WO2003065480A1 - Fibroid separator and energy storage device using the same - Google Patents

Fibroid separator and energy storage device using the same Download PDF

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Publication number
WO2003065480A1
WO2003065480A1 PCT/KR2002/000309 KR0200309W WO03065480A1 WO 2003065480 A1 WO2003065480 A1 WO 2003065480A1 KR 0200309 W KR0200309 W KR 0200309W WO 03065480 A1 WO03065480 A1 WO 03065480A1
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WO
WIPO (PCT)
Prior art keywords
fibroid
separator
polymer
film
polyvinyl
Prior art date
Application number
PCT/KR2002/000309
Other languages
French (fr)
Inventor
Jin-Young Hong
Hyo-Rang Kang
Original Assignee
Newturn Energy Co., Ltd.
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Publication date
Application filed by Newturn Energy Co., Ltd. filed Critical Newturn Energy Co., Ltd.
Publication of WO2003065480A1 publication Critical patent/WO2003065480A1/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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/44—Fibrous material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/454—Separators, membranes or diaphragms characterised by the material having a layered structure comprising a non-fibrous layer and a fibrous layer superimposed on one another
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/42—Acrylic resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/423—Polyamide resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/429—Natural polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/429—Natural polymers
    • H01M50/4295—Natural cotton, cellulose or wood
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H01M50/434—Ceramics
    • H01M50/437—Glass
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • 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

Definitions

  • the present invention relates to a separator and an energy storage device comprising the separator, and more particularly, to a fibroid separator applicable to the energy storage device such as lithium polymer secondary battery.
  • An electric reduction of an active material of a cathode and an oxidation of an active material of an anode is induced during discharging of a charged cell or battery, and as the result electrons flow from the anode to the cathode through an external circuit for generating current.
  • An electrolytic layer exists between the cathode and anode to prevent an internal flow of the electrons, which is called as an electric short, and to impart an ion transmission between the cathode and anode.
  • the electrolytic layer should be made from a non-electron conductive material and transmit ions during discharging for a primary battery and during charging and discharging for a secondary battery.
  • the electrolytic layer should be electrochemically and chemically stable with respect to the cathode and anode.
  • a laminating method of the polymer electrolyte through heating, a gelling method after impregnating a battery including a porous separator with an electrolytic solution which can form the gel, etc. can be illustrated.
  • the aluminum pouch is used, if the gel or the polymer electrolyte is used, surface between the electrode and the electrolytic layer maintained stably.
  • the separator manufactured by the conventional method in which polymer applied partially on the porous separator such as polyethylene non-woven fabric and polypropylene non-woven fabric, has problem of low ionic conductivity, electrolyte absorption and electrolyte maintenance characteristics because the separator has little porosity.
  • the polymer is applied overall on the polyolefm-based separator such as polyethylene non-woven fabric and polypropylene non-woven fabric, insufficiency of electrolyte absorption capacity of the separator causes increase of resistance and Li-deposition phenomenon likely to occur. Also, if the above-mentioned polyolefm-based separator is used, physical properties of the separator are changed in the process performed in the high temperature in the range of above 120 ⁇ 140 °C. Consequently, this brings about a serious problem of stability.
  • Electric Corp. discloses a method of adhering a cathode and anode onto a porous separator after coating a binder resin solution onto the porous separator. According to this method, the electrodes are adhered to the separator coated with the binder resin solution before an evaporation of a solvent and the solvent is evaporated at a temperature range of about 80°C or less. After evaporating the solvent, pores are formed at the resin layer and a binding layer having a porous structure is manufactured.
  • the preparation of the electrolyte and the adhering process of the electrode should be continuously implemented.
  • the adhering strength and the minute structure of the binding layer changes according to the evaporating degree of the solvent, a continuous manufacture of cells having a uniform structure is difficult.
  • U.S. Pat. Nos. 5,691,005 Mitsubishi Electric Corp.
  • 5,597,659 Mitsubishi Electric Corp.
  • some disadvantages are as follows. The electrolytic solution is evaporated and the physical properties of the separator manufactured by this method changes during storing. The remaining initiator that does not participate in the cross-linking has a negative influence on the physical properties.
  • the separator manufactured by the method may have a problem of electrolyte absorption, to avoid the problem, a separator having good electrolyte absorption capacity should be used.
  • Japanese Patent Laid-Open Publication No. Hei 10-162802 discloses a cell manufactured by impregnating a non-woven fabric or an insulating porous film with a liquid polymer material base on polyacrylonitrile to manufacture a separator and then positioning thus obtained separator between a cathode and anode.
  • U.S. Pat. Nos. 5,853,916 (Motorola), 5,716,421 (Motorola), 5,834,135 (Motorola), 5,681 ,357 (Motorola) and 5,688,293 (Motorola) disclose a separator composed of a non-gelling porous layer and a gelling polymer layer and a secondary battery manufactured by using the same. In this case, a mechanical strength is accomplished and a short induced from a contact of the cathode and anode is prevented by the non-gelling porous separator layer as a non-active material which has a low affinity to an electrolytic solution.
  • the gelling layer positioned at one or both surface of the porous separator has a good affinity to the electrolytic solution and imparts an adhesive power to the electrode.
  • the gelling layer is formed through coating onto the separator, and so, the electrolytic solution is impregnated into the cell through diffusion into the gelling layer. Accordingly, if the electrolyte absorption capacity of the separator is decreased, cell capacity may be lowered.
  • a fibroid separator comprising a fibroid film and a polymer layer having a polymer material formed on the fibroid film, and an energy storage device including the above-mentioned fibroid separator.
  • FIG. 1 A is a scanning electron microscope (SEM) photograph of surface of the solvent-spun-rayon fibroid separator and FIG. IB is a SEM photograph of surface of the polytetrafluoroethylene (PTFE) fibroid separator.
  • SEM scanning electron microscope
  • FIG. 2 is a SEM photograph of polymeric film of polyolefm of the prior art.
  • FIG. 3 is a cross sectional view of lithium secondary battery having stacked structure formed by polymer applied overall on the surface of the fibroid separator in accordance with the invention.
  • FIG. 4 is a cross sectional view of lithium secondary battery having stacked structure formed by polymer applied partially on the surface of the fibroid separator in accordance with the invention.
  • FIG. 5 is a photograph of the surface of the cathode after 300 cycles charging and discharging the lithium polymer secondary battery according to Example 1 in accordance with the invention.
  • FIG. 6 is a voltage profile dependent on time during charging and discharging the lithium polymer secondary battery by 0.2 C rate according to Example 1 in accordance with the invention.
  • FIG. 7 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 1 in accordance with the invention.
  • FIG. 8 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 2 in accordance with the invention.
  • FIG. 9 is a photograph of the surface of the cathode after 50 cycles charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
  • FIG. 10 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
  • FIG. 1 1 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 3 in accordance with the invention.
  • the present invention provides a fibroid separator comprising a) a fibroid film and b) the polymer layer having polymer material formed on the fibroid film, and an energy storage device using the same.
  • the fibroid separator includes a) the fibroid film and b) the polymer layer having polymer material formed on the surface of the fibroid film.
  • the fibroid film is not a porous polymer film having little porosity such as polyolefm-based film but a porous fiber film having much porosity such as polytetrafluoroethylene, solvent-spun-rayon fiber.
  • the fibroid film is selected from polytetrafluoroethylene, solvent-spun-rayon fiber, regenerated cellulose fiber, glass fiber, manila hemp, sisal hemp, or kraft pulp, etc.
  • porosity of the fibroid film is about 40 % to 80 %.
  • porosity of the fibroid film is lower than 40%, electrolyte absorption capacity and ionic conductivity is lowered because the porosity of the film is decreased.
  • porosity of the fibroid film exceeds 80%, mechanical strength is lowered and it may cause problem of manufacturing process.
  • a fiber diameter of the fibroid film is in the range of from feasible minimum size, for example, about 0.01 ⁇ m to 10 ⁇ m. When the fiber diameter of the fibroid film exceeds 10 ⁇ m, electrolyte absorption capacity and electrolyte maintenance characteristics at the surface of the fibroid separator may be lowered.
  • FIG. 1 A is a SEM photograph of surface of the solvent-spun-rayon fibroid separator (TF4035: trade name manufactured by Nippon Kodashi Corp.) and FIG. IB is a SEM photograph of surface of the PTFE (Gore-Tex PTFE separator: trade name manufactured by W. L. Gore & Associate) fibroid separator.
  • FIG. 2 is the SEM photograph of surface of the polymer film of polyolefin (Celgard 2500: trade name manufactured by Hoechst Corp.) of the prior art.
  • the fibroid film has more pores than a porous film used in general energy storage device, as a result, the fibroid film has a superior electrolyte absorption capacity, electrolyte maintenance characteristics, and ionic conductivity. Also, the fibroid film has a good capacity and cycle-life characteristics and a stable cell can be manufactured because the lithium deposition is not formed under the uniform surface characteristics. Furthermore, the fibroid separator, such as rayon and paper, cheaper than conventional separator by ten times, so has a price competitive power.
  • the fibroid separator such as solvent-spun-rayon and PTFE
  • the conventional separator such as polyethylene non-woven fabric and polypropylene non- woven fabric of which physical properties are changed in the process carried out above about 120-140 °C
  • physical properties of the separator are not changed in the process performed in the high temperature in the range of above about 200 °C. Consequently, adhering process having various temperature ranges can be employed.
  • the polymer layer is prepared by forming the polymer on the fibroid film.
  • butadiene-based polymer material including polyacrylonitrile-butadiene rubber (NBR), polystyrene-butadiene rubber (SBR), polystyrene-butadiene-styrene rubber (SBS), acrylonitrile-butadiene-styrene rubber (ABS), polybutadiene, ii) synthetic or natural rubber including polydimethyl siloxane, polyisoprene, polychloroprene, polyisobutylene, and ethylenepropylene rubber, iii) acryl-based resin including poly (alkyl acrylate), poly (alkyl methacrylate), poly (alkyl ethacrylate), copolymers thereof, and combinations thereof, iv) polyether-based polymer material including polyethylene oxide, polyoxymethylene, polypropylene oxide, copolymers thereof, and combinations thereof, v) polyvinylether-based polymer material
  • the polymer layer is prepared by a partial coating method or an overall coating method.
  • a solution having the polymer is doped partially on a surface of the fibroid film.
  • a solution having the polymer is doped overall on the surface of the fibroid film.
  • a spraying method, a dipping method, a doctor blade method, a silkscreen printing, an inkjet printing, etc. can be applied.
  • a space formed between the electrode and the separator therefore the electrolyte can be impregnated into the separator and the electrode through the space.
  • the spraying method is used cell can be manufactured by a simple process that the polymer-dissolved solution is sprayed on the separator and then the cell is assembled. Furthermore, the spraying method has a merit in cost because a dry room (humid control system) is need only in electrolyte injection process. Additionally, if the partial coating method is applied, contrary to a gel type or bellcore type, various electrolyte can be used because of good absorption characteristics. Also, though the separator is heated several times, physical properties of polymer and efficiency of cell is maintained uniformly, therefore mono cell can be manufactured easily when the stacked type cell is manufactured.
  • the separator should be heated only one time, consequently, cell can be manufactured in bi-cell structure. Also, if the cell is manufactured by the method that the polymer is coated overall on the fibroid separator and then the adhesive polymer is coated partially on the polymer-coated fibroid separator, thickness of the polymer coated overall on the fibroid separator is less than 10 ⁇ m, therefore extraction of plasticizer is achieved easily and promptly.
  • An energy storage device including the fibroid separator according to the present invention comprise, comprising a) an anode having positive active material, b) a cathode having negative active material, positioned from the anode with a predetermined distance, c) the fibroid separator, comprising the fibroid film and the polymer layer having polymer formed on the fibroid film, positioned between the anode and the cathode, and d) a electrolyte impregnated into the fibroid separator.
  • FIG. 3 is a cross sectional view of the lithium secondary battery having stacked structure formed by coating polymer on the surface of the fibroid separator overall in accordance with the invention.
  • a positive collector 6 coated by positive active material 5 is the anode
  • a negative collector 1 coated by negative active material 2 is the cathode, positioned from the anode with a predetermined distance.
  • FIG. 3 illustrate the fibroid separator comprising the fibroid film 4 and the polymer layer 3a having polymer formed overall on the fibroid film, positioned between the anode and the cathode.
  • more preferable embodiment of the present invention is a lithium secondary battery having stacked structure formed by polymer 3b coated partially on the surface of the fibroid separator 4 as illustrated in FIG. 4. According to FIG. 4, a positive collector 6 coated by positive active material
  • FIG. 5 is the anode, and a negative collector 1 coated by negative active material 2 is the cathode, positioned from the anode with a predetermined distance.
  • FIG. 4 illustrate the fibroid separator comprising the fibroid film 4 and the polymer layer 3b having polymer formed partially on the fibroid film, positioned between the anode and the cathode.
  • Electrolyte absorption capacity of the fibroid separator is enhanced by the polymer layer 3b coated partially on the fibroid film 4.
  • space between the fibroid separator and the electrode formed the space occur the problem of diminution of electrolyte maintenance characteristics.
  • high porosity of the fibroid separator 4 prevents electrolyte maintenance characteristics from deteriorating.
  • the lithium polymer secondary battery of the present invention is manufactured by the following steps. To begin with, the fibroid separator is manufactured by coating the polymer layer having polymer on the fibroid film overall or partially. Consequently, the fibroid separator is supplied between the cathode of negative collector 1 coated by negative active material 2 and the anode of positive collector 6 coated by positive active material 5. And then, the fibroid separator and the electrodes are adhered by using the predetermined heat and pressure.
  • the negative active material is selected from metallic lithium, lithium alloy, synthetic graphite, natural graphite, petroleum coke, or doped coke, etc.
  • the positive active material is selected from LiCoO 2 , LiNiO 2 , LiCoNiO 2 , LiMn 2 O 4 , or organic sulfide compound, etc.
  • the method of manufacturing the lithium polymer secondary battery of the present invention before the polymer layer is formed, further comprise the step of forming the polymer film by coating polyvinylidene fluoride (PVdF) copolymer, dibutylpathalate, or silica on a intensified polyester film using the acetone as solvent and the step of adhering the fibroid separator to the polymer film by heating the polymer film.
  • PVdF polyvinylidene fluoride
  • dibutylpathalate dibutylpathalate
  • silica silica
  • mixed ratio of the polymer : the acetone as solvent : the DBP as plasticizer : the silica as inorganic filler is preferable in the range of 1 : 1—30 : 1-10 : 0.5-2 at weight ratio.
  • the temperature for adhering the fibroid separator and the electrodes is in the range of from 60 to 80 °C.
  • Polybutylmethacrylate was dissolved into acetone so that the concentration of thus prepared solution was 10% by weight.
  • Polybutylmethacrylate solution was sprayed on a fibroid separator (TF4035: trade name manufactured by Nippon
  • FIG. 5 was a photograph of the surface of the cathode after 300 cycles charging and discharging the lithium polymer secondary battery according to Example 1 in accordance with the invention and FIG. 6 was a voltage profile dependent on time during charging and discharging the lithium polymer secondary battery by 0.2 C rate according to Example 1 in accordance with the invention.
  • the fibroid separator for the lithium polymer secondary battery had a good electrolyte absorption capacity and electrolyte maintenance characteristics at the surface of the fibroid separator, thus Li-deposition phenomenon of the surface of cathode was not observed.
  • FIG. 6 illustrated that the lithium polymer secondary battery using the fibroid separator had good voltage behavior because the scope of constant voltage is narrow.
  • FIG. 7 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 1.
  • cycle-life characteristics of the lithium polymer secondary battery according to Example 1 maintained 90 % of initial capacity after 300 cycles charging and discharging the lithium polymer secondary battery by using the fibroid separator having superior electrolyte absorption capacity and electrolyte maintenance characteristics.
  • Example 2> A Lithium polymer secondary battery was manufactured by the same procedure as in Example 1 except that PTFE (Gore-Tex PTFE separator: trade name manufactured by W. L. Gore & Associate) instead of the fibroid separator (TF4035: trade name manufactured by Nippon Kodashi Corp.) was used, and cycle-life characteristics of the lithium polymer secondary battery was observed in the same manner.
  • PTFE Gore-Tex PTFE separator: trade name manufactured by W. L. Gore & Associate
  • TF4035 trade name manufactured by Nippon Kodashi Corp.
  • FIG. 8 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 2.
  • cycle-life characteristics of the lithium polymer secondary battery according to Example 2 maintained 90 % of initial capacity after
  • 300 cycles charging and discharging the lithium polymer secondary battery by using the fibroid PTFE separator having superior electrolyte absorption capacity and electrolyte maintenance characteristics.
  • FIG. 9 illustrated a photograph of the surface of the cathode after 50 cycles charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
  • a lithium polymer secondary battery was manufactured by using the porous separator, electrolyte absorption capacity and electrolyte maintenance characteristics was lowered because the separator had little porosity. Consequently, as shown in FIG. 9, Li-deposition resulted from insufficiency of electrolyte of the separator caused by decrease of electrolyte maintenance capacity. That was different point from FIG. 5 according to the present invention.
  • FIG. 10 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
  • Cycle-life characteristics of the lithium polymer secondary battery according to Comparative Example 1 maintained 85 % of initial capacity after 300 cycles charging and discharging by 1.0 C rate the lithium polymer secondary battery because of the decrease of the electrolyte absorption characteristics and electrolyte maintenance characteristics.
  • PVdF copolymer (Kynar 2801 : trade name manufactured by Elf Atochem), DBP, and silica were dissolved into acetone so that a mixture was prepared. At this time, mixed ratio of the PVdF copolymer : DBP : silica : aceton was 2 : 3 : 1 : 28 at weight ratio.
  • the lithium polymer secondary battery was manufactured by using fibroid separator on which the polymer film coated overall through the process of Example 1.
  • FIG. 11 was a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 3.
  • a cycle-life characteristics of the lithium polymer secondary battery according to Example 3 maintained 90 % of initial capacity after 300 cycles charging and discharging the lithium polymer secondary battery.
  • the fibroid film was used as a separator, the lithium polymer secondary battery had good cycle-life characteristics without Li-deposition.
  • the present invention uses the fibroid separator instead of porous separator, so that it is possible to enhance the electrolyte absorption characteristics and electrolyte maintenance characteristics. Consequently, by using the fibroid film as a separator, the lithium polymer secondary battery having good cycle-life characteristics without Li-deposition can be provided.
  • the present invention employs the fibroid separator including a fibroid film and the polymer layer having polymer formed partially on the fibroid film, thereby electrolyte can be absorbed easily into the separator and electrode through area where the polymer layer is not exist.
  • energy storage device such as lithium polymer secondary battery having good Ionic conductive capacity and cycle-life characteristics can be manufactured.

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  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Inorganic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Cell Separators (AREA)

Abstract

Disclosed are a fibroid separator and an energy storage device using the fibroid separator. The fibroid separator has a fibroid film and a polymer layer having polymer formed on the fibroid film. The fibroid film has many pores, therefore the fibroid separator has a superior electrolyte absorption capacity and electrolyte maintenance characteristics. Also, by using the fibroid separator having adequate quantity of porous, energy storage device such as the lithium polymer secondary battery having good cycle-life characteristics and good adherence characteristics between the separator and the electrode without Li-deposition, can be provided.

Description

FIBROID SEPARATOR AND ENERGY STORAGE DEVICE USING THE
SAME
Technical Field
The present invention relates to a separator and an energy storage device comprising the separator, and more particularly, to a fibroid separator applicable to the energy storage device such as lithium polymer secondary battery.
Background Art
An electric reduction of an active material of a cathode and an oxidation of an active material of an anode is induced during discharging of a charged cell or battery, and as the result electrons flow from the anode to the cathode through an external circuit for generating current. An electrolytic layer exists between the cathode and anode to prevent an internal flow of the electrons, which is called as an electric short, and to impart an ion transmission between the cathode and anode.
The electrolytic layer should be made from a non-electron conductive material and transmit ions during discharging for a primary battery and during charging and discharging for a secondary battery. The electrolytic layer should be electrochemically and chemically stable with respect to the cathode and anode.
Generally, in case of cell manufactured by using a metal can, a electrode cling to a separator tightly by pressure of the metal can, consequently this result in good continuity of electrolyte and electrolyte maintenance characteristics. However, as portable electric appliances are smaller and lighter, an aluminum pouch which enable a battery to be lighter and thinner is adopted instead of the metal can. On the other hand, if the aluminum pouch is applied, electrolyte maintenance characteristics between the electrode and the separator get worse because the aluminum pouch has low pressure in comparison with the metal can.
In order to avoid the said problem, various methods for manufacturing the cell have been suggested. A laminating method of the polymer electrolyte through heating, a gelling method after impregnating a battery including a porous separator with an electrolytic solution which can form the gel, etc. can be illustrated.
Though the aluminum pouch is used, if the gel or the polymer electrolyte is used, surface between the electrode and the electrolytic layer maintained stably.
Accordingly, in case of aluminum pouch is used, energy density per weight and volume are improved in comparison with metal can, consequently, a light and thin type battery can be manufactured.
However, the separator manufactured by the conventional method, in which polymer applied partially on the porous separator such as polyethylene non-woven fabric and polypropylene non-woven fabric, has problem of low ionic conductivity, electrolyte absorption and electrolyte maintenance characteristics because the separator has little porosity.
If the polymer is applied overall on the polyolefm-based separator such as polyethylene non-woven fabric and polypropylene non-woven fabric, insufficiency of electrolyte absorption capacity of the separator causes increase of resistance and Li-deposition phenomenon likely to occur. Also, if the above-mentioned polyolefm-based separator is used, physical properties of the separator are changed in the process performed in the high temperature in the range of above 120 ~ 140 °C. Consequently, this brings about a serious problem of stability.
On the other hand, if the polymer is applied partially on the separator by using a spray method or a coating method, void space between the electrode and the separator is formed. Therefore electrolyte absorption characteristics and electrolyte maintenance characteristics of separator is decreased. By this, a problem of discontinuity of the electrolyte and Li-deposition at the electrolyte insufficiency area occur. Moreover, if the polyethylene non-woven fabric or polypropylene non-woven fabric is used, this results Li-deposition by insufficiency of electrolyte and a problem of instability by growth of Li dendrite. Japanese Patent Laid-Open Publication No. Hei 1-089054 (Mitsubishi
Electric Corp.) discloses a method of adhering a cathode and anode onto a porous separator after coating a binder resin solution onto the porous separator. According to this method, the electrodes are adhered to the separator coated with the binder resin solution before an evaporation of a solvent and the solvent is evaporated at a temperature range of about 80°C or less. After evaporating the solvent, pores are formed at the resin layer and a binding layer having a porous structure is manufactured.
However, when the electrodes are adhered to the separator while the solvent remains, the preparation of the electrolyte and the adhering process of the electrode should be continuously implemented. In addition, since the adhering strength and the minute structure of the binding layer changes according to the evaporating degree of the solvent, a continuous manufacture of cells having a uniform structure is difficult.
U.S. Pat. Nos. 5,691,005 (Mitsubishi Electric Corp.) and 5,597,659 (Mitsubishi Electric Corp.) disclose a lithium secondary battery including an electrolytic layer having a separator filled with a gel-impregnated polymer components into a separator are cross-linked by exposing UV. However, some disadvantages are as follows. The electrolytic solution is evaporated and the physical properties of the separator manufactured by this method changes during storing. The remaining initiator that does not participate in the cross-linking has a negative influence on the physical properties. The separator manufactured by the method may have a problem of electrolyte absorption, to avoid the problem, a separator having good electrolyte absorption capacity should be used.
Japanese Patent Laid-Open Publication No. Hei 10-162802 (Sony Corp.) discloses a cell manufactured by impregnating a non-woven fabric or an insulating porous film with a liquid polymer material base on polyacrylonitrile to manufacture a separator and then positioning thus obtained separator between a cathode and anode.
U.S. Pat. Nos. 5,853,916 (Motorola), 5,716,421 (Motorola), 5,834,135 (Motorola), 5,681 ,357 (Motorola) and 5,688,293 (Motorola) disclose a separator composed of a non-gelling porous layer and a gelling polymer layer and a secondary battery manufactured by using the same. In this case, a mechanical strength is accomplished and a short induced from a contact of the cathode and anode is prevented by the non-gelling porous separator layer as a non-active material which has a low affinity to an electrolytic solution. Meantime, the gelling layer positioned at one or both surface of the porous separator has a good affinity to the electrolytic solution and imparts an adhesive power to the electrode. In these patents, the gelling layer is formed through coating onto the separator, and so, the electrolytic solution is impregnated into the cell through diffusion into the gelling layer. Accordingly, if the electrolyte absorption capacity of the separator is decreased, cell capacity may be lowered.
Disclosure of Invention
It is an object in the present invention considering the above-described problems to provide a fibroid separator having superior electrolyte absorption capacity, electrolyte maintenance characteristics and cycle-life characteristics at the interface and energy storage device using the same.
To accomplish the object, there is provided in the present invention a fibroid separator comprising a fibroid film and a polymer layer having a polymer material formed on the fibroid film, and an energy storage device including the above-mentioned fibroid separator.
Brief Description of Drawings FIG. 1 A is a scanning electron microscope (SEM) photograph of surface of the solvent-spun-rayon fibroid separator and FIG. IB is a SEM photograph of surface of the polytetrafluoroethylene (PTFE) fibroid separator.
FIG. 2 is a SEM photograph of polymeric film of polyolefm of the prior art. FIG. 3 is a cross sectional view of lithium secondary battery having stacked structure formed by polymer applied overall on the surface of the fibroid separator in accordance with the invention.
FIG. 4 is a cross sectional view of lithium secondary battery having stacked structure formed by polymer applied partially on the surface of the fibroid separator in accordance with the invention. FIG. 5 is a photograph of the surface of the cathode after 300 cycles charging and discharging the lithium polymer secondary battery according to Example 1 in accordance with the invention.
FIG. 6 is a voltage profile dependent on time during charging and discharging the lithium polymer secondary battery by 0.2 C rate according to Example 1 in accordance with the invention.
FIG. 7 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 1 in accordance with the invention.
FIG. 8 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 2 in accordance with the invention.
FIG. 9 is a photograph of the surface of the cathode after 50 cycles charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
FIG. 10 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1.
FIG. 1 1 is a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 3 in accordance with the invention.
Best Mode for Carrying Out the Invention
In order to achieve the above-mentioned object of the present invention, the present invention provides a fibroid separator comprising a) a fibroid film and b) the polymer layer having polymer material formed on the fibroid film, and an energy storage device using the same. The present will be described in detail with reference to the attached drawings below.
The fibroid separator includes a) the fibroid film and b) the polymer layer having polymer material formed on the surface of the fibroid film. a) The fibroid film is not a porous polymer film having little porosity such as polyolefm-based film but a porous fiber film having much porosity such as polytetrafluoroethylene, solvent-spun-rayon fiber. Specifically, a) the fibroid film is selected from polytetrafluoroethylene, solvent-spun-rayon fiber, regenerated cellulose fiber, glass fiber, manila hemp, sisal hemp, or kraft pulp, etc.
Also, porosity of the fibroid film is about 40 % to 80 %. When porosity of the fibroid film is lower than 40%, electrolyte absorption capacity and ionic conductivity is lowered because the porosity of the film is decreased. However, when porosity of the fibroid film exceeds 80%, mechanical strength is lowered and it may cause problem of manufacturing process. Furthermore, a fiber diameter of the fibroid film is in the range of from feasible minimum size, for example, about 0.01 μm to 10 μm. When the fiber diameter of the fibroid film exceeds 10 μm, electrolyte absorption capacity and electrolyte maintenance characteristics at the surface of the fibroid separator may be lowered. FIG. 1A and FIG. IB are the SEM photograph which illustrate a surface of the fibroid film according to the present invention. Specifically, FIG. 1 A is a SEM photograph of surface of the solvent-spun-rayon fibroid separator (TF4035: trade name manufactured by Nippon Kodashi Corp.) and FIG. IB is a SEM photograph of surface of the PTFE (Gore-Tex PTFE separator: trade name manufactured by W. L. Gore & Associate) fibroid separator. On the other hand, FIG. 2 is the SEM photograph of surface of the polymer film of polyolefin (Celgard 2500: trade name manufactured by Hoechst Corp.) of the prior art.
The fibroid film has more pores than a porous film used in general energy storage device, as a result, the fibroid film has a superior electrolyte absorption capacity, electrolyte maintenance characteristics, and ionic conductivity. Also, the fibroid film has a good capacity and cycle-life characteristics and a stable cell can be manufactured because the lithium deposition is not formed under the uniform surface characteristics. Furthermore, the fibroid separator, such as rayon and paper, cheaper than conventional separator by ten times, so has a price competitive power. Still furthermore, if the fibroid separator such as solvent-spun-rayon and PTFE are adopted, unlike the conventional separator such as polyethylene non-woven fabric and polypropylene non- woven fabric of which physical properties are changed in the process carried out above about 120-140 °C, physical properties of the separator are not changed in the process performed in the high temperature in the range of above about 200 °C. Consequently, adhering process having various temperature ranges can be employed. b) The polymer layer is prepared by forming the polymer on the fibroid film. As the polymer that can be used in the present invention, i) butadiene-based polymer material including polyacrylonitrile-butadiene rubber (NBR), polystyrene-butadiene rubber (SBR), polystyrene-butadiene-styrene rubber (SBS), acrylonitrile-butadiene-styrene rubber (ABS), polybutadiene, ii) synthetic or natural rubber including polydimethyl siloxane, polyisoprene, polychloroprene, polyisobutylene, and ethylenepropylene rubber, iii) acryl-based resin including poly (alkyl acrylate), poly (alkyl methacrylate), poly (alkyl ethacrylate), copolymers thereof, and combinations thereof, iv) polyether-based polymer material including polyethylene oxide, polyoxymethylene, polypropylene oxide, copolymers thereof, and combinations thereof, v) polyvinylether-based polymer material including polyvinylether, polyvinylethylether, polyvinyl n-propyl ether, polyvinyl n-butyl ether, copolymers thereof, and combinations thereof, vi) a fluoride-based polymer including polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropane, polychloro trifluoroethylene and a copolymer with ethylene, polytetrafluoro ethylene, polyvinyl fluoride and copolymers thereof, vii) chloride-based polymer including poly (vinyl chloride), and poly (vinylidene chloride), viii) benzene group-containing polymer including polystyrene and phenol resin, ix) OH group-containing polymer including polyvinylalcohol, polyhydroxy ethyl methacrylate, and ethylene-vinyl alcohol copolymer, x) acid group-containing polymer including polyacrylic acid, polystyrene sulfonic acid, and polyamic acid, xi) photo-synthesizable polymer including polyvinyl cinnamate, xii) nitrile group-containing polymer including polyacrylonitrile, polymethacrylonitrile, copolymers thereof, and combinations thereof, xiii) polyolefin polymer including polyethylene and polypropylene; xiv) polyvinyl acetal, xv) polyvinyl ketal, xvi) polyvinyl butyral, xvii) polyvinyl formal, xviii) polyvinyl ester, xix) polycarbonate, xx) polyurethane, xxi) poly amide, and xxii) poly imide, etc. may be mentioned. These can be used alone or in a combination thereof. b) The polymer layer is prepared by a partial coating method or an overall coating method. In the partial coating method, a solution having the polymer is doped partially on a surface of the fibroid film. In the overall coating method, a solution having the polymer is doped overall on the surface of the fibroid film. As for the partial coating method, a spraying method, a dipping method, a doctor blade method, a silkscreen printing, an inkjet printing, etc. can be applied. In case of partial coating using the spraying method, a space formed between the electrode and the separator, therefore the electrolyte can be impregnated into the separator and the electrode through the space. Accordingly, efficiency of manufacturing process and uniformity of cell characteristics can be achieved in mass production. Also, if the spraying method is used cell can be manufactured by a simple process that the polymer-dissolved solution is sprayed on the separator and then the cell is assembled. Furthermore, the spraying method has a merit in cost because a dry room (humid control system) is need only in electrolyte injection process. Additionally, if the partial coating method is applied, contrary to a gel type or bellcore type, various electrolyte can be used because of good absorption characteristics. Also, though the separator is heated several times, physical properties of polymer and efficiency of cell is maintained uniformly, therefore mono cell can be manufactured easily when the stacked type cell is manufactured. On the contrary, in bellcore type, if the separator is heated several times, physical properties of polymer is changed and minor-short may occur, consequently, these causes damage of cell and it is impossible to make a reliable cell in large quantities. Therefore, in using bellcore type, the separator should be heated only one time, consequently, cell can be manufactured in bi-cell structure. Also, if the cell is manufactured by the method that the polymer is coated overall on the fibroid separator and then the adhesive polymer is coated partially on the polymer-coated fibroid separator, thickness of the polymer coated overall on the fibroid separator is less than 10 μm, therefore extraction of plasticizer is achieved easily and promptly. On the contrary, if the bellcore type is applied, thickness of the polymer is 50 to 100 μm, therefore it is impossible to extract the plasticizer absolutely and time for extraction takes about one day. Moreover, If the bellcore type is used, consecutive process is not feasible because extraction of plasticizer takes long time, on the contrary, if the above-described method is applied, extraction of plasticizer is carried out promptly, therefore, consecutive process is feasible. Also, in the above-described method, by using the fibroid separator having rough surface as the supporter, shrink phenomenon of the polymer layer can be reduced. However, in bellcore type, it is impossible to manufacture a reliable cell because of shrink phenomenon resulted from decrease of adhesive strength between electrode and the polymer layer. Further more, in bellcore type, electrode used as supporter that prevent polymer layer from shrinking, therefore extraction of plasticizer is carried out after lamination of electrode and polymer separator.
Accordingly, extraction of plasticizer is carried out difficultly and slowly. However, in the above-described method, extraction of plasticizer is carried out before lamination of the electrode and the polymer separator, therefore, extraction of plasticizer is carried out easily and mass production is feasible. Further more, in the above-described method, a electrode using foil-type or mesh-type substrate can be adopted as electrode, conseqently, various type of a electrode can be applied. And by employing the partial coating method, a space is provided after adhering the electrode and the separator. Through the space formed between the electrode and the separator, an electrolyte can be absorbed into the separator and the electrode. Superior electrolyte absorption enhances efficiency of manufacturing process and uniformity of cell characteristics in mass production.
An energy storage device, including the fibroid separator according to the present invention comprise, comprising a) an anode having positive active material, b) a cathode having negative active material, positioned from the anode with a predetermined distance, c) the fibroid separator, comprising the fibroid film and the polymer layer having polymer formed on the fibroid film, positioned between the anode and the cathode, and d) a electrolyte impregnated into the fibroid separator.
FIG. 3 is a cross sectional view of the lithium secondary battery having stacked structure formed by coating polymer on the surface of the fibroid separator overall in accordance with the invention. According to FIG. 3, a positive collector 6 coated by positive active material 5 is the anode, and a negative collector 1 coated by negative active material 2 is the cathode, positioned from the anode with a predetermined distance. Also, FIG. 3 illustrate the fibroid separator comprising the fibroid film 4 and the polymer layer 3a having polymer formed overall on the fibroid film, positioned between the anode and the cathode. If the polymer layer 3a is coated the fibroid film 4 overall, adhesive strength to the electrode is enhanced, but electrolyte absorption capacity of the fibroid separator decreased. Though, high porosity of the fibroid separator prevents electrolyte absorption capacity from decreasing. Accordingly, more preferable embodiment of the present invention is a lithium secondary battery having stacked structure formed by polymer 3b coated partially on the surface of the fibroid separator 4 as illustrated in FIG. 4. According to FIG. 4, a positive collector 6 coated by positive active material
5 is the anode, and a negative collector 1 coated by negative active material 2 is the cathode, positioned from the anode with a predetermined distance. Also, the FIG. 4 illustrate the fibroid separator comprising the fibroid film 4 and the polymer layer 3b having polymer formed partially on the fibroid film, positioned between the anode and the cathode.
Electrolyte absorption capacity of the fibroid separator is enhanced by the polymer layer 3b coated partially on the fibroid film 4. However, space between the fibroid separator and the electrode formed, the space occur the problem of diminution of electrolyte maintenance characteristics. Though, high porosity of the fibroid separator 4 prevents electrolyte maintenance characteristics from deteriorating. The lithium polymer secondary battery of the present invention is manufactured by the following steps. To begin with, the fibroid separator is manufactured by coating the polymer layer having polymer on the fibroid film overall or partially. Consequently, the fibroid separator is supplied between the cathode of negative collector 1 coated by negative active material 2 and the anode of positive collector 6 coated by positive active material 5. And then, the fibroid separator and the electrodes are adhered by using the predetermined heat and pressure.
The negative active material is selected from metallic lithium, lithium alloy, synthetic graphite, natural graphite, petroleum coke, or doped coke, etc. Also, the positive active material is selected from LiCoO2, LiNiO2, LiCoNiO2, LiMn2O4, or organic sulfide compound, etc.
The method of manufacturing the lithium polymer secondary battery of the present invention, before the polymer layer is formed, further comprise the step of forming the polymer film by coating polyvinylidene fluoride (PVdF) copolymer, dibutylpathalate, or silica on a intensified polyester film using the acetone as solvent and the step of adhering the fibroid separator to the polymer film by heating the polymer film. At this time, mixed ratio of the polymer : the acetone as solvent : the DBP as plasticizer : the silica as inorganic filler is preferable in the range of 1 : 1—30 : 1-10 : 0.5-2 at weight ratio. Also, the temperature for adhering the fibroid separator and the electrodes is in the range of from 60 to 80 °C.
The preferred example of the present invention will be described in more detail, below. However, is should be understood that the present invention is not limited to the following examples.
<Example 1>
Polybutylmethacrylate was dissolved into acetone so that the concentration of thus prepared solution was 10% by weight. Polybutylmethacrylate solution was sprayed on a fibroid separator (TF4035: trade name manufactured by Nippon
Kodashi Corp.) by using a spray gun. Thus obtained polybutylmethacrylate deposited fibroid separator passed through a drying furnace to remove acetone.
On thus obtained separator, polybutylmethacrylate was partially dispersed. The polybutylmethacrylate material did not exhibit an adhering property at a room temperature, however, exhibited that at a temperature of 60 °C or over. An integrated cell was obtained by compressing the separator, a cathode and an anode with pressure at 80 °C. LiCoO2 active material was used for the manufacture of the cathode and mesocarbon microbead (MCMB) active material was used for the manufacture of the cathode. Then, 1M of LiPF6 in EC/PC/DMC = 2/1/2 solution was added into the cell and thus obtained cell was put into an aluminum laminated plastic pack. Then, a sealing process was implemented.
FIG. 5 was a photograph of the surface of the cathode after 300 cycles charging and discharging the lithium polymer secondary battery according to Example 1 in accordance with the invention and FIG. 6 was a voltage profile dependent on time during charging and discharging the lithium polymer secondary battery by 0.2 C rate according to Example 1 in accordance with the invention.
As shown in FIG. 5, the fibroid separator for the lithium polymer secondary battery had a good electrolyte absorption capacity and electrolyte maintenance characteristics at the surface of the fibroid separator, thus Li-deposition phenomenon of the surface of cathode was not observed. Also, FIG. 6 illustrated that the lithium polymer secondary battery using the fibroid separator had good voltage behavior because the scope of constant voltage is narrow.
FIG. 7 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 1. As shown in FIG. 7, cycle-life characteristics of the lithium polymer secondary battery according to Example 1 maintained 90 % of initial capacity after 300 cycles charging and discharging the lithium polymer secondary battery by using the fibroid separator having superior electrolyte absorption capacity and electrolyte maintenance characteristics. <Example 2> A Lithium polymer secondary battery was manufactured by the same procedure as in Example 1 except that PTFE (Gore-Tex PTFE separator: trade name manufactured by W. L. Gore & Associate) instead of the fibroid separator (TF4035: trade name manufactured by Nippon Kodashi Corp.) was used, and cycle-life characteristics of the lithium polymer secondary battery was observed in the same manner.
FIG. 8 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 2.
As shown in FIG. 8, cycle-life characteristics of the lithium polymer secondary battery according to Example 2 maintained 90 % of initial capacity after
300 cycles charging and discharging the lithium polymer secondary battery by using the fibroid PTFE separator having superior electrolyte absorption capacity and electrolyte maintenance characteristics.
<Comparative Example 1> A Lithium polymer secondary battery was manufactured by the same procedure as in Example 1 except that the conventional porous separator (Celgard
2400: trade name manufactured by Hoechst Corp.) instead of the fibroid separator (TF4035: trade name manufactured by Nippon Kodashi Corp.) was used, and a cycle-life characteristics of the lithium polymer secondary battery was observed in the same manner.
FIG. 9 illustrated a photograph of the surface of the cathode after 50 cycles charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1. When a lithium polymer secondary battery was manufactured by using the porous separator, electrolyte absorption capacity and electrolyte maintenance characteristics was lowered because the separator had little porosity. Consequently, as shown in FIG. 9, Li-deposition resulted from insufficiency of electrolyte of the separator caused by decrease of electrolyte maintenance capacity. That was different point from FIG. 5 according to the present invention.
FIG. 10 illustrated a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Comparative Example 1. Cycle-life characteristics of the lithium polymer secondary battery according to Comparative Example 1 maintained 85 % of initial capacity after 300 cycles charging and discharging by 1.0 C rate the lithium polymer secondary battery because of the decrease of the electrolyte absorption characteristics and electrolyte maintenance characteristics. <Example 3>
PVdF copolymer (Kynar 2801 : trade name manufactured by Elf Atochem), DBP, and silica were dissolved into acetone so that a mixture was prepared. At this time, mixed ratio of the PVdF copolymer : DBP : silica : aceton was 2 : 3 : 1 : 28 at weight ratio. The polymer film formed by casting the mixture on a mylar film (one species of a intensified polyester film) after stirring the mixture. And then, the fibroid separator was manufactured by laminating the polymer film on a fibroid film (TF4035: trade name manufactured by Nippon Kodashi Corp.) at 140 °C. Consequently, The polymer film was endowed with porosity by the extraction of DBP with methanol. Successively, the lithium polymer secondary battery was manufactured by using fibroid separator on which the polymer film coated overall through the process of Example 1. FIG. 11 was a discharging capacity dependent on cycle during charging and discharging the lithium polymer secondary battery by 1.0 C rate according to Example 3. A cycle-life characteristics of the lithium polymer secondary battery according to Example 3 maintained 90 % of initial capacity after 300 cycles charging and discharging the lithium polymer secondary battery. As described above, when the fibroid film was used as a separator, the lithium polymer secondary battery had good cycle-life characteristics without Li-deposition.
While the present invention is described in detail referring to the attached embodiments, various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the present invention.
Industrial Applicability
As described above, the present invention uses the fibroid separator instead of porous separator, so that it is possible to enhance the electrolyte absorption characteristics and electrolyte maintenance characteristics. Consequently, by using the fibroid film as a separator, the lithium polymer secondary battery having good cycle-life characteristics without Li-deposition can be provided.
Moreover, the present invention employs the fibroid separator including a fibroid film and the polymer layer having polymer formed partially on the fibroid film, thereby electrolyte can be absorbed easily into the separator and electrode through area where the polymer layer is not exist.
Consequently, energy storage device such as lithium polymer secondary battery having good Ionic conductive capacity and cycle-life characteristics can be manufactured.

Claims

Claims
1. A fibroid separator comprising: a) a fibroid film; and b) a polymer layer having a polymer material formed on the fibroid film.
2. A fibroid separator as claimed in claim 1, wherein a porosity of the fibroid film is about 40 % to 80 % and a fiber diameter of the fibroid film is about 0.01 μm to 10 μm.
3. A fibroid separator as claimed in claim 1, wherein the fibroid film is any one selected from the group consisting of polytetrafluoroethylene, solvent-spun-rayon fiber, regenerated cellulose fiber, glass fiber, manila hemp, sisal hemp, and kraft pulp.
4. A fibroid separator as claimed in claim 1, wherein the polymer material is any one selected from the group consisting of i) butadiene-based polymer material including polyacrylonitrile-butadiene rubber (NBR), polystyrene-butadiene rubber (SBR), polystyrene-butadiene-styrene rubber (SBS), acrylonitrile-butadiene-styrene rubber (ABS), polybutadiene; ii) synthetic or natural rubber including polydimethyl siloxane, polyisoprene, polychloroprene, polyisobutylene, and ethylenepropylene rubber; iii) acryl-based resin including poly (alkyl acrylate), poly (alkyl methacrylate), poly (alkyl ethacrylate), copolymers thereof, and a combination thereof; iv) polyether-based polymer material including polyethylene oxide, polvoxymethylene. polypropylene oxide, copolymers thereof, and a combination thereof; v) polyvinylether-based polymer material including polyvinylether, polyvinylethylether, polyvinyl n-propyl ether, polyvinyl n-butyl ether, a copolymer thereof, and a combination thereof; vi) fluoride-based polymer including polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropane, polychloro trifluoroethylene and a copolymer with ethylene, polytetrafluoro ethylene, polyvinyl fluoride, and copolymers thereof; vii) chloride-based polymer including poly (vinyl chloride), and poly (vinylidene chloride); viii) benzene group-containing polymer including polystyrene and phenol resin; ix) OH group-containing polymer including polyvinylalcohol, polyhydroxy ethyl methacrylate, and ethylene-vinyl alcohol copolymer; x) acid group-containing polymer including polyacrylic acid, polystyrene sulfonic acid, and polyamic acid; xi) photo-synthesizable polymer including polyvinyl cinnamate; xii) nitrile group-containing polymer including polyacrylonitrile, polymethacrylonitrile, a copolymer thereof, and a combination thereof ; xiii) polyolefin polymer including polyethylene and polypropylene; xiv) polyvinyl acetal; xv) polyvinyl ketal; xvi) polyvinyl butyral; xvii) polyvinyl formal; xviii) polyvinyl ester; xix) polycarbonate; xx) polyurethane; xxi) poly amide; and xxii) poly imide.
5. A fibroid separator as claimed in claim 1, wherein a dispersion coating is performed so that a solution having the polymer is doped dispersedly on a surface of the fibroid film, to thereby preparing the polymer layer.
6. A fibroid separator as claimed in claim 5, wherein the dispersion coating is carried out by a spraying method, a dipping method, a doctor blade method, a silk screen printing, or an inkjet printing.
7. A fibroid separator as claimed in claim 1, wherein an overall coating is performed so that a solution having the polymer is doped overall on a surface of the fibroid film, to thereby preparing the polymer layer.
8. An energy storage device including the fibroid separator as claimed in claim 1.
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CN109244341A (en) * 2018-09-28 2019-01-18 青岛大学 A kind of composite lithium ion cell diaphragm
CN109301132A (en) * 2018-09-28 2019-02-01 青岛大学 A kind of composite diaphragm of lithium ion battery sheath-core fiber structures
CN110706928A (en) * 2019-09-25 2020-01-17 富之庆电子（深圳）有限公司 Guide pin type aluminum electrolytic capacitor and production method thereof
CN110706928B (en) * 2019-09-25 2021-08-13 富之庆电子（深圳）有限公司 Guide pin type aluminum electrolytic capacitor and production method thereof

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