The welding method of power battery module connecting sheets
Power batteries are the core component of electric vehicles. They are called the heart of electric vehicles and are the top priority in the automotive industry chain. As the world’s environmental awareness and related policies strengthen, the demand for power batteries will increase in the future.
For the safe use of power batteries, the welding of battery module connectors is very important. This article will introduce you to the common welding methods of power battery module connectors.
What is power battery
Most electric vehicles use lithium batteries as power batteries. Power batteries are the power sources that provide power for tools. They mostly refer to the batteries that provide power for electric cars, electric trains, electric bicycles, and also used as golf cart batteries. The main difference is the starting battery used to start the car engine.
As the core component of electric vehicles, the power battery’s configuration for conductive connection is its top priority.
The connection method between the power battery cells and the module busbar not only affects the manufacturing efficiency of the power battery, but also determines whether the power battery production can be automated. It also has an impact on the performance of the power battery module after assembly.
Power battery module connecting sheets
Most of the connecting sheets of power battery modules adopt a multi-layer material composite method. One layer of material is the connecting layer between the connector and the pole to ensure the welding performance. Multiple layers of materials are used to ensure the conductivity of the connecting sheet.
The connecting plate substrate is processed and formed after stacking multiple layers of foil to form a flexible area, which is used to compensate for the displacement caused by the expansion of the power battery core and reduce the impact on the low-strength interface.
The connectors of power battery modules are generally rectangular, trapezoidal, triangular, or table-shaped. The connection surface is pasted with 1-3mm nickel-plated copper foil.
The surface is easily oxidized and discolored at high temperatures during welding, and must be polished without damaging the surface coating of the product. Such products not only solve the problem of overall electroplating, but also solve the problem of maximizing conductivity.
Nickel-plated copper connectors are the best, followed by pure nickel connectors, but they are more expensive, and finally nickel-plated steel connectors. Nickel-plated steel connectors are relatively cheap and easy to weld.
Each power battery manufacturer chooses different thicknesses of connecting sheets, because the thickness of the connecting sheets is related to the weight of materials consumed and the weight of the overall power battery module. Reducing the thickness is the direction of lightweight design of power battery modules.
Commonly used busbars for power battery modules include: nickel sheets, copper-aluminum composite busbars, copper busbars, total positive and total negative busbars, aluminum busbars, copper soft connectors, aluminum soft connectors, copper foil soft connectors, etc.
Welding methods for power battery module connectors
The connection method between the power battery cells and the module busbar not only affects the manufacturing efficiency of the power battery, but also determines whether the power battery production can be automated. It also has an impact on the performance of the power battery module after assembly.
The main welding methods used in connecting power battery modules are:
Resistance welding
Resistance welding is a welding method that uses resistance heat as the energy. Resistance welding uses the resistance heating effect generated by current flowing through the contact surface and adjacent areas of the workpiece to heat it to a molten or plastic state, while applying pressure to form a metal bond.
Resistance welding does not require filler metal during welding, has high productivity, small deformation of the weldment, and is easy to automate.
To prevent arcing and forge welding of metal on the contact surface, pressure should always be applied when welding. During the resistance welding process, the contact surface of the workpiece to be welded is crucial to obtain stable welding quality. Therefore, before welding, the contact surfaces between the electrode and the workpieces must be cleaned.
In the grouping process of power batteries, resistance welding is a relatively mature process and is used in the welding of power battery connecting sheets and bus bars, the connection of power battery poles and parallel conductive bars, etc.
Due to its simple equipment and low cost, it was widely used in the early stages of the development of the power battery industry. In recent years, it has been gradually replaced by more advanced laser welding and polymer diffusion welding.
Laser welding
Laser welding is highly efficient and easy to realize automated production. After continuously improving the welding process and limiting the thermal impact during the molding process, it is increasingly used in actual production. Laser welding combined with industrial robots is gradually becoming the main force in automated power battery module production lines.
Laser welding is an efficient and precise welding method that uses a high-energy-density laser beam as a heat source. Laser welding is mainly used to weld thin-walled materials and low-speed welding.
The laser welding process is a heat conduction type, that is, the laser radiation heats the surface of the workpiece, and the surface heat passes through the heat conduction diffuses to the inside, and by controlling parameters such as laser pulse width, energy, peak power, and repetition frequency, the workpiece is melted and a specific molten pool is formed.
Polymer diffusion welding
Polymer diffusion welding is a new generation of diffusion welding machine. It is a soft connection equipment for conductive strips. It is mainly composed of a host and a control part. It can realize diffusion welding between lithium polymer battery materials.
It is widely used in electric power, chemical industry, smelting and other industries and production industries. The urgently needed busbar expansion joints and soft connection conductive tape products can realize diffusion welding between soft busbars, soft busbars and hard busbars.
The principle is to bring the welding surfaces of the materials to be welded into contact with each other under a certain temperature and pressure, and expand the physical contact of the surfaces to be welded through microscopic plastic deformation or the generation of trace liquid phase through the welding surface.
Through that, the distance reaches (1~5)×10-8cm (so that the gravitational force between atoms can form a metallic bond), and then the atoms continue to diffuse and penetrate each other over a long period of time to achieve metallurgical bonding.
Polymer diffusion welding is a special welding process that can use 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.
It is mainly used for soft connection to the power battery. 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.
For the welding of electric vehicle battery module connectors, the polymer process does not require solder to achieve welding, and the quality after welding is qualified and the appearance is smooth.
In addition, the polymer diffusion welding machine uses a high-frequency transformer with low voltage, which can effectively reduce the insulation and sparking problems caused by high voltage battery and enhance the reliability of the equipment.
