High capacity surface-modified LiCoO2 cathodes for lithium-ion batteries

The surface of LiCoO2 cathodes was modified with Al2O3,TiO2, and ZrO2 by a chemical processing procedure followed by heat treatment at 300degreesC in air for 4 h. The surface-modified LiCoO2 samples show much better capacity retention at both 25 and 60degreesC than the unmodified LiCoO2 cathode to higher cutoff charge voltages of as high as 4.7 V vs. lithium. For example, Al2O3-modified LiCoO2 shows approximately 180 mAh/g at 4.5 to 3.2 V with a capacity fade of only 8% in 100 cycles, compared to 32% for the unmodified LiCoO2. Transmission electron microscopic studies reveal that the guest materials are present as loose oxides (Al2O3 and ZrO2) or as monolayers (TiO2) on the surface of LiCoO2 particles. The improved capacity retention and the higher reversible capacity (180 mAh/g) of the surface-modified LiCoO2 compared to the unmodified LiCoO2 (140 mAh/g) could be due to a suppression of the chemical and structural instabilities of the charged Li1-xCoO2 cathodes and/or reduction of interparticle stresses and strains. (C) 2002 The Electrochemical Society.