Yolk-shell-structured (Fe0.5Ni0.5)(9)S-8 solid-solution powders: Synthesis and application as anode materials for Na-ion batteries

Abstract

Multicomponent metal sulfide materials with a yolk-shell structure and a single phase were studied for the first time as anode materials for sodium-ion batteries. Yolk-shell-structured Fe-Ni-O powders with a molar ratio of iron and nickel components of 1/1 were prepared via one-pot spray pyrolysis. The prepared Fe-Ni-O powders were transformed into yolk-shell-structured (Fe0.5Ni0.5)(9)S-8 solid-solution powders via a sulfidation process. The initial discharge and charge capacities of the (Fe0.5Ni0.5)(9)S-8 powders at a current density of 1 A.g(-1) were 601 and 504 mA.h.g(-1), respectively. The discharge capacities of the (Fe0.5Ni0.5)(9)S-8 powders for the 2nd and 100th cycle were 530 and 527 mA.h.g(-1), respectively, and their corresponding capacity retention measured from the 2nd cycle was 99%. The (Fe0.5Ni0.5)(9)S-8 powders had high initial discharge and charge capacities at a low current density of 0.1 A.g(-1), and the reversible discharge capacity decreased slightly from 568 to 465 mA.h.g(-1) as the current density increased from 0.1 to 5.0 A.g(-1). The synergetic effect of the novel yolk-shell structure and the multicomponent sulfide composition of the (Fe0.5Ni0.5)(9)S-8 powders resulted in excellent sodium-ion storage performance.