As the demand for large scale batteries has grown, considerations such as earth abundance, cost, and toxicity have assumed a greater significance.  Metal oxides such as magnetite (Fe₃O₄) are worthy of evaluation as active materials for electrochemical energy storage due to its earth abundance, low cost, environmentally benign iron metal centers and high theoretical capacity, 926 mAh/g.  Implementation in the future will require understanding of the fundamental electrochemical reduction-oxidation mechanisms of the electroactive materials is required, coupled with characterization at the mesoscale to understand the underlying contributors to localized resistance which must be addressed in order to achieve significant improvements to current capability and reversibility.

An emerging paradigm for the implementation of close-packed materials in higher current applications is the tuning of the materials crystallite dimensions, where the reduction of crystallite size should minimize the path length for ion transport upon discharge, resulting in a reduction of both internal cell resistance and the resultant structural strain associated with lithium insertion.  The electrochemical impact of controlled crystallite size of magnetite will be described.

In addition to the crystallite size of the electroactive material, a complete study of an electroactive nanomaterial in the complex mesoscale environment of a composite battery electrode should also consider the level of electroactive particle agglomeration, and agglomerate distribution within the battery electrode.  Nanocrystalline magnetite (Fe₃O₄) powders and composite electrodes with different crystallite sizes were prepared, characterized, and electrochemically evaluated.  Transmission electron microscopy (TEM) examination of cross-sectioned electrodes was used to quantify the aggregate size of the Fe₃O₄ active material.  Notably, although the crystallite sizes of two magnetite samples Fe₃O₄ are different (28 and 9 nm), the observed sizes of the aggregates and aggregate distribution within the electrodes were similar, see TEM images of sectioned electrodes fabricated with the 28 nm (A,B) and 9 nm (C,D) sized Fe₃O₄ in the Figure.  Transmission x-ray microscopy (TXM) combined with x-ray absorption near edge spectroscopy (XANES) at the National Synchrotron Light Source (NSLS) were used to determine the distribution of the iron oxidation states within the electrodes before and after electrochemical testing.  The impact of both crystallite size and agglomeration on electrochemical performance were assessed.