sheet is any selected from the group consisting of polyethylene terephthalate, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate and glass A multilayer separator comprising one fiber or a mixture of two or more of them. (S1) applying a polymer solution in which a gel-forming polymer, which is gelled by an electrolyte solution, is dissolved in a solvent to one surface of a porous polymer film or a porous nonwoven fabric sheet made of a polyolefin-based polymer; (S2) laminating a porous nonwoven fabric sheet on the surface of the porous polymer film to which the polymer solution is applied, or laminating a porous polymer film on the surface of the porous nonwoven fabric sheet to which the polymer solution is applied; And (S3) Method of manufacturing a multi-layer separator comprising the step of adhering the polymer film and the porous nonwoven sheet by pressing the resultant of the step (S2). The method of claim 6, The gel-forming polymer may be vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polyurethane, polyethylene oxide, polyacrylonitrile, polymethyl A method for producing a multilayer separator, characterized in that any one selected from the group consisting of methacrylate, polyacrylamide, polyacetate and mixtures thereof. delete The method of claim 6, The polyolefin-based polymer is at least one selected from the group consisting of ethylene homopolymer, propylene homopolymer, ethylene / propylene copolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer Method of manufacturing a multilayer separator. The method of claim 6, The porous nonwoven sheet is selected from the group consisting of polyethylene terephthalate, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate and glass Method for producing a multi-layer separator, characterized in that consisting of any one fiber or a mixture of two or more of them. An electrode structure comprising an anode, a cathode, and a separator interposed between the anode and the cathode; And a nonaqueous electrolyte injected into the electrode structure and containing a lithium salt and an organic solvent. A secondary battery according to any one of claims 1 to 2 and 4 to 5, wherein the separator is a multilayer separator.

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