Battery Performance and Reaction Mechanism in Tin Sulfide as Negative Electrode: First-Principles Calculations

Sodium (Na) ion batteries have been recently expected as a next-generation battery in which Li-ion batteriesis replaced with Na. Tin sulfide (SnS) has beenexpected to have a high energy density and bea candidate for anodematerials of Na-ion batteries. In this study, weinvestigate the battery characteristics of SnS as a negative electrode for Na-ion batteriesby first-principles calculations. We calculate a phase diagram of Na-Sn-S ternary systems from energy analyses, and clarify a possible reaction route considering intermediate products in charge anddischarge reactions. We theoretically estimatethe voltage-capacity curves of Na/SnS half-cell systemsbased on the Na–SnSreaction path obtained from the ternary phase diagram, and compare with the experimental result. From the comparison between calculated and experimental results, the Na₂S reaction productcan precipitate in the SnS electrodes after discharging, and it is expected that the electrode can recover to be SnS again after charging. Therefore, the conversion reactions in which Na₂S precipitates in the SnS electrodes are consideredto occur reversibly.