Construction of Porous Co9S8 Hollow Boxes with Double Open Ends toward High-Performance Half/Full Sodium-Ion Batteries

Herein, uniform Co9S8 hollow boxes (Co9S8-HB) with double open ends have been fabricated by a facile technique involving a solvothermal and subsequent calcination process. On the basis of a time-dependent morphological evolution, the generation mechanism of novel Co9S8-HBs came from the self-assembly process of nanoparticles along their height direction. The novel hollow architecture with openings at both ends offers a short ion/electron transport path, enhances the diffusion ability of sodium ion, as well as relaxes mechanical stress upon cycling. Consequently, the unique structure and pseudocapacitive effect endow the Co9S8-HB electrode with long-term cyclic capability and an impressive rate performance for sodium-ion storage. It delivers a reversible specific capacity of 520 mAh g–1 at 0.5 A g–1 after 100 cycles. Notably, it preserves a high capacity of 464 and 405.6 mAh g–1 at 5 and 10 A g–1, after 3000 and 7000 cycles, respectively, indicating an ultralong cyclic performance. Besides, the galvanostatic intermittent titration technique (GITT) result reveals that the porous hollow structures of Co9S8-HB boost the Na+ diffusion coefficient, ensuring a glorious cycling performance and exceptional rate capability. Most importantly, the successfully paired Na3V2(PO4)3||Co9S8-HB full cell remains at a stably reversible capacity of 101 mAh g–1 at 1 A g–1 after 600 cycles. The above results show that the novel Co9S8-HB can be a prospective candidate for high-performance sodium-ion batteries in future applications.