WO2001091222A1

WO2001091222A1 - A lithium secondary battery comprising a polymer electrolyte fabricated by a spray method and its fabrication method

Info

Publication number: WO2001091222A1
Application number: PCT/KR2000/000515
Authority: WO
Inventors: Kyung Suk Yun; Byung Won Cho; Won Il Cho; Hyung Sun Kim; Un Seok Kim
Original assignee: Korea Institute Of Science And Technology
Priority date: 2000-05-22
Filing date: 2000-05-22
Publication date: 2001-11-29

Abstract

The present invention provides a lithium secondary battery and its fabrication method. More particularly, the present invention provides a lithium secondary battery comprising a porous polymer electrolyte and its fabrication method, wherein the polymer electrolyte is fabricated by the following process: a) dissolving at least one polymer with plasticizers and organic electrolyte solvents to obtain at least one polymeric electrolyte solution; b) adding the obtained polymeric electrolyte solution to a barrel of a spray machine, and c) spraying the polymeric electrolyte solution onto a substrate using a nozzle to form a porous polymer electrolyte film. The lithium secondary battery of the present invention has advantages of better adhesion with electrodes, good mechanical strength, better performance at low and high temperatures, better compatibility with organic electrolytes of a lithium secondary battery.

Description

A LITHIUM SECONDARY BATTERY COMPRISING A POLYMER ELECTROLYTE FABRICATED BY A SPRAY METHOD AND ITS FABRICATION METHOD

TECHNICAL FIELD

The present invention relates to a lithium secondary battery comprising a polymer electrolyte fabricated by a spray method, and to its fabrication method.

BACKGROUND ART

Recently electronic apparatus are becoming miniaturized and light- weighted, and accordingly research for the development of energy sources having high power and high energy is being performed intensively. A lithium secondary battery has been proposed as one energy source in the aspect that the higher integration of energy is possible because the molecular weight of lithium used in a lithium secondary battery is very low but its energy density is relatively high.

The early lithium secondary batteries were fabricated by using metallic lithium or a lithium alloy as an anode. However, the cycle characteristic of the secondary battery using metallic lithium or a lithium alloy is lowered significantly due to dendrite formation on the anode as a result of repeated charging and discharging of the battery.

A lithium ion battery was proposed in order to solve the problem caused by the dendrites. The lithium ion battery developed by SONY Company in Japan and widely used all over the world comprises a cathode active material, an anode active material, an organic electrolyte solution and a separator film.

The separator film functions to prevent internal short-circuiting of the lithium ion battery caused by contacting of a cathode and an anode, and to permeate ions. Separator films generally used at the present time are polyethylene (hereinafter referred to as "PE") or polypropylene (hereinafter referred to as "PP") separator films. However, the lithium ion battery using the PE or PP separator film still has problems such as instability, intricacy of the fabrication process, restriction of battery shape and limitation of capacity. There have been attempts to solve those problems, but there is no clear result until now.

On the contrary, a lithium polymer battery uses a polymer electrolyte having two functions, as a separator film and as an electrolyte, and it is now being viewed with keen interest as a battery being able to solve all of the problems. The lithium polymer battery has an advantage in view of productivity because the electrodes and polymer electrolytes can be laminated in a flat-plate shape and its fabrication process is similar to the fabrication process of a polymer film. A conventional polymer electrolyte is mainly prepared with polyethylene oxide (hereinafter referred to as "PEO"), but its ionic conductivity is merely 10^"8 S/cm at room temperature, and accordingly it can not be used commonly.

Recently, a gel or hybrid type polymer electrolyte having an ionic conductivity above 10^"3 S/cm at room temperature has been developed.

A polymer electrolyte of a gel type polyacrylonitrile (hereinafter referred to as "PAN") group was disclosed in U.S. Patent No. 5,219,679 to K. M. Abraham et al. and U.S. Patent No.5, 240,790 to D. L. Chua et al. The gel type PAN group polymer electrolyte is prepared by injecting a solvent compound (hereinafter referred to as an "organic electrolyte solution") prepared with a lithium salt and organic solvents, such as ethylene carbonate and propylene carbonate, etc., into a polymer matrix. It has an advantage in that the contact resistance is small in charging/discharging of a battery and desorption of the active materials rarely takes place because the adhesive strength of the polymer electrolyte is good, and accordingly adhesion between a composite electrode and a metal substrate is well developed. However, such polymer electrolyte has a problem in that its mechanical stability, namely, its strength, is low because the electrolyte is a little bit soft. Especially, such deficiency of strength may cause many problems in fabrication of electrodes and batteries. A polymer electrolyte of a hybrid type polyvinylidenedifluoride (hereinafter referred to as "PVdF") group was disclosed in U.S. Patent No. 5,460,904 to A. S. Gozdz et al. The polymer electrolyte of hybrid type PVdF group is prepared by preparing a polymer separator film having a porosity of below submicron and followed by injecting an organic electrolyte solution into the pores. It has advantages in that its compatibility with an organic electrolyte solution is good, the electrolyte injected into the small pores is not leaked so as to be safe in use and the polymer separator film can be fabricated in the atmosphere because the organic solvent electrolyte is injected later. However it has a disadvantage in that the fabrication process is intricate because in preparation of the polymer electrolyte, an extraction process of a plasticizer and an impregnation process of the organic solvent electrolyte are required. In addition, it has a serious disadvantage in that a process for forming a thin layer by heating and an extraction process are required in fabrication of electrodes and batteries because mechanical strength of the PVdF group electrolyte is good, but its adhesive strength is poor.

Recently, a polymer electrolyte of a polymethylmethacrylate (hereinafter referred to as "PMMA") group was described in Solid State Ionics, 66, 97, 105 (1993) by O. Bohnke and G. Frand et al. The PMMA polymer electrolyte has advantages in that its ionic conductivity is 10^"3 S/cm at room temperature, and its adhesive strength and compatibility with the organic electrolyte solution are good. However, it is not suitable for lithium polymer batteries because its mechanical strength is very poor. In addition, a polymer electrolyte of a polyvinylchloride (hereinafter referred to as "PVC") group, which has good mechanical strength and has an ionic conductivity of 10^"3 S/cm at room temperature, was described in J. Electrochem. Soc, 140, L96 (1993) by M. Alamgir and K. M. Abraham. However, its low-temperature characteristic is poor and its contact resistance is high.

SUMMARY OF THE INVENTION

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

Another object of the present invention is to provide a lithium secondary battery having good adhesion with electrodes, good mechanical strength, good low- and high-temperature characteristics, and good compatibility with organic electrolyte solution used for a lithium secondary battery.

The above-described and other objects can be achieved by providing a polymer electrolyte fabricated by a spray method.

BRIEF DESCRIPTION OF DRAWINGS

Figures 1a to 1c illustrate embodiments of a spray method by an electrostatic induction.

Figures 2a and 2b illustrate the fabrication method of a polymer electrolyte using a spraying machine. Figures 3a to 3c illustrate process flow for fabricating lithium secondary batteries according to the present invention.

Figure 4 is a graph illustrating charge/discharge characteristics of the lithium secondary batteries of Examples 1-6 and Comparative Examples 1 and 2. Figures 5a and 5b are graphs illustrating low- and high-temperature characteristics of the lithium secondary batteries of Example 2 and Comparative Example 2.

Figures 6a and 6b are graphs illustrating high-rate discharge characteristics of the lithium secondary batteries of Example 2 and Comparative Example 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a lithium secondary battery comprising a polymer electrolyte fabricated by a spray method, and to its fabrication method. More particularly, it relates to a lithium secondary battery comprising a cathode active material, an anode active material, an organic electrolyte solution in which a lithium salt is dissolved and a polymer electrolyte, wherein the polymer electrolyte is characterized as being one fabricated by a spray method.

A polymer electrolyte fabricated by a spray method has a form in which particles or fibers, or a combination thereof having a diameter of 1-3000nm are built up three-dimensionally. Due to the small diameter, the ratio of surface area to volume and the void ratio are very high compared to those of a conventional electrolyte. Therefore, due to the high void ratio, the amount of electrolyte impregnated is large and the ionic conductivity is increased, and due to the large surface area, the contact area with the electrolyte can be increased and the leakage of electrolyte can be minimized in spite of the high void ratio. The process for fabrication of a polymer electrolyte by a spray method comprises a step of obtaining a polymeric solution and a step of fabricating a polymer electrolyte using the obtained polymeric solution.

The step of obtaining a polymeric solution can be achieved by dissolving a polymer or polymer mixture in a mixture of plasticizer and an organic electrolyte solution.

The examples of the polymer used for forming the polymer electrolyte include polyethylene, polypropylene, cellulose, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, polyvinylpyrrolidone- vinylacetate, poly[bis(2-(2-methoxyethoxyethoxy))phosphagene], poly- ethyleneimide, polyethyleneoxide, polyethylenesuccinate, polyethylenesulfide, poly(oxymethylene-oligo-oxyethylene), polypropyleneoxide, polyvinylacetate, polyacrylonitrile, poly(acrylonitrile-co-methylacrylate), polymethylmethacrylate, poly(methylmethacrylate-co-ethylacrylate), polyvinylchloride, poly(vinylidene- chloride-co-acrylonitrile), polyvinylldenedifluoride, poly(vinylidenefluoride-co- hexafluoropropylene) or mixtures thereof. However the polymer which may be used is not limited to the above examples and any polymer which can be applied to a spray method is applicable.

The examples of a plasticizer used for the present invention include propylene carbonate, butylene carbonate, 1 ,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1 ,2-dimethoxyethane, 1 ,3-dimethyl-2- imidazolidinone, dimethylsulfoxide, ethylene carbonate, ethylmethyl carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2- pyrrolidone, polyethylenesulforane, tetraethylene glycol dimethyl ether, acetone, alcohol or mixtures thereof, but it is not particularly limited on the above examples.

The organic electrolyte solution used for the present invention means a solution in which a lithium salt is dissolved in an organic solvent which does not affect the characteristics of electrodes. The lithium salt used for the lithium secondary battery of the present invention is the same as generally used in the conventional lithium secondary battery. Examples include LiPF₆, LiCI0₄, LiAsF₆, LiBF₄ and LiCF₃SO₃, and among them LiPF₆ is more preferable. Examples of the organic solvent used for the organic electrolyte solution can include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or mixtures thereof. In order to improve the low-temperature characteristic, an additional solvent, such as methyl acetate,

methyl propionate, ethyl acetate, ethyl propionate, butylene carbonate, γ-

butyrolactone, 1 ,2-dimethoxyethane, 1 ,2-dimethoxyethane, dimethyl- acetamide, tetrahydrofuran or mixtures thereof, can be added to the above organic solvent.

The dissolving step of a polymer or polymer mixture in a mixture of a plasticizer and an organic electrolyte solution will now be described in more detail. A polymer, a plasticizer and an organic electrolyte solution are mixed in a ratio of 1 : 0.1 - 5 : 1 - 20 by weight. The resulting mixture is stirred at a temperature range of 20-150°C for 30 minutes to 24 hours to obtain a clear polymeric solution. The temperature and stirring time may be changed in accordance with the types of polymers.

The step of fabricating a polymer electrolyte with the obtained polymeric solution can be achieved by filling the polymeric solution into a barrel of a spray machine and then by spraying the polymeric solution onto a metal plate or Mylar film electrode using a nozzle at a suitable rate. In order to simplify the fabrication process, the polymeric solution can be sprayed directly onto the electrode. As illustrated in Figures 1a, 1b and 1c, when spraying the polymeric solution using a nozzle, they can be sprayed by electrostatic induction. Embodiments of spraying by electrostatic induction can include the following methods. One method is that a nozzle and an electrode are connected to be each given an electrical potential in order that the polymeric solution coming out from the nozzle has an electrostatic charge (Figure 1a). Another method is that an additional electrode for electrostatic induction is located between the nozzle and an electrode in order to charge the polymeric solution sprayed by the nozzle (Figure 1 b). Another method is to combine the above two methods (Figure 1c).

A variety of methods can be applied in spraying the polymeric solution using a nozzle. Examples can include a method of spraying the polymeric solutions all together, and another method of installing the spraying nozzles separately, followed by spraying the respective polymeric solutions sporadically and continually to get a multi-layered polymer electrolyte. Figures 2a and 2b illustrate the fabrication of a polymer electrolyte using a spray machine. Figure 2a illustrates the fabrication method by spraying all together using a nozzle to get a polymer electrolyte. Figure 2b illustrates the fabrication method by spraying sporadically and continually using separately installed nozzles to get a multi-layered polymer electrolyte.

The thickness of the polymer electrolyte can be adjusted by changing the spray rate and spray time. The thickness of the polymer electrolyte is preferably adjusted in the range of 1 μm - 100 μm, more preferably in the

range of 5 μm - 70 μm, and most preferably in the range of 10 μm - 50 μm. The diameter of the polymer forming the polymer electrolyte is preferably adjusted in the range of 1 nm - 3000 nm, more preferably 10 nm - 1000nm, and the most preferably 50 nm - 500 nm.

The polymer electrolyte fabricated by a spray method can comprise two or more polymers. The polymer electrolyte comprising two or more polymers can be obtained by the following methods. One method is by dissolving two or more polymers in a mixture of a plasticizer and an organic electrolyte solution, filling the resulting solution into a barrel of a spray machine and then spraying the solution using a nozzle, to fabricate the polymer electrolyte. Another method is by respectively dissolving two or more polymers in a mixture of a plasticizer and an organic electrolyte, filling the resulting solutions into separate barrels of a spray machine, and then spraying the respective solutions using nozzles, to fabricate the polymer electrolyte. The polymer electrolyte of the present invention can additionally include a filling agent in order to improve the porosity and mechanical strength. Preferable examples of a filling agent can include TiO₂, BaTiO₃, Li₂O, LiF, LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃, LiAIO₂, Si0₂, AI₂O₃, PTFE or mixtures thereof. It is preferable that the content of the filling agent is below 20% by weight of the total polymer electrolyte.

Typical anode and cathode active materials used in the conventional lithium secondary battery can be used in the lithium secondary battery of the present invention. Examples of the anode active material can include graphite, cokes, hard carbon, tin oxide, lithiated compounds thereof, metallic lithium or lithium alloys. Examples of the cathode active material can include LiCIO₂, LiNiO₂, LiNiCoO₂, LiMn₂O₄, V₂O₅ or V₆O₁₃.

The lithium secondary battery of the present invention can further comprise conducting materials and bonding agents as in the conventional lithium secondary battery. The anode and cathode of the lithium secondary battery are typically fabricated by mixing a certain amount of active materials, conducting materials and bonding agents with an organic solvent, casting the resulting mixture onto both sides of a copper or aluminum foil plate grid, and then drying and compressing all of them. The present invention relates to a fabrication method of a lithium secondary battery, and Figures 3a through 3c illustrate the fabrication process in detail. Figure 3a illustrates a process to fabricate a battery comprising inserting a polymer electrolyte fabricated by a spray method between an anode and a cathode, making the electrolytes and the electrodes into one body by a certain heat lamination process, inserting the resulting plate into a battery casing after laminating or rolling it, injecting an organic electrolyte solution into the battery casing, and then finally sealing the casing. Figure 3b illustrates a process to fabricate a lithium secondary battery comprising coating a polymer electrolyte by spraying polymeric solutions directly onto both sides of a cathode or anode, adhering an electrode having opposite polarity to the coated electrode onto the polymer electrolyte, making the electrolytes and the electrodes into one body by a certain heat lamination process, inserting the resulting plate into a battery casing after laminating or rolling it, injecting an organic electrolyte solution into the battery casing, and then finally sealing the battery casing. Figure 3c illustrates a process to fabricate a lithium secondary battery comprising coating a polymer electrolyte by spraying polymeric solutions directly onto both sides of one of two electrodes and onto one side of the other electrode respectively, adhering the electrodes closely together so the polymer electrolytes are faced to each other, making the electrolytes and the electrodes into one body by a certain heat lamination process, inserting the resulting plate into a battery casing after laminating or rolling it, injecting an organic electrolyte solution into the battery casing, and then finally sealing the battery casing. Examples of the organic electrolyte solution used for the fabrication of the above lithium secondary battery are the same as the examples of the organic electrolyte solution used for dissolving polymers.

Examples

The present invention will be better understood from the below examples, but those examples are given only to illustrate the present invention, not to limit the scope of it.

Example 1

1-1) Fabrication of a polymer electrolyte

To a mixture of 100g of 1 M LiPF₆ solution in EC-DMC and 10g of PC as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761) was added, and the resulting mixture was stirred at 80°C for 2 hours to give a clear polymeric solution. The obtained polymeric solution was filled into a barrel of a spray machine and sprayed onto a metal plate using a nozzle at a constant rate, and the resulting film was detached from the metal plate to prepare a polymer electrolyte film of 50 μm thickness.

1-2) Fabrication of a lithium secondary battery

The polymer electrolyte prepared in Example 1-1 was inserted between a graphite anode and a LiCoO₂ cathode. The resulting plates were

cut so as to be 3 cm x 4 cm in size and laminated. Terminals were welded

onto the electrodes and the laminated plate was inserted into a vacuum casing. A 1 M LiPF₆ solution in EC-DMC was injected into the casing, and the casing was then finally vacuum-sealed to give a lithium secondary battery.

Example 2 2-1 ) To a mixture of 10Og of 1 M LiPF₆ solution in EC-DMC and 10g of

PC as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761) was added, and the resulting mixture was stirred at 80°C for 2 hours to give a clear polymeric solution. The obtained polymeric solution was filled into a barrel of a spray machine and sprayed onto both sides of a graphite anode using a nozzle at a constant rate, to fabricate a graphite anode coated with polymer electrolytes

of 50 μm thickness on both sides of it.

2-2) A LiCoO₂ cathode was adhered onto the polymer electrolyte

obtained in Example 2-1. The resulting plate was cut so as to be 3 cm x 4 cm

in size and laminated. Terminals were welded onto the electrodes, and then the laminated plate was inserted into a vacuum casing. A 1M LiPF₆ solution in EC-DMC was injected into the casing, and the casing was then finally vacuum-sealed to give a lithium secondary battery.

Example 3

3-1) To a mixture of 100g of 1 M LiPF₆ solution in EC-DMC and 10g of PC as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761) was added, and the resulting mixture was stirred at 80°C for 2 hours to give a clear polymeric solution. The obtained polymeric solution was filled into a barrel of a spray machine and sprayed onto one side of a LiCo0₂ cathode using a nozzle at a constant rate, to fabricate a LiCoO₂ cathode coated with a polymer

electrolyte film of 50 μm thickness on one side of it.

3-2) The LiCoO₂ cathode obtained in Example 3-1 was adhered onto both sides of the graphite anode obtained in Example 2-1 so as to face the polymer electrolyte films to each other. The resulting plate was made into one

body by heat lamination at 110°C, cut so as to be 3 cm x 4 cm in size and

then laminated. Terminals were welded onto the electrodes, and then the laminated plate was inserted into a vacuum casing. A 1M LiPF₆ solution in EC- DMC was injected into the casing, and the casing was then finally vacuum- sealed to give a lithium secondary battery. Example 4

4-1) To a mixture of 100g of 1M LiPF₆ solution in EC-DMC-PC and 10g of BC as a plasticizer, 10g of PAN (prepared by Polyscience Company, molecular weight of about 150,000) was added. The resulting mixture was

stirred at 100°C for 2 hours to give a clear polymeric solution. The obtained

polymeric solution was filled into a barrel of a spray machine and sprayed onto both sides of a graphite anode using a nozzle at a constant rate, to

fabricate a graphite anode coated with polymer electrolytes of 50 μm

thickness.

4-2) The process described In Example 4-1 was applied to one side of a LiCoO₂ cathode instead of to both sides of a graphite anode, to fabricate a LiCoO₂ cathode coated with a polymer electrolyte film on one side of it.

4-3) The LiCoO₂ cathode obtained in Example 4-2 was adhered onto both sides of the graphite anode obtained in Example 4-1 so as to face the polymer electrolyte films to each other. The resulting plate was made into one

body by heat lamination at 110°C, cut so as to be 3 cm x 4 cm in size and

then laminated. Terminals were welded onto the electrodes, and then the laminated plate was inserted into a vacuum casing. A 1 M LiPF₆ solution in EC- DMC was injected into the casing, and the casing was then finally vacuum- sealed to give a lithium secondary battery. Example 5

5-1) To a mixture of 100g of 1 M LiPF₆ solution in EC-DMC and 10g of PC as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761) and 20g of PAN (fabricated by Polyscience Company, molecular weight of about 150,000) were respectively added, to prepare two mixtures. The respective mixtures

were stirred at 100°C for 2 hours to give clear polymeric solutions. Then the

respective solutions were filled into separate barrels of a spray machine and sprayed onto both sides of a graphite anode using respective nozzles at a constant rate, to fabricate a graphite anode coated with polymer electrolyte

films of 50 μm thickness.

5-2) A LiCoO₂ cathode was adhered onto the polymer electrolyte

obtained in Example 5-1 , and the resulting plate was cut so as to be 3 cm x

4 cm in size and laminated. Terminals were welded onto the electrodes and then the laminated plate was inserted into a vacuum casing. A 1 M LiPF₆ solution in EC-DMC was injected into the casing, and the casing was then finally vacuum-sealed to give a lithium secondary battery.

Example 6

6-1) To a mixture of 100g of 1 M LiPF₆ solution in EC-DMC and 10g of PC as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761), 20g of PAN (fabricated by Polyscience Company, molecular weight of about 150,000) and 20g of polymethyl-methacrylate (fabricated by Polyscience Company, molecular weight of about 150,000) were respectively added, to prepare three

mixtures. The respective mixtures were stirred at 100°C for 2 hours to give

clear polymeric solutions. Then the respective solutions were filled into separate barrels of spray machine and sprayed onto both sides of a graphite anode using respective nozzles at a constant rate, to fabricate a graphite

anode coated with polymer electrolyte films of 50 μm thickness.

6-2) The process described In Example 6-1 was applied to one side of a LiCoO₂ cathode instead of to both sides of a graphite anode, to fabricate a LiCoO₂ cathode coated with polymer electrolyte films on one side of it.

6-3) The LiCoO₂ cathode obtained in Example 6-2 was adhered onto both sides of the graphite anode obtained in Example 6-1 so as to face the polymer electrolyte films to each other. The resulting plate was made into one

body by heat lamination at 110°C, and then cut so as to be 3 cm x 4 cm in

size and laminated. Terminals were welded onto the electrodes, and then the laminated plate was inserted into a vacuum casing. A 1M LiPF₆ solution in EC- DMC was injected into the casing, and the casing was then finally vacuum- sealed to give a lithium secondary battery. Comparative Examples

Comparative Example 1

A lithium secondary battery was fabricated by laminating electrodes and separator films in order of an anode, a PE separator film, a cathode, a PE separator film and an anode, inserting the resulting laminated plate into a vacuum casing, injecting a 1M LiPF₆ solution in EC-DMC into the casing, and then finally vacuum-sealing the casing.

Comparative Example 2

According to the conventional preparation method of a gel-polymer electrolyte, 9g of a 1M LiPF₆ solution in EC-PC was added to 3g of PAN, and the resulting mixture was blended for 12 hours. After blending, the resulting

mixture was heated at 130°C for 1 hour to give a clear polymeric solution.

When a 10,000cps viscosity suitable for casting was obtained, the polymeric solution was cast by die-casting to give a polymer electrolyte film. A lithium secondary battery was fabricated by laminating in order of a graphite anode, an electrolyte, a LiCoO₂ cathode, an electrolyte and a graphite anode, welding terminals onto the electrodes, inserting the resulting laminated plate into a vacuum casing, injecting a 1M LiPF₆ solution in EC-DMC into the casing, and then finally vacuum-sealing the casing. Example 7

Charge/discharge characteristics of the lithium secondary batteries fabricated in Examples 1 - 6 and Comparative Examples 1 and 2 were tested, and Figure 4 shows the results. The tests for obtaining charge/discharge characteristics were performed by the charge/discharge method of, after charging the batteries with a C/2 constant current and a 4.2V constant voltage, discharging with a C/2 constant current, and the electrode capacities and life cycles based on the cathode were tested. Figure 4 shows that the electrode capacities and life cycles of the lithium secondary batteries of Examples 1 - 6 were improved compared to the lithium secondary batteries of Comparative Examples 1 and 2. It is considered that those results came about from the decrease of an interface resistance and the increase of an ionic conductivity by good adherence of the electrodes with the polymer electrolyte. Example 8

Low- and high-temperature characteristics of the lithium secondary batteries of Example 4 and Comparative Example 2 were tested, and Figures 5a and 5b illustrate the respective results (wherein Figure 5a is for the battery of Example 4 and Figure 5b is for the battery of Comparative Example 2). The tests for obtaining the low- and high-temperature characteristics of the lithium secondary batteries were performed by the charge/discharge method of, after charging the lithium batteries with a C/2 constant current and a 4.2 V constant voltage, discharging with a C/5 constant current. As depicted in Figures 5a and 5b, the low- and high-temperature characteristics of the lithium secondary battery of Example 4 were better than those of the lithium secondary battery of Comparative Example 2. In particular, it shows that the battery of Example

2 had an outstanding characteristic of 91 % even at -10°C.

Example 9 High rate discharge characteristics of the lithium secondary batteries of Example 2 and Comparative Example 2 were tested, and Figures 6a and 6b illustrate the results (wherein Figure 6a is for the battery of Example 2 and Figure 6b is for the lithium secondary battery of Comparative example 2). The tests for obtaining the high rate discharge characteristics of the lithium secondary batteries were performed by the charge/discharge method of, after charging the lithium batteries with a C/2 constant current and a 4.2 V constant voltage, discharging while varying the constant current to C/5, C/2,1C and 2C. As depicted in Figures 6a and 6b, the lithium secondary battery of Example 2 showed capacities such as 99% at C/2 discharge, 96% at 1 C discharge and 90% at 2C discharge based on the value at C/5 discharge. However, the lithium secondary battery of Comparative Example 2 showed low capacities such as 87% at 1C discharge and 56% at 2C discharge based on the value at C/5 discharge. Accordingly, it was discovered that the high rate discharge characteristic of the lithium secondary battery of Example 2 was better than that of the lithium secondary battery of Comparative Example 2.

Claims

1. A lithium secondary battery comprising a cathode active material, an anode active material, a polymer electrolyte and an organic electrolyte solution dissolving a lithium salt, wherein said polymer electrolyte comprises a polymer electrolyte of particlulate or fibrous form, or a combination thereof, having a diameter of 1 nm - 3000nm.

2. The lithium secondary battery according to claim 1 , wherein the polymer electrolyte is fabricated by a spray method.

3. The lithium secondary battery according to claim 1 , wherein the spray method is a spray method by electrostatic induction.

4. The lithium secondary battery according to claim 1 , wherein the polymer electrolyte is fabricated by obtaining a polymeric solution by dissolving a polymer or polymer mixture in a mixture of a plasticizer and an organic electrolyte solution, filling the obtained polymeric solution into a barrel of a spray machine, and spraying the polymeric solution using a nozzle.

5. The lithium secondary battery according to claim 1 , wherein the polymer electrolyte is fabricated by obtaining two or more polymeric solutions by respectively dissolving two or more polymers for forming polymer electrolytes in a mixture of a plasticizer and an organic electrolyte solution to obtain two or more polymeric solutions, filling the polymeric solutions into separate barrels of a spray machine respectively, and spraying the polymeric solutions using nozzles.

6. The lithium secondary battery according to claim 4 or claim 5, wherein the plasticizer is one selected from the group consisting of 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-dimethyl- formamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylene- sulforane, tetraethylene glycol dimethyl ether, acetone, alcohol and mixtures thereof.

7. The lithium secondary battery according to claim 1 , wherein the

polymer electrolyte is characterized by having a thickness of 1 μm - 100 μm.

8. The lithium secondary battery according to claim 1 , wherein a polymer for forming the polymer electrolyte is one selected from the group consisting of polyethylene, polypropylene, cellulose, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, polyvinylpyrrolidone-vinylacetate, poly[bis(2-(2-methoxyethoxyethoxy))-phosphagene], polyethyleneimide, polyethyleneoxide, polyethylenesuccinate, polyethylenesulfide, poly(oxy- methylene-oligo-oxyethylene), polypropyleneoxide, polyvinylacetate, poly- acrylonitrile, poly(acrylonitrile-co-methylacrylate), polymethylmethacrylate, poly(methylmethacrylate-co-ethylacrylate), polyvinylchloride, poly(vinylidene- chloride-co-acrylonitrile), polyvinylidenedifluoride, poly(vinylidenefluoride-co- hexafluoropropylene) and mixtures thereof.

9. The lithium secondary battery according to claim 1 , wherein the lithium salt used in the polymer electrolyte is LiPF₆, LiCIO₄, LiAsF₆, LiBF₄ or

LiCF₃SO₃.

10. The lithium secondary battery according to claim 1 , wherein an organic solvent used in the organic electrolyte solution is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate or mixtures thereof.

11. The lithium secondary battery according to claim 10, wherein the organic electrolyte solution further comprises methyl acetate, methyl

propionate, ethyl acetate, ethyl propionate, butylene carbonate, γ-

butyrolactone, 1 ,2-dimethoxyethane, 1 ,2-dimethoxyethane, dimethyl- acetamide, tetrahydrofuran or mixtures thereof in order to increase a low- temperature characteristic.

12. The lithium secondary battery according to claim 1 , wherein the polymer electrolyte further comprises a filling agent.

13. The lithium secondary battery according to claim 12, wherein the filling agent is one selected from the group consisting of TiO₂, BaTiO₃, Li₂O, LiF, LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃, LiAIO₂, SiO₂, AI₂O₃, PTFE and mixtures thereof, and the content of the filling agent is below 20% (wherein 0% is excluded) of total weight of the polymer electrolyte.

14. A method for fabricating a lithium secondary battery, comprising: inserting a polymer electrolyte fabricated by a spray method between an anode and a cathode; inserting the resulting plates into a battery casing after laminating or rolling them; injecting an organic electrolyte solution into the casing; and sealing the battery casing.

15. A method for fabricating a lithium secondary battery, comprising: inserting a polymer electrolyte fabricated by a spray method between an anode and a cathode; making the electrolytes and the electrodes into one body by a heat lamination process; inserting the resulting plate into a battery casing after laminating or rolling it; injecting an organic electrolyte solution into the battery casing; and sealing the battery casing.

16. A method for fabricating a lithium secondary battery, comprising: coating polymer electrolytes fabricated by a spray method onto both sides of an anode or cathode; adhering an electrode having opposite polarity to the coated electrode closely onto the electrolytes; inserting the resulting plate into a battery casing after laminating or rolling it; injecting an organic electrolyte solution into the battery casing; and sealing the battery casing.

17. A method for fabricating a lithium secondary battery, comprising: coating polymer electrolytes fabricated by a spray method onto both sides of an anode or cathode; adhering an electrode having opposite polarity to the coated electrode closely onto the electrolytes; making the electrolytes and the electrodes into one body by a heat lamination process; inserting the resulting plate into a battery casing after laminating or rolling it; injecting an organic electrolyte solution into the battery casing; and sealing the battery casing.

18. A method for fabricating a lithium secondary battery, comprising: coating polymer electrolytes fabricated by a spray method onto both sides of one of two electrodes and onto one side of the other electrode; adhering the electrodes closely so as to face the polymer electrolytes to each other; inserting the resulting plate into a battery casing after laminating or rolling it; injecting an organic electrolyte solution into the battery casing; and sealing the battery casing.

19. A method for fabricating a lithium secondary battery, comprising: coating polymer electrolytes fabricated by a spray method onto both sides of one of two electrodes and onto one side of the other electrode; adhering the electrodes closely so as to face the polymer electrolytes to each other; making the electrolytes and the electrodes into one body by a heat lamination process; inserting the resulting plate into a battery casing after laminating or rolling it; injecting an organic electrolyte solution into the battery casing; and sealing the battery casing.