Disclosed is a rechargeable lithium ion battery including a positive electrode including a positive active material and a negative electrode including a negative active material. The positive active material includes a lithium-manganese-based compound core and a heat resistant polymer disposed on the lithium-manganese-based compound core. The heat resistance polymer has a glass transition temperature (Tg) ranging from about 80 to about 400° C. The positive active material includes a lithium-manganese-based compound core and an inorganic metal compound as well as the heat resistant polymer with a glass transition temperature (Tg) ranging from about 80 to about 400° C. disposed on the lithium-manganese-based compound core.