Crystallochemical Tailoring of Ternary Sb 2 TeSe 2 Anodes Enables Fast and Durable Sodium‐Ion Storage

ABSTRACT Sesquichalcogenides have emerged as promising alloy–conversion‐type anodes for sodium‐ion batteries due to their tunable electronic structure and unconventional bonding characteristics. However, conventional binary sesquichalcogenides suffer from sluggish Na + kinetics and rapid structural degradation, primarily caused by crystallographic anisotropy and high defect densities. Herein, we craft a single‐phase ternary diantimony telluride diselenide (Sb 2 TeSe 2 ) anode through a precise anion transmutation strategy, where the deliberate introduction of selenium atomic layers serves as a powerful lever to reorient the crystal framework, heal structural flaws, and generate a wealth of Na + anchoring sites. This intricate structural orchestration not only strengthens Na‐ion affinity but also accelerates their migration highways, enabling fast and efficient storage dynamics. Guided by the density functional theory (DFT) insights and in situ visualizations, the atomistic Na + storage mechanism is unveiled, underscoring how anion substitution reshapes the energy landscape and unlocks optimized ion transport pathways. Consequently, the Sb 2 TeSe 2 /C anode delivers superior rate capability and remarkable cycling stability, maintaining a high capacity over 1200 cycles at 2.0 A g − 1 , far outperforming its binary counterparts (Sb 2 Te 3 /C and Sb 2 Se 3 /C). Furthermore, when coupled with a Na 3 V 2 (PO 4 ) 3 /C cathode in a full‐cell configuration, it delivers a high energy density of 191 Wh kg − 1 along with outstanding long‐term durability.