CoS nanosheets wrapping on bowl-like hollow carbon spheres with enhanced compact density for sodium-ion batteries

Transition metal sulfides have long suffered from poor conductivity and large volume change when valued as an anode material for sodium-ion batteries. Hollow carbon nanohybrids prove to be the highly effective materials to solve these problems. While the low inherent compact density of hollow material leads to the low volume energy density of batteries. Herein, we employ a bowl-like hollow carbon sphere as the carbon substrate to promote compact density. Owing to the smaller cavity size and compact arrangement of bowl-like hollow spheres, the well-designed CoS@bowl-like hollow carbon spheres ultimately upgrade the compact density to 122% compare with that of CoS@hollow carbon spheres. Meanwhile, the hierarchical and interconnected CoS nanosheets tightly wrapped on the surface of the spheres, which can not only prevent self-aggregation of CoS but also provide shorter transmission path of both ions and electronics. This novel CoS@bowl-like hollow carbon spheres exhibit a good cycling performance: a reversible capacity of 543 mAh g-1 after 400 cycles and 452 mAh g-1 after 1000 cycles at 1 A g-1. The Na3V2(PO4)3//CoS@ bowl-like hollow carbon spheres full cell shows a reversible capacity of 320 mAh g-1 at 0.5 A g-1.