Theoretical and experimental understanding of Li₂S crystal structure and its isotropic ion conduction mechanism

Lithium sulfide is a crucial material for Li-S solid electrolytes, as it serves as the costly precursor in the research and development of solid-state batteries. This study introduces an economical carbothermal reduction method for synthesizing Li₂S powder. Physicochemical studies are conducted to assess the crystallinity, morphology, homogeneity, and oxidation state of the produced Li₂S powders. DFT calculations are utilized to visualize the crystal structure and atomic sites in Li₂S. Electrochemical impedance spectroscopy analysis examines the ionic conductivity of the prepared pellets at specific temperatures. NVT-Molecular Dynamics method is applied to evaluate the diffusion coefficient of Li₂S crystal structure at both low and high temperatures. A high concentration of disordered defects correlates with excellent ionic behavior at T = 700 K. The Nudged Elastic Band study demonstrates the activation energy (E_Li+) for Li ion hopping between neighboring and distant Li sites. The low activation barrier and identification of lithium ion conduction channels confirm that Li₂S is an isotropic ionic conductor.