The citric acid aided synthesis, physico-chemical and electrochemical characterization of the nanosized nickel-doped lithium manganese spinel, LiNi0.5Mn1.5O4 having excellent high-rate properties is described. An optimal electrode material represented by perfectly shaped, well-faceted particles of 100-400nm size containing crystallites of the 15-22nm size could be obtained upon the thermal treatment at 700°C. In spite of a reduced specific capacity (102 mAh·g−1) it is able to retain a half of it upon the discharge current of 4400 mA·g−1 (30C) and to endure the current load of 5870 mAh·g−1 (40C) delivering the reversible specific capacity of 25 mAh·g−1. It is suggested that the reduced specific capacity is determined primarily by the aggregation of material's particles, whereas the good high-rate capability is governed not only by the size of crystallites but also by the perfectness of crystals, and imperfections in big, well-shaped crystals (like dislocations, grain boundaries, etc.) less retard the diffusion of lithium ions than particle boundaries in small, randomly oriented, accreted crystals.