Potassium cation storage and diffusion in SnS, SnS2, and at SnS/SnS2 interfaces

Due to their promising performance, tin sulfide and tin disulfide have been investigated as anode materials in various types of batteries, such as Li-, Na-, and K-ion batteries. Understanding the thermodynamics and kinetics of processes involving metal ions at the atomistic level, and how these processes differ between tin sulfide and tin disulfide, is crucial for improving their electrochemical performance in respective applications. However, a direct comparison between these two materials during battery operation has been limited so far. Here, we report on potassium cation diffusion barriers in bulk tin sulfide and tin disulfide, as well as parallel and perpendicular to several SnS/SnS2 interfaces by means of density functional theory calculations. We also investigate the thermodynamics of potassium storage in these materials. Our results demonstrate that while K+ diffusion in SnS occurs through elemental processes involving lower energy barriers, potassium storage in SnS2 is thermodynamically more favorable. These observations suggest strategies to improve the overall electrochemical performance of SnS/SnS2 heterostructures in battery applications.