Surface analytical characterization of LiNi0.8-yMnyCo0.2O2 (0 ≤ y ≤ 0.4) compounds for lithium-ion battery electrodes

This study presents the quantitative chemical state elucidation of newly developed LiNi0.8-yMnyCo0.2O2 (0 <= y <= 0.4) cathode materials for Li-ion batteries utilizing X-ray photoelectron spectroscopy. For reliable quantification of the chemical states of the transition metals, namely Mn, Co, and Ni, in particular, the complex peak structures consisting of significant photoelectron multiplet splitting, shake-up satellites, and additional Auger and photoelectron peak overlaps were incorporated. The template approach that has been used enables the unambiguous elucidation of the transition metals' oxidation states; even gradual changes in the Ni2+/Ni3+ ratio depending on the Ni content in the novel LiNi0.8-yMnyCo0.2O2 compound series can clearly be evidenced. In all cases, special care was taken with respect to air sensitivity, contamination during sample handling, and probable method-induced sample decomposition.