WO2001089021A1 - A composite polymer electrolyte, a lithium secondary battery comprising the composite polymer electrolyte and their fabrication methods - Google Patents

A composite polymer electrolyte, a lithium secondary battery comprising the composite polymer electrolyte and their fabrication methods Download PDF

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Publication number
WO2001089021A1
WO2001089021A1 PCT/KR2000/000499 KR0000499W WO0189021A1 WO 2001089021 A1 WO2001089021 A1 WO 2001089021A1 KR 0000499 W KR0000499 W KR 0000499W WO 0189021 A1 WO0189021 A1 WO 0189021A1
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Prior art keywords
polymer electrolyte
composite polymer
solution
poly
composite
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PCT/KR2000/000499
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French (fr)
Inventor
Kyung Suk Yun
Byung Won Cho
Seong Mu Jo
Wha Seop Lee
Won Il Cho
Kun You Park
Hyung Sun Kim
Un Seok Kim
Seok Ku Ko
Sung Won Choi
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Korea Institute Of Science And Technology
Chun, Suk, Won
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Priority to PCT/KR2000/000499 priority Critical patent/WO2001089021A1/en
Publication of WO2001089021A1 publication Critical patent/WO2001089021A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0015—Electro-spinning characterised by the initial state of the material
    • D01D5/003—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0085—Immobilising or gelification of electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0088—Composites
    • H01M2300/0091—Composites in the form of mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/14—Cells with non-aqueous electrolyte
    • H01M6/16—Cells with non-aqueous electrolyte with organic electrolyte
    • H01M6/162—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte
    • H01M6/168—Cells with non-aqueous electrolyte with organic electrolyte characterised by the electrolyte by additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/14—Cells with non-aqueous electrolyte
    • H01M6/18—Cells with non-aqueous electrolyte with solid electrolyte
    • H01M6/188—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/40—Printed batteries, e.g. thin film batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a composite polymer electrolyte, a lithium secondary battery using the same, and to its fabrication method.
  • Lithium secondary batteries are typified by a lithium ion battery and a lithium polymer battery.
  • a lithium ion battery uses a polyethylene (hereinafter
  • PE polypropylene
  • PP polypropylene
  • 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.
  • PEO polyethylene oxide
  • K. M. Abraham et at. 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 polymer matrix.
  • A.S.Gozdz et al. discloses a polymer electrolyte of hybrid type polyvinylidenedifluoride (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 the advantages in that its compatibility with the 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 prepared in the atmosphere because the organic electrolyte solution is injected afterwards.
  • the fabrication process is intricate because when the polymer electrolyte is prepared, an extraction process of a plasticizer and an impregnation process of the organic electrolyte solution are required.
  • 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.
  • PMMA polymethylmethacrylate
  • PVC polyvinylchloride
  • Figure 1 is a photograph of the polymer electrolyte matrix of the present invention taken with a transmission electronic microscope.
  • Figures 2a - 2c are process flow diagrams illustrating fabrication processes of lithium secondary batteries according to the present invention.
  • Figure 3 is a graph showing charge and discharge characteristics of
  • Figure 4 is a graph showing low- and high-temperature characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2.
  • Figure 5 is a graph showing high-rate discharge characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2.
  • the present invention relates to a composite polymer electrolyte comprising a polymer electrolyte matrix having a diameter of 1 nm ⁇ 3000 nm and a polymer electrolyte.
  • the present invention relates to a composite polymer electrolyte comprising a polymer electrolyte matrix which is made of super fine fibers having a diameter of 1 nm ⁇ 3000 nm and a polymer electrolyte incorporated into the polymer electrolyte matrix.
  • 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 and a lithium salt. The polymer electrolyte matrix can be fabricated by dissolving a polymer for forming a matrix in a mixture of an organic electrolyte solution and a plasticizer, and then by generating the resulting solution (hereinafter referred to as "polymeric solution”) into a fibrous form with an electrospinning apparatus.
  • Polymer electrolyte solution means a solution in which a polymer incorporated into the polymer electrolyte matrix is dissolved in a mixture of an organic electrolyte solution and a plasticizer.
  • Polymer electrolyte generically refers the organic electrolyte solution and the polymers, which are incorporated into the polymer matrix.
  • a polymer electrolyte matrix constructed with super fine fibers has a structure in which super fine fibers with a diameter of 1 ⁇ 3000nm are grouped disorderly and three-dimensionally. Due to the small diameter of the fibers, the ratio of surface area to volume and the void ratio are very high compared to those of a conventional matrix. Accordingly, due to the high void ratio, the amount of electrolyte incorporated is large and the ionic conductivity can be 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, if a polymer electrolyte matrix is fabricated by electrospinning, it has an advantage in that it can be prepared in the form of a film directly.
  • electrolyte matrix it is preferable to have a thickness of 1 ⁇ m -100 ⁇ m. It is more preferable to have a thickness of 5 ⁇ m - 70 ⁇ m and most preferable to
  • the fibrous material has a thickness of 10 ⁇ m - 50 ⁇ m. Furthermore, the diameter of the fibrous
  • polymer for forming the polymer electrolyte matrix is preferably adjusted to a range of 1 ⁇ 3000nm, more preferably to a range of 10nm ⁇ 1000nm, and most preferably to a range of 50nm ⁇ 500nm.
  • Polymers for forming the polymer electrolyte matrix are not limited, on condition that they can be formed into super fine fibers; in more particularity that they can be formed into super fine fibers by electrospinning.
  • Examples 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-
  • polymers used in the polymer electrolyte include 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,
  • 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.
  • organic electrolyte solution used in the polymer electrolyte matrix and the polymer electrolyte is an organic solvent dissolving a lithium salt.
  • examples of the organic solvent can include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or mixtures thereof.
  • the lithium salt used in the organic electrolyte solution can be exemplified as LiPF 6 , LiCIO 4 , LiAsF 6 , LiBF 4 or LiCF 3 SO 3 , more preferably as LiPF 6 , but not limited to these.
  • Examples of the pasticizer used in the preparation of the polymer electrolyte matrix and the polymer electrolyte 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, ethymethyl carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylenesulforane, tetraethylene glycol dimethyl ether, acetone, alcohol or mixtures thereof.
  • plasticizers there is no specific limitation on the kinds of plasticizers because they can be removed while fabricating a battery.
  • the composite polymer electrolyte of the present invention can further include a filling agent in order to improve porosity and mechanical strength.
  • a filling agent may include substances, such as TiO 2 , BaTiO 3 , Li 2 O, LiF, LiOH, Li 3 N, BaO, Na 2 O, MgO, Li 2 CO 3 , LiAIO 2 , SiO 2 , AI 2 O 3 , PTFE or mixtures thereof.
  • the content of the filling agent is not greater than 20wt% of the total composite polymer electrolyte.
  • the present invention relates to a method for fabricating the composite polymer electrolyte.
  • the method comprises the steps of obtaining a polymeric solution in which a polymer is dissolved in a mixture of a plasticizer and an organic electrolyte solution, fabricating a polymer electrolyte matrix with the obtained polymeric solution by electrospinning and injecting a polymer electrolyte solution into the obtained polymer electrolyte matrix.
  • the step of obtaining a polymeric solution is achieved by adding a polymer to a mixture of a plasticizer and an organic electrolyte solution and then raising the temperature of the resulting mixture to obtain a clear polymeric solution.
  • the plasticizer is not particularly limited on condition that it can dissolve polymers substantially and be applied to electrospinning. Solvents which might influence on the characteristics of a battery can even be used because they are removed while fabricating the polymer electrolyte matrix by electrospinning.
  • the fabrication of the polymer electrolyte matrix of the present invention is generally achieved by electrospinning.
  • a polymer electrolyte matrix can be fabricated by filling the polymeric solution for forming the polymer electrolyte matrix into a barrel of an electrospinning apparatus, applying a high voltage to a nozzle of the electrospinning apparatus and discharging the polymeric solution onto a metal substrate or a Mylar film through the nozzle at a constant rate.
  • the thickness of the polymer electrolyte matrix can be optionally adjusted by varying the discharging rate and time.
  • the preferable thickness range is within 1 - 100 ⁇ m. If
  • the above-described method is used, not just the polymer fibers for constructing the matrix, but a polymer electrolyte matrix built up three- dimensionally with fibers having a diameter of 1 ⁇ 3000nm can be fabricated directly. If it is necessary, a polymer electrolyte matrix can be fabricated onto electrodes directly. Accordingly, although the above-mentioned method is a fabrication in fibrous form, no additional apparatus is required and an economical efficiency can be achieved by simplifying the fabrication process because the final product can be fabricated not just as fibers but as a film directly.
  • a polymer electrolyte matrix using two or more polymers can be obtained by the following two fabrication methods:
  • the resulting polymeric solution is filled into a barrel of an electrospinning apparatus and then discharged using a nozzle to fabricate a polymer electrolyte matrix in a state that polymer fibers consisting of two or more polymers are entangled with each other;
  • a composite polymer electrolyte is obtained by injecting a polymer electrolyte solution into the polymer electrolyte matrix fabricated by electrospinning.
  • it is prepared by dissolving a polymer for forming a polymer electrolyte in a mixture of a plasticizer and an organic electrolyte solution to obtain a polymer electrolyte solution, and then injecting the obtained polymer electrolyte solution into the polymer electrolyte matrix by a die-casting.
  • the weight ratio of the polymer to the organic solvent used for polymer electrolyte solution is preferably in the range of 1 : 1 - 1 : 20.
  • the weight ratio of the polymer to the plasticizer is preferably in the range of 1 : 1 - 1 : 20.
  • the present invention also relates to a fabrication method of a lithium secondary battery comprising the above-described composite polymer electrolyte.
  • Figures 2a to 2c illustrate the fabrication processes for lithium secondary batteries of the present invention in detail.
  • Figure 2a illustrates a fabrication process for a battery comprising inserting a composite polymer electrolyte fabricated by incorporating a polymer electrolyte solution into a polymer electrolyte matrix fabricated by electrospinning between an anode and a cathode, 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 then finally sealing the casing.
  • Figure 2b illustrates a fabrication process for a battery comprising coating a composite polymer electrolyte onto both sides of an anode or a cathode, adhering an electrode having the 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 then finally sealing the battery casing.
  • Figure 2c 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, 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 then finally sealing the battery
  • the anode and cathode used for the lithium secondary battery of the present invention are prepared by mixing an appropriate amount of active materials, a conducting material and a bonding agent with an organic solvent, casting the resulting mixture on both sides of a copper or aluminum foil plate grid, and then dry-compressing the plate.
  • the anode active material comprises one or more materials selected from the group consisting of graphite, cokes, hard carbon, tin oxide and lithiated compounds thereof.
  • the cathode active material comprises one or more materials selected from the group consisting of LiCIO 2 , LiNiO 2 , LiNiCoO 2 , LiMn 2 O 4 , V 2 O 5 , and V 6 O 13 .
  • metallic lithium or lithium alloys can be used as an anode of the present invention.
  • polymeric solution was filled into a barrel of an electrospinning apparatus and discharged onto a metal plate at a constant rate using a nozzle charged with
  • the polymer electrolyte solution was cast onto the polymer matrix obtained 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.
  • Example 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 LiCoO 2 cathode, and the resulting
  • Example 2 A 1M LiPF 6 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 A 1M LiPF 6 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 2-1 When a viscosity of several thousands cps suitable for casting was obtained, the polymer electrolyte solution was cast onto the polymer matrix obtained in Example 2-1 by die-casting, to generate a composite polymer electrolyte on both sides of the graphite. 2-3) A LiCoO 2 cathode was adhered onto the composite polymer electrolyte obtained in Example 2-2. The resulting plate was cut so as to be
  • the resulting polymeric solution was filled into a barrel of an electrospinning apparatus and discharged onto one side of a LiCoO 2 cathode at a constant rate using a nozzle charged with 9kV, to fabricate a LiCoO 2 cathode coated with a polymer electrolyte matrix film
  • the polymer electrolyte solution was cast onto the polymer matrix obtained in Example 3-1 by die-casting, to generate a composite polymer electrolyte on one side of the LiCoO 2 cathode.
  • Example 3-2 The LiCoO 2 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
  • Example 4 20g of polyvinylidenefluoride, 20g of PAN (prepared by
  • the obtained polymeric solutions were filled into separate barrels of an electrospinning apparatus and discharged onto both sides of a graphite anode using different nozzles charged with 9kV respectively at a constant rate, to fabricate a graphite anode coated with a
  • polymer electrolyte matrix film having a thickness of 50 ⁇ m.
  • An ultraviolet lamp having power of 100W was irradiated onto the polymer electrolyte matrix for about 1.5 hours in order to induce a polymerization of the oligomer, to fabricate a composite polymer electrolyte in which the polymer electrolyte solution was incorporated into the polymer matrix.
  • Example 4-3 The composite polymer electrolyte fabricated in Example 4-2 was inserted between a graphite anode and a LiCoO 2 cathode. The resulting composite polymer electrolyte fabricated in Example 4-2 was inserted between a graphite anode and a LiCoO 2 cathode. The resulting composite polymer electrolyte fabricated in Example 4-2 was inserted between a graphite anode and a LiCoO 2 cathode. The resulting
  • 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 LiPF 6 solution in EC-DMC into the casing, and then finally vacuum-sealing the casing.
  • a lithium secondary battery was fabricated by laminating, in order, a graphite anode, an electrolyte, a LiCoO 2 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 LiPF 6 solution in EC-DMC into the casing, and then finally vacuum-sealing the casing.
  • Figures 4a and 4b illustrate the results (wherein Figure 4a is for Example 1 and Figure 4b 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 charging the lithium batteries with a C/2 constant current and 4.2 V constant voltage, and then discharging with a C/5 constant current.
  • Figures 4a and 4b show that the low- and high-temperature characteristics of the lithium secondary battery of Example 1 are better than those of the battery of Comparative Example 2. In particular, it shows that the
  • Example 7 High rate discharge 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 high rate discharge characteristics of the lithium secondary batteries were performed by a charge/discharge method of charging the lithium batteries with a C/2 constant current and 4.2 V constant voltage, and then discharging while varying the current to C/5, C/2.1C and 2C constant currents.
  • 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.
  • the lithium secondary battery of Comparative Example 2 exhibited low capacities such as 87% at 1C 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.

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 super fine fibrous porous polymer electrolyte matrix with particles having diameter of 1 - 3000 nm, polymers and lithium salt-dissolved organic electrolyte solutions incorporated into the porous polymer electrolyte 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. 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 at first 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 at. 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 polymer matrix. It has the 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 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 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 polyvinylidenedifluoride (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 the advantages in that its compatibility with the 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 prepared in the atmosphere because the organic electrolyte solution is injected afterwards. However, it has a disadvantage in that the fabrication process is intricate because when the polymer electrolyte is prepared, 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 compatibility with an organic electrolyte solution are good. However, its mechanical strength is very poor, and accordingly it is unfeasible for a lithium polymer battery.
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 presented in J. Electrochem. Soc, 140, L96 (1993) by M. Alamgir and K. M. Abraham. However, it has problems in that its low-temperature characteristic is poor and its contact resistance is high.
Accordingly, development of a polymer electrolyte having 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 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 advantages of a simple fabrication process, easiness in scaling-up of the 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
Figure 1 is a photograph of the polymer electrolyte matrix of the present invention taken with a transmission electronic microscope.
Figures 2a - 2c are process flow diagrams illustrating fabrication processes of lithium secondary batteries according to the present invention. Figure 3 is a graph showing charge and discharge characteristics of
the lithium secondary batteries of Examples 1-4 and Comparative Examples 1 and 2.
Figure 4 is a graph showing low- and high-temperature characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2.
Figure 5 is a graph showing high-rate discharge characteristics of the lithium secondary batteries of Example 1 and Comparative Example 2.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a composite polymer electrolyte comprising a polymer electrolyte matrix having a diameter of 1 nm ~ 3000 nm and a polymer electrolyte. In more detail, the present invention relates to a composite polymer electrolyte comprising a polymer electrolyte matrix which is made of super fine fibers having a diameter of 1 nm ~ 3000 nm and a polymer electrolyte incorporated into the polymer electrolyte matrix.
Hereinafter, "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 and a lithium salt. The polymer electrolyte matrix can be fabricated by dissolving a polymer for forming a matrix in a mixture of an organic electrolyte solution and a plasticizer, and then by generating the resulting solution (hereinafter referred to as "polymeric solution") into a fibrous form with an electrospinning apparatus. "Polymer electrolyte solution" means a solution in which a polymer incorporated into the polymer electrolyte matrix is dissolved in a mixture of an organic electrolyte solution and a plasticizer. "Polymer electrolyte" generically refers the organic electrolyte solution and the polymers, which are incorporated into the polymer matrix.
As depicted in Figure 1 , a polymer electrolyte matrix constructed with super fine fibers has a structure in which super fine fibers with a diameter of 1 ~ 3000nm are grouped disorderly and three-dimensionally. Due to the small diameter of the fibers, the ratio of surface area to volume and the void ratio are very high compared to those of a conventional matrix. Accordingly, due to the high void ratio, the amount of electrolyte incorporated is large and the ionic conductivity can be 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, if a polymer electrolyte matrix is fabricated by electrospinning, it has an advantage in that it can be prepared in the form of a film directly.
Although there is no specific limitation on the thickness of the polymer
electrolyte matrix, it is preferable to have a thickness of 1 μm -100 μm. It is more preferable to have a thickness of 5 μm - 70 μm and most preferable to
have a thickness of 10 μm - 50 μm. Furthermore, the diameter of the fibrous
polymer for forming the polymer electrolyte matrix is preferably adjusted to a range of 1 ~ 3000nm, more preferably to a range of 10nm ~ 1000nm, and most preferably to a range of 50nm ~ 500nm.
Polymers for forming the polymer electrolyte matrix are not limited, on condition that they can be formed into super fine fibers; in more particularity that they can be formed into super fine fibers by electrospinning. Examples 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.
Examples of the polymers used in the polymer electrolyte include 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,
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. An example of the organic electrolyte solution used in the polymer electrolyte matrix and the polymer electrolyte is an organic solvent dissolving a lithium salt. In more particularly, examples of the organic solvent can include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or mixtures thereof. In order to improve the low-temperature characteristic of the battery, a 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 further added. The lithium salt used in the organic electrolyte solution can be exemplified as LiPF6, LiCIO4, LiAsF6, LiBF4 or LiCF3SO3, more preferably as LiPF6, but not limited to these.
Examples of the pasticizer used in the preparation of the polymer electrolyte matrix and the polymer electrolyte 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, ethymethyl carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylenesulforane, tetraethylene glycol dimethyl ether, acetone, alcohol or mixtures thereof. However, there is no specific limitation on the kinds of plasticizers because they can be removed while fabricating a battery.
The composite polymer electrolyte of the present invention can further include a filling agent in order to improve porosity and mechanical strength. Examples of a filling agent may include substances, such as TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, MgO, Li2CO3, LiAIO2, SiO2, AI2O3, PTFE or mixtures thereof. Generally, the content of the filling agent is not greater than 20wt% of the total composite polymer electrolyte.
The present invention relates to a method for fabricating the composite polymer electrolyte. The method comprises the steps of obtaining a polymeric solution in which a polymer is dissolved in a mixture of a plasticizer and an organic electrolyte solution, fabricating a polymer electrolyte matrix with the obtained polymeric solution by electrospinning and injecting a polymer electrolyte solution into the obtained polymer electrolyte matrix.
The step of obtaining a polymeric solution is achieved by adding a polymer to a mixture of a plasticizer and an organic electrolyte solution and then raising the temperature of the resulting mixture to obtain a clear polymeric solution. The plasticizer is not particularly limited on condition that it can dissolve polymers substantially and be applied to electrospinning. Solvents which might influence on the characteristics of a battery can even be used because they are removed while fabricating the polymer electrolyte matrix by electrospinning.
The fabrication of the polymer electrolyte matrix of the present invention is generally achieved by electrospinning. In more detail, a polymer electrolyte matrix can be fabricated by filling the polymeric solution for forming the polymer electrolyte matrix into a barrel of an electrospinning apparatus, applying a high voltage to a nozzle of the electrospinning apparatus and discharging the polymeric solution onto a metal substrate or a Mylar film through the nozzle at a constant rate. The thickness of the polymer electrolyte matrix can be optionally adjusted by varying the discharging rate and time.
As mentioned before, the preferable thickness range is within 1 - 100 μm. If
the above-described method is used, not just the polymer fibers for constructing the matrix, but a polymer electrolyte matrix built up three- dimensionally with fibers having a diameter of 1 ~ 3000nm can be fabricated directly. If it is necessary, a polymer electrolyte matrix can be fabricated onto electrodes directly. Accordingly, although the above-mentioned method is a fabrication in fibrous form, no additional apparatus is required and an economical efficiency can be achieved by simplifying the fabrication process because the final product can be fabricated not just as fibers but as a film directly.
A polymer electrolyte matrix using two or more polymers can be obtained by the following two fabrication methods:
1) After dissolving two or more polymers in a mixture of a plasticizer and an organic solvent, the resulting polymeric solution is filled into a barrel of an electrospinning apparatus and then discharged using a nozzle to fabricate a polymer electrolyte matrix in a state that polymer fibers consisting of two or more polymers are entangled with each other; and
2) After dissolving two or more polymers in mixtures of a plasticizer and an organic electrolyte solution in separate bowls respectively, the resulting polymeric solutions are filled into different barrels of an electrospinning apparatus respectively and then discharged using different nozzles to fabricate polymer electrolyte matrices in a state that the respective polymer fibers are entangled with each other.
A composite polymer electrolyte is obtained by injecting a polymer electrolyte solution into the polymer electrolyte matrix fabricated by electrospinning. In more detail, it is prepared by dissolving a polymer for forming a polymer electrolyte in a mixture of a plasticizer and an organic electrolyte solution to obtain a polymer electrolyte solution, and then injecting the obtained polymer electrolyte solution into the polymer electrolyte matrix by a die-casting.
The weight ratio of the polymer to the organic solvent used for polymer electrolyte solution is preferably in the range of 1 : 1 - 1 : 20. The weight ratio of the polymer to the plasticizer is preferably in the range of 1 : 1 - 1 : 20.
The present invention also relates to a fabrication method of a lithium secondary battery comprising the above-described composite polymer electrolyte. Figures 2a to 2c illustrate the fabrication processes for lithium secondary batteries of the present invention in detail. Figure 2a illustrates a fabrication process for a battery comprising inserting a composite polymer electrolyte fabricated by incorporating a polymer electrolyte solution into a polymer electrolyte matrix fabricated by electrospinning between an anode and a cathode, 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 then finally sealing the casing. Figure 2b illustrates a fabrication process for a battery comprising coating a composite polymer electrolyte onto both sides of an anode or a cathode, adhering an electrode having the 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 then finally sealing the battery casing. Figure 2c 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, 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 then finally sealing the battery
casing.
The anode and cathode used for the lithium secondary battery of the present invention are prepared by mixing an appropriate amount of active materials, a conducting material and a bonding agent with an organic solvent, casting the resulting mixture on both sides of a copper or aluminum foil plate grid, and then dry-compressing the plate. The anode active material comprises one or more materials selected from the group consisting of graphite, cokes, hard carbon, tin oxide and lithiated compounds thereof. The cathode active material comprises one or more materials selected from the group consisting of LiCIO2, LiNiO2, LiNiCoO2, LiMn2O4, V2O5, and V6O13. And, metallic lithium or lithium alloys can be used as an anode of 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 10g of propylene carbonate as a plasticizer and 100g of 1M LiPF6 solution in EC-DMC as an organic electrolyte solution, 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 resulting
polymeric solution was filled into a barrel of an electrospinning apparatus and discharged onto a metal plate at a constant rate using a nozzle charged with
9kV, to fabricate a polymer electrolyte matrix film having a thickness of 50μm.
1-2) Fabrication of a composite polymer electrolyte 0.5g of PAN (prepared by Polyscience Company, molecular weight of about 150,000), 2g of PVdF (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added to a mixture of 15g of 1M LiPF6 solution in EC-DMC and 1g of DMA solution (plasticizer). The resulting mixture was blended for 12 hours. After blending, the resulting mixture was 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 matrix obtained 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 onto the electrodes and the laminated plates were 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 10g of propylene carbonate (PC) as a plasticizer and 100g of 1 M LiPF6 solution in EC-DMC as an organic electrolyte solution, 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
resulting polymeric solution was filled into a barrel of an electrospinning apparatus and discharged onto both sides of a graphite anode at a constant rate using a nozzle charged with 9kV, 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 PVdF (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added. The resulting mixture was blended for 12 hours. After blending, the resulting
mixture was 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 matrix obtained in Example 2-1 by die-casting, to generate a composite polymer electrolyte on both sides of the graphite. 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 onto the
electrodes and the laminated plates were inserted into a vacuum casing. A 1 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 1M LiPF6 solution in EC-DMC and 10g of propylene carbonate 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 resulting polymeric solution was filled into a barrel of an electrospinning apparatus 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 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 PVdF (Atochem Kynar 761) and 0.5g of PMMA (prepared by Polyscience Company) were added. The resulting mixture was blended for 12 hours. After blending, the resulting
mixture was 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 matrix obtained in Example 3-1 by die-casting, to generate a composite polymer electrolyte on one side of the LiCoO2 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 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 vacuum-sealed to fabricate a lithium secondary battery. Example 4 4-1) 20g of polyvinylidenefluoride, 20g of PAN (prepared by
Polyscience Company, molecular weight of about 150,000) and 20g of polymethyl-methacrylate (prepared by Polyscience Company, molecular weight of 100,000) were added respectively to a mixture of 100g of 1M LiPF6 solution in EC-DMC and 10g of propylene carbonate as a plasticizer. The resulting mixtures were stirred at 100 °C for 2 hours to give three respective
clear polymeric solutions. The obtained polymeric solutions were filled into separate barrels of an electrospinning apparatus and discharged onto both sides of a graphite anode using different nozzles charged with 9kV respectively at a constant rate, to fabricate a graphite anode coated with a
polymer electrolyte matrix film 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 PVdF (Atochem Kynar 761) were added to 20g of 1 M LiPF6 solution in EC-EMC, and the resulting mixture was blended enough to be homogeneous for 3 hours. After blending, the obtained mixture was cast onto the polymer electrolyte matrix obtained in Example 4-1. An ultraviolet lamp having power of 100W was irradiated onto the polymer electrolyte matrix for about 1.5 hours in order to induce a polymerization of the oligomer, to fabricate a composite polymer electrolyte in which the polymer electrolyte solution was incorporated into the polymer matrix.
4-3) The composite polymer electrolyte fabricated in Example 4-2 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 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. 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 1 M 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 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 3 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 3 shows that the electrode capacities and cycle life of the lithium secondary batteries of Examples 1 - 8 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 4a and 4b illustrate the results (wherein Figure 4a is for Example 1 and Figure 4b 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 charging the lithium batteries with a C/2 constant current and 4.2 V constant voltage, and then discharging with a C/5 constant current. Figures 4a and 4b show that the low- and high-temperature characteristics of the lithium secondary battery of Example 1 are better than those of the battery of Comparative Example 2. In particular, it shows that the
battery of Example 2 has 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 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 high rate discharge characteristics of the lithium secondary batteries were performed by a charge/discharge method of charging the lithium batteries with a C/2 constant current and 4.2 V constant voltage, and then discharging while varying the current to C/5, C/2.1C and 2C constant currents. As depicted in Figures 5a and 5b, 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 1C 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 the form of super fine fibers having a diameter of 1 nm ~ 3000 nm and an organic electrolyte solution which dissolves a polymer and a lithium salt incorporated into the polymer electrolyte matrix.
2. The composite polymer electrolyte according to claim 1 , wherein the diameter of the polymer electrolyte matrix in the form of fibers is 10 nm ~ 1000 nm.
3. The composite polymer electrolyte according to claim 1 , wherein the polymer electrolyte matrix is fabricated by an electrospinning.
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 the 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], poly- ethyleneimide, polyethyleneoxide, polyethylenesuccinate, polyethylenesulfide, poly(oxymethylene-oligo-oxyethylene), polypropyleneoxide, polyvinyl acetate, polyacrylonitrile, poly(acrylonitrile-co-methylacrylate), polymethylmethacrylate, poly(methylmethacr late-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], poly-
ethyleneimide, polyethyleneoxide, polyethylenesuccinate, polyethylenesulfide, poly(oxymethylene-oligo-oxyethylene), polypropyleneoxide, polyvinyl acetate, polyacrylonitrile, poly(acrylonitrile-co-methylacrylate), polymethylmethacrylate, poly(methylmethacrylate-co-ethylacrylate), polyvinylchloride, poly(vinylidene- chloride-co-acrylonitrile), polyvinylldenedifluoride, poly(vinylidenefluoride-co- hexafluoropropylene), polyethylene glycol diacrylate, polyethylene glycol
dimethacrylate or mixtures thereof.
7. The composite polymer electrolyte according to claim 1 , wherein the lithium salt dissolved in the organic electrolyte solution for the polymer electrolyte matrix and polymer electrolyte is LiPF6, LiCIO4, LiAsF6, LiBF4 or LiCF3SO3.
8. The composite polymer electrolyte according to claim 1 , wherein an organic solvent used for the organic electrolyte solution for the polymer electrolyte matrix and the polymer electrolyte 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, UAIO2, 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 a polymer mixture which can be formed into fibers in a mixture of plasticizer and organic electrolyte solution; a step of filling the obtained polymeric solution into a barrel of an electrospinning apparatus and then discharging the polymeric solution onto a substrate including a metal plate, a Mylar film and electrodes using a nozzle charged with a high voltage, to generate a polymer electrolyte matrix in a state that the polymer electrolyte fibers are entangled with each other respectively; and a step of injecting a polymer electrolyte solution containing 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 obtaining two or more polymeric solutions by dissolving two or more polymers which can be formed into fibers in a mixture of a plasticizer and an organic solvent respectively; a step of filling the obtained polymeric solutions into different barrels of an electrospinning apparatus respectively and then discharging the polymeric solutions onto a substrate including a metal plate, a Mylar film and electrodes with different nozzles charged with a high voltage, to generate polymer electrolyte matrices in a state that the two or more polymer fibers are entangled with each other respectively; and a step of injecting a polymer electrolyte solution containing a polymer and an organic electrolyte solution into the polymer electrolyte matrices.
14. The 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, tetra- ethylene glycol dimethyl ether, acetone, alcohol and mixtures thereof.
15. The composite polymer electrolyte according to claim 14, wherein the weight ratio of the polymer to the plasticizer contained in the polymer solution and polymer electrolyte solution is in the range of 1 : 1 - 1 : 20 and the weight ratio of the polymer to the organic solvent is in the range of 1 : 1 - 1 : 20.
16. The composite polymer electrolyte according to claim 15, wherein the polymer solution and polymer electrolyte solution are prepared by stirring the organic electrolyte solution which dissolves the polymer, the plasticizer and the lithium salt.
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 an anode and a cathode; 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 an anode and a cathode; making the electrolyte 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 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 an anode and a cathode; 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 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.
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US8097136B2 (en) * 2004-02-19 2012-01-17 Niigata Tlo Corporation Hydrogen gas sensor
CN117175141A (en) * 2023-07-31 2023-12-05 中国科学院大连化学物理研究所 Lithium battery diaphragm and preparation method and application thereof

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CN117175141B (en) * 2023-07-31 2024-03-19 中国科学院大连化学物理研究所 Lithium battery diaphragm and preparation method and application thereof

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