Carbon Metal Fluoride Nanocomposites

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Abstract
The structure and electrochemistry of FeF3:CFeF3:C -based carbon metal fluoride nanocomposites (CMFNCs) was investigated in detail from 4.5 to 1.5 V, revealing a reversible metal fluoride conversion process. These are the first reported examples of a high-capacity reversible conversion process for positive electrodes. A reversible specific capacity of approximately 600 mAh/g of CMFNCs was realized at 70°C. Approximately one-third of the capacity evolved in a reaction between 3.5 and 2.8 V related to the cathodic reduction reaction of Fe3+Fe3+ to Fe2+.Fe2+. The remainder of the specific capacity occurred in a two-phase conversion reaction at 2 V resulting in the formation of a finer Fe:LiF nanocomposite. Upon oxidation, selective area electron diffraction characterization revealed the reformation of a metal fluoride. Evidence presented suggested that the metal fluoride is related to FeF2FeF2 in structure. A pseudocapacitive reaction is proposed as a possible mechanism for the subsequent Fe2+→Fe3+Fe2+→Fe3+ oxidation reaction. Preliminary results of FeF2,FeF2, NiF2,NiF2, and CoF2CoF2 CMFNCs were used in the discussion of the electrochemical properties of the reconverted metal fluoride. © 2003 The Electrochemical Society. All rights reserved.