The invention discloses a lithium ion battery. The lithium ion battery comprises a battery casing, a battery top cap mounted on the battery casing and a pressure relief valve arranged on the battery casing and/or the battery top cap and further comprises a safeguard device, wherein the safeguard device is arranged on the battery casing and/or the battery top cap and fixed corresponding to the pressure relief valve; the safeguard device comprises a baffle plate corresponding to the pressure relief valve, a side wall and an air channel structure; the side wall extends towards the battery casing or the battery top cap from the baffle plate and is connected with the battery casing or the battery top cap; the air channel structure is formed on the side wall. Through the forming of the air channel structure on the side wall, the baffle plate and the air channel structure form relatively separating design, solid spark particles can be effectively blocked by the baffle plate, air can be efficiently discharged through the side air channel structure, and the safety performance of the lithium ion battery is improved.