Dry- and wet-process separators

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.

Polyethylene and polypropylene

The two commodity polyolefins of a cell. Almost every separator is PE, PP or a layered combination: PE melts near 130 °C and closes its pores, while PP keeps its shape to about 165 °C. PP also forms the heat-sealing inner layer of pouch foil, and both appear in packs as insulating films and moulded parts.

Porosity

The fraction of a layer’s volume that is empty space. In a lithium-ion electrode the pores — roughly 20–35 % of the volume after calendering — are filled with electrolyte, which carries ions to the particles.

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.