2024 AIChE Annual Meeting
Computational Studies of Phase Transformations in Sulfur Cathodes for Li/S Batteries
Lithium/Sulfur (Li/S) batteries are promising high energy density technologies because of the high theoretical specific capacity of S cathodes. However, the complex chemistry of the lithiation (discharge) reactions where Li is stored in Li-S compounds, and the de-lithiation (charge) reactions where Li leaves the Li- S compounds yielding plain sulfur, face significant challenges. Sulfur (S8) is stable at room temperature in a crystal rhombic configuration known as the α-phase. However, other S allotropes can exist as metastable phases at room temperature, such as β (monoclinic) and γ (amorphous). The monoclinic phase can become stable at higher temperatures. The transformation between stable and metastable phases is of interest because each crystalline S structure is also associated with a specific electronic configuration. Since the cathode material requires good electronic conductivity, converting the S electrode material into specific phases that may be better conductors of electrons is of high interest.
Here we use classical molecular dynamics (MD) and a temperature ramp in a low T range to investigate sulfur phase transitions at solid-solid interfaces, and in a higher T range we evaluate solid to liquid transitions such as b → disordered → liquid, or a → b → liquid. During the temperature ramp, we select trajectory frames to perform theoretical X Ray diffraction (XRD) analyses that can help determine the establishment of a new phase.