Electrochemical discharge of nanocrystalline magnetite: Structure analysis using X-ray diffraction and X-ray absorption spectroscopy

Magnetite (Fe₃O₄) is an abundant, low cost, environmentally benign material with potential application in batteries. Recently, low temperature coprecipitation methods have enabled preparation of a series of nanocrystalline magnetite samples with a range of crystallite sizes. Electrochemical cells based on Li/Fe₃O₄ show a linear increase in capacity with decreasing crystallite size at voltages ≥1.2 V where a 2× capacity improvement relative to commercial (26.2 nm) magnetite is observed. In this report, a combination of X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) is used to measure magnetite structural changes occurring upon electrochemical reduction, with parent Fe ₃O₄ crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction.