Enhancing kinetic and electrochemical performance of layered MoS₂ cathodes with interlayer expansion for Mg-ion batteries

Layered materials such as transition metal dichalcogenides (TMDs) are actively pursued as promising candidates for Mg-ion batteries. However, the sluggish kinetics of Mg intercalation caused by strong binding interactions remains an on-going challenge for layered electrodes. Here using first-principles calculations, we investigate the thermodynamic and electrochemical performance of MoS₂ as a prototypical example of layered TMD cathodes with controllable interlayer spacing. Our calculations demonstrate that at equilibrium spacing (∼6 Å), the intercalation of Mg ions results in the H- to T-phase transformation of MoS₂ at the critical Mg concentration of ∼0.22. For higher concentrations, the H-phase of magnesiated MoS₂ is metastable and can co-exist with the T-phase one up to the maximum Mg concentration of 0.5. Enlarging interlayer spacing (from equilibrium 6 Å to 8 Å) significantly boosts Mg diffusivities-, and can enhance the specific capacity from 155 to 225 mAhg⁻¹ with the maximum Mg concentration of 0.75. While the weakened binding interaction between Mg and expanded MoS₂ layers reduces electrode voltages, the key findings obtained from this work provide crucial insights into an optimal balance between enhanced capacity/kinetics and reduced voltage window for the practical application of layer-expanded cathodes for Mg-ion batteries.