Effect of Vertically Structured Porosity on Electrochemical Performance of FeF2 Films for Lithium Batteries

Iron fluoride (FeF2) is an attractive material for use as nanocomposite conversion reaction based cathodes in lithium ion batteries because of its high specific theoretical capacity of 571 mA hg(-1). However, despite the optimistic potential of FeF2 to advance battery cathodes, the cycling performance of the material requires further development for it to be a viable cathode candidate. A deeper understanding is required of how orientation, selective reaction fronts, and morphology impact the electrochemical performance through subsequent enhancement of ionic and/or electronic transport. FeF2 films of various degrees of vertical porosity and thickness were fabricated through the use of dynamic glancing angle deposition. Respectable performance was obtained with film thicknesses of 850 nm, well above the nanodimensions typically required to trigger electrochemical activity. Significant, systematic changes in the cycling stability of the films were induced by changes in the morphology. The structure - electrochemical relationships were utilized to formulate insights on the electronic and ionic transport limitations observed in typical nanocomposite powders. (C) 2014 Published by Elsevier Ltd.