Electrochemical discharge of nanocrystalline magnetite: structure analysis using X-ray diffraction and X-ray absorption spectroscopyElectronic supplementary information (ESI) available: Fig. S1. X-ray diffraction pattern of polyimide tape. See DOI: 10.1039/c3cp52870g

Magnetite (Fe 3 O 4 ) 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/Fe 3 O 4 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 3 O 4 crystallite size as a variable. Notably, XAS provides evidence of metallic iron formation at high levels of electrochemical reduction. Structural analysis of electrochemically reduced Fe 3 O 4 prepared by coprecipitation provides evidence of metallic iron formation and insight into crystallite size impact.