Fe₂GeS₄/exfoliated graphite composite anodes with enhanced performance for SIBs

As a new type of negative electrode material for SIBs, (iron germanium sulfide) Fe2GeS4 is considered a highly promising negative electrode material for SIBs owing to its high theoretical capacity, fast Na+ diffusion kinetics, and good thermal stability. In practical applications, it is crucial to synthesize the high-capacity/reversible nanostructured Fe2GeS4-based negative electrodes through an easily executable method. In this study, a two-step synthesis method to prepare nanostructured Fe2GeS4 anchored on graphite (Fe2GeS4/G-15%) was employed: the commercial FeS, S, and Ge powders were mixed and heated, and then graphite was added for ball milling. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that there is a strong interaction between the nanostructured Fe2GeS4 powder and the exfoliated graphite, forming a highly stable nanocomposite material, which is beneficial for improving the reversible charge-discharge performance of the material. When used as a negative electrode material for SIBs, the prepared Fe2GeS4/G-15% exhibited a capacity of 665.5 mAh g(-1) during the second cycle at 0.1 A g(-1) and could maintain a capacity of 519 mAh g(-1) even after the 60th cycle. Considering the simple synthesis process employed in this study, it provides a reference for the production of high-performance Fe2GeS4-based negative electrode materials for SIBs.