The connection method of power battery cells into modules and then into PACKs not only affects the efficiency and production mode of power battery manufacturing, but also directly determines the performance of the power battery after installation in the vehicle. From traditional welding methods to the current advanced laser welding, the welding types of power battery busbars have undergone many years of development and evolution, and can be summarized into the following categories. Below, we will analyze the characteristics of various welding methods.

1. Resistance welding.

Resistance welding is a type of welding method that uses resistance heat as energy. Resistance welding uses the resistance heat effect generated by current flowing through the contact surface of the work piece and adjacent areas to heat it to a molten or plastic state, and at the same time pressurizes it to form a metal bond. Welding method. Resistance welding does not require filler metal during welding, has high productivity, small deformation of the welded parts, and is easy to automate.

To prevent arcing at the contact surface and to forge the weld metal, pressure is always applied during welding. When welding with resistance welding, the contact surface of the work piece to be welded is of paramount importance for obtaining stable welding quality.

Therefore, the contact surfaces between the electrode and the work piece and between the work piece and the work piece must be cleaned before welding. In the power battery assembly process, resistance welding is a relatively mature process and is used in the welding of power battery cells and busbars, the connection of power battery tabs and parallel conductive strips, etc. Due to the simple equipment and low cost, it was widely used in the early development of the power battery industry. In recent years, it has been gradually replaced by more advanced laser welding and ultrasonic welding.

2. Polymer diffusion welding.

Polymer diffusion welding is a method of contacting the welding surfaces of substances to be welded with each other in a vacuum environment at a certain temperature and pressure. The physical contact of the surfaces to be welded is expanded through microscopic plastic deformation or the generation of trace liquid phases on the welding surface, making the distance between them Within (1~5) × 10-8cm (in this way, the gravitational force between atoms can form a metallic bond), and then after a long period of time, the atoms continue to diffuse and penetrate each other to achieve a metallurgical bonding. Method.

Polymer diffusion welding is a special welding process that uses copper foils of different strengths to weld together in specific areas. This welding process does not require the use of any form of flux and can achieve perfect molecular connectivity. The main reason is that it does not require the use of any form of flux. Soft connection for power batteries. The mounting contact surface can withstand any form of extrusion, bending, or impact. Since the mounting contact surface is custom-made, it can be installed into a space of only 2mm.

3. Ultrasonic welding.

Ultrasonic welding uses high-frequency vibration waves to transmit to the surfaces of two objects to be welded. Under pressure, the surfaces of the two objects rub against each other to form fusion between the molecular layers. The ultrasonic generator converts 50/60 Hz AC power into 15, 20, 30 or 40 kHz high-frequency power. The converted high-frequency electrical energy is converted again into mechanical motion of the same frequency through the transducer, and then the mechanical motion is transmitted to the welding head through a set of horn devices that can change the amplitude. The welding head transmits the received vibration energy to the joint of the work piece to be welded. In this area, the vibration energy is converted into heat energy through friction, melting the metal.

Advantages of ultrasonic metal welding:

1. Compared with the resistance welding method, ultrasonic welding has a long mold life, less mold repair and replacement time, and is easy to realize automation.

2. The welding material does not melt and has no fragile metal properties. After welding, the conductivity is good and the resistivity is extremely low or nearly zero.

3. Ultrasonic welding can be performed between different types of metals of the same type, and consumes much less energy than resistance welding. The requirements for the surface of the welding metal are low and can be welded by oxidation or electroplating.

4. Compared with other pressure welding, ultrasonic welding requires smaller pressure and deformation below 10%, while cold pressure welding has a work piece deformation of 40% to 90%. The welding time is short and no flux, gas or solder is required.