Nearly barrier-free cascaded sulfur reduction reaction realizes 2-Ah-level stable lithium-sulfur pouch cell

Sulfur reduction reaction (SRR) in lithium-sulfur (Li-S) batteries involves 16 electrons (e⁻) to transform S₈ to Li₂S, yielding a theoretical specific capacity of 1675 mAh·g⁻¹. However, the insulating nature of sulfur and multi-phase transitions results in sluggish kinetics of SRR, which causes several lithium polysulfides (LiPSs) to remain unconverted and dissolve in the electrolyte, creating the “shuttle effect”, further leading to rapid capacity fading. Here, we propose an electron-injection-softened strategy to construct the Co₉S₈-Mn₃O₄@CNF (CNF = carbon nanofiber) heterostructure as the sulfur cathode to achieve a nearly barrier-free cascaded SRR, which enables the direct injection of electrons into S–S bonds and promotes the continuous formation of solid Li₂S₂ from the beginning of discharge, ultimately yielding abundant Li₂S. Density functional theory (DFT) calculations of the electronic structure and X-ray absorption spectroscopy (XAS) analysis of coordination environment have proven the electron injection from Co₉S₈ to Mn₃O₄, softening the surface of Co₉S₈-Mn₃O₄@CNF, inducing “soft to soft” orbital interactions between Mn₃O₄ and LiPSs based on the hard and soft acids and bases (HSAB) theory. Therefore, a nearly barrier-free cascaded SRR can be attained to minimize the loss of the liquid LiPSs. The Ah-level pouch cell with a Co₉S₈-Mn₃O₄@CNF cathode exhibited a capacity retention of 81.8% after 50 cycles. Moreover, a 2.22 Ah pouch cell with an energy density of 389 Wh·kg⁻¹ and a sulfur loading of 5.95 mg_S·cm⁻² was successfully fabricated, achieving stable cycling for 60 cycles.