Pisiform Homojunction with Energy Band Bending Induced via Co-Implantation Design Enabling Fast-Charging Sodium-Sulfur Battery

Abstract A novel “induced-homojunction” concept proposed here is of great significance to alleviate the severe shuttling effects and poor rate-capability behavior, where the sandwiched p-n Mo 2 C homojunction/carbon composite is constructed by the co-implantation design of Fe and Mo-vacancy (v 6 Fe–Mo 2 C/C), enabling heterogeneous variation in n/p-type characteristics among adjacent crystal structure. Encouringly, the p-n homojunction formation with continuous band bending favors the rapid carrier transmission across the interface to endow reactive sites with high activity and strengthen polysulfides capture, hence promoting original S–S bonds cleavage, which is regarded as the critical step to suppress the shuttling-behavior and trigger conversion reactions occurrence. Crucially, high-speed ions/electrons transport effectively driven by the formed large-range internal-electric-field during the energy band alignment, ensures they timely reach the above-mentioned highly active sites and react fully, enabling the ultrafast conversion kinetics process. A conspicuous sulfur utilization (1508 mAh g −1 at 0.1 A g −1 ) and especially the superior rate performance (1337 mAh g −1 at 1 A g −1 ) are presented by the battery with v 6 Fe–Mo 2 C/C@S cathode. And the battery delivers a stable discharge capacity independently from the charging rate (even at 5 A g −1 ). This “induced-homojunction” concept achieves the significant reaction kinetics advantage to provide new insight for the exploitation of fast-charging Na–S batteries.