MoP QDs@Graphene as Highly Efficient Electrocatalyst for Polysulfide Conversion in Li-S Batteries

Abstract The shuttle effect of lithium polysulfides (LiPSs) and sluggish redox conversion significantly hinder practical implementation of lithium-sulfur batteries (LSBs). To overcome these issues, herein, we present MoP quantum dots anchored N, P-doped graphene (MPQ@G) as a multifunctional LSB cathode. The N, P-doped graphene layers serve as a conductive skeleton to support the MoP QDs which can accelerate the electron transfer, physically hinder the polysulfide migration and thus enhance the electrochemical performance. More importantly, as a polar and conductive catalyst, MoP QDs provide catalytically active sites for the conversion of LiPSs. As a result, the LSBs with MPQ@G/S cathodes deliver an elevated initial capacity of 1220.2 mA h g−1 at 0.2 C and remain 98.9% after rate cycles, signifying its exceptional cycling stability. Moreover, it displays a large capacity of 681.2 mA h g−1 even at a high rate of 1 C. The Li-S pouch cell also presents high specific capacities and preeminent cycling stabilities, confirming its great potential for high-rate applications. Density functional theory calculations demonstrate the improved absorptivity and redox conversion reversibility of LiPSs. This work provides an efficient strategy to improve composite with highly adsorptive and catalytic properties for high-performance Li-S batteries.