Monitoring Redox Pathways and Performance Limitations in Lithium-Sulfur Batteries Using In Situ ^7/6Li and ³³S NMR...

Area of Science:

• Electrochemistry
• Materials Science
• Spectroscopy

Background:

• Lithium-sulfur (Li-S) batteries promise higher capacity and lower cost than lithium-ion systems.
• Complex redox mechanisms and structural changes in Li-S batteries lead to cell failure.
• Understanding these mechanisms is vital for accelerating Li-S battery development.

Purpose of the Study:

• To provide real-time structural insights into sulfur redox processes in Li-S batteries.
• To identify performance-limiting mechanisms and degradation routes.
• To establish a fundamental understanding of Li-S battery chemistry.

Main Methods:

• Operando ^6/7Li and ³³S NMR spectroscopy were combined for the first time.
• ⁷Li and ⁶Li NMR tracked polysulfide evolution and dendrite formation.
• ³³S NMR determined the onset of Li₂S formation.

Main Results:

• The entire redox pathway was tracked by monitoring polysulfide and Li₂S evolution.
• Accumulation of soluble polysulfides from incomplete reduction during charging causes capacity fade.
• Polysulfide shuttle degradation was found to be negligible in initial cycles.

Conclusions:

• Operando NMR spectroscopy effectively elucidates Li-S battery reaction mechanisms.
• Incomplete polysulfide reduction is a primary cause of capacity fade.
• Further research can focus on optimizing the charge process to mitigate polysulfide accumulation.