Separators for enhanced flooded batteries, batteries, and related methods
A battery separator has performance enhancing additives or coatings, fillers with increased friability, increased ionic diffusion, decreased tortuosity, increased wettability, reduced oil content, reduced thickness, decreased electrical resistance, and/or increased porosity. The separator in a battery reduces the water loss, lowers acid stratification, lowers the voltage drop, and/or increases the CCA. The separators include or exhibit performance enhancing additives or coatings, increased porosity, increased void volume, amorphous silica, higher oil absorption silica, higher silanol group silica, reduced electrical resistance, a shish-kebab structure or morphology, a polyolefin microporous membrane containing particle-like filler in an amount of 40% or more by weight of the membrane and ultrahigh molecular weight polyethylene having shish-kebab formations and the average repetition periodicity of the kebab formation from 1 nm to 150 nm, decreased sheet thickness, decreased tortuosity, separators especially well-suited for enhanced flooded batteries.
1. A separator for a lead acid battery comprising a polyolefin microporous membrane, wherein the polyolefin microporous membrane comprises:
polyethylene, a silica filler, and a processing plasticizer; wherein the silica filler is present in an amount of 40% or more by weight and has a molecular ratio of OH to Si groups, measured by 29 Si-NMR, within a range of 21:100 to 35:100;
the polyethylene comprises polymer in a shish-kebab formation comprising a plurality of extended chain crystals and a plurality of folded chain crystals and wherein the average repetition of the folded chain crystals is from 1 nm to 150 nm.
2. The separator for a lead acid battery according to claim 1 , wherein
the average repetition of the extended chain crystals is defined by: taking an image of the surface of the polyolefin microporous membrane with a SEM, indicating at least three rectangular regions where the shish-kebab formation is continuously extended in the length of at least 0.5 μm or longer in the same SEM image, and specifying the repetition by Fourier Transform of contrast profile projected in the vertical direction to the length direction of the each indicated rectangular region to calculate the average of the repetition periods.
3. The separator for a lead acid battery according to claim 1 , wherein the silica filler is selected from the group consisting of silica, precipitated silica, fumed silica, and precipitated amorphous silica.
4. The separator for a lead acid battery according to claim 1 , wherein the processing plasticizer is selected from the group consisting of:
processing oil, paraffin-based oil, and mineral oil.
5. The separator according to claim 1 , wherein silica is present at the folded chain crystals of polymer.
6. The separator according to claim 1 , wherein the silica filler is friable to such a degree that after 30 seconds of ultrasonication, a median silica particle size is approximately 5.2 μm or less.
7. The separator according to claim 1 , wherein the silica filler is friable to such a degree that after 60 seconds of ultrasonication, a median silica particle size is approximately 0.5 pμm or less.
8. The separator according to claim 1 , comprising:
a mean pore size of at least approximately 120 nm.
9. The separator according to claim 1 , comprising:
a diffusion coefficient of at least approximately 1.6·10 31 10 at −5° C., and
an electrical resistance of approximately 40 mΩ·cm 2 or lower.
10. The separator according to claim 1 , comprising:
a diffusion coefficient of at least approximately 8.8·10 −10 at 30° C., and
an electrical resistance of approximately 40 mΩ·cm 2 or lower.