Prussian blue-derived multiple yolk–single shell-structured Se-doped Fe7S8@NC@C microcube composites as high-rate anodes for sodium-ion batteries

Abstract

Iron sulfides possess a high theoretical capacity and rich natural abundance, making them promising anode materials for sodium-ion batteries (SIBs); however, their inferior rate of cycling performance stemming from intrinsic inferior electrical conductivity and the huge volume change are the main hindrances to practical applications at present. Herein, spatially dual-confined Se-doped Fe₇S₈ multiple yolk–single shell (Se-Fe₇S₈@NC@C) microcubes are designed via heteroatom-doping and carbon confinement engineering. The yolk–shell structure provides sufficient void space to alleviate the effects of volume change; the dual-carbon layer acts as a rigid skeleton to ensure the structural integrity and confines active materials to avoid agglomeration during sodiation/desodiation. Meanwhile, the introduction of Se modulates the electronic structure, improving the electrical conductivity of the material and enlarging the interlayer distance to accelerate Na⁺ diffusion. Accordingly, the as-prepared Se-Fe₇S₈@NC@C shows satisfactory sodium storage properties: a superb initial capacity of 828.5 mA h g⁻¹ at 0.1 A g⁻¹, an exceptional rate capability of 448.2 mA h g⁻¹ at 5 A g⁻¹ and an admirable cycling stability with 390.9 mA h g⁻¹ at 5 A g⁻¹ after 800 cycles. This study provides an innovative idea to fabricate advanced anodes for SIBs and other alkali metal-ion batteries by morphology design and electronic structure modulation.