Correlating the dispersion of Li@Mn6 superstructure units with the oxygen activation in Li-rich layered cathode

The oxygen activation, contributing to the high capacity (>  250 mA h g −1 ) of Li-rich transition metal (TM) layered oxides xLi 2 MnO 3 •yLiTMO 2 (TM = Mn, Ni, Co, Fe, etc.), is rooted in the unique 180 o Li-O-Li configuration due to the ordering arrangement of Li@Mn 6 superstructure units in Li 2 MnO 3 component (equivalent to Li[Li 1/3 Mn 2/3 ]O 2 ), but the relationship between the oxygen activation and the distribution of Li@Mn 6 superstructure units has not established. Herein, we comprehensively investigated the dispersion behavior of Li@Mn 6 superstructure units during the synthesis of a model compound Li[Li 1/6 Mn 1/3 Ni 1/3 Sb 1/6 ]O 2 (0.5 Li[Li 2/3 Mn 1/3 ]O 2 •0.5 Li[Ni 2/3 Sb 1/3 ]O 2 ) combining ex-situ X-ray diffraction (XRD) and in-situ / ex-situ transmission electron microscope (TEM). It revealed the entire process from the formation of Li@Mn 6 superstructure units, to the gradual fusion with Sb@Ni 6 superstructure units, eventually to the complete dispersion at 1100 °C. The systemic electrochemical tests demonstrated that, the dispersion of Li@Mn 6 superstructure units effectively suppressed the irreversible oxygen activation, and the best capacity and voltage retentions were obtained in the solid solution with the complete dispersion of Li@Mn 6 superstructure units. This work benefits the design of high performance Li-rich layered oxides with the modest anionic redox activity through the local structural tuning.