Li[Ni1/3Mn1/3-zCo1/3Zrz]O-2 (0 <= z <= 0.1) samples were prepared from hydroxide precursors. The hydroxide precursors were heated with Li2CO3 at 900 degrees C to prepare the oxides. X-ray diffraction results suggest that single phase samples can be prepared for 0 <= z <= 0.02. Chemical analysis using atomic absorption spectroscopy showed that the samples had some excess Li. Rietveld refinements of X-ray diffraction data show that Zr substitution for Mn does not induce substantial cation mixing in the Li layer. Electrochemical studies of single phase samples, Li[Ni1/3Mn1/3-zCo1/3Zrz]O-2 (0 <= z <= 0.02), show a small reduction in capacity and no advantage in capacity retention as Zr is substituted for Mn. The impact of Zr substitution on the thermal stability of the Li[Ni1/3Mn1/3-zCo1/3Zrz]O-2 samples was studied via accelerating rate calorimetry. The accelerating rate calorimetry results show that the substitution of Zr into the layered structure of Li[Ni1/3Mn1/3-zCo1/3Zrz]O-2 does not improve the thermal stability of the samples. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3552603]