The separator permits ion flow from one electrode to the other while preventing any electron flow, essentially separating the anode from the cathode.
The typical separator is made up of polyolefins, usually polypropylene and/or polyethylene, along with other polymers, ceramics, and ceramic/polymer blends.
Separators are highly porous, typically
>40% porosity, approximately 25 μm thick and exhibit low ionic resistivity. Layered or composite separators are used as safety devices to prevent thermal runaway
of the cell.
Binder materials are used to hold the active electrode material particles together and in contact with the current collectors, i.e. the Aluminum Foil of the cathode or the Copper Foil of the anode.