Healable and conductive sulfur iodide for solid-state Li-S batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• Solid-state lithium-sulfur batteries (SSLSBs) offer high theoretical energy density for electric vehicles.
• Key challenges include sulfur's insulating nature and poor interfacial contact due to volume changes during cycling.
• These issues impede charge transfer and limit battery performance.

Purpose of the Study:

• To engineer a conductive sulfur-based material for improved SSLSB performance.
• To address the limitations of traditional sulfur cathodes.
• To enable practical application of SSLSBs in electric vehicles.

Main Methods:

• Synthesis of an S_9.3I molecular crystal by inserting iodine into crystalline sulfur.
• Characterization of the material's electrical conductivity and electrochemical properties.
• Fabrication and testing of an Li-S_9.3I battery to evaluate cycling stability and capacity retention.

Main Results:

• The S_9.3I crystal exhibits semiconductor-level electrical conductivity (5.9 × 10^-7 S cm^-1), an 11-order-of-magnitude increase over sulfur.
• Iodine incorporation creates new states in sulfur's band gap, promoting reactive polysulfide formation.
• The material has a low melting point (~65°C), allowing for interface self-repair during cycling.
• An Li-S_9.3I battery achieved 400 stable cycles with 87% capacity retention.

Conclusions:

• The conductive, low-melting-point sulfur-iodine material significantly advances sulfur-based battery chemistry.
• This design overcomes critical barriers to charge transfer and interfacial stability in SSLSBs.
• The findings open new avenues for the practical realization of high-energy-density solid-state lithium-sulfur batteries.