MoP Quantum Dot-Modified N,P-Carbon Nanotubes as a Multifunctional Separator Coating for High-Performance Lithium–Sulfur Batteries

Lithium-sulfur batteries (LSBs) have the advantages of high energy density and low cost and are considered promising next-generation energy storage systems, but the shuttle effect and slow sulfur redox kinetics severely limit their practical applications. Herein, MoP quantum dot-modified N,P-doped hollow PPy substrates are adopted as separator modification coatings for LSBs. The MoP quantum dots exhibit excellent chemisorption and catalytic conversion capabilities for polysulfides, while the N,P-doped PPy substrates can provide flexible channels for Li+/electron transport and act as a physical barrier to suppress the shuttle effect. As a result, LSBs assembled with modified separators exhibit excellent rate capability (739 mAh/g at 3 C) and cycle performance (600 mAh/g at 1 C after 600 cycles, 0.052% decay per cycle). Moreover, even under a high sulfur loading of 3.68 mg/cm2, areal capacities of 3.58 and 2.92 mAh/cm2 for the 1st cycle and 110th cycle are achieved. In addition, according to density functional theory calculations, MoP quantum dots have large adsorption energy for S8 and Li2Sn, which further confirms the possibility of lowering the initial nucleation energy barrier of Li2S and helps to improve the kinetics of the subsequent Li2S reaction. This study proposes a novel method for using transition-metal phosphides as catalysts in high-performance LSBs.