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 S^2? 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.