Structural,magnetic and electrochemical properties of LiNi0.5Mn0.5O2 as positive electrode for Li-ion batteries

The layered LiNi0.5Mn0.5O2 was synthesized by wet-chemical method and characterized by X-ray diffraction and SQUID magnetometry. The powders adopted the alpha-NaFeO2 structure. The ferromagnetism observed below Tc = 140 K is attributed to the linear Ni2+(3a)-O-Mn4+(3b)-O-Ni-2+(3a) magnetic paths, from which we derive that 7% of the nickel occupies the (3a) Wyckoff position in place of Li, constituting a Ni2+(3a) defect. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie-Weiss law agrees well with the combination of Ni2+ (S = 1) and Mn4+ (S= 3/2) spin-only values. Results of structural and magnetic properties of chemically delithiated sample are consistent with the electronic state Mn4+/Ni4+ and the high-spin configuration for Ni4+ ions. The LiNi0.5Mn0.5O2 electrode sintered at 900 degrees C delivers a capacity 166 mAh/g at 0.1 C rate which is capacity retention of 95%. (c) 2007 Published by Elsevier Ltd.