Mechanically Robust FeIn₂S₄ Nanosheets on rGO for Fast and Durable Sodium Storage

Indium-based bimetallic sulfides are one of the attractive anode materials for sodium-ion batteries (SIBs) but suffer from severe volume changes and sluggish kinetic process, resulting in fast capacity fading and inferior rate capability. While compounding with carbon is a common strategy, achieving mechanical robustness through rational hierarchical design and understanding the underlying stress dissipation mechanism remains a challenge. In this work, ultrathin FeIn₂S₄ nanosheets anchored on reduced graphene oxide (FIS@rGO) are rationally designed to create a stress-buffering architecture, and structural characterization confirms strong interfacial coupling between FIS and rGO. In situ XRD and finite element analysis collaboratively reveal that the remarkable stability originates from a highly reversible phase transition pathway and a unique stress-homogenizing effect within the hierarchical structure. Benefiting from the well-designed structure, FIS@rGO exhibits excellent sodium storage performance, achieving a high reversible capacity (503 mAh g^-1 at 1 A g^-1 over 200 cycles), superb rate capability (358 mAh g^-1 at 15 A g^-1), and durable stability (1300 cycles with 299 mAh g^-1 at 10 A g^-1). Furthermore, full cells paired with Na₃V₂(PO₄)₃F₃ (NVPF) cathodes manifest outstanding cyclic stability with 92.4% capacity retention at 1 A g^-1 after 100 cycles, demonstrating significant potential for practical applications.