Co–Fe Mixed Metal Phosphide Nanocubes with Highly Interconnected-Pore Architecture as an Efficient Polysulfide Mediator for Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been regarded as one of the most promising candidates for next-generation energy storage owing to their high energy density and low cost. However, the practical deployment of Li-S batteries has been largely impeded by the low conductivity of sulfur, the shuttle effect of polysulfides, and the low areal sulfur loading. Herein, we report the synthesis of uniform Co-Fe mixed metal phosphide (Co-Fe-P) nanocubes with highly interconnected-pore architecture to overcome the main bottlenecks of Li-S batteries. With the highly interconnected-pore architecture, inherently metallic conductivity, and polar characteristic, the Co-Fe-P nanocubes not only offer sufficient electrical contact to the insulating sulfur for high sulfur utilization and fast redox reaction kinetics but also provide abundant adsorption sites for trapping and catalyzing the conversion of lithium polysulfides to suppress the shuttle effect, which is verified by both the comprehensive experiments and density functional theory calculations. As a result, the sulfur-loaded Co-Fe-P (S@Co-Fe-P) nanocubes delivered a high discharge capacity of 1243 mAh g^-1 at 0.1 C and excellent cycling stability for 500 cycles with an average capacity decay rate of only 0.043% per cycle at 1 C. Furthermore, the S@Co-Fe-P electrode showed a high areal capacity of 4.6 mAh cm^-2 with superior stability when the sulfur loading was increased to 5.5 mg cm^-2. More impressively, the prototype soft-package Li-S batteries based on S@Co-Fe-P cathodes also exhibited superior cycling stability with great flexibility, demonstrating their great potential for practical applications.