Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes, the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox. Herein, a Co-free Li-rich layered oxide Li1.286Ni0.071Mn0.643O2 has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects. A significant O2 release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy (DEMS) and electron energy loss spectroscopy (EELS), respectively. Scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li2MnO3 domain upon cycling. Combined with the quantitative analysis conducted by the energy dispersive spectrometer (EDS), existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity. Overall, this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.