Mechanically Robust FeIn ₂ S ₄ Nanosheets on rGO for Fast and Durable Sodium Storage

Abstract 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 FeIn ₂ S ₄ 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 Na ₃ V ₂ (PO ₄ ) ₃ F ₃ (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.