Li(Mn1/3Ni1/3Co1/3)O2 cathode materials were fabricated by a hydroxide precursor method. Al2O3 was coated on the surface of the Li(Mn1/3Ni1/3Co1/3)O2 through a simple and effective one-step electrostatic self-assembly method. In the coating process, a NHCO3-H2CO3 buffer was formed spontaneously when CO2 was introduced into the NaAlO2 solution. Compared with bare Li(Mn1/3M1/3Co1/3)O2, the surface-modified samples exhibited better cycling performance, rate capability and rate capability retention. The Al2O3-coated Li(Mn1/3Ni1/3Co1/3)O2 electrodes delivered a discharge capacity of about 115 mAh·g−1 at 2 A·g−1, but only 84 mAh·g−1 for the bare one. The capacity retention of the Al2O3-coated Li(Mn1/3Ni1/3Co1/3)O2 was 90.7% after 50 cycles, about 30% higher than that of the pristine one.