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

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 (∼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.

[1]  M. Isaacson,et al.  Electronic and chemical analysis of fluoride interface structures at subnanometer spatial resolution , 1986 .

[2]  R. Brydson,et al.  Determination of the local chemistry of iron in inorganic and organic materials , 2005 .

[3]  J. Galy,et al.  Structural aspects of amorphous iron(III) fluorides , 1988 .

[4]  P. Buseck,et al.  Ratios of ferrous to ferric iron from nanometre-sized areas in minerals , 1998, Nature.

[5]  P. V. van Aken,et al.  Quantitative determination of iron oxidation states in minerals using Fe L2,3-edge electron energy-loss near-edge structure spectroscopy , 1998 .

[6]  J. Silcox,et al.  Effects of high-energy electron irradiation on heavy-metal fluoride glass , 2004 .

[7]  C. Colliex,et al.  Electron-energy-loss-spectroscopy near-edge fine structures in the iron-oxygen system. , 1991, Physical review. B, Condensed matter.

[8]  R. Egerton,et al.  Electron Energy-Loss Spectroscopy in the Electron Microscope , 1995, Springer US.

[9]  K. Krishnan.  Iron L3,2 near-edge fine structure studies , 1990 .

[10]  B. Fultz,et al.  Measurements of 3d state occupancy in transition metals using electron energy loss spectrometry , 1988 .

[11]  John B. Goodenough,et al.  LixCoO2 (0, 1980 .

[12]  M. Malac,et al.  Exposure characteristics of cobalt fluoride (CoF2) self-developing electron-beam resist on sub-100 nm scale , 2002 .

[13]  W. M. Stobbs,et al.  Quantification of the EELS near‐edge structures to study Mn doping in oxides , 1995 .

[14]  Glenn G. Amatucci,et al.  Structure and Electrochemistry of Carbon-Metal Fluoride Nanocomposites Fabricated by Solid-State Redox Conversion Reaction , 2005 .

[15]  C. Boothroyd,et al.  Electron energy loss spectroscopy studies of the amorphous to crystalline transition in FeF3 , 1999 .

[16]  M. Malac,et al.  Energy-loss near-edge fine structures of iron nanoparticles. , 2006, Micron.

[17]  J. Spence,et al.  Interpretation of Oxygen K pre-edge peak in complex oxides. , 2006, Ultramicroscopy.

[18]  J. Tarascon,et al.  CoO2, the end member of the LixCoO2 solid solution , 1996 .

[19]  C. Humphreys,et al.  Investigation of the proximity effect in amorphous AlF3 electron-beam resists , 1997 .

[20]  C. Boothroyd,et al.  Electron‐beam induced crystallization transition in self‐developing amorphous AlF3 resists , 1996 .

[21]  M. Scheinfein,et al.  Magnetic nanostructures produced by electron beam patterning of direct write transition metal fluoride resists , 1998 .

[22]  Z. Wang,et al.  Mapping the Valence States of Transition-Metal Elements Using Energy-Filtered Transmission Electron Microscopy , 1999 .

[23]  Nathalie Pereira,et al.  Carbon-Metal Fluoride Nanocomposites Structure and Electrochemistry of FeF3: C , 2003 .

[24]  A. Putnis,et al.  Laterally resolved EELS for ELNES mapping of the Fe L 2,3 - and O K-edge. , 2003, Ultramicroscopy.

[25]  Richard D. Leapman,et al.  Study of the L 23 edges in the 3 d transition metals and their oxides by electron-energy-loss spectroscopy with comparisons to theory , 1982 .

[26]  K. S. Nanjundaswamy,et al.  Phospho‐olivines as Positive‐Electrode Materials for Rechargeable Lithium Batteries , 1997 .

[27]  P. Bruce,et al.  Structural transformation on cycling layered Li(Mn1−yCoy)O2 cathode materials , 1999 .

[28]  O. Krivanek,et al.  Elnes of 3d transition-metal oxides. II, Variations with oxidation state and crystal structure , 1990 .

[29]  P. V. van Aken,et al.  Quantification of ferrous/ferric ratios in minerals: new evaluation schemes of Fe L23 electron energy-loss near-edge spectra , 2002 .

[30]  Glenn G. Amatucci,et al.  Carbon Metal Fluoride Nanocomposites High-Capacity Reversible Metal Fluoride Conversion Materials as Rechargeable Positive Electrodes for Li Batteries , 2003 .

[31]  V. K. Adamchuk,et al.  Low-lying unoccupied electronic states in 3d transition-metal fluorides probed by NEXAFS at the F 1s threshold , 2005 .