Speaker
Description
Layered 3d transition-metal oxides LiMO₂ (M = Ni, Mn, Co) are archetypical positive-electrode materials for Li-ion batteries. During electrochemical cycling, Li⁺ deintercalation and accompanying redox reactions generate pronounced stoichiometric gradients between the surface and bulk. Probing the associated evolution of the electronic structure within the first ~20 nm of these materials remains a significant experimental challenge.
Soft and hard X-ray photoemission spectroscopy (XPS and HAXPES) provide non-destructive access to both chemical composition and electronic structure. Here, we introduce a quantitative XPS/HAXPES methodology combining soft (Al Kα, 1.5 keV) and hard (Cr Kα, 5 keV) monochromatic sources to investigate the characteristic transition-metal signatures (M 2p and M 3p core and valence levels) from the surface toward the bulk. We examine the role of satellite features and metal-dependent orbital contributions in stoichiometric quantification.
The approach is validated across three layered-oxide archetypes—LiCoO₂, LiNiO₂, and Li₂MnO₃—in both powder and electrode form, along with reference compounds (NiO, NaNiO₂, and Co₃O₄) representing well-defined oxidation states.
Finally, the protocol is applied to NMC811 powder and electrode materials, demonstrating its relevance for complex, industrially relevant battery chemistries.