Scalable synthesis of a foam-like FeS₂ nanostructure by a solution combustion-sulfurization process for high-capacity sodium-ion batteries

Pyrite-type FeS₂ is regarded as a promising anode material for sodium ion batteries. The synthesis of FeS₂ in large quantities accompanied by an improved cycling stability, as well as retaining high theoretical capacity, is highly desirable for its commercialization. Herein, we present a scalable and simple strategy to prepare a foam-like FeS₂ (F-FeS₂) nanostructure by combining solution combustion synthesis and solid-state sulfurization. The obtained F-FeS₂ product is highly uniform and built from interconnected FeS₂ nanoparticles (∼50 nm). The interconnected feature, small particle sizes and porous structure endow the product with high electrical conductivity, good ion diffusion kinetics, and high inhibition capacity of volume expansion. As a result, high capacity (823 mA h g⁻¹ at 0.1 A g⁻¹, very close to the theoretical capacity of FeS₂, 894 mA h g⁻¹), good rate capability (581 mA h g⁻¹ at 5.0 A g⁻¹) and cyclability (754 mA h g⁻¹ at 0.2 A g⁻¹ with 97% retention after 80 cycles) can be achieved. The sodium storage mechanism has been proved to be a combination of intercalation and conversion reactions based on in situ XRD. Furthermore, high pseudocapacitive contribution (i.e. ∼87.5% at 5.0 mV s⁻¹) accounts for the outstanding electrochemical performance of F-FeS₂ at high rates.