The power battery is composed of countless single cells according to a certain number and requirements, and finally forms a complete battery pack, so the smallest unit of the power battery of a single battery. So how is the battery pack specifically composed of batteries? Specifically, a battery module is composed of several battery cells assembled and welded in parallel, which is a PACK module; communicate with one battery cell;
The vehicle power supply usually exceeds 300V, 200A. The current basic method is to connect the single batteries in parallel to form a module, connect the module batteries in series to form a battery pack, and connect the battery packs in series to form a power supply system.
PACK refers to the battery pack of new energy vehicles, which provides "energy" for the operation of the whole vehicle. We can briefly understand which systems the power battery PACK assembly is composed of, and which parts are each system composed of? In order to let everyone understand more intuitively Battery PACK, take the PACK of the Audi A3 Sportback-etron hybrid vehicle as an example. Generally speaking, electric vehicle power battery PACK is composed of the following parts: power battery module system, structural system, thermal management system, BMS, if the battery PACK is compared to a human body, then the module is the "heart", responsible for storage and release Energy, which powers the car. PACK mainly refers to the processing, assembly and packaging of battery packs. It can be a single battery or a PaCK of a series-parallel lithium battery pack, including battery packs, busbars, soft connections, protective board outer packaging, plastic brackets and other auxiliary materials. These items together form a PACK. The system uses The mechanical structure connects many individual batteries in series and parallel, and considers issues such as mechanical strength, thermal management, and BMS matching. Its main technology is reflected in the overall structure, design, welding and processing process control protection level, and active thermal management system. wait.
CCS is an essential part in the battery pack process.
CCS (Cells Contact System, integrated busbar, wiring harness board integrated parts) products are composed of FPC, plastic structural parts, copper and aluminum bars, etc. The power battery of new energy vehicles is generally composed of multiple battery modules, and a single battery module corresponds to one CCS, 1 CCS is generally equipped with 1-2 FPCs, and CCS integrates plastic structural parts, copper and aluminum bars and other structural parts. In the field of power battery application, FPC is mainly used for the traditional wiring harness replacement in the pack link, and assists in the information collection of the battery pack.
When welding the FPC of the power battery module, the welding material involves nickel and nickel-plated copper, mainly nickel-aluminum welding. During welding, it is easy to have false welding, welding penetration, bursting points, and welding deviation. The specific manifestations are:
Dissimilar metals have different melting points: when the low melting point material is melted, the high melting point material is still in a solid state. At this time, the melted material is easy to penetrate into the grain boundary of the overheating zone, resulting in the loss of low melting point material, burning loss and evaporation of alloying elements, making the weld chemical The composition changes, and the mechanical properties are 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 the molten pool crystallizes. Due to the different stress states on both sides of the weld, it is easy to cause cracks in the weld and heat-affected zones, and even Cause the weld metal to peel off from the parent metal;
The thermal conductivity and specific heat capacity of the material are different: it causes the crystallization condition of the weld metal to deteriorate, the grains are coarse, and affects the wettability of the refractory metal;
The welding of dissimilar metals is prone to produce intermetallic compounds and microstructure changes at the same time, resulting in a decrease in the mechanical properties of welded joints, especially cracks in the heat-affected zone.
In addition, thermal physical parameters such as linear expansion coefficient, thermal conductivity and specific heat capacity of materials change with temperature, which makes the laser welding process of dissimilar metal materials more complicated.
Therefore, the high-quality power battery FPC welding process, in addition to solving the series of dissimilar metal welding problems, must also avoid problems such as virtual welding, welding penetration, bursting points, and welding deviation while improving the automation, intelligence, and high efficiency of FPC welding.