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 300°C in air for 4 h. The surface-modified LiCoO₂ samples show much better capacity retention at both 25 and 60°C 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 Li_1-xCoO₂ cathodes and/or reduction of interparticle stresses and strains.