Preparation and electrochemical properties of layer-structured LiNi1/3Co1/3Mn1/3−yAlyO2

Layer-structured LiNi_1/3Co_1/3Mn_1/3−yAl_yO₂ has been synthesized via a sol–gel method. The lattice constants of LiNi_1/3Co_1/3Mn_1/3−yAl_yO₂ decrease with the concentration of aluminum ions. XANES analysis further confirms that the valence of cobalt ion is 3+, and that of Ni is between 2+ and 3+ in LiNi_1/3Co_1/3Mn_1/3−yAl_yO₂. With doping aluminum ions, the redox centers for the electrochemical reaction change from nickel ions alone to both nickel and cobalt ions. The amounts of de-intercalatable lithium ions are affected by the concentration of aluminum ions; however, the extracting efficiency of lithium ions is improved by doping aluminum ions. Among all the samples, LiNi_1/3Co_1/3Mn_0.23Al_0.1O₂ exhibits the best capacity retention and the least irreversible capacity.