Layer-structured LiNi1/3Co1/3Mn1/3−y Al y O2 has been synthesized via a sol–gel method. The lattice constants of LiNi1/3Co1/3Mn1/3−y Al y O2 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 LiNi1/3Co1/3Mn1/3−y Al y O2. 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, LiNi1/3Co1/3Mn0.23Al0.1O2 exhibits the best capacity retention and the least irreversible capacity.