Insulator-to-metal transition of lithium-sulfur battery

Abstract

Li2S is a promising battery material due to the high theoretical capacity and high energy density. However, the improvement of insulation of Li2S is a challenge for its application. Naturally, the insulator-to-metal transition strongly depends on the electronic overlap between the conduction band and the valence band at the Fermi level (EF). To solve this key problem, this work investigates the insulator-to-metal transition of Li2S under high pressure. We identify a stable structure based on the phonon dispersion and thermodynamic model. It is found that Li2S with CaF2-type, Br2O-type and Cs2S-type structures are dynamically stable in the ground state. Importantly, the band gap of Li2S decreases gradually with increasing pressure. We predict that pressure leads to the insulator-to-metal transition of Li2S owing to the Li atomic pairing and the existence of Li-Li metallic bonds.