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

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.