Efficient Synthesis and Characterization of Robust MoS₂ and S Cathode for Advanced Li–S Battery: Combined Experimental and Theoretical Studies

Abstract

Here, we report that in situ MoS₂ and S cathodes (MGC) prepared by simple decomposition of (NH₄)₂MoS₄ facilitate direct formation of Li₂S and suppress the long-term problem associated with polysulphide shuttling in Li-S batteries. For comparison, we prepared ex situ MoS₂ and S cathodes (EMS) with a similar S/MoS₂ mole ratio to that of in situ-prepared cathodes. Discharge capacity of EMS cathodes dropped by 80% after first few cycles, while assembled MGC cells demonstrated an initial discharge capacity of 1649 mA h/g, achieving close to theoretical capacity of elemental sulfur (1675 mA h/g) at C/3 and a reversible capacity of 1500 mA h/g was obtained in further cycles. The MoS₂ nanostructure evolution after initial discharge helped in extending the cycle life of assembled cells even at a high C rate. Density functional theory (DFT) calculation was performed to understand the structural stability of intermediate MoS₃ and possible electrochemical reactions pertaining to Li⁺ insertion in MoS₂ and S. Based on DFT studies, MoS₃ undergoes stoichiometric decomposition to stable MoS₂ and S. Furthermore, electrochemical analysis confirmed the redox activity of MoS₂ and S at 1.3 and 1.8 V against Li/Li⁺, respectively.