First-Principles Insights into Layered Li₂MS₂ (M = Mn, Fe, Co, and Ni) Electrodes for Lithium-Ion Batteries

In this paper, the properties of layered dichalcogenide electrode materials Li 2 MnS 2 , Li 2 FeS 2 , Li 2 CoS 2 , and Li 2 NiS 2 , with two Li atoms per formula, are investigated using density functional theory (DFT) and molecular dynamics (MD). These materials deliver high theoretical capacities, exceeding that of graphite. The evaluated descriptors include structural stability, phonon dispersion, electrochemical potential, electrical conductivity, diffusion coefficient, and voltage-ranges/profiles. Unlike previous studies focused on individual compounds—especially Li 2 FeS 2 —this work provides a systematic comparative analysis of a Li 2 MS 2 series under a unified computational framework, enabling the identification of intrinsic trade-offs among the related properties as a function of the transition metal. The theoretical voltage is assessed via Fermi and internal energy approaches, confirming the validity of the Fermi method according to available experiments for Li 2 FeS 2 . The materials exhibit promising electrical properties and rate capability, and their discharge voltage profiles and ranges indicate electrochemical suitability. Notably, the distinct theoretical voltage profiles implies that appropriately designed chargers could render them highly promising for next-generation commercial Li-ion batteries. A qualitative multi-criteria screening framework is further proposed to integrate the calculated descriptors into a unified assessment. This framework identifies Li 2 FeS 2 as the most balanced candidate while offering a practical strategy for screening layered intercalation electrodes. Overall, all assessed dichalcogenides show considerable promise, each with its own advantages. This study paves the way for future research on layered electrode materials.