Multi-region battery separators
Disclosed is a battery separator, comprising two fiber regions comprising glass fibers, and a middle fiber region disposed between them comprising larger average diameter fibers and specified amounts of silica, or fine fibers, or both; and processes for making the separator. Also disclosed is a battery separator, comprising a fiber region and either one or two silica-containing region(s) adjacent thereto, each of the regions containing a specified amount of silica; and processes for making the separator. Such separators are useful, e.g., in lead-acid batteries.
1. A battery separator, comprising:
a middle fiber region;
a first peripheral fiber region; and
a second peripheral fiber region;
wherein the middle fiber region comprises fibers having an average diameter of greater than or equal to about 2 μm; and
wherein each of the first and second peripheral fiber regions independently comprises glass fibers having an average diameter from about 0.1 to about 2 μm;
provided that the average diameter of the fibers of the middle fiber region is larger than the average diameter of the fibers of each of the first and second peripheral fiber regions;
wherein the middle fiber region is disposed between the first peripheral fiber region and the second peripheral fiber region;
wherein the thickness of the middle fiber region constitutes 10-40% of the total fiber region thickness; and
wherein the thickness of the first peripheral fiber region is different from the thickness of the second peripheral fiber region.
2. A lead-acid battery comprising a negative plate, a positive plate, and a battery separator according to claim 1 , wherein the battery separator is disposed between the negative and positive plates.
3. The battery separator according to claim 1 , wherein the middle fiber region comprises glass fibers having an average diameter from 2 to about 50 μm.
4. The battery separator according to claim 1 , wherein the middle fiber region comprises fibers having an average diameter from about 3 to about 15 μm.
5. The battery separator according to claim 1 , wherein the middle fiber region comprises glass fibers having an average diameter from about 3 to about 15 μm.
6. The battery separator according to claim 1 , wherein each of the first and second peripheral fiber regions independently comprises glass fibers having an average diameter from about 0.4 to about 1.8 μm.
7. The battery separator according to claim 1 , wherein the thickness of the middle fiber region constitutes 10-30% of the total fiber region thickness.
8. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 10 to about 30% by weight fibers having an average diameter from about 0.8to about 1.6 μm.
9. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 2 to about 30% by weight silica.
10. The battery separator according to claim 1 , wherein the average glass fiber diameter of the first peripheral fiber region differs from the average glass fiber diameter of the second peripheral fiber region by greater than or equal to 0.5 μm.
11. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 1 to 50% by weight fibers having an average diameter from about 0.1 to less than 2 μm, and wherein the tensile strength (machine direction) of the separator is about 2.00 to about 2.40 lbs/inch.
12. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 1 to 50% by weight fibers having an average diameter from about 0.1 to less than 2 μm, and wherein the tensile strength (cross direction) of the separator is about 1.75 to about 2 . 20 lbs/inch.
13. The battery separator according to claim 1 , wherein the separator exhibits an acid filling time of about 3 0 to about 70 seconds.
14. The battery separator according to claim 1 , wherein the separator exhibits an acid filling time of about 17 to about 50 seconds.
15. The battery separator according to claim 1 , wherein the separator exhibits an acid stratification distance from about 2.5 to about 16 cm.
16. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 5 to about 50% by weight glass fibers having an average diameter from about 0.1 to less than 2 μm.
17. The battery separator according to claim 1 , wherein the middle fiber region comprises from about 5 to about 50% by weight glass fibers having an average diameter from about 0.8 to about 1.6 μm.
18. A battery separator, comprising:
a middle fiber region;
a first peripheral fiber region; and
a second peripheral fiber region;
wherein the middle fiber region comprises fibers having an average diameter of greater than or equal to about 2 μm; and
wherein each of the first and second peripheral fiber regions independently comprises glass fibers having an average diameter from about 0.1 to about 2 μm;
provided that the average diameter of the fibers of the middle fiber region is larger than the average diameter of the fibers of each of the first and second peripheral fiber regions;
wherein the middle fiber region is disposed between the first peripheral fiber region and the second peripheral fiber region;
wherein the thickness of the middle fiber region constitutes 10-40% of the total fiber region thickness;
wherein the thickness of the first peripheral fiber region is different from the thickness of the second peripheral fiber region; and
wherein formation of the battery separator involves a process comprising:
(a) providing a first slurry of fibers having an average diameter from about 0.1 μm to about 2 μm;
(b) laying down the first slurry on a wire of a papermaking machine;
(c) providing a second slurry of fibers having an average diameter of greater than or equal to about 2 μm;
(d) laying down the second slurry on top of the first slurry; and
(e) dewatering the first and second slurries to form a 2-layer structure comprising the first peripheral region and at least a portion of the middle fiber region.