Method for testing secondary battery and method for manufacturing secondary battery including the same

1. A method for testing a secondary battery, the method comprising:

applying laser to the secondary battery after a manufacturing process is completed to generate an ultrasonic signal;

detecting the ultrasonic signal;

converting the detected ultrasonic signal to generate a digital signal; and

processing and analyzing the digital signal to determine defects in the secondary battery;

wherein the secondary battery comprises:

an electrode assembly;

a can surrounding the electrode assembly; and

a cap covering a top surface of the can, wherein the top surface of the can and a bottom surface of the cap are coupled by a welding process,

wherein the secondary battery for which the manufacturing process is completed is provided in plurality,

wherein the secondary batteries move in one direction along a rail and are sequentially tested by a fixed test device,

wherein the test device comprises a mount, a laser head fixed by the mount, a fiber laser connected to the laser head, and an ultrasonic sensor disposed at one side of the laser head,

wherein the secondary batteries move into a space between the laser head and the rail,

wherein the fiber laser applies the laser to a top surface of the cap to generate an ultrasonic signal at an edge of the cap, and

wherein the ultrasonic sensor is disposed adjacent to the edge of the cap to detect the ultrasonic signal generated at the edge of the cap.

2. The method of claim 1 , wherein the processing and analyzing of the digital signal determines defects in the secondary battery by determining a difference between the digital signal and a normal signal or by directly detecting a specific signal generated when the defects occur.

3. The method of claim 1 , wherein the applying of the laser to generate the ultrasonic signal comprises:

emitting the laser from a laser source; and

applying the laser emitted from the laser source to a portion of the secondary battery through a transmission part and a focusing part.

4. The method of claim 3 , wherein the transmission part is configured to adjust a position, to which the laser is applied, by controlling a path of the laser, and

the focusing part is configured to focus the laser to control a size of a focal point.

5. The method of claim 1 ,

wherein the secondary battery is a jelly-roll type, and

wherein applying the laser to a top surface of the cap comprises focusing the laser on welding regions defined as a position at which the welding process is performed.

6. The method of claim 5 , wherein the can has a cylindrical shape having a height greater than a diameter of the top surface thereof, and

the laser is applied to at least one of the welding regions.

7. The method of claim 6 , wherein the laser generates the ultrasonic signal at an edge of the cap.

8. The method of claim 5 , wherein the can has a coin shape having a diameter of the top surface, which is greater than a height thereof, and

the laser is applied to a sidewall of the can.

9. The method of claim 8 , wherein the laser generates the ultrasonic signal to the top surface of the cap.

10. The method of claim 1 , wherein rotating the secondary battery in one direction at a predetermined time interval and the applying of the laser to generate the ultrasonic signal are repeatedly performed.

11. The method of claim 1 , wherein the secondary battery for which the manufacturing process is completed is provided in plurality, and

the secondary batteries move in one direction along a rail and are sequentially tested by a fixed test device.

12. The method of claim 11 , wherein the test device comprises a mount, a laser head fixed by the mount, a fiber laser connected to the laser head, and an ultrasonic sensor disposed at one side of the laser head, and

the secondary batteries move into a space between the laser head and the rail.

13. The method of claim 1 , wherein the ultrasonic signal is temporally and spatially synchronized with the applied laser.