Jelly-roll of improved productivity and battery cell comprising the same
Disclosed herein is a jelly roll for a secondary battery configured by winding a cathode sheet, a separator, and an anode sheet, wherein electrode tabs are connected to uncoated portions of the electrode sheets, to which electrode active materials are not applied, by welding, and each of the electrode tabs is configured to have an embossed structure protruding toward the uncoated portion to improve weldability.
1. A method of manufacturing a jelly roll, the method comprising:
(a) winding a cathode sheet and an anode sheet in a state in which a separator is disposed between the cathode sheet and the anode sheet;
(b) positioning electrode tabs each having an embossed structure formed at a surface thereof on uncoated portions of the cathode sheet and the anode sheet such that protruding parts of the embossed structure faces a corresponding one of the uncoated portions; and
(c) positioning horn tips of a welding device in depressed parts of the embossed structure of each of the electrode tabs and applying ultrasonic waves to the depressed parts, wherein the embossed structure is formed prior to positioning the horn tips in the depressed parts.
2. The method according to claim 1 , wherein the electrode tabs are made of aluminum or nickel.
3. The method according to claim 1 , wherein the embossed structure comprises a plurality of micro protrusions configured to have a structure having the protruding parts formed at one side thereof facing the uncoated portion and the depressed parts formed at the other side thereof so as to correspond to the micro protrusions.
4. The method according to claim 3 , wherein each of the micro protrusions has a protruding height of 50 to 500 microns.
5. The method according to claim 3 , wherein each of the micro protrusions has a protruding height of 100 to 150 microns.
6. The method according to claim 1 , wherein the electrode tabs are connected to the uncoated portions by ultrasonic welding.
7. The method according to claim 6 , wherein the embossed structure comprises a plurality of micro protrusions, and wherein the horn tips of the welding device are arranged at intervals corresponding to the micro protrusions of the embossed structure.
8. The method according to claim 7 , wherein the depressed parts correspond to the micro protrusions of the embossed structure, and wherein the ultrasonic welding is performed by applying ultrasonic waves in a state in which the horn tips are located in the depressed parts of the respective micro protrusions.
9. The method according to claim 1 , wherein uncoated portions of the cathode sheet and the anode sheet are flat prior to applying ultrasonic waves to the depressed parts of the electrode tabs.