SHINHOP laser

Connecting the battery cells in series and parallel through welding is a key step in the production of battery modules. Welding technology has become one of the most critical factors limiting the quality, production efficiency, and cost of module products to some extent.
The following discusses the focus of this technology in the field, using the patented technologies of several excellent module manufacturing companies as examples.
Company A
Due to the large current-carrying capacity of the total output terminal, copper material is generally used. However, the welding strength between copper electrode sheets and aluminum poles is low, and stability is poor.

Company A's earliest solution was to first ultrasonically weld the copper electrode sheet to an aluminum sheet, and then weld the aluminum sheet to the pole. This method has three problems:
1. When welding the aluminum connecting sheet and the aluminum pole, it affects the stability of the already welded copper-aluminum joint.
2. The welding area of the copper-aluminum electrode sheets is asymmetric, affecting the welding strength.
3. After connecting the copper electrode sheet to the connector, it introduces shear force at the copper-aluminum interface, affecting the bonding strength.

In response to these three issues, Company A made three improvements.
First improvement:
A hole is opened on the copper electrode sheet, and ultrasonic welding is performed on the copper-aluminum electrode sheets in a circular area around the hole. Then, laser welding is performed on the aluminum sheet and aluminum pole in the hole area. This method solves the problems of multiple welds and asymmetric welding areas, but there is still shear force caused by the connector on the copper electrode sheet.

Second improvement:
Based on the above partitioned welding, the copper electrode sheet is transformed into a copper platform, which has a concentric copper column with external threads or a cylindrical hole with internal threads, and is connected to the connector by threaded connection. This reduces the impact of shear force and lowers the production difficulty of the connector, achieving self-production.

Third improvement:
Based on the first partitioned welding technology, a retractable aluminum electrode sheet was developed, which is formed by stacking multiple layers of aluminum foil, stamping, and then segmental hot pressing and welding. The arched section is a multi-layer dispersed state that is not bonded between layers, while the flat section is a single-layer state that is bonded together through hot pressing between layers, thus forming a flexible aluminum electrode connecting sheet that compensates for the displacement caused by battery expansion and reduces the stress at the copper-aluminum joint. It is speculated that the improvements in the first two methods may not fully meet the requirements for interface bonding strength, which is why this flexible aluminum connecting sheet method is adopted to compensate for the insufficient strength of the copper-aluminum interface.
Company B:
Company B connects using nickel sheets with the poles, which has good weldability but insufficient conductivity and high cost.

In response to this issue, a copper-nickel composite electrode sheet was developed, with corresponding holes opened, and nickel protrusions at the holes for welding with the poles, thus combining the welding performance of nickel with the conductivity of copper. However, this method does not completely solve the problem of insufficient conductivity. For example, optimizing by increasing the thickness of the connecting sheet affects welding performance, increases the weight of the battery module, and raises costs.

Therefore, a composite connecting sheet consisting of thick and thin aluminum electrode sheets was developed. The thick electrode sheet has a hole, and the thin electrode sheet has a circular groove corresponding to the hole, which is the welding area between the thin electrode sheet and the pole. At this time, the thick electrode sheet can be increased to a sufficient thickness to ensure conductivity, while the thin electrode sheet can be reduced to a sufficient thinness to ensure weldability. Additionally, aluminum has a low density and low price, which can also meet the overall quality and cost requirements.
Company C:
In order to achieve good connection strength, Company C opens holes in the connecting sheet, allowing the battery cell pole to pass through the hole for fitting, and then uses laser welding to melt the metal around the hole for welding. The problem is that if the hole is too large, the welding effect will be affected. If it is too small, it increases the difficulty of assembly.

In response to this issue, Company C divided the hole into two segments of different sizes, using an interference fit mode to reduce the requirements for hole shape and size.

To improve the conductivity of the connecting sheet, Company C developed a multi-layer stacked connecting sheet. Two layers of material are welded together, with one or several layers having holes, and the remaining layer corresponding to the hole area being the welding part of the connecting sheet and the pole, balancing the functions of thin welding and thick conductivity. It is worth noting that the base materials of both technologies are made of multi-layer foil welded together, and both types of connecting sheets are formed by a one-time stamping process.
To summarize the common points of each company:
1. Connecting sheets mostly use a method of multi-layer material composite + opening holes, where one layer of material is the connecting layer between the connecting sheet and the pole, ensuring welding performance. Multi-layer material stacking is used to ensure the conductivity of the connecting sheet.
2. The base material of the connecting sheet is processed into shape after stacking multi-layer foils, which can form a flexible area to compensate for the displacement caused by battery expansion, reducing the impact on low-strength interfaces.
The three companies mentioned above are all battery module manufacturing companies, and their problem-solving ideas are basically similar, which is to find ways to circumvent the problems. When the welding quality of two materials cannot meet the requirements, they try to use different alternative materials and then use more refined structures or processes to compensate for the performance loss caused by changing materials.
In addition to understanding the characteristics of various materials, module welding also requires a good set of laser welding equipment and support for welding technology. Therefore, when users are looking for battery module welding solutions, they need to contact equipment suppliers with battery welding experience to better solve their product welding problems, such as: Han's Laser, SHINHOP Laser, shinhoplaser, etc., all have good battery module welding solutions and equipment!