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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries offer high theoretical energy density but suffer from polysulfide shuttling and low sulfur utilization.
• The deposition of Li2S on the cathode is kinetically limited by a surface nucleation barrier, hindering electrochemical performance.

Purpose of the Study:

• To investigate the effect of preloaded trace lithium sulfide (tLi2S) on carbon fiber (CF) as nucleation sites for enhancing Li-S battery performance.
• To improve the electrokinetics of Li2S deposition and mitigate polysulfide loss.

Main Methods:

• Modification of carbon fiber (CF) with trace amounts of Li2S (tLi2S@CF) to serve as preloaded crystal nuclei.
• Electrochemical testing of Li-S cells using tLi2S@CF cathodes with Li2S6 catholytes.

Main Results:

• The tLi2S@CF electrode exhibited a high initial capacity of 1423 mAh g-1 at 0.2 C, achieving nearly 100% Li2S6 utilization.
• Preloaded tLi2S nuclei reduced the nucleation barrier, promoting uniform redeposition of active materials and enhancing cycle stability.
• The Li-S battery maintained a capacity of 1106 mAh g-1 at 1 C after 100 cycles.

Conclusions:

• Preloading trace Li2S on CF is an effective strategy to overcome nucleation limitations in Li-S batteries.
• This approach significantly improves initial capacity, sulfur utilization, and long-term cycling stability.
• The tLi2S@CF matrix offers a promising pathway for designing advanced sulfur cathodes.