General metal-organic framework-derived strategy to synthesize yolk-shell carbon-encapsulated nickelic spheres for sodium-ion batteries

Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal-organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal-organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbonencapsulated Ni2P (Ni2P/C), NiS2 (NiS2/C) and NiSe2 (NiSe2/C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni2P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g1) and reversible capacity of 765.4 mAh g-1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transitionmetal compound electrodes via MOFs template for advanced battery systems. (c) 2022 Elsevier Inc. All rights reserved.

Automated summary

Transition-metal compounds have potential as energy storage materials, but their capacity decay and rate capability are still limited. In this study, hierarchical carbon-encapsulated yolk-shell nickelic spheres were fabricated as anode materials for sodium-ion batteries using a metal-organic framework-derived route. The Ni-MOF precursors were converted into carbon-encapsulated Ni2P, NiS2, and NiSe2 while maintaining their sphere-like morphology. The Ni2P/C sample exhibited lower polarization, smaller voltage gap, and faster kinetics, resulting in higher initial specific capacity and reversible capacity.