Since its advent in the early 1990s, lithium batteries have been welcomed by 3C digital, power equipment and other industries for their energy density, environmental protection, high voltage, long service life and the ability to achieve fast charging, especially for new energy sources in recent years. The development of the automobile industry provides an irreplaceable contribution. As its power source, the lithium battery industry has huge market development potential and is an important part of the national strategic development. According to relevant statistics, in the next 5-10 years, lithium batteries will serve as the quality of the core components of new energy vehicle power is directly related to the safety and performance of the entire vehicle. At this stage, our equipment for manufacturing lithium battery products is divided into three stages of equipment, namely front-end equipment, mid-end equipment, and rear-end equipment. These three kinds of end equipment, the manufacturing accuracy and automation level of their equipment will affect the production efficiency and quality consistency of battery products, and laser welding equipment and its advanced welding technology are exactly suitable for the current and future needs of lithium battery production, and have been widely used.

The following describes the laser welding process through the application of laser in the power battery industry, analyzes the difficulties of laser welding of aluminum alloys and the impact of welding modes on welding quality, lists the characteristics of prismatic power batteries and battery PACK processes, and the future development of equipment. trend.

1. Lithium battery laser welding process

From lithium battery cell manufacturing to battery PACK assembly, welding is a very important process, because this process will directly determine the strength, conductivity, air tightness, metal fatigue and corrosion resistance of the lithium battery, which is a typical Battery welding quality evaluation standard, and battery products that fail to meet such standards will be strictly prohibited from being sold on the market, which is a loss for the company.

Judging from a large amount of actual production experience of lithium batteries, laser welding is the only welding processing quality requirement that can be trusted for such products. It is a processing equipment that cannot be replaced by other equipment. It has the following major advantages:

1. Laser welding has high energy density, small welding deformation and small heat-affected zone, which can effectively improve the accuracy of parts. The welding seam is smooth, free of impurities, uniform and dense, and does not require additional grinding work;

2. Laser welding can be precisely controlled, with a small focused light spot and high-precision positioning. It is easy to realize automation with a robotic arm, improve welding efficiency, reduce working hours, and reduce costs;

3. When laser welding thin plates or thin-diameter wires, it is not as susceptible to meltback as arc welding;

4. Significantly improve product quality, safety and battery consistency;

There are many kinds of materials used in manufacturing batteries, including steel, aluminum, copper, nickel, etc. These metals can be used to make electrodes, wires or casings. Therefore, in the actual welding process, we often encounter the same material or multiple materials. Previous welding has put forward more stringent requirements on welding process requirements, and the process advantage of laser welding is that it can weld multiple materials and weld between multiple materials.

2. Difficulties in welding process

Power batteries generally follow the "thin and light" principle, and among many materials, only aluminum can meet such requirements. Generally, the thickness of the shell, cover, and bottom is basically required to be below 1.0mm. Currently, more advanced manufacturers require it to be around 0.8mm. , it can be seen that the aluminum alloy battery case accounts for more than 92% of the entire power battery.

The difficulties in welding aluminum alloys are reflected in the following points:

1. Aluminum alloy is a non-ferrous metal with higher thermal conductivity and is a highly reflective material, so its sensitivity to laser is relatively low. At the same time, due to the low ionization energy of aluminum, separation is not easy to spread during the welding process, making it Poor welding stability;

2. The burning loss of alloy elements during the welding process reduces the mechanical properties of aluminum alloy welded joints;

3. The pores are highly sensitive during the welding process, and some problems and defects will inevitably occur during welding, the most important of which are pores and thermal cracks;

4. The pores produced during the laser welding process of aluminum alloys mainly include hydrogen pores and pores caused by keyhole destruction. Because the cooling speed of laser welding is too fast, the problem of hydrogen pores is more serious, and there is another type of pores in laser welding due to Holes caused by the collapse of small holes.

5. Thermal crack problem. Aluminum alloy is a typical eutectic alloy. It is prone to hot cracks during welding, including weld crystal cracks and HAZ liquefaction cracks. Due to the component segregation in the weld area, eutectic segregation will occur and grain boundary melting will occur. Under the action of stress, it will Liquification cracks form at grain boundaries, reducing the performance of welded joints.

6. Explosion (also called splashing) problem. There are many factors that cause explosions, such as the cleanliness of the material, the purity of the material itself, the characteristics of the material itself, etc. The decisive factor is the stability of the laser. The main reasons for the bulges, pores, and internal bubbles on the shell surface are that the fiber core diameter is too small or the laser energy setting is too high.

In view of the above problems, finding suitable process parameters is the key to solving the problem.