Mechanistic Origins of Structural Failure in Deeply-Lithiated Li_xMoS₂

MoS₂ is a promising high-capacity anode for Li-ion batteries due to its layered structure and theoretical capacity of ∼670 mAh g⁻¹, but its practical performance is limited by structural degradation under deep lithiation. Here, we employ a combination of global optimization and ab initio molecular dynamics (aiMD) to investigate the phase stability and structural failure mechanisms of Li-intercalated MoS₂ over a wide range of Li concentrations. Our results reveal that upon lithiation, MoS₂ undergoes a phase transformation from the 2H phase to a distorted 1T′ phase, with 1T′ Li_xMoS₂ emerging as the most stable polymorph for x > 0.4. We further clarify how the initial Li distribution affects phase stability and structural fracture behavior. Through aiMD simulations, we find that pre-lithiated (ground-state) 1T′-Li_xMoS₂ under the deep lithiation condition x > 1.0 exhibits enhanced structural integrity compared with a randomly-lithiated (high-energy) configuration. During aiMD simulation, the pre-lithiated Li_xMoS₂ preserves the layered S–Mo–S framework up to higher Li concentrations (x ≃ 1.5), showing almost no S dislodgement while opening out-of-plane Li-ion diffusion channels via localized Mo–S bond cleavage. By contrast, dynamically-lithiated structures suffer from Mo–S bond breaking, early S dislodgement, and Li_xS_y cluster formation at the interfaces (notably around x in Li_xMoS₂ ≃ 1.25). These findings suggest that controlling the initial Li intercalation geometry can significantly mitigate mechanical degradation in MoS₂ anodes, offering design guidelines for next-generation high-performance anodes with improved cycling stability and rate capability.