Improvement of Li-Sulfur Cell Cycling Performance by Use of Fe_1-xS@NC as a Functional Additive for Chemical Confinement of Lithium Polysulfides

Abstract

Lithium-sulfur cells using sulfur as an active cathode material offer high energy density and low-cost. However, dissolution and migration of lithium polysulfides (the 'shuttle effect') remain key obstacles for the practical development of lithium-sulfur cells. Here, we demonstrate that Fe1-xS (pyrrhotite) coated by N-doped carbon (Fe1-xS@NC) with high affinity for polysulfides and high electronic conductivity can be used as a functional additive to trap lithium polysulfides and reutilize reaction intermediates in the sulfur cathode during cycling. The addition of Fe1-xS@NC into the sulfur cathode results in the enhancement of cycling performance of the lithium-sulfur cell in terms of initial discharge capacity, capacity retention and rate capability. This superior cycling performance can be attributed to strong chemical interactions between electrically conductive Fe1-xS@NC particles and lithium polysulfides, which suppress the dissolution of lithium polysulfides and enhance the utilization of active sulfur during repeated cycling.