Vertically Stacked 2H-1T Dual-Phase MoS2Microstructures during Lithium Intercalation: A First Principles Study

Layered transition-metal dichalcogenides (TMDs) have shown promise to replace carbon-based compounds as suitable anode materials for Lithium-ion batteries (LIBs) owing to facile intercalation and de-intercalation of lithium (Li) during charging and discharging, respectively. While the intercalation mechanism of Li in mono- and bi-layer TMDs has' been thoroughly examined, mechanistic understanding of Li intercalation-induced phase transformation in bulk or films of TMDs is still largely unexplored. This study investigates possible scenarios during sequential Li intercalation and aims to gain a mechanistic understanding of the phase transformation in bulk MoS(2)using density functional theory (DFT) calculations. The manuscript examines the role of concentration and distribution of Li-ions on the formation of dual-phase 2H-1T microstructures that have been observed experimentally. The study demonstrates that lithiation would proceed in a systematic layer-by-layer manner wherein Li-ions diffuse into successive interlayer spacings to render local phase transformation of the adjacent MoS(2)layers from 2H-to-1T phase in the multilayered MoS2. This local phase transition is attributed to partial ionization of Li and charge redistribution around the metal atoms and is followed by subsequent lattice straining. In addition, the stability of single-phase vs. multiphase intercalated microstructures, and the origins of structural changes accompanying Li-ion insertion are investigated at atomic scales.