A power battery is the smallest unit of a power battery with countless single cells combined according to a certain number and requirements to finally form a complete battery pack. So how exactly is the battery pack made up of batteries? Specifically, a battery module consisting of a plurality of battery cells assembled in parallel and welded together is a PACK module; A plurality of battery modules are connected in series to communicate with a battery unit;

The vehicle-mounted power supply usually exceeds 300 V and 200A A. At present, the basic method is that single batteries are connected in parallel to form modules, module batteries are connected in series to form battery packs, and battery packs are connected in series to form a power supply system.

PACK refers to the battery PACK of a new energy vehicle, which provides "energy" for the operation of the whole vehicle. We can simply understand which systems the power battery pack assembly consists of and which parts each system consists of. In order to let people know the battery PACK more intuitively, take the PACK of Audi A3 Sportback-etron hybrid car as an example. Generally speaking, the power battery PACK of electric vehicle consists of the following parts: power battery module system, structural system, thermal management system and BMS. If the battery PACK is compared to a human body, then the module is the "heart", which is responsible for storing and releasing energy and providing power for the car. PACK mainly refers to the processing, assembly and packaging of battery packs. It can be a single battery or a PaCK of series-parallel lithium batteries, including battery PACK, bus bar, soft connection, protective plate packaging, plastic bracket and other auxiliary materials, which together form a pack. The system uses mechanical structure to connect many single batteries in series and parallel, and considers mechanical strength thermal management, BMS matching and other issues. Its main technologies are embodied in the overall structure, design, welding and processing technology control protection level, and active thermal management system.

In the process of battery pack, CCS is an essential part.

CCS(Cells Contact System) products are composed of FPC, plastic structural parts, copper-aluminum bars, etc. The power batteries of new energy vehicles are generally composed of multiple battery modules, each battery module corresponds to one CCS, and one CCS is generally equipped with 1-2 FPCs. CCS integrates plastic structural parts, copper-aluminum bars and other structural parts. In the field of power battery application, FPC is mainly used to replace the traditional wiring harness in the pack link and assist in the information collection of battery packs;

When the FPC of power battery module is welded, the welding material involves nickel, copper and nickel plating, mainly nickel-aluminum welding, and the phenomena such as virtual welding, welding penetration, explosion point and welding deviation are easy to occur during welding, which are as follows:

Different metals have different melting points: when the low melting point material is melted, the high melting point material is still in a solid state, and then the melted material easily penetrates into the grain boundary in the overheated area, resulting in the loss of the low melting point material, the burning and evaporation of alloy elements, which changes the chemical composition of the weld and makes the mechanical properties difficult to control;

Different linear expansion coefficients of dissimilar metals: different linear expansion coefficients of dissimilar metals lead to greater welding stress and welding deformation when molten pool crystallizes. Due to different stress states on both sides of the weld, it is easy to cause cracks in the weld and heat affected zone, and even lead to peeling of the weld metal from the parent metal;

The thermal conductivity and specific heat capacity of materials are different: it leads to the deterioration of crystallization conditions of weld metal and coarse grains, and affects the wettability of refractory metals;

Intermetallic compounds are easy to be produced in dissimilar metal welding, and at the same time, the microstructure changes, which leads to the decline of mechanical properties of welded joints, especially in the heat affected zone.

In addition, the thermal parameters such as linear expansion coefficient, thermal conductivity and specific heat capacity of materials change with the temperature, which makes the laser welding process of dissimilar metal materials more complicated.

Therefore, the FPC welding process of high-quality power battery not only solves the series of welding problems of dissimilar metals, but also improves the automation, intelligence and efficiency of FPC welding, and at the same time, it must avoid the problems of virtual welding, welding penetration, explosion point and welding deviation.

According to the laser welding requirements of CCS components, laser equipment manufacturers have introduced corresponding laser welding equipment, which has good welding performance and welding quality, and has been well received by end customers through practical application.