In this work, the high voltage LiMn1.5Ni0.5O4 cathode material has been synthesized as octadecahedron crystals with a disordered spinel structure and has been coated with a carbon layer from two different precursors (sucrose and Xerogel carbon) to improve its performance in Li-ion batteries. The effect of carbon coating on the physical and electrochemical properties of the crystals has been evaluated using X-ray diffraction (XRD), Infrared (IR) and Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental and surface area (BET) analyses and battery cycling at different charge/discharge rates and temperatures. It was found that the amount of carbon, present as a thin layer (5–10 nm) and estimated at <1 w.t.%, causes an increase in electronic conductivity with no effect on crystal structure. Battery results of the cathode material in half cells show that carbon coating greatly improves the discharge capacity, rate capability at room temperature and 60 °C as well as cycling stability. Moreover, the material coated from Xerogel carbon shows the highest capacity at 10 C rate and 60 °C.