This invention discloses a type of mixed additives for electrolyte of lithium-ion secondary batteries, having the following characteristics: in weight percentage: biphenyl series: 0.5% to 95.4%; cyclohexylbenzene series: 1.1% to 93.8%; vinylene carbonate: 0.4% to 93.2%; phenyl vinyl sulfone: 0.5% to 96.5%; ethenyl sulfonyl benzene: 0.5% to 95.8%. This invention also discloses an electrolyte for lithium-ion secondary batteries comprising organic solvents and lithium saline, wherein the special characteristic is that it comprises 2% to 20% weight percentage of said mixed additives. The distinctive advantage of the mixed additives for lithium-ion secondary batteries of this invention is to effectively enhance the overcharging, low-temperature, and cycle properties of lithium-ion batteries. A lithium-ion battery having the mixed additives of this invention remains explosion-free, ignition-free and reliably safe when the lithium-ion secondary battery is overcharging. A battery of this invention's exemplary embodiment, when discharging at temperatures of -10.degree. C. and -20.degree. C., has high capacity, high medium voltage and low terminal inner resistance.