Amorphous transformation of FeP enabling enhanced sulfur catalysis and anchoring in High-performance Li-S batteries

Abstract

• Amorphous transformation of FeP enables enhanced catalytic activities in sulfur cathodes. • aFeP overcomes the downsides of structural anisotropy in sulfur catalysis. • aFeP presents abundant and stronger binding sites for active sulfur species. • aFeP enhances the liquid–solid conversions for higher sulfur utilization. • A high-capacity pouch cell (6.3 mAh cm −2 and 305 mAh in total) is demonstrated. Catalytic materials have recently been demonstrated to be effective in addressing the critical challenges of polysulfide shuttling and low utilization of sulfur in Li-S batteries. Although amorphous materials show advantages in typical electrocatalysis processes such as water splitting, the vast majority of catalytic materials developed for the sulfur cathodes are crystalline. Herein, we demonstrate the enhanced electrochemical performance of the amorphous FeP phase (aFeP) derived from a self-oxidation process of its crystalline counterpart. Electrochemical measurements and theoretical calculation reveal that the structural anisotropy of crystalline FeP is not in favour of important properties such as polysulfide binding energy, catalytic activity and electrical conductivity. Amorphous aFeP effectively overcomes these issues. Moreover, amorphous aFeP provides additional and stronger binding sites, enhanced electron exchanging between Fe-S and P-S atoms, as well as reduced HOMO-LUMO gap of the aFeP-Li 2 S 4 adsorption system, leading to significantly improved catalytic effects especially for the capacity-limiting liquid–solid conversions. High specific capacities are achieved up to 5C and pouch cells with a high areal capacity (6.3 mAh cm −2 ) are also demonstrated. This study provides useful insights for the future development of amorphous catalytic materials in high-performance Li-S cathodes.