Dreamweaver separators contain cellulose nanofibers, and generally are shipped with less than 3% water content. Hand sheets should be dried for 1 hour at 120 C in a vacuum oven. Roll drying will depend on the size of the roll and the level of moisture required, with larger rolls requiring more time, and a requirement for very low moisture levels also requiring more time. We suggest 120 C for 24-48 hours, though more aggressive parameters may be appropriate for certain situations.
Dreamweaver separators look and feel like paper, and will compress several microns up to 25 psi of pressure. Dreamweaver reports thickness at 12 and 25 psi.
We measure thickness by stacking 10 sheets and measuring the thickness between two platens under known pressure, then dividing by 10, which gives results that are more relevant to multilayer batteries.
Polyolefin separators generally have a porosity ranging between 35 – 45%, while Dreamweaver separators have a porosity of 55-65%, and thus require more electrolyte. In addition, the amount of electrolyte needed will depend on the geometry and assembly of the specific cell in question. This additional porosity and electrolyte increase the conductivity of the separator/electrolyte, reducing internal resistance and providing longer cycle life in some cell.
If the deficit not too high, the internal resistance will be higher and the rate capability lower. If the deficit is more, then soft shorts may appear.
Dreamweaver Silver™ contains polyacrylonitrile nanofibers, which will swell with carbonate solvents commonly used in lithium ion batteries, giving performance similar to gelled electrolytes used in lithium polymer batteries. Dreamweaver Silver™ AR contains cellulose fibers, which will swell in some concentrations of alkaline aqueous electrolytes used in metal electrode and alkaline batteries. When swollen, the fibers become somewhat conductive to ions.
The SEI layer has been known to need different conditions to form properly, depending on the electrode system and the battery geometry. Dreamweaver’s internal studies show that if the final voltage, time of initial charge, and the constant voltage threshold are chosen judiciously, the SEI layer will form properly, but the parameters may be different than those used with polyolefin separators.
The mean flow pore size varies between 0.4 and 1.5 microns, depending on the separator. It is reported on the brochures for each product. This is measured in a liquid that does not swell the fibers. In electrolytes where the fibers swell, the mean flow pore size will be smaller.
Dreamweaver Silver and Gold separators are designed to work in common lithium ion battery electrolytes, and have high electrolytic stability having now been put through over 1000 cycles at 60 C. One component of the Dreamweaver Silver separator is soluble in pure propylene carbonate, and so Dreamweaver Silver is not recommended for supercapacitors that use pure PC. Blends of PC with other carbonates that are commonly used as electrolytes for lithium ion batteries do not dissolve this component, but may swell the fibers. It is believed that these swollen fibers are ionic conductors, which contributes to the enhanced rate capability of the Dreamweaver Silver separator.
