Method of producing negative electrode
A method of producing a negative electrode is disclosed which is capable of preventing volume expansion and structural deformation caused by pre-lithiation, maintaining proximity and contact between negative electrode active materials, preventing an increase in resistance of a negative electrode, and realizing an excellent capacity retention rate by performing pre-lithiation while pressurizing a negative electrode at a specific pressure. In addition, the method of producing a negative electrode is capable of improving quality consistency of a product and processability by performing pre-lithiation of a negative electrode in a roll-to-roll manner.
1. A method of producing a negative electrode, comprising:
providing a negative electrode roll on which a negative electrode structure including a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector is wound;
providing a pre-lithiation bath containing a pre-lithiation solution, the pre-lithiation bath being sequentially divided into an impregnation section and a pre-lithiation section;
impregnating the negative electrode structure with the pre-lithiation solution while unwinding the negative electrode structure from the negative electrode roll and moving the negative electrode structure through the impregnation section; and
pre-lithiating the impregnated negative electrode structure by disposing the impregnated negative electrode structure in the pre-lithiation section,
wherein the pre-lithiating the impregnated negative electrode structure includes:
(a) disposing the impregnated negative electrode structure between two pre-lithiation structures, each pre-lithiation structure including a separator layer disposed to face the negative electrode active material layer and a lithium counter electrode layer located on the separator layer;
(b) electrochemical charging the impregnated negative electrode structure while pressurizing the impregnated negative electrode structure at a pressure of 10 kPa to 3,500 kPa with the two pre-lithiation structures to form a pre-lithiated negative electrode structure; and
(c) separating the two pre-lithiation structures from the pre-lithiated negative electrode structure and moving the pre-lithiated negative electrode structure out of the pre-lithiation section.
2. The method of claim 1 , wherein step (b) is performed for 5 minutes to 120 minutes.
3. The method of claim 1 , wherein a time taken for the negative electrode structure to move through the impregnation section is 1 times to 10 times a time taken to perform step (b).
4. The method of claim 1 , wherein the pre-lithiation bath is sequentially divided into the impregnation section, the pre-lithiation section, and an aging section, and
wherein the method further comprises aging the pre-lithiated negative electrode structure having passed through the pre-lithiation section by conveying the pre-lithiated negative electrode structure to the aging section.
5. The method of claim 4 , wherein a time taken for the pre-lithiated negative electrode structure to move through the aging section is 0.5 times to 21 times the time taken to perform step (b).
6. The method of claim 4 , further comprising washing the aged negative electrode structure by taking the aged negative electrode structure out of the pre-lithiation bath, introducing the aged negative electrode structure into a washing bath containing an organic solvent, and moving the aged negative electrode structure through the washing bath to form a washed negative electrode structure.
7. The method of claim 6 , further comprising drying the washed negative electrode structure.
8. The method of claim 1 , further comprising washing the pre-lithiated negative electrode structure by taking the pre-lithiated negative electrode structure out of the pre-lithiation bath, introducing the pre-lithiated negative electrode structure into a washing bath containing an organic solvent, and moving the pre-lithiated negative electrode structure through the washing bath to form a washed negative electrode structure.
9. The method of claim 8 , wherein a time taken for the pre-lithiated negative electrode structure to move through the washing bath is 0.1 times to 5 times a time taken to perform step (b).
10. The method of claim 8 , further comprising drying the washed negative electrode structure.
11. The method of claim 10 , wherein the time taken to dry the washed negative electrode structure is 0.1 times to 5 times the time taken to perform step (b).
12. The method of claim 1 , wherein a temperature of the pre-lithiation bath ranges from 10° C. to 80° C.
13. The method of claim 1 , wherein each of the pre-lithiation structures further includes a supporting plate located on the lithium counter electrode layer and an insulating plate located on the supporting plate.
14. The method of claim 13 , wherein the pre-lithiation structures are connected by a plurality of supports such that the pre-lithiation structures are movable along the plurality of supports.