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J Am Chem Soc. 2015 Apr 15;137(14):4804-14. doi: 10.1021/jacs.5b01424. Epub 2015 Apr 7.

Understanding the roles of anionic redox and oxygen release during electrochemical cycling of lithium-rich layered Li4FeSbO6.

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†Chimie du Solide et de l'Energie, FRE 3677, Collège de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France.
‡ALISTORE-European Research Institute, FR CNRS 3104, 80039 Amiens, France.
§Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, 80039 Amiens, France.
∥National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
⊥Institut Charles Gerhardt, CNRS UMR 5253, Université Montpellier 2, 34 095 Montpellier, France.
#Sorbonne Universités - UPMC Univ Paris 06, 4 Place Jussieu, F-75005 Paris, France.
∇Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
○EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium.
◆LRCS, CNRS UMR 7314, Université de Picardie Jules Verne, 80039 Amiens, France.
¶CSIR-CECRI Chennai unit, CSIR-Madras Complex, Taramani, Chennai 600 113, India.


Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.


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