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Open Access Publications from the University of California

How Bulk Sensitive is Hard X-ray Photoelectron Spectroscopy: Accounting for the Cathode-Electrolyte Interface when Addressing Oxygen Redox.

  • Author(s): Lebens-Higgins, Zachary W
  • Chung, Hyeseung
  • Zuba, Mateusz J
  • Rana, Jatinkumar
  • Li, Yixuan
  • Faenza, Nicholas V
  • Pereira, Nathalie
  • McCloskey, Bryan D
  • Rodolakis, Fanny
  • Yang, Wanli
  • Whittingham, M Stanley
  • Amatucci, Glenn G
  • Meng, Ying Shirley
  • Lee, Tien-Lin
  • Piper, Louis FJ
  • et al.

Sensitivity to the "bulk" oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes-Li2MnO3, Li-rich NMC, and NMC 442-that shows no clear link to oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer.

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