Li1.02Ni0.5Mn1.5O4 spinel cathode materials were successfully synthesized by a citric acid-assisted sol–gel method. The structure and morphology of the materials have been examined by X-ray diffraction and scanning electron microscopy, respectively. Electrochemical properties of the materials were investigated using cyclic voltammetry and galvanostatic charge/discharge measurements at two different temperatures (25 and 55°C) using lithium anode. The initial capacity and capacity retention are highly dependent on the particle size, particle size distribution, crystallinity and purity of the materials. The Li1.02Ni0.5Mn1.5O4 materials synthesized both at 800 and 850°C have shown best electrochemical performance in terms of capacity and capacity retention between 3.5 and 4.9V with a LiPF6 based electrolyte.