Sufficient cathode infiltration for stable 500 Wh kg−1 level lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries are promising next-generation high-energy-density energy storage devices. However, the failure mechanism of 500 Wh kg⁻¹ level Li–S pouch cells has not been well understood. Herein, quantitative and systematic failure analysis is conducted on 500 Wh kg⁻¹ level Li–S pouch cells to understand the underlying failure mechanism. Focusing on electrolyte exhaustion as the primary cause of cell failure, quantitative analysis methods are established to determine electrolyte occupation by physical infiltration of the cathode, separator, and anode as well as chemical consumption by lithium metal. Insufficient physical infiltration of the cathode caused by irreversible cathode volume expansion is identified as the main cause of electrolyte exhaustion. In comparison, chemical consumption of electrolytes by lithium metal and insufficient anode infiltration have limited influence on cell operations. To address the insufficient cathode infiltration, macropore-rich sulfur cathodes are fabricated to suppress the irreversible volume expansion and prolong the cycling lifespan of Li–S pouch cells by 2.4 times. This work elucidates that the sulfur cathode dominates the cycling lifespan of high-energy-density Li–S batteries and highlights cathode structural design to mitigate irreversible volume expansion for cycling performance improvement.