LiNi0.5Mn1.5O4, a cathode material for high potential applications, rapidly deteriorates at high temperatures. In this study, fluoride-containing additives are found to offer protection to the material in damaging temperature ranges. The results of investigations using a fluoride-rich pyrazole, fluoro-ethylene carbonate, trially cyanurate with multiple double bonds, and LiF explain the combined action of the protective layer and fluoride in promoting longer life cycles. Both fluoride in a protective film and free fluoride ions prevent LiF accumulation on the electrode, extending the life of the cathode material at high temperatures.