Revealing key structures for reversible sulfur redox in amorphous polymeric sulfur

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Amorphous polymeric sulfur cathodes like sulfurized polyacrylonitrile (SPAN) offer high-energy lithium-sulfur batteries using abundant sulfur.
• Limited in situ understanding of SPAN synthesis and electrochemistry hinders optimization.

Purpose of the Study:

• To elucidate the real-time formation and electrochemical cycling mechanisms of SPAN.
• To guide mechanism-based engineering for improved lithium-sulfur battery performance.

Main Methods:

• Operando high-energy total scattering techniques.
• Sulfur K-edge X-ray absorption spectroscopy (XAS).

Main Results:

• S-C bond formation in SPAN prevents polyacrylonitrile fusion, promoting π-π stacking and short-chain sulfur vital for redox.
• Optimized SPAN demonstrates high capacity retention (>1,000 cycles) by minimizing polysulfide dissolution and charge-transfer resistance.
• Operando XAS identified residual protons driving thiol-thione tautomerism, contributing to initial irreversible capacity loss.

Conclusions:

• Mechanism-guided engineering, focusing on minimizing -NH groups and expanding pyridine networks, is crucial for SPAN optimization.
• These advancements pave the way for lithium-sulfur batteries with energy densities competitive with lithium-ion technology.