Page 21

THE TECH

Unrestrained Shrinkage at 130˚C

Image courtesy of Porous Power Technologies

Using test method ASTM D1204

Original size

Wet process Wet process 12 micron 20 micron polyolefin polyolefin

Dry process 20 micron polyolefin shutdown trilayer

Dry process 25 micron polyolefin monolayer

Charged: What is the role of ceramics in battery separators? BP: Virtually all large-format cells are using battery separators that contain ceramics. It reduces shrinkage, adds thermal stability and higher temperature performance. When a polyolefin separator gets up to about 110 degrees C, it starts shrinking quite a bit - up to 5%. If it shrinks away from the electrode edges, there are problems. So, they put ceramics on top to reduce the shrinkage and add thermal stability. The problem is that when you overcoat a porous structure, you fill up the pores, and it’s very difficult to maintain high or effective porosity. We don’t overcoat ceramics. We actually mix ceramic particles into the solution before we cast the separator. When the pores are formed, the ceramics are embedded into the wall system and not in the pores. So our separa-

Porous Power’s SYMMETRIX HPX

Porous Power’s SYMMETRIX HPXF

We don’t overcoat ceramics. We actually mix ceramic particles into the solution before we cast the separator.

tors with a high loading of ceramics are about the same porosity as our separators without ceramics. With a polyolefin separator, the maximum you can really get them to is about 55 percent porous. Overcoat them with ceramics on two sides, and you net out at about an effective 40 percent porosity. Not only do they lose a lot of effective porosity, but most start with a lower porosity to begin with. We start with about 65 percent porosity. After the addition of the ceramics, we only lose a couple of percent

SUBSCRIBE NOW www.chargedevs.com/subscribe

DEC 2013 21

CHARGED Electric Vehicles Magazine - Iss 11 DEC 2013  

CHARGED Electric Vehicles Magazine - Iss 11 DEC 2013