“First-Cycle Effect” of Trace Li₂S in a High-Performance Sulfur Cathode

Lithium–sulfur battery is one of the most promising choices for next-generation batteries due to its high theoretical energy density and natural abundance. However, the sulfur cathode undergoes a stepwise reduction process and generates multiple soluble polysulfide intermediates; for the further conversion from the dissolved intermediates to the final solid product (Li₂S), the surface nucleation barrier limits the speed of the electrochemical precipitation, resulting in serious polysulfide diffusion loss and low sulfur utilization. Herein, the trace Li₂S (tLi₂S) is modified on the carbon fiber (CF) skeleton as preloaded crystal nuclei to boost the electrokinetics of Li₂S deposition in the initial cycle. The trace Li₂S decreases the nucleation barrier on the modified electrode (tLi₂S@CF), resulting in a high initial capacity of 1423 mAh g^–1 for the Li₂S₆ catholyte (0.2 C), which corresponds to a nearly 100% utilization of Li₂S₆. Furthermore, the trace Li₂S nuclei induce a uniform distribution of the redeposited active materials, and the uniform distribution persists in the following cycles, which benefits the cycle life significantly. The sulfur cathode based on the tLi₂S@CF matrix maintains a capacity of 1106 mAh g^–1 at 1 C rate after 100 cycles. The strategy can provide a new avenue for the rational design of the sulfur cathode.