Failure analysis of high-energy-density lithium‒sulfur pouch cells

Lithium‒sulfur (Li‒S) batteries are one of the most promising energy storage devices to achieve practical energy density of 400 Wh kg−1 beyond lithium-ion batteries. However, limited understanding on the failure mechanism of high-energy-density Li‒S batteries restricts their further development. Herein, systematic failure analysis on 400 Wh kg−1 Li‒S pouch cells is conducted. The failure of the pouch cells originates from the peak-shaped polarization at the second discharge plateau that renders rapid capacity decay. The cycled cathodes and anodes maintain their structural integrity and afford considerable residual capacity. After reinjecting electrolyte into the failed pouch cells, the peak-shaped polarization diminishes and the discharge capacity recovers. Consequently, electrolyte exhaustion is identified as the key limiting factor that renders cell failure. This work highlights electrolyte exhaustion as the key issue that limits the cycling lifespan of 400 Wh kg−1 Li‒S pouch cells and provides guidelines for designing targeted promotion strategies to achieve long-cycling Li‒S batteries.