Microsized fayalite Fe2SiO4 as anode material: the structure, electrochemical properties and working mechanism

Fayalite Fe2SiO4 is synthesized by the solid-state reaction without ball milling. The obtained powder is further structurally and electrochemically examined. Field emission scanning electron microscopy (FESEM) showed that microsized powder is obtained. X-ray powder diffraction (XRD) pattern is used for both phase identification and crystal structure Rietveld refinement. The structure is refined in the orthorhombic Pbnm space group. Mossbauer spectroscopy revealed traces of Fe3+ impurity. The bond valence mapping method is applied for the first time on Fe2SiO4 framework. It shows isolated, non-connected isosurfaces of constant E(Li), which further supports the assumptions of the conversion reactions. Electrochemical performances are investigated through galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Ex-situ XRD and Fourier transform infrared spectroscopy (FTIR) analyses are combined to monitor phase change after galvanostatic cycling and to reveal the working mechanism during electrochemical lithiation.