The welding process requirements for lithium battery packs are analyzed as follows:

Selection of welding methods

The main methods used for welding lithium battery packs include resistance welding, laser welding, spot welding, ultrasonic welding and hot-press welding, etc. Among them, spot welding and laser welding are widely used in the manufacturing of lithium batteries. Spot welding is a process that uses an electric current passing through electrodes to generate an instantaneous high temperature, which instantly melts the welding material and forms a welding point. Laser welding uses a high-energy laser beam to heat the welding area, causing the welding material to melt instantly and form a welding point. Both of these two methods can achieve high-precision and high-efficiency welding.

Welding parameter setting

Welding current: It is set according to the thickness of the welding material and the power of the welding equipment. Generally speaking, the greater the welding current, the deeper the welding depth. However, excessive current can cause the electrode to overheat, affecting the welding quality.

Welding time: It refers to the time during which the electrode comes into contact with the welding material. The longer the welding time, the greater the welding strength. However, an overly long welding time can cause the electrode to overheat, affecting the welding quality.

Welding pressure: It refers to the pressure exerted by the electrode on the welding material. The greater the welding pressure, the greater the welding strength. However, excessive pressure can cause electrode deformation and affect the welding quality.

Welding speed: It refers to the speed at which the electrode moves. The faster the welding speed, the higher the welding efficiency. However, if the speed is too fast, the contact time between the electrode and the welding material will be too short, affecting the welding quality.

Preparation before welding

Material inspection: Inspect the dimensions and quality of materials such as tabs, battery cells, and solder sheets to ensure they meet the requirements.

Equipment preparation: Prepare appropriate welding equipment, such as spot welding machines, ultrasonic welding machines, etc., and ensure the normal operation of the equipment.

Environmental requirements: Ensure that the welding environment meets the requirements, such as temperature, humidity, and cleanliness, to reduce the risk of poor welding.

Welding process control

Selection of welding pins: The model and specification of the welding pins should be chosen based on the thickness of the nickel sheet and the process design requirements of the battery pack. For example, the 1.7 straight-through welding needle is suitable for nickel sheets ranging from 0.12mm to 0.18mm, and the 3.0 eccentric spot welding needle is suitable for welding thicker nickel sheets (the thickness of conventional welding nickel sheets is between 0.15 and 2.0mm).

Keep clean: During the welding process, ensure that there are no other impurities remaining on the surface of the nickel sheet and the battery cell; otherwise, poor welding conditions such as explosion may occur.

Safety precautions: During the welding process, protective equipment such as goggles and insulating gloves should be worn to prevent electric shock or scalding and other safety accidents.

Welding quality inspection

Visual inspection: Check whether there are any missed welds, false welds, or loose welds at the welding points. The weld points should be bright, uniform, firm, free of pores and coating issues.

Strength test: Conduct strength tests on the welded areas to ensure the quality of the welding.

Electrical performance test: Check the electrical connection performance of the welded parts to ensure normal current transmission.

Other tests: Depending on specific requirements, air tightness tests, durability tests, etc. may also be needed.

Post-welding treatment

Cleaning: Remove residues, oxides, etc. from the welding area to ensure the surface of the TAB is clean.

Packaging: Package the welded battery cells to ensure they are not damaged during transportation and storage.