Abstract:

Ferrous sulfide (FeS) is a promising anode material for next-generation lithium-ion batteries due to its high theoretical specific capacity, safe lithium storage voltage plateau (1.5 V), abundant mineral reserves, and environmental compatibility. However, the material suffers from significant volume expansion during charge-discharge cycles, resulting in irreversible capacity loss and poor cycling performance. A coating layer can provide additional mechanical support, helping the electrode accommodate volume changes and thereby mitigating expansion effects. In this study, FeS was synthesized via a solid-phase method, and FeS@FeOOH composite materials were prepared by coating FeOOH onto the FeS surface through wet ball milling. The crystal structure and morphology were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Results show that at a ball milling speed of 300 r/min, the coating consists of tetragonal β-FeOOH, while at 600 r/min, the coating comprises both orthorhombic α-FeOOH and tetragonal β-FeOOH phases. Electrochemical tests demonstrate that the composite prepared at 600 r/min achieves 100% capacity retention after 100 cycles at 1 A/g, owing to the synergistic effect of α-FeOOH and β-FeOOH in the coating layer. Furthermore, it exhibits a low charge transfer resistance (R_ct) of 68.84 Ω. Low-temperature discharge testing reveals that at -40 ℃ and a current density of 100 mA/g, the discharge specific capacity retention reaches 99.8% of that at 0 ℃. This study proposes a straightforward and effective FeS surface modification strategy, providing a reference for the commercial application of FeS-based anodes in energy storage systems.

Key words: ferrous sulfide, anode material, double coating, wet ball milling, hydroxyl iron oxides