0013-4651/2013/160(11)/A2293/6/$31.00 © The Electrochemical Society Characterization of the Surface of LiCoO2 Particles Modified by Al and Si Oxide Using Analytical TEM

LiCoO2 particles about 300 nm in size were synthesized by the Pechini method. LiCoO2 modified using Al oxide and Si oxide were also prepared by the sol-gel method. These samples allowed direct TEM observation without sampling damage, and homogeneous distribution of coating materials on the surface was confirmed. The cycling properties of LiCoO2 coated with Al oxide were improved compared with pristine LiCoO2. Samples modified with Si oxide showed poor electrochemical performance. From an analytical TEM study, there was a thin layer of Co and Al mixture on the LiCoO2 surface in the Al oxide coated LiCoO2. By Si oxide coating, a homogeneous layer about 5 nm in thickness was formed. Using an EELS study, the Li ion concentration in particles was mapped under monochromatized electron beam conditions. Homogeneous Li distribution was confirmed in the cycled particles in LiCoO2 coated by Al oxide. In contrast, an inhomogeneous Li distribution was found in pristine and LiCoO2 with Si oxide coating