Insight into the Atomic Structure of Cycled Lithium-Rich Layered Oxide Li1.20Mn0.54Co0.13Ni0.13O2 Using HAADF STEM and Electron Nanodiffraction

Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) and electron nanodiffraction investigations have been carried out to follow changes in the local atomic structure of three Li-rich layered oxides recovered after a single chargedischarge cycle, performed in different conditions. The structure of the pristine material Li1.20Mn0.54Co0.13Ni0.13O2 was fully characterized. It was then compared to those of the materials recovered after one electrochemical cycle in a lithium battery, with the upper voltage limit being either just below the voltage of the irreversible plateau typical of Li-rich layered oxides or just above. An in-depth study of the material obtained chemically, after oxidation to deintercalate Li and then reduction to reintercalate Li, was also performed for comparison. The main message of this paper is that the plateau is not associated with an extended structural reorganization of the material. The irreversible processes associated with cation migration are restricted to the external part of the particles. The results reported here support the oxidation of oxygen ions we earlier proposed to occur reversibly in the core of the particles and to be the actual origin for the exceptional capacity of Li- and Mn-rich layered oxides.