Spinel LiNi0.5Mn1.5O4 materials are synthesized by one-step precipitation method. Ammonium carbonate is used as the precipitating agent to obtain a more precise feed ratio without recourse to traditional washing. After annealing at high temperature, the spherical particles become angular and show high levels of crystallinity. The synthesized samples are evaluated using powder X-ray diffraction, scanning electron microscopy, and electrochemical testing. The samples synthesized with different metal ion concentrations yield different morphologies and rate performances. The sample synthesized with 0.2molL−1 gives the most uniform particle distribution and the best electrochemical performance. The specific discharge capacity values of the sample at 10 and 15C are as high as 109.5 and 88.7mAhg−1, respectively. After the high-rate cycling, its discharge capacity at 0.2C can be reverted to 97.67% of its initial capacity.