SHINHOP laser

The lithium power battery module is assembled from multiple individual cells in series and parallel. The connection and fastening between individual cells require that the connecting piece has a low contact resistance with the battery's terminal, is resistant to vibration, and has a high degree of reliability. Whether using laser welding, resistance welding, or bolt mechanical locking, it is essential to ensure the reliability and durability of the battery system during the actual operation of electric vehicles. In different design requirements for power battery systems, parameters such as volume energy density, mass-specific energy density, and volume power density are related to the connection structure and process between individual batteries in the power battery system.

The lithium power battery module connects several individual cells in series and parallel through conductive connectors, fixed in the designed position by processes and structures, working together to store and release electrical energy. It can be said that the basic functions of the module are connection, fixation, and safety protection. Common module types can be divided into three forms based on the connection method between the cells and the conductive bus: welding, screw connection, and mechanical crimping. Research shows that the connection method between the individual cells and the module bus not only affects manufacturing efficiency and the possibility of automation but also has a significant impact on the performance of the battery after installation.
However, ensuring reliable electrical connections in lithium power battery modules is not easy, as the electrical connections are closely related to several individual cells, connectors, connection methods, processes, and materials. The reliability of the connections depends not only on the materials, structures, and geometric dimensions of the connectors themselves but also on atmospheric pollution at the electrical connection points, such as dust, corrosive gases, humidity, and temperature, which can directly affect connection reliability. During the conduction of current at the electrical connection points in the lithium power battery module, various random factors can influence the reliability of the electrical connection, such as current thermal effects, electrodynamics, external atmospheric pollution, temperature, humidity, and electromagnetic interference, all of which can lead to unreliable electrical contact.
Currently, the connection processes for polymer cells mainly include two methods: welding and non-welding (mechanical compression contact type).

1) Welding. Welding includes two types: laser welding or soldering.
Due to the large area of the power battery pack, it is not easy for the ultrasonic welding head to make contact, so ultrasonic welding is rarely used. Laser welding is a more ideal welding method. The high-temperature process of soldering poses certain risks to the sealing at the polymer cell's terminal, and the heavy weight of solder increases the mass of the battery pack; whether laser welding or soldering, the grouping process is not conducive to replacing individual batteries.

2) Mechanical crimping.
The non-welding connection structure and method that allows for the disassembly and replacement of polymer cell modules treat each cell as an independent unit, connecting each unit in series and parallel while ensuring that each battery can be disassembled and replaced. The main advantage of this process is that individual batteries can be replaced, solving the problem of difficulty in replacing individual cells after grouping, thus improving the safety of the battery pack.

The connection process between individual batteries usually employs mechanical locking. The advantage of this process is that assembly connections can use various methods, making disassembly and assembly simple and flexible; the disadvantage is that due to structural limitations, compared to flat terminal types, the assembly process requires additional metal components, increasing the mass of the battery module.

The connection resistance of welding is less than that of screw connections, which is a clear advantage of welding. At the same time, there is significant room for improvement in the production efficiency of welding, so overall, welding is superior to screw connections. However, it can also be seen that screw connections are generally applied in large batteries, where their stronger conductivity is highlighted, while the disadvantage of low efficiency is mitigated.
The benefits of mechanical crimping lie in flexible disassembly and a high success rate for later maintenance and secondary recycling. The downside is that assembly efficiency is difficult to significantly improve, and if the design of the mechanical connection structure is not reasonable, there is a high possibility of changes in contact resistance under long-term road vehicle operating conditions.

SHINHOP laser - square aluminum shell battery module laser welding equipment.