Insight of Enhanced Redox Chemistry for Porous MoO2 Carbon-Derived Framework as Polysulfide Reservoir in Lithium-Sulfur Batteries.

As a promising energy-storage system, lithium-sulfur batteries (LSBs) with a high energy density suffer from the polysulfide shuttle effect and sluggish reaction kinetics, which have been studied for a few decades. Incorporation of polar metal oxides is an efficient addition for LSBs to suppress the dissolution of soluble polysulfides, increase the utilization of sulfur, and improve cycling stability. Herein, a model (MoO2/C-NCs) based on a porous octahedral carbon framework decorated with MoO2 nanoparticles (MoO2 NPs) as a sulfur host is proposed. Adsorption experiments of lithium polysulfides (LiPSs) to MoO2/C-NCs and cyclic voltammetry analysis showed that the MoO2 NPs facilitate interfacial charge transfer and provide numerous active sites for the electrochemical redox reactions of LiPSs. Density functional theory calculations further reveal that LiPSs are diffused and strongly adsorbed on the surface of MoO2 NPs because of the powerful van der Waals forces via Mo-S and Li-O bonds, which helps achieve a stable long-term cycling performance. As a result, the fabricated LSBs display a high initial specific capacity of 1317 mA h g-1 at 0.2C and a promising capacity of 602 mA h g-1 and a capacity retention of 65.6% at 1C when proceeding to 500 cycles.