Accelerating the Catalytic Conversion of Polysulfides in Lithium–Sulfur Batteries from Both the Cathode and the Separator Perspectives

Abstract

Lithium–sulfur (Li–S) batteries have a high theoretical energy density and are regarded to be an ideal choice for the next generation of electrochemical energy storage systems. However, their practical application is hindered by several bottlenecks, including the insulating nature of sulfur and its discharge products (Li₂S₂/Li₂S), the shuttling behavior of intermediate polysulfides, and slow redox reactions. Herein, we propose a highly efficient bimetallic selenide electrocatalyst featuring a hollow porous core–shell spherical structure, which serves as both a cathode host and a modified separator coated on a commercially available polypropylene separator to address the above issues. The bimetallic selenide enhances cathode conductivity, and its unique hollow porous core–shell spherical structure provides rapid ion transport channels, along with ample spatial confinement for lithium polysulfides. Additionally, the abundant reactive sites on the bimetallic selenides exhibit high intrinsic electrocatalytic activity, accelerating polysulfide conversion and improving redox kinetics. Density functional theory calculations indicate that bimetallic selenides interact more strongly with polysulfides and present lower reaction barriers compared to those of their sulfide counterparts. Consequently, these bimetallic selenide materials demonstrate superior rate performance and cycling stability in Li–S batteries, achieving an impressive lifespan of 1400 cycles with a minimal decay rate of 0.030% per cycle at 1.0 C. This work provides unique insights into enhancing the performance of transition metal compounds in Li–S batteries.