Higher-order polysulfides induced thermal runaway for 1.0 Ah lithium sulfur pouch cells

We found the reactions between dissolved higher-order polysulfides and Li metal were the origins for thermal runaway of 1.0 Ah cycled Li–S pouch cells. 16-cycle pouch cell indicates high safety, heating from 30 to 300 °C without thermal runaway, while 16-cycle pouch cell with additional electrolyte undergoes severe thermal runaway at 147.9 °C, demonstrating the key roles of electrolyte on the thermal safety of batteries.

On the contrary, thermal runaway does not occur for 45-cycle pouch cell despite the addition of electrolyte. It is found that the higher-order polysulfides (Li2Sx≥6) are discovered in 16-cycle electrolyte while the sulfur species in 45-cycle electrolyte are Li2Sx≤4. In addition, strong exothermic reactions are discovered between cycled Li and dissolved higher-order polysulfide (Li2S6 and Li2S8) at 153.0 °C, driving the thermal runaway of cycled Li–S pouch cells.