Al-doped Li[Ni1/3Mn1/3Co(1/3-z)Alz]O-2 (0 <= z <= 0.14) samples were synthesized using a coprecipitation method followed by calcination with LiOH center dot H2O at 500 degrees C for 3 h and 900 degrees C for 3 h. Electrochemical testing showed that Li[Ni1/3Mn1/3Co(1/3-z)Alz]O-2 had a high initial discharge capacity and good charge-discharge cycle performance in the voltage ranges of either 2.5-4.3 or 2.5-4.6 V. The impact of Al doping on the thermal stability of Li[Ni1/3Mn1/3Co(1/3-z)Alz]O-2 was studied by accelerating rate calorimetry. Al substitution for Co in Li[Ni1/3Mn1/3Co1/3]O-2 caused a dramatic improvement in thermal stability over the material without aluminum. Al-doped Li{Ni1/3Mn1/3Co(1/3-z)Alz]O-2 with z=0.1 displays an energy density greater than LiMn2O4 and equivalent or higher thermal stability, making it a possible choice as an electrode material for large Li-ion batteries.