Multi-layer negative electrode with different binder content and different particle size of active material in each layer and lithium secondary battery comprising the same
A multi-layer negative electrode according to an embodiment of the present disclosure includes: a current collector configured to transmit electrons between an outer lead and a negative electrode active material; a first negative electrode mixture layer formed on one surface or both surfaces of the current collector and including a first negative electrode active material and a first binder; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second negative electrode active material, wherein the first negative electrode mixture layer has an electrode density of about 0.9 to 2.0 g/cc and the second negative electrode mixture layer has an electrode density of about 0.2 to 1.7 g/cc, which is a range lower than that of the electrode density of the first negative electrode mixture layer. The multi-layer negative electrode can be included in a lithium secondary battery.
1. A multi-layer negative electrode comprising:
a current collector configured to transmit electrons between an outer lead and a negative electrode active material;
a first negative electrode mixture layer formed on one surface or both surfaces of the current collector and including a first negative electrode active material and a first binder; and
a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second negative electrode active material,
wherein the first negative electrode mixture layer has an electrode density of about 0.9 to 2.0 g/cc and the second negative electrode mixture layer has an electrode density of about 0.2 to 1.7 g/cc, and the electrode density of the second negative electrode mixture layer is lower than the electrode density of the first negative electrode mixture layer.
2. The multi-layer negative electrode of claim 1 , wherein an average electrode density of the multi-layer negative electrode is more than 1.0 g/cc and is 1.6 g/cc or less.
3. The multi-layer negative electrode of claim 1 , wherein the second negative electrode mixture layer further includes a second binder, and a weight ratio of the first binder and the second binder (the first binder/the second binder) is about 1.2 to 10.
4. The multi-layer negative electrode of claim 3 , wherein the second negative electrode mixture layer further includes a second binder, and a weight ratio of the first binder and the second binder (the first binder/the second binder) is about 3 to 8.
5. The multi-layer negative electrode of claim 1 , wherein the first binder has a content of about 1 to 10 wt % based on the weight of the entire first negative electrode mixture layer.
6. The multi-layer negative electrode of claim 3 , wherein the second binder has a content of about 0.1 to 5 wt % based on the weight of the entire second negative electrode mixture layer.
7. The multi-layer negative electrode of claim 3 , wherein the first binder and the second binder are the same or different kinds of materials.
8. The multi-layer negative electrode of claim 1 , wherein the first negative electrode mixture layer and the second negative electrode mixture layer are not mixed with each other and form an interface.
9. The multi-layer negative electrode of claim 1 , wherein solids of each layers are intermixed between the first negative electrode mixture layer and the second negative electrode mixture layer and an interface is not formed.
10. The multi-layer negative electrode of claim 1 , wherein the first negative electrode mixture layer and the second negative electrode mixture layer have a thickness ratio of 1:9 to 7:3.
11. The multi-layer negative electrode of claim 1 , wherein the first negative electrode active material is in a form of an elliptical particle whose major axis is parallel to the surface of the current collector as a vertical cross section, and the second negative electrode active material is in a form of a spherical particle.
12. The multi-layer negative electrode of claim 1 , wherein the first negative electrode active material and the second negative electrode active material are in forms of elliptical particles whose major axes are parallel to the surface of the current collector as a vertical cross section, and the particle major axis of the first negative electrode active material is relatively larger than the particle major axis of the second negative electrode active material.
13. The multi-layer negative electrode of claim 1 , wherein the first negative electrode active material and the second negative electrode active material are the same or different kinds of compounds.
14. The multi-layer negative electrode of claim 1 , wherein the first negative electrode active material has an average particle diameter (D50) of about 10 to 30 μm, and the second negative electrode active material has an average particle diameter (D50) of about 5 to 25 μm.
15. The multi-layer negative electrode of claim 1 , wherein each of the first binder and the second binder is selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch; hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluorine rubber.
16. The multi-layer negative electrode of claim 1 , wherein the first negative electrode mixture layer and the second negative electrode mixture layer further include a conductive material.
17. A method of preparing the multi-layer negative electrode of claim 1 , comprising:
(i) a process of coating a first negative electrode slurry including a first negative electrode active material and a first binder on one surface or both surfaces of a negative electrode current collector and forming a first coating layer; and
(ii) a process of coating a second negative electrode slurry including a second negative electrode active material on the first coating layer and forming a second coating layer,
wherein an electrode density of the first coating layer is about 0.9 to 2.0 g/cc, and an electrode density of the second coating layer is about 0.2 to 1.7 g/cc, which is a range lower than that of the electrode density of the first coating layer.
18. The method of claim 17 , further comprising:
a process of drying the first coating layer between processes (i) and (ii), and a process of drying the second coating layer after process (ii) and rolling the coating layers;
a process of drying and rolling the first coating layer between processes (i) and (ii, and a process of drying and rolling the second coating layer after process (ii); or
a process of drying and rolling both coating layers at once after process (ii).
19. The method of claim 18 , wherein when a process of drying and rolling the first coating layer between processes (i) and (ii), and a process of drying and rolling the second coating layer after process (ii) are further comprised, a rolling strength of the first coating layer is higher than that of the second coating layer.
20. The method of claim 17 , wherein the second negative electrode slurry further includes a second binder, and a weight ratio of the first binder and the second binder (the first binder/the second binder) is about 1.2 to 10.