Novel Metallic Crystalline Phase of Li2S3

Poor electrical conductivity of the redox end solid products is one of the most important reasons impeding commercialization of Li-S battery. One of the solid intermediate products, Li2S2, is well-characterized, but the nature of the higher-order polysulfides is still somewhat unknown. In this paper, we focus on Li2S3, investigating its structural and electronic properties. The calculated results based on density functional theory find the cubic phase to be the ground state of Li2S3. Analysis of the vibrational spectrum suggests the cubic Li2S3 to be dynamically stable. The calculated density of states predicts the cubic Li2S3 to be metallic, which is due to excess S-2 dimers relative to Li atoms in the unit cell. Moreover, a signature peak at 2471 eV observed in the X-ray absorption near-edge structure spectrum of Li polysulfides has been identified. Overall, the calculated results provide insight into the nature of one of the intermediate Li-S redox solid products, thereby facilitating efforts via a controlled synthesis of conducting Li-S redox species to advance the design of the cathode material for Li-S battery.