"Li-1.04(Ni0.40Mn0.40Co0.20-zAlz)(0.96)O-2" (z = 0; 0.05 and 0.10) samples were synthesized using a coprecipitation method followed by calcinations at 500 degrees C for 5 h and then at 950 degrees C for 2 h. Structural and physico-chemical characterizations have shown that these materials were obtained pure with a small overlithiation ratio (Li/M 1.01-1.03) and thus a significant exchange between the divalent nickel ions from the slabs and the lithium ions from the interslab spaces (between 4% for the non substituted material and 8% for the aluminum substituted ones). Aluminum substitution induces a decrease of the reversible capacity, but also a major improvement of the thermal stability in the deintercalated state (corresponding to the charge state of the battery). These results have thus shown that the composition Li-1.01(Ni0.39Mn0.40Co0.15Al0.06)(0.99)O-2 is very attractive for large scale lithium-ion batteries to be developed for EV and HEV applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3571479]