The effect of Ti substitution for Mn on the structure and electrochemical properties of the LiNi0.5Mn1.5-xTixO4 was studied. The LiNi0.5Mn1.5-xTixO4 (x = 0-1.0) was successfully synthesized at 900degreesC by solid-state reaction method. Additional annealing was used for the ordering of transition metals in octahedral sites. X-ray diffraction (XRD) and selected-area electron diffraction study clearly showed that Ti substitution leads to the disordering of the transition metals and consequently lowers the symmetry from primitive simple cubic structure (P43(3)2) to face-centered spinel (Fd (3) over barm). Electron diffraction patterns of the LiNi0.5Mn1.5-xTixO4 showed stacking faults which came from the localized incorporation of Ti atoms in the lattice. LiNi0.5Mn1.5-xTixO4 exhibited higher operating voltages, faster lithium ion diffusion, and better rate capability than Ti-free LiNi0.5Mn1.5O4 confirmed by electrochemical tests including galvanostatic intermittent titration technique measurement. In addition, ex situ XRD data of the delithiated LiNi0.5Mn1.5-xTixO4 (x = 0, 0.3, and 0.5) showed that phase transition was suppressed with increasing Ti content. A large amount of Ti substitution in LiNi0.5Mn1.5-xTixO4, however, exhibited low discharge capacity, which would be due to the blocking migration pathway of electrons by the Ti4+ (d(0)) ions in octahedral sites. (C) 2004 The Electrochemical Society.