KR100362280B1 - Separator for lithium secondary battery and the method thereof - Google Patents

Abstract

The present invention provides a separator and a method of manufacturing the lithium secondary battery. The separator is a porous polyolefin film made of polyethylene or polypropylene; And one adhesive polymer resin formed on both sides of the porous polyolefin film and selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin; And a porous adhesive polymer film made of an inorganic filler. Separator of the present invention is excellent in mechanical properties can be applied to the continuous lamination process mass production is possible. In addition, since the ion conductivity is excellent and the pores are formed by spraying the fine particles by the spray method, it is unnecessary to add an undesired plasticizer in terms of environmental and worker health. Therefore, there is an advantage that the extraction process for removing such plasticizers is unnecessary and the manufacturing process is simplified.

Description

Separator for lithium secondary battery and manufacturing method thereof

The present invention relates to a separator of a lithium secondary battery and a method for manufacturing the same. More specifically, the mechanical properties of the lithium secondary battery are excellent and not only can be manufactured according to a continuous lamination process but also do not include a plasticizer, and thus a process of removing the lithium secondary battery is unnecessary. The present invention relates to a separator of a lithium secondary battery in which a manufacturing process is simplified, and a manufacturing method thereof.

Lithium secondary batteries can be divided into lithium ion batteries using liquid electrolytes and lithium ion polymer batteries using solid electrolytes, depending on the type of electrolyte. Among them, the lithium ion polymer battery uses a solid electrolyte, so there is little risk of leakage of the electrolyte, and the processability can be made into a battery pack. It is light in weight, low in volume, and has a very small self-discharge rate. Due to these characteristics, lithium ion polymer batteries are not only safer than lithium ion batteries, but also easy to manufacture into square and large cells.

1 is a view showing an example of a conventional lithium ion polymer battery.

Referring to this, the lithium ion polymer battery includes a battery assembly 11 formed by stacking a cathode, an anode, and a separator, and a case 12 surrounding and sealing the battery assembly 11. In addition, the electrode tab 13 serving as an external electrical passage between the battery assembly 11 is connected to a connection tab 13 ′ provided at the cathode and the anode, and the electrode tab 13 has a predetermined length out of the case 12. Exposed.

In the lithium ion polymer battery having the structure as described above, the separator is manufactured according to the following method.

First, a polymer resin such as polyvinylidene fluoride, an inorganic filler such as silica, and a plasticizer such as dibutyl phthalate are dissolved in a solvent to prepare a separator composition in a slurry state. This separator composition is then directly coated and dried on top of the electrode or cast on a separate support to produce a film, the film is peeled from this support and laminated onto the electrode to complete the separator. Later, the plasticizer contained in the separator is extracted and removed by an organic solvent to form pores inside the separator.

By the way, the separator formed as described above, although the mechanical strength is improved to some extent by the addition of the inorganic filler, there is room for improvement because it does not reach the level enough to be able to perform a continuous lamination process. In addition, since the deformation occurs in the separator film itself, it is impossible to be transported by a roll when the film itself is continuously produced. In addition, in order to improve battery performance, the thickness of the separator is gradually thinned. However, reducing the thickness of the separator results in a lot of difficulties in handling because of easy surface damage.

The technical problem to be solved by the present invention is to improve the mechanical properties to solve the above problems can be carried out a continuous lamination process and do not use a plasticizer can be omitted because of this additional process as well as improved lithium ion conductivity characteristics It is to provide a separator of a secondary battery.

Another object of the present invention is to provide a method of manufacturing the separator.

1 is a view showing the structure of a conventional lithium ion polymer battery,

2 is a view showing a process of continuously manufacturing a separator according to the present invention.

<Description of Major Symbols in Drawing>

11 ... battery assembly 12 ... case

13 ... electrode tab 13 '... connection tab

22 .. Nozzle part 23. Storage container

24 ... drying furnace 25 ... unwinding

26 ... Feed roll 27 ... Winding part

In order to achieve the above technical problem, in the present invention, a porous polyolefin film made of polyethylene or polypropylene; And one adhesive polymer resin formed on both sides of the porous polyolefin film and selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin; The present invention provides a separator for a lithium secondary battery comprising a porous adhesive polymer film made of an inorganic filler.

Another technical problem of the present invention is a polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid, and styrene-butadiene resin on both sides of a porous polyolefin film made of polyethylene or polypropylene. Spray coating and drying a composition comprising one adhesive polymer resin, an inorganic filler and a solvent selected from to form a separator comprising a porous polyolefin film and a porous adhesive polymer film formed on both sides of the porous polyolefin film. It is made by the method of manufacturing a separator of a lithium secondary battery.

The separator of the present invention has a structure in which an adhesive polymer film is laminated on both sides of the porous polyethylene film. In this case, the porous polyethylene film is particularly preferably made of polyethylene (PE) or polypropylene (PP) with excellent mechanical strength. And such a porous polyethylene film, in addition to the basic structure, such as the one-layer structure such as PE layer, PP layer, two-layer structure such as PE layer / PP layer, PE layer / PP layer / PE layer, PP layer / PE layer / PP layer It may also be in the form of a composite film having a three-layer structure such as.

The adhesive polymer film laminated on both sides of the porous polyethylene film is composed of an adhesive polymer resin and an inorganic filler, and pores are formed by spraying fine particles of the coating composition by the spray method. The adhesive polymer resin herein uses at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin.

In the separator of the present invention, the thickness ratio of the porous polyethylene film and the adhesive polymer film is preferably 1:10 to 10: 1.

Hereinafter, a separator manufacturing method according to the present invention will be described with reference to the accompanying drawings.

2 is a view for explaining a process of continuously manufacturing a separator according to the present invention. Referring to this, first, an adhesive polymer resin, an inorganic filler and a solvent are sufficiently mixed to prepare a composition for forming an adhesive polymer film. This mixing process is more effective in a ball mill or screw mixer. Subsequently, the composition for forming the adhesive polymer film is placed in the storage container 23.

As the adhesive polymer resin, at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin is used. The content of hexafluoropropylene in the vinylidene fluoride-hexapropylene fluoride copolymer is preferably 0.1 to 40% by weight. In addition, as the inorganic filler, at least one selected from the group consisting of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Ga ₂ O ₃ , TiO _2, and SnO ₂ may be used, and 20 to 50 based on 100 parts by weight of the polymer resin. Preference is given to using parts by weight. And it is preferable to use acetone or alcohol solvents such as methanol, ethanol, isopropyl alcohol, etc., because these solvents are volatile and easy to remove when drying. The content of the solvent is 100 to 10000 parts by weight based on 100 parts by weight of the polymer resin.

As shown in FIG. 2, the porous polyethylene film 21, which is a separator forming material, is moved from the unwinding portion 25 by a feed roll 26 and wound around the winding-up portion 27. The polyethylene film 21 is continuously sprayed with a composition for forming the adhesive polymer film in the storage container 26 at the nozzle portion 22 during the movement to coat the adhesive polymer film composition on one surface of the polyethylene film 21. After that, the resultant spray-coated adhesive polymer film composition is transferred to a drying furnace and dried. This drying process is carried out in a hot air atmosphere at a temperature of 25 to 100 ℃, especially 45 ℃.

After the coating process on one side of the porous polyethylene film 21 as described above, by repeating the above-described spray coating and drying process on the other side of the porous polyethylene film 21, the adhesive polymer film on both sides of the porous polyethylene film The separator formed by laminating | stacking is completed. At this time, the thickness ratio of the porous polyethylene film and the adhesive polymer resin film is adjusted to be 1:10 to 10: 1. At this time, the factors influencing the thickness of both films include coating amount, dilution ratio and the like.

The separator is then cut to the desired electrode plate size and laminated with the electrode plate. Winding it or stacking it in a bi-cell structure to make a lithium secondary battery as desired.

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples.

Example 1

A mixture of 5 g of fume silica (Cabot, Usa), 6 g of vinylidene fluoride-hexafluoropropylene copolymer Kinar 2801 (Elf Atochem) and 100 g of acetone was thoroughly mixed in a ball mill. Excess acetone was added to this mixture, diluted 10 times, and then placed in the storage container 23 of the spray machine of FIG.

Thereafter, the feed roll 26 of FIG. 2 was driven to continuously spray the composition for forming an adhesive polymer film on one surface of a polyethylene film (thickness: 20 μm). Then, it was transferred to a drying furnace 24 and hot air dried at 45 ° C.

Then, the separator was completed by spray-coating and drying the composition for forming an adhesive polymer film on the other side of the polyethylene film in the same manner as described above to form an adhesive polymer film (thickness: 10 μm).

60 g of N-methylpyrrolidone (NMP) was added to dissolve 6 g of polyvinylidene fluoride (PVDF), and then 25 g of propylene carbonate was added thereto and mixed. 1300 g of LiCoO ₂ and 90 g of SuperP were added to the mixture, which was then mixed for 2 hours to form a cathode active material composition.

The cathode active material composition was directly coated on an aluminum expanded metal and then dried at 120 ° C. to form a cathode.

Separately, 6 g of PVDF was added and dissolved in 60 g of NMP, and then 25 g of propylene carbonate was added thereto and mixed. 1200 g of mesocarbon fiber (MCF) and 90 g of super blood were added to the mixture, which was then mixed for 2 hours to form an anode active material composition.

The anode active material composition was directly coated on a copper expanded metal and then dried at 120 ° C. to form an anode.

The separator and the anode plate were laminated in a bicell structure on the cathode plate obtained according to the above procedure. An electrolyte solution (1.15 M LiPF ₆ in ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 3: 3: 4) was injected into the battery structure to complete a lithium ion polymer battery.

Example 2

Separators were completed in the same manner as in Example 1, except that a polypropylene film was used instead of a polyethylene film.

Example 3

Seperita was completed in the same manner as in Example 1, except that the polyethylene / polypropylene / polyethylene three-layer composite film was used instead of the polyethylene film.

Comparative Example 1

The separator was prepared according to the following procedure, and the lithium ion polymer battery was completed in the same manner as in Example 1 except that the process of extracting the plasticizer from the battery structure was further performed.

6 g PVDF, 20 g dibutyl phthalate and 60 g NMP were mixed. 40 g of silica was added thereto and sufficiently mixed for 24 hours to form a composition for forming a separator.

The composition for forming a separator was cast on a PET electrode plate having a thickness of 45 μm using a doctor blade having a 320 μm gap, and then dried at 80 ° C. for 10 minutes to separate the separator film from the PET electrode plate.

Comparative Example 2

A lithium ion polymer battery was completed in the same manner as in Comparative Example 1 except that a polyethylene film (Asahi, Mw = 300,000) was used as the separator.

In the lithium ion polymer battery prepared according to Example 1-3 and Comparative Example 1-2, the internal resistance and the constant current charging characteristics were investigated.

As a result, in the lithium ion polymer battery according to Example 1-3, the internal resistance was reduced by about 20% or more compared with the case of Comparative Example 1-2, and it was found that the ion conductivity characteristics were improved and the constant current charging characteristics were also improved.

Meanwhile, a nail test was performed on the lithium ion polymer batteries prepared according to Examples 1-3 and Comparative Examples 1-2 to evaluate the penetration of the separator.

As a result, the separator of Example 1-3 is excellent in the elongation of the separator so that the separator does not penetrate through the nail test and wraps around the nail tip to prevent contact between the cathode and the anode collector. The shot could be suppressed. On the contrary, in the case of Comparative Example 2, the separator penetrates, and the cathode current collector and the anode current collector are likely to explode.

In addition, the separator of Example 1-3 is excellent in mechanical strength, when produced in a continuous roll process as shown in Figure 2, it was not difficult to handle. And since the plasticizer is not used in the separator, it is not necessary to go through the process of removing the plasticizer, thereby simplifying the manufacturing process.

Separator of the present invention is excellent in mechanical properties can be applied to the continuous lamination process mass production is possible. In addition, since the ion conductivity is excellent and the pores are formed by spraying the fine particles by the spray method, it is unnecessary to add an undesired plasticizer in terms of environmental and worker health. Therefore, there is an advantage that the extraction process for removing such plasticizers is unnecessary and the manufacturing process is simplified.

According to the present invention, since the pores are formed by spraying the fine particles by the spray method, it is not necessary to use a plasticizer. Therefore, it is more preferable in terms of environmental protection and worker's health, it is possible to omit the plasticizer extraction process using an organic solvent, thereby reducing the manufacturing cost. In addition, the separator of the present invention can be applied to the continuous lamination process by improving the mechanical strength, mass production is possible, and excellent ion conductivity characteristics.

Claims (5)

Porous polyolefin films made of polyethylene or polypropylene; And One adhesive polymer resin formed on both sides of the porous polyolefin film and selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin, Separator of a lithium secondary battery comprising a porous adhesive polymer film of an inorganic filler. One adhesive polymer resin selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexapropylene fluoride copolymer, polyethylene acrylic acid and styrene-butadiene resin on both sides of the porous polyolefin film made of polyethylene or polypropylene Spray coating and drying a composition comprising an inorganic filler and a solvent to form a separator comprising a porous polyolefin film and a porous adhesive polymer film formed on both sides of the porous polyolefin film. The manufacturing method of the separator of a battery. delete According to claim 1 or 2, wherein the inorganic filler is at least one selected from the group consisting of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , Ga ₂ O ₃ , TiO ₂ and SnO ₂ , Separator and a method for producing a lithium secondary battery, characterized in that the solvent is an acetone or an alcohol solvent. The separator and the method of manufacturing the lithium secondary battery according to claim 1 or 2, wherein the porous polyolefin film and the porous adhesive polymer resin film have a thickness ratio of 1:10 to 10: 1.