P-doped Co9S8 nanoparticles embedded on 3D spongy carbon-sheets as electrochemical catalyst for lithium-sulfur batteries

Abstract

Co9S8 can catalyze polysulfides conversion in Lithium sulfur batteries (LSBs) owing to its metallic nature and rich catalytic sites. However, its catalytic activity and chemical adsorption is not strong enough to suppress the shuttle effect of Lithium polysulfides (LiPS) under high sulfur loading. Herein, Phosphorous (P)-doped Co9S8 nanoparticle was synthesized and embedded into 3D Spongy carbon (SC) sheets as electrochemical catalyst for LSBs. Our Density functional theory (DFT) calculations and experimental results revealed that moderate P doping can modulate the electronic structure of Co9S8 and simultaneously improve its interaction with LiPS and promote LiPS conversion. When P-doped Co9S8 nanoparticles are in situ formed and homogeneously distributed on 3D spongy carbon sheet matrix, the resulting P-Co9S8@SC can ensure good exposure of their adsorption and catalytic sites. As a result, the LSB based on an optimized P-Co9S8@SC modified polypropylene separator exhibited excellent cycling stability (capacity decay of 0.05% per cycle over 900 cycles at 1 C) and high areal capacity (4.38 mAh cm−2 at 5.6 mg cm−2 sulfur loading at 0.1 C). Our work demonstrates that moderate heteroatom doping is a promising strategy to develop effective polysulfides catalysis.