Effect of ball-milling on 3-V capacity of lithium-manganese oxospinel cathodes

Ball-milling for a sufficient period of time of lithium-manganese oxide spinels, prepared either by a sol-gel method or by solid-state reaction, gave cathode materials of a lithium cell with excellent capacity retention in the 3-V range at room temperature and elevated temperatures despite an apparent Jahn-Teller distortion. In a 50-cycle test with 0.5 mA/cm(2), a sample ball-milled for 1 h gave a constant capacity of 122 mAh/g at a constant voltage 2.9 V versus lithium. X-ray diffraction and transmission electron microscopy were performed on the ball-milled spinel powders; they were found to contain significant strain and to consist of nanometer-scale grains. Furthermore, partial oxidation of manganese ions took place during the ball-milling process.