A series of samples of LiNi_1/2Mn_3/2O₄ were prepared by different synthetic methods. They displayed a variety of particle sizes and shapes, from nanometric to micrometric, with different anisotropies and assemblies. The evaluation of their performance as electrodes in lithium metal half cells showed that the best performance at a fast rate of 1 C is obtained with BM900C, which consisted of micron-size octahedral particles. It outperformed samples that showed nanometric particle sizes, which, at the same time, also showed worse coulombic efficiencies. Nonetheless, a low efficiency of 88.9% for the first cycle, and 99.6% in subsequent cycles, was still observed for the best sample. Low coulombic efficiencies are likely behind the poor performance of a Li-ion cell containing BM900C and a MCMB anode. The most critical issue to be solved to make LiNi_1/2Mn_3/2O₄ a viable electrode material for Li-ion batteries is related to these inefficiencies, as the material has inherently good life, even at high rates. It is concluded that microstructure has an important role on the performance of LiNi_1/2Mn_3/2O₄, with micron-sized particles having the best properties.