Polyethylene and polypropylene

Example

Use in Lemonergy

Connect transport with electronic isolation.

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Ceramic-coated separator

A polyolefin separator coated with a thin layer of alumina or boehmite particles. The ceramic raises the temperature at which the film shrinks, so the electrodes stay apart longer in a thermal event.

Dry- and wet-process separators

The two routes to a porous polyolefin film. The dry process extrudes polypropylene or a PP/PE/PP trilayer, anneals it and stretches it lengthwise so slit-like pores open, with no solvent. The wet process mixes polyethylene with paraffin oil, stretches the sheet both ways and extracts the oil, giving thinner, stronger, more uniform films — the usual choice for EV cells.

Pouch foil

The flexible case of a pouch cell: a thin aluminium layer laminated between a polyamide outer film and a heat-sealable polypropylene inner film. It is light and cheap but offers no mechanical support and can swell.

Separator

A porous, electronically insulating film between the electrodes. Electrons cannot cross it; ions move through the electrolyte in its pores.

Separator shutdown

A built-in safety feature of polyolefin separators: around 130 °C the polyethylene layer melts and closes its pores, stopping ion flow and the current with it. It helps only if the separator does not also shrink and let the electrodes touch, so shutdown behavior is not universal.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. Electrolytes and Interphases in Li-Ion Batteries and Beyond

   Kang Xu · Chemical Reviews · 2014

   Topic background · Electrolyte salts, solvents, additives and electrode interphases.