LiNi0.5Mn1.5O4 powders were prepared through polymer-pyrolysis method. XRD and TEM analysis indicated that the pure spinel structure was formed at around 450 °C due to the very homogeneous intermixing of cations at the atomic scale in the starting precursor in this method, while the well-defined octahedral crystals appeared at a relatively high calcination temperature of 900 °C with a uniform particle size of about 100 nm. When cycled between 3.5 and 4.9 V at a current density of 50 mA/g, the as prepared LiNi0.5Mn1.5O4 delivered an initial discharge capacity of 112.9 mAh/g and demonstrated an excellent cyclability with 97.3% capacity retentive after 50 cycles.