ENTEK is the world leader in battery separator technology. Our deep knowledge of battery chemistry, separator properties and in-application uses is what sets us apart from the competition.
Separators are an integral part of the performance, safety, and cost of lithium batteries. The term “lithium batteries” refers to both (1) non-rechargeable, lithium metal-based batteries and (2) rechargeable lithium-ion batteries which are widely used in portable electronic devices. During normal operation, the principal functions of the separator are to prevent electronic conduction (i.e., shorts or direct contact) between the anode and cathode while permitting ionic conduction via the electrolyte.
For small commercial cells under abuse conditions, such as external short circuit or overcharge, the separator is required to shut down at temperatures well below where thermal runaway can occur. Shutdown results from collapse of the pores in the separator due to melting and viscous flow of the polymer, thus slowing down or stopping ion flow between the electrodes. Nearly all Li-ion battery separators contain polyethylene as part of a single- or multi-layer construction so that shutdown begins at ~135 °C, the melting point of polyethylene. Battery failures in the field, however, have demonstrated that shutdown is not a guarantee of safety. The principle reason is that, after shutting down, the internal temperature of the battery is often high enough to cause residual stress and reduced mechanical properties leading to shrinkage, tearing, or pinhole formation.