The separator is a porous polymer-based membrane with a thickness of 15-25 µm that acts as an electronic insulator and prevents the direct electronic contact between both electrodes to avoid an internal short circuit. The majority of the microporous separators are either based on polyolefins polypropylene or polyethylene in single- or multi-layer design. Microporous separators may be additionally coated with ceramics, for example, Al2O3 to support higher temperature tolerance and, thus, safety. Further, ceramic particles also improve the wettability of the separator with the electrolyte.