Generally speaking, the welding of power lithium battery casings mainly involves two methods: side welding and top welding. Each has its advantages and disadvantages. Due to the special properties of its material, the aluminum casing of power lithium batteries is prone to problems such as bulges, pores, and cracks. Problems are particularly common when welding square batteries at corners. Below, we will analyze some of the difficulties in the welding of power lithium battery packaging:
1. Technological challenges in welding power lithium batteries
Generally, the thickness of the aluminum casing for power lithium batteries is required to be below 1.0 mm. Mainstream manufacturers currently use 0.6 mm and 0.8 mm thicknesses for the casing material, depending on the battery capacity. Welding methods are mainly divided into side welding and top welding. A significant advantage of side welding is that it has less impact on the inside of the battery cell, preventing spatter from easily entering the inside of the casing.
Because welding may cause protrusions, which can slightly affect subsequent assembly processes, the side welding process places high demands on the stability of the laser, the cleanliness of the materials, and the fit clearance between the top cover and the aluminum shell of the power lithium battery. The top welding process, because it welds to one surface, can employ a more efficient galvanometer scanning welding method, but it requires very high standards for the preceding shell insertion and positioning processes, as well as a high degree of equipment automation.
2. Welding difficulties of aluminum casing for power lithium batteries
Currently, aluminum casings account for over 90% of the entire power lithium battery. Laser welding of aluminum is quite challenging, presenting problems such as surface protrusions, porosity, sparking, and internal bubbles. Surface protrusions, porosity, and internal bubbles are fatal flaws in laser welding, forcing many applications to cease or find alternative solutions due to these issues.
Many battery manufacturers struggle with this issue during the early stages of research and development. The main reason is that the fiber core diameter is too small or the laser energy setting is too high. There are many factors that can cause sparking (also known as splashing), such as the cleanliness of the materials, the purity of the materials themselves, and the inherent properties of the materials. However, the stability of the laser is the decisive factor in its application.
In the welding of power lithium batteries, welding technicians will select appropriate lasers and welding process parameters based on the customer's battery material, shape, thickness, tensile strength requirements, etc., including welding speed, waveform, peak value, welding head tilt angle, etc., to set reasonable welding process parameters to ensure that the final welding effect meets the requirements of the power lithium battery manufacturer.
3. Welding difficulties of square power lithium batteries
Due to factors such as the precision of incoming material fitting, square batteries are most prone to problems at the corners during welding. These issues can be addressed by continuously exploring and adjusting the welding speed based on actual conditions. Round batteries do not have this problem, but their subsequent integration into battery modules is more difficult.
