Synthesis of Cobalt Sulfide Multi‐shelled Nanoboxes with Precisely Controlled Two to Five Shells for Sodium‐Ion Batteries

We report the synthesis of cobalt sulfide multi-shelled nanoboxes through metal-organic framework (MOF)-based complex anion conversion and exchange processes. The polyvanadate ions react with cobalt-based zeolitic imidazolate framework-67 (ZIF-67) nanocubes to form ZIF-67/cobalt polyvanadate yolk-shelled particles. The as-formed yolk-shelled particles are gradually converted into cobalt divanadate multi-shelled nanoboxes by solvothermal treatment. The number of shells can be easily controlled from 2 to 5 by varying the temperature. Finally, cobalt sulfide multi-shelled nanoboxes are produced through ion-exchange with S2- ions and subsequent annealing. The as-obtained cobalt sulfide multi-shelled nanoboxes exhibit enhanced sodium-storage properties when evaluated as anodes for sodium-ion batteries. For example, a high specific capacity of 438 mAh g-1 can be retained after 100 cycles at the current density of 500 mA g-1 .