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 angstrom), 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 Tphase one up to the maximum Mg concentration of 0.5. Enlarging interlayer spacing (from equilibrium 6 angstrom to 8 angstrom) 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.