Multi-layer, microporous membrane, battery separator and battery
View Patent ↗Disclosed herein is a multi-layer, microporous polyolefin membrane comprising a first porous layer of a polyethylene, and a second porous layer comprising a polyethylene, and polypropylene having a weight-average molecular weight of 6×10 5 or more and a fraction having a molecular weight of 1.8×10 6 or more being 10% or more by mass.
1. A multi-layer, microporous membrane comprising a first porous layer comprising primarily polyethylene, and a second porous layer comprising 0.1 to 99.9 wt % polyethylene and 0.1 to 99.9 wt % polypropylene, the polypropylene having (1) a weight-average molecular weight of 6×10 5 or more, (2) the fraction having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene, and (3) a heat of fusion of 90 J/g or more.
2. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a heat of fusion of 100 J/g or more.
3. The multi-layer, microporous membrane of claim 1 wherein the fraction of polypropylene having a molecular weight of 1.8×10 6 or more being 10% or more by mass of the polypropylene.
4. The multi-layer, microporous membrane of claim 1 wherein the polyethylene of the first and/or second layer has a weight-average molecular weight of 2×10 5 or more.
5. The multi-layer, microporous membrane of claim 4 wherein the polyethylene of the first and/or second layer has a weight-average molecular weight of 5×10 5 or more.
6. The multi-layer, microporous membrane of claim 5 wherein the polyethylene of the first and/or second layer has a weight-average molecular weight of from 1×10 6 to 15×10 6 .
7. The multi-layer, microporous membrane of claim 1 wherein the polyethylene of the first and/or second layer has a weight-average molecular weight of 1×10 4 or more and less than 5×10 5 .
8. The multi-layer, microporous membrane of claim 1 wherein the polyethylene of the first and/or second layer has an Mw/Mn of 5 to 300.
9. The multi-layer, microporous membrane of claim 1 wherein the polypropylene of the second layer has a weight-average molecular weight of 6.5×10 5 or more and a heat of fusion of 95 J/g or more, the fraction of the polypropylene having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene.
10. The multi-layer, microporous membrane of claim 1 wherein the polypropylene content of the second layer is from 5 to 95% by mass.
11. The multi-layer, microporous membrane of claim 1 wherein the polypropylene content of the second layer is from 20 to 80% by mass.
12. The multi-layer, microporous membrane of claim 1 wherein the polypropylene content of the second layer is from 30 to 70% by mass.
13. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a weight-average molecular weight of 6×10 5 to 1×10 6 .
14. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a Mw/Mn of 2.5 or less.
15. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a weight-average molecular weight of 1×10 6 to 1.5×10 6 .
16. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a Mw/Mn of 3 or less.
17. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a weight-average molecular weight of 1.5×10 6 to 2×10 6 .
18. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a Mw/Mn of 4 or less.
19. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a weight-average molecular weight of greater than 2×10 6 .
20. The multi-layer, microporous membrane of claim 1 wherein the polypropylene has a Mw/Mn of 5 or less.
21. The multi-layer, microporous membrane of claim 1 having a porosity of 25 to 80%, an air permeability of 20 to 2,000 seconds/100 cc (converted to the value at 20-μm thickness), a pin puncture strength of 2,000 mN/20 μm or more, a shut down temperature of 120 to 140° C., and a meltdown temperature of 170° C. or higher.
22. The multi-layer, microporous membrane of claim 1 having a thickness of 3-200 μm.
23. The multi-layer, microporous membrane of claim 1 comprising a two-layer structure comprising the first porous layer and the second porous layer; a three-layer structure comprising the first porous layer, the second porous layer and the first porous layer; or a three-layer structure comprising the second porous layer, the first porous layer and the second porous layer.
24. A method for producing a multi-layer, microporous membrane comprising the steps of
(1) preparing a first melt-blend polyolefin solution comprising polyethylene and a diluent;
(2) preparing a second melt-blend polyolefin solution comprising a diluent and a polyolefin composition comprising a 0.1 to 99.9 wt % polyethylene and 0.1 to 99.9 wt % polypropylene having a weight-average molecular weight of 6×10 5 or more, the fraction having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene; and wherein the heat of fusion of the polypropylene is 90 J/g or more;
(3) extruding the first and second polyolefin solutions through separate dies to form a first extrudate and a second extrudate;
(4) cooling each of the resultant first and second extrudates to form first and second gel-like sheets;
(5) stretching the first and second gel-like sheets in at least one direction to form first and second films;
(6) removing the diluent from the first and second films;
(7) drying the first and second films to form first and second membranes;
(8) heat-treating the first and second membranes; and
(9) laminating the resultant first and second membranes to form the multi-layer, microporous polyolefin membrane.
25. The method of claim 24 wherein the heat of fusion of the polypropylene is 90 J/g or more.
26. The method of claim 24 wherein the polypropylene has a weight-average molecular weight of 6×10 5 to 1×10 6 .
27. The method of claim 24 wherein the polypropylene has a Mw/Mn of 2.5 or less.
28. The method of claim 24 wherein the polypropylene has a weight-average molecular weight of 1×10 6 to 1.5×10 6 .
29. The method of claim 24 wherein the polypropylene has a Mw/Mn of 3 or less.
30. The method of claim 24 wherein the polypropylene has a weight-average molecular weight of 1.5×10 6 to 2×10 6 .
31. The method of claim 24 wherein the polypropylene has a Mw/Mn of 4 or less.
32. The method of claim 24 wherein the polypropylene has a weight-average molecular weight of greater than 2×10 6 .
33. The method of claim 24 wherein the polypropylene has a Mw/Mn of 5 or less.
34. The method of claim 24 wherein the fraction of polypropylene having a molecular weight of 5×10 4 or less is 3% or less by mass of the polypropylene.
35. The method of claim 24 wherein the polypropylene has a heat of fusion of 100 J/g or more.
36. The method of claim 24 wherein the polyethylene of the first and/or second polyolefin solution has a weight-average molecular weight of 2×10 5 or more.
37. The method of claim 24 wherein the polyethylene of the first and/or second polyolefin solution has a weight-average molecular weight of 5×10 5 or more.
38. The method of claim 37 wherein the polyethylene of the first and/or second polyolefin solution has a weight-average molecular weight of from 1×10 6 to 15×10 6 .
39. The method of claim 24 wherein the polyethylene of the first and/or second polyolefin solution has a weight-average molecular weight of 1×10 4 or more and less than 5×10 5 .
40. The method of claim 24 wherein the polypropylene of the second polyolefin solution has a weight-average molecular weight of 6.5×10 5 or more and a heat of fusion of 95 J/g or more, the fraction having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene.
41. The method of claim 24 wherein the polypropylene content of the second polyolefin solution is from 5 to 95% by mass.
42. The method of claim 24 wherein the polypropylene content of the second polyolefin solution is from 20 to 80% by mass.
43. The method of claim 24 wherein the polypropylene content of the second polyolefin solution is from 30 to 70% by mass.
44. The method of claim 24 wherein step (9) comprises forming an at least three layer microporous membrane by laminating the resultant first gel-like sheet to each opposite side of the second gel-like sheet to form the multi-layer, microporous polyolefin membrane.
45. The method of claim 24 wherein step (9) comprises forming an at least three layer microporous membrane by laminating the resultant second gel-like sheet to each opposite side of the first gel-like sheet to form the multi-layer, microporous polyolefin membrane.
46. The method of claim 24 wherein the polyethylene in the first melt-blend polyolefin solution and the polyolefin composition in the second melt-blend polyolefin solution are 1 to 50% by mass of the respective melt-blend polyolefin solution.
47. A method for producing a multi-layer, microporous membrane comprising the steps of
(1) preparing a first melt-blend polyolefin solution comprising a polyethylene and a diluent;
(2) preparing a second melt-blend polyolefin solution comprising a diluent and a polyolefin composition comprising a polyethylene and polypropylene having a weight-average molecular weight of 6×10 5 or more and a heat of fusion (measured by a differential scanning calorimeter) of 90 J/g or more; the fraction of polypropylene having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene;
(3) simultaneously extruding the first and second polyolefin solutions through dies to form a laminar coextrudate;
(4) cooling each of the laminar coextrudate to form a multi-layer gel-like sheet;
(5) stretching the multi-layer gel-like sheet in at least one direction to form a multi-layer film;
(6) removing the diluent from the stretched multi-layer film;
(7) drying the multi-layer film to form a multi-layer membrane; and
(8) heat-treating the multi-layer membrane to form the multi-layer, microporous polyolefin membrane.
48. The method of claim 47 wherein the laminar coextrudate product of step (3) comprises layers of the first gel-like sheet on each opposite side of the second gel-like sheet to form the multi-layer, microporous polyolefin membrane.
49. The method of claim 47 wherein the laminar coextrudate product of step (3) comprises layers of the second gel-like sheet on each opposite side of the first gel-like sheet to form the multi-layer, microporous polyolefin membrane.
50. A battery separator composed of a multi-layer, microporous membrane comprising a first porous layer comprising primarily polyethylene, and a second porous layer comprising polyethylene and polypropylene, the polypropylene having a weight-average molecular weight of 6×10 5 or more, a heat of fusion (measured by a differential scanning calorimeter) of 90 J/g or more; the fraction of polypropylene having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene.
51. The battery separator of claim 50 wherein said microporous membrane comprises a two-layer structure comprising the first porous layer and the second porous layer; a three-layer structure comprising the first porous layer, the second porous layer and the first porous layer; or a three-layer structure comprising the second porous layer, the first porous layer and the second porous layer.
52. The battery separator of claim 50 having a porosity of 25 to 80%, an air permeability of 20 to 2,000 seconds/100 cc (converted to the value at 20-μm thickness), a pin puncture strength of 2,000 mN/20 μm or more, a shut down temperature of 120 to 140° C., and a meltdown temperature of 170° C. or higher.
53. The battery separator of claim 52 having a thickness of 3-200 μm.
54. A battery comprising a battery separator comprising of a multi-layer, microporous polyolefin membrane comprising a first porous layer comprising primarily polyethylene, and a second porous layer comprising a polyethylene and polypropylene, the polypropylene having a weight-average molecular weight of 6×10 5 or more and a heat of fusion (measured by a differential scanning calorimeter) of 90 J/g or more; the fraction of polypropylene having a molecular weight of 1.8×10 6 or more being 10% or more by mass by mass of the polypropylene.
55. The battery of claim 54 wherein the battery separator comprises a two-layer structure comprising the first porous layer and the second porous layer; a three-layer structure comprising the first porous layer, the second porous layer and the first porous layer; or a three-layer structure comprising the second porous layer, the first porous layer and the second porous layer.
56. The battery of claim 54 wherein the battery separator has a porosity of 25 to 80%, an air permeability of 20 to 2,000 seconds/100cc (converted to the value at 20 μm thickness), a pin puncture strength of 2,000 mN/20 μm or more, a shut down temperature of 120 to 140° C., and a meltdown temperature of 170° C. or higher.
57. The battery of claim 54 wherein the battery separator has a thickness of 3-200 μm.