Synthesis, crystal structure, and electrochemical properties of Li1.2+xMn0.3Co0.2Ni0.3O2 (x > 0) for lithium-ion battery cathodes

Abstract

Li1.2+xMn0.3Co0.2Ni0.3O2 (x = 0, 0.2, 0.4) with a Li-rich layered rock salt type structure were synthesized by a highpressure method. Rietveld analysis using neutron diffraction data elucidated that the Li atoms were located at the octahedral sites in the Li and transitional metal (TM) layers. Furthermore, additional Li was detected at the tetrahedral site in the TM layer for the x = 0.4 sample. The tetrahedral Li caused vacancies at the neighboring TM sites and a structural distortion of the (Li,M)O6 octahedra. The x = 0.4 sample exhibited larger and smaller charge and discharge capacities of 388 and 135mAhg?1 at the first cycle, respectively, than the x = 0.2 sample (296 and 151mAhg?1). The structural modification caused by the introduction of the tetragonal Li affects the initial activation process of the Li-rich layered rock salt type electrodes.