Enhancing lithium-ion battery safety: A comparative study of separator performance under mechanical abuse

Batteries serve as the primary energy storage solution for a wide range of applications. However, the high energy density of these batteries presents significant safety challenges. The separator in a battery cell plays a crucial role since damage to the separator will cause an internal short circuit and can trigger a thermal runaway. To evaluate the differences in the response of a separator to mechanical stress five distinct polyolefin and nonwoven separators were tested in two separator material level tests. Battery cells were then fabricated with these separators and tested for mechanical stability and thermal runaway behavior during crush tests with a hemispherical punch. The results disclose that internal short circuits occur in the dry processed polyolefin-based separators at low mechanical loads. The incorporation of ceramic particles within the nonwovens and the elevated thermal stability impart a heightened short-circuit load capacity of 17 % and a notable delay in the onset of thermal runaway. The most promising outcome is observed in the wet-processed PE separator with a ceramic coating, exhibiting a 33 % increase in load and a 25 % increase in deformation compared to the polyolefin separators. In addition, CO concentrations doubled between nonwoven and pure polyolefin based separators.