Olivine-Type Fe 2 GeX 4 (X = S, Se, and Te): A Novel Class of Anode Materials for Exceptional Sodium Storage Performance

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 GeX (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 GeX . Fe GeS exhibits a high capacity of 477.9 mA h g after 2660 cycles at 8 A g , and excellent rate capability. Furthermore, the Na V (PO ) //Fe GeS full cell delivers a capacity of 375.5 mA h g at 0.5 A g , 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 GeS and Fe GeSe . Upon reaching a specific cycle threshold, the assessment of the kinetic properties of Fe GeX primarily relies on the ion diffusion process that occurs during charging. This work demonstrates that Fe GeX possesses promising practical potential to outperform hard carbon, offering valuable insights and impetus for the advancement of ternary germanium-based anodes.