Reversible and Irreversible Redox Processes in Li-Rich Layered Oxides

Reversible and irreversible charge exchange reactions of Li- and Mn-rich layered oxides (Li1.15Ni0.2Co0.1Mn0.55O2, LLO) are investigated with bulk and surface-sensitive near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Ni L2,3, Co L2,3, Mn L2,3, and O K edges; mass spectrometry (MS); and operando synchrotron X-ray powder diffraction (SXPD). The present work shows the relation between O–O formation in the bulk and Ni, Co, and Mn reduction/oxidation processes, which in turn deliver outstanding capacities of Li-rich layered oxides (LLO). Moreover, the reversibility of charge compensation reactions is discussed and differences between O–O formation and oxygen release, both occurring mainly upon the first charge (so-called activation), are identified.