Multivalent Ion Mobility in Layered NbS₂ and NbSe₂ Structures with Trigonal Prismatic Transition Metal Coordination

The development of multivalent energy-storage systems is hindered by the scarcity of electrode materials capable of supporting the reversible intercalation of multivalent ions. Layered structures containing trigonal prismatic polyhedra offer a promising framework for efficient ion diffusion, leveraging the favorable coordination environments predicted by Pauling’s theory. Thus, this study is aimed at systematically examining the migration mechanisms of divalent ions (Ca and Mg) within NbS2 and NbSe2 layered structures, focusing on the influence of structural phases (2H and 3R) and coordination geometries (prismatic and octahedral). The migration behavior is modulated by coordination environments, ionic interactions, and local structural distortions, which collectively determine the energy barriers and diffusion pathways. Results demonstrate that trigonal prismatic coordination significantly reduces migration barriers compared with octahedral coordination, owing to the absence of coordination fluctuations during diffusion. Additionally, the choice of chalcogenide species affects migration barriers, with Se ions generally exhibiting lower migration barriers than those associated with S ions except in specific structural contexts. This work elucidates the intricate interplay among structural phases, coordination geometries, and chalcogenide composition, offering valuable insights into the design of advanced materials for multivalent ion storage.