Two samples of LiNi0.5Mn1.5O4 with surface areas of 0.5 and 1.8 m(2)/g were synthesized from a co-precipitated hydroxide precursor. LiNi0.5Mn1.5O4 electrodes with different ratios of active material, carbon black and PVDF were used in LiNi0.5Mn1.5O4/Li cells. The cells were tested at currents corresponding to C/10, C/21 and C/43 and at temperatures of 30, 40 and 50 C on the High Precision Charger at Dalhousie University. Accurate measurements of the coulombic efficiency (CE) as well as the charge and discharge end point capacity slippages were made. There was a significant decrease of the CE as the active material surface area increased. The CE decreased proportionally to the increase in charge-discharge cycle time indicating that parasitic reactions at the positive electrode in these cells occur at a fixed rate at a given temperature. The CE decreased with increasing temperature showing that the parasitic reactions increased with temperature. More research is needed to improve the CE, along with suppression of electrolyte oxidation, before the commercial application of this electrode material can be contemplated. (C) 2013 The Electrochemical Society. All rights reserved.