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EELS Spectroscopy of Iron Fluorides and FeF x /C Nanocomposite Electrodes Used in Li-Ion Batteries

2007; Oxford University Press; Volume: 13; Issue: 2 Linguagem: Inglês

10.1017/s1431927607070183

1435-8115

Frederic Cosandey, Jafar F. Al‐Sharab, Fadwa Badway, Glenn G. Amatucci, Pierre Stadelmann,

Semiconductor materials and devices

A new type of positive electrode for Li-ion batteries has been developed recently based on FeF3/C and FeF2/C nanocomposites. The microstructural and redox evolution during discharge and recharge processes was followed by electron energy loss spectroscopy (EELS) to determine the valence state of Fe by measuring the Fe L3 line energy shift and from Fe L3/L2 line intensity ratios. In addition, transition metal fluorides were found to be electron beam sensitive, and the effect of beam exposure on EELS spectra was also investigated. The EELS results indicate that for both FeF3/C and FeF2/C nanocomposite systems, a complete reduction of iron to FeO is observed upon discharge to 1.5 V with the formation of a finer FeO/LiF subnanocomposite ( approximately 7 nm). Upon complete recharging to 4.5 V, EELS data reveal a reoxidation process to a Fe2+ state with the formation of a carbon metal fluoride nanocomposite related to the FeF2 structure.