Se‐Rich Functionalized FeS_x Hollow Nanospheres for Accelerated and Long‐Lasting Sodium Storage

Abstract Transition metal sulfides are emerging as promising anode materials for sodium‐ion batteries (SIBs) due to their high theoretical capacity and low cost, their practical application yet face critical issues of sluggish kinetics and poor cycling stability. In this study, a reliable approach is introduced to overcome these challenges by fabrication of Se_0.75‐Fe_1‐xS_0.25@SC hollow nanospheres thanks to the enriched robust Fe─S─C, C─S, and C─Se bonding, which greatly benefit for enhancing both reaction kinetics and structural stability. Kinetic study combining with in situ characterization reveals that the incorporation of rich‐Se into FeS_x induces the formation of cationic Fe and Se vacancies, leading to abundant sites and optimized path for sodium storage. Density functional theory calculations also demonstrate how Se‐rich engineering weakens carbonaceous polar C─S─Fe bonds and accelerates reaction dynamics. The as‐prepared Se_0.75‐Fe_1‐xS_0.25@SC can deliver a high reversible capacity of 515 mAh g⁻¹ at 2 A g⁻¹ over 1250 cycles and achieve superior rate capability with maintaining capacity of 418 mAh g⁻¹ at 10 A g⁻¹. This work pioneers the concept of vacancy‐rich functionalized nanostructures, offering a new pathway for designing advanced electrode materials for energy storage devices.