Enhanced Surface Pseudocapacitance in 3D Hierarchical FeSe₂ Rod-Clusters Enabling High-Rate and Long-Term Sodium Storage

FeSe₂ is highly prone to structural degradation during repeated (de)sodiation reactions, leading to inferior rate performance and poor cycling stability, which significantly limits its application. Herein, 3D hierarchical rod-clusters assembled from FeSe₂ submicron rods are successfully synthesized through seleniumization with dissolution-reassembly and the subsequent annealing process. The submicron rods can facilitate rapid sodium-ion diffusion and release structural stress, which is conducive to maintaining structural integrity during prolonged cycling. Importantly, the unique 3D hierarchical architecture provides an open and interconnected framework, enabling plentiful active sites for sodium storage and enhancing surface-controlled pseudocapacitive behavior. These synergistic advantages endow FeSe₂ rod-clusters with high capacity, excellent rate property, and outstanding cycling stability. Specifically, the optimized A-FS-2 delivers a high specific capacity of 453.0 mAh g^-¹ even after 900 cycles under 1.0 A g^-¹, as well as retains a reversible specific capacity of 356.1 mAh g^-¹ after 1800 cycles under 3.0 A g^-¹ and 361.1 mAh g^-¹ after 1100 cycles under 5.0 A g^-¹. This work demonstrates a promising anode material for SIBs and provides a worthy guide for designing conversion-type anode materials with high-rate capability and long-term cycling stability.