New high-performance battery designs need to be developed to feed the growing needs of electrostatic energy storage. Magnesium-Sulphur (Mg-S) batter- ies are fast emerging as a promising candidate in the last few years. However, they are plagued by viability issues due to the ‘Shuttle Effect’ slowing down the reaction kinetic and causing rapid decay of battery capacity. The shuttle effect is due to the formation of meta-stable Mg polysulphides (MgSx) that are soluble in the battery electrolyte. The formation of these polysulphides reduce the efficiency of the cell reaction, and cause a loss of electrode material since the ploysulfides cannot be recycled. To combat these issues, vanadium tetrasulphide (VS4) has been identified as a potential adsorbent for the MgSx, which can help recycle them and act as a catalyst. In this project, the adsorption capacity of the  surface of VS4 towards various MgSx has been computationally investigated by performing ab initio Density Functional Theory (DFT) calculations. The adsorption energies of various MgSx upon adsorption on (VS4) have been calculated using this method. The results are promising, the adsorption energies of (MgSx) is in range of (−1.40 → −0.14) (eV/atom) with the highest and lowest adsorption energies in case of MgS and MgS8 respectively. The adsorbate and adsorbent structure is not substantially altered by adsorption, which is crucial to eliminate capacity fading and promote battery life cycle. There could be seen a significant amount of charge transfer from (MgSx) to VS4 thus suggesting good performance of VS4 in mitigating the shuttle effect in magnesium sulfur batteries.The electronic properties discloses that all the adsorbed system possess indirect band gaps. We believe that the thorough investigation presented in this work offers a practical theory for creating a suitable separator that in- corporates VS4 , which can promote good cycle and material usage in Mg-S batteries.
Dr. Priya Johari