K.J. Takeuchi, A.C. Marschilok, E.S. Takeuchi
Stony Brook University,
Keywords: energy storage, nanoscale, iron oxide
Summary:Improved battery technology is needed to meet the future energy demands for grid storage, electric vehicles, and portable electronics. As the demand for large scale batteries grows, considerations such as earth abundance, cost, and toxicity gain increased significance. Iron oxides are potentially attractive active materials for electrochemical energy storage as they are abundant, low cost, environmentally benign materials, have very low toxicity, and have high theoretical gravimetric capacity of >900 mAh/g. Many iron oxides adopt close-packed coordination environments. Close-packing optimizes ion density, but rapid ion and electron transfer are challenges as a result. 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. As a result, the size of the particles of active electrode materials can have a large effect on the cycling performance and discharge characteristics of batteries as well as the rate capability in particular for materials limited by low ionic conductivity, such as magnetite. By reducing the crystallite dimension of magnetite, the total path length for Li ions can be decreased, allowing for an increase in capacity at higher discharge currents by increasing the utilization of the active material by 30 to 200%. Significant improvements in current capability of iron oxides via direct crystallite size control will be described. Stable cycling performance has also been elusive for iron oxide based systems, where some of the best results have been achieved through the formation of composite materials and mesoscale composite electrodes. Here, a composite iron oxide based bimetallic material prepared by direct synthesis is described. A synthetic paradigm for concomitant control of crystallite size and composition is introduced, with a marked benefit on reversible capacity and capacity retention. In addition, characterization approaches lending insight for composite materials and electrodes have been developed. The synthetic and characterization approaches described in this presentation will provide new strategies which may be applicable toward development of other new classes of materials with energy or energy storage applications.