KR20030007633A - A lithium secondary battery comprising a super fine fibrous polymer separator film and its fabrication method - Google Patents

Abstract

PURPOSE: Provided are a lithium secondary battery which comprises a super fine fibrous porous polymer separator film and has the advantages of better adhesion with electrodes, good mechanical strength, better performance at low and high temperatures, better compatibility with organic electrolyte solution of a lithium secondary battery, and its fabrication method. CONSTITUTION: The lithium secondary battery comprises a cathode active material, an anode active material, a porous polymer separator film and an organic electrolyte solution dissolving a lithium salt, wherein the porous polymer separator film is constructed with super fine fibrous polymer having a diameter of 1-3000nm and is fabricated by the steps of: (a) melting at least one polymer or dissolving at least one polymer with organic solvents to obtain at least one polymeric melt or at least one polymeric solution; (b) adding the obtained polymeric melt or polymeric solution to barrels of an electrospinning machine; and (c) discharging the polymeric melt or polymeric solution onto a substrate using a nozzle to form a porous separator film.

Description

Lithium secondary battery comprising a superfine fibrous porous polymer separator and its manufacturing method {A LITHIUM SECONDARY BATTERY COMPRISING A SUPER FINE FIBROUS POLYMER SEPARATOR FILM AND ITS FABRICATION METHOD}

Recently, as electronic devices and the like have become smaller and lighter, development of energy sources having high density and high energy has been intensively studied. Lithium secondary batteries have been suggested as one of the methods in that the molecular weight of lithium is very small and the density is relatively high, and energy integration is possible.

Early lithium secondary batteries were manufactured using lithium metal or lithium alloy as a negative electrode. However, secondary batteries using lithium metal or lithium alloy have a problem in that a cycle characteristic is remarkably low because dendrite is formed on the negative electrode as charge and discharge are repeated.

In order to solve the problems caused by the formation of the dendrite is a lithium ion battery. The lithium ion battery, first developed by Sony Japan and commercialized worldwide, is composed of a negative electrode active material, a positive electrode active material, an organic electrolyte and a separator.

The separator serves to prevent internal short circuit caused by contact between the cathode and the anode of the lithium ion battery and to permeate ions. Currently, the separator is generally used as polyethylene (hereinafter referred to as "PE") or polypropylene (hereinafter as "PP") separator. However, lithium ion batteries using PE or PP separators still have problems such as battery instability, difficulty in battery manufacturing process, battery shape limitation, and limitation on high capacity. Efforts have been made to solve these problems, but there are no clear results.

In contrast, lithium polymer batteries use polymer electrolytes having two functions of a separator and an electrolyte at the same time, and are currently attracting the most attention as a battery that is expected to solve the above problems. This lithium polymer battery has the advantage that the electrode and the polymer electrolyte can be laminated on a flat plate, and the manufacturing process is similar to the manufacturing process of the polymer membrane, which is very advantageous in terms of productivity.

Conventional polymer electrolytes are mainly prepared using polyethylene oxide (hereinafter referred to as "PEO") as a polymer matrix, but have not been commercialized because their ionic conductivity is only about 10 ^-8 S / cm at room temperature.

Recently, gel or hybrid polymer electrolytes having an ionic conductivity of 10 ⁻³ S / cm or more at room temperature have been developed.

US Pat. No. 5,219,679 to K. M. Abraham et al. And US Pat. No. 5,240,790 to D. L. Chua et al. Disclose gel-based polyacrylonitrile (hereinafter referred to as "PAN") polymer electrolytes. The gel PAN polymer electrolyte is prepared by injecting a solvent compound (hereinafter referred to as "organic electrolyte") formed between a lithium salt and an organic solvent such as ethylene carbonate and propylene carbonate in a PAN polymer matrix, and has excellent adhesion. Since the adhesion between the composite electrode and the metal substrate is good, there is an advantage in that the contact resistance is small and the detachment of the active material occurs less during charging and discharging of the battery. However, in spite of these advantages, the polymer electrolyte has a disadvantage in that the electrolyte is somewhat withdrawn and thus the mechanical stability, that is, the strength is lowered. In particular, such weak strength properties can cause significant problems in the manufacture of electrodes and batteries.

U.S. Patent No. 5,460,904 to A. S. Gozdz et al. Discloses a polyvinylidene difluoride (hereinafter referred to as "PVdF") based polymer electrolyte in hybrid form. The hybrid PVdF polymer electrolyte is prepared by preparing a polymer matrix to have a porosity of submicron or less, and then injecting an organic electrolyte into the small pores, and having excellent compatibility with the organic electrolyte. The electrolyte has the advantage that it can be used as a safe electrolyte without leakage, and since the organic solvent electrolyte is injected later, there is an advantage that the polymer matrix can be prepared in the air. However, there is a disadvantage in that the manufacturing process is difficult because the extraction process of the plasticizer and the impregnation process of the organic solvent electrolyte are required in the preparation of the polymer electrolyte. In addition, the PVdF-based electrolyte has excellent mechanical strength but poor adhesive strength, and thus, a critical disadvantage is that a heating thinning process and an extraction process are required in manufacturing an electrode and a battery.

Recently, Solid State Ionics, 66, 97, 105 (1993) published by O. Bohnke and G. Frand et al. Disclose a polymethyl methacrylate (hereinafter referred to as "PMMA") polymer electrolyte. have. The PMMA-based polymer electrolyte has an ion conductivity of about 10 ⁻³ S / cm at room temperature, and has an advantage of excellent adhesion and compatibility with an organic electrolyte. However, this electrolyte has a disadvantage in that its mechanical strength is very weak and unsuitable for lithium polymer batteries.

See also J. Electrochem., Published by M. Alamgir and KM Abraham. Soc., 140, L96 (1993) disclose a polyvinyl chloride (hereinafter referred to as "PVC") polymer electrolyte having excellent mechanical strength and an ionic conductivity of about 10 ^-3 S / cm at room temperature. In addition, the low temperature characteristics are bad, there is a disadvantage that the contact resistance is large.

The present invention relates to a lithium secondary battery including a superfine fibrous porous polymer separator and a method of manufacturing the same.

1 shows a transmission electron micrograph of a porous polymer membrane.

Figure 2 shows a process chart for manufacturing a lithium secondary battery of the present invention.

3 is a graph showing charge and discharge characteristics of the lithium secondary batteries obtained in Examples 1-8 and Comparative Examples 1 and 2;

Figure 4 is a graph showing the low temperature and high temperature characteristics of the lithium secondary battery obtained in Example 5 and Comparative Example 2.

5 is a graph showing the high rate discharge characteristics of the lithium secondary battery obtained in Example 3 and Comparative Example 2.

Summary of the Invention

Accordingly, an object of the present invention is to provide a new lithium secondary battery utilizing the advantages of a lithium ion battery and a lithium polymer battery.

It is still another object of the present invention to provide a lithium secondary battery having all of bonding properties with an electrode, mechanical strength, low temperature and high temperature characteristics, compatibility with an organic electrolyte solution for a lithium secondary battery, and the like.

The above and other objects can be achieved by providing a porous polymer membrane composed of ultra-fine fibrous shape.

Detailed description of the invention

The present invention relates to a lithium secondary battery including a superfine fibrous porous polymer separator and a method of manufacturing the same. More specifically, the present invention relates to a lithium secondary battery including a cathode active material, an anode active material, an organic electrolyte in which lithium salt is dissolved, and an ultrafine fibrous porous polymer separator.

As shown in FIG. 1, the porous polymer membrane made of ultrafine polymer fibers has a form in which three-dimensionally superfine fibers of 1-3000 nm diameter are randomly stacked three-dimensionally, compared to conventional membranes due to the small diameter of the fibers. It has been found that the surface area to volume ratio is very high and the porosity is large. Therefore, the amount of impregnation of the electrolyte is high due to the high porosity, thereby increasing the ion conductivity, and despite the high porosity, the contact area with the electrolyte may be increased due to the large surface area, thereby minimizing leakage of the electrolyte. In the case of manufacturing a porous polymer membrane by electrospinning, there is an advantage that it can be manufactured directly in the form of a membrane, not just pieces of fiber.

The polymer forming the porous polymer membrane is not particularly limited as long as it can be formed into ultra-fine fibers as described above, more specifically, it can be formed into ultra-fine fibers by charge-induced radiation, and examples thereof include polyethylene, polypropylene, cellulose, and cellulose. Acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylpyrrolidone-vinylacetate, poly [bis (2- (2-methoxyethoxyethoxy)) phosphazene], polyethyleneimide, polyethylene oxide, Polyethylene succinate, polyethylene sulfide, poly (oxymethylene-oligo-oxyethylene), polypropylene oxide, polyvinylacetate, polyacrylonitrile, poly (acrylonitrile-co-methylacrylate), polymethylmethacrylate Poly (methyl methacrylate-co-ethylacrylate), Polyvinyl chloride, poly (vinylidene chloride-co-acrylonitrile), polyvinylidene dendi fluoride, poly (vinylidene fluoride-co-hexafluoropropylene), or a mixture thereof.

The thickness of the porous polymer separator is not particularly limited, but is preferably 1-100 μm. More preferably 5 μm to 70 μm, most preferably 10 μm to 50 μm. In addition, the diameter of the fibrous polymer forming the polymer membrane is preferably controlled within the range of 1-3000 nm, more preferably 10 nm-1000 nm, most preferably 50 nm-500 nm. .

As the lithium salt used in the lithium secondary battery of the present invention, a lithium salt usually used in a lithium secondary battery is used. Examples thereof include LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and the like, and LiPF ₆ is more preferable.

Examples of the organic solvent used in the organic electrolyte include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, or a mixed solvent thereof, and methyl acetate, methyl pro in these solvents to improve low temperature characteristics. Cypionate, ethyl acetate, ethyl propionate, butylene carbonate, γ -butyrolactone, 1,2-dimethoxyethane, 1,2-dimethoxyethane, dimethylacetamide, tetrahydrofuran or a mixed solvent thereof It may be added additionally.

The porous polymer membrane of the present invention may further contain a filler to enhance porosity and mechanical strength, for example, TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O , MgO, Li ₂ CO ₃ , LiAlO ₂ , SiO ₂ , Al ₂ O ₃ , PTFE or mixtures thereof. The content of the filler is usually 20% by weight or less based on the porous separator.

The method for preparing an ultra-fine fibrous porous polymer separator of the present invention includes dissolving a polymer forming a porous polymer separator in a hot melt or an organic solvent and forming a porous polymer separator.

Melting or dissolving the polymer forming the porous polymer separator is accomplished by heating the polymer to melt it, or mixing it with a suitable organic solvent and raising the temperature to obtain a transparent polymer solution.

In the case of dissolving the polymer using an organic solvent, the usable organic solvent is not particularly limited as long as it dissolves the polymer sufficiently and is a solvent applicable to the charge induction spinning method. Since is almost eliminated, it can be used to affect the characteristics of the battery. Examples include propylene carbonate, butylene carbonate, 1,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, Ethylene carbonate, ethylmethyl carbonate, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylenesulfuran, tetraethylene glycol dimethyl ether, acetone, alcohols or mixtures thereof Can be mentioned.

Formation of the porous polymer separator is usually accomplished by the charge induction radiation method. More specifically, a polymer solution dissolved in a molten polymer or an organic solvent forming a polymer separator is introduced into a barrel of a charge induction spinning device, a high voltage is applied to a nozzle, and then discharged onto a metal plate or a mylar film at a predetermined speed. By the porous polymer membrane can be prepared. The thickness of the porous separator can be arbitrarily adjusted by changing the discharge rate and the discharge time, the appropriate thickness is in the range of 1-100 ㎛ as described above. When using this method, it is possible to directly prepare a separator in which the polymer forming the separator is not a fiber but a three-dimensionally laminated fiber having a diameter of 1 to 3000 nm. If necessary, a highly porous separator may be directly formed on the electrode. Therefore, despite the fibrous manufacturing method, the final product can be manufactured directly in the form of a film instead of the fiber, so that no additional device is required, and the manufacturing process is simplified to improve economic efficiency.

Porous polymer membranes using two or more polymers are prepared by heating or melting two or more polymers in one or more organic solvents, injecting them into one barrel of a charge-inducing spinning device, and spinning them with a nozzle to entangle the polymer fibers. Method, and 2) heating each of two or more polymers in different containers or dissolving them in an organic solvent, and then injecting them into different barrels of the charge-inducing device and spinning them with a nozzle to make each polymer fiber entangled with each other. It is obtained by the method.

The present invention also relates to a method for manufacturing a lithium secondary battery, Figure 2 describes in detail the manufacturing process of the lithium secondary battery. Figure 2a is prepared by the charge induction radiation method, the porous polymer separator is placed between the negative electrode and the positive electrode, optionally the electrolyte and the electrode by integrating the heat lamination process, then laminated or rolled into a battery case and put the organic electrolyte solution The process of sealing and manufacturing a battery is shown. FIG. 2B shows that the porous polymer separator is coated on both sides of the cathode or the anode, and then the electrode having the other pole is coated on the porous polymer separator, and optionally the electrolyte and the electrode are integrated by a heating lamination process, and then laminated or rolled to form a battery case. And a process of manufacturing a battery by injecting and then injecting an organic electrolyte solution and sealing the same. Figure 2c is a porous polymer membrane is coated on both sides of one of the two electrodes and one side of the other electrode of the two electrodes, the porous polymer membrane is faced to contact with each other, and optionally the electrolyte and the electrode by the heating lamination process, A process of manufacturing a battery by laminating or rolling it in a battery case, injecting an organic electrolyte, and sealing the same is illustrated.

The negative electrode and the positive electrode used in the lithium secondary battery are mixed with an appropriate amount of an active material, a conductive material, a binder, and an organic solvent in the same manner as a conventional lithium secondary battery, and then cast on both sides of a copper or aluminum sheet grid and dry rolled. Is made. Specifically, the negative electrode active material is composed of one or more materials selected from the group consisting of graphite, coke, hard carbon, tin oxide, their lithiated ones, lithium and lithium alloys, and the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiNiCoO ₂ , At least one substance selected from the group consisting of LiMn ₂ O ₄ , V ₂ O ₅ and V ₆ O ₁₃ .

The present invention is described in more detail by the following examples, but these examples are merely illustrative of the present invention and do not limit the scope of the present invention.

Example 1

1-1) Preparation of Porous Polymer Membrane

20 g of polyvinylidene fluoride (Kynar 761) was added to 100 g of dimethylacetamide and stirred at room temperature for 24 hours to obtain a clear polymer solution. The obtained polymer solution was introduced into a barrel of a charge-inducing radiator, and a charge of 9 kV was applied to the nozzle and discharged to a metal plate at a predetermined rate to prepare a porous polymer membrane film having a thickness of 50 μm.

1-2) Manufacturing of Lithium Secondary Battery

The porous polymer separator prepared in Example 1-1 was placed between the graphite anode and the LiCoO ₂ anode, cut and laminated to a size of about 3 cm × 4 cm, and then the terminals were welded to an electrode in a vacuum package and 1M LiPF ₆ was added. After injecting the dissolved EC-DMC solution, and vacuum sealed to prepare a lithium secondary battery.

Example 2

2-1) 20 g of polyvinylidene fluoride (Kynar 761) was added to 100 g of dimethylacetamide and stirred at room temperature for 24 hours to obtain a clear polymer solution. The obtained polymer solution was introduced into the barrel of the charge-inducing radiator and charged to the nozzle at a rate of 9 kV to be discharged on both sides of the graphite cathode at a constant rate, thereby obtaining a graphite cathode coated with a porous polymer membrane film having a thickness of 50 μm. Prepared.

2-2) The LiCoO ₂ positive electrode was brought into close contact with the porous polymer separator obtained in Example 2-1, cut and laminated to a size of about 3 cm × 4 cm, and then the terminals were welded to an electrode in a vacuum package and placed in 1M LiPF _6. After dissolving the dissolved EC-DMC solution, and vacuum sealed to prepare a lithium secondary battery.

Example 3

3-1) 20 g of polyvinylidene fluoride (Kynar 761) was added to 100 g of dimethylacetamide and stirred at room temperature for 24 hours to obtain a clear polymer solution. The obtained polymer solution was introduced into a barrel of a charge-inducing radiator, charged to the nozzle with a charge of 9 kV, and discharged to one side of the LiCoO ₂ anode at a constant rate, so that a porous polymer membrane film having a thickness of 50 μm was coated on one side. A LiCoO ₂ positive electrode was prepared.

3-2) The LiCoO ₂ positive electrode obtained in Example 3-1 was adhered to both surfaces of the graphite negative electrode obtained in Example 2-1 such that the porous polymer separators faced each other, and integrated at 110 ° C. by heating lamination. After the integrated electrode body is cut and laminated to a size of about 3 cm × 4 cm, the terminals are welded to the electrode in a vacuum package, and then injected with an EC-DMC solution in which 1M LiPF ₆ is dissolved, followed by vacuum sealing to obtain a lithium secondary battery. Paper was prepared.

Example 4

4-1) 10 g of polyvinylidene fluoride (Kynar 761) and 10 g of PAN (manufactured by polyscience, molecular weight 150,000) were added to 100 g of dimethylacetamide and stirred at room temperature for 24 hours to provide a clear polymer solution. Got. The obtained polymer solution was introduced into the barrel of the charge-inducing radiator and charged to the nozzle at a rate of 9 kV to be discharged on both sides of the graphite cathode at a constant rate, thereby obtaining a graphite cathode coated with a porous polymer membrane film having a thickness of 50 μm. Prepared.

4-2) Instead of applying the process of Example 4-1 to both sides of the graphite anode, a LiCoO ₂ anode having a porous polymer membrane film coated on one side was prepared by applying it to one side of the LiCoO ₂ anode.

4-3) The LiCoO ₂ positive electrode obtained in Example 4-2 was adhered to both surfaces of the graphite negative electrode obtained in Example 4-1 such that the porous polymer separator films faced each other, and integrated at 110 ° C. by heating lamination. After the integrated electrode body is cut and laminated to a size of about 3 cm × 4 cm, the terminals are welded to the electrode in a vacuum package, and then injected with an EC-DMC solution in which 1M LiPF ₆ is dissolved, followed by vacuum sealing to obtain a lithium secondary battery. Paper was prepared.

Example 5

5-1) A polymer solution in which 20 g of polyvinylidene fluoride (Kynar 761) is dissolved in 100 g of dimethylacetamide and 20 g of PAN (manufactured by polyscience, molecular weight 150,000) in 100 g of dimethylacetamide The dissolved polymer solution is introduced into different barrels of the charge induction radiator, and 9 kV is charged to the nozzles and discharged on both sides of the graphite cathode at a predetermined rate, thereby forming a porous polymer membrane film having a thickness of 50 μm. Coated graphite cathodes were prepared.

5-2) The LiCoO ₂ positive electrode was brought into close contact with the porous polymer separator obtained in Example 5-1, cut and laminated to a size of about 3 cm × 4 cm, and the terminals were welded to an electrode in a vacuum package and placed in 1M LiPF _6. After dissolving the dissolved EC-DMC solution, and vacuum sealed to prepare a lithium secondary battery.

Example 6

6-1) A polymer solution in which 20 g of polyvinylidene fluoride (Kynar 761) is dissolved in 100 g of dimethylacetamide and 20 g of PAN (manufactured by polyscience, molecular weight 150,000) in 100 g of dimethylacetamide The dissolved polymer solution is introduced into different barrels of the charge induction radiator, and 9 kV is charged to the nozzles and discharged on both sides of the graphite cathode at a predetermined rate, thereby forming a porous polymer membrane film having a thickness of 50 μm. Coated graphite cathodes were prepared.

6-2) Instead of applying the process of Example 6-1 to both sides of the graphite anode, a LiCoO ₂ anode having a porous polymer separator coated on one side was prepared by applying it to one side of the LiCoO ₂ anode.

6-3) The LiCoO ₂ positive electrode obtained in Example 6-2 was adhered to both surfaces of the graphite negative electrode obtained in Example 6-1 so that the porous polymer separators faced each other, and was integrated at 110 ° C. by heating lamination. After the integrated electrode body is cut and laminated to a size of about 3 cm × 4 cm, the terminals are welded to the electrode in a vacuum package, and then injected with an EC-DMC solution in which 1M LiPF ₆ is dissolved, followed by vacuum sealing to obtain a lithium secondary battery. Paper was prepared.

Example 7

7-1) 10 g of polyvinylidene fluoride (Kynar 761), 5 g of PAN (manufactured by polyscience, molecular weight 150,000) and 5 g of polymethyl methacrylate (manufactured by polyscience, molecular weight 100,000) of 100 g A polymer solution dissolved in dimethylacetamide was introduced into a barrel of a charge induction radiator, and a charge of 9 kV was applied to the nozzle and discharged to both sides of the graphite cathode at a constant rate, thereby having a thickness of 50 μm. This coated graphite negative electrode was prepared.

7-2) The LiCoO ₂ positive electrode was brought into close contact with the porous polymer separator obtained in Example 7-1, cut and laminated to a size of about 3 cm × 4 cm, and the terminals were welded to an electrode in a vacuum package and placed in 1M LiPF _6. After dissolving the dissolved EC-DMC solution, and vacuum sealed to prepare a lithium secondary battery.

Example 8

8-1) 10 g of polyvinylidene fluoride (Kynar 761), 5 g of PAN (manufactured by polyscience, molecular weight 150,000) and 5 g of polymethyl methacrylate (manufactured by polyscience, molecular weight 100,000) of 100 g A polymer solution dissolved in dimethylacetamide was introduced into a barrel of a charge induction radiator, and a charge of 9 kV was applied to the nozzle and discharged to both sides of the graphite cathode at a constant rate, thereby having a thickness of 50 μm. This coated graphite negative electrode was prepared.

8-2) Instead of applying the process of Example 8-1 to both sides of the graphite anode, a LiCoO ₂ anode having a porous separator coated on one side was prepared by applying it to one side of the LiCoO ₂ anode.

8-3) The LiCoO ₂ positive electrode obtained in Example 8-2 was adhered to both surfaces of the graphite negative electrode obtained in Example 8-1 so that the porous polymer separator films faced each other, and integrated at 110 ° C. by heating lamination. After the integrated electrode body is cut and laminated to a size of about 3 cm × 4 cm, the terminals are welded to the electrode in a vacuum package, injected with an EC-DMC solution in which 1M LiPF ₆ is dissolved, and then vacuum sealed to form a lithium secondary battery. Paper was prepared.

Comparative Example 1

The electrode and the separator are sequentially stacked in the order of the negative electrode, the PE separator, the positive electrode, the PE separator, and the negative electrode, and then placed in a vacuum package, and injected with an EC-DMC solution in which 1M LiPF ₆ is dissolved, followed by vacuum sealing to form a lithium secondary battery. Prepared.

Comparative Example 2

According to a conventional gel polymer electrolyte preparation method, 9 g of an EC-PC solution in which 1 M LiPF ₆ was dissolved was added to 3.0 g of PAN, and mixed for 12 hours. After mixing, the mixture was heated at 130 ° C. for 1 hour to obtain a transparent polymer solution. Thereafter, when the viscosity became about 10,000 cps, which was good for casting, casting was performed by a die casting method to obtain a polymer electrolyte film. After stacking sequentially in order of graphite cathode, electrolyte, LiCoO ₂ anode, electrolyte, graphite cathode, the terminals were welded to electrodes and placed in vacuum packaging, and then injected with EC-DMC solution in which 1M LiPF ₆ was dissolved. A secondary battery was manufactured.

Example 9

Using the lithium secondary batteries obtained in Example 1-8 and Comparative Examples 1 and 2, the charge and discharge characteristics were tested, and the results are shown in FIG. The charge / discharge test was performed by the charge / discharge method of charging with C / 2 constant current and 4.2V constant voltage and then discharging with C / 2 constant current. The electrode capacity and cycle life based on the anode were investigated. 3 shows that the lithium secondary batteries obtained in Examples 1-8 have improved electrode capacity and battery life than the lithium secondary batteries obtained in Comparative Examples 1 and 2. FIG. This improvement in battery characteristics is attributed to the fact that the electrode and the separator are in close contact with each other, the interface resistance is reduced, and the ion conductivity is improved.

Example 10

The low temperature and high temperature characteristics were tested using the lithium secondary battery obtained in Example 5 and the lithium secondary battery obtained in Comparative Example 2, and the results are shown in FIGS. 4A and 4B (but FIG. 4A is applied to the lithium secondary battery of Example 5). 4b is a test result for the lithium secondary battery of Comparative Example 2). The low temperature and high temperature characteristics tests were performed by a charge / discharge method of charging with C / 2 constant current and 4.2V constant voltage and then discharging with C / 5 constant current. 4A and 4B show that the lithium secondary battery obtained in Example 5 has superior low temperature and high temperature characteristics than the lithium secondary battery obtained in Comparative Example 2. In particular, even at -10 ℃ appeared to have excellent properties of about 91%.

Example 11

The high-rate discharge characteristics were tested using the lithium secondary battery obtained in Example 3 and the lithium secondary battery obtained in Comparative Example 2, and the results are shown in FIGS. 5A and 5B (where, FIG. 5A is for the lithium secondary battery of Example 3). 5B is a test result of the lithium secondary battery of Comparative Example 2). The high rate discharge characteristic test was performed by charging and discharging by charging with a C / 2 constant current and 4.2V constant voltage, and then converting the C / 5, C / 2, 1C and 2C constant current to discharge. As can be seen in FIGS. 5A and 5B, the lithium secondary battery obtained in Example 3 exhibited a capacity of 99% at C / 2 discharge and 96% and 90% at 1C and 2C discharge, respectively, for C / 5 discharge. The lithium secondary battery obtained in Comparative Example 2 showed low performance of 87% and 56% at 1C and 2C discharges, respectively, for the C / 5 discharge. Therefore, it can be seen that the lithium secondary battery obtained in Example 3 is superior in high rate discharge characteristics to the lithium secondary battery obtained in Comparative Example 2.

Claims (18)

A lithium secondary battery comprising a cathode active material, an anode active material, a porous polymer separator, and an organic electrolyte in which lithium salt is dissolved, wherein the porous polymer separator is made of a ultrafine fibrous polymer having a diameter of 1 to 3000 nm. battery. The lithium secondary battery according to claim 1, wherein the porous polymer separator is manufactured by a charge induction spinning method. The method of claim 1, wherein the porous polymer membrane is heated or melted or dissolved in a suitable organic solvent to obtain a molten polymer or a polymer solution to form a porous polymer membrane, the resulting molten polymer or polymer solution is charged induction radiator Lithium secondary battery, characterized in that is produced by spinning in a nozzle after the injection into the barrel. The method of claim 1, wherein the porous polymer membrane is melted or dissolved in each of two or more polymers forming a porous polymer membrane in a suitable organic solvent to obtain two or more molten polymer or two or more polymer solution, the charge of the obtained molten polymer or polymer solution Lithium secondary battery, characterized in that it is produced by spinning into a nozzle after each injection into the barrel of the induction spinning device. The organic solvent according to claim 3 or 4, wherein the organic solvent for dissolving the polymer is propylene carbonate, butylene carbonate, 1,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,3 -Dimethyl-2-imidazolidinone, dimethyl sulfoxide, ethylene carbonate, ethylmethyl carbonate, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylenesulfuran And tetraethylene glycol dimethyl ether, acetone, alcohol, and mixtures thereof. The lithium secondary battery according to claim 1, wherein the porous polymer separator has a thickness of 1-100 μm. The method of claim 1, wherein the polymer forming the porous polymer membrane is polyethylene, polypropylene, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylpyrrolidone-vinylacetate, poly [bis (2- (2-methoxyethoxyethoxy)) phosphazene], polyethyleneimide, polyethylene oxide, polyethylenesuccinate, polyethylenesulfide, poly (oxymethylene-oligo-oxyethylene), polypropylene oxide, polyvinylacetate, poly Acrylonitrile, poly (acrylonitrile-co-methylacrylate), polymethylmethacrylate, poly (methylmethacrylate-co-ethylacrylate), polyvinylchloride, poly (vinylidene chloride-co-acrylic Ronitrile), polyvinylidenedifluoride, poly (vinylidenefluoride-co-hexafluoroprop Alkylene), and a lithium secondary battery, characterized in that selected from the group consisting of a mixture thereof. The lithium secondary battery according to claim 1, wherein the lithium salt embedded in the porous polymer separator is LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF _4, or LiCF ₃ SO ₃ . The lithium secondary battery according to claim 1, wherein the organic solvent used in the organic electrolyte is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, or a mixed solvent thereof. The method of claim 9, wherein the organic solvent is methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, butylene carbonate, γ -butyrolactone, 1,2-dimethoxyethane, A lithium secondary battery further comprising 1,2-dimethoxyethane, dimethylacetamide, tetrahydrofuran, or a mixed solvent thereof. The lithium secondary battery of claim 1, wherein the porous polymer separator further comprises a filler. The method of claim 11, wherein the filler is TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, MgO, Li ₂ CO ₃ , LiAlO ₂ , SiO ₂ , Al ₂ O ₃ , Lithium secondary battery, characterized in that selected from the group consisting of PTFE and mixtures thereof, the content is 20% by weight or less (but does not include 0) relative to the porous separator. A method of manufacturing a lithium secondary battery comprising placing a porous polymer separator prepared by a charge induction radiation method between a cathode and an anode, laminating them, rolling them in a battery case, injecting an organic electrolyte solution, and sealing the same. Inserting the porous polymer membrane prepared by the charge induction radiation method between the cathode and the anode, the electrolyte and the electrode by integrating the electrode by the heating lamination process, laminated or rolled and put into the battery case and injecting the organic electrolyte solution and sealing Method of manufacturing a lithium secondary battery. After coating on both sides of the cathode or the anode of the porous polymer membrane prepared by the charge induction radiation method, the electrode having the other pole is in close contact with the electrolyte, laminated or rolled them, put into a battery case and inject the organic electrolyte solution and then sealed Method for manufacturing a lithium secondary battery comprising the. After coating on both sides of the porous polymer membrane cathode or anode prepared by the charge induction radiation method, the electrode having the other pole is brought into close contact with the electrolyte, the electrolyte and the electrode are integrated by a heating lamination process, and then laminated or rolled The method of manufacturing a lithium secondary battery comprising putting in an organic electrolyte solution in a battery case and sealing. The porous polymer separator prepared by the charge-induced radiation method was coated on both sides of one of the two electrodes of the battery and on one side of the other electrode, and the polymer electrolytes were brought into close contact with each other, stacked or rolled, and placed in a battery case. Method of manufacturing a lithium secondary battery comprising the sealing after injecting the electrolyte solution. The porous polymer separator prepared by the charge induction radiation method was coated on both sides of one of the two electrodes of the battery and on one side of the other electrode, and the polymer electrolytes were brought into close contact with each other, and the electrolyte and the electrodes were integrated by a heating lamination process. After that, laminated or rolled, rolled into a battery case, a method of manufacturing a lithium secondary battery comprising injecting an organic electrolyte solution and sealing.