Murat Yavuz

A novel high-throughput setup for in situ powder diffraction on coin cell batteries

A new setup for in situ experiments with up to eight electrochemical cells, especially battery coin cells, and the corresponding custom-made in situ cells are presented. The setup is primarily optimized for synchrotron powder diffraction measurements. As a newly constructed experimental setup, the in situ coin cell holder was tested for positional errors of the cells and the reliability of the diffraction as well as electrochemical measurements. The overall performance characteristics of the sample holder are illustrated by measurements on LiMn2O4 and LiNi0.35Fe0.3Mn1.35O4 spinel-based positive electrode materials.

Sol-gel processing and electrochemical characterization of monoclinic Li 3 FeF 6

To find new cathode materials for future applications in lithium-ion batteries, lithium transition metal fluorides represent an interesting class of materials. In principle the Li intercalation voltage can be increased by replacing oxygen in the cathode host structure with the more electronegative fluorine. A facile pyrolytic sol–gel process with trifluoroacetic acid as fluorine source was established to synthesize monoclinic Li3FeF6 using nontoxic chemicals. The acicular Li3FeF6 powder was characterized with X-ray diffraction and a detailed structure model was calculated by Rietveld analysis. For the preparation of cathode films to cycle versus lithium monoclinic Li3FeF6 was ball milled with carbon and binder down to nanoscale. After 100 cycles galvanostatic cycling (C/20) 47xa0% fully reversible capacity of the initial capacity (129xa0mAh/g) could be retained. To the best of our knowledge the results presented in this work include the first rate performance test for monoclinic Li3FeF6 up to 1 C maintaining a capacity of 71xa0mAh/g. The redox reaction involving Fe3+/Fe2+ during Li insertion/extraction was confirmed by post-mortem XPS and cyclic voltammetry.

Li+intercalation in isostructural Li2VO3and Li2VO2F with O2−and mixed O2−/F−anions

Mixed-anion materials for Li-ion batteries have been attracting attention in view of their tunable electrochemical properties. Herein, we compare two isostructural (Fm3̅m) model intercalation materials Li2VO3 and Li2VO2F with O(2-) and mixed O(2-)/F(-) anions, respectively. Synchrotron X-ray diffraction and pair distribution function data confirm large structural similarity over long-range and at the atomic scale for these materials. However, they show distinct electrochemical properties and kinetic behaviour arising from the different anion environments and the consequent difference in cationic electrostatic repulsion. In comparison with Li2VO3 with an active V(4+/5+) redox reaction, the material Li2VO2F with oxofluoro anions and the partial activity of V(3+/5+) redox reaction favor higher theoretical capacity (460 mA h g(-1)vs. 230 mA h g(-1)), higher voltage (2.5 V vs. 2.2 V), lower polarization (0.1 V vs. 0.3 V) and faster Li(+) chemical diffusion (∼10(-9) cm(2) s(-1)vs. ∼10(-11) cm(2) s(-1)). This work not only provides insights into the understanding of anion chemistry, but also suggests the rational design of new mixed-anion battery materials.

X-ray total scattering investigation of Al0.57Sn0.43O1.71nanoparticles

X-ray pair distribution function (PDF) analysis of Al0.57Sn0.43O1.71, a promising candidate as anode material for Li ion batteries, has been carried out using synchrotron radiation at 60 keV. The average and short-range ordering of nanocrystalline Al0.57Sn0.43O1.71 was investigated both with the traditional Rietveld refinement method and with X-ray PDF analysis. The instrumental parameters of the high-resolution powder diffraction beamline P02.1, Petra III, have been characterized. Reverse Monte Carlo (RMC) refinements based on PDF data indicate that Al substitution induces local distortions around the Al/Sn atoms and that oxygen vacancies, induced by the Al substitution, are mostly located on an anion site around the Al atoms. Additionally, RMC refinements hint at a clustering of Al atoms.