LiNi0.5Mn1.5O4 spinels coated with various amounts of fumed silica have been synthesized and investigated as cathode materials for high-voltage lithium-ion batteries at the elevated temperature (55°C). The morphology and structure of the coated LiNi0.5Mn1.5O4 samples were characterized by XRD, TEM and EDX. It was found that the surfaces of the coated LiNi0.5Mn1.5O4 samples are covered with a porous, amorphous, nanostructured SiO2 layer. The results of electrochemical experiments showed that the SiO2-coated LiNi0.5Mn1.5O4 samples display obviously improved capacity retention rate, and the improvement effect enhances with the increase of SiO2 content. The XPS results revealed that the surfaces of the SiO2-coated LiNi0.5Mn1.5O4 cathode materials have relatively low content of LiF, and this is mainly responsible for their improved electrochemical cycling stability.