Layered Li-0.7[M1/6Mn5/6]O-2 (M = Li, Ni) was synthesized using a sol-gel method. P2-Na-0.7[M1/6Mn5/6]O-2 precursor was first synthesized by a sol-gel method, and then O2-Li-0.7[M1/6Mn5/6]O-2 was prepared by an ion exchange of Li for Na in P2-Na-0.7[M1/6Mn5/6]O-2 precursor. From charge/discharge curves, it was seen that Li-0.7[Li1/6Mn5/6]O-2 has two plateaus similar to those observed from a spinel structure, but Li-0.7[Ni1/6Mn5/6]O-2 holds a single plateau as observed from a typical layered structure. It was considered that Li-0.7[Li1/6Mn5/6]O-2 undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li-0.7[Ni1/6Mn5/6]O-2 maintains O2-layered structure after the cycles. Li-0.7[Ni1/6Mn5/6]O-2 was higher in discharge capacity and retention rate than Li-0.7[Li1/6Mn5/6]O-2.