N, S Co-doped carbon-enhanced FeS2 yolk–shell structure: Overcoming volume expansion and polysulfide shuttle issues in sodium-ion battery anodes

Abstract

Pyrite FeS₂ has the advantages of high theoretical capacity, environmental friendliness, and low cost as an anode material for sodium-ion batteries, but it suffers from large volume expansion during cycling as well as the problem of polysulfide shuttling, which seriously affects its cycling stability and rate performance. Therefore, in this paper, a yolk–shell FeS₂@NSC composite was synthesized by using Prussian blue (PB) as a precursor through dopamine coating and subsequent carbonization and vulcanization processes. The as-prepared FeS₂@NSC structure not only has sufficient internal space to mitigate the volume expansion but also effectively blocks the shuttling of polysulfides through the physical barrier and chemical adsorption of the N, S co-doped carbon layer, which effectively improves the cycling stability and rate performance of the electrode. As a result, it exhibits a high specific capacity of 939 mAh g⁻¹ after 200 cycles at 0.5 A g⁻¹ with a superior rate capability of 575.5 mAh g⁻¹ at 10 A g⁻¹. Most impressively, a stable capacity of 592 mAh g⁻¹ can still be retained even after 800 cycles at 5 A g⁻¹. The structure provides an idea for designing high-performance anode materials for sodium-ion batteries.