Improvement of Ultra Soft X-ray Absorption Spectroscopy and Photoelectron Spectroscopy Beamline for Studies on Related Materials and Cathodes of Lithium Ion Batteries (original) (raw)
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In situ X-ray absorption spectroscopy—A probe of cathode materials for Li-ion cells
Fluid Phase Equilibria, 2006
In situ X-ray absorption spectroscopy is a powerful emerging technique that has the capability to observe the changes in ongoing electrochemical reactions. It is already well established in materials science, and it is becoming a significant tool for the electrochemical community. As with all X-ray absorption spectroscopies, extended X-ray absorption fine structure (EXAFS) has the advantage of being element specific. Interpretation of the spectra at different states of charge can provide very useful quantitative and qualitative information about the valence change of the constituent elements in the cathode material during the ongoing electrochemical reaction, the degree of distortion or changes in structure from the initial state of charge to the final state of charge and provide valuable information about the extent of degradation of the cathode material during continuous cycling. It can also provide valuable insight about how the nature of the electrochemical reactions changes when one of the transition metal constituents is removed or increased in content in the cathode material. It is often important to adjust the composition of the cathode material in order to achieve high specific capacity and long-term stability in Li-ion cells. This article details the development of the in situ XAS techniques to study electrochemical reactions using various X-ray absorption spectroscopies which are now possible with the advent of third generation synchrotron radiation sources and improved end stations. The strength of in situ EXAFS techniques is illustrated using examples of various interesting transition metal oxides. In this way, we aim to encourage chemists, chemical engineers and materials scientists to consider in situ X-ray absorption spectroscopy as an effective tool for developing an understanding the electronic structure of materials and the changes that it undergoes during electrochemical reactions. (A. Deb).
Applied Spectroscopy, 2003
We applied soft X-ray absorption spectroscopy (XA S) and two-dimensional (2D) correlation analysis to the rst lithium insertionextraction cycle in a Li 11 x V 3 O 8 /Li cell in order to investigate the electrochemical reactions of lithium with the Li 11 x V 3 O 8 electrod e. The V L I I,I II -edge and O K-edge spectra of the Li 11x V 3 O 8 electrod e were obtained for varying electrode lithium content. The insertion of lithium leads to the reduction of the V 51 species presen t in the pristine Li 11 x V 3 O 8 electrode, and to the red shift and the broadening of the spectral features of the V L II ,I II edge compared to those of the pristine electrode. In the extraction process, the main spectral features at the highest value of the extraction of lithium show some differences compared to the features of the pristine electrode spectrum due to the residual lithium ions in the Li 11 x V 3 O 8 structure.
Journal of Power Sources, 2007
The lithium(1s) K-edge X-ray absorption spectra of lithium-ion battery relevant materials (Li metal, Li 3 N, LiPF 6 , LiC 6 , and LiMn 1.90 Ni 0.10 O 4 ) are presented. The Li and LiC 6 spectra are discussed and compared with literature data. The Li in lithium-intercalated carbon LiC 6 , typically used as anode battery electrode material, could be clearly identified in the spectrum, and a presumed purely metallic character of the Li can be ruled out based on the chemical shift observed. The Li in corresponding cathode electrode materials, LiMn 1.90 Ni 0.10 O 4 , could be detected with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, but the strong (self-) absorption of the spinel lattice provides an obstacle for quantitative analysis. Owing to its ionic bonding, the spectrum of the electrolyte salt LiPF 6 contains a sharp -resonance at 61.8 eV, suggesting a distinct charge transfer between Li and the hexafluorophosphate anion. In addition, LiPF 6 resembles many spectral features of LiF, making it difficult to discriminate both from each other.
Energies
The main challenges facing rechargeable batteries today are: (1) increasing the electrode capacity; (2) prolonging the cycle life; (3) enhancing the rate performance and (4) insuring their safety. Significant efforts have been devoted to improve the present electrode materials as well as to develop and design new high performance electrodes. All of the efforts are based on the understanding of the materials, their working mechanisms, the impact of the structure and reaction mechanism on electrochemical performance. Various operando/in-situ methods are applied in studying rechargeable batteries to gain a better understanding of the crystal structure of the electrode materials and their behaviors during charge-discharge under various conditions. In the present review, we focus on applying operando X-ray techniques to investigate electrode materials, including the working mechanisms of different structured materials, the effect of size, cycling rate and temperature on the reaction mech...
Designing High-Capacity, Lithium-Ion Cathodes Using X-ray Absorption Spectroscopy
Chemistry of Materials, 2011
We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucidate the chemical and structural details of a surface treatment intended for the protection of high-capacity cathode materials. Electrochemical data have shown that surface treatments of 0.5Li 2 MnO 3 •0.5LiCoO 2 (Li 1.2 Mn 0.4 Co 0.4 O 2) with an acidic solution of lithium− nickel-phosphate significantly improves electrode capacity, rate, and cycling stability. XAS data reveal that the surface treatment results in a modification of the composite structure itself, where Ni 2+ cations, intended to be present in a lithium−nickel-phosphate coating, have instead displaced lithium in the transition metal layers of Li 2 MnO 3-like domains within the 0.5Li 2 MnO 3 •0.5LiCoO 2 structure. X-ray diffraction data show the presence of Li 3 PO 4 , suggesting that phosphate ions from the acidic solution are responsible for lithium extraction and nickel insertion with the formation of vacancies and/or manganese reduction for charge compensation. Furthermore, we show that the above effects are not limited to lithium−nickelphosphate treatments. The studies described are consistent with a novel approach for synthesizing and tailoring the structures of high-capacity cathode materials whereby a Li 2 MnO 3 framework is used as a precursor for synthesizing a wide variety of composite metal oxide insertion electrodes for Li-ion battery applications.
Journal of Physical Chemistry B, 1997
Electronic and structural properties of materials generated by the reduction and subsequent oxidation of pyrite in a lithium-based solid polymer electrolyte have been examined by i n s i t u fluorescence Fe K-edge X-ray absorption fine structure (XAFS) in a FeS2/Li battery environment. The XAFS results obtained are consistent with the formation of metallic iron as one of the products of the full (4-electron) discharge, in agreement with information reported in other laboratories. Extended X-ray absorption fine structure (EXAFS) data reveal that a subsequent 2-electron or 4electron recharge generates a species with a Fe-S bond distance identical to that of pyrite, d(Fe-S)-2.259 A, with no other clearly detectable interactions due to more distant atoms. Based on the similarities between the metrical parameters and other features in the X-ray absorption near edge structure (XANES), the ferrous sites in these species appear to be tetrahedrally coordinated, as in chalcopyrite (CuFeS2), for which d(Fe-S) is 2.257 A, and, thus, different than in Li2FeS2, a material that exhibits longer Fe-S distances. The electrochemical reactivity of pyrite in non-aqueous, lithiumbased electrolytes continues to receive attention from both scientifi~l-~ and industrial6 communities. Much of the impetus for research in this area is derived from the prospects of developing high energy densicy, low cost, and environmentally safe rechargeable Li/FeS2 batteries with potential use in vehicular propulsion and other applications. A number of structural and spectroscopic techniques, including i n s i t u X-ray diffraction (XRD),2 i n s i t u 57Fe Mossbauer effect spectroscopy (MES)2 ,3 and i n s i t u X-ray absorption fine structure (X4FS)5 have been employed to establish the identity of cell Accordingly, the U. S Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U. S. Government purposes. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liability or responsiiility for the accluacy, completeness, or dulness of any information, apparatus, product, or process disdosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, p~ocess, or service by trade name, trademark, manufacturer, or otherwise does not necessanly'coilstitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.