Lithium Secondary Battery with Improved Safety

A lithium secondary battery is disclosed herein. The secondary battery has improved high temperature safety and may prevent generation of a large amount of gas under a high temperature condition, which prevents an increase in resistance and a decrease in capacity due to the elution of metal ions from an electrode by uniformly forming a coating film on an electrode surface during activation of the battery. A positive electrode active material of the battery includes a high concentration(s) of nickel and/or manganese and a non-aqueous electrolyte including an additive are used, which improves performance and high-temperature safety of the battery.