Study on the lithium dendrite puncturing resistance of nonwoven separators

The occurrence of an internal short circuit caused by lithium dendrite puncturing the separators is a critical safety issue for lithium batteries. While the investigation of dendrite puncturing resistance of commercial polyolefin separators is well-established, nonwoven separators have received fewer relevant studies. Therefore, we assembled lithium-symmetric cells, lithium-sulfur batteries, and lithium-lithium iron phosphate batteries using three commercial nonwoven separators and a homemade micro-fibrillated cellulose nonwoven separator to verify the ability of the nonwoven separator to resist lithium dendrite penetration. The results reveal that even under low current densities, all four types of nonwoven separators are susceptible to dendrite puncturing, leading to both hard short circuits with significant voltage drops, as well as soft short circuits with charging currents or voltage fluctuations. Moreover, the impedance of lithium-symmetric cells is significantly reduced after short circuit, while the charge transfer resistance of lithium-sulfur batteries increases substantially after short circuit. Our findings provide valuable insights for the development of nonwoven separators for use in lithium metal batteries, highlighting the need for further reduction in pore size.