Charging-Discharging Phenomena on P2-Na2/3Co2/3Mn1/3O2 Observed by X-ray Absorption Spectroscopy

Thursday, 9 October 2014: 11:20
Sunrise, 2nd Floor, Galactic Ballroom 1 (Moon Palace Resort)
B. J. Hwang (National Synchrotron Radiation Research Center, National Taiwan University of Science and Technology), J. H. Cheng (National Taiwan University of Science and Technology), C. J. Pan (National Taiwan University of Science and Technology, Taiwan), J. F. Lee, J. M. Chen (National Synchrotron Radiation Research Center), M. Guignard, C. Delmas (CNRS, Université de Bordeaux, ICMCB), and D. Carlier (ICMCB-CNRS, Université de Bordeaux; RS2E, Réseau Français sur le Stockage Electrochimique de l’Energie)
Charging-discharging phenomena of P2-Na2/3Co2/3Mn1/3O2 prepared by a co-precipitation method were investigated by ex situ and in situ X-ray absorption spectroscopy [1, 2]. The electronic transitions at the O K-edge and the charge compensation mechanism, during the sodium intercalation process, were elucidated by combining Density Function Theory (DFT) calculations and X-ray absorption spectroscopy (XAS) data. The pre-edge of the oxygen K-edge moves to higher energy while the integrated intensity dramatically decreases, indicating that the population of holes in O 2p states is reduced with increasing numbers of sodium ions. From the K-edge and L-edge observations, the oxidation states of pristine Co and Mn were determined to be +III and +IV, respectively. The absorption energy shifts to lower positions during the discharging process for both the Co and Mn edges, suggesting that the redox pairs, i.e. Co3+/Co2+ and Mn4+/Mn3+, are both involved in the reaction.

[1] J.-H. Cheng, C.-J. Pan, J.-F. Lee, J.-M. Chen, M. Guignard, C. Delmas, D. Carlier, and B.-J. Hwang, Chem. Mater., 26 (2014) 1219–1225.

[2] D. Carlier, J. H. Cheng, R. Berthelot, M. Guignard, M. Yoncheva, R. Stoyanova, B. J. Hwang and C. Delmas,  Dalton Trans.,40 (2011), 9306.