Nanosized Lithium-Rich Cobalt Oxide Particles and Their Transformation to Lithium Cobalt Oxide Cathodes with Optimized High-Rate Morphology

摘要

We report the formation of crystalline dispersible LixCo1-xOy (with y <= 1) nanoparticles with an unusual rock-salt phase containing similar to 15 at. % Li in the crystalline structure. This is the first time that this composition was formed at temperatures as low as 150 degrees C under conditions of a solvothermal process, although it is referred to as a high-temperature metastable phase in a very limited number of known publications. The Li0.15Co0.85Oy nanoparticles of 2-3 nm size completely transform to high-temperature LiCoO2 (HT-LCO) nanoparticlec at 560 degrees C-in presence of slightly overstoichiometric amounts of Li source. The presence of lithium in the CoO lattice slows down the kinetics of its phase transformation, enabling to obtain very small HT-LCO nanocrystals during the subsequent calcination. The HT-LCO particles formed after this transformation have an elongated shape with a mean size of about 17 x 60 nm, which is targeted as an optimum size for battery applications. An attractive feature of the Li0.15Co O-0.85(y) nanoparticles is their high dispersibility enabling their assembly into different nanostructures with optimized morphology. Open porous HT-LCO electrodes prepared via self-assembly of Li0.15Co0.85Oy nanoparticles and Pluronic F127 as a structure-directing agent demonstrate very good performances at high current densities representing short charge/discharge times below 10 min. Even at a charge/discharge time of 72 s (50C), 50% of the theoretical capacity has been preserved. After 250 cycles at a charge/discharge time of 6 min (10C), over 60% of the initial discharge capacity was retained.