CN116900528A - Welding device and welding method of lithium battery - Google Patents

Abstract

The application provides a welding device and a welding method of a lithium battery, wherein the welding device is used for welding the lithium battery, the welding device comprises a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat, the resistance welding mechanism comprises an upper resistance welding needle, the cylinder is connected with the resistance welding needle, the ultrasonic welding mechanism comprises an ultrasonic welding head, the upper resistance welding needle is in clearance fit with the ultrasonic welding head, the upper resistance welding needle and the ultrasonic welding head are arranged opposite to the welding seat, and the cylinder is used for driving the upper resistance welding needle to move towards the welding seat, so that the situation of poor welding when the lithium battery is welded is reduced, and the reliability of the lithium battery is further improved.

Description

Welding device and welding method of lithium battery

Technical field

The present application relates to the technical field of lithium-ion batteries, and specifically to a welding device and a welding method for lithium batteries.

Background technique

In recent years, lithium-ion batteries have been widely used in the field of new energy vehicles. With the continuous development of new energy vehicles, lithium-ion batteries with high energy density, long life and high safety have become the main research in the field of lithium-ion battery technology. direction.

In the existing technology, ultrasonic welding is usually used for welding lithium batteries, but ultrasonic welding is solid phase welding and is only suitable for welding metal foils with smaller thicknesses, that is, it is suitable for lithium batteries with a small number of tabs, protective sheets and When the thickness of the adapter sheet is small. However, when the number of lithium battery tabs is large and the protective sheet and adapter sheet are thick, using ultrasonic welding to weld the lithium battery will easily lead to poor welding problems such as weak welding, cracked protective sheet welding or cracked tabs, which can lead to The reliability of lithium batteries is reduced.

Contents of the invention

In view of this, this application provides a welding device to improve the reliability of lithium batteries.

The present application provides a welding device. The welding device is used for welding lithium batteries. The welding device includes a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat. The resistance welding mechanism includes an upper resistance welding needle. The cylinder Connected to the resistance welding needle, the ultrasonic welding mechanism includes an ultrasonic welding head, the upper resistance welding needle has a clearance fit with the ultrasonic welding head, the upper resistance welding needle and the ultrasonic welding head are in contact with the welding seat Arranged oppositely, the air cylinder is used to drive the upper resistance welding pin to move toward the welding seat.

In some embodiments, the resistance welding mechanism further includes a connection block, and the cylinder and the upper resistance welding pin are connected through the connection block.

In some embodiments, the resistance welding mechanism further includes a positive terminal and a negative terminal, the positive terminal is threadedly connected to the connection block, and the negative terminal is threadedly connected to the welding seat.

In some embodiments, the connection block includes an upper connection part, a lower connection part and an insulating connection part disposed between the upper connection part and the lower connection part, the upper connection part is connected to the cylinder, and the The lower connecting part is connected to the upper resistance welding pin, and the positive terminal is threadedly connected to the insulating connecting part and connected to the lower connecting part.

In some embodiments, the welding base includes a lower base, an upper base, and an insulating portion disposed between the upper base and the lower base, and the upper base and the upper resistance welding pin And the ultrasonic welding head is arranged oppositely, and the negative terminal is threadedly connected to the insulating part and connected to the upper base.

In some embodiments, the ultrasonic welding head includes a plurality of via holes that penetrate the ultrasonic welding head to expose the welding seat, and the upper resistance welding pin passes through the through holes toward the welding The seat moves.

In some embodiments, the ultrasonic welding head is provided with first welding teeth on one side facing the welding base, the first welding teeth are staggered with the through holes, and the welding base is provided on one side facing the cylinder. There are second welding teeth, and the second welding teeth are arranged in one-to-one correspondence with the first welding teeth.

In some embodiments, a lower resistance welding pin is provided on a side of the welding seat facing the cylinder, the lower resistance welding pin is arranged in one-to-one correspondence with the upper resistance welding pin, and the lower resistance welding pin is connected to the upper resistance welding pin. The second welding teeth are arranged in a staggered manner.

In some embodiments, the ultrasonic welding mechanism further includes an adapter connected to the ultrasonic welding head.

This application also provides a welding method for lithium batteries, using the welding device as mentioned above for welding, including:

Place the tab, adapter piece and protective piece of the lithium battery between the welding seat, the upper resistance welding pin and the ultrasonic welding head;

Driving at least one of the ultrasonic welding head and the upper resistance welding pin to move toward the welding seat, and making one of the ultrasonic welding head and the upper resistance welding pin contact the pole of the lithium battery The ears, the adapter piece and the protective piece are welded for the first time;

The other one of the ultrasonic welding head and the upper resistance welding needle is used to weld the tab, the adapter piece and the protective piece of the lithium battery for a second time to complete the welding of the lithium battery.

This application provides a welding device and a welding method for lithium batteries. The welding device is used for welding lithium batteries. The welding device includes a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat. The resistance welding mechanism includes an upper resistance welding needle, a cylinder and a resistor. Welding pin connection, the ultrasonic welding mechanism includes an ultrasonic welding head, the upper resistance welding needle has a gap fit with the ultrasonic welding head, the upper resistance welding needle and the ultrasonic welding head are set opposite to the welding base, and the cylinder is used to drive the upper resistance welding needle to move toward the welding base. Reduce the occurrence of poor welding when welding lithium batteries, thereby improving the reliability of lithium batteries.

Description of the drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic three-dimensional structural diagram of the welding device improved by the present application;

Figure 2 is a schematic structural diagram of the welding device in Figure 1, viewed from above;

Figure 3 is a schematic top structural view of the welding seat of the welding device in Figure 1;

Figure 4 is a schematic side view of the welding device in Figure 1;

Figure 5 is a schematic flow chart of the welding method of the lithium battery provided.

Reference signs:

10. Welding device; 20. Protective sheet; 30. Battery lug; 40. Adapter piece; 100. Cylinder; 200. Resistance welding mechanism; 210. Upper resistance welding pin; 220. Connection block; 221. Upper connection 222. Lower connection part; 223. Insulating connection part; 230. Positive terminal; 240. Negative terminal; 300. Ultrasonic welding mechanism; 310. Ultrasonic welding head; 311. First welding tooth; 312. Via hole; 320. Adapter; 400, welding seat; 410, lower base; 420, upper base; 430, insulation part; 440, lower resistance welding needle; 450, second welding tooth.

Detailed ways

The technical solutions in the embodiments of the present application are clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of this application. The following embodiments and their technical features may be combined with each other without conflict.

This application provides a welding device. The welding device is used for welding lithium batteries. The welding device includes a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat. The resistance welding mechanism includes an upper resistance welding needle. The cylinder is connected to the resistance welding needle. Ultrasonic welding The mechanism includes an ultrasonic welding head, the upper resistance welding needle has a gap fit with the ultrasonic welding head, the upper resistance welding needle and the ultrasonic welding head are arranged opposite to the welding base, and the cylinder is used to drive the upper resistance welding needle to move toward the welding base.

In this application, the welding device is mainly composed of a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat, and the cylinder is connected to the resistance welding needle of the resistance welding mechanism, and the upper resistance welding needle has a gap fit with the ultrasonic welding head of the ultrasonic welding mechanism. , the upper resistance welding needle and the ultrasonic welding head are set opposite to the welding base, so that the resistance welding mechanism can soften the lithium battery foil through the resistance heat generated by the current, so as to form an effective connection point in the welding area of the foil, thereby improving the welding The regional metal atom diffusion activation energy allows the ultrasonic welding joint to use only a small practical power to improve the plastic flow of metal in the welding area, thereby allowing the welding area to quickly form a welding joint, thereby reducing the occurrence of welding during lithium battery welding. adverse conditions, thereby improving the reliability of lithium batteries.

Please refer to Figures 1 to 4. Figure 1 is a schematic three-dimensional structural diagram of the welding device improved by the present application; Figure 2 is a schematic structural diagram of position A of the welding device in Figure 1, viewed from above; Figure 3 is a welding seat of the welding device in Figure 1 A schematic top view of the structure; Figure 4 is a schematic side view of the welding device in Figure 1. This application provides a welding device 10. The welding device 10 is used for welding lithium batteries. The welding device 10 includes a cylinder 100, a resistance welding mechanism 200, an ultrasonic welding mechanism 300 and a welding base 400. The welding device 10 is specifically described as follows.

The resistance welding mechanism 200 includes an upper resistance welding needle 210 , a cylinder 100 is connected to the resistance welding needle, and the cylinder 100 is used to drive the upper resistance welding needle 210 to move toward the welding seat 400 . Specifically, the cylinder 100 has a connecting rod, and the outer part of the connecting rod has external threads. The resistance welding mechanism 200 includes an upper resistance welding pin 210 , a connection block 220 , a positive terminal 230 and a negative terminal 240 . The connection block 220 includes an upper connection part 221, a lower connection part 222, and an insulating connection part 223 provided between the upper connection part 221 and the lower connection part 222. The upper connection part 221 is provided with a connection hole, and the connection hole of the upper connection part 221 is The inner wall has internal threads, and the connecting rod of the cylinder 100 is inserted into the connecting hole. At this time, the external threads on the outside of the connecting rod of the cylinder 100 match the internal threads on the inner wall of the connecting hole of the upper connecting part 221, that is, the cylinder 100 is connected to the upper connecting part 221. The connection between the parts 221 is a threaded connection, so that the cylinder 100 and the upper resistance welding pin 210 form a detachable connection. There is a connection hole in the insulating connection part 223. The inner wall of the connection hole of the insulating connection part 223 is provided with internal threads. The outside of one end of the positive terminal 230 has external threads. One end of the positive terminal 230 is placed in the connection hole of the insulating connection part 223. , that is, the positive terminal 230 and the insulating connecting part 223 are threadedly connected, so that the external thread of the positive terminal 230 matches the internal thread of the connecting hole of the insulating connecting part 223 , that is, the positive terminal 230 and the connecting block 220 are detachable. For connection, a connection groove is provided on the side of the insulating connection part 223 close to the lower connection part 222. The connection groove communicates with the connection hole of the insulating connection part 223, and the positive terminal 230 is electrically connected to the lower connection part 222 through the connection groove. The lower connecting part 222 is provided with a resistance welding pin hole, and the inner wall of the resistance welding pin hole is provided with an internal thread. One end of the upper resistance welding pin 210 is provided with an external thread, and one end of the upper resistance welding pin 210 is placed in the resistance welding pin hole. The internal thread of the resistance welding needle hole matches the external thread of the upper resistance welding needle 210 , that is, the connection between the upper resistance welding needle 210 and the lower connection part 222 is a threaded connection, that is, the connection between the upper resistance welding needle 210 and the lower connection part 222 A detachable connection is formed between them, that is, the upper connecting part 221 is connected to the cylinder 100, the lower connecting part 222 is connected to the upper resistance welding pin 210, and the positive terminal 230 is threadedly connected to the insulating connecting part 223 and connected to the lower connecting part 222.

The ultrasonic welding mechanism 300 includes an ultrasonic welding head 310. The upper resistance welding needle 210 is clearance-fitted with the ultrasonic welding head 310. The upper resistance welding needle 210 and the ultrasonic welding head 310 are arranged opposite to the welding seat 400. Specifically, the ultrasonic welding mechanism 300 includes an ultrasonic welding head 310 and an adapter 320 connected to the ultrasonic welding head 310. The ultrasonic welding head 310 is connected to the welding machine. The adapter 320 is used to hold it to move the ultrasonic welding head 310. The ultrasonic welding head 310 is connected to the ultrasonic welding head 310. The welding head 310 includes a plurality of via holes 312 , the via holes 312 penetrate the ultrasonic welding head 310 to expose the welding base 400 , the upper resistance welding needle 210 moves through the through holes 312 toward the welding base 400 , and the ultrasonic welding head 310 faces one side of the welding base 400 And the area where the via hole 312 is not provided is the ultrasonic welding area, and the area where the ultrasonic welding head 310 faces the welding seat 400 and is also provided with the via hole 312 is the resistance welding area. The welding base 400 includes a lower base 410, an upper base 420, and an insulating portion 430 disposed between the upper base 420 and the lower base 410. The upper base 420 is disposed opposite to the upper resistance welding needle 210 and the ultrasonic welding head 310. The insulating part 430 is provided with a plug hole, the inner wall of the plug hole is provided with internal threads, and the outside of one end of the negative terminal 240 is provided with an external thread that matches the internal thread of the plug hole, so that the negative terminal 240 is connected to the insulating part 430 The connection between them is a threaded connection. The insulating part 430 is provided with a slot connected to the insertion hole, so that the negative terminal 240 is connected to the upper base 420 through the slot. During operation, the positive terminal 230, the lower connecting part 222, The resistance welding pin, the protective sheet 20, the tab 30 of the battery core, the adapter sheet 40, the upper base 420 and the negative terminal 240 pass a certain amount of current to form a closed loop circuit. Furthermore, the ultrasonic welding head 310 is provided with first welding teeth 311 on one side facing the welding base 400. The first welding teeth 311 are staggered with the through holes 312. The second welding teeth 450 are provided on the side of the welding base 400 facing the cylinder 100. The second welding teeth 450 are arranged in one-to-one correspondence with the first welding teeth 311 . Further, a lower resistance welding pin 440 is provided on the side of the welding seat 400 facing the cylinder 100. The lower resistance welding pin 440 is arranged in one-to-one correspondence with the upper resistance welding pin 210, and the lower resistance welding pin 440 is staggered with the second welding tooth 450. Specifically, the second welding teeth 450 and the lower resistance welding pins 440 are disposed on a side of the upper base 420 facing the cylinder 100 . Further, the lower resistance welding pin 440 and the second welding tooth 450 are integrally formed with the upper base 420 . Optionally, the side of the lower resistance welding pin 440 close to the cylinder 100 is flush with the side of the second welding tooth 450 close to the cylinder 100 .

In this application, the welding device 10 is mainly composed of a cylinder 100, a resistance welding mechanism 200, an ultrasonic welding mechanism 300 and a welding seat 400. The cylinder 100 is connected to the resistance welding needle of the resistance welding mechanism 200, and the upper resistance welding needle 210 is connected to the ultrasonic welding needle. The ultrasonic welding head 310 of the welding mechanism 300 has a clearance fit, and the upper resistance welding needle 210 and the ultrasonic welding head 310 are arranged opposite to the welding seat 400, so that the resistance welding mechanism 200 can soften the foil of the lithium battery through the resistance heat generated by passing the current. Effective connection points are formed in the welding area of the foil, thereby increasing the diffusion activation energy of metal atoms in the welding area, thereby allowing the ultrasonic welding joint to increase the plastic flow of metal in the welding area with only a small practical power, thereby allowing the welding area to Quickly form welding joints, thereby reducing the occurrence of poor welding during lithium battery welding, thereby improving the reliability of lithium batteries.

In this application, the resistance welding needle and the ultrasonic welding head 310 adopt a clearance fit and share a welding seat 400, so that the upper resistance welding needle 210 can pass through the ultrasonic welding head 310 without contact and obstruction to perform welding operations and return to the origin, that is, It can realize ultrasonic welding and resistance welding of lithium batteries, so that the resistance heat softens the foil of the lithium battery and forms effective connection points in the welding area of the foil, thereby increasing the diffusion activation energy of metal atoms in the welding area, thereby making the ultrasonic welding joint Only a small amount of practical power is needed to improve the plastic flow of metal in the welding area, allowing the welding area to quickly form welding joints, thus reducing the occurrence of poor welding during lithium battery welding, thereby improving the reliability of lithium batteries.

In this application, the cylinder 100 and the connecting block 220, the connecting block 220 and the upper resistance welding pin 210, and the connecting block 220 and the positive terminal 230 are connected through threads, so that the subsequent cylinder 100, the connecting block 220, the upper resistance welding pin 210 And when the positive terminal 230 is damaged and needs to be replaced, or needs to be cleaned, components can be easily replaced or cleaned to improve component replacement or cleaning efficiency.

In this application, a first welding tooth 311 is provided on the side of the ultrasonic welding head 310 facing the welding seat 400 and a second welding tooth 450 is provided on the side of the welding seat 400 facing the cylinder 100 that corresponds to the first welding tooth 311 one by one. , to further improve the plastic flow of metal in the welding area, thereby allowing the welding area to quickly form a welding joint, thereby reducing the occurrence of poor welding during lithium battery welding, and thereby improving the reliability of the lithium battery.

In this application, the lower resistance welding pin 440 and the second welding tooth 450 are integrally formed with the upper base 420, so that when the welding device 10 is in operation, the lower resistance welding pin 440, the second welding tooth 450 and the upper base 420 The risk of shaking during the welding operation is ensured to ensure the normal progress of the welding operation, thereby further reducing the occurrence of poor welding during lithium battery welding and thereby improving the reliability of the lithium battery.

In this application, the side of the lower resistance welding pin 440 close to the cylinder 100 is flush with the side of the second welding tooth 450 close to the cylinder 100 to further improve the plastic flow of metal in the welding area, thereby allowing the welding area to quickly form a welding joint. , thereby reducing the occurrence of poor welding during lithium battery welding, thereby improving the reliability of lithium batteries.

In this application, an insulating connection part 223 is provided between the upper connection part 221 and the lower connection part 222 and the positive terminal 230 to prevent current from flowing to the upper connection part 221 and thereby avoid leakage between the lower connection part 222 and the positive terminal 230 , thereby ensuring the normal progress of the welding operation, to further reduce the occurrence of poor welding during lithium battery welding, and thereby improve the reliability of the lithium battery.

In this application, an insulating portion 430 is provided between the upper base 420 and the negative terminal 240 and the lower base 410 to prevent current from flowing to the lower base 410 and thereby avoid the gap between the upper base 420 and the negative terminal 240. Leakage conditions, thereby ensuring the normal progress of welding operations, to further reduce the occurrence of poor welding during lithium battery welding, thereby improving the reliability of lithium batteries.

Please refer to Figure 5, which is a schematic flow chart of the welding method of the lithium battery provided. This application also provides a welding method for lithium batteries, which is welded by using the welding device 10 provided by this application. The welding method includes:

B11. Place the tabs, adapter piece and protective piece of the lithium battery between the welding base, the upper resistance welding pin and the ultrasonic welding head.

B12. Drive at least one of the ultrasonic welding head and the upper resistance welding needle to move toward the welding seat, and make one of the ultrasonic welding head and the upper resistance welding needle carry out the first operation on the tabs, adapter sheets and protective sheets of the lithium battery. One weld.

B13. Use the other one of the ultrasonic welding head and the upper resistance welding needle to weld the tab, adapter piece and protective piece of the lithium battery for the second time to complete the welding of the lithium battery.

Specifically, during the welding operation, the tabs 30, the protective sheet 20 and the adapter sheet 40 of the battery core are placed in the welding area, and the ultrasonic welding head 310, the upper resistance welding needle 210 and the welding seat 400 are moved toward the battery core together. The welding areas of the tabs 30 , the protective sheet 20 and the adapter sheet 40 are moved to press the tabs 30 , the protective sheet 20 and the adapter sheet 40 of the battery core. Then, the cylinder 100 drives the connecting block 220 and the upper resistance welding pin 210 to press down until the resistance welding pin contacts the protective sheet 20 and maintains a certain pressure value.

Then, a certain amount of current flows through the positive terminal 230, the connecting block 220, the upper resistance welding pin 210, the protective sheet 20, the pole lug 30 of the battery core, the adapter piece 40, the lower resistance welding pin 440 of the welding base 400 and the negative terminal 240. And a closed loop circuit is formed for the first welding. At this time, a matrix point-like effective welding joint is formed in the welding area.

Then, the cylinder 100 drives the connecting block 220 and the upper resistance welding needle 210 to rise to the origin position. The ultrasonic welding head 310 and the second welding tooth 450 of the welding base 400 pressurize the battery core, the protective sheet 20 and the adapter sheet 40 at a certain value. The second welding is performed under compression. At this time, the metal in the welding area quickly forms a high-strength welded joint through good plastic flow. Finally, the ultrasonic welding head 310, the welding base 400 and the negative terminal 240 return to the origin, and the welding of the lithium battery is completed.

The present application provides a welding method for lithium batteries. Current is passed through the welding areas of the cell tabs 30, the protective sheet 20 and the adapter sheet 40 under compression conditions. When the resistance welding needle 440 is energized and pressurized for the first welding operation, effective connection points after the diffusion of metal atoms will be formed in the entire welding area, and the resistance heat generated at the same time will soften the unconnected metal foil in the welding area, so that The diffusion activation energy of metal atoms and the vacancy diffusion concentration of metal atoms in the welding area are increased, so that when the ultrasonic welding head 310 performs the second welding operation, it only needs to use less power to produce better metal plastic flow in the welding area, thus This allows the welding area to quickly form a high-strength welding joint, thereby reducing the occurrence of poor welding during lithium battery welding, thereby improving the reliability of the lithium battery.

The above are only embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the description and drawings of the present application, such as the mutual exchange of technical features between the various embodiments. Combination, or direct or indirect application in other related technical fields, are all equally included in the scope of patent protection of this application.

Claims (10)

1. The welding device is used for welding a lithium battery and comprises a cylinder, a resistance welding mechanism, an ultrasonic welding mechanism and a welding seat, wherein the resistance welding mechanism comprises an upper resistance welding needle, the cylinder is connected with the resistance welding needle, the ultrasonic welding mechanism comprises an ultrasonic welding head, the upper resistance welding needle is in clearance fit with the ultrasonic welding head, the upper resistance welding needle and the ultrasonic welding head are oppositely arranged with the welding seat, and the cylinder is used for driving the upper resistance welding needle to move towards the welding seat.

2. The welding device of claim 1, wherein the resistance welding mechanism further comprises a connection block through which the cylinder and the upper resistance welding pin are connected.

3. The welding device of claim 2, wherein the resistance welding mechanism further comprises a positive terminal and a negative terminal, the positive terminal being threadably connected to the connection block, the negative terminal being threadably connected to the weld block.

4. The welding device according to claim 3, wherein the connection block includes an upper connection portion connected to the cylinder, a lower connection portion connected to the upper resistance welding pin, and an insulating connection portion provided between the upper connection portion and the lower connection portion, and the positive electrode terminal is screwed to the insulating connection portion and connected to the lower connection portion.

5. The welding device of claim 3, wherein the welding base comprises a lower base, an upper base, and an insulating portion disposed between the upper base and the lower base, the upper base is disposed opposite to the upper resistance welding needle and the ultrasonic welding head, and the negative terminal is screwed with the insulating portion and connected with the upper base.

6. The welding device of claim 1, wherein the ultrasonic horn includes a plurality of vias extending therethrough to expose the weld mount, the upper resistance wire moving through the vias toward the weld mount.

7. The welding device of claim 6, wherein a first welding tooth is arranged on one surface of the ultrasonic welding head facing the welding seat, the first welding tooth is staggered with the through hole, a second welding tooth is arranged on one surface of the welding seat facing the cylinder, and the second welding tooth is arranged in one-to-one correspondence with the first welding tooth.

8. The welding device according to claim 7, wherein a lower resistance welding needle is arranged on one surface of the welding seat facing the cylinder, the lower resistance welding needle is arranged in one-to-one correspondence with the upper resistance welding needle, and the lower resistance welding needle is arranged in a staggered manner with the second welding teeth.

9. The welding device of claim 1, wherein the ultrasonic welding mechanism further comprises an adapter member coupled to the ultrasonic horn.

10. A welding method of a lithium battery, characterized in that the welding is performed by using the welding device according to any one of claims 1 to 9, comprising:

arranging a tab, a switching sheet and a protection sheet of a lithium battery between the welding seat and the upper resistance welding needle as well as between the welding seat and the ultrasonic welding head;

driving at least one of the ultrasonic welding head and the upper resistance welding needle to move towards the welding seat, and enabling one of the ultrasonic welding head and the upper resistance welding needle to weld the lug of the lithium battery, the switching piece and the protection piece for the first time;

and adopting the other one of the ultrasonic welding head and the upper resistance welding needle to weld the lug, the switching piece and the protection piece of the lithium battery for the second time, so as to finish the welding of the lithium battery.