Study On The First Principle Of TiS ₂ For Cathode Materials Of Magnesium Ion Batteries

Magnesium-based rechargeable batteries might be an important future alternative to be used for mass storage and high power applications. Recently, most of theoretical and experimental pay close attention to the discovery of ideal cathode materials. TiS2 materials have shown a fine phenomenon to be used as cathode for Li ion battery, which also is expected to be a good cathode material for Mg ion battery. In the past few years, low-dimensional nanomaterials have been proposed for electrode of batteries by other researcher, which is expected to eliminate the drawback to using Mg-ion batteries with the slow kinetics. In our work, first-principles calculations based various recently proposed van der waals (vdw) density functionals, and the standard exchange-correlation functional are adopted to analyze the features of the crystal structure, electronic structure, dissociation curve, and diffusion kinetics on this material.Titanium Disulfide TiS2 bulk is a typical layered structure with the weak vdw forces between two layers. We find that the standard exchange-correlation functional fail to reproduce the lattice parameter c of TiS2 bulk as it is absence of describing long-range vdw interaction between the planes. However, the optB88-vdw functional can give a best describing to crystal structure of TiS2 bulk with less 1% modification. Further, electronic structure obtained by GGA-PBE, LDA, and optB88-vdw functional are compared. The results clearly indicate the fact that electronic structure is main dominated by the covalent one and the function of vdw bond is tiny. Moreover, we find that the electronic structure obtained by optB88-vdw functional is influenced significantly when TiS2 monolayer is intercalated with Mg ion.We have computed the potential energy curve of two TiS2 layers separation by GGA-PBE, optB88-vdw, and rpw86-vdw function. The results show that the vdw functional is more reliable than the GGA-PBE in describing properties for TiS2 materials. Activation barriers for Mg ion diffusion were calculated using the nudged elastic band (NEB) method. It is strange to find that the diffusion barrier of Mg obtained with GGA-PBE on the monolayer and in bulk TiS2 have very similar values, which are 0.624 and 0.608eV, respectively. In order to get accurate theoretical estimates of diffusion barrier, vdw functional is very necessary to employ in our calculation. As expected the results obtained by vdw functional show that the diffusion barrier of Mg in the monolayer is lower than that in the bulk. It is found that electrostatic interaction between the two layers for TiS2 bulk can produce a notable retard in Mg ion diffusion, and cutting TiS2 bulk into monolayer can improve ion mobility. Above all, our study shows that the TiS2 monolayer is a hopeful cathode in terms of ion mobility for Mg ion battery by comparison with commercial Li rechargeable batteries.