Dependence of Properties, Crystal Structure and Electrode Characteristics on Li Content for Li_xCo_1/3Ni_1/3Mn_1/3O_2+δ as a Cathode Active Material for Li Secondary Battery

Abstract

We investigated the dependence of the properties, crystal structure and electrode characteristics on the Li content of Li_xCo_1/3Ni_1/3Mn_1/3O_2+δ. The crystal structure was determined by Rietveld analysis using neutron diffraction. The electron density images were determined by X-ray diffraction, Rietveld analysis and Maximum Entropy Method. The cycle performance was slightly lower, but the discharge capacity increased at x=1.122. From the crystal structure analysis, the amount of cation mixing was changed by the Li content, that is, a small amount of Ni²⁺ ions is present in the lithium layers (3a) and extra Li is located in transition metal layer (3b). Ni²⁺ ions occupied about 4% of the 3a site and Li is located in the 3b site at 0.915≤x≤1.052. On the other hand, Ni²⁺ ions occupied about 1.2% of the 3a site for x=1.122. In other words, 12% of the total amount of Ni existed in the 3a site at 0.915≤x≤1.052, but, 3.8% of the total amount of Ni existed in the 3a site for x=1.122. The bond length between 3b and 6c (oxygen site) increased with the increasing Li content. From the results, the discharge capacity increased with the decreasing Ni in the 3a site.