Thermodynamic and Mechanical Stability of Crystalline Phases of Li₂S₂

Lithium-sulfur battery is considered as promising substitute of Li-ion battery for the next generation energy storage system. However, the intermediate process during charging and discharging cycles is not clear. It is believed that Li₂S₂ is one of the most important intermediate products which may present as insoluble solid phase in the system. In this talk, we considered three phases of crystalline Li₂S₂ (tetrahedra, triclinic and hexagonal) to investigate their thermodynamic and mechanical stability based on density functional theory. The results show that the hexagonal Li₂S₂ is relatively stable than the other two phases. The highly anisotropic mechanical characteristics of Li₂S₂ are shown to be due to the unique arrangement of S-S bonds in these crystalline structures.