Polyethylene microporous film and process for producing the same

• US 6,127,438 A
• Filed: 08/26/1997
• Issued: 10/03/2000
• Est. Priority Date: 03/03/1995
• Status: Expired due to Term

• Current Assignee: Asahi Kasei Kogyo Kabushiki Kaisha
• Original Assignee: Asahi Kasei Kogyo Kabushiki Kaisha
• Inventors: Kondo, Takahiko, Hasegawa, Takuya
• Primary Examiner(s): COONEY, JOHN M
• Application Number:
  US08/894,714
• Time in Patent Office: 1,134 Days
• Field of Search: 429/249, 429/254, 521/64, 521/143, 264/41, 264/210.3, 264/210.4, 264/210.5, 264/210.7, 264/211, 264/211.13, 264/211.2, 210/500.27, 210/500.36, 210/500.42, 428/315.5
• US Class Current: 521/64
• 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 2300/0025 Organic electrolyte
• CPC Class Codes: H01M 50/417 Polyolefins
• 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
• CPC Class Codes: Y10T 428/249978 Voids specified as micro

Abstract

A polyethylene microporous film excellent in mechanical strength, permeability and productivity and having a very high reliability such that the safety of a battery may be secured even under severe circumstances which film has a crosslinked structure and has a porosity of 20-80%, a gel fraction of 1% or more, and an average pore diameter determined by the permeation method of 0.001-0.1 μm, and a process for producing the polyethylene microporous film.

Claims

1. A polyethylene microporous film having high strength and excellent heat resistance which has a crosslinked structure and has a porosity of 20-80%, a gel fraction of 1% or more and an average pore diameter determined by the permeation method of 0.001-0.1 μ

m.

2. The polyethylene microporous film according to claim 1 which has a residual contraction rate of 15% or more.

3. The polyethylene microporous film according to claim 1 or 2 which has a fuse speed of 5.0 or more.

4. The polyethylene microporous film according to claim 1 which has a piercing strength of 300 g or more.

5. The polyethylene microporous film according to claim 1 which has a piercing strength of 400 g or more.

6. The polyethylene microporous film according to claim 1 which has a breaking time in silicone oil at 160°

C. of 20 seconds or more.

11. A separator for batteries made from the polyethylene microporous film according to claim 1.

12. A battery containing the separator of claim 11.

13. A separator according to claim 11, wherein said batteries are lithium ion batteries.

14. A lithium ion battery containing the separator of claim 13.

17. The polyethylene microporous film of claim 1, wherein the film has an air permeability, converted to a thickness of 25 μ

m, of not more than 2,000 seconds.

7. A process for producing a polyethylene microporous film comprising the steps of preparing a hot solution consisting essentially of polyethylene and a plasticizer, cooling and solidifying the hot solution to form a sheet, stretching the sheet in at least a uniaxial direction to obtain an oriented film, and removing by extraction the plasticizer contained in the oriented film wherein at least one crosslinking treatment is applied to the sheet or film during any one of the process steps or after the process steps.

8. The process for producing a polyethylene microporous film according to claim 7 wherein the crosslinking treatment is applied after the stretching.

9. The process for producing a polyethylene microporous film according to claim 7 or 8 wherein the crosslinking treatment is electron beam irradiation.

10. The process for producing a polyethylene microporous film according to claim 7 wherein electron beam irradiation is conducted after removing the plasticizer by extraction.

15. The process for producing a polyethylene microporous film according to claim 7, wherein the plasticizer is selected from the group consisting of decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane and paraffin oil.

16. The process for producing a polyethylene microporous film according to claim 7, wherein the plasticizer concentration is in the range of from 20 to 90 wt. %, based upon the total mass of plasticizer plus polyethylene.