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

Publication Type

Journal Article

Date Published

02/2020

Abstract

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.

Journal

The Journal of Physical Chemistry Letters

Volume

11

Year of Publication

2020

Short Title

J. Phys. Chem. Lett.

Refereed Designation

Refereed

Pagination

2106 - 2112

Issue

6

ISSN

1948-7185