The spinel LiNi0.5Mn1.5O4 has been surface modified separately with 1.0wt.% ZrO2 and ZrP2O7 for the purpose of improving its cycle performance as a cathode in a 5-V lithium-ion cell. Although the modifications did not change the crystallographic structure of the surface-modified samples, they exhibited better cyclability at elevated temperature (55°C) compared with pristine LiNi0.5Mn1.5O4. The material that was surface modified with ZrO2 gave the best cycling performance, only 4% loss of capacity after 150 cycles at 55°C. Electrochemical impedance spectroscopy demonstrated that the improved performance of the ZrO2-surface-modified LiNi0.5Mn1.5O4 is due to a small decrease in the charge transfer resistance, indicating limited surface reactivity during cycling. Differential scanning calorimetry showed that the ZrO2-modified LiNi0.5Mn1.5O4 exhibits lower heat generation and higher onset reaction temperature compared to the pristine material. The excellent cycling and safety performance of the ZrO2-modified LiNi0.5Mn1.5O4 electrode was found to be due to the protective effect of homogeneous ZrO2 nano-particles that form on the LiNi0.5Mn1.5O4, as shown by transmission electron microscopy.