Core–shell polyoxometalate-based zeolite imidazole framework-derived multi-interfacial MoSe2/CoSe2@NC enabling multi-functional polysulfide anchoring and conversion in lithium–sulfur batteries

Abstract

The realistic application of lithium–sulfur batteries (LSBs) as a competitive candidate for next-generation electrochemical energy storage systems is still hampered by the severe polysulfide shuttle effect and sluggish redox kinetics. Designing multi-functional host materials for a cathode that takes into account both adsorption ability to the polysulfide and bidirectional acceleration for sulfur conversion is crucial for the deployment of LSBs. Herein, for the first time, core–shell MoSe₂/CoSe₂@NC are proposed to effectively adsorb soluble polysulfides and simultaneously manipulate the kinetics during charging and discharging. Such cathode host material is derived from a polyoxometalate (POM)-based ZIF as the precursor, and the abundant MoSe₂/CoSe₂ heterojunction structures are embedded in the conductive N-doped carbon polyhedron skeleton. Adsorption test, Li₂S oxidation test and density functional theory (DFT) simulation results collectively demonstrate that CoSe₂ has a chemical adsorption effect on polysulfides, and can catalyze the reduction reaction of long-chain polysulfides, while MoSe₂ possesses the bidirectional conversion catalytic activities on sulfur, particularly the oxidation reaction of short-chain polysulfides. Furthermore, in situ UV-vis experiments indicate that MoSe₂ can greatly promote the generation of S₃˙⁻ radicals, which is beneficial for the polysulfide conversion. Benefiting from the excellent characteristics of each component in the heterostructures, the S@MoSe₂/CoSe₂@NC electrode with the sulfur loading of 1.5 mg cm⁻² exhibits a high initial capacity of 1352.54 mA h g⁻¹ and satisfactory cycling stability (low average capacity attenuation of 0.075% in 500 cycles at the high rate of 3C). More encouragingly, it also exhibits good battery performance even at a high sulfur loading of 3.6 mg cm⁻². This study offers a deeper insight into the fabrication of transition metal selenide (TMSe)-based heterostructures for designing multi-functional cathode materials for LSBs.