Capacity Fade Analysis of Sulfur Cathodes in Lithium–Sulfur Batteries

Rechargeable lithium–sulfur (Li–S) batteries are receiving ever‐increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S‐cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly‐shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li–S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li–S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li–S batteries. Sulfur undergoes a multistep reaction during cycling. In discharge, sulfur is reduced to Li2S by accepting the Li‐ions and electrons at cathode; in charge, a reversed reaction takes place. The electrolyte viscosity and polarization in cells influence the discharge and charge curves and therefore influence capacity and capacity fade of liquid‐type lithium sulfur batteries.