Theoretical Investigation of the Intercalation Chemistry of Lithium/Sodium Ions in Transition Metal Dichalcogenides

Among various two-dimensional compounds, transition metal dichalcogenides (TMDs or MX2) are a group of materials attracting growing research interest for potential applications as battery electrodes. Here we systematically investigate the electrochemical performance of a series of MX2 (M = Mo, W, Nb, Ta; X = S, Se) upon Li/Na intercalation through first-principles calculations. MOX2 arid WX2 were found to have lower voltages while those of NbX2 and TaX2 were higher than 1.5 V. By applying the rigid-band model, we found that the energy gained for electrons to transfer from Li/Na to MX2 could serve as a descriptor for characterizing voltages of MX2.The linear relation between the descriptor and voltages is useful for screening candidates for electrodes with desired voltage. Migration barriers for Li/Na ions were approximately 0.3 eV in MoX2/WX2 and 0.5 eV in NbX2/TaX2. The low barriers suggest a reasonable rate performance when these TMDs are used as electrodes. By Stacking different MX2, with distinct properties, TMDs heterostructures could be adopted to provide tunable electrochemical properties, including voltage, capacity and electronic conductivity while keeping barriers for Li/Na ions little changed. Thus, this strategy offers another degree of freedom for rational design of layered electrode materials.