Structural and Electrochemical Properties of Layered Li[Ni1/2Mn1/2]1-xCoxO2 Cathode materials synthesized by spray pyrolysis method

Abstract

Recently, various attempts have been made to enhance the electrochemical performance of LiNiO2-LiCoO2-LiMnO2 solid solution. Among them, LiNi1/3Co1/3Mn1/3O2 has been suggested as an alternative to LiCoO2 because Ni and Mn can substitute each other to form a solid solution of any percentage without disturbing the layer structure. Dahn et al. reported that Li[NixCo1-2xMnx]O2 (x in 1/4, 3/8) materials can delivered a discharge capacity of 160 mAh/g when cycled between 2.5 V and 4.4 V. In this work, we synthesized of Li[Ni1/2Mn1/2]1-xCoxO2 (x = 0~1/3) compounds by a spray pyrolysis method. The Li[Ni1/2Mn1/2]1-xCoxO2 compounds are considered to be a solid solution of LiNiO2, LiMnO2, and LiCoO2. We investigate the optimum substitute amount of cobalt in the Li[Ni1/2Mn1/2]1-xCoxO2 materials. Spherical morphology layered Li[Ni1/2Mn1/2]1-xCoxO2 (0≤x≤0.33) powders have been synthesized by ultrasonic spray pyrolysis method. Single phase of Li[Ni1/2Mn1/2]1-xCoxO2 could be prepared in 0≤x≤0.33 region. Structural and electrochemical properties of the Li[Ni1/2Mn1/2]1-xCoxO2 materials were characterized by means of powder X-ray diffraction, Rietveld refinements, and galvanostatic charge/discharge test. . All materials have a phase-pure layered structure with a space group of R-3m (No. 166). The discharge capacity linearly increased as increase of cobalt substituted content. However, 20 mol% cobalt substituted electrode was exhibited a high discharge capacity over 175 mAh/g between 2.8 and 4.4 V with a good capacity retention.