Optimized architectural engineering and interface modulation in metallic-phase selenide for exceptional sodium-storage performance

Transition metal selenides (TMSs) exhibit promise as anode materials for sodium-ion batteries (SIBs) due to their high specific capacity and diverse electronic properties. However, practical implementation faces challenges such as structural deterioration, solid-electrolyte interphase (SEI) instability, and diminished coulombic efficiency, especially at the nanoscale. Here, we introduce a novel approach that combines surface engineering of Fe₃Se₄ with an interface engineering strategy (Fe₃Se₄@NC) to effectively address these issues. By incorporating engineered void spaces and an electrolyte-blocking layer within micrometer-sized secondary clusters, Fe₃Se₄ nanoparticles gain the ability to expand and contract freely during cycling, thereby preserving interparticle connections and enhancing the structural integrity. The synergy of surface engineering with a nitrogen-doped carbon layer and interface engineering through electrolyte modulation leads to an outstanding 95.1 % initial Coulombic efficiency in the Fe₃Se₄@NC electrode. Even after 2000 cycles at 5 A g⁻¹, the electrode retains over 89.2 % of its initial capacity with an average specific capacity of 450 mAh g⁻¹. In situ transmission electron microscopy (TEM) and in situ X-ray diffraction (XRD) analysis shed light on the structural evolution and sodiation dynamics during charge/discharge process. Experimental investigations and DFT calculations provide a comprehensive understanding of the SEI composition and the structural stability of the composite.