WO2001091221A1

WO2001091221A1 - A composite polymer electrolyte fabricated by a spray method, a lithium secondary battery comprising the composite polymer electrolyte and their fabrication methods

Info

Publication number: WO2001091221A1
Application number: PCT/KR2000/000514
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 novel composite polymer electrolyte, lithium secondary battery comprising the composite polymer electrolyte and their fabrication methods. More particularly, the present invention provides the composite polymer electrolyte comprising a porous polymer electrolyte matrix with particles, fibers or mixture thereof having diameters of 1 - 3000 nm, polymers and lithium salt-dissolved organic electrolyte solutions incorporated into the porous polymer matrix. The composite polymer electrolyte 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 lithium secondary battery and it can be applied to the manufacture of lithium secondary batteries.

Description

A COMPOSITE POLYMER ELECTROLYTE FABRICATED BY A SPRAY METHOD. A LITHIUM SECONDARY BATTERY COMPRISING THE COMPOSITE POLYMER ELECTROLYTE AND THEIR FABRICATION METHODS

TECHNICAL FIELD

The present invention relates to a composite polymer electrolyte, a lithium secondary battery using the same, and to its fabrication method.

BACKGROUND ART

Lithium secondary batteries are typified by a lithium ion battery and a lithium polymer battery. A lithium ion battery uses a polyethylene (hereinafter referred to as "PE") or polypropylene (hereinafter referred to as "PP") separator film besides an electrolyte. Because it is difficult to fabricate the lithium ion battery by laminating electrodes and separator films in a flat-plate shape, it is fabricated by rolling the electrodes with separator films and by inserting them into a cylindrical or rectangular casing (D. Linden, Handbook of Batteries, McGraw-Hill Inc., New York (1995)). The lithium ion battery was developed by SONY Company in Japan and has been widely used all over the world; however, it has problems such as instability of the battery, intricacy of its fabrication process, restriction on battery shape and limitation of capacity.

On the contrary, a lithium polymer battery uses a polymer electrolyte having two functions, as a separator film and as an electrolyte at the same time, 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 a polymer electrolyte can be laminated in a flat-plate shape and its fabrication process is similar to a 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.

K. M. Abraham et al. and D. L. Chua et al. disclose a polymer electrolyte of a gel type polyacrylonitrile (hereinafter referred to as "PAN") group in U.S. Patent No. 5,219,679 and in U.S. Patent No.5, 240,790 respectively. 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 PAN-group polymer matrix. It has advantages 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 force of the polymer electrolyte is good, and accordingly adhesion between a composite electrode and a metal substrate is well developed. However, such a polymer electrolyte has a disadvantage in that its mechanical stability, namely its strength, is low because the electrolyte is a little bit soft. Especially, such deficiency in strength may cause many problems in the fabrication of an electrode and battery.

A. S. Gozdz et al. discloses a polymer electrolyte of hybrid type polyvmylidenedifluoride (hereinafter referred to as "PVdF") group in U.S. Patent No. 5,460,904. The polymer electrolyte of the hybrid type PVdF group is prepared by fabricating a polymer matrix having a porosity not greater than submicron and then injecting an organic electrolyte solution into the small pores in the polymer matrix. It has advantages in that its compatibility with an organic electrolyte solution is good, the organic electrolyte solution injected into the small pores is not leaked so as to be safe in use and the polymer matrix can be fabricated in the atmosphere because the organic electrolyte solution is injected later. However, it has disadvantages 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 electrolyte solution are required. In addition, it has a critical 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 the mechanical strength of the PVdF group electrolyte is good but its adhesive force is poor. Recently, a polymer electrolyte of a polymethylmethacrylate

(hereinafter referred to as "PMMA") group was presented in Solid State Ionics, 66, 97, 105 (1993) by O. Bohnke and G. Frand, et al. The PMMA polymer electrolyte has advantages in that it has an ionic conductivity of 10^"3

S/cm at room temperature and its adhesive force and its compatibility with an 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 a good mechanical strength and has an ionic conductivity of 10^"3 S/cm at room temperature, was presented in J. Electrochem. Soc, 140, L96 (1993) by M. Alamgir and K. M. Abraham. However, it has problems in that a low-temperature characteristic is poor and a contact resistance is high.

Accordingly, development of a polymer electrolyte having a good adhesion with electrodes, good mechanical strength, good low- and high- temperature characteristics and good compatibility with an organic electrolyte solution for a lithium secondary battery, etc. has been required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel composite polymer electrolyte.

It is another object of the present invention to provide a composite polymer electrolyte having a good adhesion with electrodes, good mechanical strength, good low- and high-temperature characteristics and good compatibility with an organic electrolyte solution for a lithium secondary battery, etc, and its fabrication method.

It is yet another object of the present invention to provide a lithium secondary battery having a simplified fabrication process, an advantage in scaling-up of a battery size, and superiority in energy density, cycle characteristics, low- and high-temperature characteristics, high rate discharge characteristics and stability, and its fabrication method.

BRIEF DESCRIPTION OF DRAWINGS Figures 1a to 1c illustrate embodiments of a spray method by an electrostatic induction.

Figures 2a and 2b illustrate fabrication methods of a polymer electrolyte matrix using a spray 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 composite polymer electrolyte comprising a polymer electrolyte matrix in particulate or fibrous form, or a combination thereof having a diameter of 1-3000nm and a polymer electrolyte incorporated into the polymer electrolyte matrix. In more detail, the present invention relates to a composite polymer electrolyte obtained by dissolving a polymer in a mixture of a plasticizer and an organic electrolyte solution, fabricating a polymer electrolyte matrix in particulate or fibrous form, or a combination thereof having a diameter of 1-3000nm by a spray method and then injecting a polymer electrolyte solution, in which a polymer, a plasticizer and an organic electrolyte solution are mixed and dissolved with each other, into the pores in the polymer matrix. In the present invention, "composite polymer electrolyte" means an electrolyte in which a polymer electrolyte is incorporated into a polymer electrolyte matrix. "Polymer electrolyte matrix" means a matrix comprising a polymer, an organic solvent and a lithium salt. The polymer electrolyte matrix can be fabricated by dissolving a polymer for forming the matrix in a mixture of an organic electrolyte solution dissolving a lithium salt and a plasticizer, and then spraying the obtained solution (hereinafter, it is referred to as a "polymeric solution") onto a metal plate, a Mylar film or electrodes. "Polymer electrolyte solution" means a solution which dissolves a polymer to be incorporated into the polymer electrolyte matrix in a mixture of an organic electrolyte solution and a plasticizer. "Polymer electrolyte" generically means an organic electrolyte solution and a polymer incorporated into the polymer electrolyte matrix.

A polymer electrolyte matrix fabricated by a spray method has a form in which particles or fibers, or a combination thereof with 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.

Furthermore, in spite of the fabrication method in particulate or fibrous form or a combination thereof, the fabrication equipment and processes can be simplified, and the fabrication time can be shortened because the final product is fabricated in the form of a film directly, and accordingly the economic efficiency is high and as well the fabrication of the film is easy. In addition, because the particles or fibers, or combination thereof, are built up to form a structure having pores of effective size, closed pores can not be formed structurally, and there is no possibility of closing the pores during the lamination process applied in order to fabricate batteries. Furthermore, because DBP, which is used in the conventional process of Bellcore Co. for forming pores, is not used, there is no problem of residual DBP.

The examples of the polymer for forming the polymer electrolyte matrix 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 formed into a polymer electrolyte matrix by a spray method is applicable. Although there is no limitation on the thickness of the polymer

electrolyte matrix, it is preferable to be 1 μm - 100 μm, more preferably 5 μm

- 70 μm and most preferably 10 μm - 50 μm. The diameter of the particles and

fibers forming the polymer electrolyte matrix is preferably adjusted in the range of 1 nm - 3000 nm, more preferably 10 nm - 1000nm and most preferably 50 nm - 500 nm.

The polymers incorporated into the polymer electrolyte matrix function as a polymer electrolyte, and examples of the polymer can include polyethylene, polypropylene, cellulose, cellulose acetate, cellulose acetate butylate, cellulose acetate propionate, polyvinylpyrrolidone-vinylacetate, poly[bis(2-(2-methoxyethoxyethoxy))phosphagene], polyethyleneimide, poly- ethyleneoxide, polyethylenesuccinate, polyethylenesulfide, poly(oxy- methylene-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), polyethylene glycol diaciNlate, polyethylene glycol dimethacrylate or mixtures thereof.

Examples of an organic electrolyte solution used in the polymer electrolyte matrix and the polymer electrolyte 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 selected from the group consisting of methyl acetate, methyl propionate, ethyl acetate, ethyl propionate, butylene

carbonate, γ-butyrolactone, 1 ,2-dimethoxyethane, 1 ,2-dimethoxyethane,

dimethylacetamide, tetrahydrofuran and mixtures thereof can be added to the above organic solvent. And, the examples of a lithium salt used for the organic electrolyte solution can include LiPF₆, LiCIO₄, LiAsF₆, LiBF₄ or UCF₃SO₃. Among them LiPF₆ is more preferable. However, the lithium salt is not particularly limited to the above-mentioned examples.

The examples of the plasticizer used for the fabrication of the polymer electrolyte matrix and the polymer electrolyte solution can 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-dimethyl- formamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylene- sulforane, tetraethylene glycol dimethyl ether, acetone, alcohol or mixtures thereof. However, because the plasticizer can be removed in the fabrication of a battery, the kind of plasticizer is not particularly limited to the above examples.

The composite polymer electrolyte of the present invention can additionally include a filling agent in order to improve the porosity and mechanical strength. Examples of a filling agent can include TiO₂, BaTiO₃,

Li₂O, LiF, LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃, LiAIO₂, SiO₂, AI₂O₃, PTFE or mixtures thereof. It is preferable that the content of the filling agent is typically below 20% by weight of the total composite polymer electrolyte.

The present invention relates to a fabrication method of a composite polymer electrolyte. The method comprises a step of obtaining a polymeric solution in which a polymer is dissolved in a mixture of a plasticizer and an organic electrolyte solution, a step of fabricating a polymer electrolyte matrix by a spray method, and a step of injecting a polymer electrolyte solution into the fabricated polymer electrolyte matrix.

The step of obtaining a polymeric solution can be achieved by dissolving a polymer in a mixture of a plasticizer and an organic electrolyte solution and then raising the temperature of the mixture to obtain a clear polymeric solution. The possible plasticizer used for obtaining the polymeric solution is not particularly limited on condition that it can dissolve the polymer substantially and be applicable to a spray method. In addition, a plasticizer which might influence on the characteristics of the battery can even be used, because it is almost completely removed while fabricating a polymer electrolyte matrix by a spray method.

The step of fabricating a polymer electrolyte matrix can be achieved by a spray method. In more detail, the polymer electrolyte matrix can be obtained by filling the polymeric solution for forming the polymer electrolyte matrix into a barrel of a spray machine and then spraying the polymeric solution using a nozzle at a constant rate onto a metal plate or Mylar film. In order to simplify the process, the polymeric solution can be sprayed directly onto electrodes. The thickness of the polymer electrolyte matrix can be adjusted by changing a spray speed and time, and the preferable thickness range is 1 - 100 μm as mentioned before.

As illustrated in Figures 1a to 1c, when spraying the polymeric solution using a nozzle, the polymeric solution 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 a nozzle and an electrode, to charge the polymeric melt or polymeric solution sprayed by the nozzle (Figure 1b). Another method is to combine the above two methods (Figure 1c).

A variety of methods can be applied in spraying a 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 and then spraying the respective polymeric solutions sporadically and continually to get a multi-layered polymer electrolyte matrix. Figures 2a and 2b illustrate the fabrication of a polymer matrix using a spray machine.

Figure 2a illustrates the fabrication method by spraying all together using a nozzle to get a polymer matrix, and Figure 2b illustrates the fabrication method by spraying sporadically and continually using separately installed nozzles to get a multi-layered polymer matrix.

The polymer electrolyte matrix using two or more polymers can be obtained by the following methods. One method is that two or more polymers are dissolved in a mixtures of a suitable plasticizer and organic electrolyte solution, and the obtained solution is filled into a barrel of a spray machine and sprayed using a nozzle, to fabricate the polymer electrolyte matrix. Another method is that two or more polymers are dissolved respectively in a mixture of a suitable plasticizer and organic electrolyte solution, and the obtained solutions are filled into separate barrels of a spray machine respectively and sprayed using different nozzles, to fabricate the polymer electrolyte matrix.

The composite polymer electrolyte is obtained by injecting a polymer electrolyte solution into the polymer electrolyte matrix fabricated by a spray method. In more detail, a polymer is dissolved in a mixture of an organic electrolyte solution and a plasticizer to give a polymer electrolyte solution, and the obtained polymer electrolyte solution is injected into the polymer electrolyte matrix by die-casting. The weight ratio of a polymer, plasticizer and organic electrolyte solution used for the polymer electrolyte solution is preferably in the range of 1 : 1 - 20 : 1 - 20, and the kinds are the same as mentioned before.

The present invention relates to a lithium secondary battery comprising the composite polymer electrolyte, and Figures 3a to 3c illustrate the fabrication process in detail. Figure 3a illustrates a fabrication process for a battery comprising inserting a composite polymer electrolyte, obtained by incorporating a polymer electrolyte solution into a polymer electrolyte matrix 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 fabrication process for a battery comprising coating a composite polymer electrolyte onto both sides of a cathode or anode; adhering an electrode having opposite polarity to the coated electrode onto the composite 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 fabrication process for a battery comprising coating a composite polymer electrolyte onto both sides of one of two electrodes and onto one side of the other electrode respectively; adhering the electrodes closely together so the composite 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.

The anode and cathode for the lithium secondary battery are fabricated in the same way as in the conventional method, such as 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 anode active material consists of a material selected from the group consisting of graphite, cokes, hard carbon, tin oxide and lithiated compounds thereof. The cathode active material is a material selected from the group consisting of LiCIO₂, LiNiO₂, LiNiCoO₂, LiMn₂O₄, V₂O₅ and V₆O₁₃. Metallic lithium or lithium alloys can also be used for the anode in the present invention.

Examples

The present invention will be described in more detail by way of the following examples, but those examples are given for the purpose to illustrate the present invention, not to limit the scope of it. Example 1

1-1) Fabrication of a polymer electrolyte matrix To a mixture of 100g of 1 M LiPF₆ solution in EC-DMC and10g of propylene carbonate (hereinafter referred to as "PC") as a plasticizer, 20g of polyvinylidenefluoride (Kynar 761) was added. 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 discharged onto a metal plate at a constant rate, to fabricate a polymer electrolyte matrix

having a thickness of 50μm.

1-2) Fabrication of a composite polymer electrolyte

To a mixture of 15g of 1M LiPF₆ solution in EC-DMC and 1g of DMA solution as a plasticizer, 0.5g of PAN (prepared by Polyscience Company, molecular weight of about 150,000), 2g of polyvinylidenedifluoride (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added. The resulting mixture was blended for 12 hours and then heated at

130°C for one hour to give a clear polymer electrolyte solution. When a

viscosity of several thousands cps suitable for casting was obtained, the polymer electrolyte solution was cast onto the polymer electrolyte matrix fabricated in Example 1-1 by die-casting, to fabricate a composite polymer electrolyte in which the polymer electrolyte solution was incorporated into the polymer electrolyte matrix.

1-3) Fabrication of a lithium secondary battery The composite polymer electrolyte fabricated in Example 1-2 was inserted between a graphite anode and a LiCoO₂ cathode, and the resulting

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

were welded on to the electrodes and the laminated plate was inserted into a vacuum casing. A 1M LiPF₆ solution in EC-DMC was injected into the vacuum casing, and then the vacuum casing was vacuum-sealed to fabricate a lithium secondary battery. Example 2

2-1) 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 resulting polymeric solution was filled into a barrel of a spray machine and discharged onto both sides of a graphite anode at a constant rate using a nozzle, to fabricate a graphite anode coated with a polymer

electrolyte matrix film having a thickness of 50 μm.

2-2) To a mixture of 15g of 1 M LiPF₆ solution in EC-DMC and 1g of DMA solution as a plasticizer, 0.5g of PAN (prepared by Polyscience Company, molecular weight of about 150,000), 2g of polyvinylidenedifluoride (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added. The resulting mixture was blended for 12 hours and then heated

at 130°C for one hour to give a clear polymer electrolyte solution. When a

viscosity of several thousands cps suitable for casting was obtained, the polymer electrolyte solution was cast onto the polymer electrolyte matrix obtained in Example 2-1 by die-casting, to generate a composite polymer electrolyte on both sides of the graphite anode 2-3) A LiCoO₂ cathode was adhered onto the composite polymer electrolyte obtained in Example 2-2. The resulting plate was cut so as to be

3 cm x 4 cm in size and laminated. Terminals were welded on to the

electrodes, and the laminated plate was inserted into a vacuum casing. A 1M LiPF₆ solution in EC-DMC was injected into the vacuum casing, and the casing was then vacuum-sealed to fabricate 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 discharged onto one side of a LiCoO₂ cathode at a constant rate using a nozzle charged with 9kV, to fabricate a LiCoO₂ cathode coated with

a polymer electrolyte matrix film having a thickness of 50 μm on one side of

it. 3-2) To 15g of 1M LiPF₆ solution in EC-DMC and 1g of DMA solution as a plasticizer, 0.5g of PAN (prepared by Polyscience Company, molecular weight of about 150,000), 2g of polyvinylidenedifluoride (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added. The

resulting mixture was blended for 12 hours and then heated at 130°C for one

hour to give a clear polymer electrolyte solution. When a viscosity of several thousands cps suitable for casting was obtained, the polymer electrolyte solution was cast onto the polymer electrolyte matrix obtained in Example 3-1 by die-casting, to generate a composite polymer electrolyte on one side of a LiCo0₂ cathode.

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

into one body by heat lamination at 110°C, followed by cutting so as to be 3

cm x 4 cm in size and then laminated. Terminals were welded on to the

electrodes, and then the laminated plate was inserted into a vacuum casing. A 1 M LiPFg solution in EC-DMC was injected into the casing, and the casing was then vacuum-sealed to fabricate a lithium secondary battery. Example 4 4-1) Three mixtures, in which 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 dissolved in a mixture of 100g of 1M LiPF₆ solution in EC-DMC and 10g of plasticizer PC, were prepared in separate bowls. The resulting mixtures were

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

polymeric solutions were filled into separate barrels of spray machine respectively and then 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 having a thickness of 50 μm.

4-2) 2g of an oligomer of polyethylene glycol diacrylate (hereinafter referred to as "PEGDA", prepared by Aldrich Company, molecular weight of 742) and 3g of polyvinylidenedifluoride (Atochem Kynar 761) were added to 20g of 1 M LiPF₆ solution in EC-DMC. The resulting mixture was blended enough to be homogeneous for 3 hours and then cast onto the polymer electrolyte matrix obtained in Example 4-1. An ultraviolet lamp having a power of 100W was irradiated onto the polymer electrolyte matrix for about 1.5 hours in order to induce polymerization of the oligomer, to fabricate a composite polymer electrolyte in which a polymer electrolyte was incorporated into a polymer electrolyte matrix.

4-3) The composite polymer electrolyte fabricated in Example 4-2 was inserted between a graphite anode and a LiCoO₂ cathode, and then the

resulting plates were cut so as to be 3 cm x 4 cm in size and laminated.

Terminals were welded on to the electrodes, and the laminated plate was inserted into a vacuum casing. A 1 M LiPF₆ solution in EC-DMC was injected into the vacuum casing, and then the vacuum casing was vacuum-sealed to fabricate 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 vacuum-sealing the casing.

Comparative example 2

According to the conventional preparation method of a gel-polymer electrolyte, 9g of 1 M LiPF₆ solution in EC-PC was added to 3g of PAN. The

resulting mixture was blended for 12 hours and then heated at 130°C for 1

hour to give a clear polymeric solution. When a viscosity of 10,000cps 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, a graphite anode, an electrolyte, a LiCoO₂ cathode, an electrolyte and a graphite anode, welding terminals on to 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 5

Charge/discharge characteristics of the lithium secondary batteries obtained in Examples 1 - 4 and Comparative Examples 1 and 2 were tested, and Figure 4 shows the results. The tests for obtaining the charge/discharge characteristics were performed by a charge/discharge method of, after charging the batteries with a C/2 constant current and 4.2V constant voltage, discharging with a C/2 constant current, and the electrode capacities and cycle life based on the cathode were tested. Figure 4 shows that the electrode capacities and cycle life of the lithium secondary batteries of Examples 1 - 4 were improved compared to the lithium secondary batteries of Comparative Examples 1 and 2. Example 6

Low- and high-temperature characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2 were tested, and Figures 5a and 5b illustrate the results (wherein Figure 5a is for Example 1 and Figure 5b is for Comparative Example 2). The tests for obtaining the low- and high- temperature characteristics of the lithium secondary batteries were performed by a charge/discharge method of, after charging the lithium batteries with a C/2 constant current and 4.2 V constant voltage, discharging with a C/5 constant current. Figures 5a and 5b show that the low- and high-temperature characteristics of the lithium secondary battery of Example 1 were better than those of the battery of Comparative Example 2. In particular, it shows that the

battery of Example 1 had an outstanding characteristic of 91 % even at -10°C.

Example 7 High rate discharge characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2 were tested, and Figures 6a and 6b illustrate the results (wherein Figure 6a is for Example 1 and Figure 6b is for Comparative Example 2). The tests for obtaining the high rate discharge characteristics of the lithium secondary batteries were performed by a charge/discharge method of, after charging the lithium batteries with a C/2 constant current and 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 1 exhibited capacities such as 99% at C/2 discharge, 96% at 1C discharge and 90% at 2C discharge based on the value of C/5 discharge. However, the lithium secondary battery of Comparative Example 2 exhibited low capacities such as 87% at 1 C discharge and 56% at 2C discharge based on the value of C/5 discharge. Accordingly, it was discovered that the high rate discharge characteristic of the lithium secondary battery of Example 1 was better than that of the lithium secondary battery of Comparative Example 2.

Claims

1. A composite polymer electrolyte comprising a polymer electrolyte matrix in particulate or fibrous form or a combination thereof having a diameter of 1-3000nm and an organic electrolyte solution dissolving a polymer and a lithium salt incorporated into the polymer electrolyte matrix.

2. The composite polymer electrolyte according to claim 1 , wherein the polymer electrolyte matrix is fabricated by a spray method.

3. The composite polymer electrolyte according to claim 2, wherein the spray method is an electrostatic induction spray method.

4. The composite polymer electrolyte according to claim 1 , wherein the

polymer electrolyte matrix has a thickness of 1 μm - 100 μm.

5. The composite polymer electrolyte according to claim 1 , wherein a polymer for forming the polymer electrolyte matrix is 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(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) and mixtures thereof.

6. The composite polymer electrolyte according to claim 1 , wherein the polymer incorporated into the polymer electrolyte matrix is 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(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), polyetylene glycol diacrylate, polyethylene glycol dimethacrylate or mixtures thereof.

7. The composite polymer electrolyte according to claim 1 , wherein the lithium salt incorporated into the polymer electrolyte matrix is LiPF₆, LiCIO₄, LiAsF₆, LiBF₄ or LiCF₃SO₃.

8. The composite polymer electrolyte according to claim 1 , wherein an organic solvent used in the organic electrolyte solution is ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or mixtures thereof.

9. The composite polymer electrolyte according to claim 8, wherein the organic solvent further comprises methyl acetate, methyl propionate, ethyl

acetate, ethyl propionate, butylene carbonate, γ-butyrolactone, 1 ,2-

dimethoxyethane, 1 ,2-dimethoxyethane, dimethylacetamide, tetrahydrofuran or mixtures thereof in order to improve a low-temperature characteristic.

10. The composite polymer electrolyte according to claim 1 , wherein the composite polymer electrolyte further comprises a filling agent.

11. The composite polymer electrolyte according to claim 10, wherein the filling agent is selected from the group consisting of TiO₂, BaTiO₃, Li₂O, LiF, LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃, LiAIO₂, SiO₂, AI₂O₃, PTFE and mixtures thereof, and its content is not greater than 20wt% (excluding 0%) of the total composite polymer electrolyte.

12. A fabrication method of a composite polymer electrolyte comprising: a step of obtaining a polymeric solution by dissolving a polymer or polymeric mixture in a mixture of a plasticizer and an organic electrolyte solution; a step of filling the obtained polymeric solution into a barrel of a spray machine and then discharging the polymeric solution onto a substrate including a metal plate, a Mylar film and electrodes with a nozzle to fabricate a polymer electrolyte matrix; and a step of injecting a polymer electrolyte solution in which a polymer is dissolved in a mixture of a plasticizer and an organic electrolyte solution into the polymer electrolyte matrix.

13. A fabrication method of a composite polymer electrolyte comprising: a step of dissolving two or more polymers in a mixture of a plasticizer and an organic electrolyte solution in different bowls respectively, to obtain two or more clear polymeric solutions; a step of filling the obtained polymeric solutions into different barrels of a spray machine respectively and then discharging the polymeric solutions onto a substrate including a metal plate, a Mylar film and electrodes with different nozzles in order to fabricate polymer electrolyte matrices; and a step of injecting a polymer electrolyte solution in which polymer is dissolved in a mixture of a plasticizer and an organic electrolyte solution into the polymer electrolyte matrices.

14. The fabrication method of a composite polymer electrolyte according to claim 12 or 13, wherein the plasticizer is 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, dimethylsulfoxide, ethylene carbonate, ethylmethyl carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2- pyrrolidone, polyethylenesulforane, tetraethylene glycol dimethyl ether, acetone, alcohol and mixtures thereof.

15. The fabrication method of a composite polymer electrolyte according to claim 14, wherein the weight ratio of the polymer to the plasticizer is 1 : 1 - 1 : 20 and the weight ratio of the polymer to the organic electrolyte solution is 1 : 1 - 1 : 20.

16. The fabrication method of a composite polymer electrolyte according to claim 15, wherein the polymer electrolyte solution is prepared by, after mixing the polymer, the plasticizer and an organic electrolyte solution, stirring

the mixture at 20 - 150°C for 30 minutes - 24 hours.

17. A lithium secondary battery comprising the composite polymer electrolyte according to claim 1.

18. A fabrication method of a lithium secondary battery, comprising: inserting the composite polymer electrolyte according to claim 1 between a cathode and an anode; 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 casing.

19. A fabrication method of a lithium secondary battery, comprising: inserting the composite polymer electrolyte according to claim 1 between a cathode and an anode; making the electrolyte and 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 sealing the casing.

20. A fabrication method of a lithium secondary battery, comprising: coating the composite polymer electrolyte according to claim 1 onto both sides of a cathode or an anode; adhering an electrode having opposite polarity to the coated electrode onto the composite polymer electrolyte; 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.

21. A fabrication method of a lithium secondary battery, comprising: coating the composite polymer electrolyte according to claim 1 onto both sides of a cathode or an anode; adhering an electrode having opposite polarity to the coated electrode onto the composite polymer electrolyte; making the electrolytes and 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.

22. A fabrication method of a lithium secondary battery, comprising: coating the composite polymer electrolyte according to claim 1 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 composite 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.

23. A fabrication method of a lithium secondary battery, comprising: coating the composite polymer electrolyte according to claim 1 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 composite polymer electrolytes to each other; making the electrolytes and 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 sealing the battery casing.