In Situ Formation of Co₉S₈/N‐C Hollow Nanospheres by Pyrolysis and Sulfurization of ZIF‐67 for High‐Performance Lithium‐Ion Batteries

Abstract

Co₉ S₈ is considered a promising candidate as the anode material in lithium-ion batteries (LIBs) because of its remarkable electrical conductivity, high theoretical capacity, and low cost. However, the practical application of Co₉ S₈ is greatly restricted because of its poor cycling stability and rate performance, which result mainly from the large volume expansion and dissolution of the polysulfide intermediates during the charge/discharge process. In this report, Co₉ S₈ embedded in N-rich carbon hollow spheres are successfully designed and synthesized through an in situ pyrolysis and sulfurization process, employing the well-known ZIF-67 as the precursor and ethanethiol as the sulfur source. Co₉ S₈ nanoparticles embedded in the N-rich hollow carbon shell exhibit excellent lithium storage properties at a high charge/discharge rate. A discharge capacity of 784 mAh g^-1 is obtained upon battery testing at a current density of 1 C (544 mA g^-1 ). Even upon cycling at a current density of 4 C, the as-prepared Co₉ S₈ /N-C can still deliver a discharge capacity of 518 mAh g^-1 . The excellent battery performance can be attributed to the hollow structure as well as the N-rich carbon encapsulation. Moreover, this metal-organic framework sulfurization route also shows good generality for the synthesis of other metal sulfide-carbon composites such as ZnS/N-C and Cu₂ S/C.