Applied in a battery with a silicon-oxide (SiO) anode, a non-flammable triethyl-phosphate (TEP)-based electrolyte with fluoroethylene carbonate (FEC) improved the safety and energy density of the battery. This TEP:FEC-based battery demonstrated almost the same performance, namely, capacity retention of 78% after 250 cycles, as that of a flammable electrolyte such as an ethylene carbonate (EC)/diethyle carbonate (DEC)-mixed electrolyte (79%). Moreover, this non-flammable electrolyte significantly enhanced the safety of the battery. This improved performance and safety is attributed to the disappearance of the exothermic peak around 120–160 °C derived from the reaction between the electrolyte and charged anode. Accordingly, this non-flammable (TEP)-based electrolyte can enhance the safety of lithium-ion batteries.