The citric acid-assisted sol-gel method was used to produce the high-voltage cathodes LiNi0.5Mn1.5O4 and LiNi0.4Ru0.05Mn1.5O4 at 800 degrees C and 1000 degrees C final calcination temperatures. High resolution powder diffraction using synchrotron radiation, inductively coupled plasma - optical emission spectroscopy and scanning electron microscopy analyses were carried out to characterize the structure, chemical composition and morphology. X-ray absorption spectroscopy studies were conducted to confirm Ru doping inside the spinel as well as to compare the oxidation states of transition metals. The formation of an impurity LixNi1-xO in LiNi0.5Mn1.5O4 powders annealed at high temperatures (T >= 800 degrees C) can be suppressed by partial substitution of Ni2+ by Ru4+ ion. The LiNi0.4Ru0.05Mn1.5O4 powder synthesized at 1000 degrees C shows the highest performance regarding the rate capability and cycling stability. It has an initial capacity of similar to 139 mAh g(-1) and capacity retention of 84% after 300 cycles at C/2 charging-discharging rate between 3.5 and 5.0 V. The achievable discharge capacity at 20 degrees C for a charging rate of C/2 is similar to 136 mAh g(-1) (similar to 98% of the capacity delivered at C/2). Since the electrode preparation plays a crucial role on parameters like the rate capability, the influence of the mass loading of active materials in the cathode mixture is discussed. (C) 2014 Elsevier B.V. All rights reserved.