A novel additive is investigated as a bifunctional electrolyte additive for 5 V-class lithium ion batteries. It was found that the additive can be electro-polymerized at 5.05 V (vs. Li/Li⁺), which would protect the batteries from voltage runaway. Moreover, this additive could lower the electrolyte's self-extinguishing time (SET). The influence of this additive on cycling performance and capacity is positive, which makes it promising.