The effects of Al substitution for Ni or (and) Mn in LiNi0.5Mn1.5O4 spinel on the structures and electrochemical properties are investigated. Powders of LiNi0.5Mn1.5O4, Li0.95Ni0.45Mn1.5Al0.05O4, LiNi0.475Mn1.475Al0.05O4 and Li1.05Ni0.5Mn1.45Al0.05O4 are synthesized by a thermopolymerization method. Their structures and electrochemical properties are studied by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, cyclic voltammetry and galvanostatic charge–discharge testing. The introduction of Al in these LiNi0.5Mn1.5O4 samples has resulted in structure variation, and greatly improved their cyclic performance and rate capability. The effects of Al substitutions for Ni and Mn in the LiNi0.5Mn1.5O4 are different. Compared with LiNi0.5Mn1.5O4, Li0.95Ni0.45Mn1.5Al0.05O4 demonstrates higher specific capacity at room temperature but faster capacity fading at elevated temperatures. Li1.05Ni0.5Mn1.45Al0.05O4 displays a lower discharge capacity but better capacity retention at 55°C. Moreover, the cyclic performance and rate capability of the Ni-substituted Li0.95Ni0.45Mn1.5Al0.05O4, Ni/Mn co-substituted LiNi0.475Mn1.475Al0.05O4 and Mn-substituted Li1.05Ni0.5Mn1.45Al0.05O4 at room temperature are similar, and have improved substantially compared with the Al-free LiNi0.5Mn1.5O4 sample.