Ionically conductive polymer electrolytes

• US 6,828,065 B2
• Filed: 07/02/2002
• Issued: 12/07/2004
• Est. Priority Date: 06/28/1999
• Status: Expired due to Fees

• Current Assignee: Alfred J. Longhi Jr, Government of the United States of America
• Original Assignee: Lithium Werks Technology BV
• Inventors: Munshi, M. Zafar A.
• Primary Examiner(s): WEINER, LAURA S
• Application Number:
  US10/187,483
• Publication Number:
  US 20030091904A1
• Time in Patent Office: 889 Days
• Field of Search: 429/309, 429/317, 429/316, 429/315, 429/314, 429/306, 429/310
• US Class Current: 429/309
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 10/0565 Polymeric materials, e.g. gel-type or solid-type
• CPC Class Codes: H01M 10/0585 of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
• CPC Class Codes: H01M 4/04 Processes of manufacture in general
• CPC Class Codes: H01M 4/131 Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• CPC Class Codes: H01M 4/133 Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• CPC Class Codes: H01M 4/134 Electrodes based on metals, Si or alloys
• CPC Class Codes: H01M 4/137 Electrodes based on electro-active polymers
• CPC Class Codes: H01M 4/622 being polymers
• CPC Class Codes: H01M 4/661 Metal or alloys, e.g. alloy coatings H01M4/669 take precedence
• CPC Class Codes: H01M 4/667 in the form of layers, e.g. coatings
• CPC Class Codes: H01M 4/668 Composites of electroconductive material and synthetic resins
• CPC Class Codes: H01M 6/10 with wound or folded electrodes
• CPC Class Codes: H01M 6/168 by additives
• CPC Class Codes: H01M 6/188 Processes of manufacture
• CPC Class Codes: H01M 6/40 Printed batteries , e.g. thin film batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y10T 29/49108 Electric battery cell making
• CPC Class Codes: Y10T 29/49115 : including coating or impregnating

Abstract

A dimensionally stable, highly resilient, hybrid copolymer solid-solution electrolyte-retention film for use in a lithium ion battery in one preferred embodiment has a predominantly amorphous structure and mechanical strength despite contact with liquid solvent electrolyte. The film is a thinned (stretched), cast film of a homogeneous blend of two or more polymers, one of which is selected for its pronounced solvent retention properties. A very high surface area inorganic filler dispersed in the blend during formation thereof serves to increase the porosity of the film and thereby enhance electrolyte retention. The film is soaked in a solution of liquid polymer with liquid organic solvent electrolyte and lithium salt, for absorption thereof. Use of a cross-linked liquid polymer enhances trapping of molecules of the electrolyte into pores of the film. The electrolyte film is sandwiched between flexible active anode and cathode layers to form the lithium ion battery. Novel methods are provided for forming the electrodes, the polymer substrate, and other elements of the battery.

Claims

1. An ionically conductive polymer electrolyte, comprising

at least two constituent polymers homogeneously mixed in a hybrid copolymer solid solution blend of predominantly amorphous structure constituting a base polymer,

one of said constituent polymers selected from a polar group of polymers adapted for pronounced solvent retention.

another of said constituent polymers selected from a group consisting of one or more of polyester (PET) polypropylene (PP), polyethylene napthalate (PEN), polycarbonate (PC), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE) in a ratio of concentrations of said constituent polymers in said solid solution to infuse said base polymer with a predetermined property among enhanced strength, processing capability, thermal stability, and mechanical stability, and

an electrolyte solution heavily absorbed within said base polymer without substantial swelling thereof, wherein

said hybrid copolymer solid solution blend comprises a thin film that includes:

a very high surface area inorganic filler consisting of one of fumed silica or alumina in a concentration range from about 0.1% to about 30% by weight dispersed into said hybrid copolymer solid solution blend to create porosity therein and to enhance the mechanical stability of said thin film; and

said electrolyte solution is a liquid solvent electrolyte absorbed into said thin film.

2. The polymer electrolyte of claim 1, wherein:

said one constituent polymer is polyvinylidene fluoride (PVDF).

3. The polymer electrolyte of claim 1, wherein:

said homogeneously mixed constituent polymers are co-extruded, and

said inorganic filler is dispersed therein as the constituent polymers are co-extruded.

4. The polymer electrolyte of claim 1, wherein:

said inorganic filler is fumed silica in the form of highly pure silica in amorphous crystalline structure with fine particle size less than 0.05 micron and high specific surface area greater than 100 m₂/g, said fumed silica inorganic filler thereby being substantially evenly distributed in said dispersal throughout the hybrid copolymer solid solution blend.

5. The polymer electrolyte of claim 1, wherein:

said inorganic filler is alumina with fine particle size less than 0.05 micron and high specific surface area greater than 100 m₂/g, said alumina inorganic filler thereby being substantially evenly distributed in said dispersal throughout the hybrid copolymer solid solution blend.

6. An ionically conductive polymer electrolyte, comprising

at least two constituent polymers homogeneously mixed in a hybrid copolymer solid solution blend of predominantly amorphous structure constituting a base polymer,

one of said constituent polymer selected from a polar group of polymers adapted for pronounced solvent retention,

another of said constituent polymers selected from a group consisting of one or more of polyester (PET), polypropylene (PP), polyethylene napthalate (PEN), polycarbonate (PC), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE) in a ratio of concentrations of said constituent polymers in said solid solution to infuse said base polymer with a predetermined property among enhanced strength, processing capability, thermal stability, and mechanical stability, and

an electrolyte solution heavily absorbed within said base polymer without substantial swelling thereof, wherein

said base polymer comprises a thin film that includes:

a very high surface area inorganic filler contained therein for porosity and enhanced mechanical stability of said thin film; and

said electrolyte solution contains lithium salt for ionic conduction and enhanced absorption of said electrolyte solution into said thin film.

7. The polymer electrolyte of claim 6, wherein

said lithium salt is dispersed in said electrolyte solution in a solvent mixture of at least one of ethylenecarbonate-diethyl carbonate (EC-DEC), ethylenecarbonate-dimethyl carbonate (EC-DMC), PC-EC-DMC or PC-DEC.

8. The polymer electrolyte of claim 6, wherein

said lithium salt is selected from a group including lithium hexafluorophosphase LiPF₆, lithium perchlorate LiClO₄, lithium tetrafluoro-borate LiBF₄, lithium hexafluoroarsenate LiAsF₆, lithium tetrachloroaluminate LiAlCl₄, lithium trifluoromethane sulfonate LiCF₃SO₃, lithium bis(trifluoromethane sulfonyl) imide (lithium imide) LiN(CF₃SO₂)₂, and lithium methide LiC(SO₂CF₃)₃.

10. The polymer electrolyte of claim 6, wherein:

said one constituent polymer is polyvinylidene fluoride (PVDF).

9. A thin film lithium ion battery, comprising:

a pair of spaced-apart flexible thin film electrodes, each including a polymer substrate having an adherent electrically conductive layer thereon, and

a polymer electrolyte tightly sandwiched between said pair of thin film electrodes, said polymer electrolyte being ionically conductive and comprising

at least two constituent polymers homogeneously mixed in a hybrid copolymer solid solution blend of predominantly amorphous structure constituting a base polymer,

one of said constituent polymers selected from a polar group of polymers adapted for pronounced solvent retention,

another of said constituent polymers selected from a group consisting of one or more of polyester (PET), polypropylene (PP), polyethylene napthalate (PEN), polycarbonate (PC), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE) in a ratio of concentrations of said constituent polymers in said solid solution to infuse said base polymer with a predetermined property among enhanced strength, processing capability, thermal stability, and mechanical stability, and

an electrolyte solution heavily absorbed within said base polymer without substantial swelling thereof.