Facile synthesis of uniform yolk–shell structured FeS@mesoporous carbon spheres for high-performance sodium-ion batteries

Abstract

Iron sulfide is a promising candidate anode material for high performance Na-ion batteries because of its high theoretical capacity and low price. Unfortunately, it usually shows frustrating performance because of its inherent low conductivity and large volume expansion during charge–discharge processes. Here, we have synthesized uniform yolk–shell structured FeS@mesoporous carbon spheres (FeS@meso-C) by combining a facile one-pot coating strategy with a sulfuration method. The resultant yolk–shell structured FeS@meso-C with a diameter of ∼200 nm possess ∼120 nm single crystalline FeS yolks, ∼40 nm void space and uniform mesoporous carbon shells (∼15 nm thickness and ∼5 nm mesopores). In this unique structure, the void spaces provide enough room to buffer the FeS expansion, the mesopores in the carbon shells facilitate the transport of Na ions and the mesoporous carbon shells can improve the conductivity of the active composites. When used as the anode for Na-ion batteries, the yolk–shell structured FeS@meso-C show a high specific capacity of 596 mA h g⁻¹ even after 100 cycles at 0.2 A g⁻¹ and show an excellent rate capability (capabilities of 578, 438, 420, 358, 320, 256 and 214 mA h g⁻¹ at 0.2, 0.5, 1, 2, 4, 8 and 10 A g⁻¹)