Bi-Metallic Phosphide Electrocatalyst-Integrated Li2S Cathode for High-Performance Anode-Free Li–S Batteries

Abstract

Sluggish redox kinetics and severe polysulfide shuttling are major hurdles for the commercialization of lithium–sulfur (Li–S) batteries. Transition-metal compound catalysts offer a promising solution by providing excellent polysulfide adsorption capabilities, outstanding catalytic activities, and homogeneous nucleation control of Li2S2/Li2S. The electronic structure of transition-metal sites in catalysts can also be fine-tuned through bi-metallic coupling, which can further improve the catalytic activities. In this study, bi-metallic nickel molybdenum phosphide is co-synthesized with Li2S and carbon through a carbothermal reduction process, forming a cathode composite (Li2S @ NixMoyPz @ C). This process is not only advantageous for large-scale manufacturing due to its simplicity, but also ensures homogeneous integration and distribution of the catalyst within the cathode composite. Furthermore, applying Li2S as an active material allows the creation of an anode-free cell configuration, enhancing the overall cell energy density. The anode-free cell with the Li2S @ NixMoyPz @ C composite cathode demonstrates an outstanding capacity retention of 50% over 300 cycles at a negative-to-positive capacity (N/P) ratio of 1. Additionally, the bi-metallic phosphide integrated Li2S cathode composite delivers a remarkable anode-free pouch cell performance of 703 mA h g−1 (on Li2S basis) under the challenging conditions of an E/Li2S ratio of 4.5.