An electrolyte for a lithium-ion battery and a lithium-ion battery. The electrolyte for a lithium-ion battery comprises a non-aqueous organic solvent, a lithium salt, and an electrolyte additive. The additive is selected from compounds of formula 1, wherein R1 is selected from unsaturated alkyls having three to six carbon atoms, and R2 is selected from alkylenes having two to five carbon atoms. Because the molecular structure of the additive comprises both unsaturated carbon-carbon bonds and cyanos, polymerization can occur on an electrode surface to form a compound containing multiple cyanos. The compound can be complexed with metal ions on a surface of a cathode material, thereby inhibiting electrolyte decomposition on an electrode surface to improve high-temperature storage and cyclability of a battery.