Synthesis of spinel LiMn2O4 by the sol-gel method for a cathode-active material in lithium secondary

Spinel LiMn2O4 powders were synthesized by a sol-gel method using an aqueous solution of metal acetates containing poly(acrylic acid) (PAA) as a chelating agent. The dependence of the physicochemical properties of the spinel LiMn2O4 powders, such as crystallinity, lattice constant, and specific surface area, on the calcination temperature and the PAA quantity was investigated. It was found that a pure crystalline phase of spinel LiMn2O4 without impurities could be formed at 250 degrees C in air from the gel precursors. Polycrystalline LiMn2O4 powders calcined at 300-800 degrees C for 10 h were found to be composed of very uniformly-sized particulates with an average particle size of 30-600 nm and a specific surface area of 3.3-65 m(2)/g, depending on the processing conditions. Therefore, the sol-gel method required much lower calcination temperature and shorter calcination time than the conventional solid-state reaction. Electrochemical studies on the charge/discharge characteristics of the Li/LiMn2O4 cells show that LiMn2O4 powders calcined at 800 degrees C delivered a high initial capacity of 135 mA h/g and exhibited a good cycling behavior with only 9.5% loss from the initial discharge capacity at the 168 cycles during the charge/ discharge experiments.