NANOFIBERS & MICROFIBERS: Spider Webs and Scaffolding

THE PROBLEM:
No One Thing Works

Nanofibers:  Nanofibers give small pore sizes, but pack at very high densities, leaving little room for ions to pass through a membrane. 

Microfibers:  Microfibers provide high strength and pack at high porosity, but the pore size is too large to be useful for supercapacitors and lithium ion batteries.

"Middlefibers": Fibers with sizes around a micron deliver the worst of both worlds.  While the pore size is too large, because the fibers must be short to process, the strength also goes down.

THE SOLUTION:
A Combination of Approaches

Layered Approach:  Some university labs and others have made suitable separators by electrospinning nanofibers onto a nonwoven substrate.  However, electrospinning is a production infant in the nonwoven world, with slow throughput yielding highly nonuniform products with a very light, weak coating performing a the critical task of delivering consistently small pores.

Dreamweaver Solution: Nanofibers and microfibers intimately blended in high shear mixing, then cast together in high speed, high quality wet laid nonwoven manufacturing. 

In Dreamweaver's separators, the microfibers form a scaffolding over which the nanofiber "spider webs" drape, giving strength and dimensional stability as well as small pore size.

At higher magnification, it is clear the nanofibers form a barrier to dendrite growth and other cross contamination.

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Outstanding Separator Properties

Outstanding Thermal Performance

Dreamweaver separators combine microfibers that melt with nanofibers that do not melt, and are stable to 300 C.  We then press them together to form a coherant network which is stable in even the most harsh conditions. The result is a separator with extraordinarily low shrinkage even above 300 C.  See the comparison to conventional materials in the chart on the right.

The pictures (below right) show a conventional polyolefin separator and Dreamweaver Gold before and after 5 minutes at 150 C, and again after 5 minutes at 190 C.  While the Gold separator is unchanged, the polypropylene separator shrinks dramatically at 150 C, and nearly disappears after 190 C.  Can you find it in the picture?

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Small Pores, Narrow Distribution

In modern wet laid nonwoven manufacturing, as the water is drained from the slurry of fibers, the fibers are drawn to any areas of low density.  This results in very uniform sheets with a naturally low pore size distribution.  See the chart to the right, showing most pores at 0.4 microns with only 0.05 micron width of the peak at half the maximum value.

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Superior Wettability

With a porosity as much as 10% higher, highly polar nanofibers, and an incredibly high surface area, the wet out of electrolyte is exceptional.

In a wicking test with different common solvents for lithium ion battery and supercapacitors, Dreamweaver separators averaged between 1.5 and 3 times the wick height.

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Dreamweaver International
18-B Brozzini Court Greenville, SC 29615