Deciphering the Degradation Mechanism of High‐Rate and High‐Energy‐Density Lithium–Sulfur Pouch Cells

Abstract Lithium–sulfur (Li–S) batteries are widely regarded as promising next‐generation battery systems due to their impressive theoretical energy density of 2600 Wh kg −1 . However, practical high‐energy‐density Li–S pouch cells suffer from rapid performance degradation under high working rates. Herein, the performance degradation mechanism of 400 Wh kg −1 Li–S pouch cells is systematically investigated under a high cycling rate of 0.2 C. Focusing on the reduced specific capacity and increased cell polarization, the sluggish cathodic sulfur redox kinetics under lean‐electrolyte and high‐rate conditions is identified as the main limitation. Further polarization decoupling indicates the cathodic activation polarization contributes dominantly to the increased cell polarization. Accordingly, a delicately designed electrolyte using dimethyl diselenide as the kinetic promoter is proposed to enable the Li–S pouch cells to work at 0.2 C with reduced cell polarization. This work clarifies the sluggish cathodic interfacial charge transfer kinetics as the main challenge for high‐energy‐density Li–S batteries at high rates and is expected to inspire rational strategy design for achieving advanced Li–S batteries.