A bidirectional electrocatalyst for enhancing Li2S nucleation and decomposition kinetics in lithium–sulfur batteries

Abstract

Accelerating sulfur redox reactions and suppressing the shuttle effect of lithium polysulfide (LiPSs) are crucial for high-performance lithium–sulfur (Li–S) batteries. Herein, we develop a highly efficient bidirectional electrocatalyst (Ti₃C₂/(NiCo)_0.85Se) consisting of 2D Ti₃C₂ nanosheets loaded with well-dispersed (NiCo)_0.85Se nanoparticles. Based on electrochemical analysis and theoretical calculations, the Ti₃C₂/(NiCo)_0.85Se heterostructure is demonstrated to provide abundant active sites for steady bidirectional electrocatalysis and abundant lithiophilic–sulfiphilic anchoring points for the immobilization of LiPSs. Ti₃C₂ promotes the reduction process of LiPSs to Li₂S, and (NiCo)_0.85Se enhances the decomposition of Li₂S. Moreover, the (NiCo)_0.85Se nanoparticles prevent the Ti₃C₂ nanosheets from aggregating, ensuring a hierarchical porous framework endowed with good structural robustness and fast electron/ion transportation. Li–S batteries with Ti₃C₂/(NiCo)_0.85Se modified separators exhibit an ultralong cycling lifespan with a capacity decay rate of only 0.03% per cycle over 2000 cycles at 1C and improved rate capability. When equipped with a high sulfur loading of 6.4 mg cm⁻² and a low electrolyte/sulfur ratio of 8 μL mg⁻¹, the cell maintains a distinguished area capacity of 9.7 mA h cm⁻². This work provides a general strategy for the design of bidirectional electrocatalysts for high-performance Li–S batteries with especially remarkable cycling stability.