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 2x 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 Fe3O4 crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction.