Charge compensation in 3d transition metal oxide intercalation cathodes through the generation of localized electron holes on oxygen.
During the charging and discharging of lithium ion battery cathodes through the de and reintercalation of lithium ions, electroneutrality is maintained by transition metal redox chemistry, which limits the charge that can be stored. However, for some transition metal oxides this limit can be broken and oxygen loss and/or oxygen redox reactions have been proposed to explain the phenomenon. We present operando mass spectrometry of (18)O labelled Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+]O2, which demonstrates that oxygen is extracted from the lattice on charging a Li1.2[Ni0.13(2+)Co0.13(3+)Mn0.54(4+]O2 cathode, although we detected no O2 evolution. Combined soft X ray absorption spectroscopy, resonant inelastic X ray scattering spectroscopy, X ray absorption near edge structure spectroscopy and Raman spectroscopy demonstrates that, in addition to oxygen loss, Li( removal is charge compensated by the formation of localized electron holes on O atoms coordinated by Mn(4+ and Li( ions, which serve to promote the localization, and not the formation, of true O2(2 (peroxide, O O ~1.45 A) species. The quantity of charge compensated by oxygen removal and by the formation of electron holes on the O atoms is estimated, and for the case described here the latter dominates.
Nature chemistry