The separator is a thin, porous membrane placed between the battery’s anode and cathode. Its primary function is to keep the positive and negative electrodes apart to prevent short-circuiting, while still permitting ions (like lithium ions) to flow through it back and forth during charge and discharge. Separators are usually made of polymers like polyethylene (PE), polypropylene (PP), or trilayer PP/PE/PP. They are typically 10 – 30 micrometers thick. They have a microscopic pore structure where the pores fill with the liquid electrolyte. The electrolyte-soaked separator allows ionic conduction through the pores while being an electronic insulator. Key properties of separators include mechanical strength, uniform pore structure and thermal stability below 130°C. Some separators are designed to close the pores at a certain temperature to stop ion flow to help improve cell safety.
NOVONIX assesses separators when evaluating cell performance and safety. They may test cells with different separator types to see how it impacts internal resistance and rate capability (different separators have different thicknesses and porosities, affecting ion transport). In R&D, if a new separator is introduced, NOVONIX will quantify any performance metrics compared to standard separators.
