Manufacturing method of lithium secondary battery

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

performing a pretreatment in which an SEI (solid electrolyte interface) 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 two 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,

wherein the combination process of electrolyte injection and charging comprises:

a first injection step of preparing a battery cell by injecting a first electrolyte into a battery case;

a first charging step of charging the battery cell;

a second injection step of injecting a second electrolyte into the charged battery cell; and

a second charging step of charging the battery cell into which the second electrolyte is injected,

wherein the second electrolyte comprises an imide-based lithium salt.

2. The method of claim 1 , wherein the SEI film-forming agent comprises one selected from the group consisting of a cyclic carbonate-based compound containing an unsaturated bond; a cyclic or chain carbonate-based compound containing a halogen atom; a lithium salt containing an oxalato complex as an anion; an imide-based lithium salt; a fluorophosphate-based lithium salt; a 6-membered aromatic heterocyclic compound containing at least two nitrogen atoms in a molecule; and a sultone-based compound, or a mixture of two or more thereof.

3. The method of claim 1 , wherein the SEI film-forming agent is included in an amount of 0.1 wt % to 10 wt % based on a total weight of the composition for forming an SEI film.

4. The method of claim 1 , wherein the forming of the SEI film is performed by applying a voltage of 0.005 V to 4.5 V at a constant current of 0.01 C to 5 C.

5. The method of claim 1 , wherein the first electrolyte comprises at least one lithium salt selected from the group consisting of LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , and LiSO 3 CF 3 ,

the electrode comprises an aluminum current collector, and

an AlF 3 film is formed on the current collector after the first charging step.

6. The method of claim 1 , wherein the first electrolyte further comprises a sulfonic acid ester-based additive.

7. The method of claim 1 , wherein the first charging step is performed by applying a voltage of 1.0 V to 4.5 V at a constant current of 0.01 C to 5 C.

8. The method of claim 1 , wherein the second charging step is performed by applying a voltage of 2.0 V to 4.5 V at a constant current of 0.01 C to 5 C in a state in which the battery case is sealed after the injection of the second electrolyte.

9. The method of claim 1 , wherein the SEI film-forming agent comprises a cyclic carbonate-based compound containing an unsaturated bond, and

the first electrolyte comprises at least one lithium salt selected from the group consisting of LiPF 6 , LiAsF 6 , LiBF 4 , LiSbF 6 , and LiSO 3 CF 3 .

10. The method of claim 9 , wherein the first electrolyte further comprises a sulfonic acid ester-based additive.

11. A lithium secondary battery prepared by the method of claim 1 , comprising an electrode including an SEI film derived from a cyclic carbonate-based compound containing an unsaturated bond formed on a surface of the electrode, a sulfonic acid ester-based additive derived film formed on the SEI film, and an imide-based lithium salt derived film formed on the sulfonic acid ester-based additive derived film.

12. A battery module comprising the lithium secondary battery of claim 11 as a unit cell.

13. A battery pack comprising the battery module of claim 12 .