Highly stable rare earth YS2 and ScS2 monolayers for potassium-ion batteries: first-principles calculations†
Abstract
Most currently reported anode materials for potassium-ion batteries (KIBs) face a significant trade-off between high potassium capacity and stability, limiting their practical applications. It is widely recognized that reversible potassium intercalation during potassiation and depotassiation processes offers a promising approach to achieving long-term cycle stability. In this study, we conducted a comprehensive investigation of the MS2 monolayer family as anodes for K-ion batteries, utilizing density functional theory (DFT) computations. We demonstrated that the lowest unoccupied states (ELUS) of MS2 monolayers can serve as a simple yet effective descriptor for evaluating potassium adsorption ability. It was revealed that a lower ELUS of the material can lead to more energetically favourable electron occupation, resulting in stronger K adsorption. The proposed potassiation mechanisms were largely dependent on the delicate competition between the K–MS2 interaction (Eads) and the M–S bonding interaction (ΔHf) within the MS2 structure. Our computations indicated that most of the MS2 monolayers (except for CoS2, NiS2, and PdS2) could suppress the conversion reaction after K-ion insertion owing to the less electrovalent K–S bond. By evaluating the theoretical capacities, diffusion barriers, and electronic characteristics, the rare earth Sc- and Y-mediated MS2 monolayers were identified as the most promising intercalation candidates for KIB anodes with maximum theoretical capacities of 509.28 and 461.09 mA h g−1 and exceptionally low ion diffusion barriers of 0.11 eV and 0.12 eV, respectively. This study provides an effective strategy for designing stable and high-performance electrodes for potassium-ion batteries, thereby advancing the development of next-generation energy storage systems.