Synthesis, Crystal Structure, and Electrochemical Properties of Li_1.2+xMn_0.3Co_0.2Ni_0.3O₂ (x > 0) for Lithium-ion Battery Cathodes

Abstract

Li_1.2+xMn_0.3Co_0.2Ni_0.3O₂ (x = 0, 0.2, 0.4) with a Li-rich layered rock salt type structure were synthesized by a high-pressure 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 135 mAh g⁻¹ at the first cycle, respectively, than the x = 0.2 sample (296 and 151 mAh g⁻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.