Two dimensional WS₂/C nanosheets as a polysulfides immobilizer for high performance lithium-sulfur batteries

A dual function cathode consisting of tungsten disulfide and porous carbon nanosheets (WS2/C) was synthesized to improve the performance of lithium sulfur batteries. The well-defined structure is composed of ≤5 layers with 0.62 nm interlayer spacing corresponding to the (002) facial plane of WS₂. The composite depicted very strong affinity toward lithium polysulfides. Rapid transport of lithium ions was also revealed. The cathode demonstrated excellent cycling stability and rate capability by delivering a reversible specific capacity of 419mAh g⁻¹ at 8C after 500 cycles with low capacity fading at 0.04% per cycle. At high sulfur loading of 4.7mg cm⁻² the batteries delivered 3.4mAh cm⁻² areal capacity after 100 cycles at 0.5C. The synergistic effect of strong chemical interaction between lithium polysulfides and WS₂, and the superior electronic conductivity of carbon nanosheets are responsible for the enhanced performance. It also suppressed the self-discharge phenomenon by maintaining 94.5% of its initial capacity after 10 days resting. The electrochemical impedance spectroscopy (EIS) analysis demonstrated that even after 400 cycles, the interfacial and charge transfer resistances only increased by 1.2 and 1.7, respectively, describing faster electrochemical kinetics by inhibiting the formation of insulating layer of lithium sulfide (Li2S) on the surface of the electrodes.