Elucidating the Potassiation Mechanism in SnS2 from a First-Principles Perspective

As a typical transition-metal dichalcogenide (TMD), SnS2 has received significant interest as an anode material for potassium-ion batteries (KIBs) due to its high safety and environmental friendliness. However, according to previous experimental results, the amount of K ions that can be reversibly inserted/extracted per SnS2 is limited, and detailed information about the reaction mechanisms during subsequent conversion and alloying processes is still poorly investigated. In this work, we performed first-principles calculations by density functional theory (DFT) to elucidate the potassiation reaction pathways of SnS2 as well as phase transformation caused by conversion and alloying. A variety of K x SnS2 (0 ≤ x ≤ 5) with nonequilibrium structural configurations as the anode material are systematically examined to understand the diffusion energetics, charge transfer, and lattice evolution. It is found that reversible intercalation occurs for K x SnS2 (0 ≤ x ≤ 1), which transforms to SnS, Sn, K2S, and KSn intermediate phases after the intercalation of K ions in tetrahedral interstitial sites. Based on these findings, the potassiation voltage profile of SnS2 is predicted to have a high theoretical capacity of 750 mAh g–1. Our work opens a new avenue for understanding the architectural evolution and potassium storage chemistry for TMDs and provides important guidance for the design of energy-dense two-dimensional anodes in KIBs.