Metal-Organic Framework Template Synthesis of NiCo2S4@C Encapsulated in Hollow Nitrogen-Doped Carbon Cubes with Enhanced Electrochemical Performance for Lithium Storage.

Owing to its richer redox reaction and remarkable electrical conductivity, bimetallic nickel cobalt sulfide (NiCo2S4) is considered as an advanced electrode material for energy-storage applications. Herein, nanosized NiCo2S4@C encapsulated in a hollow nitrogen-doped carbon cube (NiCo2S4@D-NC) has been fabricated using a core@shell Ni3[Co(CN)6]2@polydopamine (PDA) nanocube as the precursor. In this composite, the NiCo2S4 nanoparticles coated with conformal carbon layers are homogeneously embedded in a 3D high-conduction carbon shell from PDA. Both the inner and the outer carbon coatings are helpful in increasing the electrical conductivity of the electrode materials and prohibit the polysulfide intermediates from dissolving in the electrolyte. When researched as electrode materials for lithium storage, owing to the unique structure with double layers of nitrogen-doped carbon coating, the as-obtained NiCo2S4@D-NC electrode maintains an excellent specific capacity of 480 mAh g-1 at 100 mA g-1 after 100 cycles. Even after 500 cycles at 500 mA g-1, a reversible capacity of 427 mAh g-1 can be achieved, suggesting an excellent rate capability and an ultralong cycling life. This remarkable lithium storage property indicates its potential application for future lithium-ion batteries.