Introduction of SnS₂ to Regulate the Ferrous Disulfide Phase Evolution for the Construction of Triphasic Heterostructures Enabling Kinetically Accelerated and Durable Sodium Storage

Abstract Transition metal sulfides (TMSs) still confront the challenges of capacity fading and inferior fast‐charging capability for sodium storage. The rational design of heterostructures enables a new approach to conquer these drawbacks. In this work, a hierarchical structure consisting of SnS₂ nanosheets and FeS₂ microrods with triphasic heterostructures is proposed by the facile secondary growth and sulfidation process. The introduction of tin sources regulates the proportion of pyrite and marcasite phases, thereby achieving the triphasic heterostructures comprising pyrite, marcasite FeS_2, and SnS₂. When served as anode material for sodium‐ion batteries, the optimized sample exhibits a high reversible capacity (901 mAh g⁻¹) and durable cycling performances (827 mAh g⁻¹ after 200 cycles at 1 A g⁻¹ and 742 mAh g⁻¹ after 700 cycles at 5 A g⁻¹). Paring with the commercial Na₃V₂(PO₃)₃ cathodes, the full‐cell also delivers extraordinary cyclic stability with a high capacity of 618 mAh g⁻¹ (based on the weight of anode material) after 200 cycles at 1 A g⁻¹ (98.7% capacity retention). The hierarchical structure with adjustably triphasic heterogeneous interfaces alleviates the volumetric expansion and interfacial passivation of active material, while modulating the energy band structure and inducing the build‐in electric fields to boost Na⁺/electrons transport rate.