Structural and electrochemical properties of Li1+xNi0.5Mn0.5O2+delta (0 <= x <= 0.7) cathode materials for lithium-ion batteries

Abstract

A comparative analysis of the properties of LiNi0.5Mn0.50O2 and Li1-xNi0.5Mn0.5O2 (0.2 less than or equal to x less than or equal to 0.7) powders, obtained by the freeze drying method, was performed. Lattice parameters of Li1+xNi0.5Mn0.5O2 decreased considerably with growing amounts of Li until x = 0.3: at x > 0.5 trace amounts of Li2MnO3 are observed by X-ray diffraction (XRD) patterns. X-ray photoelectron spectroscopy (XPS) analysis displayed an increase of Ni3+/Ni2+ ratio at 0.3 < x < 0.5, while Mn 2p spectra were almost identical in all samples. Rechargeable capacity values (V = 2.5-4.6 V) increased systematically with x reaching its maximum (185-190 mAh g(-1)) at x = 0.5. Samples with supersioichiometric lithium content also demonstrated good C rate characteristics. (C) 2004 Elsevier B.V. All fights reserved.