First-principles calculation of discharge reaction products in Na/SnS batteries

Li-ion batteries have been widely used as power sources in mobile electronics devices because of their high energy density. To extend them to much wider usage, it is necessary to develop batteries without high-cost rare-metals such as Li and Co. Recently Na-ion batteries have been highly recognized as one of the next-generation secondary batteries, in which high-cost Li is replaced with ubiquitous Na. As an anode material suitable for Na batteries, we focus our attention on tin compound SnS_x. Possible reaction products such as ternary Na-Sn-S and binary Na-Sn systems during the discharge reaction processes are searched by using a crystal structure prediction tool and the electrochemical properties are evaluated from first principles. Voltages of Na/SnS discharge process are calculated and compared with experiments. To clarify the phases of intermediate products, x-ray absorption spectra are computed by applying Fermi golden rule for calculated electronic structure with explicit core hole.