In Situ Encapsulation of Cobalt Selenide Nanoparticles in N-Doped Carbon Nanotubes with a Full Sulfiphilic Surface as a Catalytic Interlayer for Lithium–Sulfur Batteries

The shuttle effect of lithium–sulfur batteries (LSBs) caused by the dissolution and migration of lithium polysulfides (LiPSs) leads to rapid capacity decay of sulfur cathodes. Modifying the separator with a catalytic layer becomes an effective strategy to inhibit LiPS shuttling and promote the conversion kinetics of sulfur active materials. Herein, we propose a carbon nanotube (CNT)-encapsulation strategy to fabricate a composite of CoSe nanoparticles encapsulated in N-doped CNT (CoSe@NCNT). The as-prepared CoSe@NCNT is endowed with a full sulfiphilic surface to trap LiPSs by Co–S and Se–Li bonds and catalyze sulfur redox reactions (SRRs) of the discharge/charge processes. In addition, the encapsulated structure effectively inhibits the aggregation of CoSe nanoparticles and enables its persistent adsorption–catalysis ability on regulating the kinetics of SRRs. When equipped with a CoSe@NCNT catalytic interlayer, the LSB shows a high specific capacity of 768.3 mAh g–1 at 2 C and superior cycle stability with the capacity decay rate of 0.06% per cycle over 1000 cycles at 1 C. In addition, when operated with an electrolyte/sulfur ratio of 5 μL mg–1, the modified battery with a sulfur loading of 4.0 mg cm–2 delivers a specific capacity of 746.9 mAh g–1 at 0.2 C. Our studies provide a CNT-encapsulation strategy to develop transition metal-based catalytic materials for high-performance LSBs.