Low electrical resistance microporous battery separator membranes, separators, cells, batteries, and related methods
Novel or improved microporous battery separator membranes, separators, cells, batteries including such membranes, separators, or cells, and/or methods of making such membranes and/or separators, and/or methods of using such membranes and/or separators. In accordance with at least certain embodiments, an improved or novel battery separator for a secondary or rechargeable lithium battery may have low Electrical resistance of less than 0.95 ohm-cm 2 , or in some cases, less than 0.8 ohm-cm 2 . Furthermore, the inventive battery separator membrane may provide a means to achieve an improved level of battery performance in a rechargeable or secondary lithium battery based on a possibly synergistic combination of low Electrical resistance, low Gurley, low tortuosity, and/or a unique trapezoid shaped pore. In accordance with at least certain multilayer embodiments (by way of example only, a trilayer membrane made of two polypropylene layers with a polyethylene layer in between), the inventive microporous membrane or battery separator may have excellent onset and rate of thermal shutdown performance.
1. A biaxially-stretched dry-process microporous membrane, wherein the membrane was stretched in the machine direction (MD) and in the transverse direction (TD), and stretching in the TD uses a stretch ratio of 15% to 100%; wherein the biaxially-stretched dry-process microporous membrane has an electrical resistance less than 0.95 ohm-cm 2 .
2. The biaxially-stretched dry-process microporous membrane of claim 1 , wherein stretching in the TD uses a stretch ratio of 20% to 100%.
3. The biaxially-stretched dry-process microporous membrane of claim 2 , wherein the membrane comprises non-round shaped pores.
4. The biaxially-stretched dry-process microporous membrane of claim 2 , wherein the membrane comprises trapezoidal pores.
5. The biaxially-stretched dry-process microporous membrane of claim 1 , wherein stretching in the TD uses a stretch ratio of 25% to 100%.
6. The biaxially-stretched dry-process microporous membrane of claim 5 , wherein the membrane comprises non-round shaped pores.
7. The biaxially-stretched dry-process microporous membrane of claim 5 , wherein the membrane comprises trapezoidal pores.
8. The biaxially-stretched dry-process microporous membrane of claim 1 , wherein the membrane comprises non-round shaped pores.
9. The biaxially-stretched dry-process microporous membrane of claim 1 , wherein the membrane comprises trapezoidal pores.
10. The biaxially-stretched dry-process microporous membrane of claim 1 , having a Gurley less than 500 sec/100 cc.
11. The biaxially-stretched dry-process microporous membrane of claim 1 , having a tortuosity less than 1.5.
12. A battery separator comprising the biaxially-stretched dry-process microporous membrane of claim 1 .
13. A battery comprising the separator of claim 12 .
14. A battery cell comprising the separator of claim 12 .
15. A battery separator for a rechargeable or secondary lithium battery comprising the biaxially-stretched dry-process microporous membrane of claim 1 and having Gurley of less than 150 seconds/100cc, tortuosity of less than 1.2, trapezoid shaped pores, or combinations thereof.
16. A multilayer battery separator for a rechargeable or secondary lithium battery comprising the biaxially-stretched dry-process microporous membrane of claim 1 .
17. The biaxially-stretched dry-process microporous membrane of claim 1 having an electrical resistance of less than 0.70 ohm-cm 2 .
18. The biaxially-stretched dry-process microporous membrane of claim 1 having an electrical resistance of less than 0.60 ohm-cm 2 .