X-ray absorption spectroscopy study of the Li x FePO 4 cathode during cycling using a novel electrochemical in situ reaction cell (original) (raw)
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Structural investigations of LiFEPO-4 electrodes by Fe x-ray absorption spectroscopy
J Phys Chem B, 2004
Fe K-edge X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) have been performed on electrodes containing LiFePO 4 to determine the local atomic and electronic structure and their stability with electrochemical cycling. A versatile electrochemical in situ cell has been constructed for long-term soft and hard X-ray experiments for the structural investigation on battery electrodes during the lithium-insertion/extraction processes. The device is used here for an X-ray absorption spectroscopic study of lithium insertion/extraction in a LiFePO 4 electrode, where the electrode contained about 7.7 mg of LiFePO 4 on a 20 m thick Al-foil. Fe K-edge X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) have been performed on this electrode to determine the local atomic and electronic structure and their stability with electrochemical cycling. The initial state (LiFePO 4 ) showed iron to be in the Fe 2+ state corresponding to the initial state (0.0 mAh) of the cell, whereas in the delithiated state (FePO 4 ) iron was found to be in the Fe 3+ state corresponding to the final charged state (3 mAh). XANES region of the XAS spectra revealed a high spin configuration for the two states (Fe (II), d 6 and Fe (III), d 5 ). The results confirm that the olivine structure of the LiFePO 4 and FePO 4 is retained by the electrodes in agreement with the XRD observations reported previously. These results confirm that LiFePO 4 cathode material retains good structural short-range order leading to superior cycling capability.
Journal of Solid State Chemistry, 2010
is a powerful tool to investigate redox reactions during in electrochemical lithium insertion/extraction processes. Electrochemical oxidation of LiFe II PO 4 (triphylite) in Li-ion batteries results in Fe III PO 4 (heterosite). LiFePO 4 was synthesized by solid state reaction at 800 1C under Ar flow from Li 2 CO 3 , FeC 2 O 4 Á 2H 2 O and NH 4 H 2 PO 4 precursors in stoichiometric composition. FePO 4 was prepared from chemical oxidation of LiFePO 4 using bromine as oxidative agent. For both materials a complete 57 Fe Mössbauer study as a function of the temperature has been carried out. The Debye temperatures are found to be y M = 336 K for LiFePO 4 and y M =359 K for FePO 4 , leading to Lamb-Mössbauer factors f 300 K = 0.73 and 0.77, respectively. These data will be useful for a precise estimation of the relative amounts of each species in a mixture.
Soft X-ray XANES studies of various phases related to LiFePO4 based cathode materials
Energy & Environmental Science, 2012
LiFePO 4 has been a promising cathode material for rechargeable lithium ion batteries. Different secondary or impurity phases, forming during either synthesis or subsequent redox process under normal operating conditions, can have a significant impact on the performance of the electrode. The exploration of the electronic and chemical structures of impurity phases is crucial to understand such influence. We have embarked on a series of synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy studies for the element speciation in various impurity phase materials relevant to LiFePO 4 for Li ion batteries. In the present report, soft-X-ray XANES spectra of Li K-edge, P L 2,3-edge, O K-edge and Fe L 2,3-edge have been obtained for LiFePO 4 in crystalline, disordered and amorphous forms and some possible ''impurities'', including LiPO 3 , Li 4 P 2 O 7 , Li 3 PO 4 , Fe 3 (PO 4) 2 , FePO 4 , and Fe 2 O 3. The results indicate that each element from different pure reference compounds exhibits unique spectral features in terms of energy position, shape and intensity of the resonances in its XANES. In addition, inverse partial fluorescence yield (IPFY) reveals the surface vs. bulk property of the specimens. Therefore, the spectral data provided here can be used as standards in the future for phase composition analysis.
In-situ battery measurement of LiFePO4 cathode during charge mechanism using x-ray diffraction
Journal of Physics: Conference Series
Lithium-ion batteries (LIB) as one of the essential rechargeable energy storage for supporting renewable technologies is currently a big issue. It is important to understand the mechanism of lithium-ion batteries in order to improve more durable batteries, long cyclable ability and better efficiency. This work aimed to use in-situ X-ray diffraction (XRD) as a powerful technique for acquiring a fundamental understanding of structure and phase transformations of lithium-ion battery during charge mechanism. The battery consists of LiFePO4 as cathode and graphite as anode material. The results show that some new Bragg peaks occur at 2 of 39.97 and 47.26. These indicate a phase transformation occurred from LiFePO4 to FePO4 during the charging mechanism. It can be concluded that in-situ XRD is a powerful tool to understand the phase transformation of lithium-ion batteries during the charging mechanism.
2011
CITATIONS 3 READS 69 4 authors, including: Some of the authors of this publication are also working on these related projects: Synthesis and studies on controlled porosity composite thin layers and systems for energy storage and conversion applications View project Research Cooperation Project: Synthesis and studies on controlled porosity composite thin layers and systems for energy storage and conversion applications (2014-2017) View project
Energy & Fuels, 2020
The study on the two-phase (LiFePO 4 /FePO 4) transformation mechanism of LiFePO 4 during charge−discharge is reported. The study is conducted using ex situ and in situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The Rietveld refinements are performed on ex situ XRD data of electrode materials collected at various stages of the first charge−discharge cycle. The results reveal the existence of solid solution at room temperature in the narrow nanophase region (0 < x < μ and 1 − η < x < 1). The biphase Li x FePO 4 is a mixture of Li-deficient phase Li μ FePO 4 and Li-rich phase Li 1−η FePO 4 in μ < x < 1 − η, where μ = 0.056 and η = 0.043. The present study is conducted on samples prepared by electrochemical reaction, which provides a more realistic situation than the previous study reported on samples prepared by the chemical process. Moreover, a similar study is also repeated by in situ XRD and XPS techniques, which also confirm the transformation of LiFePO 4 into the FePO 4 phase during charging and vice versa during discharging. Furthermore, the study also conducted on the fully charged state (at different current rates from 0.1 to 5C) of various electrodes by ex situ XRD found that phase transformation (LiFePO 4 to FePO 4) depends on the charging current rate. At the lower current, complete transformation of the LiFePO 4 phase into FePO 4 is observed, whereas at the higher current rate, a trace amount of residual phase LiFePO 4 along with FePO 4 is found in the fully charged state. Therefore, the findings of the study reveal the time-dependent lithium-ion diffusion phenomenon in LiFePO 4 causing lower capacity at the higher current rate.
Characterization of LiFePO4/C Cathode for Lithium Ion Batteries
Industrial & Engineering Chemistry Research, 2011
LiFePO 4 /C was synthesized from a mixture of different precursors of Li, Fe, and C by solid-state reaction. The initial mixture obtained was heated in different calcination conditions under inert atmosphere. The precursor of LiFePO 4 doped with carbon was studied using different techniques such as thermal analysis, chemical and physical characterizations, and M€ osbauer spectroscopy. A calculation of the crystallinity of the final product with two different methods is also presented. The chemical analysis techniques used were IRTF, XRD, and SEM. This characterization confirmed that we obtained a well-crystallized LiFePO4/ C in all the operating conditions tested. The SEM showed aggregation and sintering during the calcination process, which were confirmed by the particle-size distribution measurements and by the physical characterizations. M€ osbauer spectroscopy was used to determine the quantity of Fe(II) and Fe(III) contained in the final product. Our calcination conditions did not significantly modify the quantity of the two oxidation states.
High-throughput studies of Li1−xMgx/2FePO4 and LiFe1−yMgyPO4 and the effect of carbon coating
Journal of Power Sources, 2008
A two-dimensional sample array synthesis has been used to screen carbon-coated Li (1−x) Mg x/2 FePO 4 and LiFe (1−y) Mg y PO 4 powders as potential positive electrode materials in lithium ion batteries with respect to x, y and carbon content. The synthesis route, using sucrose as a carbon source as well as a viscosity-enhancing additive, allowed introduction of the Mg dopant from solution into the sol-gel pyrolysis precursor. High-throughput XRD and cyclic voltammetry confirmed the formation of the olivine phase and percolation of the electronic conduction path at sucrose to phosphate ratios between 0.15 and 0.20. Measurements of the charge passed per discharge cycle showed that the capacity deteriorated on increasing magnesium in Li (1−x) Mg x/2 FePO 4 , but improved with increasing magnesium in LiFe (1−y) Mg y PO 4 , especially at high scan rates. Rietveld-refined XRD results on samples of LiFe (1−y) Mg y PO 4 prepared by a solid-state route showed a single phase up to y = 0.1 according to progressive increases in unit cell volume with increases in y. Carbon-free samples of the same materials showed conductivity increases from 10 −10 to 10 −8 S cm −1 and a decrease of activation energy from 0.62 to 0.51 eV. Galvanostatic cycling showed near theoretical capacity for y = 0.1 compared with only 80% capacity for undoped material under the same conditions.