2019 Volume 18 Issue 1 Pages 78-83
We investigate the Na-ion battery characteristics of SnS as a negative electrode for Na ion battery by first-principles calculations. Using energy analyses, we show a phase diagram of Na-Sn-S ternary systems by convex-hull curves, and clarify a possible reaction route considering intermediate products in discharge reactions. We calculate the voltage-capacity curves based on the Na / SnS reaction path obtained from the ternary phase diagram, and compare with the experimental result. It is found that the conversion reactions and subsequently the alloying reactions proceed in the SnS electrode, contributing to its high capacity compared with the metallic Sn electrode, in which only the alloying reactions progresses stepwise. To verify our calculation result, x-ray absorption spectra (XAS) are computed and compared with experimental XAS at S K-edge. The Na2S reaction product can precipitate in the SnS electrodes during the discharge process, and it is expected that the electrode is recovered to be SnS again after charging.
