Bidirectional tandem catalysis coupled with interface engineering and Se vacancies for accelerating the polysulfide conversion

Abstract

The shuttling of long-chain LiPSs (Li₂S_n, 4 ≤ n ≤ 8) and the sluggish conversion from Li₂S₄ to Li₂S represent two primary challenges hindering the fast multi-step transformations of lithium-sulfur (Li-S) batteries. Here, we propose a bidirectional tandem catalytic strategy to promote polysulfide conversions. A novel nanostructured catalyst consisting of hollow bimetallic selenide (ZnSe/SnSe₂) cubes with dual-active centers, heterogeneous interfaces and selenium-rich vacancies was synthesized. Experimental and theoretical calculations confirmed that ZnSe and SnSe₂ selectively reduced the thermodynamic transition energy barrier of S₈→Li₂S₄ and Li₂S₄→Li₂S to achieve baton-relay-like conversion of polysulfides. Moreover, the synergistic effect of ZnSe and SnSe₂ significantly reduced the activation barrier of Li₂S reoxidation during the charging process, and achieved an efficient bidirectional catalytic conversion. In situ Raman analysis confirmed that ZnSe/SnSe₂ effectively inhibited the shuttle effect. As a result, a battery with ZnSe/SnSe₂ interlayer delivered high specific capacity of 1269.5 mAh g⁻¹ at 0.2 C, and excellent rate capability (680.4 mAh g⁻¹ at 4 C). Remarkably, the battery maintained cycling stability with only 0.086% capacity degradation per cycle after 500 cycles at 2 C. This work provides a new path for designing electrocatalyst towards precise control of catalytic processes in Li-S batteries.