Carbon-Metal Fluoride Nanocomposites

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Abstract
The practical electroactivity of electrically insulating iron fluoride was enabled through the use of carbon-metal fluoride nanocomposites (CMFNCs). The nanocomposites were fabricated through the use of high energy mechanical milling and resulted in nanodomains of FeF3FeF3 on the order of 1-20 nm encompassed in a matrix of carbon as characterized by transmission electron microscopy and X-ray diffraction (XRD). Electrochemical characterization of CMFNCs composed of 85/15 wt % FeF3/CFeF3/C resulted in a nanocomposite specific capacity as high as 200 mAh/g (235 mAh/(g of FeF3)FeF3) with the electrochemical activity associated with the Fe3+→Fe2+Fe3+→Fe2+ occurring in the region of 2.8-3.5 V. The CMFNCs revealed encouraging rate capability and cycle life with <10%ex situ and in situ XRD. Initial results suggest that xx from 0 to 0.5 in LixFeF3LixFeF3 proceeds in a two-phase reaction resulting in a phase with significant redistribution of the Fe atoms within a structure very similar to the base FeF3.FeF3. FeF3FeF3 -based CMFNCs also exhibited a very high specific capacity of 600 mAh/g at 70°C due to a reversible reaction at approximately 2 V. © 2003 The Electrochemical Society. All rights reserved.