First-principles methods are used to calculate the miscibility of eight aluminum-doped transition-metal oxides in the layered alpha-NaFeO2 structure. This study finds that for all Li(Al,M)O-2 compounds investigated(M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu) the enthalpy of mixing is positive. In addition, detailed analyses were performed on LiA(1-x)Co(x)O(2) and LiA(1-x)Cr(x)O(2) by calculating full temperature-composition phase diagrams. For the Li(Al,Co)O-2 system, we find regions of immiscibility below - 173 degrees C and above 600 degrees C. For both Li(Al,Co)O-2 and Li(A1,Cr)O-2 above 600 degrees C, Al-doping is limited by the formation of gamma-LiAlO2.