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

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 Mo₂C homojunction/carbon composite is constructed by the co-implantation design of Fe and Mo-vacancy (v₆Fe-Mo₂C/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 v₆Fe-Mo₂C/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.