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Anion Redox Chemistry in the Cobalt Free 3d Transition Metal Oxide Intercalation Electrode Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2

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  • Kun Luo
  • Matthew R. Roberts
  • Niccoló Guerrini
  • Nuria Tapia-Ruiz
  • Rong Hao
  • Felix Massel
  • David M Pickup
  • Silvia Ramos
  • Yi-Sheng Liu
  • Jinghua Guo
  • Alan V. Chadwick
  • Laurent C. Duda
  • Peter G. Bruce
<mark>Journal publication date</mark>7/09/2016
<mark>Journal</mark>Journal of the American Chemical Society
Issue number35
Number of pages8
Pages (from-to)11211-11218
Publication StatusPublished
<mark>Original language</mark>English


Conventional intercalation cathodes for lithium batteries store charge in redox reactions associated with the transition metal cations, e.g. Mn 3+/4+ in LiMn 2 O 4 , and this limits the energy storage of Li-ion batteries. Compounds such as Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 exhibit a capacity to store charge in excess of the transition metal redox reactions. The additional capacity occurs at and above 4.5 V vs. Li + /Li. The capacity at 4.5 V is dominated by oxidation of the O 2-anions accounting for ~0.43 e -/formula unit, with an additional 0.06 e -/formula unit being associated with O loss from the lattice. In contrast, the capacity above 4.5 V, is mainly O loss, ~ 0.08 e -/formula. The O redox reaction involves the formation of localized hole states on O during charge, which are located on O coordinated by (Mn 4+ /Li +). The results have been obtained by combining operando electrochemical mass spec on 18 O labelled Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 with XANES, soft X-ray spectroscopy, Resonant Inelastic X-ray spectroscopy and Raman spectroscopy. Finally the general features of O-redox are described with discussion about the role of comparatively ionic (less covalent) 3d metal-oxygen interaction on anion redox in lithium rich cathode materials.