KR20140067370A - Separator comprising engineering plastic layers and a method of making the same - Google Patents

Abstract

The present invention relates to a separator for an electrochemical device where an engineering plastic layer made of engineering plastic fiber web which has a preset diameter and is formed by the electronspinning of engineering plastic touches one surface or both surfaces of a polyolefin-based substrate, and a method of manufacturing the same. The engineering plastic according to the present invention is used as the engineering plastic fiber web, thereby securing constant porous property. A hardened engineering plastic fiber web touches the polyolefin-based substrate, thereby preventing the thermal contraction of the polyolefin-based substrate at a high temperature. Moreover, the polyolefin-based substrate and the engineering plastic layer are manufactured by a bonding method, thereby facilitating manufacturing processes.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator for an electrochemical device including an engineering plastic layer and a method of manufacturing the separator.

The present invention relates to a separator for an electrochemical device including an engineering plastic layer and a method for producing the separator, and more particularly, to a separator for an electrochemical device including an engineering plastic layer, To a separator for an electrochemical device and a method of manufacturing the same.

As the demand for batteries as an energy source increases, interest in electrochemical devices capable of charging and discharging is increasing, and in particular, demand and interest in lithium secondary batteries are increasing.

A separation membrane for an electrochemical device is a component interposed between an anode and a cathode to electrically insulate the anode and the cathode, and a porous substrate having pores capable of smoothly moving lithium ions is generally used.

Since the pores of the separator substrate are the movement path of an active component that causes a cell reaction in the electrochemical device, for example, lithium ion (Li ⁺ ), the size and porosity of the pore become an important factor in controlling the ion conductivity in the cell In addition, it directly affects battery performance. That is, when lithium ions, which are a kind of electrochemical device, cause a cell reaction and move between the positive electrode and the negative electrode, the separation membrane pores located between the positive electrode and the negative electrode are theoretically acting as passages when they are larger than the diameter of lithium ions . For reference, the diameter of the lithium ion is several angstroms. However, when lithium ions actually move, lithium ions migrate solely in an electrolyte, for example, a large number of carbonate-based compound molecules, rather than moving solely. Therefore, the pore size and porosity Has a range similar to the diameter of the lithium ion, the performance of the battery can not be exhibited due to the reduction of movement of the lithium ion and the decrease of the ion conductivity in the battery. Therefore, the pore size of the separator is one of the important evaluation factors of the separator.

Polyolefin resin has been widely used in the art as a separator material since it is relatively in conformity with the above conditions. However, there is a problem that an internal short circuit occurs when the electrochemical device is overcharged due to a low melting point and the electrochemical device explodes.

Engineering plastics are excellent in heat resistance and chemical resistance, but they have disadvantages in that adequate air permeability and mechanical strength can not be secured when used as a membrane component.

Therefore, although a separator for an electrochemical device having only the advantages of a polyolefin resin and an engineering plastic has been studied, there is still a need for improvement.

Disclosure of the Invention The present inventors have intensively studied on the above problems and intend to provide a separator for electrochemical devices and a method for producing the same, which can provide heat resistance and chemical resistance of engineering plastics while ensuring air permeability of the polyolefin-based substrate.

According to one aspect of the present invention, there is provided a separation membrane for an electrochemical device in which an engineering plastic layer is bonded to one or both surfaces of a polyolefin-based substrate.

The engineering plastic layer may comprise an engineering plastic fiber web formed by electrospinning.

The engineering plastic layer may be formed from one or a mixture of two or more selected from the group consisting of polyamideimide-based polymers, polyetherimide-based polymers, polyphenylsulfone-based polymers, and copolymers thereof.

The engineering plastic layer may have a mass per unit area of 1.0 to 3.0 g / m < ² >. Here, the 'mass per unit area' of the engineering plastic layer is a numerical value based on an engineering plastic layer bonded to one surface of a polyolefin-based substrate, that is, an engineering plastic layer forming one layer.

The engineering plastic fiber web may have a diameter of 1 to 5 탆.

The separation membrane may have an air permeability of 100 to 2000 sec / 100 cc in terms of gully value.

A binder polymer may be applied to the interface between the engineering plastic layer and the polyolefin-based substrate.

According to an aspect of the present invention, there is provided an electrochemical device including a cathode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte, wherein the separator is the separator described above.

The electrochemical device may be a lithium secondary battery.

According to one aspect of the present invention, there is provided a method of manufacturing an engineering plastic fiber web, comprising: electrospinning an engineering plastic to produce an engineering plastic fiber web having an average diameter of 300 to 1000 nm; Solidifying the engineering plastic fiber web to form an engineering plastic layer; And joining the engineering plastic layer to one or both surfaces of the polyolefin-based substrate.

And applying a binder polymer to the interface of the polyolefin-based substrate and the engineering plastic layer prior to bonding the engineering plastic layer to the polyolefin-based substrate.

According to the present invention, by using the engineering plastic in the form of a fibrous web, it is possible to secure the required air permeability in the separator and at the same time, since the solidified engineering plastic fiber web is bonded to the polyolefin-based substrate, the polyolefin- So that the heat shrinkage phenomenon of the separator can be remarkably improved. In addition, the polyolefin-based substrate and the engineering plastic layer are manufactured by the bonding method, so that the manufacturing process is easy.

1 is a photograph of an engineering plastic layer before it is electrospun on a polyolefin substrate and then rolled.
Fig. 2 is a photograph of the engineering layer after electrospinning the polyolefin-based substrate and roll-pressing the engineering layer.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Accordingly, the drawings described in the present specification or the constitutions described in the embodiments are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents It should be understood that water and variations may be present.

The separation membrane for an electrochemical device according to the present invention has a structure in which an engineering plastic layer is bonded to one or both surfaces of a polyolefin-based substrate.

In the present specification, the term "polyolefin-based substrate" is understood to refer to a polyolefin-based film, a polyolefin-based sheet, and a polyolefin-based nonwoven fabric.

Examples of the material of the polyolefin base material include high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMWPE), polypropylene, polyethyleneterephthalate, But are not limited to, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone ), Polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. However, the present invention is not limited thereto. The polyolefin-based substrate can be manufactured by a dry method or a wet method known in the art using the above materials. Representative commercially available examples include Celgard ^™ 2400, 2300, C210 (manufactured by Hoechest Celanese Corp.), polypropylene membrane (manufactured by Ube Industries Ltd. or Pall RAI), polyethylene (Tonen or Entek) And the like, but are not limited thereto.

Non-limiting examples of the engineering plastics constituting the engineering plastic layer include a mixture of one or more selected from the group consisting of a polyamideimide-based polymer, a polyetherimide-based polymer, a polyphenylsulfone-based polymer, and a copolymer thereof have.

The engineering plastic layer may be in the form of a solidified engineering plastic fiber web having a fibrous web shape by electrospinning. The engineering plastic layer may have a mass per unit area of 1.0 to 3.0 g / m < ² > and a thickness of 1 to 5 mu m, and the engineering plastic fiber web constituting the engineering plastic layer may have a diameter of 300 to 1000 nm. As described above, the 'mass per unit area' of the engineering plastic layer is a numerical value based on an engineering plastic layer bonded to one surface of a polyolefin-based substrate, that is, an engineering plastic layer forming one layer.

The joining of the engineering plastic layer to the polyolefin-based substrate can be laminated by a method such as joining by a thermal bonding, a roll press, or the like, which is common in the art. Alternatively, the joining of the engineering plastic layer to the polyolefin-based substrate may be performed by a binder polymer. The binder polymer can be selectively applied to the interface between the polyolefin-based substrate and the engineering plastic layer to enhance the adhesion. The binder polymer may be a conventional binder polymer used in the art. Non-limiting examples of the binder polymer include (meth) acrylic copolymer, polyurethane, polyol, polyvinylidene fluoride, polysiloxane, polyurea, cellulose acetate, Styrene-butadiene rubber, or a mixture of two or more thereof.

The separation membrane for an electrochemical device comprises electrospun engineering plastic to produce an engineering plastic fiber web having an average diameter of 300 to 1000 nm; Solidifying the engineering plastic fiber web to obtain an engineering plastic layer; And bonding the engineering plastic layer to one or both sides of the polyolefin-based substrate.

The electrospinning of engineering plastics can be carried out using a polyethylene substrate as the support under conditions of, for example, an applied voltage of 5 to 20 kV, a distance of 5 to 15 cm from the tip of the support to the support, and a discharge rate of 0.5 to 1.5 ml / hr , But is not limited thereto.

The separator of the present invention prepared as described above can be used in an electrochemical device according to a conventional method known in the art.

As a non-limiting example of the positive electrode active material among the electrode active materials usable in the electrochemical device employing the separator of the present invention, a conventional positive electrode active material that can be used for a positive electrode of a conventional electrochemical device can be used. In particular, lithium manganese oxide, Oxides, lithium nickel oxides, lithium iron oxides, or lithium composite oxides combining these may be used.

As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials, and the like.

Non-limiting examples of the positive electrode current collector include aluminum, nickel, or a foil produced by a combination of these. Non-limiting examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil and so on.

Electrolyte that may be used in the present invention is A ⁺ B ^- and been made of the electrolyte salt of the structure is dissolved or dissociated in an electrolyte solvent, the electrolyte salt A ⁺ is Li ^+, Na ^+, a cation or the alkali metal such as K ⁺ And B ^- is an ion selected from the group consisting of PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N (CF ₃ SO ₂ ) ₂ ^- , C (CF ₂ SO ₂ ) ₃ ^- , or an ion composed of a combination thereof. The electrolyte solvent includes propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DMP), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl- Methyl carbonate (EMC), gamma butyrolactone, or mixtures thereof. And, thus it is not limited thereto.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

The electrode according to the present invention may optionally further include components such as a conductive material, a binder and a filler material, if necessary.

The conductive material may be acetylene black or carbon black, but is not limited thereto.

The binder used for the negative electrode and the positive electrode is selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyacrylonitrile, nitrile rubber, polybutadiene, polystyrene, styrene butadiene rubber, polysulfide rubber, butyl rubber, hydrogenated styrene butadiene Rubber, nitrocellulose, and carboxymethylcellulose is preferable.

The battery according to the present invention can be manufactured by a conventional method known in the art, for example, by dispersing an electrode active material and a binder in an organic solvent to prepare a slurry, coating the electrode slurry on the electrode collector, followed by drying and pressing, And a non-aqueous electrolyte is injected into the electrode assembly.

Hereinafter, the separator of the present invention and the method for producing an electrochemical device including the same will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

Example  1-1: Preparation of Membrane

25 g of polyamideimide was dissolved in 80 ml of dimethylacetamide solution and stirred at room temperature for 1 to 2 days to prepare a spinning solution of 25% by weight. The electrospinning conditions were set at an applied voltage of 16 kV, a discharge rate of 0.9 ml / hr per 1 hole, and a distance of 10 cm from the spinneret to the support, and the spinning solution was directly electrospun on the substrate using a polyethylene substrate as a support. At this time, the used nozzle gauge was 25 gauge and it was radiated by using a single nozzle. For uniform coating, a moving nozzle robot was used and the maximum coating width was 200 cm2. The microfine fibers were spun on a support with a mass of 1.8 to 1.9 g / m 2 and solidified to obtain a polyamideimide layer of polyamideimide fiber web. The diameter of the resulting polyamideimide fiber web was 500 to 700 nm, and the thickness of the polyamideimide layer was 3 占 퐉.

The polyamideimide layer was spun on both sides of polyethylene (Celgard ^TM , C210), rolled at room temperature and then dried to bond the three layers to obtain a separator for electrochemical devices. The total thickness of the obtained separation membrane was 22 mu m. The permeability of the obtained membrane was 500 to 600 sec / 100 cc, tensile strength was 160 to 180 MPa, and average pore diameter was 0.032 mu m, and these values were the same as or similar to those of the polyolefin substrate.

Example  1-2: The lithium secondary battery  Produce

Cathode manufacturing

(PVDF) as a binder polymer, and carbon black as a conductive material in an amount of 96% by weight, 3% by weight and 1% by weight, respectively, and a solvent N-methyl-2 Pyrrolidone (NMP) to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 .mu.m and dried to prepare a negative electrode, followed by roll pressing.

Manufacture of anode

92% by weight of a lithium cobalt composite oxide as a positive electrode active material, 4% by weight of carbon black as a conductive material and 4% by weight of PVdF as a binder polymer were added to a solvent N-methyl-2-pyrrolidone (NMP) Slurry. The anode mixture slurry was applied to an aluminum (Al) thin film of a cathode current collector having a thickness of 20 μm and dried to produce a cathode, followed by roll pressing.

Manufacture of batteries

The prepared positive electrode, negative electrode and separator were assembled in a stacking manner, and an electrolytic solution (ethylene carbonate (EC) / ethylmethyl carbonate (EMC) = 1/2 (volume ratio), lithium hexafluorophosphate (LiPF ₆ ) 1 mole) was injected to prepare a battery.

Comparative Example  1-1: Preparation of Membrane

A composition consisting of 25 g of polyamideimide (Solvay, torlon-400T), 80 ml of dimethylacetamide and 5 g of poly (vinylidene fluoride-co-hexafluoropropylene) was laminated on both sides of a polyethylene substrate (Celgard ^TM , C210) Followed by roll pressing at 70 to 100 DEG C, followed by drying to prepare a separator. The thickness of the obtained separation membrane was 22 mu m.

Comparative Example  1-2: The lithium secondary battery  Produce

An electrochemical device was produced in the same manner as in Example 1-2, except that the separator obtained in Comparative Example 1-1 was used.

Experimental Example : Heat shrinkage  Experiment

When the separator obtained in Example 1-1 was allowed to stand at 150 ° C for 1 hour, it was determined that the separator shrank 20% in the MD direction. The same experiment was carried out on the membrane obtained in Comparative Example 1-1, and as a result, it was measured to be 20% shrinkage in the MD direction.

Claims (11)

A separator for an electrochemical device in which an engineering plastic layer is bonded to one or both sides of a polyolefin-based substrate.
The method according to claim 1,
Wherein the engineering plastic layer comprises an engineering plastic fiber web formed by electrospinning.
The method according to claim 1,
Wherein the engineering plastic layer is formed from a mixture of one or more selected from the group consisting of a polyamideimide-based polymer, a polyetherimide-based polymer, a polyphenylsulfone-based polymer, and a copolymer thereof.
The method according to claim 1,
Wherein the engineering plastic layer has a mass per unit area of 1.0 to 3.0 g / m < ² >.
3. The method of claim 2,
Wherein the engineering plastic fiber web has a diameter of 1 to 5 탆.
The method according to claim 1,
Wherein the separation membrane has an air permeability of 100 to 2000 sec / 100cc as a gravel value.
The method according to claim 1,
Wherein a binder polymer is applied to an interface between the engineering plastic layer and the polyolefin-based substrate.
An electrochemical device comprising an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte,
The electrochemical device according to any one of claims 1 to 7, wherein the separator is a separator.
9. The method of claim 8,
Wherein the electrochemical device is a lithium secondary battery.
Electrospinning an engineering plastic to produce an engineering plastic fiber web having an average diameter of 300 to 1000 nm; Solidifying the engineering plastic fiber web to form an engineering plastic layer; And joining the engineering plastic layer to one or both surfaces of the polyolefin-based substrate.
11. The method of claim 10,
And applying a binder polymer to an interface between the polyolefin-based substrate and the engineering plastic layer before the step of bonding the engineering plastic layer to the polyolefin-based substrate.

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