Six spinel LiNi0.5Mn1.5O4 (LNMS) samples with different morphologies were synthesized via a PVP (polyvinylpyrrolidone)-assisted gel combustion method by varying the calcination temperature from 800°C to 1050°C. XRD tests were used to characterize the crystal structure and phase purity. SEM images clearly revealed the evolution of the particle size (from sub-micrometer to micrometer), shape and degree of agglomeration with increasing calcination temperature. Charge/discharge tests indicated that the LNMS samples composed of larger primary particles had better cyclic performance than those composed of smaller primary particles. Among the six samples, LNMS1050-6 (calcined at 1050°C) and LNMS1000-6 (calcined at 1000°C) demonstrated excellent capacity retentions of 97.6% and 97.3%, respectively, after 200 cycles with a 1C rate at room temperature. The cyclic performance of LNMS1050-6 and LNMS1000-6 at 55°C was also remarkable, showing capacity retentions of 97.1% and 96.0%, respectively, after 50 cycles at a 1C rate. Rate capability tests indicated that among the six LNMS samples, the single-crystal-like LNMS1000-6 with a moderate particle size (1–3μm) showed the best rate capability. It delivered 132.9mAhg−1, 130.2mAhg−1, 128.1mAhg−1 and 124.5mAhg−1 at rates of 1C, 5C, 10C and 15C, respectively. Electrochemical impedance spectroscopy (EIS) measurements showed that larger primary particles exhibited slower interface impedance increases upon cycling than smaller particles.