Structurally stable fusible battery separators and method of making same

• US 6,346,350 B1
• Filed: 04/20/1999
• Issued: 02/12/2002
• Est. Priority Date: 04/20/1999
• Status: Expired due to Term

• Current Assignee: Celgard LLC (Asahi Kasei Corporation)
• Original Assignee: Celgard LLC (Asahi Kasei Corporation)
• Inventors: Call, Ronald W., Yu, Wei-Ching, Hux, Shawn E., Nguyen, Khuy Van, Cook, Pierre C.
• Primary Examiner(s): Dunn, Tom
• Assistant Examiner(s): EDMONDSON, LYNNE RENEE
• Application Number:
  US09/296,682
• Time in Patent Office: 1,029 Days
• Field of Search: 429/249, 429/206, 429/62, 429/144
• US Class Current: 429/249
• CPC Class Codes: B29C 2071/022 Annealing
• CPC Class Codes: B29C 48/09 Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
• CPC Class Codes: B29C 48/10 flexible, e.g. blown foils
• CPC Class Codes: B29C 48/21 the layers being joined at their surfaces
• CPC Class Codes: B29C 48/335 Multiple annular extrusion nozzles in coaxial arrangement, e.g. for making multi-layered tubular articles
• CPC Class Codes: B29C 48/91 Heating, e.g. for cross linking
• CPC Class Codes: B29C 48/912 of tubular films
• CPC Class Codes: B29C 48/9125 internally
• CPC Class Codes: B29C 48/913 externally
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B29K 2023/06 PE, i.e. polyethylene
• CPC Class Codes: B29K 2023/12 PP, i.e. polypropylene
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: B29L 2031/3468 Batteries, accumulators or fuel cells battery cases B29L2031/7146
• CPC Class Codes: B32B 27/32 comprising polyolefins comprising vinyl (co)polymers or acrylic (co)polymers B32B27/30
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 50/406 Moulding; Embossing; Cutting
• CPC Class Codes: H01M 50/417 Polyolefins
• CPC Class Codes: H01M 50/451 comprising layers of only organic material and layers containing inorganic material
• CPC Class Codes: H01M 50/457 comprising three or more layers
• CPC Class Codes: H01M 50/489 : Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
• CPC Class Codes: H01M 50/491 : Porosity
• CPC Class Codes: Y02E 60/10 : Energy storage using batteries

Abstract

A fusible, structurally stabilized battery separator is disclosed. The separator is formed by extruding a cylindrical parison of a polymer film and quenching the film on both sides with a low temperature fluid stream prior to processing the film to impart microporosity. Most preferably, the film includes at least a polyethylene layer and polypropylene layer.

Claims

1. A battery separator comprising a microporous polyolefinic membrane capable of maintaining an electrical resistance through the separator of greater than about 10,000 ohms-square centimeter at a temperature of at least about 185°

C. as measured at a scan rate of 60°

C. per minute.

2. The battery separator according to claim 1, wherein said polyolefinic membrane is capable of maintaining an electrical resistance greater than about 10,000 ohms-square centimeter at a temperature of at least about 185°

C. as measured as a scan rate of 2°

C. per minute.

3. The battery separator according to claim 1, wherein said polyolefinic membrane is characterized by maintaining an electrical resistance greater than about 10,000 ohms-square centimeter over a temperature range of from about 130°

C. to about 185°

C. as measured at a scan rate of 60°

C. per minute.

4. The battery separator according to claim 2, wherein said polyolefinic membrane is characterized by maintaining an electrical resistance greater than about 10,000 ohms-square centimeter over a temperature range of from about 130°

C. to about 185°

C. as measured at a scan rate of 2°

C. per minute.

5. The battery separator according to claim 1 wherein said polyolefinic membrane is formed of a polymer selected from the group consisting of polyethylene, polypropylene and mixtures thereof.

6. The battery separator according to claim 5 wherein said polyolefinic membrane comprises a microporous polyolefinic formed of isotactic polypropylene.

7. The battery separator according to claim 5 wherein said polyolefinic membrane comprises a microporous membrane formed of high density polyethylene.

8. The battery separator according to claim 1 wherein said polyolefinic membrane is a multilayer polyolefinic membrane including at least one layer formed of polypropylene and at least one layer formed of polyethylene.

9. The battery separator according to claim 8, wherein said polyolefinic membrane is a bi-layer membrane.

10. The battery separator according to claim 8, wherein said membrane is a polypropylene-polyethylene-polypropylene tri-layer membrane.

11. A method of making a battery separator comprising:

(a) extruding a cylindrical parison of a polymer film in a molten state having inner and outer surfaces;

(b) quenching the molten parison with a low temperature fluid stream applied to both surfaces of the parison such that it is in a substantially solidified state; and

(c) imparting porosity to said polymer film to make said microporous separator.

12. The method according to claim 11, wherein said method of extruding said polymer film includes co-extruding a polymer film with at least 2 layers of different composition.

13. The method according to claim 12, wherein said polymer film includes a polyethylene layer and a polypropylene layer.

14. The method according to claim 13, wherein said polyethylene layer is formed of high density polyethylene and said polypropylene layer is formed of isotactic polypropylene.

15. A method of making a battery separator comprising:

(a) extruding a cylindrical parison of a polymer film in a molten state having inner and outer surfaces;

(b) quenching the molten parison with a low temperature fluid stream applied to both surfaces of the parison such that it is in a substantially solidified state;

(c) annealing said polymer film to enhance its crystalline structure;

(d) elongating said film to impart porosity to the film; and

(e) heat setting said film.

16. The method according to claim 15, wherein said step of elongating said film comprises:

(f) elongating said film by at least about 20 per cent at a low temperature followed by;

(g) elongating said film at an elevated temperature by at least about 100 per cent.

17. The method according to claim 16, wherein said low temperature is from about 15 to about 35°

C.

18. The method according to claim 16, wherein said high temperature is from about 110°

C. to about 135°

C.

19. The method according to claim 15, wherein said polymer film includes a polyethylene layer and a polypropylene layer.

20. The method according to claim 19, wherein said polypropylene layer is formed of isotactic polypropylene.