Negative electrode and method for manufacturing same

1. A negative electrode comprising:

a current collector;

a first active material layer formed on the current collector; and

a second active material layer formed on the first active material layer,

wherein the first active material layer includes carbon-based negative electrode active material particles, and the second active material layer includes silicon nitride,

wherein the silicon nitride is represented by SiN X where x satisfies 0.73<x<0.90 and a portion of silicon which is not covalently bonded to nitrogen is present in the form of a silicon (Si) nanocrystal.

2. The negative electrode of claim 1 , wherein the second active material layer has a thickness of less than 1 μm.

3. The negative electrode of claim 1 , wherein a thickness ratio of the first active material layer and the second active material layer is 70:1 to 500:1.

4. The negative electrode of claim 1 , wherein the second active material layer includes first byproduct particles including a Si nanocrystal core and a lithium nitride (Li 3 N) shell surrounding the Si nanocrystal core after at least one cycle of charging and discharging.

5. The negative electrode of claim 1 , wherein the second active material layer includes second byproduct particles including a lithium silicide core and a lithium nitride (Li 3 N) shell surrounding the lithium silicide core after at least one cycle of charging and discharging.

6. The negative electrode of claim 5 , wherein the lithium silicide is represented by Li x Si where x satisfies 0<x<3.75.

7. The negative electrode of claim 1 , wherein the carbon-based negative electrode active material particles of the first active material layer is natural graphite.

8. The negative electrode of claim 1 , wherein the first active material layer further includes a conductive material and a binder.

9. A method of manufacturing the negative electrode of claim 1 , comprising:

forming the first active material layer on the current collector by using a negative electrode slurry including the carbon-based negative electrode active material particles, a conductive material, and a binder (Step 1); and

forming the silicon nitride layer on the first active material layer through a plasma-enhanced chemical vapor deposition process (Step 2).

10. The method of claim 9 , wherein, in the plasma-enhanced chemical vapor deposition process in step 2, nitrogen gas diluted with silane gas is used as a raw material, a flow rate of nitrogen gas diluted with silane gas is 30 sccm to 70 sccm, and a molar ratio of the nitrogen gas and silane gas is 97:3 to 99:1.

11. The method of claim 9 , wherein the plasma-enhanced chemical vapor deposition process in step 2 is performed at a plasma power of 25 watts to 100 watts and a deposition time of 0.5 hour to 2 hours.

12. The method of claim 9 , wherein the plasma-enhanced chemical vapor deposition process in step 2 is performed at a temperature of 100° C. to 300° C.

13. A secondary battery comprising the negative electrode of claim 1 , a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

14. A battery module comprising the secondary battery of claim 13 as a unit cell.

15. A battery pack comprising the battery module of claim 14 and used as a power source for medium- to large-sized devices.

16. The battery pack of claim 15 , wherein the medium- to large-sized device is selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.