Electrode having a dual layer structure, method for manufacturing thereof, and lithium secondary battery comprising the same

1. An electrode having a dual layer structure, comprising:

an electrode current collector;

a middle layer formed on at least one side of the electrode current collector; and

an electrode active material layer formed on the middle layer,

wherein the middle layer comprises a first binder,

wherein the electrode active material comprises an electrode active material and a second binder, and wherein the first binder and the second binder are the same kind of material but have different crystalline phases and different molecular weights.

2. The electrode having a dual layer structure according to claim 1 , wherein the first binder has an α/β ratio ranging from 0.3 to 0.8.

3. The electrode having a dual layer structure according to claim 1 , wherein the second binder has an α/β ratio ranging from 0.05 to 0.25.

4. The electrode having a dual layer structure according to claim 1 , wherein the first binder has a weight average molecular weight ranging from 60,000 to less than 270,000.

5. The electrode having a dual layer structure according to claim 1 , wherein the second binder has a weight average molecular weight ranging from 330,000 to 1,000,000.

6. The electrode having a dual layer structure according to claim 1 , wherein the first binder and the second binder are at least one selected from the group consisting of: poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber.

7. The electrode having a dual layer structure according to claim 1 , wherein the electrode is a positive electrode and the electrode active material is a positive electrode active material.

8. The electrode having a dual layer structure according to claim 7 , wherein the positive electrode active material is at least one selected from the group consisting of:

an oxide of the following formulae 1 to 3; V2O5, TiS, and MoS

Li1+x[NiaCobMnc]O2  [Formula 1]

(where −0.5≦x≦0.6; 0≦a, b, c≦1; x+a+b+c=1)

LiMn2−xMxO4  [Formula 2]

(where M is one or more elements selected from the group consisting of: Ni, Co, Fe, P, S, Zr, Ti, and Al; 0≦x≦2)

Li1+aFe1−xMx(PO4−b)Xb  [Formula 3]

(where M is one or more elements selected from the group consisting of: Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X is one or more elements selected from the group consisting of: F, S, and N; −0.5≦a≦+0.5; 0≦x≦0.5; 0≦b≦0.1).

9. The electrode having a dual layer structure according to claim 7 , wherein the positive electrode active material is at least one selected from the group consisting of: LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li[Ni a Co b Mn c ]O 2 (where 0<a, b, c≦1; a+b+c=1), and LiFePO 4 .

10. The electrode having a dual layer structure according to claim 1 , wherein the middle layer has a thickness ranging from 0.5 μm to 5 μm.

11. The electrode having a dual layer structure according to claim 1 , wherein the electrode active material layer has a thickness ranging from 40 μm to 120 μm.

12. A method for manufacturing an electrode having a dual layer structure according to claim 1 , comprising the steps of:

1) preparing a predispersed slurry comprising a third binder;

2) forming a middle layer by coating at least one side of an electrode current collector with the predispersed slurry; and

3) forming an electrode active material by coating the middle layer with an electrode active material slurry comprising a fourth binder,

wherein the third binder and the fourth binder are the same kind of material but have different molecular weights.

13. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the predispersed slurry of step 1) is prepared by addition of a conductive agent to the fourth binder and high-shear mixing of the same.

14. The method for manufacturing an electrode having a dual layer structure according to claim 13 , wherein the high-shear mixing is carried out under a pressure condition of 20,000 psi to 40,000 psi.

15. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the coating of step 2) comprises a painting step and a drying step, wherein the drying is carried out by conducting heat treatment for 10 to 24 hours at a temperature range of 140° C. to 160° C.

16. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the coating of step 3) comprises a painting step and a drying step, wherein the drying is carried out by conducting heat treatment for 10 to 24 hours at a temperature range of 120° C. to 140° C.

17. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the middle layer comprises a first binder, the electrode active material layer comprises a second binder, and the first binder and the second binder are the same kind of material but have different crystalline phases.

18. The method for manufacturing an electrode having a dual layer structure according to claim 17 , wherein the first binder is formed by heat treating the third binder, and the first binder has an α/β ratio ranging from 0.3 to 0.8.

19. The method for manufacturing an electrode having a dual layer structure according to claim 17 , wherein the second binder is formed by heat treating the fourth binder, and the second binder has an α/β ratio ranging from 0.05 to 0.25.

20. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the third binder has a weight average molecular weight ranging from 60,000 to less than 270,000.

21. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the fourth binder has a weight average molecular weight ranging from 330,000 to 1,000,000.

22. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the electrode is a positive electrode and the electrode active material is a positive electrode active material.

23. The method for manufacturing an electrode having a dual layer structure according to claim 12 , wherein the positive electrode active material is a mixture of: at least one selected from the group consisting of: an oxide of the following formulae 1 to 3; V2O5, TiS, and MoS

Li1+x[NiaCobMnc]O2  [Formula 1]

(where −0.5≦x≦0.6; 0≦a, b, c≦1; x+a+b+c=1)

LiMn2−xMxO4  [Formula 2]

(where M is one or more elements selected from the group consisting of: Ni, Co, Fe, P, S, Zr, Ti, and Al; 0≦x≦2)

Li1+aFe1−xMx(PO4−b)Xb  [Formula 3]

(where M is one or more elements selected from the group consisting of: Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X is one or more elements selected from the group consisting of: F, S, and N; −0.5≦a≦+0.5; 0≦x≦0.5; 0≦b≦0.1).

24. The method for manufacturing an electrode having a dual layer structure according to claim 22 , wherein the positive electrode active material is at least one selected from the group consisting of: LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li[Ni a Co b Mn c ]O 2 (where 0<a, b, c≦1; a+b+c=1), and LiFePO 4 .

25. A lithium secondary battery comprising an electrode having a dual layer structure according to claim 1 .