Bimetallic zinc-cobalt sulfides embedded within N, S-codoped hollow carbon polyhedra for superior lithium-ion batteries

Abstract

Binary transitional metal sulfides, as the anodes for lithium-ion batteries, have attracted increasing attention due to their high specific capacity, low cost, and environmental benignity. However, their relatively large volume variation and inferior reaction kinetics always result in unsatisfactory electrochemical performance. Herein, an approach is presented to facilely fabricate Zn-Co-S nanoparticles embedded in N, S-codoped carbon polyhedra (Zn-Co-S@NS-CP) using dopamine-coated metal–organic-frameworks as sacrificial precursors. During pyrolysis process, Co2+/Co3+ is introduced to ZnS lattice by partially substitution of Zn2+, and the Zn-Co-S nanoparticles are evenly anchored close to sulfur sites in the porous hollow carbon shell. The as-synthesized product inherits a unique hierarchical structure with interconnected conductive network. As a result, the optimized Zn-Co-S@NS-CP exhibits excellent lithium storage performance, including a high reversible capacity of 740 mAh g-1 at a current density of 1.12 Ag-1 as well as superior cyclic stability. Meanwhile, a notable capacity increasement upon cycling is observed, which can be ascribed to the phase separation of the lithiated products, creating more reactive sites and promoting lithium ion transportation as well as the reversible growth of polymer layer over the electrodes, further facilitating the capacity increment in the long-term cycling.