M. Bervas, L. Klein, G. Amatucci
2006
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73
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Journal
Journal of The Electrochemical Society
Abstract
For the first time, the effect of the oxygen anion substitution on the reversible electrochemical activity of metal fluorides was investigated through the use of bismuth oxyfluorides. We demonstrate that a reversible conversion occurs in BiO x F 3 - 2 - x ( x = 0 , 0 . 5 , 1 , 1 . 5 ) /C nanocomposites with the formation of Bi°, Li 2 O, and/or LiF during lithiation and the reformation of BiO x F 3 - 2 x during subsequent delithiation as opposed to a two-phase mixture of Bi 2 O 3 + BiF 3 . We also show evidence that in BiOF and BiO 0 . 5 F 2 the fluoride component reacts first at higher voltage during lithiation to form Bi°, LiF, and Bi 2 O 3 . The newly formed Bi 2 O 3 is then subsequently reduced into Li 2 O and Bi° on a second plateau at lower voltage. During delithiation the process is reversed, Li 2 O reacting first at low voltage followed by LiF. Although cycling is presently poor, our results show that a relatively low oxygen content can significantly improve the electrochemical activity of the metal fluoride, suggesting that optimized metal oxyfluorides could be an attractive alternative to metal fluorides for applications as positive electrode materials in lithium batteries.