Comprehensive evaluation of safety performance and failure mechanism analysis for lithium sulfur pouch cells

Abstract

Here, we first propose a comprehensive evaluation method of lithium sulfur (Li-S) pouch cells safety performance, including nail penetration, impact, external short circuit and overcharge tests. Using high definition IR imaging combined with a temperature-voltage data acquisition system, XPS and SEM, careful analysis of the thermal and electrochemical behaviors, chemical compositions and evolution of electrode structure of Li-S pouch cells is performed. Furthermore, the failure mechanism of Li-S pouch cells has been proposed for the first time. Based on the mechanism, an important self-protection “insulated seal” and overcharge without triggering safety hazards in Li-S pouch cells are identifed and elucidated in detal. Meanwhile, a pivotal strategy to address thermal runaway in Li-S pouch cells under abuse conditions is proposed by designing and fabricating a thermally conductive separator accordingly. The as-made carbon coated (LA132-C) separator shows in-plane thermal conductivity of 8.43 ​W ​m−1 ​K−1, which is 228% of commercial separators. The practical application of the as-made separator is highlighted by evaluating Li-S pouch cell to meet the standards for all abuse tests and delivers a high capacity retention rate of 87.7% over 30 cycles at 0.05C under lean electrolyte condition (E/S ​= ​4.3).