Rational Design of Bi 2 Se 3 @NiSe 2 Heterostructures on N-Doped CNTs as a Dual-Functional Polysulfide Mediator for High-Performance Li–S Batteries

The practical implementation of lithium–sulfur (Li–S) batteries is still impeded by two fundamental challenges: the low conductivity of lithium sulfide species (Li 2 S 2 /Li 2 S) and the shuttling of soluble lithium polysulfides (LiPSs). To tackle these issues, we propose an efficient polysulfide regulation strategy via a functional separator coated with Bi 2 Se 3 @NiSe 2 heterostructures anchored on nitrogen-doped carbon nanotubes (N-CNTs). The rationally constructed Bi 2 Se 3 @NiSe 2 interfaces not only offer strong chemisorption toward LiPSs but also act as highly active electrocatalysts to facilitate their conversion kinetics, particularly the nucleation and decomposition of Li 2 S. Coupled with the three-dimensional conductive network of N-CNTs, which ensures rapid electron/ion transport, the designed separator significantly suppresses the shuttle effect and enhances redox efficiency. As a result, Li–S batteries equipped with the Bi 2 Se 3 @NiSe 2 /N-CNT-modified separator achieve a remarkable initial discharge capacity of 1418.24 mAh g –1 at 0.1 C and outstanding long-term cyclability with a minimal decay rate of 0.083% per cycle over 500 cycles at 1 C. In situ X-ray diffraction further verifies the reversible phase evolution between α-S 8 and Li 2 S during cycling. This work highlights the potential of bimetallic selenide heterostructures as multifunctional catalytic interlayers and provides a feasible pathway toward advanced separators for durable Li–S batteries.