Olivine‐Type Fe2GeX4 (X = S, Se, and Te): A Novel Class of Anode Materials for Exceptional Sodium Storage Performance

Abstract The introduction of abundant metals to form ternary germanium‐based chalcogenides can dilute the high price and effectively buffer the volume variation of germanium. Herein, olivine‐structured Fe 2 GeX 4 (X = S, Se, and Te) are synthesized by a chemical vapor transport method to compare their sodium storage properties. A series of in situ and ex situ measurements validate a combined intercalation‐conversion‐alloying reaction mechanism of Fe 2 GeX 4 . Fe 2 GeS 4 exhibits a high capacity of 477.9 mA h g −1 after 2660 cycles at 8 A g −1 , and excellent rate capability. Furthermore, the Na 3 V 2 (PO 4 ) 3 //Fe 2 GeS 4 full cell delivers a capacity of 375.5 mA h g −1 at 0.5 A g −1 , which is more than three times that of commercial hard carbon, with a high initial Coulombic efficiency of 93.23%. Capacity‐contribution and kinetic analyses reveal that the alloying reaction significantly contributes to the overall capacity and serves as the rate‐determining step within the reaction for both Fe 2 GeS 4 and Fe 2 GeSe 4 . Upon reaching a specific cycle threshold, the assessment of the kinetic properties of Fe 2 GeX 4 primarily relies on the ion diffusion process that occurs during charging. This work demonstrates that Fe 2 GeX 4 possesses promising practical potential to outperform hard carbon, offering valuable insights and impetus for the advancement of ternary germanium‐based anodes.