This application provides a lithium-ion battery and an apparatus. The lithium-ion battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. A positive active material of the positive electrode plate includes Lix1Coy1M1-y1O2-z1Qz1, where 0.5≤x1≤1.2, 0.8≤y1≤1.0, 0≤z1≤0.1, M is selected from one or more of Al, Ti, Zr, Y, and Mg, and Q is selected from one or more of F, Cl, and S. The electrolyte contains an additive A that is a polynitrile six-membered nitrogen-heterocyclic compound with a relatively low oxidation potential. The lithium-ion battery has superb cycle performance and storage performance, especially under high-temperature and high-voltage conditions.