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

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.