In Situ High Resolution Synchrotron X-Ray Powder Diffraction Studies of Lithium Batteries
The understanding of structural and compositional changes of bulk electrodes in batteries is undoubtedly important. However, it is often transport of electrons and ions across and through interfaces  (e.g., between lithiated and delithiated domains) which limits the obtainable power density and battery life time. A challenging and important task is to obtain in situ information about the formation and evolution of interfaces in an operating battery system. This work addresses these challenges and for this purpose we have developed a special microcapillary battery cell allowing diffraction information to be obtained from only the active material during battery operation . High resolution synchrotron x-ray powder diffraction technique has been undertaken to obtain detailed structural and compositional information during lithiation/delithiation of commercial LiFePO4 materials .
We report results from the first in situ time resolved high resolution powder diffraction experiments at beamline ID22/31 at the European Synchrotron Radiation Facility, ESRF. We follow the structural changes during charge of commercial LiFePO4 based battery materials using the Rietveld method. Conscientious Rietveld analysis shows slight but continuous deviation of lattice parameters from those of the fully stoichiometric end members LiFePO4 and FePO4 indicating a subsequent variation of stoichiometry during cathode delithiation. The application of an intermittent current pulses during charge using GITT technique shows an oscillation of lattice constants that correlates with the applied current and electrochemical relaxation sequence and may indicate the existence of metastable non-stoichiometric states.
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