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 (E_F). 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.