Manufacturing method of lithium secondary battery

A method of preparing a lithium secondary battery, the method comprising:

• performing a pretreatment in which an SEI (solid electrolyte interphase) film is formed on an electrode by impregnating the electrode in a composition for forming an SEI film and applying a voltage to the electrode;
• and
• preparing an electrode assembly using the electrode having the SEI film formed thereon, putting the electrode assembly in a battery case, and performing a combination process of electrolyte injection and charging one or more times,
• wherein the composition for forming an SEI film comprises a lithium salt, a non-aqueous organic solvent, and an SEI film-forming agent forming the SEI film by an electrochemical oxidation or reduction decomposition reaction.