Dual-Conductive CoSe2 @TiSe2 -C Heterostructures Promoting Overall Sulfur Redox Kinetics under High Sulfur Loading and Lean Electrolyte.

ABSTRACT

Although lithium-sulfur batteries (LSBs) possess a high theoretical specific capacity and energy density, the inherent problems including sluggish sulfur conversion kinetics and the shuttling of soluble lithium polysulfides (LiPSs) have severely hindered the development of LSBs. Herein, cobalt selenide (CoSe2 ) polyhedrons anchored on few-layer TiSe2 -C nanosheets derived from Ti3 C2 Tx MXenes (CoSe2 @TiSe2 -C) are reported for the first time. The dual-conductive CoSe2 @TiSe2 -C heterostructures can accelerate the conversion reaction from liquid LiPSs to solid Li2 S and promote Li2 S dissociation process through high conductivity and lowered reaction energy barriers for promoting overall sulfur redox kinetics, especially under high sulfur loadings and lean electrolyte. Electrochemical analysis and density functional theory calculation results clearly reveal the catalytic mechanisms of the CoSe2 @TiSe2 -C heterostructures from the electronic structure and atomic level. As a result, the cell with CoSe2 @TiSe2 -C interlayer maintains a superior cycling performance with 842.4 mAh g-1  and a low-capacity decay of 0.031% per cycle over 800 cycles at 1.0 C under a sulfur loading of 2.5 mg cm-2 . More encouragingly, it with a high sulfur loading of ≈7.0 mg cm-2  still harvests a high areal capacity of ≈6.25 mAh cm-2  under lean electrolyte (electrolyte/sulfur, E/S ≈ 4.5 µL mg-1 ) after 50 cycles at 0.05 C.