Improvement of structural stability of LiMn2O4 cathode material on 55°C cycling by sol-gel coating of LiCoO2

A significant improvement in high temperature performance of LiMn2O4 cathode material has been achieved by sol-gel coating its particle surface with LiCoO2. Although the LiCoO2 coating completely disappeared by reacting with LiMn2O4 at 800 degrees C, a newly formed spinel phase, Li1+xMn2-xCoxO4, having a higher Co concentration at the particle surface, provided excellent structural stability on cycling at 55 degrees C. Although the initial capacity at 55 degrees C was reduced to 109 from 113 mAh/g by the coating, the stability on cycling was noticeably improved. The coated LiMn2O4 retains approximately 91% of its initial capacity after 100 cycles at 0.2 C rate at 55 degrees C while the uncoated LiMn2O4 suffered nearly 50% loss of the initial capacity in the same condition. These results indicate that higher concentration of Co ions at the surface is effective in protecting the active material from Mn3+ dissolution into electrolytes, resulting in the performance improvement. (C) 1999 The Electrochemical Society. S1099-0062(99)07-084-4. All rights reserved.