The coprecipitation process, using either mixed nitrate or sulfate solutions, to produce Al-doped Ni1/3Mn1/3Co1/3(OH)(2) has been studied in detail. Using X-ray diffraction (XRD) and thermal gravimetric analysis (TGA), it has been determined that charge-compensating NO3- or SO42- ions accompany the incorporated Al3+ ions into the structure to form layered double hydroxides (LDHs). The phases formed were determined for 0 < z < 1/3 in Ni1/3Mn1/3Co1/3-zAlz(OH)(2)(NO3)(z) and Ni1/3Mn1/3Co1/3-zAlz(OH)(2)(SO4)(z/2). For 0 < z < 1/6, two phase mixtures between M(OH)(2) (M=Ni, Mn, and Co) and the LDH phase with z approximate to 1/6 were formed. For aluminum contents greater than z=1/6, XRD and TGA experiments suggest that the excess Al is present as Al(OH)(3) and that the product is a mixture of M5/6Al1/6(OH)(2)(NO3)(z) or M5/6Al1/6(OH)(2)(SO4)(z/2) and Al(OH)(3), where M represents the mixture of Ni, Mn, and Co. Alternatively, the data can also be explained assuming that samples with z>1/6 are single phase Ni1/3Mn1/3Co1/3-zAlz(OH)(2)(NO3)(1/6)(OH)(z-1/6). TGA experiments show that the NO3- in the NO3--containing LDH is eliminated at lower temperature than the SO42- in the SO42--containing LDH. Thus coprecipitations using nitrates may be preferred in situations where excellent cation mixing is desired in the production of Al-doped Li[Ni1/3Mn1/3Co1/3-zAlz]O-2. (C) 2008 The Electrochemical Society.