Web Release Date: February 16,
Electrochemical Reactions of Iron Borates with Lithium: Electrochemical and in Situ Mössbauer and X-ray Absorption Studies
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Laboratoire de Cristallographie, CNRS, BP 166, 38042 Grenoble Cedex 9, France, and Laboratoire des Agrégats Moléculaires et Matériaux Inorganiques (UMR 5072 CNRS), Université Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, and Laboratoire de Réactivité et Chimie des Solides, Université de Picardie Jules Verne, 80039 Amiens Cedex, France
Received August 3, 2001
Revised Manuscript Received November 26, 2001
Abstract:
Upon electrochemical reduction in a lithium cell, crystalline FeBO3 and Fe3BO6 give amorphous compounds, which can be cycled reversibly at low potential (Rowsell, J. Power Sources 2001, 97-98, 254). We report here capacities as high as 300 Ah/kg at the 14th cycle. The mechanism of reaction was investigated by step-potential electrochemical spectroscopy and in situ Mössbauer and X-ray absorption spectroscopies on electrochemical cells encapsulated in thin sealed plastic bags. These techniques confirm the reduction mechanism consisting of the early destruction of the crystallized borates and a direct FeIII-Fe0 multiphase reduction on first discharge. On recharge and subsequent cyclings, a reversible redox reaction occurs between Fe0 and FeII/III in an amorphous or nanocrystalline matrix.
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