Storage Characteristics of LiNi[sub 0.8]Co[sub 0.1+x]Mn[sub 0.1−x]O[sub 2] (x=0, 0.03, and 0.06) Cathode Materials for Lithium Batteries

cathodes with , 0.03, and 0.06 were prepared by firing a mixture of stoichiometric amounts of and coprecipitated powders at for 15 h. Using these powders, their storage characteristics upon exposure to air and electrolytes at were compared before charging and after charging to 4.3 V with a variation of the storage time. The discharge capacities of the cathodes with , 0.03, and 0.06 were 192, 186, and 184 mAh/g, respectively, while their irreversible capacity ratios were 13, 12, and , respectively. As the Co content increased in the cathode, both the content in the lithium 3a sites, and the contents of the LiOH and impurity phases decreased. In particular, changes in the oxidation state of the Ni and Mn ions after 4.3 V charging upon storage at were monitored using X-ray absorption near-edge spectra, and was found to reduce to while the oxidation state of the predominant did not change. However, residual ions in the cathodes dissolved into the electrolytes. Moreover, the cathodes stored at for 7 days were transformed into a spinel phase , regardless of the Co content. In an effort to resolve this dissolution problem, and nanoparticles were coated onto the cathode with the highest amounts of metal dissolution at . The results showed that the -coated cathode exhibited a greatly decreased metal dissolution and decreased its irreversible capacity by , compared with a bare and -coated cathode.