Lithium ion battery and formation method thereof

The invention discloses a lithium ion battery formation method. A negative electrode active substance of a lithium ion battery comprises a lithium-rich manganese-based positive electrode material. Theformation method includes at least three times of charge-discharge cycles; in the two former charge-discharge cycles, charge cut-off voltage is lower than 4.4V, discharge current is higher than charge current, and the second-time charge current is higher than the first-time charge current; in the last charge-discharge cycle, the charge cut-off voltage is not lower than 4.4V, and the charge current is not lower than the second-time charge current. By the step voltage charge-discharge formation method, a stable SEI film can be formed on the surface of a negative electrode in repeated low-voltage charge-discharge processes while a stable CEI film is formed on the surface of a positive electrode, side reaction between electrolyte and an electrode piece can be inhibited, gas generation is reduced, and accordingly the