In order to understand the origin of high capacity of Li-rich cathode materials, systematic investigation is required to understand the structural changes in the bulk materials during electrochemical cycling. In this study, we synthesized Li2Ir0.75Sn0.25O3 electrode material that delivered first cycle charge and discharge capacity of 214mAh/g (corresponds to removal of ~2 moles of Li+) and 188mAh/g, respectively and after 100 cycles, it was still able to deliver 128mAh/g of discharge capacity with 71% capacity retention. We performed synchrotron radiation-based high-resolution X-ray powder diffraction (HRPD) and hard & soft X-ray absorption spectroscopy (XAS) along with several electrochemical characterization techniques, to investigate the redox reaction in Li2Ir0.75Sn0.25O3 electrode in terms of local and bulk crystal structural changes, variations in the oxidation states of transition metal and oxygen ions in Li2Ir0.75Sn0.25O3, respectively. Sn K-edge XANES spectra do not show any edge shift implying that Sn-ions are not participating in the electrochemical reaction. However, we found that there is minimal contribution from Ir-ions in the charge compensation, as inferred by small changes in the Ir L3-edge XANES edge position. So the charge is mostly compensated by anionic redox chemistry mainly involving oxygen. O K-edge soft XAS spectra were measured to quantify the charge compensation by oxygen and metals. However, anionic redox chemistry is very complex as it involves significant structural changes. Understanding these structural changes during lithium extraction and insertion is a key to investigate the charge compensation mechanism of 4d and 5d metals-based Li-rich cathode materials. Rietveld refinement and profile refinement by FAULTS  were performed on the measured HRPD pattern to understand the detailed crystal structure variations and formation of stacking faults during charge and discharge. Detailed findings will be presented at the time of the meeting.
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