Ab initio characterization of layered MoS₂ as anode for sodium-ion batteries

Identifying suitable layered materials as electrodes with desirable electrochemical properties remains a key challenge for rechargeable Na-ion batteries (NIBs). Using first principles methods, here we examine the efficacy of layered molybdenum disulphide (MoS₂) as a host electrode material for NIBs. We identify various low energy Na adsorption sites and evaluate the stability of the hexagonal and tetragonal polytypes of MoS₂ upon Na intercalation. Our results illustrate a moderately strong binding between Na and MoS₂ that is thermodynamically favorable against the cluster formation and phase separation of Na. We find that while Na intercalation in MoS₂ results in a phase transformation from the hexagonal phase to the tetragonal phase, it gives rise to a maximum theoretical capacity of 146 mAh g^-1 and a low average electrode potential in the range of 0.75-1.25 V. Our calculations of Na diffusion kinetics indicates a moderately fast mobility of Na in the van der Waals interlayer spaces of MoS₂. These results highlight the promise of MoS₂ as an appealing negative electrode (anode) for rechargeable NIBs.