FeNb 2 O 6 as a High‐Performance Anode for Sodium‐Ion Batteries Enabled by Structural Amorphization Coupled with NbO 6 Local Ordering

Abstract Pseudocapacitance‐type transition metal oxides have been extensively investigated as anodes for lithium‐ion batteries (LIBs). Currently, they are also gaining attention for sodium‐ion batteries (SIBs) due to their low volume change and safety. However, their performance in sodium storage remains limited, primarily due to the larger Na + ion radius. Here, for the first time, an iron niobate is reported with a columbite structure as a high‐performance sodium storage anode. The presence of iron triggers the loss of long‐range order through disorder of the FeO 6 octahedra local structure, subsequently allowing reversible sodium storage in an amorphous phase. Simultaneously, the formation of short‐range ordered zigzag‐chain structures within the NbO 6 planes creates a “skeleton” that offers abundant active sites for pseudocapacitive ion storage and enhanced ion diffusion pathways. These characteristics of FeNb 2 O 6 make it an effective intercalation host, offering high capacity along with fast Na + kinetics, as demonstrated through operando and ex situ characterizations. It leads to an applicable reversible capacity (>300 mAh g −1 ) with a favorable average voltage of ≈0.6 V and excellent rate capability (180.4 mAh g −1 at a current density of 2 A g −1 ). This study provides insights into the development of intrinsically active transition metal oxides for Na + ‐ion intercalation.