Efficient Activation of Li₂S by Transition Metal Phosphides Nanoparticles for Highly Stable Lithium–Sulfur Batteries

Abstract

Considerable research efforts have been devoted to the lithium–sulfur battery due to its advantages such as high theoretical capacity, high energy density, and low cost. However, the shuttle effect and the irreversible deposition of Li2S result in severe capacity decay and low Coulombic efficiency. Herein, we discovered that the transition metal phosphides cannot only trap the soluble polysulfides but also effectively catalyze the decomposition of Li2S to improve the utilization of active materials. Compared with the cathodes without transition metal phosphides, the cathodes based on Ni2P, Co2P, and Fe2P all exhibit higher reversible capacity and improved cycling performance. The Ni2P-added electrode delivers capacities of 1165, 1024, 912, 870, and 812 mAh g–1 at 0.1, 0.2, 0.5, 1.0, and 2.0 C, respectively, and high capacity retention of 96% after 300 cycles at 0.2 C. Even with a high sulfur mass loading of 3.4 mg cm–2, the capacity retention remains 90.3% after 400 cycles at 0.5 C. Both density functional theory calculations and electrochemical tests reveal that the transition metal phosphides show higher adsorption energies and lower dissociation energies of Li2S than those of carbon materials.